Effect of ethanol and chlorpromazine on transhepatic transport and biliary secretion of horseradish peroxidase

Effect of S-adenosyl-L-methionine on ethanol cholestasis and hepatotoxicity in isolated perfused rat liver

We investigated whether S-adenosyl-L-methionine (SAMe) influences the inhibitory effect of ethanol on bile secretion and ethanol hepatotoxicity in the isolated perfused rat liver. SAMe (25 mg/kg intramuscularly three times a day) was administered for three days consecutively. Liver was then isolated and perfused with taurocholate to stabilize bile secretion and exposed to 1% ethanol for 70 min. The effect of ethanol on bile flow, bile salt biliary secretion, oxygen liver consumption, AST and LDH release in the perfusate, and hepatic concentration of glutathione, malondialdehyde, and diene conjugates was compared between SAMe-treated livers (N = 11) and paired controls (N = 11). Control experiments without ethanol were also performed (N = 6). Exposure to 1% ethanol induced a significantly (P < 0.03) higher inhibition of bile flow (-35% vs 17%) and bile salt secretion (-28% vs 16%) in untreated compared with SAMe-treated livers. During 1% ethanol exposure, the release of LDH and AST in the perfusate was significantly lower (P < 0.02) in SAMe-treated livers. Oxygen liver consumption was markedly inhibited by 1% ethanol administration (P < 0.02 vs controls without ethanol), an effect almost totally prevented by SAMe treatment (P < 0.02 vs ethanol controls). The hepatic concentration of total glutathione was significantly (P < 0.02) decreased by 1% ethanol exposure, but this effect was less pronounced in SAMe-treated than in untreated controls (P < 0.02). The hepatic levels of malondialdehyde and diene conjugates were not significantly changed by ethanol exposure in either SAMe-treated or control livers in comparison to ethanol-free controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrahepatic cholestasis: a review of biochemical-pathological mechanisms

Intrahepatic cholestasis involves impaired excretion of bile via the hepatobiliary system as a consequence of one or more lesions within the liver. In humans, intrahepatic cholestasis most often results as a side-effect of drug therapy and the clinical manifestation of this condition, jaundice, has been estimated to account for hospitalization in 2 to 5% of the cases for the general population and approaches as much as 20% in the elderly. With the aging of the population and the common occurrence of poly-drug therapy in geriatric patients, it is to be expected that jaundice due to drug-induced intrahepatic cholestasis will become even more prevalent, and accordingly the need to understand the basic mechanisms of this disease condition will become more urgent. The list of culprit agents implicated in the induction of intrahepatic cholestasis in humans is continually expanding. These include various steroid hormones, bile acids, drugs and other chemicals. Experimentally, a wide spectrum of agents has been shown to precipitate intrahepatic cholestasis. Over the years, a number of hypotheses on the biochemical and pathological mechanisms of intrahepatic cholestasis has emerged, including the following: impaired sinusoidal membrane function; interference with the distribution and binding of cytoplasmic endogenous carrier proteins; interference with mitochondrial energy supply; defects in the canalicular membrane including altered Na+/K+ -ATP-ase activity; impairment of microfilament and microtubule functions; interference with bile secretion involving bile acid dependent and independent fractions, and altered bile acid metabolism due to "hypoactive hypertrophic smooth endoplasmic reticulum". In partial agreement with the latter hypothesis, our studies indicated that impairment of the endoplasmic reticulum might represent one of the early stages in the development of intrahepatic cholestasis. Various experimental conditions that induce intrahepatic cholestasis to different degrees resulted in an interference of the synthesis of microsomal phospholipids and altered microsomal function. The conditions included the administration of various hepatotoxic compounds or steroids, pregnancy, delayed development of the endoplasmic reticulum in neonates, and dietary methyl donor or choline deficiency. This review reports the biochemical-pathological mechanisms postulated to be involved in the genesis of intrahepatic cholestasis with specific reference to experimental models of drug-induced intrahepatic cholestasis. The important practical implications of cholestasis are also briefly surveyed.

