Cholestatic Hepatocytes Research Articles

Does lithium attenuate the liver damage due to oxidative stress and liver glycogen depletion in experimental common bile duct obstruction?

In extrahepatic cholestasis, the molecular mechanisms of liver damage due to bile acid accumulation remain elusive. In this study, the activation of glutamatergic receptors was hypothesized to be responsible for bile acid-induced oxidative stress and liver damage. Recent evidence showed that lithium, as an N-methyl-d-aspartate receptor (NMDAR) GluN2B subunit inhibitor, may act on the glutamate/NMDAR signaling axis. Guinea pigs were assigned to four groups, as sham laparotomy (SL), bile duct ligated (BDL), lithium-treated SL (SL + Li) and lithium-treated BDL (BDL + Li) groups. Cholestasis-induced liver injury was evaluated by aspartate aminotransferase (AST), alanine transaminase (ALT), interleukin-6 (IL-6), tissue malondialdehyde (MDA), copper‑zinc superoxide dismutase and reduced glutathione levels. The liability of glutamate/NMDAR signaling axis was clarified by glutamate levels in both plasma and liver samples, with the production of nitric oxide (NO), as well as with the serum calcium concentrations. Blood glucose, glucagon, insulin levels and glucose consumption rates, in addition to tissue glycogen were measured to evaluate the liver glucose-glycogen metabolism. A high liver damage index (AST/ALT) was calculated in BDL animals in comparison to SL group. In the BDL animals, lithium reduced plasma NO and glutamate in addition to tissue glutamate concentrations, while serum calcium increased. The antioxidant capacities and liver glycogen contents significantly increased, whereas blood glucose levels unchanged and tissue MDA levels decreased 3-fold in lithium-treated cholestatic animals. It was concluded that lithium largely protects the cholestatic hepatocyte from bile acid-mediated damage by blocking the NMDAR-GluN2B subunit.

S2919 Bile Duct Injury Due to Ketamine Use

Introduction: Ketamine is used routinely in the hospital for anesthesia, but is also used recreationally for its hallucinogenic and dissociative side effects. Chronic recreational use has been linked to bile duct damage and ulcerative cystitis. We report a case of ketamine induced sclerosing cholangiopathy. Case Description/Methods: A 42-year-old Cantonese woman with past medical history of bilateral hydronephrosis with stents leading to chronic kidney disease presented with abdominal pain associated with abnormal transaminases. Alkaline phosphatase was high at 1,017 IU/L with gamma glutamyl transferase of 2,310 IU/L with normal bilirubin. Abdominal imaging showed diffuse dilatation of the common bile duct. Viral serologies and anti-mitochondrial antibody were negative. She reported chronically elevated liver tests of unknown etiology. Social history was notable for prior alcohol abuse. She denied family history of liver diseases. Her pain resolved and plan was for outpatient follow-up, but she re-presented with sepsis with a rise in bilirubin to 2.9 mg/dL (Table 1). Given prior abnormal imaging, a magnetic resonance cholangiopancreatography was obtained, which showed increased intra- and extrahepatic bile duct dilation with irregular appearance of the central intrahepatic ducts with possible stricture. Differential diagnoses were recurrent pyogenic cholangitis, sclerosing cholangitis, and IgG4 disease. Her IgG level was high at 2,779 mg/dL with IgG4 elevated at 213 mg/dL. Liver biopsy showed chronic cholestatic liver injury consistent with sclerosing cholangitis (Image 1). IgG4 stain was negative. Upon further investigation, patient admitted to at least a decade of daily ketamine use, which was likely the culprit of both her kidney and liver diseases. Discussion: Due to her age, race, gender and rarity of ketamine induced cholangiopathy, she was not directly asked about ketamine use. Since the early 2000s, ketamine has emerged as the illicit drug of choice in Hong Kong and has seen increased use throughout Asia. The biliary damage from ketamine has been studied by a Chinese group that found 62% of the 257 chronic ketamine users had biliary tract anomalies. The greater the alkaline phosphatase, the higher the likelihood of finding biliary tract anomalies on imaging. Ketamine cessation has resulted in normalization of liver tests and imaging, however worsening cholangiopathy has been seen despite abstinence. In patients who present with unexplained cholangiopathy, chronic ketamine use should be considered.Figure 1.: Liver biopsy: A mild lymphoplasmacytic inflammation is noted in some triads with focal and mild interface activity. The bile ducts are injured (irregular contour, unevenly distributed nuclei, intracytoplasmic vacuoles) with focal periportal cholestasis. Immunohistochemical stain for keratin 7 confirms predominantly periportal cholestatic hepatocytes. Keratin 19 shows widespread loss of canals of Hering and focal bile duct loss. Rhodanine stain confirms periportal hepatocellular copper accumulation compatible with a chronic cholestatic process. Table 1. - Patient's hepatic function panels during initial encounter, subsequent encounter, and at least 6 months after subsequent encounter Liver Tests Reference Range & Units Initial Hospitalization Subsequent Hospitalization Most Recent Liver Tests Total bilirubin 0.2 – 1.2 mg/dL 0.8 2.9 4.5 Direct bilirubin 0 – 0.5 mg/dL 0.7 1.8 3.3 Aspartate aminotransferase 5 – 34 IU/L 75 104 88 Alanine transaminase 0 – 37 IU/L 74 129 91 Alkaline phosphatase 40 – 150 IU/L 1017 1106 845 Gamma glutamyl transferase 12 – 43 IU/L 2310 2516 1897

