The histone deacetylase inhibitor sodium butyrate decreases excessive ethanol intake in dependent animals

New therapeutics for the prevention or amelioration of fetal alcohol spectrum disorders: a narrative review of the preclinical literature

Background: Ethanol consumption during pregnancy induces enduring detrimental effects in the offspring, manifesting as a spectrum of symptoms collectively termed as Fetal Alcohol Spectrum Disorders (FASD). Presently, there is a scarcity of treatments for FASD.Objectives: To analyze current literature, emphasizing evidence derived from preclinical models, that could potentially inform therapeutic interventions for FASD.Methods: A narrative review was conducted focusing on four prospective treatments: nutritional supplements, antioxidants, anti-inflammatory compounds and environmental enrichment. The review also highlights innovative therapeutic strategies applied during early (e.g. folate administration, postnatal days 4-9) or late (e.g. NOX2 inhibitors given after weaning) postnatal stages that resulted in significant improvements in behavioral responses during adolescence (a critical period marked by the emergence of mental health issues in humans).Results: Our findings underscore the value of treatments centered around nutritional supplementation or environmental enrichment, aimed at mitigating oxidative stress and inflammation, implying shared mechanisms in FASD pathogenesis. Moreover, the review spotlights emerging evidence pertaining to the involvement of novel molecular components with potential pharmacological targets (such as NOX2, MCP1/CCR2, PPARJ, and PDE1).Conclusions: Preclinical studies have identified oxidative imbalance and neuroinflammation as relevant pathological mechanisms induced by prenatal ethanol exposure. The relevance of these mechanisms, which exhibit positive feedback loop mechanisms, appear to peak during early development and decreases in adulthood. These findings provide a framework for the future development of therapeutic avenues in the development of specific clinical treatments for FASD.

Short-chain fatty acid valerate reduces voluntary alcohol intake in male mice

BACKGROUND

Despite serious health and social consequences, effective intervention strategies for habitual alcohol binge drinking are lacking. The development of novel therapeutic and preventative approaches is highly desirable. Accumulating evidence in the past several years has established associations between the gut microbiome and microbial metabolites with drinking behavior, but druggable targets and their underlying mechanism of action are understudied.

RESULTS

Here, using a drink-in-the-dark mouse model, we identified a microbiome metabolite-based novel treatment (sodium valerate) that can reduce excessive alcohol drinking. Sodium valerate is a sodium salt of valeric acid short-chain fatty acid with a similar structure as γ-aminobutyric acid (GABA). Ten days of oral sodium valerate supplementation attenuates excessive alcohol drinking by 40%, reduces blood ethanol concentration by 53%, and improves anxiety-like or approach-avoidance behavior in male mice, without affecting overall food and water intake. Mechanistically, sodium valerate supplementation increases GABA levels across stool, blood, and amygdala. It also significantly increases H4 acetylation in the amygdala of mice. Transcriptomics analysis of the amygdala revealed that sodium valerate supplementation led to changes in gene expression associated with functional pathways including potassium voltage-gated channels, inflammation, glutamate degradation, L-DOPA degradation, and psychological behaviors. 16S microbiome profiling showed that sodium valerate supplementation shifts the gut microbiome composition and decreases microbiome-derived neuroactive compounds through GABA degradation in the gut microbiome.

CONCLUSION

Our findings suggest that sodium valerate holds promise as an innovative therapeutic avenue for the reduction of habitual binge drinking, potentially through multifaceted mechanisms. Video Abstract.

Epigenetic drugs and psychedelics as emerging therapies for alcohol use disorder: insights from preclinical studies

Alcohol use disorder (AUD) is a public health issue that affects millions of people worldwide leading to physical, mental and socio-economic consequences. While current treatments for AUD have provided relief to individuals, their effectiveness on the long term is often limited, leaving a number of affected individuals without sustainable solutions. In this review, we aim to explore two emerging approaches for AUD: psychedelics and epigenetic drugs (i.e., epidrugs). By examining preclinical studies, different animal species and procedures, we delve into the potential benefits of each of these treatments in terms of addictive behaviors (alcohol drinking and seeking, motivation to drink alcohol and prevention of relapse). Because psychedelics and epidrugs may share common and complementary mechanisms of action, there is an exciting opportunity for exploring synergies between these approaches and their parallel effectiveness in treating AUD and the diverse associated psychiatric conditions.

Gut-liver axis: Recent concepts in pathophysiology in alcohol-associated liver disease

The growing recognition of the role of the gut microbiome's impact on alcohol-associated diseases, especially in alcohol-associated liver disease, emphasizes the need to understand molecular mechanisms involved in governing organ-organ communication to identify novel avenues to combat alcohol-associated diseases. The gut-liver axis refers to the bidirectional communication and interaction between the gut and the liver. Intestinal microbiota plays a pivotal role in maintaining homeostasis within the gut-liver axis, and this axis plays a significant role in alcohol-associated liver disease. The intricate communication between intestine and liver involves communication between multiple cellular components in each organ that enable them to carry out their physiological functions. In this review, we focus on novel approaches to understanding how chronic alcohol exposure impacts the microbiome and individual cells within the liver and intestine, as well as the impact of ethanol on the molecular machinery required for intraorgan and interorgan communication.

Gut-Liver-Brain Axis and Alcohol Use Disorder: Treatment Potential of Fecal Microbiota Transplantation

PURPOSE

Chronic alcohol use is a major cause of liver damage and death. In the United States, multiple factors have led to low utilization of pharmacotherapy for alcohol use disorder (AUD), including lack of provider knowledge and comfort in prescribing medications for AUD. Alcohol consumption has direct effects on the gut microbiota, altering the diversity of bacteria and leading to bacterial overgrowth. Growing evidence suggests that alcohol's effects on the gut microbiome may contribute to increased alcohol consumption and progression of alcohol-associated liver disease (ALD). This article reviews human and preclinical studies investigating the role of fecal microbiota transplantation (FMT) in ameliorating alcohol-associated alterations to the liver, gut, and brain resulting in altered behavior; it also discusses the therapeutic potential of FMT.

SEARCH METHODS

For this narrative review, a literature search was conducted in September 2022 of PubMed, Web of Science Core Collection, and Google Scholar to identify studies published between January 2012 and September 2022. Search terms used included "fecal microbiota transplantation" and "alcohol."

SEARCH RESULTS

Most results of the literature search were review articles or articles on nonalcoholic fatty liver disease; these were excluded. Of the remaining empirical manuscripts, very few described clinical or preclinical studies that were directly investigating the effects of FMT on alcohol drinking or related behaviors. Ultimately, 16 studies were included in the review.

DISCUSSION AND CONCLUSIONS

The literature search identified only a few studies that were directly investigating the effect of FMT on ALD or alcohol drinking and related behaviors. Largely proof-of-concept studies, these findings demonstrate that alcohol can alter the gut microbiome and that the microbiome can be transferred between humans and rodents to alter affective behaviors frequently associated with increased alcohol use. Other studies have shown promise of FMT or other probiotic supplementation in alleviating some of the symptoms associated with ALD and drinking. These results show that the implementation of FMT as a therapeutic approach is still in the investigatory stages.

Epidrugs in the Therapy of Central Nervous System Disorders: A Way to Drive on?

