Inhibitory effect of alcohol on ghrelin secretion in normal man

The glucagon-like peptide-1 and other endocrine responses to alcohol ingestion in women with versus without metabolic surgery

Glucagon-like peptide-1 (GLP-1)-based therapies, effective in treating obesity and type 2 diabetes, hold potential for reducing alcohol-seeking behaviour. However, the understanding of how alcohol consumption affects endogenous GLP-1 responses-important for understanding GLP-1-based therapies' potential in addressing alcohol misuse-is limited, given the absence of placebo-controlled studies examining these effects. This study aimed to determine the acute effects of alcohol ingestion on GLP-1 and other peptides and evaluate whether metabolic surgery, which increases GLP-1 responses, blood alcohol concentrations (BAC) and alcohol misuse risk, influences this effect. Additionally, we assessed the acute effects of alcohol on plasma glucose and insulin concentrations. Using a placebo-controlled crossover study, we examined hormonal and glucose responses after oral alcohol consumption (0.5 g/kg of fat-free mass) versus placebo drinks in 18 women who underwent metabolic surgery <5 years ago and in 14 non-operated controls (equivalent in age, body mass index [BMI], race and alcohol consumption patterns). Women had a mean (SD) age of 41 (10) years and a BMI of 33 (5) kg/m2. Compared with the control group, the surgery group exhibited a higher peak BAC (0.99 [0.20] g/L vs. 0.75 [0.16] g/L; P < 0.005). Alcohol decreased GLP-1 by 34% (95% CI, 16%-52%) in both groups and decreased ghrelin more in the control (27%) than in the surgery group (13%). Alcohol modestly decreased plasma glucose and transiently increased insulin secretion in both groups (P < 0.05). However, alcohol lowered blood glucose concentrations to the hypoglycaemic range in 28% of the women in the surgery group versus none in the control group. These findings provide compelling evidence that acute alcohol consumption decreases GLP-1, a satiation signal, elucidating alcohol's 'apéritif' effect. This study also highlights the potential increase in alcohol-related hypoglycaemic effects after metabolic surgery.

Alcohol and the dopamine system

The mesolimbic dopamine pathway plays a major role in drug reinforcement and is likely involved also in the development of drug addiction. Ethanol, like most addictive drugs, acutely activates the mesolimbic dopamine system and releases dopamine, and ethanol-associated stimuli also appear to trigger dopamine release. In addition, chronic exposure to ethanol reduces the baseline function of the mesolimbic dopamine system. The molecular mechanisms underlying ethanol´s interaction with this system remain, however, to be unveiled. Here research on the actions of ethanol in the mesolimbic dopamine system, focusing on the involvement of cystein-loop ligand-gated ion channels, opiate receptors, gastric peptides and acetaldehyde is briefly reviewed. In summary, a great complexity as regards ethanol´s mechanism(s) of action along the mesolimbic dopamine system has been revealed. Consequently, several new targets and possibilities for pharmacotherapies for alcohol use disorder have emerged.

Pharmacological GHSR (ghrelin receptor) blockade reduces alcohol binge-like drinking in male and female mice

Ghrelin is a peptide that is produced by endocrine cells that are primarily localized in the stomach. Ghrelin receptors (GHSR) are expressed in the brain and periphery. Preclinical and clinical studies support a role for ghrelin in alcohol drinking and seeking. The GHSR has been suggested to be a potential pharmacotherapeutic target for alcohol use disorder (AUD). However, the role of the ghrelin system and its potential modulation by biological sex on binge-like drinking has not been comprehensively investigated. The present study tested six GHSR antagonists in an alcohol binge-like drinking procedure in male and female mice. Systemic administration of the GHSR antagonists JMV2959, PF-5190457, PF-6870961, and HM-04 reduced alcohol intake in both male and female mice. YIL-781 decreased intake in males, and LEAP2 (likely peripherally restricted) did not reduce intake in mice of either sex. We also administered LEAP2 and JMV2959 intracerebroventricularly to investigate whether the effects of GHSR blockade on alcohol intake are mediated by central receptors. The central administration of LEAP2 and JMV2959 decreased alcohol intake, particularly in high-drinking animals. Finally, in a preliminary experiment, an anti-ghrelin vaccine was examined for its potential effect on binge-like drinking and had no effect. In all experiments, there was a lack of meaningful sex differences. These findings suggest that central GHSR mediates binge-like alcohol intake. These data reveal novel pharmacological compounds with translational potential in the treatment of AUD and provide further evidence of the GHSR as a potential treatment target for AUD.

Role of the ghrelin system in alcohol use disorder and alcohol-associated liver disease: A narrative review

Unhealthy alcohol consumption is a global health problem. Adverse individual, public health, and socioeconomic consequences are attributable to harmful alcohol use. Epidemiological studies have shown that alcohol use disorder (AUD) and alcohol-associated liver disease (ALD) are the top two pathologies among alcohol-related diseases. Consistent with the major role that the liver plays in alcohol metabolism, uncontrolled drinking may cause significant damage to the liver. This damage is initiated by excessive fat accumulation in the liver, which can further progress to advanced liver disease. The only effective therapeutic strategies currently available for ALD are alcohol abstinence or liver transplantation. Any molecule with dual-pronged effects at the central and peripheral organs controlling addictive behaviors and associated metabolic pathways are a potentially important therapeutic target for treating AUD and ALD. Ghrelin, a hormone primarily derived from the stomach, has such properties, and regulates both behavioral and metabolic functions. In this review, we highlight recent advances in understanding the peripheral and central functions of the ghrelin system and its role in AUD and ALD pathogenesis. We first discuss the correlation between blood ghrelin concentrations and alcohol use or abstinence. Next, we discuss the role of ghrelin in alcohol-seeking behaviors and finally its role in the development of fatty liver by metabolic regulations and organ crosstalk. We propose that a better understanding of the ghrelin system could open an innovative avenue for improved treatments for AUD and associated medical consequences, including ALD.

Pathogenesis of Alcohol-Associated Liver Disease

Excessive alcohol consumption is a global healthcare problem with enormous social, economic, and clinical consequences. While chronic, heavy alcohol consumption causes structural damage and/or disrupts normal organ function in virtually every tissue of the body, the liver sustains the greatest damage. This is primarily because the liver is the first to see alcohol absorbed from the gastrointestinal tract via the portal circulation and second, because the liver is the principal site of ethanol metabolism. Alcohol-induced damage remains one of the most prevalent disorders of the liver and a leading cause of death or transplantation from liver disease. Despite extensive research on the pathophysiology of this disease, there are still no targeted therapies available. Given the multifactorial mechanisms for alcohol-associated liver disease pathogenesis, it is conceivable that a multitherapeutic regimen is needed to treat different stages in the spectrum of this disease.

Therapeutic potential of GHSR-1A antagonism in alcohol dependence, a review

Growth hormone secretagogue receptor type 1A (GHSR-1A) is a functional receptor of orexigenic peptide ghrelin and is highly expressed in mesolimbic dopaminergic systems that regulate incentive value of artificial reward in substance abuse. Interestingly, GHSR-1A has also shown ligand-independent constitutive activity. Alcohol use disorder (AUD) is one of the growing concerns worldwide as it involves complex neuro-psycho-endocrinological interactions. Positive correlation of acylated ghrelin and alcohol-induced human brain response in the right and left ventral striatum are evident. In the last decade, the beneficial effects of ghrelin receptor (GHSR-1A) antagonism to suppress artificial reward circuitries and induce self-control for alcohol consumption have drawn significant attention from researchers. In this updated review, we summarize the available recent preclinical, clinical, and experimental data to discuss functional, molecular actions of central ghrelin-GHSR-1A signaling in different craving levels for alcohol as well as to promote "GHSR-1A antagonism" as one of the potential therapies in early abstinence.