Inhibition of biliary cholesterol and phospholipid secretion by cefmetazole. The role of vesicular transport and of canalicular events

A number of organic anions selectively inhibit the biliary secretion of cholesterol and phospholipids without affecting bile acid secretion. We studied the effect of cefmetazole, a third-generation cephalosporin, on biliary lipid secretion in the rat. Injection of cefmetazole at a dose of 200 mumol/kg body wt. induced a choleretic effect and a significant decrease in the biliary output of cholesterol and phospholipid, without changes in bile acid secretion. The decrease was more marked for cholesterol than for phospholipid secretion, with a significant decrease in their molar ratio in bile. The effects were apparently unrelated to an inhibition of intracellular vesicular transport because, after injection of horseradish peroxidase, both the time course and total amount secreted of the protein did not significantly differ between control animals and those receiving cefmetazole. The secretory rate of the lysosomal marker acid phosphatase was not affected by cefmetazole administration. Biliary outputs of the plasma-membrane enzymes alkaline phosphatase and gamma-glutamyltransferase were significantly decreased by the antibiotic. These results point to an effect of cefmetazole at the level of the canalicular membrane.

Chemical-induced interference with hepatocellular transport. Role in cholestasis

Transport of endogenous chemicals both into (at the basolateral membrane) and out of (at the canalicular membrane) hepatocytes plays an important role in bile formation. Hence, interference with these processes, for example by chemicals, may result in reduced bile output. Several different systems are available for the study of transport and hence chemicals that may interfere with the process. These have been used to varying degrees with isolated hepatocytes probably being the most popular over recent years. It is likely that hepatocyte couplets and highly purified plasma membrane vesicles will be increasingly employed over the ensuing years. The inhibitory effects of several chemicals on the transport of bile acids have been demonstrated with indications that this may help to account for some aspects of chemical-induced hepatobiliary dysfunction. For example, the inhibition of transport of bile acids by cyclosporin A is consistent with the reported pattern of liver dysfunction in patients on high doses of this immunosuppressant. Investigation into chemical-induced interference with electrolyte transport has yet to receive the same degree of attention. This and other aspects have been suggested as deserving of and likely to be subjected to more intensive experimentation over the next few years.

Taurocholate stimulates transcytotic vesicular pathways labeled by horseradish peroxidase in the isolated perfused rat liver

The effect of taurocholate on transcytotic vesicular pathways labeled with horseradish peroxidase was assessed in isolated perfused rat liver preparations. Forty-five minutes after a horseradish peroxidase load in a recirculating system, continuous infusion of taurocholate but not taurodehydrocholate significantly increased horseradish peroxidase excretion in bile by 50% compared with controls. When horseradish peroxidase (25 mg) was pulse loaded for 1 minute in control perfusions, it appeared in bile in early (4-6 minutes) and late (20-25 minutes) peaks, the latter accounting for 90% of total horseradish peroxidase output. Taurocholate infusion significantly increased horseradish peroxidase output in both early and late peaks, whereas only a small increase in the early peak was observed with taurodehydrocholate. Colchicine pretreatment increased the early peak in bile but abolished the second peak. Electron micrographs from control livers revealed the accumulation of horseradish peroxidase-containing vesicles in pericanalicular regions at early (2 minutes) as well as late (18 minutes) periods. When a morphometric analysis of electron micrographs was performed from pericanalicular regions 2 minutes after a 1-minute pulse of horseradish peroxidase (500 mg), taurocholate but not taurodehydrocholate increased both the density and percent area of horseradish peroxidase-containing vesicles compared with controls. In contrast, colchicine pretreatment had no effect on the density of the early-appearing vesicles, although their individual sizes were reduced. Taurocholate but not taurodehydrocholate also increased the percent of tubular structures in the pericanalicular region. These findings indicate that taurocholate stimulates both early and late transcytotic vesicle pathways and therefore probably microtubule-independent vesicle pathway is present in hepatocytes that must be distinguished from paracellular routes.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

