Differential association between the GLP1R gene variants and brain functional connectivity according to the severity of alcohol use

Glucagon-like peptide-1 receptor agonists, but not dipeptidyl peptidase-4 inhibitors, reduce alcohol intake

BACKGROUNDDespite growing preclinical evidence that glucagon-like peptide1 receptor agonists (GLP-1RAs) could be repurposed to treat alcohol use disorder (AUD), clinical evidence is scarce. Additionally, the potential impact of dipeptidyl peptidase-4 inhibitors (DPP-4Is) on alcohol intake is largely unknown.METHODSWe conducted a large cohort study using 2008-2023 electronic health records data from the U.S. Department of Veterans Affairs. Changes in Alcohol Use Disorders Identification Test-Consumption (AUDIT-C) scores were compared between propensity-score-matched GLP-1RA recipients, DPP-4I recipients, and unexposed comparators. We further tested the effects of 2 DPP-4Is, linagliptin and omarigliptin, on binge-like alcohol drinking in mice and operant oral alcohol self administration in alcohol-dependent rats, models previously used to show a significant effect of the GLP-1RA semaglutide in reducing alcohol intake.RESULTSGLP-1RA recipients reported a greater reduction in AUDIT-C scores than unexposed individuals (difference-in-difference [DiD]: 0.09 [95% CI: 0.03, 0.14], P = 0.0025) and DPP-4I recipients (DiD: 0.11 [95% CI: 0.05,0.17], P = 0.0002). Reductions in drinking were more pronounced among individuals with baseline AUD (GLP-1RA versus unexposed: 0.51 [95% CI: 0.29,0.72], P < 0.0001; GLP-1RA versus DPP-4I: 0.65 [95% CI: 0.43,0.88], P < 0.0001) and baseline hazardous drinking (GLP-1RA versus unexposed: 1.38 [95% CI: 1.07,1.69], P < 0.0001; GLP-1RA versus DPP-4I: 1.00 [95% CI: 0.68,1.33], P < 0.0001). There were no differences between DPP-4I recipients and unexposed individuals. The latter results were confirmed via a reverse translational approach. Specifically, neither linagliptin nor omarigliptin reduced alcohol drinking in mice or rats. The rodent experiments also confirmed target engagemhent, as both DPP-4Is reduced blood glucose levels.CONCLUSIONConvergent findings across humans, mice, and rats indicated that GLP-1RAs, but not DPP-4Is, reduce alcohol consumption and may be efficacious in treating AUD.FUNDINGThis work was supported by the National Institutes of Health Intramural Research Program (ZIA DA000635, ZIA DA000644, ZIA DA000602), National Institute on Alcohol Abuse and Alcoholism extramural funding (R01 AA030041, P01 AA029545, U01 AA026224, U24 AA020794, U01 AA020790, U10 AA013566), the U.S. Department of Veterans Affairs (I01BX004820), and an Alkermes Pathways Research Award.

An inhibitory GLP-1 circuit in the lateral septum modulates reward processing and alcohol intake in rodents

BACKGROUND

Alcohol use disorder (AUD) is a complex psychiatric condition with limited effective treatment options. Glucagon-like peptide-1 receptor (GLP-1R) agonists have emerged as potential AUD treatment, as they have been shown to modulate reward-related behaviours, including those linked to alcohol consumption. However, the underlying mechanisms and neurocircuitry remain unclear. This study investigated the role of GLP-1R in the lateral septum (LS), a brain region highly expressing GLP-1R and implicated in reward-related behaviours, including alcohol-induced reward and consumption.

METHODS

Behavioural, neurochemical, molecular, and electrophysiological methods were used to investigate the effect of LS GLP-1R signalling in alcohol-mediated responses in rodents.

