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

Alcohol and IL-6 Alter Expression of Synaptic Proteins in Cerebellum of Transgenic Mice with Increased Astrocyte Expression of IL-6

Recent studies indicate that neuroimmune factors, including the cytokine interleukin-6 (IL-6), play a role in the CNS actions of alcohol. The cerebellum is a sensitive target of alcohol, but few studies have examined a potential role for neuroimmune factors in the actions of alcohol on this brain region. A number of studies have shown that synaptic transmission, and in particular inhibitory synaptic transmission, is an important cerebellar target of alcohol. IL-6 also alters synaptic transmission, although it is unknown if IL-6 targets are also targets of alcohol. This is an important issue because alcohol induces glial production of IL-6, which could then covertly influence the actions of alcohol. The persistent cerebellar effects of both IL-6 and alcohol typically involve chronic exposure and, presumably, altered gene and protein expression. Thus, in the current studies we tested the possibility that proteins involved in inhibitory and excitatory synaptic transmission in the cerebellum are common targets of alcohol and IL-6. We used transgenic mice that express elevated levels of astrocyte produced IL-6 to model persistently elevated expression of IL-6, as would occur in alcohol use disorders, and a chronic intermittent alcohol exposure/withdrawal paradigm (CIE/withdrawal) that is known to produce alcohol dependence. Multiple cerebellar synaptic proteins were assessed by Western blot. Results show that IL-6 and CIE/withdrawal have both unique and common actions that affect synaptic protein expression. These common targets could provide sites for IL-6/alcohol exposure/withdrawal interactions and play an important role in cerebellar symptoms of alcohol use such as ataxia.

Pulcinelli R, Bandiera S, Caletti G, Bitencourt PER, Quincozes-Santos A, Gomez R. Combined Exposure to Alcohol and Tobacco Smoke Changes Oxidative, Inflammatory, and Neurotrophic Parameters in Different Areas of the Brains of Rats

Devastating effects of exposure to alcohol and tobacco smoke on health are extensively reported in the literature. However, few studies have attempted to elucidate the consequences of their combined use on the central nervous system. Here we studied the effect of this combined use on some oxidative, inflammatory, and neurotrophic parameters in the hippocampus, striatum, and frontal cortex of rats. Adult Wistar rats were allocated into control (CT), alcohol (AL), tobacco smoke (TB), or combined (ALTB) groups. Rats were exposed to environmental air (CT and AL groups) or to the smoke from six cigarettes (TB and ALTB groups) immediately after tap water (CT and TB) or 2 g of alcohol/kg (AL and ALTB) oral gavage administration, twice a day, for 4 weeks. On day 28, rats were euthanized and areas of the brain were dissected to evaluate some cellular redox parameters, pro-inflammatory cytokine levels, and brain-derived neurotrophic factor (BDNF) levels. A one-way analysis of variance showed that the ALTB combined treatment significantly increased oxidative stress levels in the hippocampus. ALTB also increased interleukin-1β levels in the striatum and frontal cortex and tumoral necrosis factor-α levels in the frontal cortex compared with those of AL, TB, and CT rats. Combined treatment also decreased the BDNF levels in the frontal cortex of rats. Oxidative damage was found, more importantly, in the hippocampus, and inflammatory parameters were extended to all areas of the brain that were studied. Our results showed an interaction between alcohol and tobacco smoke according to the area of the brain, suggesting an additional risk of neural damage in alcoholics who smoke.

Does Oxidative Stress Induced by Alcohol Consumption Affect Orthodontic Treatment Outcome?

HIGHLIGHTS Ethanol, Periodontal ligament, Extracellular matrix, Orthodontic movement. Alcohol is a legal drug present in several drinks commonly used worldwide (chemically known as ethyl alcohol or ethanol). Alcohol consumption is associated with several disease conditions, ranging from mental disorders to organic alterations. One of the most deleterious effects of ethanol metabolism is related to oxidative stress. This promotes cellular alterations associated with inflammatory processes that eventually lead to cell death or cell cycle arrest, among others. Alcohol intake leads to bone destruction and modifies the expression of interleukins, metalloproteinases and other pro-inflammatory signals involving GSKβ, Rho, and ERK pathways. Orthodontic treatment implicates mechanical forces on teeth. Interestingly, the extra- and intra-cellular responses of periodontal cells to mechanical movement show a suggestive similarity with the effects induced by ethanol metabolism on bone and other cell types. Several clinical traits such as age, presence of systemic diseases or pharmacological treatments, are taken into account when planning orthodontic treatments. However, little is known about the potential role of the oxidative conditions induced by ethanol intake as a possible setback for orthodontic treatment in adults.

