The apical conjugate efflux pump ABCC2 (MRP2)

Cholangiogenic potential of human deciduous pulp stem cell-converted hepatocyte-like cells

Background

Stem cells from human exfoliated deciduous teeth (SHED) have been reported to show the in vivo and in vitro hepatic differentiation, SHED-Heps; however, the cholangiogenic potency of SHED-Heps remains unclear. Here, we hypothesized that SHED-Heps contribute to the regeneration of intrahepatic bile duct system in chronic fibrotic liver.

Methods

SHED were induced into SHED-Heps under cytokine stimulation. SHED-Heps were intrasplenically transplanted into chronically CCl₄-treated liver fibrosis model mice, followed by the analysis of donor integration and hepatobiliary metabolism in vivo. Immunohistochemical assay was examined for the regeneration of intrahepatic bile duct system in the recipient liver. Furthermore, SHED-Heps were induced under the stimulation of tumor necrosis factor alpha (TNFA).

Results

The intrasplenic transplantation of SHED-Heps into CCl₄-treated mice showed that donor SHED-Heps behaved as human hepatocyte paraffin 1- and human albumin-expressing hepatocyte-like cells in situ and ameliorated CCl₄-induced liver fibrosis. Of interest, the integrated SHED-Heps not only expressed biliary canaliculi ATP-binding cassette transporters including ABCB1, ABCB11, and ABCC2, but also recruited human keratin 19- (KRT19-) and KRT17-positive cells, which are considered donor-derived cholangiocytes, regenerating the intrahepatic bile duct system in the recipient liver. Furthermore, the stimulation of TNFA induced SHED-Heps into KRT7- and SRY-box 9-positive cells.

Conclusions

Collectively, our findings demonstrate that infused SHED-Heps showed cholangiogenic ability under the stimulation of TNFA in CCl₄-damaged livers, resulting in the regeneration of biliary canaliculi and interlobular bile ducts in chronic fibrotic liver. Thus, the present findings suggest that SHED-Heps may be a novel source for the treatment of cholangiopathy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-020-02113-8.

Effects of psoralen on hepatic bile acid transporters in rats

Fructus Psoraleae (FP), widely used in traditional medicine, is increasingly reported to cause serious hepatotoxicity in recent years. However, the main toxic constituents responsible for hepatotoxicity and the underlying mechanisms are poorly understood. In the present study, psoralen, a main and quality-control constituent of FP, was intragastrically administered to Sprague-Dawley rats at a dose of 60 mg/kg for 1, 3 and 7 days. Blood and selected tissue samples were collected and analyzed for biochemistry and histopathology to evaluate hepatotoxicity. The results showed that psoralen could induce hepatotoxicity by enhanced liver-to-body weight ratio and alterations of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and total cholesterol after administration for 3 days. In addition, histopathological examinations also indicated the hepatotoxicity induced by psoralen. Furthermore, the mRNA and protein levels of hepatic bile acid transporters were significantly changed, in which MRP4, ABCG5 and ABCG8 were repressed, while the protein level of NTCP tended to increase in the rat liver. Taken together, psoralen caused liver injury possibly through affecting bile acid transporters, leading to the disorder of bile acid transport and accumulation in hepatocytes.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

Mutation spectrum and biochemical features in infants with neonatal Dubin-Johnson syndrome

Background

Dubin-Johnson syndrome (DJS) is an autosomal recessive disorder presenting as isolated direct hyperbilirubinemia.DJS is rarely diagnosed in the neonatal period. The purpose of this study was to clarify the clinical features of neonatal DJS and to analyze the genetic mutation of adenosine triphosphate-binding cassette subfamily C member 2 (ABCC2).

Methods

From 2013 to 2018, 135 infants with neonatal cholestasis at Seoul National University Hospital were enrolled. Genetic analysis was performed by neonatal cholestasis gene panel. To clarify the characteristics of neonatal DJS, the clinical and laboratory results of 6 DJS infants and 129 infants with neonatal cholestasis from other causes were compared.

Results

A total of 8 different ABCC2 variants were identified among the 12 alleles of DJS. The most common variant was p.Arg768Trp (33.4%), followed by p.Arg100Ter (16.8%). Three novel variants were identified (p.Gly693Glu, p.Thr394Arg, and p.Asn718Ser). Aspartate transaminase (AST) and alanine transaminase (ALT) levels were significantly lower in infants with DJS than in infants with neonatal cholestasis from other causes. Direct bilirubin and total bilirubin were significantly higher in the infants with DJS.

Conclusions

We found three novel variants in 6 Korean infants with DJS. When AST and ALT levels are normal in infants with neonatal cholestasis, genetic analysis of ABCC2 permits an accurate diagnosis.

Role of membrane-embedded drug efflux ABC transporters in the cancer chemotherapy

One of the major problems being faced by researchers and clinicians in leukemic treatment is the development of multidrug resistance (MDR) which restrict the action of several tyrosine kinase inhibitors (TKIs). MDR is a major obstacle to the success of cancer chemotherapy. The mechanism of MDR involves active drug efflux transport of ABC superfamily of proteins such as Pglycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) that weaken the effectiveness of chemotherapeutics and negative impact on the future of anticancer therapy. In this review, the authors aim to provide an overview of various multidrug resistance (MDR) mechanisms observed in cancer cells as well as the various strategies developed to overcome these MDR. Extensive studies have been carried out since last several years to enhance the efficacy of chemotherapy by defeating these MDR mechanisms with the use of novel anticancer drugs that could escape from the efflux reaction, MDR modulators or chemosensitizers, multifunctional nanotechnology, and RNA interference (RNAi) therapy.

SOD2 promotes the expression of ABCC2 through lncRNA CLCA3p and improves the detoxification capability of liver cells

Superoxide dismutase 2 (SOD2) is a key enzyme for scavenging reactive oxygen species produced by mitochondria, which plays an important role in maintaining cellular homeostasis. However, its effects on the detoxification capability of liver cells have not been reported. In this study, we found that change in SOD2 expression affects the proliferation of liver cells. Genome-wide microarray analysis showed that SOD2 positively regulates the drug transporter ABCC2, and co-expression analysis suggested that lncRNA CLCA3P participates in the process. Further experiments showed that SOD2 can promote the expression of CLCA3P, which increases the transcription of ABCC2 by interacting with the transcription factor IRF1. By increasing ABCC2 expression SOD2 facilitates drugs efflux of liver cells and thus promotes their survival under a drug-toxic environment. This study elucidates the improvement of the detoxification of liver cells by a regulatory axis, SOD2-CLCA3P-IRF1-ABCC2, and provides novel insight into the modification of human liver cells that can be applied to bioartificial liver system or the study of SOD2 in drug metabolism.

