Faculty Bibliography

Tetracyclines have recently been shown to have 'chondroprotective' effects in inflammatory arthritides in animal models. Since nitric oxide (NO) is spontaneously released from human cartilage affected by osteoarthritis (OA) or rheumatoid arthritis in quantities sufficient to cause cartilage damage, we evaluated the effect of tetracyclines on the expression and function of human OA-affected nitric oxide synthase (OA-NOS) and rodent inducible NOS (iNOS). Among the tetracycline group of compounds, doxycycline > minocycline blocked and reversed both spontaneous and interleukin 1 beta-induced OA-NOS activity in ex vivo conditions. Similarly, minocycline > or = doxycycline inhibited both lipopolysaccharide- and interferon-gamma-stimulated iNOS in RAW 264.7 cells in vitro, as assessed by nitrite accumulation. Although both these enzyme isoforms could be inhibited by doxycycline and minocycline, their susceptibility to each of these drugs was distinct. Unlike acetylating agents or competitive inhibitors of L-arginine that directly inhibit the specific activity of NOS, doxycycline or minocycline has no significant effect on the specific activity of iNOS in cell-free extracts. The mechanism of action of these drugs on murine iNOS expression was found to be, at least in part, at the level of RNA expression and translation of the enzyme, which would account for the decreased iNOS protein and activity of the enzyme. Tetracyclines had no significant effect on the levels of mRNA for beta-actin and glyceraldehyde-3-phosphate dehydrogenase nor on levels of protein of beta-actin and cyclooxygenase 2 expression. These studies indicate that a novel mechanism of action of tetracyclines is to inhibit the expression of NOS. Since the overproduction of NO has been implicated in the pathogenesis of arthritis, as well as other inflammatory diseases, these observations suggest that tetracyclines should be evaluated as potential therapeutic modulators of NO for various pathological conditions

OBJECTIVE: The migration of cells of chondrocyte lineage is believed to play a role in cartilage growth and repair. The present study examined 1) whether chondrocytes are capable of migration in vitro; and 2) the effects of nitric oxide (NO) on chondrocyte migration, adhesion, and cytoskeletal assembly. METHODS: Chondrocyte migration was evaluated by 2 assays: 1) 'centrifugal' migration within a 3-dimensional collagen matrix (dot culture); and 2) directed migration under agarose in response to bone morphogenetic protein. To assess the effects of NO, chondrocytes were treated with either exogenous NO (S-nitrosoglutathione [SNO-GSH]) or a mixture of cytokines known to induce endogenous NO production. The effects of NO on chondrocyte adhesion to fibronectin-coated surfaces, as well as on actin polymerization (determined by indirect immunofluorescence), were also examined. RESULTS: The capacity of chondrocytes to migrate was demonstrated both by the dot culture and by agarose methods. Both SNO-GSH and endogenous NO induced by cytokines inhibited this migration. Exposure to NO also inhibited attachment of chondrocytes to fibronectin and disrupted assembly of actin filaments. These effects of SNO-GSH and cytokine-induced NO production were reversed in the presence of hemoglobin and the NO synthase inhibitor NG-monomethyl arginine, respectively. CONCLUSION: NO interferes with chondrocyte migration and attachment to fibronectin, an extracellular matrix protein, probably via effects on the actin cytoskeleton. These effects of NO may result in impairment of cartilage repair, by interfering with the extracellular matrix regulation of chondrocyte function