The Role of Ghrelin/GHS-R1A Signaling in Nonalcohol Drug Addictions

A case control study investigating the methylation levels of GHRL and GHSR genes in alcohol use disorder

BACKGROUND

Alcohol use disorder (AUD) is a relapsing disease described as excessive use of alcohol. Evidence of the role of DNA methylation in addiction is accumulating. Ghrelin is an important peptide known as appetite hormone and its role in addictive behavior has been identified. Here we aimed to determine the methylation levels of two crucial genes (GHRL and GHSR) in ghrelin signaling and further investigate the association between methylation ratios and plasma ghrelin levels.

METHODS

Individuals diagnosed with (n = 71) and without (n = 82) AUD were recruited in this study. DNA methylation levels were measured through methylation-sensitive high-resolution melting (MS-HRM). Acylated ghrelin levels were detected by ELISA. The GHRL rs696217 polymorphism was analyzed by the standard PCR-RFLP method.

RESULTS

GHRL was significantly hypermethylated (P < 0.0022) in AUD between 25 and 50% methylation than in control subjects but no significant changes of GHSR methylation were observed. Moreover, GHRL showed significant positive correlation of methylation ratio between 25 and 50% with age. A significant positive correlation between GHSR methylation and ghrelin levels in the AUD group was determined (P = 0.037). The level of GHRL methylation and the ghrelin levels showed a significant association in the control subjects (P = 0.042).

CONCLUSION

GHSR and GHRL methylation levels did not change significantly between control and AUD groups. However, GHRL and GHSR methylations seemed to have associations with plasma ghrelin levels in two groups. This is the first study investigating the DNA methylation of GHRL and GHSR genes in AUD.

Shared Mechanisms of GABAergic and Opioidergic Transmission Regulate Corticolimbic Reward Systems and Cognitive Aspects of Motivational Behaviors

The functional interplay between the corticolimbic GABAergic and opioidergic systems plays a crucial role in regulating the reward system and cognitive aspects of motivational behaviors leading to the development of addictive behaviors and disorders. This review provides a summary of the shared mechanisms of GABAergic and opioidergic transmission, which modulate the activity of dopaminergic neurons located in the ventral tegmental area (VTA), the central hub of the reward mechanisms. This review comprehensively covers the neuroanatomical and neurobiological aspects of corticolimbic inhibitory neurons that express opioid receptors, which act as modulators of corticolimbic GABAergic transmission. The presence of opioid and GABA receptors on the same neurons allows for the modulation of the activity of dopaminergic neurons in the ventral tegmental area, which plays a key role in the reward mechanisms of the brain. This colocalization of receptors and their immunochemical markers can provide a comprehensive understanding for clinicians and researchers, revealing the neuronal circuits that contribute to the reward system. Moreover, this review highlights the importance of GABAergic transmission-induced neuroplasticity under the modulation of opioid receptors. It discusses their interactive role in reinforcement learning, network oscillation, aversive behaviors, and local feedback or feedforward inhibitions in reward mechanisms. Understanding the shared mechanisms of these systems may lead to the development of new therapeutic approaches for addiction, reward-related disorders, and drug-induced cognitive impairment.

Ghrelin/GHS-R1A antagonism in memory test and its effects on central molecular signaling involved in addiction in rats

Central ghrelin signaling seems to play important role in addiction as well as memory processing. Antagonism of the growth hormone secretagogue receptor (GHS-R1A) has been recently proposed as a promising tool for the unsatisfactory drug addiction therapy. However, molecular aspects of GHS-R1A involvement in specific brain regions remain unclear. The present study demonstrated for the first time that acute as well as subchronic (4 days) administration of the experimental GHS-R1A antagonist JMV2959 in usual intraperitoneal doses including 3 mg/kg, had no influence on memory functions tested in the Morris Water Maze in rats as well as no significant effects on the molecular markers linked with memory processing in selected brain areas in rats, specifically on the β-actin, c-Fos, two forms of the calcium/calmodulin-dependent protein kinase II (CaMKII, p-CaMKII) and the cAMP-response element binding protein (CREB, p-CREB), within the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum, and hippocampus (HIPP). Furthermore, following the methamphetamine intravenous self-administration in rats, the 3 mg/kg JMV2959 pretreatment significantly reduced or prevented the methamphetamine-induced significant decrease of hippocampal β-actin and c-Fos as well as it prevented the significant decrease of CREB in the NAC and mPFC. These results imply, that the GHS-R1A antagonist/JMV2959 might reduce/prevent some of the memory-linked molecular changes elicited by methamphetamine addiction within brain structures associated with memory (HIPP), reward (NAc), and motivation (mPFC), which may contribute to the previously observed significant JMV2959-induced reduction of the methamphetamine self-administration and drug-seeking behavior in the same animals. Further research is necessary to corroborate these results.

Impaired Ghrelin Signaling Does Not Lead to Alterations of Anxiety-like Behaviors in Adult Mice Chronically Exposed to THC during Adolescence

As marijuana use during adolescence has been increasing, the need to understand the effects of its long-term use becomes crucial. Previous research suggested that marijuana consumption during adolescence increases the risk of developing mental illnesses, such as schizophrenia, depression, and anxiety. Ghrelin is a peptide produced primarily in the gut and is important for feeding behavior. Recent studies have shown that ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR), play important roles in mediating stress, as well as anxiety and depression-like behaviors in animal models. Here, we investigated the effects of chronic tetrahydrocannabinol (THC) administration during late adolescence (P42-55) in GHSR (GHSR ^-/-) knockout mice and their wild-type littermates in relation to anxiety-like behaviors. We determined that continuous THC exposure during late adolescence did not lead to any significant alterations in the anxiety-like behaviors of adult mice, regardless of genotype, following a prolonged period of no exposure (1 month). These data indicate that in the presence of intact or impaired ghrelin/GHSR signaling, THC exposure during late adolescence has limited if any long-term impact on anxiety-like behaviors in mice.