Ethanol-Associated Changes in Glutamate Reward Neurocircuitry: A Minireview of Clinical and Preclinical Genetic Findings

Herein, we have reviewed the role of glutamate, the major excitatory neurotransmitter in the brain, in a number of neurochemical, -physiological, and -behavioral processes mediating the development of alcohol dependence. The findings discussed include results from both preclinical as well as neuroimaging and postmortem clinical studies. Expression levels for a number of glutamate-associated genes and/or proteins are modulated by alcohol abuse and dependence. These changes in expression include metabotropic receptors and ionotropic receptor subunits as well as different glutamate transporters. Moreover, these changes in gene expression parallel the pharmacologic manipulation of these same receptors and transporters. Some of these gene expression changes may have predated alcohol abuse and dependence because a number of glutamate-associated polymorphisms are related to a genetic predisposition to develop alcohol dependence. Other glutamate-associated polymorphisms are linked to age at the onset of alcohol-dependence and initial level of response/sensitivity to alcohol. Finally, findings of innate and/or ethanol-induced glutamate-associated gene expression differences/changes observed in a genetic animal model of alcoholism, the P rat, are summarized. Overall, the existing literature indicates that changes in glutamate receptors, transporters, enzymes, and scaffolding proteins are crucial for the development of alcohol dependence and there is a substantial genetic component to these effects. This indicates that continued research into the genetic underpinnings of these glutamate-associated effects will provide important novel molecular targets for treating alcohol abuse and dependence.

Quantification of glutamate and glutamine using constant-time point-resolved spectroscopy at 3 T

Separate quantification of glutamate (Glu) and glutamine (Gln) using conventional MRS on clinical scanners is challenging. In previous work, constant-time point-resolved spectroscopy (CT-PRESS) was optimized at 3 T to detect Glu, but did not resolve Gln. To quantify Glu and Gln, a time-domain basis set was constructed taking into account metabolite T(2) relaxation times and dephasing from B(0) inhomogeneity. Metabolite concentrations were estimated by fitting the basis one-dimensional CT-PRESS diagonal magnitude spectra to the measured spectrum. This method was first validated using seven custom-built phantoms containing variable metabolite concentrations, and then applied to in vivo data acquired in rats exposed to vaporized ethanol and controls. Separate metabolite quantification revealed increased Gln after 16 weeks and increased Glu after 24 weeks of vaporized ethanol exposure in ethanol-treated compared with control rats. Without separate quantification, the signal from the combined resonances of Glu and Gln (Glx) showed an increase at both 16 and 24 weeks in ethanol-exposed rats, precluding the determination of the independent and differential contribution of each metabolite at each time.

Oxidative stress in anxiety and comorbid disorders

Anxiety disorders, depression, and alcohol use disorder are common neuropsychiatric diseases that often occur together. Oxidative stress has been suggested to contribute to their etiology. Oxidative stress is a consequence of either increased generation of reactive oxygen species or impaired enzymatic or non-enzymatic defense against it. When excessive it leads to damage of all major classes of macromolecules, and therefore affects several fundamentally important cellular functions. Consequences that are especially detrimental to the proper functioning of the brain include mitochondrial dysfunction, altered neuronal signaling, and inhibition of neurogenesis. Each of these can further contribute to increased oxidative stress, leading to additional burden to the brain. In this review, we will provide an overview of recent work on oxidative stress markers in human patients with anxiety, depressive, or alcohol use disorders, and in relevant animal models. In addition, putative oxidative stress-related mechanisms important for neuropsychiatric diseases are discussed. Despite the considerable interest this field has obtained, the detailed mechanisms that link oxidative stress to the pathogenesis of neuropsychiatric diseases remain largely unknown. Since this pathway may be amenable to pharmacological intervention, further studies are warranted.

