The role of glucosamine and chondroitin sulfate in treatment for and prevention of osteoarthritis in animals

J disease, in particular osteoarthritis, is an important cause of lameness and debilitation for humans and other animals. Presently, a number of pharmacologic agents are available for treatment for osteoarthritis, including nutraceuticals containing glucosamine and chondroitin sulfate. Although to date clinical trials in veterinary patients are limited, trials conducted in humans have for the most part provided encouraging results. Results of in vitro studies suggest that these compounds may impede the progression of joint degeneration in osteoarthritis. The purpose of this review is to provide veterinary practitioners with up-to-date information regarding the mechanism of action, pharmacokinetics, clinical efficacy, and safety of glucosamine and chondroitin sulfate. Structure of Articular Cartilage and Pathophysiology of Osteoarthritis Chondrocytes, the cellular component of articular cartilage, are responsible for the synthesis and maintenance of the extracellular matrix in which they are embedded. The extracellular matrix is composed of collagen (predominantly type II collagen) and proteoglycans, with a smaller percentage of glycoproteins (Figure 1). Type II collagen arranged in fibrils is responsible for the tensile strength of articular cartilage. Proteoglycans consist of a central protein core to which 1 or more glycosaminoglycan (GAG) side chains are attached. In turn, GAGs are composed of repeating disaccharide units of hexosamine (glucosamine or galactosamine) alternating with another residue of glucuronate, iduronate, or galactose. The largest and most predominant proteoglycan in cartilage is aggrecan. Chondrocytes synthesize aggrecan by covalently attaching GAGs (chondroitin sulfate and keratan sulfate) to a central protein core of proteoglycans in an organized manner. This core protein of the proteoglyThe role of glucosamine and chondroitin sulfate in treatment for and prevention of osteoarthritis in animals