Effect of acute ethanol administration on the subcellular distribution of iron in rat liver and cerebellum

MRI texture-based radiomics analysis for the identification of altered functional networks in alcoholic patients and animal models

Alcohol use disorder (AUD) is a complex condition representing a leading risk factor for death, disease and disability. Its high prevalence and severe health consequences make necessary a better understanding of the brain network alterations to improve diagnosis and treatment. The purpose of this study was to evaluate the potential of resting-state fMRI 3D texture features as a novel source of biomarkers to identify AUD brain network alterations following a radiomics approach. A longitudinal study was conducted in Marchigian Sardinian alcohol-preferring msP rats (N = 36) who underwent resting-state functional and structural MRI before and after 30 days of alcohol or water consumption. A cross-sectional human study was also conducted among 33 healthy controls and 35 AUD patients. The preprocessed functional data corresponding to control and alcohol conditions were used to perform a probabilistic independent component analysis, identifying seven independent components as resting-state networks. Forty-three radiomic features extracted from each network were compared using a Wilcoxon signed-rank test with Holm correction to identify the network most affected by alcohol consumption. Features extracted from this network were then used in the machine learning process, evaluating two feature selection methods and six predictive models within a nested cross-validation structure. The classification was evaluated by computing the area under the ROC curve. Images were quantized using different numbers of gray-levels to test their influence on the results. The influence of ageing, data preprocessing, and brain iron accumulation were also analyzed. The methodology was validated using structural scans. The striatal network in alcohol-exposed msP rats presented the most significant number of altered features. The radiomics approach supported this result achieving good classification performance in animals (AUC = 0.915 ± 0.100, with 12 features) and humans (AUC = 0.724 ± 0.117, with 9 features) using a random forest model. Using the structural scans, high accuracy was achieved with a multilayer perceptron in both species (animals: AUC > 0.95 with 2 features, humans: AUC > 0.82 with 18 features). The best results were obtained using a feature selection method based on the p-value. The proposed radiomics approach is able to identify AUD patients and alcohol-exposed rats with good accuracy, employing a subset of 3D features extracted from fMRI. Furthermore, it can help identify relevant networks in drug addiction.

Association between iron accumulation in the dorsal striatum and compulsive drinking in alcohol use disorder

RATIONALE

Brain iron accumulation has been observed in neuropsychiatric disorders and shown to be related to neurodegeneration.

OBJECTIVES

In this study, we used quantitative susceptibility mapping (QSM), an emerging MRI technique developed for quantifying tissue magnetic susceptibility, to examine brain iron accumulation in individuals with alcohol use disorder (AUD) and its relation to compulsive drinking.

METHODS

Based on our previous projects, QSM was performed as a secondary analysis with gradient echo sequence images, in 186 individuals with AUD and 274 healthy participants. Whole-brain susceptibility values were calculated with morphology-enabled dipole inversion and referenced to the cerebrospinal fluid. Then, the susceptibility maps were compared between AUD individuals and healthy participants. The relationship between drinking patterns and susceptibility was explored.

RESULTS

Whole-brain analyses showed that the susceptibility in the dorsal striatum (putamen and caudate) among AUD individuals was higher than healthy participants and was positively related to the Obsessive Compulsive Drinking Scale (OCDS) scores and the amount of drinking in the past three months.

CONCLUSIONS

Increased susceptibility suggests higher iron accumulation in the dorsal striatum in AUD. This surrogate for the brain iron level was linearly associated with the compulsive drinking pattern and the recent amount of drinking, which provides us a new clinical perspective in relation to brain iron accumulation, and also might indicate an association of AUD with neuroinflammation as a consequence of brain iron accumulation. The iron accumulation in the striatum is further relevant for functional imaging studies in AUD by potentially producing signal dropout and artefacts in fMRI images.

