Neuroendocrine response to GABA-B receptor agonism in alcohol-dependent individuals: Results from a combined outpatient and human laboratory experiment

Chronic alcohol-induced long-lasting working memory deficits are associated with altered histone H3K9 dimethylation in the prefrontal cortex

Introduction

Epigenetic modifications have emerged as key contributors to the enduring behavioral, molecular and epigenetic neuroadaptations during withdrawal from chronic alcohol exposure. The present study investigated the long-term consequences of chronic alcohol exposure on spatial working memory (WM) and associated changes of transcriptionally repressive histone H3 lysine 9 dimethylation (H3K9me2) in the prefrontal cortex (PFC).

Methods

Male C57BL/6 mice were allowed free access to either 12% (v/v) ethanol for 5 months followed by a 3-week abstinence period or water. Spatial WM was assessed through the spontaneous alternation T-maze test. Alcoholic and water mice received daily injections of GABAB agonist baclofen or saline during alcohol fading and early withdrawal. Global levels of histone modifications were determined by immunohistochemistry.

Results

Withdrawal mice displayed WM impairments along with reduced prefrontal H3K9me2 levels, compared to water-drinking mice. The withdrawal-induced decrease of H3K9me2 occurred concomitantly with increased level of permissive H3K9 acetylation (H3K9ac) in the PFC. Baclofen treatment rescued withdrawal-related WM deficits and fully restored prefrontal H3K9me2 and H3K9ac. Alcohol withdrawal induced brain region-specific changes of H3K9me2 and H3K9ac after testing, with significant decreases of both histone marks in the dorsal hippocampus and no changes in the amygdala and dorsal striatum. Furthermore, the magnitude of H3K9me2 in the PFC, but not the hippocampus, significantly and positively correlated with individual WM performances. No correlation was observed between H3K9ac and behavioral performance. Results also indicate that pre-testing intraperitoneal injection of UNC0642, a selective inhibitor of histone methyltransferase G9a responsible for H3K9me2, led to WM impairments in water-drinking and withdrawal-baclofen mice. Collectively, our results demonstrate that alcohol withdrawal induced brain-region specific alterations of H3K9me2 and H3K9ac, an effect that persisted for at least three weeks after cessation of chronic alcohol intake.

Conclusion

The findings suggest a role for long-lasting decreased H3K9me2 specifically in the PFC in the persistent WM impairments related to alcohol withdrawal.

Hypothalamic-pituitary-adrenocortical response in alcohol-dependent patients during baclofen treatment and association with clinical outcome: Preliminary results

Baclofen has been shown to reduce alcohol consumption in some individuals with alcohol use disorder. This preliminary study aimed to evaluate i) the effect of baclofen versus placebo on hypothalamic-pituitary-adrenocortical activity (HPA axis), as measured by cortisol, and ii) the relationship between clinical outcomes such as alcohol consumption on a randomized controlled trial of baclofen (BAC) versus placebo (PL) (Kirsten C. Morley et al., 2018; K. C. Morley, Leung, Baillie, & Haber, 2013). We hypothesized that baclofen will reduce HPA-axis activity following a mild stressor in patients with alcohol dependence. Plasma cortisol levels were taken from N = 25 alcohol-dependent patients at two time points, approximately 60 (pre-MRI scan: PreCortisol) and 180 min (post MRI scan: PostCortisol) following administration of PL, BAC 10 mg, or BAC 25 mg. Participants were followed up for the remaining 10 weeks as part of the trial for clinical outcome (percentage days abstinent). Mixed models revealed a significant main effect of medication on cortisol levels (F = 3.88, p = 0.037), no significant effect of time (F = 0.04, p = 0.84), and a significant time × medication interaction (F = 3.54, p = 0.049). Linear regression (F = 6.98, p = 0.01, R2 = 0.66) revealed that abstinence at follow-up, weighted by gender, was predicted by blunted cortisol response (β = -0.48 p = 0.023), in addition to medication (β = 0.73 p = 0.003). In conclusion, our preliminary data suggest that baclofen moderates HPA-axis activity, as measured by blood cortisol, and that these alterations may play a role in long-term treatment response.

