Nympha B. D'Souza

Chronic alcohol exposure of rats exacerbates apoptosis in hepatocytes and sinusoidal endothelial cells

Background/aims: The liver apoptotic response to chronic alcohol consumption remains poorly characterized. The purpose of this study was to determine in rats the effects of chronic alcohol consumption on the relative magnitude of apoptosis in two major targets of alcohol-induced liver injury: the hepatocyte (Hep) and sinusoidal endothelial cell (SEC). Methods: Rats were fed a liquid diet containing either alcohol or isocaloric amounts of maltose-dextrin for 14 weeks. Hep and SEC were isolated by liver perfusion with collagenase followed by centrifugal elutriation. The state of the liver was assessed on the basis of light microscopic appearance, plasma liver enzymes (alanine and aspartate:2-oxoglutarate amino transferases), and the content of malondialdehyde in Hep. Apoptosis was assessed on the basis of DNA fragmentation in the whole organ (TUNEL), and caspase-3 and -8 activity in isolated cells. A mechanistic approach was also undertaken by measuring mRNA expression and the amount of protein for Fas/CD95, Fas ligand, caspase-3, Bax, Bcl-X(L), and Bcl-2 in the isolated Hep and SEC. Results: The livers of alcohol-fed rats displayed prominent steatosis. Oxidative stress was also present as reflected by an increase in the malondialdehyde content of Hep. Alcohol consumption increased apoptosis in the whole liver assessed on the basis of TUNEL procedure and in Hep and SEC as reflected by significant increase in caspase-3 activity. Of the multiple pro- and anti-apoptotic factors determined in this study, significant changes as assessed by both mRNA expression and the amount of proteins, were observed only in the SEC compartment. Conclusions: The data presented in this study indicate that: (1) chronic alcohol consumption in rats leads to a moderate augmentation of apoptosis in the whole liver and in two liver cell types which are targets for injury in alcoholic liver disease: Hep and SEC; (2) the mechanisms recruited/activated by these two types of liver cells to initiate and execute apoptosis in response to alcohol vary with the cell type.

Effects of acute alcohol intoxication on gluconeogenesis and its hormonal responsiveness in isolated, perfused rat liver

Rats were acutely administered ethanol as a primed constant infusion in order to produce sustained blood ethanol levels of 8-12 or 55-65 mM. At the end of ethanol infusion the livers were either freeze-clamped in vivo or isolated and perfused for metabolic studies. The rate of gluconeogenesis and its responsiveness to phenylephrine (10 microM), prostaglandin F2 alpha (5 microM) and glucagon (10 nM), as well as the redox state of the cytosolic NAD(+)-NADH system were assessed in livers isolated from acutely ethanol-treated rats, and subsequently perfused without ethanol. For liver clamped in vivo, high- but not low-ethanol treatment decreased the ATP content by 31% and slightly increased ADP and AMP content, resulting in a decreased energy charge (11%). Glutamate and aspartate content was also increased in high-dose ethanol-infused rats with no changes in malate and 2-oxoglutarate content. Gluconeogenesis with saturating concentrations of lactate (4 mM)+pyruvate (0.4 mM) was delayed in reaching a plateau in the livers of high-dose ethanol-treated rats and its response to all three stimulators was impaired. Low-dose ethanol treatment only decreased the liver response to phenylephrine. While the perfused livers of low-dose ethanol-treated rats displayed no changes in adenine nucleotide content, the livers of high-dose ethanol-treated rats had a decreased ATP (35%) and an increased AMP (77%) content, paralleled by a fall in the total adenine nucleotides (14%) and energy charge (14%). No differences were observed between the saline- and ethanol-treated rats with respect to malate-aspartate shuttle intermediate concentration in perfused livers. Also, the livers of high-, but not low-dose ethanol-treated rats had a more negative value of NAD(+)-NADH redox state as compared to the livers of control rats. The data suggest that acute ethanol intoxication produces changes in liver metabolism and its responsiveness to hormones/agonists that are demonstrable for at least 2 hr after isolation and perfusion of the liver.

