Effects of glycyrrhizin and glycyrrhetinic acid on damage to isolated hepatocytes by transient exposure to tert-butyl hydroperoxide

We investigated the effects of glycyrrhizin (GL) and glycyrrhetinic acid (GA) which are applied to allergic reaction and inflammatory disease, on the damage to isolated rat hepatocytes transiently exposed to 75 μM tert-butyl hydroperoxide (t-BuOOH). In t-BuOOH-exposed cells, the level of phosphatidylcholine hydroperoxide (PCOOH), a peroxidative product of biomembranes in the hepatocytes, and the leakage of acid phosphatase (AP), a lysosomal enzyme, AST, ALT and LDH into the culture medium, were significantly increased above the background levels found in control experiments. In t-BuOOH-exposed cells, the level of phosphatidylcholine (PC) was significantly (p < 0.05) decreased. By electron spin resonance spectroscopy (ESR) analysis using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), spin adducts of carbon center radicals and hydroxyl radicals (DMPO-OH) were detected after t-BuOOH exposure for 15 minutes. GL and GA (2, 20 nM) added to culture medium before and during the t-BuOOH exposure, could not changed the increased PCOOH level, but improved the decreased PC level in hepatocytes and the leakage of AP, AST, ALT and LDH into the culture medium. GL and GA also reduced the DMPO-OH formation in hepatocyte suspension, although they have not radical scavenging abilities. These results suggest that GL and GA exert their protective effects by the membrane stabilization which results in inhibiting the prolongation of oxidative stress.