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N F Larusso

Publications and source records attributed to N F Larusso.

16 recordsLinked to original sources
PubMed2005

Membrane microdomains in hepatocytes: potential target areas for proteins involved in canalicular bile secretion.

The formation of hepatic bile requires that water be transported across liver epithelia. Rat hepatocytes express three aquaporins (AQPs): AQP8, AQP9, and AQP0. Recognizing that cholesterol and sphingolipids are thought to promote the assembly of proteins into specialized membrane microdomains, we hypothesized that canalicular bile secretion involves the trafficking of vesicles to and from localized lipid-enriched microdomains in the canalicular plasma membrane. Hepatocyte plasma membranes were sonicated in Triton and centrifuged overnight on a sucrose gradient to yield a Triton-soluble pellet and a Triton-insoluble, sphingolipid-enriched microdomain fraction at the 5%/30% sucrose interface. The detergent-insoluble portion of the hepatocyte plasma membrane was enriched in alkaline phosphatase (a microdomain-positive marker) and devoid of amino-peptidase N (a microdomain-negative marker), enriched in caveolin, both AQP8 and AQP9, but negative for clathrin. The microdomain fractions contained chloride-bicarbonate anion exchanger isoform 2 and multidrug resistance-associated protein 2. Exposure of isolated hepatocytes to glucagon increased the expression of AQP8 but not AQP9 in the microdomain fractions. Sphingolipid analysis of the insoluble fraction showed the predominant species to be sphingomyelin. These data support the presence of sphingolipid-enriched microdomains of the hepatocyte membrane that represent potential localized target areas for the clustering of AQPs and functionally related proteins involved in canalicular bile secretion.

Animals↗
PubMed2001

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. Both UDCA and its taurine conjugate stimulated secretion of ATP by isolated rat hepatocytes, and produced measurable increases in ATP in bile of isolated rat liver. Perfusion of ATP into microdissected bile-duct segments induced Ca(2+) signalling in bile-duct epithelia, while perfusion of bile acid did not. Thus UDCA may promote bile flow by inducing hepatocytes to release ATP into bile, which then stimulates fluid and electrolyte secretion by bile-duct epithelia downstream via changes in cytosolic Ca(2+). Moreover, these findings demonstrate the feasibility of using pharmacological means to induce secretion of endogenous ATP. Since the liver and other epithelial organs express luminal ATP receptors, these findings more generally suggest that a mechanism exists for pharmacological activation of this paracrine signalling pathway. This strategy may be useful for treatment of cystic fibrosis and other secretory disorders of the liver and other epithelial tissues.

Adenosine Triphosphate↗
PubMed2001

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. RESULTS: A marked improvement in serum alkaline phosphatase activity (1265+/-172 vs 693+/-110 U/L, p < 0.001), AST (161+/-037 vs 77+/-13 U/L, p = 0.001), albumin (4.0+/-0.1 vs 4.2+/-0.1 g/dl, p = 0.03), and total bilirubin (1.6+/-0.3 vs 1.3+/-0.2 mg/dl, p = 0.1) occurred at 1 yr of therapy with high-dose UDCA. Changes in the Mayo risk score after 1 yr of treatment were significantly different among the three groups (p < 0.001), and these changes would be translated into a significantly different expected survival at 4 yr (p = 0.05). This expected survival at 4 yr was significantly different between placebo and the dose of 25-30 mg/kg per day (p = 0.04), but not between placebo and the dose of 13-15 mg/kg per day (p = 0.4). High-dose UDCA was well tolerated. CONCLUSIONS: UDCA at a dose of 25-30 mg/kg per day may be of benefit for patients with PSC, and this regimen deserves further evaluation in a long-term, randomized, placebo-controlled trial.

Adult↗
PubMed2000

Biliary tract physiology.

Cholangiocytes, the cells lining the bile ducts, are now recognized as important contributors to and modulators of bile formation. During the last few years, remarkable insights have been made into the mechanisms of fluid, electrolyte, and solute transport by biliary epithelia, as well as increasing knowledge of the complex endocrine, paracrine, and neurologic factors regulating bile formation. Advances in the past year include an increased understanding of the interaction between bile acids and cholangiocytes in the regulation of bile formation in normal and cholestatic states and greater insight into the pathogenic mechanisms of biliary diseases. References to recent comprehensive reviews of specific areas of biliary physiology are provided, and new experimental models are also described.

Journal Article↗
PubMed1999

Oral nicotine in treatment of primary sclerosing cholangitis: a pilot study.

