A novel mechanism of action of tetracyclines: Effects on nitric oxide synthases

Abstract

Tetracyclines have recently been shown to have ''chondroprotective'' effects in inf lammatory 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␤-induced OA-NOS activity in ex vivo conditions. Similarly, minocycline > doxycycline inhibited both lipopolysaccharide-and interferon-␥-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 ␤-actin and glyceraldehyde-3-phosphate dehydrogenase nor on levels of protein of ␤-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 inf lammatory diseases, these observations suggest that tetracyclines should be evaluated as potential therapeutic modulators of NO for various pathological conditions.

Superinduction of cyclooxygenase-2 activity in human osteoarthritis-affected cartilage. Influence of nitric oxide.

“…The production of both NO and PGE 2 by OA cartilage explants can be attenuated by inhibitors of protein synthesis (cycloheximide) and NF-B (PDTC). An interesting divergence in the regulation of COX-2 and NOS in chondrocytes, however, is reflected in their sensitivity to glucocorticoids: in OA chondrocytes expression of COX-2, but not NOS, is inhibited by prior exposure to dexamethasone (11,38).…”

Acyclovir Reduces the Duration of Fever in Patients with Infectious Mononucleosis-like Illness

“…Interestingly, a previous study has reported that acyclovir blocks the expression of inflammatory cytokines (Halford et al 1997). Moreover, recent reports have shown that antibiotics such as minocycline or macrolides demonstrate antiinflammatory activity in addition to their known function (Amin et al 1996).…”

Use of the plasma stromelysin (matrix metalloproteinase 3) concentration to predict joint space narrowing in knee osteoarthritis

“…In vitro, when doxycycline is present during activation of the proenzyme, MMPs are degraded into catalytically inactive fragments (33). In addition, doxycycline inhibits messenger RNA for inducible nitric oxide synthase, a potent stimulus for MMP production by chondrocytes (34).…”