Interviewee: Salomon Amar
Obese versus Lean Mice
Boston University Associate Dean for research, Salomon Amar has found that obese mice are not as effective as lean mice in mounting a counterattack against an infection. In research published in the Proceedings of the National Academy of Sciences, Amar found that the mice’s inflammatory response, part of the body’s defense against infection, was blunted.
Amar fed mice a diet that was many times greater than they needed, and then infected both the now obese mice and a similar group of lean mice that grew up on a normal diet. Amar found that if a lean animal “Would take seven days to eliminate the microorganism, the obese animal would take about 10 days or 12 to 13 days.”
Amar also found that this reduced response had a second problem. Even though it the obese mice had a blunted inflammatory response, it lasted longer than necessary. He says, “You have to understand that the inflammatory response is very bad for the body when it stays longer. It’s there to clean up the damages and then it needs to be removed.” As examples, he notes that extended inflammation is an important problem for diabetics and that in some cases extended inflammation can result in fatal septic shock.
Amar pointed out that in his experiments, he was able to take diabetes out of the equation by infecting the obese mouse before the onset of diabetes. The experiments were also specific to obesity caused by diet, and not some sort of genetic situation.
Amar performed the tests on two different groups of obese mice. One received a general infection, while the other was infected with an infection specific to the mouth. In the mouth-specific infection, the mice showed a greater loss of bone density in the mouth due to the infection.
Amar notes that the connection between infections and obesity is a relatively new area of study and that much still needs to be learned. One area of research is learning better what is it about obesity that reduces the infection response. He says that nothing has been completely established, but adds, “We have ideas and evidence that the signals using the same mechanism that the high fat diets are using.” In other words, the high fat is producing a chemical signal to the body to which the body learns to adapt. He adds, “The high fat diet activates the signal on a chronic basis and the system is too tolerant to the microorganism.”
A second area of research, and one that Amar is working on now, is whether losing the weight will allow the body to return to a normal immune response rate. Amar says at the moment he’s putting obese mice on a weight loss and exercise program, adding, “You’re probably going to laugh, but there is a treadmill that is specifically made for mice.” He says they want to, “See if the ability to fight the infectious agent is regained.”
“I would venture to say that we could regain what has been lost as a result of the diet,” he says, but adds that, “at some point the body probably loses its ability to regain normal infection-fighting function.”
This research appears in the Proceedings of the National Academy of Sciences Online Early Edition for the week of December 10, 2007 and was funded by the National Institute of Dental and Craniofacial Research.
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