Role of feeding-related pathways in alcohol dependence: A focus on sweet preference, NPY, and ghrelin

The glucagon-like peptide-1 (GLP-1) analogue semaglutide reduces alcohol drinking and modulates central GABA neurotransmission

Growing evidence indicates that the glucagon-like peptide-1 (GLP-1) system is involved in the neurobiology of addictive behaviors, and GLP-1 analogues may be used for the treatment of alcohol use disorder (AUD). Here, we examined the effects of semaglutide, a long-acting GLP-1 analogue, on biobehavioral correlates of alcohol use in rodents. A drinking-in-the-dark procedure was used to test the effects of semaglutide on binge-like drinking in male and female mice. We also tested the effects of semaglutide on binge-like and dependence-induced alcohol drinking in male and female rats, as well as acute effects of semaglutide on spontaneous inhibitory postsynaptic currents (sIPSCs) from central amygdala (CeA) and infralimbic cortex (ILC) neurons. Semaglutide dose-dependently reduced binge-like alcohol drinking in mice; a similar effect was observed on the intake of other caloric/noncaloric solutions. Semaglutide also reduced binge-like and dependence-induced alcohol drinking in rats. Semaglutide increased sIPSC frequency in CeA and ILC neurons from alcohol-naive rats, suggesting enhanced GABA release, but had no overall effect on GABA transmission in alcohol-dependent rats. In conclusion, the GLP-1 analogue semaglutide decreased alcohol intake across different drinking models and species and modulated central GABA neurotransmission, providing support for clinical testing of semaglutide as a potentially novel pharmacotherapy for AUD.

Prospective Associations between Attitudes toward Sweet Foods, Sugar Consumption, and Cravings for Alcohol and Sweets in Early Recovery from Alcohol Use Disorders

Sweet liking (heightened preference for highly-sweet solutions) is linked to Alcohol Use Disorder (AUD) and relapse, as well as attitudes towards sweet foods - use of sugar to cope with negative affect (sweet-cope), and impaired control over sweets consumption (sweet-control). This prospective analysis of individuals with AUD (N=26) participating in an Alcohol and Drug partial hospitalization program observed increases in self-reported sugar consumption and sweet craving from Time 1 (T1) to Time 2 (T2; 4 weeks later). Sweet-cope (T1) predicted T2 sweet craving. In an exploratory cross-lagged panel model, sweet-cope predicted sugar consumption and sweet craving at T1 and T2, and alcohol craving at T2. This pattern of results suggests the hypothesis that use of sugar to regulate negative affect may prove a novel, modifiable risk mechanism of the association between sweet liking and relapse. Sweet-cope may also prove an intervention target for improving nutrition and weight-related factors in early recovery. Future research in larger sample sizes is needed.

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

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

Body mass index and serum levels of soluble leptin receptor are sex-specifically related to alcohol binge drinking behavior

OBJECTIVE

Binge drinking is a highly prevalent behavior in adolescents and young adults and a risk factor to develop alcohol use disorder. Body mass index (BMI) and blood levels of leptin peptide and its soluble receptor have been implicated in alcohol use disorder; however, their role in binge drinking remains to be investigated.

METHOD

We studied associations of BMI, serum levels of soluble leptin receptor (ObRe) and leptin as well as the free leptin index with binge drinking in 93 male and 99 female young adults.

RESULTS

In men, binge drinkers showed significantly higher BMI (kg/m²) than non-binge drinkers (23.67 vs. 22.08) and higher BMI correlated significantly with more severe binge drinking episodes (ρ = 0.251). In women, we found significantly higher ObRe (ng/ml) / BMI (kg/m²) values in binge drinkers than in non-binge drinkers (0.52 vs. 0.44) and ObRe/BMI values correlated significantly with more severe binge drinking episodes (ρ = 0.210).

CONCLUSION

This study confirms that higher BMI associates with binge drinking in men and shows for the first time a role of ObRe/BMI in binge drinking in women. Our data emphasize the importance of further research in the field of metabolic markers and implications in neurobiological processes of binge drinking.

Dietary fiber deficiency as a component of malnutrition associated with psychological alterations in alcohol use disorder

BACKGROUND & AIMS

Chronic alcohol consumption can cause malnutrition that may contribute to alcohol-induced organ injury and psychological disorders. We evaluated the link between nutrient intake, especially dietary fibers (DF) and different parameters reflecting mental health and well being, namely anxiety, depression, alcohol craving, sociability, fatigue and intestinal comfort in alcohol use disorder (AUD) patients.

METHODS

Cross-sectional data from 50 AUD patients, hospitalized for a 3-week detoxification program were used. Three 24-h recalls allowed to calculate dietary habits and nutrient intakes, that was also assessed in healthy subjects (HS). Diet quality was measured using the NOVA score. Psychological factors and intestinal discomfort were evaluated using validated self-administered questionnaires.

RESULTS

Energy intake (excluding alcoholic beverage), total fat, monounsaturated and polyunsaturated fatty acids, protein and DF intakes were lower in AUD subjects compared to HS. Ninety percent of patients had a DF intake below the recommendation. AUD patients consumed more than twice as much ultra-processed food than HS. Fructan intake was negatively associated with anxiety (p = 0.04) adjusted for main confounders. Total DF, insoluble, soluble DF and galacto-oligosaccharide intakes were associated with higher sociability score. Soluble DF intake was associated with better satisfaction of bowel function (p = 0.02) and a lower intestinal discomfort (p = 0.04).

CONCLUSIONS

This study reveals that insufficient DF intake is part of AUD-related malnutrition syndrome, and is associated with higher anxiety, lower sociability score and intestinal discomfort. Our results suggest that an adequate intake of DF might be beneficial for recovery from AUD.

TRIAL REGISTRATION

NCT03803709, https://clinicaltrials.gov/ct2/show/NCT03803709.

Interventions and Manipulations of Interoception

Interoceptive pathways may be manipulated at various levels to develop interventions to improve symptoms in a range of disorders. Primarily through the lens of the respiratory system, we outline various pathways that can be manipulated at neural, behavioral, and psychological levels to change the representation of and attention to interoceptive signals, which can alter interconnected physiological systems and improve functioning and adaptive behavior. Interventions can alter interoception via neuromodulation of the vagus nerve, slow breathing to change respiratory rate and depth, or awareness processes such as mindfulness-based interventions. Aspects of this framework may be applied to other physiological systems and future research may integrate interventions across multiple levels of manipulation or bodily systems.

