Interactions between inducible nitric oxide synthase and heme oxygenase-1 in glomerulonephritis

Background. In anti-glomerular basement membrane (GBM) nephritis, inducible nitric oxide synthase (iNOS) and heme oxygenase (HO-1) are co-induced. Moreover, in glomerular mesangial cells iNOS-derived nitric oxide (NO) production stimulates HO-1 while HO-1 activation reduces iNOS expression/ activity. These observations prompted us to explore regulatory interactions between iNOS and HO-1 in anti-GBM nephritis. Methods. Rats with anti-GBM nephritis were pretreated with the iNOS inhibitor L-N-6-(1-iminoethyl) lysine (L-NIL) or with the HO-1 inducer hemin, Glomerular HO-1 levels were assessed by Western blot analysis. iNOS activity was assessed by calculating conversion Of L-arginine to L-Citrulline. Results. iNOS inhibition reduced glomerular HO-1 levels without altering the inflammatory response to anti-GBM antibody induced injury. Induction of HO-1 reduced glomerular iNOS activity. Conclusions. In anti-GBM nephritis iNOS up-regulates HO-1 presumably via high output NO production. Suprainduction of HO-1 attenuates iNOS activity. This negative feedback interaction points to HO-1 as a target for pharmacologic manipulation to reduce activity of prooxidant heme containing enzymes such as iNOS.