Ethanol withdrawal provokes mitochondrial injury in an estrogen preventable manner

Chronic alcohol consumption shifts learning strategies and synaptic plasticity from hippocampus to striatum-dependent pathways

Introduction

The hippocampus and striatum have dissociable roles in memory and are necessary for spatial and procedural/cued learning, respectively. Emotionally charged, stressful events promote the use of striatal- over hippocampus-dependent learning through the activation of the amygdala. An emerging hypothesis suggests that chronic consumption of addictive drugs similarly disrupt spatial/declarative memory while facilitating striatum-dependent associative learning. This cognitive imbalance could contribute to maintain addictive behaviors and increase the risk of relapse.

Methods

We first examined, in C57BL/6 J male mice, whether chronic alcohol consumption (CAC) and alcohol withdrawal (AW) might modulate the respective use of spatial vs. single cue-based learning strategies, using a competition protocol in the Barnes maze task. We then performed in vivo electrophysiological studies in freely moving mice to assess learning-induced synaptic plasticity in both the basolateral amygdala (BLA) to dorsal hippocampus (dCA1) and BLA to dorsolateral striatum (DLS) pathways.

Results

We found that both CAC and early AW promote the use of cue-dependent learning strategies, and potentiate plasticity in the BLA → DLS pathway while reducing the use of spatial memory and depressing BLA → dCA1 neurotransmission.

Discussion

These results support the view that CAC disrupt normal hippocampo-striatal interactions, and suggest that targeting this cognitive imbalance through spatial/declarative task training could be of great help to maintain protracted abstinence in alcoholic patients.

Alcohol Withdrawal Is an Oxidative Stress Challenge for the Brain: Does It Pave the Way toward Severe Alcohol-Related Cognitive Impairment?

Alcohol use is a leading cause of mortality, brain morbidity, neurological complications and minor to major neurocognitive disorders. Alcohol-related neurocognitive disorders are consecutive to the direct effect of chronic and excessive alcohol use, but not only. Indeed, patients with severe alcohol use disorders (AUD) associated with pharmacological dependence suffer from repetitive events of alcohol withdrawal (AW). If those AW are not managed by adequate medical and pharmacological treatment, they may evolve into severe AW, or be complicated by epileptic seizure or delirium tremens (DT). In addition, we suggest that AW favors the occurrence of Wernicke's encephalopathy (WE) in patients with known or unknown thiamine depletion. We reviewed the literature on oxidative stress as a core mechanism in brain suffering linked with those conditions: AW, epileptic seizure, DT and WE. Thus, we propose perspectives to further develop research projects aiming at better identifying oxidative stress brain damage related to AW, assessing the effect of repetitive episodes of AW, and their long-term cognitive consequences. This research field should develop neuroprotective strategies during AW itself or during the periwithdrawal period. This could contribute to the prevention of severe alcohol-related brain damage and cognitive impairments.

Different brain oxidative and neuroinflammation status in rats during prolonged abstinence depending on their ethanol relapse-like drinking behavior: Effects of ethanol reintroduction

RATIONALE

Accumulating evidence suggests that chronic alcohol consumption is associated with excessive oxidative damage and neuroinflammatory processes and these events have been associated to early alcohol withdrawal. In the present research we wonder if brain oxidative stress and neuroinflammation remains altered during prolonged withdrawal situations and whether these alterations can be correlated with relapse behavior in alcohol consumption. The effects of alcohol reintroduction were also evaluated METHODS: We have used a model based on the alcohol deprivation effect (ADE) within a cohort of wild-type male Wistar rats. Two subpopulations were identified according to the alcohol relapse-like drinking behavior displayed (ADE and NO-ADE subpopulations). Oxidized and reduced glutathione content was determined within the hippocampus and the amygdala using a mass spectrometry method. The levels of mRNA of seven different inflammatory mediators in the prefrontal cortex of rats were quantified. All the analyses were performed in two different conditions: after 21-day alcohol deprivation (prolonged abstinence) and after 24 h of ethanol reintroduction in both subpopulations.

RESULTS

ADE and NO-ADE rats showed different endophenotypes. ADE rats always displayed a significant lower alcohol intake rate and ethanol preference than NO-ADE rats. The results also demonstrated the existence of altered brain redox and neuroinflammation status after prolonged abstinence exclusively in ADE rats. Moreover, when ethanol was reintroduced in the ADE subpopulation, altered oxidative stress and neuroinflammatory markers were restored.

