Methylation of the Oxytocin, Oxytocin Receptor, and Vasopressin Gene Promoters in Tobacco Use Disorder during Cessation.

INTRODUCTION: Vasopressin (AVP) and oxytocin (OT) exert sex-specific effects on social pair bonding and stress reactions while also influencing craving in substance use disorders. In this regard, intranasal oxytocin (OT) and AVP antagonists present potential treatments for tobacco use disorder (TUD). Since transcription of both hormones is also regulated by gene methylation, we hypothesized sex-specific changes in methylation levels of the AVP, OT, and OT receptor (OXTR) gene during nicotine withdrawal. METHODS: The study population consisted of 49 smokers (29 males, 20 females) and 51 healthy non-smokers (25 males, 26 females). Blood was drawn at day 1, day 7, and day 14 of smoking cessation. Craving was assessed with the questionnaire on smoking urges (QSU). RESULTS: Throughout cessation, mean methylation of the OT promoter gene increased in males and decreased in females. OXTR receptor methylation decreased in females, while in males it was significantly lower at day 7. Regarding the AVP promoter, mean methylation increased in males while there were no changes in females. Using mixed linear modeling, CpG position, time point, sex, and the interaction of time point and sex as well as time point, sex, and QSU had a significant fixed effect on OT and AVP gene methylation. The interaction effect suggests that sex, time point, and QSU are interrelated, meaning that, depending on the sex, methylation could be different at different time points and vice versa. There was no significant effect of QSU on mean OXTR methylation. DISCUSSION: We identified differences at specific CpGs between controls and smokers in OT and AVP and in overall methylation of the AVP gene. Furthermore, we found sex-specific changes in mean methylation levels of the mentioned genes throughout smoking cessation, underlining the relevance of sex in the OT and vasopressin system. This is the first study on epigenetic regulation of the OT promoter in TUD. Our results have implications for research on the utility of the AVP and OT system for treating substance craving. Future studies on both targets need to analyze their effect in the context of sex, social factors, and gene regulation.

DNA-methylation of the dopamin receptor 2 gene is altered during alcohol withdrawal.

The dopaminergic neurotransmission is known to be of crucial importance in addictive behavior. Epigenetic regulation like methylation of DNA influences the function of dopaminergic transmission. The present study investigated alterations of DNA methylation in the dopamine D2 receptor (DRD2)-gene in patients suffering from alcohol dependence. The study sample consists of 99 alcohol dependent males admitted for alcohol withdrawal treatment and a control group of 33 healthy participants. Blood samples underwent bisulfite sequencing to determine levels of DNA-methylation of the promoter region of the DRD2 gene. Mixed linear modeling was used to test differences between patients and controls, course of methylation during detoxification. While DRD2-gene methylation did not differ significantly between patients and controls, we found a significant increase of DRD2-gene methylation during alcohol withdrawal/early abstinence. Craving, measured with the Obsessive Compulsive Drinking Scale (OCDS), was significantly associated with DRD2-gene methylation. Furthermore, smoking significantly influenced DRD2-gene methylation in both, patients and controls. As in other types of addictive disorders, DRD2-gene methylation is altered during alcohol withdrawal/early abstinence. The findings regarding an association with alcohol craving and tobacco consumption point towards a crucial role of DRD2-gene methylation in the neurobiology of addictive behavior.

Alcohol Withdrawal and Proopiomelanocortin Neuropeptides in an Animal Model of Alcohol Dependence.

BACKGROUND: Alcohol is one of the leading threats to health worldwide. Craving for alcohol makes abstinence a difficult challenge by maintaining alcohol dependence. Many studies suppose the hypothalamic-pituitary-adrenal axis, especially the proopiomelanocortin (POMC)-derived neuropeptides, to mediate craving during withdrawal in alcohol dependence. Evidence is available that the two POMC proteins, α-melanocyte-stimulating hormone (α-MSH) and ß-endorphin (ß-END) are altered by alcohol consumption and influence alcohol consumption, respectively. OBJECTIVES: We investigated the dynamics of α-MSH and ß-END during alcohol withdrawal and the influence of intraperitoneal administration of either α-MSH or ß-END in an established rodent model (Wistar rats) for alcohol dependence. RESULTS: After long-term alcohol self-administration over 12 months and repeated deprivation periods for 3 days, we found a significant decrease in α-MSH levels during withdrawal in rodents (p = 0.006) compared to controls, while ß-END levels remained unchanged. Treatment with intraperitoneally administered α-MSH and ß-END did not affect alcohol drinking behavior after deprivation. CONCLUSION: We demonstrate the effects of alcohol deprivation on α-MSH in alcohol-dependent rodents, which appear to mimic α-MSH alteration found after fasting periods during appetite regulation. Therefore, low α-MSH levels are a possible indicator for craving in alcohol-dependent individuals and hence would be a potential target for anti-craving treatment.

CAGn repeat of the androgen receptor is linked to proopiomelanocortin promoter methylation-relevance for craving of male alcohol-dependent patients?

RATIONALE: Previous findings of the Franconian Alcoholism Research Studies showed that both the CAGn of the androgen receptor (AR) and the promoter methylation of the hypothalamic peptide proopiomelanocortin (POMC) were associated with craving of male alcohol-dependent patients. OBJECTIVES: Based on the strong interactions between the hypothalamic-pituitary-gonadal (HPG) and the hypothalamic-pituitary-adrenal axis (HPA), this study investigated the relationships between the CAGn repeat of the AR, POMC promoter methylation and craving of male alcohol-dependent patients. METHODS: This analysis covers 84 male patients with a diagnosis of alcohol dependence (DSM-IV). We sequenced the POMC gene promoter using bisulfite modified DNA to display the methylation status. Furthermore, we sequenced the CAGn repeat within exon 1 of the AR gene. Craving was quantified by the Obsessive Compulsive Drinking Scale. RESULTS: We found an inverse correlation between the number of CAGn repeats of the AR and the POMC methylation status in this study. Altogether, the POMC promoter methylation accounted for 33 % of the relationship between CAGn AR polymorphism and craving. CONCLUSIONS: This work shows that the AR and the POMC gene might functionally interact with each other and subsequently mediate craving in alcohol-dependent patients. The paper discusses different mechanisms which might underlie our findings involving sex hormones' and sex determining region of Y-gene's regulatory function on DNA-methyltransferase activity. In conclusion, the results give insight in the interaction between HPG and HPA axis. This study is a further step on the way to a better understanding of genetic and non-genetic factors underlying craving for alcohol.

DNA methylation of the POMC gene promoter is associated with craving in alcohol dependence.

Hypothalamic-pituitary-adrenal (HPA) axis dysfunction has been implicated in the pathogenesis of addictive behaviour and especially in alcohol craving. The pro-opiomelanocortin gene (POMC), encoding a 241 amino acids stretching polypeptide hormone precursor, plays an important role in the regulation of the HPA, and is prone to epigenetic regulation due to promoter-related DNA methylation. Aim of the present study therefore was to investigate possible differences in promoter-related DNA methylation in patients suffering from alcohol dependence compared to healthy controls. We analysed the DNA methylation of the 5' promoter of the POMC gene that is embedded in a CpG island using bisulfite sequencing in 145 alcohol-dependent patients and 37 healthy controls taken from the Franconian Alcoholism Research Studies. We found only marginal, hence significant differences at single CpG sites between patients and controls. We identified a cluster of CpGs showing a significant association with alcohol craving in the patients group. These results implicate that epigenetic changes possibly due to alcohol intake may contribute to craving via promoting HPA-axis dysfunction. Further studies should more closely investigate the impact of these changes on the several derivatives of the POMC gene.