Liver X receptor α and farnesoid X receptor are major transcriptional regulators of OATP1B1

Investigational farnesoid X receptor agonists for the treatment of primary biliary cholangitis

INTRODUCTION

Up to 40% of Primary biliary cholangitis (PBC) patients have a suboptimal response to Ursodeoxycholic acid (UDCA). Close to half of such patients show a remarkable improvement when additionally treated with Obeticholic acid (OCA) but have a dose-dependent increase of pruritus. This relative success of OCA, a first-in-class Farnesoid receptor (FXR) agonist, has positioned FXR as an attractive target for drug development. Novel candidates have since emerged, providing hope for this subgroup of patients who lack effective and safe treatments.

AREAS COVERED

We discussed the role of bile acids in PBC pathogenesis and how the FXR agonists provide therapeutic value by affecting bile acid synthesis and transport. Novel FXR agonists undergoing pre-clinical and clinical trials for PBC were enlisted via literature search by including the terms 'FXR agonists,' 'FXR PBC,' 'PBC clinical trials' on PubMed, MEDLINE via Ovid, and Clinicaltrials.gov.

EXPERT OPINION

Novel FXR agonists currently under investigation for PBC improve the disease surrogate markers in early trials. However, as with OCA, pruritus remains a concern with the newer drugs despite targeted chemical modifications to increase FXR specificity. Directing future resources toward studying the molecular mechanisms behind pruritus may lead to better drug design and efficacious yet safer drugs.

Intestinal stearoyl-CoA desaturase-1 regulates energy balance via alterations in bile acid homeostasis

Background and Aims

Stearoyl-CoA desaturase-1 (SCD1) converts saturated fatty acids into monounsaturated fatty acids and plays an important regulatory role in lipid metabolism. Previous studies have demonstrated that mice deficient in SCD1 are protected from diet-induced obesity and hepatic steatosis due to altered lipid esterification and increased energy expenditure. Previous studies in our lab have shown that intestinal SCD1 modulates intestinal and plasma lipids and alters cholesterol metabolism. Here we investigated a novel role for intestinal SCD1 in the regulation of systemic energy balance.

Methods

To interrogate the role of intestinal SCD1 in modulating whole body metabolism, intestine-specific Scd1 knockout (iKO) mice were maintained on standard chow diet or challenged with a high-fat diet (HFD). Studies included analyses of bile acid content and composition, metabolic phenotyping including body composition, indirect calorimetry, glucose tolerance analyses, and assessment of bile acid signaling pathways.

Results

iKO mice displayed elevated plasma and hepatic bile acid content and decreased fecal bile acid excretion, associated with increased expression of the ileal bile acid uptake transporter, Asbt . These increases were associated with increased expression of TGR5 targets, including Dio2 in brown adipose tissue and elevated plasma glucagon-like peptide-1 levels. Upon HFD challenge, iKO mice had reduced metabolic efficiency apparent through decreased weight gain despite higher food intake. Concomitantly, energy expenditure was increased, and glucose tolerance was improved in HFD-fed iKO mice.

Conclusion

Our results indicate that deletion of intestinal SCD1 has significant impacts on bile acid metabolism and whole-body energy balance, likely via activation of TGR5.

The regulation of tissue-specific farnesoid X receptor on genes and diseases involved in bile acid homeostasis

Bile acids (BAs) facilitate the absorption of dietary lipids and vitamins and have also been identified as signaling molecules involved in regulating their own metabolism, glucose and lipid metabolism, as well as immunity. Disturbances in BA homeostasis are associated with various enterohepatic and metabolic diseases, such as cholestasis, nonalcoholic steatohepatitis, inflammatory bowel disease, and obesity. As a key regulator, the nuclear orphan receptor farnesoid X receptor (FXR, NR1H4) precisely regulates BA homeostasis by transcriptional regulation of genes involved in BA synthesis, metabolism, and enterohepatic circulation. FXR is widely regarded as the most potential therapeutic target. Obeticholic acid is the only FXR agonist approved to treat patients with primary biliary cholangitis, but its non-specific activation of systemic FXR also causes high-frequency side effects. In recent years, developing tissue-specific FXR-targeting drugs has become a research highlight. This article provides a comprehensive overview of the role of tissue-specific intestine/liver FXR in regulating genes involved in BA homeostasis and briefly discusses tissue-specific FXR as a therapeutic target for treating diseases. These findings provide the basis for the development of tissue-specific FXR modulators for the treatment of enterohepatic and metabolic diseases associated with BA dysfunction.

The Role of Adopted Orphan Nuclear Receptors in the Regulation of an Organic Anion Transporting Polypeptide 1B1 (OATP1B1) under the Action of Sex Hormones

Organic anion transporting polypeptide 1B1 (OATP1B1) is an influx transporter protein of the SLC superfamily, expressed mainly in the liver and some tumor cells. The mechanisms of its regulation are being actively studied. In the present study, the effect of sex hormones (estradiol, progesterone and testosterone) on OATP1B1 expression in HepG2 cells was examined. The role of adopted orphan receptors, farnasoid X receptor (FXR), constitutive androstane receptor (CAR), pregnane X receptor (PXR) and liver X receptor subtype alpha (LXRa), was also evaluated. Hormones were used in concentrations of 1, 10 and 100 μM, with incubation for 24 h. The protein expression of OATP1B1, FXR, CAR, PXR and LXRa was analyzed by Western blot. It was shown that estradiol (10 and 100 μM) increased the expression of OATP1B1, acting through CAR. Testosterone (1, 10 and 100 μM) increased the expression of OATP1B1, acting through FXR, PXR and LXRa. Progesterone (10 and 100 μM) decreased the expression of OATP1B1 (10 and 100 μM) and adopted orphan receptors are not involved in this process. The obtained results have important practical significance and determine ways for targeted regulation of the transporter, in particular in cancer.

Effects of short-chain per- and polyfluoroalkyl substances (PFAS) on toxicologically relevant gene expression profiles in a liver-on-a-chip model

Short-chain per- and polyfluoroalkyl substances (PFAS) are highly stable and widely used environmental contaminants that pose potential health risks to humans. Aggregating reliable mechanistic information for safety assessments necessitates physiologically relevant high-throughput screening approaches. Here, we demonstrated the utility of a liver-on-a-chip model to investigate the effects of five short-chain PFAS at low (1 nM) and high (1 μM) concentrations on toxicologically-relevant gene expression profiles using the QuantiGene® Plex Assay. We found that the short-chain PFAS tested in this study modulated the expression of ABCG2, a gene encoding for the breast cancer resistance protein (BCRP), with marked and significant upregulation (up to 4-fold) observed for all but one of the short-chain PFAS tested. PFBS and HFPO-DA repressed SLCO1B3 expression, a gene that encodes for an essential liver-specific organic anion transporter. High concentrations of PFBS, PFHxA, and PFHxS upregulated the expression of genes encCYP1A1,CYP2B6 and CYP2C19 with the same treatments resulting in the repression of the expression of the gene encoding CYP1A2. This dysregulation could have consequences for the clearance of endogenous compounds and xenobiotics. However, we acknowledge that increased expression of genes encoding for transporters and biotransformation enzymes may or may not indicate changes to their protein expression or activity. Overall, our study provides important insights into the effects of short-chain PFAS on liver function and their potential implications for human health. The use of the liver-on-a-chip model in combination with the QuantiGene® Plex Assay may be a valuable tool for future high-throughput screening and gene expression profiling in toxicology studies.

Pharmacogenomics of response to statin treatment and susceptibility to statin-induced adverse drug reactions in Asians: a scoping review

Background

Statins are the most widely used lipid-lowering agents for patients with hyperlipidemia. However, interindividual variations in efficacy and risk of adverse drug reactions to statin treatment have been widely reported. Ethnicity is well known to be one of the contributing factors to this variation, particularly among Asians.

