Induction of genes for metabolism and transport by trans-stilbene oxide in livers of Sprague-Dawley and Wistar-Kyoto rats

Enhanced absorption and inhibited metabolism of emodin by 2, 3, 5, 4'-tetrahydroxystilbene-2-O-β-D-glucopyranoside: Possible mechanisms for Polygoni Multiflori Radix-induced liver injury

Polygoni Multiflori Radix (PMR) has been commonly used as a tonic in China for centuries. However, PMR-associated hepatotoxicity is becoming a safety issue. In our previous in vivo study, an interaction between stilbenes and anthraquinones has been discovered and a hypothesis is proposed that the interaction between stilbene glucoside-enriching fraction and emodin may contribute to the side effects of PMR. To further support our previous in vivo results in rats, the present in vitro study was designed to evaluate the effects of 2, 3, 5, 4'-tetrahydroxystilbene-2-O-β-D-glucopyranoside (TSG) on the cellular absorption and human liver microsome metabolism of emodin. The obtained results indicated that the absorption of emodin in Caco-2 cells was enhanced and the metabolism of emodin in human liver microsomes was inhibited after TSG treatment. The effects of the transport inhibitors on the cellular emodin accumulation were also examined. Western blot assay suggested that the depressed metabolism of emodin could be attributed to the down-regulation of UDP-glucuronosyltransferases (UGTs) 1A8, 1A10, and 2B7. These findings definitively demonstrated the existence of interaction between TSG and emodin, which provide a basis for a better understanding of the underlying mechanism for PMR-induced liver injury.

Chemical-induced coordinated and reciprocal changes in heme metabolism, cytochrome P450 synthesis and others in the liver of humans and rodents

A wide variety of drugs and chemicals have been shown to produce induction and inhibition of heme-metabolizing enzymes, and of drug-metabolizing enzymes, including cytochrome P450s (P450s, CYPs), which consist of many molecular species with lower substrate specificity. Such chemically induced enzyme alterations are coordinately or reciprocally regulated through the same and/or different signal transductions. From the toxicological point of view, these enzymatic changes sometimes exacerbate inherited diseases, such as precipitation of porphyrogenic attacks, although the induction of these enzymes is dependent on the animal species in response to the differences in the stimuli of the liver, where they are also metabolized by P450s. Since P450s are hemoproteins, their induction and/or inhibition by chemical compounds could be coordinately accompanied by heme synthesis and/or inhibition. This review will take a retrospective view of research works carried out in our department and current findings on chemical-induced changes in hepatic heme metabolism in many places, together with current knowledge. Specifically, current beneficial aspects of induction of heme oxygenase-1, a rate-limiting heme degradation enzyme, and its relation to reciprocal and coordinated changes in P450s, with special reference to CYP2A5, in the liver are discussed. Mechanistic studies are also summarized in relation to current understanding on these aspects. Emphasis is also paid to an example of a single chemical compound that could cause various changes by mediating multiple signal transduction systems. Current toxicological studies have been developing by utilizing a sophisticated "omics" technology and survey integrated changes in the tissues produced by the administration of a chemical, even in time- and dose-dependent manners. Toxicological studies are generally carried out step by step to determine and elucidate mechanisms produced by drugs and chemicals. Such approaches are correct; however, current "omics" technology can clarify overall changes occurring in the cells and tissues after treating animals with drugs and chemicals, integrate them and discuss the results. In the present review, we will discuss chemical-induced similar changes of heme synthesis and degradation, and of P450s and finally convergence to similar or different directions.

Stilbene glucoside inhibits the glucuronidation of emodin in rats through the down-regulation of UDP-glucuronosyltransferases 1A8: application to a drug-drug interaction study in Radix Polygoni Multiflori

ETHNOPHARMACOLOGICAL RELEVANCE

The integrated effects of herbal medicines were the outcome of all of the inherent components. Currently, few studies have focused on the multicomponent interactions in an herbal medicine to elucidate its pharmacological and/or toxicological effects. In this study, an attempt was made to investigate the interaction between stilbene glucosides and the anthraquinones contained in Radix Polygoni Multiflori (RPM) and to explore the interaction's mechanism from the perspective of UDP-glucuronosyltransferase (UGT) regulation.

