Selasa, 31 Agustus 2010

Injunction Against Human Stem Cell Research

In March of 2009 President Obama issued an executive order permitting the use of federal funds for research on stem cells lines derived previously from human embryos, arguing that the researchers had not destroyed the embryos themselves. The Obama executive order effectively overturned the ban of the Bush administration on the use of human embryonic stem cells for research. At the time, I reported in this blog that the Obama order might still face a legal challenge, based on a federal law called the Dickey-Wicker Amendment of 1999.

Last week it finally happened. As the result of a lawsuit filed by several Christian groups and two doctors opposed to human stem cell research, a U.S. District Court judge issued an injunction which blocks the National Institutes of Health (NIH) from implementing the Obama order. The judge argued that the Obama executive order clearly violates the language of the Dickey-Wicker Amendment, and even some supporters of the Omama order grudgingly agree. According to Harvard ethicist Louis Guenin, allowing research on cell lines merely derived from human embryonic stem cells would be like allowing research on dead bald eagles. It’s illegal to kill bald eagles, and therefore anyone doing research on bald eagles killed by someone else would be considered complicit in the crime.

If research on stem cells derived from human embryos is to continue, it appears that Congress will have to overturn the Dickey-Wicker Amendment. Whether there are sufficient votes in both houses of Congress to do so is anybody’s guess. In the meantime, funding for future projects is on hold. And while NIH’s interpretation is that currently-funded research projects can continue for now, not everyone seems to agree. We’ll have to see how this one shakes out. For starters, I’m sure we can expect the ruling to be appealed.

Rabu, 25 Agustus 2010

The Benefits of Human Breast Milk

Colonization of the human infants’ gastrointestinal tract by bacteria occurs only after birth. It is known that human breast milk encourages colonization of the newborn’s gut by beneficial bacteria and discourages colonization by harmful ones, but how exactly does it do that? An article in the Proceedings of the National Academy of Sciences provides a tantalizing glimpse into the likely mechanisms.

About 4-12% of the macronutrient composition of human milk consists of a structurally diverse group of complex sugars called oligosaccharides. These oligosaccharides are indigestible by the infant, and so for many years scientists thought they had no function. It turns out that they are digestible by a particular group of beneficial bacteria called bifidobacteria. The presence of these oligosaccharides in human milk gives the bifidobacteria a nutritional advantage over less desirable bacteria in the human infant’s gut. In other words, these oligosaccharides are produced in human milk specifically to provide nutrients to beneficial bacteria, rather than to nourish the infant.

Some of these oligosaccharides have another interesting property; they bind to certain harmful bacteria, thus preventing them from attaching to the epithelial cells lining the gut. Researchers think that these oligosaccharides may flush out harmful bacteria during that very vulnerable time in early life when the infant’s immune system has not yet developed fully.

Selasa, 24 Agustus 2010

Oral Immunotherapy for Food Allergies

Some people have food allergies so severe that even the slightest contact with the food can lead to a life-threatening allergic response. A rare but potentially fatal allergic response to peanuts, for example, is why most airlines no longer serve peanuts on their flights. Other sufferers are equally allergic to milk or to eggs, commonly used as ingredients in many food products and recipes. Is there anything that can be done for people with life-threatening food allergies aside from having them try to avoid the food?

Current research efforts are focused on oral immunotherapy (OIT). OIT consists of exposing the patient to miniscule quantities of the allergen in a supervised research setting (under close medical supervision), and then if an allergic reaction fails to occur or remains mild, slowly increasing the dose over days or months to “desensitize” the patient.

Researchers caution that the technique is not yet ready for widespread clinical use, however. The risk of an adverse reaction to the first dose is fairly high, and little is known about the safety of OIT when done at home under a variety of conditions. In addition, it is not known how long desensitization lasts if/when regular desensitizing dosing is ended. There is a danger that desensitized patients might develop a false sense of security once they become partially desensitized or quit their therapy altogether.

Nevertheless, OIT might become a useful therapy for severe food allergies in the future, once we better understand how to perform it safely. For sufferers of truly severe food allergies, the risks associated with desensitization would have to be balanced against the risk of accidental exposure to the allergen and perhaps even death.

Minggu, 22 Agustus 2010

Kidney Disease and African Sleeping Sickness

Natural selection can actually favor an otherwise harmful allele of a gene, if that allele somehow confers a survival advantage in some individuals and populations. The one textbook example of this phenomenon has always been sickle cell disease, a genetically inherited disease that results in deformed red blood cells and can lead to early death. Sickle cell disease is prevalent in persons of African ancestry because the allele that causes sickle cell disease also protects the person with that allele from malaria, a disease which is widespread in Africa.

Now there’s a second example of this phenomenon. Researchers have found that two different alleles for a gene involved in the production of a blood protein can; a) lead to kidney disease, and b) protect against the parasite that causes African sleeping sickness. Not surprisingly, the two abnormal alleles and the kidney diseases they cause are four to five times more common in African Americans than in persons of European descent.

