Role and mechanisms of action of acetylcholine in the regulation of rat cholangiocyte secretory functions.

UNLABELLED: We investigated, in isolated bile duct units (IBDU) and cholangiocytes isolated from normal rat liver, the occurrence of acetylcholine (ACh) receptors, and the role and mechanisms of ACh in the regulation of the Cl-/HCO3- exchanger activity. The Cl-/HCO3- exchanger activity was evaluated measuring changes in intracellular pH induced by acute Cl- removal/readmission. M3 subtype ACh receptors were detected in IBDU and isolated cholangiocytes by immunofluorescence, immunoelectron microscopy, and reverse transcriptase PCR. M1 subtype ACh receptor mRNA was not detected by reverse transcriptase PCR and M2 subtype was negative by immunofluorescence. ACh (10 microM) showed no effect on the basal activity of the Cl-/HCO3- exchanger. When IBDU were exposed to ACh plus secretin, ACh significantly (P < 0.03) increased the maximal rate of alkalinization after Cl- removal and the maximal rate of recovery after Cl- readmission compared with secretin alone (50 nM), indicating that ACh potentiates the stimulatory effect of secretin on the Cl-/HCO3- exchanger activity. This effect of ACh was blocked by the M3 ACh receptor antagonist, 4-diphenyl-acetoxy-N-(2-chloroethyl)-piperidine (40 nM), by the intracellular Ca2+ chelator, 1,2-bis (2-Aminophenoxy)- ethane-N,N,N', N'-tetraacetic acid acetoxymethylester (50 microM), but not by the protein kinase C antagonist, staurosporine (0.1 microM). Intracellular cAMP levels, in isolated rat cholangiocytes, were unaffected by ACh alone, but were markedly higher after exposure to secretin plus ACh compared with secretin alone (P < 0.01). The ACh-induced potentiation of the secretin effect on both intracellular cAMP levels and the Cl-/HCO3- exchanger activity was individually abolished by two calcineurin inhibitors, FK-506 and cyclosporin A (100 nM). CONCLUSIONS: M3 ACh receptors are markedly and diffusively represented in rat cholangiocytes. ACh did not influence the basal activity of the Cl-/HCO3- exchanger, but enhanced the stimulation by secretin of this anion exchanger by a Ca2+-dependent, protein kinase C-insensitive pathway that potentiates the secretin stimulation of adenylyl cyclase. Calcineurin most likely mediates the cross-talk between the calcium and adenylyl cyclase pathways. Since secretin targets cholangiocytes during parasympathetic predominance, coordinated regulation of Cl-/HCO3- exchanger by secretin (cAMP) and ACh (Ca2+) could play a major role in the regulation of ductal bicarbonate excretion in bile just when the bicarbonate requirement in the intestine is maximal.

Membrane heterogeneity in isolated rat hepatocytes and liver plasma membrane subfractions: a comparative study using DPH and its cationic derivative TMA-DPH.

The fluorescence decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) and of 1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) has been studied in hepatocytes isolated from rat liver and in isolated plasma membrane subfractions (cLPM, canalicular membranes and bLPM, basolateral membranes) using frequency domain fluorometry. The decay has been analyzed either by using a model of discrete exponential components or a model that assumes a continuous distribution of lifetime values in order to study different aspects of membrane heterogeneity. The results obtained by the two analyses are practically superimposable but the distributional approach allows an evaluation of membrane heterogeneity through the width of the distribution that has shown particularly significant differences when freshly hepatocytes are compared with in vitro aged hepatocytes. Moreover, the comparison of the distributional analysis of the two probes has shown in cLPM a tendency to higher values of the main lifetime component and a narrower distribution width with respect to bLPM. These results indicate changes of membrane domain organization that have been discussed in relation with the specific lipid composition that characterizes the two membrane subfractions. Our results indicate that frequency domain fluorometry may be used to study membrane heterogeneity in intact cells and isolated membranes.

An interleukin-1 receptor antagonist decreases fibrosis induced by dimethylnitrosamine in rat liver.

