Metabolic evidence for the involvement of enzymatic bioactivation in the cataractogenicity of acetaminophen in genetically susceptible (C57BL/6) and resistant (DBA/2) murine strains.
Acetaminophen has been shown to be cataractogenic in mice and rabbits. C57BL/6 and DBA/2 mice respectively are genetically susceptible and resistant to the induction of cytochrome P-448 by 3-methylcholanthrene (3-MC). This isoenzyme is thought to bioactivate acetaminophen to a toxic reactive intermediate. These two murine strains also are correspondingly susceptible and resistant to acetaminophen cataractogenesis. To evaluate the potential role of enzymatic bioactivation as a determinant of acetaminophen cataractogenesis, C57BL/6 and DBA/2 mice were treated with acetaminophen, 300 or 400 mg/kg intraperitoneally (ip), with or without pretreatment 48 hr earlier using 3-MC, 200 mg/kg ip. Lenticular cataracts were evaluated using the unaided eye and a slit lamp, and hepatotoxicity was evaluated by determination of peak plasma concentration of alanine aminotransferase (ALT). Plasma concentrations of acetaminophen and metabolites, particularly the glutathione (GSH)-derived conjugates (cysteine and mercapturic acid) reflecting enzymatic bioactivation, were measured by high-performance liquid chromatography. Cataracts developed only in C57BL/6 mice pretreated with 3-MC, occurring in 1 of 5 and 5 of 5 animals treated respectively with 300 and 400 mg/kg of acetaminophen. Comparing these two groups of induced C57BL/6 mice, production of the cysteine conjugate of acetaminophen was 2.5-fold higher with the 400 mg/kg dose of acetaminophen (p less than 0.05). Compared to their respective dose-matched, noninduced controls, cysteine conjugate production in the 300 and 400 mg/kg dose groups of induced C57BL/6 mice respectively was 3-fold and 4-fold higher (p less than 0.05). No DBA/2 mice developed cataracts. No mercapturic acid conjugate was detectable in the plasma of DBA/2 mice, and production of the cysteine conjugate was not altered in this strain by increasing the dose of acetaminophen or by pretreatment with 3-MC. The mean peak plasma concentration of the cysteine conjugate, reflecting acetaminophen bioactivation, was 5-fold higher in animals developing cataracts compared with those without cataracts (p less than 0.001). Plasma concentrations of unmetabolized acetaminophen were similar in all groups and unrelated to the development of cataracts. All mice of both strains pretreated with 3-MC showed evidence of hepatotoxicity, indicating a dissociation between hepatotoxic and cataractogenic susceptibility.(ABSTRACT TRUNCATED AT 400 WORDS)
Lubek
B M
BM
Faculty of Pharmacy, University of Toronto, Ontario, Canada.
Basu
P K
PK
Wells
P G
PG
D000082:Acetaminophen / Q000378:metabolism / Q000633:toxicity*; D000818:Animals; D001711:Biotransformation; D002386:Cataract / Q000139:chemically induced*; D019388:Cytochrome P-450 CYP1A2; D003580:Cytochromes / Q000096:biosynthesis; D005965:Glucuronates / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D013045:Species Specificity
D003580:Cytochromes; D005965:Glucuronates; D000082:Acetaminophen; D008748:Methylcholanthrene; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D005978:Glutathione