Expression and function of renal and hepatic organic anion transporters in extrahepatic cholestasis

Natural sporopollenin microcapsules: biological evaluation and application in regulating hepatic toxicity of diclofenac sodium in vivo

Diclofenac sodium (DIC) is a pain reliever and anti-nociceptive medication. Significant limitations of DIC treatment stem from its adverse effects. This study investigates the feasibility of using natural Lycopodium clavatum sporopollenin (LCS) microcapsules loaded with DIC to mitigate the hepatotoxicity associated with DIC treatment. In addition, LCS microcapsules were tracked in the blood, stomach, small intestine, and feces of rats to demonstrate their morphological integrity and uptake behavior. Four groups (6 per group) of adult male albino rats were administered normal saline (control), empty LCS (30 mg kg-1), plain DIC (10 mg kg-1), and DIC-loaded LCS (40 mg kg-1) orally for seven consecutive days. The first comprehensive histological examination of the rat stomach demonstrated the robustness and bioadhesion ability of LCS under severe conditions. The findings suggested that these versatile microcapsules are unlikely to be digested in the gastrointestinal tract (GIT). The administration of DIC-loaded LCS was found to play a potential protective role in regulating DIC-induced substantially increased serum levels of transaminases, alkaline phosphatase, total bilirubin, and pro-inflammatory cytokines. In addition, DIC-loaded LCS restored the antioxidant enzymes, DNA damage, and liver histological architecture abnormalities caused by DIC. Microencapsulation of DIC into pollen-derived biomaterials could be employed as an efficient platform with enough safety coverage on rat liver, pending further clinical studies.

Pathophysiology of sepsis‐induced cholestasis: A review

Sepsis is a critical condition resulting from the excessive activation of the inflammatory/immune system in response to an infection, with high mortality if treatment is not administered promptly. One of the many possible complications of sepsis is liver dysfunction with consequent cholestasis. The aim of this paper is to review the main mechanisms involved in the development of cholestasis in sepsis. Cholestasis in a septic patient must raise the suspicion that it is the consequence of the septic condition and limit the laborious attempts of finding a hepatic or biliary disease. Prompt antibiotic administration when sepsis is suspected is essential and may improve liver enzymes. Cholestasis is a syndrome with a variety of etiologies, among which sepsis is frequently overlooked, despite a number of studies and case reports in the literature demonstrating not only the association between sepsis and cholestasis but also the role of cholestasis as a prognostic factor for sepsis‐induced death.

Molecular Properties of Drugs Handled by Kidney OATs and Liver OATPs Revealed by Chemoinformatics and Machine Learning: Implications for Kidney and Liver Disease

In patients with liver or kidney disease, it is especially important to consider the routes of metabolism and elimination of small-molecule pharmaceuticals. Once in the blood, numerous drugs are taken up by the liver for metabolism and/or biliary elimination, or by the kidney for renal elimination. Many common drugs are organic anions. The major liver uptake transporters for organic anion drugs are organic anion transporter polypeptides (OATP1B1 or SLCO1B1; OATP1B3 or SLCO1B3), whereas in the kidney they are organic anion transporters (OAT1 or SLC22A6; OAT3 or SLC22A8). Since these particular OATPs are overwhelmingly found in the liver but not the kidney, and these OATs are overwhelmingly found in the kidney but not liver, it is possible to use chemoinformatics, machine learning (ML) and deep learning to analyze liver OATP-transported drugs versus kidney OAT-transported drugs. Our analysis of >30 quantitative physicochemical properties of OATP- and OAT-interacting drugs revealed eight properties that in combination, indicate a high propensity for interaction with "liver" transporters versus "kidney" ones based on machine learning (e.g., random forest, k-nearest neighbors) and deep-learning classification algorithms. Liver OATPs preferred drugs with greater hydrophobicity, higher complexity, and more ringed structures whereas kidney OATs preferred more polar drugs with more carboxyl groups. The results provide a strong molecular basis for tissue-specific targeting strategies, understanding drug-drug interactions as well as drug-metabolite interactions, and suggest a strategy for how drugs with comparable efficacy might be chosen in chronic liver or kidney disease (CKD) to minimize toxicity.

Inflammation Induces Changes in the Functional Expression of P-gp, BCRP, and MRP2: An Overview of Different Models and Consequences for Drug Disposition

The ATP-binding cassette (ABC) transporters play a key role in drug pharmacokinetics. These membrane transporters expressed within physiological barriers can be a source of pharmacokinetic variability. Changes in ABC transporter expression and functionality may consequently affect the disposition of substrate drugs, resulting in different drug exposure. Inflammation, present in several acute and chronic diseases, has been identified as a source of modulation in drug transporter expression leading to variability in drug response. Its regulation may be particularly dangerous for drugs with a narrow therapeutic index. In this context, numerous in vitro and in vivo models have shown up- or downregulation in the expression and functionality of ABC transporters under inflammatory conditions. Nevertheless, the existence of contradictory data and the lack of standardization for the models used have led to a less conclusive interpretation of these data.