FINDINGS

LS GLP-1R activation attenuated alcohol's rewarding effects, reducing locomotor stimulation, place preference, and accumbal dopamine release. Intra-LS infusion of the GLP-1R agonist exendin-4 (Ex4) reduced alcohol intake dose-dependently without affecting food or water consumption, while GLP-1R inhibition increased alcohol intake. Furthermore, LS GLP-1R expression correlated with alcohol intake in male but not female rats, suggesting sex-specific effects of long-term alcohol exposure. Ex vivo electrophysiology indicated that GLP-1R activation depressed LS neurotransmission via a gamma-aminobutyric acid (GABA)A receptor-dependent mechanism.

INTERPRETATION

This study provides new insights into how GLP-1R agonists may reduce alcohol intake. Overall, the findings underscore the potentially inhibitory neuromodulatory role of LS GLP-1R in regulating alcohol consumption through the modulation of dopaminergic reward processes tentatively involving GABA transmission.

FUNDING

Swedish Research Council (2023-2600), Sahlgrenska University HospitalLUA/ALF (grant no. 723941), Adlerbertska Research Foundation and Professor Bror Gadelius Foundation.

GLP-1 Receptor Agonists: Promising Therapeutic Targets for Alcohol Use Disorder

Glucagon-like peptide-1 (GLP-1) is abundant in the circulation, and it is well-known to regulate glucose homeostasis, feeding, and body weight. GLP-1 receptor agonists are therefore approved for treating type 2 diabetes and obesity. However, more recent research has demonstrated that GLP-1 acts within the brain to modulate reward responses, thereby highlighting GLP-1 as a potential target for addiction. Specifically, preclinical studies demonstrated that GLP-1 receptor agonists decrease alcohol intake, reduce the motivation to consume alcohol, and prevent relapse drinking by potentially lowering alcohol-induced reward. These preclinical results have been confirmed and extended in human studies in which GLP-1 receptor agonists reduce alcohol intake in patients with alcohol use disorder (AUD) who have a regular weight or comorbidity of obesity or type 2 diabetes. On a similar note, genetic variations in genes encoding for the GLP-1 receptor are associated with AUD and heavy drinking. The central mechanisms by which GLP-1 regulates alcohol-related behaviors are not fully defined, but may involve areas central to reward as well as regions projecting to these reward areas, such as the nucleus tractus solitarius of the brainstem. Together, existing preclinical and clinical data suggest that GLP-1 is involved in the AUD process and implies its role as a tentative treatment for AUD.

A systematic review in effects of glucagon-like peptide-1 (GLP-1) mono-agonists on functional connectivity: Target engagement and rationale for the development in mental disorders

INTRODUCTION

The mechanistic role of glucagon-like peptide-1 (GLP-1) and GLP-1 receptor agonists (GLP-1RAs) in modulating brain functional activity has been inadequately examined. Mental disorders are characterized by dysregulated functional connectivity in brain circuits that subserve phenomenology. We conducted a comprehensive synthesis of known effects of GLP-1 and GLP-1RAs on functional connectivity.

METHODS

We conducted a systematic review examining studies that investigate changes in functional connectivity mediated by GLP-1 and GLP-1RAs in human adults. Relevant articles were retrieved from OVID (MedLine, Embase, AMED, PsychINFO, JBI EBP Database), PubMed, and Web of Science from database inception to April 26, 2024. Primary or secondary studies (n = 8) investigating the role of GLP-1 and GLP-1RAs on functional connectivity were included for analysis.

RESULTS

GLP-1 and GLP-1RAs modulate functional connectivity within the dorsal default mode network (DMN), visuospatial network, right frontal parietal network, and the salience network. GLP-1 agonism is also associated with decreased functional connectivity within the hypothalamus, lateral orbitofrontal cortex, and amygdala. Contrastingly, some GLP-1RAs (e.g. exenatide) increase functional connectivity in the hypothalamus, nucleus tractus solitarius, and thalamus. Moreover, liraglutide is associated with increased functional connectivity within the hippocampus in healthy individuals suggesting that GLP-1RAs may have differential effects on brain functional connectivity.