Effects of naltrexone on alcohol, sucrose, and saccharin binge-like drinking in C57BL/6J mice: a study with a multiple bottle choice procedure

Chronic alcohol (ethyl alcohol, EtOH) binging has been associated with long-term neural adaptations that lead to the development of addiction. Many of the neurobiological features of EtOH abuse are shared with other forms of binging, like pathological feeding. The drinking-in-the-dark (DID) paradigm has been used extensively to study the neurobiology of EtOH binge-like drinking due to its ability to promote high intakes relevant to human behavior. DID can also generate high consumption of other tastants, but this procedure has not been fully adapted to study forms of binging behavior that are not alcohol-driven. In the present study, we used a modified version of DID that uses multiple bottle availability to promote even higher levels of EtOH drinking in male C57BL/6J mice and allows a thorough investigation of tastant preferences. We assessed whether administration of systemic naltrexone could reduce binging on EtOH, sucrose, and saccharin separately as well as in combination. Our multiple bottle DID procedure resulted in heightened levels of consumption compared with previously reported data using this task. We found that administration of the opioid receptor antagonist naltrexone reduced intakes of preferred, highly concentrated EtOH, sucrose, and saccharin. We also report that naltrexone was able to reduce overall intakes when animals were allowed to self-administer EtOH, sucrose, or saccharin in combination. Our modified DID procedure provides a novel approach to study binging behavior that extends beyond EtOH to other tastants (i.e. sucrose and artificial sweeteners), and has implications for the study of the neuropharmacology of binge drinking.

A long non-coding RNA (Lrap) modulates brain gene expression and levels of alcohol consumption in rats

LncRNAs are important regulators of quantitative and qualitative features of the transcriptome. We have used QTL and other statistical analyses to identify a gene coexpression module associated with alcohol consumption. The "hub gene" of this module, Lrap (Long non-coding RNA for alcohol preference), was an unannotated transcript resembling a lncRNA. We used partial correlation analyses to establish that Lrap is a major contributor to the integrity of the coexpression module. Using CRISPR/Cas9 technology, we disrupted an exon of Lrap in Wistar rats. Measures of alcohol consumption in wild type, heterozygous and knockout rats showed that disruption of Lrap produced increases in alcohol consumption/alcohol preference. The disruption of Lrap also produced changes in expression of over 700 other transcripts. Furthermore, it became apparent that Lrap may have a function in alternative splicing of the affected transcripts. The GO category of "Response to Ethanol" emerged as one of the top candidates in an enrichment analysis of the differentially expressed transcripts. We validate the role of Lrap as a mediator of alcohol consumption by rats, and also implicate Lrap as a modifier of the expression and splicing of a large number of brain transcripts. A defined subset of these transcripts significantly impacts alcohol consumption by rats (and possibly humans). Our work shows the pleiotropic nature of non-coding elements of the genome, the power of network analysis in identifying the critical elements influencing phenotypes, and the fact that not all changes produced by genetic editing are critical for the concomitant changes in phenotype.

Combined alcoholic and non-alcoholic steatohepatitis

While metabolic syndrome and alcohol consumption are the two main causes of chronic liver disease, one of the two conditions is often predominant, with the other acting as a cofactor of morbimortality. It has been shown that obesity and alcohol act synergistically to increase the risk of fibrosis progression, hepatic carcinogenesis and mortality, while genetic polymorphisms can strongly influence disease progression. Based on common pathogenic pathways, there are several potential targets that could be used to treat both diseases; based on the prevalence and incidence of these diseases, new therapies and clinical trials are needed urgently.

Role of Molybdenum-Containing Enzymes in the Biotransformation of the Novel Ghrelin Receptor Inverse Agonist PF-5190457: A Reverse Translational Bed-to-Bench Approach

(R)-2-(2-methylimidazo[2,1-b]thiazol-6-yl)-1-(2-(5-(6-methylpyrimidin-4-yl)-2,3-dihydro-1H-inden-1-yl)-2,7-diazaspiro[3.5]nonan-7-yl)ethan-1-one (PF-5190457) was identified as a potent and selective inverse agonist of the ghrelin receptor [growth hormone secretagogue receptor 1a (GHS-R1a)]. The present translational bed-to-bench work characterizes the biotransformation of this compound in vivo and then further explores in vitro metabolism in fractions of human liver and primary hepatocytes. Following oral administration of PF-5190457 in a phase 1b clinical study, hydroxyl metabolites of the compound were observed, including one that had not been observed in previously performed human liver microsomal incubations. PF-6870961 was biosynthesized using liver cytosol, and the site of hydroxylation was shown to be on the pyrimidine using nuclear magnetic resonance spectroscopy. The aldehyde oxidase (AO) inhibitor raloxifene and the xanthine oxidase inhibitor febuxostat inhibited the formation of PF-6870961 in human liver cytosol, suggesting both enzymes were involved in the metabolism of the drug. However, greater inhibition was observed with raloxifene, indicating AO is a dominant enzyme in the biotransformation. The intrinsic clearance of the drug in human liver cytosol was estimated to be 0.002 ml/min per milligram protein. This study provides important novel information at three levels: 1) it provides additional new information on the recently developed novel compound PF-5190457, the first GHS-R1a blocker that has moved to development in humans; 2) it provides an example of a reverse translational approach where a discovery in humans was brought back, validated, and further investigated at the bench level; and 3) it demonstrates the importance of considering the molybdenum-containing oxidases during the development of new drug entities. SIGNIFICANCE STATEMENT: PF-5190457 is a novel ghrelin receptor inverse agonist that is currently undergoing clinical development for treatment of alcohol use disorder. PF-6870961, a major hydroxyl metabolite of the compound, was observed in human plasma, but was absent in human liver microsomal incubations. PF-6870961 was biosynthesized using liver cytosol, and the site of hydroxylation on the pyrimidine ring was characterized. Inhibitors of aldehyde oxidase and xanthine oxidase inhibited the formation of PF-6870961 in human liver cytosol, suggesting both enzymes were involved in the metabolism of the drug. This information is important for patient selection in subsequent clinical studies.

Do Associations Between Alcohol Use and Alcohol Use Disorder Vary by Weight Status? Results From the National Epidemiologic Survey on Alcohol and Related Conditions-III

BACKGROUND

Understanding whether the associations between alcohol use and alcohol use disorder (AUD) differ by weight status may be useful in screening for AUD in populations where obesity is common. We aimed to determine whether the associations between alcohol use and AUD differ by weight status.

