Koji Sakamoto

Inhibitory actions of glucosamine, a therapeutic agent for osteoarthritis, on the functions of neutrophils.

Glucosamine, an amino monosaccharide naturally occurring in the connective and cartilage tissues, contributes to maintaining the strength, flexibility, and elasticity of these tissues. In recent years, glucosamine has been used widely to treat osteoarthritis in humans and animal models. Neutrophils, which usually function as the primary defenders in bacterial infections, are also implicated in the destructive, inflammatory responses in arthritis. In this study, we have evaluated the effects of glucosamine on neutrophil functions using human peripheral blood neutrophils. Glucosamine (0.01–1 mM) dose‐dependently suppressed the superoxide anion generation induced by formyl‐Met‐Leu‐Phe (fMLP) or complement‐opsonized zymosan and inhibited the phagocytosis of complement‐opsonized zymosan or IgG‐opsonized latex particles. Furthermore, glucosamine inhibited the release of granule enzyme lysozyme from phagocytosing neutrophils and suppressed neutrophil chemotaxis toward zymosan‐activated serum. In addition, glucosamine inhibited fMLP‐induced up‐regulation of CD11b significantly, polymerization of actin, and phosphorylation of p38 mitogen‐activated protein kinase (MAPK). In contrast, N‐acetyl‐glucosamine, an analogue of glucosamine, did not affect these neutrophil functions (superoxide generation, phagocytosis, granule enzyme release, chemotaxis, CD11b expression, actin polymerization, and p38 MAPK phosphorylation) at the concentrations examined (1–10 mM). Together these observations likely suggest that glucosamine suppresses the neutrophil functions, thereby possibly exhibiting anti‐inflammatory actions in arthritis.

Evaluation of the effect of glucosamine on an experimental rat osteoarthritis model

AIMS To investigate the in vivo effect of glucosamine on articular cartilage in osteoarthritis (OA), we evaluated serum biomarkers such as CTX-II (type II collagen degradation) and CPII (type II collagen synthesis) as well as histopathological changes (Mankin score, toluidine blue staining of proteoglycans in an experimental OA model using rats. MAIN METHODS OA was surgically induced in the knee joint by anterior cruciate ligament transection (ACLT) in rats. Animals were divided into three groups: sham-operated group (Sham), ACLT group without GlcN administration (-GlcN) and ACLT group with oral administration of glucosamine hydrochloride (+GlcN; 1000mg/kg/day for 56days). KEY FINDINGS ACLT induced macroscopic erosive changes on the surfaces of articular cartilage and histological damages such as increase of Mankin score. Of note, glucosamine administration substantially suppressed the macroscopic changes, although the effect on Mankin score was not significant. In addition, serum CTX-II levels were elevated in -GlcN group compared to that in Sham group after the operation. Of importance, the increase of CTX-II was significantly suppressed by GlcN administration. Moreover, serum CP-II levels were substantially increased in +GlcN group compared to those in Sham and -GlcN groups after the operation. SIGNIFICANCE GlcN has a potential to exert a chondroprotective action on OA by inhibiting type II collagen degradation and enhancing type II collagen synthesis in the articular cartilage.

Biological Activities of Glucosamine and Its Related Substances

Glucosamine (GlcN) has been widely used to treat osteoarthritis (OA) in humans. We revealed that among GlcN-derivatives (GlcN and N-acetyl-d-glucosamine) and uronic acids (d-glucuronic acid and d-galacturonic acid), only GlcN induces the production of hyaluronic acid (HA) by synovial cells and chondrocytes, and the production level is much higher (>10-fold) in synovial cells compared with chondrocytes. Moreover, GlcN increases the expression of HA-synthesizing enzymes (HAS) in synovial cells and chondrocytes. These observations indicate that GlcN likely exhibits the chondroprotective action on OA by modulating the expression of HAS and inducing the production of HA (a major component of glycosaminoglycans contained in the synovial fluid) especially by synovial cells. The pathological change of subchondral bone is implicated in the initiation and progression of cartilage damage in OA. Thus, we further determined the effect of GlcN on the bone metabolism (osteoblastic cell differentiation). The results indicated that GlcN increases the mineralization of mature osteoblasts and the expression of middle and late stage markers (osteopontin and osteocalcin, respectively) during osteoblastic differentiation, and reduces the expression of receptor activator of NF-κB ligand (RANKL), a differentiation and activation factor for osteoclasts. These observations likely suggest that GlcN has a potential to induce the osteoblastic cell differentiation and suppress the osteoclastic cell differentiation, thereby increasing bone matrix deposition and decreasing bone resorption to modulate bone metabolism in OA.