Association of inflammation genes with alcohol dependence/abuse: a systematic review and a meta-analysis

Going beyond risk factor: Childhood maltreatment and associated modifiable targets to improve life-long outcomes in mood disorders

Childhood maltreatment increases risk for mood disorders and is associated with earlier onset-and more pernicious disease course following onset-of mood disorders. While the majority of studies to date have been cross-sectional, longitudinal studies are emerging and support the devastating role(s) childhood maltreatment has on development of, and illness course in, mood disorders. This manuscript extends prior reviews to emphasize more recent work, highlighting longitudinal data, and discusses treatment studies that provide clues to mechanisms that mediate disease risk, course, relapse, and treatment response. Evidence suggesting systemic inflammation, alterations in hypothalamic-pituitary-adrenal (HPA) axis function and corticotropin-releasing factor (CRF) neural systems, genetic and other familial factors as mechanisms that mediate risk and onset of, and illness course in, mood disorders following childhood maltreatment is discussed. Risky behaviors following maltreatment, e.g., substance use and unhealthy lifestyles, may further exacerbate alterations in the HPA axis, CRF neural systems, and systematic inflammation to contribute to a more pernicious disease course. More research on sex differences and the impact of maltreatment in vulnerable populations is needed. Future research needs to be aimed at leveraging knowledge on modifiable targets, going beyond childhood maltreatment as a risk factor, to inform prevention and treatment strategies and foster trauma-informed care.

The Etiologic, Theory-Based, Ontogenetic Hierarchical Framework of Alcohol Use Disorder: A Translational Systematic Review of Reviews

Modern nosologies (e.g., ICD-11, DSM-5) for alcohol use disorder (AUD) and dependence prioritize reliability and clinical presentation over etiology, resulting in a diagnosis that is not always strongly grounded in basic theory and research. Within these nosologies, DSM-5 AUD is treated as a discrete, largely categorical, but graded, phenomenon, which results in additional challenges (e.g., significant phenotypic heterogeneity). Efforts to increase the compatibility between AUD diagnosis and modern conceptualizations of alcohol dependence, which describe it as dimensional and partially overlapping with other psychopathology (e.g., other substance use disorders) will inspire a stronger scientific framework and strengthen AUD's validity. We conducted a systematic review of 144 reviews to integrate addiction constructs and theories into a comprehensive framework with the aim of identifying fundamental mechanisms implicated in AUD. The product of this effort was the Etiologic, Theory-Based, Ontogenetic Hierarchical Framework (ETOH Framework) of AUD mechanisms, which outlines superdomains of cognitive control, reward, as well as negative valence and emotionality, each of which subsume narrower, hierarchically-organized components. We also outline opponent processes and self-awareness as key moderators of AUD mechanisms. In contrast with other frameworks, we recommend an increased conceptual role for negative valence and compulsion in AUD. The ETOH framework serves as a critical step towards conceptualizations of AUD as dimensional and heterogeneous. It has the potential to improve AUD assessment and aid in the development of evidence-based diagnostic measures that focus on key mechanisms in AUD, consequently facilitating treatment matching.

Converging vulnerability factors for compulsive food and drug use

Highly palatable foods and substance of abuse have intersecting neurobiological, metabolic and behavioral effects relevant for understanding vulnerability to conditions related to food (e.g., obesity, binge eating disorder) and drug (e.g., substance use disorder) misuse. Here, we review data from animal models, clinical populations and epidemiological evidence in behavioral, genetic, pathophysiologic and therapeutic domains. Results suggest that consumption of highly palatable food and drugs of abuse both impact and conversely are regulated by metabolic hormones and metabolic status. Palatable foods high in fat and/or sugar can elicit adaptation in brain reward and withdrawal circuitry akin to substances of abuse. Intake of or withdrawal from palatable food can impact behavioral sensitivity to drugs of abuse and vice versa. A robust literature suggests common substrates and roles for negative reinforcement, negative affect, negative urgency, and impulse control deficits, with both highly palatable foods and substances of abuse. Candidate genetic risk loci shared by obesity and alcohol use disorders have been identified in molecules classically associated with both metabolic and motivational functions. Finally, certain drugs may have overlapping therapeutic potential to treat obesity, diabetes, binge-related eating disorders and substance use disorders. Taken together, data are consistent with the hypotheses that compulsive food and substance use share overlapping, interacting substrates at neurobiological and metabolic levels and that motivated behavior associated with feeding or substance use might constitute vulnerability factors for one another. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Chemokines, cytokines and substance use disorders