The main pathological feature of liver fibrosis is the accumulation of extracellular matrix associated with hyperplasia and activation of perisinusoidal (Ito) cells (PSC) to myofibroblast-like cells. Interleukin-1 enhances collagen synthesis by increasing the proliferative activity of cultured PSC and has been implicated in the pathogenesis of hepatic fibrosis. Interleukin-1 receptor antagonist (IL-1ra) can block the binding of IL-1 to its receptors and act as a natural inhibitor of IL-1. We have examined whether the administration of IL-1ra can interfere with the development of experimental cirrhosis induced by dimethylnitrosamine (DMN). Rats were divided in three groups and received respectively DMN, DMN + IL-1ra and IL-1ra. For each group the collagen content of the hepatic tissue and the volume density of the inflammatory infiltrate were measured. Immunostaining for laminin and alpha-smooth muscle actin were also performed. In animals given DMN + IL-1ra we observed a decreased deposition of laminin and collagen, and a decreased number of laminin-positive PSC and of alpha-smooth muscle actin reactive cells, compared with animals receiving DMN alone. The present findings suggest that the early activation of PSC in vivo is at least in part mediated by IL-1 and confirm that the administration of IL-1ra may be of interest in modifying the biological effects of IL-1.

Ethanol-induced alterations of matrix network in the duodenal mucosa of chronic alcohol abusers.

Excessive consumption of alcoholic beverages may be associated with gastrointestinal symptoms, including dyspepsia and diarrhoea. It is not clear whether or not chronic alcohol ingestion damages the mucosa of the small intestine. We investigated the effect of chronic alcohol abuse on the duodenal mucosa, and particularly on its extracellular matrix (ECM) network. Duodenal biopsy specimens were obtained during upper gastrointestinal endoscopy from 50 chronic alcoholics without cirrhosis and 10 healthy subjects. Morphological studies were performed by routine histology, immunohistochemistry and electron microscopy. Morphometry of duodenal tissues was performed with a computerized image analyser. No significant duodenal epithelial changes were found in alcoholics, despite an evident reduction in the enterocyte turnover. Myofibroblast-like cells were significantly increased in the villus stroma of alcoholics in comparison to controls. These cells stained positively for desmin, alpha-smooth muscle actin and for several ECM components. In alcohol abusers the thickness of the mucosal basement membrane was greater and the staining for collagen I and III was enhanced both in the basement membrane and in the villus stroma. A higher expression of tenascin was also seen at the base of villi of alcoholics. Chronic alcohol abuse may induce fibrosis of duodenal villi which is associated with a transformation of villus juxta-parenchymal cells into active subepithelial myofibroblast-like cells able to produce different ECM components.

Primary biliary cirrhosis: modalities of injury and death in biliary epithelium.

BACKGROUND/AIM: Despite the number of studies on primary biliary cirrhosis, contrasting data remain concerning modalities of cholangiocyte death. Liver biopsies obtained from 40 patients with anti mitochondrial antibody-positive primary biliary cirrhosis, at various stages of the disease, were examined, and special attention was paid to the expression of subcellular damage and evidence of apoptosis. METHODS: Liver sections were stained with haematoxylin/eosin or Sirius red. Ductular mass was evaluated on sections after cytokeratin 7 staining. Apoptosis was evaluated on haematoxylin/eosin stained material or after processing for terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling assay. In 16 patients, part of the biopsy was processed for electron microscopy. Twenty histologically normal liver biopsies were used for control purposes. RESULTS: According to Scheuer's classification, 29 patients were classified as stage I-II, and 11 as stage III-IV. A strong staining of bile ducts was evident after immunohistochemistry for cytokeratin 7, often associated with ductular metaplasia in lobular zone 1. Cytokeratin 7-positive cells occupied 3.0+/-1.3% of liver mass as compared to 0.25+/-0.03% in controls. Ductular metaplasia accounted for 1.4+/-0.07% of all cytokeratin 7-positive cells. Regardless of staging, apoptotic bodies were seen only exceptionally in epithelial wall of bile ducts, whereas cholangiocyte damage leading to extensive lytic necrosis appeared responsible for most of the bile duct mass loss, as also confirmed by ultrastructural studies. A few terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling-positive nuclei were occasionally associated with the inflammatory infiltrate and evidence of apoptosis in hepatocytes was frequent, especially in zone 1. CONCLUSION: Regardless of staging, lytic necrosis and not apoptosis accounts for most of the bile duct loss in primary biliary cirrhosis. Furthermore, ductular metaplasia appears as a late event with highly variable pattern being observed between patients.