Objectives

To identify genetic variants associated with statin treatment responses among Asian populations with a focus on four commonly prescribed statins: atorvastatin, rosuvastatin, simvastatin, and pravastatin.

Methods

A literature search was conducted in Medline and Embase databases. Studies published from 2008 to 2021 were included. The title and abstract of each article were screened by two reviewers and verified by another two reviewers. Data charted include information on authors, year of study, study population, statin studied, gene studied, study findings, and data of significant statistical value.

Results

A total of 35 articles were included from the 1,939 original studies related to treatment efficacy and 5 articles out of the 284 original studies related to adverse effects. Genetic variants in transmembrane transporters, cytochrome P450 isoenzymes, and apolipoproteins are the most extensively studied among Asian populations, with a main focus on ethnic Chinese. However, Asia consists of genetically different populations, and the results of this review indicated that there is a paucity of studies on other ethnic groups within Asia.

Conclusions

Considering the ethnicity of patients could provide a potential value to personalized medicine in statin therapy.

The Role of Solute Carrier Transporters in Efficient Anticancer Drug Delivery and Therapy

Transporter-mediated drug resistance is a major obstacle in anticancer drug delivery and a key reason for cancer drug therapy failure. Membrane solute carrier (SLC) transporters play a crucial role in the cellular uptake of drugs. The expression and function of the SLC transporters can be down-regulated in cancer cells, which limits the uptake of drugs into the tumor cells, resulting in the inefficiency of the drug therapy. In this review, we summarize the current understanding of low-SLC-transporter-expression-mediated drug resistance in different types of cancers. Recent advances in SLC-transporter-targeting strategies include the development of transporter-utilizing prodrugs and nanocarriers and the modulation of SLC transporter expression in cancer cells. These strategies will play an important role in the future development of anticancer drug therapies by enabling the efficient delivery of drugs into cancer cells.

Drug metabolism and drug transport of the 100 most prescribed oral drugs

Safe and effective use of drugs requires an understanding of metabolism and transport. We identified the 100 most prescribed drugs in six countries and conducted a literature search on in vitro data to assess contribution of Phase I and II enzymes and drug transporters to metabolism and transport. Eighty-nine of the 100 drugs undergo drug metabolism or are known substrates for drug transporters. Phase I enzymes are involved in metabolism of 67 drugs, while Phase II enzymes mediate metabolism of 18 drugs. CYP3A4/5 is the most important Phase I enzyme involved in metabolism of 43 drugs followed by CYP2D6 (23 drugs), CYP2C9 (23 drugs), CYP2C19 (22 drugs), CYP1A2 (14 drugs) and CYP2C8 (11 drugs). More than half of the drugs (54 drugs) are known substrates for drug transporters. P-glycoprotein (P-gp) is known to be involved in transport of 30 drugs, while breast cancer resistance protein (BCRP) facilitates transport of 11 drugs. A considerable proportion of drugs are subject to a combination of Phase I metabolism, Phase II metabolism and/or drug transport. We conclude that the majority of the most frequently prescribed drugs depend on drug metabolism or drug transport. Thus, understanding variability of drug metabolism and transport remains a priority.

Isotretinoin and its Metabolites Alter mRNA of Multiple Enzyme and Transporter Genes In Vitro, but Downregulation of Organic Anion Transporting Polypeptide Does Not Translate to the Clinic

Isotretinoin [13-cis-retinoic acid (13cisRA)] is widely used for the treatment of neuroblastoma and acne. It acts via regulating gene transcription through binding to retinoic acid receptors. Yet, the potential for isotretinoin to cause transcriptionally mediated drug-drug interactions (DDIs) has not been fully explored. We hypothesized that isotretinoin and its active metabolites all-trans-retinoic acid (atRA) and 4-oxo-13cisRA would alter the transcription of enzymes and transporters in the human liver via binding to nuclear receptors. The goal of this study was to define the DDI potential of isotretinoin and its metabolites resulting from transcriptional regulation of cytochrome P450 and transporter mRNAs. In human hepatocytes (n = 3), 13cisRA, atRA, and 4-oxo-13cisRA decreased OATP1B1, CYP1A2, CYP2C9, and CYP2D6 mRNA and increased CYP2B6 and CYP3A4 mRNA in a concentration-dependent manner. The EC50 values for OATP1B1 mRNA downregulation ranged from 2 to 110 nM, with maximum effect (Emax ) ranging from 0.17- to 0.54-fold. Based on the EC50 and Emax values and the known circulating concentrations of 13cisRA and its metabolites after isotretinoin dosing, a 55% decrease in OATP1B1 activity was predicted in vivo. In vivo DDI potential was evaluated clinically in participants dosed with isotretinoin for up to 32 weeks using coproporphyrin-I (CP-I) as an OATP1B1 biomarker. CP-I steady-state serum concentrations were unaltered following 2, 8, or 16 weeks of isotretinoin treatment. These data show that isotretinoin and its metabolites alter transcription of multiple enzymes and transporters in vitro, but translation of these changes to in vivo drug-drug interactions requires clinical evaluation for each enzyme. SIGNIFICANCE STATEMENT: Isotretinoin and its metabolites alter the mRNA expression of multiple cytochrome P450s (CYPs) and transporters in human hepatocytes, suggesting that isotretinoin may cause clinically significant drug-drug interactions (DDIs). Despite the observed changes in organic anion transporting polypeptide 1B1 (OATP1B1) mRNA in human hepatocytes, no clinical DDI was observed when measuring a biomarker, coproporphyrin-I. Further work is needed to determine whether these findings can be extrapolated to a lack of a DDI with CYP1A2, CYP2B6, and CYP2C9 substrates.

Regulation of Drug Transport Proteins-From Mechanisms to Clinical Impact: A White Paper on Behalf of the International Transporter Consortium

Membrane transport proteins are involved in the absorption, disposition, efficacy, and/or toxicity of many drugs. Numerous mechanisms (e.g., nuclear receptors, epigenetic gene regulation, microRNAs, alternative splicing, post‐translational modifications, and trafficking) regulate transport protein levels, localization, and function. Various factors associated with disease, medications, and dietary constituents, for example, may alter the regulation and activity of transport proteins in the intestine, liver, kidneys, brain, lungs, placenta, and other important sites, such as tumor tissue. This white paper reviews key mechanisms and regulatory factors that alter the function of clinically relevant transport proteins involved in drug disposition. Current considerations with in vitro and in vivo models that are used to investigate transporter regulation are discussed, including strengths, limitations, and the inherent challenges in predicting the impact of changes due to regulation of one transporter on compensatory pathways and overall drug disposition. In addition, translation and scaling of in vitro observations to in vivo outcomes are considered. The importance of incorporating altered transporter regulation in modeling and simulation approaches to predict the clinical impact on drug disposition is also discussed. Regulation of transporters is highly complex and, therefore, identification of knowledge gaps will aid in directing future research to expand our understanding of clinically relevant molecular mechanisms of transporter regulation. This information is critical to the development of tools and approaches to improve therapeutic outcomes by predicting more accurately the impact of regulation‐mediated changes in transporter function on drug disposition and response.

