Inhibition and activation of acetaminophen reactive metabolite formation by caffeine. Roles of cytochromes P-450IA1 and IIIA2.
Caffeine has previously been shown to diminish or potentiate acetaminophen (APAP) hepatotoxicity in rats, depending on induction state. To elucidate the P-450 forms involved in these divergent effects, rat liver microsomes, prepared after pretreatment with various inducers, were used to examine the effect of caffeine on N-acetyl-p-benzoquinone imine (NAPQI) formation. The addition of caffeine to incubations with 3-methylcholanthrene (MC)-induced microsomes resulted in a biphasic effect on the formation of NAPQI. A 43% decrease in NAPQI formation was observed as caffeine concentration was increased from 0 to 0.5 mM; however, NAPQI formation was accelerated as caffeine concentration increased, exceeding the control (no caffeine) value, at caffeine concentrations greater than 2.5 mM. Incubations with purified P-450IA1 showed that as caffeine concentration increased from 0 to 5 mM, a 50% inhibition was observed with no evidence of acceleration. In contrast to MC microsomes, the addition of caffeine to incubations with uninduced and phenobarbital-induced adult rat microsomes resulted in a marked (3- to 4-fold) acceleration of NAPQI formation with no evidence of inhibition. Caffeine (5 mM) also accelerated NAPQI formation in microsomes isolated from diabetic rats, but to a substantially lesser extent (120%), suggesting a modest (if any) effect on P-450IIE1, a form previously shown to form NAPQI from APAP. Interestingly, caffeine caused a 3- to 4-fold increase in NAPQI formation by juvenile male and female rat microsomes, but no activation was observed with adult female rat microsomes. These results suggested that caffeine activated a member of the cytochrome P-450IIIA subfamily.(ABSTRACT TRUNCATED AT 250 WORDS)
Lee
C A
CA
Department of Pharmaceutics, University of Washington, Seattle 98195.
Thummel
K E
KE
Kalhorn
T F
TF
Nelson
S D
SD
Slattery
J T
JT
D000082:Acetaminophen / Q000378:metabolism* / Q000633:toxicity; D000818:Animals; D016227:Benzoquinones / Q000378:metabolism; D001711:Biotransformation / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology*; D056486:Chemical and Drug Induced Liver Injury / Q000201:enzymology / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D006801:Humans; D007097:Imines / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D016227:Benzoquinones; D007097:Imines; D000082:Acetaminophen; D002110:Caffeine; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D009251:NADPH-Ferrihemoprotein Reductase; C028473:N-acetyl-4-benzoquinoneimine