The genetics of nicotine addiction liability: ethical and social policy implications

Ethics of early detection of disease risk factors: A scoping review

BACKGROUND

Scientific and technological advancements in mapping and understanding the interrelated pathways through which biological and environmental exposures affect disease development create new possibilities for detecting disease risk factors. Early detection of such risk factors may help prevent disease onset or moderate the disease course, thereby decreasing associated disease burden, morbidity, and mortality. However, the ethical implications of screening for disease risk factors are unclear and the current literature provides a fragmented and case-by-case picture.

METHODS

To identify key ethical considerations arising from the early detection of disease risk factors, we performed a systematic scoping review. The Scopus, Embase, and Philosopher's Index databases were searched for peer-reviewed, academic records, which were included if they were written in English or Dutch and concerned the ethics of (1) early detection of (2) disease risk factors for (3) disease caused by environmental factors or gene-environment interactions. All records were reviewed independently by at least two researchers.

RESULTS

After screening 2034 titles and abstracts, and 112 full papers, 55 articles were included in the thematic synthesis of the results. We identified eight common ethical themes: (1) Reliability and uncertainty in early detection, (2) autonomy, (3) privacy, (4) beneficence and non-maleficence, (5) downstream burdens on others, (6) responsibility, (7) justice, and (8) medicalization and conceptual disruption. We identified several gaps in the literature, including a relative scarcity of research on ethical considerations associated with environmental preventive health interventions, a dearth of practical suggestions on how to address expressed concerns about overestimating health capacities, and a lack of insights into preventing undue attribution of health responsibility to individuals.

CONCLUSIONS

The ethical concerns arising with the early detection of risk factors are often interrelated and complex. Comprehensive ethical analyses are needed that are better embedded in normative frameworks and also assess and weigh the expected benefits of early risk factor detection. Such research is necessary for developing and implementing responsible and fair preventive health policies.

Nicotine Motivated Behavior in C. elegans

To maximize the advantages offered by Caenorhabditis elegans as a high-throughput (HTP) model for nicotine dependence studies, utilizing its well-defined neuroconnectome as a robust platform, and to unravel the genetic basis of nicotine-motivated behaviors, we established the nicotine conditioned cue preference (CCP) paradigm. Nicotine CCP enables the assessment of nicotine preference and seeking, revealing a parallel to fundamental aspects of nicotine-dependent behaviors observed in mammals. We demonstrated that nicotine-elicited cue preference in worms is mediated by nicotinic acetylcholine receptors and requires dopamine for CCP development. Subsequently, we pinpointed nAChR subunits associated with nicotine preference and validated human GWAS candidates linked to nicotine dependence involved in nAChRs. Functional validation involves assessing the loss-of-function strain of the CACNA2D3 ortholog and the knock-out (KO) strain of the CACNA2D2 ortholog, closely related to CACNA2D3 and sharing human smoking phenotypes. Our orthogonal approach substantiates the functional conservation of the α2δ subunit of the calcium channel in nicotine-motivated behavior. Nicotine CCP in C. elegans serves as a potent affirmation of the cross-species functional relevance of GWAS candidate genes involved in nicotine seeking associated with tobacco abuse, providing a streamlined yet comprehensive system for investigating intricate behavioral paradigms within a simplified and reliable framework.

Synthetic Methods for the Preparation of Conformationally Restricted Analogues of Nicotine

In the context of naturally occurring nitrogen heterocycles, nicotine is a chiral alkaloid present in tobacco plants, which can target and stimulate nicotinic acetylcholine receptors (nAChRs), a class of ligand-gated ion channels commonly located throughout the human brain. Due to its well-known toxicity for humans, there is considerable interest in the development of synthetic analogues; in particular, conformationally restricted analogues of nicotine have emerged as promising drug molecules for selective nAChR-targeting ligands. In the present mini-review, we will describe the synthesis of the conformationally restricted analogues of nicotine involving one or more catalytic processes. In particular, we will follow a systematic approach as a function of the heteroarene structure, considering: (a) 2,3-annulated tricyclic derivatives; (b) 3,4-annulated tricyclic derivatives; (c) tetracyclic derivatives; and (d) other polycyclic derivatives. For each of them we will also consider, when carried out, biological studies on their activity for specific nAChR subunits.