A systems-level analysis of bile acids effects on rat colon epithelial cells

Bile acid diarrhea is a chronic condition caused by increased delivery of bile acids to the colon. The underlying mechanisms remain to be elucidated. To investigate genes involved in bile acid diarrhea, systems-level analyses were used on a rat bile acid diarrhea model. Twelve male Wistar Munich rats, housed in metabolic cages, were fed either control or bile acid-mixed (1% wt/wt) diets for 10 days. Food intake, water intake, urine volume, body weight, and fecal output were monitored daily. After euthanasia, colonic epithelial cells were isolated using calcium chelation and processed for systems-level analyses, that is, RNA-sequencing transcriptomics and mass spectrometry proteomics. Bile acid-fed rats suffered diarrhea, indicated by increased drinking, feces weight, and fecal water content compared with control rats. Urine output was unchanged. With bile acid feeding, RNA-sequencing revealed 204 increased and 401 decreased mRNAs; mass spectrometry revealed 183 increased and 111 decreased proteins. Among the altered genes were genes associated with electrolyte and water transport (including Slc12a7, Clca4, and Aqp3) and genes associated with bile acid transport (Slc2b1, Abcg2, Slc51a, Slc51b, and Fabps). Correlation analysis showed a significant positive correlation (Pearson's r = 0.28) between changes in mRNA expression and changes in protein expression. However, caution must be exercised in making a direct correlation between experimentally determined transcriptomes and proteomes. Genes associated with bile acid transport responded to bile acid feeding, suggesting that colonic bile acid transport also occur by regulated protein facilitated mechanisms in addition to passive diffusion. In summary, the study provides annotated rat colonic epithelial cell transcriptome and proteome with response to bile acid feeding.NEW & NOTEWORTHY Feeding rats with a bile acid caused changes in fecal output, underlining this bile acid diarrhea model's usefulness. Colonic epithelial expression of genes associated with facilitated transport of bile acids was altered during bile acid feeding. The study raises the possibility of regulated colonic transepithelial transport of bile acids in response to luminal bile acids. In addition, this study provides annotated rat colonic epithelial cell transcriptome and proteome with response to bile acid feeding.

Dill Shows Potential for Herb-Drug Interactions via Up-Regulation of CYP1A2, CYP2C19, SULT1A1, NAT2 and ABCB1 in Caco-2 Cells

<b>Background and Objective:</b> Dill<i> </i>(<i>Anethum graveolens</i> L.) has the potential to develop as a new alternative medicine due to its pharmacological activities. However, studies into its safety regarding herb-drug interactions have been neglected. This study investigated the risk of dill-induced herb-drug interactions (HDI) by examining its effect on the expression of phase I and II drug-metabolizing enzyme and transporter genes in Caco-2 cells. <b>Materials and Methods:</b> Caco-2 cells (5×10<sup>5</sup> cells/well) were treated with 10 μM ketoconazole, 20 μM rifampicin or dill extract (60-240 μg mL<sup>1</sup>) for 72 hrs. Cell viability was assessed using the resazurin assay and reactive oxygen species (ROS) content was determined with 2 ,7 -dichlorofluorescein diacetate. Aspartate (AST) and alanine aminotransferase (ALT) levels were measured using L-aspartate and L-alanine with α-ketoglutarate as substrate. Expression of phase I (<i>CYP1A2</i>, <i>CYP2C19</i>, <i>CYP2D6</i>, <i>CYP2E1 </i>and <i>CYP3A4</i>) and II (<i>UGT1A6</i>,<i> SULT1A1</i>,<i> NAT1</i>,<i> NAT2 </i>and<i> GSTA1/2</i>) metabolizing genes and transporters (<i>ABCB1</i>,<i> ABCC2</i>,<i> ABCG2 </i>and <i>SLCO1B1</i>) were determined by RT/qPCR. <b>Results:</b> All tested concentrations of dill did not affect cell viability or AST and ALT levels. The highest concentration of dill extract (240 μg mL<sup>1</sup>) significantly lowered the ROS level. Expression of <i>CYP1A2</i>, <i>CYP2C19</i>, <i>SULT1A1</i>, <i>NAT2 </i>and <i>ABCB1 </i>mRNA was significantly up-regulated by dill extract. <b>Conclusion:</b> Dill extract did not directly damage Caco-2 cells but prolonged use of dill may increase the risk of HDI via the up-regulation of the drug-metabolizing genes <i>CYP1A2</i>, <i>CYP2C19</i>, <i>SULT1A1</i>, <i>NAT2 </i>and the transporter <i>ABCB1</i>.

Acute and Chronic Effects of Rifampin on Letermovir Suggest Transporter Inhibition and Induction Contribute to Letermovir Pharmacokinetics

Rifampin has acute inhibitory and chronic inductive effects that can cause complex drug-drug interactions. Rifampin inhibits transporters including organic-anion-transporting polypeptide (OATP)1B and P-glycoprotein (P-gp), and induces enzymes and transporters including cytochrome P450 3A, UDP-glucuronosyltransferase (UGT)1A, and P-gp. This study aimed at separating inhibitory and inductive effects of rifampin on letermovir disposition and elimination (indicated for cytomegalovirus prophylaxis in hematopoietic stem cell transplant recipients). Letermovir is a substrate of UGT1A1/3, P-gp, and OATP1B, with its clearance primarily mediated by OATP1B. Letermovir (single-dose) administered with rifampin (single-dose) resulted in increased letermovir exposure through transporter inhibition. Chronic coadministration with rifampin (inhibition plus potential OATP1B induction) resulted in modestly decreased letermovir exposure versus letermovir alone. Letermovir administered 24 hours after last rifampin dose (potential OATP1B induction) resulted in markedly decreased letermovir exposure. These data suggest rifampin may induce transporters that clear letermovir; the modestly reduced letermovir exposure with chronic rifampin coadministration likely reflects the net effect of inhibition and induction. OATP1B endogenous biomarkers coproporphyrin (CP) I and glycochenodeoxycholic acid-sulfate (GCDCA-S) were also analyzed; their exposures increased after single-dose rifampin plus letermovir, consistent with OATP1B inhibition and prior reports of inhibition by rifampin alone. CP I and GCDCA-S exposures were substantially reduced with letermovir administered 24 hours after the last dose of rifampin versus letermovir plus chronic rifampin coadministration, This study suggests that OATP1B induction may contribute to reduced letermovir exposure after chronic rifampin administration, although given the complexity of letermovir disposition, alternative mechanisms are not fully excluded.

GPR43 regulation of mitochondrial damage to alleviate inflammatory reaction in sepsis

Sepsis is a common critical illness in ICU and always a great difficulty in clinical treatment. GPR43 (G protein-coupled receptor 43) participates in regulating appetite and gastrointestinal peptide secretion to modulate fat decomposition and formation. However, the biological contribution of GPR43 on inflammation of sepsis has not been previously investigated. We investigated the mechanisms of GPR43 gene, which plays a possible role in distinguishing sepsis and contributes to the pathogenesis of sepsis-induced inflammatory reaction. Furthermore, we performed studies with mice induced to sepsis by Cecal Ligation and Puncture (CLP), Knockout GPR43 (GPR43-/-) mice, and Wild Type (WT) mice induced with CLP. In addition, lung tissues and cell samples were analyzed by histology, Quantitative Polymerase Chain Reaction (Q-PCR), Enzyme-linked Immunosorbent (ELISA) Assay, and western blot. GPR43 agonist could significantly reduce inflammation reactions and trigger lung injury in mice with sepsis. As for GPR43-/- mice, the risks of sepsis-induced inflammatory reactions and corresponding lung injury were promoted. On the one hand, the up-regulation of GPR43 gene reduced ROS mitochondrial damage to inhibit inflammatory reactions via the inactivation of NLRP3 Inflammasome by PPARγ/ Nox1/EBP50/ p47phox signal channel. On the other hand, the down-regulation of GPR43 promoted inflammatory reactions in vitro model through the acceleration of ROS-dependently mitochondrial damage by PPARγ/ Nox1/EBP50/ p47phox/ NLRP3 signal channel. These findings indicate that the inhibition of GPR43 as a possible important factor of sepsis may shed lights on the mechanism of sepsis-induced inflammation reaction.

Classification of drugs for evaluating drug interaction in drug development and clinical management

During new drug development, clinical drug interaction studies are carried out in accordance with the mechanism of potential drug interactions evaluated by in vitro studies. The obtained information should be provided efficiently to medical experts through package inserts and various information materials after the drug's launch. A recently updated Japanese guideline presents general procedures that are considered scientifically valid at the present moment. In this review, we aim to highlight the viewpoints of the Japanese guideline and enumerate drugs that were involved or are anticipated to be involved in evident pharmacokinetic drug interactions and classify them by their clearance pathway and potential intensity based on systematic reviews of the literature. The classification would be informative for designing clinical studies during the development stage, and the appropriate management of drug interactions in clinical practice.

