Kupffer cell-mediated downregulation of hepatic transporter expression in rat hepatic ischemia-reperfusion

Are Selected Cytokines and Epstein-Barr Virus DNA Load Predictors of Hepatological Complications of Epstein-Barr Virus Infection in Children?

The aim of the study was to evaluate tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), soluble intracellular adhesion molecules 1 (s-ICAM-1) and Epstein-Barr virus (EBV) DNA load levels as predictors of hepatological complications of EBV infection in children. The study group consisted of 54 children aged one to eighteen years, who were hospitalised from 1 December 2018 to 31 December 2020 in the Department of Paediatrics, Infectious Diseases and Hepatology and who had hepatological complications in the course of serologically and molecularly confirmed EBV infection. It was shown that IL-6, TNF-α, and s-ICAM-1 concentrations were the highest in patients with hepatitis and biliary pole damage. Higher EBV DNA viremia positively correlated with increased C-reactive protein (CRP) and TNF-α levels and increased leukocyte, lymphocyte, and monocyte counts. Increases in lymphocyte counts and TNF-α concentrations were observed along with increases in gamma-glutamyl transpeptidase (GGTP) activity. Increased concentrations of IL-6, TNF-α, and s-ICAM-1 may indicate the risk of hepatitis with concomitant biliary pole damage during EBV infection.

A transcriptional regulatory network of HNF4α and HNF1α involved in human diseases and drug metabolism

HNF4α and HNF1α are core transcription factors involved in the development and progression of a variety of human diseases and drug metabolism. They play critical roles in maintaining the normal growth and function of multiple organs, mainly the liver, and in the metabolism of endogenous and exogenous substances. The twelve isoforms of HNF4α may exhibit different physiological functions, and HNF4α and HNF1α show varying or even opposing effects in different types of diseases, particularly cancer. Additionally, the regulation of CYP450, phase II drug-metabolizing enzymes, and drug transporters is affected by several factors. This article aims to review the role of HNF4α and HNF1α in human diseases and drug metabolism, including their structures and physiological functions, affected diseases, regulated drug metabolism genes, influencing factors, and related mechanisms. We also propose a transcriptional regulatory network of HNF4α and HNF1α that regulates the expression of target genes related to disease and drug metabolism.

Treprostinil Supplementation Ameliorates Hepatic Ischemia Reperfusion Injury and Regulates Expression of Hepatic Drug Transporters: An Isolated Perfused Rat Liver (IPRL) Study

Purpose

IR injury is an unavoidable consequence in deceased donor liver transplantation. Cold preservation and warm reperfusion may change the expression and function of drug transporters in the liver due to vasoconstriction, infiltration of neutrophils and release of cytokines. We hypothesize that vasodilation, anti-platelet aggregation and proinflammatory downregulation activities of treprostinil will diminish the IR injury and its associated effects.

Methods

Livers obtained from male SD rats (n = 20) were divided into 1) Control, 2) IR, 3) Treprostinil-1 (preservation only), and 4) Treprostinil-2 (preservation and reperfusion) groups. Control livers were procured and immediately reperfused. Livers in the other groups underwent preservation for 24 h and were reperfused. All the livers were perfused using an Isolated Perfused Rat Liver (IPRL) system. Periodic perfusate, cumulative bile samples and liver tissue at the end of perfusion were collected. Liver injury markers, bile flow rates, m-RNA levels for uptake and efflux transporters (qRT-PCR) were measured.

Results

Cold preservation and warm reperfusion significantly increased the release of AST and ALT in untreated livers. Treprostinil supplementation substantially reduced liver injury. Bile flow rate was significantly improved in treprostinil-2 group. m-RNA levels of Slc10a1, Slc22a1, and Slc22a7 in liver were increased and m-RNA levels of Mdr1a were decreased by IR. Treprostinil treatment increased Abcb11 and Abcg2 m-RNA levels and maintained Slc22a1m-RNA similar to control livers.

Conclusions

Treprostinil treatment significantly reduced liver injury. IR injury changed expression of both uptake and efflux transporters in rat livers. Treprostinil significantly altered the IR injury mediated changes in m-RNA expression of transporters.

Anticholestatic Effect of Bardoxolone Methyl on Hepatic Ischemia-reperfusion Injury in Rats

Supplemental Digital Content is available in the text.

Background.

