Hepatic lipid peroxidation and mitochondrial susceptibility to peroxidative attacks during ethanol inhalation and withdrawal

Hepatoprotective Effects of the Cichorium intybus Root Extract against Alcohol-Induced Liver Injury in Experimental Rats

The effects of the Cichorium intybus root extract (Cii) on alcohol-induced liver disease were investigated using Chang liver cells and male Sprague Dawley rats. Silymarin, a liver-protective agent, was used as a positive control. In cell experiments, after 24 h of treatment with the extract, no cytotoxicity was noted, and death by alcohol was avoided. Migration of Chang liver cells increased after exposure to the extract at a concentration of 400 μg/mL. In animal experiments, alcohol was injected into 6-week-old rats for 1, 3, and 50 days. Oral administration of the drug was performed 30 min before alcohol administration. The control was treated with distilled water, and the drug groups were administered EtOH (40% EtOH + 2.5 mL/kg), EtOH + Cii L (low concentration, 2 mg/kg), EtOH + Cii H (high concentration, 10 mg/kg), or EtOH + silymarin (100 mg/kg). Increased liver weight was observed in the alcohol group, as were increased blood-alcohol concentration and liver damage indicators (glutamic oxalacetic transaminase (GOT), glutamic pyruvate transaminase (GPT), and triglycerides (TG)), decreased alcoholysis enzymes (ADH and ALDH), and increased CYP2E1. In the Cii treatment group, liver weight, blood-alcohol concentration, liver damage indicators (GOT, GPT, and TG), and CYP2E1 were decreased, while alcoholysis enzymes (ADH and ALDH) were increased. The degree of histopathological liver damage was compared visually and by staining with hematoxylin and eosin and oil red O. These results indicated that ingestion of Cii inhibited alcohol-induced liver damage, indicating Cii as a useful treatment for alcohol-induced liver injury.

Alcohol Withdrawal and Cerebellar Mitochondria

Cerebellar disorders trigger the symptoms of movement problems, imbalance, incoordination, and frequent fall. Cerebellar disorders are shown in various CNS illnesses including a drinking disorder called alcoholism. Alcoholism is manifested as an inability to control drinking in spite of adverse consequences. Human and animal studies have shown that cerebellar symptoms persist even after complete abstinence from drinking. In particular, the abrupt termination (ethanol withdrawal) of long-term excessive ethanol consumption has shown to provoke a variety of neuronal and mitochondrial damage to the cerebellum. Upon ethanol withdrawal, excitatory neurotransmitter molecules such as glutamate are overly released in brain areas including cerebellum. This is particularly relevant to the cerebellar neuronal network as glutamate signals are projected to Purkinje neurons through granular cells that are the most populated neuronal type in CNS. This excitatory neuronal signal may be elevated by ethanol withdrawal stress, which promotes an increase in intracellular Ca(2+) level and a decrease in a Ca(2+)-binding protein, both of which result in the excessive entry of Ca(2+) to the mitochondria. Subsequently, mitochondria undergo a prolonged opening of mitochondrial permeability transition pore and the overproduction of harmful free radicals, impeding adenosine triphosphate (ATP)-generating function. This in turn provokes the leakage of mitochondrial molecule cytochrome c to the cytosol, which triggers a cascade of adverse cytosol reactions. Upstream to this pathway, cerebellum under the condition of ethanol withdrawal has shown aberrant gene modifications through altered DNA methylation, histone acetylation, or microRNA expression. Interplay between these events and molecules may result in functional damage to cerebellar mitochondria and consequent neuronal degeneration, thereby contributing to motoric deficit. Mitochondria-targeting research may help develop a powerful new therapy to manage cerebellar disorders associated with hyperexcitatory CNS disorders like ethanol withdrawal.

