Interleukin-1 beta down-regulates the expression of glucuronosyltransferase I, a key enzyme priming glycosaminoglycan biosynthesis - Influence of glucosamine on interleukin-1 beta-mediated effects in rat chondrocytes

Objective. To assess the variations of galactose-beta -1,3-glucuronosyltran sferase I (GIcAT-I) expression related to the decrease in proteoglycan synt hesis mediated by interleukin-1 beta (IL-1 beta) in rat chondrocytes, and t o evaluate the influence of glucosamine on the effects elicited by this pro inflammatory cytokine. Methods. Rat articular chondrocytes in primary monolayer cultures or encaps ulated into alginate beads were treated with recombinant IL-1 beta in the a bsence or presence (1.0-4.5 gm/liter) of glucosamine. Variations of GIcAT-I and expression of stromelysin I (matrix metalloproteinase 3 [MMP-3]) messe nger RNA (mRNA) were evaluated by quantitative multistandard reverse transc riptase-polymerase chain reaction. In vitro enzymatic activity of GIcAT-I w as measured by thin-layer chromatography, with radiolabeled UDP-glucuronic acid and a digalactoside derivative as substrates. Proteoglycan synthesis w as determined by ex vivo incorporation of (Na2-SO4)-S-35. Nitric oxide synt hase and cyclooxygenase activities were monitored by the evaluation of nitr ite (NO2-) and prostaglandin E-2 (PGE(2)) produced in the culture medium, r espectively. Results. IL-1 beta treatment resulted in a marked inhibition of GIcAT-I mRN A expression and in vitro catalytic activity, together with a decrease in p roteoglycan synthesis. In addition, glucosamine was able to prevent, in a d ose-dependent manner, the inhibitory effects of IL-1 beta. In the same way, the amino sugar reduced NO2- and PGE(2) production induced by IL-1 beta. F inally, the up-regulation of stromelysin 1 (MMP-3) mRNA expression by IL-1 beta was fully prevented by glucosamine. Conclusion. The results of this study suggest that the deleterious effect o f IL-1 beta on the anabolism of proteoglycan could involve the repression o f GIcAT-I, a key enzyme in the biosynthesis of glycosaminoglycan. Glucosami ne was highly effective in preventing these IL-1 beta -mediated suppressive effects. The amino sugar also prevented the production of inflammatory med iators induced by the cytokine. This action could account for a possible be neficial effect of glucosamine on osteoarthritic articular cartilage.