Ebselen prevents chronic alcohol-induced rat hippocampal stress and functional impairment

BACKGROUND

Most of the previously published data suggest a role for oxidative or nitrosative stress in ethanol-induced nervous system damage. Moreover, ethanol is able to impair learning abilities in adult mammalian brain, a process suggested to be directly related to hippocampal neurogenesis. Ebselen, a synthetic compound with antioxidant properties, is able to prevent ethanol-induced impairment of neurogenesis in adult rats. The aim of the present work was to further demonstrate the ability of ebselen to prevent biochemical alterations, and preserve long-term potentiation (LTP) and learning abilities, in the hippocampus of chronic alcoholic adult rats.

METHODS

Biochemical markers of oxidative stress (glutathione and malondialdehyde) were assayed in hippocampi of control rats and animals fed a liquid alcoholic diet (Lieber-De Carli) supplemented or not with ebselen. Long-term potentiation and hippocampal-dependent tests were studied in all animal groups.

RESULTS

The hippocampal concentrations of glutathione and malondialdehyde were decreased and increased, respectively, in alcohol-treated animals, and did not differ from those of the control and the alcohol+ebselen groups. Long-term potentiation in hippocampal slices from ethanol-treated animals was prevented, when compared with controls, and occurred with a similar profile in control animals and in the alcohol+ebselen groups. Learning ability was tested with the Morris water maze test. Escape latencies were higher in ethanol-treated rats than in control animals or the ones treated with ethanol+ebselen.

CONCLUSIONS

The results herein strongly suggest that oxidative mechanisms may underlie the hippocampal effects of ethanol in adult rats, in view of the protective effect of ebselen.

The Application of Proteomics to the Human Alcoholic Brain

Alcoholism results in changes in the human brain that reinforce the cycle of craving and dependency, and these changes are manifest in the pattern of expression of proteins in key cells and brain areas. Described here is a proteomics-based approach aimed at determining the identity of proteins in the superior frontal cortex (SFC) of the human brain that show different levels of expression in autopsy samples taken from healthy and long-term alcohol abuse subjects. Soluble protein fractions constituting pooled samples combined from SFC biopsies of four well-characterized chronic alcoholics (mean consumption > 80 g ethanol/day throughout adulthood) and four matched controls (<20 g/day) were generated. Two-dimensional electrophoresis was performed in triplicate on alcoholic and control samples and the resultant protein profiles analyzed for differential expression. Overall, 182 proteins differed by the criterion of twofold or more between case and control samples. Of these, 139 showed significantly lower expression in alcoholics, 35 showed significantly higher expression, and 8 were new or had disappeared. To date, 63 proteins have been identified using MALDI-MS and MS-MS. The finding that the expression level of differentially expressed proteins is preponderantly lower in the alcoholic brain is supported by recent results from parallel studies using microarray mRNA transcript.

Ethanol modifies differently aspartyl- and glutamyl-aminopeptidase activities in mouse frontal cortex synaptosomes

Aminopeptidase A activity (aspartyl aminopeptidase (AspAP) and glutamyl aminopeptidase (GluAP) exerts angiotensinase activity due to its relation to the metabolism of angiotensins in the regional brain renin-angiotensin system (RAS). This activity may also modify the free amino acid pool through the release of N-terminal acidic amino acids. Ethanol (EtOH) exerts profound effects on the brain, inducing important neurological damages. Our purpose is to study the influence of EtOH on AspAP and GluAP activities on basal and K(+)-stimulated conditions, at the synapse level. We used mouse frontal cortex synaptosomes and their incubation supernatant in a Ca(2+)-containing or Ca(2+)-free artificial cerebrospinal fluid. We evaluate the possible contribution of these enzymatic activities on brain blood pressure regulation through RAS and/or the free acidic amino acid pool. The results obtained are correlated with several parameters of oxidative stress, such as free radical generation, lipid peroxidation, and protein oxidation. Under basal conditions, in synaptosomes, EtOH inhibits AspAP and GluAP activities independently of Ca(2+). In the supernatant, however, EtOH differently modulates the two enzyme activities under the various concentrations. Under K(+)-stimulated conditions, EtOH inhibits the K(+)-stimulated increase on AspAP and GluAP differently depending on the presence or absence of Ca(2+) and the concentration of EtOH used. These results invalidate the idea that excess free acidic amino acids could be released by AspAP and GluAP to induce neurodegeneration. The changes in AspAP and GluAP activities as a consequence of EtOH administration and their role in the brain RAS are discussed.