The effects of acetaldehyde in vitro on proteasome activities and its potential involvement after alcoholization of rats by inhalation of ethanol vapours

BACKGROUND/AIMS

Some models of chronic ethanol administration resulted in decreased proteasome activities. The mechanisms still remain speculative. In the present study, we tested another model of alcoholization with high blood alcohol levels (BALs) and high acetaldehyde fluxes as well as the in vitro effect of acetaldehyde on proteasome. Methods/

RESULTS

Ethanol vapour chronically inhaled by adult Wistar rats up to a specific protocol, can reach high BALs (200 mg/dl) with significant circulating acetaldehyde levels. After 4 weeks of ethanol intoxication, although cytochrome CYP2E1 was increased, liver lipid peroxidation remained unchanged when protein carbonyls augmented selectively for high molecular weight with a decrease of the proteasome activities in ethanol rats. Several aldehydes inhibit proteasome function; we specifically explored the effects of acetaldehyde, the first alcohol metabolite. Adduction of acetaldehyde in vitro to cytosolic proteins inhibits proteasome in a dose-dependent manner. Acetaldehyde adducted to purified proteasome also exhibits a decrease in its activities. Furthermore, an acetaldehyde-adducted protein, i.e. bovine serum albumin (BSA) is less degraded than a native BSA by purified proteasome. These findings suggest that acetaldehyde, if overproduced, can inhibit proteasome activities and reduce the proteolysis of acetaldehyde-adducted proteins.

CONCLUSIONS

Our study, for the first time, provided the evidence that acetaldehyde by itself inhibits proteasome activities. As the chronic inhalation model used in this study is not associated with an overt lipid peroxidation, one can suggest that high BALs and their subsequent high acetaldehyde fluxes contribute to impairment of proteasome function and accumulation of carbonylated proteins. This early phenomenon may have relevance in experimental alcohol liver disease.

Lipid hydroperoxide induced mitochondrial dysfunction following acute ethanol intoxication in rats. The critical role for mitochondrial reduced glutathione

It has been found that acute ethanol (EtOH) intoxication of rats caused depletion of mitochondrial reduced glutathione (GSH) of approximately 40%. A GSH reduction of similar extent was also observed after the administration to rats of buthionine sulphoximine (BSO), a specific inhibitor of GSH synthesis. Combined treatment with BSO plus EtOH further decreased mitochondrial GSH up to 70% in comparison to control. Normal functional efficiency was encountered in BSO-treated mitochondria, as evaluated by membrane potential measurements during a complete cycle of phosphorylation. In contrast a partial loss of coupled functions occurred in mitochondria from EtOH- and BSO plus EtOH-treated rats. The presence in the incubation system of either GSH methyl monoester (GSH-EE), which normalizes GSH levels, or of EGTA, which chelates the available Ca2+, partially restores the mitochondrial phosphorylative efficiency. Following EtOH and BSO plus EtOH intoxication, the presence of fatty-acid-conjugated diene hydroperoxides, such as octadecadienoic acid hydroperoxide (HPODE), was detected in the mitochondrial membrane. Exogenous HPODE, when added to BSO-treated mitochondria, induced, in a concentration-dependent system, membrane potential derangement. The presence of either GSH-EE or EGTA fully prevented a drop in membrane potential. The results obtained suggest that fatty acid hydroperoxides, endogenously formed during EtOH metabolism, brought about non-specific permeability changes in the mitochondrial inner membrane whose extent was strictly dependent on the level of mitochondrial GSH.

Changes in microsomal phospholipases and arachidonic acid in experimental alcoholic liver injury: relationship to cytochrome P-450 2E1 induction and conjugated diene formation

We evaluated the role of changes in microsomal phospholipases (A and C) and arachidonic acid in the intragastric rat feeding model. The experimental animals (male Wistar rats), divided into 4-5 rats/group, were fed the following diets: corn oil and ethanol and corn oil plus dextrose. One set of groups was killed after 2 weeks of feeding, and the second set was killed after 1 month. For each animal, microsomal analysis of cytochrome P-450 2E1 (CYP 2E1) and fatty acids was done. Fourteen animals had analyses of phospholipase C (PLC) and phospholipase A (PLA), and 10 animals had measurements of conjugated dienes. A significant correlation was obtained between the level of CYP 2E1 and the decrease in arachidonic acid (AA) from baseline levels (r = 0.69, p < 0.01). The decrease in AA also correlated with the increase in conjugated dienes (r = 0.70, p < 0.05). PLA and PLC activities were both significantly increased in the corn oil and ethanol groups. The activity of PLC correlated with the decline in AA (r = 0.69, p < 0.01). The correlations noted between the decrease in microsomal AA and CYP 2E1 induction and conjugated diene formation suggest that these processes may be interlinked especially in regard to generation of lipid peroxides that may play a role in alcoholic liver injury.