Cholestasis is a sign of hepatic ischemia-reperfusion injury (IRI), which is caused by the dysfunction of hepatocyte membrane transporters (HMTs). As transcriptional regulation of HMTs during oxidative stress is mediated by nuclear factor erythroid 2-related factor 2, we hypothesized that bardoxolone methyl (BARD), a nuclear factor erythroid 2-related factor 2 activator, can mitigate cholestasis associated with hepatic IRI.

Methods.

BARD (2 mg/kg) or the vehicle was intravenously administered into rats immediately before sham surgery, 60 min of ischemia (IR60), or 90 min of ischemia (IR90); tissue and blood samples were collected after 24 h to determine the effect on key surrogate markers of bile metabolism and expression of HMT genes (Mrp (multidrug resistance-associated protein) 2, bile salt export pump, Mrp3, sodium-taurocholate cotransporter, and organic anion-transporting polypeptide 1).

Results.

Significantly decreased serum bile acids were detected upon BARD administration in the IR60 group but not in the IR90 group. Hepatic tissue analyses revealed that BARD administration increased mRNA levels of Mrp2 and Mrp3 in the IR60 group, and it decreased those of bile salt export pump in the IR90 group. Protein levels of multidrug resistance–associated protein 2, multidrug resistance–associated protein 3, and sodium-taurocholate cotransporter were higher in the IR90 group relative to those in the sham or IR60 groups, wherein the difference was notable only when BARD was administered. Immunohistochemical and morphometric analyses showed that the area of expression for multidrug resistance–associated protein 2 and for sodium-taurocholate cotransporter was larger in the viable tissues than in the necrotic area, and the area for multidrug resistance–associated protein 3 was smaller; these differences were notable upon BARD administration.

Conclusions.

BARD may have the potential to change HMT regulation to mitigate cholestasis in hepatic IRI.

Hepatic Stellate Cells Play a Functional Role in Exacerbating Ischemia-Reperfusion Injury in Rat Liver

PURPOSE

The involvement of hepatic stellate cells (HSCs) with ischemia-reperfusion (I/R) injury in rat liver was examined using gliotoxin, which is known to induce HSC apoptosis.

METHODS

Male Sprague-Dawley rats were used. HSC was represented by a glial fibrillary acidic protein (GFAP)-positive cell. Liver ischemia was produced by cross-clamping the hepatoduodenal ligament. The degree of I/R injury was evaluated by a release of aminotransferases. Sinusoidal diameter and sinusoidal perfusion rates were examined using intravital fluorescence microscopy.

RESULTS

Gliotoxin significantly decreased the number of GFAP-positive cells 48 h after dosing (2.50 ± 0.19% [mean ± SD] in the nontreated group vs. 1.91 ± 0.46% in the gliotoxin-treated group). Liver damage was significantly suppressed by the pretreatment with gliotoxin. Sinusoidal diameters in zone 3 were wider in the gliotoxin group (10.25 ± 0.35 µm) than in the nontreated group (8.21 ± 0.50 µm). The sinusoidal perfusion rate was maintained as well in the gliotoxin group as in normal livers, even after I/R.

CONCLUSIONS

Pretreatment with gliotoxin significantly reduced the number of HSCs in the liver and further suppressed liver injury following I/R. It is strongly suggested that HSCs play a functional role in exacerbating the degree of I/R injury of the liver.

Effects of Hepatic Ischemia-Reperfusion Injuries and NRF2 on Transcriptional Activities of Bile Transporters in Rats

BACKGROUND

The effect of hepatic ischemia-reperfusion injury (IRI) on bile transporter (BT) gene expression is unknown. We hypothesized that abnormal expression of BTs during hepatic IRI is dependent on nuclear factor erythroid 2-related factor 2 (NRF2), which contributes to the cholestasis after reperfusion.

METHODS

Sham surgery and short (60 min) or long (90 min) periods of warm ischemia time (WIT) with or without reperfusion for 24 h were applied to wild-type Sprague-Dawley rats and Nrf2 knockout rats (n = 5 per group). At each stage of IRI, the serum levels of aminotransferase, total bilirubin, and bile acids were measured. In addition, hepatic tissue was sampled to determine the histologic score of IRI (Suzuki score), measure adenosine triphosphate (ATP), and identify the quantitative real-time polymerase chain reactions of BTs (Oatp1, Ntcp, Mrp2, Bsep, and Mrp3).

