Month: June 2010

A safe reaction

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Nuclear reactors might one day be constructed using materials that can self-heal following radiation damage, thanks to a materials study by scientists at Los Alamos National Laboratory.

In computer simulations, the LANL scientists have observed a surprising mechanism that allows copper nanocrystalline materials to heal themselves after suffering radiation-induced damage. [Bai et al., Science (2010) 327, 1631]. The phenomenon exploits the mix of grains and the grain boundaries between them in such materials.

An important considering in the design, construction and operation of nuclear reactors is the effect of high levels of radiation on the materials from which the reactor is constructed. In addition to constant bombardment, reactor materials might also be exposed to high temperatures, physical stresses, and corrosive conditions. Radiation itself can cause dislocations and interstitial atoms and vacancies to form that insidiously weaken the structure at the nanoscale. The accumulation of defects leads to swelling and hardening leading to brittleness and the potential for catastrophic failure.

Nanocrystalline materials contain a large fraction of grain boundaries, which can absorb and remove defects, and so scientists presumed that such materials might be more radiation tolerant than equivalent materials with larger grain sizes. However, few specific details have been obtained regarding the complex behaviour of such solids under different conditions.

Xian-Ming Bai and colleagues explain that they have now used three atomistic simulation methods to investigated defect-grain boundary interactions in copper on the picosecond to microsecond timescales. They found that grain boundaries have a surprising “loading-unloading” effect in which irradiation leads to interstitials being loaded, or trapped, in the boundary on the short timescale. The loaded boundary then acts as a source unloading, or emitting on the long timescale, interstitials back into the bulk, which eradicates vacancies. The simulations reveal that this recombination mechanism, “has a much lower energy barrier than conventional vacancy diffusion and is efficient for annihilating immobile vacancies in the nearby bulk”. The net effect is the surprising self-healing, the efficient annealing, in other words, of material defects caused by radiation exposure.

The team adds that this “loading-unloading” role of grain boundaries might explain the behaviour of irradiated nanocrystalline materials that runs counter to expectations, but more importantly could provide new opportunities for engineering nanocrystalline materials to be self-healing in high-radiation environments.

Team member Blas Pedro Uberuaga told Materials Today that the researchers have compared their simulated data with literature experiments, which he says explains very nicely those results. “In terms of more direct validation, we have some experiments in progress on Au and on metal composites (Cu/Nb), that will indirectly connect to these results, but may or may not be able to directly validate these simulation results. So, we have ongoing experimental activities in related areas,” he adds.

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Dronedarone for the treatment of atrial fibrillation and atrial flutter: approval and efficacy

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Dronedarone is an amiodarone analog with multichannel blocking electrophysiologic properties similar to those of amiodarone, but several structural differences. Dronedarone’s lack of the iodine moiety reduces its potential for thyroid and pulmonary toxicity. Preliminary data from the DIONYSOS trial, and an indirect meta–analysis comparing amiodarone with dronedarone, showed amiodarone to be more effective in maintaining sinus rhythm, while dronedarone was associated with fewer adverse effects resulting in early termination of the drug. Dronedarone is the first antiarrhythmic drug for the treatment of atrial fibrillation and atrial flutter shown to reduce cardiovascular hospitalizations. In patients with structural heart disease who have an ejection fraction >35% and no recent decompensated heart failure, dronedarone should be considered earlier than amiodarone in the treatment algorithm.

Vitamin D Concentrations in Blood Not Linked to Risk of Less Common Cancers

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A large prospective study has found that levels of vitamin D circulating in the bloodstream are not associated with subsequent risk of developing seven rare cancers, including endometrial, esophageal, stomach, ovarian, pancreatic, and kidney cancers and non-Hodgkin lymphoma. Although each of these cancers is individually uncommon, they collectively account for about a quarter of all deaths from cancer in the United States. The results were reported in a series of studies published online in the American Journal of Epidemiology on June 18.

“These cancer sites were chosen because there was a paucity of previous epidemiological studies, though basic research and biological evidence had suggested vitamin D may play a role in altering risk for these cancers,” said Dr. Demetrius Albanes of NCI’s Division of Cancer Epidemiology and Genetics. “Because these cancers are relatively rare, no one study could address risk; by pooling data from 10 studies, we had greater power to rigorously test the vitamin D hypothesis for these cancer outcomes.”