Increased ethane exhalation, an in vivo index of lipid peroxidation, in alcohol-abusers

Ethane exhalation was measured in 42 control subjects, 52 patients with various non-alcoholic liver diseases, and 89 alcohol abusers who had been admitted to hospital for alcohol withdrawal and assessment of liver disease (six with normal liver tests, 10 with steatosis with or without fibrosis, six with alcoholic hepatitis, 29 with cirrhosis, 34 with both cirrhosis and alcoholic hepatitis, and four with both cirrhosis and a hepatocellular carcinoma). Ethane exhalation was similar in control subjects and in patients with non-alcoholic liver diseases, but was five times higher in alcohol abusers. Ethane exhalation in alcohol abusers was significantly, but very weakly, correlated with the daily ethanol intake before hospital admission, and the histological score for steatosis, but not with the inflammation or alcoholic hepatitis scores. Ethane exhalation was inversely correlated with the duration of abstinence before the test. In nine alcoholic patients, the exhalation of ethane was measured repeatedly, and showed slow improvement during abstinence. Ethane exhalation was significantly but weakly correlated with the Pugh's score in patients with alcoholic cirrhosis. It is concluded that the mean ethane exhalation is increased in alcohol abusers. One of the possible mechanisms may be the presence of oxidizable fat in the liver. The weak correlation with the Pugh's score is consistent with the contribution of many other factors in the progression to severe liver disease.

Implication of free radical mechanisms in ethanol-induced cellular injury

Numerous experimental data reviewed in the present article indicate that free radical mechanisms contribute to ethanol-induced liver injury. Increased generation of oxygen- and ethanol-derived free radicals has been observed at the microsomal level, especially through the intervention of the ethanol-inducible cytochrome P450 isoform (CYP2E1). Furthermore, an ethanol-linked enhancement in free radical generation can occur through the cytosolic xanthine and/or aldehyde oxidases, as well as through the mitochondrial respiratory chain. Ethanol administration also elicits hepatic disturbances in the availability of non-safely-sequestered iron derivatives and in the antioxidant defense. The resulting oxidative stress leads, in some experimental conditions, to enhanced lipid peroxidation and can also affect other important cellular components, such as proteins or DNA. The reported production of a chemoattractant for human neutrophils may be of special importance in the pathogenesis of alcoholic hepatitis. Free radical mechanisms also appear to be implicated in the toxicity of ethanol on various extrahepatic tissues. Most of the experimental data available concern the gastric mucosa, the central nervous system, the heart, and the testes. Clinical studies have not yet demonstrated the role of free radical mechanisms in the pathogenesis of ethanol-induced cellular injury in alcoholics. However, many data support the involvement of such mechanisms and suggest that dietary and/or pharmacological agents able to prevent an ethanol-induced oxidative stress may reduce the incidence of ethanol toxicity in humans.

Mitochondrial and microsomal lipid peroxidation in rat liver after acute acetaldehyde and ethanol intoxication

The effects of acetaldehyde and ethanol treatments on hepatic lipid peroxidation are compared in rats after the administration of toxically corresponding doses. Wistar rats were given a single dose of acetaldehyde (0.5 g/kg) or ethanol (5 g/kg) intraperitoneally. The animals were killed 1/2, 1, 2, 4, 6, 9, 12 and 24 h after treatments. The results indicate that acetaldehyde, like ethanol, stimulates hepatic lipid peroxidation and also selectively affects the hepatic mitochondria.