RESULTS

In short periods of WIT, BT expression increased during the ischemia stage and returned to the baseline after reperfusion. However, in long periods of WIT, BT expression did not increase after ischemia and decreased further after reperfusion. Short WIT did not increase BT expression in Nrf2 knockout animals. The level of BT expression was correlated with the Suzuki score, the serum levels of aminotransferase, bilirubin, and bile acids, and tissue ATP level. Stepwise multiple regression analysis derived equations to predict the Suzuki score (R² = 76.8, P < 0.001), serum total bilirubin (R² = 61.2, P < 0.001), and tissue ATP (R² = 61.1, P < 0.001).

CONCLUSIONS

Short WIT induces the transcriptional activities of BT, whereas long WIT depresses them, and the effect was blunted by Nrf2 knockout status. BT expression can be considered a surrogate marker for hepatic IRI.

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.

Gd-EOB-DTPA-enhanced MRI for quantitative assessment of liver organ damage after partial hepatic ischaemia reperfusion injury: correlation with histology and serum biomarkers of liver cell injury

OBJECTIVE

To evaluate Gd-EOB-DTPA-enhanced MRI for quantitative assessment of liver organ damage after hepatic ischaemia reperfusion injury (IRI) in mice.

METHODS

Partial hepatic IRI was induced in C57Bl/6 mice (n = 31) for 35, 45, 60 and 90 min. Gd-EOB-DTPA-enhanced MRI was performed 1 day after surgery using a 3D-FLASH sequence. A subgroup of n = 9 animals with 60 min IRI underwent follow-up with MRI and histology 7 days after IRI. The total liver volume was determined by manual segmentation of the entire liver. The volume of functional, contrast-enhanced liver parenchyma was quantified by a region growing algorithm (visual threshold) and an automated segmentation (Otsu's method). The percentages of functional, contrast-enhanced and damaged non-enhanced parenchyma were calculated according to these volumes. MRI data was correlated with serum liver enzyme concentrations and histologically quantified organ damage using periodic acid-Schiff (PAS) staining.

RESULTS

The percentage of functional (contrasted) liver parenchyma decreased significantly with increasing ischaemia times (control, 94.4 ± 3.3%; 35 min IRI, 89.3 ± 4.1%; 45 min IRI, 87.9 ± 3.3%; 60 min IRI, 68 ± 10.5%, p < 0.001 vs. control; 90 min IRI, 55.9 ± 11.5%, p < 0.001 vs. control). The percentage of non-contrasted liver parenchyma correlated with histologically quantified liver organ damage (r = 0.637, p < 0.01) and serum liver enzyme elevations (AST r = 0.577, p < 0.01; ALT r = 0.536, p < 0.05). Follow-up MRI visualized recovery of functional liver parenchyma (71.5 ± 8.7% vs. 84 ± 2.1%, p < 0.05), consistent with less histological organ damage on day 7.

CONCLUSION

We demonstrated the feasibility of Gd-EOB-DTPA-enhanced MRI for non-invasive quantification of damaged liver parenchyma following IRI in mice. This novel methodology may refine the characterization of liver disease and could have application in future studies targeting liver organ damage.

KEY POINTS

• Prolonged ischaemia times in partial liver IRI increase liver organ damage. • Gd-EOB-DTPA-enhanced MRI at hepatobiliary phase identifies damaged liver volume after hepatic IRI. • Damaged liver parenchyma quantified with MRI correlates with histological liver damage. • Hepatobiliary phase Gd-EOB-DTPA-enhanced MRI enables non-invasive assessment of recovery from liver injury.

Trafficking and other regulatory mechanisms for organic anion transporting polypeptides and organic anion transporters that modulate cellular drug and xenobiotic influx and that are dysregulated in disease

Organic anion transporters (OATs) and organic anion-transporting polypeptides (OATPs), encoded by a number of solute carrier (SLC)22A and SLC organic anion (SLCO) genes, mediate the absorption and distribution of drugs and other xenobiotics. The regulation of OATs and OATPs is complex, comprising both transcriptional and post-translational mechanisms. Plasma membrane expression is required for cellular substrate influx by OATs/OATPs. Thus, interest in post-translational regulatory processes, including membrane targeting, endocytosis, recycling and degradation of transporter proteins, is increasing because these are critical for plasma membrane expression. After being synthesized, transporters undergo N-glycosylation in the endoplasmic reticulum and Golgi apparatus and are delivered to the plasma membrane by vesicular transport. Their expression at the cell surface is maintained by de novo synthesis and recycling, which occurs after clathrin- and/or caveolin-dependent endocytosis of existing protein. Several studies have shown that phosphorylation by signalling kinases is important for the internalization and recycling processes, although the transporter protein does not appear to be directly phosphorylated. After internalization, transporters that are targeted for degradation undergo ubiquitination, most likely on intracellular loop residues. Epigenetic mechanisms, including methylation of gene regulatory regions and transcription from alternate promoters, are also significant in the regulation of certain SLC22A/SLCO genes. The membrane expression of OATs/OATPs is dysregulated in disease, which affects drug efficacy and detoxification. Several transporters are expressed in the cytoplasmic subcompartment in disease states, which suggests that membrane targeting/internalization/recycling may be impaired. This article focuses on recent developments in OAT and OATP regulation, their dysregulation in disease and the significance for drug therapy.

