Science News and Notes
Monday, April 26, 2004
Rate Of Ocean Circulation Directly Linked To Abrupt Climate Change
Source: Woods Hole Oceanographic Institution
Date: 2004-04-26 URL Link
A new study strengthens evidence that the oceans and climate are linked in an intricate dance, and that rapid climate change may be related to how vigorously ocean currents transport heat from low to high latitudes.
A new study, reported April 22 in the journal Nature, suggests that when the rate of the Atlantic Ocean's north-south overturning circulation slowed dramatically following an iceberg outburst during the last deglaciation, the climate in the North Atlantic region became colder. When the rate of the ocean's overturning circulation subsequently accelerated, the climate warmed abruptly.
Study author Jerry McManus and colleagues Roger Francois, Jeanne Gherardi, Lloyd Keigwin and Susan Brown-Leger at the Woods Hole Oceanographic Institution and in France report that the coldest interval of the last 20,000 years occurred when the overturning circulation collapsed following the discharge of icebergs into the North Atlantic 17,500 years ago. This regional climatic extreme began suddenly and lasted for two thousand years. Another cold snap 12,700 years ago lasting more than a thousand years and accompanied another slowdown of overturning circulation. Each of these two cold intervals was followed by a rapid acceleration of the overturning circulation and dramatically warmer climates over Northern Europe and the North Atlantic region. (See map-diagram at link)
McManus and colleagues studied a seafloor sediment core from the subtropical North Atlantic that was retrieved from an area known as the Bermuda Rise. The core contains sediments deposited over tens of thousands of years that include shells of small animals called foraminifera that record surface water conditions in their shells when alive. The researchers measured oxygen isotope ratios in each individual sandgrain-sized shell to determine climatic changes that occurred since the last ice age. They used a new tool, based on two daughter isotopes of uranium that occur naturally in seawater, as a proxy for changes in the rate of ocean circulation. The technique has been used for other purposes in the past, but this is the first time it has been used to generate a detailed time series that provides a history of variations in the strength of ocean circulation.
The isotopes, protactinium and thorium, are produced at constant rates in seawater by radioactive decay from dissolved uranium and are removed quickly by adhering to particles settling to the ocean floor. Thorium is removed so rapidly by particles that it resides in the water column no more than a few decades before nearly all of it is buried on the sea floor below where it was produced. Protactinium is removed less readily and thus remains in the water column 100 to 200 years. As a result, about half of the protactinium produced in North Atlantic water today is exported into the Southern Ocean as part of the ocean circulation system known as the great conveyor. At times when the rate of overturning circulation slows, the proportion of protactinium buried in the North Atlantic sediments increases, thus preserving the record of such changes in the accumulating sediments. The research team found that the rate of ocean circulation varied remarkably following the last ice age, with strong reductions and abrupt reinvigorations closely tied to regional climate changes. McManus says this is the best demonstration to date of what many paleoclimatologists and ocean scientists have long suspected. "Strong overturning circulation leads to warm conditions in the North Atlantic region, and weak overturning circulation leads to cold conditions," he said. "We've known for some time from changes in the chemistry of the seawater itself that something was different about the ocean's circulation at times of rapid climate changes, and it now appears that the difference was related to changes in the rate of ocean circulation. One big question is why the circulation would collapse in the first place and possibly trigger abrupt climate change. We think it is the input of fresh water to the surface ocean at a particularly sensitive location."
McManus says the team is now applying this same technique to sea floor cores collected in other regions of the North Atlantic. "We've made a little step forward in understanding the ocean's role in the climate puzzle, but there are more pieces to fill in." The WHOI study was funded by the National Science Foundation, the Institution's Ocean and Climate Change Institute and an Interdisciplinary and Independent Study Award, and by the Comer Science and Education Foundation.
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Researchers Discover Cold Virus Can 'Hit And Hide'
Source: Imperial College Of Science, Technology And Medicine
Date: 2004-04-26
URL: http://www.sciencedaily.com/releases/2004/04/040426055429.htm
An international team of researchers has discovered that respiratory syncytial virus (RSV), a common cold virus causing bronchiolitis in children, can act as a 'hit and hide' virus. It was thought that the virus could only survive in the body for a few days, but these new results show that the virus can survive for many months or years, perhaps causing long-term effects on health, such as damage to the lungs.
The research, published in this month's American Journal of Respiratory and Critical Care Medicine, was a joint project between Imperial College London, St Mary's Hospital, London and the Ruhr-Universitat Bochum, Germany. Professor Peter Openshaw, from Imperial College London and St Mary's Hospital, and one of the papers authors, comments: "These studies show that RSV is a 'hit and hide' virus, rather like HIV, herpes or some hepatitis viruses. The symptoms seem to go away but the virus is just hiding, waiting for a chance to re-emerge and begin infecting other people."