Social learning promotes nicotine self-administration by facilitating the extinction of conditioned aversion in isogenic strains of rats

Both social environment and genetic factors are critical for smoking initiation and nicotine addiction. We reported that rats developed conditioned flavor (i.e., taste and odor) aversion to intravenously self-administered (IVSA) nicotine, and that social learning promoted nicotine IVSA with flavor cues. We thus tested the hypothesis that socially acquired nicotine IVSA is a heritable trait by using female rats of six inbred strains and six F1 hybrids. Each strain was tested for 10 daily IVSA sessions. We found that the intake of nicotine (15 and 30 μg/kg/inf) varied among these strains by 33.7–56.6-fold. The heritability of nicotine intake was estimated to be 0.54–0.65. Further, there was a strong correlation in nicotine intake (R² = 0.85, p < 0.0001) between the two nicotine doses. Another cohort of rats was given three daily IVSA sessions followed by five sessions that tested conditioned flavor aversion. Nicotine intake was highly correlated with the extinction of the conditioned aversion (R² = 0.58, p < 0.005). These data showed that nicotine intake in the socially acquired nicotine self-administration model is controlled by genetic factors and that the role of social learning is likely in facilitating the extinction of conditioned aversive response to nicotine.

The biology of addiction

In this narrative review, the neurobiological mechanisms underlying substance abuse and addiction are discussed with a particular emphasis on the mechanisms that promote ongoing use and relapse. Addiction is estimated to affect 10-15% or more of the adult population, including physicians. Genetic predisposition, psychological and environmental risk factors, the timing of exposure to the substance, the type of substance used, and the frequency of use influence the individual's susceptibility to addiction. Abused substances act on the brain's reward system, a neural circuit that produces pleasurable feelings in response to stimuli that promote survival, thereby modifying future behavior to seek out similar stimuli. Endogenous activators include food, sex, and social interaction. Drugs of abuse hijack the reward circuit, producing intense activation. Repetitive exposure to substances leads to persistent, altered genetic expression and accumulation of ΔFos-B and corticotropin-releasing factor. High levels of these substances suppress the reward circuit and activate the endogenous stress response, resulting in a generalized state of discord. These changes are enduring and can trigger substance use relapse even after long periods of abstinence.

The media and behavioral genetics: Alternatives coexisting with addiction genetics

To understand public discourse in the U.S. on genetic causation of behavioral disorders, we analyzed media representations of genetic research on addiction published between 1990 and 2010. We conclude first that the media simplistically represent biological bases of addiction and willpower as being mutually exclusive: behaviors are either genetically determined, or they are a choice. Second, most articles provide only cursory or no treatment of the environmental contribution. A media focus on genetics directs attention away from environmental factors. Rhetorically, media neglect the complexity underlying of the etiology of addiction and direct focus back toward individual causation and responsibility.

Unwarranted optimism in media portrayals of genetic research on addiction overshadows critical ethical and social concerns

The cost of addiction in the United States, in combination with a host of new tools and techniques, has fueled an explosion of genetic research on addiction. Because the media has the capacity to reflect and influence public perception, there is a need to examine how treatments and preventive approaches projected to emerge from addiction genetic research are presented to the public. The authors conducted a textual analysis of 145 news articles reporting on genetic research on addiction from popular print media in the United States and from popular news and medical internet sites. In articles that report on prevention, the media emphasize vaccine development and identifying individuals at genetic risk through population screening. Articles that emphasize treatment often promote current pharmaceutical solutions and highlight the possibility of tailoring treatments to specific genetic variants. The authors raise concerns about the tendency of this coverage to focus on the benefits of pharmaceutical treatments and genetic-based approaches to prevention while neglecting or downplaying potential risks and ethical issues. This analysis suggests a need for more balanced, evidence-based media reporting on the potential outcomes of genetic research.

The brain disease model of addiction: is it supported by the evidence and has it delivered on its promises?

