Role of multidrug resistance-associated protein 4 in the basolateral efflux of hepatically derived enalaprilat

Impact of liver diseases and pharmacological interactions on the transportome involved in hepatic drug disposition

The liver plays a pivotal role in drug disposition owing to the expression of transporters accounting for the uptake at the sinusoidal membrane and the efflux across the basolateral and canalicular membranes of hepatocytes of many different compounds. Moreover, intracellular mechanisms of phases I and II biotransformation generate, in general, inactive compounds that are more polar and easier to eliminate into bile or refluxed back toward the blood for their elimination by the kidneys, which becomes crucial when the biliary route is hampered. The set of transporters expressed at a given time, i.e., the so-called transportome, is encoded by genes belonging to two gene superfamilies named Solute Carriers (SLC) and ATP-Binding Cassette (ABC), which account mainly, but not exclusively, for the uptake and efflux of endogenous substances and xenobiotics, which include many different drugs. Besides the existence of genetic variants, which determines a marked interindividual heterogeneity regarding liver drug disposition among patients, prevalent diseases, such as cirrhosis, non-alcoholic steatohepatitis, primary sclerosing cholangitis, primary biliary cirrhosis, viral hepatitis, hepatocellular carcinoma, cholangiocarcinoma, and several cholestatic liver diseases, can alter the transportome and hence affect the pharmacokinetics of drugs used to treat these patients. Moreover, hepatic drug transporters are involved in many drug-drug interactions (DDI) that challenge the safety of using a combination of agents handled by these proteins. Updated information on these questions has been organized in this article by superfamilies and families of members of the transportome involved in hepatic drug disposition.

Development of pharmacophore models for AcrB protein and the identification of potential adjuvant candidates for overcoming efflux-mediated colistin resistance

Growing multi-drug resistance (MDR) among ESKAPE pathogens is a huge challenge. Increased resistance to last-resort antibiotics, like colistin, has further aggravated this. Efflux is identified as a major route of colistin resistance. So, finding an FDA-approved efflux inhibitor for potential application as an adjuvant to colistin was the primary objective of this study. E. coli-AcrB pump inhibitors and substrates were used to develop and validate the pharmacophoric model. Drugs confirming this pharmacophore were subjected to molecular docking to identify hits for the AcrB binding pocket. The efflux inhibition potential of the top hit was validated through the in vitro evaluation of the minimum inhibitory concentration (MIC) in combination with colistin. The checkerboard assay was done to demonstrate synergism, which was further corroborated by the Time-kill assay. Ten common pharmacophore hypotheses were successfully generated using substrate/inhibitors. Following enrichment analysis, AHHNR.100 was identified as the top-ranked hypothesis, and 207 unique compounds were found to conform to this hypothesis. The multi-step docking of these compounds against the AcrB protein revealed argatroban as the top non-antibiotic hit. This significantly inhibited the efflux activity of colistin-resistant clinical isolates K. pneumoniae (n = 1) and M. morganii (n = 2). Further, their combination with colistin enhanced the susceptibility of these isolates, and the effect was found to be synergistic. Accordingly, the time-kill assay of this combination showed 8-log and 2-log reductions against K. pneumoniae and M. morganii, respectively. In conclusion, this study found argatroban as a bacterial efflux inhibitor that can be potentially used to overcome efflux-mediated resistance.

Hepatic Transporters Alternations Associated with Non-alcoholic Fatty Liver Disease (NAFLD): A Systematic Review

BACKGROUND AND OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) is a progressive liver disorder and is usually accompanied by obesity, metabolic syndrome, and diabetes mellitus. NAFLD progression can lead to impaired functions of hepatocytes such as alternations in expression and function of hepatic transporters. The present study aimed to summarize and discuss the results of clinical and preclinical human studies that investigate the effect of NAFLD on hepatic transporters.

METHODS

The databases of PubMed, Scopus, Embase, and Web of Science were searched systematically up to 1 March 2022. The risk of bias was assessed for cross-sectional studies through the Newcastle-Ottawa Scale score.

RESULTS

Our review included ten cross-sectional studies consisting of 485 participants. Substantial alternations in hepatic transporters were seen during NAFLD progression to non-alcoholic steatohepatitis (NASH) in comparison with control groups. A significant reduction in expression and function of several hepatic uptake transporters, upregulation of many efflux transporters, downregulation of cholesterol efflux transporters, and mislocalization of canalicular transporter ABCC2 are associated with NAFLD progression.

CONCLUSION

Since extensive changes in hepatic transporters could alter the pharmacokinetics of the drugs and potentially affect the safety and efficacy of drugs, close monitoring of drug administration is highly suggested in patients with NASH.