The researchers infected mice with the human RSV, and found that after 14 days, the virus could no longer be found in samples taken from the airways, but tell-tale traces of the virus's genetic material (viral RNA) were still found lying dormant in lung tissue over 100 days later. The team believes that this may also be the case in humans, and that long after the initial symptoms, such as coughs and sneezes, have disappeared, the virus could lie dormant in the body. It is possible that the recurrent wheezing which occurs in children who have suffered from bronchiolitis may be due to virus hidden in the lung.
Professor Openshaw says: "Some people may be 'carriers', able to act as a source of new outbreaks in children. If RSV is a 'hit and hide' virus, this could explain where this virus goes in the summer and where it comes from each winter. If the virus is able to lie dormant in previously infected individuals, it could re-emerge when the conditions are right and cause the outbreaks that fill our children's wards each winter."
RSV is very common infecting most children during their first year of life and for some infants RSV leads to bronchiolitis, one of the major causes of infant hospitalisation in the Western world. Around 40 percent of infants who experience bronchiolitis as a result of RSV infection are subsequently affected by recurring wheeze and up to a third can also suffer with childhood asthma.
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Wednesday, April 14, 2004
Star Making Peaked Five Billion Years Ago; Expect Darkness
PHILADELPHIA -- The universe reached the climax of its star-building activity five billion years ago -- more recently than previously thought -- according to researchers at the University of Pennsylvania and the University of Edinburgh.
The astronomers sifted through the fossil record of 96,545 nearby galaxies to chronicle the complete history of star formation over time. Their findings, reported in the April 8 issue of the journal Nature, also determined that the more massive a galaxy the earlier its stars were formed, indicating that galaxies form stars differently depending on weight.
"If we want to understand how structure in the Universe formed and evolved, then we need to understand the history of the stars," said Raul Jimenez, an assistant professor in Penn Department of Physics and Astronomy. "Fortunately we can read the history of the stars. By analyzing all of the light coming out of a particular galaxy that is, the entire spectrum of visible light we can effectively see the entire 'fossil record' of that galaxy at one glance."
While paleontologists generally need to dig down to find their fossil record, Jimenez and his colleagues needed only to look up, in this case to look up data from the Sloan Digital Sky Survey. To sift through data from nearly 100,000 galaxies, Jimenez and Edinburgh astronomer Alan Heavens created a program called Multiple Optimized Parameter Estimation and Data Compression (MOPED) that analyzes spectrum data quickly by compressing information into more manageable blocks.
"Stars of different masses evolve with different luminosities, so by looking at the integrated spectrum of a galaxy we can track those different luminosities, their masses and, therefore, how long ago they were born," Jimenez said. "Our method takes into account all the stars that are present in the observed galaxies today and allows us to create the most complete history of star formation yet assembled."
According to the researchers' findings, star formation in the universe peaked, on average, about five billion years ago. By the time our own sun was born, about 4.7 billion years ago, almost half of the stellar mass in the universe since the big bang was already created. Star formation has drastically dropped off since then and, as new stars are not being created faster than old stars are dying, this will lead to the gradual dimming of the universe.
The findings also show a difference in star formation between low-mass and high-mass galaxies. Galaxies with a higher mass, our own Milky Way among them, formed most of their stars well before galaxies of a lower mass did.
"The mass-dependence of the star-formation history explains why previous surveys showed a much earlier date for star formation, since those studies were only able to examine more massive galaxies," Jimenez said.
In an accompanying paper submitted to the Monthly Notices of the Royal Astronomical Society, Jimenez and his colleagues have explored how these results shed light on the assembly of dark matter, the mysterious component of the universe that holds galaxies together.
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Statins And Aspirin May Protect Against Severe Vision Loss In Elderly
Cholesterol-busting statins, the largest-selling prescription drugs in the U.S., may protect older people from blindness, a new study shows. Aspirin also appears to provide significant protection, according to the research.
Scientists at UCSF assessed the use of statins and aspirin among more than 300 elderly patients with age-related macular degeneration, or AMD, a common condition among people over 70. About one in eight cases of AMD deteriorates into what is called wet AMD, the leading cause of irreversible severe vision loss in older people.
The scientists found that those patients already taking statins were half as likely as those without statins to develop the more severe wet AMD, caused by the growth of new blood vessels underneath the retina. Those already on aspirin were about 40 percent less likely to develop this new blood vessel growth, technically called choroidal neovascularization (CNV).
The research is reported in the April issue of the American Journal of Ophthalmology.
"Standard treatments for wet AMD often result in stabilization of vision loss, rather than improved vision, so it's important to identify treatments that may prevent the disease," said Jacque L. Duncan, MD, assistant professor of ophthalmology at UCSF and senior author of the study.