Efficacious pharmacotherapies for the treatment of substance use disorders need to be expanded and improved. Non-neuronal cells, particularly astrocytes and microglia, have emerged as therapeutic targets for the development of pharmacotherapies to treat dependence and relapse that accompanies chronic drug use. Cytokines and chemokines are neuroimmune factors expressed in neurons, astrocytes, and microglia that demonstrate promising clinical utility as therapeutic targets for substance use disorders. In this review, we describe a role for cytokines and chemokines in the rewarding and reinforcing effects of alcohol, opioids, and psychostimulants. We also discuss emerging cytokine- and chemokine-based therapeutic strategies that differ from conventional strategies directed toward transporters and receptors within the dopamine, glutamate, GABA, serotonin, and GABA systems.

Tumour Necrosis Factor in Neuroplasticity, Neurogenesis and Alcohol Use Disorder

Alcohol use disorder is a pervasive and detrimental condition that involves changes in neuroplasticity and neurogenesis. Alcohol activates the neuroimmune system and alters the inflammatory status of the brain. Tumour necrosis factor (TNF) is a well characterised neuroimmune signal but its involvement in alcohol use disorder is unknown. In this review, we discuss the variable findings of TNF's effect on neuroplasticity and neurogenesis. Acute ethanol exposure reduces TNF release while chronic alcohol intake generally increases TNF levels. Evidence suggests TNF potentiates excitatory transmission, promotes anxiety during alcohol withdrawal and is involved in drug use in rodents. An association between craving for alcohol and TNF is apparent during withdrawal in humans. While anti-inflammatory therapies show efficacy in reversing neurogenic deficit after alcohol exposure, there is no evidence for TNF's essential involvement in alcohol's effect on neurogenesis. Overall, defining TNF's role in alcohol use disorder is complicated by poor understanding of its variable effects on synaptic transmission and neurogenesis. While TNF may be of relevance during withdrawal, the neuroimmune system likely acts through a larger group of inflammatory cytokines to alter neuroplasticity and neurogenesis. Understanding the individual relevance of TNF in alcohol use disorder awaits a more comprehensive understanding of TNF's effects within the brain.

Neuroimmune signaling in alcohol use disorder

Alcohol use disorder (AUD) is a widespread disease with limited treatment options. Targeting the neuroimmune system is a new avenue for developing or repurposing effective pharmacotherapies. Alcohol modulates innate immune signaling in different cell types in the brain by altering gene expression and the molecular pathways that regulate neuroinflammation. Chronic alcohol abuse may cause an imbalance in neuroimmune function, resulting in prolonged perturbations in brain function. Likewise, manipulating the neuroimmune system may change alcohol-related behaviors. Psychiatric disorders that are comorbid with AUD, such as post-traumatic stress disorder, major depressive disorder, and other substance use disorders, may also have underlying neuroimmune mechanisms; current evidence suggests that convergent immune pathways may be involved in AUD and in these comorbid disorders. In this review, we provide an overview of major neuroimmune cell-types and pathways involved in mediating alcohol behaviors, discuss potential mechanisms of alcohol-induced neuroimmune activation, and present recent clinical evidence for candidate immune-related drugs to treat AUD.

