Regulatory frameworks governing the supply of therapeutic goods

Last lecture for the year- and possibly for my undergrad!

What is a therapeutic good?

A therapeutic good is anything that is used for a therapeutic use, such as treatment, prevention or diagnosis of diseases, testing susceptibility to diseases, contraception and pregnancy tests. Even stuff like band-aids and thermometers are considered to be therapeutic goods.

Sometimes things can get a bit complicated. Let's start with foods. If you have a clove of garlic, that is food. If you concentrate part of the garlic, put it into capsule form and make a therapeutic claim (e.g. "can relieve cold and flu symptoms"), you now have a therapeutic good. Cosmetics can also be a bit confusing: moisturisers are normally cosmetics, but if they contain a sunscreen agent and claim to protect from UV radiation, they become classified as a therapeutic good. In short: the principal use and presentation of a product are important in determining whether something should be classified as a "therapeutic good" or not.

To make things even more confusing, there are some products that you would think should be therapeutic goods, but aren't. Hair products, such as bleaches and dyes, as well as some dental products, such as whiteners, are excluded from being classified as therapeutic goods. Breath testers used by police are also exempt, as is reproductive tissue for use in assisted reproductive therapy. Fresh, viable organs are exempt, though an organ that has been stored for a while is classified as a therapeutic good.

Why is regulation of therapeutic goods important?

It is important to regulate therapeutic goods so that we can (hopefully) prevent dodgy drugs from making it to market, or we can at least recall them quickly if they turn out to be problematic. Here are some examples of therapeutic goods that turned out to be problematic:

• Thalidomide- Perhaps the most well-known example. Thalidomide was originally created to treat morning sickness. However, it also caused babies to be born without limbs (or with deformed limbs), due to anti-angiogenic effects. Interestingly, thalidomide is sometimes used as an anti-cancer drug because of its anti-angiogenic effects.
• Vioxx- Originally created to treat rheumatoid arthritis and other forms of chronic inflammation, Vioxx was withdrawn when it was found to increase the risk of cardiovascular disease.
• Porcine small intestine submucosa (SIS)- SIS was advertised as an acellular scaffold for cell therapies. However, it was found to contain porcine DNA, resulting in inflammatory responses.
• Metal-on-metal hip implants- Metal-on-metal implants were found to release small metal particles into the bloodstream.
• Poly implant prosthesis (PIP) breast implants- These breast implants had the risk of exploding.

Regulation of therapeutic goods

To be honest, I mainly just zoned out here. Main points are that the main regulator in Australia is the Therapeutic Goods Administration (TGA). Their main concerns are quality, safety, efficacy and cost. All of these factors are taken into consideration when evaluating a new therapeutic good and when monitoring an existing good.

There are three main categories of therapeutic goods: medicines, medical devices and biologicals. Medicines include prescription and over-the-counter drugs, vaccines, blood and blood components, and animal cell and tissue-derived products. Medical devices include blood pressure monitors, cardiac pacemakers, surgical gloves, breast implants, condoms and human tissues used in diagnostics. Biologicals are things that are made from human cells and/or human tissues (aside from human tissues used in diagnostics).

And that's the last post for the semester! Good luck in exams!!

Infant Nutrition and Functional Foods

Last post for PHYL3003!

Definitions

First up, some definitions for some extra clarity:

• Infant- A child aged between 0-12 months.
• Newborn or neonate- An infant in the first 28 days of life.
• Preterm- Infant born before 37 weeks gestation.
• Very preterm- Infant born between 28 weeks and 31 weeks + 6 days gestation.
• Extremely preterm- Infant born before 28 weeks gestation.

Babies who are born very or extremely preterm may need to be fed parentally at first, and then drip-fed milk. Premature babies may have underdeveloped GI tracts that cannot handle a rapid feed, so feeding them rapidly may increase the risk of necrotising enterocolitis (NEC).

Breastmilk

You've probably heard the saying that "breast is best." In fact, the World Health Organisation and UNICEF recommend that babies are fed exclusively breast milk in the first six months of life, and that breast milk continues to be the primary food for the first year of life. It is also recommended to continue to breastfeed for two years or even longer.

Why is breast milk so good? It's got lots of good stuff in it, such as:

Proteins

Proteins, which are found in higher concentrations in colostrum (milk in first few days after giving birth) as compared to regular breast milk, are needed for growth of lean tissue. The main proteins in breast milk are caseins, whey proteins and milk fat globule proteins. Important whey proteins include lactoferrin, alpha-lactalbumin, lysozyme, secretory IgA and bile-salt-stimulated lipase. Lactoferrin binds to iron, reducing the amount of iron available for pathogens, and thus has bacteriostatic effects. Alpha-lactalbumin has a good amino acid profile, making it suitable for promoting the growth of the gut microbiome. Lysozyme and secretory IgA both have important immune functions, while bile-salt-stimulated lipase aids in the digestion of milk lipids. Whey proteins are somewhat resistant to digestion by the baby's gut, so they can hang around and exert their goodness for a while.

Carbohydrates

The main carbohydrate in breast milk is lactose, but it isn't the only one. Other important carbohydrates include the human milk oligosaccharides (HMO), which consist of a large variety of oligosaccharides (3-10 monosaccharides) that are resistant to digestion. HMOs are prebiotic (support growth of the gut microbiome), inhibit virus and bacteria binding, and are a source of sialic acid, which supports brain development and cognition. At least one HMO is associated with reduced risk of necrotising enterocolitis.

Fats

Breast milk contains plenty of saturated and polyunsaturated long-chain fatty acids. The total fat content is independent of the maternal diet, but the fatty acid profile depends on maternal diet, so mothers should make sure to eat a diet with a good fatty acid profile. Fats are actively transported from the maternal blood through lactocytes in order to get to the milk.

The main saturated fatty acids in breast milk are palmitic and stearic acids, which are important energy sources. Around 60% of palmitic acid in human breast milk is esterified at the sn-2 position of glycerol, which is different to cow's milk and formula in which esterification occurs at sn-1 and sn-3. It is thought that the esterification in cow's milk and formula may increase calcium binding to palmitate, leading to hard stools in babies fed formula (as opposed to breast milk).

The main polyunsaturated fatty acids in breast milk include linoleic and linolenic acids (both essential fatty acids), decosahexanoic acid (DHA) and eicosapentanoic acid (EPA) (incorporated into cell membranes and are essential for retinal and brain development), and arachidonic acid. The optimal ω-6/ω-3 ratio is around 5.

Micronutrients

Breast milk contains a lot of micronutrients such as vitamins, iron and iodine. However, the concentrations of such nutrients depends on the mother's diet.

Prebiotics?

Breast milk contains bacteria that may be important for the gut health of the infant. This is still a growing area of research, so watch this space...

"Nutritional supplements" for infants

Unfortunately, not all mothers can breastfeed, for various reasons. As such, other possible "supplements" are being researched. Bovine colostrum has been shown to be beneficial in neonatal growth, digestive function and gut immunity, while bovine lactoferrin (which is 70% homologous with human lactoferrin) may reduce the risk of necrotising enterocolitis.

Formula

Formula is pretty much always the go-to for mothers who cannot breastfeed. All formulae have certain nutrients that are required by law. In addition, there are laws that state that no health claims can be made for formulae designed for infants (i.e. <12 months of age).

Introducing solids

Solids can be introduced at around 6 months, or even slightly earlier. It is important that the first foods given are rich in protein and iron, as these are the first nutrients to become deficient. Foods can be introduced in pretty much any order, at a rate that suits the infant. Once the child is older than 12 months, they can usually eat the same foods as the rest of the family.

Only one more content lecture left for the rest of semester (for PATH3304)! Almost there!

The Future of Infectious Diseases

Last post for MICR3350! This semester's been a wild ride!

We've come a long way in diagnosis and treatment of infectious diseases. Diseases that used to be major causes of death and disability are not as bad today, and one (smallpox) has been eradicated entirely (well, unless you count smallpox samples in labs). That being said, there's always room for improvement with regards to diagnosis, treatment, prevention and eradication.

Diagnosis

The quicker we diagnose something, the quicker we can give appropriate treatment. Therefore, we are always looking to find ways to diagnose diseases more rapidly.

Sepsis

Traditional diagnosis of sepsis ("a toxic inflammatory condition arising from the spread of bacteria or bacterial toxins from the focus of infection") relies on culture, which normally takes at least 24-48 hours. Possible rapid diagnostic tests that can be done instead include direct detection of biomarkers and point-of-care testing. Point-of-care testing might be done at a dedicated point-of-care lab that is closer than a central diagnostic lab, or it might be done at the bedside via a range of hand-held devices. For example, a portable "microscope" has been developed that sends light through a blood drop and can detect the interaction of light with blood components. Another possible device is the CD64 biochip which detects CD64 expression on neutrophils. The CD64 biochip can provide results after around 30 minutes.

Tuberculosis

Conventional TB diagnosis requires chest X-ray as well as sputum microscopy and culture. Since mycobacteria take a long time to grow, quicker tests, such as urine and breath tests, are being developed. Urine tests can be done to detect lipoarabinomannan (LAM), a component of the M. tuberculosis cell wall. These tests can give results in 25 minutes. Breath tests can look for metabolic products of M. tuberculosis, such as naphthalene derivatives, benzene and alkanes. Such breath tests can give results in six minutes- a far cry from the weeks required to culture M. tuberculosis!

Treatments

Unfortunately, not much has happened in the way of developing new antibiotics, despite new technologies for drug discovery, such as "iChips." One antibiotic that has been developed using the "iChip" is teixobactin, which was derived from soil microbes. Another relatively recent antibiotic is Baxdela, or delafloxacin, which is a fluoroquinolone.

Prevention

Public health campaigns and other preventative measures such as vaccines have helped to bring down the rate of infectious diseases. Unfortunately, there are many diseases that we don't have vaccines for yet, such as HIV/AIDS. HIV is highly mutable and very variable, making it difficult to produce a vaccine. There is also a lack of natural immunity to HIV that can be exploited with a vaccine. Other production issues for an HIV vaccine include a lack of an animal model, non-antigenicity of heat-killed HIV-1, and safety concerns with a live attenuated vaccine.

