Associations of serum leptin concentration with gender, fat mass, interleukins, and growth factors in patients with osteoarthritis of the knee

Aging, obesity, and female gender are risk factors for osteoarthritis (OA) of the knee. Basic research has suggested that leptin may play an important role in the pathological process of OA, and that interleukins (ILs) and growth factors may be related to this process. The objective of the present clinical study was to examine the possible correlations between the serum leptin concentration and gender, fat mass, and the IL and growth factor levels in synovial fluid among patients with knee OA. Forty-four patients with knee OA and hydrarthrosis (age: 50-88 yr) were recruited in our outpatient clinic. Plain radiographs of the knee were taken, and blood and synovial fluid of the knee joint were collected. The serum leptin concentration was significantly higher in women than in men. A simple linear regression analysis showed that body weight, body mass index, and total fat mass, but not age, height, radiographic grade of knee OA, lean body mass, or the levels of IL-6, transforming growth factor-beta (TGF-beta), or insulin-like growth factor-1 (IGF-1) in synovial fluid were significantly correlated with the serum leptin concentration. A multiple regression analysis showed that among gender and the three above-mentioned significant factors, only gender and total fat mass were significantly associated with the serum leptin concentration. These results suggested that the serum leptin concentration was higher in women than in men and that it was related only to an increased total fat mass in patients with knee OA. However, the present clinical study failed to show a significant correlation between the serum leptin concentration and the IL or growth factor levels in synovial fluid.