Seeing the world differently

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Out of this world

"It is absolutely astonishing that these scientists are able to start to tease out the details of what planets around other stars are made of," he said.

"The planet is thousands of times fainter than the star it orbits. So the scientists have to perform an amazing feat of precision measurement to extract anything at all. The fact that they are able to tell us something about the composition of this particular planet is quite literally out of this world."

To date astronomers have discovered more than 500 planets around other stars. These distant worlds are known as exoplanets. It is only recently that instruments and analysis methods have become powerful enough to discern their composition.

This new planet, Wasp 12b, is the first to have more carbon than oxygen. It is a so-called gas giant, like Jupiter, and is mostly made from hydrogen gas. But the planet's core could be composed of some form of diamond, graphite and other carbon compounds, possibly in liquid form.

Tar pools

This discovery suggests there may well be many Earth-sized planets in our galaxy that are ultra-rich in carbon.

But these worlds would be unlike our planet: "Theoretical studies suggest that they could be dominated by diamond and graphite rocks," according to Dr Madhusudhan.

"That would mean that in the mountains, a large fraction of the rock mass could instead be made of diamonds and lots of land masses rich in diamonds, much more than we see on Earth."

These planets would be lacking in water So, if temperatures were sufficiently high, liquid on their surface would consist of carbon-rich compounds, such as tar, he says.

So how common are these diamond planets? The short answer is that astronomers simply don't know. But the fact that they've discovered one means that they'll now start to try and find an answer. Dr Madhusudhan believes that they could be common.

"It's my strong belief that a fair fraction of the exoplanets we have discovered could be carbon-rich and it's a very interesting thought that on such rocky planets, sand could be a rare commodity and diamonds would be plentiful. The more important question is how such planets could form."

An immediate question that is raised is why Wasp 12b is so much higher in carbon than the planets we know about. The prevalent theory is that plenty of water ice was available when the planets in our Solar System formed. That could not have been the case for Wasp 12b.

Do Free Radicals Really Cause Aging?

These much maligned molecules may not be entirely harmful after all. In fact, a new study suggests they could help us live longer.

By Jessica Marshall

Conventional wisdom has held for decades that free radicals cause aging, and that antioxidants, which squelch the reactivity of these highly reactive molecules, are a way to slow the process. But new work adds to a growing body of research that suggests the story is not so simple.

In the new study published in PLoS Biology, worms that made more free radicals or that were treated with a free-radical-producing herbicide actually lived longer than normal worms. What's more, when the longer-lived mutant worms were given antioxidants, the effects were reversed, and the worms had a conventional worm lifespan. The finding flies in the face of the idea that antioxidants battle the effects of aging.

According to study author Siegfried Hekimi of McGill University in Montreal and others, what is emerging from this and other experiments is a view of free radicals - or, more precisely, reactive oxygen species - as a normal part of the body's stress response, with beneficial effects at certain levels.

"Maybe the reason why free radicals and aging are correlated is because free radical production in the mitochondria (part of the cell) is a stress reaction to the damage of aging," Hekimi said. "The organism tries to counter with free radical production." Hekimi and others point out that part of exercise's benefit may be because exercise causes mild increases in the levels of reactive oxygen species that are actually good for us.

The emerging view casts a pall on the idea of popping antioxidant pills in hopes of slowing the aging process or protecting against disease. "When clinical trials have been done with antioxidants, they have not shown benefits," Hekimi said. "If we're right that reactive oxygen species are fundamental to maintain normal fitness and also adaptation to stress, then you don't want to take too many antioxidants," said Navdeep Chandel of Northwestern Medical School in Chicago.

Indeed, Chandel suspects that the beneficial effects of limited alcohol consumption come not from antioxidants in red wine but from the mild oxidative stress the alcohol provides.

"Who am I to say if you should take antioxidants or not," he added. "All I would say is there is no evidence that taking more antioxidants than you get through diet is needed."

Free radicals do cause damage, Hekimi said, but at normal levels their beneficial effects are perhaps more important. If the stress of aging or disease increases sufficiently, he said, the damage caused by the free radicals might overwhelm their positive effects.

"You cannot live without them, nor should you wish to, but they will probably help to kill you in the end," agreed Barry Halliwell of the National University of Singapore, of reactive oxygen species. "Learning how to stop the latter whilst preserving the useful functions of reactive oxygen species should be a major research priority in the next few years." Halliwell said that evidence supports that reactive oxygen species probably contribute to the progression of cancer and neurodegenerative diseases, despite having beneficial effects at lower levels. They also probably cause skin wrinkling, he added.

