The Change of Plasma Ghrelin and Leptin Levels by the Development of Type 2 Diabetes Mellitus in Patients With Alcohol Dependence

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The prevalence of diabetes mellitus type 2 in people with alcohol use disorders: a systematic review and large scale meta-analysis

Type 2 Diabetes Mellitus (T2DM) is highly predictive of cardiovascular diseases and is associated with worse quality of life and increased healthcare utilisation. The current meta-analysis aimed to (i) describe the pooled prevalence of T2DM in people with alcohol use disorders (AUDs), (ii) investigate the impact of demographic, clinical and treatment factors, and (iii) compare T2DM prevalences in AUDs versus the general population. The trim and fill adjusted pooled T2DM prevalence among 3998 people with AUDs (age range 34.8-51.1 years; 76.6% male) (N studies=7) was 12.4% (95%CI=11.8-13.9%). Higher T2DM prevalences were observed in studies with a higher mean age and a higher percentage of male participants, and in studies with self- or physician reported T2DM assessment. A trend for higher T2DM prevalences was found in inpatient settings, in studies assessing T2DM with the gold-standard oral glucose tolerance test compared with fasting glucose only, and with studies including patients with a higher percentage of physical co-morbidity. Although healthy control data are lacking, the pooled prevalence is similar to that observed in people with severe mental illness who are considered a high-risk group. Routine screening and multidisciplinary management of T2DM in people with AUDs is needed.

Ghrelin knockout mice show decreased voluntary alcohol consumption and reduced ethanol-induced conditioned place preference

Recent work suggests that stomach-derived hormone ghrelin receptor (GHS-R1A) antagonism may reduce motivational aspects of ethanol intake. In the current study we hypothesized that the endogenous GHS-R1A agonist ghrelin modulates alcohol reward mechanisms. For this purpose ethanol-induced conditioned place preference (CPP), ethanol-induced locomotor stimulation and voluntary ethanol consumption in a two-bottle choice drinking paradigm were examined under conditions where ghrelin and its receptor were blocked, either using ghrelin knockout (KO) mice or the specific ghrelin receptor (GHS-R1A) antagonist "JMV2959". We showed that ghrelin KO mice displayed lower ethanol-induced CPP than their wild-type (WT) littermates. Consistently, when injected during CPP-acquisition, JMV2959 reduced CPP-expression in C57BL/6 mice. In addition, ethanol-induced locomotor stimulation was lower in ghrelin KO mice. Moreover, GHS-R1A blockade, using JMV2959, reduced alcohol-stimulated locomotion only in WT but not in ghrelin KO mice. When alcohol consumption and preference were assessed using the two-bottle choice test, both genetic deletion of ghrelin and pharmacological antagonism of the GHS-R1A (JMV2959) reduced voluntary alcohol consumption and preference. Finally, JMV2959-induced reduction of alcohol intake was only observed in WT but not in ghrelin KO mice. Taken together, these results suggest that ghrelin neurotransmission is necessary for the stimulatory effect of ethanol to occur, whereas lack of ghrelin leads to changes that reduce the voluntary intake as well as conditioned reward by ethanol. Our findings reveal a major, novel role for ghrelin in mediating ethanol behavior, and add to growing evidence that ghrelin is a key mediator of the effects of multiple abused drugs.

Genome-wide DNA methylation patterns in discordant sib pairs with alcohol dependence

INTRODUCTION

Alcohol dependence is a complex disease caused by a confluence of environmental and genetic factors. Epigenetic mechanisms have been shown to play an important role in the pathogenesis of alcohol dependence.

METHODS

To determine if alterations in gene-specific methylation were associated with alcohol dependence, a genome-wide DNA methylation analysis was performed on peripheral blood mononuclear cells from alcohol-dependent patients and siblings without alcohol dependence as controls. The Illumina Infinium Human Methylation450 BeadChip was used and gene-specific methylation of DNA isolated from peripheral blood mononuclear cells was assessed. Genes ALDH1L2, GAD1, DBH and GABRP were selected to validate beadchip results by pyrosequencing.

RESULTS

Compared to normal controls, 865 hypomethylated and 716 hypermethylated CG sites in peripheral blood mononuclear cell DNA in alcohol-dependent patients were identified. The most hypomethylated CG site is located in the promoter of SSTR4 (somatostatin receptor 4) and the most hypermethylated CG site is GABRP (gamma-aminobutyric acid A receptor). The results from beadchip analysis were consistent with that of pyrosequencing.

DISCUSSION

DNA methylation might be associated with alcohol dependence. Genes SSTR4, ALDH1L2, GAD1, DBH and GABRP may participate in the biological process of alcohol dependence.

Alcoholism and diabetes mellitus

Chronic use of alcohol is considered to be a potential risk factor for the incidence of type 2 diabetes mellitus (T2DM), which causes insulin resistance and pancreatic β-cell dysfunction that is a prerequisite for the development of diabetes. However, alcohol consumption in diabetes has been controversial and more detailed information on the diabetogenic impact of alcohol seems warranted. Diabetes, especially T2DM, causes dysregulation of various metabolic processes, which includes a defect in the insulin-mediated glucose function of adipocytes, and an impaired insulin action in the liver. In addition, neurobiological profiles of alcoholism are linked to the effects of a disruption of glucose homeostasis and of insulin resistance, which are affected by altered appetite that regulates the peptides and neurotrophic factors. Since conditions, which precede the onset of diabetes that are associated with alcoholism is one of the crucial public problems, researches in efforts to prevent and treat diabetes with alcohol dependence, receives special clinical interest. Therefore, the purpose of this mini-review is to provide the recent progress and current theories in the interplay between alcoholism and diabetes. Further, the purpose of this study also includes summarizing the pathophysiological mechanisms in the neurobiology of alcoholism.