Primary biliary cholangitis: pathogenesis and therapeutic opportunities

Primary biliary cholangitis is a chronic, seropositive and female-predominant inflammatory and cholestatic liver disease, which has a variable rate of progression towards biliary cirrhosis. Substantial progress has been made in patient risk stratification with the goal of personalized care, including early adoption of next-generation therapy with licensed use of obeticholic acid or off-label fibrate derivatives for those with insufficient benefit from ursodeoxycholic acid, the current first-line drug. The disease biology spans genetic risk, epigenetic changes, dysregulated mucosal immunity and altered biliary epithelial cell function, all of which interact and arise in the context of ill-defined environmental triggers. A current focus of research on nuclear receptor pathway modulation that specifically and potently improves biliary excretion, reduces inflammation and attenuates fibrosis is redefining therapy. Patients are benefiting from pharmacological agonists of farnesoid X receptor and peroxisome proliferator-activated receptors. Immunotherapy remains a challenge, with a lack of target definition, pleiotropic immune pathways and an interplay between hepatic immune responses and cholestasis, wherein bile acid-induced inflammation and fibrosis are dominant clinically. The management of patient symptoms, particularly pruritus, is a notable goal reflected in the development of rational therapy with apical sodium-dependent bile acid transporter inhibitors.

Alternative Polyadenylation of ABC Transporters of the C-Family (ABCC1, ABCC2, ABCC3) and Implications on Posttranscriptional Micro-RNA Regulation

ATP-binding cassette (ABC) transporters represent a large group of efflux pumps that are strongly involved in the pharmacokinetics of various drugs and nutrient distribution. It was recently shown that micro-RNAs (miRNAs) may significantly alter their expression as proven, e.g., for miR-379 and ABCC2 However, alternative mRNA polyadenylation may result in expression of 3'-untranslated regions (3'-UTRs) with varying lengths. Thus, length variants may result in presence or absence of miRNA binding sites for regulatory miRNAs with consequences on posttranscriptional control. In the present study, we report on 3'-UTR variants of ABCC1, ABCC2, and ABCC3 mRNA. Applying in vitro luciferase reporter gene assays, we show that expression of short ABCC2 3'-UTR variants leads to a significant loss of miR-379/ABCC2 interaction and subsequent upregulation of ABCC2 expression. Furthermore, we show that expression of ABCC2 3'-UTR lengths varies significantly between human healthy tissues but is not directly correlated to the respective protein level in vivo. In conclusion, the presence of altered 3'-UTR lengths in ABC transporters could lead to functional consequences regarding posttranscriptional gene expression, potentially regulated by alternative polyadenylation. Hence, 3'-UTR length variability may be considered as a further mechanism contributing to variability of ABCC transporter expression and subsequent drug variation in drug response. SIGNIFICANCE STATEMENT: micro-RNA (miRNA) binding to 3'-untranslated region (3'-UTR) plays an important role in the control of ATP-binding cassette (ABC)-transporter mRNA degradation and translation into proteins. We disclosed various 3'-UTR length variants of ABCC1, C2, and C3 mRNA, with loss of mRNA seed regions partly leading to varying and tissue-dependent interaction with miRNAs, as proven by reporter gene assays. Alternative 3'-UTR lengths may contribute to variable ABCC transporter expression and potentially explains inconsistent findings in miRNA studies.

The importance of transporters and cell polarization for the evaluation of human stem cell-derived hepatic cells

One of the most promising applications of human pluripotent stem cells is their utilization for human-based pharmacological models. Despite the fact that membrane transporters expressed in the liver play pivotal role in various hepatic functions, thus far only little attention was devoted to the membrane transporter composition of the stem cell-derived liver models. In the present work, we have differentiated HUES9, a human embryonic stem cell line, toward the hepatic lineage, and monitored the expression levels of numerous differentiation marker and liver transporter genes with special focus on ABC transporters. In addition, the effect of bile acid treatment and polarizing culturing conditions on hepatic maturation has been assessed. We found that most transporter genes crucial for hepatic functions are markedly induced during hepatic differentiation; however, as regards the transporter composition the end-stage cells still exhibited dual, hepatocyte and cholangiocyte character. Although the bile acid treatment and sandwich culturing only slightly influenced the gene expressions, the stimulated cell polarization resulted in formation of bile canaliculi and proper localization of transporters. Our results point to the importance of membrane transporters in human stem cell-derived hepatic models and demonstrate the relevance of cell polarization in generation of applicable cellular models with correctly localized transporters. On the basis of our observations we suggest that conventional criteria for the evaluation of the quality of stem cell-derived hepatocyte-like cells ought to be augmented with additional elements, such as polarized and functional expression of hepatic transporters.

Probing the Role of the Chloroplasts in Heavy Metal Tolerance and Accumulation in Euglena gracilis

The E. gracilis Zm-strain lacking chloroplasts, characterized in this study, was compared with the earlier assessed wild type Z-strain to explore the role of chloroplasts in heavy metal accumulation and tolerance. Comparison of the minimum inhibitory concentration (MIC) values indicated that both strains tolerated similar concentrations of mercury (Hg) and lead (Pb), but cadmium (Cd) tolerance of the Z-strain was twice that of the Zm-strain. The ability of the Zm-strain to accumulate Hg was higher compared to the Z-strain, indicating the existence of a Hg transportation and accumulation mechanism not depending on the presence of chloroplasts. Transmission electron microscopy (TEM) showed maximum accumulation of Hg in the cytosol of the Zm-strain and highest accumulation of Cd in the chloroplasts of the Z-strain indicating a difference in the ability of the two strains to deposit heavy metals in the cell. The highly abundant heavy metal transporter MTP2 in the Z-strain may have a role in Cd transportation to the chloroplasts. A multidrug resistance-associated protein highly increased in abundance in the Zm-strain could be a potential Hg transporter to either cytosol or mitochondria. Overall, the chloroplasts appear to have major role in the tolerance and accumulation of Cd in E. gracilis.

