Role of CYP3A and CYP2E1 in Alcohol-Mediated Increases in Acetaminophen Hepatotoxicity: Comparison of Wild-Type andCyp2e1(–/–) Mice

Abstract

ABSTRACT:CYP2E1 is widely accepted as the sole form of cytochrome P450 responsible for alcohol-mediated increases in acetaminophen (APAP) hepatotoxicity. However, we previously found that alcohol [ethanol and isopentanol (EIP)] causes increases in APAP hepatotoxicity in Cyp2e1(؊/؊) mice, indicating that CYP2E1 is not essential. Here, using wild-type and Cyp2e1(؊/؊) mice, we investigated the relative roles of CYP2E1 and CYP3A in EIP-mediated increases in APAP hepatotoxicity. We found that EIP-mediated increases in APAP hepatotoxicity occurred at lower APAP doses in wild-type mice (300 mg/kg) than in Cyp2e1(؊/؊) mice (600 mg/kg). Although this result suggests that CYP2E1 has a role in the different susceptibilities of these mouse lines, our findings that EIP-mediated increases in CYP3A activities were greater in wild-type mice compared with Cyp2e1(؊/؊) mice raises the possibility that differential increases in CYP3A may also contribute to the greater APAP sensitivity in EIP-pretreated wild-type mice. At the time of APAP administration, which followed an 11 h withdrawal from the alcohols, alcohol-induced levels of CYP3A were sustained in both mouse lines, whereas CYP2E1 was decreased to constitutive levels in wild-type mice. The CYP3A inhibitor triacetyloleandomycin (TAO) decreased APAP hepatotoxicity in EIP-pretreated wild-type and Cyp2e1(؊/؊) mice. TAO treatment in vivo resulted in inhibition of microsomal CYP3A-catalyzed activity, measured in vitro, with no inhibition of CYP1A2 and CYP2E1 activities. In conclusion, these findings suggest that both CYP3A and CYP2E1 contribute to APAP hepatotoxicity in alcohol-treated mice.Acetaminophen (APAP) is considered to be a relatively safe drug and is widely prescribed and used for its analgesic and antipyretic properties. The first reports of hepatotoxicity in humans resulting from APAP overdose were in 1966 ( Thomson and Prescott, 1966). Today, APAP is a frequent cause of liver failure and the leading cause of death due to accidental and deliberate overdose (for review, see Bromer and Black, 2003). APAP is mainly glucuronidated and sulfated in the liver by phase II metabolic pathways, leading to excretion of the drug. However, APAP is also metabolized by certain forms of cytochromes P450 (P450s) to N-acetyl-p-benzoquinone imine (NAPQI), a highly electrophilic metabolite that is considered to be responsible for triggering the ensuing liver damage. CYP1A2, CYP2E1, and CYP3A are three forms of rat and human P450s active in the conversion of APAP to NAPQI, with CYP2E1 and CYP3A having greater intrinsic activity than CYP1A2 (Patten et al., 1993;Thummel et al., 1993). Reduced glutathione (GSH) reacts with NAPQI, resulting in the inactivation of this reactive metabolite. When GSH levels become depleted, liver damage can occur as a result of the

Wuzhi Tablet (Schisandra SphenantheraExtract) Protects against Acetaminophen-Induced Hepatotoxicity by Inhibition of CYP-Mediated Bioactivation and Regulation of NRF2-ARE and p53/p21 Pathways

“…It is known that the reactive metabolite NAPQI derived from APAP is generated by P450-catalyzed oxidation mainly involving CYP2E1, CYP3A4, and CYP1A2 (Zaher et al, 1998;Wolf et al, 2007). Previous reports showed that Schisandra chinensis extract and its lignans activated PXR and induced the expression of CYP3A and CYP2C by reporter gene assays in primary hepatocyte cultures (Mu et al, 2006), which was consistent with our observations.…”

Identification of Novel Toxicity-associated Metabolites by Metabolomics and Mass Isotopomer Analysis of Acetaminophen Metabolism in Wild-type and Cyp2e1-null Mice

“…The importance of CYP1A2 in the metabolism of high dose APAP in vivo was further demonstrated by the increased covalent binding in ␤-napthaflavone-pretreated mice (28) and the exceptional resistance to the APAP-induced toxicity in CYP2E1 and CYP1A2 double knock-out mice (29). The potential involvement of CYP3A in the in vivo bioactivation of APAP was also implied by the studies on alcohol-enhanced APAP toxicity (30,31) and the pregnane X receptor-null mouse model (32). In fact, it was recently reported that liver microsomes from wild-type and Cyp2e1-null mice had comparable activities for generating GS-APAP (30).…”

“…The potential involvement of CYP3A in the in vivo bioactivation of APAP was also implied by the studies on alcohol-enhanced APAP toxicity (30,31) and the pregnane X receptor-null mouse model (32). In fact, it was recently reported that liver microsomes from wild-type and Cyp2e1-null mice had comparable activities for generating GS-APAP (30). Therefore, it is highly possible that, in the high dose APAP treatments, CYP1A2 and CYP3A as well as other P450s with high K m values can compensate for the deficiency of CYP2E1 in Cyp2e1-null mice for converting APAP to NAPQI, resulting in a metabolite profile similar to wild-type mice.…”

CYP2E1 and oxidative liver injury by alcohol

“…Mice lacking both CYP2E1 and 1A2 were almost completely resistant to acetaminophen toxicity (189). The combination of ethanol plus isopentanol caused an increase in acetaminophen hepatotoxicity in CYP2E1 knockout mice which was sensitive to the CYP3A inhibitor, triacetyloleandomycin, leading to the suggestion that both CYP2E1 and CYP3A contribute to acetaminophen toxicity in ethanol plus isopentanol-treated mice (190). Recently, a CYP2E1-humanized transgenic mouse model that expresses functional and inducible human CYP2E1 was described (191).…”