Rat liver microsomal NADPH-supported oxidase activity and lipid peroxidation dependent on ethanol-inducible cytochrome P-450 (P-450IIE1)

The liver microsomal ethanol-inducible cytochrome P-450 (P-450IIE1) form is known to exhibit a high rate of oxidase activity in the absence of substrate and it was therefore of interest to evaluate whether this form of P-450 could contribute to microsomal and liposomal NADPH-dependent oxidase activity and lipid peroxidation. The rate of microsomal NADPH-consumption, O2--formation, H2O2-production and generation of thiobarbituric acid (TBA) reactive substances correlated to the amount of P-450IIE1 in 28 microsomal samples from variously treated rats. Anti-P-450IIE1 IgG inhibited, compared to control IgG, microsomal H2O2-formation by 45% in microsomes from acetone-treated rats and by 22% in control microsomes. NADPH-dependent generation of TBA-reactive products was completely inhibited by these antibodies, whereas preimmune IgG was essentially without effect. Liposomes containing reductase and P-450IIE1 were peroxidized in a superoxide dismutase (SOD) sensitive reaction at a 5-10-fold higher rate than membranes containing 3 other forms of cytochrome P-450. Lipid peroxidation in reconstituted vesicles dependent on the presence of P-450IIB1 was by contrast not inhibited by SOD. Microsomal peroxidase activities, using 15-(S)-hydroperoxy-5-cis-8,11,13-trans-eicosatetraenoic acid as a substrate were high in microsomes from phenobarbital- or ethanol-treated rats but low in membranes from isoniazid-treated rats, having the highest relative level of P-450IIE1. It is suggested that the oxidase activity of P-450IIE1 contributes to microsomal NADPH-dependent lipid peroxidation. The combined action of the oxidase activity by P-450IIE1 and the peroxidase activities by P-450IIB1 and other forms of P-450 may be important for the high rate of lipid peroxidation observed in e.g. microsomes from ethanol- or acetone-treated rats. The possible importance of cytochrome P-450IIE1-dependent lipid peroxidation in vivo after ethanol abuse is discussed.

Biochemical basis for alcohol-induced liver injury

Chronic ethanol ingestion leads to hepatocellular injury and alcoholic liver disease (ALD) only if multiple factors combine to favor centrilobular hepatocellular hypoxia. It is hypothesized that these factors include a shift in the redox state, the induction of the microsomal ethanol oxidizing system (MEOS), a high blood alcohol level (BAL), a high polyunsaturated fat diet and episodic decreased O2 supply to the liver. The shift in the redox state favors a low cellular pH, decreased fatty acid oxidation and increased triglyceride formation. The increased MEOS activity increases O2 consumption and portal-central O2 gradient as well as favors acetaldehyde toxic effects including retention of hepatic lipids and export proteins causing cell swelling. The resultant increase in the concentration of acetaldehyde and lactate may stimulate fibrosis as they stimulate collagen synthesis in vitro. The resultant fatty liver narrows the sinusoids slowing sinusoid blood flow. The combination of events reduces available O2 leading to decreased levels of ATP and cellular pH making the liver vulnerable to episodes of systemic hypoxia. The role of membrane changes are reviewed, i.e., 1) membrane fluidity as related to changes in the species of phospholipids, 2) mitochondrial function as related to the changes in the lipid environment of the electron transport chain, and 3) linoleic acid-prostaglandin metabolism. Acute ethanol in vitro has been shown to affect liver cell metabolism regulation by triggering and increasing protein phosphorylation through the Ca2+-phospholipase C pathway. A high fat diet enhances the liver injury caused by chronic ethanol ingestion.

Flow cytometric analysis of oxidative product formation in phytohemagglutinin-stimulated ethanol-treated immune mononuclear cells

Oxidative products formed by immune mononuclear cells were studied by flow cytometry. JURKAT T cells and peripheral blood mononuclear cells were incubated with 2,7-dichlorofluorescin diacetate. This substance was hydrolysed in the cells, leading to a non-fluorescent product which was oxidized into highly fluorescent 2,7-dichlorofluorescein by oxygen reactive species. These latter products were analysed by flow cytometry in phytohemagglutinin (PHA)-stimulated ethanol (ETH)-treated mononuclear cells. The level of fluorescence intensity (FI) was found higher in stimulated cells than in non-stimulated cells. ETH displayed two different effects on the cells: either a decrease of FI associated with a decrease of the number of fluorescent cells (FC) or an increase in FI. Both effects were dose-dependent. ETH is an effective scavenger of .OH radicals, but it is also oxidized by the microsomal ETH oxidizing system with production of oxygen reactive species, which probably explains the opposite effects of ETH. In the presence of desferal, an iron-chelating agent, and nordihydroguaiaretic acid, an inhibitor of the lipooxygenase pathway, the cells showed a decrease of FI and FC. These results suggest that .OH and other oxygen reactive species are involved in stimulation by PHA of ETH-treated immune mononuclear cells.