Prognostic significance and molecular mechanisms of adenosine triphosphate-binding cassette subfamily C members in gastric cancer

Gastric cancer (GC) is one of the major leading causes of tumor-related deaths worldwide. Adenosine triphosphate-binding cassette subfamily C (ABCC) consists of 13 members, ABCC1 to 13, which were examined for their associations with GC.The online Kaplan-Meier Plotter database was used to determine the prognostic significance of ABCC subfamily members in GC. Stratified analyses were performed using gender, disease stage, degree of tumor differentiation, expression of human epidermal growth factor receptor 2 (HER2), and Lauren classification. Molecular mechanisms were examined using the database for annotation, visualization, and integrated discovery database.ABCC1, ABCC3, ABCC7, ABCC8, ABCC9, and ABCC10 expression showed prognostic significance in the whole population and in male and female subpopulations (all P ≤ .05). Furthermore, high expression of most ABCC family members always suggested a poor prognosis, except for ABCC7 (P > .05). Stratified analyses revealed that ABCC1, ABCC3, ABCC7, ABCC8, ABCC9, and ABCC10 expression showed prognostic significance for the whole population, as well as male and female populations. ABCC2 and ABCC9 were significantly correlated with all disease stages, while ABCC2 and ABCC6 were significantly correlated with all Lauren classifications. Expression of ABCC1, ABCC3, ABCC5, ABCC7, ABCC8, ABCC9, and ABCC10 was significantly correlated with either negative or positive of HER2 status (all P ≤ .05). Enrichment analysis indicated that these genes were involved in ATPase activity, transmembrane transport, or were ABC transporters (all P ≤ .05).ABCC1, ABCC3, ABCC7, ABCC8, ABCC9, and ABCC10 may be potential prognosis biomarkers for GC, acting as ABC transporters and via ATPase activity.

Current insights in the complexities underlying drug-induced cholestasis

Drug-induced cholestasis (DIC) poses a major challenge to the pharmaceutical industry and regulatory agencies. It causes both drug attrition and post-approval withdrawal of drugs. DIC represents itself as an impaired secretion and flow of bile, leading to the pathological hepatic and/or systemic accumulation of bile acids (BAs) and their conjugate bile salts. Due to the high number of mechanisms underlying DIC, predicting a compound's cholestatic potential during early stages of drug development remains elusive. A profound understanding of the different molecular mechanisms of DIC is, therefore, of utmost importance. Although many knowledge gaps and caveats still exist, it is generally accepted that alterations of certain hepatobiliary membrane transporters and changes in hepatocellular morphology may cause DIC. Consequently, liver models, which represent most of these mechanisms, are valuable tools to predict human DIC. Some of these models, such as membrane-based in vitro models, are exceptionally well-suited to investigate specific mechanisms (i.e. transporter inhibition) of DIC, while others, such as liver slices, encompass all relevant biological processes and, therefore, offer a better representation of the in vivo situation. In the current review, we highlight the principal molecular mechanisms associated with DIC and offer an overview and critical appraisal of the different liver models that are currently being used to predict the cholestatic potential of drugs.

Roles of Hepatic Drug Transporters in Drug Disposition and Liver Toxicity

Hepatic drug transporters are mainly distributed in parenchymal liver cells (hepatocytes), contributing to drug's liver disposition and elimination. According to their functions, hepatic transporters can be roughly divided into influx and efflux transporters, translocating specific molecules from blood into hepatic cytosol and mediating the excretion of drugs and metabolites from hepatic cytosol to blood or bile, respectively. The function of hepatic transport systems can be affected by interspecies differences and inter-individual variability (polymorphism). In addition, some drugs and disease can redistribute transporters from the cell surface to the intracellular compartments, leading to the changes in the expression and function of transporters. Hepatic drug transporters have been associated with the hepatic toxicity of drugs. Gene polymorphism of transporters and altered transporter expressions and functions due to diseases are found to be susceptible factors for drug-induced liver injury (DILI). In this chapter, the localization of hepatic drug transporters, their regulatory factors, physiological roles, and their roles in drug's liver disposition and DILI are reviewed.

Natural products as multidrug resistance modulators in cancer

Cancer is a prominent cause of death globally. Currently, many drugs that are in clinical practice are having a high prevalence of side effect and multidrug resistance. Risk of tumors acquiring resistance to chemotherapy (multidrug resistance) remains a significant hurdle to the successful treatment of various types of cancer. Membrane-embedded drug transporters, generally overexpressed in cancer, are the leading cause among multiple mechanisms of multidrug resistance (MDR). P-glycoprotein (P-gp) also MDR1/ABCB1, multidrug resistance associated protein 1 (MRP1/ABCC1), MRP2 and breast cancer resistance protein (BCRP/ABCG2) are considered to be a prime factor for induction of MDR. To date, several chemical substances have been tested in a number of clinical trials for their MDR modulatory activity which are not having devoid of any side effects that necessitates to find newer and safer way to tackle the current problem of multidrug resistance in cancer. The present study systematically discusses the various classes of natural products i.e flavonoids, alkaloids, terpenoids, coumarins (from plants, marine, and microorganisms) as potential MDR modulators and/or as a source of promising lead compounds. Recently a bisbenzyl isoquinoline alkaloid namely tetrandrine, isolated from Chinese herb Stephania tetrandra (Han-Fang-Chi) is in clinical trials for its MDR reversal activity.

What "The Cancer Genome Atlas" database tells us about the role of ATP-binding cassette (ABC) proteins in chemoresistance to anticancer drugs

Introduction: Chemotherapy remains the only option for advanced cancer patients when other alternatives are not feasible. Nevertheless, the success rate of this type of therapy is often low due to intrinsic or acquired mechanisms of chemoresistance. Among them, drug extrusion from cancer cells through ATP-binding cassette (ABC) proteins plays an important role. ABC pumps are primary active transporters involved in the barrier and secretory functions of many healthy cells. Areas covered: In this review, we have used The Cancer Genome Atlas (TCGA) database to explore the relationship between the expression of the major ABC proteins involved in cancer chemoresistance in the most common types of cancer, and the drugs used in the treatment of these tumors that are substrates of these pumps. Expert opinion: From unicellular organisms to humans, several ABC proteins play a major role in detoxification processes. Cancer cells exploit this ability to protect themselves from cytostatic drugs. Among the ABC pumps, MDR1, MRPs and BCRP are able to export many antitumor drugs and are expressed in several types of cancer, and further up-regulated during treatment. This event results in the enhanced ability of tumor cells to reduce intracellular drug concentrations and hence the pharmacological effect of chemotherapy.

