Inhibition by tetranactin of interleukin 1 beta- and cyclic AMP-induced nitric oxide synthase expression in rat renal mesangial cells.

1. We have investigated whether tetranactin, a cyclic antibiotic produced by Streptomyces aureus with a molecular structure related to cyclosporin 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 two principal classes of activating signals comprising inflammatory cytokines such as interleukin 1 (IL-1) or tumour necrosis factor alpha and agents that elevate cellular levels of cyclic AMP. Treatment of mesangial cells with IL-1 beta or the membrane-permeable cyclic AMP analogue, N6, 0-2'-dibutyryladenosine 3',5'-phosphate (Bt2 cyclic AMP) for 24 h induces iNOS activity measured as nitrite levels in cell culture supernatants by 44 fold or 33 fold, respectively. Incubation of mesangial cells with tetranactin inhibits IL-1 beta- and cyclic AMP-dependent production of nitrite in a dose-dependent fashion with IC50 values of 50 nM and 10 nM, respectively. 3. Western-blot analyses of mesangial cell extracts reveal that the inhibition of nitrite synthesis by tetranactin is due to a suppression of iNOS protein levels. This effect is preceded by a reduction of iNOS mRNA steady state levels as demonstrated by Northern blot analyses of total cellular RNA isolated from stimulated mesangial cells. 4. Thus, tetranactin is a potent inhibitor of iNOS expression in cytokine- and cyclic AMP-stimulated mesangial cells and represents a new class of iNOS inhibitors with IC50s in the low nanomolar range. This compound may be useful in the therapy of diseases associated with pathological NO overproduction due to iNOS expression.