Hepatocyte tight-junctional permeability is increased in rat experimental colitis

TNF-α Mediated the Disruption of Hepatic Tight Junction Expression in Blood-Biliary Barrier of Colitis via Downregulating PI3K/AKT Signaling Pathway

Hepatocyte tight junctions (TJ) constituted blood-biliary barrier is the most important hepatic barrier for separating bile from the bloodstream, disruption or dysfunction of TJ barrier is involved in hepatobiliary manifestations of colitis, but the underlying mechanism is still not clear. This study aims to investigate the effect and underlying mechanism of tumor necrosis factor alpha (TNF-α) on hepatic TJ protein expression in blood-biliary barrier and identify its role in the pathogenesis of acute colitis-related cholestasis. Acute colitis rat model was induced by trinitrobenzene sulfonic acid (TNBS) intra-colonic administration. TJs expression of blood-biliary barrier was tested in colitis rats, the serum TNF-α level was also determined in order to elucidate the correlation of TNF-α and TJs. HepaRG cells were used to investigate the effect of TNF-α on TJs, and the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway were also evaluated in rats and TNF-α treated HepaRG cells. Acute colitis was induced in rats at 5 d post TNBS, which is accompanied with cholestasis-like alteration. Serum TNF-α level was increased in colitis rats and positively correlated with the alteration of total bile acids and bilirubin, marked decrease in TJs was found in TNF-α treated HepaRG cells and the rats, down-regulated PI3K/AKT signaling pathway were also identified in TNF-α treated HepaRG cells and the rats. The study concluded that serum TNF-α mediated the down-regulation of PI3K/AKT signaling pathway, which contributed to the reduction of TJ protein expression in acute colitis-related intrahepatic cholestasis. These findings suggest that TNF-α plays an important role in the pathogenesis of intrahepatic cholestasis of colitis.

Colitis ameliorates cholestatic liver disease via suppression of bile acid synthesis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by chronic inflammation and progressive fibrosis of the biliary tree. The majority of PSC patients suffer from concomitant inflammatory bowel disease (IBD), which has been suggested to promote disease development and progression. However, the molecular mechanisms by which intestinal inflammation may aggravate cholestatic liver disease remain incompletely understood. Here, we employ an IBD-PSC mouse model to investigate the impact of colitis on bile acid metabolism and cholestatic liver injury. Unexpectedly, intestinal inflammation and barrier impairment improve acute cholestatic liver injury and result in reduced liver fibrosis in a chronic colitis model. This phenotype is independent of colitis-induced alterations of microbial bile acid metabolism but mediated via hepatocellular NF-κB activation by lipopolysaccharide (LPS), which suppresses bile acid metabolism in-vitro and in-vivo. This study identifies a colitis-triggered protective circuit suppressing cholestatic liver disease and encourages multi-organ treatment strategies for PSC.

ZO-2 favors Hippo signaling, and its re-expression in the steatotic liver by AMPK restores junctional sealing

ZO-2 is a peripheral tight junction (TJ) protein whose silencing in renal epithelia induces cell hypertrophy. Here, we found that in ZO-2 KD MDCK cells, in compensatory renal hypertrophy triggered in rats by a unilateral nephrectomy and in liver steatosis of obese Zucker (OZ) rats, ZO-2 silencing is accompanied by the diminished activity of LATS, a kinase of the Hippo pathway, and the nuclear concentration of YAP, the final effector of this signaling route. ZO-2 appears to function as a scaffold for the Hippo pathway as it associates to LATS1. ZO-2 silencing in hypertrophic tissue is due to a diminished abundance of ZO-2 mRNA, and the Sp1 transcription factor is critical for ZO-2 transcription in renal cells. Treatment of OZ rats with metformin, an activator of AMPK that blocks JNK activity, augments ZO-2 and claudin-1 expression in the liver, reduces the paracellular permeability of hepatocytes, and serum bile acid content. Our results suggest that ZO-2 silencing is a common feature of hypertrophy, and that ZO-2 is a positive regulator of the Hippo pathway that regulates cell size. Moreover, our observations highlight the importance of AMPK, JNK, and ZO-2 as therapeutic targets for blood-bile barrier dysfunction.

Identification of pathology from diesel exhaust particles in the bladder in a rat model by aspiration of particles from the pharynx

To determine whether diesel exhaust particles (DEPs) could be a toxic agent to the bladder, rats were exposed to different concentrations of DEPs for one month or three months. When the rats were sacrificed, morphologic changes of the urothelium were investigated. The antioxidase activity and the levels of lipid peroxidation in the bladder were assayed. In the three-month group, DEPs at doses of 21.03 μg/μl insulted the structural integrity of surface glycosaminoglycans, widened the gap between urothelial cells, increased levels of lipid peroxidation, and decreased antioxidase activities in the urinary bladder (p<0.05). Furthermore, DEPs at a dose of 5.61 μg/μl decreased glutathione, catalase, and glutathione peroxidase activities (p<0.05). These results led to the conclusion that DEPs were a toxic agent in the bladder. The toxic effects might be attributed to oxidative damage mediated by pro-oxidant/antioxidant imbalance or excessive free radicals.