DISCUSSION

We observed that GLP-1 and GLP-1 RAs are associated with changes in functional connectivity known to subserve phenomenology of many mental disorders (e.g. anhedonia). Future research should aim to further examine neural circuits and networks affected by GLP-1 receptor activity and how they may affect cognitive and psychopathological domains in psychiatric disorders.

Relating Functional Connectivity and Alcohol Use Disorder: A Systematic Review and Derivation of Relevance Maps for Regions and Connections

Alcohol Use Disorder (AUD), a prevalent and potentially severe psychiatric condition, is one of the leading causes of morbidity and mortality. This systematic review investigates the relationship between AUD and resting-state functional connectivity (rsFC) derived from functional magnetic resonance imaging data. Following the PRISMA guidelines, a comprehensive search yielded 248 papers, and a screening process identified 39 studies with 73 relevant analyses. Using the automated anatomical labeling atlas for whole-brain parcellation, relevance maps were generated to quantify associations between brain regions and their connections with AUD. These outcomes are based on the frequency with which significant findings are reported in the literature, to deal with the challenge of methodological diversity between analyses, including sample sizes, types of independent rsFC features, and AUD measures. The analysis focuses on whole-brain studies to mitigate selection biases associated with seed-based approaches. The most frequently reported regions include the middle and superior frontal gyri, the anterior cingulate cortex, and the insula. The generated relevance maps can serve as a valuable tool for formulating hypotheses and advancing our understanding of AUD's neural correlates in the future. This work also provides a template on how to quantitatively summarize a diverse literature, which could be applied to more specific aspects of AUD, including craving, relapse, binge drinking, or other diseases.

Immunology and treatments of fatty liver disease

Alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) are two major chronic liver diseases worldwide. The triggers for fatty liver can be derived from external sources such as adipose tissue, the gut, personal diet, and genetics, or internal sources, including immune cell responses, lipotoxicity, hepatocyte death, mitochondrial dysfunction, and extracellular vesicles. However, their pathogenesis varies to some extent. This review summarizes various immune mechanisms and therapeutic targets associated with these two types of fatty liver disease. It describes the gut-liver axis and adipose tissue-liver crosstalk, as well as the roles of different immune cells (both innate and adaptive immune cells) in fatty liver disease. Additionally, mitochondrial dysfunction, extracellular vesicles, microRNAs (miRNAs), and gastrointestinal hormones are also related to the pathogenesis of fatty liver. Understanding the pathogenesis of fatty liver and corresponding therapeutic strategies provides a new perspective for developing novel treatments for fatty liver disease.

Anti-consumption agents: Tirzepatide and semaglutide for treating obesity-related diseases and addictions, and improving life expectancy

American culture encourages overconsumption, fueled by ubiquitous availability and pervasive marketing of ultra-processed foods and other addictive substances. This chronic overindulgence has contributed to rising rates of obesity, type 2 diabetes (T2D), substance abuse, mental health disorders and premature mortality. Glucose-like peptide-1 agonists (GLP-1RAs) affect the brain's reward pathway that mediates addiction to foods and various other substances. Evolving data suggest that tirzepatide and semaglutide may be the first effective "anti-consumption" agents with potential applications in reducing food cravings, obesity, alcohol consumption, nicotine addiction, recreational drug use, and even uncontrollable shopping behaviors. Tirzepatide and semaglutide, unlike prior weight-loss drugs, are effective and relatively safe/well-tolerated medications that are associated with reduced risks for myocardial infarction, stroke, cardiovascular death, heart failure, progressive kidney and liver disease, obstructive sleep apnea, debilitating osteoarthritis, polycystic ovarian syndrome, neurodegenerative disease and premature mortality. Observational studies show that GLP-1RAs are associated with spontaneous nonvolitional reductions in use of alcohol, nicotine, and recreational drugs. Because obesity and substance abuse are so prevalent in the United States, GLP-1RA drugs may be uniquely helpful in addressing overconsumption and addiction issues thereby improving overall health and life expectancy.