Since 1997 the US National Institute on Drug Abuse has advocated a brain disease model of addiction (BDMA). We assess the strength of evidence for the BDMA in animals, neuroimaging studies of people with addiction, and current research on the role of genetics in addiction. We critically assess claims about the medical and social benefits of use of the BDMA because the social implications are often implied as a reason to accept this model. Furthermore, we argue that the BDMA is not supported by animal and neuroimaging evidence to the extent its advocates suggest; it has not helped to deliver more effective treatments for addiction; and its effect on public policies toward drugs and people with addiction has been modest. The focus of the BDMA is on disordered neurobiology in a minority of severely addicted individuals, which undermines the implementation of effective and cost-effective policies at the population level to discourage people from smoking tobacco and drinking heavily. The pursuit of high technology direct brain interventions to cure addiction when most individuals with addiction do not have access to effective psychosocial and drug treatments is questionable.

Framing Nicotine Addiction as a "Disease of the Brain": Social and Ethical Consequences

OBJECTIVES

In this article, we seek to better understand how a genomic vision of addiction may influence drug prevention and treatment. Though social influences on substance use and abuse (e.g., peer and family influence, socioeconomic status) are well documented, biomedical intervention is becoming increasingly technoscientific in nature. We wish to elucidate how emphasizing biological influences on substance use may lead to a vision of addiction as a phenomenon isolated within our bodies and neurochemistry, not lived daily within a complex social web of relationships and a particular political economy, including the tobacco industry, which aggressively markets products known to cause harm.

METHODS

We explore the emerging view of addiction as a "disease of the brain" in open-ended interviews with 86 stakeholders from the fields of nicotine research and tobacco control. Interview data were analyzed using standard qualitative techniques.

RESULTS

Most stakeholders hold a medicalized view of addiction. Though environmental variables are understood to be a primary cause of smoking initiation, the speed and strength with which addiction occurs is understood to be a largely biological process. Though stakeholders believe that an increased focus on addiction as a disease of the brain is not likely to lead to widespread unrealistic expectations for cessation therapies, they remain concerned that it may reinforce teenagers' expectations that quitting is not difficult. Finally, stakeholder responses indicate that genetic and neuroscientific research is unlikely to increase or decrease stigmatization, but will be used by interest groups to buttress their existing views of the stigma associated with smoking.

CONCLUSION

We argue that the main potential harms of focusing on biological etiology stem from a concept of addiction that is disassociated from social context. Focusing on genetic testing and brain scans may lead one to overemphasize pharmaceutical "magic bullet cures" and underemphasize, and underfund, more traditional therapies and public health prevention strategies that have proven to be effective. Genetic research on addiction may fundamentally change our conception of deviance and our identities, and may thus transform our susceptibility to substance use into something isolated in our biology, not embedded in a biosocial context.

Integrating genetic studies of nicotine addiction into public health practice: stakeholder views on challenges, barriers and opportunities

OBJECTIVE

Will emerging genetic research strengthen tobacco control programs? In this empirical study, we interview stakeholders in tobacco control to illuminate debates about the role of genomics in public health.

METHODS

The authors performed open-ended interviews with 86 stakeholders from 5 areas of tobacco control: basic scientists, clinicians, tobacco prevention specialists, health payers, and pharmaceutical industry employees. Interviews were qualitatively analyzed using standard techniques.

RESULTS

The central tension is between the hope that an expanding genomic knowledge base will improve prevention and smoking cessation therapies and the fear that genetic research might siphon resources away from traditional and proven public health programs. While showing strong support for traditional public health approaches to tobacco control, stakeholders recognize weaknesses, specifically the difficulty of countering the powerful voice of the tobacco industry when mounting public campaigns and the problem of individuals who are resistant to treatment and continue smoking.

CONCLUSIONS

In order for genetic research to be effectively translated into efforts to minimize the harm of smoking-related disease, the views of key stakeholders must be voiced and disagreements reconciled. Effective translation requires honest evaluation of both the strengths and limitations of genetic approaches.

Personalized medicine and tobacco-related health disparities: is there a role for genetics?