A closer look at alcohol-induced changes in the ghrelin system: novel insights from preclinical and clinical data

Ghrelin is a gastric-derived peptide hormone with demonstrated impact on alcohol intake and craving, but the reverse side of this bidirectional link, that is, the effects of alcohol on the ghrelin system, remains to be fully established. To further characterize this relationship, we examined (1) ghrelin levels via secondary analysis of human laboratory alcohol administration experiments with heavy-drinking participants; (2) expression of ghrelin, ghrelin receptor, and ghrelin-O-acyltransferase (GOAT) genes (GHRL, GHSR, and MBOAT4, respectively) in post-mortem brain tissue from individuals with alcohol use disorder (AUD) versus controls; (3) ghrelin levels in Ghsr knockout and wild-type rats following intraperitoneal (i.p.) alcohol administration; (4) effect of alcohol on ghrelin secretion from gastric mucosa cells ex vivo and GOAT enzymatic activity in vitro; and (5) ghrelin levels in rats following i.p. alcohol administration versus a calorically equivalent non-alcoholic sucrose solution. Acyl- and total-ghrelin levels decreased following acute alcohol administration in humans, but AUD was not associated with changes in central expression of ghrelin system genes in post-mortem tissue. In rats, alcohol decreased acyl-ghrelin, but not des-acyl-ghrelin, in both Ghsr knockout and wild-type rats. No dose-dependent effects of alcohol were observed on acyl-ghrelin secretion from gastric mucosa cells or on GOAT acylation activity. Lastly, alcohol and sucrose produced distinct effects on ghrelin in rats despite equivalent caloric value. Our findings suggest that alcohol acutely decreases peripheral ghrelin concentrations in vivo, but not in proportion to alcohol's caloric value or through direct interaction with ghrelin-secreting gastric mucosal cells, the ghrelin receptor, or the GOAT enzyme.

A population-based investigation of the association between alcohol intake and serum total ghrelin concentrations among cigarette-smoking, non-alcohol-dependent male individuals

BACKGROUND

Ghrelin plays significant roles in regulating appetite, food intake, and metabolism. Furthermore, the ghrelin system is increasingly being studied in relation to alcohol seeking behaviors. To this end, it is important to understand the possible effects of alcohol intake on the ghrelin system. The aim of the present study was to investigate the association between alcohol drinking and circulating ghrelin levels in a large sample of cigarette-smoking, non-alcohol-dependent male individuals.

METHODS

We utilized data from two nested case-control studies (study A, n = 807; study B, n = 976) based within the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) trial. Data on alcohol consumption (grams of pure alcohol consumed per day) were obtained via a food frequency questionnaire. Blood samples were also collected (after 12 h of fasting), and serum concentrations of total ghrelin were measured by radioimmunoassay.

RESULTS

Dichotomous comparison between alcohol drinkers (>0 g/day of alcohol intake) and non-drinkers (0 g/day of alcohol intake) found higher total ghrelin levels among individuals who drank alcohol than those who did not, with statistically significant results in study A [F (1, 798) = 4.32, P = 0.03] and less robust results in study B [F (1, 966) = 2.62, P = 0.10], controlling for a list of factors that may influence ghrelin levels and/or differ between drinkers and non-drinkers. Bivariate correlational analysis among drinkers found no association between the quantity of daily alcohol intake and blood total ghrelin concentrations.

CONCLUSION

These results indicate elevated ghrelin levels among alcohol drinkers and provide additional/relevant information on the complex interaction between alcohol use and the ghrelin system.

The association of plasma acyl ghrelin level with alcohol craving in early abstinent alcohol dependent patients

Background

Craving plays an important role in maintenance of alcohol dependence. Earlier studies have analyzed the role of ghrelin in craving and their results have been heterogenous. Acyl ghrelin is its more active form as it crosses the blood brain barrier. Hence we aimed to examine the relationship between plasma acyl ghrelin and craving in Indian patients having alcohol dependence syndrome.

Methods

The present study was a hospital-based prospective study. A total of 60 drug-naive patients of alcohol dependence and 30 healthy controls were included. After taking informed consent fasting blood samples were collected from them on day 1 and tested for plasma acyl ghrelin level. Fasting blood samples were repeated in all cases on day 14. During this time, we also assessed the patients' cravings by obsessive compulsive drinking scale, and alcohol craving questionnaire; and withdrawal by clinical institute withdrawal assessment for alcohol scale. These scales were repeated on day 14. Data analysis was done by SPSS version 25.0.

Results

Plasma concentrations of acyl ghrelin increased significantly during early abstinence in patients from day 1 to day 14 (P < 0.0001). Pearson correlation test revealed a trend of positive correlation between plasma concentration of acyl ghrelin on day 14 and severity of craving on day 1.

Conclusion

Our results suggest the plasma concentration of acyl ghrelin may be a predictor of severity of alcohol craving during early abstinence. Anti-craving drugs acting on acyl ghrelin level in brain may open an innovative avenue for optimum treatment of alcohol dependence.

Microbiota-gut-brain axis as a regulator of reward processes

Our gut harbours trillions of microorganisms essential for the maintenance of homeostasis and host physiology in health and disease. In the last decade, there has been a growing interest in understanding the bidirectional pathway of communication between our microbiota and the central nervous system. With regard to reward processes there is accumulating evidence from both animal and human studies that this axis may be a key factor in gating reward valence. Focusing on the mesocorticolimbic pathway, we will discuss how the intestinal microbiota is involved in regulating brain reward functions, both in natural (i.e. eating, social or sexual behaviours) and non-natural reinforcers (drug addiction behaviours including those relevant to alcohol, psychostimulants, opioids and cannabinoids). We will integrate preclinical and clinical evidence suggesting that the microbiota-gut-brain axis could be implicated in the development of disorders associated with alterations in the reward system and how it may be targeted as a promising therapeutic strategy. Cover Image for this issue: https://doi.org/10.1111/jnc.15065.

THE INTRIGUING LIGAND-DEPENDENT AND LIGAND-INDEPENDENT ACTIONS OF THE GROWTH HORMONE SECRETAGOGUE RECEPTOR ON REWARD-RELATED BEHAVIORS

The growth hormone secretagogue receptor (GHSR) is a G-protein-coupled receptor (GPCR) highly expressed in the brain, and also in some peripheral tissues. GHSR activity is evoked by the stomach-derived peptide hormone ghrelin and abrogated by the intestine-derived liver-expressed antimicrobial peptide 2 (LEAP2). In vitro, GHSR displays ligand-independent actions, including a high constitutive activity and an allosteric modulation of other GPCRs. Beyond its neuroendocrine and metabolic effects, cumulative evidence shows that GHSR regulates the activity of the mesocorticolimbic pathway and modulates complex reward-related behaviors towards different stimuli. Here, we review current evidence indicating that ligand-dependent and ligand-independent actions of GHSR enhance reward-related behaviors towards appetitive stimuli and drugs of abuse. We discuss putative neuronal networks and molecular mechanisms that GHSR would engage to modulate such reward-related behaviors. Finally, we briefly discuss imaging studies showing that ghrelin would also regulate reward processing in humans. Overall, we conclude that GHSR is a key regulator of the mesocorticolimbic pathway that influences its activity and, consequently, modulates reward-related behaviors via ligand-dependent and ligand-independent actions.

Effects of ethanol on plasma ghrelin levels in the rat during early and late adolescence

Ghrelin is an appetite-regulating peptide that is primarily secreted by endocrine cells in the stomach and is implicated in regulation of alcohol consumption and alcohol-reinforced behaviors. In the present study, adolescent Sprague-Dawley rats received intermittent ethanol (AIE) exposure by intragastric intubation (5 g/kg) or vapor inhalation, manipulations conducted between postnatal days (PD) 28-43. On the first and last day of AIE exposure, the level of intoxication was examined 1 h after ethanol gavage or upon removal from the vapor chamber. This was immediately followed by a blood draw for determination of the blood ethanol concentration (BEC) and plasma levels of acylated ghrelin (acyl-ghrelin; active). On PD29, plasma levels of acyl-ghrelin were significantly elevated in male (but not female) rats in response to acute ethanol exposure by both gastric gavage and vapor inhalation. Importantly, assessment of plasma acyl-ghrelin in response to repeated ethanol exposure revealed a complex interaction of both sex and method of AIE exposure. On PD43, vapor inhalation increased plasma acyl-ghrelin in both males and females compared to their air-control counterparts, whereas there was no change in plasma levels of acyl-ghrelin in either male or female rats in response to exposure by intragastric gavage. Assessment of plasma acyl-ghrelin following a 30-day ethanol-free period revealed AIE exposure did not produce a change in basal levels. In addition, an acute ethanol challenge in adult rats of 5 g/kg via gastric gavage had no effect on plasma ghrelin levels when assessed 1 h after initiation of exposure. Collectively, these observations suggest that acyl-ghrelin, a primary gut-brain signaling hormone, is elevated by ethanol during early adolescence independent of administration route, and in gender-dependent fashion.