Pharmacological Activation of PXR and CAR Downregulates Distinct Bile Acid-Metabolizing Intestinal Bacteria and Alters Bile Acid Homeostasis

The gut microbiome regulates important host metabolic pathways including xenobiotic metabolism and intermediary metabolism, such as the conversion of primary bile acids (BAs) into secondary BAs. The nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known regulators for xenobiotic biotransformation in liver. However, little is known regarding the potential effects of PXR and CAR on the composition and function of the gut microbiome. To test our hypothesis that activation of PXR and CAR regulates gut microbiota and secondary BA synthesis, 9-week-old male conventional and germ-free mice were orally gavaged with corn oil, PXR agonist PCN (75 mg/kg), or CAR agonist TCPOBOP (3 mg/kg) once daily for 4 days. PCN and TCPOBOP decreased two taxa in the Bifidobacterium genus, which corresponded with decreased gene abundance of the BA-deconjugating enzyme bile salt hydrolase. In liver and small intestinal content of germ-free mice, there was a TCPOBOP-mediated increase in total, primary, and conjugated BAs corresponding with increased Cyp7a1 mRNA. Bifidobacterium, Dorea, Peptociccaceae, Anaeroplasma, and Ruminococcus positively correlated with T-UDCA in LIC, but negatively correlated with T-CDCA in serum. In conclusion, PXR and CAR activation downregulates BA-metabolizing bacteria in the intestine and modulates BA homeostasis in a gut microbiota-dependent manner.

Heme oxygenase-1 induction by hemin prevents oxidative stress-induced acute cholestasis in the rat

We previously demonstrated in in vitro and ex vivo models that physiological concentrations of unconjugated bilirubin (BR) prevent oxidative stress (OS)-induced hepatocanalicular dysfunction and cholestasis. Here, we aimed to ascertain, in the whole rat, whether a similar cholestatic OS injury can be counteracted by heme oxygenase-1 (HO-1) induction that consequently elevates endogenous BR levels. This was achieved through the administration of hemin, an inducer of HO-1, the rate-limiting step in BR generation. We found that BR peaked between 6 and 8 h after hemin administration. During this time period, HO-1 induction fully prevented the pro-oxidant tert-butylhydroperoxide (tBuOOH)-induced drop in bile flow, and in the biliary excretion of bile salts and glutathione, the two main driving forces of bile flow; this was associated with preservation of the membrane localization of their respective canalicular transporters, bile salt export pump (Bsep) and multidrug resistance-associated protein 2 (Mrp2), which are otherwise endocytosed by OS. HO-1 induction counteracted the oxidation of intracellular proteins and membrane lipids induced by tBuOOH, and fully prevented the increase in the oxidized-to-total glutathione (GSHt) ratio, a sensitive parameter of hepatocellular OS. Compensatory elevations of the activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were also prevented. We conclude that in vivo HO-1 induction protects the liver from acute oxidative injury, thus preventing consequent cholestasis. This reveals an important role for the induction of HO-1 and the consequently elevated levels of BR in preserving biliary secretory function under OS conditions, thus representing a novel therapeutic tool to limit the cholestatic injury that bears an oxidative background.

ABC Family Transporters

The transport of specific molecules across lipid membranes is an essential function of all living organisms. The processes are usually mediated by specific transporters. One of the largest transporter families is the ATP-binding cassette (ABC) family. More than 40 ABC transporters have been identified in human, which are divided into 7 subfamilies (ABCA to ABCG) based on their gene structure, amino acid sequence, domain organization, and phylogenetic analysis. Of them, at least 11 ABC transporters including P-glycoprotein (P-GP/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2) are involved in multidrug resistance (MDR) development. These ABC transporters are expressed in various tissues such as the liver, intestine, kidney, and brain, playing important roles in absorption, distribution, and excretion of drugs. Some ABC transporters are also involved in diverse cellular processes such as maintenance of osmotic homeostasis, antigen processing, cell division, immunity, cholesterol, and lipid trafficking. Several human diseases such as cystic fibrosis, sitosterolemia, Tangier disease, intrahepatic cholestasis, and retinal degeneration are associated with mutations in corresponding transporters. This chapter will describe function and expression of several ABC transporters (such as P-GP, BCRP, and MRPs), their substrates and inhibitors, as well as their clinical significance.

Transporter and Lysosomal Mediated (Multi)drug Resistance to Tyrosine Kinase Inhibitors and Potential Strategies to Overcome Resistance

Tyrosine kinase inhibitors are a class of chemotherapeutic drugs that target specific protein kinases. These tyrosine kinase inhibitors constitute a relatively new class of drugs which target for instance Bcr-Abl, Epidermal Growth Factor Receptor (EGFR) and Vascular Endothelial Growth Factor Receptor (VEGFR). Despite some initial successes, the overall therapeutic benefit of tyrosine kinase inhibitors in the clinic has been mixed. Next to mutations in the target, multidrug resistance is a major obstacle for which still no clinically effective strategies have been developed. Major mechanisms of multidrug resistance are mediated by drug efflux transporter proteins. Moreover, there is accumulating evidence that multidrug resistance can also be caused by lysosomal sequestration of drugs, effectively trapping tyrosine kinase inhibitors and preventing them from reaching their target. Lysosomal drug sequestration seems to work together with ATP-binding cassette transporters, increasing the capacity of lysosomes to mediate sequestration. Both membrane efflux transporter proteins and lysosomes present potential therapeutic targets that could reverse multidrug resistance and increase drug efficacy in combination therapy. This review describes both mechanisms and discusses a number of proposed strategies to circumvent or reverse tyrosine kinase inhibitor-related multidrug resistance.

Pesticide toxicity: a mechanistic approach

Pesticides are known for their high persistence and pervasiveness in the environment, and along with products of their biotransformation, they may remain in and interact with the environment and living organisms in multiple ways, according to their nature and chemical structure, dose and targets. In this review, the classifications of pesticides based on their nature, use, physical state, pathophysiological effects, and sources are discussed. The effects of these xenobiotics on the environment, their biotransformation in terms of bioaccumulation are highlighted with special focus on the molecular mechanisms deciphered to date. Basing on targeted organisms, most pesticides are classified as herbicides, fungicides, and insecticides. Herbicides are known as growth regulators, seedling growth inhibitors, photosynthesis inhibitors, inhibitors of amino acid and lipid biosynthesis, cell membrane disrupters, and pigment biosynthesis inhibitors, whereas fungicides include inhibitors of ergosterol biosynthesis, protein biosynthesis, and mitochondrial respiration. Insecticides mainly affect nerves and muscle, growth and development, and energy production. Studying the impact of pesticides and other related chemicals is of great interest to animal and human health risk assessment processes since potentially everyone can be exposed to these compounds which may cause many diseases, including metabolic syndrome, malnutrition, atherosclerosis, inflammation, pathogen invasion, nerve injury, and susceptibility to infectious diseases. Future studies should be directed to investigate influence of long term effects of low pesticide doses and to minimize or eliminate influence of pesticides on non-target living organisms, produce more specific pesticides and using modern technologies to decrease contamination of food and other goods by pesticides.