A survey of chemicals inducing lipid peroxidation in biological systems

A great number of drugs and chemicals are reviewed which have been shown to stimulate lipid peroxidation in any biological system. The underlying mechanisms, as far as known, are also dealt with. Lipid peroxidation induced by iron ions, organic hydroperoxides, halogenated hydrocarbons, redox cycling drugs, glutathione depleting chemicals, ethanol, heavy metals, ozone, nitrogen dioxide and a number of miscellaneous compounds, e.g. hydrazines, pesticides, antibiotics, are mentioned. It is shown that lipid peroxidation is stimulated by many of these compounds. However, quantitative estimates cannot be given yet and it is still impossible to judge the biological relevance of chemical-induced lipid peroxidation.

Synergism of organic zinc salts and sulfhydryl compounds (thiols) in the protection of mice against acute ethanol toxicity, and protective effects of various metal salts

Organic zinc salts such as zinc aspartate, zinc orotate, zinc histidine and zinc acetate protected mice against the lethality of an acute intraperitoneal challenge with ethanol. A similar activity was also provided by salts of cobalt, zirconium, lithium and magnesium. Organic zinc salts acted synergistically with sulfhydryl compounds in protecting the mice and potentiation between the two categories of agents was seen. The results are in analogy to radioprotective effects by zinc and thiols and imply that organic zinc salts may, alone or in conjunction with thiols, reduce in a wider context tissue injury caused by free radical-mediated mechanisms.

Lipid peroxidation and mechanisms of toxicity

Aerobic organisms by definition require oxygen, and the importance of iron in aerobic respiration has long been recognized, but despite their beneficial roles, these elements can pose a real threat to the organism. During oxygen reduction, reactive species such as O2-. and H2O2 are formed readily. Iron can combine with these species, or with molecular oxygen itself, to generate free radicals which will attack the polyunsaturated fatty acids of membrane lipids. This oxidative deterioration of membrane lipids is known as lipid peroxidation. To protect itself against this form of attack, the organism possesses several types of defense mechanisms. Under normal conditions, these defenses appear to offer adequate protection for cell membranes, but the possibility exists that certain foreign compounds may interfere with or even overwhelm these defenses, and herein could lie a general mechanism of toxicity. This possible cause of toxicity is discussed in relation to other suggested causes.

The role of the hepatocellular redox state in the hepatic triglyceride accumulation following acute ethanol administration

The role of the increased hepatocellular redox-state [( NADH]/[NAD+] ratio) as a mechanism underlying hepatic triglyceride deposition after acute ethanol dosing has been investigated in the rat. Following a single dose of ethanol (2 g/kg i.p.) in fasted rats, increases were observed at 1.5 hr in the hepatic [lactate]/[pyruvate] (133%), [3-hydroxybutyrate]/[acetoacetate] (69%) ratios, and the liver triglyceride concentration (129%). At the same time point, ethanol increased radioactivity incorporated into hepatic total lipid and triglyceride, after an injection of [U-14C] palmitic acid, by 76% and 158% respectively. Treatment of animals with Naloxone hydrochloride (2 mg/kg i.p.) at 1.0 hr and 2.5 hr after ethanol abolished these ethanol-mediated redox-state changes, without inhibiting ethanol oxidation or affecting hepatic acetaldehyde levels. This, however, did not prevent completely the triglyceride accumulation in the liver or reverse the enhanced uptake of radio-labelled palmitate caused by ethanol. Administration of sorbitol (3.5 g/kg i.p.) caused 109%, 57% and 200% increases in the hepatic [lactate]/[pyruvate], [3-hydroxybutyrate]/[acetoacetate] ratios and glycerol-3-phosphate concentrations respectively. However, the hepatic triglyceride concentration and the incorporation of [U-14C] palmitic acid into hepatic lipids were not influenced by this treatment. In vitro studies in which rat liver slices were incubated with [1-14C] palmitic acid also indicated that the altered [NADH]/[NAD+] ratio was not responsible for the decreased rate of fatty acid oxidation seen after ethanol administration or after the addition of ethanol to the incubation medium. In conclusion, these experiments indicate that increases in the hepatic [NADH]/[NAD+] ratio resulting from ethanol oxidation may not be directly implicated in the altered hepatic fatty acid utilisation and triglyceride deposition observed after acute ethanol administration in rats.