Peripheral TNFα elevations in abstinent alcoholics are associated with hepatitis C infection

Substantial evidence supports the view that inflammatory processes contribute to brain alterations in HIV infection. Mechanisms recently proposed to underlie neuropathology in Alcohol Use Disorder (AUD) include elevations in peripheral cytokines that sensitize the brain to the damaging effects of alcohol. This study included 4 groups: healthy controls, individuals with AUD (abstinent from alcohol at examination), those infected with HIV, and those comorbid for HIV and AUD. The aim was to determine whether inflammatory cytokines are elevated in AUD as they are in HIV infection. Cytokines showing group differences included interferon gamma-induced protein 10 (IP-10) and tumor necrosis factor α (TNFα). Follow-up t-tests revealed that TNFα and IP-10 were higher in AUD than controls but only in AUD patients who were seropositive for Hepatitis C virus (HCV). Specificity of TNFα and IP-10 elevations to HCV infection status was provided by correlations between cytokine levels and HCV viral load and indices of liver integrity including albumin/globulin ratio, fibrosis scores, and AST/platelet count ratio. Because TNFα levels were mediated by HCV infection, this study provides no evidence for elevations in peripheral cytokines in "uncomplicated", abstinent alcoholics, independent of liver disease or HCV infection. Nonetheless, these results corroborate evidence for elevations in IP-10 and TNFα in HIV and for IP-10 levels in HIV+HCV co-infection.

Alcohol abstinence in patients surviving an episode of alcoholic hepatitis: Prediction and impact on long-term survival

Alcoholic hepatitis (AH) is the most severe form of alcoholic liver disease. Most studies have focused on short-term prognosis, whereas factors associated with long-term survival are largely unknown. The aims of our study were to (1) determine the impact of complete abstinence from alcohol on long-term survival and (2) identify prognostic factors at admission capable of predicting abstinence during long-term follow-up in patients with AH. One hundred forty-two patients with biopsy-proven AH that survived the first episode were included. Demographic, psychiatric, and biochemical variables at admission and drinking status during follow-up were obtained. Cox regression, logistic regression, and classification and regression trees (CART) analyses were used for statistical analysis. Overall mortality was 38% with a median follow-up of 55 months. During follow-up, complete abstinence was reported in 39% and was associated with better long-term survival (hazard ratio, 0.53; P = 0.03). After adjustment for baseline prognostic scoring systems (Model for End-Stage Liver Disease and age, bilirubin, international normalized ratio, creatinine scores), complete abstinence was independently associated with survival (P < 0.05). Age and lack of past alcoholism treatments were independently associated with complete abstinence (P < 0.001 and P = 0.02, respectively) during follow-up. CART analysis generated a simple and practical algorithm based on the combination of past alcoholism treatments and age. Using CART analysis, we stratified 2 subgroups of patients with high (65%) and low (26%-29%) rates of complete abstinence after an episode of AH.

CONCLUSION

Complete abstinence after an episode of AH positively impacts long-term survival. The combination of 2 variables easily obtained at admission might be useful to predict long-term abstinence after an episode of AH. Strategies aimed at promoting alcohol abstinence in these patients are necessary. (Hepatology 2017;66:1842-1853).

Associations between the tumor necrosis factor-α gene and interleukin-10 gene polymorphisms and risk of alcoholic liver disease: A meta-analysis

BACKGROUND

The critical roles of tumor necrosis factor-α (TNF-α) and interleukin-10 (IL-10) in the pathogenesis of alcoholic liver diseases (ALD) suggest that functional variations in the TNF-α (TNFA) and IL-10 genes may be related to individual susceptibility to ALD. As available studies examining the associations between TNFA or IL-10 polymorphisms and ALD risk have yielded conflicting results, a meta-analysis was conducted to clarify the potential relation between TNFA and IL-10 polymorphisms and the risk of ALD.

METHODS

A comprehensive literature search was conducted to identify relevant studies. Pooled odds ratios and 95% confidence intervals were calculated using a random-effects model. The heterogeneity between studies was assessed using the Cochran's Q statistic and the I(2) statistic. Publication bias was assessed using funnel plots and the Egger's regression test.