Ethanol- and Cigarette Smoke-Related Alternations in Oral Redox Homeostasis

Alcohol abuse as well as smoking cigarettes has been proven to negatively affect the oral environment. The aim of this work was to provide a systematic review of the literature on the influence of ethanol and cigarette smoking on oral redox homeostasis. A search was performed for scientific articles indexed in the PubMed, Medline and Web of Science databases. We identified 32,300 articles, of which 54 were used for the final review, including the results from 2000 to 2021. Among the publications used to write this article, n = 14 were related to the influence of alcohol consumption (clinical studies n = 6, experimental studies n = 8) and n = 40 were related to the influence of smoking (clinical studies n = 33, experimental studies n = 7) on oral redox homeostasis. The reviewed literature indicates that alcohol abusers and smokers are more likely to suffer from salivary gland dysfunction, as well as develop precancerous lesions due to DNA damage. Compared to alcohol abstainers and non-smokers, alcohol drinkers and smokers are also characterized by a deterioration in periodontal health measured by various indicators of periodontal status. In summary, alcohol abuse and smoking are associated with disrupted oral redox homeostasis, which may lead not only to tooth loss, but also contribute to various adverse effects related to mental health, digestive processes and chronic inflammation throughout the human body.

Deep grey matter iron accumulation in alcohol use disorder

PURPOSE

Evaluate brain iron accumulation in alcohol use disorder (AUD) patients compared to controls using quantitative susceptibility mapping (QSM).

METHODS

QSM was performed retrospectively by using phase images from resting state functional magnetic resonance imaging (fMRI). 20 male AUD patients and 15 matched healthy controls were examined. Susceptibility values were manually traced in deep grey matter regions including caudate nucleus, combined putamen and globus pallidus, combined substantia nigra and red nucleus, dentate nucleus, and a reference white matter region in the internal capsule. Average susceptibility values from each region were compared between the patients and controls. The relationship between age and susceptibility was also explored.

RESULTS

The AUD group exhibited increased susceptibility in caudate nucleus (+8.5%, p=0.034), combined putamen and globus pallidus (+10.8%, p=0.006), and dentate nucleus (+14.9%, p=0.022). Susceptibility increased with age in two of the four measured regions - combined putamen and globus pallidus (p=0.013) and combined substantia nigra and red nucleus (p=0.041). AUD did not significantly modulate the rate of susceptibility increase with age in our data.

CONCLUSION

Retrospective QSM computed from standard fMRI datasets provides new opportunities for brain iron studies in psychiatry. Substantially elevated brain iron was found in AUD subjects in the basal ganglia and dentate nucleus. This was the first human AUD brain iron study and the first retrospective clinical fMRI QSM study.

Anti-inflammatory role of naringenin in rats with ethanol induced liver injury

The aim of the study was to investigate the antiinflammatory effects of naringenin in rats induced liver damage by exposure to ethanol. Rats were divided into four groups, groups 1 and 2 received isocaloric glucose; groups 3 and 4 received 20% ethanol equivalent to 6 g/kg body weight everyday for the total experimental period of 60 days. In addition, groups 2 and 4 were supplemented with naringenin (50 mg/kg p.o.) everyday for the last 30 days of the experiment. The results showed significantly elevated levels/activities/expression of serum aspartate and alanine transaminases, iron, ferritin, transforming growth factor-alpha (TNF-α), interleukin-6 (IL-6), nuclear factor-kappa B (NF-κB), cyclooxygenase-2 (COX-2), macrophage inflammatory protein 2 (MIP-2) and CD14 in ethanol fed rats as compared to those of the control. Ethanol-fed rats exhibited increased staining for the presence of inducible nitric oxide (iNOS) protein adducts in the liver. Supplementation with naringenin for the last 30 days to ethanol-fed rats, significantly decreased the levels/activities/expression of serum aspartate and alanine transaminases, iron, ferritin, TNF-α, IL-6, NF-κB, COX-2, MIP-2, CD14 and iNOS protein adducts in the liver as compared to the untreated ethanol fed rats. The inhibition of TNF-α, IL-6, NF-κB, COX-2, MIP-2, iNOS and CD14 by naringenin may contribute to its antiinflammatory activity in ethanol fed rats.

