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Obesity Virus: More, Bigger Fat Cells

Common Virus Boosts Fat-Cell Production -- and Makes Fat Cells Fatter

By Daniel J. DeNoon
WebMD Medical News

Reviewed by Louise Chang, MD

Aug. 20, 2007 - Infection with a virus linked to human obesity ups fat-cell production and makes fat cells fatter.

"Infectobesity" is the term coined by Louisiana State University researcher Nikhil Dhurandhar, PhD, and colleagues to describe the phenomenon. Their research strongly links a common human virus -- adenovirus-36 or Ad-36 -- to human obesity.

Previous research showed that nearly 30% of obese people, but only 11% of lean people, have been infected with Ad-36. Monkeys experimentally infected with Ad-36 gain significant weight.

Now Dhurandhar's team finds evidence that Ad-36 has a direct effect on human fat cells. Infection of adult stem cells from human fat triggers their transition into pre-fat cells. And these virus-infected cells hold much more fat than normal pre-fat cells.

The end result: more, fatter fat cells.

Dhurandhar colleague Magdalena Pasarica, MD, PhD, presented the findings at the 234th national meeting of the American Chemical Society, held Aug. 19-23 in Boston.

"We're not saying that a virus is the only cause of obesity, but this study provides stronger evidence that some obesity cases may involve viral infections," Pasarica says in a news release. "We would ultimately like to identify the underlying factors that predispose some obese people to [the effects of] this virus and eventually find a way to treat it."

It's not entirely clear how the virus acts on fat stem cells. But Pasarica reported a major clue: One specific Ad-36 gene, called E4Orfl, is responsible for the virus's obesity-related effects.

The researchers are now trying to figure out why some people seem to become obese after Ad-36 infection while others don't.

There are some 50 adenovirus strains. Various strains cause some 5% of respiratory infections every year, ranging from mild colds to serious pneumonia. Some of these viruses also cause eye infections. Ad-36 was originally isolated from a German girl with diabetes; however, it has not been linked to any specific disease.

A vaccine, used by the military, can prevent some types of adenovirus infection. However, the adenovirus strains used in this vaccine are very different from the Ad-36 strain.

Dhurandhar first became interested in obesity-related viruses while working in India. There he investigated a peculiar phenomenon: Chickens infected with a deadly avian adenovirus became fatter, not thinner, before they died.

When Dhurandhar moved to the U.S. to pursue his studies, he found that agriculture authorities were not going to allow him to import the chicken virus. So he began looking for human adenovirus strains that might have the same effect. That led to the discovery of the obesity-related effects of Ad-36.

Interestingly, other researchers have implicated another human adenovirus -- Ad-37 -- in human obesity.

SOURCES: 234th national meeting of the American Chemical Society, Boston, Aug. 19-23, 2007. News release, American Chemical Society. Atkinson, R.L. International Journal of Obesity, March 2005; vol 29: pp 281-286. Whigham, L.D. American Journal of Physiology: Regulatory, Integrative, and Comparative Physiology, January 2006; vol: 290 pp: R190-R194. Dhurandhar, N.V. Journal of Nutrition, 2002; vol: 132 pp: 3155-3160.

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