Formaldehyde formation as a metabolite of methoxyflurane
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Abstract:
The production of formaldehyde as a metabolite of enzymatic biotransformation of methoxyflurane was observed in vitro in hepatic microsomal preparations derived from Japanese monkeys, rabbits and Wistar strain rats. Production rates of formaldehyde were 0.80-2.50 n moles/mg protein/min in the induced group which was pretreated with phenobarbitone, and 0.15-0.68 n moles/mg protein/min in the non-induced group. This reaction needed the presence of NADPH and oxygen. Formaldehyde production was almost completely inhibited by addition of 25% CO. Further degradation of formaldehyde did not occur in microsomal suspension. No detectable species difference was observed among the animals used in this study. These results indicate that the biotransformation of methoxyflurane is preceded by interaction with cytochrome p-450 in hepatic microsomes in the presence of NADPH and oxygen.
Insights
Methoxyflurane biotransformation in liver microsomes produces formaldehyde, requiring NADPH and oxygen. This metabolic pathway involves cytochrome P450, with no significant species differences observed in monkeys, rabbits, or rats.
Area of Science:
- Pharmacology and Toxicology
- Biochemistry
- Drug Metabolism
Background:
- Methoxyflurane is an anesthetic agent with known metabolic pathways.
- Hepatic microsomes are key sites for drug biotransformation.
- Understanding methoxyflurane metabolism is crucial for assessing its safety and efficacy.
Purpose of the Study:
- To investigate the in vitro biotransformation of methoxyflurane.
- To identify metabolites produced during methoxyflurane metabolism.
- To elucidate the enzymatic systems involved in methoxyflurane biotransformation.
Main Methods:
- In vitro incubation of methoxyflurane with hepatic microsomal preparations from Japanese monkeys, rabbits, and Wistar rats.
- Measurement of formaldehyde production using spectrophotometric assays.
- Assessment of cofactor requirements (NADPH, oxygen) and inhibitory effects (CO) on formaldehyde production.
Main Results:
- Formaldehyde was identified as a metabolite of methoxyflurane biotransformation.
- Higher formaldehyde production rates were observed in phenobarbitone-induced hepatic microsomes compared to non-induced.
- The reaction was dependent on NADPH and oxygen, and inhibited by carbon monoxide, indicating cytochrome P450 involvement.
Conclusions:
- Methoxyflurane undergoes enzymatic biotransformation to formaldehyde in hepatic microsomes.
- Cytochrome P450 enzymes, in the presence of NADPH and oxygen, mediate this initial step.
- No significant species-specific differences in methoxyflurane biotransformation were noted among the tested animal models.