Metabolism of ethanol by rat hepatocytes results in generation of a lipid chemotactic factor: studies using a cell-free system and role of oxygen-derived free radicals

Synergistic and Detrimental Effects of Alcohol Intake on Progression of Liver Steatosis

Nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are the most common liver disorders worldwide and the major causes of non-viral liver cirrhosis in the general population. In NAFLD, metabolic abnormalities, obesity, and metabolic syndrome are the driving factors for liver damage with no or minimal alcohol consumption. ALD refers to liver damage caused by excess alcohol intake in individuals drinking more than 5 to 10 daily units for years. Although NAFLD and ALD are nosologically considered two distinct entities, they show a continuum and exert synergistic effects on the progression toward liver cirrhosis. The current view is that low alcohol use might also increase the risk of advanced clinical liver disease in NAFLD, whereas metabolic factors increase the risk of cirrhosis among alcohol risk drinkers. Therefore, special interest is now addressed to individuals with metabolic abnormalities who consume small amounts of alcohol or who binge drink, for the role of light-to-moderate alcohol use in fibrosis progression and clinical severity of the liver disease. Evidence shows that in the presence of NAFLD, there is no liver-safe limit of alcohol intake. We discuss the epidemiological and clinical features of NAFLD/ALD, aspects of alcohol metabolism, and mechanisms of damage concerning steatosis, fibrosis, cumulative effects, and deleterious consequences which include hepatocellular carcinoma.

Oxidative damage in rat erythrocyte membranes following ethanol intake: effect of ethyl pyruvate

Alcoholic patients and experimental animals exposed to ethanol display biochemical signs of oxidative damage, suggesting a possible role of free radicals in causing some of the toxic effects of alcohol. The ester derivative, ethyl pyruvate (EP) is stable in solution and should function as an antioxidant and energy precursor. In the present study, the effect of ethanol intake on plasma membrane fluidity, lipid oxidation and antioxidant enzyme activities (GPx, CAT and SOD) were first evaluated. Secondly, the consequences of ethyl pyruvate treatment on the physico-chemical properties of erythrocyte plasma membranes were investigated. The results obtained demonstrate that ethanol induces an increase in lipid peroxidation, a reduction of GPx activity and fluidity in the hydrophilic-hydrophobic region of the bilayer, moreover an increase of fluidity in hydrophobic part of the plasma membrane was measured. When rats were treated with ethyl pyruvate a partially protective effect can be observed for the hydrophilic-hydrophobic region tested by Laurdan, while EP cannot restore the DPH anisotropy values to the control values. In summary, our data indicate that treatment with EP can only partially reduce ethanol plasma membrane perturbation. Since this study shows an ethyl pyruvate dose-dependent effect, it is important to consider the amount of EP required to maintain the right level of membrane fluidity and polarity. These results could be interesting in order to investigate if EP, due to its radical scavenging effect, can prevent oxidative damage induced by ethanol intake and can protect against injure related with ethanol intake.

Chronic ethanol ingestion-induced changes in open-field behavior and oxidative stress in the rat

The effects of chronic ethanol intoxication on the open-field behavior, on antioxidant enzyme activities, and the degree of lipid peroxidation were investigated. Rats consuming a liquid diet containing 7% ethanol for 4, 7, 14, or 21 days exhibited a significantly decreased ambulation activity, accompanied by a reduced frequency and duration of explorative rearing in an open-field task 4, 7, and 14 days after chronic ethanol ingestion, whereas presumed adaptation to the neurologic effects of ethanol was observed on day 21. Changes in the activities of glutathione peroxidase (GSH-Px): glutathione reductase (GSH-R), and catalase, and in the content of reduced glutathione (GSH) in blood samples were determined by means of biochemical methods. The degree of lipid peroxidation was measured via thiobarbituric acid assays. Chronic ethanol ingestion elicited a significant increase in GSH-Px activity (by a maximum of approximately 32% on day 14), whereas opposite alterations in GSH-R and catalase activities were recorded (49% of the control value on day 4 and 17% on day 21, respectively). Highly elevated contents of thiobarbituric acid reactive substances reflected extensive lipid peroxidation processes throughout the experiment. These changes indicate that ethanol toxicity induces profound changes in explorative behavior, mediated, at least partly, by changes in the free radical metabolism.