The researchers, part of the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers, measured blood concentrations of 25-hydroxy vitamin D, which is the primary form of this vitamin circulating in the bloodstream. Lower cancer risk was not observed in persons with high vitamin D blood concentrations compared with normal concentrations for any of these cancers. At the other end of the spectrum, higher cancer risk was not seen in participants with low vitamin D concentrations. However, researchers did observe an increased risk of pancreatic cancer for a small number of patients (2.3 percent) with very high blood concentrations of vitamin D (100 nmol/L or greater). “This finding needs to be followed up in further studies,” said Dr. Albanes.

Dr. Kathy J. Helzlsouer of the Prevention and Research Center at Mercy Medical Center in Baltimore, MD, who served as the chair of the project’s steering committee, wrote in the overview of the importance of optimum concentrations of vitamin D, particularly for bone health. A message of the study, she suggested, was “all things in moderation. You don’t want vitamin D levels that are too low, and you don’t want levels that are too high.”

“These studies offer compelling evidence against the hypothesis that circulating levels of vitamin D are relevant to risk of these cancers,” wrote Dr. Tim Byers of the University of Colorado Cancer Center, Aurora, in an accompanying editorial. This new information is important, he continued, because a review by the International Agency for Research on Cancer had decided that evidence was previously insufficient to draw conclusions about these cancer sites.

source: NCI bulletin

Genome Studies Start to Unravel Prostate Cancer’s Complexity

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Illustration of a DNA strand

Researchers at Memorial Sloan-Kettering Cancer Center (MSKCC) have completed the largest genomic analysis of prostate tumors to date. The results, based on clinical and genomic information collected from 218 patients, provide an overview of the common genetic changes in the disease and point to new directions for research, including a way to potentially differentiate aggressive tumors from those that are not life threatening. The researchers have made the data available to the community through a public Web site, and a summary of the results appeared online last week in Cancer Cell.

“We now have a much better picture of the common genetic alterations in prostate cancer,” said lead investigator Dr. Charles Sawyers. Although more samples need to be analyzed, he continued, the results could provide a roadmap for designing future clinical trials in this disease. “When it comes to developing and testing targeted cancer drugs, you need to be able to subclassify patients, and you can’t do this intelligently until you know what the alterations are.”

This would change how doctors talk to patients about the disease and the need for adjuvant therapy or not, which is why this finding is so exciting.

—Dr. Jonathan Simons

Genome studies have yielded insights into glioblastoma and cancers of the lung, colon, pancreas, and breast, but prostate cancer has been a challenge. Prostate tumors are relatively small, and expert pathologists are needed to obtain adequate samples of tumor tissue. With a large prostate cancer program and skilled pathologists, MSKCC was able to overcome these challenges.

“Dr. Sawyers and his colleagues have made an extraordinarily important contribution to the field of prostate cancer research,” said NCI Deputy Director Dr. Anna Barker. “Certain tumors are going to be difficult to collect and analyze, but this study—which used high-quality samples and multidimensional data—now gives the community new opportunities to understand the disease.”

The researchers sequenced 157 genes that were known to be associated with prostate and other cancers. Mutations in these genes were rare. But when the researchers included additional information, such as DNA copy-number changes (gains and losses of DNA), they identified several genetic pathways, including the PI3K pathway, that were altered in nearly all metastatic tumors and many primary tumors.

“Just as we’ve seen in brain tumors, when you combine all these different sources of information, there is a uniform consistency of pathways that are altered in the disease,” said co-author Dr. Peter Scardino, chairman of the Department of Surgery at MSKCC. “We found many more abnormalities in localized prostate cancer than we expected.”

The researchers also identified a gene called NCOA2 that appears to play an important role in about 11 percent of prostate tumors. The protein encoded by this gene may drive prostate cancer by amplifying signals from the androgen-receptor pathway; this pathway plays a critical role in early- and late-stage prostate cancer.

Potential Biomarker

The analysis also revealed a striking association between changes in DNA copy number and the risk of recurrence after surgery, and this association could not be explained entirely by Gleason score. “This was one of the most exciting findings from the study,” said Dr. Scardino. “It offers the possibility of a biomarker that could be used to characterize the aggressiveness of prostate cancer, which is something we greatly need.”