The pathogenesis of renal injury in obstructive jaundice: A review of underlying mechanisms, inducible agents and therapeutic strategies

Kidney injury is one of the main complications of obstructive jaundice (OJ) and its pathogenesis has not been clarified. As an independent risk factor for OJ associated with significant morbidity and mortality, it can be mainly divided into two types of morphological injury and functional injury. We called these dysfunctions caused by OJ-induced kidney injury as OJKI. However, the etiology of OJKI is still not fully clear, and research studies on how OJKI becomes a facilitated factor of OJ are limited. This article reviews the underlying pathological mechanism from five aspects, including metabolisms of bile acids, hemodynamic disturbances, oxidative stress, inflammation and the organic transporter system. Some nephrotoxic drugs and measures that can enhance or reduce the renal function with potential intervention in perioperative periods to alleviate the incidence of OJKI were also described. Furthermore, a more in-depth study on the pathogenesis of OJKI from multiple aspects for exploring more targeted treatment measures were further put forward, which may provide new methods for the prevention and treatment of clinical OJKI and improve the prognosis.

Distribution of the organic anion transporters Oat1 and Oat3 between renal membrane microdomains in obstructive jaundice

Relation between the renal function and the membrane environment where the organic anion transporters Oat1 and Oat3 are localized is scarce. The aim of this study was to examine the Oat1 and Oat3 distribution in different cellular fractions under physiological conditions as well as the effects of extrahepatic cholestasis on membrane distribution of both proteins. Besides, the potential role of jaundice serum on the Oat1 and Oat3 expression in suspensions of renal tubular cells was evaluated. Cellular and membrane fractions of renal cortex were obtained from control rats to evaluate Oat1 and Oat3 protein expressions. Other rats were subjected to bile duct ligation (BDL) or Sham operation to determine the membrane distribution of Oat1 and Oat3 between lipid raft domains (LRD) and non-LRD. Incubation of renal cortical cells with serum from Sham and BDL were also performed to study Oat1 and Oat3 protein expressions. In physiological conditions, Oat1 and Oat3 were concentrated in LRD. The pathology induced a shift of Oat1 from LRD to non-LRD, while Oat3 showed no changes in its distribution. In cells exposed to BDL serum, Oat1 protein expression in membranes significantly increased. For Oat3, no difference between groups was observed. The Oat1 redistribution to non-LRD in BDL could be favoring the increase in renal transport of organic anions previously observed. This change was specific to Oat1. The in vitro experiment allows to conclude that some component present in BDL serum is responsible for the alterations observed in Oat1 expression in cortical membranes.

Kolaviron Diminishes Diclofenac-Induced Liver and Kidney Toxicity in Wistar Rats Via Suppressing Inflammatory Events, Upregulating Antioxidant Defenses, and Improving Hematological Indices

Diclofenac (DF) is widely used in the treatment of pain and fever. Despite it therapeutic benefits, it triggered hepatorenal injury. Thus, the present study investigated the protective roles of kolaviron (KV) against DF-induced hepatic and renal toxicity in rats. The rats were allotted into groups: control group received propylene glycol and treatment groups received DF, which induced hepatorenal toxicity in rats and different doses of KV that prevented systemic toxicity of DF in rats. Twenty-four hours after the last treatment, all the rats were killed. Pro-inflammatory levels, markers of liver and kidney functions, oxidative stress, hematological indices, and histopathological alterations were evaluated. Diclofenac caused significant increase in the plasma levels of creatinine and urea and activities of liver enzymes, including bilirubin level, pro-inflammatory markers, and plasma prostaglandin E₂ (PGE₂). It also caused significant alteration in renal and hepatic PGE₂, antioxidants, lipid peroxidation (malondialdehyde), and hematological indices. These toxic effects were confirmed by histological studies and levels of inflammatory infiltration (myeloperoxidase). However, KV significantly prevented or reduced the adverse effects of DF in the plasma, liver, and kidney of the rats pretreated with KV before DF administration. This study showed the efficacy of KV as hepatic and renal protector in DF-induced hepatorenal toxicity through reduction of oxidative stress and suppression of inflammation.