Hesperidin alleviates cholestasis via activation of the farnesoid X receptor in vitro and in vivo

Cholestasis causes the intrahepatic accumulation of bile acids leading to hepatobiliary injury. Recently obeticholic acid, a farnesoid X receptor (FXR) agonist, was FDA-approved to treat cholestatic liver diseases, providing a new therapeutic strategy for cholestasis. The purpose of the current study was to characterize a novel FXR agonist and verify the anti-cholestatic effect of hesperidin (HP) in vivo and in vitro. Based on a molecular docking study that predicted that HP would bind to FXR, the hepatoprotective effect of HP against cholestasis and hepatotoxicity was evaluated in mice and in normal and FXR-suppressed HepaRG cells. HP prevented bile acid toxicity in HepaRG cells, and this effect was blocked by FXR silencing. HP appears to activate FXR to prevent cholestatic liver injury. Dynamic change analysis of bile acids revealed that HP promoted bile acid excretion into feces and reduced hepatic accumulation via the regulation of the FXR-target genes bile salt export pump, multi-drug resistance-associated protein 2, and Na+-taurocholate cotransporting polypeptide. Furthermore, HP down-regulated enzymes involved in bile acid synthesis including cholesterol 7α-hydroxylase and sterol 27-hydroxylase. HP produced a protective effect against cholestasis via FXR activation, and may be an effective approach for the prevention and treatment of cholestatic liver diseases.

Culture density contributes to hepatic functions of fresh human hepatocytes isolated from chimeric mice with humanized livers: Novel, long-term, functional two-dimensional in vitro tool for developing new drugs

Chimeric mice with humanized livers are considered a useful animal model for predicting human (h-) drug metabolism and toxicity. In this study, the characteristics of fresh h-hepatocytes (cFHHs, PXB-cells^®) isolated from chimeric mice (PXB-mice^®) were evaluated in vitro to confirm their utility for drug development. cFHHs cultured at high density (2.13 × 10⁵ cells/cm²) displayed stable production of h-albumin and cytochrome P450 (CYP) 3A activities for at least 21 days. The mRNA expression levels of 10 of 13 CYP, UDP-glucuronosyltransferase (UGT), and transporters were maintained at >10% of the levels of freshly isolated cFHHs after 21 days. From 1 week, many bile canaliculi were observed between cFHHs, and the accumulation of the multidrug resistance-associated protein and bile salt export pump substrates in these bile canaliculi was clearly inhibited by cyclosporin A. Microarray analysis of cFHHs cultured at high density and at low density (0.53 × 10⁵ cells/cm²) revealed that high density culture maintained high expressions of some transcription factors (HNF4α, PXR, and FXR) perhaps involved in the high CYP, UGT and transporter gene expressions of cFHHs. These results strongly suggest that cFHHs could be a novel in vitro tool for drug development studies.

Absence of OATP1B (Organic Anion-Transporting Polypeptide) Induction by Rifampin in Cynomolgus Monkeys: Determination Using the Endogenous OATP1B Marker Coproporphyrin and Tissue Gene Expression

Organic anion-transporting polypeptide (OATP) 1B induction is an evolving mechanism of drug disposition and interaction. However, there are contradictory reports describing OATP1B expression in hepatocytes and liver biopsies after administration of an inducer. This study investigated the in vivo effects of the common inducer rifampin (RIF) on the activity and expression of cynomolgus monkey OATP1B1 and OATP1B3 transporters, which are structurally and functionally similar their human OATP1B counterparts. Multiple doses of oral RIF (15 mg/kg) resulted in a steady 3.9-fold increase of CYP3A biomarker, 4β-hydroxycholesterol (4βHC), in the plasma samples collected before each RIF dose during the treatment period (i.e., predose). In contrast, the predose plasma levels of OATP1B biomarkers coproporphyrin (CP) I and CPIII did not change when compared with RIF treatment. The trough concentration, area under plasma concentration-time curve (AUC), and half-life of RIF decreased markedly during RIF treatment, suggesting that RIF induced its own clearance. Consequently, RIF treatment increased CPI and CPIII AUCs substantially after a single administration and, to a lesser extent, after multiple administrations compared with preadministration AUCs. In addition, OATP1B1 and OATP1B3 mRNA expressions were not modulated by RIF treatment (0.85-1.3-fold), whereas CYP3A8 expression was increased 3.7-5.0-fold, which correlated well with the predose levels of CP and 4βHC. Rifampin treatment showed 2.0-3.3-fold increases in P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 2 (MRP2) expression in the small intestine. Collectively, these findings indicate that monkey OATP1B and OATP1B3 are not induced by RIF, and further investigation of OATP1B induction by RIF and other nuclear receptor activators in humans is warranted. SIGNIFICANCE STATEMENT: In this study, combined endogenous biomarker and gene expression data suggested that RIF did not induce OATP1B in cynomolgus monkeys. For the first time, the study determines transporter gene expression in the nonhuman primate liver, gut, and kidney tissues after administration of RIF for 7 days, leading to a better understanding of the induction of OATP1B and other major drug transporters. Finally, it provides evidence to strengthen the claim that coproporphyrin is a suitable endogenous probe of OATP1B activity.

Berberine Promotes OATP1B1 Expression and Rosuvastatin Uptake by Inducing Nuclear Translocation of FXR and LXRα

Berberine, a quinoline alkaloid, can be used in combination with statins to enhance hypolipidemic effects and reduce the dose and side effects of statins. The hypolipidemic effects of statins in the liver are mainly regulated by organic anion transporting polypeptides (OATPs), and the expression of OATPs is regulated by nuclear receptors. Berberine has been reported to affect nuclear receptors. However, whether berberine affects the uptake of statins by regulating nuclear receptor-mediated expression of OATPs remains to be determined. The aim of this study was to investigate the effects of berberine on the expression of OATP1B1 in HepG2 and explore the underlying mechanism. In HepG2 cells, 10-50 μM berberine significantly increased the uptake of rosuvastatin by inducing the expression of OATP1B1 mRNA and protein. Dual-Luciferase reporter assay showed that luciferase activity of hFXR and hLXRα activated OATP1B1 promoter was increased by 2.5-50 μM berberine in a concentration-dependent manner, with half-maximal effective concentration (EC₅₀) of 12.19 ± 0.86 and 32.15 ± 2.32 μM, respectively. In addition, after silencing FXR or LXRα by small interfering RNA (siRNA), berberine-induced OATP1B1 expression was significantly attenuated. Western blot analysis of FXR and LXRα protein levels in the cytoplasm and nucleus of HepG2 cells after treatment with berberine showed that berberine induced nuclear translocation and activation of FXR and LXRα. In conclusion, berberine-induced nuclear translocation of FXR and LXRα could activate OATP1B1 promoter, resulting in enhanced expression of OATP1B1 and increased uptake of rosuvastatin.

microRNA-206 modulates the hepatic expression of the organic anion-transporting polypeptide 1B1

BACKGROUND & AIMS

The organic anion-transporting polypeptide 1B1 (OATP1B1) is an anion exchanger expressed at the hepatocyte sinusoidal membrane, which mediates the uptake of several endogenous metabolites and drugs. OATP1B1 expression level and activity are major sources of inter-patient variability of pharmacokinetics and pharmacodynamics of several drugs. Besides the genotype, factors that contribute to the inter-individual variability in OATP1B1 expression level are practically unknown. The aim of this work was to uncover novel epigenetic mechanisms of OATP1B1 regulation.