Metabolite profiling of plasma and urine from rats with TNBS-induced acute colitis using UPLC-ESI-QTOF-MS-based metabonomics--a pilot study

The incidence of inflammatory bowel disease, a relapsing intestinal condition whose precise etiology is still unclear, has continually increased over recent years. Metabolic profiling is an effective method with high sample throughput that can detect and identify potential biomarkers, and thus may be useful in investigating the pathogenesis of inflammatory bowel disease. In this study, using a metabonomics approach, a pilot study based on ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOF-MS) was performed to characterize the metabolic profile of plasma and urine samples of rats with experimental colitis induced by 2,4,6-trinitrobenzene sulfonic acid. Acquired metabolic profile data were processed by multivariate data analysis for differentiation and screening of potential biomarkers. Five metabolites were identified in urine: two tryptophan metabolites [4-(2-aminophenyl)-2,4-dioxobutanoic acid and 4,6-cihydroxyquinoline], two gut microbial metabolites (phenyl-acetylglycine and p-cresol glucuronide), and the bile acid 12α-hydroxy-3-oxocholadienic acid. Seven metabolites were identified in plasma: three members of the bile acid/alcohol group (cholic acid, 12α-hydroxy-3-oxocholadienic acid and cholestane-3,7,12,24,25-pentol) and four lysophosphatidylcholines [LysoPC(20:4), LysoPC(16:0), LysoPC(18:1) and LysoPC(18:0)]. These metabolites are associated with damage of the intestinal barrier function, microbiota homeostasis, immune modulation and the inflammatory response, and play important roles in the pathogenesis of inflammatory bowel disease. Our results positively support application of the metabonomic approach in study of the pathophysiological mechanism of inflammatory bowel disease.

Injury of the hepatic barrier and intestinal barrier in patients with small-for-size graft syndrome after partial liver transplantation: mechanisms and protective measures

The intestinal barrier can resist the invasion of pathogens and prevent harmful substances from going into blood circulation to maintain the stability of internal environment, while the hepatic barrier is a vital structure that can protect liver function and prevent endotoxin and virus from entering the liver to damage hepatocytes. Both the two barrier structures are most vulnerable to damage after partial liver transplantation due to the occurrence of postoperative 'small-for-size graft syndrome'. The pathogenesis of 'small-for-size graft syndrome' is associated with postoperative portal hypertension and hyperperfusion. How to effectively control the occurrence of 'small-for-size graft syndrome' and to protect the intestinal barrier and hepatic barrier postoperatively are key to the maintenance of intestinal and hepatic functions. The primary aim of this paper is to review the mechanisms underlying the development of injury of the hepatic barrier and intestinal barrier in patients with small-for-size graft syndrome after partial liver transplantation and to propose the corresponding protective measures.

Effects of oral Lactobacillus plantarum on hepatocyte tight junction structure and function in rats with obstructive jaundice

Surgery and infection are prominent risk factors for the development of obstructive cholestasis which in turn is associated with failure of the liver barrier. We studied the effects of oral Lactobacillus plantarum (LP) supplementation on endotoxemia, oxidative stress, apoptosis, and tight junctions of hepatocytes in an experimental model of obstructive jaundice. Fifty male Wistar rats were randomly divided into five groups of 10 each: group I, sham-operated; group II, ligation and division of the common bile duct (BDL); group III, BLD followed by oral LP treatment; group IV, BDL followed by internal biliary drainage (IBD); group V, BDL followed by IBD and oral LP treatment. Hepatocyte apoptosis, plasma reduced glutathione (GSH) and oxidized glutathione (GSSG) levels, and portal blood endotoxin levels were measured and changes in tight junction-associated proteins occludin, claudin-1, claudin-4, and ZO-1 were observed. Compared to the sham-operated group I, significant increases in endotoxemia, apoptosis, and GSSG were observed in group II and significant decreases were observed in group V. Tight junctions were destroyed in group II animals but were not in animals treated with oral LP (groups III and V). An increase in occludin, claudin-1, claudin-4, and ZO-1 mRNA and protein levels were detected in livers in LP-treated animals (group V) compared with group II levels. Oral LP treatment of rats with obstructive jaundice assisted in the return of active hepatic barrier function. These results may lead to treatments to prevent the deleterious effects of obstructive jaundice.

Impact of experimental colitis on hepatobiliary transporter expression and bile duct injury in mice

BACKGROUND AND AIMS

The pathogenetic link between ulcerative colitis and sclerosing cholangitis (SC) is unclear. We hypothesized that colitis induces changes in bile composition via inflammation-induced reduction of hepatobiliary transporter gene expression, ultimately resulting in cholestasis and bile duct injury.

METHODS

Alterations in transporter expression and bile secretion in acute dextran sulphate sodium (DSS)-induced colitis were compared with lipopolysaccharide (LPS)-treated mice serving as positive control. Whether chronic DSS-colitis elicits cholangitis in genetically predisposed animals was studied in heterozygous multidrug resistance gene 2 knockout mice (Mdr2(+/-)).

RESULTS

LPS but not DSS-colitis changed major hepatobiliary transporters (Ntcp, Bsep, Mrp2-4, Ostalpha/beta, Abcg5/8, Oatp1-4, Mdr1b and Mdr2), enzymes (Cyp3a11 and Cyp7a1), nuclear receptors (RXRalpha, FXR, CAR and PXR) and proinflammatory mediators (tumour necrosis factor alpha and inducible nitric oxide synthase). Formation of toxic bile reflected by an increased bile acid/phospholipid ratio was observed neither in acute nor in chronic colitis, although heterozygous Mdr2(+/-) mice developed mild portal inflammation after chronic colitis.

CONCLUSIONS

In contrast to LPS, DSS-colitis has a minor impact on hepatobiliary gene expression and bile secretion. Therefore, intestinal inflammation-associated changes of hepatobiliary transporter expression do not play a pathogenetic role in SC.

Changes in hepatic cell junctions structure during experimental necrotizing enterocolitis: effect of EGF treatment

Necrotizing enterocolitis (NEC) is a devastating disease of premature babies. Previously, we have shown that EGF reduces NEC and that overproduction of hepatic TNF-alpha is associated with intestinal damage. Leakage of TNF-alpha may be a consequence of epithelial hepatic cellular junction dysfunction. The aim of this study was to investigate changes in the composition of hepatic tight junctions (TJs) and adherens junctions (AJs). Using an established rat model of NEC, animals were divided into the following groups: dam fed (DF), formula fed (NEC), or fed with formula supplemented with EGF (EGF). Serum EGF and histologic localization of major TJ and AJ proteins were evaluated. Distribution patterns of hepatic TJ and AJ proteins were significantly altered in the NEC group compared with those in DF or EGF groups. Cytoplasmic accumulation of occludin, claudin-2, and ZO-1 with reduction of claudin-3 signal was detected in the liver of NEC rats. Localization of beta-catenin was associated with the hepatocyte membrane in EGF and DF groups, but diffused in the NEC group. These data show that hepatic cellular junctions are significantly altered during NEC pathogenesis. EGF-mediated reduction of experimental NEC is associated with protection of hepatic integrity and structure.

The immunobiology of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease histologically characterized by the presence of intrahepatic and/or extrahepatic biliary duct concentric, obliterative fibrosis, eventually leading to cirrhosis. Approximately 75% of patients with PSC have inflammatory bowel disease. The male predominance of PSC, the lack of a defined, pathogenic autoantigen, and the potential role of the innate immune system suggest that it may be due to dysregulation of immunity rather than a classic autoimmune disease. However, PSC is associated with several classic autoimmune diseases, and the strongest genetic link to PSC identified to date is with the human leukocyte antigen DRB01*03 haplotype. The precise immunopathogenesis of PSC is largely unknown but likely involves activation of the innate immune system by bacterial components delivered to the liver via the portal vein. Induction of adhesion molecules and chemokines leads to the recruitment of intestinal lymphocytes. Bile duct injury results from the sustained inflammation and production of inflammatory cytokines. Biliary strictures may cause further damage as a result of bile stasis and recurrent secondary bacterial cholangitis. Currently, there is no effective therapy for PSC and developing a rational therapeutic strategy demands a better understanding of the disease.

5-lipoxygenase modulates the alteration of paracellular barrier function in mice ileum during experimental colitis

Small intestine permeability is frequently altered in inflammatory bowel disease and may be caused by the translocation of intestinal toxins through leaky small intestine tight junctions (TJs) and adherence. Recently, it has been shown that 5-lipoxygenase (5-LO) plays an important role in the development of various inflammatory conditions like inflammatory bowel disease. In the present study, by comparing the responses in wild-type mice (5-LOWT) with those of mice lacking the 5-lipoxygenase (5-LOKO), we investigated the role played by this enzyme in the permeability and structure of small intestine TJs in an animal model of experimental colitis. To address this question, we used an experimental model of colitis, induced by dinitrobenzene sulfonic acid (DNBS). Four days after colitis induction by DNBS, the ileal TJs were studied by means of transmission electron microscopy using lanthanum nitrate and immunohistochemistry of occludin and ZO-1. When compared with DNBS-treated 5-LOWT mice, DNBS-treated 5-LOKO mice experienced a reduced rate of the extent and severity of the histological signs of colon injury. After administration of DNBS, 5-LOWT mice showed a significant increase of ileal permeability (88.3% +/- 1.2%) compared with sham (5.6% +/- 0.5%). In colitis, the percentage of "leaky" junctions in terminal ilea correlated positively with the macroscopic colon damage score. Distal colitis in 5-LOWT mice induces an increase of TJ permeability throughout the entire small intestine, and the extent of alterations correlates with colonic damage. On the contrary, a significant reduction of (1) the degree of colon injury, (2) the alteration of ZO-1 and occludin localization (immunohistochemistry), and (3) ileal permeability (8.1% +/- 0.7%) caused by DNBS in the colon was observed in 5-LOKO mice. Similarly, the treatment of 5-LOWT with zileuton (50 mg/kg per oral gavage twice a day), a 5-LO inhibitor, resulted in a significant reduction of all the previously described parameters. Taken together, our results clearly demonstrate that 5-LO modulates small intestinal permeability in experimental colitis through the regulation of TJ protein.

Involvement of cell junctions in hepatocyte culture functionality

In liver, like in other multicellular systems, the establishment of cellular contacts is a prerequisite for normal functioning. In particular, well-defined cell junctions between hepatocytes, including adherens junctions, desmosomes, tight junctions, and gap junctions, are known to play key roles in the performance of liver-specific functionality. In a first part of this review article, we summarize the current knowledge concerning cell junctions and their roles in hepatic (patho)physiology. In a second part, we discuss their relevance in liver-based in vitro modeling, thereby highlighting the use of primary hepatocyte cultures as suitable in vitro models for preclinical pharmaco-toxicological testing. We further describe the actual strategies to regain and maintain cell junctions in these in vitro systems over the long-term.

Hepatobiliary Disposition in Primary Cultures of Dog and Monkey Hepatocytes

Hepatobiliary transporters are a major route for elimination of xenobiotics and endogenous products. In vitro hepatobiliary models have been reported for human and rat, but not for the other preclinical species used in safety evaluation. We have established methodologies for culturing dog and monkey hepatocytes with optimal bile canalicular formation and function, using a sandwich culture comprising rigid collagen substratum and gelled collagen overlay. Hepatic uptake utilizing sinusoidal transporters and biliary excretion through canalicular transporters were assessed using the bile salt taurocholate, salicylate (negative control), and the Bsep inhibitors cyclosporin A (CsA) and glyburide. There was significant taurocholate and salicylate canalicular efflux in dog and monkey hepatocytes, although the amount of salicylate transported was one thousandth that of taurocholate. Species differences were observed, as glyburide significantly inhibited taurocholate uptake in monkey (64% at 10 microM) but not dog hepatocytes, and inhibited taurocholate efflux in dog (100% at 10 microM) but not monkey hepatocytes. CsA did not inhibit bile salt uptake and significantly inhibited canalicular efflux in dog (at 0.1 microM) and monkey (at 1 and 10 microM) hepatocyte cultures. These results suggest that glyburide is a bile salt uptake inhibitor in monkey but not in dog hepatocytes and that CsA inhibits bile salt canalicular efflux but not basolateral uptake in these species. We have established dog and monkey hepatocytes in sandwich culture with intact bile canalicular formation and function. The differences observed in taurocholate transport between dog and monkey hepatocytes may be indicative of in vivo species differences.

THALIDOMIDE TREATMENT REDUCES THE ALTERATION OF PARACELLULAR BARRIER FUNCTION IN MICE ILEUM DURING EXPERIMENTAL COLITIS

Small intestine permeability is frequently altered in inflammatory bowel diseases and may be caused by the translocation of intestinal toxins through leaky small intestine tight junctions (TJs) and adherence. Thus, the aim of the present study was to examine the effects of thalidomide treatment on the permeability and structure of small intestine TJs in an animal model of experimental colitis induced by dinitrobenzene sulfonic acid (DNBS). Four days after colitis induction with DNBS, the ileal TJs were studied by means of transmission electron microscopy using lanthanum nitrate and immunohistochemistry of occludin and zonula occludens 1. When compared with DNBS-treated mice, thalidomide-treated (200 mg/kg orally starting 30 min after the administration of DNBS) mice subjected to DNBS-induced colitis experienced a significantly reduced rate of the extent and severity of the histological signs of colon injury associated with a significant reduction of plasma and colon tumor necrosis factor alpha levels. After administration of DNBS to the mice induced a significant increase of ileal permeability was observed. Distal colitis in mice induced an increase of TJ permeability throughout the entire small intestine, and the extent of alterations correlates with colonic damage. In particular, we have observed that thalidomide treatment resulted in a significant reduction of the following: (1) the degree of colon injury, (2) the alteration of zonula occludens 1 and occludin localization (immunohistochemistry), and (3) intestinal permeability caused by DNBS in the colon. Taken together, our results clearly show that thalidomide treatment reduced small intestinal permeability in experimental colitis through the regulation of TJ protein.

Intestinal permeability in rats with CCl4-induced portal hypertension

AIM: To investigate the intestinal barrier changes in rats with CCl₄-induced portal hypertension.

METHODS: The permeability of intestinal barrier detected by Lanthanum as a tracer was evaluated in rats. Bacterial translocation and plasma endotoxin were also determined.

RESULTS: The incidence of bacterial translocation was 85% in rats with CCl₄-induced portal hypertension, which was significantly higher than that in control rats (20%, P<0.01). Plasma endotoxin level was significantly higher in experimental group than in control group. Permeability of the epithelial mucosa and pathological alteration were increased in the ileum and the microvilli became shorter and thinner in rats with portal hypertension.

CONCLUSION: Bacterial translocation occurs in rats with CCl₄-induced portal hypertension and increased permeability between epithelial cells contributes to the translocation.

The multiple organ dysfunction syndrome and late-phase mortality in sepsis

Sepsis is a devastating and common syndrome characterized by systemic inflammation. Sepsis accounts for considerable morbidity and mortality among intensive care unit patients. Although the inflammatory response generated by the immune system represents the body's attempt to clear invading pathogens, it is the failure to modulate this response that leads to dysregulated inflammation and the injury of healthy tissue. A great deal of research has characterized many of the early events and mediators that lead to systemic inflammation and sepsis. However, substantially less is known about the pathogenesis of the late phase of sepsis, which accounts for the vast majority of sepsis-related mortality (ie, the dysfunction and subsequent failure of the major parenchymal organs).

Epithelial Barrier Dysfunction: A Unifying Theme to Explain the Pathogenesis of Multiple Organ Dysfunction at the Cellular Level

The multiple organ dysfunction syndrome (MODS) is the most common cause of death among patients requiring care in an ICU. There is widespread agreement that MODS is the clinical manifestation of a dysregulated inflammatory response. This article, however, summarizes some tantalizing data to support the view that derangements in the formation or function of specialized structures in epithelial cells, tight junctions, may be a key factor leading to lung, liver, gut, and perhaps kidney dysfunction associated with such conditions as sepsis and acute lung injury syndrome that are caused by dysregulated inflammatory processes.

Lanthanum Effect on the Dynamics of Tight Junction Opening and Closing

We present a comparative study in frog urinary bladders (FUB) and A6 cell monolayers (A6CM) on the effect of La3+ on tight junction (TJ) dynamics. These tissues react similarly to changes of basolateral Ca2+ (Ca(2+)bl), while responding differently to the action of La3+(bl). In FUB, La(3+)bl shows a Ca(2+)-antagonistic effect that promotes TJ opening in the presence of a normal Ca(2+)bl concentration. In A6CM, in contrast, La(3+)bl always shows a clear Ca(2+)-agonistic effect. The fact that a concentration of La(3+)bl one fifth of the normal Ca(2+)bl leads in FUB to TJ opening and in A6CM to a complete recovery of the TJ seal indicates a high affinity of La3+ for the Ca(2+)-binding sites in both tissues. In FUB, apical La3+ (La(3+)ap) exhibits, differently from its basolateral effect, an evident Ca(2+)-agonistic effect, suggesting a dual effect of La3+, depending on which side of the bladder La3+ is applied. In A6CM La(3+)ap has a Ca(2+)-agonistic effect similar to La(3+)bl. The effects of La(3+)bl in FUB and in A6CM are consistent, according to our previous publications, with La3+ acting antagonistically or agonistically, respectively, on the Ca2+ binding sites of zonula adhaerens. Despite the fact that the effect of La(3+)ap is clear in both tissues, its site of action is yet to be determined. Protonation of the Ca(2+)-binding sites causes a decrease of its agonistic effect on A6CM, consistent with a negatively charged binding site. In A6CM La3+ apparently replaces Ca2+, mimicking the effect of Ca2+ triggering the cascade of events leading to TJ closure. In FUB, La3+ interacts with the binding sites, dislodging Ca2+, with a high affinity, but this interaction is inadequate to initiate or sustain the process of junction closing. Possibly, the difference between the two preparations resides in subtle conformation differences of the outer segment of E-cadherin molecules.

Time-dependent morphological alterations of cold-stored small bowel in Euro-Collins and Ringer's lactate solutions

Small bowel is one of the organs that can in principle be transplanted. Optimum preservation of the organ is essential for the success of transplantation. The aim of the present study is the investigation of time-related morphological changes of rat small bowel during preservation in hypothermic Euro-Collins (EC) and Ringer's lactate (RL) solution using light microscopy and transmission electron microscopy to evaluate the integrity of intercellular complexes of mucosal epithelium, one of the tissues of the intestine that is most susceptible to ischemia. Small bowels were perfused with either EC, RL solution or physiological saline solution and were placed in the different preservation solutions at 4 degrees C for 0, 3, 6 and 12 h. The results of our study suggest that both preservation solutions are suitable for short-term preservation of the small bowel although RL solution is more effective than EC solution. However, we conclude that further improvement of preservation solutions and/or techniques are needed to perform long-term preservation.

Increased iNOS activity is essential for hepatic epithelial tight junction dysfunction in endotoxemic mice

We tested the hypothesis that increased production of nitric oxide (NO*) by inducible NO* synthase (iNOS) is a key factor responsible for alterations in the expression, localization, and function of key tight junction (TJ) proteins in mice challenged with lipopolysaccharide (LPS, endotoxin). Endotoxemia was associated with hepatobiliary epithelial barrier dysfunction, as evidenced by increased plasma-to-bile leakage of FITC-labeled dextran (relative molecular mass 40 kDa) and increased circulating levels of bile acids and conjugated bilirubin. Immunoblotting revealed decreased expression of zonula occludens (ZO)-1, ZO-2, ZO-3, and occludin in liver after injection of C57Bl/6J mice with 2 mg/kg Escherichia coli 0111:B4 LPS. Nonidet P-40-insoluble (i.e., TJ-associated) occludin and ZO-1 were virtually undetectable 12 and 18 h after injecting LPS. Immunofluorescence microscopy also revealed deranged subcellular localization of ZO-1 and occludin in endotoxemic mice. Pharmacological inhibition of iNOS activity using l-N6-(1-iminoethyl)lysine (5 mg/kg) or genetic ablation of iNOS ameliorated LPS-induced changes in hepatobiliary barrier function, and these strategies partially preserved TJ protein expression and localization. Steady-state levels of occludin and ZO-3 transcripts decreased transiently after injecting LPS but returned toward normal by 12 and 24 h after induction of endotoxemia, respectively. These results support the view that iNOS-dependent NO* production is an important factor contributing to hepatobiliary epithelial barrier dysfunction resulting from systemic inflammation and suggest that iNOS induction may play a role in the development of cholestatic jaundice in patients with severe sepsis.

Tumor necrosis factor-alpha and interleukin-6 reduce bile canalicular contractions of rat hepatocytes

BACKGROUND

Surgeons sometimes encounter hyperbilirubinemia without mechanical obstruction of the biliary tree postoperatively. Many of these patients have bacterial infections and endotoxemia. Kupffer's cells stimulated by endotoxin secrete inflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-6. We hypothesized that TNF-alpha and IL-6 might be involved in the pathogenesis of hyperbilirubinemia.

METHODS

Effects of TNF-alpha and IL-6 on the contractions of bile canaliculi (BC) of rat hepatocyte couplets were examined and time-lapse images using phase-contrast microscopy were taken. Bile was collected from rats treated with or without the cytokines. The livers, perfused with lanthanum after the injection of cytokines, were examined ultrastructurally using electron microscopy.

RESULTS

The number of BC contractions decreased in the couplets treated with both cytokines. The rapid movement of a droplet from BC was observed at the intercellular space of the hepatocyte couplet treated with TNF-alpha. Systolic blood pressure and hepatic tissue blood flow of rats injected with TNF-alpha were not changed, whereas the hepatic tissue blood flow of rats treated with IL-6 decreased (Dunnett test, P <.05). Bile secretion was reduced in both groups of rats (Dunnett test, P <.05). In rats treated with TNF-alpha the total serum bile acid concentration increased and lanthanum temporarily accumulated in BC.

CONCLUSIONS

These results suggest that TNF-alpha and IL-6 may reduce BC contractions and thereby decrease bile flow.

Indomethacin-induced morphologic changes in the rat urinary bladder epithelium

OBJECTIVES

To evaluate the morphologic changes in rat urothelium induced by indomethacin. Nonsteroidal anti-inflammatory drug-induced cystitis is a poorly recognized and under-reported condition. In addition to tiaprofenic acid, indomethacin has been reported to be associated with this condition.

METHODS

Three groups were established: a control group (n = 10), a high-dose group (n = 10), treated with one intraperitoneal injection of indomethacin 20 mg/kg, and a therapeutic dose group (n = 10) in which oral indomethacin was administered 3.25 mg/kg body weight daily for 3 weeks. The animals were then killed and the bladders removed for light and electron microscopic studies.

RESULTS

The light microscopic findings showed some focal epithelial degeneration that was more prominent in the high-dose group. When compared with the control group, both indomethacin groups revealed statistically increased numbers of mast cells in the mucosa (P <0.0001) and penetration of lanthanum nitrate through intercellular areas of the epithelium. Furthermore, the difference in mast cell counts between the high and therapeutic dose groups was also statistically significant (P <0.0001).

CONCLUSIONS

Indomethacin resulted in histopathologic findings typical of interstitial cystitis, such as leaky bladder epithelium and mucosal mastocytosis. The true incidence of nonsteroidal anti-inflammatory drug-induced cystitis in humans must be clarified by prospective clinical trials.

Experimental colitis attenuates development of toxin-induced cholangitis in rats

Primary sclerosing cholangitis frequently occurs in association with ulcerative colitis. This close association may be due to colitis predisposing patients to bile ductular injury. Therefore, we determined the susceptibility of rats with experimental colitis to toxin-induced cholangitis. Sprague-Dawley rats received 2,4,6-trinitrobenzene-sulfonic-acid (TNBS) or ethanol vehicle intracolonically. Seven days later, rats received either the biliary epithelial cell toxin alpha-naphthylisothiocyanate (ANIT) or vehicle and were killed 24 hr later. Liver histology, serum biochemistries and tumor-necrosis factor-alpha (TNF-alpha), and hepatic interleukin-10 (IL-10) mRNA were determined. TNBS-treated rats showed extensive macroscopic colonic damage and a 10-fold increase in myeloperoxidase activity compared to ethanol-treated controls. ANIT-treated noncolitic rats showed portal inflammation centered on damaged bile ducts (cholangitis), which was markedly attenuated in ANIT-treated colitic rats. Hepatic IL-10 mRNA was twofold higher in colitic compared to noncolitic rats, with no difference in serum TNF-alpha. In conclusion, experimental colitis attenuates the development of toxin-induced cholangitis in rats, possibly by up-regulating hepatic IL-10 expression.

Regulation of organic anion transporters in a new rat model of acute and chronic cholangitis resembling human primary sclerosing cholangitis

BACKGROUND/AIMS

Primary sclerosing cholangitis (PSC) is a cholestatic liver disease of unknown etiology. Although the primary defect affects cholangiocytes, cholestatic injury of hepatocytes may promote further liver damage. Since down-regulation of hepatocellular organic anion transporters is implicated in the molecular pathogenesis of cholestasis, expression of these transporters was determined in a novel rat model, which closely resembles human PSC.

METHODS

Hepatic protein and mRNA expression of basolateral (Ntcp, Oatp1, 2 and 4) and canalicular (Mrp2, Bsep) organic anion transporters were analyzed 1, 4 and 12 weeks after induction of experimental PSC by 2,4,6-trinitrobenzenesulfonic acid (TNBS).

RESULTS

Specific down-regulation of basolateral and canalicular transport systems except Oatp4 and Bsep proteins occurred during the acute phase of inflammation. In chronic cholangitis 12 weeks after TNBS Mrp2 protein and mRNA remained down-regulated by 40-50% of controls (P<0.05). In addition Oatp1 protein was also reduced by 40+/-13% (P<0.05), whereas all other transporters returned to control values.

CONCLUSIONS

In chronic cholangitis only canalicular Mrp2 expression remained down-regulated. This might represent the first injury to hepatocytes in chronic cholangitis as an extension of liver injury from the level of cholangiocytes to hepatocytes in PSC.

Cholestasis with altered structure and function of hepatocyte tight junction and decreased expression of canalicular multispecific organic anion transporter in a rat model of colitis

Cholestasis is frequently associated with inflammatory bowel disease. Because some cholestasis is resulted from altered hepatocyte tight junctions (TJs) or the canalicular multispecific organic anion transporter, we have investigated the following topics in a rat model of inflammatory bowel disease: (1) alterations in hepatocyte TJs and in the canalicular multispecific organic anion transporter, (2) etiologic factors for cholestasis, and (3) effects of antibiotics on cholestasis. Rats with trinitrobenzene sulfonic acid-induced colitis were studied 24 hours after treatment. Hepatocyte TJs and the canalicular multispecific organic anion transporter were evaluated by immunostaining for TJ-associated proteins, 7H6 and ZO-1, and multidrug resistance protein 2 (mrp2). To investigate etiologic factors causing cholestasis, portal endotoxin and proinflammatory cytokines were examined. The effects of polymyxin B, penicillin G, or metronidazole on immunostaining for 7H6, ZO-1, mrp2, and cholestasis were investigated. (1) Immunostaining for 7H6 and ZO-1 colocalized outlining the bile canaliculi and immunostaining for mrp2 localized on the canalicular membrane in controls. Treatment with trinitrobenzene sulfonic acid induced significant cholestasis and caused translocation of immunostaining for 7H6, but not that for ZO-1, to the cytoplasm and diminished immunostaining for mrp2 on the canaliculus membrane. (2) The levels of portal endotoxin, but not proinflammatory cytokines, was increased. (3) Polymyxin B, but not the other antibiotics, prevented alterations in immunostaining for both 7H6 and mrp2, and cholestasis. We described that both hepatocyte TJs and the canalicular multispecific organic anion transporter were altered and that gut-derived endotoxin levels in the portal blood were increased in this rat colitis model.

Disturbed bile secretion and cytochrome P450 function during the acute state of experimental colitis in rats

BACKGROUND/AIMS

A variety of hepatobiliary abnormalities has been described in patients with inflammatory bowel diseases. However, the pathophysiological mechanisms leading to these liver alterations are poorly understood. The aim of the present study was to investigate parameters of liver function in a trinitrobenzenesulfonic acid (TNB)-induced rat colitis model.

METHODS

Glucose output, bile acid secretion, bile acid uptake, and the cytochrome P-450 metabolic capacity during TNB-colitis were studied in the perfused liver model. Furthermore, hepatic bile acid- and glycogen content was measured. To evaluate the inflammatory response in the colon and liver, NF-kappaB/Rel was quantified by electrophoretic mobility shift assays. As an NF-kappaB/Rel regulated gene the inducible NO-synthase (NOS2) was evaluated by Western blot analysis. As possible mediators released from the inflamed colon into the portal vein, endotoxin and the stable metabolite of prostaglandin I2 (6-keto-prostaglandin-F1alpha) were determined.

RESULTS

Glucose output, bile acid secretion, bile acid uptake, and cytochrome P-450 metabolic capacity decreased on the first and second day of TNB-colitis. Hepatic bile acid content increased at day 14 of colitis. Glycogen content was reduced, most likely due to an inadequate chow intake of these animals. A low level of portal endotoxin was detectable during the first 2 days of colitis. In addition, 6-keto-prostaglandin-F1alpha was clearly increased in portal blood. NF-kappaB/Rel binding activity and inducible NOS2 were strongly positive in the colon during colitis. Although low levels of portal endotoxin were measured during the first 2 days of colitis, no significant NF-kappaB/Rel activity and NOS2 induction were detected in the liver.

CONCLUSION

Our results indicate that during the acute state of the TNB-colitis, bile acid secretion and cytochrome P-450 function are disturbed in the absence of distinct inflammatory changes in the liver.

Requirement for Ras and phosphatidylinositol 3-kinase signaling uncouples the glucocorticoid-induced junctional organization and transepithelial electrical resistance in mammary tumor cells

In Con8 rat mammary epithelial tumor cells, the synthetic glucocorticoid dexamethasone stimulates the remodeling of the apical junction (tight and adherens junctions) and the transepithelial electrical resistance (TER), which reflects tight junction sealing. Indirect immunofluorescence revealed that dexamethasone induced the recruitment of endogenous Ras and the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase to regions of cell-cell contact, concurrently with the stimulation of TER. Expression of dominant-negative RasN17 abolished the dexamethasone stimulation in TER, whereas, dexamethasone induced the reorganization of tight junction and adherens junction proteins, ZO-1 and beta-catenin, as well as F-actin, to precise regions of cell-cell contact in a Ras-independent manner. Confocal microscopy revealed that RasN17 and the p85 regulatory subunit of PI 3-kinase co-localized with ZO-1 and F-actin at the tight junction and adherens junction, respectively. Treatment with either of the PI 3-kinase inhibitors, wortmannin or LY294002, or the MEK inhibitor PD 098059, which prevents MAPK signaling, attenuated the dexamethasone stimulation of TER without affecting apical junction remodeling. Similar to dominant-negative RasN17, disruption of both Ras effector pathways using a combination of inhibitors abolished the glucocorticoid stimulation of TER. Thus, the glucocorticoiddependent remodeling of the apical junction and tight junction sealing can be uncoupled by their dependence on Ras and/or PI 3-kinase-dependent pathways, implicating a new role for Ras and PI 3-kinase cell signaling events in the steroid control of cell-cell interactions.

Inflammation-induced cholestasis

Inflammatory cytokines produced in response to various infectious and non-infectious stimuli are potent inducers of intrahepatic cholestasis (inflammation-induced cholestasis). The cholestatic effect of cytokines results mainly from inhibition of expression and function of hepatocellular transport systems which normally mediate hepatic uptake and biliary excretion of bile salts and various non-bile salt organic anions (e.g. bilirubin). These cytokine effects are reversible and bile secretory function is restored upon disappearance of the inflammatory injury. This review summarizes the clinical, pathophysiological and molecular aspects of inflammation-induced cholestasis.

Different lobular distributions of altered hepatocyte tight junctions in rat models of intrahepatic and extrahepatic cholestasis

Hepatocyte tight junctions (TJs), the only intercellular barrier between the sinusoidal and the canalicular spaces, play a key role in bile formation. Although hepatocyte TJs are impaired in cholestasis, attempts to localize the precise site of hepatocyte TJ damage by freeze-fracture electron microscopy have produced limited information. Recently, several TJ-associated proteins like ZO-1 and 7H6 have been identified and characterized. Immunolocalization of 7H6 appears to closely correlate with paracellular permeability. We used rat models of intrahepatic cholestasis by ethinyl estradiol (EE) treatment and extrahepatic cholestasis by bile duct ligation (BDL) to precisely determine the site of TJ damage. Alterations in hepatocyte TJs were assessed by double-immunolabeling for 7H6 and ZO-1 using a confocal laser scanning microscope. In control rats, immunostaining for 7H6 and ZO-1 colocalized to outline bile canaliculi in a continuous fashion. In contrast, 7H6 and ZO-1 immunostaining was more discontinuous, outlining the bile canaliculi after BDL. Immunostaining for 7H6, not ZO-1, decreased and predominantly appeared as discrete signals in the submembranous cytoplasm of periportal hepatocytes after BDL. After EE treatment, changes in immunostaining for 7H6 and ZO-1 were similar to those seen in periportal hepatocytes after BDL, but distributed more diffusely throughout the lobule. This study is the first to demonstrate that impairment of hepatocyte TJs occurs heterogenously in the liver lobule after BDL and suggests that BDL and EE treatments produce different lobular distributions of increased paracellular permeability.

Structural and functional regulation of tight junctions by RhoA and Rac1 small GTPases

Tight junctions (TJ) govern ion and solute diffusion through the paracellular space (gate function), and restrict mixing of membrane proteins and lipids between membrane domains (fence function) of polarized epithelial cells. We examined roles of the RhoA and Rac1 GTPases in regulating TJ structure and function in MDCK cells using the tetracycline repressible transactivator to regulate RhoAV14, RhoAN19, Rac1V12, and Rac1N17 expression. Both constitutively active and dominant negative RhoA or Rac1 perturbed TJ gate function (transepithelial electrical resistance, tracer diffusion) in a dose-dependent and reversible manner. Freeze-fracture EM and immunofluoresence microscopy revealed abnormal TJ strand morphology and protein (occludin, ZO-1) localization in RhoAV14 and Rac1V12 cells. However, TJ strand morphology and protein localization appeared normal in RhoAN19 and Rac1N17 cells. All mutant GTPases disrupted the fence function of the TJ (interdomain diffusion of a fluorescent lipid), but targeting and organization of a membrane protein in the apical membrane were unaffected. Expression levels and protein complexes of occludin and ZO-1 appeared normal in all mutant cells, although ZO-1 was more readily solubilized from RhoAV14-expressing cells with Triton X-100. These results show that RhoA and Rac1 regulate gate and fence functions of the TJ, and play a role in the spatial organization of TJ proteins at the apex of the lateral membrane.