Enhancement of epoxide hydrolase activity in hepatic microsomes of mice given heterocyclic compounds.

The effects of dietary administration of equimolar doses (5 mmol/kg body wt per day) of trimethylene oxide, trimethylene sulfide, coumaran, benzofuran, indole, and indole-3-carbinol on the activities of microsomal epoxide hydrolase and several other xenobiotic metabolizing enzymes were measured in the liver of female CD-1 mouse. Every compound, with the exception of indole, caused a significant increase (P less than 0.01) of the styrene oxide epoxide hydrolase activity over controls in hepatic microsomes. These results indicate that the enzyme activity is elevated in vivo by several heterocyclic compounds with strained bond angles to a nucleophilic hetero-atom. In addition, the ability of sulfur-containing trimethylene sulfide and nitrogen-containing indole-3-carbinol to elevate the enzyme activity indicates that the heterocyclic oxygen atom is not an absolute requirement for this effect. Data from the other xenobiotic metabolizing enzymes indicate that trimethylene oxide and trimethylene sulfide enhance the epoxide hydrolase activity rather specifically, while not affecting the activities of the other enzymes measured. While the oxygen-containing coumaran and benzofuran both increased the NADH: quinone reductase activity in hepatic cytosol, the nitrogen-containing indole and indole-3-carbinol did not. This indicated a specific requirement for the oxygen atom in elevating the quinone reductase activity, which was not the case for the elevation of microsomal epoxide hydrolase activity.