Effects of antidepressant drugs on the activity of cytochrome P-450 measured by caffeine oxidation in rat liver microsomes.
Caffeine is a marker drug for testing the activity of CYP1A2 (3-N-demethylation) in humans and rats. Moreover, it is also a relatively specific substrate of CYP3A (8-hydroxylation). In the case of 1-N- and in particular 7-N-demethylation of caffeine, apart from CYP1A2, other cytochrome P-450 isoenzymes play a considerable role. The aim of the present study was to investigate the influence of imipramine, amitriptyline and fluoxetine on cytochrome P-450 activity measured by caffeine oxidation in rat liver microsomes. The obtained results showed that imipramine exerted a most potent inhibitory effect on caffeine metabolism. Imipramine decreased the rate of 3-N-, 1-N- and 7-N-demethylations, and 8-hydroxylation of caffeine, the effect on 3-N-demethylation being most pronounced (Ki = 33 microM). Amitriptyline showed distinct inhibition of 3-N- and 1-N-demethylation of caffeine, though its effect was less potent than in the case of imipramine (Ki = 57 and 61 pM, respectively). The influence of amitriptyline on 8-hydroxylation and especially on 7-N-demethylation of caffeine was weaker (Ki = 108 and 190 pM, respectively) than on 3-N- or 1-N-demethylation, suggesting a narrower spectrum of cytochrome P-450 inhibition by amitriptyline than by imipramine, involving mainly the subfamily CYP1A2, and--to a lesser degree--CYP3A. In contrast to the tested tricyclic antidepressants, fluoxetine did not exert any considerable effect on the 3-N- or 1-N-demethylation of caffeine (Ki = 152 and 196 microM, respectively), which indicates its low affinity for CYP1A2. However, fluoxetine displayed a clear inhibitory effect on caffeine 7-N-demethylation (Ki = 72 microM), the reaction which is catalyzed mainly by other than CYP1A2 isoenzymes. Fluoxetine diminished markedly the 8-hydroxylation of the marker drug; as reflected by Ki values, the potency of inhibition of rat CYP3A by fluoxetine was similar to that of imipramine (Ki = 40 and 45 microM, respectively). In summary, CYP1A2 was distinctly inhibited by imipramine and amitriptyline, CYP3A by imipramine and fluoxetine, while other CYP isoenzymes (CYP2B and/or 2E1) by imipramine and fluoxetine.
Danie
W A
WA
Department of Pharmacokinetics and Drug Metabolism, Institute of Pharmacology, Polish Academy of Sciences, Kraków.
Syrek
M
M
Ryłko
Z
Z
Wójcikowski
J
J
D000639:Amitriptyline / Q000494:pharmacology; D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases; D002110:Caffeine / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003640:Dealkylation; D005473:Fluoxetine / Q000494:pharmacology; D006900:Hydroxylation; D007099:Imipramine / Q000494:pharmacology; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity
D000928:Antidepressive Agents; D018687:Antidepressive Agents, Second-Generation; D000929:Antidepressive Agents, Tricyclic; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D007527:Isoenzymes; D005473:Fluoxetine; D000639:Amitriptyline; D002110:Caffeine; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D007099:Imipramine