Effects of exogenous ghrelin administration and ghrelin receptor blockade, in combination with alcohol, on peripheral inflammatory markers in heavy-drinking individuals: Results from two human laboratory studies

The ghrelin system has been garnering interest for its role in different neuropsychiatric disorders, including alcohol use disorder (AUD). Accordingly, targeting the ghrelin system is under investigation as a potential novel therapeutic approach. While alcohol provokes the immune system and inflammatory responses, ghrelin has potent immunomodulatory and anti-inflammatory properties. The present study aimed to shed light on the "crosstalk" between ghrelin and inflammation by examining the effects of exogenous ghrelin administration and ghrelin receptor blockade on peripheral inflammatory markers in the context of two human laboratory studies with alcohol administration. Non-treatment-seeking, heavy-drinking individuals with alcohol dependence, the majority of whom were African American males, were enrolled. In the first randomized, crossover, double-blind, placebo-controlled human laboratory study, participants underwent two experimental paradigms - an intravenous alcohol self-administration (IV-ASA) and an intravenous alcohol clamp (IV-AC) - each consisting of two counterbalanced sessions (ghrelin, placebo). A loading dose of intravenous ghrelin (3 mcg/kg) or placebo, followed by a continuous ghrelin (16.9 ng/kg/min) or placebo infusion was administered. In the second dose-escalating, single-blind, placebo-controlled human laboratory phase 1b study, participants were dosed with an oral ghrelin receptor blocker (PF-5190457) and underwent an oral alcohol challenge. Repeated blood samples were collected, and plasma concentrations of the following inflammatory markers were measured: C-reactive protein (CRP), interleukin (IL)-6, IL-10, IL-18, and tumor necrosis factor alpha (TNF-α). During the IV-ASA experiment, significant drug × time interaction effects were observed for IL-6 (F_3,36 = 3.345, p = 0.030) and IL-10 (F_3,53.2 = 4.638, p = 0.006), indicating that ghrelin, compared to placebo, significantly reduced blood concentrations of the proinflammatory cytokine IL-6, while increasing blood concentrations of the anti-inflammatory cytokine IL-10. No significant drug × time interaction effects were observed during the IV-AC experiment, possibly because of its much shorter duration and/or smaller sample. Treatment with PF-5190457, compared to placebo, had no significant effect on the inflammatory markers investigated. In conclusion, a supraphysiologic pharmacological challenge with exogenous ghrelin in heavy-drinking individuals produced anti-inflammatory effects in the context of intravenous alcohol administration. On the contrary, ghrelin receptor blockade did not lead to any change in the inflammatory markers included in this study. Mechanistic studies are required to better understand the interaction between ghrelin, alcohol, and inflammatory processes.

The novel ghrelin receptor inverse agonist PF-5190457 administered with alcohol: preclinical safety experiments and a phase 1b human laboratory study

Rodent studies indicate that ghrelin receptor blockade reduces alcohol consumption. However, no ghrelin receptor blockers have been administered to heavy alcohol drinking individuals. Therefore, we evaluated the safety, tolerability, pharmacokinetic (PK), pharmacodynamic (PD) and behavioral effects of a novel ghrelin receptor inverse agonist, PF-5190457, when co-administered with alcohol. We tested the effects of PF-5190457 combined with alcohol on locomotor activity, loss-of-righting reflex (a measure of alcohol sedative actions), and on blood PF-5190457 concentrations in rats. Then, we performed a single-blind, placebo-controlled, within-subject human study with PF-5190457 (placebo/0 mg b.i.d., 50 mg b.i.d., 100 mg b.i.d.). Twelve heavy drinkers during three identical visits completed an alcohol administration session, subjective assessments, and an alcohol cue-reactivity procedure, and gave blood samples for PK/PD testing. In rats, PF-5190457 did not interact with the effects of alcohol on locomotor activity or loss-of-righting reflex. Alcohol did not affect blood PF-5190457 concentrations. In humans, all adverse events were mild or moderate and did not require discontinuation or dose reductions. Drug dose did not alter alcohol concentration or elimination, alcohol-induced stimulation or sedation, or mood during alcohol administration. Potential PD markers of PF-5190457 were acyl-to-total ghrelin ratio and insulin-like growth factor-1. PF-5190457 (100 mg b.i.d.) reduced alcohol craving during the cue-reactivity procedure. This study provides the first translational evidence of safety and tolerability of the ghrelin receptor inverse agonist PF-5190457 when co-administered with alcohol. PK/PD/behavioral findings support continued research of PF-5190457 as a potential pharmacological agent to treat alcohol use disorder.

Prevalence and factors associated with overweight and obesity among rural and urban women in Burkina Faso

Introduction

Low- and middle-income countries, including Burkina Faso, are facing increasing urbanization with health challenges related to nutrition transition that impact body weight change. This study reported the prevalence and factors associated with overweight/obesity among women living in rural and urban Burkina Faso.

Methods

We conducted a secondary analysis using data from the Burkina Faso 2013 WHO STEPwise survey. Data included socio-demographic, clinical (anthropometric, systolic/diastolic blood pressure (SBP/DBP), oral/dental symptoms), biological (total and high-density lipoprotein cholesterol and fasting blood sugar), and alcohol and tobacco consumption data. A total of 2191 participants with complete data were considered in the analysis. We categorized the 13 Burkinabe regions by urbanization rate quartiles. We then performed Student's t, chi-squared, and Fisher's exact tests and backward stepwise regressions.

Results

The overall prevalence of overweight/obesity was 19.6% (13.1% and 44% in rural and urban women respectively, p=0.0001). Common factors positively associated with overweight/obesity in both rural and urban women were being a resident of a region in the highest urbanization rate quartile, having a high level of total cholesterol (alone or via an interaction with age) and having a high DBP. In urban women only, overweight/obesity was also associated with a high SBP.

Conclusion

The prevalence of overweight/obesity in urban women in Burkina was among the highest levels in urban sub-Saharan Africa and roughly mimicked the urbanization profile of the country. In overweight/obesity conditions, cardiovascular concerns, such as increase in total cholesterol and blood pressure, were objective, and the blood pressure increase was more severe in urban women than in rural women.

Gut-brain axis and addictive disorders: A review with focus on alcohol and drugs of abuse

Due to the limited efficacy of existing medications for addictive disorders including alcohol use disorder (AUD), the need for additional medications is substantial. Potential new medications for addiction can be identified through investigation of the neurochemical substrates mediating the ability of drugs of abuse such as alcohol to activate the mesolimbic dopamine system. Interestingly, recent studies implicate neuropeptides of the gut-brain axis as modulators of reward and addiction processes. The present review therefore summarizes the current studies investigating the ability of the gut-brain peptides ghrelin, glucagon-like peptide-1 (GLP-1), amylin and neuromedin U (NMU) to modulate alcohol- and drug-related behaviors in rodents and humans. Extensive literature demonstrates that ghrelin, the only known orexigenic neuropeptide to date, enhances reward as well as the intake of alcohol, and other drugs of abuse, while ghrelin receptor antagonism has the opposite effects. On the other hand, the anorexigenic peptides GLP-1, amylin and NMU independently inhibits reward from alcohol and drugs of abuse in rodents. Collectively, these rodent and human studies imply that central ghrelin, GLP-1, amylin and NMU signaling may contribute to addiction processes. Therefore, the need for randomized clinical trials investigating the effects of agents targeting these aforementioned systems on drug/alcohol use is substantial.