Upregulation of glucose-6-phosphate dehydrogenase in response to hepatocellular oxidative stress: studies with diquat

The expression of hepatic glucose-6-phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) is hypothesized to be modulated by free radicals during oxidative stress. The ability of diquat, a compound known to enhance oxidative stress through generation of reactive oxygen species, to modulate the expression of G6PDH in primary cultures of Fischer-rat hepatocytes was examined. Diquat-treated hepatocytes maintained in a chemically defined medium showed both a time- and concentration-dependent increase in G6PDH enzyme activity. This increase in enzyme activity was accounted for by an increase in both G6PDH mRNA and immunoreactive protein, suggesting control at a pretranslational level. The possibility that diquat increased transcription by transfecting cells with a chimeric gene containing 935 bp of the G6PDH promoter (-878 to +57) linked to the gene for chloramphenicol acetyl-transferase (CAT) was examined. Hepatocytes transiently transfected with this chimera, and subsequently treated with diquat, exhibited an increase in CAT activity. However, hepatocytes transfected with a chimera containing 287 bp of the G6PDH promoter (-230 to +57) exhibited only basal CAT activity in the presence of diquat. These results suggest that regions in the DNA sequences required for diquat-induced expression of G6PDH lie between base pairs -878 and -230 of the G6PDH gene. These findings are suggestive that oxidative stress in hepatocytes increased the expression of G6PDH activity and protein and that the increased expression is controlled at the transcriptional level.

Chronic alcohol intoxication enhances the expression of CD18 adhesion molecules on rat neutrophils and release of a chemotactic factor by Kupffer cells

Chronic alcohol intoxication has been associated with increased migration of inflammatory leukocytes to the liver that may contribute to the development of alcoholic hepatitis in susceptible individuals. Thus, this work was performed to examine the mechanism by which neutrophils [polymorphonuclear neutrophils (PMNS)] are sequestered in the liver during prolonged consumption of alcohol. Male Sprague-Dawley rats were fed with Sustacal supplemented by 36% alcohol, or isocaloric diet for 16 weeks. Circulating blood PMNs were collected and examined for CD18 (beta 2-integrin) adhesion molecule expression. Monoclonal antibody 1F12, an anti-CD18 antibody and potent neutropenic agent, was used to detect CD18 on PMNs. More than 97% of neutrophils obtained from pair and ethanol-fed rats were positive for the antibody. Fluorescence intensity of fluorescein isothiocyanate-1F12 binding to PMNs from ethanol-fed rat was significantly enhanced 2-fold compared with the pair-fed controls. The release of chemoattractant and free radical-generating activity in culture supernatants of Kupffer cells was also examined. Twenty-four hr culture supernatants of Kupffer cells from chronic alcoholic rats enhanced the migration and superoxide anion generation by normal PMNs, compared with those of the pair-fed rats. Antirat interleukin-8 antiserum inhibited chemotactic activity and superoxide generating capacity of culture supernatants. These results suggest that upregulation of adhesion molecules on PMNs and chemotactic factor release from Kupffer cells may contribute, at least in part, to enhanced migration of inflammatory leukocytes to the liver during chronic alcohol intoxication.

Oxidant injury to hepatic mitochondria in patients with Wilson's disease and Bedlington terriers with copper toxicosis

BACKGROUND/AIMS

Copper overload leads to liver injury in humans with Wilson's disease and in Bedlington terriers with copper toxicosis; however, the mechanisms of liver injury are poorly understood. This study was undertaken to determine if oxidant (free radical) damage to hepatic mitochondria is involved in naturally occurring copper toxicosis.

METHODS

Fresh liver samples were obtained at the time of liver transplantation from 3 patients with Wilson's disease, 8 with cholestatic liver disease, and 5 with noncholestatic liver disease and from 8 control livers. Fresh liver was also obtained by open liver biopsy from 4 copper-overloaded and 4 normal Bedlington terriers and from 8 control dogs. Hepatic mitochondria and microsomes (humans only) were isolated, and lipid peroxidation was measured by lipid-conjugated dienes and thiobarbituric acid-reacting substances. In humans, liver alpha-tocopherol content was measured.

RESULTS

Lipid peroxidation and copper content were significantly increased (P < 0.05) in mitochondria from patients with Wilson's disease and copper-overloaded Bedlington terriers. More modest increases in lipid peroxidation were present in microsomes from patients with Wilson's disease. Mitochondrial copper concentrations correlated strongly with the severity of mitochondrial lipid peroxidation. Hepatic alpha-tocopherol content was decreased significantly in Wilson's disease liver.

CONCLUSIONS

These data suggest that the hepatic mitochondrion is an important target in hepatic copper toxicity and that oxidant damage to the liver may be involved in the pathogenesis of copper-induced injury.

