Vijay A. Ramchandani

A genetic determinant of the striatal dopamine response to alcohol in men

Excessive alcohol use, a major cause of morbidity and mortality, is less well understood than other addictive disorders. Dopamine release in ventral striatum is a common element of drug reward, but alcohol has an unusually complex pharmacology, and humans vary greatly in their alcohol responses. This variation is related to genetic susceptibility for alcoholism, which contributes more than half of alcoholism risk. Here, we report that a functional OPRM1 A118G polymorphism is a major determinant of striatal dopamine responses to alcohol. Social drinkers recruited based on OPRM1 genotype were challenged in separate sessions with alcohol and placebo under pharmacokinetically controlled conditions, and examined for striatal dopamine release using positron emission tomography and [11C]-raclopride displacement. A striatal dopamine response to alcohol was restricted to carriers of the minor 118G allele. To directly establish the causal role of OPRM1 A118G variation, we generated two humanized mouse lines, carrying the respective human sequence variant. Brain microdialysis showed a fourfold greater peak dopamine response to an alcohol challenge in h/mOPRM1-118GG than in h/mOPRM1-118AA mice. OPRM1 A118G variation is a genetic determinant of dopamine responses to alcohol, a mechanism by which it likely modulates alcohol reward.

Research advances in ethanol metabolism

The pharmacokinetics of alcohol determines the time course of alcohol concentration in blood after the ingestion of an alcoholic beverage and the degree of exposure of organs to its effects. The interplay between the kinetics of absorption, distribution and elimination is thus important in determining the pharmacodynamic responses to alcohol. There is a large degree of variability in alcohol absorption, distribution and metabolism, as a result of both genetic and environmental factors. The between-individual variation in alcohol metabolic rates is, in part due to allelic variants of the genes encoding the alcohol metabolizing enzymes, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). This review summarizes recent developments in the investigation of the following influences on alcohol elimination rate: gender, body composition and lean body mass, liver volume, food and food composition, ethnicity, and genetic polymorphisms in alcohol metabolizing enzymes as well as in the promoter regions of the genes for these enzymes. Evaluation of the factors regulating the rates of alcohol and acetaldehyde metabolism, both genetic and environmental, will help not only to explain the risk for development of alcoholism, but also the risk for development of alcohol-related organ damage and developmental problems.

Why We Like to Drink : A Functional Magnetic Resonance Imaging Study of the Rewarding and Anxiolytic Effects of Alcohol

People typically drink alcohol to induce euphoria or reduce anxiety, and they frequently drink in social settings, yet the effect of alcohol on human brain circuits involved in reward and emotion has been explored only sparingly. We administered alcohol intravenously to social drinkers while brain response to visual threatening and nonthreatening facial stimuli was measured using functional magnetic resonance imaging (fMRI). Alcohol robustly activated striatal reward circuits while attenuating response to fearful stimuli in visual and limbic regions. Self-ratings of intoxication correlated with striatal activation, suggesting that activation in this area may contribute to subjective experience of pleasure and reward during intoxication. These results show that the acute pharmacological rewarding and anxiolytic effects of alcohol can be measured with fMRI.

Gender differences in alcohol metabolism: Relationship to liver volume and effect of adjusting for body mass

BACKGROUND & AIMS Alcoholic liver disease purportedly develops more readily in women than in men. Some studies have demonstrated faster rates of alcohol elimination in women. This study examined whether gender differences in alcohol metabolism are related to differences in liver volume and/or differences in lean body mass. METHODS Ten men and 10 women had alcohol elimination rates determined by clamping of the breath alcohol concentration at 50 mg/dL by means of a constant rate of intravenous infusion of 6% ethanol. Liver volume was determined by computed tomography. RESULTS Mean alcohol elimination rate and mean computed liver volume were not significantly different in men and women. Lean body mass was 42% greater in men than in women. Consequently, the calculated alcohol elimination rate and liver volume per kilogram of lean body mass were 33% and 38% higher in women than in men, respectively. When the alcohol elimination rate was calculated per unit liver volume, no gender-related difference was found. CONCLUSIONS Women have greater clearance of ethanol per unit lean body mass, confirming previous oral alcohol administration studies. Women have approximately the same liver volume as men, explaining the equivalent alcohol elimination rates seen when men and women are compared on the basis of liver size.