The polygenic nature of neurological and psychiatric syndromes and the significant impact of environmental factors on the underlying developmental, homeostatic, and neuroplastic mechanisms suggest that an efficient therapy for these disorders should be a complex one. Pharmacological interventions with drugs selectively influencing the epigenetic landscape (epidrugs) allow one to hit multiple targets, therefore, assumably addressing a wide spectrum of genetic and environmental mechanisms of central nervous system (CNS) disorders. The aim of this review is to understand what fundamental pathological mechanisms would be optimal to target with epidrugs in the treatment of neurological or psychiatric complications. To date, the use of histone deacetylases and DNA methyltransferase inhibitors (HDACis and DNMTis) in the clinic is focused on the treatment of neoplasms (mainly of a glial origin) and is based on the cytostatic and cytotoxic actions of these compounds. Preclinical data show that besides this activity, inhibitors of histone deacetylases, DNA methyltransferases, bromodomains, and ten-eleven translocation (TET) proteins impact the expression of neuroimmune inflammation mediators (cytokines and pro-apoptotic factors), neurotrophins (brain-derived neurotropic factor (BDNF) and nerve growth factor (NGF)), ion channels, ionotropic receptors, as well as pathoproteins (β-amyloid, tau protein, and α-synuclein). Based on this profile of activities, epidrugs may be favorable as a treatment for neurodegenerative diseases. For the treatment of neurodevelopmental disorders, drug addiction, as well as anxiety disorders, depression, schizophrenia, and epilepsy, contemporary epidrugs still require further development concerning a tuning of pharmacological effects, reduction in toxicity, and development of efficient treatment protocols. A promising strategy to further clarify the potential targets of epidrugs as therapeutic means to cure neurological and psychiatric syndromes is the profiling of the epigenetic mechanisms, which have evolved upon actions of complex physiological lifestyle factors, such as diet and physical exercise, and which are effective in the management of neurodegenerative diseases and dementia.

Modulation of neuronal excitability by binge alcohol drinking

Drug use poses a serious threat to health systems throughout the world. The number of consumers rises every year being alcohol the drug of abuse most consumed causing 3 million deaths (5.3% of all deaths) worldwide and 132.6 million disability-adjusted life years. In this review, we present an up-to-date summary about what is known regarding the global impact of binge alcohol drinking on brains and how it affects the development of cognitive functions, as well as the various preclinical models used to probe its effects on the neurobiology of the brain. This will be followed by a detailed report on the state of our current knowledge of the molecular and cellular mechanisms underlying the effects of binge drinking on neuronal excitability and synaptic plasticity, with an emphasis on brain regions of the meso-cortico limbic neurocircuitry.

Epigenetic Dysregulation in Alcohol-Associated Behaviors: Preclinical and Clinical Evidence

Alcohol use disorder (AUD) is characterized by loss of control over intake and drinking despite harmful consequences. At a molecular level, AUD is associated with long-term neuroadaptations in key brain regions that are involved in reward processing and decision-making. Over the last decades, a great effort has been made to understand the neurobiological basis underlying AUD. Epigenetic mechanisms have emerged as an important mechanism in the regulation of long-term alcohol-induced gene expression changes. Here, we review the literature supporting a role for epigenetic processes in AUD. We particularly focused on the three most studied epigenetic mechanisms: DNA methylation, Histone modification and non-coding RNAs. Clinical studies indicate an association between AUD and DNA methylation both at the gene and global levels. Using behavioral paradigms that mimic some of the characteristics of AUD, preclinical studies demonstrate that changes in epigenetic mechanisms can functionally impact alcohol-associated behaviors. While many studies support a therapeutic potential for targeting epigenetic enzymes, more research is needed to fully understand their role in AUD. Identification of brain circuits underlying alcohol-associated behaviors has made major advances in recent years. However, there are very few studies that investigate how epigenetic mechanisms can affect these circuits or impact the neuronal ensembles that promote alcohol-associated behaviors. Studies that focus on the role of circuit-specific and cell-specific epigenetic changes for clinically relevant alcohol behaviors may provide new insights on the functional role of epigenetic processes in AUD.

Epigenetic Effects of Addictive Drugs in the Nucleus Accumbens

Substance use induces long-lasting behavioral changes and drug craving. Increasing evidence suggests that epigenetic gene regulation contributes to the development and expression of these long-lasting behavioral alterations. Here we systematically review extensive evidence from rodent models of drug-induced changes in epigenetic regulation and epigenetic regulator proteins. We focus on histone acetylation and histone methylation in a brain region important for drug-related behaviors: the nucleus accumbens. We also discuss how experimentally altering these epigenetic regulators via systemically administered compounds or nucleus accumbens-specific manipulations demonstrate the importance of these proteins in the behavioral effects of drugs and suggest potential therapeutic value to treat people with substance use disorder. Finally, we discuss limitations and future directions for the field of epigenetic studies in the behavioral effects of addictive drugs and suggest how to use these insights to develop efficacious treatments.

Targeted epigenomic editing ameliorates adult anxiety and excessive drinking after adolescent alcohol exposure

Adolescent binge drinking is a major risk factor for psychiatric disorders later in life including alcohol use disorder. Adolescent alcohol exposure induces epigenetic reprogramming at the enhancer region of the activity-regulated cytoskeleton-associated protein (Arc) immediate-early gene, known as synaptic activity response element (SARE), and decreases Arc expression in the amygdala of both rodents and humans. The causal role of amygdalar epigenomic regulation at Arc SARE in adult anxiety and drinking after adolescent alcohol exposure is unknown. Here, we show that dCas9-P300 increases histone acetylation at the Arc SARE and normalizes deficits in Arc expression, leading to attenuation of adult anxiety and excessive alcohol drinking in a rat model of adolescent alcohol exposure. Conversely, dCas9-KRAB increases repressive histone methylation at the Arc SARE, decreases Arc expression, and produces anxiety and alcohol drinking in control rats. These results demonstrate that epigenomic editing in the amygdala can ameliorate adult psychopathology after adolescent alcohol exposure.

Supplementation with sodium butyrate protects against antibiotic-induced increases in ethanol consumption behavior in mice

BACKGROUND

We have recently reported that oral treatment of adult male C57BL/6J mice with a non-absorbable antibiotic cocktail resulted in an increase in ethanol intake and in significant reductions in butyrate-producing gut microbiota populations. This work led us to hypothesize that reduction in butyrate levels within the gut is linked to antibiotic-induced increases in voluntary ethanol consumption.

OBJECTIVE

This study tested whether ad libitum sodium butyrate supplementation can prevent antibiotic-induced ethanol consumption in mice.

METHODS

Sodium butyrate was provided to adult male C57BL/6J mice in drinking water alone or in combination with antibiotic cocktail. Effects on ethanol (20%) intake were measured using drinking in the dark and modified 2-bottle choice paradigms. Body parameters, food and liquid intake, cecum, and adipose tissues were measured during and/or at the conclusion of the drinking in the dark study. Cecal 16s rRNA was analyzed for microbiota diversity and changes in specific bacterial phyla/species.

RESULTS

In drinking in the dark, sodium butyrate supplementation prevented antibiotic-induced increases in ethanol intake without altering basal ethanol consumption. Furthermore, sodium butyrate supplementation lowered ethanol preference in the 2-bottle choice study. Ethanol intake was correlated to specific bacterial phyla/species. Sodium butyrate did not affect the changes in microbiota diversity and composition induced by antibiotic cocktail.

CONCLUSIONS

The findings support a role of gut microbiota-derived butyrate in regulating alcohol-induced behaviors. Additionally, the work contributes to efforts in development of novel microbiome-based strategies as novel preventative and intervention-based therapeutics to address alcohol use disorder.