Alcohol consumption is positively associated with fasting serum ghrelin in non-dependent adults: Results from the population-based LIFE-Adult-Study

BACKGROUND

Animal experiments and studies in alcohol dependent patients indicate that ghrelin signaling in the brain is causally involved in the regulation of alcohol reward and intake. Increasing ghrelin levels enhances alcohol craving and intake, blocking ghrelin receptors abolishes these effects. If ghrelin is also involved in non-dependent alcohol consumption in humans, though, remains unknown. The aim was therefore to investigate the relationship between ghrelin serum levels and alcohol consumption in a large population-based sample.

METHODS

Total ghrelin was determined after an overnight fast in 1666 subjects participating in a population-based cross-sectional study ('LIFE') including 10,000 adults. 1521 subjects were included in this analysis. Alcohol consumption was assessed using a food frequency questionnaire (FFQ). Multiple linear regression analyses and extreme group comparisons testing for statistical differences of alcohol consumption between the highest and lowest quartile according to ghrelin levels were performed.

RESULTS

Alcohol consumption was positively associated with serum ghrelin; total sample: β = 0.003, p = 0.002; men: β = 0.005, p = 0.023; women: β = 0.002, p = 0.007, adjusted for age, BMI and smoking status. Mean alcohol consumption in men/women belonging to the highest quartile of serum ghrelin levels (men: 21.5 (21.1) g/day; women: 7.5 (11.4) g/day) was considerably higher than in those belonging to the lowest quartile (men: 16.5 (19.3) g/day p < 0.002; women: 4.59 (10.7) g/day p = 0.0001).

CONCLUSION

This is the first study showing that alcohol consumption is positively associated with serum ghrelin in a population-based sample. The study provides an initial indication that ghrelin is also involved in the regulation of alcohol consumption in non-dependent subjects.

Ghrelin is Related to Personality Differences in Reward Sensitivity and Impulsivity

Aims

Ghrelin, a feeding-related peptide mainly produced in the stomach, has been linked to reward mechanisms for food and drugs of abuse in addition to traits of impulsivity. This study is a secondary analysis of an existing data set designed to examine the direct relationships between fasting ghrelin levels and reward sensitivity/impulsivity in healthy social drinkers.

Methods

Participants (n = 20) were recruited from an original study examining the subjective effects of alcohol among social drinkers. Fasting ghrelin levels were collected at baseline. Personality measures (Behavioral Inhibition, Behavioral Activation, and Affective Response to Impending Reward and Punishment and Barratt Impulsiveness Scale) were administered at baseline to evaluate sensitivity to reward and punishment, and measure traits of impulsivity, respectively.

Results

Fasting ghrelin levels were significantly related to reward sensitivity and impulsivity traits. Specifically, those with higher ghrelin levels were more sensitive to reward and were more impulsive (have lower self-control).

Conclusions

The results indicate that individuals with higher levels of ghrelin are more sensitive to reward. In addition, they are less able to exercise self-control and to an extent more likely to act without thinking. This is the first study to report on the direct relationship between fasting ghrelin levels and personality characteristics such as reward sensitivity and aspects of impulsivity among healthy social drinkers.

Short summary

Individuals with higher levels of fasting ghrelin are more sensitive to reward, but less sensitive to punishment. Higher ghrelin levels are also related to some aspects of impulsivity such as decreased self-control and increased likelihood of acting without thinking.

Stress, Motivation, and the Gut-Brain Axis: A Focus on the Ghrelin System and Alcohol Use Disorder

Since its discovery, the gut hormone, ghrelin, has been implicated in diverse functional roles in the central nervous system. Central and peripheral interactions between ghrelin and other hormones, including the stress-response hormone cortisol, govern complex behavioral responses to external cues and internal states. By acting at ventral tegmental area dopaminergic projections and other areas involved in reward processing, ghrelin can induce both general and directed motivation for rewards, including craving for alcohol and other alcohol-seeking behaviors. Stress-induced increases in cortisol seem to increase ghrelin in the periphery, suggesting a pathway by which ghrelin influences how stressful life events trigger motivation for rewards. However, in some states, ghrelin may be protective against the anxiogenic effects of stressors. This critical review brings together a dynamic and growing literature, that is, at times inconsistent, on the relationships between ghrelin, central reward-motivation pathways, and central and peripheral stress responses, with a special focus on its emerging role in the context of alcohol use disorder.

Ghrelin is Supressed by Intravenous Alcohol and is Related to Stimulant and Sedative Effects of Alcohol

Aims

Evidence indicates that feeding-related peptides, such as ghrelin, have a role in the rewarding properties of addictive substances like alcohol. Oral alcohol administration significantly suppresses ghrelin. This study was designed to evaluate the effects of two doses of alcohol on ghrelin and examine if ghrelin levels predict the subjective effects of alcohol.

Methods

Healthy social drinkers (N = 20) participated in three, randomly assigned, and counterbalanced laboratory sessions. During each session they received a continuous IV infusion of either placebo (saline), low dose (40 mg%) or high dose (100 mg%) of alcohol. Participants were given a standardized, light breakfast 90 min before the start of the infusion. Ghrelin levels [acyl ghrelin (AG) and total ghrelin (TG)] were collected at four time points before, during and after the infusion. Subjective effects of alcohol, using the BAES, were evaluated before, during and after alcohol infusion.

Results

IV alcohol significantly reduced AG but not TG levels with no difference between the two doses of alcohol. The percent change (%∆) in AG suppression was substantial in both high dose (43.4%∆), and low dose (39.5%∆) of alcohol. Also, fasting AG and TG levels were significant predictors of alcohol stimulant and sedative effects. Higher fasting ghrelin levels were associated with longer and more intense subjective effects.

Conclusions

The results provide evidence that IV alcohol suppresses ghrelin levels similarly to oral alcohol. This study is the first to show that ghrelin predicts subjective effects of alcohol, suggesting that ghrelin may have a role in the rewarding mechanisms for alcohol.

Short summary

Intravenous alcohol infusion (low dose and high dose of alcohol) when compared to placebo (saline) significantly suppresses ghrelin in healthy social drinkers. Fasting ghrelin levels also predict subjective behavioral effects of alcohol. Those with higher fasting ghrelin levels tend to experience alcohol effects longer and more intensely.

The Role of the Ghrelin System in Drug Addiction

In the past years, a significant volume of research has implicated the appetitive hormone ghrelin in the mechanisms underlying drug use and addiction. From a neuroscientific standpoint, ghrelin modulates both reward and stress pathways, two key drivers of substance use behaviors. Previous investigations support a connection between the ghrelin system and alcohol, stimulants, and tobacco use in both animals and humans, while the research on opioids and cannabis is scarce. In general, upregulation of the ghrelin system seems to enhance craving for drugs as well as substances use. On the other hand, acute and chronic exposure to drugs of abuse influences the ghrelin system at different levels. This chapter summarizes the literature on the relationship between the ghrelin system and substance-related behaviors. We also review recent work investigating the ghrelin system as a potential pharmacological target for treating substance use disorders and discuss the need for additional research.

Prairie Voles as a Model to Screen Medications for the Treatment of Alcoholism and Addictions

Most preclinical studies of medications to treat addictions are performed in mice and rats. These two rodent species belong to one phylogenetic subfamily, which narrows the likelihood of identifying potential mechanisms regulating addictions in other species, ie, humans. Expanding the genetic diversity of organisms modeling alcohol and drug abuse enhances our ability to screen for medications to treat addiction. Recently, research laboratories adapted the prairie vole model to study mechanisms of alcohol and drugs of abuse. This development not only expanded the diversity of genotypes used to screen medications, but also enhanced capabilities of such screens. Prairie voles belong to 3-5% of mammalian species exhibiting social monogamy. This unusual trait is reflected in their ability to form lasting long-term affiliations between adult individuals. The prairie vole animal model has high predictive validity for mechanisms regulating human social behaviors. In addition, these animals exhibit high alcohol intake and preference. In laboratory settings, prairie voles are used to model social influences on drug reward and alcohol consumption as well as effects of addictive substances on social bonding. As a result, this species can be adapted to screen medications whose effectiveness could be (a) resistant to social influences promoting excessive drug taking, (b) dependent on the presence of social support, and (c) medications affecting harmful social consequences of alcohol and drug abuse. This report reviews the literature on studies of alcohol and psychostimulants in prairie voles and discusses capabilities of this animal model as a screen for novel medications to treat alcoholism and addictions.