Hepatoprotective effect of ginsenoside Rg1 from Panax ginseng on carbon tetrachloride-induced acute liver injury by activating Nrf2 signaling pathway in mice

Oxidative stress and inflammatory response are well known to be involved in the pathogenesis of acute liver injury. This study was performed to examine the hepatoprotective effect of ginsenoside Rg1 (Rg1) against CCl4 -induced acute liver injury, and further to elucidate the involvement of Nrf2 signaling pathway in vivo and in vitro. Mice were orally administered Rg1 (15, 30, and 60 mg/kg) or sulforaphane (SFN) once daily for 1 week prior to 750 μL/kg CCl4 injection. The results showed that Rg1 markedly altered relative liver weights, promoted liver repair, increased the serum level of TP and decreased the serum levels of ALT, AST and ALP. Hepatic oxidative stress was inhibited by Rg1, as evidenced by the decrease in MDA, and increases in GSH, SOD, and CAT in the liver. Further research demonstrated that Rg1 suppressed liver inflammation response through repressing the expression levels of inflammation-related genes including TNF-α, IL-1β, IL-6, COX-2, and iNOS. In addition, Rg1 enhanced antioxidative stress and liver detoxification abilities by up-regulating Nrf2 and its target-genes such as GCLC, GCLM, HO-1, NQO1, Besp, Mrp2, Mrp3, Mrp4, and down-regulating Cyp2e1. However, the changes in Nrf2 target-genes, as well as ameliorative liver histology induced by Rg1 were abrogated by Nrf2 antagonist all-transretinoic acid in vivo and Nrf2 siRNA in vitro. Overall, the findings indicated that Rg1 might be an effective approach for the prevention against acute liver injury by activating Nrf2 signaling pathway.

Conjugated hyperbilirubinemia after surgery. A diagnosis of Dubin-Johnson syndrome confirmed by genetic testing

Dubin-Johnson syndrome is a rare benign inherited disorder, caused by mutations in ABCC2 gen, and it is characterized by predominantly conjugated hyperbilirubinemia that can be increased by intercurrent infectious illnesses or surgical procedures. We report the case of a 10 year-old patient who showed, after a surgical procedure for peritonitis due to appendicitis, jaundice and predominantly conjugated hyperbilirubinemia, and he was diagnosed with Dubin-Johnson syndrome by genetic testing.

Clinical, Pathologic, and Genetic Features of Neonatal Dubin-Johnson Syndrome: A Multicenter Study in Japan

OBJECTIVE

To clarify the clinical, pathologic, and genetic features of neonatal Dubin-Johnson syndrome.

STUDY DESIGN

Ten patients with neonatal Dubin-Johnson syndrome were recruited from 6 pediatric centers in Japan between September 2013 and October 2016. Clinical and laboratory course, macroscopic and microscopic liver findings, and molecular genetic findings concerning ATP-binding cassette subfamily C member 2 (ABCC2) were retrospectively and prospectively examined.

RESULTS

All neonates exhibited cholestasis, evident as prolonged jaundice with or without acholic stools and elevations of serum direct bilirubin as well as γ-glutamyltransferase or total bile acids. Only 38% (3 of 8) of patients who underwent liver biopsy showed a grossly black liver or melanin-like pigment deposits in hepatocytes; their biopsies were performed in early infancy. Immunohistochemically, all liver specimens showed no expression of multidrug resistance-associated protein 2 but increased expression of the bile salt export pump protein. Homozygous or compound heterozygous pathogenic variants of ABCC2 were identified in all patients, representing 11 distinct pathogenic variants including 2 not previously reported.

CONCLUSIONS

Immunohistochemical staining of the liver for multidrug resistance-associated protein 2 and molecular genetic analysis of ABCC2 are crucial for accurate diagnosis of neonatal Dubin-Johnson syndrome.

A Clinical Quantitative Evaluation of Hepatobiliary Transport of [11C]Dehydropravastatin in Humans Using Positron Emission Tomography

Various positron emission tomography (PET) probes have been developed to assess in vivo activities in humans of drug transporters, which aid in the prediction of pharmacokinetic properties of drugs and the impact of drug-drug interactions. We developed a new PET probe, sodium (3R, 5R)-3, 5-dihydroxy-7-((1S, 2S, 6S, 8S)-6-hydroxy-2-methyl-8- ((1-[11C]-(E)-2-methyl-but-2-enoyl) oxy) -1, 2, 6, 7, 8, 8a-hexahydronaphthalen-1-yl) heptanoate ([11C]DPV), and demonstrated its usefulness for the quantitative investigation of Oatps (gene symbol SLCO) and Mrp2 (gene symbol ABCC2) in rats. To further analyze the species differences and verify the pharmacokinetic parameters in humans, serial PET scanning of the abdominal region with [11C]DPV was performed in six healthy volunteers with and without an OATP1Bs and MRP2 inhibitor, rifampicin (600 mg, oral), in a crossover fashion. After intravenous injection, [11C]DPV rapidly distributed to the liver and kidney followed by secretion into the bile and urine. Rifampicin significantly reduced the liver distribution of [11C]DPV 3-fold, resulting in a 7.5-fold reduced amount of excretion into the bile and the delayed elimination of [11C]DPV from the blood circulation. The hepatic uptake clearance (CLuptake, liver) and canalicular efflux clearance (CLint, bile) of [11C]DPV (544 ± 204 and 10.2 ± 3.5 µl/min per gram liver, respectively) in humans were lower than the previously reported corresponding parameters in rats (1800 and 298 µl/min per gram liver, respectively) (Shingaki et al., 2013). Furthermore, rifampicin treatment significantly reduced CLuptake, liver and CLint, bile by 58% and 44%, respectively. These results suggest that PET imaging with [11C]DPV is an effective tool for quantitatively characterizing the OATP1Bs and MRP2 functions in the human hepatobiliary transport system.