METHODS

A functional screening strategy to assess the effect of microRNAs on the uptake of estrone-3-sulphate, an OATP1B1 substrate, into human hepatocellular carcinoma (Huh-7) cells was used. microRNA-206 (miR-206) expression in human liver tissues was measured by real-time RT-PCR. OATP1B1 expression in Huh-7 and in human liver tissues was assessed by real-time RT-PCR, Western blotting and immunostaining. The mRNA-miRNA interaction was assessed by reporter assay.

RESULTS

miR-206 mimic repressed mRNA and protein expression of OATP1B1 in Huh-7 cells. The intracellular accumulation of estrone-3-sulphate was reduced by 30% in cells overexpressing miR-206. The repressive effect of miR-206 on the activity of the firefly luciferase gene 2 under the control of the OATP1B1 3' untranslated region was lost upon deletion of the predicted miR-206 binding site. Hepatic miR-206 level negatively correlated with OATP1B1 mRNA and protein levels extracted from normal human liver tissues.

CONCLUSIONS

miR-206 exerts a suppressive effect on OATP1B1 expression by an epigenetic mechanism. Individuals with high hepatic levels of miR-206 appear to display lower level of OATP1B1.

OATP1B3-1B7, a novel organic anion transporting polypeptide, is modulated by FXR ligands and transports bile acids

Organic anion transporting polypeptide (OATP) 1B3-1B7 (LST-3TM12) is a member of the OATP1B [solute carrier organic anion transporter (SLCO) 1B] family. This transporter is not only functional but also expressed in the membrane of the smooth endoplasmic reticulum of hepatocytes and enterocytes. OATP1B3-1B7 is a splice variant of SLCO1B3 in which the initial part is encoded by SLCO1B3, whereas the rest of the mRNA originates from the gene locus of SLCO1B7. In this study, we not only showed that SLCO1B3 and the mRNA encoding for OATP1B3-1B7 share the 5' untranslated region but also that silencing of an initial SLCO1B3 exon lowered the amount of SLCO1B3 and of SLCO1B7 mRNA in Huh-7 cells. To validate the assumption that both transcripts are regulated by the same promoter we tested the influence of the bile acid sensor farnesoid X receptor (FXR) on their transcription. Treatment of Huh-7 and HepaRG cells with activators of this known regulator of OATP1B3 not only increased SLCO1B3 but also OATP1B3-1B7 mRNA transcription. Applying a heterologous expression system, we showed that several bile acids interact with OATP1B3-1B7 and that taurocholic acid and lithocholic acid are OATP1B3-1B7 substrates. As OATP1B3-1B7 is located in the smooth endoplasmic reticulum, it may grant access to metabolizing enzymes. In accordance are our findings showing that the OATP1B3-1B7 inhibitor bromsulphthalein significantly reduced uptake of bile acids into human liver microsomes. Taken together, we report that OATP1B3-1B7 transcription can be modulated with FXR agonists and antagonists and that OATP1B3-1B7 transports bile acids.NEW & NOTEWORTHY Our study on the transcriptional regulation of the novel organic anion transporting polypeptide (OATP) 1B3-1B7 concludes that the promoter of solute carrier organic anion transporter (SLCO) 1B3 governs SLCO1B3-1B7 transcription. Moreover, the transcription of OATP1B3-1B7 can be modulated by farnesoid X receptor (FXR) agonists and antagonists. FXR is a major regulator in bile acid homeostasis that links OATP1B3-1B7 to this physiological function. Findings in transport studies with OATP1B3-1B7 suggest that this transporter interacts with the herein tested bile acids.

Organic Anion-Transporting Polypeptide Genes Are Not Induced by the Pregnane X Receptor Activator Rifampin: Studies in Hepatocytes In Vitro and in Monkeys In Vivo

Induction potentials of the pregnane X receptor (PXR) activator rifampin (RIF) on transporter genes [e.g., organic anion-transporting polypeptides (OATPs)] are still in its infancy or remain controversial in the field. The present investigations characterized changes in transporter gene expression by RIF in sandwich-cultured hepatocytes from multiple donors of human and cynomolgus monkey using real-time quantitative reverse transcription polymerase chain reaction method. Three-day treatment of RIF significantly induced CYP3A4 (∼60-fold induction), but not CYP1A2 and CYP2D6 genes. SLC51B was the most highly induced uptake transporter gene (>10-fold) in both human and monkey hepatocytes. A greater induction of CYP2C9 was observed in monkey hepatocytes than that in humans. ATP-binding cassette (ABC)B1 and ABCC2 were induced slightly above 2-fold in human and monkey hepatocytes and appeared to be dose-dependent. The induction of OATP and other transporter genes was generally less than 2-fold and considered not clinically relevant. SLCO2B1 was not detectable in monkey hepatocytes. To investigate in vivo OATP induction, RIF (18 mg/kg per day) was orally dosed to cynomolgus monkeys for 7 days. Pitavastatin and antipyrine were intravenously dosed before and after RIF treatment as exogenous probes of OATP and CYP activities, respectively. Plasma coproporphyrin-I (CP-I) and coproporphyrin-III (CP-III) were measured as OATP endogenous biomarkers. Although a significant increase of antipyrine clearance (CL) was observed after RIF treatment, the plasma exposures of pitavastatin, CP-I, and CP-III remained unchanged, suggesting that OATP function was not significantly altered. The results suggested that OATP transporters were not significantly induced by PXR ligand RIF. The data are consistent with current regulatory guidances that the in vitro characterization of transporter induction during drug development is not required. SIGNIFICANCE STATEMENT: Organic anion-transporting polypeptide (OATP) genes were not induced by rifampin in sandwich-cultured human and monkey hepatocytes OATP functions measured by OATP probe pitavastatin and endogenous marker coproporphyrins were not altered in monkeys in vivo by 7-day rifampin treatment. The data suggested that OATP transporters are unlikely induced by the pregnane X receptor ligand rifampin, which are consistent with current regulatory guidances that the in vitro characterization of OATP1B induction during drug development is not required.

Expanded Physiologically-Based Pharmacokinetic Model of Rifampicin for Predicting Interactions With Drugs and an Endogenous Biomarker via Complex Mechanisms Including Organic Anion Transporting Polypeptide 1B Induction

As rifampicin can cause the induction and inhibition of multiple metabolizing enzymes and transporters, it has been challenging to accurately predict the complex drug–drug interactions (DDIs). We previously constructed a physiologically‐based pharmacokinetic (PBPK) model of rifampicin accounting for the components for the induction of cytochrome P450 (CYP) 3A/CYP2C9 and the inhibition of organic anion transporting polypeptide 1B (OATP1B). This study aimed to expand and verify the PBPK model for rifampicin by incorporating additional components for the induction of OATP1B and CYP2C8 and the inhibition of multidrug resistance protein 2. The established PBPK model was capable of accurately predicting complex rifampicin‐induced alterations in the profiles of glibenclamide, repaglinide, and coproporphyrin I (an endogenous biomarker of OATP1B activities) with various dosing regimens. Our comprehensive rifampicin PBPK model may enable quantitative prediction of DDIs across diverse potential victim drugs and endogenous biomarkers handled by multiple metabolizing enzymes and transporters.

The nuclear receptors PXR and LXR are regulators of the scaffold protein PDZK1

PDZK1 (NHERF3) interacts with membrane proteins whereby modulating their spatial arrangement, membrane stability, and function. One of the membrane proteins shown to be stabilized by interaction with PDZK1 is the HDL-receptor SR-BI (SCARB1). Testing the influence of TO 901317, a known activator of liver X receptor alpha (LXRα, NR1H3) which is a central regulator of the lipid homeostasis, Grefhorst et al. reported in 2012 that administration of TO 901317 did not affect PDZK1 expression and reduced the amount of SR-BI protein in mouse liver. Considering that TO 901317 also activates the xenosensor pregnane X receptor (PXR, NR1I2), it was aim of this study to further investigate the influence of LXRα and PXR activation on transcription of PDZK1. First, we tested the transactivation of PDZK1 by LXRα or PXR in cell-based reporter gene assays comparing the effect of prototypical ligands to that of TO 901317. Ligand mediated activation of LXRα increased, while that of PXR lowered luciferase activity. Further, we located the most likely binding site for LXRα and PXR on the PDZK1 promoter between -85 bp and -54 bp. The transcriptional regulation by LXRα was further supported showing enhanced mRNA expression of PDZK1 in HepG2 cells treated with the selective LXRα-agonist GW3965, while treatment with TO 901317 reduced the protein amount of PDZK1. Taken together, we provide evidence that both LXRα and PXR are transcriptional regulators of PDZK1 supporting the previous notion that the scaffold protein is part of cholesterol homeostasis and drug metabolism.

