Increased microsomal oxidation of hydroxyl radical scavenging agents and ethanol after chronic consumption of ethanol

Interaction between fatty acid oxidation and ethanol metabolism in liver

Fatty acid oxidation (FAO) releases the energy stored in fat to maintain basic biological processes. Dehydrogenation is a major way to oxidize fatty acids, which needs NAD+ to accept the released H+ from fatty acids and form NADH, which increases the ratio of NADH/NAD+ and consequently inhibits FAO leading to the deposition of fat in the liver, which is termed fatty liver or steatosis. Consumption of alcohol (ethanol) initiates simple steatosis that progresses to alcoholic steatohepatitis, which constitutes a spectrum of liver disorders called alcohol-associated liver disease (ALD). ALD is linked to ethanol metabolism. Ethanol is metabolized by alcohol dehydrogenase (ADH), microsomal ethanol oxidation system (MEOS), mainly cytochrome P450 2E1 (CYP2E1), and catalase. ADH also requires NAD+ to accept the released H+ from ethanol. Thus, ethanol metabolism by ADH leads to increased ratio of NADH/NAD+, which inhibits FAO and induces steatosis. CYP2E1 directly consumes reducing equivalent NADPH to oxidize ethanol, which generates reactive oxygen species (ROS) that lead to cellular injury. Catalase is mainly present in peroxisomes, where very long-chain fatty acids and branched-chain fatty acids are oxidized, and the resultant short-chain fatty acids will be further oxidized in mitochondria. Peroxisomal FAO generates hydrogen peroxide (H2O2), which is locally decomposed by catalase. When ethanol is present, catalase uses H2O2 to oxidize ethanol. In this review, we introduce FAO (including α-, β-, and ω-oxidation) and ethanol metabolism (by ADH, CYP2E1, and catalase) followed by the interaction between FAO and ethanol metabolism in the liver and its pathophysiological significance.

CYP2E1 Sensitizes the Liver to LPS- and TNF α-Induced Toxicity via Elevated Oxidative and Nitrosative Stress and Activation of ASK-1 and JNK Mitogen-Activated Kinases

The mechanisms by which alcohol causes cell injury are not clear. A major mechanism is the role of lipid peroxidation and oxidative stress in alcohol toxicity. Many pathways have been suggested to play a role in how alcohol induces oxidative stress. Considerable attention has been given to alcohol elevated production of lipopolysaccharide (LPS) and TNFα and to alcohol induction of CYP2E1. These two pathways are not exclusive of each other; however, interactions between them, have not been extensively evaluated. Increased oxidative stress from induction of CYP2E1 sensitizes hepatocytes to LPS and TNFα toxicity and oxidants, activation of inducible nitric oxide synthase and p38 and JNK MAP kinases, and mitochondrial dysfunction are downstream mediators of this CYP2E1-LPS/TNFα-potentiated hepatotoxicity. This paper will summarize studies showing potentiated interactions between these two risk factors in promoting liver injury and the mechanisms involved including activation of the mitogen-activated kinase kinase kinase ASK-1. Decreasing either cytosolic or mitochondrial thioredoxin in HepG2 cells expressing CYP2E1 causes loss of cell viability and elevated oxidative stress via an ASK-1/JNK-dependent mechanism. We hypothesize that similar interactions occur as a result of ethanol induction of CYP2E1 and TNFα.

Long term ethanol consumption leads to lung tissue oxidative stress and injury

BACKGROUND

Alcohol abuse is a systemic disorder. The deleterious health effects of alcohol consumption may result in irreversible organ damage. By contrast, there currently is little evidence for the toxicity of chronic alcohol use on lung tissue. Hence, in this study we investigated long term effects of ethanol in the lung.

RESULTS

Though body weight of rats increased significantly with duration of exposure compared to its initial weight, but there was no significant change in relative weight (g/100 g body weight) of lung due to ethanol exposure. The levels of thiobarbituric acid reactive substances (TBARS), nitrite, protein carbonyl, oxidized glutathione (GSSG), redox ratio (GSSG/GSH) and GST activity elevated; while reduced glutathione (GSH) level and activities of glutathione reductase (GR), glutathione peroxidase (GPx), catalase, superoxide dismutase (SOD) and Na(+)K(+) ATPase reduced significantly with duration of ethanol exposure in the lung homogenate compared to the control group. Total matrix metalloproteinase activity elevated in the lung homogenate with time of ethanol consumption. Histopathologic examination also demonstrated that severity of lung injury enhanced with duration of ethanol exposure.

METHODS

16-18 weeks old male albino Wistar strain rats weighing 200-220 g were fed with ethanol (1.6 g/ kg body weight/ day) up to 36 weeks. At the end of the experimental period, blood samples were collected from reteroorbital plexus to determine blood alcohol concentration, and the animals were sacrificed. Various oxidative stress related biochemical parameters, total matrix metalloproteinase activity and histopathologic examinations of the lung tissues were performed.

CONCLUSIONS

Results of this study indicate that long term ethanol administration aggravates systemic and local oxidative stress, which may be associated with lung tissue injury.

CYP2E1 potentiation of LPS and TNFα-induced hepatotoxicity by mechanisms involving enhanced oxidative and nitrosative stress, activation of MAP kinases, and mitochondrial dysfunction

The mechanisms by which alcohol causes cell injury are not clear. A major mechanism that is the focus of considerable research is the role of lipid peroxidation and oxidative stress in alcohol toxicity. Many pathways have been suggested to play a role in how alcohol induces oxidative stress. Considerable attention has been given to alcohol-elevated production of lipopolysaccharide (LPS) and TNFα and to alcohol induction of CYP2E1. These two pathways are not exclusive of each other, however, associations and interactions between them, especially in vivo, have not been extensively evaluated. We have shown that increased oxidative stress from induction of CYP2E1 in vivo sensitizes hepatocytes to LPS and TNF toxicity and that oxidants, such as peroxynitrite, activation of p38 and JNK MAP kinases, inactivation of NF-kB protective pathways and mitochondrial dysfunction are downstream mediators of this CYP2E1-LPS/TNF potentiated hepatotoxicity. This review will summarize studies showing potentiated interactions between these two risk factors in promoting liver injury and the mechanisms involved.

Ferritin-dependent radical generation in rat liver homogenates

The hypothesis of this study was that mammalian ferritin (FER) has the ability of releasing Fe in the tissue to catalyze the generation of free radicals, such as ascorbyl (A) and hydroxyl radical (OH), that might lead to the damage of FER itself. The rat liver homogenates exhibited an electron paramagnetic resonance (EPR) signal with the spectral features (a(H)=1.88 G, g=2.0054) of A. The addition to the reaction medium of isolated rat liver FER increased by 3-fold the EPR signal, as compared to the recorded value in its absence. Isolated microsomes from rat liver incubated during 10 min showed a signal with the spectral features (a(H)=15G, g=2.0062) of OH. The addition of FER in the presence of either ethylenediamine-tetraacetic acid (EDTA) or adenosine-5'-triphosphate (ATP) significantly increased the recorded spectra. The labile Fe pool (LIP) in the homogenate was assessed by EPR. The rat liver homogenates exhibited an EPR signal with the spectral features (g=4.3) of the Fe(2+) and was significantly increased by the addition of FER (3-fold). The oxidation profile of the isolated FER from rat liver was analyzed after incubation with 10 mM ascorbate (AH(-)). A drastic increase in the width of the band suggested alterations to the protein structure. The FER content of tryptophan (Trp) and thiols was significantly lower when the incubation was performed in the presence of AH(-) as compared to the recorded effect in its absence. The data in tissue homogenates presented here showed that radical generation is associated to FER Fe release, and moreover that the FER protein itself was affected during this process.

Role of oxidative stress in alcohol-induced liver injury

Reactive oxygen species (ROS) are highly reactive molecules that are naturally generated in small amounts during the body's metabolic reactions and can react with and damage complex cellular molecules such as lipids, proteins, or DNA. Acute and chronic ethanol treatments increase the production of ROS, lower cellular antioxidant levels, and enhance oxidative stress in many tissues, especially the liver. Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury. Many pathways play a key role in how ethanol induces oxidative stress. This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol-induced liver injury. Special emphasis is placed on CYP2E1, which is induced by alcohol and is reactive in metabolizing and activating many hepatotoxins, including ethanol, to reactive products, and in generating ROS.

