POSTTRANSCRIPTIONAL REGULATION OF INDUCIBLE NITRIC-OXIDE SYNTHASE MESSENGER-RNA IN MURINE MACROPHAGES BY DOXYCYCLINE AND CHEMICALLY-MODIFIED TETRACYCLINES

Chemically modified tetracyclines [CMT-3 (IC50 similar to 6-13 mu M = similar to 2.5-5 mu g/ml) and CMT-8 (IC50 similar to 26 mu M = 10 mu g /ml), but not CMT-1, -2 or -5], which lack anti-microbial activity, in hibited nitrite production in LPS-stimulated macrophages, Unlike compe titive inhibitors of L-arginine which inhibited the specific activity of inducible nitric oxide synthase (iNOS) in cell-free extracts, CMTs exerted no such direct effect on the enzyme, CMTs could, however, be s hown to inhibit both iNOS mRNA accumulation and protein expression in LPS-stimulated cells, Tetracyclines (doxycycline and CMT-3) unlike hyd rocortisone had no significant effect on murine macrophages transfecte d with iNOS promoter (tagged to a luciferase reporter gene) in the pre sence of LPS, However, doxycycline and CMT-3 augmented iNOS mRNA degra dation, in LPS-stimulated murine macrophages, These studies show a nov el mechanism of action of tetracyclines which harbours properties to i ncrease iNOS mRNA degradation and decrease iNOS protein expression and nitric oxide production in macrophages, This property of tetracycline s may have beneficial effects in the treatment of various diseases whe re excess nitric oxide has been implicated in the pathophysiology of t hese diseases. (C) 1997 Federation of European Biochemical Societies.