Dioscin Protects ANIT-Induced Intrahepatic Cholestasis Through Regulating Transporters, Apoptosis and Oxidative Stress

Intrahepatic cholestasis, a clinical syndrome, is caused by excessive accumulation of bile acids in body and liver. Proper regulation of bile acids in liver cells is critical for liver injury. We previously reported the effects of dioscin against α-naphthylisothio- cyanate (ANIT)-induced cholestasis in rats. However, the pharmacological and mechanism data are limited. In our work, the animals of rats and mice, and Sandwich-cultured hepatocytes (SCHs) were caused by ANIT, and dioscin was used for the treatment. The results showed that dioscin markedly altered relative liver weights, restored ALT, AST, ALP, TBIL, GSH, GSH-Px, MDA, SOD levels, and rehabilitated ROS level and cell apoptosis. In mechanism study, dioscin not only significantly regulated the protein levels of Ntcp, OAT1, OCT1, Bsep and Mrp2 to accelerate bile acids excretion, but also regulated the expression levels of Bak, Bcl-xl, Bcl-2, Bax, Caspase 3 and Caspase 9 in vivo and in vitro to improve apoptosis. In addition, dioscin markedly inhibited PI3K/Akt pathway and up-regulated the levels of Nrf2, GCLc, GCLm, NQO1 and HO-1 against oxidative stress (OS) caused by bile acids. These results were further validated by inhibition of PI3K and Akt using the inhibitors of wortmannin and perifosine in SCHs. Our data showed that dioscin had good action against ANIT-caused intrahepatic cholestasis through regulating transporters, apoptosis and OS. This natural product can be considered as one active compound to treat intrahepatic cholestasis in the future.

Protective Mechanisms of Hypothermia in Liver Surgery and Transplantation

Hepatic ischemia/reperfusion (I/R) injury is a side effect of major liver surgery that often cannot be avoided. Prolonged periods of ischemia put a metabolic strain on hepatocytes and limit the tolerable ischemia and preservation times during liver resection and transplantation, respectively. In both surgical settings, temporarily lowering the metabolic demand of the organ by reducing organ temperature effectively counteracts the negative consequences of an ischemic insult. Despite its routine use, the application of liver cooling is predicated on an incomplete understanding of the underlying protective mechanisms, which has limited a uniform and widespread implementation of liver-cooling techniques. This review therefore addresses how hypothermia-induced hypometabolism modulates hepatocyte metabolism during ischemia and thereby reduces hepatic I/R injury. The mechanisms underlying hypothermia-mediated reduction in energy expenditure during ischemia and the attenuation of mitochondrial production of reactive oxygen species during early reperfusion are described. It is further addressed how hypothermia suppresses the sterile hepatic I/R immune response and preserves the metabolic functionality of hepatocytes. Lastly, a summary of the clinical status quo of the use of liver cooling for liver resection and transplantation is provided.

Effects of Pringle maneuver and partial hepatectomy on the pharmacokinetics and blood-brain barrier permeability of sodium fluorescein in rats

Liver diseases are known to affect the function of remote organs. The aim of the present study was to investigate the effects of Pringle maneuver, which results in hepatic ischemia-reperfusion (IR) injury, and partial hepatectomy (Hx) on the pharmacokinetics and brain distribution of sodium fluorescein (FL), which is a widely used marker of blood-brain barrier (BBB) permeability. Rats were subjected to Pringle maneuver (total hepatic ischemia) for 20 min with (HxIR) or without (IR) 70% hepatectomy. Sham-operated animals underwent laparotomy only. After 15 min or 8h of reperfusion, a single 25-mg/kg dose of FL was injected intravenously and serial (0-30 min) blood and bile and terminal brain samples were collected. Total and free (ultrafiltration) plasma, total brain homogenate, and bile concentrations of FL and/or its glucuronidated metabolite (FL-Glu) were determined by HPLC. Both IR and HxIR caused significant reductions in the biliary excretions of FL and FL-Glu, resulting in significant increases in the plasma AUC of the marker. Additionally, the free fraction of FL in plasma was significantly increased by HxIR. Although the brain concentrations of FL were increased by almost twofold in both IR and HxIR animals, the brain concentrations corrected by the free FL AUC (and not the total AUC) were similar in both groups at either time points. It is concluded that Pringle maneuver and/or partial hepatectomy substantially alters the hepatobiliary disposition, plasma AUC, plasma free fraction, and brain accumulation of FL without altering the BBB permeability to the marker.