Completing the Enalaprilat Excretion Pathway-Renal Handling by the Proximal Tubule

BACKGROUND

Enalapril is often used in the treatment of cardiovascular diseases. Clinical data suggest that the urinary excretion of enalaprilat, the active metabolite of enalapril, is mediated by renal transporters. We aimed to identify enalaprilat specificity for renal proximal tubular transporters.

METHODS

Baculovirus-transduced HEK293 cells overexpressing proximal tubular transporters were used to study enalaprilat cellular uptake. Uptake into cells overexpressing the basolateral transporters OCT2, OAT1, OAT2, or OAT3 and apical transporters OAT4, PEPT1, PEPT2, OCTN1, OCTN2, MATE1, MATE2k, and URAT1 was compared with mock-transduced control cells. Transport by renal efflux transporters MRP2, MPR4, P-gp, and BCRP was tested using a vesicular assay. Enalaprilat concentrations were measured using LC-MS/MS.

RESULTS

Uptake of enalaprilat into cells expressing OAT3 as well as OAT4 was significantly higher compared to control cells. The enalaprilat affinity for OAT3 was 640 (95% CI: 520-770) µM. For OAT4, no reliable affinity constant could be determined using concentrations up to 3 mM. No transport was observed for other transporters.

CONCLUSION

The affinity of enalaprilat for OAT3 and OAT4 was notably low compared to other substrates. Taking this affinity and clinically relevant plasma concentrations of enalaprilat and other OAT3 substrates into account, we believe that drug-drug interactions on a transporter level do not have a therapeutic consequence and will not require dose adjustments of enalaprilat itself or other OAT3 substrates.

Pharmacology of enalapril in children: a review

Enalapril is an angiotensin-converting enzyme (ACE) inhibitor that is used for the treatment of (paediatric) hypertension, heart failure and chronic kidney diseases. Because its disposition, efficacy and safety differs across the paediatric continuum, data from adults cannot be automatically extrapolated to children. This review highlights paediatric enalapril pharmacokinetic data and demonstrates that these are inadequate to support with certainty an age-related effect on enalapril/enalaprilat pharmacokinetics. In addition, our review shows that evidence to support effective and safe prescribing of enalapril in children is limited, especially in young children and heart failure patients; studies in these groups are either absent or show conflicting results. We provide explanations for observed differences between age groups and indications, and describe areas for future research.

Mathematical modeling analysis of hepatic uric acid disposition using human sandwich-cultured hepatocytes

Uric acid is biosynthesized from purine by xanthine oxidase (XO) mainly in the liver and is excreted into urine and feces. Although several transporters responsible for renal and intestinal handling of uric acid have been reported, information on hepatic transporters is limited. In the present study, we studied quantitative contribution of transporters for hepatic handling of uric acid by mathematical modeling analysis in human sandwich-cultured hepatocytes (hSCH). Stable isotope-labeled hypoxanthine, hypoxanthine-¹³C2,¹⁵N (HX), was incubated with hSCH and formed ¹³C2,¹⁵N-labeled xanthine (XA) and uric acid (UA) were measured by LC-MS/MS time dependently. Rate constants for metabolism and efflux and uptake transport across sinusoidal and bile canalicular membranes of HX, XA and UA were estimated in the presence of inhibitors of XO and uric acid transporters. An XO inhibitor allopurinol significantly decreased metabolisms of HX and XA. Efflux into bile canalicular lumen was negligible and sinusoidal efflux was considered main efflux pathway of formed UA. Transporter inhibition study highlighted that GLUT9 strongly and MRP4 intermediately contribute to the sinusoidal efflux of UA with minor contribution of NPT1/4. Modeling analysis developed in the present study should be useful for quantitative prediction of uric acid disposition in liver.

Multidrug resistance-associated protein 4 in pharmacology: Overview of its contribution to pharmacokinetics, pharmacodynamics and pharmacogenetics

MRP4 is an ABC membrane transporter involved in clinical outcomes as it is located in many tissues that manages the transport and the elimination of many drugs. This review explores the implication of MRP4 in clinical pharmacology and the importance of its genetic variability. Although there is no specific recommendation regarding the study of MRP4 in drug development, it should be considered when drugs are eliminated by the kidney or liver or when drug-drug interactions are expected.

Evaluation of Drug Biliary Excretion Using Sandwich-Cultured Human Hepatocytes

Evaluation of hepatobiliary transport of drugs is an important challenge, notably during the development of new molecular identities. In this context, sandwich-cultured human hepatocytes (SCHH) have been proposed as an interesting and integrated tool for predicting in vitro biliary excretion of drugs. The present review was therefore designed to summarize key findings about SCHH, including their establishment, their main functional features and their use for the determination of canalicular transport and the prediction of in vivo biliary clearance and hepatobiliary excretion-related drug-drug interactions. Reviewed data highlight the fact that SCHH represent an original and probably unique holistic in vitro approach to predict biliary clearance in humans, through taking into account sinusoidal drug uptake, passive drug diffusion, drug metabolism and sinusoidal and canalicular drug efflux. Limits and proposed refinements for SCHH-based analysis of drug biliary excretion, as well as putative human alternative in vitro models to SCHH are also discussed.