The role of alcohol intake in the pharmacogenetics of treatment with clozapine

Clozapine (CLZ) is an atypical antipsychotic reserved for patients with refractory psychosis, but it is associated with a significant risk of severe adverse reactions (ADRs) that are potentiated with the concomitant use of alcohol. Additionally, pharmacogenetic studies have explored the influence of several genetic variants in CYP450, receptors and transporters involved in the interindividual response to CLZ. Herein, we systematically review the current multiomics knowledge behind the interaction between CLZ and alcohol intake, and how its concomitant use might modulate the pharmacogenetics. CYP1A2*1F, *1C and other alleles not yet discovered could support a precision medicine approach for better therapeutic effects and fewer CLZ ADRs. CLZ monitoring systems should be amended and include alcohol intake to protect patients from severe CLZ ADRs.

Epigenetic modification in alcohol use disorder and alcoholic cardiomyopathy: From pathophysiology to therapeutic opportunities

Alcohol consumption prompts detrimental psychological, pathophysiological and health issues, representing one of the major causes of death worldwide. Alcohol use disorder (AUD), which is characterized by compulsive alcohol intake and loss of control over alcohol usage, arises from a complex interplay between genetic and environmental factors. More importantly, long-term abuse of alcohol is often tied with unfavorable cardiac remodeling and contractile alterations, a cadre of cardiac responses collectively known as alcoholic cardiomyopathy (ACM). Recent evidence has denoted a pivotal role for ethanol-triggered epigenetic modifications, the interface between genome and environmental cues, in the organismal and cellular responses to ethanol exposure. To-date, three major epigenetic mechanisms (DNA methylation, histone modifications, and RNA-based mechanisms) have been identified for the onset and development of AUD and ACM. Importantly, these epigenetic changes induced by alcohol may be detectable in the blood, thus offering diagnostic, therapeutic, and prognostic promises of epigenetic markers for AUD and alcoholic complications. In addition, several epigenetic drugs have shown efficacies in the management of alcohol abuse, loss of control for alcohol usage, relapse, drinking-related anxiety and behavior in withdrawal. In this context, medications targeting epigenetic modifications may hold promises for pharmaceutical management of AUD and ACM.

Targeting Epigenetic Mechanisms to Treat Alcohol Use Disorders (AUD)

BACKGROUND

The impact of abusive alcohol consumption on human health is remarkable. According to the World Health Organization (WHO), approximately 3.3 million people die annually because of harmful alcohol consumption (the figure represents around 5.9% of global deaths). Alcohol Use Disorder (AUD) is a chronic disease where individuals exhibit compulsive alcohol drinking and present negative emotional states when they do not drink. In the most severe manifestations of AUD, the individuals lose control over intake despite a decided will to stop drinking. Given the multiple faces and the specific forms of this disease, the term AUD often appears in the plural (AUDs). Since only a few approved pharmacological treatments are available to treat AUD and they do not apply to all individuals or AUD forms, the search for compounds that may help to eliminate the burden of the disease and complement other therapeutical approaches is necessary.

METHODS

This work reviews recent research focused on the involvement of epigenetic mechanisms in the pathophysiology of AUD. Excessive drinking leads to chronic and compulsive consumption that eventually damages the organism. The central nervous system is a key target and is the focus of this study. The search for the genetic and epigenetic mechanisms behind the intricated dysregulation induced by ethanol will aid researchers in establishing new therapy approaches.

CONCLUSION

Recent findings in the field of epigenetics are essential and offer new windows for observation and research. The study of small molecules that inhibit key epienzymes involved in nucleosome architecture dynamics is necessary in order to prove their action and specificity in the laboratory and to test their effectivity and safety in clinical trials with selected patients bearing defined alterations caused by ethanol.

The Gut Microbiome and Substance Use Disorder

Substance use disorders (SUDs) remain a significant public health challenge, affecting tens of millions of individuals worldwide each year. Often comorbid with other psychiatric disorders, SUD can be poly-drug and involve several different substances including cocaine, opiates, nicotine, and alcohol. SUD has a strong genetic component. Much of SUD research has focused on the neurologic and genetic facets of consumption behavior. There is now interest in the role of the gut microbiome in the pathogenesis of SUD. In this review, we summarize current animal and clinical evidence that the gut microbiome is involved in SUD, then address the underlying mechanisms by which the gut microbiome interacts with SUD through metabolomic, immune, neurological, and epigenetic mechanisms. Lastly, we discuss methods using various inbred and outbred mice models to gain an integrative understanding of the microbiome and host genetic controls in SUD.

Effect of histone acetylation on maintenance and reinstatement of morphine-induced conditioned place preference and ΔFosB expression in the nucleus accumbens and prefrontal cortex of male rats

Recently, epigenetic mechanisms are considered as the new potential targets for addiction treatment. This research was designed to explore the effect of histone acetylation on ΔFosB gene expression in morphine-induced conditioned place preference (CPP) in male rats. CPP was induced via morphine injection (5 mg/kg) for three consecutive days. Animals received low-dose theophylline (LDT) or Suberoylanilide Hydroxamic acid (SAHA), as an histone deacetylase (HDAC) activator or inhibitor, respectively, and a combination of both in subsequent extinction days. Following extinction, a priming dose of morphine (1 mg/kg) was administered to induce reinstatement. H4 acetylation and ΔFosB expression in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) were assessed on the last day of extinction and the following CPP reinstatement. Our results demonstrated that daily administration of SAHA (25 mg/kg; i.p.), facilitated morphine-extinction and decreased CPP score in reinstatement of place preference. Conversely, injections of LDT (20 mg/kg; i.p.) prolonged extinction in animals. Co-administration of LDT and SAHA on extinction days counterbalanced each other, such that maintenance and reinstatement were no different than the control group. The gene expression of ΔFosB was increased by SAHA in NAc and mPFC compared to the control group. Administration of SAHA during extinction days, also altered histone acetylation in the NAc and mPFC on the last day of extinction, but not on reinstatement day. Collectively, administration of SAHA facilitated extinction and reduced reinstatement of morphine-induced CPP in rats. This study confirms the essential role of epigenetic mechanisms, specifically histone acetylation, in regulating drug-induced plasticity and seeking behaviors.

Sugar, a powerful substitute for ethanol in ethanol postdependent rats: Relevance for clinical consideration?

Sugar has been shown to be a powerful substitute for drugs in preclinical studies on addiction. However, the link between sugar intake and alcohol use disorder (AUD) is poorly understood. We assessed the influence of sucrose on ethanol drinking in both nondependent (ND) and dependent (D) Long-Evans rats during acute withdrawal using the postdependent state model. Ethanol (10%-40%) and sucrose (1%-4%) solutions were offered in an operant paradigm either independently or concurrently under ratio schedules of reinforcement. We showed that D rats displayed an enhanced motivation for both 10% ethanol solution (10E) and 4% sucrose solution (4S) as compared with ND rats, and a clear preference for 4S was observed in both groups. During acute withdrawal, D rats showed a strong motivation for 30% ethanol (30E), even when adulterated with quinine, but still preferred 4S despite the fact that a high level of negative reinforcement could be expected. However, when a premix solution (30E4S) was offered concurrently with 4S, the preference for 4S was lost in D animals, which consumed as much premix as 4S, whereas ND animals displayed preference for 4S. Altogether, those results suggest that reinforcing properties of sucrose surpass those of ethanol in D rats under acute withdrawal, which indicates that sugar is a powerful substitute for ethanol. Our results suggest that craving for sugar may be increased in AUD patients during withdrawal and raise the issue of dependence transfer from alcohol to sugar.