Physiological and biochemical basis of clinical liver function tests: a review

OBJECTIVE

To review the literature on the most clinically relevant and novel liver function tests used for the assessment of hepatic function before liver surgery.

BACKGROUND

Postoperative liver failure is the major cause of mortality and morbidity after partial liver resection and develops as a result of insufficient remnant liver function. Therefore, accurate preoperative assessment of the future remnant liver function is mandatory in the selection of candidates for safe partial liver resection.

METHODS

A MEDLINE search was performed using the key words "liver function tests," "functional studies in the liver," "compromised liver," "physiological basis," and "mechanistic background," with and without Boolean operators.

RESULTS

Passive liver function tests, including biochemical parameters and clinical grading systems, are not accurate enough in predicting outcome after liver surgery. Dynamic quantitative liver function tests, such as the indocyanine green test and galactose elimination capacity, are more accurate as they measure the elimination process of a substance that is cleared and/or metabolized almost exclusively by the liver. However, these tests only measure global liver function. Nuclear imaging techniques ((99m)Tc-galactosyl serum albumin scintigraphy and (99m)Tc-mebrofenin hepatobiliary scintigraphy) can measure both total and future remnant liver function and potentially identify patients at risk for postresectional liver failure.

CONCLUSIONS

Because of the complexity of liver function, one single test does not represent overall liver function. In addition to computed tomography volumetry, quantitative liver function tests should be used to determine whether a safe resection can be performed. Presently, (99m)Tc-mebrofenin hepatobiliary scintigraphy seems to be the most valuable quantitative liver function test, as it can measure multiple aspects of liver function in, specifically, the future remnant liver.

Role of cholangiocyte bile Acid transporters in large bile duct injury after rat liver transplantation

BACKGROUND

The pathogenesis of nonanastomotic strictures with a patent hepatic artery remains to be investigated. This study focuses on the role of cholangiocyte bile acid transporters in bile duct injury after liver transplantation.

METHODS

Sprague-Dawley rats were divided into three groups (n=20 for each): the sham-operated group (Sham), the transplant group with 1-hr donor liver cold preservation (CP-1h), and the transplant group with 12-hr donor liver cold preservation (CP-12h). Bile was collected for biochemical analysis. The histopathologic evaluation of bile duct injury was performed and the cholangiocyte bile acid transporters apical sodium-dependent bile acid transporter (ASBT), ileal lipid binding protein (ILBP), and Ostalpha/Ostbeta were investigated. RESULTS.: The immunohistochemical assay suggested that ASBT and ILBP were expressed exclusively on large bile duct epithelial cells, whereas Ostalpha and Ostbeta were expressed on both small and large bile ducts. Western blot and quantitative polymerase chain reaction analysis showed that the expression levels of these transporters dramatically decreased after transplantation. It took seven to 14 days for ILBP, Ostalpha, and Ostbeta to recover, whereas ASBT recovered within 3 days and even reached a peak above the normal level seven days after operation. In the CP-12h group, the ratios of the ASBT/ILBP, ASBT/Ostalpha and ASBT/Ostbeta expression levels were correlated with the injury severity scores of large but not small bile ducts.

CONCLUSIONS

The results suggest that the unparallel alteration of cholangiocyte bile acid transporters may play a potential role in large bile duct injury after liver transplantation with prolonged donor liver preservation.

Bile duct ligation: step-by-step to cholangiocyte inflammatory tumorigenesis

Chronic liver inflammation after murine bile duct ligation could evolve according to three interrelated phenotypes, which would have different metabolic, functional and histologic characteristics. Liver injury secondary to extrahepatic cholestasis would induce an early ischemic-reperfusion phenotype with cholangiocyte depolarization, abnormal ion transport, hypometabolism with anaerobic glycolysis and hepatocytic apoptosis. This phenotype, in turn, could trigger the switch to a leukocytic phenotype by the cholangiocytes, with an intense anaplerotic activity, hypermetabolism, extracellular matrix degradation and moderated proliferation to create a pseudotissue with metabolic autonomy and paracrine functions. In the long-term cholestasis-drive tumorigenesis, the tumorous tissue would principally consist of cholangiocyte parenchyma, with an impressive biosynthetic activity through the tricarboxylic cell cycle. In terms of the tumorous stroma, made up by fibroplasia and angiogenesis, it would favor the tumor trophism. In conclusion, the great intensity and persistence in the expression of these phenotypes by the cholestatic cholangiocyte would favor chronic inflammatory tumorigenesis.