Simultaneous Semi-Mechanistic Population Pharmacokinetic Modeling Analysis of Enalapril and Enalaprilat Serum and Urine Concentrations From Child Appropriate Orodispersible Minitablets

Enalapril is recommended as the first line of therapy and is proven to improve survival rates for treatment of Pediatric Heart Failure; however, an approved drug and child appropriate dosage formulation is still absent. The present analysis was conducted to perform a detailed model informed population pharmacokinetic analysis of prodrug enalapril and its active metabolite enalaprilat in serum and urine. Further, a model informed dosage form population-pharmacokinetic analysis was conducted to evaluate differences in pharmacokinetics of enalapril and its active metabolite enalaprilat when prodrug was administered to 24 healthy adults in a crossover, two periods, two treatments, phase I clinical trial using child-appropriate orodispersible mini-tablets (ODMT) and reference (Renitec®) dosage formulation. A simultaneous semi-mechanistic population-pharmacokinetic model was developed using NONMEM software, which predicted full profile serum and urine concentrations of enalapril and enalaprilat. First-order conditional estimation with interaction was used for parameter estimation. Transit compartments added using Erlang distribution method to predicted enalapril absorption and enalaprilat formation phases. Normalized body weight was identified as covariate related to enalapril volume of distribution. Visual predictive check (VPC) plots and conducted bootstrap analysis validated the model. The data from the two formulations were pooled for population-pharmacokinetic analysis and covariate effect of the formulation was found on mean transit time (MTT1) of enalapril absorption. In addition, data of each formulation were modeled separately and the estimated parameters of each individual administered both formulations were correlated using paired samples Wilcoxon rank test (p < 0.05 = significant) which also showed only a significant difference (p = 0.03) in MTT1 i.e., 5 min early appearance of enalapril from ODMT compared to reference tablets. No difference in the pharmacokinetics of active enalaprilat was found from the ODMT compared to the reference formulation. The population pharmacokinetic analysis provided detailed information about the pharmacokinetics of enalapril and enalaprilat, which showed that the ODMT formulation might have similar pharmacodynamic response compared to the reference formulation.

Effect of Cryopreservation on Enzyme and Transporter Activities in Suspended and Sandwich Cultured Rat Hepatocytes

Freshly-isolated rat hepatocytes are commonly used as tools for hepatic drug disposition. From an ethical point of view, it is important to maximize the use of isolated hepatocytes by cryopreservation. The present study compared overall hepatocyte functionality as well as activity of the organic anion transporting polypeptide (Oatp), multidrug resistance-associated protein 2 (Mrp2), and UDP-glucuronosyltransferase 1 (Ugt1), in in vitro models established with cryopreserved and freshly-isolated hepatocytes. A similar culture time-dependent decline in cellular functionality, as assessed by urea production, was observed in sandwich-cultured hepatocytes (SCH) obtained from freshly-isolated and cryopreserved cells. Concentration-dependent uptake kinetics of the Oatp substrate sodium fluorescein in suspended hepatocytes (SH) or SCH were not significantly affected by cryopreservation. Mrp2-mediated biliary excretion of 5 (and 6)-carboxy-2',7'-dichlorofluorescein by SCH was assessed with semi-quantitative fluorescence imaging: biliary excretion index values increased between day 3 and day 4, but did not differ significantly between cryopreserved and freshly-isolated hepatocytes. Finally, telmisartan disposition was evaluated in SCH to simultaneously explore Oatp, Ugt1, and Mrp2 activity. In order to distinguish between the susceptibilities of the individual disposition pathways to cryopreservation, a mechanistic cellular disposition model was developed. Basolateral and canalicular efflux as well as glucuronidation of telmisartan were affected by cryopreservation. In contrast, the disposition parameters of telmisartan-glucuronide were not impacted by cryopreservation. Overall, the relative contribution of the rate-determining processes (uptake, metabolism, efflux) remained unaltered between cryopreserved and freshly-isolated hepatocytes, indicating that cryopreserved hepatocytes are a suitable alternative for freshly-isolated hepatocytes when studying these cellular disposition pathways.