Eradication

As you most likely know, smallpox has been declared eradicated. Factors contributing towards smallpox eradication include an effective vaccine, good surveillance and the fact that humans are the only host. (If animals are also hosts, then you have to vaccinate all of the animals too, which can be tricky.) There are current global eradication programs for polio, malaria, Guinea worms and Yaws (caused by T. pallidum pertenue). Wild poliovirus type 2 has already been eradicated worldwide and type 3 hasn't been seen since 2012 (so it may be declared eradicated soon), but type 1 is still circulating in some countries, notably Pakistan, Nigeria and Afghanistan. The Democratic Republic of the Congo and Syria have also experienced outbreaks.

And that's it for MICR3350!! Good luck in the exam!

TB and HIV

Second last post for MICR3350!

Tuberculosis (TB)

TB has been around for a while (there are 5000-year-old mummies that have evidence of TB infection), but it wasn't always called TB. It used to be called phthisis pulmonalis or consumption, and may have been transmitted between animals and humans. The causative agent, M. tuberculosis, was first identified by Robert Koch, who was awarded the Nobel Prize in Physiology or Medicine for his discovery.

Presentation

M. tuberculosis is an aerobic, non-motile, rod-shaped bacterium. It has a unique cell wall structure, which makes it resistant to most typical stains, such as the Gram stain. The main defining feature of the M. tuberculosis cell wall is the presence of mycolic acids, which resist drying, acids, alcohol and lytic enzymes. M. tuberculosis cell walls also have a unique component called lipoarabinomannan (LAM), which has been investigated as a possible diagnostic sign.

The most common form of tuberculosis is pulmonary tuberculosis. Pulmonary TB is characterised by chronic cough, haemoptysis (coughing up blood), fever, night sweats, loss of appetite and weight loss. It can be diagnosed by the presence of "Ghon foci" in a lung X-ray, as well as granulomatous lesions and caseous necrosis (especially in active infection). Pulmonary TB can persist for months. Extra-pulmonary TB, which is more common in patients who are also HIV+, affects all organs and may cause meningitis and lymph node disease. "Potts Disease" is TB that affects the spine.

TB can be transmitted via respiratory droplet nuclei, which is why most infections are in the lungs. TB can grow within macrophages to evade the immune system, and from there it can spread via the blood to various organs of the body. Around 10% of infections will become symptomatic, but the remaining ~90% remain latent. It is estimated that around 1/3 of the world's population have latent TB. Only people with active TB can transmit the disease, and it is estimated that every active case results in around 10-15 transmissions per year.

Diagnosis

Specimens used for TB diagnosis include sputum and biopsy. Tests done include microscopy and culture, though culture of mycobacteria can take a long time. Therefore, molecular tests such as PCR and special blood tests such as the Quantiferon TB-Gold blood test (which detects cell-mediated immune response) are increasingly being used.

Treatment

Treatment of tuberculosis requires prolonged therapy (6 months or more). The first phase, the induction phase, lasts around 2 months. In this phase, patients are given rifampicin, isoniazid, pyrazinamide and sometimes ethambutol (if the organism is not sensitive to rifampicin and isoniazid). This cocktail of drugs results in a cure rate of over 90%. In the consolidation phase, which lasts for around 4 months, patients are given rifampicin and isoniazid. The consolidation phase may continue for over a year if patients present with meningitis.

Drug resistance

Unfotunately, TB is gaining resistance to many treatments. MDR-TB (multi-drug resistant TB) is resistant to at least rifampicin and isoniazid. XDR-TB (extensively drug resistant TB) is resistant to rifampicin, isoniazid, fluoroquinolones and at least one anti-TB injectable drug. Finally, XXDR-TB is totally drug resistant.

Human Immunodeficiency Virus (HIV)

HIV is a lentivirus of the retroviridae (retrovirus) family. As such, it is an RNA virus that uses reverse transcriptase to convert its genome into DNA and integrate into the host genome.

The two types of HIV are HIV-1 and HIV-2. HIV-1 is the most common cause, and is very similar to a chimpanzee retrovirus called SIVcpz. HIV-2 is much less common as it is less transmissible and less severe, and is largely confined to West Africa. It is similar to a virus in Sooty Mangabey monkeys called SIVsm. The most common forms of HIV transmission are sexual intercourse, intra-uterine, childbirth and sharing needles. Breastfeeding may also pose a risk, but there is still some controversy surrounding this.

As I have stated in other posts, HIV infects many cells, but particularly CD4+ cells, such as T-helper cells. CD4 falls by around 40-80 cells/μL per year, leading to impaired cell-mediated immunity and a higher risk of opportunistic infections. Opportunistic infections mainly appear when CD4+ cell count falls beneath 200 cells/μL, which normally happens around 6-10 years after diagnosis.

HIV is diagnosed primarily through detection of HIV antibodies or HIV p24 antigen via ELISA. These tests are then confirmed by a Western blot assay which has high specificity. The Western Blot used for HIV detects antibodies to all three major HIV gene products: gag, pol and env. Treatment response can be monitored by looking at CD4 count and at HIV RNA PCR. The goal for HIV RNA PCR is for an "undetectable viral load," or less than 40 copies/mL.

There are a range of treatments for HIV. These include NRTIs, NNRTIs, protease inhibitors, integrase inhibitors and entry inhibitors. However, I will not go into these drugs in further detail in this post.

TB and HIV

There is a profound interaction between TB and HIV. Over 25% of TB deaths are in patients who are HIV+, and around 80% of TB infections are co-infected with HIV. TB patients who are HIV+ have a 10% chance of TB reactivation every year, which is very different to HIV- patients who have a less than 5% risk of reactivation in their lifetime. HIV+ patients also have an increased risk of drug-resistant TB. Nevertheless, treatment for TB is the same in HIV+ and HIV- patients.

The Ins and Outs of Ethanol

Last post for PHYL3004! This post will discuss the favourite drug of many students worldwide- ethanol!

What factors govern absorption of ethanol into the blood stream?

Ethanol is quite water-soluble due to its -OH group. It is also fairly lipid-soluble due to its CH₃CH₂- group. As ethanol is a small, uncharged molecule, it is also able to cross cell membranes and have an effect on the various tissues of our body without requiring any kind of chemical modification.

Ethanol is absorbed into the circulation via passive diffusion. Most (~80%) is absorbed through the small intestine, whereas the remaining 20% is absorbed in the stomach wall. As such, factors governing ethanol absorption are the same as factors governing diffusion in general: concentration gradient, permeability, and surface area. Most ethanol is absorbed in the intestines because the intestines have a much larger surface area than the stomach.

You've probably heard the advice to "never drink on an empty stomach." But why is this? Ethanol is absorbed more slowly after eating. This is because the presence of food in the stomach delays gastric emptying, allowing ethanol to remain in the stomach longer, where it is absorbed at a slower rate. The slower rate of ethanol absorption allows the body more time to metabolise any ethanol that has already been absorbed, which also reduces the peak of blood alcohol concentration.

The distribution of ethanol into various tissues depends on the relative water content of the tissue. Ethanol is both water- and lipid-soluble, as I said earlier, but it is more water-soluble than lipid-soluble. Therefore, it is highly soluble in the blood but has low solubility in fats. Females tend to have a reduced body water compared to males due to increased fat mass and decreased muscle mass (muscle cells have more water than fat cells). Therefore, blood alcohol concentration increases more for females than for males, which is why females are recommended to have fewer drinks than males. Similarly, other populations with reduced muscle mass (e.g. elderly) may also be more susceptible to the effects of alcohol.

What are the determinants of peak blood alcohol concentration?

Blood alcohol concentration is, well, the concentration of alcohol in the blood. It is usually given as a percentage. The legal driving limit in Australia is 0.05%, or 0.05g per 100mL of blood.

I've already hinted at a couple of determinants of peak blood alcohol concentration: stomach fullness and the proportion of fat and muscle. The obvious other determinant of blood alcohol concentration is the number of standard drinks consumed. 1 standard drink is equivalent of 10g of pure alcohol.

Why is the brain susceptible to the effects of ethanol (beginning with the blood-brain barrier)?

Before ethanol gets anywhere near the central nervous system, it already has effects on sensory nerves. Remember how capsaicin stimulates the sensation of heat? Ethanol works through the same pathway, stimulating TRPV1 receptors (i.e. vallinoid receptors, the same receptors stimulated by capsaicin).

Ethanol can cross the blood-brain barrier as it is a small, uncharged molecule. Once in the brain, it causes inhibition by enhancing the activation of inhibitory GABA_A receptors and suppressing the activation of excitatory glutamate receptors. Alcoholics have an adaptive response in which their brain increases its level of excitation. During withdrawal, these compensatory excitatory effects persist long after inhibition by alcohol has ceased, causing withdrawal symptoms.

How is ethanol removed from the body?

Ethanol is not stored- it just hangs around until it gets removed. Most of this removal (~90%) is via metabolism, most of which occurs in the liver. In the liver, alcohol is converted into acetaldehyde by alcohol dehydrogenase (ADH), and acetaldehyde is then converted into acetate via aldehyde dehydrogenase (ALDH). Both of these reactions require NAD+ as a cofactor. As ADH is also expressed in the stomach, a small amount of ethanol is metabolised in the stomach before absorption, reducing the total amount of ethanol absorbed. Interestingly enough, the efficacy of ADH is reduced in alcoholics.

The remaining ~10% of ethanol is excreted unchanged in the urine, breath or sweat. The concentration of ethanol in the blood is the same as in the urine. Urinary clearance is only around 1mL/min, so it's a good thing that we have so many other mechanisms to get rid of alcohol.

Removal of alcohol via the breath is quite unique. While oxygen and carbon dioxide enter the alveoli via the pulmonary circulation, ethanol actually diffuses across the airways from the bronchial circulation. We know this because a graph of breath ethanol concentration shows an exhalation pattern more similar to airway gas exchange than alveolar gas exchange. In alveolar gas exchange, there is an initial plateau (dead space air), a steep increase in concentration (due to transition from dead space air to alveolar air) and a final plateau (alveolar air). In airway gas exchange, like in ethanol, the initial plateau is absent, the steep increase represents the conducting airways, and the plateau phase represents alveolar air that has been modified in the exchange zone. Furthermore, the location of gas exchange appears to depend on the liquid to gas partition ratio, or λ. The blood and water solubility for ethanol (which is exchanged in the airways) is far greater than for oxygen or carbon dioxide (which are absorbed in the alveoli).