S2905 Prolonged Cholestasis After COVID-19

Introduction: The coronavirus SARS-CoV-2 (COVID-19) is known to cause both pulmonary and hepatic injury. Cholangiocytes have an abundance of angiotensin-converting enzyme 2 receptors, which are the main mode of entry for the virus. Whether the liver injury is caused directly by the virus or as a result of the cytokine storm remains unknown. We present a case of prolonged cholestatic liver injury secondary to COVID-19. Case Description/Methods: A 55-year-old woman presented to our institution with sudden onset of right leg pain and swelling. She had hypertension, diabetes, obesity, and hypothyroidism. She denied any history of liver disease, toxic habits and was not taking any hepatotoxic medications or supplements. Two months prior to presentation, she was admitted to another hospital with severe COVID-19 pneumonia requiring mechanical ventilation. She had received Remdesivir, Convalescent Plasma, Extra Corporeal Membrane Oxygenation (ECMO), and hemodialysis for acute renal failure, before being discharged. During this admission, she was found to have a right lower extremity thrombus and was started on Enoxaparin. Her liver function tests were significant for a markedly elevated alkaline phosphatase level. An ultrasound abdomen was significant only for a fatty liver. CT scan of the abdomen with contrast and an MRCP did not reveal any hepatobiliary abnormalities. Viral hepatitis serology and autoimmune workup were negative. She underwent a liver biopsy which demonstrated cholestasis, mild lobular necroinflammation, and macrovesicular steatosis. There was no PCR evidence of SARS-CoV-2. Her hospital course was complicated by MRSA and pseudomonas pneumonia. She suffered a cardiac arrest and ultimately succumbed to her infection 2 months later. Her Alkaline phosphatase remained elevated throughout her hospital stay. Discussion: Although our patient’s liver biopsy did not demonstrate PCR evidence of SARS-COV-2, it was consistent with histological features of COVID-19 related hepatic injury. Macrovesicular steatosis is the most common histological finding, followed by lobular necroinflammation, according to a case series of 40 patients who died of COVID-19. PCR for SARS-COV-2 in liver biopsy was positive in only 55% of patients. Recent reports have identified ECMO as a cause of secondary sclerosing cholangitis in critically ill patients, which remains a possibility in our case. However, a normal bilirubin level and MRCP did not support this diagnosis in our patient.Figure 1.: (A) 4 x magnification, (B) 10 x magnification, and (C) 40 x magnification of a liver biopsy specimen demonstrating hepatocellular cholestasis with feathery degeneration of hepatocytes, mild lobular neuroinflammation, and mild macrovesicular steatosis. There is sinusoidal dilatation and glycogenated nuclei. Portal tracts show mild to moderate mixed cellular infiltration, including eosinophils, endothelilitis, ductular reaction, and focal mild bile duct damage. There is no pericellular fibrosis to indicate non-alcoholic chronic steatohepatitis, although rare perivenular ballooned hepatocytes are noted on the H&E slide. CK7 immunostain shows moderate to marked ductular reaction, rare cholestatic hepatocytes, and damaged bile ducts. Findings are those of subacute cholestatic hepatitis.Table 1.: Laboratory values from the previous hospitalization, on admission day of this hospitalization, at 1-month of hospitalization, and prior to death.

Single-Cell Transcriptomes Reveal Characteristic Features of Mouse Hepatocytes with Liver Cholestatic Injury.

