Jérôme Jeanblanc

The Class I-Specific HDAC Inhibitor MS-275 Decreases Motivation to Consume Alcohol and Relapse in Heavy Drinking Rats

Background: New strategies for the treatment of alcohol dependence are a pressing need, and recent evidence suggests that targeting enzymes involved in epigenetic mechanisms seems to have great potential. Among these mechanisms, alteration of histone acetylation by histone deacetylases is of great importance for gene expression and has also been implicated in addiction. Here, we examined whether intra-cerebroventricular administration of MS-275, a class I-specific histone deacetylase inhibitor, could alter ethanol self-administration, motivation to consume ethanol, and relapse in heavy drinking rats. Methods: Male Long Evans rats trained to self-administer high levels of ethanol received intra-cerebroventricular micro-infusions of MS-275 (250 µM, 500 µM, and 1000 µM) 3 hours prior to the self-administration sessions. Results: First, we demonstrated that intra-cerebroventricular infusion of MS-275 increases acetylation of Histone 4 within the nucleus accumbens nucleus accumbens and the dorsolateral striatum. Second, we observed that MS-275 decreases ethanol self-administration by about 75%. We found that 2 consecutive daily injections are necessary to decrease ethanol self-administration. Additionally, the dose-response curve test indicated that MS-275 has a U-shape effect on ethanol self-administration with the dose of 500 µM as the most efficient dose. Furthermore, we showed that MS-275 also diminished the motivation to consume ethanol (25% decrease), and finally, we demonstrated that MS-275 reduced relapse (by about 50%) and postponed reacquisition even when the treatment was stopped. Conclusions: Our study confirms the potential therapeutic interest of targeting epigenetic mechanisms in excessive alcohol drinking and strengthens the interest of focusing on specific isoforms of histone deacetylases.

Brain‐derived neurotrophic factor mediates the suppression of alcohol self‐administration by memantine

Brain‐derived neurotrophic factor (BDNF) within the striatum is part of a homeostatic pathway regulating alcohol consumption. Memantine, a non‐competitive antagonist of N‐methyl‐D‐aspartate receptors, induces expression of BDNF in several brain regions including the striatum. We hypothesized that memantine could decrease ethanol (EtOH) consumption via activation of the BNDF signalling pathway. Effects of memantine were evaluated in Long‐Evans rats self‐administering moderate or high amounts of EtOH 6, 30 and 54 hours after an acute injection (12.5 and 25 mg/kg). Motivation to consume alcohol was investigated through a progressive ratio paradigm. The possible role for BDNF in the memantine effect was tested by blockade of the TrkB receptor using the pharmacological agent K252a and by the BDNF scavenger TrkB‐Fc. Candidate genes expression was also assessed by polymerase chain reaction array 4 and 28 hours after memantine injection. We found that memantine decreased EtOH self‐administration and motivation to consume EtOH 6 and 30 hours post‐injection. In addition, we found that inhibition or blockade of the BDNF signalling pathway prevented the early, but not the delayed decrease in EtOH consumption induced by memantine. Finally, Bdnf expression was differentially regulated between the early and delayed timepoints. These results demonstrate that an acute injection of memantine specifically reduces EtOH self‐administration and motivation to consume EtOH for at least 30 hours. Moreover, we showed that BDNF was responsible for the early effect, but that the delayed effect was BDNF‐independent.

Light alcohol intake during adolescence induces alcohol addiction in a neurodevelopmental model of schizophrenia.

Schizophrenia is a mental disorder characterized by a series of positive, negative or cognitive symptoms but with also the particularity of exhibiting a high rate of co‐morbid use of drugs of abuse. While more than 80% of schizophrenics are smokers, the second most consumed drug is alcohol, with dramatic consequences on frequency and intensity of psychotic episodes and on life expectancy. Here we investigated the impact of light alcohol intake during adolescence on the subsequent occurrence of alcohol addiction‐like behavior in neonatal ventral hippocampal lesion (NVHL) rats, a neurodevelopmental model of schizophrenia. Our findings demonstrated an increased liability to addictive behaviors in adult NVHL rats after voluntary alcohol intake during adolescence. NVHL rats displayed several signs of alcohol use disorder such as a loss of control over alcohol intake and high motivation to consume alcohol, associated with a higher resistance to extinction. In addition, once NVHL rats relapsed, they maintained higher drinking levels than controls. We finally showed that the anti‐addictive drug naltrexone is efficient in reducing excessive alcohol intake in NVHL rats. Our results are in accordance with epidemiological studies underlying the particular vulnerability to alcohol addiction after adolescent exposure to alcohol and highlight the fact that schizophrenic subjects may be particularly at risk even after light alcohol consumption. Based on these results, it seems particularly relevant to prevent early onset of alcohol use in at‐risk subjects and thus to reduce the incidence of co‐morbid alcohol abuse in psychotic patients.