Xenobiotic, bile acid, and cholesterol transporters: function and regulation

Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

ANIT-induced intrahepatic cholestasis alters hepatobiliary transporter expression via Nrf2-dependent and independent signaling

Alpha-naphthylisothiocyanate (ANIT) causes intrahepatic cholestasis by injuring biliary epithelial cells. Adaptive regulation of hepatobiliary transporter expression has been proposed to reduce liver injury during cholestasis. Recently, the oxidative stress transcription factor Nrf2 (nf-e2-related factor 2) was shown to regulate expression of hepatobiliary transporters. The purpose of this study was to determine whether ANIT-induced hepatotoxicity and regulation of hepatobiliary transporters are altered in the absence of Nrf2. For this purpose, wild-type and Nrf2-null mice were administered ANIT (75 mg/kg po). Surprisingly, ANIT-induced hepatotoxicity was similar in both genotypes at 48 h. Accumulation of bile acids in serum and liver was lower in Nrf2-null mice compared with wild-types treated with ANIT. Transporter mRNA profiles differed between wild-type and Nrf2-null mice after ANIT. Bsep (bile salt export pump), Mdr2 (multidrug resistance gene), and Mrp3 (multidrug resistance-associated protein) efflux transporters were increased by ANIT in wild-type, but not in Nrf2-null mice. In contrast, mRNA expression of two hepatic uptake transporters, Ntcp (sodium-taurocholate cotransporting polypeptide) and Oatp1b2 (organic anion transporting peptide), were decreased in both genotypes after ANIT, with larger declines in Nrf2-null mice. mRNA expression of the transcriptional repressor of Ntcp, small heterodimeric partner (SHP), was increased in Nrf2-null mice after ANIT. Furthermore, hepatocyte nuclear factor 1alpha (HNF1alpha), which regulates Oatp1b2, was downregulated in ANIT-treated Nrf2-null mice. Preferential upregulation of SHP and downregulation of HNF1alpha and uptake transporters likely explains why Nrf2-null mice exhibited similar injury to wild-types after ANIT. A subsequent study revealed that treatment of mice with the Nrf2 activator oltipraz protects against ANIT-induced histological injury. Despite compensatory changes in Nrf2-null mice to limit ANIT toxicity, pharmacological activation of Nrf2 may represent a therapeutic option for intrahepatic cholestasis.

Relation of endotoxic hepatic injury with expression of scavenger receptor A in liver tissue during severe acute cholangitis

AIM: To investigate the relationship of endotoxic hepatic injury with the expression of scavenger receptor A (SR-A) in liver tissue during acute cholangitis of severe type (ACST).

METHODS: A rat model of ACST was established by ligating choledochus and injecting escherichia coli O₁₁₁B4 into Wistar rats. At 0, 4, 8, 16, 24 h after operation, the expressions of SR-A protein and mRNA in liver tissue were assayed by western blot and RT-PCR respectively; the levels of plasma endotoxin and interleukin-6 (IL-6) were measured using limulus test and ELISA. Pathological changes in liver tissue were detected by light microscopy, while ALT and TB were determined too.

RESULTS: The plasma endotoxin levels in ACST were progressively increased with time (0-24 h: 0.058 ± 0.009, 0.207 ± 0.024, 0.433 ± 0.049, 0.645 ± 0.077, 0.784 ± 0.097, P < 0.01). With elevated endotoxin, the levels of IL-6, ALT and TB were markedly increased; hepatic histopathological injury was gradually aggravated, while the SR-A expression was obviously decreased. There was significant difference between the expression of SR-A and expression of BLD at 24 h (protein: 0.156 ± 0.014 vs 0.809 ± 0.107, P < 0.01; mRNA: 0.138 ± 0.019 vs 0.578 ± 0.068, P < 0.01).

CONCLUSION: Endotoxic hepatic injury is related with the progressively decreased expression of SR-A in liver tissue during ACST. With the Kupffer cells abilities of clearing endotoxin down-regulated, endotoxic hepatic injury is gradually aggravated.