CYP2E1 and oxidative liver injury by alcohol

Ethanol-induced oxidative stress seems to play a major role in mechanisms by which ethanol causes liver injury. Many pathways have been suggested to contribute to the ability of ethanol to induce a state of oxidative stress. One central pathway seems to be the induction of cytochrome P450 2E1 (CYP2E1) by ethanol. CYP2E1 metabolizes and activates many toxicological substrates, including ethanol, to more reactive, toxic products. Levels of CYP2E1 are elevated under a variety of physiological and pathophysiological conditions and after acute and chronic alcohol treatment. CYP2E1 is also an effective generator of reactive oxygen species such as the superoxide anion radical and hydrogen peroxide and, in the presence of iron catalysts, produces powerful oxidants such as the hydroxyl radical. This review article summarizes some of the biochemical and toxicological properties of CYP2E1 and briefly describes the use of cell lines developed to constitutively express CYP2E1 and CYP2E1 knockout mice in assessing the actions of CYP2E1. Possible therapeutic implications for treatment of alcoholic liver injury by inhibition of CYP2E1 or CYP2E1-dependent oxidative stress will be discussed, followed by some future directions which may help us to understand the actions of CYP2E1 and its role in alcoholic liver injury.

Effects of pyridine exposure upon structural lipid metabolism in Swiss Webster mice

Pyridine is a prototypical inducer of cytochrome P450 (CYP) 2E1, an enzyme associated with cellular oxidative stress and membrane damage. To better understand the effect of this treatment on cellular lipids, the influence of pyridine exposure (100 mg/kg/day i.p. for 5 days) on fatty acids, fatty esters, and fatty alcohol ethers in brain, heart, liver, and adipose tissue from male Swiss Webster mice was investigated. Lipid levels in cholesterol esters, triglycerides, free fatty acids, cardiolipin, sphingomyelin, and glycerylphospholipids were quantified. Pyridine altered the level and composition of lipids involved in membrane structure (i.e., sphingomyelin, phosphatidylethanolamines, and plasmalogens), energy metabolism (i.e., free fatty acids), and long-chain fatty acid transport (i.e., cholesterol esters) in a tissue-specific manner. Subtle changes in cholesterol esters were observed in all tissues. Sphingomyelin in the brain and heart were depleted in monounsaturated fatty acids (1.4- and 1.5-fold, respectively), while the liver sphingomyelin concentrations increased (1.5-fold). Pyridine exposure also increased heart free fatty acids by 1.3-fold, enriched cardiac phosphatidylethanolamine in long-chain polyunsaturated fatty acids by 1.3-fold, and depleted cardiolipin-associated plasmalogens by 3.8-fold. Phosphatidylethanolamines in the brain were also enriched in both saturated fatty acids (1.2-fold) and polyunsaturated fatty acids (1.3-fold) but were depleted in plasmalogens (2.9-fold). In particular, the levels of phosphatidylethanolamine-associated arachidonic (AA) and docosahexaenoic acid (DHA) in both brain and cardiac tissues significantly decreased following pyridine exposure. Considering the hypothetical role of plasmalogens as membrane-bound reactive oxygen scavengers, the current findings suggest that the brain and heart should be the focus of future studies on the toxicity of pyridine, as well as other CYP 2E1 inducers.

In vivo supplementation with Ginkgo biloba protects membranes against lipid peroxidation

The effect of Ginkgo biloba (Gb) supplementation in vivo was studied on lipid peroxidation of microsomal membranes. Administration of up to 100 mg/kg/day Gb to rats did not significantly affect either the activity of microsomal enzymes, the rate of generation of superoxide anion or the iron reduction rate by rat liver microsomes. Lipid peroxidation, assessed by the generation of lipid radicals measured by electron paramagnetic resonance (EPR) spectroscopy using POBN as the spin trap, was reduced by 39.7% and thiobarbituric acid reactive substances (TBARS) generation by 30% after Gb supplementation (100 mg/kg/day) for 10 days. Moreover, membranes from Gb treated animals showed a significant lower content of lipid radicals and TBARS after exposure to oxidative stress both in vitro (t-butyl hydroperoxide) and in vivo (acute iron overload). The data presented here showed that Gb extracts were able to limit lipid peroxidation and scavenge lipid radicals in vivo and actively protect membranes from oxidative damage.

Effects of seasonal and latitudinal cold on oxidative stress parameters and activation of hypoxia inducible factor (HIF-1) in zoarcid fish

Acute, short term cooling of North Sea eelpout Zoarces viviparus is associated with a reduction of tissue redox state and activation of hypoxia inducible factor (HIF-1) in the liver. The present study explores the response of HIF-1 to seasonal cold in Zoarces viviparus, and to latitudinal cold by comparing the eurythermal North Sea fish to stenothermal Antarctic eelpout (Pachycara brachycephalum). Hypoxic signalling (HIF-1 DNA binding activity) was studied in liver of summer and winter North Sea eelpout as well as of Antarctic eelpout at habitat temperature of 0 degrees C and after long-term warming to 5 degrees C. Biochemical parameters like tissue iron content, glutathione redox ratio, and oxidative stress indicators were analyzed to see whether the cellular redox state or reactive oxygen species formation and HIF activation in the fish correlate. HIF-1 DNA binding activity was significantly higher at cold temperature, both in the interspecific comparison, polar vs. temperate species, and when comparing winter and summer North Sea eelpout. Compared at the low acclimation temperatures (0 degrees C for the polar and 6 degrees C for the temperate eelpout) the polar fish showed lower levels of lipid peroxidation although the liver microsomal fraction turned out to be more susceptible to lipid radical formation. The level of radical scavenger, glutathione, was twofold higher in polar than in North Sea eelpout and also oxidised to over 50%. Under both conditions of cold exposure, latitudinal cold in the Antarctic and seasonal cold in the North Sea eelpout, the glutathione redox ratio was more oxidised when compared to the warmer condition. However, oxidative damage parameters (protein carbonyls and thiobarbituric acid reactive substances (TBARS) were elevated only during seasonal cold exposure in Z. viviparus. Obviously, Antarctic eelpout are keeping oxidative defence mechanisms high enough to avoid accumulation of oxidative damage products at low habitat temperature. The paper discusses how HIF could be instrumental in cold adaptation in fish.

Alcohol-induced oxidative stress

Alcohol-induced oxidative stress is linked to the metabolism of ethanol involving both microsomal and mitochondrial systems. Ethanol metabolism is directly involved in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). These form an environment favourable to oxidative stress. Ethanol treatment results in the depletion of GSH levels and decreases antioxidant activity. It elevates malondialdehyde (MDA), hydroxyethyl radical (HER), and hydroxynonenal (HNE) protein adducts. These cause the modification of all biological structures and consequently result in serious malfunction of cells and tissues.

Oxidative stress, toxicology, and pharmacology of CYP2E1

This review describes some of the biochemical and toxicological properties of CYP2E1, especially as it relates to alcohol metabolism and toxicity and the establishment of human hepatoma HepG2 cell lines that overexpress human CYP2E1. Ethanol, polyunsaturated fatty acids, and iron were found to be cytotoxic in HepG2 cells that overexpress CYP2E1. GSH appears to be essential in protecting HepG2 cells against the CYP2E1-dependent cytotoxicity, and GSH levels were elevated owing to a twofold increase in activity and expression of glutamate cysteine ligase. We suggest that this up-regulation of GSH synthesis was an adaptive response to attenuate CYP2E1-dependent oxidative stress and toxicity. Induction of a state of oxidative stress appears to play a central role in the CYP2E1-dependent cytotoxicity. Mitochondrial membrane potential decreased in the CYP2E1-expressing HepG2 cells, and this decrease shared similar characteristics with the developing toxicity. Alcohol-dependent liver injury is likely to be a multifactorial process involving several mechanisms. We believe that the linkage between CYP2E1-dependent oxidative stress, mitochondrial injury, and GSH homeostasis contribute to the toxic actions of ethanol on the liver.

