Some Obesity Linked to Virus

BOSTON, Aug. 23 -- Obesity may be caused -- at least in some cases -- by a virus, researchers said here.
Adenovirus-36, one of a family of about 50 common viruses, appears to cause stem cells in fat tissue to develop into adipocytes rather than other forms of cell, according to Nikhil Dhurandhar, Ph.D., of Louisiana State University in Baton Rouge, told attendees at the American Chemical Society meeting.
What's more, the new fat cells accumulate more fat than similar cells that develop from uninfected stem cells, said Dr. Dhurandhar, the study's senior author.
"Obesity is multi-factorial," Dr. Dhurandhar said. "Infections may be one of the causes."
In the long run, he said, the implication for clinicians is that therapy based on a specific cause of obesity may be more successful than the "blanket therapy" now employed.
Dr. Dhurandhar said the finding opens up the possibility of preventing at least some obesity by targeting the virus with a vaccine. But, he added, fat people shouldn't take the finding to mean that they can blame their condition on a virus.
"This only explains how you got there," he said. "It doesn't absolve you of the responsibility to take care of yourself."
The researchers took adult stem cells from fatty tissue from a broad cross-section of patients who had undergone liposuction.
Half of the stem cells were exposed to adenovirus-36 and half were not, according to Magdalena Pasarica, M.D., Ph.D., also of the Pennington Biomedical Research Center, who presented the study.
After about a week in culture, most of the infected stem cells had developed into adipocytes, but only a few of the uninfected cells did, Dr. Pasarica said in a statement.
What's more, the infected adipocytes accumulated 2.5 times more fat on average than fat cells that developed from non-infected stem cells, Dr. Dhurandhar said. The difference was statistically significant at P<0.05.
Lipid accumulation was higher in cells with a higher viral load, Dr. Pasarica said, and the response was "observed regardless of the donor gender and over an age range of 22 to 57."
The key player in the process is a viral gene, dubbed E4 Orf-1, that's both "necessary and sufficient" to cause the lipidogenic response, Dr. Dhurandhar said.
The researchers showed that using a technique called RNA interference they were able to reduce the expression of the gene in infected cells, he said.
"This is the only gene that causes the effect," he said.
The finding follows epidemiological studies, also carried out by Dr. Dhurandhar's group, that showed that the rate of infection with adenovirus-36 was about 30% in a sample of obese Americans, but only 11% among lean people.
The difference was significant at P<0.05, he said.
"That showed an association with obesity, but still doesn't prove a cause-and-effect relationship," he said.
The group followed with animal studies showing that infection with the virus caused animals to become fatter, he said.