Hepatocytes are the main parenchymal cells of the liver and play important roles in liver homeostasis and disease process. The heterogeneity of normal hepatocytes has been reported, but there is little knowledge about hepatocyte subtype and distinctive functions during liver cholestatic injury. Bile duct ligation (BDL)-induced mouse liver injury model was employed, and single-cell RNA sequencing was performed. Western blot and qPCR were used to study gene expression. Immunofluoresence was employed to detect the expressions of marker genes in hepatocytes. We detected a specific hepatocyte cluster (BDL-6) expressing extracellular matrix genes, indicating these hepatocytes might undergo epithelia-mesenchymal transition. Hepatocytes of BDL-6 also performed tissue repair functions (such as angiogenesis) during cholestatic injury. We also found that four clusters of cholestatic hepatocytes (BDL-2, BDL-3, BDL-4, and BDL-5) were involved in inflammatory process in different ways. To be specific, BDL-2/3/5 were inflammation-regulated hepatocytes, while BDL-4 played a role in cell chemotaxis. Among these four clusters, BDL-5 was special. because the hepatocytes of BDL-5 were proliferating hepatocytes. Our analysis provided more knowledge of hepatocyte distinctive functions in injured liver and gave rise to future treatment aiming at hepatocytes.

PERSPECTIVE FOR EVALUATION OF MICRORNA IN PLASMA AND BILE FOR DIFFERENTIAL DIAGNOSIS OF OBSTRUCTIVE BILIARY TRACT DISEASE

Introduction: Cholelithiasisis diagnosed in 10-25% of the adult population. The manifestation of cholelithiasis in the form of acute cholecystitis, cholangitis, jaundice etc. occurs with a probability of 2-3% or more per year depending on the risk factors. Most often, it manifests it self as acute calculous cholecystitis. Up to 20% of such patients have additional calculi in extrahepatic bile ducts requiring simultaneous surgical intervention. Currently, the algorithm for diagnosis of concomitant choledocholithiasis in acute cholecystitis is multilevel and it needs to be simplified and improved. Conventional non-invasive diagnostic techniques have low specificity and sensitivity. A new safe diagnostic test is needed for the diagnosis of choledocholithiasis in cholecystitis in order to improve the results of surgical treatment of patients. The aim of the study - to determine the prospects for diagnosis of microRNA for differential diagnosis of obstructive diseases of the biliary tract on the basis of the literature data. Materials and methods: The analysis of the selected international literature in the period of 1991-2018 concerning the studies of microRNA in cholestatic liver diseases was carried out. The search for literature was conducted using Google Scholar and PubMed search engines for the following keywords: microRNA, cholestasis, choledocholithiasis, acute cholecystitis, biliary obstruction in their various combinations. Review: MicroRNA is a specific post-transcriptional regulator of gene expression in all organs and systems of the body. There are specific types of miRNAs for different tissues. The most studied type of liver miRNA is miR-122. The studies showed better sensitivity and specificity of the detection of miR-122 both in the plasma and in the bile for the diagnosis of pathological liver conditions compared with conventional liver tests (aminotransferase, alkaline phosphatase, gamma-glutamyltransferase). Regarding the cholestatic hepatocyte injury occurring in choledocholithiasis, the following types of miRNA were identified: 122, 21, 29, 125, 222, let-7, 98 etc. Their concentrations in plasma and bile can be used as a diagnostic test for the presence of concomitant benign cholestasis in acute cholecystitis. Moreover, these markers can be used for the differential diagnosis of cholestasis of different etiology. Conclusions: Quantitative and qualitative characteristics of microRNA in bile and plasma can be used as an additional non-invasive method for diagnosis of cholestasis induced by choledocholithiasis in acute calculous cholecystitis. Further studyis needed to identify the most optimal algorithm for the administration of microRNA in clinical practice.

Hepatic Notch2 deficiency leads to bile duct agenesis perinatally and secondary bile duct formation after weaning