Iron and CYP2E1-dependent oxidative stress and toxicity

Iron plays a critical role in catalyzing the formation of potent oxidants. Increases in iron content enhance oxidative stress, whereas removal of iron deceases such stress. An association between iron and alcoholic liver injury has been proposed. The ability of iron to modulate the biochemical and toxicologic actions of cytochrome P450 2E1 (CYP2E1) has been evaluated by using isolated microsomes and intact liver cells. The ability of different iron complexes to stimulate microsomal lipid peroxidation and hydroxyl radical production during reduced form of nicotinamide adenine dinucleotide phosphate (NADPH)- and reduced form of nicotinamide adenine dinucleotide (NADH)-dependent electron transfer has been characterized. Certain iron complexes have been shown to be effective in promoting lipid peroxidation; others are better catalysts of hydroxyl radical production as a complex pattern has been found. Reactive oxygen production, lipid peroxidation, and interaction with iron chelates have been shown to be enhanced with microsomes isolated from ethanol-treated rats with elevated levels of CYP2E1. This increase was prevented by anti-CYP2E1 immunoglobulin (Ig)G or chemical inhibitors of CYP2E1. Thus, in the presence of iron complexes, microsomes enriched in CYP2E1 are especially reactive in generation of reactive oxygen species. To assess the toxicologic significance of this iron-CYP2E1 interaction, iron (ferric-nitrilotriacetate) was added to HepG2 cells, which were engineered to express the human CYP2E1. Ferric-nitrilotriacetate produced a greater toxicity in the CYP2E1-expressing HepG2 cells than that in control HepG2 cells. This enhanced, synergistic toxicity was blocked by antioxidants and inhibitors of CYP2E1. Mitochondrial membrane potential and ATP levels were decreased, and damage to the mitochondria played a critical role in the CYP2E1-plus-iron-dependent toxicity. These results support the suggestion that low concentrations of iron and polyunsaturated fatty acids can act as priming or sensitizing factors for CYP2E1-induced injury in HepG2 cells and hepatocytes. Such interactions may play a role in alcohol-induced liver injury.

A review of the role of reactive oxygen and nitrogen species in alcohol-induced mitochondrial dysfunction

Our understanding of the mechanisms involved in the development of alcohol-induced liver disease has increased substantially in recent years. Specifically, reactive oxygen and nitrogen species have been identified as key components in initiating and possibly sustaining the pathogenic pathways responsible for the progression from alcohol-induced fatty liver to alcoholic hepatitis and cirrhosis. Ethanol has been demonstrated to increase the production of reactive oxygen and nitrogen species and decrease several antioxidant mechanisms in liver. However, the relative contribution of the proposed sites of ethanol-induced reactive species production within the liver is still not clear. It has been proposed that chronic ethanol-elicited alterations in mitochondria structure and function might result in increased production of reactive species at the level of the mitochondrion in liver from ethanol consumers. This in turn might result in oxidative modification and inactivation of mitochondrial macromolecules, thereby contributing further to mitochondrial dysfunction and a loss in hepatic energy conservation. Moreover, ethanol-related increases in reactive species may shift the balance between pro- and anti-apoptotic factors such that there is activation of the mitochondrial permeability transition, which would lead to increased cell death in the liver after chronic alcohol consumption. This article will examine the critical role of these reactive species in ethanol-induced liver injury with specific emphasis on how chronic ethanol-associated alterations to mitochondria influence the production of reactive oxygen and nitrogen species and how their production may disrupt hepatic energy conservation in the chronic alcohol abuser.

Effect of zinc on hepatic lipid peroxidation and antioxidative enzymes in ethanol-fed rats

A 3-ml aliquot of 30% ethanol was fed daily to normal as well as zinc-treated (227 mg l(-1)) rats for periods of 2, 4 and 8 weeks. A highly significant increase in the levels of hepatic lipid peroxidation was observed in ethanol-fed rats after 4 and 8 weeks of treatment. On the other hand, the levels of lipid peroxidation came down significantly following ethanol feeding to zinc-treated rats. The activities of glutathione peroxidase (GPx), catalase and superoxide dismutase (SOD) in liver were elevated significantly after ethanol administration to rats for durations of 2, 4 and 8 weeks. Interestingly, zinc treatment to rats given ethanol was able to bring down the elevated levels of SOD, catalase and GPx to within normal limits, However, zinc administration alone did not cause any significant alteration in the activities of these antioxidative enzymes.

Soymilk products affect ethanol absorption and metabolism in rats during acute and chronic ethanol intake

In this study we evaluated the effects of soy products on ethanol metabolism during periods of acute and chronic consumption in rats. Gastric ethanol content and blood ethanol and acetaldehyde concentrations were investigated after the oral administration of ethanol (34 mmol/kg) plus soy products such as soymilk (SM) or fermented soymilk (FSM). The gastric ethanol concentration of the FSM group was greater than that of the control group, whereas portal and aortal blood ethanol concentrations of the FSM group were lower than in controls. The aortal acetaldehyde concentration in the FSM group was lower than that of the control group. The direct effect of isoflavones on liver function was investigated by using hepatocytes isolated from untreated rats. Genistein (5 micromol/L) decreased ethanol (P = 0.045) and tended to decrease acetaldehyde (P = 0.10) concentrations in the culture filtrate. Some variables of ethanol metabolism in the liver were investigated after chronic ethanol exposure for 25 d. Rats consumed a 5% ethanol fluid plus the SM diet, the FSM diet or a control diet. Microsomal ethanol oxidizing activity was significantly lower in the FSM group than the control group. Furthermore, cytosolic glutathione S-transferase activity was higher in the SM and FSM groups than in the control group. Acetaldehyde dehydrogenase activity (low K(m)) in the FSM group (P = 0.15), but not in the SM group (P = 0.31), tended to be greater than in the control group. The amount of thiobarbituric acid reacting substances in the liver of the SM and FSM groups tended to be less than that of the control group (P = 0.18 and 0.10, respectively). These results demonstrate that soymilk products inhibit ethanol absorption and enhance ethanol metabolism in rats.

Modulating effect of Liv.100, an ayurvedic formulation on antituberculosis drug-induced alterations in rat liver microsomes

The influence of Liv.100 on the hepatotoxicity of antituberculosis drugs [isoniazid (INH), rifampicin (RMP) pyrazinamide (PZA)] was studied in male albino rats. INH, RMP, and PZA were proved to be the most hepatotoxic. Rats were treated with antituberculosis drugs daily for a period of 6 weeks by intragastric administration. The combined use of antituberculosis drugs elevated the levels of cytochrome P-450 and cytochrome-b5. A significant increase was observed in the levels of NADPH-cytochrome P-450 reductase and NADH-cytochrome-b5 reductases after antitubercular drug administration. During antitubercular drug treatment a significant decrease was also observed in the activity of glucose-6-phosphatase. The extent of NADPH-induced and ascorbic acid-induced lipid peroxides were marked in antitubercular drug treatment, when compared with normal control animals. Oral Liv.100 co-administration, for the same period, modulated the alterations in the xenobiotic metabolizing system and microsomal lipid peroxidation in experimental animals. The results are discussed with reference to drug metabolizing enzymes, lipid peroxidation and the hepatoprotective nature of Liv.100.

Effect of dietary fat on chronic ethanol-induced oxidative stress in hepatocytes

BACKGROUND

Although oxidative stress and deficits in hepatic energy metabolism have been implicated as important factors in the initiation of alcoholic liver disease, their relative contribution to ethanol-induced cell death is not known. The purpose of this study was to examine the effects of chronic ethanol administration on hepatocyte reactive oxygen species (ROS) generation, energy state, and viability, as well as the effect of dietary fat on these parameters.

METHODS

Male Sprague-Dawley rats were fed liquid diets that provided 36% total calories as ethanol, with fat as either 12% (low fat) or 35% (high fat) of total calories. Pair-fed controls received liquid diets in which maltose-dextrin was substituted for ethanol calories. The fluorescent probe 2',7'-dichlorofluorescin diacetate was used to detect ROS, lactate dehydrogenase leakage was used to assess viability, and ATP levels were used as a measure of the energy state. The effect of chronic ethanol feeding on these parameters was determined by incubating hepatocytes under a 5% oxygen-containing atmosphere or an atmosphere < or = 1% oxygen for 60 min.

