Osteoarthritis, or degenerative joint disease, may be worsened by metabolic syndrome in obese individuals. A group of Spanish researchers investigated whether high cholesterol is linked to osteoarthritis independently of weight.
Osteoarthritis, or degenerative joint disease, is a common joint disorder that results in joint pain, immobility, and serious changes to the structure of the joints. The main feature of osteoarthritis is the destruction of joint cartilage, but all aspects of the joint, from the bone to the muscle, are affected. Although it appears to be a localized disease, osteoarthritis is linked to many system-wide processes, and some osteoarthritis may be linked to metabolic syndrome.
Metabolic syndrome refers to a cluster of metabolic conditions including insulin resistance, high blood pressure, and high cholesterol. Although some have suggested that osteoarthritis and metabolic syndrome are associated primarily because they are both frequently found in obese persons, obese persons tend to show osteoarthritis in non-weight-bearing joints, suggesting underlying metabolic factors.
To understand whether metabolic syndrome is independently associated with osteoarthritis, Spanish researcher Larrañaga-Vera and colleagues investigated the relationship between high cholesterol and osteoarthritis. Their results were recently published in Arthritis Research and Therapy.
They studied 36 male white rabbits, of which 16 received a high-fat diet and 20 received a normal diet. After six weeks, osteoarthritis was surgically induced in 10 of the high-fat diet animals and 10 of the normal diet animals. Twelve weeks after osteoarthritis induction, the researchers assessed the condition of the joint, the cartilage, and blood lipid levels.
At six weeks, when osteoarthritis was surgically induced, the two groups of rabbits did not differ in weight. After the surgery, rabbits who had undergone surgery gained less weight than those who had not. Although there were no differences between groups in most metabolic factors, the rabbits fed a high-fat diet had significantly higher blood cholesterol levels.
Rabbits on a high-fat diet with induced osteoarthritis had significantly higher inflammation in the synovial cartilage than either rabbits with osteoarthritis and a normal diet, or rabbits with no osteoarthritis and a high-fat diet. Rabbits with osteoarthritis and a high-fat diet also had a consistently higher degree of atherosclerotic cells than any other group, as well as more vascularized cartilage. Fat cells were much more irregularly shaped in the osteoarthritis groups, and most irregularly shaped in the osteoarthritis high-fat diet group.
High-fat diets and high cholesterol in turn seriously worsened osteoarthritis in rabbits without other symptoms of metabolic syndrome. This occurred through inflammation of the synovial membrane, rather than direct damage to the cartilage itself. This strongly suggests that there is a metabolic component to osteoarthritis and that osteoarthritis is worsened in obese individuals not only through the mechanical pressures of extra weight on joints but through inflammation and other metabolic conditions.
Written by C.I. Villamil
Reference: Larranaga-Vera et al. 2017. Increased synovial lipodystrophy induced by high fat diet aggravates synovitis in experimental osteoarthritis. Arthritis Research and Therapy 19:264.