Gambogic acid prevents angiotensin II‑induced abdominal aortic aneurysm through inflammatory and oxidative stress dependent targeting the PI3K/Akt/mTOR and NF‑κB signaling pathways

Gamboge is the dry resin secreted by Garcinia hanbaryi Hook.f, with the function of promoting blood circulation and anti‑cancer effects, detoxification, hemostasis and killing insects. It is also used for the treatment of cancer, brain edema and other diseases. Gambogic acid is the main effective constituent of Gamboge. The present study tested the hypothesis that the effect of Gambogic acid prevents angiotensin II‑induced abdominal aortic aneurysm (AAA), and explored its underlying mechanism. It was demonstrated that gambogic acid significantly inhibited AAA incidence rate, and reduced edge leading aortic diameter and aortic wall thickness in AAA mice. Gambogic acid treatment markedly decreased the levels of proinflammatory cytokines and oxidative stress factors, and transforming growth factor‑β (TGF‑β) and matrix metalloproteinase (MMP)‑2 and MMP‑9 protein expression in AAA mice. Furthermore, Gambogic acid decreased expression of phosphatidylinositol 3‑kinase (PI3K), and phosphorylation of protein kinase B (Akt), mechanistic target of rapamycin (mTOR) and p70‑S6 kinase 1. It also suppressed nuclear factor (NF)‑κB protein expression in AAA mice. The findings of the present study indicated that Gambogic acid prevents angiotensin II‑induced AAA through inflammatory and oxidative stress‑dependent targeting of the PI3K/Akt/mTOR and NF‑κB signaling pathways.

Disease-Associated Changes in Drug Transporters May Impact the Pharmacokinetics and/or Toxicity of Drugs: A White Paper From the International Transporter Consortium

Drug transporters are critically important for the absorption, distribution, metabolism, and excretion (ADME) of many drugs and endogenous compounds. Therefore, disruption of these pathways by inhibition, induction, genetic polymorphisms, or disease can have profound effects on overall physiology, drug pharmacokinetics, drug efficacy, and toxicity. This white paper provides a review of changes in transporter function associated with acute and chronic disease states, describes regulatory pathways affecting transporter expression, and identifies opportunities to advance the field.

Fat-specific protein 27 is a novel target gene of liver X receptor α

Fat-specific protein 27 (FSP27) is highly expressed in the fatty liver of genetically obese ob/ob mice and promotes hepatic triglyceride (TG) accumulation. The nuclear hormone receptor liver X receptor α (LXRα) also plays a critical role in the control of TG levels in the liver. The present study demonstrated transcriptional regulation of Fsp27a and Fsp27b genes by LXRα. Treatment with the LXR ligand T0901317 markedly increased Fsp27a and Fsp27b mRNAs in wild-type C57BL/6J and ob/ob mouse livers. A reporter assay indicated that two LXR-responsive elements (LXREs) are necessary for LXRα-dependent induction of Fsp27a and Fsp27b promoter activities. Furthermore, the LXRα/retinoid X receptor α complex is capable of directly binding to the two LXREs both in vitro and in vivo. These results suggest that LXRα positively regulates Fsp27a and Fsp27b expression through two functional LXREs. Fsp27a/b are novel LXR target genes in the ob/ob fatty liver.

Update on FXR Biology: Promising Therapeutic Target?

Farnesoid X receptor (FXR), a metabolic nuclear receptor, plays critical roles in the maintenance of systemic energy homeostasis and the integrity of many organs, including liver and intestine. It regulates bile acid, lipid, and glucose metabolism, and contributes to inter-organ communication, in particular the enterohepatic signaling pathway, through bile acids and fibroblast growth factor-15/19 (FGF-15/19). The metabolic effects of FXR are also involved in gut microbiota. In addition, FXR has various functions in the kidney, adipose tissue, pancreas, cardiovascular system, and tumorigenesis. Consequently, the deregulation of FXR may lead to abnormalities of specific organs and metabolic dysfunction, allowing the protein as an attractive therapeutic target for the management of liver and/or metabolic diseases. Indeed, many FXR agonists have been being developed and are under pre-clinical and clinical investigations. Although obeticholic acid (OCA) is one of the promising candidates, significant safety issues have remained. The effects of FXR modulation might be multifaceted according to tissue specificity, disease type, and/or energy status, suggesting the careful use of FXR agonists. This review summarizes the current knowledge of systemic FXR biology in various organs and the gut–liver axis, particularly regarding the recent advancement in these fields, and also provides pharmacological aspects of FXR modulation for rational therapeutic strategies and novel drug development.

An update on efflux and uptake transporters as determinants of statin response

INTRODUCTION

Statins are used in the treatment of dyslipidemia promoting primary and secondary prevention against detrimental cardiovascular events. ATP-binding cassette (ABC) and solute carrier (SLC) membrane transporters transport statins across the cell membrane. Differences in drug transporter tissue expression and activity contribute to variability in statin pharmacokinetics (PK) and response. Areas covered: The purpose of this review is to discuss factors impacting transporter expression and the effect this has on statin efficacy and safety. Previous studies have demonstrated that genetic polymorphisms, drug-drug interactions (DDI), nuclear receptors, and microRNAs affect statin PK and pharmacodynamics. Expert opinion: Genetic variants of ABCG2 and SLCO1B1 transporters affect statin PK and, as a result, the intended lipid-lowering response. However, the effect size is small, limiting its applicability in clinical practice. Furthermore, genetic variants do not totally explain the observed intervariability in statin response. Thus, it is likely that transcriptional and post-transcriptional regulation of drug transporters are also highly involved. Further studies are required to understand the contribution of each of these new factors in statin disposition and toxicity.

Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.

PDZ domain containing protein 1 (PDZK1), a modulator of membrane proteins, is regulated by the nuclear receptor THRβ

Genome wide association studies revealed single nucleotide polymorphisms (SNP) located within the promoter of PDZ domain containing protein 1 (PDZK1) to be associated with serum uric acid levels. Since modulation of transporters and particularly of membrane proteins involved in uric acid handling by PDZK1 has previously been reported, the aim of this study was to analyze the impact of the polymorphisms rs1967017, rs1471633, and rs12129861 on promoter activity and thereby transcription of PDZK1. Cell-based reporter gene assays showed transactivation of the PDZK1-promoter by triiodothyronine mediated by thyroid hormone receptors (THR) α and β. In silico analysis verified localization of the polymorphism rs1967017 within the most likely THR binding site whose deletion reduced THR-mediated transactivation. Furthermore, our study shows regulation of PDZK1 by thyroid hormones, thereby providing a mechanistic basis for the previously reported associations between thyroid hormone status and uric acid homeostasis.