Researchers are wondering how many other genetic diseases we’ll find that also confer protective advantages against certain infectious diseases. Researchers are also hoping to develop new treatments for African sleeping sickness that are based on the proteins these abnormal alleles produce.

Sabtu, 14 Agustus 2010

Maximum Heart Rate for Women

Many serious exercisers pay close attention to their heart rates while exercising. That’s because they generally are advised to keep their heart rates within 65-85% of their maximum heart rate for a safe but relatively strenuous workout designed to improve aerobic capacity and endurance.

According to a formula for maximum heart rate that is now 40 years old (it was developed in the 17970s), your maximum heart rate should be around 220 beats per minute (bpm) minus your age. The formula is a population average, of course, and shouldn’t be taken as an absolute number for each individual. More importantly, the old formula was based solely on men subjects. Now a new study of over 5,000 healthy women indicates that a better population-based formula for women is:

Maximum Heart Rate for Women = 206 – (0.88 x age)

Admittedly the new formula has the disadvantage that it can’t be calculated in your head, but it’s easy enough to do with a calculator. And the difference may be significant: By the old formula, a 40-year-old’s 65-85% target range would have been 117-153 bpm. By the new formula, the target range for a 40-yr-old woman would be 111-145 bpm. Six to eight beats per minute might not sound like much, but over an hour’s workout it could make the difference between pushing yourself too far and getting discouraged, and just getting a good healthy workout.

The new study focused only on women subjects. Perhaps someone ought to confirm or revise the old formula for men, too!

Reference: Gulati, M. et al., Heart Rate Response to Exercise Stress Testing in Asymptomatic Women: The St. James Women Take Heart Project. Circulation 122:130-137, 2010.

Minggu, 08 Agustus 2010

Rapid Eye Movement (REM) Sleep

Humans go through several stages of sleep during a typical night. One of them is the period during which we have complex dreams, called rapid eye movement (REM) sleep. During REM sleep our eyes move about rapidly beneath closed eyelids, even though our bodies typically remain completely motionless.

The explanation for rapid eye movement during REM sleep has always remained somewhat of a mystery - until now. In the June issue of Brain, researchers report that the most likely explanation is that our eyes are trying to follow the action in our dreams. They came to this conclusion after studying the direction of eye movements in a group of subjects who have a particular sleep disorder in which they physically act out their dreams while sleeping. The patients’ eye movements tracked their physical actions with a consistency of nearly 90%. The eye movements in these patients were no different than in normal subjects who did not move physically during sleep, leading the authors to suggest that the “follow-the-dream-action” explanation for REM activity may hold for normal subjects as well.

Kamis, 05 Agustus 2010

Dietary Supplements Deceptive Sales Practices

Dietary supplements are regulated as food products, not as drugs. Manufacturers are free to make vague claims of effectiveness, such as “improves heart health” or “boosts brain function”, but they cannot make medical claims such as “lowers high blood pressure” or “prevents Alzheimer’s”. And although their products are supposed to be safe, they’re not required to submit any data to prove it.

Now a Senate document reveals that even though the products may be labelled correctly, in sales conversations (“off-label”, so to speak) retail sales representatives of dietary supplements products are openly engaging in “deceptive and questionable sales tactics” – in other words, they’re lying to make a sale.

In testimony before a U.S. Senate committee, the General Accounting Office (GAO) reported that it had staff members ask questions of sales representatives such as: Is ginkgo biloba safe to take with aspirin? Can ginseng cure cancer? Is it okay to replace my blood pressure medication with garlic supplements? All too often they got “yes” answers when the correct answers are “no”. These answers are not just harmless sales advice – they are potentially dangerous advice and they are against the law. Action may be taken against some sellers as a result of the investigation. But for all practical purposes, it’s still “buyer beware” when it comes to the safety and efficacy of dietary supplements.

You can hear clips of some of the undercover calls at

Minggu, 01 Agustus 2010

First Human Stem Cell Therapy Trial

The first clinical trial of a therapy based on human stem cells has received final approval from the Food and Drug Administration (FDA) and will get underway shortly, according to a press release from Geron Corporation, the company sponsoring the research. During the first phase of the trial, researchers will inject precursor cells to neural support cells called oligodendrocytes into the spinal cords of patients who have suffered recent spinal cord injuries and who have almost no chance of recovery of function otherwise. The hope is that the precursor cells will differentiate into mature oligodendrocytes (the cells that produce myelin) and that the myelin will form new sheaths around damaged nerves.

The trial was planned several years ago but held up by the FDA over concerns that the therapy could increase the risk of tumors forming in the spinal cord if the injected cells were not free of embryonic stem cells. The first phase of the trial is designed to test the safety of the procedure. It will be years before the technique becomes widely available for the repair of spinal cord injuries, even if it does eventually prove to be both safe and effective.

Stem cell researchers will be holding their breath. A failure in this first approved trial could set back the whole field of stem cell therapy research for years.
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