Currently, no accepted medical therapy for patients with primary sclerosing cholangitis (PSC) is available. Case-control studies have shown an inverse association between PSC and smoking behavior, suggesting that nicotine might have a beneficial effect in PSC. The aim of this study was to evaluate the safety and estimate the efficacy of oral nicotine in the treatment of PSC. Eight PSC patients who had never smoked received oral nicotine at a maximum dose of 6 mg four times a day for up to one year. Liver biochemistries and plasma cotinine levels were determined at entry and at three-month intervals during the study duration. Five patients completed one year of treatment, but three of them had to temporarily reduce the dose due to side effects. One patient completed only four months of treatment due to dizziness and heart palpitations. Two patients completed only one month of treatment due to reactivation of colitis requiring corticosteroid therapy. No significant changes in liver biochemistries were noted during the treatment period despite a significant increase in plasma cotinine levels. In conclusion, oral nicotine seems to have no beneficial effects in the treatment of PSC, and it is frequently associated with side effects necessitating permanent drug cessation.

Administration, Oral↗
PubMed1999

Biliary tract physiology.

Largely because of the recent development of new experimental models, cholangiocytes--the cells lining the bile ducts--are now recognized as important contributors to and modulators of bile formation. Recent work elucidating the mechanisms and regulation of fluid, solute, and electrolyte transport indicates that the biliary epithelium influences bile formation through both autocrine and paracrine mechanisms. Novel roles for bile acids in cholangiocyte physiology have been proposed, and insight into the anatomic and functional differences of cholangiocytes along the biliary tree has been gained. Improved understanding of these concepts and the pathophysiologic response of the biliary tree to injury should provide new therapies for biliary diseases.

Journal Article↗
PubMed1999

The Fifth Carlos E. Rubio Memorial Lecture. Sclerosing cholangitis: pathogenesis, pathology, and practice.

Primary sclerosing cholangitis is a generally progressive, sometimes fatal, chronic hepatobiliary disorder for which no effective medical or surgical therapy now exists. The syndrome occurs most frequently in young men and is characterized by chronic cholestasis, frequent association with CUC, a paucity of serologic markers, hepatic copper overload, and characteristic abnormalities in some liver biopsy specimens and in virtually all cholangiograms. The natural history of the syndrome is still somewhat unclear; the disease likely progresses slowly and relentlessly over a decade or longer from an asymptomatic stage to a condition characterized by symptoms of cholestasis and complicated by cirrhosis and portal hypertension and carcinoma of the bile ducts. Management should first involve a thoughtful decision to observe, which is reasonable in the asymptomatic patient with early disease, or to intervene, particularly in patients with symptoms. Therapeutic goals should be defined and should concentrate on either alleviating symptoms, dealing with complications, or attempting to affect the underlying hepatobiliary disease. Symptomatic treatment and therapy for complications is similar to that employed in other chronic liver diseases, but also involves balloon dilatation of dominant strictures in appropriately selected symptomatic patients. Biliary tract reconstructive surgery may alleviate symptoms in selected patients with PSC, but its effect on the natural history of the syndrome has not been determined. Proctocolectomy for CUC in a patient with CUC and PSC does not beneficially affect the progression of the underlying hepatobiliary disease. In contrast, orthotopic liver transplantation may be life-saving for patients with advanced disease. Medical therapy directed at arresting the progression of the underlying hepatobiliary disease is currently experimental and includes cupruretic, immunosuppressive, antifibrogenic, and choleretic agents. Although a single recently completed controlled trial makes it unlikely that cupruretic agents will be helpful in this syndrome, immunosuppressive (i.e. cyclosporin A and methotrexate) and choleretic (i.e. ursodeoxycholic acid) agents alone or in combination are currently undergoing evaluation in randomized trials.

Adrenal Cortex Hormones↗
PubMed1997

The pathobiology of biliary epithelia.

Our understanding of the pathobiology of biliary epithelia is rapidly growing because of a surge of investigative activity. This became possible after suitable experimental models and techniques were developed with which to study cholangiocyte biology. Although the molecular mechanisms of bile formation by cholangiocytes and the role of these cells as a major cellular target in a variety of severe hepatobiliary diseases are currently being investigated, many questions remain unanswered, particularly regarding cholangiocellular functions, both in normal and abnormal conditions. As current experimental models become more refined, scientists with interests as diverse as cell biology and physiology, morphology, pharmacology, immunology, genetics, and oncology can be expected to further clarify the pathobiology of biliary epithelia.

Autoimmune Diseases↗
PubMed1996

Solute and water transport pathways in cholangiocytes.

