Alcohol Dependence and Genetic Variability in the Serotonin Pathway among Currently and Formerly Alcohol-Dependent Males

Association Study of Serotonin 1A Receptor Gene, Personality, and Anxiety in Women with Alcohol Use Disorder

Alcohol use disorder is considered a chronic and relapsing disorder affecting the central nervous system. The serotonergic system, mainly through its influence on the mesolimbic dopaminergic reward system, has been postulated to play a pivotal role in the underlying mechanism of alcohol dependence. The study aims to analyse the association of the rs6295 polymorphism of the 5HTR1A gene in women with alcohol use disorder and the association of personality traits with the development of alcohol dependence, as well as the interaction of the rs6295, personality traits, and anxiety with alcohol dependence in women. The study group consisted of 213 female volunteers: 101 with alcohol use disorder and 112 controls. NEO Five-Factor and State-Trait Anxiety Inventories were applied for psychometric testing. Genotyping of rs6295 was performed by real-time PCR. We did not observe significant differences in 5HTR1A rs6295 genotypes (p = 0.2709) or allele distribution (p = 0.4513). The AUD subjects scored higher on the anxiety trait (p < 0.0001) and anxiety state (p < 0.0001) scales, as well as on the neuroticism (p < 0.0001) and openness (p = 0134) scales. Significantly lower scores were obtained by the AUD subjects on the extraversion (p < 0.0001), agreeability (p < 0.0001), and conscientiousness (p < 0.0001) scales. Additionally, we observed a significant effect of 5HTR1A rs6295 genotype interaction and alcohol dependency, or lack thereof, on the openness scale (p = 0.0016). In summary, this study offers a comprehensive overview of alcohol dependence among women. It offers valuable insights into this complex topic, contributing to a more nuanced understanding of substance use among this specific demographic. Additionally, these findings may have implications for developing prevention and intervention strategies tailored to individual genetic and, most importantly, personality and anxiety differences.

The association between the CCDC88A gene polymorphism at rs1437396 and alcohol use disorder, with or without major depression disorder

Girdin is a protein involved in neuronal migration and hippocampal development. It is encoded by the coiled-coil domain-containing 88A (CCDC88A) gene, located on the short arm of chromosome 2 (2p). The CCDC88A gene is modulated by the intergenic single-nucleotide polymorphism (SNP) of the rs1437396, situated 9.5 kb downstream from its transcription stop site. As recent genome-wide research has associated the T allele of the SNP with increased risk of alcohol use disorder (AUD), we wanted to validate this finding in an independent cohort and to test further for an association with comorbid major depressive disorder (MDD). The study included 226 AUD patients (AUD group), 53 patients with comorbid MDD, and 391 controls selected randomly. The participants were genotyped for the rs1437396 polymorphism using the real-time polymerase chain reaction. The association between the rs1437396 polymorphism and increased risk of AUD and AUD+MDD was tested with logistic regression. Our results show significantly higher frequency of the T risk allele in the AUD group (p=0.027) and even higher in the AUD+MDD group (p=0.016). In conclusion, this is the first study that has validated the association between the rs1437396 polymorphism of the CCDC88A gene and AUD with or without MDD. Studies on larger samples of patients are needed to further investigate the mechanism of this association.

Serotonin disruption at gestation alters expression of genes associated with serotonin synthesis and reuptake at weaning

RATIONALE

Serotonin (5-HT) is a monoamine neuromodulator that plays a key role in the organization of the central nervous system. 5-HT alterations may be associated to the emergence of social deficits and psychiatric disorders, including anxiety, depression, and substance abuse disorders. Notably, disruption of the 5-HT system during sensitive periods of development seems to exert long-term consequences, including altered anxiety responses and problematic use of alcohol.

OBJECTIVE

We analyzed, in mice, the effects of transient 5-HT depletion at gestation (a developmental stage when medial prefrontal cortex (mPFC) 5-HT levels depend exclusively on placental 5-HT availability) on 5-HT central synthesis and reuptake at weaning. We also explored if 5-HT disruption at the embryonic stage influences behavioral outcomes that may serve as a proxy for autistic- or anxiety-like phenotypes.