Translating the neuroscience of alcoholism into clinical treatments : from blocking the buzz to curing the blues

Understanding the pathophysiology of addictive disorders is critical for development of new treatments. A major focus of addiction research has for a long time been on systems that mediate acute positively reinforcing effects of addictive drugs, most prominently the mesolimbic dopaminergic (DA) system and its connections. This research line has been successful in shedding light on the physiology of both natural and drug reward, but has not led to therapeutic breakthroughs. The role of classical reward systems is perhaps least clear in alcohol addiction. Here, recent work is summarized that points to some clinically important conclusions. First, important pharmacogenetic differences exist with regard to positively reinforcing effects of alcohol and the ability of this drug to activate classical reward pathways. This offers an opportunity for personalized treatment approaches in alcoholism. Second, brain stress and fear systems become pathologically activated in later stages of alcoholism and their activation is a major influence in escalation of alcohol intake, sensitization of stress responses, and susceptibility to relapse. These findings offer a new category of treatment mechanisms. Corticotropin-releasing hormone (CRH) signaling through CRH1 receptors is a major candidate target in this category, but recent data indicate that antagonists for substance P (SP) neurokinin 1 (NK1) receptors may have a similar potential.

Alcohol‐Related Olfactory Cues Activate the Nucleus Accumbens and Ventral Tegmental Area in High‐Risk Drinkers: Preliminary Findings

BACKGROUND The mesocorticolimbic dopamine system is implicated in motivation and reward and may be involved in the development of alcoholism. METHODS We used functional magnetic resonance imaging to study the blood oxygen level-dependent (BOLD) response to alcohol-related olfactory stimuli (AROS; odors of beer and whiskey) and non-alcohol-related olfactory stimuli (NAROS; odors of grass and leather) in 10 high-risk (HR) drinkers (average drinks per week, 19.99; SD, 6.99; all with > or = 2 first- or second-degree alcoholic relatives) and 5 low-risk (LR) social drinking controls (drinks per week, 2.82; SD, 2.87; 1 subject had 1 second-degree alcoholic relative). Data were analyzed with SPM99 and random effects analysis by using regions of interest and corrected cluster statistics (p < 0.05) to focus on the nucleus accumbens (NAc) and ventral tegmental area (VTA). RESULTS In HR subjects, there was a greater BOLD signal increase in the NAc during AROS than during clean air. BOLD signal increases during AROS were also greater in the NAc than the signal increases induced by NAROS. The AROS signal was significantly greater than the NAROS signal in a small number of voxels in the VTA. Finally, the AROS/NAROS difference signal was larger in HR drinkers in both the NAc and VTA. CONCLUSIONS Alcoholic olfactory cues may invoke the dopaminergic mesocorticolimbic system to a greater degree than nonalcoholic odors and could be effective tools in exploring the role of the dopamine system in susceptibility to alcoholism.

Effect of Food and Food Composition on Alcohol Elimination Rates in Healthy Men and Women

Several studies have evaluated the effect of food on alcohol pharmacokinetics; however, most studies have used oral alcohol administration, which cannot separate the influence of food on absorption from its influence on alcohol elimination. Alcohol clamping uses intravenous alcohol and provides a direct measure of the alcohol elimination rate (AER). Two studies, using alcohol clamping at 50 mg%, were conducted to investigate the effect of food and food composition on AER (g/h) in healthymenand women. In the first study, 20 subjects underwent two clamping sessions, one after a 12‐hour fast and another 1 hour after consuming a 530‐calorie breakfast. In the second study, 8 subjects underwent four clamping sessions: one after a 12‐hour fast and, in each of three “fed” sessions, 1 hour after a 550‐calorie high‐fat, high‐protein, or high‐carbohydrate breakfast. Comparison of AERs from the first study showed an average 25% increase following food compared to that following fasting. Men showed significantly higher AERs compared to women; however, the food effect was similar in both genders. In the second study, the AER showed a significant average 45% increase following the meal, regardless of composition, compared with that following fasting. These findings indicate that food intake results in increased alcohol elimination rates. The increase was similar for meals of different compositions, suggesting that the food effect is not due to specific interactions with meal constituents. Probable mechanisms for the increased alcohol elimination include food‐induced increases in hepatic blood flow and in the activity of alcohol‐metabolizing enzymes.

Impact of Multiple Types of Childhood Trauma Exposure on Risk of Psychiatric Comorbidity Among Alcoholic Inpatients

