The roles played by crucial free radicals like lipid free radicals, nitric oxide, and enzymes NOS and NADPH in CCl 4-induced acute liver injury of mice

Abstract

Mice were administered a single dose of carbon tetrachloride (CCl 4) to induce acute liver injury. We found that lactate dehydrogenase (LDH) and glutamic pyruvic transaminase (GPT) levels in serum, as well as the level of thiobarbituric acid reaction substances (TBARS) in liver homogenate increased significantly in a manner both dose dependent and time dependent after CCl 4 administration. Such results suggest that the liver is susceptible to CCl 4 treatment and that lipid peroxidation is associated with CCl 4-induced liver injury. The spin-trapping electron paramagnetic resonance (EPR) method was used to detect nitric oxide (NO) level in liver. The chemiluminescence method was also employed to measure the NO 2 −/NO 3 − concentration in serum. The NO levels in liver tissues and NO 2 −/NO 3 − concentration in serum were found to decrease significantly both in a dose-dependent manner and in time course after CCl 4 treatment. The nitric oxide synthase (NOS) II activity in the liver, in contrast, was found to increase significantly. Our study suggests that not only should the expression of NOS be analyzed but NO organ and blood concentration must be measured in the study of diseases involving nitric oxide. l-arginine treatment had no significant effect on the liver function of CCl 4-treated mice. It was found that NO donor sodium nitroprusside (SNP; 50 or 100 μg/kg) treatment resulted in decreases of LDH, GPT, and TBARS levels, leading to a protective effect on CCl 4-treated mice. On the other hand, N G-nitro- l-arginine methyl ester ( l-NAME, 100 or 300 mg/kg) treatment caused more severe liver damage. Moreover, we have found in an in vitro EPR study that SNP could scavenge lipid peroxyl radical LOO . The above results together suggest that NO may protect CCl 4-induced liver injury through scavenging lipid radical, inhibiting the lipid peroxidation chain reaction. On the basis of our analysis, we put forth two explanations for the stated discrepancy between NOS II and NO production: (i) NO was used up gradually in terminating lipid peroxidation and (ii) NADPH was depleted (on the basis of correlation evidence only).