Emerging pharmacological targets for alcohol use disorder

Alcohol Use Disorder (AUD) remains a challenging condition with limited effective treatment options; however new technology in drug delivery and advancements in pharmacology have paved the way for discovery of novel therapeutic targets. This review explores emerging pharmacological targets that offer new options for the management of AUD, focusing on the potential of somatostatin (SST), vasoactive intestinal peptide (VIP), glucagon-like peptide-1 (GLP-1), nociceptin (NOP), and neuropeptide S (NPS). These targets have been selected based on recent advancements in preclinical and clinical research, which suggest their significant roles in modulating alcohol consumption and related behaviors. SST dampens cortical circuits, and targeting both the SST neurons and the SST peptide itself presents promise for treating AUD and various related comorbidities. VIP neurons are modulated by alcohol and targeting the VIP system presents an unexplored avenue for addressing alcohol exposure at various stages of development. GLP-1 interacts with the dopaminergic reward system and reduces alcohol intake. Nociceptin modulates mesolimbic circuitry and agonism and antagonism of nociceptin receptor offers a complex but promising approach to reducing alcohol consumption. NPS stands out for its anxiolytic-like effects, particularly relevant for the anxiety associated with AUD. This review aims to synthesize the current understanding of these targets, highlighting their potential in developing more effective and personalized AUD therapies, and underscores the importance of continued research in identifying and validating novel targets for treatment of AUD and comorbid conditions.

Genetic variability of incretin receptors affects the occurrence of neurodegenerative diseases and their characteristics

Background

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative diseases. Their treatment options are rather limited, and no neuroprotective or disease-modifying treatments are available. Anti-diabetic drugs, such as glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) agonists, have been suggested as a potential therapeutic option.

Aims

Assess GLP1R and GIPR genetic variability in relation to AD- and PD-related phenotypes.

Methods

AD, PD patients and healthy control subjects were included in the study. Cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease were measured in AD patients, while cognitive impairment was evaluated in PD. All participants were genotyped for three SNPs: GLP1R rs10305420, GLP1R rs6923761 and GIPR rs1800437.

Results

GLP1R rs10305420 genotypes were associated with increased odds for AD and PD development. GLP1R rs10305420 and GLP1R rs6923761 genotypes were significantly associated with Aβ42/40 ratio (p = 0.041 and p = 0.050), while GLP1R rs6923761 was also associated with p-tau levels (p = 0.022). Finally, GIPR rs1800437 heterozygotes as well as carriers of at least one GIPR rs1800437 C allele presented with increased odds for the development of dementia in PD (OR = 1.92; 95 % CI = 1.05-3.51; p = 0.034 and OR = 1.95; 95 % CI = 1.08-3.52; p = 0.027, respectively).

Conclusion

GLP1R and GIPR genetic variability may affect the occurrence of AD and PD and is also associated with AD CSF biomarkers for Alzheimer's disease and dementia in PD. The data on GLP1R and GIPR genetic variability may support the function of incretin receptors in neurodegeneration.

IUPHAR review - Glucagon-like peptide-1 (GLP-1) and substance use disorders: An emerging pharmacotherapeutic target

