Abstract
Dietary restriction (DR) reduced the metabolic activation of aflatoxin B I (afb 1) in rats. This reduction may be attributed to the decrease of cytochrome P-450-mediated afb 1 epoxidation and/or increase in the detoxification of AFB 1 catalyzed by hepatic glutathione S-transferase (GST) and other phase II detoxification enzymes. In this study the effect of DR on male rat liver cytosolic GST activity toward AFB 1-8,9-epoxide was studied. The chemically-synthesized AFB 1-8,9-epoxide was used as the substrate in this assay, and the formation ofAFB 1-GSH conjugate was analyzed by HPLC. Male Fischer 344 rats fed DR diets (60% of the food consumption of ad libitum (AL)-fed rats) showed a 2.4-fold increase in GST activity when AFB 1-epoxide was used as the substrate. The results from the enzyme kinetic study showed that DR increased V max of the liver cytosolic GST but not the K m. Acute DR has little or no impact on GST activity when l-chloro-2,4-dinitrobenzene and 2,4-dichloronitrobenzene were used as substrates. The mouse liver GST activity toward AFB 1-epoxide was 3-fold greater than that of phenobarbital-induced rats, 4.5-fold greater than DR rats, and 14.7-fold greater than the GST activity of AL rats. This direct assay of liver GST activity using AFB 1-epoxide as the substrate is useful for studying AFB 1-induced biomarkers, such as afb 1-gsh conjugation and AFB 1-DNA adducts.
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