MATERIALS AND METHODS

The extract of RPM was separated into a stilbene glucoside fraction and a emodin fraction. A rapid high-performance liquid chromatography-mass spectrometry method was developed and validated to disclose the influence of stilbene glucoside on the pharmacokinetics of emodin in rats. Drug and Statistics 2.0 was used for the estimation of the pharmacokinetic parameters. Gene expression analysis in liver and intestinal tissues was performed by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS

The analytical method appeared to be suitable for the analysis of emodin with desirable linearity, accuracy, precision and stability, and the total analysis time was less than 2 min on a short column. Glucuronide of emodin, which is the major metabolite of emodin, was determined after β-glucuronidase hydrolysis. As the in vivo pharmacokinetic studies had indicated, the AUC, Cmax and T1/2 of emodin were increased after the stilbene glucoside treatment, and the glucuronidation of emodin was significantly inhibited. The mRNA levels from UGT1A8 and UGT1A2 were decreased by stilbene glucoside treatment. In contrast, the expression of UGT1A1, UGT1A6 and UGT1A9 mRNA was increased in the liver following treatment.

CONCLUSIONS

The influence of stilbene glucoside on the pharmacokinetics of emodin may be attributed to the inhibition of UGT1A8 mRNA expression. Thus, it is important to extend this research to deepen our understanding of the pharmacological and/or toxicological effects of RPM.

Constitutive activation of nuclear factor-E2-related factor 2 induces biotransformation enzyme and transporter expression in livers of mice with hepatocyte-specific deletion of Kelch-like ECH-associated protein 1

Chemicals that activate nuclear factor-E2-related factor 2 (Nrf2) often increase multidrug-resistance-associated protein (Mrp) expression in liver. Hepatocyte-specific deletion of Kelch-like ECH-associated protein 1 (Keap1) activates Nrf2. Use of hepatocyte-specific Keap1 deletion represents a nonpharmacological method to determine whether constitutive Nrf2 activation upregulates liver transporter expression in vivo. The mRNA, protein expression, and localization of several biotransformation and transporters were determined in livers of wild-type and hepatocyte-specific Keap1-null mice. Sulfotransferase 2a1/2, NADP(H):quinone oxidoreductase 1, cytochrome P450 2b10, 3a11, and glutamate-cysteine ligase catalytic subunit expression were increased in livers of Keap1-null mice. Organic anion-transporting polypeptide 1a1 expression was nearly abolished, as compared to that detected in livers of wild-type mice. By contrast, Mrp 1-5 mRNA and protein levels were increased in Keap1-null mouse livers, with Mrp4 expression being more than 15-fold higher than wild types. In summary, Nrf2 has a significant role in affecting Oatp and Mrp expressions.

Regulation of hepatic ABCC transporters by xenobiotics and in disease states

The subfamily of ABCC transporters consists of 13 members in mammals, including the multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and the cystic fibrosis transmembrane conductance regulator (CFTR). These proteins play roles in chemical detoxification, disposition, and normal cell physiology. ABCC transporters are expressed differentially in the liver and are regulated at the transcription and translation level. Their expression and function are also controlled by post-translational modification and membrane-trafficking events. These processes are tightly regulated. Information about alterations in the expression of hepatobiliary ABCC transporters could provide important insights into the pathogenesis of diseases and disposition of xenobiotics. In this review, we describe the regulation of hepatic ABCC transporters in humans and rodents by a variety of xenobiotics, under disease states and in genetically modified animal models deficient in transcription factors, transporters, and cell-signaling molecules.