HGF induces protective effects in α-naphthylisothiocyanate-induced intrahepatic cholestasis by counteracting oxidative stress

Cholestasis is a clinical syndrome common to a large number of hepatopathies, in which either bile production or its transit through the biliary tract is impaired due to functional or obstructive causes; the consequent intracellular retention of toxic biliary constituents generates parenchyma damage, largely via oxidative stress-mediated mechanisms. Hepatocyte growth factor (HGF) and its receptor c-Met represent one of the main systems for liver repair damage and defense against hepatotoxic factors, leading to an antioxidant and repair response. In this study, we evaluated the capability of HGF to counteract the damage caused by the model cholestatic agent, α-naphthyl isothiocyanate (ANIT). HGF had clear anti-cholestatic effects, as apparent from the improvement in both bile flow and liver function test. Histology examination revealed a significant reduction of injured areas. HGF also preserved the tight-junctional structure. These anticholestatic effects were associated with the induction of basolateral efflux ABC transporters, which facilitates extrusion of toxic biliary compounds and its further alternative depuration via urine. The biliary epithelium seems to have been also preserved, as suggested by normalization in serum GGT levels, CFTR expression and cholangyocyte primary cilium structure our results clearly show for the first time that HGF protects the liver from a cholestatic injury.

The SLC22 Transporter Family: A Paradigm for the Impact of Drug Transporters on Metabolic Pathways, Signaling, and Disease

The SLC22 transporter family consists of more than two dozen members, which are expressed in the kidney, the liver, and other tissues. Evolutionary analysis indicates that SLC22 transporters fall into at least six subfamilies: OAT (organic anion transporter), OAT-like, OAT-related, OCT (organic cation transporter), OCTN (organic cation/carnitine transporter), and OCT/OCTN-related. Some-including OAT1 [SLC22A6 or NKT (novel kidney transporter)] and OAT3 (SLC22A8), as well as OCT1 (SLC22A1) and OCT2 (SLC22A2)-are widely studied drug transporters. Nevertheless, analyses of knockout mice and other data indicate that SLC22 transporters regulate key metabolic pathways and levels of signaling molecules (e.g., gut microbiome products, bile acids, tricarboxylic acid cycle intermediates, dietary flavonoids and other nutrients, prostaglandins, vitamins, short-chain fatty acids, urate, and ergothioneine), as well as uremic toxins associated with chronic kidney disease. Certain SLC22 transporters-such as URAT1 (SLC22A12) and OCTN2 (SLC22A5)-are mutated in inherited metabolic diseases. A new systems biology view of transporters is emerging. As proposed in the remote sensing and signaling hypothesis, SLC22 transporters, together with other SLC and ABC transporters, have key roles in interorgan and interorganism small-molecule communication and, together with the neuroendocrine, growth factor-cytokine, and other homeostatic systems, regulate local and whole-body homeostasis.

Renal expression of organic anion transporters is modified after mercuric chloride exposure: Gender-related differences

Mercuric ions (Hg⁺²) gain access to proximal tubule cells primarily by the Organic Anion Transporter 1 (Oat1) and 3 (Oat3) in the basolateral plasma membrane. The removal process of Hg⁺² ions from cells into the lumen involves an efflux process mainly mediated by the Multidrug Resistance-Associated Protein 2 (Mrp2). The aim of this study was to compare the sex-related differences in the renal expression of Oat1, Oat3, and Mrp2 after mercuric chloride (HgCl₂) treatment and analyze their relevance in the mercury-induced nephrotoxicity. Control and Hg-treated male and female Wistar rats were used. Animals received a dose of HgCl₂ (4 mg/kg bw, ip) 18 h before the experiments. Tubular injury was assessed by histopathological studies. The renal expression of Oat1, Oat3, and Mrp2 was analyzed by Western Blotting. Mercury levels were determined in urine by cold vapour atomic absorption spectroscopy. HgCl₂ treatment increased the expression of renal Oat1 and Mrp2 in both sexes, being more evident in females than in males. The Oat3 renal expression only increased in female rats. The higher expressions of Oat1, Oat3, and Mrp2 could explain the higher renal excretion of mercury and consequently, the lesser renal tubular damage in female rats than in male rats.

Gender differences in mercury-induced hepatotoxicity: Potential mechanisms

The accumulation of mercury in the liver causes hepatotoxicity. The organic anion transporter 3 (Oat3) and the multidrug-resistance associated protein 2 (Mrp2) are involved in the hepatic excretion of toxins and drugs and in the hepatic handling of mercury. The aim of this work was to study if there are gender-related differences in mercuric chloride (HgCl₂)-induced hepatotoxicity in rats. Total mercury levels and protein expressions of Oat3 and Mrp2 in liver samples were also assessed to clarify the mechanisms underlying mercury-induced liver damage in male and female rats. Control and HgCl₂-treated male and female Wistar rats were used. Hepatotoxicity was evaluated by plasma activity of transaminases and alkaline phosphatase, as well as by histopathological analysis. Oat3 and Mrp2 expression was assessed by immunoblotting. Female rats displayed a higher HgCl₂-induced hepatotoxicity than male rats as demonstrated by the higher alterations in the plasma markers of liver damage and in the histopathology. The sex-related differences observed in the hepatic damage can be explained by the higher accumulation of mercury in liver from female rats. In this connection, after mercury treatment the expression of Mrp2 decreased in both sexes and the expression of Oat3 decreased only in males. The decreased in Oat3 abundance in the hepatocytes membranes in mercury-treated males would limit the uptake of mercuric ions into the liver protecting them from mercury hepatotoxicity.