Notch signaling plays an acknowledged role in bile-duct development, but its involvement in cholangiocyte-fate determination remains incompletely understood. We investigated the effects of early Notch2 deletion in Notch2fl/fl/Alfp-Cretg/− (“Notch2-cKO”) and Notch2fl/fl/Alfp-Cre−/− (“control”) mice. Fetal and neonatal Notch2-cKO livers were devoid of cytokeratin19 (CK19)-, Dolichos-biflorus agglutinin (DBA)-, and SOX9-positive ductal structures, demonstrating absence of prenatal cholangiocyte differentiation. Despite extensive cholestatic hepatocyte necrosis and growth retardation, mortality was only ~15%. Unexpectedly, a slow process of secondary cholangiocyte differentiation and bile-duct formation was initiated around weaning that histologically resembled the ductular reaction. Newly formed ducts varied from rare and non-connected, to multiple, disorganized tubular structures that connected to the extrahepatic bile ducts. Jaundice had disappeared in ~30% of Notch2-cKO mice by 6 months. The absence of NOTCH2 protein in postnatally differentiating cholangiocyte nuclei of Notch2-cKO mice showed that these cells had not originated from non-recombined precursor cells. Notch2 and Hnf6 mRNA levels were permanently decreased in Notch2-cKO livers. Perinatally, Foxa1, Foxa2, Hhex, Hnf1β, Cebpα and Sox9 mRNA levels were all significantly lower in Notch2-cKO than control mice, but all except Foxa2 returned to normal or increased levels after weaning, coincident with the observed secondary bile-duct formation. Interestingly, Hhex and Sox9 mRNA levels remained elevated in icteric 6 months old Notch2-cKOs, but decreased to control levels in non-icteric Notch2-cKOs, implying a key role in secondary bile-duct formation. ConclusionCholangiocyte differentiation becomes progressively less dependent on NOTCH2 signaling with age, suggesting that ductal-plate formation is dependent on NOTCH2, but subsequent cholangiocyte differentiation is not.

Concentrations of Gd-BOPTA in cholestatic fatty rat livers: role of transport functions through membrane proteins

Gd-BOPTA (gadobenate dimeglumine) is a magnetic resonance (MR) contrast agent that, after i.v. administration, distributes within the extracellular space, enters rat hepatocytes through the sinusoidal transporters organic anion transporting peptides (Oatps) and is excreted unchanged into bile through the multidrug resistance-associated protein 2 (Mrp2). It is unclear how the hepatobiliary contrast agent would accumulate in cholestatic fatty livers from obese rats with bile flow impairment. Indeed, the expression of both Oatps and Mrp2 transporters is decreased in cholestatic hepatocytes. To assess this question, we measured on-line the hepatic concentrations of ¹⁵³Gd-BOPTA with a gamma probe placed over perfused rat livers. During the perfusion of ¹⁵³Gd-BOPTA, we obtained a similar maximal hepatic concentration in normal and fatty livers despite the decreased expression and function of membrane transporters in fatty livers. By pharmacokinetic modeling and mathematical simulations, we show how changes of transport into and out of hepatocytes modify the concentrations of ¹⁵³Gd-BOPTA within hepatocytes. Mathematical simulations help to understand how each parameter (entry into hepatocytes, bile excretion, or efflux back to sinusoids) interferes with the hepatic concentrations. The hepatic concentrations of ¹⁵³Gd-BOPTA within hepatocytes rely on the entry into hepatocytes through the sinusoidal membrane and on two paths of exit, the efflux back to sinusoids and the elimination into bile. Understanding how ¹⁵³Gd-BOPTA accumulates in hepatocytes is then complex. However, such understanding is important to analyze liver imaging with hepatobiliary contrast agents in cholestatic fatty livers.

Altered membrane glycoprotein targeting in cholestatic hepatocytes

Hepatocytes are polarized epithelial cells with three morphologically and functionally distinct membrane surfaces: the sinusoidal, lateral and canalicular surface domains. These domains differ from each other in the expression of integral proteins, which concur to their polarized functions. We hypothesize that the cholestasis-induced alterations led to partial loss of hepatocyte polarity. An altered expression of membrane proteins may be indicative of functional disorders. Alkaline liver phosphatase (ALP), one of the most representative plasma membrane glycoproteins in hepatocytes, is expressed at the apical (canalicular) pole of the cell. Because the release of ALP protein in the bloodstream is significantly increased in cholestasis, the enzymatic levels of plasma ALP have major relevance in the diagnosis of cholestatic diseases. Here we assess the cholestasis-induced redistribution of membrane glycoproteins to investigate the ALP release. We performed enzymatic histochemistry, immunohistochemistry, lectin histochemistry, immunogold and lectin-and immunoblotting studies. Experimental cholestasis was induced in rats by ligation of common bile duct (BDL). The BDL led to altered membrane sialoglycoprotein targeting as well as to ultrastructural and functional disorders. Disarrangement of the microtubular system, thickening of the microfilamentous pericanalicular ectoplasm and disturbance of the vectorial trafficking of membrane glycoprotein containing vesicles were found. Altogether, results indicate that the cholestasis-induced partial loss of hepatocyte cell polarity leads to mistranslocation of ALP to the sinusoidal plasma membrane from where the enzyme is then massively released into the bloodstream.