Doctors currently do not have a way to distinguish between prostate cancers that require aggressive treatment and those that will cause no harm if left alone. Consequently, many men receive treatment unnecessarily. Genomic tests can provide prognostic information in breast cancer, for example, but none yet exists in this disease.

The new findings, if confirmed, represent a prototype for developing these kinds of prognostic tests for prostate cancer, said Dr. Jonathan Simons, CEO and president of the Prostate Cancer Foundation. “This would change how doctors talk to patients about the disease and the need for adjuvant therapy or not, which is why this finding is so exciting,” he added.

Dr. Scardino runs the Specialized Program of Research Excellence (SPORE) in prostate cancer at MSKCC, and his group has launched follow-up studies. The current work was done using frozen tumor specimens collected during prostatectomies. The researchers will now see whether copy-number changes are informative using paraffin-embedded tissues. If the answer is yes, they will test cells obtained from a needle biopsy.

The genome analysis also revealed that some patients whose tumors include a fusion of the genes TMPRSS2 and ERG are also missing part of chromosome 3. This fusion gene occurs in about half of all prostate cancers, and researchers have suspected that other genes also play a role in these cases.

“This deletion on chromosome 3 appears to be very strongly associated with the fusion,” said Dr. Sawyers. “The next steps are to see which genes in the region that is deleted are involved in the disease. We have a clear path forward.”

The TMPRSS2-ERG fusion was discovered in 2005 by University of Michigan researchers supported by NCI’s Early Detection Research Network. At the time, fusions were thought to be limited to cancers of the blood, but it is now known that these alterations are present in common cancers as well. About two dozen have been identified in prostate cancer.

New Class of Gene Fusions

Earlier this month, the Michigan group, led by Dr. Arul Chinnaiyan, reported a new class of prostate cancer gene fusions derived from the RAF pathway. One of these fusions involves the gene BRAF, which plays a role in melanoma. Drugs targeting BRAF are in clinical trials, and it appears, based on experiments in cells, that these drugs may be active in up to 2 percent of patients with prostate cancer, the researchers reported.

“The clinical promise of this discovery is that patients who have these RAF gene fusions may be candidates for drugs that target these changes,” said Dr. Chinnaiyan. “Some of the newer inhibitors, in particular, might be useful in treating this molecular subtype of prostate cancer as well as some other cancers.”

In the future, every man whose prostate cancer is biopsied is going to have his DNA read for gene fusions, just as women have their breast cancers tested for overexpression of the HER2 protein to determine whether they should receive trastuzumab (Herceptin), predicted Dr. Simons. “To cure every man of advanced prostate cancer, we’ll need at least 24 strategies,” he continued. “Now that we know what we’re facing, we can make research plans and do the work.”

Two prostate cancer genome sequences have been presented at scientific meetings and will likely be published later this year, Dr. Simons said. “It’s a complicated disease, but key properties of the disease are going from being in total darkness to full clarity. And that’s what is so amazing.”

For Dr. Barker, a founder of The Cancer Genome Atlas (TCGA) project with colleagues from the National Human Genome Research Institute, the MSKCC study is both exciting and gratifying. Dr. Sawyers and his colleagues essentially followed the TCGA approach by profiling high-quality tumor samples and integrating clinical and multiple kinds of genomic information into their analysis. As with TCGA, they made the results public so that investigators in the community can now mine the information for new insights.

The hope from the beginning of TCGA has been that the approach would be adopted by investigators performing cancer genomics studies in the community, said Dr. Barker. And now that this study has been completed, TCGA investigators will use the data when they launch an even larger study of prostate tumors in the future.

“This study gives us a much better starting point for prostate cancer than we’ve ever had before,” Dr. Barker said. “It’s a great day for cancer research, and an even better day for patients.”

source:NCI bulletin

Pramipexole for Depression in Parkinson Disease

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The largest study of depression in PD to date demonstrates that pramipexole is a statistically better treatment than placebo, but not by a lot.


Is pramipexole better than placebo for the treatment of mildly to moderately depressed, nondemented people with Parkinson disease (PD)? To find out, researchers conducted a 12-week, double blind, placebo-controlled, multicenter, manufacturer-sponsored trial involving 296 patients with mild-to-moderate depressive symptoms and PD without motor fluctuations.