Taurine enhances the metabolism and detoxification of ethanol and prevents hepatic fibrosis in rats treated with iron and alcohol

The study examines the effects of taurine on the metabolism and detoxification of ethanol in liver fibrosis induced by simultaneous administration of iron carbonyl (0.5%, w/w) and ethanol (6g/(kgday)). Ethanol and iron administration caused liver damage and fibrosis as evidenced by liver histology and biochemical profile in plasma. Over accumulation of iron and a loss in taurine in hepatic tissue was observed in fibrotic animals. The activities of alcohol dehydrogenase and aldehyde dehydrogenase were significantly reduced in these rats compared to control. Adaptive induction of activities of Cytochrome P4502E1 (CYP2E1) and aniline hydroxylase accompanied by the reduction in glutathione-S-transferase, DT-diaphorase and glyoxalases I and II was observed. Taurine administration (2% in drinking water) ameliorated the effects of ethanol and iron. Hepatic damage and fibrosis were reduced in taurine-supplemented rats. Thus taurine has the potential for the treatment of alcoholic liver fibrosis.

Alcohol and oxidative liver injury

Acute and chronic ethanol treatment has been shown to increase the production of reactive oxygen species, 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. Many of the seminal reports in this topic have been published in Hepatology , and it is fitting to review this research area for the 25th Anniversary Issue of the Journal.

Role of the GABA-A system in estrogen-induced protection against brain lipid peroxidation in ethanol-withdrawn rats

BACKGROUND

Our previous study showed that 17 beta-estradiol (E2) treatment protects against cerebellar neuronal death and related motor deficits in ethanol-withdrawn rats, in part through the GABAergic system. In this study, we examined the effect of the GABA-A antagonist bicuculline on the neuroprotective effect of E2 by assessing the oxidative marker thiobarbituric acid reactive substances (TBARS) during ethanol withdrawal (EW).

METHODS

Ovariectomized animals that had implants of E2 (EW/E2) or oil (EW/Oil) pellets received liquid ethanol (7.5% w/v) or dextrin for 7 days by gavage. The GABA-A antagonist bicuculline (1.25 mg/kg) was administered (three times a day intraperitoneally) for 4 days starting 3 days before the onset of EW. After testing for overt EW signs at 7 hr of EW, one set of the animals was immediately killed for the collection of the cerebellum, hippocampus, and cortex. The brain homogenates were further processed for TBARS assay to detect TBARS in the presence or absence of FeCl(3). For assessing motor capacity, the other set of animals was tested for the latency to fall from a rotarod after 1 week of EW.

RESULTS

The EW/Oil animals had enhanced endogenous and FeCl(3)-stimulated TBARS levels in the cerebellum and the hippocampus in a manner potentiated by bicuculline but inhibited by E2. Bicuculline counteracted the protective effect of E2 when administered along with E2. Pearson correlation coefficients indicated that the latency to fall from the rotarod covaried with TBARS levels in the cerebellum and the hippocampus.

CONCLUSION

These data suggest that E2 protects against lipid peroxidation in vulnerable brain areas of ethanol-withdrawn rats, in part through the GABAergic system.

Estrogen protects against brain lipid peroxidation in ethanol-withdrawn rats

This study examined whether 17beta-estradiol (E2) administration protects against ethanol withdrawal (EW)-associated oxidative insults by assessing oxidative markers thiobarbituric-acid-reacting-substances (TBARS). Ovariectomized rats implanted with E2 (EW/E2) or oil pellets (EW/Oil) received chronic ethanol (7.5% wt./vol., 5 weeks) or control dextrin diet (Dextrin/Oil). At 24 or 48 h of EW, rats were tested for overt EW signs and the cerebellum, hippocampus, and cortex were prepared for TBARS assessment in the presence and absence of FeCl3. For control experiments, we assessed E2 effects on blood ethanol concentrations and TBARS levels during ethanol exposure prior to EW. The EW/Oil group showed enhanced endogenous- and FeCl3-stimulated membrane TBARS levels in the cerebellum and hippocampus in a manner inhibited by E2 treatment. There was a relationship between the severity of EW and elevation of TBARS levels, particularly in the cerebellum. The enhanced TBARS levels at 24 h of EW appeared to diminish at 48 h in the hippocampus, but persisted in the cerebellum. E2 treatment did not alter blood ethanol concentrations and ethanol exposure alone did not enhance TBARS levels. These data suggest that EW rather than ethanol enhances brain lipid peroxidation that is transient and brain-region specific. Estrogens protect against the brain lipid peroxidation in a manner independent of blood ethanol concentrations.