Sandwich-Cultured Hepatocytes for Mechanistic Understanding of Hepatic Disposition of Parent Drugs and Metabolites by Transporter-Enzyme Interplay

Functional interplay between transporters and drug-metabolizing enzymes is currently one of the hottest topics in the field of drug metabolism and pharmacokinetics. Uptake transporter-enzyme interplay is important to determine intrinsic hepatic clearance based on the extended clearance concept. Enzyme and efflux transporter interplay, which includes both sinusoidal (basolateral) and canalicular efflux transporters, determines the fate of metabolites formed in the liver. As sandwich-cultured hepatocytes (SCHs) maintain metabolic activities and form a canalicular network, the whole interplay between uptake and efflux transporters and drug-metabolizing enzymes can be investigated simultaneously. In this article, we review the utility and applicability of SCHs for mechanistic understanding of hepatic disposition of both parent drugs and metabolites. In addition, the utility of SCHs for mimicking species-specific disposition of parent drugs and metabolites in vivo is described. We also review application of SCHs for clinically relevant prediction of drug-drug interactions caused by drugs and metabolites. The usefulness of mathematical modeling of hepatic disposition of parent drugs and metabolites in SCHs is described to allow a quantitative understanding of an event in vitro and to develop a more advanced model to predict in vivo disposition.

Importance of Hepatic Transporters in Clinical Disposition of Drugs and Their Metabolites

This review provides a practical clinical perspective on the relevance of hepatic transporters in pharmacokinetics and drug-drug interactions (DDIs). Special emphasis is placed on transporters with clear relevance to clinical DDIs, efficacy, and safety. Basolateral OATP1B1 and 1B3 emerged as important hepatic drug uptake pathways, sites for systemic DDIs, and sources of pharmacogenetic variability. As the first step in hepatic drug removal from the circulation, OATPs are an important determinant of systemic pharmacokinetics, specifically influencing systemic absorption, clearance, and hepatic distribution for subsequent metabolism and/or excretion. Biliary excretion of parent drugs is a less prevalent clearance pathway than metabolism or urinary excretion, but BCRP and MRP2 are critically important to biliary/fecal elimination of drug metabolites. Inhibition of biliary excretion is typically not apparent at the level of systemic pharmacokinetics but can markedly increase liver exposure. Basolateral efflux transporters MRP3 and MRP4 mediate excretion of parent drugs and, more commonly, polar metabolites from hepatocytes into blood. Basolateral excretion is an area in need of further clinical investigation, which will necessitate studies more complex than just systemic pharmacokinetics. Clinical relevance of hepatic uptake is relatively well appreciated, and clinical consequences of hepatic excretion (biliary and basolateral) modulation remain an active research area.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Sandwich-Cultured Hepatocytes as a Tool to Study Drug Disposition and Drug-Induced Liver Injury

Sandwich-cultured hepatocytes (SCH) are metabolically competent and have proper localization of basolateral and canalicular transporters with functional bile networks. Therefore, this cellular model is a unique tool that can be used to estimate biliary excretion of compounds. SCH have been used widely to assess hepatobiliary disposition of endogenous and exogenous compounds and metabolites. Mechanistic modeling based on SCH data enables estimation of metabolic and transporter-mediated clearances, which can be used to construct physiologically based pharmacokinetic models for prediction of drug disposition and drug-drug interactions in humans. In addition to pharmacokinetic studies, SCH also have been used to study cytotoxicity and perturbation of biological processes by drugs and hepatically generated metabolites. Human SCH can provide mechanistic insights underlying clinical drug-induced liver injury (DILI). In addition, data generated in SCH can be integrated into systems pharmacology models to predict potential DILI in humans. In this review, applications of SCH in studying hepatobiliary drug disposition and bile acid-mediated DILI are discussed. An example is presented to show how data generated in the SCH model were used to establish a quantitative relationship between intracellular bile acids and cytotoxicity, and how this information was incorporated into a systems pharmacology model for DILI prediction.

Insights into solute carriers: physiological functions and implications in disease and pharmacokinetics

SLCs transport many endogenous and exogenous compounds including drugs; SLCs dysfunction has implications in pharmacokinetics, drug toxicity or lack of efficacy.

The Pharmacological and Physiological Role of Multidrug-Resistant Protein 4

Multidrug-resistant protein 4 (MRP4), a member of the C subfamily of ATP-binding cassette transporters, is distributed in a variety of tissues and a number of cancers. As a drug transporter, MRP4 is responsible for the pharmacokinetics and pharmacodynamics of numerous drugs, especially antiviral drugs, antitumor drugs, and diuretics. In this regard, the functional role of MRP4 is affected by a number of factors, such as genetic mutations; tissue-specific transcriptional regulations; post-transcriptional regulations, including miRNAs and membrane internalization; and substrate competition. Unlike other C family members, MRP4 is in a pivotal position to transport cellular signaling molecules, through which it is tightly connected to the living activity and physiologic processes of cells and bodies. In the context of several cancers in which MRP4 is overexpressed, MRP4 inhibition shows striking effects against cancer progression and drug resistance. In this review, we describe the role of MRP4 more specifically in both healthy conditions and disease states, with an emphasis on its potential as a drug target.