Chemically modified tetracyclines inhibit inducible nitric oxide synthase expression and nitric oxide production in cultured rat mesangial cells.

Tetracyclines inhibit matrix metalloproteinases (MMP) and attenuate connective tissue degradation in a wide variety of human and animal disorders. Chemically modified tetracyclines (CMT) have been synthesized in which the antibacterial potency has been eliminated but in which the anti-MMP efficacy is retained. Nitric oxide (NO) modulates MMP synthesis and activity in mesangial cells in vitro. Therefore, we examined whether CMT inhibit iNOS gene and protein expression and NO production in cultured rat mesangial cells. Mesangial cells were maintained in media containing IFN-gamma and LPS for 24-72 h. Test media contained either no further additives or CMT-1, 3, 5, or 8 at concentrations of 1, 2.5, 5, and 10 micrograms/ml. iNOS gene and protein expression were assessed and NO production was determined by the Griess reaction. Incubation of mesangial cells with CMT-3 and CMT-8 resulted in time- and dose-dependent inhibition of NO production that was maximal at 48 h (< 20% of control) and at a drug concentration of 5 micrograms/ml (P < 0.05). Addition of CMT-1 had a modest (40%) inhibitory effect and CMT-5 did not alter NO production. The impact of CMT on NO production was directly related to their potency as collagenase inhibitors. Moreover, CMT-induced changes in NO synthesis were associated with parallel alterations in steady-state iNOS mRNA abundance and protein expression. These agents may be useful to ameliorate NO-dependent glomerular inflammation.