Enzymic and chemical demethylenation of (methylenedioxy)amphetamine and (methylenedioxy)methamphetamine by rat brain microsomes

Rat brain microsomes convert MDA and MDMA into dihydroxyamphetamine (DHA) and dihydroxymethamphetamine (DHMA), respectively. This demethylenation requires NADPH and is strongly inhibited by carbon monoxide/oxygen, indicating involvement of cytochrome P450. The process is inhibited by desipramine, imipramine, and methimazole but not by SKF-525A or alpha-naphthoflavone. Biphasic Lineweaver-Burk plots suggest multiple isozymes may be involved, and no significant stereoselectivity is observed. Catechol formation is 2.6 times greater in phosphate buffer than HEPES buffer, but this difference disappears with desferal and hydroxyl radical scavengers. Sensitivity to catalase and stimulation by ferric ion and EDTA indicate both a cytochrome P450-mediated component and a chemical component involving hydroxyl radicals.

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Abstract

The metabolism of (methylenedioxy)amphetamine (MDA) and (methylenedioxy)methamphetamine (MDMA) was examined in microsomal preparations from rat brains. The products generated from MDA and MDMA were identified as dihydroxyamphetamine (DHA) and dihydroxymethamphetamine (DHMA), respectively. The demethylenation reaction required NADPH and was strongly inhibited by CO/O2 (4:1 v/v), suggesting that the formation of DHA and DHMA is mediated by cytochrome P450. The conversion was inhibited by desipramine, imipramine, and methimazole, whereas SKF-525A and alpha-naphthoflavone had little effect. Lineweaver-Burk plots of MDA and MDMA demethylenation were biphasic in both cases, indicating that multiple isozymes may participate in the oxidation. The microsomal preparation showed no significant stereoselectivity in the demethylenation of either MDA or MDMA. Catechol formation differed with the incubation buffer and was 2.6 times greater when phosphate rather than HEPES buffer was used. This difference disappeared, however, when desferrioxamine B methanesulfonate (desferal) and hydroxyl radical (.OH) scavenging agents were added to either buffer. The demethylenation was also sensitive to catalase and was stimulated by the addition of ferric ion and EDTA to the microsomal incubation mixture. These results indicate that the demethylenation of MDA and MDMA by rat brain microsomes has a cytochrome P450-mediated component as well as a chemical component involving .OH.