Hepatic fibrosis--role of hepatic stellate cell activation

Hepatic fibrosis is a reversible wound healing response characterized by accumulation of extracellular matrix (ECM), or "scar," that follows chronic but not self-limited liver disease. The ECM components in fibrotic liver are similar regardless of the underlying cause. Activation of hepatic stellate cells is the central event in hepatic fibrosis. These perisinusoidal cells orchestrate an array of changes including degradation of the normal ECM of liver, deposition of scar molecules, vascular and organ contraction, and release of cytokines. Not only is hepatic fibrosis reversible, but it is also increasingly clear that cirrhosis may be reversible as well. The exact stage at which fibrosis/cirrhosis becomes truly irreversible is not known. Antifibrotic therapies will soon be a clinical reality. Emerging therapies will be targeted to those patients with reversible disease. The paradigm of stellate cell activation provides an important framework for defining therapeutic targets.     

Reversible phosphorylation of 3-hydroxy-3-methylglutaryl CoA reductase in Morris hepatomas

The reversible phosphorylation of microsomal 3-hydroxy-3-methylglutaryl CoA reductase in host liver and hepatoma 5123C has been investigated. The percentage of the total enzyme activity in vivo was similar in the normal liver, host liver and hepatoma 5123C. The inclusion of 30 mM EDTA and 10 mM mevalonic acid in assays of 3-hydroxy-3-methylglutaryl CoA reductase inactivation in vitro eliminated artifacts generated by the presence of mevalonate kinase. Inactivation of 3-hydroxy-3-methylglutaryl CoA reductase from normal liver, host liver and hepatoma occurred at a similar rate with similar half-times. We conclude that phosphorylation/dephosphorylation of 3-hydroxy-3-methylglutaryl CoA reductase occurs in hepatomas and that the lack of dietary cholesterol feedback inhibition in the hepatomas is not a result of a defect in this particular aspect of the reversible phosphorylation system.     

Hydrogen ion dependent reversible fibrillarization and hydration of chromatin in divalent cation-depleted isolated rat liver nuclei

Rat liver cell nuclei isolated in the presence of Ca++ and Mg++ ions were exposed to citrate buffer at different pH levels. Their morphology was studied with the electron microscope and the water content measured. At a low pH the chromatin remained compact, but at neutral pH an intense fibrillarization of the chromatin was observed; and, seemed to be reversible, because of deoxyribonucleoproteins (DNP) filaments which dispersed at a pH of 7 were repacked to their previous site at a pH of 3. The ribonucleo-proteins (RNP)-containing structures did not show the same reversible fibrillarization. In addition to the morphological changes, a large increase in the water content ("water-holding capacity") of the chromatin structures was observed.     

Functional restructurings of the mononuclear phagocyte system in experimental liver cirrhosis

In rats with CCl4-induced liver cirrhosis the clearance rate of colloid carbon particles was more than 2 times lower than in control animals. Simultaneously the uptake capacity of liver Kupffer calls falls. The number of phagocytizing liver macrophages decreased. Along with the diminished functional activity of liver macrophages in cirrhotic liver, the total number of lung and spleen macrophages increased 1.5-fold, with their uptake capacity increasing 10- and 3-fold, respectively. The nitroblue tetrazolium dye reduction and methacrylate particles uptake by alveolar macrophages in vitro rises. The liver, lung, spleen and peritoneal macrophages during liver fibrosis become less sensitive to zymosan stimulation. The incidence of zymosan-induced liver infiltrates decreases 50-fold, while in the lungs they do not develop at all. Such a decreased macrophage reactivity may be closely linked with progressing, poorly reversible liver fibrosis.     

Binding of heparin and heparan sulphate to rat liver cells

The binding of pig mucosal heparin and rat liver heparan sulphate to rat liver cells is demonstrated. The process is shown to be time dependent, reversible and saturable. The maximal amount of heparin bound to the cells exceeds that of heparan sulphate, on a molar basis.The binding of both polysaccharides is specific, in that excess amounts of glycosaminoglycans other than heparin-related do not affect the binding reaction.The binding of heparin to cells was markedly reduced when incubations were performed at low temperature or after trypsin treatment of the cells.     

Regulation of canalicular bile formation by alpha-adrenergic action and by external ATP in the isolated perfused rat liver

In isolated perfused rat liver, addition of adrenaline induced a complex response of bile flow including rapid, reversible stimulation (1/2-2 min), reversible inhibition (2-10 min), and prolonged stimulation. Both the reversible stimulation and the inhibition were mimicked by the alpha-sympathomimetic agonist phenylephrine but not by the beta-agonist isoproterenol. The reversible stimulation was a very early effect being terminated prior to all other alpha-adrenergic responses of liver. External ATP considerably lowered bile flow while inducing release of glucose and lactate, inhibition of respiration, and a reversible efflux of Ca2+. Variations of mannitol clearance parallel to those of bile flow indicate a canalicular origin of all changes.     

