| Osteoarthritis (OA) is a significant problem for both humans and animals. Nutraceuticals such as glucosamine and chondroitin sulfate (CS) are widely used to alleviate symptoms of OA. However, the mechanism(s) of action of these nutraceuticals remains unclear. Bovine articular cartilage explants added with 50 ng/ml interleukin-1 (IL-1) to stimulate cartilage catabolism were used to determine the molecular events of the nutraceuticals. Glucosamine (5 mug/ml) and CS (20 mug/ml), at concentrations attainable in vivo, were supplemented individually or in combination. Glucosamine and CS regulated transiently nitric oxide (NO) synthesis and the expression of genes encoding inducible nitric oxide synthase (iNOS) and microsomal prostaglandin E synthase-1 (mPGEs1). There was concomitant repression of IL-1 induced expression of cyclooxgenase-2 (COX-2) transcript with prostaglandin E2 (PGE 2) production. Glucosamine and CS reduced cytokine up-regulated expressions of matrix metalloproteinase (MMP)-3, MMP-13, aggrecanase (Agg)-1 and Agg-2. The nutraceutical combination was more effective in antagonizing some gene expression than if glucosamine and CS were used individually. There were no treatment effects on gene expression of tissue inhibitor of metalloproteinase (TIMP)-1, TIMP-2, type II collagen and aggrecan although the glucosamine and CS combination tended to elevate TIMP-3 transcript. In a separate study, bovine articular cartilage explants were induced with a subsaturating dose of IL-1 (15 ng/ml) and treated with glucosamine (10 mug/ml) and CS (20 mug/ml). The regulation of molecular events was also characterized at 8, 16 and 24 hours after culture. The combination abrogated IL-1 induced gene expression of iNOS, COX-2, mPGEs1 and nuclear factor kappa beta p65 subunit at all time points. This was accompanied by decreases in NO and PGE2 synthesis. Stimulated MMP-13, Agg-1 and Agg-2 mRNA abundance were down-regulated while TIMP-3 was increased by the nutraceutical combination at all time points. TIMP-3 protein abundance was elevated by the combination. Proteoglycan release, an indicator of proteoglycan loss was suppressed by glucosamine and CS combination. Thus, glucosamine and CS in combination repress the synthesis and expression of genes encoding inflammatory mediators and matrix catabolic enzymes while up-regulating TIMP-3. This provides a plausible mechanism for their mild anti-inflammatory and chondroprotective properties. |