Inhibition of N-methyl-D-aspartic acid-nitric oxide synthase in rat hippocampal slices by ethanol. Evidence for the involvement of tetrahydrobiopterin but not lipid peroxidation

The ionotropic glutamatergic receptor system, especially the subtype mediated by N-methyl-D-aspartic acid (NMDA), is known to exhibit special sensitivity to the effect of ethanol. This is due partly to the ability of ethanol to modulate the production of nitric oxide through the NMDA-nitric oxide synthase (NOS) pathway. In this study, we examined the effects of ethanol on basal and NMDA-stimulated NOS activity in rat hippocampal slices by measuring the conversion of [(14)C]-arginine into [(14)C]-citrulline in an incubation system containing the necessary cofactors. Stimulation of hippocampal slices with NMDA (100 microM) enhanced NOS activity by 43% (n = 12). Although ethanol did not alter NOS activity when added to the incubation system during NMDA stimulation, it dose-dependently inhibited NMDA-NOS activity when added to the slices during the 90-min preincubation period. Further assay of NOS activity with brain cytosolic fraction indicated an inhibitory effect of ethanol (200 mM) when the assay was carried out in the absence of exogenous tetrahydrobiopterin (BH4), a redox-active cofactor for NOS. Incubation of brain homogenates resulted in a time-dependent increase in the levels of lipid peroxidation products, but ethanol did not further enhance these products. Taken together, these results provide evidence for the role of BH4 but not oxidative stress in the inhibitory effect of ethanol on NMDA-NOS activity in rat hippocampal slices.

Application of DNA microarrays to study human alcoholism

An emerging idea is that long-term alcohol abuse results in changes in gene expression in the brain and that these changes are responsible at least partly for alcohol tolerance, dependence and neurotoxicity. The overall goal of our research is to identify genes which are differentially expressed in the brains of well-characterized human alcoholics as compared with non-alcoholics. This should identify as-yet-unknown alcohol-responsive genes, and may well confirm changes in the expression of genes which have been delineated in animal models of alcohol abuse. Cases were carefully selected and samples pooled on the basis of relevant criteria; differential expression was monitored by microarray hybridization. The inherent diversity of human alcoholics can be exploited to identify genes associated with specific pathological processes, as well as to assess the effects of concomitant disease, severity of brain damage, drinking behavior, and factors such as gender and smoking history. Initial results show selective changes in gene expression in alcoholics; of particular importance is a coordinated reduction in genes coding for myelin components.

Metabolic changes in rat brain after prolonged ethanol consumption measured by 1H and 31P MRS experiments

1. In vivo 1H and 31P magnetic resonance spectroscopy techniques were applied to reveal biochemical changes in the rat brain caused by prolonged ethanol consumption. 2. Three models of ethanol intoxication were used. 3. 1H MRS showed a significant decrease in the concentration of myo-inositol in the brain of rats fed with 20% ethanol for 8 weeks. This change is consistent with perturbances in astrocytes. On the other hand, N-acetyl aspartate and choline content did not differ from controls. 4. 31P MRS did not reveal any significant changes in the high-energy phosphates or intracellular free Mg2+ content in the brain of rats after 14 weeks of 20% ethanol drinking. The intracellular pH was diminished. 5. By means of a 31P saturation transfer technique, a significant decrease was observed for the pseudo first-order rate constant k(for) of the creatine kinase reaction in the brain of rats administered 30% ethanol for 3 weeks using a gastric tube. 6. The 1H MRS results may indicate that myo-inositol loss, reflecting a disorder in astrocytes, might be one of the first changes associated with alcoholism, which could be detected in the brain by means of in vivo 1H MRS. 7. The results from 31p MRS experiments suggest that alcoholism is associated with decreased brain energy metabolism. 8. 31P saturation transfer, which provides insight into the turnover of high-energy phosphates, could be a more suitable technique for studying the brain energetics in chronic pathological states than conventional 31P MRS.