METHODS

C57/BL6 male and female mice, born from dams treated with a 5-HT synthesis inhibitor (PCPA; 4-Chloro-DL-phenylalanine methyl ester hydrochloride) at gestational days (G)13.5-16.5, were subjected to a behavioral battery that assesses social preference and novelty, compulsive behavior, stereotypies, and ethanol's anti-anxiety effects, at postnatal days (P) 21-28. Afterwards, expression of the genes that encode for 5-HT synthesis (Tph2) and SERT (5-HT transporter) were analyzed in mPFC via real-time RT-PCR. Dopamine 2 receptor (D2R) expression was also analyzed via RT-PCR to further explore possible effects of PCPA on dopaminergic transmission.

RESULTS

Transient 5-HT disruption at G13.5-16.5 reduced Tph2 expression of both male and female mice in mPFC at P23. Notably, female mice also exhibited higher SERT expression and reduced D2R expression in mPFC. Mice derived from 5-HT depleted dams displayed heightened compulsive behavior at P21, when compared to control mice. Alcohol anti-anxiety effects at early adolescence (P28) were exhibited by mice derived from 5-HT depleted dams, but not by control counterparts. No social deficits or stereotyped behaviors were observed.

CONCLUSION

Transient 5-HT inhibition at gestation resulted in altered expression of genes involved in 5-HT synthesis and reuptake in mPFC at weaning, a period in which the 5-HT system is still developing. These alterations may exert lingering effects, which translate to significant compulsivity and heightened sensitivity to the anxiolytic effects of alcohol at early adolescence.

Genetics of social anxiety disorder: a systematic review

Social anxiety disorder (SAD) is a common psychiatric disorder, often associated with avoidant temperament. Research studies have implicated a strong genetic architecture of SAD. We have conducted a systematic review on the genetics of SAD and yielded 66 articles. In general, prior research studies have focused on the serotonin transporter, oxytocin receptor, brain-derived neurotrophic factor and catechol-O-methyltransferase genes. Mixed and inconsistent results have been reported. Additional approaches and phenotypes have also been investigated, including pharmacogenetics of treatment response, imaging genetics and gene-environment interactions. Future directions warrant further international collaborative efforts, deep-phenotyping of clinical characteristics including consistent and reliable measurement-based symptom severity, and larger sample sizes to ensure sufficient power for stratification due to the heterogeneity of this chronic and often debilitating condition.

Transient serotonin depletion at adolescence, but not at early infancy, reduced subsequent anxiety-like behavior and alcohol intake in female mice

RATIONALE

Serotonin (5-HT) plays an important role in the organization of the central nervous system and in the development of social interaction deficits and psychiatric disorders, including anxiety, depression, and addiction disorders. Notably, disruption of the 5-HT system during sensitive periods of development exerts long-term consequences, including altered anxiety response and problematic use of alcohol.

OBJECTIVE

we analyzed, in mice, the effects of transient 5-HT depletion at infancy or adolescence on subsequent anxiety-like behavior and alcohol intake during adolescence.

METHODS

C57/BL6 male and female mice were administered a 5-HT synthesis inhibitor (PCPA; 4-chloro-DL-phenylalanine methyl ester hydrochloride) at infancy (postnatal days 14-16 [PD14-16]) or adolescence (PD40-42). Eleven (± 1) days after treatment, mice were assessed for ethanol intake in daily two-bottle choice tests and for anxiety response via the elevated plus maze.

RESULTS

Female, but not male, mice transiently depleted of 5-HT at adolescence (but not those depleted at the perinatal stage) exhibited a significant reduction in anxiety response, which was accompanied by a significant reduction on alcohol intake.

CONCLUSION

Transient 5-HT inhibition at adolescence may act, in females, as a protective factor for the emergence of anxiety disorders and problematic use of alcohol during adolescence.