Pramipexole was statistically superior to placebo in reducing scores on the Beck Depression Inventory (the primary outcome) and on two other depression scales, while also improving motor function. Path analysis suggested that depression benefit was mostly independent of improved motor function. Although improvements on two quality-of-life (QOL) measures correlated with reduced depression, the QOL improvements did not differ significantly between the treatment groups, nor did changes on two measures of pleasure and pain. The drug was well tolerated.

Comment: This is the largest study ever done of drug therapy for depression in PD and appears to have been well designed and well performed. The results showed a surprisingly good tolerance of pramipexole, with scant hallucinations and a suspiciously low incidence of impulse-control problems. The depression benefits were not large but appeared to correlate with improvement in QOL. These results suggest that pramipexole has antidepressant effects, which may explain puzzling observations of reduced depressive symptoms in other blinded studies in which pramipexole was underdosed for treating motor dysfunction. In the current study, the benefits may have been dampened by the exclusion of severely depressed patients. However, even in antidepressant trials in the general population, effects are generally only mildly better than those of placebo.

As of this writing, some evidence suggests that tricyclics are helpful in treating depression in patients with PD, but very little evidence supports the use of selective serotonin reuptake inhibitors. These new results suggest that using pramipexole to treat depression in the setting of PD is reasonable, but only for appropriate patients who are at lowest risk for the common adverse effects of this drug.

— Joseph H. Friedman, MD

Dr. Friedman is Director, Movement Disorders Program, Butler Hospital, and Professor and Chief, Division of Movement Disorders, Department of Neurology, Warren Alpert Medical School of Brown University, Providence, RI. He has received funds for lectures from the manufacturer that sponsored this trial.

Published in Journal Watch Neurology June 29, 2010

High Thyroxine Levels and Risk for Venous Thrombosis

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Hyperthyroidism is associated with a hypercoagulable state. Conversely, hypothyroidism is associated with reduced levels of von Willebrand factor and increased risk for bleeding. To investigate the relation between hyperthyroidism and risk for venous thrombosis, researchers in the Netherlands measured thyroid-hormone and thyroid-antibody levels in 190 patients with a first deep venous thrombosis (DVT) and 379 sex-matched controls.

The mean level of free thyroxine was significantly higher among DVT patients than among controls (16.2 pmol/L vs. 15.4 pmol/L; P<0.01), as was the mean T3 level (1.90 nmol/L vs. 1.79 nmol/L; P<0.01). The higher the thyroxine level, the greater the risk for DVT, such that a level above the reference threshold (>24 pmol/L) was associated with an age- and sex-adjusted odds ratio for DVT of 13.0 (95% confidence interval, 1.1–154.1).

Thyrotropin levels tended to be higher in DVT patients than in controls, but they were not significantly associated with risk for DVT, particularly after adjustment for free thyroxine levels. Levels of thyroid peroxidase antibodies did not differ significantly between DVT patients and controls. Three DVT patients and no controls had overt hyperthyroidism (P=0.02).

Comment: The observational finding that increased thyroid activity is a risk factor for DVT is not intuitively obvious. Patients with hyperthyroidism usually have a hyperdynamic circulation rather than the sluggish blood flow that characterizes venous thrombosis. The investigators suggest that thyroid hormone–induced increases in factor VIII are responsible for the thrombophilia, but they did not use clotting-factor assays to confirm this. It is also possible that thyroid hormone is a surrogate for some other thrombogenic factor. Only large epidemiologic studies can confirm whether a high level of thyroid hormones is a risk factor for DVT. Until then, clinicians confronted with unexplained venous thrombosis might simply consider hyperthyroidism as a possibility.

— David Green, MD, PhD

Published in Journal Watch Oncology and Hematology June 29, 2010

Intensive Glucose Control Reduces Some Microvascular Complications — At the Cost of Increased Mortality

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Intensive glucose control in high-risk diabetes offers mixed results, according to two new analyses from the ACCORD trial.

In ACCORD, patients with type 2 diabetes and elevated cardiovascular risk were randomized to intensive glucose control or standard therapy. About half were also assigned to intensive or standard blood pressure control, and the other half to combination or standard lipid therapy. Intensive glucose control was stopped early, in 2008, because of increased mortality.