Functional shift with maintained regenerative potential following portal vein ligation

Selective portal vein ligation (PVL) allows the two-stage surgical resection of primarily unresectable liver tumours by generating the atrophy and hypertrophy of portally ligated (LL) and non-ligated lobes (NLL), respectively. To evaluate critically important underlying functional alterations, present study characterised in vitro and vivo liver function in male Wistar rats (n = 106; 210-250 g) before, and 24/48/72/168/336 h after PVL. Lobe weights and volumes by magnetic resonance imaging confirmed the atrophy-hypertrophy complex. Proper expression and localization of key liver transporters (Ntcp, Bsep) and tight junction protein ZO-1 in isolated hepatocytes demonstrated constantly present viable and well-polarised cells in both lobes. In vitro taurocholate and bilirubin transport, as well as in vivo immunohistochemical Ntcp and Mrp2 expressions were bilaterally temporarily diminished, whereas LL and NLL structural acinar changes were divergent. In vivo bile and bilirubin-glucuronide excretion mirrored macroscopic changes, whereas serum bilirubin levels remained unaffected. In vivo functional imaging (indocyanine-green clearance test; ^99mTc-mebrofenin hepatobiliary scintigraphy; confocal laser endomicroscopy) indicated transitionally reduced global liver uptake and -excretion. While LL functional involution was permanent, NLL uptake and excretory functions recovered excessively. Following PVL, functioning cells remain even in LL. Despite extensive bilateral morpho-functional changes, NLL functional increment restores temporary declined transport functions, emphasising liver functional assessment.

Membrane Transporters for Bilirubin and Its Conjugates: A Systematic Review

Background: Bilirubin is a highly-hydrophobic tetrapyrrole which binds to plasma albumin. It is conjugated in the liver to glucuronic acid, and the water-soluble glucuronides are excreted in urine and bile. The membrane transporters of bilirubin diglucuronide are well-known. Still undefined are however the transporters performing the uptake of bilirubin from the blood into the liver, a process known to be fast and not rate-limited. The biological importance of this process may be appraised by considering that in normal adults 200–300 mg of bilirubin are produced daily, as a result of the physiologic turnover of hemoglobin and cellular cytochromes. Nevertheless, research in this field has yielded controversial and contradicting results. We have undertaken a systematic review of the literature, believing in its utility to improve the existing knowledge and promote further advancements.

Methods: We have sourced the PubMed database until 30 June 2017 by applying 5 sequential searches. Screening and eligibility criteria were applied to retain research articles reporting results obtained by using bilirubin molecules in membrane transport assays in vitro or by assessing serum bilirubin levels in in vivo experiments.

Results: We have identified 311 articles, retaining 44, reporting data on experimental models having 6 incremental increases of complexity (isolated proteins, membrane vesicles, cells, organ fragments, in vivo rodents, and human studies), demonstrating the function of 19 membrane transporters, encoded by either SLCO or ABC genes. Three other bilirubin transporters have no gene, though one, i.e., bilitranslocase, is annotated in the Transporter Classification Database.

Conclusions: This is the first review that has systematically examined the membrane transporters for bilirubin and its conjugates. Paradoxically, the remarkable advancements in the field of membrane transport of bilirubin have pointed to the elusive mechanism(s) enabling bilirubin to diffuse into the liver as if no cellular boundary existed.

Resveratrol modifies biliary secretion of cholephilic compounds in sham-operated and cholestatic rats

AIM

To investigate the effect of resveratrol on biliary secretion of cholephilic compounds in healthy and bile duct-obstructed rats.

METHODS

Resveratrol (RSV) or saline were administered to rats by daily oral gavage for 28 d after sham operation or reversible bile duct obstruction (BDO). Bile was collected 24 h after the last gavage during an intravenous bolus dose of the Mdr1/Mrp2 substrate azithromycin. Bile acids, glutathione and azithromycin were measured in bile to quantify their level of biliary secretion. Liver expression of enzymes and transporters relevant for bile production and biliary secretion of major bile constituents and drugs were analyzed at the mRNA and protein levels using qRT-PCR and Western blot analysis, respectively. The TR-FRET PXR Competitive Binding Assay kit was used to determine the agonism of RSV at the pregnane X receptor.