Effects of Polymorphisms in NR1H4, NR1I2, SLCO1B1, and ABCG2 on the Pharmacokinetics of Rosuvastatin in Healthy Chinese Volunteers

The nuclear receptors (NR)-farnesoid X receptor (FXR, NR1H4) and pregnane X receptor (PXR, NR1I2)-have important effects on the expression of genes related to the pharmacokinetics (PKs) of rosuvastatin. This study was designed to investigate whether the genetic variants in drug disposition genes (SLCO1B1 and ABCG2) combined with their upstream regulators (NR1H4 and NR1I2) would affect the PKs of rosuvastatin in a Chinese population. Sixty-one healthy male volunteers were enrolled and the plasma concentrations of rosuvastatin were measured using the liquid chromatographic-tandem mass spectrometry/MS method. All subjects were analyzed and grouped according to the genotypes of NR1H4, NR1I2, SLCO1B1, and ABCG2. The exposure of rosuvastatin was higher in subjects carrying the SLCO1B1 521C or ABCG2 421A allele compared with noncarriers. No association was observed of single-nucleotide polymorphisms in NR1H4 or NR1I2 genes with the PKs of rosuvastatin. After adjusting for the 421C>A and 521T>C variants, the Cmax in subjects with NR1I2 63396TT wild type were about 2-fold of those of NR1I2 mutant type (63396CC and CT) (10.7 vs. 20.4 ng/mL, P = 0.023), whereas no significant differences were observed for other parameters. Polymorphisms investigated in the genes of NR1H4 and NR1I2 seemed to play no significant role in the disposition of rosuvastatin.

Doxorubicin enhances oxysterol levels resulting in a LXR-mediated upregulation of cardiac cholesterol transporters

The anthracycline-mediated cardiotoxicity is still not completely understood. To examine the impact of cholesterol metabolism and transport in this context, cholesterol and oxysterol levels as well as the expression of the cholesterol transporters ABCA1 and ABCG1 were analyzed in doxorubicin-treated HL-1 murine cardiomyocytes as well as in mouse model for acute doxorubicin-induced cardiotoxicity. Doxorubicin-treated HL-1 cells exhibited enhanced cholesterol (153±20% of control), oxysterol (24S-hydroxycholesterol: 206±29% of control) and cholesterol precursor levels (lathosterol: 122±12% of control; desmosterol: 188±10% of control) indicating enhanced cholesterol synthesis. Moreover, abca1 and abcg1 were upregulated on mRNA, protein and functional level caused by a doxorubicin-mediated activation of the nuclear receptor LXR. In addition, the oxysterols not only induced the abca1 and abcg1 in HL-1 cells but also enhanced the expression of endothelin-1 and transforming growth factor-β, which have already been identified as important factors in doxorubicin-induced cardiotoxicity. These in vitro findings were verified in a murine model for acute doxorubicin-induced cardiotoxicity, demonstrating elevated cardiac (2.1±0.2vs. 3.6±1.0ng/mg) and systemic cholesterol levels (105.0±8.4vs. 130.0±4.3mg/dl), respectively, as well as enhanced oxysterol levels such as cardiac 24S-hydroxycholesterol (2.1±0.2vs. 3.6±1.0ng/mg). In line with these findings cardiac mRNA expression of abca1 (303% of control) and abcg1 (161% of control) was induced. Taken together, our data demonstrate enhanced cholesterol and oxysterol levels by doxorubicin, resulting in a LXR-dependent upregulation of abca1 and abcg1. In this context, the cytotoxic effects of oxysterols and their impact on cardiac gene expression should be considered as an important factor in doxorubicin-induced cardiotoxicity.

The regulation of human hepatic drug transporter expression by activation of xenobiotic-sensing nuclear receptors

INTRODUCTION

If a drug is found to be an inducer of hepatic drug metabolizing enzymes via activation of nuclear receptors such as pregnane X receptor (PXR) or constitutive androstane receptor (CAR), it is likely that drug transporters regulated through these same receptors will be induced as well. This review highlights what is currently known about the molecular mechanisms that regulate transporter expression and where the research is directed. Areas covered: This review is focused on publications that describe the role of activated hepatic nuclear receptors in the subsequent regulation of drug uptake and/or efflux transporters following exposure to xenobiotics. Expert opinion: Many of the published studies on the role of nuclear receptors in the regulation of drug transporters involve non-human test animals. But due to species response differences, these associations are not always applicable to humans. For this reason, some relevant human in vitro models have been developed, such as primary or cryopreserved human hepatocytes, human liver slices, or HepG2 or HuH7 cell lines transiently or stably transfected with PXR expression and reporter constructs as well as in vivo models such as PXR-humanized mice. These human-relevant test systems will continue to be developed and applied for the testing of investigational drugs.

Role of farnesoid X receptor in cholestasis

The nuclear receptor farnesoid X receptor (FXR) plays an important role in physiological bile acid synthesis, secretion and transport. Defects of FXR regulation in these processes can cause cholestasis and subsequent pathological changes. FXR regulates the synthesis and uptake of bile acid via enzymes. It also increases bile acid solubility and elimination by promoting conjugation reactions and exports pump expression in cholestasis. The changes in bile acid transporters are involved in cholestasis, which can result from the mutations of transporter genes or acquired dysfunction of transport systems, such as inflammation-induced intrahepatic cholestasis. The modulation function of FXR in extrahepatic cholestasis is not identical to that in intrahepatic cholestasis, but the discrepancy may be reduced over time. In extrahepatic cholestasis, increasing biliary pressure can induce bile duct proliferation and bile infarcts, but the absence of FXR may ameliorate them. This review provides an update on the function of FXR in the regulation of bile acid metabolism, its role in the pathophysiological process of cholestasis and the therapeutic use of FXR agonists.

Disruption of BSEP Function in HepaRG Cells Alters Bile Acid Disposition and Is a Susceptive Factor to Drug-Induced Cholestatic Injury

In the present study, we characterized in vitro biosynthesis and disposition of bile acids (BAs) as well as hepatic transporter expression followed by ABCB11 (BSEP) gene knockout in HepaRG cells (HepaRG-KO cells). BSEP KO in HepaRG cells led to time-dependent BA accumulation, resulting in reduced biosynthesis of BAs and altered BA disposition. In HepaRG-KO cells, the expression of NTCP, OATP1B1, OATP2B1, BCRP, P-gp, and MRP2 were reduced, whereas MRP3 and OCT1 were up-regulated. As a result, BSEP KO altered the disposition of BAs and subsequently underwent adaptive regulations of BA synthesis and homeostasis to enable healthy growth of the cells. Although BSEP inhibitors caused no or slight increase of BAs in HepaRG wild type cells (HepaRG-WT cells), excessive intracellular accumulation of BAs was observed in HepaRG-KO cells exposed to bosentan and troglitazone, but not dipyridamole. LDH release in the medium was remarkably increased in HepaRG-KO cultures exposed to troglitazone (50 μM), suggesting drug-induced cellular injury. The results revealed that functional impairment of BSEP predisposes the cells to altered BA disposition and is a susceptive factor to drug-induced cholestatic injury. In total, BSEP inhibition might trigger the processes but is not a sole determinant of cholestatic cellular injury. As intracellular BA accumulation is determined by BSEP function and the subsequent adaptive gene regulation, assessment of intracellular BA accumulation in HepaRG-KO cells could be a useful approach to evaluate drug-induced liver injury (DILI) potentials of drugs that could disrupt other BA homeostasis pathways beyond BSEP inhibition.

Farnesoid x receptor in human metabolism and disease: the interplay between gene polymorphisms, clinical phenotypes and disease susceptibility

INTRODUCTION

Farnesoid x receptor (FXR) belongs to the group of nuclear receptors (NRs), which regulate the expression of various genes by binding to DNA either as a monomer or a heterodimer with retinoid x receptor.

AREAS COVERED

FXR affects several metabolic pathways through its specific target genes, regulating bile acid (BA) synthesis and homeostasis, glucose and lipid metabolism, also exhibiting a crucial role in intestinal bacterial growth and liver regeneration. Additionally, FXR is involved in the pathogenesis of different cholestatic diseases, as well as non-alcoholic fatty liver disease, inflammatory bowel disease (IBD) and primary idiopathic BA malabsorption.