Genetic testing has been proposed as a means to increase smoking cessation rates and thus reduce smoking prevalence. To understand how that might be practically possible, with appreciation of the current social context of tobacco use and dependence, we performed a contextual analysis of smoking-related genetics and smoking cessation. To provide added value, genetics would need to inform and improve existing interventions for smokers (including behavioral and pharmacological treatments). Pharmacogenetics offers the most promising potential, because it may improve the efficacy of medication-based smoking cessations strategies. All proven interventions for treating tobacco dependence, however, including simple cost-effective measures, such as quit lines and physician counseling, are underutilized. As tobacco use occurs disproportionately among disadvantaged populations, efforts to improve smokers' access to health care, and to the tools that are known to help them quit, represent the most promising approaches for reducing smoking prevalence within these groups. Similar considerations apply to other chronic diseases contributing to population-level health disparities. We conclude that although genetics offers increasing opportunities to tailor drug treatment, and may in some cases provide useful risk prediction, other methods of personalizing care are likely to yield greater benefit to populations experiencing health disparities related to tobacco use.

Being more realistic about the public health impact of genomic medicine

Wayne Hall and colleagues discuss the limitations of genomic risk prediction for population-level preventive health care.

Substance use disorder genetic research: investigators and participants grapple with the ethical issues

OBJECTIVE

This qualitative research examined the ethical concerns regarding the psychosocial issues, research design and implementation, and application of psychiatric genetic research on substance use disorders (SUD) from multiple perspectives.

METHODS

A literature review of the bioethics literature related to psychiatric genetics and focus groups explored the ethical implications of SUD genetic research. Twenty-six National Institute on Drug Abuse funded principal investigators in the field of psychiatric genetic research, nine adolescent patients in residential SUD treatment, and 10 relatives of patients participated in focus groups (held separately). The focus groups were recorded, transcribed, and the content was analyzed. The themes that emerged from the literature and the focus group transcripts were organized by using NVIVO7, a software package designed to manage, analyze, and compare narrative data.

RESULTS

Investigators and the literature expressed similar concerns regarding the ethical concerns associated with psychiatric genetic research including violation of privacy, misunderstanding about psychiatric genetics, stigmatization, commercialization, discrimination, eugenics, consequences of research on illegal behavior, unforeseen consequences, altered notion of individual responsibility, and others. Patients and their relatives showed little familiarity with the ethical issues as identified by professionals and little concern regarding most of the potential risks. The exception was apprehension associated with potential criminal justice uses of stored genetic information, in particular enforced therapy and stigmatization, which elicited some concern from all perspectives.

CONCLUSION

The challenge for further research is to identify risks and benefits of SUD research that are germane in a behaviorally disinhibited population and devise effective tools to communicate information to participants through an improved informed consent process.

The issue of consent in research that administers drugs of addiction to addicted persons

In addiction, impaired control over drug use raises questions about the capacity of addicted persons to consent to participate in research studies in which they are given their drug of addiction. We review the case for doing such research, and the arguments that addiction does, and does not, prevent addicted persons from consenting to such research. We argue for a more nuanced view that acknowledges that while in some situations addiction impairs decision-making capacity, it does not eliminate such capacity. We conclude with some suggestions for recruiting addicted subjects and designing experiments in ways to obtain free and informed consent.

Multiple genetic tests for susceptibility to smoking do not outperform simple family history

AIMS

To evaluate the utility of using predictive genetic screening of the population for susceptibility to smoking.

METHODS

The results of meta-analyses of genetic association studies of smoking behaviour were used to create simulated data sets using Monte Carlo methods. The ability of the genetic tests to screen for smoking was assessed using receiver operator characteristic curve analysis. The result was compared to prediction using simple family history information. To identify the circumstances in which predictive genetic testing would potentially justify screening we simulated tests using larger numbers of alleles (10, 15 and 20) that varied in prevalence from 10 to 50% and in strength of association [relative risks (RRs) of 1.2-2.1].

RESULTS

A test based on the RRs and prevalence of five susceptibility alleles derived from meta-analyses of genetic association studies of smoking performed similarly to chance and no better than the prediction based on simple family history. Increasing the number of alleles from five to 20 improved the predictive ability of genetic screening only modestly when using genes with the effect sizes reported to date.

CONCLUSIONS

This panel of genetic tests would be unsuitable for population screening. This situation is unlikely to be improved upon by screening based on more genetic tests. Given the similarity with associations found for other polygenic conditions, our results also suggest that using multiple genes to screen the general population for genetic susceptibility to polygenic disorders will be of limited utility.