RESULTS

A total of 17studies and 12studies were identified and included in the meta-analysis of the associations between TNFA polymorphisms and ALD risk, and IL-10 polymorphisms and ALD risk, respectively. The pooled results showed that the "A" allele of the TNFA-238G>A polymorphism was significantly associated with an increased risk of ALD. Significant differences in the allele and genotype distributions of the IL-10-1082A>G polymorphism were detected in the comparison between ALD patients and healthy controls, but not when comparing ALD patients and alcohol dependent individuals without ALD. No significant associations between other polymorphic loci and ALD risks were detected.

CONCLUSIONS

The TNFA-238G>A polymorphism was significantly associated with ALD risk, while the TNFA-308G>A polymorphism and IL-10 polymorphisms (-1082A>G and -592C>A) may not be associated with the individual susceptibility to ALD. The impact of combined TNFA and IL-10 polymorphisms on individual susceptibility to ALD needs to be investigated in future studies.

Neuroimmune signaling: a key component of alcohol abuse

Molecular and behavioral studies corroborate a pivotal role for the innate immune system in mediating the acute and chronic effects of alcohol and support a neuroimmune hypothesis of alcohol addiction. Changes in expression of neuroimmune genes and microglial transcripts occur in postmortem brain from alcoholics and animals exposed to alcohol, and null mutant animals lacking certain innate immune genes show decreased alcohol-mediated responses. Many of the differentially expressed genes are part of the toll like receptor (TLR) signaling pathway and culminate in an increased expression of pro-inflammatory immune genes. Compounds known to inhibit inflammation, microglial activation, and neuroimmune gene expression have shown promising results in reducing alcohol-mediated behaviors in animal models, indicating that neuroimmune signaling pathways offer unexplored targets in the treatment of alcohol abuse.

The genetics of alcohol dependence

Alcohol consumption dates back to the Neolithic period, and alcohol dependence contributes substantially to the current global burden of disease. Despite this, optimal therapies and preventive strategies are lacking. Formal genetic studies of alcohol dependence have shown that genetic factors play as large a role in disease etiology as environmental factors. Molecular genetic studies may identify causal factors and facilitate the development of novel preventive and therapeutic approaches. Whereas earlier studies involved the use of linkage- and candidate-gene approaches, recent years have witnessed the introduction of genome-wide association studies (GWAS). The present review provides a brief overview of the findings of formal genetic studies, summarizes the results of earlier molecular-genetic investigations, and presents a detailed overview of all published GWAS in the field of alcohol dependence research. To date, few genome-wide significant findings have been reported. However, through the polygenic approach, GWAS have both confirmed the existence of a multitude of novel risk genes and indicated interesting new candidates.

Family-based and case-control study of glutamate receptor GRIK3 Ser310Ala polymorphism in alcohol dependence

AIM

The aim of this study was to evaluate the role of the glutamate receptor subunit-7 (GluR7, GRIK 3) rs6691840 (Ser310Ala, T928G) in the pathogenesis of alcohol dependence (AD).

METHODS

DNA was provided from AD patients (n = 209) and healthy control subjects (n = 308) all of Polish descent. The history of alcoholism was obtained using the Polish version of the SSAGA (Semi-Structured Assessment for the Genetics of Alcoholism). We conducted case-control association study and transmission disequilibrium test (TDT). GRIK3 functional polymorphism was genotyped by the PCR-RFLP method.

RESULTS

Analyses revealed that polymorphism Ser310Ala of GRIK3 gene is not associated with AD or any of its subgroups. TDT reveled an adequate transmission of both alleles in the group of alcohol families.

CONCLUSIONS

These findings replicate and extend our previous research results that do not support the hypothesis of the role of rs6691840 in the pathogenesis of AD.