Effects of chlorpromazine and low calcium on the cytoskeleton and the secretory function of hepatocytes in vitro

It has been established that the cytoskeleton plays an important role in the secretory function of hepatocytes. We studied the effect of chlorpromazine (CPZ) and low calcium (LC) on the cytoskeleton of primary cultured hepatocytes using double-labelling immunofluorescence and secretion of fluorescein diacetate (FD) into the bile canaliculi (BC). The hepatocytes were obtained from 14-day-old male rats. They were cultured for 24 h in serum-free William's E medium with insulin and dexamethasone added to induce differentiation including bile canaliculus formation. After incubation with CPZ (200 microM) for 1 h, the BC became dilated and distorted and formed diverticula. Actin filaments around the BC became more prominent and the stress fibers decreased. CPZ did not affect the microtubules or cytokeratin filaments. Exposure to LC (20 microM) for 24 h caused a slight dilation of the BC. Actin spread out over the cell periphery and appeared non-filamentous. Actin filaments around the BC appeared unchanged and the stress fibers disappeared. Microtubules and cytokeratin filaments were unaffected. Secretion of FD into the BC occurred normally after treatment with CPZ or LC. These results support the idea that the integrity of actin is not necessary for secretory function and that microtubules and intermediate filaments play a role in this process. The dilatation and diverticular formation in the BC induced by CPZ treatment suggests that a cytochalasin-like loss of contraction of the BC may explain the CPZ-induced decrease in bile flow observed in vivo.

Drug-induced jaundice

A large number of drugs may be associated with impaired bile flow. Drug-associated cholestasis presents like other forms of cholestasis with pale stools, dark urine, pruritus and jaundice. Abdominal pain may be present in some instances and can be so severe as to lead to a false diagnosis of acute cholecystitis. Biochemically, drug-associated cholestasis resembles other forms of cholestasis although the presence of eosinophilia may suggest drug involvement. Many types of drug-induced cholestasis run a benign course with resolution of signs and symptoms within 3 months but occasionally the jaundice can take a year or more to resolve. Progression to cirrhosis is uncommon. Some patients may develop a syndrome resembling primary biliary cirrhosis. The mechanisms of drug-associated cholestasis are uncertain but may arise from alteration of bile formation within the hepatocyte or bile excretion at the level of the canaliculus or the extrahepatic ducts. Histological examination of the liver may be helpful in classifying the types of jaundice but the diagnosis of drug-induced cholestasis is usually one of temporal association and exclusion of other causes.

Interaction of intermediate filaments with nuclear lamina and cell periphery

Ultrastructural observations of the cytoskeleton suggest that the connection of the intermediate filaments (IFs) to actin microfilaments (MFs) at the plasma membrane and the nuclear lamina inside the nuclear membrane link signals received at the cell periphery to the nucleus. When these connections are viewed in three dimensions using detergent extracted cytoskeletal preparations from tissue cultures or slices made from tissue, the IFs are seen to run without interruption from the cell periphery to the nucleus and back. The IFs form side to side connections with the nuclear lamina and pore complexes. The nucleus and the centrioles are supported and held suspended in these extracted cells where all organelles and cytosol have been removed. The IFs are particularly dense in the ectoplasm where they form a sheet and provide the scaffolding which maintains the shape of the extracted cells. The IFs in the ectoplasm are attached to desmoplakin at cell-cell desmosome adhesions and to MFs where the cells are attached to the fibronectin substratum possibly through integrin linkages at adhesion plaques. This was graphically shown by immunogold labelling of IF cells treated with nickel. In this way, it was possible to visualize the loss of the cell-cell connections at desmosomes and the disruption of the IF-MF connections in the ectoplasm. The MFs after losing their connections with the IFs, redistribute to cover the entire cell periphery. The nickel treatment of primary liver cell cultures lead to the loss of several functions including formation of the bile canaliculus, the ability to secrete fluorescein diacetate and the ability to take up horseradish peroxidase (HRP) by endocytosis. These observations support the conclusion that the IF-MF connections at the cell periphery provide both structural and functional polarity of the liver cells including uptake and secretion and the formation of bile canaliculi.

