Effect of physiologic leptin ± IL-1α and fatty acid on healthy cartilage extracellular matrix homeostasis. Forty-eight-hour in vitro tissue culture experiments were performed on macroscopically intact porcine femoral articular cartilage explants to determine the acute effect of leptin stimulation on extracellular matrix synthesis and degradation. (a) Effect of leptin stimulation on collagen and sulfated glycosaminoglycan (S-GAG) synthesis rates determined by radioisotope incorporation of [3H]proline and [35S]sulfate, respectively (N = 9 joints, n = 5 explants per joint). Data are normalized to the average control value per joint. (b) S-GAG release from cartilage explants due to leptin stimulation (N = 12, n = 5). (c) Nitrite and nitrate (NOx) production from cartilage explants due to leptin stimulation (N = 9, n = 5). Leptin-stimulated conditions were not significantly different from control values (P > 0.05). Effect of leptin stimulation on cartilage (d) collagen synthesis, (e) S-GAG synthesis, (f) S-GAG release, and (g) NOx production when co-treated with 0.5 mM fatty acids (FA) or 0.1 ng/ml IL-1α separately or combined (N = 3, n = 5). FA treatment was a 1:1 ratio of palmitic:oleic acids. y axes are on a log scale. *P < 0.05 versus untreated control (dashed line). #P < 0.05 versus zero leptin condition. Data shown are mean ± standard error of the mean.