Copper deficiency increases cytochrome P450-dependent 7-ethoxyresorufin-O-deethylase activity in rat small intestine

Although impaired heme synthesis during copper deficiency may limit the production and function of hemoproteins, little is known about the effects of copper deficiency on the cytochromes P450, an important family of hemoproteins, in the small intestine. A series of experiments was conducted to examine the effects of copper deficiency on cytochrome P450 content, ethoxyresorufin-O-deethylase (EROD) activity, and NADPH-cytochrome P450 reductase activity in rat small intestine. Sixteen hours after a single oral administration of 5,6-benzoflavone (BF), an inducer of cytochromes P4501A1 and P4501A2, intestinal cytochrome P450 content was elevated as indicated by the CO-difference spectrum of the reduced cytochrome and by immunoblotting using anticytochrome P4501A1/1A2. However, cytochrome P450 content, measured by either method following BF induction, was not affected by copper deficiency. Thus, copper deficiency did not impair the availability of heme for cytochrome P450 synthesis in the small intestine. Even though copper deficiency did not affect intestinal cytochrome P450 content, EROD activity, which is a cytochrome P450-associated monooxygenase activity, was 9-fold higher in copper-deficient rats compared with controls following BF treatment. The finding that copper deficiency has no effect on intestinal cytochrome P450 content suggests that the increased EROD activity results from an effect of copper deficiency on the cytochrome P450 reductase component of the monooxygenase system. Measurement of cytochrome P450 reductase activity showed a 2-fold increase in the small intestines of copper-deficient rats compared with controls. It is possible, therefore, that increased intestinal cytochrome P450 reductase activity during copper deficiency increases EROD activity by facilitating the flow of electrons to cytochrome P450 during the redox cycle that cytochrome P450 undergoes during the O-deethylation of ethoxyresorufin.