RESULTS

RSV increased bile flow in sham-operated rats due to increased biliary secretion of bile acids (BA) and glutathione. This effect was accompanied by the induction of the hepatic rate-limiting transporters for bile acids and glutathione, Bsep and Mrp2, respectively. RSV also induced Cyp7a1, an enzyme that is crucial for bile acid synthesis; Mrp4, a transporter important for BA secretion from hepatocytes to blood; and Mdr1, the major apical transporter for xenobiotics. The findings were supported by increased biliary secretion of azithromycin. The TR-FRET PXR competitive binding assay confirmed RSV as a weak agonist of the human nuclear receptor PXR, which is a transcriptional regulator of Mdr1/Mrp2. RSV demonstrated significant hepatoprotective properties against BDO-induced cirrhosis. RSV also reduced bile flow in BDO rats without any corresponding change in the levels of the transporters and enzymes involved in RSV-mediated hepatoprotection.

CONCLUSION

Resveratrol administration for 28 d has a distinct effect on bile flow and biliary secretion of cholephilic compounds in healthy and bile duct-obstructed rats.

Metabolomic and Genome-wide Association Studies Reveal Potential Endogenous Biomarkers for OATP1B1

Transporter-mediated drug-drug interactions (DDIs) are a major cause of drug toxicities. Using published genome-wide association studies (GWAS) of the human metabolome, we identified 20 metabolites associated with genetic variants in organic anion transporter, OATP1B1 (P < 5 × 10-8 ). Of these, 12 metabolites were significantly higher in plasma samples from volunteers dosed with the OATP1B1 inhibitor, cyclosporine (CSA) vs. placebo (q-value < 0.2). Conjugated bile acids and fatty acid dicarboxylates were among the metabolites discovered using both GWAS and CSA administration. In vitro studies confirmed tetradecanedioate (TDA) and hexadecanedioate (HDA) were novel substrates of OATP1B1 as well as OAT1 and OAT3. This study highlights the use of multiple datasets for the discovery of endogenous metabolites that represent potential in vivo biomarkers for transporter-mediated DDIs. Future studies are needed to determine whether these metabolites can serve as qualified biomarkers for organic anion transporters. Quantitative relationships between metabolite levels and modulation of transporters should be established.

Resveratrol Protects Oxidative Stress-Induced Intestinal Epithelial Barrier Dysfunction by Upregulating Heme Oxygenase-1 Expression

BACKGROUND/AIM

Obstructive jaundice (OJ) is frequently complicated by infections and has been associated with increased bacterial translocation, intestinal epithelial hyperpermeability, and oxidative stress, but the mechanism remains unclear. The potential effect of resveratrol (Res) on modifying intestinal epithelial dysfunction was evaluated both in vitro and in vivo.

METHODS

Caco-2 cells (in vitro) and male Wistar rats (n = 60; in vivo) were used to evaluate the role of Res on intestinal epithelial dysfunction. Hydrogen peroxide was used to induce oxidative stress in the Caco-2 cells. In bile duct-ligated group, OJ was successfully established on Day 7 after bile duct ligation, whereas sham-operated and vehicle-treated rats served as controls. Western blot and RT-qPCR were performed to analyze TJ proteins expression in epithelium isolated from rat intestine.

RESULTS

Intestinal hyperpermeability was associated with decreased expression and phosphorylation of occludin and zonula occluden (ZO-1), but increased oxidation in Caco-2 cells and the intestinal epithelium. Res treatment increased the epithelial expression and phosphorylation of occludin and ZO-1 in a concentration-dependent manner. Moreover, Res which protected Caco-2 cells from H2O2-induced oxidative damage clearly reduced malondialdehyde level and intracellular reactive oxygen species accumulation, but increased the expression levels of superoxide dismutase and heme oxygenase-1 (HO-1). Further studies showed that Res also inhibited H2O2-induced protein kinase C activity and p38 phosphorylation. Interestingly, these effects of Res were abolished by the HO-1 inhibitor zinc protoporphyrin or knockdown of HO-1 by siRNA.

CONCLUSIONS

Res protected gut barrier function possibly by initiating HO-1-dependent signaling which is essential for common expression of key tight junction proteins. It also provides a rationale to develop Res clinical applications of intestinal disorders.

