The human embryonic stem cells available for research are contaminated with nonhuman molecules from the culture medium used to grow the cells, researchers report.
According to AP, the nonhuman cell-surface sialic acid can compromise the potential uses of the stem cells in humans, say scientists at the University of California, San Diego. Their study was published Sunday in the online edition of Nature Medicine.
Stem cells form very early in an embryo's development. They can develop into numerous types of cells to form organs and other parts of the body. Researchers hope to use these cells to repair damaged organs and cure diseases.
The work is controversial because the cells are taken from days-old embryos, which then die. Opponents say this is unethical.
"People have always been concerned about the possibility that something deleterious might be transferred from feeder cells to stem cells. This puts a face on that substance," Dr. James Battey, chairman of the stem cell task force at the National Institutes of Health, said about the new report.
This is a safety consideration, along with many others that will need to be addressed, Battey said in a telephone interview.
The paper suggests that growing new stem cell lines in ways that avoid animal contaminants. Battey also suggested that existing cells might be isolated from animal products for a time, allowing the acid to be diluted.
The study reports that the cell lines currently approved for study under federal funding contain a sialic acid called N-glycolylneuraminic acid, or Neu5Gc.
Human embryonic stem cells are contaminated by this acid "even when grown in special culture conditions with commercially available serum replacements, apparently because these are also derived from animal products," said the lead researcher, Dr. Ajit Varki.

High cholesterol, hypertension, diabetes and smoking have long been considered--and aggressively treated--as risk factors for cardiovascular disease. These same cardiovascular (CV) risk factors in middle age may also increase significantly the risk of dementia in old age, according to Kaiser Permanente researchers.
According to psychport.com, the study, of nearly 9,000 northern Californians, appears in the January 25 issue of Neurology, the scientific journal of the American Academy of Neurology.
Compared to those with no risk factors, those with two of the risk factors were 1.7 times more likely to be diagnosed with dementia. Those with three risk factors were more than twice as likely, and those with all four risk factors had a 2.37 times greater risk of being diagnosed with dementia, according to lead investigator Rachel A. Whitmer, PhD, a researcher with the Kaiser Permanente Division of Research in Oakland, California.
Correspondingly, treating one's risk factors for heart disease may also reduce the risk for dementia, said Whitmer. And earlier treatment may have an even greater benefit by virtue of the cumulative effect of longer exposure to protective therapies, she said.
Each of these four CV risk factors identified at mid-life (age 40 to 44) was associated with a 20 to 40 percent increased risk of dementia in later life. Those with diabetes were 46 percent more likely than those without diabetes to develop dementia. Similarly, those with high total cholesterol were 42 percent more likely, and those with hypertension were 24 percent more likely. Participants who reported ever smoking at mid-life were 26 percent more likely to develop dementia. The effects of cardiovascular risk factors on risk of dementia were the same across race and gender groups.

Physicists have trapped 50 times more antiprotons than ever before at the Antiproton Decelerator (AD) at CERN. Moreover, Yasunori Yamazaki and co-workers from Japan, Hungary and CERN have also been able to extract antiproton beams with lower energies than achieved.
According to PhysicsWeb.org, the ultraslow antiprotons could be used in a variety of experiments in fundamental physics.
The antiprotons are produced when high-energy protons collide with an iridium target, and are then decelerated from 3.5 GeV to 5.3 MeV by the AD, which delivers about 20 million antiprotons in short pulses or "shots" at 100 second intervals.
However, these antiprotons are still too energetic for most experiments, including the "recombination" of antiprotons and positrons to form antihydrogen. Previous efforts to reduce the energy to the keV range by passing the beam through a "degrader" foil have only been able to capture about 25000 antiprotons in a typical AD shot.
Yamazaki and colleagues replaced the degrader foil with a radio-frequency quadrupole decelerator (RFQD) -- a device that slows the particles with a series of electric fields. This allowed the team to decelerate between 5 and 9 million antiprotons to keV energies in a single AD shot.
The antiprotons were then injected into a multiring trap (MRT), where they were confined by a combination of an electric field and a strong magnetic field. Since the antiprotons have already been decelerated by the RFQD, it is easier to contain them in the MRT. The antiprotons can be cooled further through collisions with cold electrons that have been preloaded into the trap.
Yamazaki and co-workers obtained as many as 1.2 million cold antiprotons per AD shot using this method. Moreover, they were able to extract a small number of monoenergetic antiprotons with energies in the range 10 to 250 eV as the particles continued cooling.

A team of US scientists claims to have created petrified wood in just a few days, mimicking a natural process that normally takes millions of years, BBC News website said.
Researchers from Pacific Northwest National Laboratory turned wood into mineral by soaking poplar and pine in a solution and then cooking them.
The process could provide new ways of filtering pollutants, soaking up contaminants and separating chemicals.
Details of the research appear in the journal Advanced Materials.
Petrified forests can form when trees are buried without oxygen, leaching out their woody compounds and sponging up the soil's minerals over millions of years.
To mimic this process in the lab, the team led by Yongsoon Shin bought pine and poplar boards. A 1cm cube cut from these boards is placed in acid for two days, before being soaked in a silica solution for two more.
Next, the cube is air-dried, placed in a furnace filled with argon gas which is gradually raised to 1,400C and left to cook for two hours.
Finally, the cube is left to cool in argon to room temperature.
Silica takes up permanent residence with the carbon left in the wood's cellulose to form silicon carbide, a ceramic.