Carcinogenesis Advance Access originally published online on August 29, 2003
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Carcinogenesis, Vol. 25, No. 5, 787-791,
May 2004
Carcinogenesis vol.25 no.5 © Oxford University Press 2004; all rights reserved.
ARTICLE |
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
1 Environmental Toxicology Program, College of Pharmacy and Pharmaceutical Sciences and 2 Biology Department, College of Arts and Sciences, Florida A&M University, Tallahassee, FL 32307, USA
3 To whom correspondence should be addressed Email: ronald.thomas{at}famu.edu
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 Km remained constant whereas the Vmax decreased with increasing DAS (0, 186 and 373 µM) concentrations (microsomes Km = 80 µM; Vmax = 5.56, 4.16 and 3.33 nmol/mg protein/min; mitochondria Km = 35.7 µM; Vmax = 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 µM DAS inhibited the mitochondrial, microsomal and nuclear oxidation by 27, 35 and 40%, respectively. A concentration of 373 µM 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.