Glutamate-mediated transmission, alcohol, and alcoholism

Glutamate-mediated neurotransmission may be involved in the range of adaptive changes in brain which occur after ethanol administration in laboratory animals, and in chronic alcoholism in human cases. Excitatory amino acid transmission is modulated by a complex system of receptors and other effectors, the efficacy of which can be profoundly affected by altered gene or protein expression. Local variations in receptor composition may underlie intrinsic regional variations in susceptibility to pathological change. Equally, ethanol use and abuse may bring about alterations in receptor subunit expression as the essence of the adaptive response. Such considerations may underlie the regional localization characteristic of the pathogenesis of alcoholic brain damage, or they may form part of the homeostatic change that constitutes the neural substrate for alcohol dependence.

Acetaldehyde cytotoxicity in cultured rat astrocytes

The effect of acetaldehyde on astrocytes have been investigated because not only do they play an important role in brain maturation but also recent reports have shown their delayed proliferation following both 'in vivo' and 'in vitro' ethanol exposure. Biochemical parameters related to apoptotic and necrotic processes were examined in primary cultures of rat astrocytes exposed for 4 days to acetaldehyde generated from ethanol by co-cultured alcohol dehydrogenase-transfected Chinese hamster ovary cells. Acetaldehyde levels in the culture media attained concentrations of approximately 450 microM. To study ethanol effects, alcohol oxidation was inhibited by 4-methylpyrazole (an inhibitor of alcohol dehydrogenase). Acetaldehyde but not ethanol increased intracellular calcium levels by 155%. Moreover, significant DNA fragmentation was detected using a random oligonucleotide primed synthesis assay, by flow cytometry and when using agar gel electrophoresis. Transglutaminase activity was elevated in the cells treated with acetaldehyde but when acetaldehyde formation was inhibited by 4-methylpyrazole the enzyme activity was unaffected. Nitrate levels in the culture media were unchanged. Additionally, microscopic examination of cell nuclei revealed chromatin condensation in astrocytes exposed to acetaldehyde. It can be concluded, that in 'in vitro' acetaldehyde exposed rat astrocytes apoptotic pathways are activated.

Regulation of prostaglandin biosynthesis in vivo by glutathione

Intraperitoneal administration of urate crystals to mice reduced subsequent macrophage conversion of arachidonic acid (AA) to prostaglandins (PGs) and 12-hydroxyeicosatetraenoic acid for up to 6 h. In contrast, levels of 12-hydroxyheptadecatrienoic acid (12-HHT) were markedly elevated. This metabolic profile was previously observed in vitro when recombinant cyclooxygenase (COX) enzymes were incubated with reduced glutathione (GSH). Analysis of peritoneal GSH levels revealed a fivefold elevation after urate crystal administration. The GSH synthesis inhibitor L-buthionine-[S,R]-sulfoximine partially reversed the urate crystal effect on both GSH elevation and PG synthesis. Moreover, addition of exogenous GSH to isolated peritoneal macrophages shifted AA metabolism from PGs to 12-HHT. Urate crystal administration reduced COX-1, but induced COX-2 expression in peritoneal cells. The reduction of COX-1 may contribute to the attenuation of PG synthesis after 1 and 2 h, but PG synthesis remained inhibited up to 6 h, when COX-2 levels were high. Overall, our results indicate that elevated GSH levels inhibit PG production in this model and provide in vivo evidence for the role of GSH in the regulation of PG biosynthesis.

Binge ethanol-induced brain damage in rats: effect of inhibitors of nitric oxide synthase

Testing the possible role of endogenous nitric oxide (NO) in the neurotoxicity of ethanol, we examined how two different NO synthase (NOS) inhibitors affected the extent cerebrocortical and olfactory neuronal damage in a modified "binge intoxication" rat model (Collins et al., Alcohol Clin. Exp. Res. 20:284-292, 1996). Male rats intragastrically fed ethanol (6.5 to 12 g/kg/day) in nutrient solution three times daily for 4 days also received NG-nitro-L-arginine methyl ester by chronic intracerebroventricular infusion or 7-nitro-indazole by daily intraperitoneal injection; control rats were given nutrient solution only and/or vehicles. Blood ethanol levels did not differ among the ethanol-treated groups. The amount of ethanol-dependent neuronal degeneration in the entorihinal cortex, dentate gyrus, and olfactory bulb glomeruli--visualized with the de Olmos cupric silver stain and quantitatively assessed in the binge-intoxicated rats--was either unchanged or significantly increased by the NOS inhibitors. Although the efficacies of the inhibitors cannot be directly compared because of various NOS forms were probably inhibited to differing extents, the results do not support the idea that endogenous NO is a neurotoxic mediator of ethanol's effects. Rather NO may have a modest neuroprotectant role in this model of early brain damage induced by ethanol. In addition, the NOS that is localized histochemically as NADPH diaphorase was present primarily in regions and/or cells not damaged by binge ethanol treatment. Assuming that NADPH diaphorase represents most of the NO forming enzyme(s) this suggests a transcellular mechanism for NO. A further observation was that hippocampal CA pyramidal neuron degeneration was extensive in rats infused centrally with NG-nitro-L-arginine methyl ester.

