INHIBITION BY TETRANACTIN OF INTERLEUKIN 1-BETA-INDUCED AND CYCLIC AMP-INDUCED NITRIC-OXIDE SYNTHASE EXPRESSION IN RAT RENAL MESANGIAL CELLS

1 We have investigated whether tetranactin, a cyclic antibiotic produc ed by Streptomyces aureus with a molecular structure related to cyclos porin A, influences inducible nitric oxide synthase (iNOS; EC 1.14.13. 39) induction in rat glomerular mesangial cells. 2 Previously we have shown that iNOS is expressed in renal mesangial cells in response to t wo principal classes of activating signals comprising inflammatory cyt okines such as interleukin 1 (IL-1) or tumour necrosis factor alpha an d agents that elevate cellular levels of cyclic AMP. Treatment of mesa ngial cells with IL-1 beta or the membrane-permeable cyclic AMP analog ue, N-6, 0-2'-dibutyryladenosine 3',5'-phosphate (Bt(2) cyclic AMP) fo r 24 h induces iNOS activity measured as nitrite levels in cell cultur e supernatants by 44 fold or 33 fold, respectively. Incubation of mesa ngial cells with tetranactin inhibits IL-1 beta- and cyclic AMP-depend ent production of nitrite in a dose-dependent fashion with IC50 values of 50 nM and 10 nM, respectively. 3 Western-blot analyses of mesangia l cell extracts reveal that the inhibition of nitrite synthesis by tet ranactin is due to a suppression of iNOS protein levels. This effect i s preceded by a reduction of iNOS mRNA steady state levels as demonstr ated by Northern blot analyses of total cellular RNA isolated from sti mulated mesangial cells. 4 Thus, tetranactin is a potent inhibitor of iNOS expression in cytokine- and cyclic- AMP-stimulated mesangial cell s and represents a new class of iNOS inhibitors with IC(50)s in the lo w nanomolar range. This compound may be useful in the therapy of disea ses associated with pathological NO overproduction due to iNOS express ion.