Memantine reduces alcohol drinking but not relapse in alcohol-dependent rats.

Alcoholism is a chronic relapsing disorder with consequences on health and that requires more effective treatments. Among alternative therapies, the therapeutic potential of the non‐competitive N‐methyl‐D‐aspartate receptor antagonist memantine has been suggested. Despite promising results, its efficiency in the treatment of alcoholism remains controversial. Currently, there is no pre‐clinical data regarding its effects on the motivation for ethanol in post‐dependent (PD) animals exposed to intermittent ethanol vapor, a validated model of alcoholism. Thus, the objectives of this study were to evaluate the effects of acute injections of memantine (0, 12.5, 25 and 50 mg/kg) on operant ethanol self‐administration in non‐dependent (ND) and PD rats tested either during acute withdrawal or relapse after protracted abstinence. Our results showed that memantine (25 mg/kg) abolished ethanol self‐administration in ND rats and reduced by half the one of PD rats during acute withdrawal. While this effect was observed only 6 hours after treatment in ND rats, it was long lasting in PD rats (at least 30 hours after injection). Furthermore, our results indicated that memantine did not modify the breaking point for ethanol. This suggests that memantine probably act by potentiating the pharmacological effect of ethanol but not by reducing motivation for ethanol. Finally, memantine was also ineffective in reducing relapse after protracted abstinence. Altogether, our pre‐clinical results highlighted a potential therapeutic use of memantine that may be used as a replacement therapy drug but not as relapse‐preventing drug.

Effect of N-acetylcysteine on motivation, seeking and relapse to ethanol self-administration

Alcohol use disorder is a chronic and highly relapsing disorder, characterized by a loss of control over alcohol consumption and craving. Several studies suggest a key role of glutamate in this disorder. In recent years, the modulation of cystine/glutamate exchange via the xc− system has emerged as a new therapeutic alternative for reducing the excitatory glutamatergic transmission observed after ethanol self‐administration in both rats and humans. The objective of this study was to determine whether a treatment with N‐acetylcysteine (NAC), a cystine prodrug, could reduce ethanol self‐administration, ethanol‐seeking behavior and reacquisition of ethanol self‐administration. Male Long Evans rats were trained to self‐administer 20 percent ethanol in operant cages for several weeks. Once the consumption surpassed 1 g of ethanol/kg body weight/15 minutes, the effect of an acute intraperitoneal injection of NAC (0, 25, 50 or 100 mg/kg) 1 hour before the beginning of each test was evaluated on different aspects of the operant self‐administration behavior. We demonstrated antimotivational properties of NAC (100 mg/kg), as ethanol‐reinforced responding was reduced in a fixed ratio (−35 percent) and in a progressive ratio schedule (−81 percent). NAC also reduced ethanol‐seeking behavior (−77 percent) evaluated as extinction responding in a single extinction session. NAC was able to reduce reacquisition in rats that were abstinent for 17 days, while NAC had no effect on ethanol relapse in rats previously exposed to six extinction sessions. Overall, our results demonstrate that NAC limits motivation, seeking behavior and reacquisition in rats, making it a potential new treatment for the maintenance of abstinence.

Deciphering the relationship between vulnerability to ethanol-induced behavioral sensitization and ethanol consumption in outbred mice.