Investigations of the total flavonoids extracted from flowers of Abelmoschus manihot (L.) Medic against α-naphthylisothiocyanate-induced cholestatic liver injury in rats

ETHNOPHARMACOLOGY RELEVANCE

The decoction of the flowers of Abelmoschus manihot (L.) Medic was traditionally used for the treatment of jaundice and various types of chronic and acute hepatitis in Anhui and Jiangsu Provinces of China for hundreds of years. Phytochemical studies have indicated that total flavonoids extracted from flowers of A. manihot (L.) Medic (TFA) were the major constituents of the flowers. Our previous studies have investigated the hepatoprotective effects of the TFA against carbon tetrachloride (CCl4) induced hepatocyte damage in vitro and liver injury in vivo. This study aimed to investigate the protective effects and mechanisms of TFA on α-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury in rats.

MATERIAL AND METHODS

The hepatoprotective activities of TFA (125, 250 and 500mg/kg) were investigated on ANIT-induced cholestatic liver injury in rats. The serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) were used as indices of hepatic cell damage and measured. Meanwhile, the serum levels of alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), total bilirubin (TBIL), direct bilirubin (DBIL), and total bile acid (TBA) were used as indices of biliary cell damage and cholestasis and evaluated. Hepatic malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD), glutathione transferase (GST), tumor necrosis factor-α (TNF-α) and nitric oxide (NO) were measured in the liver homogenates. The bile flow in 4h was estimated and the histopathology of the liver tissue was evaluated. Furthermore, the expression of transporters, bile salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2), and Na(+)-taurocholate cotransporting polypeptide (NTCP) were studied by western blot and reverse transcription-quantitative real-time polymerase chain reaction (RT-PCR) to elucidate the protective mechanisms of TFA against ANIT-induced cholestasis.

RESULTS

The oral administration of TFA to ANIT-treated rats could reduce the increases in serum levels of ALT, AST, LDH, ALP, GGT, TBIL, DBIL and TBA. Decreased bile flow by ANIT was restored with TFA treatment. Concurrent administration of TFA reduced the severity of polymorphonuclear neutrophil infiltration and other histological damages, which were consistent with the serological tests. Hepatic MDA and GSH contents in liver tissue were reduced, while SOD and GST activities, which had been suppressed by ANIT, were elevated in the groups pretreated with TFA. With TFA intervention, levels of TNF-α and NO in liver were decreased. Additionally, TFA was found to increase the expression of liver BSEP, MRP2, and NTCP in both protein and mRNA levels in ANIT-induced liver injury with cholestasis.

CONCLUSION

TFA exerted protective effects against ANIT-induced liver injury. The possible mechanisms could be related to anti-oxidative damage, anti-inflammation and regulating the expression of hepatic transporters. It layed the foundation for the further research on the mechanisms of cholestasis as well as the therapeutic effects of A. manihot (L.) Medic for the treatment of jaundice.

Expression of renal Oat5 and NaDC1 transporters in rats with acute biliary obstruction

AIM: To examine renal expression of organic anion transporter 5 (Oat5) and sodium-dicarboxylate cotransporter 1 (NaDC1), and excretion of citrate in rats with acute extrahepatic cholestasis.

METHODS: Obstructive jaundice was induced in rats by double ligation and division of the common bile duct (BDL group). Controls underwent sham operation that consisted of exposure, but not ligation, of the common bile duct (Sham group). Studies were performed 21 h after surgery. During this period, animals were maintained in metabolic cages in order to collect urine. The urinary volume was determined by gravimetry. The day of the experiment, blood samples were withdrawn and used to measure total and direct bilirubin as indicative parameters of hepatic function. Serum and urine samples were used for biochemical determinations. Immunoblotting for Oat5 and NaDC1 were performed in renal homogenates and brush border membranes from Sham and BDL rats. Immunohistochemistry studies were performed in kidneys from both experimental groups. Total RNA was extracted from rat renal tissue in order to perform reverse transcription polymerase chain reaction. Another set of experimental animals were used to evaluate medullar renal blood flow (mRBF) using fluorescent microspheres.

RESULTS: Total and direct bilirubin levels were significantly higher in BDL animals, attesting to the adequacy of biliary obstruction. An important increase in mRBF was determined in BDL group (Sham: 0.53 ± 0.12 mL/min per 100 g body weight vs BDL: 1.58 ± 0.24 mL/min per 100 g body weight, P < 0.05). An increase in the urinary volume was observed in BDL animals. An important decrease in urinary levels of citrate was seen in BDL group. Besides, a decrease in urinary citrate excretion (Sham: 0.53 ± 0.11 g/g creatinine vs BDL: 0.07 ± 0.02 g/g creatinine, P < 0.05) and an increase in urinary excretion of H⁺ (Sham: 0.082 ± 0.03 μmol/g creatinine vs BDL: 0.21 ± 0.04 μmol/g creatinine, P < 0.05) were observed in BDL animals. We found upregulations of both proteins Oat5 and NaDC1 in brush border membranes where they are functional. Immunohistochemistry technique corroborated these results for both proteins. No modifications were observed in Oat5 mRNA and in NaDC1 mRNA levels in kidney from BDL group as compared with Sham ones.

