Nicotine dependence and comorbid psychiatric disorders: examination of specific genetic variants in the CHRNA5-A3-B4 nicotinic receptor genes

Tobacco use, trauma exposure and PTSD: a systematic review

Tobacco use remains one of the most significant preventable public health problems globally and is increasingly concentrated among vulnerable groups, including those with trauma exposure or diagnosed with PTSD. The goal of this systematic review was to update and extend previous reviews. Of the 7224 publications that met the initial criteria, 267 were included in the review. Summary topic areas include conceptual frameworks for the relation between trauma or PTSD and tobacco use; associations between trauma exposure or PTSD and tobacco use; number and type of trauma exposures and tobacco use; PTSD symptoms and tobacco use; Treatment-related studies; and the examination of causal relations. Evidence continues to indicate that individuals exposed to trauma or diagnosed with PTSD are more likely to use tobacco products, more nicotine dependent and less likely to abstain from tobacco even when provided evidence-based treatments than individuals without trauma. The most commonly cited causal association proposed was use of tobacco for self-regulation of negative affect associated with trauma. A small proportion of the studies addressed causality and mechanisms of action. Future work should incorporate methodological approaches and measures from which we can draw causal conclusions and mechanisms to support the development of viable therapeutic targets.

[Comorbidity of posttraumatic stress disorder and addiction from a biopsychosocial perspective]

Posttraumatic stress disorder and substance use disorder often co-occur within the health care system. Their comorbidity is associated with more serious acute clinical symptomatology, more frequent hospital admissions in state of emergency and significantly lower chances of improvement by psychological and pharmacological treatment. Their comorbidity contributes to dramatically unfavourable courses of illness as regards all biopsychosocial levels. The survey presented will discuss empirical findings from various perspectives: general epidemiology, substance use disorder as risk factor of trauma and PTSD, trauma and PTSD as risk factor of SUD, neurobiological effects of SUD converging towards neurobiology of PTSD, shared common factors of genetics/epigenetics, personality traits, and early developmental stress and trauma. The main focus of analysis will be put on processes that are intrinsically linked to the development and course of both disorders.

Association Between Nicotine-dependent Gene Polymorphism and Smoking Cessation in Patients With Lung Cancer

BACKGROUND

Patients with lung cancer continue to smoke owing to complex factors. Failure to quit smoking (defined as nicotine dependence) is significantly associated with genetic status. This study aimed to investigate the relationship between polymorphisms in nicotine dependence genes and smoking status after the diagnosis of lung cancer.

PATIENTS AND METHODS

A total of 240 patients with lung cancer were included from July 2017 to March 2018. According to the actual smoking condition after lung cancer diagnosis, eligible patients were divided into 3 groups: the never-smoking group, the failure to quit smoking group, and the successful smoking cessation group. Fagerstrom Test for Nicotine Dependence scores were used to evaluate the smoking status of each group. Three nicotine-dependent genes with 6 loci were detected.

RESULTS

Among the 240 patients, 86 were never-smokers, 51 failed to quit smoking, and 104 successfully quit smoking. The initial age of smoking in the failure to quit smoking group was significantly younger than those in the successful smoking cessation group (P = .001). There was a significant difference in the GG and AG and AA genotype distributions of CHRNA3 (rs578776) among the 3 groups (P = .003). There was also a significant difference in the distribution of CHRNA4 (rs2229959) genotypes among the 3 groups (P = .003). However, there was no significant difference in the genotype distribution of CHRNA5 (rs588765) among the 3 groups (P = .277).

CONCLUSIONS

Gene polymorphisms of CHRNA3 (rs578776) and CHRNA4 (rs1044396 and rs2229959) were associated with the success of smoking cessation after the diagnosis of lung cancer, which should be considered in the management of smoking cessation after patients are diagnosed with lung cancer.

Negative affective states and cognitive impairments in nicotine dependence

Smokers have substantial individual differences in quit success in response to current treatments for nicotine dependence. This observation may suggest that different underlying motivations for continued tobacco use across individuals and nicotine cessation may require different treatments in different individuals. Although most animal models of nicotine dependence emphasize the positive reinforcing effects of nicotine as the major motivational force behind nicotine use, smokers generally report that other consequences of nicotine use, including the ability of nicotine to alleviate negative affective states or cognitive impairments, as reasons for continued smoking. These states could result from nicotine withdrawal, but also may be associated with premorbid differences in affective and/or cognitive function. Effects of nicotine on cognition and affect may alleviate these impairments regardless of their premorbid or postmorbid origin (e.g., before or after the development of nicotine dependence). The ability of nicotine to alleviate these symptoms would thus negatively reinforce behavior, and thus maintain subsequent nicotine use, contributing to the initiation of smoking, the progression to dependence and relapse during quit attempts. The human and animal studies reviewed here support the idea that self-medication for pre-morbid and withdrawal-induced impairments may be more important factors in nicotine addiction and relapse than has been previously appreciated in preclinical research into nicotine dependence. Given the diverse beneficial effects of nicotine under these conditions, individuals might smoke for quite different reasons. This review suggests that inter-individual differences in the diverse effects of nicotine associated with self-medication and negative reinforcement are an important consideration in studies attempting to understand the causes of nicotine addiction, as well as in the development of effective, individualized nicotine cessation treatments.