[Alcohol and oxidative stress]

There is accumulating evidence pointing oxidative stress as a mechanism of ethanol toxicity. Oxidative stress takes place when the balance between the antioxidant defenses and the generation of reactive oxygen species (ROS) is tipped in favour of the latter. Ethanol metabolism is directly involved in the production of ROS, but ethanol also participated to the formation of an environment favourable to oxidative stress such as hypoxia, endotoxemia and cytokine release. Following ethanol intoxication, balance between prooxidants and antioxidants is disturbed to such an extent that it results in an oxidative damage of biomolecules. The ability of ethanol to induce peroxidation of membrane lipids is widely reviewed in literature. More recently it has also been described that ethanol can oxidize proteins and ADN. In this review, is also discussed the impairment of cellular function resulting from this situation of oxidative stress.

Oxidative stress and cytotoxicity induced by ferric-nitrilotriacetate in HepG2 cells that express cytochrome P450 2E1

Iron can potentiate the toxicity of ethanol. Ethanol increases the content of cytochrome P450 2E1 (CYP2E1), which generates reactive oxygen species, and transition metals such as iron are powerful catalysts of hydroxyl radical formation and lipid peroxidation. Experiments were carried out to attempt to link CYP2E1, iron, and oxidative stress as a potential mechanism by which iron increases ethanol toxicity. The addition of ferric-nitrilotriacetate (Fe-NTA) to a HepG2 cell line expressing CYP2E1 decreased cell viability, whereas little effect was observed in control cells not expressing CYP2E1. Toxicity in the CYP2E1-expressing cells was markedly enhanced after the depletion of glutathione. Lipid peroxidation was increased by Fe-NTA, especially in cell extracts and medium from the CYP2E1-expressing cells. Toxicity was completely prevented by vitamin E or by 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, which also decreased the lipid peroxidation. Levels of ATP were lowered by Fe-NTA, and this was associated with a decreased rate of oxygen consumption by permeabilized cells with substrates donating electrons to complexes I, II, and IV of the respiratory chain. This mitochondrial damage was prevented by vitamin E. Toxicity was accompanied by DNA fragmentation, and this fragmentation was prevented by antioxidants. Overexpression of bcl-2 decreased the toxicity and DNA fragmentation produced by the combination of CYP2E1 plus Fe-NTA, as did a peptide inhibitor of caspase 3. These results suggest that elevated generation of reactive oxygen species in HepG2 cells expressing CYP2E1 leads to lipid peroxidation in the presence of iron, and the ensuing prooxidative state damages mitochondria, releasing factors that activate caspase 3, leading to a loss in cell viability and DNA fragmentation.

Relative and combined effects of ethanol and protein deficiency on zinc, iron, copper, and manganese contents in different organs and urinary and fecal excretion

The relative contribution of protein deficiency to the altered metabolism of certain trace elements in chronic alcoholics is not well defined, so this study was performed to analyse the relative and combined effects of ethanol and protein deficiency on liver, bone, muscle, and blood cell content of copper, zinc, iron, and manganese, and also on serum levels and urinary and fecal excretion of these elements in four groups of eight animals each that were pair-fed during 8 weeks with a nutritionally adequate diet, a 36% (as energy) ethanol-containing isocaloric diet, a 2% protein isocaloric diet, and a 36% ethanol 2% protein isocaloric diet, respectively, following the Lieber-DeCarli model. Five additional rats were fed ad lib the control diet. Protein malnutrition, but not ethanol, leads to liver zinc depletion. Both ethanol and protein malnutrition cause muscle zinc depletion and increase urinary zinc and manganese excretion, whereas ethanol also increases urinary iron excretion and liver manganese content. No differences were observed regarding copper metabolism.