Interstrain differences in voluntary binge-like drinking behavior and in two acute ethanol injections-induced synaptic plasticity deficits in rats

Propensity to drink alcohol and to initiate binge drinking behavior is driven by genetic factors. Recently, we proposed an original animal model useful in the study of voluntary binge-like drinking (BD) in outbred Long-Evans rats by combining intermittent access to 20% ethanol in a two-bottle choice (IA2BC) paradigm to 15-min daily sessions of 20% ethanol operant self-administration. We sought to compare three strains of outbred rats (Long-Evans, Sprague-Dawley, and Wistar) in our BD model. Because we found different propensity to BD between strains, we also sought to test interstrain differences using another procedure of two acute ethanol exposures known to alter long-term depression of hippocampal synaptic plasticity. Our results demonstrate that in both IA2BC and operant procedures, the Long-Evans strain consumed the highest, Wistar the lowest amount of ethanol, and the Sprague-Dawley was intermediate. Long-Evans rats were also the fastest consuming with the shortest time to reach 50% of their maximum consumption in 15 min. When we tested the acute effects of ethanol, long-term depression in hippocampus was abolished specifically in Long-Evans rats with no impact in the two other strains. Thus, our study reveals that the Long-Evans strain is the ideal strain in our recently developed animal model useful in the study of BD. In addition, with the other paradigm of forced acute ethanol exposure, the Long-Evans strain displayed an increase in sensitivity to the deleterious effect of BD on hippocampal synaptic plasticity. Further studies are needed in order to investigate why Long-Evans rats are more prone to BD.

Exposure to Running Wheels Prevents Ethanol Rewarding Effects: The Role of CREB and Deacetylases SIRT-1 and SIRT-2 in the Nucleus Accumbens and Prefrontal Cortex

Alcohol use disorder is one of the most prevalent addictions, strongly influenced by environmental factors. Voluntary physical activity (VPA) has proven to be intrinsically reinforcing and we hypothesized that, as a non-drug reinforcer, VPA could mitigate ethanol-induced rewarding effects. The transcriptional factor cAMP response element binding protein (CREB), and deacetylases isozymes sirtuins 1 and 2 (SIRT-1 and SIRT-2) have a complex interplay and both play a role in the rewarding effects of ethanol. To test whether the exposure of mice to running wheels inhibits the development of ethanol-induced conditioned place preference (CPP), mice were assigned into four groups: housed in home cages with locked ("Sedentary") or unlocked running wheels (VPA), and treated with saline or 1.8 g/kg ethanol during the conditioning phase. The groups were referred as Saline-Sedentary, Saline-VPA, Ethanol-Sedentary and Ethanol-VPA. The expression of CREB, SIRT-1 and SIRT-2 were evaluated in the prefrontal cortex (PFC) and nucleus accumbens (NAc). VPA prevented the development of ethanol-induced CPP. VPA, ethanol and the combination of both inhibited pCREB and pCREB/CREB ratio in the NAc, suggesting that both reward stimuli can share similar patterns of CREB activation. However, we have found that ethanol-induced increased CREB levels were prevented by VPA. Both VPA groups presented lower SIRT-1 levels in the NAc compared to the Sedentary groups. Thus, exposure to running wheels prevented ethanol-rewarding effects and ethanol-induced increases in CREB in the NAc. The molecular alterations underlying CPP prevention may be related to a lower expression of CREB in the NAc of Ethanol-VPA compared to the respective Sedentary group, given the positive correlation between CPP and CREB levels in the Ethanol-Sedentary group.

Evidence for Modulation of Substance Use Disorders by the Gut Microbiome: Hidden in Plain Sight

The gut microbiome modulates neurochemical function and behavior and has been implicated in numerous central nervous system (CNS) diseases, including developmental, neurodegenerative, and psychiatric disorders. Substance use disorders (SUDs) remain a serious threat to the public well-being, yet gut microbiome involvement in drug abuse has received very little attention. Studies of the mechanisms underlying SUDs have naturally focused on CNS reward circuits. However, a significant body of research has accumulated over the past decade that has unwittingly provided strong support for gut microbiome participation in drug reward. β-Lactam antibiotics have been employed to increase glutamate transporter expression to reverse relapse-induced release of glutamate. Sodium butyrate has been used as a histone deacetylase inhibitor to prevent drug-induced epigenetic alterations. High-fat diets have been used to alter drug reward because of the extensive overlap of the circuitry mediating them. This review article casts these approaches in a different light and makes a compelling case for gut microbiome modulation of SUDs. Few factors alter the structure and composition of the gut microbiome more than antibiotics and a high-fat diet, and butyrate is an endogenous product of bacterial fermentation. Drugs such as cocaine, alcohol, opiates, and psychostimulants also modify the gut microbiome. Therefore, their effects must be viewed on a complex background of cotreatment-induced dysbiosis. Consideration of the gut microbiome in SUDs should have the beneficial effects of expanding the understanding of SUDs and aiding in the design of new therapies based on opposing the effects of abused drugs on the host's commensal bacterial community. SIGNIFICANCE STATEMENT: Proposed mechanisms underlying substance use disorders fail to acknowledge the impact of drugs of abuse on the gut microbiome. β-Lactam antibiotics, sodium butyrate, and high-fat diets are used to modify drug seeking and reward, overlooking the notable capacity of these treatments to alter the gut microbiome. This review aims to stimulate research on substance abuse-gut microbiome interactions by illustrating how drugs of abuse share with antibiotics, sodium butyrate, and fat-laden diets the ability to modify the host microbial community.

Is R(+)-Baclofen the best option for the future of Baclofen in alcohol dependence pharmacotherapy? Insights from the preclinical side

For several decades, studies conducted to evaluate the efficacy of RS(±)-Baclofen in the treatment of alcohol dependence yielded contrasting results. Human and animal studies recently questioned the use of the racemic drug in patients since a potential important role of the different enantiomers has been revealed with an efficacy thought to reside with the active R(+)-enantiomer. Here we conducted experiments in the postdependent rat model of alcohol dependence to compare the efficacy of R(+)-Baclofen or S(-)-Baclofen to that of RS(±)-Baclofen on ethanol intake, seeking, and relapse. R(+)-Baclofen was more effective than RS(±)-Baclofen in reducing ethanol intake and seeking during acute withdrawal and during relapse after abstinence. We also used an original population approach in order to identify drug responders. We found a significant proportion of responders to S(-)-Baclofen and RS(±)-Baclofen, displaying an increase in ethanol intake, and this increasing effect on alcohol intake was not seen in the R(+)-Baclofen group. At an intermediate dose of R(+)-Baclofen, devoid of any motor side effects, we identified a very large proportion of responders (75%) with a large decrease in ethanol intake (90% decrease). Finally, the response to RS(±)-Baclofen on ethanol intake was correlated to plasma level of Baclofen. R(+)-Baclofen and RS(±)-Baclofen were effective in reducing sucrose intake. Our study has important clinical implication since it suggests that the wide variability in the therapeutic responses of patients to RS(±)-Baclofen may come from the sensitivity to the R(+)-Baclofen but also to the one of the S(-)-Baclofen that can promote an increase in ethanol intake.

