1. Baclofen The GABA-B receptor agonist baclofen has been identified as a possible medication able to reduce alcohol craving and intake in alcohol dependent individuals. In keeping with preclinical studies, most of the clinical studies have demonstrated baclofens effects in reducing alcohol craving and intake (Addolorato et al, Lancet 2007, Alcohol Alcohol 2011;Leggio et al, Addict Behav 2012, Pharmacol Biochem Behav 2013). However, one trial found a robust treatment effect, but no differences between baclofen and placebo (Garbutt et al., ACER 2010). This suggests that different alcoholic individuals may respond differently to baclofen. Baclofen has been demonstrated to consistently reduce anxiety in alcoholic patients, and analyses of positive vs. null findings with baclofen suggest that alcoholic patients with higher levels of anxiety may represent a sub-population responsive to baclofen treatment (Leggio et al., CNS Neurol Disord Drug Targets 2010). Thus, the Section developed a clinical protocol (AA-13-0040) that is currently ongoing and that will systematically test the role of baclofen on alcohol-related outcomes in alcoholic individuals with high anxiety levels. The design is a between-subject randomized double-blind controlled study with the medication conditions as the between subjects factor. Dr. Leggio received a NARSAD Award from the Brain &Behavior Research Foundation to conduct this study. 2. Ghrelin Ghrelin is a 28-amino acid peptide acting as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Animal experiments demonstrate that the central ghrelin action not only stimulates the reward processing but is also required for stimulation of that system by alcohol (Jerlhag et al., PNAS 2009;Suchankova et al., PLoS One 2013). Human studies show a positive correlation between ghrelin level and alcohol craving scores, and that intravenous ghrelin acutely increases alcohol craving in alcoholic individuals. Altogether, preclinical and clinical studies provide preliminary evidence that ghrelin might represent a novel pharmacological target for treatment (reviewed in: Leggio, Drug News Perspect 2010). There are three studies conducted or under way within this theme of the CPN Section research agenda. a. Previous studies have shown that oral alcohol acutely suppresses circulating ghrelin level. As ghrelin is primarily produced in the stomach, one question never previously explored is whether alcohol administered intravenously (IV) results in similar decrease in ghrelin levels. Thus, in collaboration with Dr. Ramchandani (HP Section/LCTS), the CPN Section analyzed the potential effects of IV alcohol administration on plasma ghrelin levels in healthy nonsmoking social drinkers who received either an IV infusion of alcohol or saline in two separate counterbalanced sessions. This study (Leggio et al., Psychoneuroendocrinology in press) indicated a trend toward significance in percent change ghrelin in the alcohol condition compared to the placebo condition (p = 0.07), suggesting that, while alcohol did not reduce ghrelin, on the other hand, despite bypassing the stomach, alcohol still attenuated circulating ghrelin levels, i.e. the fasting-induced increase in circulating ghrelin was blunted by IV alcohol administration. These findings lead us to hypothesize that alcohol might affect ghrelin signaling not only via a local effect on the stomach mucosa, but also via a systemic effect. b. Previous studies indicate that ghrelin administration may result in increased alcohol-seeking behaviors, but there is no direct human evidence that ghrelin increases alcohol administration in humans. As such, we are currently conducting a within-subject, double-blind, placebo-controlled study human laboratory study (AA-13-0043) whose primary objectives are to investigate whether IV ghrelin, as compared to placebo, increases motivation for alcohol reward, as measured by a progressive ratio schedule paradigm with IV alcohol self-infusion;and whether IV ghrelin, as compared to placebo, will increase the BOLD activation in the ventral striatum during an fMRI session. c. Unlike in rodents, the hypothesis that GHS-R antagonism results in reduced alcohol use as never been tested in humans. In order to test this hypothesis, we have developed a translational project that will assess the role of a GHS-R antagonist manufactured by Pfizer as a novel medication for alcoholism. This project was developed by Dr. Leggio in collaboration with Fatemeh Akhlaghi, Pharm.D., Ph.D., from URI and was recently awarded with a NCATS grant award. This project will allow us to generate preliminary evidence on the safety and efficacy of such pharmacological agent via three projects, i.e.: (P1) a set of experiments testing the effect of this drug in well-validated animal models of alcohol-seeking behavior;(P2) a drug/alcohol interaction study to establish safety in humans (Phase 1b);and (P3) a human laboratory proof-of-concept study to assess the efficacy of this drug on alcohol-seeking behaviors (Phase 2a). These projects will be conducted at the NIH Intramural Program under the leadership of Dr. Leggio. Furthermore, all three projects will include pharmacokinetics (PK) and pharmacodynamic (PD) investigations conducted at University of Rhode Island (URI) by Dr. Akhlaghi. In summary, this research will investigate the tolerability, efficacy and mechanism of this novel pharmacological approach for AD thus leading to the potential identification of a new treatment for AD. 3.GLP-1 The glucagon-like peptide-1 (GLP-1) is an incretin hormone involved in the regulation of food intake. Recent preclinical studies have shown that a GLP-1 receptor (GLP1R) agonist, attenuates the reinforcing properties of alcohol in rodents (Egecioglu et al, Psychoneuroendocrinology 2013;Shirazi et al., PLoS One 2013). Given that alcohol use disorder (AUD) is a partly heritable, complex, psychiatric disorder, the Section designed a study aimed to investigate whether single nucleotide polymorphisms (SNPs) in GLP1R are associated with AUD. This study included three components: a) a case-control analysis (n=908) was performed using logistic regression and controlling for self-reported race;b) the SAGE GWAS sample was used for replication purposes by splitting the sample into controls, heavy drinking controls and alcohol dependent individuals;and c) data from a human laboratory study served to conduct a post-hoc analysis of SNPs against parameters recorded during a computer-assisted self-infusion of ethanol (CASE) experiment, thus with an intravenous alcohol self-administration (IV-ASA) paradigm. The main results of this study (Suchankova et al. manuscript in preparation) indicated that five SNPs located in the GLP1R were significantly associated with AUD. Furthermore, a trend towards association between the previously reported functional SNP (rs6923761;Ser168Gly) and AUD (p=0.004) was observed. Splitting the sample according to self-reported race revealed replications (rs7766663, rs7341356, rs2235868 and rs7769547) and a trend toward replication (rs10305512) between all five SNPs and AUD. Despite large discrepancies between the cohorts we were able to replicate these findings in the male sample of SAGE (one-sided p=0.033). In the IV-ASA experiment, the 168Ser-allele was associated with increased peak breath alcohol concentrations (p=0.045). As such, these findings provide support to the possible role of GLP1R as a possible pharmacotherapy target for AUD.
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