EXPERT OPINION

Analyses of certain FXR polymorphisms revealed associations with clinical phenotypes and susceptibility to various human diseases. FXR single-nucleotide polymorphisms seem to be correlated with differences in glucose homeostasis, gallstone formation, intrahepatic cholestasis of pregnancy, IBD and therapeutic response to hypolipidemic therapy, among studied populations. Unfortunately, little data are still available and more studies remain to be done to determine the contribution of FXR polymorphisms in estimating risk factors and clinical outcomes for several diseases.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

Organic anion-transporting polypeptides

Organic anion-transporting polypeptides or OATPs are central transporters in the disposition of drugs and other xenobiotics. In addition, they mediate transport of a wide variety of endogenous substrates. The critical role of OATPs in drug disposition has spurred research both in academia and in the pharmaceutical industry. Translational aspects with clinical questions are the focus in academia, while the pharmaceutical industry tries to define and understand the role these transporters play in pharmacotherapy. The present overview summarizes our knowledge on the interaction of food constituents with OATPs and on the OATP transport mechanisms. Further, it gives an update on the available information on the structure-function relationship of the OATPs and, finally, covers the transcriptional and posttranscriptional regulation of OATPs.

Effect of drug transporter pharmacogenetics on cholestasis

INTRODUCTION

The liver is the central place for the metabolism of drugs and other xenobiotics. In the liver cell, oxidation and conjugation of compounds take place, and at the same time, bile formation helps in extrusion of these compounds via the biliary route. A large number of transporters are responsible for drug uptake into the liver cell and excretion into bile or efflux to the sinusoidal blood.

AREAS COVERED

Genetic variants of these transporters and their transactivators contribute to changes in drug handling and are also responsible for cholestatic syndromes of different severity. This review summarizes the current knowledge regarding the influence of these genetic changes. The review covers progressive hereditary cholestatic syndromes as well as recurrent or transient cholestatic syndromes such as drug-induced liver injury, intrahepatic cholestasis of pregnancy, and benign recurrent intrahepatic cholestasis.

EXPERT OPINION

Polymorphisms in transporter genes are frequent. For clinically relevant cholestatic syndromes, it often requires a combination of genetic variants or acquired triggers such as pregnancy or drug treatment. In combination with other pathogenetic aspects, genetic variants in drug transporters may contribute to our understanding of not only cholestatic diseases such as primary sclerosing cholangitis or primary biliary cirrhosis, but also the natural course of chronic liver disease in general.

The SLCO (former SLC21) superfamily of transporters

The members of the organic anion transporting polypeptide superfamily (OATPs) are classified within the SLCO solute carrier family. All functionally well characterized members are predicted to have 12 transmembrane domains and are sodium-independent transport systems that mediate the transport of a broad range of endo- as well as xenobiotics. Substrates are mainly amphipathic organic anions with a molecular weight of more than 300Da, but some of the known transported substrates are also neutral or even positively charged. Among the well characterized substrates are numerous drugs including statins, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, antibiotics, antihistaminics, antihypertensives and anticancer drugs. Based on their amino acid sequence identities, the different OATPs cluster into families (in general with more than 40% amino acid sequence identity) and subfamilies (more than 60% amino acid identity). With the sequencing of genomes from different species and the computerized prediction of encoded proteins more than 300 OATPs can be found in the databases, however only a fraction of them have been identified in humans, rodents, and some additional species important for pharmaceutical research like the rhesus monkey (Macaca mulatta), the dog (Canis lupus familiaris) and the pig (Sus scrofa). These OATPs form 6 families (OATP1-OATP6) and 13 subfamilies. In this review we try to summarize what is currently known about OATPs with respect to endogenous substrates, tissue distribution, transport mechanisms, regulation of expression, structure-function relationship and mutations and polymorphisms.

The inhibitory effects of the bioactive components isolated from Scutellaria baicalensis on the cellular uptake mediated by the essential solute carrier transporters

Solute carrier transporters (SLCs), in particular the organic anion transporters (OATs), OAT polypeptides (OATPs), and organic cation transporters (OCTs/OCTNs), are the important membrane proteins responsible for the cellular influx of various drugs. Baicalein (BA), baicalin (BG), and wogonin (WG) are the three major bioactive components of Scutellaria baicalensis. In this study, we evaluated the inhibitory effects of BA, BG, and WG on the cellular uptake of specific substrates mediated by the essential SLCs in human embryonic kidney-293 cells. Our data demonstrated that BA and WG significantly inhibit the OAT1-, OAT3-, and OATP1B3-mediated uptake; BG effectively reduces the influx of substrates of OAT3, OAT4, OATP1B3, and OATP2B1; WG is a potent inhibitor of OCT3. Our further kinetic analysis derived the IC50 values of these compounds with pronounced inhibitory effects on SLCs, particularly the inhibitions of WG on OAT1 and OCT3 and that of BA and WG on OAT3. Our study comprehensively evaluated the inhibitory effects of three bioactive components of Scutellaria baicalensis on the uptake of specific substrates mediated by the essential SLC transporters, which suggested that precautions will be needed when coadministrating drugs with Scutellaria baicalensis so as to prevent the unfavorable drug-drug/herb interactions in human.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Nuclear-receptor-mediated regulation of drug- and bile-acid-transporter proteins in gut and liver

Adverse drug events (ADEs) are a common cause of patient morbidity and mortality and are classically thought to result, in part, from variation in expression and activity of hepatic enzymes of drug metabolism. It is now known that alterations in the expression of genes that encode drug- and bile-acid-transporter proteins in both the gut and liver play a previously unrecognized role in determining patient drug response and eventual clinical outcome. Four nuclear receptor (NR) superfamily members, including pregnane X receptor (PXR, NR1I2), constitutive androstane receptor (NR1I3), farnesoid X receptor (NR1H4), and vitamin D receptor (NR1I1), play pivotal roles in drug- and bile-acid-activated programs of gene expression to coordinately regulate drug- and bile-acid transport activity in the intestine and liver. This review focuses on the NR-mediated gene activation of drug and bile-acid transporters in these tissues as well as the possible underlying molecular mechanisms.

Genetics is a major determinant of expression of the human hepatic uptake transporter OATP1B1, but not of OATP1B3 and OATP2B1

BACKGROUND

Organic anion transporting polypeptide (OATP) 1B1, OATP1B3, and OATP2B1 (encoded by SLCO1B1, SLCO1B3, SLCO2B1) mediate the hepatic uptake of endogenous compounds like bile acids and of drugs, for example, the lipid-lowering atorvastatin, thereby influencing hepatobiliary elimination. Here we systematically elucidated the contribution of SLCO variants on expression of the three hepatic OATPs under consideration of additional important covariates.

METHODS

Expression was quantified by RT-PCR and immunoblotting in 143 Caucasian liver samples. A total of 109 rare and common variants in the SLCO1B3-SLCO1B1 genomic region and the SLCO2B1 gene were genotyped by MALDI-TOF mass spectrometry and genome-wide SNP microarray technology. SLCO1B1 haplotypes affecting hepatic OATP1B1 expression were associated with pharmacokinetic data of the OATP1B1 substrate atorvastatin (n = 82).

RESULTS

Expression of OATP1B1, OATP1B3, and OATP2B1 at the mRNA and protein levels showed marked interindividual variability. All three OATPs were expressed in a coordinated fashion. By a multivariate regression analysis adjusted for non-genetic and transcription covariates, increased OATP1B1 expression was associated with the coding SLCO1B1 variant c.388A > G (rs2306283) even after correction for multiple testing (P = 0.00034). This held true for haplotypes harboring c.388A > G but not the functional variant c.521T > C (rs4149056) associated with statin-related myopathy. c.388A > G also significantly affected atorvastatin pharmacokinetics. SLCO variants and non-genetic and regulatory covariates together accounted for 59% of variability of OATP1B1 expression.

CONCLUSIONS

Our results show that expression of OATP1B1, but not of OATP1B3 and OATP2B1, is significantly affected by genetic variants. The SLCO1B1 variant c.388A > G is the major determinant with additional consequences on atorvastatin plasma levels.