METHODS

A total of 24,869 adult participants of the National Epidemiologic Survey on Alcohol and Related Conditions-III with a body mass index ≥18.5 kg/m² who reported past-year alcohol use were included. The AUD and Associated Disabilities Interview Schedule-5 were administered to identify past-year AUD. Logistic regression was used to test the associations between weight status and levels and patterns of alcohol use with AUD; interactions between weight status and alcohol use variables in relation to AUD were examined. Analyses were stratified by gender.

RESULTS

For males and females, the odds of AUD were higher with greater frequency of any alcohol use and heavy drinking, higher average quantity of drinks per drinking day, and past-year high-risk drinking. Among males, at the same average quantity of drinks per drinking day, frequency of heavy drinking, or presence of high-risk drinking, those with class 3 obesity had higher odds of AUD versus lower classes or no obesity (p for all interactions <0.01). Among females, at the same frequency of any alcohol use, those with healthy weight had the highest odds of AUD, while females with class 3 obesity had the lowest odds of AUD (p for interaction <0.001); interactions between weight status and other alcohol use variables were not significant (p ≥ 0.05).

CONCLUSIONS

The associations between some measures of alcohol use and AUD differed by weight status, with inconsistent results between males and females. Alcohol use thresholds typically used in AUD screening may be too high in males with class 3 obesity.

Activation of amylin receptors attenuates alcohol-mediated behaviours in rodents

Alcohol expresses its reinforcing properties by activating areas of the mesolimbic dopamine system, which consists of dopaminergic neurons projecting from the ventral tegmental area to the nucleus accumbens. The findings that reward induced by food and addictive drugs involve common mechanisms raise the possibility that gut-brain hormones, which control appetite, such as amylin, could be involved in reward regulation. Amylin decreases food intake, and despite its implication in the regulation of natural rewards, tenuous evidence support amylinergic mediation of artificial rewards, such as alcohol. Therefore, the present experiments were designed to investigate the effect of salmon calcitonin (sCT), an amylin receptor agonist and analogue of endogenous amylin, on various alcohol-related behaviours in rodents. We showed that acute sCT administration attenuated the established effects of alcohol on the mesolimbic dopamine system, particularly alcohol-induced locomotor stimulation and accumbal dopamine release. Using the conditioned place preference model, we demonstrated that repeated sCT administration prevented the expression of alcohol's rewarding properties and that acute sCT administration blocked the reward-dependent memory consolidation. In addition, sCT pre-treatment attenuated alcohol intake in low alcohol-consuming rats, with a more evident decrease in high alcohol consumers in the intermittent alcohol access model. Lastly, sCT did not alter peanut butter intake, blood alcohol concentration and plasma corticosterone levels in mice. Taken together, the present data support that amylin signalling is involved in the expression of alcohol reinforcement and that amylin receptor agonists could be considered for the treatment of alcohol use disorder in humans.

Eating disorders and substance use in adolescents: How substance users differ from nonsubstance users in an outpatient eating disorders treatment clinic

OBJECTIVE

The relationship between eating disorders (EDs) and substance use (SU) has only been briefly described in literature using mainly adult populations. This study examined the prevalence and characteristics of SU among patients of an adolescent ED outpatient treatment program.

METHOD

A retrospective chart analysis was conducted to determine and subsequently compare medical status, psychosocial factors, treatment course and outcome between patients with and without SU.

RESULTS

Over 60% of patients with SU status (n = 203) reported regularly consuming substances. 33.4% of substance users received a diagnosis involving purging behaviors compared to 5.9% of nonusers. Females composed 96.4% and 81.7% of users and nonusers, respectively. Users reported significantly more self-harm (57.7% of users vs. 38.6% of nonusers) but did not differ significantly in terms of trauma (abuse or victimization; 48.3% of users vs. 44.9% of nonusers). The percentage of ideal body weight significantly improved throughout treatment and did not differ by SU with a mean increase of 5.29% (SD = 13.6) among nonusers compared to 5.45% (SD = 7.5) of users. While users and nonusers did not differ before and after treatment in ED severity, users were more likely than nonusers to drop-out of treatment (41.5% of users vs. 25.2% of nonusers).

DISCUSSION

Adolescents with SU benefit from ED outpatient treatment as much as those without SU, however, users are more likely to drop-out. Therefore, treatment should target these adolescents' emotional dysregulation to improve treatment compliance. Further research is necessary to determine the efficacy of such an approach.

Identifying and Characterizing Subpopulations of Heavy Alcohol Drinkers Via a Sucrose Preference Test: A Sweet Road to a Better Phenotypic Characterization?

Aims

Sweet preference in individuals with alcohol use disorder (AUD) has been associated with family history of AUD and personality traits. Therefore, testing sweet preference may help identify subpopulations of AUD individuals.

Short summary

Sweet preference has been associated with family history of AUD and personality traits. We compared heavy drinkers based on their sweet liker status and using two cutoffs. Our findings support the role of sweet preference in heavy drinkers and point to the importance of how sweet likers are defined.

Methods

This study aimed at describing and comparing heavy drinkers based on their sweet liker status, through demographic, neuroendocrine, inflammatory, behavioral and drinking characteristics. Participants rated the pleasantness and intensity of sucrose solutions (0.05, 0.10, 0.21, 0.42 and 0.83 M). Two cutoffs were used to identify likers versus dislikers: Grouping A likers preferred 0.83 M and Grouping B likers preferred 0.83 or 0.42 M; the rest were dislikers.

Results

Sweet likers were 36% (n = 20) using Grouping A and 58.2% (n = 32) using Grouping B. Grouping B, but not Grouping A, sweet likers had higher BMI (P = 0.01). In Grouping B, sweet likers had higher plasma leptin and insulin concentrations and higher insulin resistance (P's < 0.05). C-reactive protein concentrations were higher in sweet likers in Grouping A (P = 0.0015) and at a trend level in Grouping B (P = 0.07). Grouping A sweet likers had higher alcohol craving (P = 0.0004). Sweet likers preferred spirits compared to nonspirits (wine and beer) across both grouping (P's < 0.05).

Conclusions

These results provide further support for the role of sweet liking phenotype in identifying subpopulations of AUD individuals. These findings also point to the importance of how sweet likers are defined, therefore highlighting the need for further research.

Pharmacological manipulation of the ghrelin system and alcohol hangover symptoms in heavy drinking individuals: Is there a link?