Effect of oral alcohol administration on plasma cytokine concentrations in heavy drinking individuals

BACKGROUND

Alcohol is known to modulate the immune system, including cytokines, under conditions of both acute consumption and chronic use. The specific pro- and anti-inflammatory effects and mechanisms whereby alcohol consumption modulates circulating cytokine concentrations are not well understood. Few studies in humans have investigated the effect of acute alcohol consumption on plasma cytokine concentrations in individuals who are heavy drinkers.

METHODS

Data were pooled from two studies involving a total of 25 non-treatment seeking, heavy drinking individuals who undertook an oral alcohol administration procedure. Plasma cytokine [Interleukin-10 (IL-10), Interleukin-6 (IL-6), Interleukin-18 (IL-18) and Tumor Necrosis Factor-alpha (TNF-α)] concentrations were measured at two baseline timepoints, then three hours after alcohol administration, and finally when breath alcohol concentrations returned to zero. Linear mixed models were conducted to determine whether there was a significant effect of time on cytokine concentrations.

RESULTS

There was a significant reduction in TNF-α concentration (F [3, 20.42] = 4.96, p = 0.01, η²_p = 0.42) post alcohol administration, compared to baseline concentrations, and a significant increase in IL-6 concentrations (F [3, 27.81] = 9.06, p < 0.001, η²_p = 0.49) post alcohol administration, compared to baseline. There were no significant changes in IL-18 or IL-10 concentrations.

CONCLUSIONS

To our knowledge, this is the first study to examine the acute effect of oral alcohol consumption on peripheral inflammatory markers in individuals with alcohol use disorder. Results indicate a clinically relevant increase in proinflammatory cytokines approximately 3 h after initial alcohol ingestion. Further research should be done to elucidate the complex interaction between alcohol and the immune system.

High-dose baclofen attenuates insula activation during anticipatory anxiety in treatment-seeking alcohol dependant individuals: Preliminary findings from a pharmaco-fMRI study

The GABA _B agonist, baclofen, has been shown to reduce alcohol consumption in patients with alcohol use disorder and also those with comorbid anxiety. This study aimed to evaluate the effect of baclofen versus placebo on the BOLD response during an anticipatory anxiety fMRI task in treatment seeking alcohol patients. Participants included 28 alcohol dependant individuals who had received daily baclofen 30 mg (n = 10), 75 mg (n = 8) or placebo (n = 10) for at least 2 week on a randomized controlled trial (Morley, Leung et al. 2013, Morley, Baillie et al. 2018). Using functional magnetic resonance imaging (fMRI), we examined threat cue-elicited neural activation during a threat reactivity task 120 min following administration of BAC (30 mg or 75 mg) or placebo. Whole-brain analyses revealed no significant differences between the combined BAC doses versus PL. However, there were significant decreases in anticipatory threat cue-elicited activation observed in BAC 75 mg/day compared to PL participants in the insula. In response to threat cues, high dose (75 mg/day) baclofen administration attenuates activation in the insula and inferior frontal gyrus, relative to placebo. These preliminary findings suggests that modulating emotional regulation and attentional allocation during high threat stimuli may be mediated by GABA _B receptors and may be a potential mechanism of action for baclofen's beneficial treatment effects for alcohol use disorder.

A deeper insight into how GABA-B receptor agonism via baclofen may affect alcohol seeking and consumption: lessons learned from a human laboratory investigation

Previous studies suggest that GABA-B receptor agonism may represent an effective pharmacological approach to treat addictive disorders. Baclofen is a selective GABA-B receptor agonist which has been investigated as a potential treatment for alcohol use disorder. However, research is needed to understand the biobehavioral mechanisms underlying baclofen's effect on alcohol use. In the present randomized, double-blind, placebo-controlled study, thirty-four alcohol-dependent individuals were randomized to receive baclofen (30 mg/d) or placebo for a week, and then participated in a laboratory experiment consisting of three procedures: alcohol cue-reactivity, priming, and self-administration. During the experiment, craving and other subjective responses to alcohol were assessed, and blood samples were collected for pharmacokinetic measurements. The effects of baclofen on the relationships between different alcohol-related laboratory parameters were investigated. Baclofen pharmacokinetic parameters and their correlations with behavioral measures were also examined. Results showed that baclofen disrupted the link between alcohol priming and self-administration, as indicated by significant interaction effects between drug condition (baclofen vs. placebo) and some of the priming variables (alcohol craving: F3,9 = 6.03, p = 0.01; alcohol sedation: F3,6 = 7.16, p = 0.01) on the total amount of alcohol self-administered. Considerable interindividual variability in baclofen pharmacokinetic parameters was observed. Maximum plasma concentrations of baclofen negatively correlated with cue-induced alcohol craving (r = -0.57, p = 0.03) and priming-induced ratings of 'like more' (r = -0.59, p = 0.02). In conclusion, baclofen may work by dissociating the link between an initial drink (priming) and subsequent alcohol consumption (self-administration). Considerable pharmacokinetic variability is an important factor to take into account when employing baclofen as a treatment for alcohol use disorder.