Experimental obstructive cholestasis: the wound-like inflammatory liver response

Obstructive cholestasis causes hepatic cirrhosis and portal hypertension. The pathophysiological mechanisms involved in the development of liver disease are multiple and linked. We propose grouping these mechanisms according to the three phenotypes mainly expressed in the interstitial space in order to integrate them.Experimental extrahepatic cholestasis is the model most frequently used to study obstructive cholestasis. The early liver interstitial alterations described in these experimental models would produce an ischemia/reperfusion phenotype with oxidative and nitrosative stress. Then, the hyperexpression of a leukocytic phenotype, in which Kupffer cells and neutrophils participate, would induce enzymatic stress. And finally, an angiogenic phenotype, responsible for peribiliary plexus development with sinusoidal arterialization, occurs. In addition, an intense cholangiocyte proliferation, which acquires neuroendocrine abilities, stands out. This histopathological finding is also associated with fibrosis.It is proposed that the sequence of these inflammatory phenotypes, perhaps with a trophic meaning, ultimately produces a benign tumoral biliary process - although it poses severe hepatocytic insufficiency. Moreover, the persistence of this benign tumor disease would induce a higher degree of dedifferentiation and autonomy and, therefore, its malign degeneration.

Hepatic Mrp4 induction following acetaminophen exposure is dependent on Kupffer cell function

During acetaminophen (APAP) hepatotoxicity, increased expression of multidrug resistance-associated proteins 2, 3, and 4 (Mrp2-4) occurs. Mrp4 is the most significantly upregulated transporter in mouse liver following APAP treatment. Although the expression profiles of liver transporters following APAP hepatotoxicity are well characterized, the regulatory mechanisms contributing to these changes remain unknown. We hypothesized that Kupffer cell-derived mediators participate in the regulation of hepatic transporters during APAP toxicity. To investigate this, C57BL/6J mice were pretreated with clodronate liposomes (0.1 ml iv) to deplete Kupffer cells and then challenged with APAP (500 mg/kg ip). Liver injury was assessed by plasma alanine aminotransferase and hepatic transporter protein expression was determined by Western blot and immunohistochemistry. Depletion of Kupffer cells by liposomal clodronate increased susceptibility to APAP hepatotoxicity. Although increased expression of several efflux transporters was observed after APAP exposure, only Mrp4 was found to be differentially regulated following Kupffer cell depletion. At 48 and 72 h after APAP dosing, Mrp4 levels were increased by 10- and 33-fold, respectively, in mice receiving empty liposomes. Immunohistochemistry revealed Mrp4 staining confined to centrilobular hepatocytes. Remarkably, Kupffer cell depletion completely prevented Mrp4 induction by APAP. Elevated plasma levels of TNF-alpha and IL-1beta were also prevented by Kupffer cell depletion. These findings show that Kupffer cells protect the liver from APAP toxicity and that Kupffer cell mediators released in response to APAP are likely responsible for the induction of Mrp4.

Post-transcriptional regulation of breast cancer resistance protein after intestinal ischemia-reperfusion

Breast cancer resistance protein (BCRP), the product of the ABCG2 gene, is a recently identified ATP binding cassette half-transporter. BCRP is expressed in a variety of tumor cells and many normal human tissues. In the small intestine, BCRP can limit the influx and facilitate the efflux to prevent intracellular accumulation of BCRP substrates. Ischemia-reperfusion (I/R) induces the release of reactive oxygen species, and organs are severely damaged by I/R. It has been shown that the expression of transporters was altered in the organ after I/R. The present study was undertaken to clarify the expression of BCRP after intestinal I/R. We showed that the expression level of Bcrp was significantly decreased at 1 h after I/R. Bcrp mRNA level was not altered at 1 h after I/R. These results suggest that Bcrp expression was regulated by a post-transcriptional regulation mechanism after intestinal I/R. Bcrp mRNA level was increased at 24 h after I/R, and the expression level of Bcrp protein was of the same level or slightly increased compared with sham operated-rats. Bcrp was slightly located at the intestinal membrane at 24 h after intestinal I/R. These results suggested that Bcrp was not translocated to the intestinal membrane after intestinal I/R. There is little information on post-transcriptional regulation compared with information on transcriptional regulation. In this study, it was shown that Bcrp expression is regulated by post-transcriptional regulation after intestinal I/R. These results of this study may provide important information for further studies aimed at revealing the biological function of Bcrp.