Free radical production after exposure of astrocytes and astrocytic C6 glioma cells to ethanol. Preliminary results

Formation of the alpha-hydroxyethyl radical (CH3 degree CHOH) has already been extensively demonstrated after ethanol metabolism in the liver. Despite favourable conditions, this formation in the brain has remained speculative since there is no direct experimental evidence in intact brain cells. In this preliminary study, the formation of such a radical was observed after exposure of astrocytes and astrocytic C6 glioma cells to ethanol. These cells were studied because astrocyte integrity is essential for normal growth and functioning of neurons. The free radicals were detected by EPR spectroscopy using the spin trapping technique. Astrocytes appeared to be more sensitive than the C6 cells to free radical formation as the intensity of the signal was higher after exposure of the astrocytes and increased with time, a fact not observed after exposure of the C6 cells.

Changes in some pro- and antioxidants in rat cerebellum after chronic alcohol intake

Some pro- and antioxidants were measured in the cerebellum from ethanol-fed rats using ethanol administration in drinking water as a model of moderate alcohol intoxication. After 4 weeks of ethanol intake, a 30% increase in the nonheme iron content in the cerebellum occurred in ethanol-fed rats as compared to control animals. The low-molecular-weight-chelated iron (LMWC-Fe) content as well as the percentage of total nonheme iron represented by LMWC-Fe were increased in the cerebellar cytosol after chronic ethanol administration. Cerebellar copper and selenium concentrations were lower and zinc concentration higher in ethanol-fed rats than in controls. Ethanol consumption decreased the cerebellar vitamin E level. Glutathione S-transferase [EC 2. 5. 1. 18] activity was higher, whereas glutathione peroxidase [glutathione: H2O2 oxidoreductase, EC 1. 11. 1. 9] activity was not altered by ethanol treatment. No significant changes in cerebellar lipid peroxidation, carbonyl protein content, or glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming) EC 6. 3. 1. 2] activity were observed. These results suggest that adaptative increases in some elements of the antioxidant defense may counteract the increase in LMWC-Fe, a pro-oxidant factor, and prevent the occurrence of overt cellular lipid and protein damage. However, after 8 weeks of ethanol intake, the activity of glutamine synthetase, an enzyme specially sensitive to inactivation by oxygen radicals, was decreased, suggesting that this prevention was not totally achieved.

Regulation of ferritin expression by alcohol in a human hepatoblastoma cell line and in rat hepatocyte cultures

Serum ferritin increases in chronic alcoholism, without clear explanation. We have previously shown that alcohol increases ferritin levels in a human hepatoblastoma cell line (HepG2). The aims of the present work were: 1) To extend our results in normal rat hepatocyte cultures, and 2) To determine the mechanism by which alcohol enhances ferritin levels. In HepG2 cells, high alcohol concentrations (300 mM) during long exposure (4 days) increased the synthesis of H and L ferritin subunits, in association with increased levels of ferritin mRNAs. In rat hepatocyte cultures, the synthesis of L ferritin increased after 24 h of exposure to lower alcohol concentrations (10 mM); alcohol had no effect on ferritin mRNAs levels. In both cell types, the alcohol effect was not related to an increase in iron intracellular incorporation. In HepG2 cells, desferrioxamine (Df), a potent iron chelator, abolished ferritin synthesis in the presence or absence of alcohol, and abolished the alcohol induction of ferritin mRNAs. In rat hepatocytes, Df decreased ferritin synthesis to a similar level in the presence or absence of alcohol. Alcohol increased ferritin synthesis differently in HepG2 cells and in normal rat hepatocyte cultures. In the latter case, the alcohol effect was observed at low concentration. Despite a striking inhibiting effect of Df on ferritin synthesis, in both cellular models a mechanism accounting for increased ferritin synthesis independently of iron is suggested. Globally, these data strongly suggest that hyperferritinemia in chronic alcoholism could be related to the induction of ferritin by alcohol.

