Diallyl sulfide inhibits the oxidation and reduction reactions of stilbene estrogens catalyzed by microsomes, mitochondria and nuclei isolated from breast tissue of female ACI rats.

Previously, it has been demonstrated that microsomal, mitochondrial and nuclear enzymes isolated from the liver of male Sprague-Dawley rats catalyzed the oxidation of diethylstilbestrol (DES) to DES quinone. In the present study we have shown that diallyl sulfide (DAS) inhibits the oxidation of DES to DES quinone in all three subcellular fractions (microsomes, mitochondria and nuclei) isolated from breast tissue of female ACI rats. UV analysis of mitochondrial and microsomal fractions revealed that DAS decreased the rate of DES oxidation to DES quinone and DAS also decreased the rate in which DES quinone was reduced to DES. Lineweaver-Burk plots of the rate of DES quinone formation at various DES and DAS concentrations demonstrated that DAS inhibited the oxidation of DES and the reduction of DES quinone in a non-competitive fashion. In both microsomal and mitochondrial oxidation reactions the K(m) remained constant whereas the V(max) decreased with increasing DAS (0, 186 and 373 microM) concentrations (microsomes K(m) = 80 microM; V(max) = 5.56, 4.16 and 3.33 nmol/mg protein/min; mitochondria K(m) = 35.7 microM; V(max) = 3.45, 2.44 and 1.82 nmol/mg protein/min). Results were similar for reduction reactions. HPLC analysis revealed that a concentration of 186 microM DAS inhibited the mitochondrial, microsomal and nuclear oxidation by 27, 35 and 40%, respectively. A concentration of 373 microM DAS inhibited the mitochondrial, microsomal and nuclear oxidation by 50, 52 and 60% respectively. The data provide direct evidence that the breast tissue contain the metabolic machinery required to oxidize DES to reactive intermediates that may lead to genetic instability and cancer. This inhibition may play a role in the chemoprevention of stilbene estrogen-induced breast cancer.