DON鈥橳 blame overeating for the obesity epidemic 鈥� blame a virus instead. It might sound like a lame excuse, but the idea that an infectious virus could be making some people fatter gained credibility this week, as researchers showed that a relative of the common cold virus, called adenovirus-36, can stimulate human fat stem cells to turn into flab.
Nikhil Dhurandhar at Louisiana State University in Baton Rouge and his colleagues had already shown that adenovirus-36 and a similar virus, called SMAM-1, could make animals put on weight. While 30 per cent of obese people and 11 per cent of people of average weight already have antibodies against the virus, suggesting prior infection, it would be unethical to deliberately infect people with adenovirus-36 to see if they fattened up. So Magdalena Pasarica, also at Louisiana State University, did the next best thing by using human stem cells isolated from fat extracted during liposuction. When she infected these stem cells with adenovirus-36 they began to multiply and became bloated with fat.
鈥淚t would be unethical to deliberately infect people with the virus to see if they fattened up鈥�
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鈥淭he end result is more, fatter, fat cells,鈥� says Pasarica, who presented her results at the American Chemical Society meeting in Boston this week. She also reported similar effects in mouse cells earlier this year (). Exposure of the human stem cells to other viruses had no effect.
As for whether virus-induced obesity could be contagious, Dhurandhar says the lab animals infected with the virus spread it to their infection-free cage mates within 12 hours. 鈥淲e can鈥檛 say this definitely happens in humans but, in theory, it can.鈥� Adenovirus-36 is already known to cause eye and respiratory infections in humans.
Pasarica鈥檚 findings suggest it may eventually be possible to combat obesity transmitted by adenovirus-36 by vaccinating people against it or killing it with antiviral drugs. Already, Pasarica has shown that cidofovir, an antiviral drug given to people with AIDS to treat genital warts and viral infections of the eye, can stop adenovirus-36 from turning cells fatty in mice. For now, however, the team鈥檚 primary objective remains to establish exactly how the virus affects fat stem cells.
Other researchers are intrigued, but stress that overeating and lack of exercise are likely to remain the major factors driving the spread of obesity, which now affects almost 100 million American adults. 鈥淚t鈥檚 fascinating, but I can鈥檛 accept that the virus is a common cause of obesity,鈥� says Steve Bloom, an obesity researcher at Hammersmith Hospital in London.
鈥淭he earlier claims about viruses causing obesity have been substantiated by the newer evidence,鈥� says Arne Astrup of the University of Copenhagen in Denmark, 鈥渂ut we need further robust evidence before we start vaccination programmes or isolation of obese people.鈥�
