Polarized expression and function of P2Y ATP receptors in rat bile duct epithelia.

Extracellular nucleotides may be important regulators of bile ductular secretion, because cholangiocytes express P2Y ATP receptors and nucleotides are found in bile. However, the expression, distribution, and function of specific P2Y receptor subtypes in cholangiocytes are unknown. Thus our aim was to determine the subtypes, distribution, and role in secretion of P2Y receptors expressed by cholangiocytes.

Water movement across rat bile duct units is transcellular and channel-mediated.

In recent studies using freshly isolated rat cholangiocytes, we established that water crosses the cholangiocyte membrane by a channel-mediated mechanism involving aquaporins, a family of water-channel proteins. Our goal was to address the importance of channel-mediated water transport in ductal bile formation by employing a physiologic experimental model, the enclosed, polarized rat intrahepatic bile duct unit (IBDU). Expansion and reduction of luminal areas as a reflection of water movement into and out of IBDUs prepared from livers of normal rats were measured by quantitative computer-assisted image analysis.

Human Ogg1, a protein involved in the repair of 8-oxoguanine, is inhibited by nitric oxide.

NO-mediated inhibition of base excision DNA repair may potentiate oxidativeDNA damage in cells and could be relevant to carcinogenesis associated with chronic inflammation. Because 8-oxoguanine, a ubiquitous oxidative DNA lesion, is repaired predominantly by human 8-oxoguanine glycosylase (hOgg1), our aim was to determine whether NO directly inhibits its repair activity. Neither induction of NO-generating enzyme inducible NO synthase nor treatment with S-nitroso-N-acetyl-D-L-pencillamine altered expression of hOgg1 in a human cholangiocarcinoma cell line (KMBC).

Nitric oxide in gastrointestinal epithelial cell carcinogenesis: linking inflammation to oncogenesis.

Chronic inflammation of gastrointestinal tissues is a well-recognized risk factor for the development of epithelial cell-derived malignancies. Although the inflammatory mediators linking chronic inflammation to carcinogenesis are numerous, current information suggests that nitric oxide (NO) contributes to carcinogenesis during chronic inflammation. Inducible nitric oxide synthase (iNOS), expressed by both macrophages and epithelial cells during inflammation, generates the bioreactive molecule NO.

Stimulation of ATP secretion in the liver by therapeutic bile acids.

ATP receptors are ubiquitously expressed and are potential targets for the therapy of a number of disorders. However, delivery of ATP or other nucleotides to specific tissues is problematic, and no pharmacological means to stimulate the release of endogenous ATP has been described. We examined the effects of the bile acid ursodeoxycholic acid (UDCA) on ATP release into bile, since this bile acid is the only agent known to be of therapeutic benefit in secretory disorders of the liver, and since its mechanism of action is not established.

Bcl-2-dependent oxidation of pyruvate dehydrogenase-E2, a primary biliary cirrhosis autoantigen, during apoptosis.

The close association between autoantibodies against pyruvate dehydrogenase-E2 (PDC-E2), a ubiquitous mitochondrial protein, and primary biliary cirrhosis (PBC) is unexplained. Many autoantigens are selectively modified during apoptosis, which has focused attention on apoptotic cells as a potential source of "neo-antigens" responsible for activating autoreactive lymphocytes. Since increased apoptosis of bile duct epithelial cells (cholangiocytes) is evident in patients with PBC, we evaluated the effect of apoptosis on PDC-E2.

Quantitative assessment of the rat intrahepatic biliary system by three-dimensional reconstruction.

The anatomical details of the biliary tree architecture of normal rats and rats in whom selective proliferation was induced by feeding alpha-naphthylisothiocyanate (ANIT) were reconstructed in three dimension using a microscopic-computed tomography scanner. The intrahepatic biliary tree was filled with a silicone polymer through the common bile duct and each liver lobe embedded in Bioplastic; specimens were then scanned by a microscopic-computed tomography scanner and modified Feldkamp cone beam backprojection algorithm applied to generate three-dimensional images. Quantitative analysis of bile duct geometry was performed using a customized software program.

Cryptosporidium parvum activates nuclear factor kappaB in biliary epithelia preventing epithelial cell apoptosis.

Background & Aims: Our previous studies have shown that Cryptosporidium parvum induces biliary epithelial cell apoptosis in vivo and causes apoptosis in bystander uninfected biliary epithelia in vitro. We analyzed C. parvum-induced nuclear factor kappa B (NF-kappaB) activation in human biliary epithelial cells and assessed its relevance to epithelial cell apoptosis.

High-dose ursodeoxycholic acid as a therapy for patients with primary sclerosing cholangitis.

Objectives: To assess the tolerability and efficacy of high-dose (25-30 mg/kg per day) ursodeoxycholic acid (UDCA) in patients with primary sclerosing cholangitis (PSC).

Methods: Thirty patients with PSC were enrolled in this pilot study and treated for 1 yr. Changes in the Mayo risk score at 1 yr of treatment and projected survival at 4 yr were compared with that observed in patients randomized to placebo (n = 52) or UDCA (n = 53) at a dose of 13-15 mg/kg per day.

The water channel aquaporin-8 is mainly intracellular in rat hepatocytes, and its plasma membrane insertion is stimulated by cyclic AMP.

We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes.

Nitric oxide-mediated inhibition of DNA repair potentiates oxidative DNA damage in cholangiocytes.

Background & Aims: Chronic inflammation, a risk factor for the development of bile duct cancer, induces inducible nitric oxide synthase (iNOS) with nitric oxide (NO) generation, which promotes oxidative damage of DNA, a process that probably is important in the initiation and progression of malignancies. Because inhibition of DNA repair is required for accumulation of oxidative DNA lesions, our aim was to determine if NO also inhibits repair of oxidative DNA damage.

Methods: A cholangiocarcinoma cell line and a cholangiocyte cell line were transfected with iNOS.

Upregulation of secretin receptors on cholangiocytes after bile duct ligation.

Secretin not only increases ductular bile secretion in vivo in rats after bile duct ligation (BDL) [1], but also increases cAMP levels and stimulates exocytosis in isolated cholangiocytes [2]. Although we have previously reported that secretin receptor mRNA was upregulated in cholangiocytes after BDL [3], the cholangiocyte secretin receptor has not been functionally characterized or quantified after BDL. In this work, we used a novel, photolabile and biologically active analogue of secretin to quantify and characterize secretin receptors on cholangiocytes isolated from normal and BDL rats.

Perfused rat intrahepatic bile ducts secrete and absorb water, solute, and ions.

Background & Aims: We report a novel approach to study biliary water, bile acid, and HCO(3)(-) transport: the microperfusion of intrahepatic bile duct units (IBDUs) isolated from normal rat liver.

Methods: To study water transport, IBDUs were perfused in vitro with a membrane-impermeant fluorescent volume marker, fluorescein sulfonate; net water movement (J(v)) and osmotic water permeability (P(f)) were then calculated. To study solute transport, IBDUs were perfused with taurocholic acid (TCA) and bile acid uptake was calculated from the concentrations of TCA in the perfused and collected solutions.

Magnetic resonance cholangiography in patients with biliary disease: its role in primary sclerosing cholangitis.

Background/aim: Magnetic resonance cholangiography (MRC) is a non-invasive diagnostic procedure whose role in the management of patients with primary sclerosing cholangitis (PSC) is unclear. The aim of this study was to determine the usefulness of MRC in the evaluation of the biliary tree in patients with suspected biliary disease, and in particular, PSC.

Methods: MRC and invasive cholangiography (ERCP or PTC) were both performed in 73 patients, (33 male, 40 female, mean age 56 years) with clinical and/or biochemical evidence of cholestasis.

A pilot study of pentoxifylline for the treatment of primary sclerosing cholangitis.

Objective: There is no effective therapy for patients with primary sclerosing cholangitis (PSC). Rats with experimental small bowel bacterial overgrowth develop hepatobiliary injury similar to PSC. The hepatobiliary injury results from peptidoglycan-polysaccharide-mediated activation of Kupffer cells, release of cytokines such as tumor necrosis factor (TNF-alpha), and is prevented by pentoxifylline.

Oral budesonide in the treatment of primary sclerosing cholangitis.

Objective: This study was designed to evaluate the safety and estimate the efficacy of oral budesonide in patients with primary sclerosing cholangitis (PSC).

Methods: Twenty-one patients with PSC were treated with 9 mg daily of oral budesonide for 1 yr.

Results: Significant, but marginally important, improvement in serum alkaline phosphatase (1,235 +/- 190 vs 951 +/-206 U/L, p = 0.

Alternative splicing of the rat sodium/bile acid transporter changes its cellular localization and transport properties.

Bile secretion involves the structural and functional interplay of hepatocytes and cholangiocytes, the cells lining the intrahepatic bile ducts. Hepatocytes actively secrete bile acids into the canalicular space and cholangiocytes then transport bile acids in a vectorial manner across their apical and basolateral plasma membranes. The initial step in the transepithelial transport of bile acids across rat cholangiocytes is apical uptake by a Na(+)-dependent bile acid transporter (ASBT).

Current therapies and clinical controversies in the management of primary sclerosing cholangitis.

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease of unknown etiology characterized by fibrosing inflammation of the intrahepatic and extrahepatic bile ducts, leading ultimately to cirrhosis and death caused by complications from liver failure if liver transplantation is not peformed. Despite a better understanding of the natural history of the disease, no significant breakthroughs have been made into its pathogenesis. Over the past decade and a half, many clinical trials of medical therapy have been conducted; however, none have demonstrated real efficacy.

Rab3D, a small GTP-binding protein implicated in regulated secretion, is associated with the transcytotic pathway in rat hepatocytes.

Rab3 isotypes are expressed in regulated secretory cells. Here, we report that rab3D is also expressed in rat hepatocytes, classic models for constitutive secretion. Using reverse transcriptase polymerase chain reaction (RT-PCR) with primers specific for rat rab3D, we amplified a 151 base pair rab3D fragment from total RNA extracted from primary cultures of rat hepatocytes.

A revised natural history model for primary sclerosing cholangitis.

Objective: To describe a natural history model for primary sclerosing cholangitis (PSC) that is based on routine clinical findings and test results and eliminates the need for liver biopsy.

Patients And Methods: Using the Cox proportional hazards analysis, we created a survival model based on 405 patients with PSC from 5 clinical centers. Independent validation of the model was undertaken by applying it to 124 patients who were not included in the model creation.

Expression of aquaporin-4 water channels in rat cholangiocytes.

We recently reported that secretin induces the exocytic insertion of functional aquaporin-1 water channels (AQP1) into the apical membrane of cholangiocytes and proposed that this was a key process in ductal bile secretion. Because AQP1 is present on the basolateral cholangiocyte membrane in low amounts, we hypothesized that another AQP must be expressed at this domain to facilitate transbasolateral water movement. Thus, we investigated the expression, subcellular localization, possible regulation by secretin, and functional activity of AQP4, a mercury-insensitive water channel expressed in other fluid transporting epithelia.

Mechanisms of attachment and internalization of Cryptosporidium parvum to biliary and intestinal epithelial cells.

Background & Aims: Although infection of the intestinal and biliary tracts by Cryptosporidium parvum is a major problem in patients with the acquired immunodeficiency syndrome, the specific microbial and host molecules involved in C. parvum infection are unknown. We tested the hypothesis that lectin-carbohydrate interactions and cytoskeleton reorganization are involved in the infection of biliary and intestinal epithelia by C.