Of the few earlier studies of the possible relationship between statins and either early or late AMD, three supported an association and one did not. All these studies involved relatively small numbers of people with wet AMD, Duncan said.
"This study is probably the strongest support we can get for the benefits of statins and aspirin against AMD," Duncan said. "A randomized controlled trial is unlikely to occur, because it would withhold statins and aspirin from the control group, and these drugs have been shown to save lives."
Some patients were on statins alone, some on aspirin alone, and some on both, Duncan noted. A statistical analysis found that both statin use and aspirin use were independently associated with reduced risk of CNV.
Earlier studies had suggested that statins' ability to lower cholesterol levels in the blood may account for their protective effect against macular degeneration, since some evidence suggests that fat deposits in eye membranes may lead to AMD. But Duncan and her colleagues found no association between cholesterol levels after statin treatment and wet AMD.
The most likely, but still unproven, explanation involves the anti-inflammatory properties of both statins and aspirin, Duncan said. Tissue studies of patients with CNV reveal chronic inflammatory cells and other evidence of inflammation. Statins inhibit production of proteins involved in inflammation and reduce the role of immune cells in inflammation. They also are antioxidants, which have been shown to reduce risk of CNV in AMD patients.
"There are lots of good reasons to be on statins and aspirin," Duncan concludes. "This study suggests yet another potential benefit. Although we are not sure of the mechanism, these drugs appear likely to have a protective effect against the leading cause of irreversible severe vision loss in older people."
The study also supported earlier findings that development of the harmful CNV is significantly more common among smokers.
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Researchers Identify Unifying Code Among Diverse Classes Of Natural Antibiotics
Torrance, Calif. (April 12, 2004) – Investigators at the Research and Education Institute (REI) at Harbor-UCLA Medical Center have identified a novel structural signature that is conserved in otherwise distinct classes of antimicrobial peptides. Antimicrobial peptides are small, naturally occurring protein antibiotics that protect organisms – including man - against infection. The discovery of such a broadly encompassing structural signature within these ancient host defense peptides could significantly accelerate development of novel molecules to fight multi-drug resistant infections.
In a research article published in the April 12 issue of the Proceedings of the National Academy of Sciences of the United States of America (PNAS), Principal Investigators Nannette Yount, PhD, and Michael Yeaman, PhD, integrated novel proteomic methods with established microbiologic techniques to reveal previously hidden structural codes common to broad classes of antimicrobial peptides from diverse organisms spanning nearly 4 billion years of evolution. Proteomics is a relatively new field of biomedical research that uses powerful computational methods to analyze molecular databases – and uncover complex structure-function codes that would otherwise remain unknown.
Using a unique combination of proteomic methods, Yount and Yeaman discovered the antimicrobial peptide signature, which integrates inverse amino acid sequence patterns and a hallmark 3-dimensional motif. This multidimensional signature is conserved in disulfide-stabilized antimicrobial peptides across biological kingdoms, and transcends motifs previously limited to defined peptide subclasses. Illustrating the promise of their findings, experimental data validating the multidimensional signature model enabled the identification of previously unrecognized antimicrobial peptides and peptide classes.
"Our work builds upon the efforts of many excellent researchers in the field. We believe this discovery offers new insights into the evolution of immune defense against infection – and drives new technology that takes advantage of the fact that antimicrobial peptides inhibit many microbial pathogens that resist conventional antibiotics," said Drs. Yount and Yeaman. "The multidimensional signature in these antimicrobial peptides provides a unifying structural code that likely reflects fundamental interactions between host and pathogen that have been taking place over profound spans of time. In addition to its potential for use in developing novel anti-infective strategies, this structural signature will facilitate the discovery of antimicrobial molecules as yet unknown, and offers a new understanding of how Nature has conserved effective molecular determinants of immune defense in diverse species, ranging from microbes to man." Yount and Yeaman are Faculty of the Division of Infectious Disease at Harbor-UCLA Medical Center, a nationally recognized teaching hospital within the Geffen School of Medicine at UCLA in Los Angeles.
Dr. Terry Smith, Investigator at the Research and Education Institute, and Chief of Molecular Medicine at Harbor-UCLA Medical Center, agrees that the potential benefits of this research are enormous. "Previous analyses distinguished antimicrobial peptides by differences in one-directional amino acid sequences, or overall secondary structures. These approaches did not uncover more comprehensive structural motifs that are conserved among diverse classes of antimicrobial peptides. The discovery of multidimensional signatures in host defense peptides by Drs. Yount and Yeamen will help to create molecules with strategic functions, potentially enabling new and effective treatments for drug-resistant infections. Moreover, it validates a new method to identify cryptic structural codes in other types of proteins that could significantly advance our ability to prevent or treat infections and non-infectious disease in man."
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