Differential effects of ghrelin antagonists on alcohol drinking and reinforcement in mouse and rat models of alcohol dependence

An effort has been mounted to understand the mechanisms of alcohol dependence in a way that may allow for greater efficacy in treatment. It has long been suggested that drugs of abuse seize fundamental reward pathways and disrupt homeostasis to produce compulsive drug seeking behaviors. Ghrelin, an endogenous hormone that affects hunger state and release of growth hormone, has been shown to increase alcohol intake following administration, while antagonists decrease intake. Using rodent models of dependence, the current study examined the effects of two ghrelin receptor antagonists, [DLys3]-GHRP-6 (DLys) and JMV2959, on dependence-induced alcohol self-administration. In two experiments adult male C57BL/6J mice and Wistar rats were made dependent via intermittent ethanol vapor exposure. In another experiment, adult male C57BL/6J mice were made dependent using the intragastric alcohol consumption (IGAC) procedure. Ghrelin receptor antagonists were given prior to voluntary ethanol drinking. Ghrelin antagonists reduced ethanol intake, preference, and operant self-administration of ethanol and sucrose across these models, but did not decrease food consumption in mice. In experiments 1 and 2, voluntary drinking was reduced by ghrelin receptor antagonists, however this reduction did not persist across days. Despite the transient effects of ghrelin antagonists, the drugs had renewed effectiveness following a break in administration as seen in experiment 1. The results show the ghrelin system as a potential target for studies of alcohol abuse. Further research is needed to determine the central mechanisms of these drugs and their influence on addiction in order to design effective pharmacotherapies.

The apéritif effect: Alcohol's effects on the brain's response to food aromas in women

OBJECTIVE

Consuming alcohol prior to a meal (an apéritif) increases food consumption. This greater food consumption may result from increased activity in brain regions that mediate reward and regulate feeding behavior. Using functional magnetic resonance imaging, we evaluated the blood oxygenation level dependent (BOLD) response to the food aromas of either roast beef or Italian meat sauce following pharmacokinetically controlled intravenous infusion of alcohol.

METHODS

BOLD activation to food aromas in non-obese women (n = 35) was evaluated once during intravenous infusion of 6% v/v EtOH, clamped at a steady-state breath alcohol concentration of 50 mg%, and once during infusion of saline using matching pump rates. Ad libitum intake of roast beef with noodles or Italian meat sauce with pasta following imaging was recorded.

RESULTS

BOLD activation to food relative to non-food odors in the hypothalamic area was increased during alcohol pre-load when compared to saline. Food consumption was significantly greater, and levels of ghrelin were reduced, following alcohol.

CONCLUSIONS

An alcohol pre-load increased food consumption and potentiated differences between food and non-food BOLD responses in the region of the hypothalamus. The hypothalamus may mediate the interplay of alcohol and responses to food cues, thus playing a role in the apéritif phenomenon.

The effects of ghrelin antagonists [D-Lys(3) ]-GHRP-6 or JMV2959 on ethanol, water, and food intake in C57BL/6J mice

BACKGROUND

Alcohol use and abuse patterns have created a need for novel treatment models. Current research has turned its focus on reward pathways associated with intrinsic necessities, such as feeding. Theories suggest that drugs of abuse seize control of natural reward pathways and dysregulate normal function, leading to chronic addiction. One such pathway involving the hunger stimulating peptide, ghrelin, is the focus of our study.

METHODS

Male C57BL/6J mice were randomly assigned to groups and treated with vehicle or a ghrelin antagonist, either [D-Lys(3) ]-GHRP-6 (DLys) or JMV2959. Three experiments tested ghrelin antagonism using different doses; experiment 1 tested 12 mg/kg JMV2959; experiment 2 tested 15 mg/kg DLys; experiment 3 tested 9 mg/kg JMV2959. Using a 2-bottle choice 24-hour access paradigm, data were collected for ethanol intake, preference, water intake, and food intake at 4 and 24 hours after injection.

RESULTS

Experiment 1 showed that 12 mg/kg of JMV2959 decreased ethanol, water, and food intake, without affecting preference. Experiment 2 showed that 15 mg/kg of DLys decreased ethanol intake, preference, and water intake only on the first day of treatment. Experiment 3 showed that 9 mg/kg of JMV2959 decreased only ethanol and food intake. No change was seen during deprivation, and JMV2959 was still effective at reducing ethanol intake upon reintroduction. Despite the change in food intake, there were no differences in body weight throughout the experiments. It should be noted that the majority of significant effects were only found 4 hours postinjection.

CONCLUSIONS

The results show that compounds that block ghrelin receptor activity are effective at decreasing ethanol intake. However, DLys was only effective at reducing intake and preference on the first day, suggesting a quick tolerance and selectivity for ethanol. JMV2959 consistently reduced ethanol intake, but at the higher dose also reduced all other consummatory behaviors. Thus, ghrelin antagonists provide a viable potential for treatment of alcohol abuse disorders, but further research is needed to determine an appropriate dose and administration paradigm.

Effects of Cigarette Smoking on Plasma Concentration of the Appetite-Regulating Peptide Ghrelin

BACKGROUND

Weight gain is a common but only a partially understood consequence of smoking cessation. Existing data suggest modulating effects of the orexigenic peptide ghrelin on food intake. The aim of the present study was to investigate the effect of tobacco withdrawal on plasma concentration of acetylated and total ghrelin.

METHODS

Fifty four normal-weighted smokers and 30 non-smoking healthy controls were enrolled in our study. Concentrations of acetylated and total ghrelin were measured in blood plasma drawn two hours after a standardized meal and three hours after the smokers smoked their last cigarette. The severity of tobacco addiction was assessed based on cotinine plasma concentration, the Fagerström Test for Nicotine Dependence (FTND) and the number of cigarettes smoked per day.

RESULTS

The plasma concentration of acetylated ghrelin, but not total ghrelin, was significantly higher in smokers than in non-smokers. Moreover, we found significant negative correlations between acetylated ghrelin and all measures of the severity of nicotine dependence.

CONCLUSIONS

Early abstinence from tobacco smoking seems to be associated with increased plasma concentration of the orexigenic peptide acetylated ghrelin. This could be one reason for increased food craving during nicotine withdrawal and subsequent weight gain. Smokers might compensate these effects by increasing tobacco intake.

Alcohol Consumption and Obesity: An Update

Recreational alcohol intake is a widespread activity globally and alcohol energy (7 kcal/g) can be a contributing factor to weight gain if not compensated for. Given that both excessive alcohol intake and obesity are of public health interest, the present paper provides an update on the association between alcohol consumption and body weight. In general, recent prospective studies show that light-to-moderate alcohol intake is not associated with adiposity gain while heavy drinking is more consistently related to weight gain. Experimental evidence is also mixed and suggests that moderate intake of alcohol does not lead to weight gain over short follow-up periods. However, many factors can explain the conflicting findings and a better characterization of individuals more likely to gain weight as a result of alcohol consumption is needed. In particular, individuals who frequently drink moderate amounts of alcohol may enjoy a healthier lifestyle in general that may protect them from weight gain. In conclusion, despite the important limitations of current studies, it is reasonable to say that alcohol intake may be a risk factor for obesity in some individuals, likely based on a multitude of factors, some of which are discussed herein.

Association of alcohol consumption and components of metabolic syndrome among people in rural China

Background

Accumulative evidence in the literature suggests alcohol consumption is a protective factor of the metabolic syndrome (MS). However, few studies investigated the relationship between alcohol consumption and components of MS. We examined association of several types of alcoholic beverage with components of MS among people in rural China.

Methods

In the Nantong Metabolic Syndrome Study (NMSS), a cross-sectional study, a total of 20,502 participants, including 13,505 women and 6,997 men aged 18–74 years, were recruited between 2007 and 2008 in Nantong, China. Socio-economic status, dietary intake, physical exercise, alcoholic beverage consumption, and smoking status information were obtained, and triglycerides (TG), high-density lipoprtein cholesterol (HDL-c), blood pressure (BP) and blood glucose level were examined for all participants. Logistic regression model and the restricted cubic spline approach were used to analyze the associations between alcoholic beverage consumption and MS components.

