Effect of naturally occurring phenolic acids on the expression of glutathione S-transferase isozymes in the rat

Naturally occurring plant phenols, protocatechuic and tannic acids, have been reported to be inhibitors of chemical mutagenesis and carcinogenesis in experimental models. Our previous studies, have shown that these compounds modulate the activity of phases 1 and 2 enzymes in rodents. The aim of the present study was to investigate whether these compounds affect protein levels of rat hepatic and renal glutathione S-transferase (GST) isozymes. Male Wistar rats were treated intraperitoneally with protocatechuic or tannic acid at 50 mg/kg body weight five times during 14 days. 3-Methylcholanthrene (MC) was administered at 20 mg/kg body weight on day 13 (the last treatment with phenolic compounds) and on day 14. Tissues were obtained from rats terminated 24 h after the last treatment. Western blot analysis with specific antibodies showed significant differences in the effect of the phenolic compounds in the liver and kidney. In the liver, protocatechuic acid significantly increased the constitutive GSTμ, while tannic acid reduced the GSTα protein level by 60%. Both plant phenols decreased all classes of constitutive GST isozymes in the kidney including GSTπ, and also the MC-induced GSTα and/or π protein levels. These results, as well as our previous reports, suggest that protocatechuic and tannic acids interfere with the pathways related to xenobiotic toxicities and carcinogenesis. This effect may be important for chemoprotective activity of these plant phenols.