Alternative transporter pathways in patients with untreated early-stage and late-stage primary biliary cirrhosis

Modulation of Hepatic MRP3/ABCC3 by Xenobiotics and Pathophysiological Conditions: Role in Drug Pharmacokinetics

Liver transporters play an important role in the pharmacokinetics and disposition of pharmaceuticals, environmental contaminants, and endogenous compounds. Among them, the family of ATP-Binding Cassette (ABC) transporters is the most important due to its role in the transport of endo- and xenobiotics. The ABCC sub-family is the largest one, consisting of 13 members that include the cystic fibrosis conductance regulator (CFTR/ABCC7); the sulfonylurea receptors (SUR1/ABCC8 and SUR2/ABCC9) and the multidrug resistanceassociated proteins (MRPs). The MRP-related proteins can collectively confer resistance to natural, synthetic drugs and their conjugated metabolites, including platinum-containing compounds, folate anti-metabolites, nucleoside and nucleotide analogs, among others. MRPs can be also catalogued into "long" (MRP1/ABCC1, -2/C2, -3/C3, -6/C6, and -7/C10) and "short" (MRP4/C4, -5/C5, -8/C11, -9/C12, and -10/C13) categories. While MRP2/ABCC2 is expressed in the canalicular pole of hepatocytes, all others are located in the basolateral membrane. In this review, we summarize information from studies examining the changes in expression and regulation of the basolateral hepatic transporter MPR3/ABCC3 by xenobiotics and during various pathophysiological conditions. We also focus, primarily, on the consequences of such changes in the pharmacokinetic, pharmacodynamic and/or toxicity of different drugs of clinical use transported by MRP3.

Effect of Liver Disease on Hepatic Transporter Expression and Function

Liver disease can alter the disposition of xenobiotics and endogenous substances. Regulatory agencies such as the Food and Drug Administration and the European Medicines Evaluation Agency recommend, if possible, studying the effect of liver disease on drugs under development to guide specific dose recommendations in these patients. Although extensive research has been conducted to characterize the effect of liver disease on drug-metabolizing enzymes, emerging data have implicated that the expression and function of hepatobiliary transport proteins also are altered in liver disease. This review summarizes recent developments in the field, which may have implications for understanding altered disposition, safety, and efficacy of new and existing drugs. A brief review of liver physiology and hepatic transporter localization/function is provided. Then, the expression and function of hepatic transporters in cholestasis, hepatitis C infection, hepatocellular carcinoma, human immunodeficiency virus infection, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and primary biliary cirrhosis are reviewed. In the absence of clinical data, nonclinical information in animal models is presented. This review aims to advance the understanding of altered expression and function of hepatic transporters in liver disease and the implications of such changes on drug disposition.

Changes in drug transport and metabolism and their clinical implications in non-alcoholic fatty liver disease

INTRODUCTION

The incidence of non-alcoholic fatty liver disease (NAFLD) is rising, especially in Western countries. Drug treatment in patients with NAFLD is common since it is linked to other conditions like diabetes, obesity, and cardiovascular disease. Consequently, changes in drug metabolism may have serious clinical implications. Areas covered: A literature search for studies in animal models or patients with obesity, fatty liver, non-alcoholic steatohepatitis (NASH) or NASH cirrhosis published before November 2016 was performed. After discussing epidemiology and animal models for NAFLD, we summarized both basic as well as clinical studies investigating changes in drug transport and metabolism in NAFLD. Important drug groups were assessed separately with emphasis on clinical implications for drug treatment in patients with NAFLD. Expert opinion: Given the frequency of NAFLD even today, a high degree of drug treatment in NAFLD patients appears safe and well-tolerated despite considerable changes in hepatic uptake, distribution, metabolism and transport of drugs in these patients. NASH causes changes in biliary excretion, systemic concentrations, and renal handling of drugs leading to alterations in drug efficacy or toxicity under specific circumstances. Future clinical drug studies should focus on this special patient population in order to avoid serious adverse events in NAFLD patients.

Geniposide attenuates ANIT-induced cholestasis through regulation of transporters and enzymes involved in bile acids homeostasis in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Geniposide (GE) is one of the major iridoid glycosides isolated from the fruit of Gardenia jasminoides Ellis that has been used to treat hepatic disorders including cholestasis. However, the underlying mechanisms for GE ameliorating the reduction in bile acids accumulation by α-naphthylisothiocyanate (ANIT) remain unclear.

AIM OF THE STUDY

The purpose of this study is to characterize the efficacy of GE in regulation of bile acids uptake, synthesis, metabolism, and transport in ANIT-induced rats.

MATERIALS AND METHODS

Sprague-Dawley rats were orally administrated with vehicle, GE (25, 50, and 100mg/kg), and ursodeoxycholic acid (UDCA) (60mg/kg) once daily for seven days. On the fifth day, a single dose of ANIT (75mg/kg) was administrated via oral gavage. Blood biochemical determination, bile flow rate and liver histopathology were measured to evaluate the protective effect of GE. The mRNA expressions and protein levels of transporters and enzymes involved in bile acids homeostasis were determined by quantitative real-time polymerase chain reaction (PCR) and western blot to study the underlying mechanism of GE against ANIT-induced rats.

RESULTS

GE (25, 50, and 100mg/kg, po) dose-dependently prevented ANIT-induced changes in serum markers for liver injury. GE treatment reduced basolateral bile acids uptake via repression of OATP2 (P<0.05). Bile acids biosynthesis was decreased through down-regulation of CYP7A1, CYP8B1, and CYP27A1 (P<0.05). GE significantly increased canalicular bile acids secretion via BSEP (P<0.05), subsequently stimulating bile flow during cholestasis. GE also markedly enhanced mRNA level of basolateral transporter OSTβ (P<0.01). Bile acids transported to the plasma were cleared into the urine, resulting in down-regulation of plasma bile acids. However, GE did not alter the mRNA levels of CYP3A2, UGT1A1 and SULT2A1. Furthermore, the gene and protein expression analysis demonstrated activation of FXR, PXR, and SHP after GE administration.