Are Signals Regulating Energy Homeostasis Related to Neuropsychological and Clinical Features of Gambling Disorder? A Case-Control Study

Gambling disorder (GD) is a modestly prevalent and severe condition for which neurobiology is not yet fully understood. Although alterations in signals involved in energy homeostasis have been studied in substance use disorders, they have yet to be examined in detail in GD. The aims of the present study were to compare different endocrine and neuropsychological factors between individuals with GD and healthy controls (HC) and to explore endocrine interactions with neuropsychological and clinical variables. A case−control design was performed in 297 individuals with GD and 41 individuals without (healthy controls; HCs), assessed through a semi-structured clinical interview and a psychometric battery. For the evaluation of endocrine and anthropometric variables, 38 HCs were added to the 41 HCs initially evaluated. Individuals with GD presented higher fasting plasma ghrelin (p < 0.001) and lower LEAP2 and adiponectin concentrations (p < 0.001) than HCs, after adjusting for body mass index (BMI). The GD group reported higher cognitive impairment regarding cognitive flexibility and decision-making strategies, a worse psychological state, higher impulsivity levels, and a more dysfunctional personality profile. Despite failing to find significant associations between endocrine factors and either neuropsychological or clinical aspects in the GD group, some impaired cognitive dimensions (i.e., WAIS Vocabulary test and WCST Perseverative errors) and lower LEAP2 concentrations statistically predicted GD presence. The findings from the present study suggest that distinctive neuropsychological and endocrine dysfunctions may operate in individuals with GD and predict GD presence. Further exploration of endophenotypic vulnerability pathways in GD appear warranted, especially with respect to etiological and therapeutic potentials.

Investigating associations between appetite-regulating hormones, aggression and craving in males with cannabis use disorder

BACKGROUND

Aggression and craving are common and important withdrawal symptoms in cannabis use disorder. The present study investigated the association between appetite-regulating hormones, aggression, and craving during cannabis withdrawal syndrome (CWS).

METHODS

Fifty-six male subjects diagnosed with cannabis withdrawal and 45 healthy males were included in the study. The Substance Craving Scale, the Buss-Perry Aggression Questionnaire, and the State-Trait Anxiety Inventory were implemented at baseline. Blood samples were drawn to measure ghrelin, leptin, adiponectin, and resistin levels in the serum. Then, the Point Subtraction Aggression Paradigm (PSAP) was applied. Bloodwork and psychometric assessment procedures were re-implemented after the PSAP. At the 7-day follow-up, psychometric assessments and hormone measurements were repeated in the CWS group.

RESULTS

Baseline serum ghrelin and adiponectin levels were lower in the CWS group than controls at baseline. After PSAP, there was a significant increase in ghrelin levels of patients with CWS compared to controls. Patients yielded higher aggression scores, while there was no significant correlation between hormonal changes and PSAP findings. At 7-day follow, ghrelin and resistin levels significantly increased, while serum leptin decreased in patients with CWS. Finally, there was a positive association between craving and resistin levels.

CONCLUSIONS

Our results present the changes in appetite-regulating hormones. Long-term follow-up studies are needed to shed light on neuroendocrinological aspects of cannabis withdrawal.

Changes in Plasma Ghrelin Levels Following Surgical and Non-Surgical Weight-Loss in Female Rats Predict Alcohol Use

The weight-loss surgery Roux-en Y gastric bypass (RYGB) is a relatively effective, long-term treatment option for patients with morbid obesity. However, accumulating clinical evidence suggests that patients receiving RYGB may be at increased risk of developing alcohol use disorder. This observation has been repeatedly supported by preclinical studies showing rodents increase intake of ethanol (EtOH) after RYGB, and has been further confirmed by human studies. A promising alternative to RYGB is sleeve gastrectomy (SG), which has resulted in decreased EtOH consumption in some rodent studies. The exact mechanism underlying the differential alcohol outcomes after RYGB versus SG has yet to be elucidated. However, the gut hormone ghrelin has emerged as a potential candidate from previous preclinical studies specific to RYGB surgeries and due to its action to stimulate food and alcohol intake and cravings. To directly assess changes in plasma ghrelin levels following weigh loss surgeries in the context of alcohol intake, 24 female rats were separated into three surgical groups receiving RYGB, SG, or Sham surgery followed by caloric restriction to produce adiposity matched controls (Sham-AM). Blood was drawn for fasted and fed plasma ghrelin (acyl and des-acyl) assays at multiple time points: while on a normal diet (ND), after 5-week exposure to a high fat diet (HFD), following surgery, and after a series of two-bottle alcohol choice test with increasing concentrations (2%, 4%, 6%, 8%) of EtOH. Consistent with previous observations, RYGB rats drank more EtOH than SG rats across all concentrations. As expected, fasted ghrelin levels were blunted after HFD feeding, compared to normal diet baseline. After RYGB, fasted ghrelin levels returned to higher levels while remained blunted after SG and Sham-AM. Fed acyl ghrelin levels were significantly increased to above "normal" levels after RYGB, but remain low after SG and Sham-AM. Given that post-RYGB acyl ghrelin levels are raised to a fasted state regardless of actual prandial status, we conclude that RYGB may results in a hormonal state reminiscence of a fasted state with the inability of feeding to inhibit ghrelin production, an effect which could potentially contribute to increased EtOH intake following the surgery. In contrast, following SG, ghrelin levels in rats remain consistent with the fed state regardless of prandial status, potentially explaining lower alcohol intake and lower risk of developing AUD.