Gut Microbiota at the Intersection of Alcohol, Brain, and the Liver

Over the last decade, increased research into the cognizance of the gut-liver-brain axis in medicine has yielded powerful evidence suggesting a strong association between alcoholic liver diseases (ALD) and the brain, including hepatic encephalopathy or other similar brain disorders. In the gut-brain axis, chronic, alcohol-drinking-induced, low-grade systemic inflammation is suggested to be the main pathophysiology of cognitive dysfunctions in patients with ALD. However, the role of gut microbiota and its metabolites have remained unclear. Eubiosis of the gut microbiome is crucial as dysbiosis between autochthonous bacteria and pathobionts leads to intestinal insult, liver injury, and neuroinflammation. Restoring dysbiosis using modulating factors such as alcohol abstinence, promoting commensal bacterial abundance, maintaining short-chain fatty acids in the gut, or vagus nerve stimulation could be beneficial in alleviating disease progression. In this review, we summarize the pathogenic mechanisms linked with the gut-liver-brain axis in the development and progression of brain disorders associated with ALD in both experimental models and humans. Further, we discuss the therapeutic potential and future research directions as they relate to the gut-liver-brain axis.

Early Life Stress- and Drug-Induced Histone Modifications Within the Ventral Tegmental Area

Psychiatric illnesses are a major public health concern due to their prevalence and heterogeneity of symptom presentation resulting from a lack of efficacious treatments. Although dysregulated dopamine (DA) signaling has been observed in a myriad of psychiatric conditions, different pathophysiological mechanisms have been implicated which impede the development of adequate treatments that work across all patient populations. The ventral tegmental area (VTA), a major source of DA neurons in the brain reward pathway, has been shown to have altered activity that contributes to reward dysregulation in mental illnesses and drug addiction. It has now become better appreciated that epigenetic mechanisms contribute to VTA DA dysfunction, such as through histone modifications, which dynamically regulate transcription rates of critical genes important in synaptic plasticity underlying learning and memory. Here, we provide a focused review on differential histone modifications within the VTA observed in both humans and animal models, as well as their relevance to disease-based phenotypes, specifically focusing on epigenetic dysregulation of histones in the VTA associated with early life stress (ELS) and drugs of abuse. Locus- and cell-type-specific targeting of individual histone modifications at specific genes within the VTA presents novel therapeutic targets which can result in greater efficacy and better long-term health outcomes in susceptible individuals that are at increased risk for substance use and psychiatric disorders.

Memory and plasticity impairment after binge drinking in adolescent rat hippocampus: GluN2A/GluN2B NMDA receptor subunits imbalance through HDAC2

Ethanol (EtOH) induces cognitive impairment through modulation of synaptic plasticity notably in the hippocampus. The cellular mechanism(s) of these EtOH effects may range from synaptic signaling modulation to alterations of the epigenome. Previously, we reported that two binge-like exposures to EtOH (3 g/kg, ip, 9 h apart) in adolescent rats abolished long-term synaptic depression (LTD) in hippocampus slices, induced learning deficits, and increased N-methyl-d-aspartate (NMDA) receptor signaling through its GluN2B subunit after 48 hours. Here, we tested the hypothesis of EtOH-induced epigenetic alterations leading to modulation of GluN2B and GluN2A NMDA receptor subunits. Forty-two days old rats were treated with EtOH or the histone deacetylase inhibitor (HDACi) sodium butyrate (NaB, 600 mg/kg, ip) injected alone or 30 minutes before EtOH. After 48 hours, learning was tested with novel object recognition while synaptic plasticity and the role of GluN2A and GluN2B subunits in NMDA-fEPSP were measured in CA1 field of hippocampus slices. LTD and memory were impaired 48 hours after EtOH and NMDA-fEPSP analysis unraveled changes in the GluN2A/GluN2B balance. These results were associated with an increase in histone deacetylase (HDAC) activity and HDAC2 mRNA and protein while Ac-H4K12 labelling was decreased. EtOH increases expression of HDAC2 and mRNA level for GluN2B subunit (but not GluN2A), while HDAC2 modulates the promoter of the gene encoding GluN2B. Interestingly, NaB pretreatment prevented all the cellular and memory-impairing effects of EtOH. In conclusion, the memory-impairing effects of two binge-like EtOH exposure involve NMDA receptor-dependent LTD deficits due to a GluN2A/GluN2B imbalance resulting from changes in GluN2B expression induced by HDAC2.

Chronic Chemogenetic Stimulation of the Nucleus Accumbens Produces Lasting Reductions in Binge Drinking and Ameliorates Alcohol-Related Morphological and Transcriptional Changes

Binge drinking is a dangerous pattern of behavior. We tested whether chronically manipulating nucleus accumbens (NAc) activity (via clozapine-N-oxide (CNO) and Designer Receptors Exclusively Activated by Designer Drugs (DREADD)) could produce lasting effects on ethanol binge-like drinking in mice selectively bred to drink to intoxication. We found chronically increasing NAc activity (4 weeks, via CNO and the excitatory DREADD, hM3Dq) decreased binge-like drinking, but did not observe CNO-induced changes in drinking with the inhibitory DREADD, hM4Di. The CNO/hM3Dq-induced reduction in ethanol drinking persisted for at least one week, suggesting adaptive neuroplasticity via transcriptional and epigenetic mechanisms. Therefore, we defined this plasticity at the morphological and transcriptomic levels. We found that chronic binge drinking (6 weeks) altered neuronal morphology in the NAc, an effect that was ameliorated with CNO/hM3Dq. Moreover, we detected significant changes in expression of several plasticity-related genes with binge drinking that were ameliorated with CNO treatment (e.g., Hdac4). Lastly, we found that LMK235, an HDAC4/5 inhibitor, reduced binge-like drinking. Thus, we were able to target specific molecular pathways using pharmacology to mimic the behavioral effects of DREADDs.

Alcohol Intoxication and Cognition: Implications on Mechanisms and Therapeutic Strategies

Binge alcohol drinking is highly prevalent in young adults and results in 30% deaths per year in young males. Binge alcohol drinking or acute alcohol intoxication is a risk factor for developing alcohol use disorder (AUD). Three FDA approved drugs are currently in use as therapy for AUD; however, all of them have contra-indications and limitations. Structural brain imaging studies in alcoholics have shown defects in the brain regions involved in memory, cognition and emotional processing. Positron emission tomography (PET) using radiotracers (e.g., 18FDG) and measuring brain glucose metabolism have demonstrated diagnostic and prognostic utility in evaluating patients with cognitive impairment. Using PET imaging, only a few exclusive human studies have addressed the relationship between alcohol intoxication and cognition. Those studies indicate that alcohol intoxication causes reduction in brain activity. Consistent with prior findings, a recent study by us showed that acute alcohol intoxication reduced brain activity in the cortical and subcortical regions including the temporal lobe consisting the hippocampus. Additionally, we have observed a strong correlation between reduction in metabolic activity and spatial cognition impairment in the hippocampus after binge alcohol exposure. We have also demonstrated the involvement of a stress response protein, cold inducible RNA binding protein (CIRP), as a potential mechanistic mediator in acute alcohol intoxication. In this review, we will first discuss in detail prior human PET imaging studies on alcohol intoxication as well as our recent study on acute alcohol intoxication, and review the existing literature on potential mechanisms of acute alcohol intoxication-induced cognitive impairment and therapeutic strategies to mitigate these impairments. Finally, we will highlight the importance of studying brain regions as part of a brain network in delineating the mechanism of acute alcohol intoxication-induced cognitive impairment to aid in the development of therapeutics for such indication.

