Diethyl ether as a substrate for acetone/ethanol-inducible cytochrome P-450 and as an inducer for cytochrome(s) P-450

The ability of diethyl ether to serve as a substrate for microsomal and purified cytochrome P-450 (P-450) and as an inducer for rat hepatic microsomal monooxygenase activities was examined. Microsomal oxidation of ether to acetaldehyde, as monitored by high pressure liquid chromatography, was elevated 3- to 5-fold by treatment of rats with acetone or ethanol, 1.5- to 2-fold by treatment with ether, and only slightly by phenobarbital treatment. Ether also induced N-nitrosodimethylamine demethylase by up to 2-fold and 7-pentoxyresorufin dealkylation by up to 10-fold. These trends agreed with immunoblot experiments in which ether was a weak inducer of the P-450 isozyme IIE1 (encoded by the rat gene P450IIE1), but a stronger inducer of IIB1. A monoclonal antibody against IIE1 inhibited the deethylation by 78% in microsomes from acetone-treated rats and by 45% in controls. N-Nitrosodimethylamine, as well as common inhibitors of IIE1 such as hexane, benzene, pyrazole, and phenylethylamine, strongly inhibited ether deethylation. Using microsomes from acetone-induced rats, the apparent Km for deethylation was 13.4 +/- 2.4 microM and the Vmax was 8.2 +/- 0.2 (nmol of acetaldehyde/min/nmol of P-450). The Km for the controls was 71.3 +/- 9.5 microM. The rates of deethylation at 1 mM ether by purified, reconstituted IIE1 and IIB1 were 4.2 and 0.42 (nmol of acetaldehyde/min/nmol of P-450), respectively. Cytochrome b5 stimulated the rate due to IIE1 apparently by a decrease in the Km. These findings, along with previous work showing marked inhibition by ether of IIE1-dependent reactions, strongly support a major role for this isozyme in ether metabolism.