Aquaporin‐9 is Downregulated in the Liver of Rat with Extrahepatic Cholestasis

Hepatocytes express aquaporin‐9 (AQP9), a basolateral channel permeable to water, glycerol and other neutral solutes. While liver AQP9 is known for mediating the uptake of glycerol its relevance in bile secretion remains elusive. Here, we evaluated whether defective expression of AQP9 is associated to secretory dysfunction of rat hepatocytes following bile duct ligation (BDL). By immunoblotting, 1‐day BDL resulted in a slight decrease of AQP9 protein in basolateral membranes and a simultaneous increase of AQP9 in intracellular membranes. This pattern was steadily accentuated in the subsequent days of BDL as at 7‐days BDL basolateral membrane AQP9 decreased by 85% whereas intracellular AQP9 increased by 115%. However, the total amount of AQP9 in the livers from day 7 of BDL rats was reduced by 49% compared to the sham counterpart. Results were confirmed by immunocytochemistry and consistent with biophysical studies showing considerable decrease of the basolateral membrane water and glycerol permeabilities of cholestatic hepatocytes. The AQP9 mRNA was slightly reduced only at day 7 of BDL indicating that the dysregulation was mainly occurring at a posttranslational level. The altered expression of liver AQP9 during BDL was not dependent on insulin, a hormone known to downregulate AQP9, since insulinemia was unchanged in 7‐days BDL rats. These results suggest that extrahepatic cholestasis leads to downregulation of liver AQP9 and dysregulated AQP channels contribute to bile flow dysfunction of cholestatic hepatocyte.

Altered expression and distribution of aquaporin-9 in the liver of rat with obstructive extrahepatic cholestasis

Rat hepatocytes express aquaporin-9 (AQP9), a basolateral channel permeable to water, glycerol, and other small neutral solutes. Although liver AQP9 is known for mediating the uptake of sinusoidal blood glycerol, its relevance in bile secretion physiology and pathophysiology remains elusive. Here, we evaluated whether defective expression of AQP9 is associated to secretory dysfunction of rat hepatocytes following bile duct ligation (BDL). By immunoblotting, 1-day BDL resulted in a slight decrease of AQP9 protein in basolateral membranes and a simultaneous increase of AQP9 in intracellular membranes. This pattern was steadily accentuated in the subsequent days of BDL since at 7 days BDL basolateral membrane AQP9 decreased by 85% whereas intracellular AQP9 increased by 115%. However, the AQP9 immunoreactivity of the total liver membranes from day 7 of BDL rats was reduced by 49% compared with the sham counterpart. Results were confirmed by immunofluorescence and immunogold electron microscopy and consistent with biophysical studies showing considerable decrease of the basolateral membrane water and glycerol permeabilities of cholestatic hepatocytes. The AQP9 mRNA was slightly reduced only at day 7 of BDL, indicating that the dysregulation was mainly occurring at a posttranslational level. The altered expression of liver AQP9 during BDL was not dependent on insulin, a hormone known to negatively regulate AQP9 at a transcriptional level, since insulinemia was unchanged in 7-day BDL rats. Overall, these results suggest that extrahepatic cholestasis leads to downregulation of AQP9 in the hepatocyte basolateral plasma membrane and dysregulated aquaporin channels contribute to bile flow dysfunction of cholestatic hepatocyte.

Obstructive cholestasis down-regulates Oatp1 by TNFα signalling without affecting Oatp2 and Oatp4 expression and Sodium-independent bile salt uptake in rat liver

Background & Aims: Hepatic uptake of bile salts is mediated by sodium-dependent and sodium-independent transport systems. During extrahepatic cholestasis both function and expression of the Na+/taurocholate cotransporting polypeptide (Ntcp) are down-regulated. To test whether hepatic sodium-independent organic anion transporting polypeptides (Oatp1/Oatp1a1, Oatp2/Oatp1a4, Oatp4/Oatp1b2) are also affected by extrahepatic cholestasis, function and expression of all three Oatps have been determined in rats subjected to common bile duct ligation (CBDL; n=4) for up to 7 days with and without anti-cytokine pretreatment with etanercept and anakinra. Results: Protein expression of Oatp1 protein mass as determined by Western blotting remained unchanged after CBDL for 1 day, but then declined by 75±7% and 90±17%, respectively, after 3 and 7 days. In contrast Oatp2 and 4 protein expression was not affected by CBDL as compared to both untreated and sham-operated controls. After CBDL, Oatp1 steady-state mRNA as determined by Northern blotting was rapidly down-regulated by 68±21% of untreated controls (P<0.05) within 24 hours, and remained at similar levels at 3 and 7 days. Cytokine-inactivation studies with etanercept pretreatment demonstrated that TNFα dependent signals mediated the down-regulation of this transporter gene at both protein and mRNA level during obstructive cholestasis. Sodium-independent uptake of taurocholate and cholate into freshly isolated hepatocyte suspensions showed neither significant differences in Km nor Vmax values. Conclusions: These results indicate that sodium-independent transport of bile salts may be mediated by Oatp2 and 4 during biliary obstruction, since its expression remains unaffected and may compensate for loss of Oatp1 expression and function in cholestatic hepatocytes. However, continous bile salt uptake through maintained Oatp2 and 4 expression under these conditions could contribute to the progressive nature of obstructive liver damage.