CONCLUSIONS

Present findings provide new mechanisms underlying the neurobiology of relapse behavior and suggest the development of new pharmacological approaches to treat alcohol-induced relapse.

Alcohol Withdrawal and Cerebellar Mitochondria

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

Aberrant histone acetylation promotes mitochondrial respiratory suppression in the brain of alcoholic rats

The acetylation of histone proteins in the core of DNA regulates gene expression, including those affecting mitochondria. Both histone acetylation and mitochondrial deficit have been implicated in neuronal damage associated with drinking problems. Many alcoholics will repeat unsuccessful attempts at abstaining, developing a pattern of repeated drinking and withdrawal. We investigated whether aberrant histone acetylation contributes to mitochondrial and cellular damage induced by repeated ethanol withdrawal (EW). We also investigated whether this effect of histone acetylation involves let-7f, a small noncoding RNA (microRNA). Male rats received two cycles of an ethanol/control diet (7.5%, 4 weeks) and withdrawal. Their prefrontal cortex was collected to measure the mitochondrial respiration and histone acetylation using extracellular flux (XF) real-time respirometry and gold immunostaining, respectively. Separately, HT22 (mouse hippocampal) cells received two cycles of ethanol exposure (100 mM, 20 hours) and withdrawal. Trichostatin A (TSA) as a histone acetylation promoter and let-7f antagomir were applied during withdrawal. The mitochondrial respiration, let-7f level, and cell viability were assessed using XF respirometry, quantitative polymerase chain reaction, TaqMan let-7f primers, and a calcein-acetoxymethyl assay, respectively. Repeated ethanol withdrawn rats showed a more than 2-fold increase in histone acetylation, accompanied by mitochondrial respiratory suppression. EW-induced mitochondrial respiratory suppression was exacerbated by TSA treatment in a manner that was attenuated by let-7f antagomir cotreatment. TSA treatment did not alter the increasing effect of EW on the let-7f level but dramatically exacerbated the cell death induced by EW. These data suggest that the multiple episodes of withdrawal from chronic ethanol impede mitochondrial and cellular integrity through upregulating histone acetylation, independent of or additively with let-7f.

Ethanol withdrawal hastens the aging of cytochrome c oxidase

We investigated whether abrupt ethanol withdrawal (EW) age-specifically inhibits a key mitochondrial enzyme, cytochrome c oxidase (COX), and whether estrogen mitigates this problem. We also tested whether this possible effect of EW involves a substrate (cytochrome c) deficiency that is associated with proapoptotic Bcl2-associated X protein (BAX) and mitochondrial membrane swelling. Ovariectomized young, middle age, and older rats, with or without 17β-estradiol (E2) implantation, underwent repeated EW. Cerebelli were collected to measure COX activity and the mitochondrial membrane swelling using spectrophotometry and the mitochondrial levels of cytochrome c and BAX using an immunoblot method. The loss of COX activity and the mitochondrial membrane swelling occurred only in older rats under control diet conditions but occurred earlier, starting in the young rats under EW conditions. E2 treatment mitigated these EW effects. EW increased mitochondrial BAX particularly in middle age rats but did not alter cytochrome c. Collectively EW hastens but E2 delays the age-associated loss of COX activity. This EW effect is independent of cytochrome c but may involve the mitochondrial overload of BAX and membrane vulnerability.

Alcohol withdrawal and brain injuries: beyond classical mechanisms

Unmanaged sudden withdrawal from the excessive consumption of alcohol (ethanol) adversely alters neuronal integrity in vulnerable brain regions such as the cerebellum, hippocampus, or cortex. In addition to well known hyperexcitatory neurotransmissions, ethanol withdrawal (EW) provokes the intense generation of reactive oxygen species (ROS) and the activation of stress-responding protein kinases, which are the focus of this review article. EW also inflicts mitochondrial membranes/membrane potential, perturbs redox balance, and suppresses mitochondrial enzymes, all of which impair a fundamental function of mitochondria. Moreover, EW acts as an age-provoking stressor. The vulnerable age to EW stress is not necessarily the oldest age and varies depending upon the target molecule of EW. A major female sex steroid, 17β-estradiol (E2), interferes with the EW-induced alteration of oxidative signaling pathways and thereby protects neurons, mitochondria, and behaviors. The current review attempts to provide integrated information at the levels of oxidative signaling mechanisms by which EW provokes brain injuries and E2 protects against it.

