Effect of leptin on the activation of the STAT pathway in chondrocytes obtained from normal or overweight (BMI <30 kg/m2) and obese (BMI >30 kg/m2) OA patients. The phosphorylation of STAT 1α, -3, -5A and -5B was determined with nuclear proteins obtained from chondrocytes exposed to leptin at 100 ng/ml or 500 ng/ml for 10 minutes. For every patient, experiments were carried out in duplicate and results were expressed as means ± standard error of the mean over control values. * P < 0.05 between leptin-treated and control chondrocytes. BMI, body mass index; OA, osteoarthritis; STAT, signal transducer and activator of transcription.