Staphylococcus aureus stimulates inducible nitric oxide synthase in articular cartilage

Objective. To determine if Staphylococcus aureus stimulates the L-arginine- nitric oxide (NO) synthase pathway in articular cartilage. Methods. A heat-killed and sonicated (denatured) S aureus preparation was a dded to cultures of bovine articular cartilage. NO production was measured as accumulated nitrite in the culture medium and by the NO synthase-depende nt conversion of H-3-L-arginine to H-3-L-citrulline in cartilage homogenate s. Inducible NO synthase (iNOS) messenger RNA (mRNA) expression was analyze d by Northern blot. Proteoglycan synthesis was measured by (SO4)-S-35 incor poration into glycosaminoglycan. Results. Nitrite accumulation and H-3-L-citrulline formation in cartilage w ere elevated by denatured S aureus (compared with unstimulated control cart ilage) and inhibited by the NO synthase inhibitor N-G-monomethyl-L-arginine . Northern blot analysis revealed increased INOS mRNA expression in bovine chondrocytes in response to denatured S aureus stimulation. Denatured S aur eus suppressed the accumulation of (SO4)-S-35-labeled macromolecules repres enting newly synthesized proteoglycans in bovine articular cartilage. The s uppressed proteoglycan synthesis was due to the presence of NO. Conclusion, These findings support the hypothesis that a component of S aur eus can stimulate iNOS in articular cartilage, and that NO generated from t his enzyme down-regulates cartilage matrix proteoglycan synthesis.