Translational strategies for therapeutic development in nicotine addiction: rethinking the conventional bench to bedside approach

Individual variations in motives for nicotine self-administration in male rats: evidence in support for a precision psychopharmacology

The significant heterogeneity in smoking behavior among smokers, coupled with the inconsistent efficacy of approved smoking cessation therapies, supports the presence of individual variations in the mechanisms underlying smoking. This emphasizes the need to shift from standardized to personalized smoking cessation therapies. However, informed precision medicine demands precision fundamental research. Tobacco smoking is influenced and sustained by diverse psychopharmacological interactions between nicotine and environmental stimuli. In the classical experimental rodent model for studying tobacco dependence, namely intravenous self-administration of nicotine, seeking behavior is reinforced by the combined delivery of nicotine and a discrete cue (nicotine+cue). Whether self-administration behavior is driven by the same psychopharmacological mechanisms across individual rats remains unknown and unexplored. To address this, we employed behavioral pharmacology and unbiased cluster analysis to investigate individual differences in the mechanisms supporting classical intravenous nicotine self-administration (0.04 mg/kg/infusion) in male outbred Sprague-Dawley rats. Our analysis identified two clusters: one subset of rats sought nicotine primarily for its reinforcing effects, while the second subset sought nicotine to enhance the reinforcing effects of the discrete cue. Varenicline (1 mg/kg i.p.) reduced seeking behavior in the former group, whereas it tended to increase in the latter group. Crucially, despite this fundamental qualitative difference revealed by behavioral manipulation, the two clusters exhibited quantitatively identical nicotine+cue self-administration behavior. The traditional application of rodent models to study the reinforcing and addictive effects of nicotine may mask individual variability in the underlying motivational mechanisms. Accounting for this variability could significantly enhance the predictive validity of translational research.

Assessment of ethanol and nicotine interactions using a reinforcer demand modeling with grouped and individual levels of analyses in a long-access self-administration model using male rats

Previous reports have indicated the reciprocal effects of nicotine and ethanol on their rewarding and reinforcing properties, but studies using methodological approaches resembling substance use in vulnerable populations are lacking. In our study, rats first self-administered ethanol, and their sensitivity to ethanol's reinforcing effects was assessed using a reinforcer demand modeling approach. Subsequently, rats were equipped with intravenous catheters to self-administer nicotine, and their sensitivity to nicotine's reinforcing effects was evaluated using the same approach. In the final phase, rats were allowed to self-administer ethanol and nicotine concurrently, investigating the influence of one substance on the rate of responding for the other substance. Group analyses revealed notable differences in demand among sucrose, sweetened ethanol, and ethanol-alone, with sucrose demonstrating the highest demand and ethanol-alone exhibiting greater sensitivity to changes in cost. At the individual level, our study finds significant correlations between rats' demand for sucrose and sweetened ethanol, suggesting parallel efforts for both substances. Our individual data also suggest interconnections in the elasticity of demand for sweetened ethanol and ethanol-alone, as well as a potential relationship in price response patterns between ethanol and nicotine. Furthermore, concurrent self-administration of ethanol and nicotine at the group level displayed reciprocal effects, with reduced responding for nicotine in the presence of ethanol and increased responding for ethanol in the presence of nicotine. This study provides valuable insights into modeling the co-use of ethanol and nicotine and assessing their interaction effects using reinforcer demand modeling and concurrent self-administration or noncontingent administration tests. These findings contribute to our understanding of the complex interplay between ethanol and nicotine and have implications for elucidating the underlying mechanisms involved in polydrug use.

Tobacco and nicotine use

Tobacco smoking is a major determinant of preventable morbidity and mortality worldwide. More than a billion people smoke, and without major increases in cessation, at least half will die prematurely from tobacco-related complications. In addition, people who smoke have a significant reduction in their quality of life. Neurobiological findings have identified the mechanisms by which nicotine in tobacco affects the brain reward system and causes addiction. These brain changes contribute to the maintenance of nicotine or tobacco use despite knowledge of its negative consequences, a hallmark of addiction. Effective approaches to screen, prevent and treat tobacco use can be widely implemented to limit tobacco's effect on individuals and society. The effectiveness of psychosocial and pharmacological interventions in helping people quit smoking has been demonstrated. As the majority of people who smoke ultimately relapse, it is important to enhance the reach of available interventions and to continue to develop novel interventions. These efforts associated with innovative policy regulations (aimed at reducing nicotine content or eliminating tobacco products) have the potential to reduce the prevalence of tobacco and nicotine use and their enormous adverse impact on population health.

Evaluation of dopamine D3 receptor occupancy by blonanserin using [11C]-(+)-PHNO in schizophrenia patients

RATIONALE

Unlike other antipsychotics, our previous positron emission tomography (PET) study demonstrated that a single dose of blonanserin occupied dopamine D₃ as well as dopamine D₂ receptors in healthy subjects. However, there has been no study concerning the continued use of blonanserin.

