| Osteoarthritis (OA), a progressive degradation of articular cartilage, is a common cause of lameness and decreased performance for athletic horses. Biochemical changes leading to OA cause an imbalance in the normal extracellular matrix (ECM) turnover process with degradation exceeding synthesis. Increased proteolytic enzyme activity is a major factor that is responsible for ECM degradation. Oral supplementation of compounds that prevent cartilage degradation and/or joint injury is an attractive potential solution for lameness. Glucosamine is a potential anti-arthritic compound currently being marketed. It is a naturally occurring, non-toxic molecule that decreased pain and improved mobility in osteoarthritic joints in a number of human studies. However, the biochemical basis to support its potential as an anti-arthritic agent is not well documented. Therefore, the objectives of this work were to (1) develop an equine explant culture system and (2) determine whether glucosamine and its derivatives (glucosamine sulfate and N-acetyl-glucosamine) could inhibit experimentally induced cartilage degradation in explant culture.;Articular cartilage was obtained from the weight bearing region of the antebrachio-carpal and middle joints of horses (2--8 years old) sacrificed for reasons unrelated to lameness. Cartilage discs (3.5mm) were collected and maintained in a modified version of media without serum 2 days prior to the start of 4 treatment days (media were exchanged daily and the recovered media stored at 4°C). On days 1 and 2 lipopolysaccharide (LPS, 10 mug/ml) or recombinant human interleukin-1beta (rhIL-1beta, 50 ng/ml) were added to induce cartilage degradation. To test the potential protective effects of glucosamine, the compound was added in three concentrations (0.25, 2.5, or 25 mg/ml) and treatments were performed in triplicate. To test the effects of the glucosamine derivatives, equimolar concentrations of glucose-3-sulfate and N-acetyl-glucosamine were added. Controls included wells without LPS, rhIL-1beta, or glucosamine. Controls for the sugar moiety included glucose and glucose-3-sulfate. Nitric oxide, proteoglycan and matrix metalloproteinase (MMP) released into conditioned media and tissue proteoglycan synthesis were measured as indicators of cartilage metabolism. Maximal nitric oxide production, proteoglycan release, and MMP activity were detected 1 day after the addition of LPS or rhIL-1beta to the media. The addition of 25 mg/ml of glucosamine HCl prevented the increase in nitric oxide production, proteoglycan release and MMP activity induced by LPS or rhIL-1. Glucosamine sulfate consistently inhibited cartilage degradation in a manner similar to glucosamine HCl, while the effects of N-acetyl-glucosamine were highly variable and generally did not inhibit cartilage degradation. These data substantiate anecdotal in vivo observations and suggest a mechanism through which glucosamine may possess chondroprotective properties in equine articular cartilage. |