RESULTS

In general, chronic ethanol feeding stimulated ROS production and decreased ATP concentrations, which were associated with decreased viability in hepatocytes isolated from rats fed either high- or low-fat, ethanol-containing diets, compared to the corresponding controls. Incubation under an atmosphere < or = 1% oxygen and/or ethanol (10 mM) augmented these effects in both high- and low-fat control and ethanol-fed hepatocytes. The addition of antimycin to the incubations increased ROS production, decreased ATP concentrations, and accelerated loss of hepatocyte viability. Viability loss under all conditions used in this study was correlated with decreases in cellular ATP.

CONCLUSIONS

Comparisons of incubations performed under the two oxygenation conditions revealed that viability loss was inversely associated with ROS production, which indicates that ATP loss and not ROS production was a better predictor of loss in cell integrity. This study also demonstrates that the level of dietary fat has only minor effects on generation of ROS and the cellular energy state. In contrast, ethanol consumption had significant effects on generation of ROS, energy state, and hepatocyte viability.

Immunohistochemical detection of 4-hydroxy-2-nonenal-modified-protein adducts in human alcoholic liver diseases

4-Hydroxy-2-nonenal (HNE) is one of the major components of lipid peroxidation product and has been shown to react with proteins to form HNE-protein adducts. HNE-protein adducts are relatively stable and can be used as a marker of radical-mediated cellular damage. We report herein the immunohistochemical analysis of HNE-protein adducts in human alcoholic liver diseases using a specific monoclonal antibody HNEJ-2. Cytoplasm of hepatocytes and bile duct epithelia was positively stained for HNE-protein adducts, and the nucleus was negligibly stained. The immunohistochemical intensity of hepatocytes was classified into three groups: strong, moderate, and faint staining. Strong staining was found in 43% of alcoholic liver diseases and in 4% of viral liver diseases. Hepatocytes of alcoholic liver diseases contained a higher amount of HNE-protein adducts than those of viral liver diseases, and the difference was statistically significant (p = 0.005; chi2 test). Semiquantitative analysis of the histological intensities of HNE-protein adducts and iron indicated a significant positive correlation (p = 0.084; Spearman's rank correlation). The localization of HNE-protein adducts and iron in hepatocytes appeared to be identical. These data suggested the correlation between HNE-protein adducts and iron. Our results indicate that HNE-protein adducts, a marker of oxidative stress-induced damage, are increased in human alcoholic liver damage, and that hepatic siderosis may act on the production of free radicals.

Complete suppresion of ethanol-induced formation of megamitochondria by 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-OH-TEMPO)

An attempt has been made to suppress the ethanol-induced formation of megamitochondria (MG) in the rat liver by 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-OH-TEMPO), a free radical scavenger, and by allopurinol (AP), a xanthine oxidase inhibitor. Changes observed in the liver of animals given ethanol (EtOH) for 1 month were remarkable decreases both in the body weight gains during the course of the experiment and in the liver weight at the time of sacrifice compared to those of the control; remarkable increases in the level of thiobarbituric acid reactive substances and lipid soluble fluorophores both in microsomes and mitochondria; decreases in the content of cytochrome a+a3 and b and lowered phosphorylating ability of mitochondria; and formation of MG in the liver. A combined treatment of animals with EtOH plus 4-OH-TEMPO completely suppressed the formation of MG in the liver induced by EtOH and distinctly improved the changes caused by EtOH, as specified above, while AP partly suppressed the MG formation. Results described herein provide additional insight into chronic hepatotoxicity of EtOH besides that previously reported. A novelty of the present work is that we were able for the first time to demonstrate reversibility of EtOH-mediated ultrastructural changes of the liver by a simple administration of aminoxyl-type free radical scavenger, 4-OH-TEMPO. Our results suggest that free radicals may be involved in the mechanism of the formation of MG induced by EtOH.

Pathogenesis of alcoholic liver disease with particular emphasis on oxidative stress

Oxidative stress is well recognized to be a key step in the pathogenesis of ethanol-associated liver injury. Ethanol administration induces an increase in lipid peroxidation either by enhancing the production of oxygen reactive species and/or by decreasing the level of endogenous antioxidants. Numerous experimental studies have emphasized the role of the ethanol-inducible cytochrome P450 in the microsomes and the molybdo-flavoenzyme xanthine oxidase in the cytosol. This review shows the putative role of ethanol-induced disturbances in iron metabolism in relation to iron as a pro-oxidant factor. Ethanol administration also affects the mitochondrial free radical generation. Many previous studies suggest a role for active oxygens in ethanol-induced mitochondrial dysfunction in hepatocytes. Recent studies in our laboratory in the Department of Internal Medicine, Keio University, using a confocal laser scanning microscopic system strongly suggest that active oxidants generated during ethanol metabolism produce mitochondrial membrane permeability transition in isolated and cultured hepatocytes. In addition, acetaldehyde, ethanol consumption-associated endotoxaemia and subsequent release of inflammatory mediators may cause hepatocyte injury via both oxyradical-dependent and -independent mechanisms. These cytotoxic processes may lead to lethal hepatocyte injury. Investigations further implicate the endogenous glutathione-glutathione peroxidase system and catalase as important antioxidants and cytoprotective machinery in the hepatocytes exposed to ethanol.

Ethanol-induced oxidative stress in the liver

Oxygen stress is well recognized to be a key step in the pathogenesis of ethanol-associated liver injury. Ethanol administration induces an increase in lipid peroxidation either by enhancing the production of oxygen-reactive species and/or by decreasing the level of endogenous antioxidants. Numerous experimental studies have emphasized the role of the ethanol-inducible cytochrome P-450 in the microsomes, as well as the molybdo-flavoenzymes xanthine oxidase in the cytosol. This review shows the putative role of ethanol-induced disturbances in iron metabolism in relation to iron as a prooxidant factor. Ethanol administration also affects the mitochondrial free radical generation. Although many previous studies suggest a role for active oxygens in ethanol-induced mitochondrial dysfunction in hepatocytes, the detailed mechanism of ethanol-induced oxidative stress on mitochondria remains to be clarified further. Studies of our laboratory using a confocal laser scanning microscopic system strongly suggest that active oxidants produced during ethanol metabolism modulate mitochondrial energy synthesis in isolated and cultured hepatocytes. In addition, our investigations implicate endogenous glutathione-glutathione peroxidase system and catalase as important antioxidants and cytoprotective machinery in the hepatocyte mitochondria exposed to ethanol. The fluorographic investigations using the confocal laser scanning microscopy may be useful to extend our knowledge and provide a new view about ethanol-associated oxidative stress and metabolic changes in hepatocytes.

Increased oxidation of ethylene glycol to formaldehyde by microsomes after ethanol treatment: role of oxygen radicals and cytochrome P450

The production of ferryl-type oxidants by microsomes from ethanol-fed rats and pair-fed controls was determined by assaying for the production of formaldehyde from ethylene glycol. Microsomes from the ethanol-fed rats were more reactive than controls in oxidizing ethylene glycol. Catalase was a powerful inhibitor for this reaction, superoxide dismutase was slightly inhibitory and hydroxyl radical scavengers had no effect. These results suggest an important role for H2O2, but not O2-. or .OH in the overall pathway for oxidizing ethylene glycol to formaldehyde. The production of H2O2 by microsomes was increased after ethanol treatment, the extent of increase corresponding to the increase in oxidation of ethylene glycol. A variety of inhibitors and ligands of cytochrome P450, including miconazole, diethyldithiocarbamate, tryptamine, and 4-methylpyrazole, inhibited formaldehyde production by both microsomal preparations. Anti-cytochrome P4502E1 IgG also inhibited the reaction with both microsomal preparations and prevented the increase caused by ethanol treatment. These results indicate that microsomes from ethanol-treated rats are more reactive than pair-fed controls in generating ferryl-type oxidants and that increased production of H2O2 by cytochrome P4502E1 plays a role in the elevated oxidation of ethylene glycol to formaldehyde.