Addiction is a chronic relapsing disease with high morbidity and mortality. Treatments for addiction include pharmacological and psychosocial interventions; however, currently available medications are limited in number and efficacy. The glucagon-like-peptide-1 (GLP-1) system is emerging as a potential novel pharmacotherapeutic target for alcohol and other substance use disorders (ASUDs). In this review, we summarize and discuss the wealth of available evidence from testing GLP-1 receptor (GLP-1R) agonist medications in preclinical models and humans with ASUDs, possible mechanisms underlying the impact of GLP-1R agonists on alcohol/substance use, gaps in knowledge, and future directions. Most of the research with GLP-1R agonists has been conducted in relation to alcohol use; psychostimulants, opioids, and nicotine have also been investigated. Preclinical evidence suggests that GLP-1R agonists reduce alcohol/substance use and other related outcomes. The main proposed mechanisms are related to reward processing, stress, and cognitive function, as well as broader mechanisms related to satiety, changes in gastric motility, and glucose homeostasis. More in-depth mechanistic studies are warranted. Clinical studies have been limited and their findings have been less conclusive; however, most support the safety and potential efficacy of GLP-1R agonists in ASUD treatment. Identifying preferred compounds, as well as possible subgroups who are most responsive to GLP-1R agonists are some of the key research questions to translate the promising preclinical data into clinical settings. Several clinical trials are underway to test GLP-1R agonists in people with ASUDs.

Ghrelin system and GLP-1 as potential treatment targets for alcohol use disorder

Peptides of the gut-brain axis have gained recent attention as potential treatment targets for addiction. While the number of gut-brain peptides is vast, ghrelin and glucagon-like peptide-1 (GLP-1) have been suggested as important players. Ghrelin is traditionally considered an orexigenic peptide, but recent studies found that it increases alcohol intake in rodents and craving for alcohol in humans. Additionally, suppression of the ghrelin receptor attenuates alcohol-related responses in animal models reflecting alcohol use disorder (AUD). For instance, a lower alcohol intake, suppressed motivation to consume alcohol, and attenuated reward from alcohol is observed after ghrelin receptor antagonism treatment. On a similar note, a partial ghrelin receptor agonist prevents hangover symptoms in humans. When it comes to the anorexigenic peptide GLP-1, agonists of its receptor are approved to treat diabetes type 2 and obesity. Extensive preclinical studies have revealed that these GLP-1 receptor agonists reduce alcohol intake, suppress the motivation to consume alcohol, and prevent relapse drink, with effects tentatively associated with a reduced alcohol-induced reward. These preclinical findings have to some extent been varied in humans, as GLP-1 receptor agonists decrease alcohol intake in overweight patients with AUD. Furthermore, genetic variations in either the genes encoding for pre-pro-ghrelin, GHSR, GLP-1, or its receptor, are associated with AUD and heavy alcohol drinking. While central mechanisms appear to modulate the ability of either ghrelin or GLP-1 to regulate alcohol-related responses the exact mechanisms have not been defined. Taken together these preclinical and clinical data imply that gut-brain peptides participate in the addiction process and should be considered as potential targets for AUD treatment.

New insights into the molecular basis of alcohol abstinence and relapse in alcohol-associated liver disease

Alcohol use disorder remains a significant public health concern, affecting around 5% of adults worldwide. Novel pathways of damage have been described during the last years, providing insight into the mechanism of injury due to alcohol misuse beyond the direct effect of ethanol byproducts on the liver parenchyma and neurobehavioral mechanisms. Thus, the gut-liver-brain axis and immune system involvement could be therapeutic targets for alcohol use disorder. In particular, changes in gut microbiota composition and function, and bile acid homeostasis, have been shown with alcohol consumption and cessation. Alcohol can also directly disrupt intestinal and blood-brain barriers. Activation of the immune system can be triggered by intestinal barrier dysfunction and translocation of bacteria, pathogen-associated molecular patterns (such as lipopolysaccharide), cytokines, and damage-associated molecular patterns. These factors, in turn, promote liver and brain inflammation and the progression of liver fibrosis. Other involved mechanisms include oxidative stress, apoptosis, autophagy, and the release of extracellular vesicles and miRNA from hepatocytes. Potential therapeutic targets include gut microbiota (probiotics and fecal microbiota transplantation), neuroinflammatory pathways, as well as neuroendocrine pathways, for example, the ghrelin system (ghrelin receptor blockade), incretin mimetics (glucagon-like peptide-1 analogs), and the mineralocorticoid receptor system (spironolactone). In addition, support with psychological and behavioral treatments is essential to address the multiple dimensions of alcohol use disorder. In the future, a personalized approach considering these novel targets can contribute to significantly decreasing the alcohol-associated burden of disease.

