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Enzymatic and chemical demethylenation of (methylenedioxy)amphetamine and (methylenedioxy)methamphetamine by rat
1Department of Pharmacology, School of Medicine, University of California, Los Angeles 90024-1735.
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.
Insights
The metabolism of (methylenedioxy)amphetamine (MDA) and (methylenedioxy)methamphetamine (MDMA) in rat brains involves cytochrome P450 and hydroxyl radicals. This demethylenation process forms dihydroxyamphetamine (DHA) and dihydroxymethamphetamine (DHMA).
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- The metabolism of psychoactive compounds like MDA and MDMA is crucial for understanding their effects and toxicity.
- Rat brain microsomes are a key model system for studying drug metabolism pathways.
- Cytochrome P450 enzymes are known to play a significant role in xenobiotic metabolism.
Purpose of the Study:
- To investigate the metabolic pathways of (methylenedioxy)amphetamine (MDA) and (methylenedioxy)methamphetamine (MDMA) in rat brain microsomes.
- To identify the specific enzymes and chemical reactions involved in the demethylenation of MDA and MDMA.
- To explore factors influencing the rate and mechanism of these metabolic processes.
Main Methods:
- Incubation of rat brain microsomes with MDA and MDMA.
- Identification of metabolic products using analytical techniques.
- Enzyme inhibition studies using specific inhibitors (CO/O2, desipramine, imipramine, methimazole, SKF-525A, alpha-naphthoflavone).
- Kinetic analysis using Lineweaver-Burk plots.
- Investigation of buffer effects and radical scavenging agents (desferal).
- Assessment of catalase activity and metal ion influence (ferric ion, EDTA).
Main Results:
- MDA and MDMA were metabolized to dihydroxyamphetamine (DHA) and dihydroxymethamphetamine (DHMA), respectively.
- Demethylenation was NADPH-dependent and inhibited by CO/O2, indicating cytochrome P450 involvement.
- Multiple P450 isozymes likely participate, as suggested by biphasic Lineweaver-Burk plots.
- No significant stereoselectivity was observed in the demethylenation process.
- Catechol formation was buffer-dependent and influenced by hydroxyl radical (.OH) scavenging agents, catalase, and metal ions.
Conclusions:
- Rat brain microsomal metabolism of MDA and MDMA involves both cytochrome P450-mediated and chemical pathways, including hydroxyl radical generation.
- The findings highlight the complex metabolic fate of these amphetamines in the brain.
- Understanding these pathways is essential for neuropharmacological and toxicological assessments.