Epigenetic pharmacotherapy for substance use disorder

Identifying novel therapeutics for the treatment of substance use disorder (SUD) is an area of intensive investigation. Prior strategies that have attempted to modify one or a few neurotransmitter receptors have had limited success, and currently there are no FDA-approved medications for the treatment of cocaine, methamphetamine, and marijuana use disorders. Because drugs of abuse are known to alter the expression of numerous genes in reward-related brain regions, epigenetic-based therapies have emerged as intriguing targets for therapeutic innovation. Here, I evaluate potential therapeutic approaches and challenges in targeting epigenetic factors for the treatment of SUD and highlight examples of promising strategies and future directions.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) alleviates depression-like behavior and normalizes epigenetic changes in the hippocampus during ethanol withdrawal

Withdrawal from chronic alcohol drinking can cause depression, leading to an inability to function in daily life and an increased risk for relapse to harmful drinking. Understanding the causes of alcohol withdrawal-related depression may lead to new therapeutic targets for treatment. Epigenetic factors have recently emerged as important contributors to both depression and alcohol use disorder (AUD). Specifically, acetylation of the N-terminal tails of histone proteins that package DNA into nucleosomes is altered in stress-induced models of depression and during alcohol withdrawal. The goal of this study was to examine depression-like behavior during alcohol withdrawal and associated changes in histone acetylation and expression of histone deacetylase 2 (HDAC2) in the hippocampus, a brain region critical for mood regulation and depression. Male Sprague-Dawley rats were treated with the Lieber-DeCarli ethanol liquid diet for 15 days and then underwent withdrawal. Rats were treated with the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA), during withdrawal and were tested for depression-like behavior. In a separate group of rats, the hippocampus was analyzed for mRNA and protein expression of HDAC2 and levels of histone H3 lysine 9 acetylation (H3K9ac) during chronic ethanol exposure and withdrawal. Rats undergoing ethanol withdrawal exhibited depression-like behavior and had increased HDAC2 and decreased H3K9ac levels in specific structures of the hippocampus. Treatment with SAHA during withdrawal ameliorated depression-like behavior and normalized changes in hippocampal HDAC2 and H3K9ac levels. These results demonstrate that ethanol withdrawal causes an altered epigenetic state in the hippocampus. Treatment with an HDAC inhibitor can correct this state and alleviate depression-like symptoms developed during withdrawal. Targeting histone acetylation may be a novel strategy to reduce ethanol withdrawal-induced depression.

The effects of histone deacetylase inhibitors on the attentional set-shifting task performance of alcohol-dependent rats

OBJECTIVES

Alcohol dependence causes extensive damage to the central nervous system, resulting in impaired brain structure and behavioral changes. Moreover, histone deacetylase (HDAC) inhibitors restrain the activity of HDAC and cause increased histone acetylation, which may be related to alcohol dependence.

METHODS

Ethanol dependence was modelled in animals by persistent alcohol exposure and tested in the conditioned place preference (CPP) paradigm. To induce CPP, the alcohol-treated rats were given orally gradient concentration (3%, 6%, and 9% v/v) alcohol administration for 20 consecutive days. The sodium butyrate (NaB)-treated rats were injected daily. Cognitive flexibility was evaluated using an attentional set-shifting task (ASST) in which the rats performed a series of seven consecutive discriminations after the final CPP paradigm.

RESULTS

Ethanol administration induced alcohol dependence behaviors, with more time spent in the ethanol-paired compartment. Compared with the CPP scores of the control group, the scores of the ethanol- and NaB-treated groups were significantly higher. In the ASST, alcohol-treated rats had significantly increased number of trials to reach criteria (TTC) in most phases, higher error rate, and lower cognitive levels compared to the control group. Moreover, the present findings demonstrated that NaB combined with ethanol caused cognitive deficits as the result of an increased number of TTC during the ASST.

CONCLUSIONS

The attentional/cognitive flexibility of the prefrontal cortex of alcohol-dependent rats was damaged and the NaB administration procedure itself did not produce cognitive deficits, but instead exacerbated cognitive impairment in alcohol-dependent rats.

Effects of a histone deacetylase 3 inhibitor on extinction and reinstatement of cocaine self-administration in rats

RATIONALE

A challenge in treating substance use disorder is that successful treatment often does not persist, resulting in relapse and continued drug seeking. One approach to persistently weaken drug-seeking behaviors is to pair exposure to drug-associated cues or behaviors with delivery of a compound that may strengthen the inhibition of the association between drug cues and behavior.

OBJECTIVES

We evaluated whether a selective histone deacetylase 3 (HDAC3) inhibitor could promote extinction and weaken contextual control of operant drug seeking after intravenous cocaine self-administration.

METHODS

Male Long-Evans rats received a systemic injection of the HDAC3 inhibitor RGFP966 either before or immediately after the first extinction session. Persistence of extinction was tested over subsequent extinction sessions, as well as tests of reinstatement that included cue-induced reinstatement, contextual renewal, and cocaine-primed reinstatement. Additional extinction sessions occurred between each reinstatement test. We also evaluated effects of RGFP966 on performance and motivation during stable fixed ratio operant responding for cocaine and during a progressive ratio of reinforcement.

RESULTS

RGFP966 administered before the first extinction session led to significantly less responding during subsequent extinction and reinstatement tests compared to vehicle-injected rats. Follow-up studies found that these effects were not likely due to a performance deficit or a change in motivation to self-administer cocaine, as injections of RGFP966 had no effect on stable responding during a fixed or progressive ratio schedule. In addition, RGFP966 administered just after the first extinction session had no effect during early extinction and reinstatement tests, but weakened long-term responding during later extinction sessions.

CONCLUSIONS

These results suggest that a systemic injection of a selective HDAC3 inhibitor can enhance extinction and suppress reinstatement after cocaine self-administration. The finding that behavioral and pharmacological manipulations can be combined to decrease drug seeking provides further potential for treatment by epigenetic modulation.

It is a complex issue: emerging connections between epigenetic regulators in drug addiction

Drug use leads to addiction in some individuals, but the underlying brain mechanisms that control the transition from casual drug use to an intractable substance use disorder (SUD) are not well understood. Gene x environment interactions such as the frequency of drug use and the type of substance used likely to promote maladaptive plastic changes in brain regions that are critical for controlling addiction-related behavior. Epigenetics encompasses a broad spectrum of mechanisms important for regulating gene transcription that are not dependent on changes in DNA base pair sequences. This review focuses on the proteins and complexes contributing to epigenetic modifications in the nucleus accumbens (NAc) following drug experience. We discuss in detail the three major mechanisms: histone acetylation and deacetylation, histone methylation, and DNA methylation. We discuss how drug use alters the regulation of the associated proteins regulating these processes and highlight how experimental manipulations of these proteins in the NAc can alter drug-related behaviors. Finally, we discuss the ways that histone modifications and DNA methylation coordinate actions by recruiting large epigenetic enzyme complexes to aid in transcriptional repression. Targeting these multiprotein epigenetic enzyme complexes - and the individual proteins that comprise them - might lead to effective therapeutics to reverse or treat SUDs in patients.