Ghrelin, an orexigenic peptide synthesized in the stomach, is a key player in the gut-brain axis. In addition to its role in regulating food intake and energy homeostasis, ghrelin has been shown to modulate alcohol-related behaviors. Alcohol consumption frequently results in hangover, an underexplored phenomenon with considerable medical, psychological, and socioeconomic consequences. While the pathophysiology of hangover is not clear, contributions of mechanisms such as alcohol-induced metabolic/endocrine changes, inflammatory/immune response, oxidative stress, and gut dysbiosis have been reported. Interestingly, these mechanisms considerably overlap with ghrelin's physiological functions. Here, we investigated whether pharmacological manipulation of the ghrelin system may affect alcohol hangover symptoms. Data were obtained from two placebo-controlled laboratory studies. The first study tested the effects of intravenous (IV) ghrelin and consisted of two experiments: a progressive-ratio IV alcohol self-administration (IV-ASA) and a fixed-dose IV alcohol clamp. The second study tested the effects of an oral ghrelin receptor inverse agonist (PF-5190457) and included a fixed-dose oral alcohol administration experiment. Alcohol hangover data were collected the morning after each alcohol administration experiment using the Acute Hangover Scale (AHS). IV ghrelin, compared to placebo, significantly reduced alcohol hangover after IV-ASA (p = 0.04) and alcohol clamp (p = 0.04); PF-5190457 had no significant effect on AHS scores. Females reported significantly higher hangover symptoms than males following the IV-ASA experiment (p = 0.04), but no gender × drug condition (ghrelin vs. placebo) effect was found. AHS total scores were positively correlated with peak subjective responses, including 'stimulation' (p = 0.08), 'sedation' (p = 0.009), 'feel high' (p = 0.05), and 'feel intoxicated' (p = 0.03) during the IV-ASA. IV ghrelin blunted the positive association between alcohol sedation and hangover as shown by trend-level drug × sedation effect (p = 0.08). This is the first study showing that exogenous ghrelin administration, but not ghrelin receptor inverse agonism, affects hangover symptoms. Future research should investigate the potential mechanism(s) underlying this effect.

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 Corticotropin Releasing Factor Receptor 1 in Alcohol Use Disorder: Still a Valid Drug Target?

Corticotropin releasing factor (CRF) is a neuropeptide that plays a key role in behavioral and physiological responses to stress. A large body of animal literature implicates CRF acting at type 1 CRF receptors (CRFR1) in consumption by alcohol-dependent subjects, stress-induced reinstatement of alcohol seeking, and possibly binge alcohol consumption. These studies have encouraged recent pilot studies of CRFR1 antagonists in humans with alcohol use disorder (AUD). It was a great disappointment to many in the field that these studies failed to show an effect of these compounds on stress-induced alcohol craving. Here, we examine these studies to explore potential limitations and discuss preclinical and human literature to ask whether CRFR1 is still a valid drug target to pursue for the treatment of AUD.

The importance of nutrition in aiding recovery from substance use disorders: A review

BACKGROUND

Nutrition is a prerequisite for health; yet, there is no special nutritional assessment or guidance for drug and alcohol dependent individuals, despite the fact that their food consumption is often very limited, risking malnutrition. Further, the premise is examined that malnutrition may promote drug seeking and impede recovery from substance use disorders (SUD).

METHOD

A narrative review addressed the relationship between substance use disorders and nutrition, including evidence for malnutrition, as well as their impact on metabolism and appetite regulation. The implications of the biopsychology of addiction and appetite for understanding the role of nutrition in SUD were also considered.

RESULTS

The literature overwhelmingly finds that subjects with alcohol use disorder (AUD) and drug use disorder (DUD) typically suffer from nutrient deficiencies. These nutrient deficiencies may be complicit in the alcoholic myopathy, osteopenia and osteoporosis, and mood disorders including anxiety and depression, observed in AUD and DUD. These same individuals have also been found to have altered body composition and altered hormonal metabolic regulators. Additionally, brain processes fundamental for survival are stimulated both by food, particularly sweet foods, and by substances of abuse, with evidence supporting confusion (addiction transfer) when recovering from SUD between cravings for a substance and craving for food.

CONCLUSION

Poor nutritional status in AUD and DUD severely impacts their physical and psychological health, which may impede their ability to resist substances of abuse and recover their health. This review contributes to a better understanding of interventions that could best support individuals with substance use disorders.

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.

Changes in circulating peptide YY and ghrelin are associated with early smoking relapse

Ghrelin and peptide YY (PYY) during ad libitum smoking have been associated with decreased reported craving (ghrelin) and increased positive affect (PYY), and higher baseline ghrelin levels predicted subsequent increased risk of smoking relapse. The current study assessed PYY and ghrelin during ad libitum smoking and again after the initial 48h of a smoking cessation attempt. The data compared smokers who abstained for 28days (n=37), smokers who relapsed (n=54), and nonsmokers (n=37). Plasma samples and subjective measures assessing craving and mood were collected at the beginning of each session. Results showed that relapsers experienced greater levels of distress (ps <0.01). While nonsmokers and abstainers showed no change in ghrelin across the initial 48h, relapsers declined (p <0.01). With PYY, relapsers increased (p <0.05) across the early abstinent phase. PYY and ghrelin may be useful predictors of relapse, specifically in reference to early withdrawal.

Hepatic, lipid and genetic factors associated with obesity: crosstalk with alcohol dependence?

OBJECTIVES

Alcohol dependence represents a leading cause of mortality and morbidity. Understanding the variables that contribute to this diagnosis and its severity is critical. An overlap between factors that may predispose people to become obese and those that may increase the risk of alcohol dependence may exist. However, data in the literature are not conclusive. Therefore, this study aimed to identify the association between alcohol dependence and obesity-related factors, including biochemical and genetic factors.

METHODS

In a case-control study with 829 participants, factors involved with metabolism and obesity were assessed, including biochemical lipid and liver markers, and the fat mass and obesity-associated (FTO) single nucleotide polymorphism (SNP) rs8050136.

RESULTS

Increased triglycerides, having one or two minor A alleles for rs8050136 and being a smoker were associated with increased risk of alcohol dependence, while increased low-density lipoprotein cholesterol was associated with decreased risk. In addition, having abnormal gamma-glutamyl transferase and being female were factors associated with an increased severity of alcohol dependence.

CONCLUSIONS

Our preliminary findings suggest a link between alcohol dependence and obesity-related biochemical and genetic factors. Future studies are needed to better understand if these factors may play a predictive role and/or may act as biomarkers for treatment response.