Drug-metabolizing enzyme and transporter expression in a mouse model of diabetes and obesity

Obesity and type II diabetes pose a serious human health risk. Obese or diabetic patients usually take prescription drugs that require hepatic and renal metabolism and transport, and these patients sometimes display different pharmacokinetics of these drugs. Therefore, mRNA and protein expression of drug-metabolizing enzymes (DMEs) and transporters was measured in livers and kidneys of adult wild-type and ob/ob mice, which model obesity and diabetes. mRNA expression of numerous DMEs increased by at least 2-fold in livers of male ob/ob mice, including Cyp4a14, Cyp2b10, NAD(P)H:quinone oxidoreductase 1 (Nqo1), and sulfotransferase 2a1/2. In general, expression of uptake transporters was decreased in livers of ob/ob mice, namely organic anion-transporting polypeptides (Oatps) and sodium/taurocholate cotransporting polypeptide (Ntcp). In particular, Oatp1a1 mRNA and protein expression in livers of ob/ob mice was diminished to <5% and <15% of that in wild-types, respectively. Generally, the mRNA and protein expression of efflux transporters multidrug resistance-associated proteins (Mrps) was increased in livers of ob/ob mice, particularly with Mrp4 expression being elevated by at least 6-fold and Mrp2 expression at least 3-fold in livers of ob/ob mice. In kidney, Nqo1, Mrp3, 4, Oatp1a1, and organic anion transporter 2 (Oat2) showed significant alterations with mRNA expression levels in ob/ob mice, being increased for Nqo1 and Mrp4 and decreased for Mrp3, Oatp1a1, and Oat2. In summary, the expression of a number of DMEs and transporters was significantly altered in livers and kidneys of ob/ob mice. Since expression of some DMEs and transporters is regulated similarly between mouse and human, the data from this study suggest that transporter expression in liver and kidney may be changed in patients presenting with obesity and/or type II diabetes.

Ischemia-reperfusion of rat livers decreases liver and increases kidney multidrug resistance associated protein 2 (Mrp2)

Hepatic ischemia-reperfusion (IR) injury during liver transplantation can lead to cholestasis and remote organ dysfunction. Multidrug resistance-associated proteins (Mrps) are efflux transporters known to transport a diverse set of substrates, such as amphipathic chemicals, organic anions, and endogenous molecules. The purpose of this study was to determine the effect of hepatic IR injury on the expression of Mrps in rat liver and kidney. Male Sprague-Dawley rats were subjected to 60 min of partial hepatic ischemia. At various times after reperfusion (0, 3, 6, 24, and 48 h), the ischemic lobes were harvested as well as kidneys. RNA and protein expression of Mrps in livers and kidneys were determined by the branched DNA method, Western blot analysis, and tissue immunofluorescence. Mrp2 mRNA and protein expression in livers decreased after IR. Conversely, Mrp2 mRNA and protein expression in kidneys increased after IR. Mrp3 mRNA expression, and Mrp4 mRNA and protein expression in kidneys transiently increased after IR. The intensity of immunofluorescent staining of Mrp2 corresponded to changes in Mrp2 expression in livers and kidneys after IR as detected by Western blot analysis and was localized to the apical membrane domain in both tissues. These results demonstrate that after hepatic IR, downregulation of hepatic Mrp2 and upregulation of renal Mrp2 occur. These decreases in hepatic Mrp2 may contribute to cholestasis, yet increases in kidney may protect from oxidative stress and/or inflammation after hepatic IR.

Role of Kupffer cells in the pathogenesis of liver disease

Kupffer cells, the resident liver macrophages have long been considered as mostly scavenger cells responsible for removing particulate material from the portal circulation. However, evidence derived mostly from animal models, indicates that Kupffer cells may be implicated in the pathogenesis of various liver diseases including viral hepatitis, steatohepatitis, alcoholic liver disease, intrahepatic cholestasis, activation or rejection of the liver during liver transplantation and liver fibrosis. There is accumulating evidence, reviewed in this paper, suggesting that Kupffer cells may act both as effector cells in the destruction of hepatocytes by producing harmful soluble mediators as well as antigen presenting cells during viral infections of the liver. Moreover they may represent a significant source of chemoattractant molecules for cytotoxic CD8 and regulatory T cells. Their role in fibrosis is well established as they are one of the main sources of TGFβ1 production, which leads to the transformation of stellate cells into myofibroblasts. Whether all these variable functions in the liver are mediated by different Kupffer cell subpopulations remains to be evaluated. In this review we propose a model that demonstrates the role of Kupffer cells in the pathogenesis of liver disease.