Flying Together: Drosophila as a Tool to Understand the Genetics of Human Alcoholism

Alcohol use disorder (AUD) exacts an immense toll on individuals, families, and society. Genetic factors determine up to 60% of an individual's risk of developing problematic alcohol habits. Effective AUD prevention and treatment requires knowledge of the genes that predispose people to alcoholism, play a role in alcohol responses, and/or contribute to the development of addiction. As a highly tractable and translatable genetic and behavioral model organism, Drosophila melanogaster has proven valuable to uncover important genes and mechanistic pathways that have obvious orthologs in humans and that help explain the complexities of addiction. Vinegar flies exhibit remarkably strong face and mechanistic validity as a model for AUDs, permitting many advancements in the quest to understand human genetic involvement in this disease. These advancements occur via approaches that essentially fall into one of two categories: (1) discovering candidate genes via human genome-wide association studies (GWAS), transcriptomics on post-mortem tissue from AUD patients, or relevant physiological connections, then using reverse genetics in flies to validate candidate genes' roles and investigate their molecular function in the context of alcohol. (2) Utilizing flies to discover candidate genes through unbiased screens, GWAS, quantitative trait locus analyses, transcriptomics, or single-gene studies, then validating their translational role in human genetic surveys. In this review, we highlight the utility of Drosophila as a model for alcoholism by surveying recent advances in our understanding of human AUDs that resulted from these various approaches. We summarize the genes that are conserved in alcohol-related function between humans and flies. We also provide insight into some advantages and limitations of these approaches. Overall, this review demonstrates how Drosophila have and can be used to answer important genetic questions about alcohol addiction.

Dietary yeast influences ethanol sedation in Drosophila via serotonergic neuron function

Abuse of alcohol is a major clinical problem with far-reaching health consequences. Understanding the environmental and genetic factors that contribute to alcohol-related behaviors is a potential gateway for developing novel therapeutic approaches for patients that abuse the drug. To this end, we have used Drosophila melanogaster as a model to investigate the effect of diet, an environmental factor, on ethanol sedation. Providing flies with diets high in yeast, a routinely used component of fly media, increased their resistance to ethanol sedation. The yeast-induced resistance to ethanol sedation occurred in several different genetic backgrounds, was observed in males and females, was elicited by yeast from different sources, was readily reversible, and was associated with increased nutrient intake as well as decreased internal ethanol levels. Inhibition of serotonergic neuron function using multiple independent genetic manipulations blocked the effect of yeast supplementation on ethanol sedation, nutrient intake, and internal ethanol levels. Our results demonstrate that yeast is a critical dietary component that influences ethanol sedation in flies and that serotonergic signaling is required for the effect of dietary yeast on nutrient intake, ethanol uptake/elimination, and ethanol sedation. Our studies establish the fly as a model for diet-induced changes in ethanol sedation and raise the possibility that serotonin might mediate the effect of diet on alcohol-related behavior in other species.

Association of serotonin and GABA pathway gene polymorphisms with alcohol dependence: A preliminary study

BACKGROUND

Alcohol dependence (AD), characterized by profound disruptions in specific circuits of the brain is influenced by both environmental, which play a significant role in developing addiction and genetic factors, which make some individuals more susceptible to disruptions. Various polymorphisms in the neurotransmitter genes are reported to increase the risk of developing dependence. The present study aimed to identify association of serotonin and GABA polymorphisms with AD in Indian subjects.

METHOD

The study group comprised of 141 AD cases recruited as per DSM IV TR criteria from the outpatient Department of Psychiatry and 110 volunteers from the general population. Clinical and family history was noted and 5 ml blood drawn for genetic studies. Polymorphisms 5-HTTLPR and STin2 of serotonin and rs2279020 and rs3219151 of the GABA pathway were analyzed and results correlated with age at first use quantity consumed, duration of use, dependence and age at onset of dependence.

RESULTS

The marker frequencies were similar between cases and controls except for rs3219151. 5-HTTLPR was significantly associated with high AUDIT scores and alcohol intake (p < 0.0001), GABA_A rs2279020 and rs3219151 with age at first use (p < 0.0001); rs2279020 with higher AUDIT score (p = 0.002) and rs3219151 with quantity (p = 0.0001). High frequency of GABRA6 rs3219151 TT genotype in AD and its association with lower age at first use, higher intake/day, and higher duration of dependence appears to confer risk.

CONCLUSIONS

This preliminary study, though on a smaller sample size, suggests an association of 5-HTTLPR and GABA_A receptor polymorphisms with AD in our population.