Hekimi hopes further experiments will determine exactly how reactive oxygen species increase lifespan in the worms. He and his colleagues used the nematode worm Caenorhabditis elegans, an organism used widely in lab studies, but Hekimi believes the findings will translate into higher organisms like mice and humans, because these systems are so fundamental.

Halliwell noted, though, that C. elegans can not be used to study the effect of free radicals on stem cells, which evidence suggests may be important. Also, the study only shows the effects of free radicals on longevity, and can say nothing about quality of life.

The importance of making a good first impression in the classroom

Researchers examine how medical students evaluate professors

MAYWOOD, Ill. - A study of how medical students evaluate their professors is illustrating the critical importance of making a good first impression.

Students in a physiology course at Loyola University Chicago Stritch School of Medicine were asked to evaluate 16 professors who lectured during the course. Students had the option of evaluating each professor concurrently during the course, or waiting until the course ended. Students were allowed to change their minds before the evaluations were finalized at the end of the course.

The study, published in the December, 2010 issue of the journal Advances in Physiology Education, included 144 students. Twenty six percent filled out evaluations during the course and 65 percent waited until the course ended. Nine percent did not submit evaluations.

The scores professors received on early evaluations were markedly similar to the scores they received on evaluations made after the course ended. (In statistical terms, the correlation was .91.) And students rarely changed their minds about professors - only 3 percent of evaluations were revised before the evaluations were finalized.

"Students tended not to change their scores and comments, regardless of the time they submitted their evaluations," researchers wrote. "Hence, first impressions appear to be important."

For decades, students in colleges and graduate schools have been evaluating their professors. Faculty promotion and tenure decisions are based in part on these evaluations.

"The first lecture a faculty member gives to a class really sets the impression," said John A. McNulty, PhD, first author of the study. "The professor is either going to click with the student's learning style, or not."

At Loyola's Stritch School of Medicine, students are asked to rate how well professors communicate, relate course content to learning objectives and add to the student's understanding. Professors are rated on a scale of 1 to 5, with 1 the worst and 5 the best. Students also can write comments. In the most recent evaluations, the average score for basic science faculty was 4.2, and the average score for clinical faculty (physicians) was 4.38.

"We have a really good faculty," McNulty said. "The distribution of scores is skewed toward the high end."

McNulty is a professor in the Department of Cell and Molecular Physiology. Co-authors of the study are Dr. Gregory Gruener, professor in the Department of Neurology; Dr. Arcot Chandrasekhar, professor in the Department of Medicine; Dr. Baltazar Espiritu, associate professor in the Department of Medicine; Amy Hoyt, manager of information technologies for Loyola University Health System, and David Ensminger, clinical assistant professor in the School of Education at Loyola University Chicago.

Estrogen alone is effective for reducing breast cancer risk

SAN ANTONIO - While endogenous estrogen (i.e., estrogen produced by ovaries and by other tissues) does have a well-known carcinogenic impact, hormone replacement therapy (HRT) utilizing estrogen alone (the exogenous estrogen) provides a protective effect in reducing breast cancer risk, according to study results presented at the 33rd Annual CTRC-AACR San Antonio Breast Cancer Symposium, held Dec. 8-12.

"Our analysis suggests that, contrary to previous thinking, there is substantial value in bringing HRT with estrogen alone to the guidelines. The data show that for selected women it is not only safe, but potentially beneficial for breast cancer, as well as for many other aspects of women's health," said lead researcher Joseph Ragaz, M.D., medical oncologist and clinical professor in the faculty of medicine, School of Population and Public Health at The University of British Columbia, Vancouver, BC, Canada.

"These findings should intensify new research into its role as a protective agent against breast cancer," he added.

Ragaz and colleagues reviewed and reanalyzed data from the Women's Health Initiative (WHI) hormone replacement therapy trials. WHI is a national health study that focuses on strategies for preventing heart disease, breast and colorectal cancer, and fracture in postmenopausal women. The WHI was launched in 1991 and includes more than 161,000 U.S. women aged 50 to 79 years.

"Over the last 30 years HRT has been used almost indiscriminately by women expecting the benefit of reducing cardiac risks, while providing a protective effect against bone fracture, and improving overall quality of life," said Ragaz. "The WHI results as originally interpreted led to a major pendulum swing against HRT."

The WHI HRT trial consisted of two cohorts of women; the estrogen-alone group of women without a uterus and the estrogen-plus-progestin group of women with a uterus.