Extrahepatic cholestasis downregulates Oatp1 by TNF‐α signalling without affecting Oatp2 and Oatp4 expression and sodium‐independent bile salt uptake in rat liver

Hepatic uptake of bile salts is mediated by sodium-dependent and sodium-independent transport systems. During extrahepatic cholestasis, both the function and the expression of the Na(+)/taurocholate cotransporting polypeptide (Ntcp) are downregulated. To test whether sodium-independent organic anion-transporting polypeptides are also affected by extrahepatic cholestasis, the function and expression of all three Oatps have been determined in common bile duct-ligated (CBDL) rats. Oatp1/Oatp1a1 protein mass remained unchanged after CBDL for 1 day, but then declined by 75+/-7% and 90+/-17%, respectively, after 3 and 7 days. In contrast, Oatp2/Oatp1a4 and Oatp4/Oatp1b2 protein expression was not affected by CBDL as compared with controls. After CBDL, Oatp1 mRNA was rapidly downregulated by 68+/-21% of untreated controls (P<0.05) within 24 h, and remained at similar levels at 3 and 7 days. Cytokine-inactivation studies with etanercept pretreatment demonstrated that TNF-alpha-dependent signals mediated the down-regulation of this transporter gene at both protein and mRNA levels during obstructive cholestasis. Sodium-independent uptake of taurocholate and cholate into freshly isolated hepatocyte suspensions showed neither significant differences in K(m) nor V(max) values. These results indicate that sodium-independent transport of bile salts may be mediated by Oatp2 and 4 during biliary obstruction, because its expression remains unaffected and may compensate for loss of Oatp1 expression and function in cholestatic hepatocytes.

Changes in GM1 ganglioside content and localization in cholestatic rat liver

(Glyco)sphingolipids (GSL) are believed to protect the cell against harmful environmental factors by increasing the rigidity of plasma membrane. Marked decrease of membrane fluidity in cholestatic hepatocytes was described but the role of GSL therein has not been investigated so far. In this study, localization in hepatocytes of a representative of GSL, the GM1 ganglioside, was compared between of rats with cholestasis induced by 17alpha-ethinylestradiol (EE) and vehicle propanediol treated or untreated animals. GM1 was monitored by histochemical reaction employing cholera toxin B-subunit. Our findings in normal rat liver tissue showed that GM1 was localized in sinusoidal and canalicular hepatocyte membranes in both peripheral and intermediate zones of the hepatic lobules, and was nearly absent in central zones. On the contrary, in EE-treated animals GM1 was also expressed in central lobular zones. Moreover, detailed densitometry analysis at high magnification showed greater difference of GM1 expression between sinusoidal surface areas and areas of adjacent cytoplasm, caused as well by increased sinusoidal staining in central lobular zone as by decreased staining in cytoplasm in peripheral zone. These differences correlated with serum bile acids as documented by linear regression analyses. Both GM1 content and mRNA corresponding to GM1-synthase remained unchanged in livers; the enhanced expression of GM1 at sinusoidal membrane thus seems to be due to re-distribution of cellular GM1 at limited biosynthesis and could be responsible for protection of hepatocytes against harmful effects of bile acids accumulated during cholestasis.

Defective hepatocyte aquaporin-8 expression and reduced canalicular membrane water permeability in estrogen-induced cholestasis