In airway exchange of ethanol, ethanol first moves into the airway surface liquid that lines the airways and humidifies inspired gas. Ethanol then moves down the airways during inspiration (as this means that it is moving down its concentration gradient). Movement of ethanol down the airways causes saturation of alveolar air with ethanol, so there is no concentration gradient in the alveoli. Therefore, there is no alveolar exchange of ethanol.

And I think that's it! Good luck in exams!

Problems with Gene Therapy

Final lecture before the test! This lecture was super light on content- most of the slides (and there were only 14) included a bunch of ethical questions to think about as well as links to other associations for students who want more information. I'm just going to deal with the content part, so this will be a short blog post.

Factors that have slowed gene therapy development

Despite decades of research into gene therapies, several factors have hindered development of actual treatments. For starters, most corrections are only short-lived, particularly when whole-cell transplantation is used as the cells may be attacked by the immune system. Therefore, multiple doses are normally needed, which might be difficult due to said immune response. Delivery to cells can also be problematic as you need a vector that can accommodate the desired gene and deliver it to its target. Furthermore, most target cells are somatic, non-dividing cells, so the correction won't be propagated. Finally, many diseases involve multiple genes, and possibly a combination of genes and environmental factors, making it difficult to design a gene therapy.

Since I just mentioned vectors, I'll go into vectors in a bit more detail. As mentioned here, the main vectors used are adenoviruses, AAVs, HSV and retroviruses. All of these (except for AAVs) can provoke immune responses. Retroviruses can be particularly problematic as they randomly integrate into the genome (unlike AAVs which always integrate into chromosome 19), which may interrupt a normally functioning gene.

New developments that are helping gene therapy

Of course, it's not all gloom and doom. Several strategies are being used to help the development of gene therapy. For example, as mentioned here, siRNAs, exon skipping, and CRISPR-Cas9 have all been explored for their potential to alter gene expression. Another factor helping gene therapy development is improved liposomal targeting of the brain, which may help treat Parkinson's and Alzheimer's. Yet another new development is Chimeric Antigen Receptor (CAR) T-cell therapy, in which T-cells are isolated from the patient, engineered to express chimeric antigen receptors (CARs) that recognise cancer cells, and reinfused into the patient.

Not many gene therapy drugs have made it through to market, but here's a few that have:

1. Glybera was the first drug to make it to market (in 2012). It is a treatment for lipoprotein lipase (LPL) deficiency, and consists of a human LPL gene delivered by an AAV1 viral vector.
2. Kymriah is a CAR drug used to treat acute lymphoblastic leukaemia (ALL).
3. Yescarta is another CAR drug used to treat large B-cell leukaemia.

Gene Therapy and Immunocontraception

This lecture was pretty interesting! Probably my favourite lecture from this unit :D

Why immunocontraception?

Immunocontraception has been proposed as a potential solution to dealing with pests. For example, mouse plagues are a problem in grain-growing regions of Australia. In the past, they used to be dealt with using a poison called strychnine, but the use of strychnine has since been banned due to the risk of contamination. Currently mouse populations are monitored by using canola cards (the more chewed up the card, the bigger the problem you have), and controlled by using zinc phosphide and bromodiolone. In the USA, wild horse populations are problematic, and control measures may be needed.

Autoimmunity and infertility

Studies have shown that antibodies against the zona pellucida (ZP) are associated with infertility. The zona pellucida is a glycoprotein layer that surrounds the oocyte, providing protection from polyspermy. In mice, the zona pellucida is formed from three genes: ZP1, ZP2 and ZP3. ZP1 is associated with structural integrity, and loss of structural integrity occurs if ZP1 is knocked out. ZP2 and ZP3 alternate to form chains that make up the bulk of the zona pellucida. If ZP2 is knocked out, the early ZP is thin, and later on it is absent entirely. If ZP3 is knocked out, the ZP fails to form. In both ZP2 and ZP3 knockout, infertility results.

Studies have shown that ZP3 from a different species can be used as an "infertility vaccine" for large animals that can be vaccinated individually, such as horses. (It's a tad harder to vaccinate individual mice during a mouse plague). To address this problem, virally vectored immunocontraception was explored instead. The idea behind this process is that the DNA encoding reproductive proteins can be inserted into a virus, which can then be used to infect mice. When mice develop an immune response against the virus, they will also develop an immune response against the protein.

rMCMV-mZP3

Many immunocontraception studies examined the use of ZP3 as an antigen. This is because monoclonal antibodies to ZP3 have been shown to prevent oocyte fertilisation (both in vivo and in vitro), and immunisation with ZP3 peptide conjugated to Keyhole limpet haemocyanin also causes infertility. The vector used was MCMV (mouse cytomegalovirus), as it has a large genome (~235kb), is a natural pathogen of mice in Australia, and mice can be infected by multiple strains. It is also a persistent, latent infection, so it'll hang around for a while. MCMV containing ZP3 DNA is also known as rMCMV-mZP3.

rMCMV-mZP3 was found to induce infertility over the long term. By day 7, degradation of the zona pellucida was evident, by day 21, primary follicles had decreased, secondary follicle morphology was abnormal and tertiary follicles were absent, and by day 100, primary and secondary follicles were markedly reduced, there were no tertiary follicles, and there were evident changes to the histology of the ovary. Gap junctions between the zona pellucida and ovary also failed to form. Induced antibody titre was found to increase the effect of infertility. Furthermore, mice who could not produce antibodies were not rendered infertile by this method.

Unfortunately, viral growth using rMCMV-mZP3 was very poor. One possible explanation is that expression of the foreign antigen led to an increased immune response from the mouse, resulting in poor viral growth. Because viral growth was poor in the saliva, mice did not spread this virus by biting each other (which is how MCMV is usually spread). Therefore, this method of immunocontraception was unable to provide widespread contraception of mice.

Another thing that was learned from this study is that the viral vector used is important. Mice who have innate resistance to the viral vector have a reduced response. The Cmv1 locus appears to be important in MCMV resistance. BALB/c mice have a more profound response to rMCMV-mZP3 as compared to C57BL/6, which have a more "resistant" allele on the Cmv1 locus. However, when C57BL/6 mice were given the G4 (Geraldton) strain of MCMV, which they were not resistant to, they had a strong response to the immunocontraceptive therapy.

Only one more lecture to cover before the test tomorrow!

Infections in the Immunocompromised

Recap the basics of the immune system

I took an entire unit on immunology last year, so you can read all about the immune system here. Otherwise, read on for the tl;dr version.

The main types of immunity are innate and adaptive immunity. Innate immunity includes anatomical barriers such as skin, the complement system, normal flora and cells such as NK cells, monocytes and neutrophils. Adaptive immunity is more specific, but needs to be primed by a previous encounter by that pathogen. Adaptive cells include the antibody-producing B-cells, as well as T-cells. T-cells come in two main flavours: the helper variety (CD4+), which mediate immune responses, and the cytotoxic variety (CD8+), which induce death of cells that have been infected by viruses.

T-helper cells can be further divided into different kinds of T-cells. In this post, we will only be looking at Th1 and Th2 cells. Th1 cells respond mainly to intracellular pathogens and viruses, and are characterised by IFNγ production. They activate macrophages and induce B-cells to make opsonising and complement-fixing antibodies, leading to "cell-mediated immunity." Th2 cells, on the other hand, respond to extracellular antigens. They are characterised by IL-4 release and activate B-cells, which make neutralising antibodies, leading to "humoral immunity."

Describe what happens when a patient’s immune system is compromised

If your immune system is compromised, you get sick more often (duh). The types of pathogens that you are more likely to get depends on the component of your immune system that is defective. If neutrophils are defective, you are more likely to get staphs, streps and some fungi such as Candida, if you have globulin defects, you are more likely to get encapsulated bacteria and Giardia, and if your skin is broken in some way (e.g. IV lines, catheters etc.) you are more likely to get S. aureus, S. pyogenes, Candida, and so on. Some immune defects, like a defect in cell-mediated immunity, predisposes you to infection from a range of different organisms.

Infections in the cancer patient (aka febrile neutropenia)

Neutropenia, a deficiency in neutrophils, may occur as a result of chemotherapy. Neutropenia can be mild (1000-1500 cells/μL), moderate (500-1000 cells/μL) or severe (less than 500 cells/μL). If a patient with severe neutropenia has a temperature of greater than 38.3°C, or a temperature of greater than 38°C for over an hour, they are considered to have neutropenic fever. Risk factors for neutropenic fever include severity and duration of neutropenia, cancer not in remission and mucositis (a side-effect of chemotherapy). Neutropenic fever, particularly neutropenic sepsis, is considered to be a medical emergency as infection can progress very quickly. Prompt empiric antibiotics are usually given as there is roughly 10% mortality per hour delay in antibiotic therapy.

Antibiotic therapy needs to be relatively broad-spectrum as a large proportion of patients (~1/2) will not have a pathogen identified. The most common bacteria in neutropenic fever are Gram-positive organisms such as S. aureus and S. epidermidis, but Gram-negative bacteria used to be more common. The pathogen associated with the highest rate of mortality is Pseudomonas, so antibiotic therapy must include cover for Pseudomonas. A commonly-used antibiotic for this purpose is Pipericillin-Tazobactam (tazocin).

If fever persists despite antibiotic therapy, other causative agents, such as fungi, should be considered. The main candidate is Candida, as risk factors for candidaemia include severe neutropenia, use of broad-spectrum antibiotics and mucocutaneous damage. Other common fungi include moulds such as Aspergillus, Fusarium and Zygomycetes, which are particularly prevalent following bone marrow transplant. These moulds usually cause pulmonary infections, but may also cause CNS or skin infections.

To diagnose the causative agent of neutropenic fever, blood cultures are usually done. Cultures are done from peripheral blood as well as from ports of IV catheters. Sputum, urine and other targeted samples may also be used. Chest X-rays and CT scans might be used to check for other signs of illness.