Beyond Competitive Inhibition: Regulation of ABC Transporters by Kinases and Protein-Protein Interactions as Potential Mechanisms of Drug-Drug Interactions

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters mediating the extrusion of an array of substrates ranging from amino acids and lipids to xenobiotics, and many therapeutic compounds, including anticancer drugs. The ABC transporters are also recognized as important contributors to pharmacokinetics, especially in drug-drug interactions and adverse drug effects. Drugs and xenobiotics, as well as pathologic conditions, can influence the transcription of ABC transporters, or modify their activity or intracellular localization. Kinases can affect the aforementioned processes for ABC transporters as do protein interactions. In this review, we focus on the ABC transporters ABCB1, ABCB11, ABCC1, ABCC4, and ABCG2 and illustrate how kinases and protein-protein interactions affect these transporters. The clinical relevance of these factors is currently unknown; however, these examples suggest that our understanding of drug-drug interactions will benefit from further knowledge of how kinases and protein-protein interactions affect ABC transporters.

A Critical Evaluation of Liver Pathology in Humans with Danon Disease and Experimental Correlates in a Rat Model of LAMP-2 Deficiency

Danon disease is a genetic deficiency in lysosome-associated membrane protein 2 (LAMP-2), a highly glycosylated constituent of the lysosomal membrane and characterized by a cardiomyopathy, skeletal muscle myopathy, and cognitive impairment. Patients, however, often manifest hepatic abnormalities, but liver function has not been well evaluated and the syndrome is relatively uncommon. Hence, we have taken advantage of a rat that has been deleted of LAMP-2 to study the relative role of LAMP-2 on liver function. Interestingly, rats deficient in LAMP-2 develop a striking increase in serum alkaline phosphatase (ALP) and a decrease in bile flow compared with wild-type littermates. Importantly and by ultrastructural analysis, deficient rats manifest dilated canaliculi that lack microvilli with evidence of bile-containing bodies. Moreover, following bile duct ligation, LAMP-2-deficient rats develop rapid and severe evidence of advanced cholestasis, with an increase in serum bilirubin, as early as 6 h later. In wild-type control rats, multidrug resistance-associated protein 2 (Mrp2) normally concentrates at the bile canalicular membranes to secrete conjugated bilirubin into bile. However, in LAMP-2^y/- rats, Mrp2 was detected in hepatocytes compared with other canalicular proteins including P-glycoproteins, dipeptidyl peptidase IV (CD26), and aminopeptidase (CD13). Our data further suggest that LAMP-2 interacts with the membrane cytoskeletal proteins radixin and F-actin in determining the localization of integral membrane proteins.

Usefulness of the MRP2 promoter to overcome the chemoresistance of gastrointestinal and liver tumors by enhancing the expression of the drug transporter OATP1B1

Tumor response to chemotherapy is often limited by drug export through ABC proteins. To overcome this problem, here we have investigated the usefulness of inducing the expression of the multidrug uptake transporter OATP1B1 under the control of the MRP2 promoter (MRP2pr). Human hepatoma cells (Alexander) were transfected with MRP2pr fragments of different length fused to the firefly luciferase ORF in order to select the shortest fragment with the highest response to dexamethasone, which was subsequently used to generate the chimeric construct MRP2pr-OATP1B1-V5. Hepatoma cells transduced with MRP2pr-OATP1B1-V5 resulted in dexamethasone-sensitive inducible OATP1B1 expression and enhanced selective antitumor response to OATP1B1 substrates (paclitaxel, Bamet-R2 and Bamet-UD2). In human colon cancer cells LS174T/R, used as a model of endogenous chemoresistance due to MRP2 overexpression, MRP2pr-OATP1B1 induced OATP1B1 expression together with chemosensitivity to OATP1B1 substrates. In nude mice, xenografted tumors formed by LS174T/R cells transduced with MRP2pr-OATP1B1 plus treatment with dexamethasone were markedly sensitized to Bamet-UD2. In conclusion, the induced expression of anticancer drug uptake transporters, under the control of promoters of ABC proteins involved in chemoresistance, constitutes an interesting approach to overcome the poor response of cancer to chemotherapy due to reduced drug uptake and/or enhanced drug export.

Cell Migration Related to MDR-Another Impediment to Effective Chemotherapy?

Multidrug resistance, mediated by members of the ATP-binding cassette (ABC) proteins superfamily, has become one of the biggest obstacles in conquering tumour progression. If the chemotherapy outcome is considered successful, when the primary tumour volume is decreased or completely abolished, modulation of ABC proteins activity is one of the best methods to overcome drug resistance. However, if a positive outcome is represented by no metastasis or, at least, elongation of remission-free time, then the positive effect of ABC proteins inhibition should be compared with the several side effects it causes, which may inflict cancer progression and decrease overall patient health. Clinical trials conducted thus far have shown that the tested ABC modulators add limited or no benefits to cancer patients, as some of them are merely toxic and others induce unwanted drug–drug interactions. Moreover, the inhibition of certain ABC members has been recently indicated as potentially responsible for increased fibroblasts migration. A better understanding of the complex role of ABC proteins in relation to cancer progression may offer novel strategies in cancer therapy.

Chorioamnionitis Induces a Specific Signature of Placental ABC Transporters Associated with an Increase of miR-331-5p in the Human Preterm Placenta

Background/Aims

The ATP-binding cassette (ABC) transporters mediate drug biodisposition and immunological responses in the placental barrier. In vitro infective challenges alter expression of specific placental ABC transporters. We hypothesized that chorioamnionitis induces a distinct pattern of ABC transporter expression.

Methods

Gene expression of 50 ABC transporters was assessed using TaqMan® Human ABC Transporter Array, in preterm human placentas without (PTD; n=6) or with histological chorioamnionitis (PTDC; n=6). Validation was performed using qPCR, immunohistochemistry and Western blot. MicroRNAs known to regulate P-glycoprotein (P-gp) were examined by qPCR.

Results

Up-regulation of ABCB9, ABCC2 and ABCF2 mRNA was detected in chorioamnionitis (p<0.05), whereas placental ABCB1 (P-gp; p=0.051) and ABCG2 (breast cancer resistance protein-BCRP) mRNA levels (p=0.055) approached near significant up-regulation. In most cases, the magnitude of the effect significantly correlated to the severity of inflammation. Upon validation, increased placental ABCB1 and ABCG2 mRNA levels (p<0.05) were observed. At the level of immunohistochemistry, while BCRP was increased (p<0.05), P-gp staining intensity was significantly decreased (p<0.05) in PTDC. miR-331-5p, involved in P-gp suppression, was upregulated in PTDC (p<0.01) and correlated to the grade of chorioamnionitis (p<0.01).

Conclusions

Alterations in the expression of ABC transporters will likely lead to modified transport of clinically relevant compounds at the inflamed placenta. A better understanding of the potential role of these transporters in the events surrounding PTD may also enable new strategies to be developed for prevention and treatment of PTD.