Failure of electron paramagnetic resonance spectroscopy studies to detect elevated free radical signals in liver biopsy specimens from patients with alcoholic liver disease

Electron paramagnetic resonance spectroscopy (EPR) was used to study free radicals and transition metal complexes in liver tissue taken from patients with liver disease. Samples were frozen to 77K directly following biopsy to prevent deterioration. Our major aim was to compare signals from patients suffering from alcohol abuse with those from patients having liver damage not induced by alcohol. Samples were obtained from 19 chronic alcohol abusers and 7 non-alcoholic liver disease patients. Of the 19 alcoholic patients, 18 had an increased fat content, 6 had Mallory's hyaline, 12 had an acute inflammatory response, 9 had increased stainable iron and 4 had evidence of fibrosis. A signal derived from free radicals with a spectroscopic splitting factor of g = 2.0045 was found in all samples. This signal in the alcoholic patients had a mean amplitude of 2.96 cm (+/- 1.42 SD), and in patients with non-alcoholic liver disease 2.12 cm (+/- 0.82) (p = 0.10 NS), measured under identical instrument settings. The molar proportion of diene conjugated linoleic acid (DCLA), a free radical marker, in the sera of alcoholic patients was 2.68% (+/- 1.93), but did not correlate with the free radical signals obtained by EPR spectroscopy. Also, there was no correlation between the free radical derived EPR signal and fat content, Mallory's hyaline, inflammatory infiltrate, iron or fibrosis in the liver biopsy specimens. Similarly the concentrations of aspartate transaminase, albumin, and gamma-glutamyl transferase in serum samples showed no correlations with free radical concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidant defense mechanisms in the male rat: interaction with alcohol, copper, and type of dietary carbohydrate

The activities of enzymes participating in cellular protection against free radical reactions were measured in hepatic tissues from copper-adequate and copper-deficient rats fed fructose or starch-based diets. Half of the rats consumed 20% ethanol in their drinking water. The consumption of ethanol depressed growth rate, reduced hematocrit, and hepatic copper concentration. Feed efficiency was greatly depressed by ethanol. Mortality due to copper deficiency occurred in fructose-fed rats and in starch-fed rats that drank ethanol. Ethanol had no effect on superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), or catalase. In contrast, copper deficiency reduced SOD and fructose feeding depressed catalase activity. GSH-Px was not affected by either the type of dietary carbohydrate, copper, or ethanol. Taken together, these data suggest that additional mechanisms to antioxidant defense systems are responsible for the metabolic changes that occur during the interactions between ethanol low copper and dietary carbohydrates.

The Mallory body: morphological, clinical and experimental studies (Part 1 of a literature survey)

To aid understanding of markers of disease and predictors of outcome in alcohol-exposed systems, we undertook a literature survey of more than 700 articles to view the morphological characteristics and the clinical and experimental epidemiology of the Mallory body. Mallory bodies are filaments of intermediate diameter that contain intermediate filament components (e.g., cytokeratins) observable by conventional light microscopy or immunohistochemical methods, identical in structure regardless of initiating factors or putative pathogenesis. Although three morphological types can be identified under electron microscopy (with fibrillar structure parallel, random or absent), they remain stereotypical manifestations of hepatocyte injury. A summary of the conditions associated with Mallory bodies in the literature and their validity and potential etiological relationships is presented and discussed, including estimates on the combined light microscopic and immunohistochemical prevalences and kinetics. Emphasis is placed on proper confounder control (in particular, alcohol history), which is highly essential but often inadequate. These conditions include (mean prevalence of Mallory bodies in parentheses): Indian childhood cirrhosis (73%), alcoholic hepatitis (65%), alcoholic cirrhosis (51%), Wilson's disease (25%), primary biliary cirrhosis (24%), nonalcoholic cirrhosis (24%), hepatocellular carcinoma (23%), morbid obesity (8%) and intestinal bypass surgery (6%). Studies in alcoholic hepatitis strongly suggest a hit-and-run effect of alcohol, whereas other chronic liver diseases show evidence of gradual increase in prevalence of Mallory bodies with severity of hepatic pathology. Mallory bodies in cirrhosis do not imply alcoholic pathogenesis. Obesity, however, is associated with alcoholism and diabetes, and Mallory bodies are only present in diabetic patients if alcoholism or obesity complicates the condition. In addition, case studies on diseases in which Mallory bodies have been identified, along with pharmacological side effects and experimental induction of Mallory bodies by various antimitotic and oncogenic chemicals, are presented. Mallory bodies occur only sporadically in abetalipoproteinemia, von Gierke's disease and focal nodular hyperplasia and during hepatitis due to calcium antagonists or perhexiline maleate. Other conditions and clinical drug side effects are still putative. Finally, a variety of experimental drugs have been developed that cause Mallory body formation, but markedly different cell dynamics and metabolic pathways may raise questions about the relevance of such animal models for human Mallory body formation. In conclusion, the Mallory body is indicative but not pathognomonic of alcohol involvement. A discussion on theories of development and pathological significance transcending the clinical frameworks will be presented in a future paper.

DNA strand cleavage as a sensitive assay for the production of hydroxyl radicals by microsomes: role of cytochrome P4502E1 in the increased activity after ethanol treatment

There is increasing interest in the role of reactive oxygen radicals in the hepatotoxicity associated with ethanol consumption. Reactive oxygen intermediates interact with DNA and can cause single-strand breaks of supercoiled DNA. Experiments were carried out to evaluate the utility of this system as a sensitive assay for the detection of potent oxidants generated by rat liver microsomes isolated from pair-fed control rats and rats treated chronically with ethanol. DNA strand cleavage was assayed by monitoring the migration of the supercoiled and open circular forms in agarose. Microsomes catalysed DNA strand breakage with either NADPH or NADH as cofactors; iron was required to catalyse the reaction and various ferric complexes were effective in promoting the reaction. DNA strand cleavage was prevented by catalase, superoxide dismutase, GSH and hydroxyl-radical-scavenging agents, suggesting that a hydroxyl-radical-like species was the oxidant responsible for the breakage. This assay system proved to be much more sensitive in detecting hydroxyl radicals than are other methods, such as e.s.r. spectroscopy or oxidation of chemical scavenging agents with respect to the amount of microsomal protein and the nature and concentration of the iron catalyst required. Microsomes from ethanol-treated rats were more reactive than control microsomes in catalysing the DNA strand cleavage with either NADPH or NADH; increased catalytic activity was observed with various ferric complexes and was sensitive to the above antioxidants. Compared with preimmune IgG, anti-(cytochrome P4502E1) IgG had no effect on DNA strand cleavage by the control microsomes, but completely prevented the NADPH- and the NADH-dependent increased activity found with microsomes from the ethanol-treated rats. Inhibitors of cytochrome P4502E1, such as diethyl dithiocarbamate and tryptamine, also lowered the extent of increase of DNA strand cleavage produced by microsomes from the ethanol-treated rats. These results indicate that DNA strand cleavage is a very sensitive assay for detecting the production of hydroxyl radicals by microsomes and to demonstrate increased activity by microsomes after chronic ethanol treatment. This increased activity with NADPH and NADH is due, at least in part, to induction of cytochrome P4502E1.

Oxygen radical formation in well-washed rat liver microsomes: spin trapping studies

The generation of hydroxyl radicals by rat liver microsomes was monitored by spin trapping with 5,5-dimethylpyrroline N-oxide (DMPO). The results confirm and extend previous data which demonstrated that hydroxyl radicals are produced by microsomes in the presence of NADPH and O2, and without the exogenous addition of iron. No EPR signals could be detected unless catalase activity which was associated with the microsomes could be substantially diminished. Addition of azide was the most effective means of eliminating catalase activity, but azide also reacted rapidly with hydroxyl radicals, forming azidyl radicals which were in turn trapped by DMPO. Extensive washing and preincubation of microsomes with 3-amino-1,2,4-triazole in the presence of H2O2 were evaluated as alternative methods of decreasing the catalase contamination of microsomes. Although neither method completely eliminated microsomal catalase activity, addition of azide was no longer necessary for hydroxyl radical detection with DMPO. When highly washed microsomal preparations were tested, weak signals of the superoxide radical adduct of DMPO could also be detected. These data indicate that the sensitivity of spin trapping in microsomal systems can be improved substantially when care is taken to eliminate cytosolic contaminants such as catalase.