Results

The MS prevalence was 21.1% in the whole population, which was significantly low among drinkers (20.6%), compared with non-drinkers (23.6%) in women, and was comparable in men (16.4% versus 17.1%). High HDL-c level was observed among drinkers, compared with non-drinkers in both men and women. Low TG level and Systolic BP (SBP) were found only among rice wine drinkers in women, and high waist circumference, high TG and BP were found among beer and liquor drinkers in men. Furthermore, we found that the highest quartile of rice wine drink in women may decrease 24% risk of high TG, 30% risk of low HDL-c and 43% risk of high glucose among MS components cases respectively, compared with non-drinkers (p for trend <0.01 for those three components). While compared non-drinkers among men, the highest quartile of liquor drink may increase 32% risk of high SBP, 55% risk of high Diastolic BP (DBP) and 34% risk of abdominal obesity among MS components cases respectively, but decrease 45% risk of low HDL-c (p for trend <0.05 for those four components).

Conclusion

Our data suggested that all alcoholic beverages increased HDL-c level. Rice wine decreased both TG level and blood glucose in women only and it could be one of healthy alcoholic beverages in MS prevention in Chinese women. While excessive liquor consumption increased BP and waist circumference level and it may lead to hypertension and central obesity in Chinese men.

Ghrelin in psychiatric disorders - A review

Ghrelin is a 28-amino-acid peptide hormone, first described in 1999 and broadly expressed in the organism. As the only known orexigenic hormone secreted in the periphery, it increases hunger and appetite, promoting food intake. Ghrelin has also been shown to be involved in various physiological processes being regulated in the central nervous system such as sleep, mood, memory and reward. Accordingly, it has been implicated in a series of psychiatric disorders, making it subject of increasing investigation, with knowledge rapidly accumulating. This review aims at providing a concise yet comprehensive overview of the role of ghrelin in psychiatric disorders. Ghrelin was consistently shown to exert neuroprotective and memory-enhancing effects and alleviated psychopathology in animal models of dementia. Few human studies show a disruption of the ghrelin system in dementia. It was also shown to play a crucial role in the pathophysiology of addictive disorders, promoting drug reward, enhancing drug seeking behavior and increasing craving in both animals and humans. Ghrelin's exact role in depression and anxiety is still being debated, as it was shown to both promote and alleviate depressive and anxiety-behavior in animal studies, with an overweight of evidence suggesting antidepressant effects. Not surprisingly, the ghrelin system is also implicated in eating disorders, however its exact role remains to be elucidated. Its widespread involvement has made the ghrelin system a promising target for future therapies, with encouraging findings in recent literature.

Gut-brain peptides in corticostriatal-limbic circuitry and alcohol use disorders

Peptides synthesized in endocrine cells in the gastrointestinal tract and neurons are traditionally considered regulators of metabolism, energy intake, and appetite. However, recent work has demonstrated that many of these peptides act on corticostriatal-limbic circuitry and, in turn, regulate addictive behaviors. Given that alcohol is a source of energy and an addictive substance, it is not surprising that increasing evidence supports a role for gut-brain peptides specifically in alcohol use disorders (AUD). In this review, we discuss the effects of several gut-brain peptides on alcohol-related behaviors and the potential mechanisms by which these gut-brain peptides may interfere with alcohol-induced changes in corticostriatal-limbic circuitry. This review provides a summary of current knowledge on gut-brain peptides focusing on five peptides: neurotensin, glucagon-like peptide 1, ghrelin, substance P, and neuropeptide Y. Our review will be helpful to develop novel therapeutic targets for AUD.

The role of ghrelin in addiction: a review

RATIONALE

Ghrelin is a fast-acting hormone that is produced primarily by the stomach and by the brain although in smaller quantities. The regulation and the secretion of ghrelin are complex and not limited to aspects of feeding. Ghrelin exerts powerful effects on multiple processes, and it has been demonstrated that it mediates the rewarding properties of food as well as of drugs of abuse.

OBJECTIVES

The purpose of this review is to summarize the findings of preclinical and clinical studies related to ghrelin's possible role in addiction for each specific class of substances. Questions related to ghrelin's involvement in addiction are highlighted. Recurrent methodological issues that render the interpretation of the findings challenging are discussed. Also, the potential of targeting ghrelin as a pharmacologic treatment strategy for addiction is explored.

RESULTS

Ghrelin signaling is implicated in the mediation of behavioral and biochemical effects of drugs of abuse that are cardinal for the development of addiction, especially for alcohol, nicotine, and stimulants. The available literature implicating ghrelin in opioid or cannabis use disorders is currently limited and inconclusive.

CONCLUSIONS

There is intriguing, although not always consistent, evidence for the involvement of ghrelin signaling in aspects of addiction, especially in the cases of alcohol, nicotine, and stimulants. Further research, particularly in humans, is recommended to replicate and expand on the findings of the current literature. Improved and novel methodologies that take into account the volatile and complex nature of ghrelin are required to clarify the inconsistencies of the findings.

Role of appetite-regulating peptides in the pathophysiology of addiction: implications for pharmacotherapy

Food intake and appetite are regulated by various circulating hormones including ghrelin and glucagon-like-peptide 1 (GLP-1). Ghrelin, mainly released from the stomach, increases food intake, induces appetite, enhances adiposity as well as releases growth hormone. Hypothalamic "ghrelin receptors" (GHS-R1A) have a critical role in food intake regulation, but GHS-R1A are also expressed in reward related areas. GLP-1 is produced in the intestinal mucosa as well as in the hindbrain in response to nutrient ingestion. This gut-brain hormone reduces food intake as well as regulates glucose homeostasis, foremost via GLP-1 receptors in hypothalamus and brain stem. However, GLP-1 receptors are expressed in areas intimately associated with reward regulation. Given that regulation of food and drug intake share common neurobiological substrates, the possibility that ghrelin and GLP-1 play an important role in reward regulation should be considered. Indeed, this leading article describes that the orexigenic peptide ghrelin activates the cholinergic-dopaminergic reward link, an important part of the reward systems in the brain associated with reinforcement and thereby increases the incentive salience for motivated behaviors via this system. We also review the role of ghrelin signaling for reward induced by alcohol and addictive drugs from a preclinical, clinical and human genetic perspective. In addition, the recent findings showing that GLP-1 controls reward induced by alcohol, amphetamine, cocaine and nicotine in rodents are overviewed herein. Finally, the role of several other appetite regulatory hormones for reward and addiction is briefly discussed. Collectively, these data suggest that ghrelin and GLP-1 receptors may be novel targets for development of pharmacological treatments of alcohol and drug dependence.

Ghrelin-Derived Peptides: A Link between Appetite/Reward, GH Axis, and Psychiatric Disorders?

Psychiatric disorders are often associated with metabolic and hormonal alterations, including obesity, diabetes, metabolic syndrome as well as modifications in several biological rhythms including appetite, stress, sleep-wake cycles, and secretion of their corresponding endocrine regulators. Among the gastrointestinal hormones that regulate appetite and adapt the metabolism in response to nutritional, hedonic, and emotional dysfunctions, at the interface between endocrine, metabolic, and psychiatric disorders, ghrelin plays a unique role as the only one increasing appetite. The secretion of ghrelin is altered in several psychiatric disorders (anorexia, schizophrenia) as well as in metabolic disorders (obesity) and in animal models in response to emotional triggers (psychological stress …) but the relationship between these modifications and the physiopathology of psychiatric disorders remains unclear. Recently, a large literature showed that this key metabolic/endocrine regulator is involved in stress and reward-oriented behaviors and regulates anxiety and mood. In addition, preproghrelin is a complex prohormone but the roles of the other ghrelin-derived peptides, thought to act as functional ghrelin antagonists, are largely unknown. Altered ghrelin secretion and/or signaling in psychiatric diseases are thought to participate in altered appetite, hedonic response and reward. Whether this can contribute to the mechanism responsible for the development of the disease or can help to minimize some symptoms associated with these psychiatric disorders is discussed in the present review. We will thus describe (1) the biological actions of ghrelin and ghrelin-derived peptides on food and drugs reward, anxiety and depression, and the physiological consequences of ghrelin invalidation on these parameters, (2) how ghrelin and ghrelin-derived peptides are regulated in animal models of psychiatric diseases and in human psychiatric disorders in relation with the GH axis.