Serum Insulin Levels Are Reduced by Intravenous Ghrelin Administration but Do Not Correlate with Alcohol Craving in Alcohol-Dependent Individuals

BACKGROUND

Increasing evidence supports a role for appetite-regulating pathways like ghrelin, insulin, and leptin in alcoholism. We previously reported that intravenous (i.v.) exogenous ghrelin increases alcohol craving. We also reported i.v. ghrelin reduces endogenous serum leptin, whose levels, in turn, negatively correlated with alcohol craving. Exogenous ghrelin administration decreases insulin secretion both in vitro and in vivo experiments. This study tested the hypothesis that i.v. ghrelin may also decrease endogenous serum insulin levels in alcoholic individuals. Additionally, we explored possible correlations between serum insulin and alcohol craving, since a correlation between insulin and alcohol craving was previously reported.

METHODS

This was a double-blind, placebo-controlled human laboratory study ( n =43). Non-treatment-seeking, alcohol-dependent, heavy drinkers were randomized to receive i.v. ghrelin or placebo, followed by an alcohol cue-reactivity procedure.

RESULTS

There was a main effect for i.v. ghrelin, compared to placebo in reducing serum insulin ( P <.05). There was also a time effect ( P <.001) but not ghrelin x time interaction ( P >.05). We did not find a correlation between the reduction of serum insulin and alcohol craving ( P >.05). The change in serum insulin was consistent with a parallel reduction in serum connective-peptide in the ghrelin group compared with placebo, although this difference did not reach statistical significance ( P =.076). No similar effects were found for other glucose-regulating hormones analyzed i.e. glucagon, glucagon-like peptide-1, and gastric inhibitory peptide ( P s>.05).

CONCLUSIONS

These findings indicate i.v. ghrelin administration has an effect on reducing serum insulin in alcohol-dependent individuals; however, the reduction of insulin did not correlate with changes in alcohol cue-elicited craving. We speculate that, unlike for leptin, the interactions between ghrelin and insulin relationship are limited at the peripheral level. However, mechanistic studies are needed to investigate this hypothesis.

Genetic variation of the growth hormone secretagogue receptor gene is associated with alcohol use disorders identification test scores and smoking

The multifaceted gut‐brain peptide ghrelin and its receptor (GHSR‐1a) are implicated in mechanisms regulating not only the energy balance but also the reward circuitry. In our pre‐clinical models, we have shown that ghrelin increases whereas GHSR‐1a antagonists decrease alcohol consumption and the motivation to consume alcohol in rodents. Moreover, ghrelin signaling is required for the rewarding properties of addictive drugs including alcohol and nicotine in rodents. Given the hereditary component underlying addictive behaviors and disorders, we sought to investigate whether single nucleotide polymorphisms (SNPs) located in the pre‐proghrelin gene (GHRL) and GHSR‐1a gene (GHSR) are associated with alcohol use, measured by the alcohol use disorders identification test (AUDIT) and smoking. Two SNPs located in GHRL, rs4684677 (Gln90Leu) and rs696217 (Leu72Met), and one in GHSR, rs2948694, were genotyped in a subset (n = 4161) of a Finnish population‐based cohort, the Genetics of Sexuality and Aggression project. The effect of these SNPs on AUDIT scores and smoking was investigated using linear and logistic regressions, respectively. We found that the minor allele of the rs2948694 SNP was nominally associated with higher AUDIT scores (P = 0.0204, recessive model) and smoking (P = 0.0002, dominant model). Furthermore, post hoc analyses showed that this risk allele was also associated with increased likelihood of having high level of alcohol problems as determined by AUDIT scores ≥ 16 (P = 0.0043, recessive model). These convergent findings lend further support for the hypothesized involvement of ghrelin signaling in addictive disorders.

A dysbiotic subpopulation of alcohol-dependent subjects

The vast majority of studies that assessed the importance of biological factors for the development of psychiatric disorders focused on processes occurring at the brain level. Alcohol-dependence is a very frequent psychiatric disorder where psycho-pharmacological interventions are only of moderate efficacy. Our laboratory has recently described that a subpopulation of alcohol-dependent subjects, that accounted for approximately 40% of individuals tested, presented with an increased intestinal permeability, with a dysbiosis, with alterations in the metabolomic content of faeces--that could play a role in the increased permeability--and finally with a more severe profile of alcohol-dependence than the other non-dysbiotic subpopulation. In this addendum, we discuss the implications of our observations for the pathophysiology of alcohol dependence where we try to discriminate which addiction dimensions are likely related to the gut microbiota alterations and whether these alterations are the cause or the consequence of drinking habits.

Changes in Nutrition-Related Behaviors in Alcohol-Dependent Patients After Outpatient Detoxification: The Role of Chocolate

BACKGROUND

Previous studies have reported changes in nutrition-related behaviors in alcohol-dependent patients after alcohol detoxification, but prospective studies assessing the effects of these changes on maintaining abstinence are lacking.

OBJECTIVES

To assess changes in craving and consumption of chocolate and other sweets over time up to six months after outpatient alcohol detoxification treatment and to detect differences in abstinent versus nonabstinent patients.

METHODS

One hundred and fifty alcohol-dependent patients were included in this prospective observational study. Participants completed self-report questionnaires on nutrition-related behaviors and craving before detoxification treatment (baseline, t1), one week (t2), one month (t3), and six months later (t4).

RESULTS

Significant changes in craving for and consumption of chocolate as well as in craving for other sweets were observed over time. Increases were most prominent within the first month. Patients who remained abstinent until t3 consumed three times more chocolate than nonabstainers. One quarter of the patients switched from being rare (t1) to frequent (t3) chocolate eaters, and 84% of these remained abstinent until t3. No significant correlations were found between craving for alcohol and craving for or consumption of chocolate or other sweets.

CONCLUSIONS/IMPORTANCE

In the first month after outpatient alcohol detoxification treatment, significant changes in nutrition-related behaviors were observed. These changes were not associated with alcohol craving. For a subgroup, increasing the frequency of chocolate consumption might be a temporary protective factor with respect to alcohol relapse.