The effect of antioxidant supplementation on a serum marker of free radical activity and abnormal serum biochemistry in alcoholic patients admitted for detoxification

Alcoholics admitted for detoxification were entered into a double blind placebo controlled trial of oral supplementation with an antioxidant cocktail (vitamin E, beta carotene, vitamin C and selenium) in order to determine the effect of this supplementation on the rate of resolution of a serum marker of free radical activity and abnormal serum biochemistry. The molar proportion of linoleic acid that was diene conjugated (a marker of free radical activity), was increased in the alcoholics 2.9% +/- 1.2 (mean +/- S.D.) compared to normal controls 1.3% +/- 0.6 (P < 0.0001) but fell at a similar rate during the first week of hospitalisation in supplemented and placebo-treated patients with a mean fall of 53.7% (+/- 16.4 S.D.) in the placebo group and 56.0% (+/- 23.7) (P = 0.32, NS) in the antioxidant supplemented group. Similarly, there was no difference in the rate of fall between serum aspartate transaminase (AST) concentration in the two groups: the placebo group falling by a mean of 68.9% (+/- 35.2) and the antioxidant supplemented group falling by 70.1% (+/- 10.0) (P = 0.41, NS) over the first 7 days of hospitalization. Alcoholics had low serum concentrations of vitamin E compared with controls (15.6 mg/l +/- 6.2 S.D.) which rose more in the supplemented group over the period of a week (7.7 mg/l +/- 4.4 to 21.6 mg/l +/- 5.1) (a mean rise of 180.5%) compared with the placebo group (8.6 mg/l +/- 6.8 to 9.6 mg/l +/- 5.7)--a mean rise of 11.6% (P = 0.006).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of cytochrome P-450 2E1 in ethanol-, carbon tetrachloride- and iron-dependent microsomal lipid peroxidation

This study investigated the role of cytochrome P-450 2E1 in enhanced microsomal lipid peroxidation in experimental alcoholic liver disease. We also examined the contribution of this isoform to the increased microsomal injury in alcoholic liver disease caused by carbon tetrachloride-induced or iron-induced oxidant stress. Adult male Wistar rats were intragastrically infused with a high-fat diet and ethanol or glucose for 16 wk; this resulted in hepatic lipid peroxidation and fibrogenesis in the ethanol-fed animals. Microsomes were isolated by differential centrifugation in the presence of 100 mumol/L deferoxamine, washed twice in buffer without deferoxamine and incubated in the absence or presence of ethanol (50 mmol/L), carbon tetrachloride (150 mumol/L), ferric citrate (50 mumol/L) or ferric citrate plus ethanol at 37 degrees C for 30 min in an NADPH-generating system. The basal rate of lipid peroxidation in microsomes isolated from ethanol-fed rats was increased by 52% compared with that in microsomes from controls. Carbon tetrachloride-induced and ferric citrate-induced lipid peroxidation were also accentuated in microsomes from ethanol-fed rats, by 76% and 108%, respectively. Ethanol added in vitro significantly reduced basal (-58%) and ferric citrate-induced (-48%) lipid peroxidation in microsomes from ethanol-fed rats, whereas it had an insignificant effect on that in control microsomes. In fact, this protective effect of ethanol on microsomes from ethanol-fed rats resulted in attenuation of the difference in the level of microsomal lipid peroxidation between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased 4-hydroxynonenal levels in experimental alcoholic liver disease: association of lipid peroxidation with liver fibrogenesis

The precise role of lipid peroxidation in the pathogenesis of alcoholic liver disease is still being debated. To explore the issue, this study was undertaken to investigate the status of lipid peroxidation, antioxidants and prooxidants at two discrete stages of experimental alcoholic liver disease. Male Wistar rats were intragastrically fed a high-fat diet plus ethanol for 5 or 16 wk (the duration that resulted in initiation of centrilobular liver necrosis or liver fibrosis, respectively). Lipid peroxidation was assessed in isolated microsomes and mitochondria with three parameters: malondialdehyde equivalents as determined by thiobarbituric acid assay, conjugated diene formation and 4-hydroxynonenal as a 2,4-dinitrophenylhydrazone derivative. To assess antioxidant systems, hepatic concentrations of glutathione, methionine and alpha-tocopherol were determined. The concentration of nonheme iron, a known prooxidant, was also measured. At wk 5, centrilobular liver necrosis was already evident in the ethanol-fed animals, with two- or threefold increases in plasma AST and ALT levels. At this stage, neither malondialdehyde equivalents nor conjugated diene values were elevated, and the 4-hydroxynonemal level was below 0.2 nmol/mg protein. Hepatic concentrations of methionine and alpha-tocopherol in these animals were increased two- and threefold, respectively, whereas the reduced glutathione level remained unchanged. When alcoholic liver disease had progressed to perivenular or bridging fibrosis at wk 16, all three parameters of lipid peroxidation showed consistent increases that were accompanied by significant reductions in the hepatic glutathione and methionine levels. Interestingly, the control animals pair-fed with the high-fat diet also had significantly elevated 4-hydroxynonenal levels at wk 16 compared to the wk 5 level.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased NADH-dependent production of reactive oxygen intermediates by microsomes after chronic ethanol consumption: comparisons with NADPH

Microsomes from chronic ethanol-fed rats were previously shown to catalyze the NADPH-dependent production of reactive oxygen intermediates at elevated rates compared to controls. Recent studies have shown that NADH can also serve as a reductant and promote the production of oxygen radicals by microsomes. The current study evaluated the influence of chronic ethanol consumption on NADH-dependent microsomal production of reactive oxygen intermediates, and compared the results with NADH to those of NADPH. Microsomal oxidation of chemical scavengers, taken as a reflection of the production of hydroxyl radical (.OH)-like species was increased about 50% with NADH as cofactor and about 100% with NADPH after chronic ethanol consumption. The potent inhibition of the production of .OH-like species by catalase suggests a precursor role for H2O2 in .OH production. Rates of NADH- and NADPH-dependent H2O2 production were increased by about 50 and 70%, respectively, after chronic ethanol consumption. A close correlation between rates of H2O2 production and generation of .OH-like species was observed for both NADH and NADPH, and increased rates of H2O2 production appear to play an important role in the elevated generation of .OH-like species after chronic ethanol treatment. Microsomal lipid peroxidation was elevated about 60% with NADH, and 120% with NADPH, after ethanol feeding. With both types of microsomal preparations, the characteristics of the NADH-dependent reactions were similar to the NADPH-dependent reactions, e.g., sensitivity to antioxidants and free radical scavengers and catalytic effectiveness of ferric complexes. However, rates with NADPH exceeded the NADH-dependent rates by 50 to 100%, and the increased production of reactive oxygen intermediates by microsomes after ethanol treatment was greater with NADPH (about twofold) than with NADH (about 50%). Oxidation of ethanol results in an increase in hepatic NADH levels and interaction of NADH, iron, and microsomes can produce potent oxidants capable of initiating lipid peroxidation and oxidizing .OH scavengers. These acute metabolic interactions produced by ethanol-derived NADH are increased, not attenuated, in microsomes from chronic ethanol-fed rats, and it is possible that such increases in NADH (and NADPH)-dependent production of reactive oxygen species play a role in the development of oxidative stress in the liver as a consequence of ethanol treatment.

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.

The role of iron in oxygen-mediated toxicities

The transition metal iron is capable of catalyzing redox reactions between biomolecules and oxygen that would not occur if catalytically active iron were not present. Although these biological oxidations (which are known collectively as "oxidative stress") have been implicated in numerous toxicities, the exact role of the iron catalyst remains to be elucidated. This review focuses on our current understanding of the role of iron in oxidative stress, discussing biologically relevant sources, biochemical forms, and reaction mechanisms of iron as a catalyst of biomolecular oxidations. Specific toxicities in which alterations in normal iron metabolism is thought to overwhelm the body's antioxidant defense system are presented, and future treatment regimens involving novel antioxidant drugs are discussed.