Serum bile acids as a sensitive biological marker for evaluating hepatic effects of organic solvents

Serum bile acids (SBAs) are suggested as a potentially sensitive and specific indicator of liver function which, accordingly, could provide an early indication of hepatobiliary dysfunction. This offers advantages over more traditional parameters of liver integrity/function. Recent studies have shown that occupational exposure to low levels of halogenated aliphatic or non-halogenated aromatic solvents is associated with significant increases in SBA levels. As this has often been evident in the absence of any effect on conventional parameters of hepatobiliary integrity/function, elevated SBA levels may well be regarded as a sensitive biological marker of exposure/effect of these compounds. In addition, it may be considered that they provide an early indicator of solvent-induced changes in hepatobiliary function. Extensive studies with experimental animals have also provided supporting evidence for these observations in solvent-exposed individuals. Investigations of the mechanisms at cellular and subcellular levels by which these increases occur have suggested that these effects are likely to be the result of selective, dose-related and reversible inhibition of bile acid uptake at the sinusoidal domain of the hepatocyte plasma membrane. Increased concentrations of SBA under low levels of exposure to different solvents have been demonstrated to be a short-lived and reversible effect which is not accompanied by any other evidence of liver damage. Therefore, it could be assumed that it is unlikely that there would be pathological sequelae to these effects, although the longer term ramifications of such effects have not been thoroughly investigated. Nevertheless, the available evidence indicates that investigation of SBA in solvent-exposed workers could provide useful indications of exposure and effect.     

Characteristics of the morphofunctional changes in the liver of C3HA mice due to immunization with a homogenate of normal syngeneic liver

Immunization of C3HA mice with homogenate of normal syngeneic liver at a dosage causing elevation of antitumor resistance damages the liver of recipients. The damage involves the formation of foci of necrosis and the alteration in activities of some tissue specific and embryonal enzymes. The damage is reversible; its degree and the rate of reverse depends on a dosage of homogenate injected.     

Serum bile acids as a sensitive biological marker for evaluating hepatic effects of organic solvents

Serum bile acids (SBAs) are suggested as a potentially sensitive and specific indicator of liver function which, accordingly, could provide an early indication of hepatobiliary dysfunction. This offers advantages over more traditional parameters of liver integrity/function. Recent studies have shown that occupational exposure to low levels of halogenated aliphatic or non-halogenated aromatic solvents is associated with significant increases in SBA levels. As this has often been evident in the absence of any effect on conventional parameters of hepatobiliary integrity/function, elevated SBA levels may well be regarded as a sensitive biological marker of exposure/effect of these compounds. In addition, it may be considered that they provide an early indicator of solvent-induced changes in hepatobiliary function. Extensive studies with experimental animals have also provided supporting evidence for these observations in solvent-exposed individuals. Investigations of the mechanisms at cellular and subcellular levels by which these increases occur have suggested that these effects are likely to be the result of selective, dose-related and reversible inhibition of bile acid uptake at the sinusoidal domain of the hepatocyte plasma membrane. Increased concentrations of SBA under low levels of exposure to different solvents have been demonstrated to be a short-lived and reversible effect which is not accompanied by any other evidence of liver damage. Therefore, it could be assumed that it is unlikely that there would be pathological sequelae to these effects, although the longer term ramifications of such effects have not been thoroughly investigated. Nevertheless, the available evidence indicates that investigation of SBA in solvent-exposed workers could provide useful indications of exposure and effect.     

Relationships between polyamine metabolism and RNA synthesis in post-ischemic liver cell repair

In liver cells recovering from reversible ischemia the increase in RNA synthesis by isolated nuclei is preceded by activation of ornithine decarboxylase, leading in turn to an increase in putrescine concentration. Treatment of the animals with 1,3-diaminopropane and putrescine prevents ornithine decarboxylase activation but does not hinder the enhancement of RNA synthesis in post-ischemic liver nuclei; therefore, ornithine decarboxylase activation does not seem to be a necessary prerequisite for the increase in RNA synthesis. Hypophysectomy does not prevent the post-ischemic increases of ornithine decarboxylase and RNA synthesis; but pre-treatment of the animals with cycloheximide—which has a dual effect on the activity of ornithine decarboxylase—abolishes the post-ischemic enhancement of RNA synthesis. In contrast with regenerating liver, changes in ornithine decarboxylase activity and putrescine concentrations in reversible ischemia are not associated to changes in S-adenosylmethionine decarboxylase activity and in spermine and spermidine concentrations that seem to be characteristic of tissues where increases in RNA synthesis are followed by DNA synthesis and cell multiplication.     