Cholangiocytes possess specific membrane transport systems for a large number of substrates. As a result of the secretion or absorption of solutes, water moves passively across plasma membranes, very likely through water channels; as a result, the volume and composition of primary bile are modified. Cholangiocytes express receptors for secretin and somatostatin, hormones that alter intracellular levels of cAMP in opposite directions; these alterations very likely alter the activation (i.e., phosphorylation state) or number (i.e., by coupled exocytic-endocytic membrane modification) of transporters in the apical or basolateral cholangiocyte membranes. Although our understanding of these mechanisms is sill embryonic, it is anticipated that accelerated research efforts by laboratories utilizing recently available experimental models will provide important advances in the knowledge of the molecular mechanisms involved in the transport of water and solutes by cholangiocytes. The challenge will be to integrate the emerging, often isolated, findings in a physiologically relevant manner to understand how cholangiocytes function normally and in pathological conditions.

Animals↗
PubMed1995

Somatostatin inhibits secretin-induced ductal hypercholeresis and exocytosis by cholangiocytes.

Previous work from our laboratory has implicated hormone-induced plasma membrane movement (i.e., endo- and exocytosis) in water and electrolyte transport by the epithelial cells that line the ducts in the liver (i.e., cholangiocytes). To further explore the cellular mechanisms regulating ductal bile secretion, we infused somatostatin and/or secretin intravenously into rats 2 wk after either bile duct ligation (BDL), a procedure that induces selective proliferation of cholangiocytes, or sham surgery and measured bile flow and biliary constituents. We also determined the effect of somatostatin on basal and secretin-induced exocytosis by purified cholangiocytes isolated from rat liver after BDL. Finally, we studied the expression of the somatostatin receptor gene by both ribonuclease (RNase) protection and nuclear run-on assays using cDNA encoding for two subtypes of the somatostatin receptor gene (i.e., SSTR1 and SSTR2). In vivo, somatostatin infusion caused a dose-dependent bicarbonate-poor decrease (57% maximal decrease below baseline; P < 0.05) in bile flow in BDL but not in sham-operated rats; in contrast, secretin caused a dose-dependent bicarbonate-rich choleresis (228% maximal increase above baseline; P < 0.05) in BDL but not in sham-operated rats. Simultaneous or prior infusion of somatostatin inhibited the secretin-induced hypercholeresis in BDL rats. In vitro, somatostatin had no effect on basal exocytosis by cholangiocytes isolated from BDL rats; however, somatostatin inhitibed (88% maximal inhibition; P < 0.05) secretin-induced exocytosis by cholangiocytes in a dose-dependent fashion. In addition, somatostatin inhibited secretin-induced increases in levels of adenosine 3',5'-cyclic monophosphate (cAMP) in cholangiocytes isolated from BDL rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Alterations in hepatocyte lysosomes in experimental hepatic copper overload in rats.

BACKGROUND: Although Wilson's disease is characterized by an accumulation of copper within hepatocyte lysosomes, the effects of excess copper on hepatic lysosomes are unknown. We studied the effects of excess copper on the structure, physicochemical properties, and pH of hepatocyte lysosomes using a rodent model. METHODS: Rats were copper loaded with 0.125% copper acetate in water for 6 weeks. Copper was measured by atomic absorption spectrophotometry. Morphology was studied by electron microscopy. Lysosomal membrane fluidity was studied by fluorescence polarization, and lipid composition was determined by gas chromatography. Hepatocyte lysosomal pH was determined by flow cytometry. RESULTS: Copper overload resulted in a 10-fold increase in hepatic copper. Hepatocyte lysosomes were enlarged and abnormally shaped with a 27-fold increase in copper, increased in vitro fragility, and decreased lysosomal membrane fluidity. Thiobarbituric acid reactive substances, a measure of lipid peroxidation, doubled in isolated lysosomal membranes. Polyunsaturated fatty acids increased, saturated fatty acids decreased, and membrane content of selected fatty acids was modified after copper overload. Lysosomal pH increased from 4.67 +/- 0.02 to 4.87 +/- 0.02. CONCLUSIONS: Copper overload causes alterations in lysosomal morphology, increases lysosomal fragility, decreases membrane fluidity, alters membrane fatty acid composition, and increases lysosomal pH. Copper catalyzed lipid peroxidation represents the likely mechanism for these alterations.

Adenosine Triphosphate↗
PubMed1993

Ulcerative colitis disease activity following treatment of associated primary sclerosing cholangitis with cyclosporin.