Increased oxidation of dimethylnitrosamine in pericentral microsomes after pyrazole induction of cytochrome P-4502E1

The cytochrome P-450IIE1 (CYP2E1) isozyme activates several toxins and procarcinogens. Recent studies employing immunohistochemical and immuno-analysis techniques have shown that this isozyme is predominantly localized in the pericentral zone of the liver acinus. Experiments were conducted to evaluate whether microsomes isolated from the pericentral region of the liver display elevated catalytic activity towards effective substrates for CYP2E1 such as dimethylnitrosamine (DMN) as compared with periportal microsomes. Rats were treated with pyrazole to induce CYP2E1 and hepatocytes prepared from periportal or pericentral zones of the livers by the digitonin-collagenase procedure. Microsomes isolated from these hepatocytes had similar total P-450 contents; however, the microsomes from the pericentral hepatocytes displayed an increased DMSO binding spectrum suggesting an increased content of CYP2E1. Low Km DMN demethylase activity (but not high Km activity) as well as the oxidation of aniline and p-nitrophenol were 2- to 3-fold higher in pericentral compared to periportal microsomes. The oxidation of DMN by both microsomal preparations, as well as the increased rates obtained with the pericentral microsomes, was sensitive to inhibition by carbon monoxide as well as to other CYP2E1 substrates such as ethanol, pyrazole, or 4-methylpyrazole. Anti-CYP2E1 IgG inhibited the oxidation of DMN by both microsomal preparations 75% to 85% and prevented most of the increase found with the pericentral microsomes. Oxidation of aniline and p-nitrophenol was elevated in pericentral hepatocytes compared with periportal hepatocytes to the same extent as in the isolated microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistent ethanol drinking increases liver injury induced by trinitrotoluene exposure: an in-plant case-control study

On the basis of a general survey conducted in a munitions plant, a case-control study was made on the various risk factors of liver damage induced by trinitrotoluene (TNT) exposure in the plant. One-hundred male cases with occupational TNT liver damage were paired with 100 male controls, one-by-one, for occupation, age and duration (years) of employment. A total of 55 possible risk factors were statistically analysed with a single factor analysis. On the basis of the single analysis, nine factors including drinking, smoking and education were further analysed with a conditional logistic regression model. A calculation was made on the odds ratio (OR) of each factor selected into the model. According to the estimated parameter of the established logistic model, the relative risk of the risk factors could be worked out. Finally, two factors, the amount of ethanol drunk on each occasion and the frequency of drinking every week were selected into the model at the level of a = 0.05. The result showed that these two factors have a dose-response relationship with their OR of occupational TNT liver damage, but there is no connection between smoking and occupational TNT liver damage and no interaction between drinking and smoking. The above results have revealed that people exposed to TNT and with a long history of heavy drinking, have a greater risk of suffering from chronic liver impairment than those that do not drink.

Electron spin resonance study of free radicals produced from ethanol and acetaldehyde after exposure to a Fenton system or to brain and liver microsomes

Free radical formation from ethanol and acetaldehyde was studied in the presence of a spin-trap and a NADPH generating system with a chemical model, Fenton's reagent, or by enzymatic oxidation of these solvents by rat liver and brain microsomes. The free radicals were detected by electron spin resonance spectroscopy (E.S.R.), using the spin-trapping agent, alpha-(4-pyridyl l-oxide)-N-tertbutyl-nitrone (POBN). Under such conditions, the hydroxyethyl radical derived from ethanol was obtained after both incubation in liver and brain microsomes as well as after exposure to the Fenton system. Enzymatic inhibition and activation showed that the mixed function oxidase system plays an important role in the generation of such a radical, even in the brain. Under all the experimental conditions acetaldehyde could also generate a free radical deriving directly from the parent molecule and modified by enzymatic activation or inhibition. A second, longer lasting radical was also observed in the presence of acetaldehyde. On the basis of a comparative study to a known process causing lipoperoxidation, its lipidic origin was suggested.

Role of iron, hydrogen peroxide and reactive oxygen species in microsomal oxidation of glycerol to formaldehyde

Rat liver microsomes can oxidize glycerol to formaldehyde. This oxidation is sensitive to catalase and glutathione plus glutathione peroxidase, suggesting a requirement for H2O2 in the overall pathway of glycerol oxidation. Hydrogen peroxide can not replace NADPH in supporting glycerol oxidation; however, added H2O2 increased the NADPH-dependent rate. Ferric chloride or ferric-ATP had no effect on glycerol oxidation, whereas ferric-EDTA was inhibitory. Certain iron chelators such as desferrioxamine, EDTA or diethylenetriaminepentaacetic acid, but not others such as ADP or citrate, inhibited glycerol oxidation. The inhibition by desferrioxamine could be overcome by added iron. Neither superoxide dismutase nor hydroxyl radical scavengers had any effect on glycerol oxidation. With the exception of propyl gallate, several antioxidants which inhibit lipid peroxidation had no effect on formaldehyde production from glycerol. The inhibition by propyl gallate could be overcome by added iron. In contrast to glycerol, formaldehyde production from dimethylnitrosamine was not sensitive to catalase or iron chelators, thus disassociating the overall pathway of glycerol oxidation from typical mixed-function oxidase activity of cytochrome P450. These studies indicate that H2O2 and nonheme iron are required for glycerol oxidation to formaldehyde. The responsible oxidant is not superoxide, H2O2, or hydroxyl radical. Cytochrome P450 may function to generate the H2O2 and reduce the nonheme iron. There may be additional roles for P450 since rates of formaldehyde production by microsomes exceed rates found with model chemical systems. Elevated rates of H2O2 production by certain P450 isozymes, e.g., P450 IIE1, may contribute to enhanced rates of glycerol oxidation.

Cytochrome P-450-dependent formation of reactive oxygen radicals: isozyme-specific inhibition of P-450-mediated reduction of oxygen and carbon tetrachloride

1. Ethanol-inducible P450 IIE1 exhibits a high rate of oxygen consumption and oxidase activity. The enzyme is selectively distributed in the liver centrilobular area, the acinar region specifically destroyed after treatment with P450 IIE1 substrates/inducers such as ethanol, carbon tetrachloride, chloroform, N-nitrosodimethylamine and paracetamol. 2. Twenty substrates and ligands for cytochrome P450 IIB4 and P450 IIE1 were evaluated for their ability to inhibit microsomal and reconstituted NADPH-dependent oxidase activity, and the P450 IIE1-catalysed reduction of carbon tetrachloride to chloroform. Type I ligands and substrates did not inhibit the processes whereas nitrogen-containing compounds such as octylamine, cimetidine, imidazole and tryptamine inhibited NADPH oxidation and H2O2 formation in microsomes from starved and acetone-treated rats by around 50%. 3. Tryptamine, octylamine, isoniazid and p-chloroamphetamine inhibited reconstituted P450 IIE1-dependent oxidase activity with half maximal effects at 14-170 microM. 4. Isoniazid, cimetidine and tryptamine inhibited the P450 IIE1-dependent reduction of carbon tetrachloride, whereas acetone was without effect. 5. The oxygen dependency of microsomal oxidase activity exhibited high-affinity and low-affinity phases, with partial saturation at 20 microM of O2. 6. It is concluded that microsomal oxidase activity takes place at physiological concentrations of O2 and that isozyme-specific type II ligands compete with oxygen or carbon tetrachloride for reduction by P-450 haem.

Insights into the pathogenesis of alcoholic liver necrosis and fibrosis: status report

The use of the Tsukamoto-French rat model of alcoholic liver disease facilitated pathological, physiological, biochemical and cell biological experiments that examined the validity of some of the existing hypotheses for pathogenesis of alcoholic liver necrosis and fibrosis. Results obtained to date strongly support the contribution of centrilobular hypoxia as a pathogenetic mechanism of alcoholic liver necrosis. The enhanced hepatic lipid peroxidation was not evident at the early stage of ethanol-induced liver necrosis but could be demonstrated at the late stage when the liver damage progressed to liver fibrosis. This suggests that the lipid peroxidation may not be an important mechanism of alcoholic liver necrosis but may be an initiation factor for liver fibrogenesis as recently proposed by others (88). The high-fat diet appears to have promoting effects on both induction of alcoholic liver necrosis and stimulation of liver fibrogenesis. The former may be related to the induction of MEOS by the high-fat diet and consequent centrilobular hypoxia caused by inadequately compensated hepatic overuse of oxygen. The latter can be mediated through sensitization of Ito cells by a high-fat diet. We propose that Kupffer cell-derived TGF beta is, at least in part, responsible for some of phenotypical changes of Ito cells associated with their activation. Our model provides maximal experimental control and induces the discrete stages of alcoholic liver injury that can be reproduced with its pathological evolution telescoped into a short time. Because of these features, replication of the experimental conditions in different laboratories is possible so that results can be validly compared through precise standardization of the experimental protocols. This model requires some training in implantation and maintenance of the gastric catheter. However, the training can be easily attained by anyone who has experience in animal surgery. Another requirement is the initial fund to acquire infusion devices and metabolism cages. Once this equipment is purchased, however, the maintenance cost is low. Even if the initial expenses are included, the cost per animal is relatively inexpensive when compared with the cost involved in the use of larger animals such as baboons or pigs. Since administration of diet and ethanol (or isocaloric glucose solution) is precisely controlled by infusion pumps, this system makes unnecessary the measurement of diet consumption that has to be done daily for each animal with other methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid peroxidation is a nonparenchymal cell event with reperfusion after prolonged liver ischemia