Now, writing in the Lancet, ACCORD researchers report that the glucose-control groups did not differ in composite outcomes measuring kidney function, diabetic eye complications, and peripheral neuropathy. However, several components of the composite outcomes (e.g., microalbuminuria, cataract extraction) were less common with intensive glucose control.

And in the New England Journal of Medicine, ACCORD researchers observe that both intensive glucose control and combination lipid therapy reduced progression of retinopathy, while intensive BP control did not.

Despite the microvascular benefits, the Lancet authors conclude, the increased mortality makes aggressive hemoglobin targets in high-risk diabetes seem “imprudent.”

Cholesterol and Alcohol

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A major focus in the battle against heart disease is lowering cholesterol levels.

Not all cholesterol is unhealthy. There are two types of cholesterol. Low-density lipoprotein (LDL) cholesterol is the “bad” type that tends to clog your arteries; high-density lipoprotein (HDL) cholesterol is the “good” kind that helps sweep cholesterol deposits out of your arteries and protects against a heart attack.

Doctors recommend keeping your LDL cholesterol levels low (optimally less than 100 mg/dL), while boosting your HDL levels (60 mg/dL or higher). You may have heard that drinking a glass or two of red wine each day can help raise HDL levels and help reduce your risk of heart disease. It’s true that alcohol has some heart-healthy benefits, but it’s important to be cautious when drinking alcohol because it also has many health risks.

Alcohol Boosts HDL Cholesterol

A few studies have found that people who drink alcohol in moderation have lower rates of heart disease, and might even live longer than those who abstain.

In particular, red wine might offer the greatest benefit for lowering heart disease risk and mortality because it contains higher levels of natural plant chemicals — such as resveratrol — which have antioxidant properties and might protect artery walls.

Many believe that the main cardiovascular benefit of alcohol is through its ability to raise HDL cholesterol levels. Alcohol has also been tied to a lower risk of blood clots and decreased levels of inflammation markers.

Risks of Drinking Alcohol

Before you order a round of wine or beer and toast to your heart, know that the news about alcohol isn’t entirely positive. Consuming too much alcohol can actually increase your risk for heart disease and stroke, raise blood pressure, contribute to obesity, and increase the levels of fats called triglycerides in the blood.

Excessive drinking also can lead to heart muscle disease (cardiomyopathy), irregular heartbeat (arrhythmia), and stroke. Eventually, heavy alcohol use can leave the heart too weak to pump efficiently, a condition called congestive heart failure.

Drinking alcohol also has other downsides, including increased risk of some cancers, cirrhosis of the liver, and an increased risk of accidents. That’s why the American Heart Association does not recommend that you start drinking wine or any other alcoholic beverages specifically to lower your cholesterol or improve your heart health. Instead, the organization advises watching your weight, eating a healthy diet, and exercising regularly to keep your cholesterol levels in check.

If you do plan to drink, check with your doctor first. Drink alcohol only in moderation — meaning a glass of wine or beer a day for women, and a glass or two a day for men. Some people — especially pregnant women and those who take certain medicines regularly — should avoid alcohol entirely.

Dendritic cells and their role in atherogenesis

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Dendritic cells (DCs) are the most potent professional antigen-presenting cells with the unique ability of primary immune response initiation. DCs originate from bone marrow progenitors, which circulate in the peripheral blood and subsequently penetrate peripheral tissues, where they give rise to immature DCs. In peripheral tissues, DCs continuously monitor the microenvironment and, when the cells encounter ‘danger’ signals, DCs undergo differentiation and maturation. Maturing DCs usually migrate to lymphatic tissues, where they form contacts with T cells to initiate a primary immune response. DCs were identified in arteries in 1995 and since then, further knowledge has been gained about the peculiarities of vascular-associated DCs and their role in atherosclerosis. Immune reactions toward modified lipoproteins and other factors ignited by resident vascular DCs as well as by newly arrived DCs, which originate from blood monocytes, are believed to destabilize arterial homeostasis from very earlier stages of atherogenesis. There is a remarkable heterogeneity of DCs in atherosclerotic lesions. Some DCs mature and become capable of forming clusters with T cells directly within the arterial wall. The predictive value of the numbers of circulating DC precursors in coronary artery disease and in atherosclerosis has been assessed, and it has been shown that DCs have a role in plaque destabilization. Over recent decades, DCs have proven to be a valuable instrument in immunotherapy approaches against cancer and various autoimmune diseases, and this explains the demand that the accumulated knowledge be applied to the field of atherosclerosis immunotherapy.

source: Nature

Evidence mounts against diabetes drug

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Studies continue to find heart-attack risk.