Caenorhabditis elegans as a Model to Study the Molecular and Genetic Mechanisms of Drug Addiction

Drug addiction takes a massive toll on society. Novel animal models are needed to test new treatments and understand the basic mechanisms underlying addiction. Rodent models have identified the neurocircuitry involved in addictive behavior and indicate that rodents possess some of the same neurobiologic mechanisms that mediate addiction in humans. Recent studies indicate that addiction is mechanistically and phylogenetically ancient and many mechanisms that underlie human addiction are also present in invertebrates. The nematode Caenorhabditis elegans has conserved neurobiologic systems with powerful molecular and genetic tools and a rapid rate of development that enables cost-effective translational discovery. Emerging evidence suggests that C. elegans is an excellent model to identify molecular mechanisms that mediate drug-induced behavior and potential targets for medications development for various addictive compounds. C. elegans emit many behaviors that can be easily quantitated including some that involve interactions with the environment. Ethanol (EtOH) is the best-studied drug-of-abuse in C. elegans and at least 50 different genes/targets have been identified as mediating EtOH's effects and polymorphisms in some orthologs in humans are associated with alcohol use disorders. C. elegans has also been shown to display dopamine and cholinergic system-dependent attraction to nicotine and demonstrate preference for cues previously associated with nicotine. Cocaine and methamphetamine have been found to produce dopamine-dependent reward-like behaviors in C. elegans. These behavioral tests in combination with genetic/molecular manipulations have led to the identification of dozens of target genes/systems in C. elegans that mediate drug effects. The one target/gene identified as essential for drug-induced behavioral responses across all drugs of abuse was the cat-2 gene coding for tyrosine hydroxylase, which is consistent with the role of dopamine neurotransmission in human addiction. Overall, C. elegans can be used to model aspects of drug addiction and identify systems and molecular mechanisms that mediate drug effects. The findings are surprisingly consistent with analogous findings in higher-level organisms. Further, model refinement is warranted to improve model validity and increase utility for medications development.

Leptin levels are reduced by intravenous ghrelin administration and correlated with cue-induced alcohol craving

Increasing evidence supports the role of appetite-regulating pathways, including ghrelin and leptin, in alcoholism. This study tested the hypothesis that intravenous exogenous ghrelin administration acutely decreases endogenous serum leptin levels, and that changes in leptin levels negatively correlate with alcohol craving. This was a double-blind, placebo-controlled human laboratory study. Non-treatment-seeking, alcohol-dependent, heavy drinkers (n=45) were randomized to receive intravenous ghrelin or placebo, followed by a cue-reactivity procedure, during which participants were exposed to neutral (juice) and alcohol trial cues. There was a main effect for intravenous ghrelin administration, compared with placebo, in reducing serum leptin levels (P<0.01). Post hoc analysis showed significant differences in serum leptin levels at the alcohol trial (P<0.05) that persisted at the end of the experiment (P<0.05). By contrast, there were no significant differences in serum leptin levels at the juice trial (P=not significant (NS)). The change of serum leptin level at the alcohol trial correlated with the increase in alcohol urge (P<0.05), whereas urge to drink juice was not correlated with the leptin change at the juice trial (P=NS). These findings provide preliminary evidence of ghrelin-leptin cross-talk in alcoholic individuals and suggest that their relationship may have a role in alcohol craving.

Microstructural analysis of rat ethanol and water drinking patterns using a modified operant self-administration model

BACKGROUND

Ethanol drinking pattern has emerged as an important factor in the development, maintenance, and health consequences of alcohol use disorders in humans. The goal of these studies was to further our understanding of this important factor through refinement of an operant rodent model of ethanol consumption capable of drinking pattern microstructural analysis. We evaluated measures of total consumption, appetitive behavior, and drinking microstructure for ethanol and water at baseline and assessed alterations induced by two treatments previously shown to significantly alter gross ethanol appetitive and consummatory behaviors in opposing directions.

METHODS

Male Long-Evans rats were trained on an FR1 operant paradigm which allowed for continuous liquid access until an 8 second pause in consumption resulted in termination of liquid access. Total appetitive and consummatory behaviors were assessed in addition to microstructural drinking pattern for both ethanol and water during a five day baseline drinking period, after chronic intermittent ethanol vapor exposure, and following administration of a cannabinoid receptor antagonist SR141716a.

RESULTS

As in previous operant studies, ethanol vapor exposure resulted in increases in ethanol-directed responding, total consumption, and rate of intake. Further, striking differential alterations to ethanol and water bout size, duration, and lick pattern occurred consistent with alterations in hedonic evaluation. Vapor additionally specifically reduced the number of ethanol-directed lever presses which did not result in subsequent consumption. SR141716a administration reversed many of these effects.

CONCLUSIONS

The addition of microstructural analysis to operant self-administration by rodents provides a powerful and translational tool for the detection of specific alterations in ethanol drinking pattern which may enable insights into neural mechanisms underlying specific components of drug consumption.

Development and validation of an UPLC-MS/MS assay for quantitative analysis of the ghrelin receptor inverse agonist PF-5190457 in human or rat plasma and rat brain

PF-5190457 is a ghrelin receptor inverse agonist that is currently undergoing clinical development for the treatment of alcoholism. Our aim was to develop and validate a simple and sensitive assay for quantitative analysis of PF-5190457 in human or rat plasma and rat brain using liquid chromatography-tandem mass spectrometry. The analyte and stable isotope internal standard were extracted from 50 μL plasma or rat brain homogenate by protein precipitation using 0.1% formic acid in acetonitrile. Chromatography was carried out on an Acquity UPLC BEH C18 (2.1 mm × 50 mm) column with 1.7 μm particle size and 130 Å pore size. The flow rate was 0.5 mL/min and total chromatographic run time was 2.2 min. The mobile phase consisted of a gradient mixture of water: acetonitrile 95:5% (v/v) containing 0.1% formic acid (solvent A) and 100% acetonitrile containing 0.1% formic acid (solvent B). Multiple reaction monitoring was carried out in positive electro-spray ionization mode using m/z 513.35 → 209.30 for PF-5190457 and m/z 518.47 → 214.43 for the internal standard. The recovery ranged from 102 to 118% with coefficient of variation (CV) less than 6% for all matrices. The calibration curves for all matrices were linear over the studied concentration range (R(2) ≥ 0.998, n = 3). The lower limit of quantification was 1 ng/mL in rat or human plasma and 0.75 ng/g in rat brain. Intra- and inter-run mean percent accuracies were between 85 and 115% and percent imprecision was ≤15%. The assays were successfully utilized to measure the concentration of PF-5190457 in pre-clinical and clinical pharmacology studies of the compound.

Impulsive choice predicts anxiety-like behavior, but not alcohol or sucrose consumption, in male Long-Evans rats

BACKGROUND

Prior human research indicates robust, positive relations between impulsive choice (i.e., preference for smaller, immediate over larger, delayed rewards) and alcohol use disorders. However, varied findings in the nonhuman literature reveal a relatively ambiguous relation between impulsive choice and alcohol consumption in rodents. In addition, few rodent studies have investigated potential relations between impulsive choice and common covariates of alcohol consumption (e.g., avidity for sweet substances or anxiety-like behavior).