The Impact of Appetite-Regulating Neuropeptide Leptin on Alcohol Use, Alcohol Craving and Addictive Behavior: A Systematic Review of Preclinical and Clinical Data

AIMS

The appetite regulating hormone leptin, which is mainly secreted from adipose tissue, is an important regulator of food intake and modulator of reward-driven behavior. Leptin exerts its biological actions via binding to the leptin receptor, which is expressed in the hypothalamus, but also in the hippocampus, the amygdala and the substantia nigra. In the ventral tegmental area (VTA), leptin attenuates the firing rate of dopaminergic neurons that project to the Nucleus accumbens (NAc), which serves as relay to other brain areas of the "addiction network", such as the prefrontal cortex. This suggests that leptin plays a role in the processing of rewards in the context of substance use disorders such as alcohol use disorder, especially through attenuation of dopaminergic activity in the mesolimbic reward system. This supports the plausibility of leptin's potential effects in alcohol use disorder.

METHODS

We searched MEDLINE from 1990 to February 2020. All abstracts were screened for relevance and we only included publications reporting original data with a full text available in English language. Studies that did not report leptin-data, reviews or case reports/series were not included.

RESULTS

We identified a total of N=293 studies of whom a total of N=55 preclinical and clinical studies met the specified criteria. N=40 studies investigated the effects of alcohol on leptin plasma levels, N=9 studies investigated the effects of leptin on alcohol craving and N=6 studies investigated the effects of leptin on relapse and alcohol consumption.

CONCLUSIONS

In this review of preclinical and clinical data, we assess the role of leptin in alcohol use and the development and maintenance of an alcohol use disorder, alcohol craving and relapse. Integrating the existing preclinical and clinical data on leptin may reveal new and innovative targets for the treatment of substance use disorders in the future.

GABAB Receptors and Alcohol Use Disorders: Clinical Studies

Harmful alcohol use and alcohol use disorders (AUD) result in major health and community burden worldwide, yet treatment options are limited. Novel pharmacotherapies are urgently required, and treatments involving GABA_B receptors have been used in treating alcohol-related disorders. This chapter will review the clinical evidence of GABA_B pharmacotherapies, such as baclofen and γ-hydroxybutyric acid. This includes the use of these treatments in individuals experiencing alcohol withdrawal symptoms and outlining the outcomes of studies of alcohol relapse prevention relapse including case studies, comparative studies and randomised controlled trials. Laboratory research investigating biobehavioural effects of baclofen will also be summarised and polymorphisms associated with baclofen treatment, and safety concerns of GABA_B treatments will be addressed. In summary, pharmacological treatments targeting GABA_B receptors such as baclofen may be modestly effective in the management of alcohol use disorder, but safety concerns limit the widespread applicability of the currently available agents.

Gut-Brain Neuroendocrine Signaling Under Conditions of Stress-Focus on Food Intake-Regulatory Mediators

The gut-brain axis represents a bidirectional communication route between the gut and the central nervous system comprised of neuronal as well as humoral signaling. This system plays an important role in the regulation of gastrointestinal as well as homeostatic functions such as hunger and satiety. Recent years also witnessed an increased knowledge on the modulation of this axis under conditions of exogenous or endogenous stressors. The present review will discuss the alterations of neuroendocrine gut-brain signaling under conditions of stress and the respective implications for the regulation of food intake.