CONCLUSION: Citrate excretion is decreased in BDL rats, at least in part, because of the higher NaDC1 expression. Using the outward gradient of citrate generated by NaDC1, Oat5 can reabsorb/eliminate different organic anions of pathophysiological importance.

The organic anion transporter (OAT) family: a systems biology perspective

The organic anion transporter (OAT) subfamily, which constitutes roughly half of the SLC22 (solute carrier 22) transporter family, has received a great deal of attention because of its role in handling of common drugs (antibiotics, antivirals, diuretics, nonsteroidal anti-inflammatory drugs), toxins (mercury, aristolochic acid), and nutrients (vitamins, flavonoids). Oats are expressed in many tissues, including kidney, liver, choroid plexus, olfactory mucosa, brain, retina, and placenta. Recent metabolomics and microarray data from Oat1 [Slc22a6, originally identified as NKT (novel kidney transporter)] and Oat3 (Slc22a8) knockouts, as well as systems biology studies, indicate that this pathway plays a central role in the metabolism and handling of gut microbiome metabolites as well as putative uremic toxins of kidney disease. Nuclear receptors and other transcription factors, such as Hnf4α and Hnf1α, appear to regulate the expression of certain Oats in conjunction with phase I and phase II drug metabolizing enzymes. Some Oats have a strong selectivity for particular signaling molecules, including cyclic nucleotides, conjugated sex steroids, odorants, uric acid, and prostaglandins and/or their metabolites. According to the "Remote Sensing and Signaling Hypothesis," which is elaborated in detail here, Oats may function in remote interorgan communication by regulating levels of signaling molecules and key metabolites in tissues and body fluids. Oats may also play a major role in interorganismal communication (via movement of small molecules across the intestine, placental barrier, into breast milk, and volatile odorants into the urine). The role of various Oat isoforms in systems physiology appears quite complex, and their ramifications are discussed in the context of remote sensing and signaling.

What do drug transporters really do?

Potential drug-drug interactions mediated by the ATP-binding cassette (ABC) transporter and solute carrier (SLC) transporter families are of clinical and regulatory concern. However, the endogenous functions of these drug transporters are not well understood. Discussed here is evidence for the roles of ABC and SLC transporters in the handling of diverse substrates, including metabolites, antioxidants, signalling molecules, hormones, nutrients and neurotransmitters. It is suggested that these transporters may be part of a larger system of remote communication ('remote sensing and signalling') between cells, organs, body fluid compartments and perhaps even separate organisms. This broader view may help to clarify disease mechanisms, drug-metabolite interactions and drug effects relevant to diabetes, chronic kidney disease, metabolic syndrome, hypertension, gout, liver disease, neuropsychiatric disorders, inflammatory syndromes and organ injury, as well as prenatal and postnatal development.

The role of canalicular ABC transporters in cholestasis

Cholestasis, a hallmark feature of hepatobiliary disease, is characterized by the retention of biliary constituents. Some of these constituents, such as bile acids, inflict damage to hepatocytes and bile duct cells. This damage may lead to inflammation, fibrosis, cirrhosis, and eventually carcinogenesis, sequelae that aggravate the underlying disease and deteriorate clinical outcome. Canalicular ATP-binding cassette (ABC) transporters, which mediate the excretion of individual bile constituents, play a key role in bile formation and cholestasis. The study of these transporters and their regulatory nuclear receptors has revolutionized our understanding of cholestatic disease. This knowledge has served as a template to develop novel treatment strategies, some of which are currently already undergoing phase III clinical trials. In this review we aim to provide an overview of the structure, function, and regulation of canalicular ABC transporters. In addition, we will focus on the role of these transporters in the pathogenesis and treatment of cholestatic bile duct and liver diseases.

Protein expression of kidney and liver bilitranslocase in rats exposed to mercuric chloride--a potential tissular biomarker of toxicity

Bilitranslocase (BTL) is a plasma membrane carrier that transports organic anions of physiological and pharmacological interest. It is expressed in basolateral plasma membrane of kidney and liver. BTL has been recently described as a marker of transition from normal tissue to its neoplastic transformation in human kidney. Inorganic mercury is a major environmental contaminant that produces many toxic effects. Previous reports have described an interaction between BTL and mercuric ions. This study was designed to evaluate the renal and hepatic expression of BTL in rats exposed to a nephrotoxic and hepatotoxic dose of HgCl2. Male rats were treated with a single injection of HgCl2 at a dose of 4mg/kg body wt, i.p. (HgCl2 group). Control rats received the vehicle alone (Control group). Studies were carried out 18h after injection. Afterwards, the kidneys and livers were excised and processed for histopathological studies or immunoblot (homogenates and crude membranes) techniques. In rats treated with HgCl2, immunoblotting showed a significant decrease in the abundance of BTL in homogenates and plasma membranes from kidney and liver. BTL decrease of expression might reflect the grade of damage in renal tubule cells and in hepatocytes. Thus, BTL might be postulated as a new biomarker of tissue toxicity induced by mercury.