Crystallization and some properties of glutamate dehydrogenase from rat liver

1. Glutamate dehydrogenase (L-glutamate:NAD(P) oxidoreductase, EC 1.4.1.3) from rat liver has been crystallized with a method carefully avoiding all denaturating agents. A 236-fold purification was achieved at a yield of 20%. The specific activity was 185 units/mg protein. The enzyme was homogeneous by analytical zone electrophoresis and sedimentation studies. The s0(20),w value was 13.2. 2. Sedimentation studies in the analytical ultracentrifuge and the behaviour of the enzyme in the disc-electrophoresis revealed that glutamate dehydrogenase from rat liver did not undergo a reversible association-dissociation reaction as reported of glutamate dehydrogenase of nearly all other mammalians. 3. Using antibodies prepared against crystalline bovine liver glutamate dehydrogenase, no immunological differences between the rat and the bovine liver enzyme could be observed.     

A validated model of in vivo electric field distribution in tissues for electrochemotherapy and for DNA electrotransfer for gene therapy

Permeabilising electric pulses can be advantageously used for DNA electrotransfer in vivo for gene therapy, as well as for drug delivery. In both cases, it is essential to know the electric field distribution in the tissues: the targeted tissue must be submitted to electric field intensities above the reversible permeabilisation threshold (to actually permeabilise it) and below the irreversible permeabilisation threshold (to avoid toxic effects of the electric pulses). A three-dimensional finite element model was built. Needle electrodes of different diameters were modelled by applying appropriate boundary conditions in corresponding grid points of the model. The observations resulting from the numerical calculations, like the electric field distribution dependence on the diameter of the electrodes, were confirmed in appropriate experiments in rabbit liver tissue. The agreement between numerical predictions and experimental observations validated our model. Then it was possible to make the first precise determination of the magnitude of the electric field intensity for reversible (362+/-21 V/cm, mean +/- S.D.) and for irreversible (637+/-43 V/cm) permeabilisation thresholds of rabbit liver tissue in vivo. Therefore the maximum of induced transmembrane potential difference in a single cell of the rabbit liver tissue can be estimated to be 394+/-75 and 694+/-136 mV, respectively, for reversible and irreversible electroporation threshold. These results carry important practical implications.     

Mitochondrial metabolism in hibernation: metabolic suppression, temperature effects, and substrate preferences

We compared liver and skeletal muscle mitochondrial function among activity states to characterize regulated reversible metabolic suppression in the mammalian hibernator Spermophilus tridecemlineatus. At 37 degrees C, succinate oxidation was 70% lower in the liver mitochondria from torpid animals than in those from summer-active animals or in animals arousing from torpor. Respiration was very sensitive to temperature (Q(10) 5.8-9.8), and when measured at 25 degrees or 5 degrees C there was no difference among the three states. Liver mitochondria from summer-active animals oxidized pyruvate and beta -hydroxybutyrate at higher rates than those from torpid animals, and flux through complex 4 of the electron transport chain was about three- and fivefold higher than flux through complexes 2-4 and complexes 1-4, respectively. In the hibernating and arousing animals there was no difference in flux through complexes 2-4 and complex 4, suggesting a downregulation of cytochrome c oxidase in liver mitochondria during the hibernation season. Muscle mitochondrial respiration did not differ between the torpid and summer-active states in any of the parameters measured. The data support a regulated, reversible decrease of liver (but not muscle) mitochondrial oxidative phosphorylation in hibernating ground squirrels.     

Effect of I.V. Injection of Small Unilamellar Liposomes of Egg Phosphatidylcholine on Cholesterol in Plasma and Erythrocytes,Serum Enzymes and Liver Function in Dogs

Abstract

Small unilamellar vesicles of egg phosphatidylcholine were prepared and injected intravenously at dose levels of 250 or 625 mg/kg into 4 adult Beagle dogs 3 times for each dose, once every other day. Plasma unesterified cholesterol increased and RBC unesterified cholesterol decreased in a dose-related manner. At the larger, but not the smaller dose, there was a reversible rise in some liver enzymes in the serum: alanine aminotransferase > > aspartate aminotransferase = sorbitol dehydrogenase > alkaline phosphatase at their peak levels. Normal bromosulfophthalein clearance, metabolite levels, and plasma protein profiles were observed following both doses of liposomes, indicating normal liver function. The rise in liver enzymes in serum may be due to changes in hepatocyte membrane permeability caused by a loss of cholesterol, resulting in enzyme leakage from the cells.     