Regional selectivity in ethanol-induced pro-oxidant events within the brain

Several biochemical parameters that reflect the presence of excess levels of reactive oxygen species were modulated in the brains of rats exposed acutely or subchronically to ethanol. These parameters included depression of cytosolic glutathione (GSH) concentration and of glutamine synthetase levels. However, using these indices, there was a significant difference in susceptibility to ethanol in different brain regions. After dietary exposure to ethanol for 12 days, these indices were selectively depressed in the striatum but not in the cerebral cortex or cerebellum. Eighteen hours after a single acute dose of ethanol (4.5 g/kg body wt), the striatum was also the only one of these areas in which proteolytic activity was elevated by ethanol treatment. Two injections of acetaldehyde (300 mg/kg), given 18 and 2 hr prior to tissue preparation, caused a specific reduction of glutamine synthetase in the striatum and a decrease of GSH levels in both striatum and cerebellum. Taken together, the results suggest a distinctive vulnerability of the striatum to ethanol-promoted oxidative events. Rather than ethanol exerting effects directly, the metabolite acetaldehyde may be the primary agent responsible for these changes.

The role of free radicals and antioxidants: how do we know that they are working?

This review briefly discusses how free radicals are formed and the possible participation of free radicals in disease. The review describes the basic radical reactions and the types of products that are formed from the free-radical reactions of cellular constituents. In many cases, in vivo free-radical oxidation can be detected by measuring products that were derived from radical reactions. Since aerobic organisms generate oxygen-containing free radicals during oxygen metabolism, they carry chemicals and enzymes that reduce the threat posed by these radicals. The more common sources of in vivo free radicals are described in the article as well as the methods used by cells to protect themselves from free-radical damage. Generation of free radicals in vivo also may be the result of exposure to certain chemical agents present in the environment. Many of these agents cause pathologic changes to the exposed tissues and organs by initiating free-radical reactions.

Increase in cellular pool of low-molecular-weight iron during ethanol metabolism in rat hepatocyte cultures. Relationship with lipid peroxidation

Ethanol-induced lipid peroxidation was studied in primary rat hepatocyte cultures supplemented with ethanol at the concentration of 50 mM. Lipid peroxidation was assessed by two indices: (1) conjugated dienes by second-derivative UV spectroscopy in lipid extract of hepatocytes (intracellular content), and (2) free malondialdehyde (MDA) by HPLC-UV detection and quantitation for the incubation medium (extracellular content). In cultures supplemented with ethanol, free MDA increased significantly in culture media, whereas no elevation of conjugated diene level was observed in the corresponding hepatocytes. The cellular pool of low-mol-wt (LMW) iron was also evaluated in the hepatocytes using an electron spin resonance procedure. An early increase of intracellular LMW iron (< or = 1 hr) was observed in ethanol-supplemented cultures; it was inhibited by 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, whereas alpha-tocopherol, which prevented lipid peroxidation, did not inhibit the increase of LMW iron. Therefore, the LMW iron elevation was the result of ethanol metabolism and was not secondarily induced by lipid hydroperoxides. Thus, ethanol caused lipid peroxidation in rat hepatocytes as shown by the increase of free MDA, although no conjugated diene elevation was detected. During ethanol metabolism, an increase in cellular LMW iron was observed that could enhance conjugated diene degradation.

Effects of acute ethanol administration on the uptake of 59Fe-labeled transferrin by rat liver and cerebellum

The uptake of iron by the liver and cerebellum was measured in rats using [59Fe]transferrin. An acute ethanol load (50 mmol/kg body wt., i.p.) elicited a significant increase in the hepatic and cerebellar non-heme iron concentration. The uptake of 59Fe by the liver and the cerebellum was significantly greater in the ethanol-treated rats than in control animals. The administration of allopurinol prior to the ethanol load prevented the changes in liver and cerebellar non-heme iron content. Moreover pretreatment with allopurinol reduced the ethanol-induced enhancement of 59Fe uptake by the liver and completely prevented the changes in 59Fe uptake by the cerebellum. These effects of allopurinol lead us to suggest that oxygen-derived free radicals are involved in the ethanol-induced disturbances of iron uptake both at the hepatic and cerebellar level.