Effects of exogenous superoxide anion and nitric oxide on the scavenging function and electron microscopic appearance of the sinusoidal endothelium in the isolated, perfused rat liver

BACKGROUND/AIMS Functional and morphological alterations of the hepatic sinusoidal endothelial cell occur in several models of experimental liver injury and in clinical settings. The causes of these alterations are multiple. The aim of this study was to test the hypothesis that the early functional impairment and morphological alterations of the sinusoidal endothelial cell and hepatic sinusoid associated with liver injury are mediated by free radical species, such as superoxide anion and nitric oxide. METHODS Isolated rat livers were perfused by recirculation with hemoglobin-free, Krebs-Henseleit bicarbonate buffer and presented with a source of superoxide anion (xanthine oxidase+hypoxanthine) or nitric oxide (S-nitroso-N-acetyl penicillamine). Hyaluronan uptake (an index of sinusoidal endothelial cell scavenging function), thiobarbituric acid-reactive substances content of the tissue (a marker of lipid peroxidation), reduced and oxidized glutathione (a marker of the thiol system oxidation/reduction state), lactate dehydrogenase and alanine aminotransferase activities (markers of cytolysis), as well as scanning and transmission electron microscopic appearance of the sinusoid were evaluated. RESULTS At the high concentrations used, both free radical generating systems suppressed hyaluronan uptake, increased malondialdehyde content of the tissue, enhanced the release of both liver enzymes, decreased the total glutathione content of the liver, and altered the ratio of reduced/oxidized glutathione. Both free radical species induced dose-dependent morphological alterations of the sinusoid, consisting of the appearance of large gaps replacing the sieve-plated fenestration. CONCLUSIONS The free radical species-induced functional impairment and morphological alterations of the liver sinusoid, presented in this study, closely resemble the early in vivo changes associated with liver injury under a variety of conditions, such as preservation and reperfusion, or administration of hepatotoxicants such as D-galactosamine, Gram-negative bacterial lipopolysaccharides, acetaminophen, alcohol and others. Therefore, we suggest that early liver sinusoid injury, observed under these conditions, can be attributed to the action of free radicals, such as superoxide anion and nitric oxide.

Effect of chronic alcohol consumption by rats on tumor necrosis factor-α and interleukin-6 clearance in vivo and by the isolated, perfused liver☆

The effects of chronic (16-week) alcohol consumption by rats on [125I]tumor necrosis factor (TNF)-α and [125I]interleukin (IL)-6 plasma clearance and organ distribution in vivo and uptake and metabolism by the isolated, perfused liver were studied. Alcohol was administered to rats in a liquid diet for 16 weeks, and caused a decreased (48%) plasma clearance rate of IL-6 and converted the plasma clearance kinetics of the cytokine from a biphasic exponential in normal rats to a monophasic exponential decay. Alcohol feeding significantly increased (101%) plasma clearance of TNF-α, which followed a biphasic exponential decay and decreased the T12 for both the α (67%) and β (76%) elimination components. The distribution of both cytokines in trichloroacetic acid precipitable and non-precipitable fractions of liver, spleen, stomach, small intestine (ileum), lung, kidney, and blood was also studied. The only effect of alcohol treatment was a significant decrease in IL-6 uptake and metabolism by the small intestine. Perfused livers, isolated from alcohol-fed rats, took up and metabolized larger amounts of IL-6 than did livers isolated from pair-fed rats. TNF-α uptake and metabolism by the isolated, perfused liver were not affected by chronic alcohol consumption. Regardless of the animal treatment, the isolated perfused liver took up and metabolized significantly larger (17-fold) amounts of TNF-α than IL-6, in spite of identical concentrations of cytokines (6 nM) in the perfusion medium. The data presented in this study along with our previous results demonstrating the effects of alcohol consumption on TNF-α and IL-6 receptors on various liver cells suggest that the effects of chronic alcohol treatment on cytokine clearance cannot be ascribed to changes in the receptors for the two cytokines. Also, no correlation was found between the effects of alcohol treatment on plasma cytokine clearance and uptake and metabolism of cytokines by the isolated, perfused liver. Experimental data and theoretical considerations suggest that cytokine receptor recycling may play an important role in mediating alcohol effects on cytokine clearance.

Alcohol-induced sinusoidal endothelial cell dysfunction in the mouse is associated with exacerbated liver apoptosis and can be reversed by caspase inhibition.