Neutropenic infection can be prevented in several different ways. Firstly, patients should be placed in a positive pressure room, free of flowers that might carry spores. A modified diet should be given, and prophylactic drugs may also be given if deemed necessary.

Infections in transplant patients

See previous post: Allograft-Transmissible Infections

Infections in splenectomy patients (sepsis)

The spleen is important for a variety of immune functions, including being the site of maturation of IgM memory B-cells, sequestering opsonised encapsulated bacteria, and modulating the effects of cytokines. Hence, removal of the spleen predisposes to a variety of infections, particularly by encapsulated bacteria such as S. pneumoniae, N. meningitidis and H. influenzae. Roughly 5% of splenectomy patients will experience an overwhelming post-splenectomy infection (OPSI) at some point, usually caused by S. pneumoniae. The greatest risk for OPSI is in the 6 months following splenectomy. Most deaths from OPSI occur within the first 24 hours of becoming unwell. OPSI can be treated with vaccination, lifelong antibiotics and extra emergency antibiotics.

The effects of acquired immune deficiency after infection by HIV

Since CD4+ cells are targeted by HIV, HIV severely weakens the immune system. Therefore, HIV/AIDS patients are at risk of many opportunistic infections. As their immune system gets weaker (CD4+ cell count decreases), they become at risk of a greater variety of infections. Here's a quick list of some opportunistic infections seen in HIV/AIDS patients:

• Kaposi's sarcoma: Related to Human Herpes Virus 8 (HHV8). It forms lesions on the skin. If untreated, it affects all organs except for the brain.
• Cytomegalovirus (CMV/HHV5): Many adults are seropositive for CMV (a.k.a. HHV5), but it is only reactivated when CD4 cell counts fall below 100. CMV may manifest as CMV retinitis in HIV/AIDS patients.
• Cryptosporidium parvum: Cryptosporidium is a protozoan that can cause acute and chronic diarrhoea. It can be life-threatening in HIV patients.
• Pneumocystis jirovecii pneumonia: Caused by a fungus. Common opportunistic infection in HIV/AIDS patients.
• Tuberculosis: Many HIV patients are co-infected with TB. TB is becoming more drug-resistant, which is a problem.
• Cryptococcus neoformans meningitis: Cryptococcus is a yeast-like fungus that can cause meningitis when CD4 counts fall below 100.
• Toxoplasma gondii cerebral toxoplasmosis: Toxoplasma is a protozoan spread in cat faeces and meat. It can cause cysts that are dormant in the brain, but are activated when CD4 counts fall below 100.

Emerging Infectious Diseases

The slides for this lecture aren't actually online yet, so I'm just going to make do with my own shitty notes. Hold on tight...

Influenza

Influenza is often seen as a common, relatively mild illness, but it has also been responsible for some major pandemics around the world. The only type of influenza responsible for pandemics is influenza A, as it can skip species and mutate in order to evade immunity from the population as a whole. Migrating birds are common vectors for influenza, as are pigs, as they have receptors for both bird and human influenza. The main types of mutations include reassortment, where packets of nucleic acid are swapped between human and animal viruses, and adaptation, in which enough mutations occur within the virus for it to be unrecognisable by human immune systems. The 1918 Spanish Flu was a result of viral adaptation.

Most influenza deaths are in the young and in the elderly. However, there are some exceptions. In 1918, there were also a lot of deaths in young adults, possibly because people of this age group were exposed to poor conditions when fighting in the war. In the 2009 swine flu pandemic, there was a peak in the 40-60-year-old age group, but the elderly were not too badly affected. It has been speculated that this is because the swine flu was similar enough to some earlier strains circulating between 1918 and 1957 for the elderly to have immunity.

The most likely candidates for future pandemics are H5N1, H7N9 and H3N2. H5N1 is mainly spread by bird migration and transport, whereas H7N9 is associated with contact with songbirds. H7N9 is mostly confined to China. It has evolved in southern China to produce a strain that is more pathogenic in birds, but it remains to be seen exactly how pathogenic this strain is in humans.

Coronaviruses

SARS

SARS is a bat virus that obtained a mutation that increased its human transmission. Bats can pass on SARS to civic cats, which in turn can pass it on to us. Thankfully, SARS is not that great at human transmission, requiring close contact for its spread. Furthermore, it is most infectious during the second week when patients are showing symptoms. As such, SARS can be readily controlled by quarantine and hygiene.

MERS

MERS, or Middle Eastern Respiratory Syndrome, may also originate from bats. Camels are the intermediate host for this virus. As you might expect from the name, most cases of MERS are in the Middle East, particularly in people with close contact with camels.

Exotic arboviruses

The good thing about arboviruses, or insect-borne viruses, is that you need that particular insect in order for the disease to spread. As such, controlling mosquito breeding can be very helpful in stopping the spread of the disease. The bad thing is that we have some of these mosquitoes in Australia: Aedes aegypti is found in northern Queensland, and Aedes albopictus is found in the Torres Strait Islands. Outbreaks of Dengue fever have occurred in northern Queensland due to the presence of Aedes aegypti.

Zika virus

Zika virus is primarily transmitted by Aedes aegypti and Aedes albopictus. Zika used to cycle between apes and these mosquitoes, but now it cycles between humans and mosquitoes. Zika can also be transmitted from human-to-human, either transplacentally, sexually or via blood transfusion. The incubation period of Zika virus is around 2 weeks, after which mild symptoms such as headache, fever and rash usually occur. Even though Zika is normally mild, it can have disastrous neurological and fetal complications. In congenital Zika syndrome, there is microcephaly (small brain due to tissue destruction), retinal damage and musculoskeletal problems.

Chikungunya

Chikungunya fever has symptoms similar to Ross River Virus, such as aches, headaches and fever. It is mainly transmitted by Aedes aegypti, but there have been some mutations that allow it to be transmitted by Aedes albopictus as well.

Nipah virus

Nipah virus originates from bats, but can be passed on to pigs and then to humans. It was originally found in Singapore and Malaysia, but there have also been outbreaks in Bangladesh and India. Symptoms include encephalitis and pneumonia, which are obviously pretty nasty, but as Nipah virus has limited person-to-person transmission, you're likely to be safe if you avoid bats.

Other viruses

Other viruses that were mentioned during the lecture include Lassa virus (from rodents), Ebola and Marburg viruses (from bats) and Congo-Crimean haemorrhagic fever (CCHF). However, the lecturer didn't go into much more detail, so that's pretty much all I'm going to say about them.

Nutrition in Pregnancy and Lactation

Second last post for PHYL3003! Hooray!

Understand the effects of maternal under- and over-nutrition on pregnancy outcomes and long-term health of the offspring

Not too many details were provided here, other than that mothers with a high BMI are more likely to give birth to very large babies, which may increase the risk of complications during delivery. Macrosomia is the term given to a birth weight above 4.5kg, and babies with macrosomia are more likely to develop metabolic syndrome later in life. On the other hand, if mothers do not gain enough weight during pregnancy, there is increased risk of low birth weight and pre-term birth.

Risk factors for inadequate fetal nutrition are age (adolescents are more likely to smoke and are more likely to have iron deficiency), multiple births (twins, triplets etc.), nausea and vomiting during pregnancy, short intervals between pregnancies, and so on. It should also be noted, however, that it is generally not necessary to consume excessive amounts of food during pregnancy as pregnancy tends to improve the efficiency of fat and energy storage.

Describe the changes in glucose metabolism in pregnancy and relevance to maternal & foetal health

Pregnancy is considered to be a state of natural insulin resistance, as insulin sensitivity usually decreases by around half over the course of pregnancy. Placenta-derived TNFα increases circulating free fatty acids and alters phosphorylation of the insulin receptor, decreasing GLUT4 expression and mobilisation (and thus decreasing glucose uptake).

If the mother began with normal insulin sensitivity, chances are that she won't be too badly affected by the decrease in insulin sensitivity. However, mothers who initially had suboptimal insulin sensitivity are at risk of developing gestational diabetes mellitus (GDM). Other risk factors for GDM include a high BMI and excessive gestational weight gain (EGWG) in the firs half of pregnancy.

Discuss physiological adaptations in maternal calcium and iron metabolism in pregnancy and lactation

Calcium

Over the course of pregnancy, around 30g of calcium goes towards fetal skeleton mineralisation (around 2-3 mg/day in the first trimester up to around 250-300mg/day in the third trimester). Nevertheless, dietary requirements remain the same throughout pregnancy and lactation. During pregnancy, total calcium decreases, but ionised calcium remains normal. Calcitriol (vitamin D3) and calcitonin tend to increase during pregnancy, but return to normal afterwards. PTH usually stays the same, but it may decrease if calcium levels are insufficient. In general, calcium requirements are met during pregnancy due to an increased absorption of calcium (due to increased calcitriol), whereas during lactation, the main method of increasing calcium is increased bone resorption.

Iron

Requirements for iron increase significantly during the second and third trimesters, but drop back to normal right after birth. Iron deficiency anaemia is relatively common, and risk factors include being vegetarian or vegan, heavy periods before pregnancy, obesity, and excessive gestational weight gain. Since half of the offspring's iron needs are supplied during gestation, and insufficient iron impairs neurodevelopment, it is important that enough iron is absorbed.

Iron uptake changes during pregnancy due to regulation of hepcidin (discussed here). After around 20 weeks, hepcidin transcription decreases, increasing iron absorption. Hepcidin returns to normal after giving birth. Inflammatory conditions such as preeclampsia, malaria and obesity may increase hepcidin, decreasing iron absorption.

Identify fortification and supplementation strategies to achieve adequate nutrition in pregnancy

Two of the main nutrients that are routinely supplemented during pregnancy are iodine and folate. Insufficient iodine can cause cretinism, so to prevent this many foods are fortified with iodine, and supplementation of 150μg/day is recommended from pre-pregnancy through to lactation. Folate, which is important for neural tube formation, is also routinely supplemented. Usually at least 400μg/day is given for at least one month prior to conception, as well as the first twelve weeks of pregnancy. Patients with an increased risk of neural tube defects and/or folate deficiency may be given more folate. Just like with iodine, many foods are fortified with folate.