Effect of glucose deprivation on rat glutamine synthetase in cultured astrocytes

Glutamine synthetase was purified from the cerebral cortex of adult rats and characterized. Polyclonal rabbit antibodies were raised against the enzyme, purified and their specific anti-(glutamine synthetase) activity determined. A primary astroglial culture was prepared from newborn Sprague-Dawley rats. Astrocytes at different ages of development were incubated in the presence and absence of glucose. In glucose-deprived conditions the specific activity of glutamine synthetase decreased. This decrease was more pronounced in 8-day-old than in 21-day-old cultures. Kinetic analysis demonstrated that the reduction in activity was mainly related to a decrease in Vmax. By immunoprecipitation, it was shown that the number of enzyme molecules in astrocytes was decreased in glucose-deprived conditions. On addition of glucose, a total recovery of glutamine synthetase was obtained after 36 h in 8-day-old culture. Rates of degradation and synthesis were investigated. When compared with an incubation in the presence of glucose, glucose deprivation increased enzyme turnover, as estimated from the first-order disappearance of radioactivity from glutamine synthetase. Synthesis rate was estimated from the incorporation of [35S]methionine during a 2 h incubation period and was decreased in glucose-deprived conditions. Trichloroacetate-precipitable proteins changed only slightly in the experimental conditions, and total protein did not vary significantly during the experimental period. A mathematical model is presented which attempts to integrate degradation and synthesis in our experimental model.

Effect of an NMDA receptor antagonist and a ganglioside GM1 derivative upon ethanol-induced modification of parameters of oxidative stress in several brain regions

Dietary administration of ethanol to rats for 2 weeks was able to depress levels of glutathione (GSH) and Cu/Zn superoxide dismutase (SOD) in several brain regions. This was indicative of the generation of excess levels of reactive oxygen in treated animals. The potentially protective effect of both an NMDA receptor blocker (MK-801) and an internally esterified derivative of ganglioside GM1 (AGF2) upon ethanol-induced changes in these indices of oxidative stress, was studied. Both of these agents are reported to have neuroprotective properties, but neither was able to prevent ethanol-induced reduction of GSH and SOD levels in any brain area studied. In fact, both agents depressed SOD and GSH levels in midbrain independently of ethanol. MK-801 had a pronounced pro-oxidant potential, and when administered in combination with ethanol. GSH and SOD were reduced in midbrain and striatum to levels below those obtained with either agent alone. The pro-oxidant properties of ethanol may thus act independently of its actions upon the NMDA receptor. The protective properties of NMDA receptor inhibitors or gangliosides cannot be attributed to any antioxidant effect.

Dietary α-tocopherol content modulates responses to moderate ethanol consumption

Rats were fed with diets containing differing amounts of α-tocopherol for 21 days. For the latter 14 days of this period, one half of the rats also received ethanol (7% v/v) in the drinking water. Treatments did not alter the rate of weight gain between groups. Hepatic glutathione levels were depressed by ethanol treatment in rats receiving diets deficient in α-tocopherol or containing normal levels of the vitamin (50 ppm). However, this depression was not found in rats maintained on a high α-tocopherol diet (1000 ppm). The high α-tocopherol diet also prevented the ethanol-induced inhibition of proteolytic activity within the liver. A dose-dependent reduction of rates of hepatic generation of reactive oxygen species was effected by this vitamin. Within the central nervous system, the only region showing an ethanol-induced lowering of glutathione levels, was the midbrain of rats receiving the α-tocopherol deficient diet.