Wine: risk factors for liver disease and antifibrotic compounds.

Wine can be considered an integral part of the Mediterranean diet and moderate alcohol intake can be beneficial for health. This health-promoting effect is presumably due to the presence of antioxidant substances. It is also known that excessive alcohol intake can lead to liver cirrhosis. A main pathogenetic mechanism in liver cirrhosis is the activation of hepatic stellate cells which acquire a myofibroblast-like phenotype. Excessive production of oxidative stress products may initiate the activation process. Phenolic compounds contained in red wine have been shown to have antifibrotic properties on activated hepatic stellate cells. In vitro and in vivo studies are needed for a better evaluation of the clinical relevance of these findings.

Bone marrow transplantation in Hunter syndrome (mucopolysaccharidosis type II): two-year follow-up of the first Italian patient and review of the literature.

A patient with Hunter syndrome, or mucopolysaccharidosis type II (MPS-osis II), was subjected to bone marrow transplantation (BMT), at the age of 2 9/12 years. A two-year follow-up ensued to the purpose of comparing clinical, biochemical, neuropsychologic status pre- and post-BMT. From the clinical standpoint, a complete normalization of hepatosplenomegaly was observed. In addition the skin decreased in thickness and joint mobility improved. The echocardiography showed normalization of left ventricle size. With the exception of verbal capabilities, there was no further deterioration of the neuropsychologic profile. The ultrastructural examination of the liver showed an almost total disappearance of storage material. Normal iduronate sulfatase levels in leukocytes and lymphoblasts were constantly found after BMT. A qualitative and quantitative improvement in urinary glycosaminoglycan (GAG) excretion was also found. The effectiveness of the BMT in our patient is also assessed in the context of the few cases of MPS-osis II that have been reported to date. A final evaluation of the efficacy of BMT in MPS-osis II will be possible only when a higher number of patients, diagnosed as early as possible and transplanted within the first months of life, can be followed-up for more extended periods of time.

A quantitative evaluation of apoptotic bodies in rat liver.

The aim of the present study was to determine if data on the number and acinar distribution of apoptotic bodies (AB) in normal liver could help in the understanding of cell kinetics in the liver, and the mechanism of early ethanol-induced liver damage. Normal male Sprague-Dawley rats were studied. They had free access to Purina chow and drinking water. Ethanol-treated rats received the drug at increasing concentration in drinking water for 5 weeks. The following parameters were measured: number of AB in the lobule, topographical localization, distance from terminal hepatic veins (THV), i.e. row of hepatocytes concerned, H1 being the closest to the THV. The results show that AB are rare in the normal liver and are always observed in zone 3, next to the THV. Of 149 THV examined, 56 showed one associated AB, exceptionally two. 74% of the AB were confined to the first row of hepatocytes (H1), 21% to H2, 4% to H3, and 1% to H4. In ethanol-treated rats the mean number of AB was 2 or 3 for each THV. 42% were found in H1, 32% in H2, 15% in H3, 7% in H4, and 4% in H5. The data show that AB are not randomly dispersed in normal liver but show a preferential acinar distribution. In addition, most AB are located in the row of liver cells immediately adjacent to the THV. If apoptosis is indeed an expression of physiological cell renewal, these findings support the concept that zone 3 contains older hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Preferential distribution of apoptotic bodies in acinar zone 3 of normal human and rat liver.

The aim of the present investigation was to study the number and acinar distribution of apoptotic bodies in normal liver as an approach to a better understanding of cell kinetics in the hepatic parenchyma. The material included 20 normal human needle liver biopsies and 20 normal male Sprague-Dawley rats. For each liver sample, the following parameters were measured: number of apoptotic bodies in the lobule, topographical localization, and distance from terminal hepatic veins (THV), i.e., the row of hepatocytes concerned, H1 being the closest to the THV. The results were strikingly similar in human and in animal material, showing that apoptotic bodies are rare in the normal liver and, when present, are always observed in zone 3, next to the THV. In fact, the first two rows of hepatocytes (H1 and H2) contained 80% of the apoptotic bodies in human liver, and 95% in rat liver. These data show that apoptotic bodies are not randomly dispersed in normal liver tissue but show a preferential acinar distribution. In addition, the vast majority of apoptotic bodies are located in the row of liver cells immediately adjacent to the THV. If apoptosis is indeed an expression of physiological cell renewal or 'programmed cell death', these findings support the concept of an aging gradient of liver cells, with zone 3 containing older hepatocytes.