Thirty five adult patients with precirrhotic primary sclerosing cholangitis were randomly allocated to treatment for at least one year with low dose (4.1 mg/kg/day) cyclosporin or placebo in a double blind trial. Thirty patients had coexisting ulcerative colitis, including three who had previously undergone colectomy and one who discontinued treatment after three months. Of the remaining 26 patients, 16 received cyclosporin and 10 received placebo. Endoscopy was performed at entry to confirm the diagnosis of inflammatory bowel disease. The ulcerative colitis disease activity was prospectively classified annually as remission/mild, moderate, or severe using the Truelove and Witt's criteria. Before treatment there were no differences between the cyclosporin and placebo groups in the number of patients with remission/mild colitis, 14/16 (88%) v 9/10 (90%), and moderate colitis, 2/16 (12%) v 1/10 (10%). During treatment, a remission/mild disease course was present in 15/16 (94%) v 6/10 (60%), p = 0.05 and a moderate disease course in 1/16 (6%) v 4/10 (40%), p = 0.05. It is concluded that patients treated with cyclosporin for primary sclerosing cholangitis who have coexisting ulcerative colitis have a more benign course of colitis resulting both from improvement of moderately active colitis and from fewer flares of remission/mildly active colitis. These findings suggest that cyclosporin may be of benefit to the colon in patients with ulcerative colitis who are being treated with cyclosporin for primary sclerosing cholangitis.

Adult↗
PubMed1982

Differing effects of ursodeoxycholic or chenodeoxycholic acid on biliary cholesterol saturation and bile acid metabolism in man. A dose-response study.

A dose-response study comparing ursodeoxycholic and chenodeoxycholic acid was carried out in six men with asymptomatic radiolucent gallstones present in well-visualizing gallbladders. The study tested the effects of a low (averaging 6 mg/kg/day) or medium dose (averaging 11 mg/kg/day) of each bile acid on the cholesterol saturation of bile as well as on bile acid metabolism, as inferred from biliary and fecal bile acid composition. Ursodeoxycholic acid, at low or medium doses, induced bile desaturation in most patients, whereas chenodeoxycholic acid did not. Despite the greater desaturation efficacy of ursodeoxycholic acid, biliary bile acids became less enriched with the administered bile acid during ursodeoxycholic acid treatment than during chenodeoxycholic acid treatment. Both bile acids were nearly completely 7-dehydroxylated to lithocholic acid by colonic bacteria, but biliary lithocholic increased only slightly (and similarly) with each bile acid. Fecal bile acid composition suggested that administered ursodeoxycholic acid suppressed endogenous bile acid synthesis much less than chenodeoxycholic acid. The results indicate that ursodeoxycholic acid and chenodeoxycholic acid have similar but not identical effects on bile acid metabolism, but that for a given dose, ursodeoxycholic acid is a more potent desaturating agent than chenodeoxycholic acid. The results suggest that cholesterol gallstone dissolution with ursodeoxycholic acid should occur with a dose of 8-10 mg/kg in most nonobese patients.

Aged↗
PubMed1982

Enzymatic determination of total 3 alpha-hydroxy bile acids in faeces. Validation in healthy subjects of a rapid method suitable for clinical routine purpose.

A method for determining faecal bile acids, suitable for clinical purposes, is introduced. The analysis uses a 0.2-g stool specimen, a simple extraction procedure, and 3 alpha-steroid dehydrogenase determination. The method, which is rapid, has been validated by gas-liquid chromatography and by recovery of internal standards. Stool examination was done in 16 healthy volunteers on free diet and in 25 patients with non-gastrointestinal diseases who were on a fat- and fibre-fixed diet. No difference was found between the two groups, so the data were pooled, and the normal reference interval (mean +/- S.D.) for faecal bile acid output was calculated to be 0-975 mumol/24h.

3-Hydroxysteroid Dehydrogenases↗
PubMed1976

Sampling intestinal content with a sequestering capsule. A noninvasive technique for determining bile acid kinetics in man.

A noninvasive technique for determining bile acid kinetics by isotope dilution in man features the intravenous injection of a radiolabeled bile acid, together with daily oral administration, for several days, of capsules of dialysis membrane containing cholestyramine and colored beads for dating. The cholestyramine traps conjugated bile acids during transit of the small intestine. Capsules are recovered from stool by sieving, sequestered bile acid is eluted, conjugated bile acids are isolated chromatographically, and their specific activity is determined. The precision and validity of this sequestering capsule technique were assessed by comparing the specific activity decay curve of chenodeoxycholyl conjugates obtained from capsule samples with that obtained from duodenal samples in seven healthy volunteers in whom the bile acid pool had been labeled with [14C]chenodeoxycholic acid. Estimates of pool size by the two methods correlated well (r = 0.98), as did the daily fractional turnover rate (r = 0.96). The mean (+/-SD) percentage differences for the kinetic parameters of pool size (8.3 +/- 13.6), fractional turnover rate (-15.2 +/- 11.5), and synthesis rate (-4.3 +/- 11.4) were fairly small, indicating that the noninvasive method has validity. However, agreement between simultaneously administered capsules was only fair, especially when the amount of bile acid trapped was small, suggesting that the precision of the capsule technique may be less than that of the conventional duodenal sampling technique; the latter probably obtains a more valid sample of the bile acid pool.

Administration, Oral↗