Relations between chondrocyte responsiveness to leptin and BMI of OA patients. Chondrocytes were exposed to leptin at (a) 100 ng/ml or (b) 500 ng/ml and mRNA levels for type 2 collagen, insulin growth factor-1 (IGF-1), tissue inhibitor of metalloproteinase (TIMP)-2 and matrix metalloproteinase (MMP)-13 were determined by quantitative real-time PCR. For every patient, experiment was carried out in triplicate, and results were expressed as means over control values. Correlations were calculated by Spearman's correlation analysis (r, correlation coefficient with p value of correlation). P < 0.05 was considered significant.