A Duke University study reveals that the absence of the appetite hormone leptin can determine whether obese mice experience arthritis, no matter how heavy they are. As such, the link between osteoarthritis and obesity may be more than the wear and tear caused by extra weight. The research team from Duke University conducted the study to learn whether or not the increased body fat of obesity causes an inflammatory response in joints, an imbalance of the immune system that signals chemicals in osteoarthritis. The researchers studied mice that were leptin-deficient or deficient in leptin receptors, and both types of mice overate and gained weight.

The study mice were then compared with normal mice to document knee osteoarthritis. The measurements included pro- and anti-inflammatory cytokines present in arthritis, and several tests to assess bone changes in the knees of the mice. The results of the study showed that the knee bones of the leptin-free, obese mice did change, but without forming osteoarthritis. The levels of inflammatory cytokines, which correlate with arthritis, were largely unchanged in this group. The results suggested that leptin might have a dual role in the development of osteoarthritis by regulating both the skeletal and immune systems, according to a Duke Medicine news release.

Farshid Guilak, PhD, of Duke University, says, “We were completely surprised to find that mice that became extremely obese had no arthritis if their bodies didn’t have leptin. Although there was some earlier evidence that leptin might be involved in the arthritis disease process, we didn’t think that there would be no arthritis at all.” Guilak adds, “However, in another study, we found that mice that gained half as much weight on a high-fat diet but processed leptin normally showed significant knee osteoarthritis.”

In regards to what this means for obesity, Guilak says, “Obesity is still the number one preventable risk factor of osteoarthritis, but now it seems body fat by itself is not what is causing it.” Guilak explains, “With obesity and osteoarthritis, there are good similarities between humans and mice. If we can find a pathway that links a high-fat diet with arthritis, then we can try to identify and block the inflammatory mediators that are linked with the dietary fat.”

[Source: Duke Medicine]