Endophenotypes for Alcohol Use Disorder: An Update on the Field

The endophenotype concept was first proposed as a strategy to use (purportedly) genetically simpler phenotypes in gene identification studies for psychiatric disorders, and is distinct from the closely related concept of intermediate phenotypes. In the area of alcohol use disorder (AUD) research, two candidate endophenotypes have produced replicable genetic associations: level of response to alcohol and neurophysiology markers (e.g., event-related oscillations and event-related potentials). Additional candidate endophenotypes from the cognitive, sensory, and neuroimaging literatures show promise, although more evidence is needed to fully evaluate their potential utility. Translational approaches to AUD endophenotypes have helped characterize the underlying neurobiology and genetics of AUD endophenotypes and identified relevant pharmacological interventions. Future research that capitalizes on the polygenic nature of endophenotypes and emphasizes endophenotypes that may change across development will enhance the usefulness of this concept to understand the genetically-influenced pathways toward AUD.

Smoking and psychopathology increasingly associated in recent birth cohorts

BACKGROUND

In recent decades, smoking has become an increasingly non-normative behavior. Because deviant behaviors are associated with greater clinical and genetic risks, current-generation smokers may have greater concentrations of psychiatric comorbidity than previous generations. We examined this question empirically by testing whether associations between measures of smoking, psychiatric diagnoses, and risk-associated personality traits, increased across seven birth-cohorts of the 20th century.

METHOD

4326 subjects from a cross-sectional NIMH control sample were categorized into one of seven groups based on birth (born before 1930, and 1930s-80s) and one of three smoking levels (lifetime dependent smoker, never dependent smoker, never smoker). Smoking and ND were assessed using the Fagerstrom Test for Nicotine Dependence; psychiatric diagnoses (drug and alcohol dependence, major depression, and generalized anxiety disorder) using the Composite International Diagnostic Interview-Short Form, and personality traits (neuroticism and extraversion) with the Eysenck Personality Questionnaire.

RESULT

Lifetime prevalence of smoking decreased across the seven cohorts. Associations between smoking and drug dependence, generalized anxiety, and neuroticism, as well as total psychiatric comorbidity, were greater in more recent cohorts [smoking-by-cohort interaction: p<0.01], with greatest increases contributed by nicotine-dependent smokers. Smoking was also independently associated with alcohol dependence and depression, but these associations did not significantly vary across cohorts.

CONCLUSIONS

More recent generations included fewer persons who smoked, but their smoking was associated with greater psychiatric morbidity. Failure to account for systematic variation in comorbidity across smoking cohorts may lead to unwanted heterogeneity in clinical, and possibly genetic, studies of nicotine dependence.

Variants in the 15q25 gene cluster are associated with risk for schizophrenia and bipolar disorder

BACKGROUND

Rates of tobacco smoking are significantly higher in patients with schizophrenia compared with the general population. The underlying mechanism for this comorbidity is unclear. One hypothesis is that there are common genetic factors that predispose to both nicotine dependence (ND) and schizophrenia. To investigate this hypothesis, we examined the association of the 15q25 gene cluster, the most significant candidate region to date implicated in ND and smoking behavior, with schizophrenia and bipolar disorder.

METHODS

Five variants in the 15q25 gene cluster (rs951266, rs16969968, rs1051730, rs8040868, and rs17477223) were selected to test for association with schizophrenia diagnosis, bipolar disorder diagnosis, and the presence of negative symptoms of schizophrenia. Effects of the variants on 15q25 gene expression were analyzed using publically available postmortem brain expression data.

RESULTS

A meta-analysis revealed four markers associated with risk for schizophrenia and bipolar disorder (rs951266, rs16969968, rs8040868, and rs17477223), and with the presence of negative symptoms of schizophrenia (rs951266, rs1051730, rs8040868, and rs17477223). The associations were in the same direction as that found for ND. Gene expression analysis indicated an association between genotypes of the rs1051730 variant and CHRNA5 expression in brain and peripheral blood mononuclear cells, and with the rs16969968 and rs17477223 variants in brain.

CONCLUSION

Variants in the 15q25 gene cluster are associated with risk for schizophrenia/bipolar illness, negative symptoms of schizophrenia, and influence CHRNA5 expression in the brain and peripheral blood mononuclear cells. These results are consistent with the notion that there are genetic mechanisms common to schizophrenia, ND, and bipolar disorder.

Neuronal nicotinic acetylcholine receptors: common molecular substrates of nicotine and alcohol dependence

Alcohol and nicotine are often co-abused. As many as 80-95% of alcoholics are also smokers, suggesting that ethanol and nicotine, the primary addictive component of tobacco smoke, may functionally interact in the central nervous system and/or share a common mechanism of action. While nicotine initiates dependence by binding to and activating neuronal nicotinic acetylcholine receptors (nAChRs), ligand-gated cation channels normally activated by endogenous acetylcholine (ACh), ethanol is much less specific with the ability to modulate multiple gene products including those encoding voltage-gated ion channels, and excitatory/inhibitory neurotransmitter receptors. However, emerging data indicate that ethanol interacts with nAChRs, both directly and indirectly, in the mesocorticolimbic dopaminergic (DAergic) reward circuitry to affect brain reward systems. Like nicotine, ethanol activates DAergic neurons of the ventral tegmental area (VTA) which project to the nucleus accumbens (NAc). Blockade of VTA nAChRs reduces ethanol-mediated activation of DAergic neurons, NAc DA release, consumption, and operant responding for ethanol in rodents. Thus, ethanol may increase ACh release into the VTA driving activation of DAergic neurons through nAChRs. In addition, ethanol potentiates distinct nAChR subtype responses to ACh and nicotine in vitro and in DAergic neurons. The smoking cessation therapeutic and nAChR partial agonist, varenicline, reduces alcohol consumption in heavy drinking smokers and rodent models of alcohol consumption. Finally, single nucleotide polymorphisms in nAChR subunit genes are associated with alcohol dependence phenotypes and smoking behaviors in human populations. Together, results from pre-clinical, clinical, and genetic studies indicate that nAChRs may have an inherent role in the abusive properties of ethanol, as well as in nicotine and alcohol co-dependence.