Ghrelin at the interface of obesity and reward

The prevalence of obesity continues to increase and has reached epidemic proportions. Accumulating data over the past few decades have given us key insights and broadened our understanding of the peripheral and central regulation of energy homeostasis. Despite this, the currently available pharmacological treatments, reducing body weight, remain limited due to poor efficacy and side effects. The gastric peptide ghrelin has been identified as the only orexigenic hormone from the periphery to act in the hypothalamus to stimulate food intake. Recently, a role for ghrelin and its receptor at the interface between homeostatic control of appetite and reward circuitries modulating the hedonic aspects of food has also emerged. Nonhomeostatic factors such as the rewarding and motivational value of food, which increase with food palatability and caloric content, can override homeostatic control of food intake. This nonhomeostatic decision to eat leads to overconsumption beyond nutritional needs and is being recognized as a key component in the underlying causes for the increase in obesity incidence worldwide. In addition, the hedonic feeding behavior has been linked to food addiction and an important role for ghrelin in the development of addiction has been suggested. Moreover, plasma ghrelin levels are responsive to conditions of stress, and recent evidence has implicated ghrelin in stress-induced food-reward behavior. The prominent role of the ghrelinergic system in the regulation of feeding gives rise to it as an effective target for the development of successful antiobesity pharmacotherapies that not only affect satiety but also selectively modulate the rewarding properties of food and reduce the desire to eat.

Fasting-induced increase in plasma ghrelin is blunted by intravenous alcohol administration: a within-subject placebo-controlled study

Ghrelin is a 28-amino acid peptide produced mainly by mucosal neuroendocrine cells lining the fundus of the stomach. Preclinical and clinical studies suggest that ghrelin plays a role in alcoholism. Furthermore, human laboratory studies indicate that acute oral administration of alcohol results in reduced circulating ghrelin. 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, this study analyzed the potential effects of IV alcohol administration on plasma ghrelin levels in healthy nonsmoking social drinkers (n=44) who received either a 180-min IV infusion of 6% (v/v) alcohol or 0.9% normal saline in two separate counterbalanced sessions. At each session, participants arrived having fasted for ~7 h and received a light breakfast 60 min before the infusion. The percent change (%Δ) in ghrelin levels was 4.5-fold less in the alcohol condition than the saline condition. In fact, there was only a modest change in ghrelin levels from baseline in the IV alcohol condition (9.6%Δghrelin) while in the IV saline condition there was a robust change (43.4%Δghrelin). There was a trend toward significance in %Δghrelin in the alcohol condition compared to the placebo condition (F[1,33]=3.3, p=0.07). While the exact mechanisms by which alcohol influences ghrelin levels are unclear, alcohol may act directly in the stomach by inhibiting ghrelin secretion and/or release, and may also attenuate ghrelin levels systemically. Although IV alcohol did not reduce circulating ghrelin levels, as seen in previous studies with oral alcohol administration, the present findings suggest that, 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.

The role of ghrelin in drug and natural reward

Ghrelin is a protein that has been given special attention in both nutrition and addiction research during the last decade. Consequently, a vast amount of information has been accumulated concerning the role of ghrelin in natural and drug reward. We are now in the position to ask whether the ghrelin system could be targeted to treat maladaptive behaviours such as obesity and drug addiction. Indeed, ghrelin research has demonstrated that blocking the activity of ghrelin receptors may be effective in reducing the consumption of both food and drugs of abuse. This review will give a short overview of our current knowledge about the ghrelin system in the context of drug and natural rewards as well as the possibility of developing potential ghrelin-based treatments.

Alcohol administration attenuates hypothalamic-pituitary-adrenal (HPA) activity in healthy men at low genetic risk for alcoholism, but not in high-risk subjects

Acute alcohol challenge studies in rodents and naturalistic observations in drinking alcoholics suggest that alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) system. The literature on respective studies in healthy volunteers is more inconsistent, suggesting differential alcohol effects depending on dosage, recent drinking history, family history of alcoholism and alcohol-induced side effects. These papers and the putative pharmacologic mechanisms underlying alcohol effects on the HPA system are reviewed here and compared with a new study, in which we investigated how secretion of adrenocorticotrophin (ACTH) and cortisol is affected by ingestion of 0.6 g/kg ethanol in 33 young healthy socially drinking males with a paternal history of alcoholism (PHP) versus 30 family history negative (FHN) males. Alcohol and placebo were administered in a 2-day, double-blind, placebo controlled crossover design with randomized administration sequence. After administration of placebo, ACTH and cortisol decreased steadily over 130 minutes. In FHN subjects, secretion of both hormones was even more attenuated after alcohol, resulting in significantly lower levels compared with placebo. In PHP subjects, no alcohol effect on hormone secretion could be detected. The ratio of cortisol to ACTH secretion, each expressed as area under the secretion curve, was significantly increased by alcohol in FHN and PHP participants. These results argue against HPA stimulation being a mechanism that promotes the transition from moderate to dependent drinking. The fact that alcohol-induced HPA suppression was not detected in PHP males is consistent with the general concept that subjects at high risk for alcoholism exhibit less-pronounced alcohol effects.

Ethanol affects acylated and total ghrelin levels in peripheral blood of alcohol-dependent rats

There is a hypothesis that ghrelin could take part in the central effects of alcohol as well as function as a peripheral indicator of the changes which occur during long-term alcohol consumption. The aim of this study was to determine a correlation between alcohol concentration and acylated and total form of ghrelin after a single administration of alcohol (intraperitoneal, i.p.) (experiment 1) and prolonged ethanol consumption (experiment 2). The study was performed using Wistar alcohol preferring (PR) and non-preferring (NP) rats and rats from inbred line (Warsaw High Preferring, WHP; Warsaw Low Preferring, WLP). It was found that ghrelin in ethanol-naive WHP animals showed a significantly lower level when compared with the ethanol-naive WLP or Wistar rats. After acute ethanol administration in doses of 1.0; 2.0 and 4.0 g/kg, i.p., the simple (WHP) or inverse (WLP and Wistar) relationship between alcohol concentration and both form of ghrelin levels in plasma were found. Chronic alcohol intake in all groups of rats led to decrease of acylated ghrelin concentration. PR and WHP rats, after chronic alcohol drinking, had lower levels of both form of ghrelin in comparison with NP and WLP rats, respectively, and the observed differences in ghrelin levels were in inverse relationship with their alcohol intake. In conclusion, it is suggested that there is a strong relationship between alcohol administration or intake, ethanol concentration in blood and both active and total ghrelin level in the experimental animals, and that ghrelin plasma concentration can be a marker of alcohol drinking predisposition.

Abnormal ghrelin secretion contributes to gastrointestinal symptoms in multiple system atrophy patients

Patients with multiple system atrophy (MSA) often have evidence of compromised gastrointestinal motility. Ghrelin is a gut hormone that influences gastrointestinal motility in humans. The aim of this study was to determine whether ghrelin secretion is affected in MSA patients, and to investigate the relation between ghrelin secretion and gastrointestinal symptoms. Plasma levels of active ghrelin and unacylated ghrelin were measured in patients with MSA (n = 30), other atypical parkinsonian disorders including progressive supranuclear palsy-Richardson syndrome and corticobasal syndrome (n = 24), and control subjects (n = 24) using enzyme-linked immunosorbent assays. Gastrointestinal symptoms were quantified in all subjects using a self-report questionnaire. The ratio of active ghrelin to total ghrelin in the plasma (active ghrelin ratio) was lower in patients with MSA (mean: 8.0 %) than in patients with other atypical parkinsonian disorders (mean: 13.7 %, P = 0.001) and control subjects (mean: 13.9 %, P = 0.001). The active ghrelin ratio was correlated with the severity of gastrointestinal symptoms in MSA (r = −0.5, P = 0.004). Our observations indicate that ghrelin secretion is affected in patients with MSA. The low active ghrelin ratio may contribute to gastrointestinal symptoms in MSA.

