Protection against carbon tetrachloride hepatotoxicity by pretreatment with indole-3-carbinol.

The effects of administering indole-3-carbinol (I-3-C) on carbon tetrachloride (CCl4)-induced hepatotoxicity were examined. Mice received by gavage 0-150 mg I-3-C/kg body wt in methanol-extracted corn oil, followed 1 h later by 15 microliters CCl4/kg body wt in corn oil. Animals were sacrificed 24 h after receiving CCl4. Pretreatment with I-3-C reduced the degree of centrolobular necrosis, as observed histologically. Additionally, CCl4-mediated elevated serum enzymes were reduced by I-3-C. Although I-3-C induced elevated levels of cytochrome P-450 and associated mixed-function oxidase activity, the CCl4 depression of these parameters was not clearly reversed by I-3-C. However, CCl4 produced decreases in hepatic levels of glutathione (GSH), total reducing equivalents, and protein sulfhydryls, all of which were restored to control levels by I-3-C. Using mouse liver microsomes in an NADPH-fortified reaction mixture, I-3-C inhibited, in a concentration-dependent manner, CCl4-initiated lipid peroxidation, with 50% inhibition at 35-40 microM I-3-C. When mice were treated by gavage with 50 mg [14C]I-3-C/kg body wt, concentrations of radiolabel in the liver were greater than 100 microM after 1 hr. This was five times the level of radioactivity measured in blood and three times the concentration of I-3-C necessary for 50% inhibition of CCl4-mediated lipid peroxidation in vitro. The data are consistent with the hypothesis that I-3-C intervenes in CCl4-mediated hepatic necrosis by combining with reactive free radical metabolites of CCl4, thereby protecting critical cellular target sites.

Indole-3-carbinol inhibits lipid peroxidation in cell-free systems.

Free radicals mediate toxicological and carcinogenic responses of tissues to many chemicals. Cellular defenses against radical mediated damage utilize endogenous substances such as tocopherol, ascorbate and GSH. Here we report a new antioxidant, indole-3-carbinol (I-3-C), a natural constituent of human diet. In chlorobenzene containing soy phospholipids, lipid oxidation was initiated with azobisisobutyronitrile; I-3-C inhibited formation of thiobarbituric acid-reactive material in a dose-dependent manner. Similar results were obtained in an aqueous system containing phospholipid vesicles initiated by Fe/ascorbate. For both systems I-3-C was less effective than tocopherol or BHT as antioxidant. To assess these antioxidant effects in vivo, mice were treated with I-3-C by gavage. A hepatic post-mitochondrial supernatant fraction isolated 2 hours after treatment showed dose-dependent decreases in NADPH-mediated lipid oxidation which correlated with decreases in 14C-nitrosodimethylamine covalent binding to protein. Although hepatotoxicity may not involve lipid oxidation per se, it does indicate that free radical damage had occurred. Inhibition of damage by I-3-C suggests that this dietary component has the potential to ameliorate radical mediated chemical toxicity.