Role of CYP2A5 and 2G1 in Acetaminophen Metabolism and Toxicity in the Olfactory Mucosa of the Cyp1a2(−/−)Mouse

doi:10.1016/S0006-2952(98)00004-5

Biochemical Pharmacology

Volume 55, Issue 11, 1 June 1998, Pages 1819-1826

https://doi.org/10.1016/S0006-2952(98)00004-5 Get rights and content

Abstract

Acetaminophen (AP) is a widely-used analgesic agent that has been linked to human liver and kidney disease with prolonged or high-dose usage. In rodents, the target organs that are affected include liver, kidney, and the olfactory mucosa. AP toxicity requires cytochrome P450(CYP)-mediated metabolic activation, and the isozymes CYP1A2, 2E1, and 3A are known to activate AP in the human. In the present study, we determined that olfactory mucosal toxicity of AP was not different between the Cyp1a2(+/+) wild-type and the Cyp1a2(−/−) knockout mouse, whereas the hepatic toxicity of AP was significantly diminished in Cyp1a2(−/−) mice. Western blots of olfactory mucosa revealed that CYP2E1 and CYP3A levels are similar between untreated Cyp1a2(+/+) and Cyp1a2(−/−) mice. Diallyl sulfide (DAS), a known inhibitor of CYP2E1 and of CYP2A10/2A11 (the rabbit orthologue of mouse CYP2A5), completely eliminated olfactory toxicity of AP in both the Cyp1a2(−/−) and wild-type mouse olfactory mucosa. We found that heterologously expressed mouse CYP2A5 and CYP2G1 enzymes (known to be present in olfactory mucosa) form 3-hydroxyacetaminophen (3-OH-AP) and 3-(glutathion-S-yl)acetaminophen (GS-AP); CYP2A5 is considerably more active than 2G1. Addition of GSH caused increases in GS-AP proportional to decreases in 3-OH-AP, suggesting that these two metabolites arise from a common precursor or are formed by way of competing pathways. We also found that both CYP2A5 and CYP2G1 are inhibitable by DAS in vitro. These studies provide strong evidence that, in addition to CYP2E1, CYP2A5 and 2G1 are important in AP bioactivation in the mouse olfactory mucosa and that CYP1A2 appears to be of minor importance for AP olfactory toxicity.

Section snippets

Chemicals

Uniformly ring-labeled[¹⁴C]-AP (6.3 Ci/mol), unlabeled AP, and DAS were obtained from Sigma. [Glycine-2-³H]-GSH (44.8 Ci/mmol) was purchased from DuPont/NEN.

Animals

Cyp1a2(+/+) wild-type homozygotes and Cyp1a2(−/−) knockout homozygotes were littermates generated by crossing the Cyp1a2(+/−) heterozygote females and males. These mice were bred in the Nebert mouse colony at the University of Cincinnati Department of Laboratory Animal Medicine and identified by PCR amplification of DNA obtained from tail

Olfactory Toxicity of AP in Cyp1a2(+/+) Wild-Type and Cyp1a2(−/−) Knockout Mice

Histopathologic evaluation (Fig. 1) revealed that acetaminophen-induced damage was observed in centrilobular hepatocytes in the Cyp1a2(+/+) wild-type mice. In contrast, the Cyp1a2(−/−) knockout mice exhibited no evidence of centrilobular necrosis (Fig. 1). Both the wild-type and the CYP1A2-deficient mice suffered similar damage to the olfactory mucosa covering the nasal turbinates. Interestingly, the nasal mucosal damage varied extensively in its severity. Approximately half of the affected

Discussion

The present study demonstrates that the liver toxicity of AP is decreased in the Cyp1a2(−/−) knockout mouse. It has been reported that CYP2E1 is important in AP-mediated liver toxicity at low AP doses, whereas CYP1A2 plays a larger role in hepatic toxicity at higher doses [35]. Because we used a high AP dose (600 mg/kg; Fig. 1), our data are consistent with those of Snawder et al. [35].

This study also demonstrates that the olfactory mucosal toxicity is not CYP1A2-dependent, suggesting that one

Acknowledgements

These studies were supported in part by NIH R01 AG13837 (M.B.G.), ES07462 (X.D.) and ES06321 (D.W.N.) and by NIH P30 ES06096 (D.W.N.).

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Original ArticlesRole of CYP2A5 and 2G1 in Acetaminophen Metabolism and Toxicity in the Olfactory Mucosa of the Cyp1a2(−/−)Mouse

Abstract

Section snippets

Chemicals

Animals

Olfactory Toxicity of AP in Cyp1a2(+/+) Wild-Type and Cyp1a2(−/−) Knockout Mice

Discussion

Acknowledgements

Toxicol Appl Pharmacol

Toxicol Appl Pharmacol

J Hepatol

Toxicol Appl Pharmacol

Biochem Pharmacol

Life Sci

J Biol Chem

J Biol Chem

Arch Biochem Biophys

Arch Biochem Biophys

Fundam Appl Toxicol

Arch Biochem Biophys

Biochem Biophys Res Comm

Biochem Pharmacol

J Biol Chem

Toxicol Appl Pharmacol

Cancer Lett

Biochem Pharmacol

Acetaminophen-induced hepatic necrosis and renal failure

JAMA

Acute renal failure associated with acetaminophen ingestionreport of a case and review of the literature

Clin Nephrol

Paracetamol-induced acute renal failure in the absence of fulminant liver damage

Br Med J

Acute renal failure after analgesic drugs including paracetamol (acetaminophen)

Nephron

Extrahepatic lesions induced by acetaminophen in the mouse

Toxicol Pathol

Original Articles
Role of CYP2A5 and 2G1 in Acetaminophen Metabolism and Toxicity in the Olfactory Mucosa of the Cyp1a2(−/−)Mouse