Iron increases ethanol toxicity in rat liver

Clinical evidence indicates that patients with iron overload are more susceptible to liver cell damage from alcohol than persons with normal iron stores. Iron may act as a co-factor to catalyze the lipid peroxidation induced by hepatotoxic compounds such as alcohol. To elucidate the role of iron in ethanol-induced hepatocellular damage, we developed a new experimental model in the rat. Following dietary carbonyl iron feeding for 8 weeks, animals were pair-fed a liquid ethanol diet for 4 weeks. In iron-fed animals the liver iron content was 6.4 vs. 0.5 micrograms Fe/mg protein in the controls. Blood alcohol concentrations were similar in all ethanol-fed animals. Serum alanine aminotransferase (ALT) levels were elevated to 269 +/- 49 U/l in the iron+alcohol group compared to 52 +/- 6 U/l in the other groups. There was a strong correlation between ALT levels and hepatic iron content in the ethanol-fed animals. Morphologically, the alcohol-fed rats displayed hepatic steatosis, whereas occasional inflammation and iron in Kupffer cells was seen in the iron+alcohol animals. Ultrastructurally, necrotic hepatocytes and cells phagocytosed by Kupffer cells were only encountered in the iron+alcohol group. Compared to controls, the liver content of hydroxyproline was significantly increased in the iron+alcohol group. No morphological evidence of fibrosis was noted. The present study demonstrates biochemical and morphological evidence of increased hepatocellular damage following the combination of iron and ethanol.

Ethanol toxicity and oxidative stress

The mechanisms underlying the toxicity of ethanol have been the subject of much study, but are not well understood. Unlike many selective pharmacological agents, ethanol clearly has several major loci of action. One deleterious factor in ethanol metabolism is the potential for generation of excess amounts of free radicals. The extent to which this activity accounts for the overall toxicity of ethanol is unknown. This review outlines the enzymic steps that have the capacity to generate reactive oxygen species. These steps are likely to differ in acute and extended exposures to ethanol. Acetaldehyde catabolism also has the likelihood of contributing to ethanol-related oxidative stress. The review focuses on the ethanol-induced production of excess amounts of pro-oxidant reactive species in both the liver and the central nervous system. The potential of various stages of ethanol catabolism to involve generation of free radicals is described.

Effects of chronic ethanol administration on free radical defence in rat myocardium

Cellular protection against free radical reactions was measured in myocardium from ethanol-fed rats using ethanol administration in drinking water as a model of moderate alcohol intoxication. The activities of Cu,Zn-superoxide dismutase (SOD) and glutathione-S-transferase were higher in ethanol-fed rats than in controls, whereas Mn-SOD, catalase and glutathione peroxidase activities were not altered by ethanol treatment. Myocardial zinc was higher and selenium concentration lower in ethanol-fed rats than in controls. Ethanol consumption, which failed to modify the myocardial vitamin E level, did not result in increased lipid peroxidation, but decreased cytosolic and membraneous protein thiols.

Iron release and membrane damage in erythrocytes exposed to oxidizing agents, phenylhydrazine, divicine and isouramil

Mouse erythrocytes were incubated with oxidizing agents, phenylhydrazine, divicine and isouramil. With all the oxidants a rapid release of iron in a desferrioxamine (DFO)-chelatable form was seen and it was accompanied by methaemoglobin formation. If the erythrocytes were depleted of GSH by a short preincubation with diethyl maleate, the release of iron was accompanied by lipid peroxidation and, subsequently, haemolysis. GSH depletion by itself did not induce iron release, methaemoglobin formation, lipid peroxidation or haemolysis. Rather, the fate of the cell in which iron is released depended on the intracellular availability of GSH. In addition, iron release was higher in depleted cells than in native ones, suggesting a role for GSH in preventing iron release when oxidative stress is imposed by the oxidants. Iron release preceded lipid peroxidation. The latter was prevented when the erythrocytes were preloaded with DFO in such a way (preincubation with 10 mM-DFO) that the intracellular concentration was equivalent to that of the released iron, but not when the intracellular DFO was lower (preincubation with 0.1 mM-DFO). Extracellular DFO did not affect lipid peroxidation and haemolysis, suggesting again that the observed events occur intracellularly (intracellular chelation of released iron). The relevance of iron release from iron complexes in the mechanisms of cellular damage induced by oxidative stress is discussed.

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.