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Metabolism of lofepramine by rat liver microsomes
Abstract:
1. The metabolism of lofepramine in vitro by rat liver microsomes was studied. The enzyme system involved was dependent on cytochrome P-450 and the main metabolites were desmethylimipramine (DMI), formaldehyde and p-chlorobenzoic acid. 2. Microsomes from rats pretreated with phenobarbital or 3-methylcholanthrene showed enhanced lofepramine metabolizing activity. The induction was reflected in increased Vmax values, whereas Km values were not changed. 3. Pretreatment of rats with lofepramine or DMI did not alter the rate of aniline hydroxylation, aminopyrine demethylation or lofepramine metabolism per mg microsomal protein. Nor was the amount of cytochrome P-450 changed. 4. Lofepramine, imipramine and DMI inhibited competitively the microsomal hydroxylation of aniline in vitro. Lofepramine was the most potent inhibitor, which probably reflects the higher lipophilicity of this compound.
Insights
Lofepramine metabolism in rats involves cytochrome P-450 enzymes, producing desmethylimipramine. Enzyme activity increased after phenobarbital or 3-methylcholanthrene pretreatment, with lofepramine inhibiting aniline hydroxylation.
Area of Science:
- Pharmacology
- Biochemistry
- Drug Metabolism
Background:
- Lofepramine is an antidepressant drug.
- Understanding its metabolic pathways is crucial for drug development and safety.
- Cytochrome P-450 enzymes play a significant role in drug metabolism.
Purpose of the Study:
- To investigate the in vitro metabolism of lofepramine using rat liver microsomes.
- To identify the key metabolites of lofepramine.
- To explore the involvement of cytochrome P-450 enzymes and the effects of enzyme induction on lofepramine metabolism.
Main Methods:
- In vitro incubation of lofepramine with rat liver microsomes.
- Analysis of metabolites using appropriate biochemical techniques.
- Enzyme kinetic studies (Vmax, Km) to assess metabolic activity.
- Investigation of enzyme induction using phenobarbital and 3-methylcholanthrene.
Main Results:
- Lofepramine is metabolized by a cytochrome P-450-dependent enzyme system.
- Major metabolites identified include desmethylimipramine (DMI), formaldehyde, and p-chlorobenzoic acid.
- Phenobarbital and 3-methylcholanthrene pretreatment enhanced lofepramine metabolism by increasing Vmax, without altering Km.
- Lofepramine, imipramine, and DMI competitively inhibited aniline hydroxylation, with lofepramine being the most potent inhibitor.
Conclusions:
- Lofepramine metabolism is mediated by cytochrome P-450 enzymes.
- Enzyme induction significantly enhances lofepramine metabolic activity.
- Lofepramine exhibits inhibitory effects on the metabolism of other drugs, such as aniline, suggesting potential drug-drug interactions.