A proposed mechanism for irreversible ischemic liver damage has been peroxidation of membrane phospholipids by free radicals. However, the hepatocyte is laden with enzymes which are antioxidants and, therefore, ought to be relatively resistant to oxidative injury. To test the hypothesis that free radical damage from ischemia and reperfusion of the liver is a nonparenchymal cell process, we studied an in vivo model of ischemia. A point of transition from reversible to irreversible ischemia was defined at greater than or equal to 60 min of total ischemia by serial measurements of ATP at control, end of ischemia, and end of reperfusion periods (n = 6 each). Nonparenchymal cells were separated out of 10 livers in each ischemic group using a Percoll gradient. Second derivative spectroscopy did not detect conjugated dienes in any hepatocellular fraction, total cellular, mitochondrial, or microsomal, but did in the nonparenchymal cell fractions of livers from the 60- and 90-min ischemia groups. This in vivo study shows that irreversible ischemia in the rat liver is associated with free radical lipid peroxidation, but that the nonparenchymal cells rather than hepatocytes are the focus of this injury.

Generation of reactive oxygen species and reduction of ferric chelates by microsomes in the presence of a reconstituted system containing ethanol, NAD+ and alcohol dehydrogenase

Many of the toxic metabolic actions of ethanol on the liver have been ascribed to the enhanced cellular production of NADH, which arises as a consequence of the oxidation of ethanol by alcohol dehydrogenase (ADH). Experiments were conducted to evaluate whether NADH generated from a reconstituted system containing ethanol plus NAD+ plus ADH could interact with ferric chelates to promote microsomal lipid peroxidation and generation of a hydroxyl radical (OH)-like species. In the presence of the reconstituted system and iron, microsomes produced.OH as assessed by the oxidation of .OH scavenging agents. This oxidation was inhibited by catalase and competitive.OH scavengers but not by superoxide dismutase. The ADH-dependent microsomal production of.OH was effectively catalyzed by ferric-EDTA and -diethylenetriamine pentaacetic acid (-DTPA), but not by ferric-ATP or -citrate. However, all these ferric chelates were reduced by the microsomes in the presence of the reconstituted system. Hydrogen peroxide (H2O2) was produced in the presence of ADH and appeared to be a limiting factor for the production of.OH. The reconstituted system also catalyzed microsomal lipid peroxidation, and the pattern of effectiveness of ferric chelates was opposite that of catalysis of.OH production. There was little effect by catalase, superoxide dismutase or dimethyl sulfoxide (DMSO) on the ADH-dependent microsomal lipid peroxidation. The reconstituted system was characterized with respect to dependence on NAD+ and ADH; ethanol could be replaced by other alcohols, which are substrates for ADH. Pyrazole, a potent inhibitor of ADH, blocked the ability of the reconstituted system to interact with iron and microsomes to produce reactive oxygen species.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of xanthine oxidase in ethanol-induced lipid peroxidation in rats

To investigate a possible role of free radical production by xanthine oxidase in the pathogenesis of ethanol-induced hepatic lipid peroxidation, chow-fed rats were given ethanol (5 g/kg) and placed at 32 degrees C for 6 h, which resulted in increased hepatic malondialdehyde levels. Pretreatment with allopurinol in amounts that effectively inhibited xanthine metabolism also significantly decreased ethanol-induced lipid peroxidation, suggesting participation of free radicals produced by xanthine oxidase in the peroxidative process. Both acetaldehyde and purine can serve as substrates for xanthine oxidase. Pretreatment with cyanamide increased hepatic acetaldehyde levels 5-fold, yet this was associated with a decrease in lipid peroxidation, indicating that acetaldehyde is not the xanthine oxidase substrate involved. By contrast, ethanol increased hepatic contents of hypoxanthine and xanthine and enhanced urinary output of allantoin (a final product of xanthine metabolism), incriminating increased metabolism of purines. Ethanol administration also enhanced hepatic nicotinamide adenine dinucleotide (reduced form). A corresponding rise of nicotinamide adenine dinucleotide (reduced form) in vitro inhibited xanthine dehydrogenase activity by 60%-76%. Increased purine degradation, possibly associated with a shift from the dehydrogenase to the xanthine oxidase pathway (secondary to nicotinamide adenine dinucleotide [reduced form]-mediated inhibition of xanthine dehydrogenase activity) is proposed as a possible mechanism for ethanol-stimulated free radical production. Because allopurinol attenuates the associated lipid peroxidation, this agent might be considered for possible therapeutic use in alcohol-induced liver damage.

Possible roles of free radicals in alcoholic tissue damage

Hepatic microsomes metabolize ethanol to a free radical metabolite which forms adducts with the spin trapping agents PBN (phenyl-N-t-butylnitrone) and DMPO (5,5-dimethyl-l-pyrroline N-oxide). This ethanol radical has been identified as the l-hydroxyethyl radical through the use of 13C-labelled ethanol. A role of the cytochrome P-450 enzymes in the generation of the l-hydroxyethyl radical was suggested by requirements for oxygen and NADPH, as well as inhibition in the presence of SKF 525-A and imidazole. In contrast, the ESR signal intensity of the l-hydroxyethyl radical was diminished when either catalase, or the iron chelating agent deferoxamine, was added to the microsomal incubations, and was increased by the addition of ADP-Fe. These observations suggest that the ethanol radicals may arise secondary to iron-catalyzed formation of hydroxyl radicals from hydrogen peroxide. This possibility was supported by enhanced rates of l-hydroxyethyl radical formation when microsomal catalase activity was inhibited by the addition of sodium azide, or by pretreatment of rats with aminotriazole. However, the reaction was relatively insensitive to scavengers of the hydroxyl radical. Thus, the mechanism of l-hydroxyethyl radical formation could involve two cytochrome P-450-dependent pathways: generation of hydrogen peroxide required for a Fenton reaction, as well as direct catalytic formation of the ethanol radical.

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.

Oxygen radical generation by microsomes: role of iron and implications for alcohol metabolism and toxicity

Experiments were carried out to evaluate whether the molecular mechanism for ethanol oxidation by microsomes, a minor pathway of alcohol metabolism, involved generation of hydroxyl radical (.OH). Microsomes oxidized chemical .OH scavengers (KMB, DMSO, t-butyl alcohol, benzoate) by a reaction sensitive to catalase, but not SOD. Iron was required for microsomal .OH generation in view of the potent inhibition by desferrioxamine; however, the chelated form of iron was important. Microsomal .OH production was effectively stimulated by ferric EDTA or ferric DTPA, but poorly increased with ferric ATP, ferric citrate, or ferric ammonium sulfate. By contrast, the latter ferric complexes effectively increased microsomal chemiluminescence and lipid peroxidation, whereas ferric EDTA and ferric DTPA were inhibitory. Under conditions that minimize .OH production (absence of EDTA, iron) ethanol was oxidized by a cytochrome P-450-dependent process independent of reactive oxygen intermediates. Under conditions that promote microsomal .OH production, the oxidation of ethanol by .OH becomes more significant in contributing to the overall oxidation of ethanol by microsomes. Experiments with inhibitors and reconstituted systems containing P-450 and NADPH-P-450 reductase indicated that the reductase is the critical enzyme locus for interacting with iron and catalyzing production of reactive oxygen species. Microsomes isolated from rats chronically fed ethanol catalyzed oxidation of .OH scavengers, light emission, and inactivation of added metabolic enzymes at elevated rates, and displayed an increase in ethanol oxidation by a .OH-dependent and a P-450-dependent pathway. It is possible that enhanced generation of reactive oxygen intermediates by microsomes may contribute to the hepatotoxic effects of ethanol.