Histone Deacetylase Inhibitor Suberanilohydroxamic Acid Treatment Reverses Hyposensitivity to γ-Aminobutyric Acid in the Ventral Tegmental Area During Ethanol Withdrawal

Background

The ventral tegmental area (VTA) is important for alcohol‐related reward and reinforcement. Mouse VTA neurons are hyposensitive to γ‐aminobutyric acid (GABA) during ethanol (EtOH) withdrawal, and GABA responsiveness is normalized by in vitro treatment with histone deacetylase inhibitors (HDACi). The present study examined the effect of a systemically administered HDACi, suberanilohydroxamic acid (SAHA) on GABA sensitivity, and related molecular changes in VTA neurons during withdrawal after chronic EtOH intake in rats.

Methods

Sprague Dawley male adult rats were fed with Lieber‐DeCarli diet (9% EtOH or control diet) for 16 days. Experimental groups included control diet‐fed and EtOH diet‐fed (0‐ or 24‐hour withdrawal) rats treated with either SAHA or vehicle injection. Single‐unit recordings were used to measure the response of VTA neurons to GABA. Immunohistochemistry was performed to examine levels of HDAC2, acetylated histone H3 lysine 9 (acH3K9), and GABA_A receptor α1 and α5 subunits in the VTA; quantitative polymerase chain reaction was performed to examine the mRNA levels of HDAC2 and GABA_A receptor subunits.

Results

VTA neurons from the withdrawal group exhibited GABA hyposensitivity. In vivo SAHA treatment 2 hours before sacrifice normalized the sensitivity of VTA neurons to GABA. EtOH withdrawal was associated with increased HDAC2 and decreased acH3K9 protein levels; SAHA treatment normalized acH3K9 levels. Interestingly, no significant change was observed in the mRNA levels of HDAC2. The mRNA levels, but not protein levels, of GABA_A receptor α1 and α5 subunits were increased during withdrawal.

Conclusions

Withdrawal from chronic EtOH exposure results in a decrease in GABA‐mediated inhibition, and this GABA hyposensitivity is normalized by in vivo SAHA treatment. Disruption of signaling in the VTA produced by alteration of GABA neurotransmission could be 1 neuroadaptive physiological process leading to craving and relapse. These results suggest that HDACi pharmacotherapy with agents like SAHA might be an effective treatment for alcoholism.

Role of Dorsal Striatum Histone Deacetylase 5 in Incubation of Methamphetamine Craving

BACKGROUND

Methamphetamine (meth) seeking progressively increases after withdrawal (incubation of meth craving). We previously demonstrated an association between histone deacetylase 5 (HDAC5) gene expression in the rat dorsal striatum and incubation of meth craving. Here we used viral constructs to study the causal role of dorsal striatum HDAC5 in this incubation.

METHODS

In experiment 1 (overexpression), we injected an adeno-associated virus bilaterally into dorsal striatum to express either green fluorescent protein (control) or a mutant form of HDAC5, which strongly localized to the nucleus. After training rats to self-administer meth (10 days, 9 hours/day), we tested the rats for relapse to meth seeking on withdrawal days 2 and 30. In experiment 2 (knockdown), we injected an adeno-associated virus bilaterally into the dorsal striatum to express a short hairpin RNA either against luciferase (control) or against HDAC5. After training rats to self-administer meth, we tested the rats for relapse on withdrawal days 2 and 30. We also measured gene expression of other HDACs and potential HDAC5 downstream targets.

RESULTS

We found that HDAC5 overexpression in dorsal striatum increased meth seeking on withdrawal day 30 but not day 2. In contrast, HDAC5 knockdown in the dorsal striatum decreased meth seeking on withdrawal day 30 but not on day 2; this manipulation also altered other HDACs (Hdac1 and Hdac4) and potential HDAC5 targets (Gnb4 and Suv39h1).

CONCLUSIONS

Results demonstrate a novel role of dorsal striatum HDAC5 in incubation of meth craving. These findings also set up future work to identify HDAC5 targets that mediate this incubation.

Histone deacetylases mediate GABAA receptor expression, physiology, and behavioral maladaptations in rat models of alcohol dependence

Alcohol use disorders are chronic debilitating diseases characterized by severe withdrawal symptoms that contribute to morbidity and relapse. GABA_A receptor (GABA_AR) adaptations have long been implicated in the chronic effects of alcohol and contribute to many withdrawal symptoms associated with alcohol dependence. In rodents, GABA_AR hypofunction results from decreases in Gabra1 expression, although the underlying mechanism controlling Gabra1 expression after chronic ethanol exposure is still unknown. We found that chronic ethanol exposure using either ethanol gavage or two-bottle choice voluntary access paradigms decreased Gabra1 expression and increased Hdac2 and Hdac3 expression. Administration of the HDAC inhibitor trichostatin A (TSA) after chronic ethanol exposure prevents the decrease in Gabra1 expression and function as well as the increase in Hdac2 and Hdac3 expression in both the cortex and the medial prefrontal cortex (mPFC). Chronic ethanol exposure and withdrawal, but not acute ethanol exposure or acute withdrawal, cause a selective upregulation of HDAC2 and HDAC3 associated with the Gabra1 promoter that accompanies a decrease in H3 acetylation of the Gabra1 promoter and the reduction in GABA_AR α1 subunit expression. TSA administration prevented each of these molecular events as well as behavioral manifestations of ethanol dependence, including tolerance to zolpidem-induced loss of righting reflex, reduced open-arm time in the elevated plus maze, reduced center-time and locomotor activity in the open-field assay, and TSA reduced voluntary ethanol consumption. The results show how chronic ethanol exposure regulates the highly prominent GABA_AR α1 subunit by an epigenetic mechanism that represents a potential treatment modality for alcohol dependence.

Ethanol actions on the ventral tegmental area: novel potential targets on reward pathway neurons

The ventral tegmental area (VTA) evaluates salience of environmental stimuli and provides dopaminergic innervation to many brain areas affected by acute and chronic ethanol exposure. While primarily associated with rewarding and reinforcing stimuli, recent evidence indicates a role for the VTA in aversion as well. Ethanol actions in the VTA may trigger neuroadaptation resulting in reduction of the aversive responses to alcohol and a relative increase in the rewarding responses. In searching for effective pharmacotherapies for the treatment of alcohol abuse and alcoholism, recognition of this imbalance may reveal novel strategies. In addition to conventional receptor/ion channel pharmacotherapies, epigenetic factors that control neuroadaptation to chronic ethanol treatment can be targeted as an avenue for development of therapeutic approaches to restore the balance. Furthermore, when exploring therapies to address reward/aversion imbalance in the action of alcohol in the VTA, sex differences have to be taken into account to ensure effective treatment for both men and women. These principles apply to a VTA-centric approach to therapies, but should hold true when thinking about the overall approach in the development of neuroactive drugs to treat alcohol use disorders. Although the functions of the VTA itself are complex, it is a useful model system to evaluate the reward/aversion imbalance that occurs with ethanol exposure and could be used to provide new leads in the efforts to develop novel drugs to treat alcoholism.

Interest of new alkylsulfonylhydrazide-type compound in the treatment of alcohol use disorders

RATIONALE

Recent preclinical research suggested that histone deacetylase inhibitors (HDACIs) and specifically class I HDAC selective inhibitors might be useful to treat alcohol use disorders (AUDs).

OBJECTIVE

The objective of this study was to find a new inhibitor of the HDAC-1 isoenzyme and to test its efficacy in an animal model of AUDs.

METHODS

In the present study, we prepared new derivatives bearing sulfonylhydrazide-type zinc-binding group (ZBG) and evaluated these compounds in vitro on HDAC-1 isoenzyme. The most promising compound was tested on ethanol operant self-administration and relapse in rats.