Avandia, used to treat type II diabetes, has attracted controversy.CUSTOM MEDICAL STOCK PHOTO/SPL

Patients who take the controversial diabetes drug Avandia are more likely to have a stroke or heart failure, or die, than those who take a rival drug, a survey of more than 200,000 insurance records has revealed.

The finding, published today1 by the Journal of the American Medical Association (JAMA), is the latest salvo in a continuing battle over Avandia (rosiglitazone).

It arrives just weeks before a US Food and Drug Administration (FDA) advisory panel meets on 13 and 14 July to evaluate whether Avandia, which is produced by the London-based pharmaceutical giant GlaxoSmithKline (GSK), should be removed from the market.

The possible health risks of Avandia were brought to light in 2007, when a meta-analysis by Steven Nissen, a cardiologist at the Cleveland Clinic in Ohio, suggested that the drug could cause heart attacks2. This is a particular concern given that diabetics already have a high risk of cardiovascular disease.

Since then, Avandia sales have fallen from £1.6 billion (US$2.4 billion) in 2006 to £771 million in 2009. In the interim, controversy surrounding the drug continued to build. The US Senate launched an investigation into the matter, and concluded this February after a two-year inquiry that GSK was aware of the adverse effects of Avandia on the heart well before the risks were made public.

Heated battle

In a paper published today in Archives of Internal Medicine3, Nissen and his colleague, statistician Kathy Wolski, repeat their 2007 meta-analysis, incorporating new clinical-trial data and addressing some criticisms of their earlier work. They again found that Avandia boosts heart-attack risk — by up to 39%3. “A drug that increases the rate of myocardial infarction by a third in a vulnerable population represents a huge public-health burden,” says Nissen.

Meanwhile, in the study in JAMA, David Graham, a drug-safety researcher at the FDA, and his colleagues analysed the insurance records of 227,571 patients who were treated with either Avandia or Actos (pioglitazone) — a similar drug produced by Takeda Pharmaceuticals, headquarted in Osaka, Japan. The team found that patients taking Avandia were 18% more likely to suffer from a stroke, heart failure, heart attack or death than those on Actos.

“The study by Graham et al. is very convincing,” says Corinne de Vries, an epidemiologist at the University of Bath, UK. “I can’t fault it, and I suspect it might be the nail in the coffin for rosiglitazone.”

Less than two days after Graham e-mailed a pre-publication draft of the article to his colleagues at the FDA, he says he received a phone call from a reporter, seeking to verify the authenticity of the manuscript they had received. The manuscript was posted in its entirety on the popular pharmaceutical blog Pharmalot.

Graham says he believes that someone leaked the draft paper in the hope that releasing the results early would discourage JAMA from publishing the work. (Many journals, including JAMA, reject articles if authors have already released the results to the media.)

“This had all the hallmarks of a dirty trick,” he says. “I was outraged.”

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In a statement issued in response to both Nissen’s and
Graham’s papers, GSK maintains that six clinical trials completed since
2007, taken together, show no increase in heart attack, stroke or
death. Furthermore, the company points to its own meta-analysis, which
uncovered no increase in heart attack. Nissen disputes these findings.

After
Nissen’s 2007 study, the FDA added a warning label to Avandia, but
decided to leave it on the market. At the time, the FDA advisory panel
was concerned that pulling the drug might indirectly implicate Actos,
says Clifford Rosen, an endocrinologist at the Maine Medical Center
Research Institute in Scarborough who served on the panel. As a result,
the panel was loath to take an action that could remove an entire class
of medications, he says.

The JAMA study could ease these
fears because it suggests that Actos is safer than Avandia but just as
effective at lowering blood sugar. The committee will still face a
tough decision, says Rosen, “but there’s not a strong rationale for
continuing to keep rosiglitazone around”.

// ]]>