Nutrition for Exercise

This lecture was kind of interesting as it explained the nutrient requirements for endurance athletes. (If you're a bodybuilder, some of this stuff might still apply, but maybe not. I don't know. Go ask an actual dietitian if you want proper advice.)

The first few slides were about energy balance, so you might want to review that if you live under a rock and have never heard of it before.

Effects of exercise on energy intake

Does exercise make you eat more? And if so, is exercise really worth it? The answers are yes and yes. In the short-term, exercise does cause a small increase in energy intake, but this is offset by the energy expenditure during exercise, so exercise is worth it. Furthermore, people who exercise regularly have been found to be better at regulating their appetite. Exercise also increases basal metabolic rate and decreases R-value, which means that more fat is burned. (A low R-value means that more fat is burned, whereas a high R-value means that more carbohydrates are burned.)

Athlete nutrition

In this post, we'll be focusing more on endurance athletes, though the requirements will probably change for bodybuilders and other types of athletes. Endurance athletes tend to have a much larger overall energy intake than us plebs, and a larger percentage of their daily energy intake is made up of carbohydrates (around 70% as compared to the usual 50-55%). This is because, as stated here, muscle glycogen is the limiting factor in how long we can exercise for.

Now for a couple of notes about protein, as protein is a nutrient of interest for many aspiring to get buff. Our general requirements are 0.8g/kg of body mass, but this can increase to 1.6g/kg in certain athletes (e.g. bodybuilders). Many athletes do consume protein powders, but if you already have adequate protein intake, protein powders provide little benefit. Furthermore, excessive protein may increase the risk of osteoporosis, colonic cancers and impaired kidney function in the long-term. However, it has been suggested that consuming a protein and a high GI snack immediately after a workout might increase the production of naturally-occurring anabolic hormones, increasing dem gainzzzzzzzzzzz. :D :D :D

For the rest of this section, I'm going to write about nutrient needs for an endurance athlete participating in a lengthy competition (>1hr). Some of this may also be applicable to shorter events. However, as I said above, if you want to know what's necessary for your specific needs, you should speak to a professional.

Pre-workout

As mentioned here, many endurance athletes participate in "carb loading" during the few days leading up to a competition. "Carb loading" involves consuming a lot of carbohydrates (10-12g/kg) while reducing your training load. If done correctly, the result is nearly doubled levels of carbohydrates.

Roughly 3-4 hours before a competition, a pre-competition meal may be consumed. This pre-competition meal is high in carbohydrates while low in fat and protein. Plenty of fluid is also consumed. Depending on the person, a liquid meal may be consumed (especially if they have a tendency to throw up during events).

Roughly 30-60 minutes before a competition, a pre-competition snack may be consumed. This snack tends to be in liquid form to prevent nausea. The foods consumed for this snack are low to medium GI foods in order to prevent rebound hypoglycaemia. In rebound hypoglycaemia, a large spike in insulin causes glucose levels to decrease rapidly, which is usually pretty great, but not if you're about to start exercising and consuming carbohydrates.

During the event

Yes, food is consumed during the event (at least in events longer than an hour). Generally athletes aim for around 30-60g/hr of carbohydrates, as well as 400-800mL/hr (100-200mL/15min) of fluid. Combining carbohydrates with fluid can be beneficial, but the percentage of carbohydrates should remain within 6-8% for optimal absorption. Cold and flavoured fluids containing electrolytes are desirable as these qualities encourage athletes to drink more and stay hydrated. Moderate to high GI carbohydrates are preferable as they result in faster release of glucose into the bloodstream.

Recovery

Post-exercise, high GI foods are consumed to accelerate glycogen replenishment. This may be followed up with low- or mid-GI foods. Plenty of fluid is also consumed, with an aim to consume 1.5x the amount of fluid lost.

Nutritional aids

There are many nutritional aids that people use but for the purposes of this post I will only focus on three: caffeine, beetroot juice and the mouth-rinsing technique.

Caffeine

Caffeine, as you probably know, improves arousal, reaction time, and so on. Caffeine increases free fatty acid metabolism, which may help preserve muscle glycogen. However, caffeine can also result in dehydration, restlessness, and so on. Also, for competition purposes, a really concentrated form of caffeine needs to be given, such as caffeine tablets.

Beetroot juice

Beetroot juice is rich in nitrates, which can increase vasodilation and muscle blood flow.

Mouth-rinsing

There is some evidence to suggest that simply rinsing the mouth with carbohydrates without actually swallowing them can stimulate carbohydrate receptors in the oral cavity, which results in the activation of performance-enhancing signalling pathways.

Obesity and the Respiratory System

Last week of PHYL3004 content! That went by quickly...

In this post, we will be talking about the effect of body fat on obesity. In particular, we will be talking about subcutaneous fat. (Visceral or intra-abdominal fat presents its own problems, as mentioned here.) Body fat distribution varies a bit between males and females- males tend to have more belly fat ("apple shape"), whereas women tend to have more fat around the hips ("pear shape"). Since fat adds mechanical load to the respiratory system, opposing the contraction of respiratory muscles, it is important to know how and why obesity impacts the respiratory system.

Before continuing further, it might help to brush up on mechanics of breathing and lung volumes if you don't remember from previous semesters.

Effect of obesity on lung volumes

In obesity, TLC (total lung capacity) decreases. Most of this decrease occurs in FRC (functional residual capacity), particularly in ERV (expiratory reserve volume).

Mechanism(s) for reduced respiratory system compliance and respiratory muscle function

In obesity, lung and chest compliance decrease for several reasons. Fat directly decreases compliance, and increased pulmonary blood flow, which is associated with high BMI, also decreases compliance. As such, lung function changes in obesity are similar to those in restrictive lung diseases, where compliance is reduced. FVC (forced vital capacity) and FEV1 (forced expiratory volume in 1 second) both decrease in both obesity and restrictive disease. However, in obesity, the FEV1/FVC ratio usually remains unchanged, whereas this ratio may increase in restrictive disease (as FVC may decrease to a greater extent than FEV1).

Respiratory muscles, such as the diaphragm, can be negatively impacted by obesity. A large abdominal mass will push the diaphragm upwards, stretching it in the process. If the diaphragm is stretched beyond its optimum length, force will decrease (I've discussed why here).

Interrelationship between obesity, lung volume, airway resistance and airway hyperresponsiveness

Obesity tends to decrease lung volume (as discussed earlier) and thus decrease the total radius of the airways. Since resistance is inversely proportional to airway radius, a decrease in radius causes an increase in airway resistance, which in turn increases difficulty in breathing, particularly during exercise. As such, tidal volume may fall in extremely obese individuals (though it generally remains unchanged).

Low lung volumes have many more negative effects. Breathing at low lung volumes causes alveoli to collapse. This is known as "atelectasis." According to the LaPlace equation (pressure = (2*tension)/(radius)), reducing the alveolar radius increases pressure and tendency to collapse.

Yet another negative impact of low lung volumes is that when lung volume is low, the amount of load placed on airway smooth muscle is also low. As decreased afterload increases shortening (see here), muscle force is more likely to become greater than the opposing load, resulting in narrowing. (If muscle force was smaller than opposing load, bronchodilation woudl result instead.) This phenomenon is also referred to as "airway hyperresponsiveness," and can be quantified using PC20 (see here). Weight loss has been shown to improve PC20.

Changes in upper airway function in obese subjects and the association with obstructive sleep apnoea

The pharynx is more prone to collapse in patients with high BMI. The pharynx, which is quite floppy compared to the nasal cavity (which is surrounded by bone) and the trachea (which is surrounded by cartilage), is supported by the genioglossus muscle (tongue) and other pharyngeal muscles. These muscles provide dilatory pressure that keeps the pharynx open, opposing negative luminal pressures and positive tissue pressures. In obesity, the tissue pressure increases, making it more likely that the pharynx will collapse. The luminal pressure that causes pharyngeal collapse is known as the Pcrit, or critical closing pressure. A lower Pcrit is better.

Pharyngeal muscles are mainly driven by reflexes. These muscles respond to negative luminal pressures (i.e. pressures that pull the lumen in), rising carbon dioxide and falling oxygen levels. Their activity is reduced during sleep, which is why obstructive sleep apnoea can be a problem in some patients, particularly in obese patients. Patients with obstructive sleep apnoea may be helped with CPAP machines, which maintain high airway pressure. Unfortunately, they are also uncomfortable to use.

The decreased lung volumes in obesity can also impact the pharynx. When lung volume decreases, tracheal tension, which is the tension of the trachea pulling on the pharynx, also decreases. As such, the compliance and tendency to collapse of the pharynx also increase.

Only one more lecture to go for this unit!

Circadian Rhythms: Adaptations to Pregnancy and Disruption by Obesity

I've already spoken about circadian rhythms here, but time to go into more detail I guess...

Control of circadian rhythms

The main "clock" involved in circadian rhythms is in the suprachiasmatic nucleus (SCN) in the anterior hypothalamus. This SCN clock is entrained by "zeitgebers," which I'm pretty sure is German for "timers" or literally "time-givers." These zeitgebers are mainly environmental cues, such as light, food and temperature. Zeitgebers induce changes in molecular clock genes, such as Bmal1 and Clock.

Just like all other genes, Bmal1 and Clock are transcribed in the nucleus and translated in the cytoplasm. In the cytoplasm, they dimerise and then return to the nucleus, where they induce transcription of Per and Cry genes. After translation in the cytoplasm, Per and Cry also dimerise, and return to the nucleus where they downregulate Bmal1 and Clock. As such, Bmal1/Clock genes tend to peak when Per/Cry is at a minimum, and vice versa. Bmal1/Clock heterodimers can also activate accessory clock genes, such as Rev-erbα and Rorα. Rev-erbα can inhibit Bmal1, whereas Rorα can stimulate Bmal1 and Clock. All of these clock genes have further effects on clock-controlled genes that are found all over the body.

Clock genes are important in metabolic homeostasis. If Clock is deleted, hyperphagia and metabolic syndrome results. Deletion of Bmal1 results in altered carbohydrate metabolism and, as mentioned here, extreme weight loss. Deletion of Cry1 and Cry2 can result in an inflammatory phenotype. Food intake can also affect clock gene expression: for example, Bmal1, Clock and Per2 have all been shown to decrease with a high-fat diet.