BACKGROUND This study examined the prevalence of single- and multiple-type childhood trauma exposure (CTE) among alcoholic patients undergoing inpatient detoxification and treatment. The relationships between various types of CTE and lifetime psychiatric comorbidities and suicide attempts were also explored. METHODS A total of 196 alcoholic inpatients were assessed by Structured Clinical Interview for DSM-IV Axis I Disorders and Childhood Trauma Questionnaire (CTQ) for CTE history. RESULTS The overall prevalence of CTE in the entire sample was high (55.1%). Specifically, the prevalence of emotional abuse was 21.4%, physical abuse 31.1%, sexual abuse 24.0%, emotional neglect 20.4%, and physical neglect 19.9%. Regarding multiple types of CTE, 31.7 and 18.9% reported at least 2 and at least 3 CTE types, respectively. Strikingly, among those with at least 1 positive CTQ category, more than half reported 2 or more CTE types. A history of emotional abuse increased the risk of mood disorder, in particular major depressive disorder, as well as posttraumatic stress disorder (PTSD). Physical abuse contributed to the prediction of suicide attempts, while sexual abuse was associated with a diagnosis of anxiety disorder, PTSD, and multiple comobidities (e.g., anxiety and mood disorder). The number of reported CTE types or the total score of the CTQ predicted an increased risk of having single or multiple psychiatric comorbidities as well as suicide attempts. CONCLUSIONS We observed high rates of a broad range of CTE types and a trend for CTE-specific enhancement of risk for various psychiatric outcomes among alcoholic inpatients. Of note, a dose-response relationship between number of CTE types and risk of psychiatric comorbidities as well as suicide attempts was found. We suggest a wide range of CTE should be included when exploring the effects of CTE or developing prevention and treatment strategies among alcoholic subjects.

Role of GABRA2 in Moderating Subjective Responses to Alcohol

BACKGROUND Human twin studies have shown that certain responses to alcohol, including subjective perceptions, are genetically influenced. Previous studies have provided evidence that a low level of response to alcohol predicts future alcohol use disorders in humans. Recent genetic studies suggest an association between alcohol dependence and genetic variation in the γ-aminobutyric acid A (GABA(A)) receptor α2 subunit gene (GABRA2). Based on a haplotypic association of alcohol dependence with GABRA2, we investigated whether GABRA2 alleles are associated with the subjective responses to clamped alcohol concentration. METHODS One hundred and ten healthy social drinkers (53 men) underwent the alcohol clamp. Fifteen minutes after the start of an intravenous infusion of alcohol, the breath alcohol concentration was clamped at a target of 50 ± 5 mg/dl for 165 minutes. Subjective physiologic responses to alcohol and stimulant and sedative effects of alcohol were measured repeatedly during the alcohol clamp. Because aldehyde dehydrogenase 2 (ALDH2) has been shown to have a great impact on the subjective responses to alcohol, we divided subjects by ALDH2 genotype for further analyses. To examine the role of genetic variation in GABRA2, 7 single nucleotide polymorphisms (SNPs) that were informative in association studies were included as factors in the analysis. RESULTS Among these 7 SNPs, 3 SNPs (rs279869, rs279858, and rs279837) located in the middle of the GABRA2 gene showed significant associations with subjective effects of alcohol. Subjects with 1 or 2 copies of the more common allele showed greater subjective responses to alcohol than did individuals homozygous for the alcohol dependence-associated allele regardless of ALDH2 genotype. CONCLUSIONS These findings confirm and extend the observation that the GABRA2 alleles affect the subjective responses to alcohol, and suggest that the genetic variations in GABRA2 might play a role in the risk of alcohol use disorders by moderating the subjective effects of alcohol.

Subjective and Neural Responses to Intravenous Alcohol in Young Adults with Light and Heavy Drinking Patterns

Heavy alcohol consumption during young adulthood is a risk factor for the development of serious alcohol use disorders. Research has shown that individual differences in subjective responses to alcohol may affect individuals’ vulnerability to developing alcoholism. Studies comparing the subjective and objective response to alcohol between light and heavy drinkers (HDs), however, have yielded inconsistent results, and neural responses to alcohol in these groups have not been characterized. We performed a double-blind, placebo-controlled, randomized crossover alcohol challenge study comparing functional magnetic resonance imaging and subjective response to intravenously administered 6% v/v ethanol to a target blood alcohol concentration of 0.08% or placebo between HDs and social drinkers (SDs). During the imaging, we presented emotional cues in order to measure how emotion modulated the effects of alcohol on the brains reward circuitry. We found that, at equivalent blood alcohol concentrations, HDs reported lower subjective alcohol effects than SDs. Alcohol significantly activated the nucleus accumbens in SDs, but not in HDs. Self-reported ratings of intoxication correlated with striatal activation, suggesting that activation may reflect subjective experience of intoxication. Fearful faces significantly activated the amygdala in the SDs only, and this activation was attenuated by alcohol. This study shows that HDs not only experience reduced subjective effects of alcohol, but also demonstrate a blunted response to alcohol in the brains reward system. Our findings indicate that reduced subjective and neural response to alcohol in HDs may be suggestive of either the development of tolerance to alcohol, or of pre-existing decreased sensitivity to alcohols effects.