The association between HTR1B gene rs13212041 polymorphism and onset of alcohol abuse

BACKGROUND

Alcohol dependence displays a wide variety of clinical phenotypes. Various typology classifications of alcoholism include age of onset of alcohol abuse as one of the major phenotypic features. Serotonergic changes have been associated with alcoholism, while serotonin receptors type 1B (5-HT1B) play an important role in regulating serotonergic neurotransmission. The rs13212041 polymorphism modulates the expression of HTR1B gene coding for 5-HT1B receptor. This study examined the association of platelet serotonin (5-HT) and HTR1B gene with the onset of alcohol abuse in alcohol-dependent subjects.

MATERIALS AND METHODS

Determination of platelet 5-HT concentration and genotyping of rs13212041 HTR1B gene polymorphism were performed in 613 alcohol-dependent patients, subdivided according to early/late onset (before/after 25 years of age) of alcohol abuse.

RESULTS

Alcohol-dependent individuals with CC genotype were more frequent in the group with early onset of alcohol abuse compared to carriers of T allele. Besides HTR1B genotype, age and gender, but not platelet 5-HT, were major variables associated with the onset of alcohol abuse. Platelet 5-HT concentration was not significantly different between patients with early and late onset of alcohol abuse, or patients carrying various HTR1B genotypes. Although we observed no influence of co-variables such as age, gender, or somatic and psychiatric comorbidities, platelet 5-HT concentration was significantly affected by smoking.

CONCLUSION

These findings support potential involvement of 5-HT1B receptors in the onset of alcohol abuse and development of alcohol dependence. Additionally, the results of our study emphasize the importance of controlling for smoking status, as one of the significant confounding factors influencing platelet 5-HT concentration.

COMT and BDNF Gene Variants Help to Predict Alcohol Consumption in Alcohol-dependent Patients

BACKGROUND

The neurobiology of alcohol dependence (AD) involves alterations in neurotransmitters and the stress response. We hypothesized that an interaction between functional variants of dopaminergic and neurotrophic genes may influence drinking in AD.

METHODS

The relationship between alcohol consumption and single-nucleotide polymorphisms, Val66Met in the brain-derived neurotrophic factor (BDNF), and Val158Met in the catechol-O-methyltransferase (COMT), was analyzed among 281 alcohol-dependent individuals.

RESULTS

Individuals carrying both the COMT Met158Met genotype and the BDNF Val66Val genotype drank more than those with other variants of these genes (P = 0.039). Those who had a family history of AD also drank more than those without a family history (P = 0.048). Patients with both Met/Met genotype in the COMT Val158Met polymorphism and Val/Val genotype in the BDNF Val66Met polymorphism suffered from more health problems than those carrying other variants (P = 0.030) and had lower motivation to change drinking patterns (P = 0.031).

CONCLUSIONS

Patients carrying both the BDNF Val66Val and COMT Met158Met variants had higher alcohol consumption. These effects may be influenced by the effects of BDNF and COMT on dopamine responses to alcohol. Motivation-enhancing strategies might benefit the group of patients identified by genotyping in this study, and also treatment aimed at reducing alcohol consumption.

A Genetic Animal Model of Alcoholism for Screening Medications to Treat Addiction

The purpose of this review is to present up-to-date pharmacological, genetic, and behavioral findings from the alcohol-preferring P rat and summarize similar past work. Behaviorally, the focus will be on how the P rat meets criteria put forth for a valid animal model of alcoholism with a highlight on its use as an animal model of polysubstance abuse, including alcohol, nicotine, and psychostimulants. Pharmacologically and genetically, the focus will be on the neurotransmitter and neuropeptide systems that have received the most attention: cholinergic, dopaminergic, GABAergic, glutamatergic, serotonergic, noradrenergic, corticotrophin releasing hormone, opioid, and neuropeptide Y. Herein, we sought to place the P rat's behavioral and neurochemical phenotypes, and to some extent its genotype, in the context of the clinical literature. After reviewing the findings thus far, this chapter discusses future directions for expanding the use of this genetic animal model of alcoholism to identify molecular targets for treating drug addiction in general.