Virus may play role in obesity and bone loss


Obesity Initiative at UGA

Source: Yale Rudd Center for Food Policy & Obesity.

Source: Yale Rudd Center for Food Policy & Obesity.

A sinister virus is creeping up to young, impressionable cells and influencing them to turn into insidious globs of fat.

Or so scientists think.

The idea that viruses are invading cells and making people fat is controversial. Researchers from the University of Georgia (UGA) are adding to a growing pile of evidence linking a virus called adenovirus 36 (Ad36) to obesity in humans.

A previous post detailed some of this research.  Earlier this year, the researchers published one study on Ad36, obesity and bone strength in Journal of Bone and Mineral Research.

The researchers reported that female obese teenagers were more likely to have antibodies against Ad36 than their normal weight counterparts. The antibodies show that the person was previously infected with the virus. In addition, obese teens with Ad36 antibodies had weaker and more brittle bones than obese teens without the antibody.

“The big picture when we had this idea [was] to prove solidly that adenovirus has an effect on obesity in humans,” said Srujana Rayalam, one of the co-authors of the study.

However, Rayalam said that the group still needs to do more studies, preferably in people of different ages and genders to truly say that bone loss and weakness in obese individuals is caused by Ad36.

Ad36 belongs to a family of adenoviruses that cause pinkeye, the common cold, gastroenteritis and other human miseries.

It is still unclear how Ad36 is involved in bone and obesity. Emma Laing, lead author of the study, thinks bone loss and weakness is due to Ad36 attacking a group of cells called mesenchymal stem cells. These stem cells are highly suggestible and have the potential to mature into bone, muscle or fat. Ad36 is thought to steer the stem cells away from a life in bone and force them to become fat instead.

A 2012 study on the same line of cells supports this idea. Researchers infected human stem cells with Ad36 and another adenovirus, Ad2. Only stem cells infected with Ad36 stored fat.

The link between Ad36 and obesity is clear in animals.

After being deliberately infected with the virus, mice, chickens and marmosets fattened up.

However, the connection is harder to demonstrate in humans. It would be unethical, of course, for researchers to infect humans with a virus to see if they gain weight.

Instead, scientists have used antibody tests to look back in time. Like the UGA researchers, others have tested blood from obese and non-obese people to see if they had been exposed to Ad36 in the past and had antibodies against it.

The first definitive link between fat and Ad36 in humans came in 2005. A group of scientists tested four different viruses and found Ad36 to be the only virus associated with increased weight.

“There is little convincing data [that viruses cause obesity],” said Ralph Tripp, the virologist for the UGA group. “However, we have made a strong association.”

In the future, Rayalam says that their study needs to be repeated at least one more time, especially to look at effects in older adults.

“Because with aging and adiposity, what you see is bone loss,” she said. “We have to see whether with adiposity and Ad36, [we] still have a positive correlation in late adults.”

Eventually, the group hopes to develop a vaccine against Ad36 to stop the production of more fat cells and keep bones strong. Tripp thinks that day will come, though it won’t be tomorrow.

“I think the future is very close for showing this academically; however, it will be a decade away from FDA approval due to compliance and related issues commonly associated with vaccinology,” he said.

The above post is a guest post by Hyacinth Empinado, a graduate student in UGA’s Health and Medical Journalism Program.