Maternal adaptations to pregnancy

There are many changes that occur during pregnancy, mostly due to the endocrine placenta. In the first phase of pregnancy, a lot of anabolism occurs in order to store nutrients for later use. In the second phase, a lot of catabolism occurs in order to supply the fetus with nutrients. Since we know that clock genes are important in metabolism, the next step is to see whether or not circadian rhythms are important in the metabolic changes during pregnancy. Most experiments have been done in rats, using cosinor analysis (kind of like a linear regression but with the cosine function rather than a straight line). The attributes that experimenters look for are the mesor (average over the cycle) and amplitude (distance from the mesor to the base or peak of the curve).

Studies in rats have shown that body temperature circadian rhythm appears to be somewhat disrupted during pregnancy (though our lecturer didn't really explain how...) and decreases over the course of pregnancy. On the other hand, circadian rhythms of glucocorticoids are maintained, but absolute levels are increased (as mentioned here, glucocorticoids are important for fetal organ maturation). Gene expression in maternal livers and adipose tissue are also altered: in early pregnancy, maternal liver Bmal1 and Per1 increase in both mesor and amplitude. At the same time, adipose Bmal1, Per1, Per2 and Rev-erbα decrease in mesor, and Bmal1 and Rev-erbα also decrease in amplitude.

Since shift workers have been found to have an increased risk of preterm birth, low birthweight and spontaneous abortion, rat studies have also looked at how disruptions to the circadian rhythm can affect pregnancy. Sure enough, corticosterone, glucose, insulin, leptin, free fatty acids, triglycerides and cholesterol have all been found to be disrupted by disrupting the circadian rhythms of rats. The maternal liver has been found to have disrupted Bmal1 and Per1 expression, while the fetal liver has been shown to have disrupted Per2 and Rev-erbα expression. The offspring were also found to have an increase in weight gain and possible insulin resistance.

Obesity

Roughly 50% of women in the USA enter pregnancy either overweight or obese, which is a real problem as obesity is associated with gestational diabetes, preeclampsia (hypertension and proteinuria), miscarriage and abnormal birth weight. Studies in rats have shown that inducing obesity with a poor diet can alter clock gene expression, which in turn can alter metabolism. Altering metabolism may in turn affect fetal growth, as detailed here. In rats fed a poor diet, the mesor and amplitude of clock genes decreased. There was also a phase advance (left shift in the graph) in hepatic clock gene expression.

Molecular Therapies for Neuromuscular Disorders

Introduction

Most of the introduction basically went over the basics of gene expression and types of mutations, which I've also written about here. Also alternative splicing is important because the exons that get included in the final product can determine the function of the protein made. This post will focus mainly on interventions that target splicing.

Here are some examples of diseases caused by mutations:

• Huntington's disease is caused by "unstable repeats" of CAG. CAG codes for glutamine, so this mutation is also known as poly-Q. It is normal to have fewer than 36 CAG repeats. People with more than 40 are affected, and those in between might have issues and are more likely to pass Huntington's on to their children. Because these repeats are unstable, disease onset is earlier and more severe with each generation.
• Fragile X mental retardation is caused by having too many CGG repeats in a noncoding region. The normal amount of CGG repeats is 26-50. Fewer repeats may cause intellectual disability, but this is relatively stable. 50-58 is listed as "intermediate" in my notes (no idea what this means), 59-200 is unstable Fragile X pre-mutation syndrome, and more than 200 repeats results in Fragile X mental retardation syndrome.
• Fascioscapulohumeral muscular dystrophy (FSHD1A) is caused by the opposite problem: too few repeats. Fewer than 10 repeats in the relevant gene (the D4Z4 repeat array in the 4q35 subtelomeric region... whatever all that means) can cause the disorder.

Overview of genetic therapy strategies

See earlier post: Introduction to Gene Therapy

Generally "gene therapy" is used to describe replacing and repairing genes, whereas "molecular therapy" is the term given to altering gene expression. For example, inducing fetal gamma-globulin with butyrate or valproate may be used to treat thalassemia. Also, nonsense mutations (mutations that result in a premature stop codon) can be bypassed by using aminoglycoside antibiotics, though these can have unwanted side-effects.

The CRISPR-Cas system, which is basically the acquired immune system of prokaryotes, can be used to help with gene editing. CRISPRs consist of DNA loci with short repeats. Each repetition is followed by "spacer DNA," which recognises and silences exogenous genetic elements. Cas genes encode proteins related to CRISPRs.

To use CRISPRs, the plasmid or virus containing cas genes and specifically designed guide RNAs (single guide RNAs, or sgRNAs) are inserted. Cas9 endonuclease forms a complex with double-stranded DNA and sgRNA. Cas9:sgRNA binds the DNA to generate an R-loop, resulting in a double-stranded break where genes can be inserted.

Another strategy that is used, and that I'll talk about a lot in this post, is using antisense oligonucleotides to alter splicing and translation. This may be done to remove selected exons to bypass a mutation, or to degrade unwanted transcripts. Two RNA-like oligonucleotides commonly used in altering splicing are 2' O methyl phosphorothioate and phosphorodiamidate morpholino oligomer (PMO). These oligonucleotides are also known as "new-generation antivirals" as they have also been found to be effective against 75% of all human viruses. Transcript degradation can be induced by inducing RNase H (which can be induced by a DNA antisense oligonucleotide binding to an RNA strand) or by using siRNA (silencing RNA). Transcript stability can also be modified with the help of micro RNA (mir).

Duchenne Muscular Dystrophy (DMD)

See previous post: Introduction to Gene Therapy. Note that carriers of DMD are not entirely unaffected: they begin life with dystrophin in only ~50% of their muscle fibres.

Mice models of DMD (mdx mice) have an early stop codon in exon 23. Antisense oligonucleotides can be used to bypass this exon and allow production of a shorter yet functional (possibly BMD-like) form of dystrophin. Unfortunately, humans are a bit more complicated, and there are many different mutations that DMD patients may have.

Some patients with DMD are missing exon 50, resulting in a premature stop codon in exon 51. To circumvent this, Exondys51 (eteplirsen) can be used to splice out exon 51. Since many BMD patients are missing exons 50 and 51, eteplirsen can be used to create a BMD-like dystrophin. Clinical trials have found that eteplirsen can help in ambulation and also increases dystrophin expression (though not to normal levels).

As I just said, humans are complicated. Not every patient with DMD is missing exon 50 and therefore not all can be treated with the same drug. In fact, it is thought that only around 13% of patients will be able to benefit from this drug, and around 20% of patients are thought to have mutations that are not amenable to exon skipping. Oh well, baby steps I guess!

Spinal Muscular Atrophy (SMA)

Spinal muscular atrophy (SMA) is caused by a loss of the SMN1 gene on chromosome 5. SMN1 is important in all cells. It is made up of 8 exons, though around 10% of the time exon 7 is spliced out to create a non-functional protein (even in healthy individuals). Humans also have a similar gene called SMN2, which only differs from SMN1 by five bases. SMN2 can also produce a functional protein, though it is far more likely to skip exon 7 and produce a non-functional protein as compared to SMN1. Treatment strategies involve using antisense oligonucleotides to turn off silencing elements around exon 7 in order to hopefully upregulate SMN2 production. The idea is that if we upregulate SMN2 enough, it might be able to produce enough protein to overcome the effects of missing SMN1. One such treatment is Nusinersan, which is a 2' O methoxyethyl oligonucleotide that induces SMN2 exon 7 inclusion.

Antiparasitic Agents

INFODUMP INCOMING!!!

I haven't written very much about parasites on this blog, but there's an introduction to them here if you need one. This lecture jumped all over the place, but hopefully I'll be able to provide some kind of coherent structure.

Malaria

For more information on malaria, see here.

Malaria can be treated with a range of antimalarials, such as quinine, mefloquine and artemisinin derivatives such as artemether and artesunate. Artemesia annua has been used in Chinese medicine for years, and the active ingredient was eventually isolated, earning Tu Youyou a Nobel Prize. The actual mechanism of action is not quite clear, but it is thought to involve increasing mitochondria-targeting endoperoxides in parasites and altering calcium metabolism. It is a well-tolerated drug and can clear parasites quickly. To prevent parasites from surviving and developing resistance, artemisinin is always given in combination with another antimalarial with a longer half-life.

Enteric protozoa and trichomonas

Enteric protozoa include Entamoeba histolytica, Giardia lamblia and Cryptosporidium, which can cause fun symptoms such as dysentery. Trichomonas, which can cause yellow-green discharge, has been discussed in further detail here. They are discussed together because amoebic dysentery, Giardia and Trichomonas can all be treated with metronidazole or tinidazole. Dientamoeba (another enteric protozoan) can also be treated with metronidazole, as well as doxycycline. Some other enteric protozoa, such as Isospora, Cyclospora and Blastocystis can be treated with co-trimoxazole (another name for trimethoprim/sulfamoxazole), or with pyrimethamine plus ciprofloxacin.

Metronidazole and Tinidazole

Metronidazole and tinidazole, which are classified as nitroimidazoles, are antibacterial and antiprotozoal. They are pretty cheap (metronidazole is 10c per tablet), well-tolerated and can be used in pregnancy (though not when breastfeeding). They can also be applied orally, topically or intravenously. Metronidazole treatment takes longer than tinidazole treatment.

Nitazoxanide

Nitazoxanide is a thiazolide mainly used to treat Cryptosporidia and other opportunistic protozoan infections in AIDS patients. It can also be used against Giardia and some viruses, such as HBV, HCV, rotavirus, influenza A, coronavirus, RSV, adenovirus and HSV1. It interferes with pyruvate ferredoxin oxidoreductase (PFOR).

Paromomycin

Paromomycin is an aminoglycoside that is also able to inhibit protozoan protein synthesis. It is effective against a wide range of protozoa, such as Entamoeba, Giardia, Dientamoeba and Leishmania.