Acute ethanol intoxication regulates f-met-leu-phe-induced chemotaxis and superoxide release by neutrophils and Kupffer cells through modulation of the formyl peptide receptor in the rat

This study was performed to assess alcohol-induced alterations in superoxide release and chemotaxis by Kupffer cells and blood neutrophils. Male Sprague-Dawley rats received a bolus injection of alcohol (1.75 g/Kg) followed by an intravenous infusion (250-300 mg/Kg/hr). Three or 24 hr after alcohol infusion, blood neutrophils and Kupffer cells were isolated and assayed for f-met-leu-phe-induced chemotaxis and superoxide release, and formyl peptide receptor expression. At 3 hr post-ethanol, f-met-leu-phe-induced-chemotaxis and superoxide release by blood neutrophils were increased 2 and 3-fold, compared to saline-treated group, and were further increased at 24 hr. The expression of formyl peptide receptors was also increased from 65,000 +/- 8,000 sites per cell to 120,000 +/- 13,000 and 200,000 +/- 16,400 sites at 3 and 24 hr post-ethanol, respectively. The equilibrium dissociation constant (KD) of these receptors on neutrophils was increased at the same time interval. In contrast, alcohol infusion for 3 hr attenuated f-met-leu-phe-induced superoxide release by Kupffer cells (0.8 +/- 0.25 nmol/10(6) cells), compared to saline-treated rats (3.7 +/- 0.3). Chemotaxis by Kupffer cells in response to f-met-leu-phe was also blunted by ethanol at 3 and 24 post-treatment. At 3 hr post-ethanol, the total number of binding sites and KD for f-met-leu-phe on these cells were reduced by almost 30%. The concentration and KD of high affinity binding sites and chemotactic activity of Kupffer cells were not significantly altered by ethanol at 3 hr. However, by 24 hr these were profoundly depressed.

Modulation of f-met-leu-phe induced chemotactic activity and superoxide production by neutrophils during chronic ethanol intoxication

Chronic alcohol consumption has been associated with increased migration of neutrophils into liver that could contribute to the development of alcoholic liver disease. Mild endotoxemia may be at least partially responsible for this condition since endotoxemia was shown to be present in virtually all chronic alcoholics. This study examines the release of superoxide anion and chemotactic activity by Kupffer cells and sequestered hepatic as well as blood neutrophils during chronic alcohol intoxication (16 weeks) alone, and following an intravenous injection of Escherichia coli lipopolysaccharide (LPS) (1 mg/kg) 3 hr before cell isolation. Chronic ethanol consumption increased the total neutrophil yield per liver, but did not change the f-met-leu-phe induced chemotactic activity by both hepatic and blood neutrophils. However, the combined insults of ethanol and LPS increased the chemotactic activity and superoxide anion generation by these cells. Plasma from ethanol-fed rats was highly chemotactic to syngeneic normal rat neutrophils. This activity was increased 1.75-fold in the plasma obtained from chronic ethanol plus endotoxin-injected rats. The chemotactic activity of Kupffer cells was not significantly modulated during ethanol intoxication plus endotoxin treatment. The f-met-leu-phe-induced superoxide anion release by Kupffer cells was enhanced after LPS treatment. Chronic ethanol consumption did not induce any effect on this parameter. These observations suggest that functional alterations in neutrophils during chronic ethanol intoxication may contribute to hepatic injury.

Characterization of a novel arachidonic acid-derived neutrophil chemoattractant

The oxidation of arachidonic acid in a superoxide-generating environment results in the formation of a potent chemoattractant that appears to be identical to a chemotactic material generated by hepatocytes when they metabolize alcohol. The product was extracted, chromatographed and characterized by physical methods including GC/MS. The physical properties are consistant with the parent structure: 19-hydroperoxy, 20-hydroxyarachidic acid. This novel saturated 20 carbon product, derived from arachidonic acid by free radical-generating reactions, may play a role in the neutrophilic infiltration observed during the course of acute alcoholic hepatitis.

Fibrogenesis in cirrhosis. Potential for therapeutic intervention

Liver cirrhosis is an end stage of several diseases that affect the liver chronically. It is characterized, among other things, by excess collagen deposition, distortion of liver architecture, tissue malfunction and hemodynamic alterations. Many of the complications of cirrhosis may result from excess matrix-deposition. Therefore, prevention of collagen accumulation or removal of collagen deposits could ameliorate the disease. In this article we discuss the pathophysiology of liver fibrosis and we describe various compounds with antiinflammatory and antifibrogenic activity. We discuss their possible mechanism of action and we describe animal and clinical studies in which these compounds have been utilized.