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Cytochrome P-450 activities in human and rat brain microsomes.
P Voirol1, M Jonzier-Perey, F Porchet
1Unité de Biochimie et Psychopharmacologie Clinique, Département Universitaire de Psychiatrie Adulte, CH-1008 Prilly, Lausanne, Switzerland.
Brain Research
|March 1, 2000
Summary
Cytochrome P450 activity in brain microsomes is low. However, psychotropic drugs may undergo local metabolism, potentially leading to significant pharmacological and toxicological effects.
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- Cytochrome P450 enzymes (CYP450) are crucial for drug metabolism.
- Their role in brain tissue, particularly in the metabolism of psychotropic medications, remains incompletely understood.
Purpose of the Study:
- To investigate the role of specific CYP450 isoforms in the metabolism of various psychotropic drugs in rat and human brain microsomes.
- To determine the potential for local cerebral metabolism of these drugs and its implications.
Main Methods:
- Utilized gas chromatography-mass spectrometry (GC-MS) for sensitive quantification of drug metabolites.
- Employed enzyme inhibition studies with specific inhibitors (ketoconazole, furafylline, etc.) and antibodies against CYP450 isoforms.
- Assessed metabolism of dextromethorphan, amitriptyline, midazolam, S-mephenytoin, citalopram, fluoxetine, and sertraline.
Main Results:
- Amitriptyline demethylation to nortriptyline was identified, primarily mediated by CYP3A4 in both rat and human brain microsomes.
- Dextromethorphan metabolism to dextrorphan was observed in rat brain microsomes, inhibited by CYP2D6-specific agents.
- Limited detection of other drug metabolites suggested low overall CYP450 activity in brain tissue, with human studies requiring exogenous reductase.
Conclusions:
- Cytochrome P450 activity in the brain is generally low.
- Psychotropic drugs can undergo local metabolism within the brain.
- This local metabolism may have significant pharmacological and/or toxicological consequences.