Regulatory effect of copper on rat adrenal cytochrome P-450 and steroid metabolism

Abstract

Accumulation of Cu 2+ in rat adrenal glands produced a biphasic response in concentrations of the mitochondrial cytochrome P-450 and heme which were, in turn, reflected in abnormal steroid biosynthesis and output. In the mitochondria, 1 day after Cu 2+ treatment, when the concentration of the metal ion was increased by 2- to 3-fold over the control value, a significant increase in cytochrome P-450-dependent steroid 11 β-hydroxylase activity was observed. These effects were accompanied by a nearly 85% increase in concentrations of cytochrome P-450 and heme. In addition, the activity of δ-aminolevulinate synthetase was increased by 3-fold. In those animals lipid peroxidation, assessed by measuring concentrations of conjugated dienes, was reduced to approximately 50% of the control value. However, after 7 days of Cu 2+ treatment (via a mini-osmotic pump), a significantly lowered rate of 11β-hydroxylase activity was noted, and the plasma concentration of corticosterone was also reduced significantly. Also, in the mitochondria, the concentrations of cytochrome P-450 and heme were decreased in comparison with the control values. These decreases were accompanied by elevated levels of the mitochondrial lipid peroxidation and a further increase in adrenal Cu 2+ content (5-fold). At this time, δ-aminolevulinate synthetase activity remained elevated but to a lower extent than that observed after 1 day of Cu 2+ treatment. In contrast to 11β-hydroxylase activity, the reduction in cytochrome P-450 content was not reflected in a decrease in the rate of cholesterol side-chain cleavage; rather this activity was increased in Cu 2+-treated animals. Adrenal heme oxygenase activity was unaffected by either Cu 2+ treatment, as was the specific content of cytochrome P-450 in the microsomal fraction. The present findings suggest that the Cu 2+-mediated regulation of cytochrome P-450-dependent steroidogenic activity in the adrenal mitochondria is predominately a reflection of the metal ion affecting heme biosynthesis and lipid peroxidation in this organ. Moreover, these actions appear to differentially affect the mitochondrial cytochrome P-450 species catalyzing different hydroxylation reactions in the adrenal steroidogenesis pathway.