METHODS

Ninety-two male Long-Evans rats completed an impulsive-choice task. From this larger sample, extreme high- and low-impulsive groups (n = 30 each) were retained for further testing. In separate tests, subsequent open-field behavior and consumption of oral alcohol (12% w/v) and isocaloric sucrose were examined. Impulsive choice was then retested to examine whether behavior remained stable over the course of the experiment.

RESULTS

No significant relations emerged between impulsive choice and either alcohol or sucrose consumption. However, impulsive choice predicted greater anxiety-like behavior (avoidance of the center field, defecation) in the open-field test. In turn, greater anxiety predicted lower alcohol and sucrose consumption. Finally, choice remained generally stable across the experiment, although high-impulsive rats tended toward less impulsive choice in the retest.

CONCLUSIONS

Although impulsive choice and alcohol consumption appear to share some variance with anxiety-like behavior, the present data offer no support for a relation between impulsive choice and alcohol consumption in Long-Evans rats. Together with mixed rodent data from prior reports, these findings attenuate cross-species comparisons to human relations between impulsive choice and alcohol use disorders.

Pharmacotherapy for alcohol use disorder: current and emerging therapies

Alcohol use disorder is a heterogeneous illness with a complex biology that is controlled by many genes and gene-by-environment interactions. Several efficacious, evidence-based treatments currently exist for treating and managing alcohol use disorder, including a number of pharmacotherapies that target specific aspects of biology that initiate and maintain dangerous alcohol misuse. This article reviews the neurobiological and neurobehavioral foundation of alcohol use disorder, the mechanisms of action and evidence for the efficacy of currently approved medications for treatment, and the literature on other emerging pharmacotherapies.

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.

Schizophrenia and Depression Co-Morbidity: What We have Learned from Animal Models

Patients with schizophrenia are at an increased risk for the development of depression. Overlap in the symptoms and genetic risk factors between the two disorders suggests a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. Understanding these shared mechanisms will be important in informing the development of new treatments. Rodent models are powerful tools for understanding gene function as it relates to behavior. Examining rodent models relevant to both schizophrenia and depression reveals a number of common mechanisms. Current models which demonstrate endophenotypes of both schizophrenia and depression are reviewed here, including models of CUB and SUSHI multiple domains 1, PDZ and LIM domain 5, glutamate Delta 1 receptor, diabetic db/db mice, neuropeptide Y, disrupted in schizophrenia 1, and its interacting partners, reelin, maternal immune activation, and social isolation. Neurotransmission, brain connectivity, the immune system, the environment, and metabolism emerge as potential common mechanisms linking these models and potentially explaining comorbid depression in schizophrenia.

Neuropeptide trefoil factor 3 attenuates naloxone-precipitated withdrawal in morphine-dependent mice

RATIONALE

The persistence of physical dependence and craving in addicts is considered to contribute to relapse. Increasing evidence indicates that neuropeptide systems are associated with several phases of drug addiction, but little is known about whether the neuropeptide trefoil factor affects withdrawal symptoms.

OBJECTIVES

This study aims to investigate the potential effects of the neuropeptide trefoil factor 3 (TFF3) on naloxone-precipitated withdrawal symptoms in morphine-dependent mice.

RESULTS

Mice received increasing doses of morphine over 3 days. On day 4, the mice were injected with TFF3 (1.0 mg/kg, i.p.) 30 min after the last dose of morphine. Thirty minutes after TFF3 treatment, naloxone (1 mg/kg, i.p.) was injected, and body weight, jumping behavior, wet-dog shakes, and locomotor activity were assessed 30 min later. Naloxone caused significant weight loss and increased jumping behavior and wet-dog shakes in morphine-dependent mice. TFF3 (1.0 mg/kg) reversed these behavioral symptoms caused by morphine withdrawal, suggesting that TFF3 might ameliorate physical dependence associated with opiate addiction. Furthermore, TFF3 pretreatment significantly reduced morphine withdrawal-induced increases in plasma corticosterone and adrenocorticotropic hormone levels. The glucocorticoid receptor agonist RU486 blocked the behavioral effects of TFF3 on morphine withdrawal symptoms. Finally, Fos expression in the medial prefrontal cortex which was decreased during morphine withdrawal was increased by TFF3 pretreatment.

CONCLUSION

These findings indicate that TFF3 might be a potential therapeutic candidate for opiate addiction by regulating glucocorticoid secretion and neuronal activation in the prefrontal cortex.

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.

Disrupted-In-Schizophrenia-1 (DISC1) interactome and mental disorders: impact of mouse models

Disrupted-In-Schizophrenia-1 (DISC1) has captured much attention because it predisposes individuals to a wide range of mental illnesses. Notably, a number of genes encoding proteins interacting with DISC1 are also considered to be relevant risk factors of mental disorders. We reasoned that the understanding of DISC1-associated mental disorders in the context of network principles will help to address fundamental properties of DISC1 as a disease gene. Systematic integration of behavioural phenotypes of genetic mouse lines carrying perturbation in DISC1 interacting proteins would contribute to a better resolution of neurobiological mechanisms of mental disorders associated with the impaired DISC1 interactome and lead to a development of network medicine. This review also makes specific recommendations of how to assess DISC1 associated mental disorders in mouse models and discuss future directions.

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.

A behavioral-genetic investigation of bulimia nervosa and its relationship with alcohol use disorder

Bulimia nervosa (BN) and alcohol use disorder (AUD) frequently co-occur and may share genetic factors; however, the nature of their association is not fully understood. We assessed the extent to which the same genetic and environmental factors contribute to liability to BN and AUD. A bivariate structural equation model using a Cholesky decomposition was fit to data from 7241 women who participated in the Swedish Twin study of Adults: Genes and Environment. The proportion of variance accounted for by genetic and environmental factors for BN and AUD and the genetic and environmental correlations between these disorders were estimated. In the best-fitting model, the heritability estimates were 0.55 (95% CI: 0.37; 0.70) for BN and 0.62 (95% CI: 0.54; 0.70) for AUD. Unique environmental factors accounted for the remainder of variance for BN. The genetic correlation between BN and AUD was 0.23 (95% CI: 0.01; 0.44), and the correlation between the unique environmental factors for the two disorders was 0.35 (95% CI: 0.08; 0.61), suggesting moderate overlap in these factors. The findings from this investigation provide additional support that some of the same genetic factors may influence liability to both BN and AUD.

