Objective: To determine the effect of avian chondroitin sulfate (CS) on interleukin-1beta (IL-1beta)-induced expression of genes related to catabolic, anabolic and inflammatory aspects in chondrocytes cultured in hypoxic alginate beads. Design: Articular chondrocytes from bovine metacarpal joint were isolated and cultured in alginate beads, using low oxygen atmosphere (5% O2). After 1-week exposure to CS (1, 10 and 100microg/ml), they were treated by recIL-1beta (10ng/ml) for 24 or 48h, in the presence of CS. RNA was extracted and used to determine, by quantitative reverse transcription-polymerase chain reaction, the steady-state levels of mRNAs encoding several genes related to anabolic, catabolic and inflammatory aspects. Glycosaminoglycan (GAG) synthesis was also assayed by 35S-sulfate incorporation. Results: CS decreased IL-1beta-induced expression of matrix metalloproteases-1, -3 and -13 and aggrecanases-1 and -2. It slightly enhanced the aggrecan core protein mRNA and the GAG synthesis. Inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) mRNA levels were found to be reduced by CS treatment. However, no CS-induced decrease of NO was observed in IL-1beta-treated chondrocytes, whereas prostaglandin E2 production was diminished in correlation with the COX-2 mRNA amounts. Furthermore, CS was capable of counteracting IL-1beta-depressed expression of transforming growth factor-beta (TGF-beta) receptors. Conclusions: CS can repress expression of genes encoding proteolytic enzymes involved in cartilage degradation. It also inhibits IL-1beta-induced expression of the pro-inflammatory genes iNOS and COX-2 and restores TGF-beta receptors I and II (TGF-betaRI and RII) mRNA levels. These data suggest that CS may exert both chondroprotective and anti-inflammatory limited effects on articular cartilage that could have long-term beneficial action on the osteoarthritic process.