OBJECTIVES

We examined D₂ and D₃ receptor occupancies in patients with schizophrenia who had been treated with blonanserin.

METHODS

Thirteen patients with schizophrenia participated. PET examinations were performed on patients treated with clinical dosage of blonanserin or olanzapine alone. A crossover design was used in which seven patients switched drugs after the first scan, and PET examinations were conducted again. D₂ and D₃ receptor occupancies were evaluated by [¹¹C]-(+)-PHNO. We used nondisplaceable binding potential (BP_ND) of 6 healthy subjects which we previously reported as baseline. To consider the effect of upregulation of D₃ receptor by continued use of antipsychotics, D₃ receptor occupancy by blonanserin in seven subjects who completed 2 PET scans were re-analyzed by using BP_ND of olanzapine condition as baseline.

RESULTS

Average occupancy by olanzapine (10.8 ± 6.0 mg/day) was as follows: caudate 32.8 ± 18.3%, putamen 26.3 ± 18.2%, globus pallidus - 33.7 ± 34.9%, substantia nigra - 112.8 ± 90.7%. Average occupancy by blonanserin (12.8 ± 5.6 mg/day) was as follows: caudate 61.0 ± 8.3%, putamen 55.5 ± 9.5%, globus pallidus 48.9 ± 12.4%, substantia nigra 34.0 ± 20.6%. EC₅₀ was 0.30 ng/mL for D₂ receptor for caudate and putamen (df = 19, p < 0.0001) and 0.70 ng/mL for D₃ receptor for globus pallidus and substantia nigra (df = 19, p < 0.0001). EC₅₀ for D₃ receptor of blonanserin changed to 0.22 ng/mL (df = 13, p = 0.0041) when we used BP_ND of olanzapine condition as baseline.

CONCLUSIONS

Our study confirmed that blonanserin occupied both D₂ and D₃ receptors in patients with schizophrenia.

Four Actionable Bottlenecks and Potential Solutions to Translating Psychiatric Genetics Research: An Expert Review

BACKGROUND

Psychiatric genetics has had limited success in translational efforts. A thorough understanding of the present state of translation in this field will be useful in the facilitation and assessment of future translational progress.

PURPOSE

A narrative literature review was conducted. Combinations of 3 groups of terms were searched in EBSCOhost, Google Scholar, and PubMed. The review occurred in multiple steps, including abstract collection, inclusion/exclusion criteria review, coding, and analysis of included papers.

RESULTS

One hundred and fourteen articles were analyzed for the narrative review. Across those, 4 bottlenecks were noted that, if addressed, may provide insights and help improve and increase translation in the field of psychiatric genetics. These 4 bottlenecks are emphasizing linear translational frameworks, relying on molecular genomic findings, prioritizing certain psychiatric disorders, and publishing more reviews than experiments.

CONCLUSIONS

These entwined bottlenecks are examined with one another. Awareness of these bottlenecks can inform stakeholders who work to translate and/or utilize psychiatric genetic information. Potential solutions include utilizing nonlinear translational frameworks as well as a wider array of psychiatric genetic information (e.g., family history and gene-environment interplay) in this area of research, expanding which psychiatric disorders are considered for translation, and when possible, conducting original research. Researchers are urged to consider how their research is translational in the context of the frameworks, genetic information, and psychiatric disorders discussed in this review. At a broader level, these efforts should be supported with translational efforts in funding and policy shifts.

Assessment of individual differences in response to acute bupropion or varenicline treatment using a long-access nicotine self-administration model and behavioral economics in female rats

Bupropion and varenicline are widely prescribed pharmacological treatments for smoking cessation. These treatments are only marginally effective in clinical populations but most preclinical studies show that they are effective in decreasing self-administration in rats on a group level. The present study investigated individual differences in responding to bupropion or varenicline in a preclinical model of long-access to nicotine (0.03 mg/kg/inf; 12 h/day) in female rats. Rats were first assessed for their individual economic demand for nicotine and for their individual performance in open field and elevated plus maze prior to nicotine access and during withdrawal. Rats were then tested for the acute effects of bupropion, varenicline, and yohimbine. We found that neither bupropion nor varenicline decreased responding for nicotine on test days. On the contrary, a moderate dose of bupropion (30 mg/kg) significantly increased responding for nicotine. We also found that rats with higher demand for nicotine were more sensitive to pretreatment with yohimbine which resulted in increased responding for nicotine during the dose-effect tests. Finally, we show that rats that had a higher demand for nicotine also were more persistent in seeking nicotine during extinction and reinstatement tests with nicotine or yohimbine as triggers. Our findings suggest that the length of access to daily nicotine may be an important factor underlying the response to pharmacological treatments like bupropion or varenicline. Future studies modeling chronic treatment approaches that include both sexes will be needed to further extend our findings.