Change in membrane lipid fluidity induced by phospholipase A activation: a mechanism of endotoxic shock

The effects of endotoxin administration on the fluidity of dog liver plasma membranes and their relationship with changes in phospholipase A2 activity were studied. Endotoxin administration decreased the fluidity of liver plasma membranes and this decrease was reversible by phosphatidylcholine. The endotoxin-induced decrease in membrane fluidity could be mimicked by digesting control liver membranes with exogenous phospholipase A2. Endotoxin administration also increased the endogenous phospholipase A2 activity. Endotoxin in vitro had no phospholipase A2-like activity but it activated the hydrolytic activity of exogenous phospholipase A2. Based on these data, it is concluded that endotoxin administration decreased the fluidity of canine liver plasma membranes by acting through activation of phospholipase A2. The decrease in membrane lipid fluidity induced by endotoxin administration may play a significant role in the development of the pathophysiology of endotoxic shock at the cellular level.     

Chromatin-bound protease: degradation of chromosomal proteins under chromatin dissociation conditions.

A chromatin-bound protease, active in 2 M NaCl-5 M urea or 5 M urea alone, was demonstrated in rat liver, kidney, testes, brain, rabbit bone marrow, chicken reticulocyte, and Ehrlich ascites chromatin. Chicken erythrocyte chromatin did not possess any detectable proteolytic activity in salt and urea. The proteolytic activity of rat liver chromatin in salt and urea was found to be independent of the methods of chromatin preparation. The protease can be inhibited by the serine specific reagents phenylmethanesulfonyl fluoride and diisopropyl fluorophosphate and the alkylating reagent, carbobenzoxyphenylalanine chloromethyl ketone, in the presence of organic solvents at 1 mM concentration. The inhibitions of chromatin-bound protease in rat liver by these compounds are irreversible. On the other hand, carbobenzoxyphenylalanine and p-nitrophenyl acetate were shown to be reversible inhibitors of rat liver chromatin-bound protease. The application of these inhibitors during the dissociation of chromatin by salt and urea may be useful to researchers interested in purifying various chromosomal proteins or to those researchers doing reconstitution studies with labile chromatins.     

Hepatic Encephalopathy: From Metabolic to Neurodegenerative

Neurochemical Research - Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of both acute and chronic liver disease. As a metabolic disorder, HE is considered to be reversible and therefore...     

Liver peptide stabilizing factor protects phosphofructokinase against inactivation by fructose-1,6-bisphosphatase.

Rabbit liver fructose-1,6-bisphosphatase (FDPase) can reversibly inactivate both rabbit muscle and rat liver phosphofructokinases (PFK) under appropriate conditions. The peptide factor which stabilizes rat liver PFK-L₂ against thermal inactivation has now been found to protect both PFKs from inactivation by FDPase. Assay at high ATP (ca. 3 mM) is necessary to demonstrate these reversible changes. In addition, the activation of FDPase by liver cytosol, by oleate plus cytosol, or by oleate plus muscle PFK is lowere about 50% in the presence of peptide factor. These observations suggest an active participation of the peptide factor in regulation of liver glycolysis and gluconeogenesis.     

Reduction of oxaloacetate by pig liver isocitrate dehydrogenase

Pure isocitrate dehydrogenase from pig liver cytoplasm catalyses the reduction of oxaloacetate by NADPH at a rate comparable with that observed for the usual substrates. The products are NADP and D-malate, the 'unatural' isomer. High concentrations of magnesium (25 mM) are necessary for maximal activity, and the reaction is not appreciably reversible. These results are discussed in connection with the inhibition of the enzyme by mixtures of glyoxylate and oxaloacetate. The reduction is not thought to be of physiological importance.     

Nucleoside mono- and nucleoside diphosphate kinase activities in rat liver and brain in radiation sickness

Activity of nucleoside di- and nucleoside triphosphates metabolism enzymes in tissues of rats gamma-irradiated by a dose of 30 Gy was studied 0.5, 1, 3, 6 and 24 hours after the radiation effect. It is shown that the nucleoside monophosphate kinase activity of the liver and brain is enhanced almost at all stages of the studies and the nucleoside diphosphate kinase activity is inhibited. A significant but reversible decrease of the nucleoside monophosphate kinase activity is observed in the liver 3 h later. By an end of the first day after irradiation the nucleoside mono- and nucleoside diphosphate kinase activities increase significantly both in the liver and brain.