Metabolism of Glutathione S-Conjugates: Multiple Pathways

Many potentially toxic electrophilic xenobiotics and some endogenous compounds are detoxified by conversion to the corresponding glutathione S-conjugate, which is metabolized to the N-acetylcysteine S-conjugate (mercapturate) and excreted. Some mercapturate pathway components, however, are toxic. Bioactivation (toxification) may occur when the glutathione S-conjugate (or mercapturate) is converted to a cysteine S-conjugate that undergoes a β-lyase reaction. If the sulfhydryl-containing fragment produced in this reaction is reactive, toxicity may ensue. Some drugs and halogenated workplace/environmental contaminants are bioactivated by this mechanism. On the other hand, cysteine S-conjugate β-lyases occur in nature as a means of generating some biologically useful sulfhydryl-containing compounds.

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.

In Vitro Transport Activity and Trafficking of MRP2/ABCC2 Polymorphic Variants

PURPOSE

Multidrug resistance-associated protein 2 (MRP2/ABCC2) is an efflux pump that removes drugs and chemicals from cells. We sought to characterize the expression, trafficking and in vitro activity of seven single nucleotide polymorphisms (SNPs) in the ABCC2 gene.

METHODS

ABCC2 SNPs were generated using site-directed mutagenesis and stably expressed in Flp-In HEK293 cells, which allows targeted insertion of transgenes within the genome. Total and cell surface expression of MRP2 as well as accumulation of substrates (calcein AM and 5(6)-carboxy-2',7'-dichlorofluorescein diacetate, CDCF) were quantified in cells or inverted membrane vesicles expressing wild-type (WT) or variant forms.

RESULTS

The cell surface expression of the C-24T-, G1249A-, G3542T-, T3563A-, C3972T- and G4544A-MRP2 variants was similar to WT-MRP2. While expression was similar, transport of calcein AM was enhanced in cells expressing the G3542T-, T3563A-, C3972T-, and G4544A-MRP2 variants. By comparison, cells expressing the C2366T-MRP2 variant had 40-50% lower surface expression, which increased the accumulation of calcein AM up to 3-fold. Accumulation of CDCF in inverted membrane vesicles expressing the C2366T-MRP2 variant was also reduced by 50%. In addition, the G1249A-MRP2 variant had decreased transport of CDCF.

CONCLUSIONS

Taken together, these data demonstrate that genetic variability in the ABCC2 gene influences the in vitro expression, trafficking, and transport activity of MRP2.

Genetic determinants of inherited susceptibility to hypercholesterolemia - a comprehensive literature review

Hypercholesterolemia is a strong determinant of mortality and morbidity associated with cardiovascular diseases and a major contributor to the global disease burden. Mutations in four genes (LDLR, APOB, PCSK9 and LDLRAP1) account for the majority of cases with familial hypercholesterolemia. However, a substantial proportion of adults with hypercholesterolemia do not have a mutation in any of these four genes. This indicates the probability of having other genes with a causative or contributory role in the pathogenesis of hypercholesterolemia and suggests a polygenic inheritance of this condition. Here in, we review the recent evidence of association of the genetic variants with hypercholesterolemia and the three lipid traits; total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C), their biological pathways and the associated pathogenetic mechanisms. Nearly 80 genes involved in lipid metabolism (encoding structural components of lipoproteins, lipoprotein receptors and related proteins, enzymes, lipid transporters, lipid transfer proteins, and activators or inhibitors of protein function and gene transcription) with single nucleotide variants (SNVs) that are recognized to be associated with hypercholesterolemia and serum lipid traits in genome-wide association studies and candidate gene studies were identified. In addition, genome-wide association studies in different populations have identified SNVs associated with TC, HDL-C and LDL-C in nearly 120 genes within or in the vicinity of the genes that are not known to be involved in lipid metabolism. Over 90% of the SNVs in both these groups are located outside the coding regions of the genes. These findings indicates that there might be a considerable number of unrecognized processes and mechanisms of lipid homeostasis, which when disrupted, would lead to hypercholesterolemia. Knowledge of these molecular pathways will enable the discovery of novel treatment and preventive methods as well as identify the biochemical and molecular markers for the risk prediction and early detection of this common, yet potentially debilitating condition.

Coproporphyrin-I: A Fluorescent, Endogenous Optimal Probe Substrate for ABCC2 (MRP2) Suitable for Vesicle-Based MRP2 Inhibition Assay

Inside-out-oriented membrane vesicles are useful tools to investigate whether a compound can be an inhibitor of efflux transporters such as multidrug resistance-associated protein 2 (MRP2). However, because of technical limitations of substrate diffusion and low dynamic uptake windows for interacting drugs used in the clinic, estradiol-17β-glucuronide (E17βG) remains the probe substrate that is frequently used in MRP2 inhibition assays. Here we recapitulated the sigmoidal kinetics of MRP2-mediated transport of E17βG, with apparent Michaelis-Menten constant (Km) and Vmax values of 170 ±17 µM and 1447 ± 137 pmol/mg protein/min, respectively. The Hill coefficient (2.05 ± 0.1) suggests multiple substrate binding sites for E17βG transport with cooperative interactions. Using E17βG as a probe substrate, 51 of 97 compounds tested (53%) showed up to 6-fold stimulatory effects. Here, we demonstrate for the first time that coproporphyrin-I (CP-I) is a MRP2 substrate in membrane vesicles. The uptake of CP-I followed a hyperbolic relationship, adequately described by the standard Michaelis-Menten equation (apparent Km and Vmax values were 7.7 ± 0.7 µM and 48 ± 11 pmol/mg protein/min, respectively), suggesting the involvement of a single binding site. Of the 47 compounds tested, 30 compounds were inhibitors of human MRP2 and 8 compounds (17%) stimulated MRP2-mediated CP-I transport. The stimulators were found to share the basic backbone structure of the physiologic steroids, which suggests a potential in vivo relevance of in vitro stimulation of MRP2 transport. We concluded that CP-I could be an alternative in vitro probe substrate replacing E17βG for appreciating MRP2 interactions while minimizing potential false-negative results for MRP2 inhibition due to stimulatory effects.