RESULTS

We showed that the alkylsulfonylhydrazide-type compound (ASH) reduced by more than 55% the total amount of ethanol consumed after one intracerebroventricular microinjection, while no effect was observed on motivation of the animals to consume ethanol. In addition, one ASH injection in the central amygdala reduced relapse.

CONCLUSIONS

Our study demonstrated that a new compound designed to target HDAC-1 is effective in reducing ethanol intake and relapse in rats and further confirm the interest of pursuing research to study the exact mechanism by which such inhibitor may be useful to treat AUDs.

Animal models of binge drinking, current challenges to improve face validity

Binge drinking (BD), i.e., consuming a large amount of alcohol in a short period of time, is an increasing public health issue. Though no clear definition has been adopted worldwide the speed of drinking seems to be a keystone of this behavior. Developing relevant animal models of BD is a priority for gaining a better characterization of the neurobiological and psychobiological mechanisms underlying this dangerous and harmful behavior. Until recently, preclinical research on BD has been conducted mostly using forced administration of alcohol, but more recent studies used scheduled access to alcohol, to model more voluntary excessive intakes, and to achieve signs of intoxications that mimic the human behavior. The main challenges for future research are discussed regarding the need of good face validity, construct validity and predictive validity of animal models of BD.

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 x_c^- 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.

Transcriptional Regulators as Targets for Alcohol Pharmacotherapies

Alcohol use disorder (AUD) is a chronic relapsing brain disease that currently afflicts over 15 million adults in the United States. Despite its prevalence, there are only three FDA-approved medications for AUD treatment, all of which show limited efficacy. Because of their ability to alter expression of a large number of genes, often with great cell-type and brain-region specificity, transcription factors and epigenetic modifiers serve as promising new targets for the development of AUD treatments aimed at the neural circuitry that underlies chronic alcohol abuse. In this chapter, we will discuss transcriptional regulators that can be targeted pharmacologically and have shown some efficacy in attenuating alcohol consumption when targeted. Specifically, the transcription factors cyclic AMP-responsive element binding protein (CREB), peroxisome proliferator-activated receptors (PPARs), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and glucocorticoid receptor (GR), as well as the epigenetic enzymes, the DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), will be discussed.

Alcohol Feeding in Mice Promotes Colonic Hyperpermeability and Changes in Colonic Organoid Stem Cell Fate

BACKGROUND

Alcohol increases intestinal permeability to proinflammatory microbial products that promote liver disease, even after a period of sobriety. We sought to test the hypothesis that alcohol affects intestinal stem cells using an in vivo model and ex vivo organoids generated from jejunum and colon from mice fed chronic alcohol.

METHODS

Mice were fed a control or an alcohol diet. Intestinal permeability, liver steatosis-inflammation, and stool short-chain fatty acids (SCFAs) were measured. Jejunum and colonic organoids and tissue were stained for stem cell, cell lineage, and apical junction markers with assessment of mRNA by PCR and RNA-seq. ChIP-PCR analysis was carried out for Notch1 using an antibody specific for acetylated histone 3.

RESULTS

Alcohol-fed mice exhibited colonic (but not small intestinal) hyperpermeability, steatohepatitis, and decreased butyrate/total SCFA ratio in stool. Stem cell, cell lineage, and apical junction marker staining in tissue or organoids from jejunum tissue were not impacted by alcohol. Only chromogranin A (Chga) was increased in jejunum organoids by qPCR. However, colonic tissue and organoid staining exhibited an alcohol-induced significant decrease in cytokeratin 20+  (Krt20+) absorptive lineage enterocytes, a decrease in occludin and E-cadherin apical junction proteins, an increase in Chga, and an increase in the Lgr5 stem cell marker. qPCR revealed an alcohol-induced decrease in colonic organoid and tissue Notch1, Hes1, and Krt20 and increased Chga, supporting an alteration in stem cell fate due to decreased Notch1 expression. Colonic tissue ChIP-PCR revealed alcohol feeding suppressed Notch1 mRNA expression (via deacetylation of histone H3) and decreased Notch1 tissue staining.

CONCLUSIONS

Data support a model for alcohol-induced colonic hyperpermeability via epigenetic effects on Notch1, and thus Hes1, suppression through a mechanism involving histone H3 deacetylation at the Notch1 locus. This decreased enterocyte and increased enteroendocrine cell colonic stem cell fate and decreased apical junctional proteins leading to hyperpermeability.

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.

Ethanol Exposure Regulates Gabra1 Expression via Histone Deacetylation at the Promoter in Cultured Cortical Neurons

γ-Aminobutyric acid A receptors (GABA_A-Rs) mediate the majority of inhibitory neurotransmission in the adult brain. The α1-containing GABA_A-Rs are the most prominent subtype in the adult brain and are important in both homeostatic function and several disease pathologies including alcohol dependence, epilepsy, and stress. Ethanol exposure causes a decrease of α1 transcription and peptide expression both in vivo and in vitro, but the mechanism that controls the transcriptional regulation is unknown. Because ethanol is known to activate epigenetic regulation of gene expression, we tested the hypothesis that ethanol regulates α1 expression through histone modifications in cerebral cortical cultured neurons. We found that class I histone deacetylases (HDACs) regulate ethanol-induced changes in α1 gene and protein expression as pharmacologic inhibition or knockdown of HDAC1-3 prevents the effects of ethanol exposure. Targeted histone acetylation associated with the Gabra1 promoter using CRISPR (clustered regularly interspaced palindromic repeat) dCas9-P300 (a nuclease-null Cas9 fused with a histone acetyltransferase) increases histone acetylation and prevents the decrease of Gabra1 expression. In contrast, there was no effect of a mutant histone acetyltransferase or generic transcriptional activator or targeting P300 to a distant exon. Conversely, using a dCas9-KRAB construct that increases repressive methylation (H3K9me3) does not interfere with ethanol-induced histone deacetylation. Overall our results indicate that ethanol deacetylates histones associated with the Gabra1 promoter through class I HDACs and that pharmacologic, genetic, or epigenetic intervention prevents decreases in α1 expression in cultured cortical neurons.

[Epigenetic mechanisms and alcohol use disorders: a potential therapeutic target]

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.

Epigenetic mechanisms of alcoholism and stress-related disorders

Stress-related disorders, such as anxiety, early life stress, and posttraumatic stress disorder appear to be important factors in promoting alcoholism, as alcohol consumption can temporarily attenuate the negative affective symptoms of these disorders. Several molecules involved in signaling pathways may contribute to the neuroadaptation induced during alcohol dependence and stress disorders, and among these, brain-derived neurotrophic factor (BDNF), corticotropin releasing factor (CRF), neuropeptide Y (NPY) and opioid peptides (i.e., nociceptin and dynorphin) are involved in the interaction of stress and alcohol. In fact, alterations in the expression and function of these molecules have been associated with the pathophysiology of stress-related disorders and alcoholism. In recent years, various studies have focused on the epigenetic mechanisms that regulate chromatin architecture, thereby modifying gene expression. Interestingly, epigenetic modifications in specific brain regions have been shown to be associated with the neurobiology of psychiatric disorders, including alcoholism and stress. In particular, the enzymes responsible for chromatin remodeling (i.e., histone deacetylases and methyltransferases, DNA methyltransferases) have been identified as common molecular mechanisms for the interaction of stress and alcohol and have become promising therapeutic targets to treat or prevent alcoholism and associated emotional disorders.