Glucagon-like peptide 1 receptor agonist, exendin-4, reduces alcohol-associated fatty liver disease

Fatty liver is the earliest response to excessive ethanol consumption, which increases the susceptibility of the liver to develop advanced stage of liver disease. Our previous studies have revealed that chronic alcohol administration alters metabolic hormone levels and their functions. Of current interest to our laboratory is glucagon-like peptide 1 (GLP-1), a widely studied hormone known to reduce insulin resistance and hepatic fat accumulation in patients with metabolic-associated fatty liver disease. In this study, we examined the beneficial effects of exendin-4 (a GLP-1 receptor agonist) in an experimental rat model of ALD. Male Wistar rats were pair-fed the Lieber-DeCarli control or ethanol diet. After 4 weeks of this feeding regimen, a subset of rats in each group were intraperitoneally injected every other day with either saline or exendin-4 at a dose of 3 nmol/kg/day (total 13 doses) while still being fed their respective diet. At the end of the treatment, rats were fasted for 6 h and glucose tolerance test was conducted. The following day, the rats were euthanized, and the blood and tissue samples collected for subsequent analysis. We found that exendin-4 treatment had no significant effect on body weight gain among the experimental groups. Exendin-4-treated ethanol rats exhibited improved alcohol-induced alterations in liver/body weight and adipose/body weight ratio, serum ALT, NEFA, insulin, adiponectin and hepatic triglyceride levels. Reduction in indices of hepatic steatosis in exendin-4 treated ethanol-fed rats was attributed to improved insulin signaling and fat metabolism. These results strongly suggest that exendin-4 mitigates alcohol-associated hepatic steatosis by regulating fat metabolism.

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.

Genetic variants of the GLP-1R gene affect the susceptibility and glucose metabolism of gestational diabetes mellitus: a two-center nested case‒control study

BACKGROUND

Gestational diabetes mellitus (GDM) is the most common complication during pregnancy, occurring under the combined action of environmental and genetic factors. Genetic variants of glucagon-like peptide-1 receptor (GLP-1R) have been reported to affect insulin secretion and susceptibility to type 2 diabetes. This study aimed to explore the role of GLP-1R polymorphisms in GDM and glucose metabolism.

METHODS

A two-center nested case‒control study was designed, including 200 pregnant women with GDM and 200 pregnant women without GDM genotyped for five tag SNPs of GLP-1R using Sanger sequencing. Logistic regression was used to evaluate the relationship between GLP-1R polymorphisms and GDM risk. Glucose and insulin concentrations were measured based upon the 75 g oral glucose tolerance test (OGTT). Beta cell function of different genotypes was estimated with the 60 min insulinogenic index (IGI₆₀) and OGTT-derived disposition index (DI).

RESULTS

Mutant genotype AG + GG of tag SNP rs6458093 nominally increased GDM risk (p = 0.049), especially among subjects younger than 35 years (p = 0.024) and with BMI no less than 24 (p = 0.041), after adjusting for confounders. Meanwhile, compared with subjects with wild genotype AA, subjects with genotype AG + GG of rs6458093 also showed nominally significantly lower IGI₆₀ (p = 0.032) and DI (p = 0.029), as well as significantly higher 75 g OGTT-based 1 h glucose load plasma glucose levels (p = 0.045). Moreover, the mutant heterozygous genotype GA of tag SNP rs3765467 nominally decreased GDM risk among subjects older than 35 years (p = 0.037) but showed no association with insulin secretion and glucose homeostasis.

CONCLUSIONS

Tag SNP rs6458093 of GLP-1R was nominally associated with increased GDM risk and affected beta cell function and postprandial glucose metabolism, while tag SNP rs3765467 of GLP-1R was nominally associated with decreased GDM risk, providing evidence for molecular markers and etiological study of GDM.