Ragaz and colleagues reanalyzed the WHI studies in more detail and found that subsets of women with no strong family history of breast cancer who received estrogen alone had a significantly reduced breast cancer incidence. In addition, the 75 percent of women without benign disease prior to the trial enrollment also had a reduced breast cancer risk.

"Reduction of rates of breast cancer in the majority of women who are candidates for estrogen-based HRT is a new finding because estrogen was always linked with a higher incidence of breast cancer," Ragaz said, "yet estrogen administered exogenously is actually protective for most women."

Based on the results of this current analysis, Ragaz suggested that "while the use of HRT with estrogen alone may reduce the risk of breast cancer and may also be appropriate to manage menopausal symptoms, further research is warranted to elaborate on the optimum treatment regimen, to refine the selection of ideal candidates for estrogen therapy, and to understand the estrogen mechanisms that support the prevention of human breast cancer."

"The recommendations based on prior analyses of the results of the WHI HRT studies was not to use HRT, but we are optimistic this will change," he said. "Our conclusion, based on the data presented, should enhance considerations for an early approval of HRT based on estrogen-alone for the majority of selected women suffering with menopausal symptoms and galvanize new research on HRT to define the optimum regimens for individual women."

Alzheimer's patients can't effectively clear sticky plaque component

Neurologists finally have an answer to one of the most important questions about Alzheimer's disease: Do rising brain levels of a plaque-forming substance mean patients are making more of it or that they can no longer clear it from their brains as effectively?

"Clearance is impaired in Alzheimer's disease," says Randall Bateman, MD, assistant professor of neurology at Washington University School of Medicine in St. Louis. "We compared a group of 12 patients with early Alzheimer's disease to 12 age-matched and cognitively normal subjects. Both groups produced amyloid-beta (a-beta) at the same average rate, but there's an average drop of about 30 percent in the clearance rates of the group with Alzheimer's." Scientists calculate this week in Science Express that it would take 10 years for this decrease in clearance to cause a build-up of a-beta equal to those seen in the brains of Alzheimer's patients.

The results have important implications for both diagnosis and treatment, according to the authors. Scientists are now interested in learning how a-beta, a byproduct of normal metabolism, is moved out of the brain for breakdown and disposal. As these details come in, they will be essential for physicians working to diagnose the disease before symptoms develop and for drug developers, who can target the problems with pharmaceuticals.

A-beta was recognized long ago as a key component of the brain plaques found during autopsies of Alzheimer's patients. One of the ways the brain clears away the a-beta normally produced by brain cell activity is by moving it to the spinal fluid for disposal. Studies have suggested that a drop in spinal fluid levels of a-beta may be a presymptomatic indicator of Alzheimer's disease, possibly because a-beta is getting stuck in the brain and starting to accumulate there.

Recent failures of therapies designed to clear a-beta from the brain have led some neurologists to speculate that a-beta may not be causatively linked to Alzheimer's. According to Bateman, though, the new data show that Alzheimer's is associated with disruption of the brain's ability to handle a-beta normally. "These findings support the idea that impaired a-beta clearance is fundamentally linked to Alzheimer's disease," Bateman says.

For the new study, scientists used stable isotope-linked kinetics (SILK), a process Bateman and his colleagues developed, to assess a-beta clearance and production rates. During SILK, researchers give test subjects an intravenous drip of the amino acid leucine that has been very slightly altered to label it.

Over the course of hours, cells in the brain pick up the labeled leucine and incorporate it into the new copies they make of a-beta and other proteins. Scientists take periodic samples of the subjects' cerebrospinal fluid through a lumbar catheter, purify the a-beta from the samples and determine how much of the a-beta includes labeled leucine.

Tracking the rise of a-beta with labeled leucine over time gives scientists the subject's a-beta production rate. When the percentage of a-beta containing labeled leucine plateaus, researchers stop introducing labeled leucine. Periodic sampling of the patients' CSF continues, allowing scientists to get a measurement of how quickly the nervous system clears out the labeled a-beta. Average clearance rate for a-beta differed significantly between the 12 normal subjects and the 12 with early Alzheimer's, but some normal subjects had lower clearance rates close to or slightly within the range seen in Alzheimer's patients.

"Cognitive tests show no signs of dementia in these participants now, but we'll be interested to see if a lower clearance rate is a predictive marker for future diagnosis of Alzheimer's disease," Bateman says.

Mawuenyega KG, Sigurdson W, Ovod V, Munsell L, Kasten T, Morris JC, Yarasheski KE, Bateman RJ. Decreased clearance of CNS amyloid-beta in Alzheimer's disease. Science Express, Dec. 9, 2010.

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