Ethanol (EtOH)‐induced behavioral sensitization (EIBS) is proposed to play a role in early and recurring steps of alcohol dependence, but its impact on alcohol abuse is not clear. EIBS development is dependent upon animal species, strain and also individual factors. We proposed here to decipher the co‐expression of EIBS and EtOH intake in individual animals among outbred Swiss mice, which exhibit heterogeneity that parallels what may occur in humans. To do so, mice were exposed to a two‐bottle choice with free access to water or 10% EtOH for 6 days just before and immediately after chronic intraperitoneal 2.5 g/kg ethanol injections once a day for 10 consecutive days. Based on their sensitization scores, mice were split into resistant and sensitized animals. First, we showed that individual susceptibility to EIBS is inversely correlated with voluntary EtOH consumption. Exposure to repeated EtOH during EIBS development increased subsequent EtOH intake among the entire population. Very interestingly, subsequent analyses suggested that the less the mice are sensitized the more they increase their EtOH intake; however, resistant mice were sensitive to EtOH adulteration with quinine, whereas sensitized ones maintained their EtOH intake levels, therefore exhibiting a compulsive‐like drinking pattern. In addition, we showed that resistant mice do not exhibit a weaker sensitivity to the aversive properties of EtOH that may contribute to their higher level of EtOH intake compared to sensitized mice. This study confirms and extends previous data showing a deep relationship between propensity for EtOH consumption and susceptibility to EIBS in Swiss mice.

Pharmacological activation of mGlu4 and mGlu7 receptors, by LSP2-9166, reduces ethanol consumption and relapse in rat

ABSTRACT Addiction is a chronic and highly relapsing disorder hypothesized to be produced by an imbalance between excitatory and inhibitory neurotransmission. For more than a decade, emerging evidence indicates that manipulation of glutamatergic neurotransmission, by group III mGlu receptors (mGlu4/7/8), could be a promising approach to develop therapeutic agents for the treatment of addiction. Thus, the aim of the present study is to determine whether LSP2‐9166, a mixed mGlu4/mGlu7 orthosteric agonist, could reduce ethanol self‐administration, ethanol motivation and reacquisition after protracted abstinence in a preclinical model of excessive ethanol intake. Male Long Evans rats were chronically trained to consume large amount of ethanol in operant cages for several weeks. Once they reached a stable level of consumption (about 1 g of pure ethanol/kg bodyweight/15min), the effect of LSP2‐9166 was evaluated on different aspects of the operant self‐administration behavior. In this study, we found that the intracerebroventricular infusion of LSP2‐9166 dose dependently reduced ethanol consumption, motivation for ethanol and reacquisition of ethanol self‐administration after abstinence. Together, these results support recent preclinical findings showing that pharmacological modulation of mGlu receptors may serve as an effective treatment for reducing ethanol consumption and relapse. HighlightsLSP2‐9166 reduced ethanol operant self‐administration.LSP2‐9166 reduced motivation to self‐administer ethanol.LSP2‐9166 reduced reacquisition after a period of abstinence.LSP2‐9166 did not change sucrose operant self‐administration.These data confirm the interest of targeting mGlu4/mGlu7 in alcohol use disorder.

Face validity of a pre-clinical model of operant binge drinking: just a question of speed: Rat operant binge drinking

Binge drinking (BD) is often defined as a large amount of alcohol consumed in a ‘short’ period of time or ‘per occasion’. In clinical research, few researchers have included the notion of ‘speed of drinking’ in the definition of BD. Here, we aimed to describe a novel pre‐clinical model based on voluntary operant BD, which included both the quantity of alcohol and the rapidity of consumption. In adult Long–Evans male rats, we induced BD by regularly decreasing the duration of ethanol self‐administration from 1‐hour to 15‐minute sessions. We compared the behavioral consequences of BD with the behaviors of rats subjected to moderate drinking or heavy drinking (HD). We found that, despite high ethanol consumption levels (1.2 g/kg/15 minutes), the total amounts consumed were insufficient to differentiate HD from BD. However, consumption speed could distinguish between these groups. The motivation to consume was higher in BD than in HD rats. After BD, we observed alterations in locomotor coordination in rats that consumed greater than 0.8 g/kg, which was rarely observed in HD rats. Finally, chronic BD led to worse performance in a decision‐making task, and as expected, we observed a lower stimulated dopaminergic release within nucleus accumbens slices in poor decision makers. Our BD model exhibited good face validity and can now provide animals voluntarily consuming very rapidly enough alcohol to achieve intoxication levels and thus allowing the study of the complex interaction between individual and environmental factors underlying BD behavior.