Ethanol withdrawal acts as an age-specific stressor to activate cerebellar p38 kinase

We investigated whether protein kinase p38 plays a role in the brain-aging changes associated with repeated ethanol withdrawal (EW). Ovariectomized young, middle-age and older rats, with or without 17β-estradiol (E2) implantation, received a 90-day ethanol with repeated withdrawal. They were tested for active pP38 expression in cerebellar Purkinje neurons and whole-cerebellar lysates using immunohistochemistry and enzyme-linked immunosorbent assay, respectively. They were also tested for the Rotarod task to determine the behavioral manifestation of cerebellar neuronal stress and for reactive oxygen species (ROS) and mitochondrial protein carbonyls to determine oxidative mechanisms. Middle-age EW rats showed higher levels of pP38-positive Purkinje neurons/cerebellar lysates, which coincided with increased mitochondrial protein oxidation than other diet/age groups. Exacerbated motor deficit due to age-EW combination also began at the middle-age. In comparison, ROS contents peaked in older EW rats. E2 treatment mitigated each of the EW effects to a different extent. Collectively, pP38 may mediate the brain-aging changes associated with pro-oxidant EW at vulnerable ages and in vulnerable neurons in a manner protected by estrogen.

Ethanol withdrawal provokes opening of the mitochondrial membrane permeability transition pore in an estrogen-preventable manner

We have reported that the major endogenous estrogen, 17beta-estradiol (E2), protects against oxidative injury during ethanol withdrawal (EW) in a cultured hippocampal cell line (HT22). Here, we investigated whether the pro-oxidant nature of EW mediates opening of the mitochondrial membrane permeability transition pore (PTP) in a manner protected by E2. Excess PTP opening provokes mitochondrial membrane swelling (MMS) and the collapse of membrane potential (DeltaPsim). HT22 cells were collected at the end of ethanol exposure (100 mM) for 24 h or at 4 h of EW to assess MMS by monitoring absorbance decline at 540 nm and to assess DeltaPsim using flow cytometry. Protective effects of E2 on PTP were compared with an antioxidant butylated hydroxytoluene (BHT) and an E2 analog, ZYC26 [(3-hydroxy-2-adamantyl(1)-4-methyl-estra-1,3,5(10)-17-one], with higher antioxidant potency than E2. To assess cellular consequences of PTP opening, effects of a PTP inhibitor (cyclosporin A) on EW-induced cell death were assessed using the calcein assay. Major findings were that: 1) EW resulted in rapid MMS and DeltaPsim collapse; 2) cyclosporin A attenuated EW-induced cell death; and 3) E2 treatment restricted to the EW phase protected against the PTP opening more prominently than BHT and to a similar degree to ZYC26. These findings suggest that EW provokes PTP opening partly but not entirely through the pro-oxidant nature and that E2 counteracts EW-associated factors to protect against the PTP opening.

Intermittent hypoxia conditioning prevents behavioral deficit and brain oxidative stress in ethanol-withdrawn rats

Intermittent hypoxia (IH) has been found to protect brain from ischemic injury. We investigated whether IH mitigates brain oxidative stress and behavioral deficits in rats subjected to ethanol intoxication and abrupt ethanol withdrawal (EW). The effects of IH on overt EW behavioral signs, superoxide generation, protein oxidation, and mitochondrial permeability transition pore (PTP) opening were examined. Male rats consumed dextrin or 6.5% (wt/vol) ethanol for 35 days. During the last 20 days, rats were treated with repetitive (5-8 per day), brief (5-10 min) cycles of hypoxia (9.5-10% inspired O2) separated by 4-min normoxia exposures. Cerebellum, cortex, and hippocampus were biopsied on day 35 of the diet or at 24 h of EW. Superoxide and protein carbonyl contents in tissue homogenates and absorbance decline at 540 nm in mitochondrial suspensions served as indicators of oxidative stress, protein oxidation, and PTP opening, respectively. Although IH altered neither ethanol consumption nor blood ethanol concentration, it sharply lowered the severity of EW signs including tremor, tail rigidity, and startle response. Compared with dextrin and ethanol per se, in the three brain regions, EW increased superoxide and protein carbonyl contents and accelerated PTP opening in a manner ameliorated by IH. Administration of antioxidant N-acetylcysteine throughout the IH program abrogated the reductions in EW signs and superoxide content, implicating IH-induced ROS as mediators of the salutary adaptations. We conclude that IH conditioning during chronic ethanol consumption attenuates oxidative damage to the brain and mitigates behavioral abnormalities during subsequent EW. IH-induced ROS may evoke this powerful protection.