Effects of chlorpromazine on taurocholate transport in isolated rat hepatocytes

Chlorpromazine has been shown to have no effect on the uptake of the endogenous bile salt substrate, taurocholate, by isolated rat hepatocytes. It has been shown, however, to inhibit directly release of taurocholate from pre-loaded cells over extended incubation. However, there was no inhibition of the efflux process per se as shown by similar initial rates of taurocholate efflux in the presence or absence of chlorpromazine. Pretreatment of rats with chlorpromazine (100 mumoles/kg) resulted in no change in the ability to transport (that is, accumulate or secrete) taurocholate by hepatocytes isolated 2, 24, 36, 48, or 60 hr later. The data indicate that, if a direct effect on bile acid transport is important in chlorpromazine induced biliary dysfunction, then it involves release rather than uptake at the cell membrane. However, as efflux itself is not inhibited chlorpromazine may interfere with release of taurocholate from intracellular sites.

Scanning electron microscopy of the hepatocyte cytoskeleton in human liver tissue

Portions of eight human livers taken by wedge biopsy or needle biopsy were extracted with 0.5% Triton X-100 and then studied by scanning electron microscopy and immunoelectron microscopy. The wedge-biopsy specimens were perfused with the detergent solution. Needle-biopsy specimens were quickly frozen and cracked and then the cracked tissue was immersed in the detergent solution. The three-dimensional filament network of hepatocytes was visualized. A dense network which consisted of intermediate filaments and microfilaments was observed within the cytoplasm of hepatocytes. These filaments were better preserved in the needle biopsies which were quick-frozen and cracked before extraction than in the wedge biopsies. Variation in the amount of the cytoskeletal filaments was less prominent in the hepatocytes treated by rapid freezing. It is concluded that freeze-cracking is the most favorable method for the study of cytoskeletal pathology in various liver diseases in man.

Drug-induced cholestasis

Intrahepatic cholestasis, defined as arrested bile flow, mimics extrahepatic obstruction in its biochemical, clinical and morphological features. It may be due to hepatocyte lesions of which there are three types, termed canalicular, hepatocanalicular and hepatocellular, respectively; or it may be due to ductal lesions at the level of the cholangiole or portal or septal ducts. Defective bile flow due to hepatic lesions reflects abnormal modification of the ductular bile. Defective formation of canalicular bile may involve bile acid-dependent or independent flow. It appears to result most importantly from defective secretion of bile acid-dependent flow secondary to defective uptake from sinusoidal blood, defective transcellular transport and defective secretion; or from regurgitation of secreted bile via leaky tight junctions. An independent defect in bile acid-independent flow is less clear. Defective flow of bile along the canaliculus may reflect increased viscosity and impaired canalicular contractility secondary to injury of the pericanalicular microfibrillar network. Impaired flow beyond the canaliculus may result from ductal injury. Sites of lesions that contribute to cholestasis include the sinusoidal and canalicular plasma membrane, the pericanalicular network and the tight junction and, less certainly, microtubules and microfilaments and Golgi apparatus. A number of drugs that lead to cholestasis have been found to lead to injury at one or more of these sites. Other agents (alpha-naphthylisothiocyanate, methylenedianiline, contaminated rapeseed oil, paraquat) lead to ductal injury resulting in cholestasis. Reports of inspissated casts in ductules (benoxaprofen jaundice) and injury to the major excretory tree (5-fluorouridine after hepatic artery infusion) have led to other forms of ductal cholestasis. Most instances of drug-induced cholestasis present as acute, transient illness, although important chronic forms also occur. The clinical features include the reflection of the cholestasis (pruritus, jaundice), systemic manifestations and extrahepatic organ involvement. While nearly all classes of medicinal agents include some that can lead to cholestasis, there are differences among the various categories. Phenothiazines and related antipsychotic and 'tranquillizer' drugs characteristically lead to cholestatic hepatic injury. The tricyclic antidepressants may lead to cholestatic or hepatocellular injury.(ABSTRACT TRUNCATED AT 400 WORDS)