Our previous work supports a role for aquaporin-8 (AQP8) water channels in rat hepatocyte bile formation mainly by facilitating the osmotically driven canalicular secretion of water. In this study, we tested whether a condition with compromised canalicular bile secretion, i.e., the estrogen-induced intrahepatic cholestasis, displays defective hepatocyte AQP8 functional expression. After 17alpha-ethinylestradiol administration (5 mg x kg body wt(-1).day(-1) for 5 days) to rats, the bile flow was reduced by 58% (P < 0.05). By subcellular fractionation and immunoblotting analysis, we found that 34 kDa AQP8 was significantly decreased by approximately 70% in plasma (canalicular) and intracellular (vesicular) liver membranes. However, 17alpha-ethinylestradiol-induced cholestasis did not significantly affect the protein level or the subcellular localization of sinusoidal AQP9. Immunohistochemistry for liver AQPs confirmed these observations. Osmotic water permeability (P(f)) of canalicular membranes, measured by stopped-flow spectrophotometry, was significantly reduced (73 +/- 1 vs. 57 +/- 2 microm/s) in cholestasis, consistent with defective canalicular AQP8 functional expression. By Northern blotting, we found that AQP8 mRNA expression was increased by 115% in cholestasis, suggesting a posttranscriptional mechanism of protein level reduction. Accordingly, studies in primary cultured rat hepatocytes indicated that the lysosomal protease inhibitor leupeptin prevented the estrogen-induced AQP8 downregulation. In conclusion, hepatocyte AQP8 protein expression is downregulated in estrogen-induced intrahepatic cholestasis, presumably by lysosomal-mediated degradation. Reduced canalicular membrane AQP8 expression is associated with impaired osmotic membrane water permeability. Our data support the novel notion that a defective expression of canalicular AQP8 contributes as a mechanism for bile secretory dysfunction of cholestatic hepatocytes.

A proteomics analysis of the cholestatic rat hepatocyte

A proteomics analysis of the cholestatic rat hepatocyte

Diagnostic and pathogenetic implications of the expression of hepatic transporters in focal lesions occurring in normal liver

Hepatocellular adenoma and focal nodular hyperplasia (FNH) are benign liver tumours. The differential diagnosis of these lesions and of well- to moderately differentiated hepatocellular carcinomas is often difficult but is very important in view of their different treatment. Although neither type of lesion is connected to the biliary tree, FNHs are cholestatic, whereas this is rarely the case for hepatocellular adenomas. This suggests that hepatocellular uptake and secretion of bile constituents is different in FNHs compared to adenomas. We therefore evaluated the expression and localization of hepatic transporters in hepatocellular adenomas, different types of FNH and well- to moderately differentiated hepatocellular carcinomas in non-cirrhotic liver and compared them with normal liver, using real-time RT-PCR and (semi-)quantitative immunohistochemistry. The parenchymal expression of the uptake transporter OATP2/8 (OATP1B1/3) was minimal or absent in adenoma, while there was strong and diffuse expression in FNH. We observed diffuse parenchymal expression of the basolateral export pump MRP3 in adenomas, while only reactive bile ductules and adjacent cholestatic hepatocytes were MRP3-positive in FNH. The MRP3/OATP2/8 expression pattern of atypical FNHs resembled that of adenomas, suggesting that both types of lesion are related. Most hepatocellular carcinomas showed decreased expression of one or more of the canalicular transporters (MDR1, MDR3, BSEP). The differences in transporter expression profile between FNHs and adenomas are most likely pathogenetically important and may explain why only FNHs are cholestatic. The finding that each type of focal lesion in non-cirrhotic liver has a specific transporter expression pattern may be useful in the establishment of a correct diagnosis by imaging or on needle biopsy.

From Alcohol Toxicity to Treatment

This article presents the proceedings of a symposium held at the meeting of the International Society for Biomedical Research on Alcoholism in Mannheim, Germany, in October 2004. This symposium was dedicated to Charles S. Lieber in recognition of his contribution in alcohol research over the last 50 years. It was divided into two parts, namely effects of alcohol on the gastrointestinal tract and effects of alcohol on the liver. Major emphasis was given to recent discoveries elucidating mechanisms of alcohol-associated carcinogenesis. M. Salaspuro (Finland) discussed the role of acetaldehyde in the saliva and in the large intestine with respect to its role in the pathogenesis of alcohol-associated cancer, and H. K. Seitz (Germany) presented new data identifying individuals homozygous for the ADH1C&1 allele as high on risk for alcohol-associated upper aerodigestive tract cancer. M. Savolainen (Finland) discussed the role phosphatidylethanol as a bioactive lipid that can mediate beneficial and harmful effects of alcohol drinking. In the second part of the symposium, alcoholic liver disease was discussed. P. Haber (Australia) presented new data on hepatic transcriptome in alcoholic liver disease with the identification of new genes possibly involved in alcohol-initiated fibrogenesis of the liver, and H. Moshage (The Netherlands) described survival mechanisms of the cholestatic hepatocytes with implications for therapy in cholestatic liver disease. The role of the hepatic microsomal ethanol oxidizing system in the metabolism of alcohol in alcoholic liver disease was summarized by R. Teschke (Germany). H. Ishii (Japan) discussed the current status and treatment of alcoholic hepatitis in Japan. Finally, in a state-of-the-art lecture, Charles S. Lieber (USA) discussed the development of the understanding of the pathophysiology of alcoholic liver disease in the last 50 years. He emphasized the role of pathophysiology as an important prerequisite for better treatment strategies.