Drug-induced perturbations of the bile acid pool, cholestasis, and hepatotoxicity: mechanistic considerations beyond the direct inhibition of the bile salt export pump

The bile salt export pump (BSEP) is located on the canalicular plasma membrane of hepatocytes and plays an important role in the biliary clearance of bile acids (BAs). Therefore, any drug or new chemical entity that inhibits BSEP has the potential to cause cholestasis and possibly liver injury. In reality, however, one must consider the complexity of the BA pool, BA enterohepatic recirculation (EHR), extrahepatic (renal) BA clearance, and the interplay of multiple participant transporters and enzymes (e.g., sulfotransferase 2A1, multidrug resistance-associated protein 2, 3, and 4). Moreover, BAs undergo extensive enzyme-catalyzed amidation and are subjected to metabolism by enterobacteria during EHR. Expression of the various enzymes and transporters described above is governed by nuclear hormone receptors (NHRs) that mount an adaptive response when intracellular levels of BAs are increased. The intracellular trafficking of transporters, and their ability to mediate the vectorial transport of BAs, is governed by specific kinases also. Finally, bile flow, micelle formation, canalicular membrane integrity, and BA clearance can be influenced by the inhibition of multidrug resistant protein 3- or ATPase-aminophospholipid transporter-mediated phospholipid flux. Consequently, when screening compounds in a discovery setting or conducting mechanistic studies to address clinical findings, one has to consider the direct (inhibitory) effect of the parent drug and metabolites on multiple BA transporters, as well as inhibition of BA sulfation and amidation and NHR function. Vectorial BA transport, in addition to BA EHR and homoeostasis, could also be impacted by drug-dependent modulation of kinases and enterobacteria.

Pathogenesis of intestinal barrier dysfunction in obstructive jaundice

Intestinal mucosal barrier is a key structure that normally prevents the passage of harmful molecules across the mucosa and into the circulation, including mechanical barrier, immunological barrier, biological barrier and chemical barrier. Obstructive jaundice (OJ) is frequently associated with infectious complications, mainly due to sepsis and renal dysfunction. The key events in the pathophysiology of these complications are endotoxemia of gut origin and increased intestinal permeability because of intestinal barrier dysfunction, as demonstrated in experimental and clinical studies. However, the mechanisms involved in this phenomenon remain obscure. Here we review recent progress in understanding the pathogenesis of intestinal barrier dysfunction in OJ.

Review article: prescribing medications in patients with cirrhosis - a practical guide

BACKGROUND

Most drugs have not been well studied in cirrhosis; recommendations on safe use are based largely on experience and/or expert opinion, with dosing recommendations often based on pharmacokinetic (PK) changes.

AIM

To provide a practical approach to prescribing medications for cirrhotic patients.

METHODS

An indexed MEDLINE search was conducted using keywords cirrhosis, drug-induced liver injury, pharmacodynamics (PDs), PKs, drug disposition and adverse drug reactions. Unpublished information from the Food and Drug Administration and industry was also reviewed.

RESULTS

Most medications have not been adequately studied in cirrhosis, and specific prescribing information is often lacking. Lower doses are generally recommended based on PK changes, but data are limited in terms of correlating PD effects with the degree of liver impairment. Very few drugs have been documented to have their hepatotoxicity potential enhanced by cirrhosis; most of these involve antituberculosis or antiretroviral agents used for HIV or viral hepatitis. Paracetamol can be used safely when prescribed in relatively small doses (2-3 g or less/day) for short durations, and is recommended as first-line treatment of pain. In contrast, NSAIDs should be used cautiously (or not at all) in advanced cirrhosis. Proton pump inhibitors have been linked to an increased risk of spontaneous bacterial peritonitis (SBP) in cirrhosis and should be used with care.

CONCLUSIONS

Most drugs can be used safely in cirrhosis, including those that are potentially hepatotoxic, but lower doses or reduced dosing frequency is often recommended, due to altered PKs. Drugs that can precipitate renal failure, gastrointestinal bleeding, SBP and encephalopathy should be identified and avoided.