The fate of electron opaque tracers (horseradish peroxidase and lanthanum chloride) during valproic acid-induced choleresis

Horseradish peroxidase (HRP) and lanthanum chloride (LaCl3) are useful tools for, respectively, the study of vesicular transport through the hepatocyte and the study of the permeability of junctional complexes. These tracers have been used to detect the changes associated with the choleresis independent of bile acids induced by valproic acid (VPA) in rats. The animals were given a single dose of VPA (600 mg/kg, ip). HRP (100 mg/kg) or 5 mM LaCl3 were given intraportally after 1 h, when bile flow had increased twofold. The excretion of HRP in bile was measured colorimetrically up to 2 h after HRP. Ultrastructural morphometry was conducted on liver of intact rats taken from 1 to 40 min after HRP. The volume density (VD) of HRP-containing vesicles and of HRP-containing multivesicular bodies (MVB) was counted. In VPA-treated rats, HRP appeared in bile with a peak showing at 5 min against 20 min in controls, but the total amount of HRP excreted was less than in controls. The intrahepatocytic vesicular transport of HRP was also modified, showing a peak at 3 min in VPA-treated rats compared to 10 min in controls, together with a decreased VD of pericanalicular vesicles. This was accompanied by an increase of HRP-containing MVB, already evident at 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol impairs biliary lysosomal enzyme release in rats

The effects of ethanol on hepatic lysosomes are poorly documented. This study examined the biliary release of lysosomal enzymes, a marker of the hepatocyte-to-bile excretory pathway, after ethanol administration in the isolated perfused rat liver model. At concentrations similar to those reached in human plasma during social drinking, ethanol markedly decreased biliary lysosomal enzyme output and bile flow in the rat. Ethanol did not affect hepatic activities or the release into perfusate of lysosomal and other subcellular marker enzymes. Hence, ethanol may potentially inhibit hepatocyte-to-bile excretion of other compounds processed through lysosomes.

Transcytosis and paracellular movements of horseradish peroxidase across liver parenchymal tissue from blood to bile. Effects of alpha-naphthylisothiocyanate and colchicine

The pathways for the entry of horseradish peroxidase (HRP) into bile have been investigated using the isolated perfused rat liver operating under one-pass conditions. Following a 1 min one-pass infusion of HRP, two peaks of HRP activity were noted in the bile. The first, at 5-7 min post-infusion, correlated with the biliary secretion of the [3H]methoxyinulin which was infused simultaneously with the HRP. The second peak of HRP activity occurred at 20-25 min, and correlated with the biliary secretion of 125I-IgA, which was also infused simultaneously with the HRP. If the isolated livers were perfused with a medium containing 2.5 microM-colchicine, the biliary secretion of IgA and the second secretion peak of HRP were inhibited by 60%. If rats were pretreated for 12h with alpha-naphthylisothiocyanate (25mg/100g body wt.) prior to liver isolation, the biliary secretion of [3H]methoxyinulin and the first secretion peak of HRP were increased. Taken together, these results suggest that HRP enters the bile via two routes. The faster route, which was increased by alpha-naphthylisothiocyanate and correlated with [3H]methoxyinulin entry into bile, was probably paracellular, involving diffusion across tight junctions. The slower route, which was inhibited by colchicine and correlated with the secretion of IgA, was probably due to transcytosis, possibly within IgA and other transport vesicles.