Changes of the smooth endoplasmic reticulum induced by rifampicin in human and guinea-pig hepatocytes.

Rifampicin induces a proliferation of the smooth endoplasmic reticulum in guinea-pig and human hepatocytes. This may support the hypothesis of enhancement of drug-metabolizing enzymes induced by the drug. However, the pattern of proliferation is not similar in man and in guinea-pig hepatocytes. Some caution is needed in the study of enzyme induction in man and in extrapolations from animal to human data.

A morphometric study of the endoplasmic reticulum in human hepatocytes. Correlation between morphological and biochemical data in subjects under treatment with certain drugs.

The distribution of the endoplasmic reticulum in human hepatocytes is defined in quantitative terms using the techniques of morphometry. The subjects of the study are liver biopsies from normal, untreated subjects and patients being treated with various drugs. In contrast to rat hepatocytes, the amount of smooth endoplasmic reticulum (SER) in man exceeds that of the rough endoplasmic reticulum (RER) and accounts for 76.3% of the total endoplasmic reticulum. This is to be taken into consideration in pharmacological or toxicological studies. In addition, two components of the SER have been identified: more prominent is the type 1 or vesicular which has a regular honeycomb pattern, made up of cisternae with patent lumina and a mean width of 1500 A; the type 2, or non-vesicular, occurs in discrete foci of densely packed smooth membranes with a spacing of about 140 A. In subjects under short-term treatment with Benzodiazepin (diazepam) the RER remained unchanged but the SER membranes were significantly increased with a remarkable, two-to threefold increase of the SER type 2 in three out of four patients. A rise in incorporation of (14)C-acetate into digitonin-precipitable sterols as measured in liver biopsy material was also noted in these three patients. The suggestion is made that the SER 2 represents the newly formed membranes whereas the SER 1 would represent ;adult' membranes. No changes were observed in two patients under short-term treatment with phenobarbital or Dilantin.

Changes of the Golgi apparatus induced by diethylmaleate in rat hepatocytes.

Ultrastructural studies of the liver of rats given diethylmaleate (DEM) (0.7 ml per kg body, i.p.) weight revealed marked alterations of the configuration of the Golgi complex in all hepatocytes. This consisted in dilatation of the cisternae leading to the formation of large cysts. The alteration was more prominent 15 min after administration of the drug, coincident with a 2-fold increase of bile flow and a decrease of hepatic glutathione to 15% of controls. The morphology returned to normal at 45 min after DEM administration together with a return of bile flow to control values whereas hepatic glutathione level remained markedly depressed for 2 hr, rising slowly afterwards. No other signs of altered hepatic morphology developed up to 5 hr. The morphological changes correlated with altered bile flow induced by DEM, suggesting involvement of the Golgi complex in biliary excretion of osmotically active glutathione conjugates of DEM.

The lipocytes in normal human liver. A quantitative study.

A quantitative analysis of lipocytes (fat-storing cells, Ito cells) has been conducted on needle liver biopsies of 8 subjects without hepatic impairment. The mean volume density of lipocytes was 1.88 +/- 0.25% of parenchymal volume, and the number of lipocytes per 1,000 hepatocytes (Ito cell index) was 63.45 +/- 19.18. A study of the zonal distribution showed that the values were significantly higher in the centrolobular than in the periportal areas. No correlation was evident between the volume density or the number of lipocytes and the volume density of parenchymal steatosis. The high coefficients of variation resulting from the present study are evidence that quantitative data are necessary to evaluate volumetrical or numerical variations of lipocytes.

Morphological features and modulation of the intrahepatic biliary epithelium.

Much has been learned in the past few years concerning the morphology and function of the intrahepatic biliary epithelium. Immunohistochemistry, together with ultrastructural studies has allowed a better identification or the smallest branches of the biliary tree and of subcellular components (cytoskeleton, specializations of the cell membrane, specific receptors). Modulation of the biliary epithelium in response to physiological or pathological stimuli has renewed the interest concerning the existence of facultative stem cells in the liver. More information is needed however concerning the mechanisms of cell loss in vanishing bile duct syndromes.