CONCLUSION

GE attenuates ANIT-induced hepatotoxicity and cholestasis in rats, due to regulation enzymes and transporters responsible for bile acids homeostasis.

Molecular changes in hepatic metabolism and transport in cirrhosis and their functional importance

Liver cirrhosis is the common endpoint of many hepatic diseases and represents a relevant risk for liver failure and hepatocellular carcinoma. The progress of liver fibrosis and cirrhosis is accompanied by deteriorating liver function. This review summarizes the regulatory and functional changes in phase I and phase II metabolic enzymes as well as transport proteins and provides an overview regarding lipid and glucose metabolism in cirrhotic patients. Interestingly, phase I enzymes are generally downregulated transcriptionally, while phase II enzymes are mostly preserved transcriptionally but are reduced in their function. Transport proteins are regulated in a specific way that resembles the molecular changes observed in obstructive cholestasis. Lipid and glucose metabolism are characterized by insulin resistance and catabolism, leading to the disturbance of energy expenditure and wasting. Possible non-invasive tests, especially breath tests, for components of liver metabolism are discussed. The heterogeneity and complexity of changes in hepatic metabolism complicate the assessment of liver function in individual patients. Additionally, studies in humans are rare, and species differences preclude the transferability of data from rodents to humans. In clinical practice, some established global scores or criteria form the basis for the functional evaluation of patients with liver cirrhosis, but difficult treatment decisions such as selection for transplantation or resection require further research regarding the application of existing non-invasive tests and the development of more specific tests.

Gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging as a useful detection method for advanced primary biliary cirrhosis

AIM

In primary biliary cirrhosis (PBC), damaged hepatocytes resulting from chronic cholestasis follow a compensatory mechanism that alters hepatobiliary transporter expression to reduce the accumulation of potentially toxic compounds such as bile acid. Organic anion transporter peptide 1B3 (OATP1B3), which transports agents such as gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA), has reduced expression in the late stages of PBC. Therefore, we investigated the use of Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) as a useful detection method for the advanced staging of PBC.

METHODS

Stage I-III PBC (non-liver cirrhosis [LC]-PBC, n = 12), stage IV (LC-PBC, n = 6), and non-PBC patients (control group, n = 4) were included in this study. We obtained liver tissue samples by percutaneous liver biopsy. Hepatic OATP1B3 expression was determined immunohistochemically, and OATP1B3 mRNA levels were assessed using real-time reverse transcription polymerase chain reaction. The relative enhancement (RE) in the hepatobiliary phase was calculated using the signal intensity of Gd-EOB-DTPA-enhanced MRI.

RESULTS

Immunohistochemistry revealed markedly reduced expression of OATP1B3 in hepatocytes around the central vein in LC-PBC patients. Hepatic OATP1B3 mRNA expression in LC-PBC patients was significantly lower than that in non-LC-PBC patients (P < 0.05). The RE on MRI was significantly decreased in the LC-PBC group (0.33 ± 0.14) compared with the non-LC-PBC (0.91 ± 0.15, P < 0.01) and control (0.92 ± 0.20, P < 0.01) groups.

CONCLUSION

Gd-EOB-DTPA-enhanced MRI may provide a useful detection method for liver disease in patients with LC-PBC.

Hepatobiliary membrane transporters in primary biliary cirrhosis

The secretion of bile normally depends on the function of a number of membrane transport systems in hepatocytes and cholangiocytes. The transport of solutes from the blood to the bile is driven by transport systems in the plasma membrane of the basolateral and canalicular surfaces of the hepatocytes. In cholestatic animal models, the expression of hepatobiliary transporters changes in response to functional impairment of the efflux of bile salts and various organic anions. In recent years, several studies have led to an improved understanding of the function and regulation of hepatobiliary transport systems in patients with primary biliary cirrhosis (PBC). This review focuses on the adaptations in hepatobiliary transporters in PBC patients.

Sustained upregulation of sodium taurocholate cotransporting polypeptide and bile salt export pump and downregulation of cholesterol 7α-hydroxylase in the liver of patients with end-stage primary biliary cirrhosis

To examine the mRNA expression of hepatobiliary transporters in primary biliary cirrhosis (PBC) patients and to compare bile acid absorption, synthesis, and efflux in patients with non-end-stage and end-stage PBC, we obtained liver samples from PBC patients by percutaneous needle biopsy. End-stage PBC was defined as follows: histological stage IV; cirrhosis; serum total bilirubin, ≥4.0 mg/dl; and Child-Pugh Class C. The mRNA expression levels of sodium taurocholate cotransporting polypeptide (NTCP), bile salt export pump (BSEP), and hepatic cholesterol 7α-hydroxylase (CYP7A1) were significantly higher in the PBC patients than in the controls (P < 0.01). The mRNA levels of NTCP and BSEP were significantly higher in the end-stage PBC patients than in the controls (P < 0.01). However, hepatic CYP7A1 mRNA expression decreased significantly (by 70%) in the patients with end-stage PBC as compared to the controls and the patients with non-end-stage PBC (P < 0.01). The hepatic expression of transporters mediating bile acid influx and efflux showed sustained elevation, whereas that of the rate-limiting enzyme for bile acid biosynthesis was attenuated in the end-stage PBC patients. Thus, mechanisms may be present preventing the accumulation of toxic bile acids in the hepatocytes of end-stage PBC patients.