Toxoplasmosis

Toxoplasmosis is caused by Toxoplasma gondii, which is spread in cat faeces and contaminated meat. It can cause cysts that can remain dormant in the brain for a while, eventually leading to cerebral disease such as fever, confusion, headache and seizures. One of the treatments for toxoplasmosis is pyrimethamine, which inhibits dihydrofolate reductase and may have synergistic activity with sulfonamides. It is also effective against malaria. Pyrimethamine can be given with sulphadiazine for effective treatment of toxoplasmosis. HIV patients may need to take pyrimethamine for life.

Leishmaniasis

Leishmaniasis is caused by leishmania, which resides in macrophages and is spread by mosquitoes. The two main forms are visceral and cutaneous leishmaniasis, but there are also mucosal, diffuse and disseminated forms.

Of the two main forms, the cutaneous form is more mild. It can self-heal within 3 months to 3 years, though it normally leaves scars. It can also be treated topically with heat, cryo or laser therapy. Other treatments include intralesional pentavalent antimonials, imiquimod, paromomycin, amphotericin B or oral miltefosine. Visceral leishmaniasis is more severe and generally requires intravenous or intramuscular pentavalent antimonials and/or amphotericin.

Pentavalent antimonials

Pentavalent antimonials, such as sodium stibogluconate and meglumine antimoniate, are first-line treatments for leishmaniasis. They have inactive Sb^V (Sb is antimony) which is converted to active Sb^III. The possible mechanism of action is inhibition of ATP synthetase, but this is still uncertain. Pentavalent antimonials are quite toxic and are linked to cardiotoxicity, elevation of pancreatic enzymes and hepatitis. Furthermore, there is some resistance to these drugs, particularly in India, where resistance to pentavalent antimonials is around 70%.

Miltefosine

Miltefosine was originally an anti-cancer drug, but has been found to have antiprotozoal activity. It is the only oral drug for leishmaniasis. It is mostly effective at treating visceral leishmaniasis, but there is increasing evidence that it may be helpful in cutaneous leishmaniasis as well.

Trypanosomiasis

There are two main kinds of trypanosomiasis: Chagas' disease and African trypanosomiasis. I have already written about African trypanosomiasis here. Chagas' disease, which is spread by the triatomine bug, can cause the Romana's sign or Chagoma acutely (a quick Google search will give you some pictures), or cardiomegaly, megaoesophagus and/or megacolon chronically. Chagas' disease can only really be treated in the acute stage by either nifurtimox or benznidazole- there are no treatments for chronic Chagas' disease.

Nifurtimox

Nifurtimox is an anti-Chagas' drug that causes free radical production. Side-effects include anorexia and neuro-psychological reactions.

Benznidazole

Benznidazole is a nitroimidazole (like metronidazole and tinidazole) that can also be used to treat Chagas' disease. Side-effects include hypersensitivity, oedema and bone marrow suppression.

Pentamidine

Pentamidine, which can be used to treat early-stage Gambiense disease, can be given as a deep IM or slow IV injection. Side-effects include hypotension, shock and renal failure.

Eflornithine

Eflornithine, which was originally developed as an anti-cancer drug, can be used to treat late-stage Gambiense disease. It is given as an IV for 14 days, which can be a bit of a problem, given that many cases of Gambiense disease occur in countries with underdeveloped healthcare systems. Side effects include GI upset, seizures and bone marrow suppression.

Suramin

Suramin is used to treat early-stage Rhodesiense disease. Side-effects include allergic reactions, nausea, vomiting, renal impairment and fever.

Melarsoprol

Melarsoprol is used to treat late-stage Rhodesiense disease. It is an arsenical, which means it comes with some nasty side-effects, such as post-treatment reactive encephalopathy. The fatality rate from this drug is 5-10%, but unfortunately it's the best treatment available for late-stage Rhodesiense disease. (You gotta wonder what the other treatments are like...)

Onchocerciasis (and other types of filariasis)

Onchocerciasis is another name for "river blindness," which is caused by subcutaneous filariasis, as detailed here. Just like with other filarial diseases, treatments involve killing microfilaria, rather than the adult worms. Hence, repeat treatments are often required.

Ivermectin

Ivermectin blocks chloride channels, paralysing microfilaria. Unfortunately, this drug may have oncogenic (cancer-causing) and sterilising effects. Other side-effects include hypotension, headache and fever.

Doxycycline

Doxycycline is a tetracycline that is used to kill Wolbachia. As mentioned here, filarial worms require Wolbachia in order to survive.

Diethylcarbamazine (DEC)

DEC kills microfilaria, as well as some adult worms. It is thought to sensitise microfilaria to phagocytosis by the immune system. DEC also inhibits arachidonic acid metabolism.

Soil-transmitted helminths

Soil-transmitted helminths, such as Ascaris and Enterobius, are mainly treated with benzimidazoles such as albendazole and mebendazole. Benzimidazoles are broad-spectrum anti-helminthics that are usually single-dose as they generally reach their target pretty well with few side-effects.

Albendazole

Albendazole binds to intracellular tubulin, impairing absorptive functions of the worm. Side-effects include transient GI upset, dizziness, itch and dry mouth. Albendazole is also potentially teratogenic, but the benefits usually outweigh the risks.

Mebendazole

Mebendazole also binds to tubulin, preventing microtubule formation, cell division and glucose uptake, which in turn leads to increased glycogen utilisation by the worm. Side-effects of mebendazole are similar to those of albendazole.

Trematodes (flukes)

I've written more about trematodes here. The main treatment is praziquantel, but albendazole, triclabendazole, nitazoxanide and chloroquine may also be used. Praziquantel increases calcium permeability of parasite membranes, but may also result in neuromuscular paralysis (presumably via the same mechanism).

Hydatid disease

Hydatid disease, as described here, is caused by tissue tapeworms. It is characterised by the formation of cysts that may rupture, so surgical intervention may be required. Before surgery, the cyst is sterilised with scolicidal agents, such as benzimidazoles and ethanol.

Taenia species

I've already written about Taenia here. T. saginata and T. solium can both be treated with praziquantel. If cysticercosis occurs (formation of cysts due to ingesting the eggs of Taenia spp.), prolonged courses may be required, as well as high-dose steroids to suppress the "immune storm" that results when worms are killed.

Infections in Returned Travellers

Fasten your seatbelts, because we're back to blogging about MICR3350!

Most travel infections result from visiting countries in tropical areas. The most common identified GI pathogens in returned travellers are Giardia, Salmonella, Shigella and Campylobacter, the most common febrile conditions include malaria, dengue, typhoid, chikungunya and so on, and the most common respiratory illnesses include flu and legionellosis. Very few people who catch a disease abroad actually die from it, and a large proportion of those deaths are from falciparum malaria (the worst form of malaria).

Diagnosis

Diagnosis can be very difficult, as most of these illnesses have non-specific and overlapping symptoms (like fever, fatigue, nausea, etc.). Therefore, it is important to obtain a thorough history that includes travel history and measures taken to avoid risk (e.g. anti-mosquito measures, pre-travel vaccinations).

Sometimes, you get lucky and find a symptom that is specific to an infection. For example, an eschar, which has a dark area in the middle surrounded by a ring of inflammation, is associated with Rickettsia infections. Chancres are associated with primary syphilis. A "migrating track" under the skin" is associated with cutaneous larva migrans (animal hookworms under the skin). A similar-shaped lesion in the eye might indicate loa loa microfilarial worms that cause loiasis. Myiasis- infection by human botflies- can be quite distinctive too.

Incubation periods can also be used to help narrow down a diagnosis. For example, the incubation period for yellow fever is only 3-6 days. If a patient visited a yellow fever-endemic country more than 6 days ago, it is unlikely that their current infection is due to yellow fever. Other incubation periods that might be helpful to know are malaria (9 days - several months), typhoid (3-60 days), dengue (3-14 days) and typhus (Rickettsia infection not to be confused with typhoid. Incubation period for this one is 6-21 days).

Malaria

Since a large proportion of deaths from travel illnesses are due to malaria, it should always be considered in a returned traveller with fever. Malaria is transmitted by Anopheles mosquitoes, and comes in five flavours: Plasmodium vivax, P. ovale, P. malariae, P. falciparum and P. knowlesi. P. falciparum is the most severe and life-threatening. P. knowlesi is not very common (originated in monkeys), but it can also be severe.

The life cycle of malaria is quite complex. The infective form, called a sporozoite, lives in the salivary gland of mosquitoes. Sporozoites are transmitted to us when mosquitoes bite. Once inside us, sporozoites move through the blood and lymphatics to the liver, where they multiply into haploid forms called merozoites, which gather in lesions called schizonts. At this stage, P. vivax and P. ovale can also produce hypnozoites, which are latent forms. Hence, P. vivax and P. ovale malaria can recur.

Eventually, liver schizonts rupture, releasing merozoites into the bloodstream. Merozoites infect red blood cells and develop into the trophozoite form. Trophozoites sometimes appear as rings under the microscope due to the presence of a large vacuole in the middle. As the trophozoites develop, a mature erythrocytic schizont that contains thousands of merozoites is formed. These erythrocytic schizonts can eventually rupture, releasing merozoites to infect fresh red cells. In untreated malaria, this cycle can cause regular waxing and waning of fever.

Some trophozoites can exit the cycle and develop into male and female gametocytes. Gametocytes can be taken up by mosquitoes. Once in the mosquito's gut, the gametocytes undergo sexual reproduction, producing new sporozoites that live in the mosquito's salivary glands. And so the process continues!

Malaria can present in many different ways. Fever is usually the main symptom, but there are many other nonspecific symptoms, from headache, to abdominal pain, to seizures. In severe cases, it may proceed to pulmonary oedema, acute renal failure, severe anaemia, and so on. Therefore, diagnosis of malaria cannot be made clinically, and diagnostic tests are necessary. These diagnostic tests include a blood film to look for parasites, PCR and antigen detection.

Dengue fever

Dengue is another common cause of fever in returned travellers. It is transmitted by Aedes mosquitoes. Just like malaria, dengue fever can present with very non-specific symptoms, mainly fever. The main symptoms of "classical" dengue are fever, rash, severe muscle and joint pain, headache, retro-orbital pain, and mild haemorrhagic phenomena. If a patient is infected twice, with a different serotype each time, they can get dengue haemorrhagic fever or dengue shock syndrome, which are very serious conditions. In dengue haemorrhagic fever, platelets are diminished, leading to haemorrhagic skin rashes, leaky blood vessels and hypotension. Diagnostic tests for Dengue fever include antibody and antigen (NS1) detection and PCR.