Bile acids and gestation

There are numerous profound maternal physiological changes that occur from conception onwards and adapt throughout gestation in order to support a healthy pregnancy. By the time of late gestation, when circulating pregnancy hormones are at their highest concentrations, maternal adaptations include relative hyperlipidemia, hypercholanemia and insulin resistance. Bile acids have now been established as key regulators of metabolism, and their role in gestational changes in metabolism is becoming apparent. Bile acid homeostasis is tightly regulated by the nuclear receptor FXR, which has been shown to have reduced activity during pregnancy. This review focuses on the gestational alterations in bile acid homeostasis that occur in normal pregnancy, which in some women can become pathological, leading to the development of intrahepatic cholestasis of pregnancy. As well as their important role in maternal metabolic health, we will review bile acid metabolism in the feto-placental unit.

Diagnosis and evaluation of hyperbilirubinemia

PURPOSE OF REVIEW

Jaundice, the physical finding associated with hyperbilirubinemia, results when the liver is unable to properly metabolize or excrete bilirubin. The purpose of this review is to examine some of the most common causes of jaundice in adults, provide insight into the diagnostic evaluation of jaundice, and review information on the outcomes of patients with jaundice.

RECENT FINDINGS

An elevated level of bilirubin almost always indicates the presence of an underlying disease state. The best approach to evaluating a patient with jaundice is to start with a careful history and physical examination, followed by imaging assessment of the biliary tree and liver. There are algorithm models that incorporate bilirubin levels in their predictor models for outcomes in patients with chronic liver disease (i.e., the model for end-stage liver disease). However, there are few studies that have examined the outcomes of patients with jaundice.

SUMMARY

Evaluation of patients with jaundice starts with a careful history and physical examination, followed by directed imaging of the biliary tree and liver. Although jaundice is generally believed to be a serious medical condition, there is little literature that addresses outcomes in patients with jaundice.

Vps33b is crucial for structural and functional hepatocyte polarity

BACKGROUND & AIMS

In the normal liver, hepatocytes form a uniquely polarised cell layer that enables movement of solutes from sinusoidal blood to canalicular bile. Whilst several cholestatic liver diseases with defects of hepatocyte polarity have been identified, the molecular mechanisms of pathogenesis are not well defined. One example is arthrogryposis, renal dysfunction and cholestasis syndrome, which in most patients is caused by VPS33B mutations. VPS33B is a protein involved in membrane trafficking that interacts with RAB11A at recycling endosomes. To understand the pathways that regulate hepatocyte polarity better, we investigated VPS33B deficiency using a novel mouse model with a liver-specific Vps33b deletion.

METHODS

To assess functional polarity, plasma and bile samples were collected from Vps33b liver knockout (Vps33bfl/fl-AlfpCre) and control (Vps33bfl/fl) mice; bile components or injected substrates were quantitated by mass spectrometry or fluorometry. For structural analysis, livers underwent light and transmission electron microscopy. Apical membrane and tight junction protein localisation was assessed by immunostaining. Adeno-associated virus vectors were used for in vivo gene rescue experiments.

RESULTS

Like patients, Vps33bfl/fl-AlfpCre mice showed mislocalisation of ATP-binding cassette proteins that are specifically trafficked to the apical membrane via Rab11a-positive recycling endosomes. This was associated with retention of bile components in blood. Loss of functional tight junction integrity and depletion of apical microvilli were seen in knockout animals. Gene transfer partially rescued these defects.

CONCLUSIONS

Vps33b has a key role in establishing structural and functional aspects of hepatocyte polarity and may be a target for gene replacement therapy.

LAY SUMMARY

Hepatocytes are liver cells with tops and bottoms; that is, they are polarised. At their bottoms they absorb substances from blood. They then, at their tops, secrete these substances and their metabolites into bile. When polarity is lost, this directional flow of substances from blood to bile is disrupted and liver disease follows. In this study, using a new mouse model with a liver-specific mutation of Vps33b, the mouse version of a gene that is mutated in most patients with arthrogryposis, renal dysfunction and cholestasis (ARC) syndrome, we investigated how the Vps33b gene product contributes to establishing hepatocyte polarity. We identified in these mice abnormalities similar to those in children with ARC syndrome. Gene transfer could partly reverse the mouse abnormalities. Our work contributes to the understanding of VPS33B disease and hepatocyte polarity in general, and may point towards gene transfer mediated treatment of ARC liver disease.

Effects of Catechins and Their Related Compounds on Cellular Accumulation and Efflux Transport of Mitoxantrone in Caco-2 Cell Monolayers

The ability of catechins and their related compounds to inhibit breast cancer resistance protein (BCRP) function in Caco-2 cell monolayers was investigated with mitoxantrone as a BCRP substrate. The gallate or pyrogallol moiety on the catechin structure seemed to promote increased cellular accumulation and inhibit efflux transport of mitoxantrone. The ability of gallate catechins such as (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) to increase cellular accumulation and inhibit efflux transport of mitoxantrone was greater than that of nongallate catechins. Gallic acid octyl ester (GAO) also increased intracellular mitoxantrone accumulation. Experiments using GAO derivatives indicated that the gallate moiety required the presence of a long carbon chain for BCRP inhibition. Cellular accumulation and reduced efflux transport of mitoxantrone were greater with epigallocatechin 3-(3″-O-butyl) gallate than with EGCG. EGCG inhibition of BCRP seemed to be restricted by hydrophobicity. The co-administration of catechins, particularly EGCG and related compounds, with greater hydrophobicity may increase the therapeutic activities of BCRP substrates such as mitoxantrone.

Pharmacokinetics of Boldine in Control and Mrp2-Deficient Rats

The aim of the present study was to describe the currently poorly understood pharmacokinetics (PK) of boldine in control rats (LW, Lewis rats), and Mrp2 transporter-deficient rats (TR-). Animals from the LW and TR- groups underwent a bolus dose study with 10 mg/kg of boldine applied either orally or intravenously in order to evaluate the major PK parameters. The TR- rats demonstrated significantly reduced total clearance with prolonged biological half-life (LW 12±4.6 versus TR- 20±4.4 min), decreased volume of distribution (LW 3.2±0.4 l/kg versus TR- 2.4±0.4 l/kg) and reduced bioavailability (LW 7 % versus TR- 4.5 %). Another set of LW and TR- rats were used for a clearance study with continuous intravenous administration of boldine. The LW rats showed that biliary and renal clearance formed less than 2 % of the total clearance of boldine. The treatment of samples with β glucuronidase showed at least a 38 % contribution of conjugation reactions to the overall clearance of boldine. The TR- rats demonstrated reduced biliary clearance of boldine and its conjugates, which was partly compensated by their increased renal clearance. In conclusion, this study presents the PK parameters of boldine and shows the importance of the Mrp2 transporter and conjugation reactions in the elimination of the compound.