Genetic variants of TNFα, IL10, IL1β, CTLA4 and TGFβ1 modulate the indices of alcohol-induced liver injury in East Indian population

Alcohol induced liver disease or alcoholic liver disease (ALD), a complex trait, encompasses a gamut of pathophysiological alterations in the liver due to continuous exposure to a toxic amount of alcohol (more than 80 g per day). Of all chronic heavy drinkers, only 15-20% develops hepatitis or cirrhosis concomitantly or in succession. Several studies revealed that inter-individual as well as inter-ethnic genetic variation is one of the major factors that predispose to ALD. The role of genetic factors in ALD has long been sought for in ethnically distinct population groups. ALD is fast emerging as an important cause of chronic liver disease in India; even in populations such as "Bengalis" who were "culturally immune" earlier. While the genetic involvement in the pathogenesis of ALD is being sought for in different races, the complex pathophysiology of ALD as well as the knowledge of population level diversity of the relevant alcohol metabolizing and inflammatory pathways mandates the need for well designed studies of genetic factors in ethnically distinct population groups. An array of cytokines plays a critical role as mediators of injury, inflammation, fibrosis and cirrhosis in ALD. We, therefore, studied the association of polymorphisms in five relevant cytokine genes with "clinically significant" ALD in an ethnic "Bengali" population in Eastern India. Compared with "alcoholic" controls without liver disease (n=110), TNFα -238AA genotype, IL1β -511CC genotype, TGFβ1 -509CC genotype and IL10 -592AA genotype were significantly overrepresented in ALD patients (n=181; OR=2.4 and 95% CI 1.2-5.5, P(genotype)=0.042, P(allelic)=0.008; OR=2.7 and 95% CI 1.2-5.9, P(genotype)=0.018, P(allelic)=0.023; OR=4.7 and 95% CI 1.7-13.1, P(genotype)=0.003, P(allelic)=0.014; and OR=2.2 and 95% CI 1.1-4.8, P(genotype)=0.04, P(allelic)=0.039 respectively). Moreover a cumulative genetic risk analysis revealed a significant trend for developing ALD with an increase in the number of risk alleles on IL10 and TGFβ1 loci among alcoholics. The risk genotype of IL1β and TGFβ1 also influences the total bilirubin, albumin and alanine aminotransferase levels among alcoholic "Bengalis". The present study is the first case-control study from Eastern India that comprehensively identified polymorphic markers in TNFα, IL10, IL1β and TGFβ1 genes to be associated with ALD in the Bengali population, accentuating the significance of genetic factors in clinical expressions of ALD.

Association of a genetic polymorphism of the alcohol-metabolizing enzyme ADH1C with alcohol dependence: results of a case-control study

OBJECTIVE

Alcohol dependence causes serious problems which may be influenced by genetic factors associated with alcohol metabolism. The aim was to investigate the allelic and genotypic difference in distribution of a polymorphism in alcohol dehydrogenase 1C gene (ADH1C) between alcohol-dependent individuals and controls, and to examine if these genotypes were associated with the age at which the patient became alcohol-dependent.

METHODS

We conducted a case-control study including 90 alcohol-dependent cases and 100 historic controls. The genomic DNA was isolated and the alleles were analyzed with an RFLP.

RESULTS

The ADH1C*1 allele frequencies were 0.89 (95% CI 0.84-0.91) in controls and 0.68 (95% CI 0.61-0.74) in alcohol-dependent patients. The frequencies of the ADH1C*2 allele were 0.11 (95% CI 0.07-0.14) and 0.32 (95% CI 0.25-0.38) among controls and alcohol-dependent patients, respectively (p < 0.0001). The ADH1C*1/*1 genotype frequency was significantly higher in the control group (77%) compared to that of the alcohol-dependents (51%, p < 0.0001). The ADH1C*1/*2 genotype frequency was significantly lower in the control group (23%) compared to that of the alcohol-dependents (42%, p < 0.0001). We obtained no statistically significant difference among the ADH1C genotype groups regarding age.

CONCLUSIONS

These findings suggest that a significantly higher presence of ADH1C*2 allele is associated with alcohol dependence in a Turkish population. Studies with other related polymorphisms are needed to more precisely estimate the association of alcohol dependence with ADH1C.