Class I HDAC Inhibitors: Potential New Epigenetic Therapeutics for Alcohol Use Disorder (AUD)

Alcohol use disorder (AUD) represents a serious public health issue, and discovery of new therapies is a pressing necessity. Alcohol exposure has been widely demonstrated to modulate epigenetic mechanisms, such as histone acetylation/deacetylation balance, in part via histone deacetylase (HDAC) inhibition. Epigenetic factors have been suggested to play a key role in AUD. To date, 18 different mammalian HDAC isoforms have been identified, and these have been divided into four classes. Since recent studies have suggested that both epigenetic mechanisms underlying AUD and the efficacy of HDAC inhibitors (HDACIs) in different animal models of AUD may involve class I HDACs, we herein report the development of class I HDACIs, including information regarding their structure, potency, and selectivity. More effort is required to improve the selectivity, pharmacokinetics, and toxicity profiles of HDACIs to achieve a better understanding of their efficacy in reducing addictive behavior.

Mécanismes épigénétiques et troubles de l’usage d’alcool : une cible thérapeutique intéressante?

Alcohol use disorder is a devastating illness with a profound health impact, and its development is dependent on both genetic and environmental factors. This disease occurs over time and requires changes in brain gene expression. There is converging evidence suggesting that the epigenetic processes may play a role in the alcohol-induced gene regulations and behavior such as the intervention of DNA methylation and histone acetylation. Histone acetylation, like histone methylation, is a highly dynamic process regulated by two classes of enzymes: histone acetyltransferases and histone deacetylases (HDACs). To date, 18 human HDAC isoforms have been characterized, and based on their sequence homologies and cofactor dependencies, they have been phylogenetically categorized into 4 main classes: classes I, II (a and b), III, and IV. In the brain, expression of the different classes of HDACs varies between cell types and also in their subcellular localization (nucleus and/or cytosol). Furthermore, we recently showed that a single ethanol exposure inhibits HDAC activity and increases both H3 and H4 histone acetylation within the amygdala of rats. In the brain of alcoholic patients, ethanol has been shown to induce histone-related and DNA methylation epigenetic changes in several reward regions involved in reward processes such as hippocampus, prefrontal cortex, and amygdala. We recently demonstrated alteration of histone H3 acetylation levels in several brain regions from the reward circuit of rats made dependent to alcohol after chronic and intermittent exposure to ethanol vapor. In neuronal cell line culture, ethanol was shown to induce HDAC expression. In mouse and rat brain, numerous studies reported epigenetic alterations following ethanol exposure. We also demonstrated that both the expression of genes and the activity of enzymes involved in epigenetic mechanisms are changed after repeated administrations of ethanol in mice sensitized to the motor stimulant effect of ethanol (a model of drug-induced neuroplasticity). Numerous studies have shown that HDAC inhibitors are able to counter ethanol-induced behaviors and the ethanol-induced changes in the levels of HDAC and/or levels of acetylated HDAC. For example, trichostatin A (TSA) treatment caused the reversal of ethanol-induced tolerance, anxiety, and ethanol drinking by inhibiting HDAC activity, thereby increasing histone acetylation in the amygdala of rats. Another study demonstrated that TSA prevented the development of ethanol withdrawal induced anxiety in rats by rescuing deficits in histone acetylation induced by increased HDAC activity in the amygdala. We have demonstrated that treatment with the HDAC inhibitor sodium butyrate blocks both the development and the expression of ethanol-induced behavioral sensitization in mice. In this context, converging evidence indicates that HDAC inhibitors could be useful in counteracting ethanol-induced gene regulations via epigenetic mechanisms, that is, HDAC inhibitors could affect different acetylation sites and may also alter the expression of different genes that could in turn counteract the effect of ethanol. Recent work in rodents has shown that systemic administration of pan HDAC class I and II inhibitors, TSA and N-hydroxy-N-phenyl-octanediamide [SuberoylAnilide Hydroxamic Acid] (SAHA), and of the more selective inhibitor (mainly HDAC1 and HDAC9) MS-275, decrease binge-like alcohol drinking in mice. SAHA selectively reduced ethanol operant self-administration and seeking in rats. Our previous study revealed that MS-275 strongly decreased operant ethanol self-administration in alcohol-dependent rats when administered 30 minutes before the session at the second day of injection. We also demonstrated that intra-cerebro-ventricular infusion of MS-275 increases acetylation of Histone 4 within the nucleus accumbens and the dorsolateral striatum, associated to a decrease in ethanol self-administration by about 75%. MS-275 also diminished both the motivation to consume ethanol (25% decrease), relapse (by about 50%) and postponed reacquisition after abstinence. Both literature and several of our studies strongly support the potential therapeutic interest of targeting epigenetic mechanisms in excessive alcohol drinking and strengthen theinterest of focusing on specific isoforms of histone deacetylases.