TARGETS OF NITRIC-OXIDE IN A MOUSE MODEL OF LIVER INFLAMMATION BY CORYNEBACTERIUM-PARVUM

Treatment of mice with Corynebacterium parvum induces chronic inflamma tion. This treatment followed by an injection of lipopolysaccharide (L PS) produces hepatic necrosis and death. We examined liver tissue by u sing electron paramagnetic resonance (EPR) spectroscopy and found that , in addition to the previously reported nonheme nitrosyl complexes, h eme nitrosyl complexes were also formed. Hemoglobin nitrosyl complexes measured in the whole blood of mice treated with C. parvum were not i ncreased after additional LPS treatment. However, this treatment signi ficantly increased the heme nitrosyl complexes in the liver, whereas t he nonheme nitrosyl complex concentration was unaffected. EPR signals from whole blood and liver tissues from mice treated with C. parvum an d C. parvum + LPS were inhibited by prolonged treatment with N-G-monom ethyl-L-arginine (L-NMA). Nitric oxide ((NO)-N-.) is known to bind to cytochrome P450 heme, and we consistently found a suppression of EPR s ignals attributable to ferric low-spin cytochrome P450/P420 peaks in t he livers of mice treated with C. parvum and C. parvum + LPS. By perfo rming analyses of EPR spectra obtained from hepatocytes exposed to (NO )-N-., we were able to unambiguously identify EPR signals attributable to cytochrome P420 and nonheme nitrosyl complexes in the livers of bo th treatments. Deconvolution of the composite in vivo EPR spectra indi cated that hemoglobin nitrosyl complexes contributed weakly in the C. parvum livers, but threefold more in the C. parvum + LPS livers, sugge sting that hemorrhage may have occurred. Experiments with L-NMA treatm ent revealed that this additional (NO)-N-. production did not correlat e with hepatic necrosis and onset of death. Immunoprecipitation of liv er cytosols from C. parvum- and (C. parvum + LPS)-treated mice using a n antibody against mouse inducible nitric oxide synthase showed that t his enzyme was indeed present in the cytosolic fractions and was absen t in those from control livers. Our novel detection of cytochrome P420 nitrosyl complex in vivo may be linked to any role of hepatic P450's functions during liver inflammation. (C) 1995 Academic Press, Inc.