The purpose of this study was to determine if a correlation exists between alcohol-induced liver sinusoidal endothelial cell (SEC) dysfunction and alcohol-induced augmented liver apoptosis in the mouse. Mice were fed an alcohol-containing liquid diet for 7 weeks. On the last day of feeding, the animals were treated with the pan-caspase inhibitor IDN1529 (N-[(indole-2-)-alaninyl]-3-amino-4-oxo-fluoropentanoic acid), killed, and plasma amino transferase activity, plasma hyaluronan, liver caspase-3 activity, the frequency of apoptotic nuclei in the liver, liver histology and electron microscopic appearance evaluated. Alcohol feeding significantly increased (2.5-fold) plasma hyaluronan levels, frequency of apoptotic nuclei (20-fold), and caspase-3 activity (1.7-fold), but did not affect plasma amino transferase activity. Transmission electron microscopy revealed that SEC was among the cell types undergoing apoptosis. Livers of alcohol-fed mice displayed marked fat accumulation without necrosis or fibrosis. Treatment of mice with IDN1529 reversed the alcohol effects on plasma hyaluronan levels, liver caspase-3 activity, and frequency of apoptotic nuclei. However, the inhibitor did not prevent fat accumulation in the liver. These data suggest that alcohol-induced exacerbation of apoptosis in the liver, which extends to the SEC, causes functional impairment of the sinusoidal lining and can be reversed by caspase inhibition.

The regulation of Fas (CD95/Apo-1)-mediated liver apoptosis in Kupffer cell-depleted mice

The purpose of this study was to further characterize Fas-mediated liver apoptosis. We investigated whether Fas-mediated apoptosis in the liver requires induction of apoptosis-related regulators and whether Kupffer cells play a role in this process. Mice were injected with GdCl(3) to deplete/suppress Kupffer cells, followed by treatment with an anti-Fas agonistic antibody, Jo2. Hepatic mRNA levels of several pro- and anti-apoptotic regulators were determined 0.5, 1.5 and 4.0 h after Jo2 injection. Liver histology, TUNEL response, the activity of caspases-3, -8, and -9, and reduced and oxidized glutathione, were also evaluated. Jo2 dramatically increased the number of apoptotic nuclei in the liver, up-regulated mRNA for Bcl-w, Bfl-1, and Bcl-X(L,) but did not affect pro-apoptotic regulator mRNA expression. Caspase-3, -8 and -9 activity increased at 1.5 h after Jo2-injection. GdCl(3) treatment was associated with an increase in the apoptotic effect of Jo2. No effect of Jo2 was recorded on redox state of the free cellular thiol system. These data suggest that: (1) the prompt apoptotic response to Fas-mediated signaling in the liver does not require induction of pro-apoptotic factors; (2) Kupffer cells may play a major role in the liver apoptotic response to Fas ligation by clearing apoptotic cells by phagocytosis; (3) oxidative stress does not seem to play an important role in Fas-mediated liver apoptosis.

The effect of ethanol infusion on the altered glucose turnover during bacterial infection

The increased glucose turnover seen during the hypermetabolic, hyperdynamic phase of sepsis is part of the bodys defense mechanisms. In contrast, the metabolism of ethanol (ETOH) is known to compromise hepatic gluconeogenesis under certain conditions. This study tested the hypothesis that acute infusion of ETOH inhibits the elevated glucose production that is manifested during infection and thereby alters the normal responses to sepsis. In catheterized conscious rats, ETOH or saline infusion was started 24 hours before the induction of sepsis, and continued throughout the experiment. In vivo glucose kinetics were assessed by the infusion of [6-3H, U-14C]-glucose 24 hours after the induction of sepsis. The characteristic sepsis-induced hyperthermia was prevented in ETOH-infused animals. Sepsis increased the plasma lactate concentration (100%), as well as the rates of glucose appearance ([Ra] 77%), recycling (213%), and metabolic clearance ([MCR] 82%) in saline-infused control animals. In contrast, ETOH infusion prevented the sepsis-induced increase in glucose Ra and markedly attenuated the increase in plasma lactate (49%) and glucose recycling (97%). The infusion of ETOH increased the lactate/pyruvate and beta-hydroxybutyrate (BHBA)/acetoacetate (AcAc) ratio in both septic and nonseptic rats. These results indicate that ETOH administration attenuates the increased glucose production, utilization, and elevated arterial lactate, and prevents the hyperthermic response seen during the hypermetabolic phase of sepsis. Thus, ethanol intoxication alters the normal metabolic responses to sepsis, thereby contributing to the compromised host defenses against the challenging bacteria.