Obese people are more likely to have osteoarthritis, but a new study from OMRF shows it could be more than just weight that’s affecting joints.
In a paper published online today in the journal Arthritis & Rheumatism, OMRF scientist Tim Griffin, Ph.D. and researchers from Duke University found that mice that became obese because they could not produce or sense the weight-regulating hormone leptin were not more likely to develop osteoarthritis than normal-weight mice. In contrast, previous research has shown that mice that become obese from being fed a high-fat diet do have increased levels of osteoarthritis, even though they weigh significantly less than the obese leptin-deficient mice.
Osteoarthritis affects the cartilage between bones. Normally, the cartilage lets bones move smoothly over one another without damage and absorbs the shocks produced by physical movement. But the cartilage breaks down in osteoarthritis patients, causing pain, swelling and loss of motion.
“We used three kinds of mice in our study: some couldn’t make a functional form of leptin, others couldn’t detect normal leptin and finally regular mice that were normal weight,” Griffin said. “While the obese mice that couldn’t produce or sense leptin weighed more than three times the normal mice, we found that the obese had mice had joints that were just as healthy as the normal weight mice.”
This suggests that osteoarthritis in obese people is not only caused by carrying too much weight, but that other obesity-related factors, such as leptin production, could play a role he said. Leptin levels are higher in obese people. These findings are consistent with prior research showing that obese people are also more likely to have osteoarthritis in their hands, a non-weight bearing joint.
Griffin found that mice that did not produce or sense leptin had altered bone thickness in the joints and less inflammation throughout the body than would be expected for mice that become obese from a high-fat diet. “We found that leptin affects numerous systems at the center of osteoarthritis—bone, inflammation, and weight,” Griffin said.
“One of the main reasons that obese patients don’t exercise is because osteoarthritis makes it so painful,” he said. “If we can stop the vicious cycle and stop the osteoarthritis, we might make it easier for people to exercise, lose weight, and live a longer, healthier life.”
Griffin said the next step in the research is to feed normal and leptin-impaired mice different types of high-fat diets to see if disabling leptin production would protect the mice from diet-induced osteoarthritis.
“Obesity is an epidemic all over the United States, but especially in Oklahoma,” he said. A study released earlier this month by the Pew Charitable Trusts found that more than 30 percent of Oklahomans are obese, the fourth highest obesity rate in the country. “Hopefully, this research will lead to a healthier and happier state.”
The research was funded by grants from the National Institute of Arthritis, Musculoskeletal and Skin Diseases and the Arthritis Foundation.