Regulatory effects of inducible nitric oxide synthase on cyclooxygenase-2 and heme oxygenase-1 expression in experimental glomerulonephritis

Background. We explored whether inducible nitric oxide synthase (iNOS) driven nitric oxide (NO) production regulates expression of iNOS, endothelial NOS (eNOS), Cyclooxygenase-2 (COX-2), and Hemeoxygenase-1 (HO-1) proteins in a rat model of glomerulonephritis induced by antibody raised in rabbits against rat glomerular basement membrane (anti-GBM). Methods. Rats were injected either with non-immune serum (control), or anti-GBM serum. In a group of rats N-6-(1-iminoethyl)-L-lysine (L-NIL) was administered prior to injection of anti-GBM serum to inhibit iNOS activity. Urinary nitrite plus nitrate (NOx) excretion was assessed to determine the extent of iNOS inhibition by L-NIL. Urinary albumin excretion was assessed to determine extent of proteinuria. Urinary PGE(2) was assessed as a marker of COX activity. Glomeruli were harvested 24 h after injection of anti-GBM serum and ED1, COX-2, iNOS, eNOS and HO-1 expression was analysed by Western blot analysis. Results. iNOS activity in glomeruli was effectively reduced in L-NIL-treated nephritic animals. In these animals, there was exacerbation of proteinuria and reduction in urinary PGE(2) levels without changes in the extent of macrophage infiltration in glomeruli. In nephritic animals, there was an increase in glomerular protein levels of COX-2, HO-1 and iNOS, but not of eNOS. While L-NIL treatment reduced glomerular HO-1, levels of COX-2 and iNOS increased; but not that of eNOS. Conclusions. The observations indicate that in glomerulonephritis iNOS-driven NO production acts as a negative feedback regulator of iNOS itself, suppresses COX-2 levels, and maintains HO-1 levels.