The relationship of appetitive, reproductive and posterior pituitary hormones to alcoholism and craving in humans

A significant challenge for understanding alcoholism lies in discovering why some, but not other individuals, become dependent on alcohol. Genetic, environmental, cultural, developmental, and neurobiological influences are recognized as essential factors underlying a person's risk for becoming alcohol dependent (AD); however, the neurobiological processes that trigger this vulnerability are still poorly understood. Hormones are important in the regulation of many functions and several hormones are strongly associated with alcohol use. While medical consequences are important, the primary focus of this review is on the underlying confluence of appetitive/feeding, reproductive and posterior pituitary hormones associated with distinct phases of alcoholism or assessed by alcohol craving in humans. While these hormones are of diverse origin, the involvement with alcoholism by these hormone systems is unmistakable, and demonstrates the complexity of interactions with alcohol and the difficulty of successfully pursuing effective treatments. Whether alcohol associated changes in the activity of certain hormones are the result of alcohol use or are the result of an underlying predisposition for alcoholism, or a combination of both, is currently of great scientific interest. The evidence we present in this review suggests that appetitive hormones may be markers as they appear involved in alcohol dependence and craving, that reproductive hormones provide an example of the consequences of drinking and are affected by alcohol, and that posterior pituitary hormones have potential for being targets for treatment. A better understanding of the nature of these associations may contribute to diagnosing and more comprehensively treating alcoholism. Pharmacotherapies that take advantage of our new understanding of hormones, their receptors, or their potential relationship to craving may shed light on the treatment of this disorder.

The association of the appetitive peptide acetylated ghrelin with alcohol craving in early abstinent alcohol dependent individuals

OBJECTIVE

Recent preclinical and clinical studies suggested ghrelin to have an orexigenic role in regulating appetite and energy balance. Preclinical studies also provided support for an important role of ghrelin in the neurobiology of addiction-related reward pathways, affecting the self-administration of alcohol and drugs as well as conditioned place preference. In contrast, clinical data have until now failed to support an association between ghrelin and alcohol craving, possibly due to the fact that these studies have analyzed the pharmacologically inactive, preprohormone ghrelin instead of ghrelin in its active, acetylated form.

MATERIALS AND METHODS

Our study sample was a group of 61 alcohol-dependent male inpatients. We assessed their plasma concentrations of both active and total ghrelin, using blood samples taken twice during the study: once at the onset of withdrawal, 12-24h after admission, and then again after 14 days of controlled abstinence. During this time, we also assessed the patients' alcohol cravings (applying the obsessive compulsive drinking scale, or OCDS), symptoms of depression (Beck Depression Inventory; BDI) and anxiety (State Trait Anxiety Inventory; STAI). The severity of alcohol dependence was assessed using the alcohol dependence scale (ADS).

RESULTS

We found a significant positive correlation between the plasma concentration of active ghrelin and alcohol craving in both blood samples. Plasma concentrations of active ghrelin increased significantly during early abstinence. In a linear regression model, the plasma concentration of active ghrelin on day one, the scores of the ADS, and the BDI explained 36% of the variance in OCDS sum score (p<0.0001). By day 14, these same factors accounted for 54% (p<0.0001). We did not detect any association between the plasma concentration of total ghrelin and patients' alcohol cravings.

CONCLUSION

Our results suggest that biologically active, acetylated ghrelin is involved in reward-associated craving during alcohol withdrawal and early abstinence in alcohol-dependent patients. Antagonizing ghrelin at its central growth-hormone secretagogue receptors (GHS-R1A) in the ventral tegmental area (VTA) may prove to be a novel pharmacological target in a future treatment for craving and relapse in alcoholics.

Ghrelin system in alcohol-dependent subjects: role of plasma ghrelin levels in alcohol drinking and craving

Animal studies suggest that the gut-brain peptide ghrelin plays an important role in the neurobiology of alcohol dependence (AD). Human studies show an effect of alcohol on ghrelin levels and a correlation between ghrelin levels and alcohol craving in alcoholics. This investigation consisted of two studies. Study 1 was a 12-week study with alcohol-dependent subjects, where plasma ghrelin determinations were assessed four times (T0-T3) and related to alcohol intake and craving [Penn Alcohol Craving Score (PACS) and Obsessive Compulsive Drinking Scale (OCDS)]. Serum growth hormone levels and assessment of the nutritional/metabolic status were also performed. Study 2 was a pilot case-control study to assess ghrelin gene polymorphisms (Arg51Gln and Leu72Met) in alcohol-dependent individuals. Study 1 showed no significant differences in ghrelin levels in the whole sample, while there was a statistical difference for ghrelin between non-abstinent and abstinent subjects. Baseline ghrelin levels were significantly and positively correlated with the PACS score at T1 and with all craving scores both at T2 and T3 (PACS, OCDS, obsessive and compulsive OCDS subscores). In Study 2, although there was a higher frequency of the Leu72Met ghrelin gene polymorphism in alcohol-dependent individuals, the distribution between healthy controls and alcohol dependent individuals was not statistically significant. This investigation suggests that ghrelin is potentially able to affect alcohol-seeking behaviors, such as alcohol drinking and craving, representing a new potential neuropharmacological target for AD.

Ghrelin receptor (GHS-R1A) antagonism suppresses both operant alcohol self-administration and high alcohol consumption in rats

The mechanisms involved in alcohol use disorders are complex. It has been shown that ghrelin is an important signal for the control of body weight homeostasis, preferably by interacting with hypothalamic circuits, as well as for drug reward by activating the mesolimbic dopamine system. The ghrelin receptor (GHS-R1A) has been shown to be required for alcohol-induced reward. Additionally, ghrelin increases and GHR-R1A antagonists reduce moderate alcohol consumption in mice, and a single nucleotide polymorphism in the GHS-R1A gene has been associated with high alcohol consumption in humans. However, the role of central ghrelin signaling in high alcohol consumption is not known. Therefore, the role of GHS-R1A in operant self-administration of alcohol in rats as well as for high alcohol consumption in Long-Evans rats and in alcohol preferring [Alko alcohol (AA)] rats was studied here. In the present study, the GHS-R1A antagonist, JMV2959, was found to reduce the operant self-administration of alcohol in rats and to decrease high alcohol intake in Long-Evans rats as well as in AA rats. These results suggest that the ghrelin receptor signaling system, specifically GHS-R1A, is required for operant self-administration of alcohol and for high alcohol intake in rats. Therefore, the GHS-R1A may be a therapeutic target for treatment of addictive behaviors, such as alcohol dependence.

The role of the central ghrelin system in reward from food and chemical drugs

Here we review recent advances that identify a role for the central ghrelin signalling system in reward from both natural rewards (such as food) and artificial rewards (that include alcohol and drugs of abuse). Whereas ghrelin emerged as a stomach-derived hormone involved in energy balance, hunger and meal initiation via hypothalamic circuits, it now seems clear that it also has a role in motivated reward-driven behaviours via activation of the so-called "cholinergic-dopaminergic reward link". This reward link comprises a dopamine projection from the ventral tegmental area (VTA) to the nucleus accumbens together with a cholinergic input, arising primarily from the laterodorsal tegmental area. Ghrelin administration into the VTA or LDTg activates the "cholinergic-dopaminergic" reward link, suggesting that ghrelin may increase the incentive value of motivated behaviours such as reward-seeking behaviour ("wanting" or "incentive motivation"). Further, direct injection of ghrelin into the brain ventricles or into the VTA increases the consumption of rewarding foods as well as alcohol in mice and rats. Studies in rodents show beneficial effects of ghrelin receptor (GHS-R1A) antagonists to suppress the intake of palatable food, to reduce preference for caloric foods, to suppress food reward and motivated behaviour for food. They have also been shown to reduce alcohol consumption, suppress reward induced by alcohol, cocaine and amphetamine. Furthermore, variations in the GHS-R1A and pro-ghrelin genes have been associated with high alcohol consumption, smoking and increased weight gain in alcohol dependent individuals as well as with bulimia nervosa and obesity. Thus, the central ghrelin signalling system interfaces neurobiological circuits involved in reward from food as well as chemical drugs; agents that directly or indirectly suppress this system emerge as potential candidate drugs for suppressing problematic over-eating that leads to obesity as well as for the treatment of substance use disorder.