Role of the nuclear receptor PXR in acetaminophen hepatotoxicity

ABSTRACT:Inulin enzymatically synthesized from sucrose is a dietary component that completely escapes glucide digestion. Supplementing inulin to a high-fat and high-sucrose diet (HF) ameliorated hypertriglycemia and hepatic steatosis in 8-week-fed rats by suppressing elevated levels of serum triacylglycerols, fatty acids, and glucose, and the accumulation of hepatic triacylglycerols and fatty acids. Inulin intake prevented phenobarbital (PB)-and dexamethasone-induced liver injuries in the HF group. No significant alteration in the baseline expression of CYP2B, CYP2C11, CYP3A, and NADPH-cytochrome P450 (P450) reductase mRNAs and proteins was found. In contrast, baseline and PB-treated expressions of CYP2E1 mRNA were reduced in HF-fed rats. The induction of P450s in response to PB was affected by the nutritional status of the rats; mRNA levels of CYP2B1 and CYP3A1 after PB treatment, as assessed by quantitative real-time polymerase chain reaction analysis were reduced in the inulin-supplemented HF (HF؉I) group, compared with those in the HF group. Western blot analysis detected the corresponding changes of CYP2B and CYP3A proteins. These alterations were correlated with changes in hepatic thiobarbituric acid-reactive substances. Furthermore, no significant difference in the expression of nuclear receptors constitutive androstane receptor, pregnane X receptor, and retinoid X receptor ␣ and coactivator peroxisome proliferator-activated receptor-␥ coactivator 1␣ proteins was found in the hepatic nucleus between the HF and HF؉I groups, but the expression of hepatocyte nuclear factor ␣ (HNF4␣) protein was significantly reduced in the HF؉I group. Taken together, these results indicate that inulin intake ameliorates PB-induced liver injury, associated with a decline in lipid accumulation and PB-induced expression of CYP2B and CYP3A, which may be related by a reduction in the nuclear expression of HNF4␣.

Section: Effect Of Inulin On Expression Of Pb-induced P450 and Hnf4␣mentioning

confidence: 99%

Dietary Inulin Alleviates Hepatic Steatosis and Xenobiotics-Induced Liver Injury in Rats Fed a High-Fat and High-Sucrose Diet: Association with the Suppression of Hepatic Cytochrome P450 and Hepatocyte Nuclear Factor 4α Expression

Sugatani

Wada²,

Osabe³

et al. 2006

“…Protein concentrations were assayed by the procedure of Lowry et al (1951), using bovine serum albumin as the standard. Glutathione peroxidase and glutathione reductase activities were measured as described previously (Wolf et al, 2005). The microsomal formation of 6␤-hydroxytestosterone was measured by HPLC analysis as described previously (Kostrubsky et al, 1999).…”

Section: Methodsmentioning

confidence: 99%

“…For CYP2E1 and CYP3A, microsomal proteins were separated by SDS-polyacrylamide gel electrophoresis (10% acrylamide) at 160 V for 1 h. A mixed anionic detergent was used during the 1 h electrophoresis of gels for CYP1A2, as described previously (Sinclair et al, 1990a). To separate the CYP3A forms, the following modifications were used (Wolf et al, 2005). The electrophoresis buffer contained 37.5 mM Tris base, 290 mM glycine, and 1.5% (w/v) SDS.…”

Section: Methodsmentioning

confidence: 99%

“…In mice, the glucuronidation of APAP is a major pathway of detoxification (Wolf et al, 2005). To determine whether a difference in the glucuronidation of APAP could contribute to the differences in APAP hepatotoxicity observed in the two mouse lines, we compared the formation of the glucuronideconjugated metabolite of APAP (APAP-Gluc) by hepatic microsomes.…”

Section: Fig 2 Effect Of Withdrawal From Eip On Hepatic Cyp1a2 Cyp2e1mentioning

confidence: 99%

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

Wolf¹,

Wood²,

Allard³

et al. 2007

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

“…Pregnenolone 16␣-carbonitrile-activated murine PXR plays a critical role in APAPinduced hepatic toxicity, probably through induction of CYP3A11 expression (Guo et al, 2004). Others have reported a reduction of APAP hepatotoxicity in Pxr-null mice (Wolf et al, 2005). However, because of species differences between human PXR and rodent PXR, rodent models cannot accurately predict inducers and potential drugdrug interactions mediated by human PXR because of different responses to PXR ligands (Jones et al, 2000).…”

mentioning

confidence: 99%

Rifampicin-Activated Human Pregnane X Receptor and CYP3A4 Induction Enhance Acetaminophen-Induced Toxicity

Cheng¹,

Ma²,

Krausz³

et al. 2009

115

ABSTRACT:Acetaminophen (APAP) is safe at therapeutic levels but causes hepatotoxicity via N-acetyl-p-benzoquinone imine-induced oxidative stress upon overdose. To determine the effect of human (h) pregnane X receptor (PXR) activation and CYP3A4 induction on APAP-induced hepatotoxicity, mice humanized for PXR and CYP3A4 (TgCYP3A4/hPXR) were treated with APAP and rifampicin. Human PXR activation and CYP3A4 induction enhanced APAPinduced hepatotoxicity as revealed by hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities elevated in serum, and hepatic necrosis after coadministration of rifampicin and APAP, compared with APAP administration alone. In contrast, hPXR mice, wild-type mice, and Pxr-null mice exhibited significantly lower ALT/AST levels compared with TgCYP3A4/ hPXR mice after APAP administration. Toxicity was coincident with depletion of hepatic glutathione and increased production of hydrogen peroxide, suggesting increased oxidative stress upon hPXR activation. Moreover, mRNA analysis demonstrated that CYP3A4 and other PXR target genes were significantly induced by rifampicin treatment. Urinary metabolomic analysis indicated that cysteine-APAP and its metabolite S-(5-acetylamino-2-hydroxyphenyl)mercaptopyruvic acid were the major contributors to the toxic phenotype. Quantification of plasma APAP metabolites indicated that the APAP dimer formed coincident with increased oxidative stress. In addition, serum metabolomics revealed reduction of lysophosphatidylcholine in the APAP-treated groups. These findings demonstrated that human PXR is involved in regulation of APAP-induced toxicity through CYP3A4-mediated hepatic metabolism of APAP in the presence of PXR ligands.