Altered Disposition of Acetaminophen in Nrf2-null and Keap1-knockdown Mice

• Published in: Toxicological sciences Vol. 109; no. 1; pp. 31 - 40
• Main Authors: Reisman, Scott A., Csanaky, Iván L., Aleksunes, Lauren M., Klaassen, Curtis D.
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01.05.2009
• Subjects: acetaminophen; Acetaminophen - administration & dosage; Acetaminophen - analogs & derivatives; Acetaminophen - analysis; Acetaminophen - blood; Acetaminophen - metabolism; Acetaminophen - pharmacokinetics; Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; Animals; Bile - chemistry; Biotransformation; Biotransformation and Toxicokinetics; Carrier Proteins - metabolism; Cytoskeletal Proteins - genetics; Cytoskeletal Proteins - metabolism; Gene Knockdown Techniques; Guinea Pigs; Kelch-Like ECH-Associated Protein 1; Liver - chemistry; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microscopy, Fluorescence; Microsomes, Liver - metabolism; NAD(P)H Dehydrogenase (Quinone); NADPH Dehydrogenase - metabolism; NF-E2-Related Factor 2 - genetics; NF-E2-Related Factor 2 - metabolism; Nrf2; pharmacokinetics; transporters; pharmacokinetics; acetaminophen; transporters; Nrf2
• ISSN: 1096-6080; 1096-0929
• DOI: 10.1093/toxsci/kfp047

Acetaminophen (AA) is a widely used antipyretic drug that causes hepatotoxicity at high doses. Nuclear factor erythroid 2–related factor 2 (Nrf2) is a transcription factor that mitigates electrophilic stress from AA by inducing genes, such as NAD(P)H:quinone oxidoreductase 1 (Nqo1), multidrug resistance–associated proteins (Mrps), and glutathione (GSH) synthesis enzymes. To determine whether Nrf2 activation alters the biotransformation and excretion of AA, male wild-type, Nrf2-null, and Keap1 (Kelch-like ECH-associated protein 1)-knockdown (Keap1-kd) mice (which have increased activation of Nrf2) were administered a single subtoxic dose of AA (50 mg/kg, iv), after which, AA and its metabolites (AA-glucuronide [AA-GLUC]; AA-sulfate [AA-SULF]; AA-glutathione [AA-GSH]) were quantified in plasma, bile, and liver. AA-GLUC concentrations were reduced in plasma and elevated in livers of Nrf2-null mice due to decreased glucuronidation activity and lower expression of the basolateral efflux transporter Mrp3. In contrast, Keap1-kd mice had higher plasma and lower hepatic AA-GLUC concentrations, due to higher Mrp3 expression. Lower glucuronidation activity of Nrf2-null mice increased the proportion of AA available for sulfation, resulting in elevated AA-SULF concentrations in plasma, bile, and liver. Decreased AA-sulfation activity in Keap1-kd mice resulted in lower AA-SULF concentrations. AA-GSH conjugates were increased in Nrf2-null mice and tended to be lower in Keap1-kd mice. Furthermore, Nqo1, an enzyme capable of detoxifying the reactive intermediate of AA metabolism, N-acetyl-p-benzoquinone imine (NAPQI), had 85% lower activity in Nrf2-null mice and 415% higher activity in Keap1-kd mice relative to wild-type. In conclusion, lack of Nrf2 results in decreased AA glucuronidation, leading to increased AA available for NAPQI formation and decreased efflux of AA-GLUC via Mrp3; however, activation of Nrf2, as in Keap1-kd mice, results in decreased sulfotransferase activity, decreased AA-SULF formation, and enhanced elimination of AA-GLUC due to increased expression of Mrp3.