Activation of xenobiotic receptors: driving into the nucleus

IMPORTANCE OF THE FIELD

Xenobiotic receptors (XRs) play pivotal roles in regulating the expression of genes that determine the clearance and detoxification of xenobiotics, such as drugs and environmental chemicals. Recently, it has become increasingly evident that most XRs shuttle between the cytoplasm and nucleus, and activation of such receptors is directly associated with xenobiotic-induced nuclear import.

AREAS COVERED IN THIS REVIEW

The scope of this review covers research literature that discusses nuclear translocation and activation of XRs, as well as unpublished data generated from this laboratory. Specific emphasis is given to the constitutive androstane receptor (CAR), the pregnane X receptor and the aryl hydrocarbon receptor.

WHAT THE READERS WILL GAIN

A number of molecular chaperons presumably associated with cellular localization of XRs have been identified. Primary hepatocyte cultures have been established as a unique model retaining inactive CAR in the cytoplasm. Moreover, several splicing variants of human CAR exhibit altered cellular localization and chemical activation.

TAKE HOME MESSAGE

Nuclear accumulation is an essential step in the activation of XRs. Although great strides have been made, much remains to be understood concerning the mechanisms underlying intracellular localization and trafficking of XRs, which involve both direct ligand-binding and indirect pathways.

Coordinate regulation of metabolic enzymes and transporters by nuclear transcription factors in human liver disease

BACKGROUND

It has been hypothesised, mainly from studies with animal models of liver disease, that the transport of substrates for metabolic enzymes and their subsequent metabolism and elimination in hepatic bile or blood is co-ordinated, but there is little information on this process in diseased human liver.

METHODS

In this study we have measured by reverse transcription polymerase chain reaction (RT-PCR) major genes involved in drug metabolism from UDP-glucuronosyltransferases (UGT1A1, UGT1A6, UGT1A9, and UGT2B4) and cytochrome P450 (CYP) families (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4), transport (OATP-C, MRP2, MRP3, and MDR1) and major transcription factors (PXR, CAR, HNF1alpha, HNF4alpha, RXR, and AHR) involved in their regulation. Liver biopsy tissue from patients with viral hepatitis was scored for inflammation and fibrosis by the METAVIR system, and separated into groups with mild (A0-1; F0-1, n = 20) or severe (A2-3; F3-4, n = 19) liver disease. Correlation analysis (Spearman rank-test, P < 0.05) was used to identify metabolic enzymes and transporters which shared significant correlation with transcription factors.

RESULTS

Our results show an extensive correlation between transcription factors, transporters, and metabolic enzymes. An unexpected finding was that this was substantially greater in the severely diseased liver. Cross-talk between transcription factors was markedly increased in tissue from patients with severe liver disease, particularly between CAR, HNF4alpha, and PXR.

CONCLUSION

Our results support the hypothesis of co-ordinate regulation of metabolic enzymes and transporters in diseased human liver, as part of a widespread co-ordinated process under the control of nuclear receptor transcription factors.

Effect of repeated administration with subtoxic doses of acetaminophen to rats on enterohepatic recirculation of a subsequent toxic dose

Development of resistance to toxic effects of acetaminophen (APAP) was reported in rodents and humans, though the mechanism is only partially understood. We examined in rats the effect of administration with subtoxic daily doses (0.2, 0.3, and 0.6g/kg, i.p.) of APAP on enterohepatic recirculation and liver toxicity of a subsequent i.p. toxic dose of 1g/kg, given 24h after APAP pre-treatment. APAP and its major metabolite APAP-glucuronide (APAP-Glu) were determined in bile, urine, serum and liver homogenate. APAP pre-treatment was not toxic, as determined by serum markers of liver damage and neither induced oxidative stress as demonstrated by assessment of ROS generation in liver or glutathione species in liver and bile. APAP pre-treatment induced a partial shift from biliary to urinary elimination of APAP-Glu after administration with the toxic dose, and decreased hepatic content and increased serum content of this conjugate, consistent with a marked up-regulation of its basolateral transporter Mrp3 relative to apical Mrp2. Preferential secretion of APAP-glu into blood decreased enterohepatic recirculation of APAP, thus attenuating liver exposition to the intact drug, as demonstrated 6h after administration with the toxic dose. The beneficial effect of interfering the enterohepatic recirculation was alternatively tested in animals receiving activated charcoal by gavage to adsorb APAP of biliary origin. The data indicated decreased liver APAP content and glutathione consumption. We conclude that selective up-regulation of Mrp3 expression by APAP pre-treatment may contribute to development of resistance to APAP hepatotoxicity, at least in part by decreasing its enterohepatic recirculation.