Prevention

Some preventative measures can be taken to reduce the risk of getting a travel illness. These include getting appropriate vaccinations, prophylactic drugs for malaria, mosquito avoidance, observing food and water safety, safe sex and avoiding animals.

Thyroid in Growth and Energy Utilisation

Explain the structure & function of the thyroid gland

The thyroid gland, which is located at the base of the neck, consists of two lateral lobes connected by an isthmus. On a microscopic level, it is made up of follicles, which in turn are made up of follicular cells surrounding a lumen, which is where thyroglobulin (thyroid hormone precursor) is stored. On the outside of the follicles are C-cells, which secrete calcitonin (see here for more information on calcitonin). The thyroid has a high blood supply to allow hormones to be readily secreted into circulation.

Explain the synthesis & secretion of thyroid hormones

Thyroid hormones come in two flavours: thyroxine (T4) and triiodothyronine (T3). Both are derived from tyrosine (as are dopamine and adrenaline). T4 is more common than T3, making up around 90% of the thyroid hormones released. However, T3 is more potent. T4 can be converted into T3 by de-iodination of the outer ring. If the inner ring is de-iodinated, as may occur during stress, then rT3 (reverse T3) is formed, which is inactive.

The main "ingredients" needed to synthesise thyroid hormones are iodine and thyroglobulin (which, as mentioned above, is a precursor for T3 and T4). Thyroglobulin is made by the follicular cells of the thyroid, whereas iodine is obtained from the diet. Absorption of iodine is poor, but it can be readily stored. In times of iodine deficiency, it can take a couple of months for symptoms to show.

Thyroid hormone synthesis kicks off by absorption of iodine. Iodine is transported into follicular cells via a Na⁺/I^- symporter. It is then pumped out the other side and into the lumen via an I^-/Cl^- antiporter called Pendrin. At the same time, thyroglobulin is produced in the endoplasmic reticulum of follicular cells before being packaged in vesicles (along with peroxidase) and exocytosed into the lumen.

Once everything is in the lumen, I^- is oxidised by that peroxidase that was packaged with the thyroglobulin. Tyrosine residues on thyroglobulin are then iodinated to form either diiodotyrosine (DIT) or monoiodotyrosine (MIT). Two DITs can combine to form T4, or one MIT and one DIT can combine to form T3.

After iodination has occurred, iodinated thyroglobulin is endocytosed by the follicular cells. It combines with lysosomes containing enzymes that cleave off T4, T3, MITs and DITs. Since MITs and DITs are non-functional, the iodine from these is removed and recycled. T4 and T3 then moves into the blood via an MCT (monocarboxylate transporter). Once in the blood, T4 and T3 are transported around by thyroxine-binding globulin (TBG), TTR/TBPA or albumin. When they get to their destination, they are brought into cells by MCTs. De-iodinases may then convert T4 to T3 with the help of tin and zinc.

Discuss the control of thyroid function

Throughout the day, we have a tonic basal release of TRH (thyrotropin-releasing hormone) from the hypothalamus. TRH stimulates release of TSH (thyroid-stimulating hormone) from the anterior pituitary. TSH then stimulates release of thyroid hormones from the thyroid. Control is by negative feedback- build-up of thyroid hormones downregulates TRH receptors in the anterior pituitary. There are also negative feedback effects on the hypothalamus, but to a lesser extent.

Aside from stimulating thyroid hormone synthesis and secretion, TSH also has other effects on the thyroid. It can cause hyperplasia and increase blood flow. This will become significant when talking about diseases involving the thyroid.

Discuss the effects of thyroid hormone on growth & metabolism

Thyroid hormone has effects across a range of different areas:

• General metabolic effects- increases basal metabolic rate by increasing the number and size of mitochondria, ATP production, VO2, active transport of ions, and heat production. Note that this means that without thyroid hormones, we produce less heat and therefore have cold intolerance (important in hypothyroidism).
• Carbohydrate metabolism- increases glucose absorption, glucose oxidation, gluconeogenesis, insulin secretion, and synthesis of specific metabolic enzymes.
• Lipid metabolism- increases lipolysis and lipogenesis, but has a stronger effect on lipolysis.
• Protein metabolism- can increase both protein synthesis and protein degradation.
• Skeletal system effects- increases bone formation (remember, thyroid hormones stimulate GH) and may play a role in bone maturation.
• CNS effects- thyroid hormones are essential for normal brain development.
• Cardiovascular effects- increases cardiac output, heart rate, contractility and tissue blood flow.

Discuss diseases of the thyroid gland

I've covered these in quite a bit of detail in an earlier post: Pituitary-Endocrine Axis Pathology. So I'm just going to list a few random fun facts that weren't covered in that earlier post.

• Deficiency of Pit-1, a transcription factor for TSH, can cause hypothyroidism
• Myxedema, which is oedema of the skin due to accumulation of polysaccharides (and water following by osmosis), is another potential symptom of hypothyroidism
• Bone and height defects in cretinism can be mostly reversed by thyroxine treatment, but this treatment has no effect on mental defects
• Methimazole is a drug used to treat Graves' disease. It lowers production of thyroid hormone
• Thyroid hormones are orally active, which means that if you eat something containing them, you can get a condition called thyrotoxicosis. This was the cause of "hamburger thyrotoxicosis" in the 1980s in USA (the patties were prepared from neck trimmings, but now such "gullet trimming" is banned).

Hormonal Regulation of Growth

Now we're onto our last topic for PHYL3003: Nutrients for Growth and Activity!

Outline how the endocrine system regulates growth and development

The main hormones involved in growth are growth hormone (GH) and insulin-like growth factors, like IGF-1. GH is stimulated by GHRH, thyroid hormones and sex steroids and inhibited by somatostatin. GH can directly stimulate growth, or stimulate IGF-1. IGF-1, which can also be stimulated by insulin, can also stimulate growth.

Describe the physiological functions of growth-regulating hormones

In this section, I'm going to focus on GH, since there's a section on IGFs coming up next. GH is the most abundant hormone in the anterior pituitary, and its secretion is stimulated by GHRH (growth-hormone releasing hormone), which in turn can be stimulated by stress, exercise and deep sleep. GH release is pulsatile and follows a circadian rhythm, peaking in the first few hours of sleep. GH is controlled by a negative feedback loop- high levels of GH inhibit further GHRH secretion.

GH has a wide variety of actions. It can increase amino acid transport and protein synthesis, stimulating growth. It can also increase lipolysis and reduce glucose transport and metabolism, which is thought to ensure that there is enough glucose to supply the brain. GH can also increase fibroblast differentiation and increase the production of IGF in the liver and fibroblasts. Time to talk about IGF in some more detail...

Describe the function and regulation of Insulin-like growth factors (IGFs)

IGF can be produced by various tissues of the body. The liver can produce and secrete it, whereas other tissues (such as skeletal muscle, heart and bone) make tissue-specific IGF-1 which they cannot secrete into the circulation (though they do have autocrine and paracrine effects). IGF-1 is the adult form of IGF, whereas IGF-II is the fetal form.

Just like GH, IGF has a range of functions. It regulates carbohydrate metabolism and stimulates amino acid uptake and protein synthesis. It also has profound effects on growth and acts as a mitogen (something that can stimulate proliferation of target cells). IGF can potentiate the effects of GH, making it more effective.

Throughout puberty, GH and IGF levels increase simultaneously. IGF peaks at adolescence- teenagers have around three times as much IGF as adults!

As I mentioned earlier, both GH and insulin can stimulate IGF release. This can be used to explain why amino acids and glucose can stimulate growth. High amino acid levels stimulate growth hormone release, increasing IGF levels. High glucose levels stimulate insulin, which also increases IGF levels. Therefore, growth occurs when nutrients are plentiful. On the other hand, if glucose is low, IGF production can decrease, impairing growth even if GH levels are high.

Just like with GH, IGF levels are also controlled by negative feedback. High IGF1 decreases GH secretion by increasing somatostatin release from the hypothalamus, suppressing release of GH from the anterior pituitary.

Other important growth factors

Steroid hormones, such as androgens, can be important in growth. Androgens can stimulate protein synthesis. Furthermore, testosterone and oestrogen can act synergistically with GH in order to stimulate growth of more GH. In turn, GH can potentiate some of the effects of the sex steroids.

Thyroid hormones, particularly T3, are also important in growth. They do not cause growth on their own, but stimulate GH synthesis and secretion. T3 may also increase the responsiveness of target cells to GH.

Outline abnormal control of growth – implications and disease states

Over-secretion of GH

Over-secretion of GH can cause gigantism if it occurs before puberty (as epiphyseal plates haven't closed yet), or acromegaly (thickening of bones) if it occurs after puberty. In acromegaly, growth of bone and cartilage can compress nerves. Therefore, symptoms of acromegaly include visual field losses due to pressure on optic nerves, Bell's palsy (facial paralysis on one side) due to pressure on the facial nerve, and carpal tunnel syndrome due to pressure on the median nerve in the wrist. Acromegaly may also increase the risk of malignant tumours.

Under-secretion of GH

Under-secretion of GH can be caused by tumours that over-secrete somatostatin, infections and irradiation. Under-secretion of GH, or some other defect in the GH signalling pathway, results in dwarfism. Not everyone with dwarfism has the same defect: Laron Dwarfs have a genetic defect in GH receptor expression, and African pygmies have normal GH levels but impaired IGF production.

Hormonal growth promoters

Synthetic hormones are being used for various processes. In food production, they are used to promote growth and productivity. (There is some controversy surrounding this, but I'm not going to go into it.) Growth hormones can also be used therapeutically in the treatment of GH deficiencies as well as muscle-wasting disorders. Such synthetic growth hormones are banned in competitive sports, but that hasn't stopped people from producing GHRH peptides, which act on the pituitary gland to stimulate GH secretion. Hormone replacement therapy has also been suggested in reducing bone and muscle loss in ageing, but there is a risk of serious side-effects since you are essentially inducing acromegaly.