Analysis of the In Vivo Functions of Mrp3

Multidrug resistance protein 3 (MRP3) is an ATP-binding cassette transporter that is able to confer resistance to anticancer agents such as etoposide and to transport lipophilic anions such as bile acids and glucuronides. These capabilities, along with the induction of the MRP3 protein on hepatocyte sinusoidal membranes in cholestasis and the expression of MRP3 in enterocytes, have led to the hypotheses that MRP3 may function in the body to protect normal tissues from etoposide, to protect cholestatic hepatocytes from endobiotics, and to facilitate bile-acid reclamation from the gut. To elucidate the role of Mrp3 in these processes, the Mrp3 gene (Abcc3) was disrupted by homologous recombination. Homozygous null animals were healthy and physically indistinguishable from wild-type mice. Mrp3(-/-) mice did not exhibit enhanced lethality to etoposide phosphate, although an analysis of transfected human embryonic kidney 293 cells indicated that the potency of murine Mrp3 toward etoposide ( approximately 2.0- to 2.5-fold) is comparable with that of human MRP3. After induction of cholestasis by bile duct ligation, Mrp3(-/-) mice had 1.5-fold higher levels of liver bile acids and 3.1-fold lower levels of serum bilirubin glucuronide compared with ligated wild-type mice, whereas significant differences were not observed between the respective sham-operated mice. Bile acid excretion, pool size, and fractional turnover rates were similar in Mrp3(-/-) and wild-type mice. We conclude that Mrp3 functions as an alternative route for the export of bile acids and glucuronides from cholestatic hepatocytes, that the pump does not play a major role in the enterohepatic circulation of bile acids and that the lack of chemosensitivity is probably attributable to functional redundancy with other pumps.

The maintenance and generation of membrane polarity in hepatocytes.

Hepatocytes, the major epithelial cells in the liver, are highly polarized. Their plasma membranes are separated by tight junctions into sinusoidal– basolateral and canalicular–apical domains, which contain distinct sets of proteins and lipids. A normal membrane polarity is vital for hepatocytes to perform many diverse functions, such as canalicular bile secretion and simultaneous sinusoidal secretion of large quantities of serum proteins into blood. Hepatocyte polarity is lost in many diseases like cholestasis. A complete understanding of the molecular mechanisms involved in hepatocyte polarity therefore is of considerable significance to both liver cell biology and the pathogenesis of liver diseases. To maintain the distinct distribution of proteins and lipids in the canalicular and sinusoidal membranes, hepatocytes have developed complex polarized trafficking and retention mechanisms. The establishment of membrane polarity in hepatocytes begins during liver embryogenesis. During hepatocyte differentiation, specific routes and mechanisms are defined for the delivery of plasma membrane proteins. How this polarity is maintained in adult hepatocytes and is generated during development are two major unanswered questions in this field. In this review, we first give an overview of the current knowledge about how membrane polarity is maintained in hepatocytes with the focus on recent developments in polarized protein trafficking.We then present a hypothetical model about how membrane polarity may be generated during liver development, and finally, we present an example of how membrane polarity is altered in cholestasis. Readers are directed to recent reviews for discussion of lipid trafficking in hepatocytes.1,2

Intracellular accumulation of pIgA-R and regulators of transcytotic trafficking in cholestatic rat hepatocytes

Bile duct ligation (BDL) impairs basolateral-to-apical transcytosis in hepatocytes, causing accumulation of transcytotic carriers for the polymeric IgA receptor (pIgA-R) and redistribution of secretory component (SC) from bile to blood. To gain insight into the mechanisms regulating transcytosis and the pathophysiology of cholestasis, we investigated nascent protein trafficking in control and BDL livers using cell fractionation in the context of in vivo pulse-chase experiments and immunoblot analysis. Control and cholestatic hepatocytes trafficked [35S]-labeled serum proteins and the pIgA-R along the secretory pathway with identical kinetics. However, BDL impaired transcytosis, causing (1) accumulation of the pIgA-R, rab3D, rab11a, and other candidate regulators of apical-directed secretion in a crude vesicle carrier fraction (CVCF) enriched in transcytotic carriers; (2) slow delivery of [35S]-labeled SC to bile; and (3) paracellular reflux of SC from bile to blood. In conclusion, these data indicate that the secretory and transcytotic pathways remain polarized in cholestatic hepatocytes and suggest that the pIgA-R traffics through postendosomal rab3D-, rab11a-, and syntaxin 2-associated compartments, implicating these proteins in the regulation of transcytosis.