Modulation of renal disease in MRL/lpr mice by pharmacologic inhibition of inducible nitric oxide synthase

Background. MRL-MPJFas(lpr) (MRL/lpr) mice spontaneously develop lupus-like disease characterized by immune complex glomerulonephritis and overproduction of nitric oxide (NO). Blocking NO production pharmacologically by a non-specific nitric oxide synthase (NOS) inhibitor ameliorated renal disease in MRL/lpr mice while genetically deficient inducible NOS (iNOS) mice developed proliferative glomerulonephritis similar to wild-type controls. Methods. To clarify the role of iNOS in the pathogenesis of nephritis in MRL/lpr mice, we treated mice with two different NOS inhibitors. Either NI-monomethyl-L-arginine (L-NMMA), a nonspecific NOS inhibitor, Or L-N-6-(1-iminoethyl)lysine (L-NIL), an iNOS specific inhibitor, was administered in the drinking water from 10 through 22 weeks of age with disease progression monitored over time. Control mice received water alone. Results. Both L-NMMA and L-NIL blocked NO production effectively in MRL/lpr mice. As expected, neither L-NNMA nor L-NIL had an effect on antibody production, immune complex deposition or complement activation. Although both NOS inhibitors decreased protein excretion, L-NMMA was more effective than L-NIL. Pathologic renal disease was significantly decreased at 19 weeks in both treatment groups. At 22 weeks the L-NIL treated mice, but not the L-NMMA mice, had significantly reduced renal disease scores compared to controls. Conclusion. These results indicate that specific inhibition of iNOS blocks the development of pathologic renal disease in MRL/lpr mice.