Ghrelin increases GABAergic transmission and interacts with ethanol actions in the rat central nucleus of the amygdala

The neural circuitry that processes natural rewards converges with that engaged by addictive drugs. Because of this common neurocircuitry, drugs of abuse have been able to engage the hedonic mechanisms normally associated with the processing of natural rewards. Ghrelin is an orexigenic peptide that stimulates food intake by activating GHS-R1A receptors in the hypothalamus. However, ghrelin also activates GHS-R1A receptors on extrahypothalamic targets that mediate alcohol reward. The central nucleus of the amygdala (CeA) has a critical role in regulating ethanol consumption and the response to ethanol withdrawal. We previously demonstrated that rat CeA GABAergic transmission is enhanced by acute and chronic ethanol treatment. Here, we used quantitative RT-PCR (qRT-PCR) to detect Ghsr mRNA in the CeA and performed electrophysiological recordings to measure ghrelin effects on GABA transmission in this brain region. Furthermore, we examined whether acute or chronic ethanol treatment would alter these electrophysiological effects. Our qRT-PCR studies show the presence of Ghsr mRNA in the CeA. In naive animals, superfusion of ghrelin increased the amplitude of evoked inhibitory postsynaptic potentials (IPSPs) and the frequency of miniature inhibitory postsynaptic currents (mIPSCs). Coapplication of ethanol further increased the ghrelin-induced enhancement of IPSP amplitude, but to a lesser extent than ethanol alone. When applied alone, ethanol significantly increased IPSP amplitude, but this effect was attenuated by the application of ghrelin. In neurons from chronic ethanol-treated (CET) animals, the magnitude of ghrelin-induced increases in IPSP amplitude was not significantly different from that in naive animals, but the ethanol-induced increase in amplitude was abolished. Superfusion of the GHS-R1A antagonists D-Lys3-GHRP-6 and JMV 3002 decreased evoked IPSP and mIPSC frequency, revealing tonic ghrelin activity in the CeA. D-Lys3-GHRP-6 and JMV 3002 also blocked ghrelin-induced increases in GABAergic responses. Furthermore, D-Lys3-GHRP-6 did not affect ethanol-induced increases in IPSP amplitude. These studies implicate a potential role for the ghrelin system in regulating GABAergic transmission and a complex interaction with ethanol at CeA GABAergic synapses.

Obesity and addiction: neurobiological overlaps

Drug addiction and obesity appear to share several properties. Both can be defined as disorders in which the saliency of a specific type of reward (food or drug) becomes exaggerated relative to, and at the expense of others rewards. Both drugs and food have powerful reinforcing effects, which are in part mediated by abrupt dopamine increases in the brain reward centres. The abrupt dopamine increases, in vulnerable individuals, can override the brain's homeostatic control mechanisms. These parallels have generated interest in understanding the shared vulnerabilities between addiction and obesity. Predictably, they also engendered a heated debate. Specifically, brain imaging studies are beginning to uncover common features between these two conditions and delineate some of the overlapping brain circuits whose dysfunctions may underlie the observed deficits. The combined results suggest that both obese and drug-addicted individuals suffer from impairments in dopaminergic pathways that regulate neuronal systems associated not only with reward sensitivity and incentive motivation, but also with conditioning, self-control, stress reactivity and interoceptive awareness. In parallel, studies are also delineating differences between them that centre on the key role that peripheral signals involved with homeostatic control exert on food intake. Here, we focus on the shared neurobiological substrates of obesity and addiction.

Neurocircuitry for modeling drug effects

The identification and functional understanding of the neurocircuitry that mediates alcohol and drug effects that are relevant for the development of addictive behavior is a fundamental challenge in addiction research. Here we introduce an assumption-free construction of a neurocircuitry that mediates acute and chronic drug effects on neurotransmitter dynamics that is solely based on rodent neuroanatomy. Two types of data were considered for constructing the neurocircuitry: (1) information on the cytoarchitecture and neurochemical connectivity of each brain region of interest obtained from different neuroanatomical techniques; (2) information on the functional relevance of each region of interest with respect to alcohol and drug effects. We used mathematical data mining and hierarchical clustering methods to achieve the highest standards in the preprocessing of these data. Using this approach, a dynamical network of high molecular and spatial resolution containing 19 brain regions and seven neurotransmitter systems was obtained. Further graph theoretical analysis suggests that the neurocircuitry is connected and cannot be separated into further components. Our analysis also reveals the existence of a principal core subcircuit comprised of nine brain regions: the prefrontal cortex, insular cortex, nucleus accumbens, hypothalamus, amygdala, thalamus, substantia nigra, ventral tegmental area and raphe nuclei. Finally, by means of algebraic criteria for synchronizability of the neurocircuitry, the suitability for in silico modeling of acute and chronic drug effects is indicated. Indeed, we introduced as an example a dynamical system for modeling the effects of acute ethanol administration in rats and obtained an increase in dopamine release in the nucleus accumbens-a hallmark of drug reinforcement-to an extent similar to that seen in numerous microdialysis studies. We conclude that the present neurocircuitry provides a structural and dynamical framework for large-scale mathematical models and will help to predict chronic drug effects on brain function.

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.

Variation in the gene TAS2R13 is associated with differences in alcohol consumption in patients with head and neck cancer

Variation in responsiveness to bitter-tasting compounds has been associated with differences in alcohol consumption. One strong genetic determinant of variation in bitter taste sensitivity is alleles of the TAS2R gene family, which encode chemosensory receptors sensitive to a diverse array of natural and synthetic compounds. Members of the TAS2R family, when expressed in the gustatory system, function as bitter taste receptors. To better understand the relationship between TAS2R function and alcohol consumption, we asked if TAS2R variants are associated with measures of alcohol consumption in a head and neck cancer patient cohort. Factors associated with increased alcohol intake are of strong interest to those concerned with decreasing the incidence of cancers of oral and pharyngeal structures. We found a single nucleotide polymorphism (SNP) located within the TAS2R13 gene (rs1015443 [C1040T, Ser259Asn]), which showed a significant association with measures of alcohol consumption assessed via the Alcohol Use Disorders Identification Test (AUDIT). Analyses with other SNPs in close proximity to rs1015443 suggest that this locus is principally responsible for the association. Thus, our results provide additional support to the emerging hypothesis that genetic variation in bitter taste receptors can impact upon alcohol consumption.