ATP-binding cassette C transporters in human pancreatic carcinoma cell lines. Upregulation in 5-fluorouracil-resistant cells

BACKGROUND

Pancreatic cancer is characterized by high resistance to chemotherapy. Such chemoresistance can be mediated by multidrug resistance proteins (MRPs), breast cancer resistance protein (BCRP), and MDR1 P-glycoprotein. However, the contribution of individual MRP isoforms to chemoresistance in pancreatic carcinoma is unclear. We studied ATP-binding cassette (ABC) transporter expression in human pancreatic carcinoma cell lines as compared to primary pancreatic duct cells, and analyzed the MRP expression profile in 5-fluorouracil-resistant cells.

METHODS

Transporter expression was analyzed by quantitative and qualitative RT-PCR, by immunoblot, and chemoresistance by cytotoxicity assay.

RESULTS

Primary pancreatic duct cells expressed MRP1, MRP3, MRP4, and MRP5, but not MRP2 mRNA. The established carcinoma cell lines expressed MRP1, MRP4, and MRP5, most of them also MRP2, MRP3, MRP7, and BCRP, but none contained detectable amounts of MRP6, MRP8, or MRP9 mRNA. Immunoblot analyses demonstrated presence of MRP1, MRP4, and MRP5 protein in all, but MRP3 and BCRP protein only in some of these cells. Compared to parental Capan-1 cells, Capan-1 cells with acquired chemoresistance towards 5-fluorouracil showed an upregulated mRNA and protein expression of MRP3, MRP4, and MRP5. In addition, silencing of MRP5 by RNA interference resulted in enhanced sensitivity of parental Capan-1 cells towards 5-fluorouracil cytotoxicity.

CONCLUSION

MRP3, MRP4, and MRP5 are upregulated in 5-fluorouracil-resistant cells, and MRP5 contributes to 5-FU resistance in pancreatic carcinoma cells.

Genes of the antioxidant response undergo upregulation in a rodent model of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease encompasses a spectrum of hepatic pathologies ranging from simple fatty liver to an inflammatory state known as nonalcoholic steatohepatitis (NASH). NASH is also characterized by severe hepatic oxidative stress. The goal of this study was to determine whether genes of the antioxidant response are induced in rodent models of nonalcoholic fatty liver disease. To simulate simple fatty liver and NASH, respectively, male Sprague-Dawley rats were fed a high-fat (HF) or a methionine and choline-deficient (MCD) diet for 8 weeks. Key marker genes of the antioxidant response that are known to undergo upregulation via activation of Nuclear Factor Erythroid 2-Related Factor 2 were measured using the branched DNA signal amplification assay. Messenger RNA levels of the antioxidant response, including NAD(P)H:quinone oxidoreductase-1 (Nqo1), Glutamate cysteine ligase catalytic (Gclc), and Heme oxygenase-1 (Ho-1), were significantly induced in MCD rat liver but not in HF rat liver. Furthermore, Nqo1 protein expression and activity underwent significant upregulation in MCD rat liver but not in HF rat liver. These data strongly indicate that the pathology induced by the MCD dietary model of NASH results in upregulation of the antioxidant response in rats.