(+)-Cyanidanol-3 prevents the functional deterioration of rat liver mitochondria induced by Fe2+ ions

The clinically effective hepatoprotective flavonoid, (+)-Cyanidanol-3, prevented the Fe2+-induced functional deterioration of rat liver mitochondria. Fe2+ treatment of mitochondria resulted in increased lipid peroxidation (MDA-formation), decreased mitochondrial membrane potential, impaired Ca2+ uptake capacity and caused large amplitude swelling of mitochondria. All of the consequences of Fe2+ treatment were inhibited by (+)-Cyanidanol-3 in a concentration dependent manner. The mitochondrial protective action of the drug is comparable with its free radical scavenging property.

Increased free-radical activity in alcoholics

The identification of the main dieneconjugated "free-radical marker" in human serum led to a study of free-radical activity in chronic alcoholics. 66 patients were investigated immediately after alcohol withdrawal and over 1-4 weeks' follow-up. The control groups were 76 normal subjects, 78 patients with liver disease, 30 patients on long-term antiepileptic drug treatment, 9 pregnant women, and 99 unselected hospital patients. 82% of chronic alcoholics had a significantly higher than normal level of phospholipid-esterified 9,11 linoleicacid isomer in blood collected within 24 h of their last alcoholic drink. The levels fell to normal over the next 2-4 days but continued to decline within the normal range for 2-3 weeks. There was no rise in the level of the isomer in normal controls after an acute alcohol load. The results suggest that chronic alcoholism may induce a specific detoxifying mechanism which is activated by alcohol and which entails or depends on greatly increased free-radical activity.

The effect of chronic ethanol ingestion on hepatic lipid peroxide, glutathione, glutathione peroxidase and glutathione transferase in rats

Water containing 20% ethanol was given for a period of 3, 6 and 9 weeks to rats, and changes in hepatic lipid peroxide, glutathione, glutathione peroxidase and glutathione transferases were investigated. Lipid peroxide levels and glutathione peroxidase activities remained unchanged after 3 weeks and started to increase thereafter. Glutathione levels and glutathione transferase activities were significantly increased following ethanol consumption. These results show that chronic ethanol consumption stimulates hepatic lipid peroxidation in rats. This stimulation is not dependent on glutathione depletion and the increased glutathione peroxidase and glutathione transferase activities may reflect an adaptive change against ethanol-induced lipid peroxide toxicity.

Fatty acid composition of rat liver mitochondrial phospholipids during ethanol inhalation

Male Sprague-Dawley rats were exposed to increasing concentrations (15-22 mg/l) of ethanol vapor over a 4-day period. Phospholipids were analyzed in liver mitochondria isolated from ethanol-treated and pair-weighted control animals. After a 2-day inhalation period, the proportion of monoenoic acids in total phospholipids increased, whereas that of arachidonic acid decreased. These changes were more striking in phosphatidylcholine (PC) than in phosphatidylethanolamine (PE). The decrease in 20:4 may be related to increased lipid peroxidation. After a 4-day inhalation period, quite different changes in phospholipid fatty acids were found. They consisted in a trend towards a more unsaturated system, the proportion of 20:4 being increased in PC and that of 22:6 in PE. This increase in polyunsaturated acids might be related to a direct ethanol effect on lipid structure and/or metabolism that would be linked to the high blood alcohol level present at this stage of ethanol intoxication.