Barriers to smoking cessation: a qualitative study from the perspective of primary care in Malaysia

OBJECTIVES

This qualitative study aims to construct a model of the barriers to smoking cessation in the primary care setting.

DESIGN

Individual in-depth, semistructured interviews were audio-taped, then verbatim transcribed and translated when necessary. The data were first independently coded and then collectively discussed for emergent themes using the Straussian grounded theory method.

PARTICIPANTS AND SETTING

Fifty-seven current smokers were recruited from a previous smoking related study carried out in a primary care setting in Malaysia. Current smokers with at least one failed quit attempts were included.

RESULTS

A five-theme model emerged from this grounded theory method. (1) Personal and lifestyle factors: participants were unable to resist the temptation to smoke; (2) Nicotine addiction: withdrawal symptoms could not be overcome; (3) Social cultural norms: participants identified accepting cigarettes from friends as a token of friendship to be problematic; (4) Misconception: perception among smokers that ability to quit was solely based on one's ability to achieve mind control, and perception that stopping smoking will harm the body and (5) Failed assisted smoking cessation: smoking cessation services were not felt to be user-friendly and were poorly understood. The themes were organised into five concentric circles based on time frame: those actionable in the short term (themes 1 and 2) and the long term (themes 3, 4, 5).

CONCLUSIONS

Five themes of specific beliefs and practices prevented smokers from quitting. Clinicians need to work on these barriers, which can be guided by the recommended time frames to help patients to succeed in smoking cessation.

Not all smokers appear to seek nicotine for the same reasons: implications for preclinical research in nicotine dependence

Tobacco use leads to 6 million deaths every year due to severe long-lasting diseases. The main component of tobacco, nicotine, is recognized as one of the most addictive drugs, making smoking cessation difficult, even when 70 percent of smokers wish to do so. Clinical and preclinical studies have demonstrated consistently that nicotine seeking is a complex behavior involving various psychopharmacological mechanisms. Evidence supports that the population of smokers is heterogeneous, particularly as regards the breadth of motives that determine the urge to smoke. Here, we review converging psychological, genetic and neurobiological data from clinical and preclinical studies supporting that the mechanisms controlling nicotine seeking may vary from individual to individual. It appears timely that basic neuroscience integrates this heterogeneity to refine our understanding of the neurobiology of nicotine seeking, as tremendous progress has been made in modeling the various psychopharmacological mechanisms driving nicotine seeking in rodents. For a better understanding of the mechanisms that drive nicotine seeking, we emphasize the need for individual-based research strategies in which nicotine seeking, and eventually treatment efficacy, are determined while taking into account individual variations in the mechanisms of nicotine seeking.

Neurobiological and Neurophysiological Mechanisms Underlying Nicotine Seeking and Smoking Relapse

Tobacco-related morbidity and mortality continue to be a significant public health concern. Unfortunately, current FDA-approved smoking cessation pharmacotherapies have limited efficacy and are associated with high rates of relapse. Therefore, a better understanding of the neurobiological and neurophysiological mechanisms that promote smoking relapse is needed to develop novel smoking cessation medications. Here, we review preclinical studies focused on identifying the neurotransmitter and neuromodulator systems that mediate nicotine relapse, often modeled in laboratory animals using the reinstatement paradigm, as well as the plasticity-dependent neurophysiological mechanisms that facilitate nicotine reinstatement. Particular emphasis is placed on how these neuroadaptations relate to smoking relapse in humans. We also highlight a number of important gaps in our understanding of the neural mechanisms underlying nicotine reinstatement and critical future directions, which may lead toward the development of novel, target pharmacotherapies for smoking cessation.

Individual differences in responding to bupropion or varenicline in a preclinical model of nicotine self-administration vary according to individual demand for nicotine

Bupropion and varenicline are the top two smoking cessation interventions that are marginally successful in increasing abstinence rates when compared to placebo. Although smokers vary in their history and pattern of tobacco use, there is a significant gap in addressing this individual variability with individually targeted treatments. The present study takes the initial step towards a better understanding of individual differences in treatment outcomes by assessing the effect of bupropion or varenicline on nicotine self-administration in rats. Rats were first assessed for their individual economic demand for sucrose and then for self-administered nicotine (0.03 mg/kg/inf; 2 h sessions). We then examined the effect of bupropion (0, 10, 30, 60 mg/kg) or varenicline (0, 0.1, 1.0, 3.0 mg/kg) pretreatment on individual rates of nicotine self-administration using progressive ratio schedule of reinforcement. Thereafter, rats were subjected to four rounds of extinction and reinstatement tests. We found that individual demand for sucrose did not predict individual demand for nicotine. Acute pretreatments with bupropion or varenicline were most effective at decreasing nicotine self-administration in rats that had a higher demand for nicotine. Rats with higher demand for nicotine also showed higher magnitude of responding in extinction and during nicotine-triggered reinstatement tests. Although the acute treatment protocol employed in this study is an important initial step towards a better understanding of individual treatment effects, future research modeling chronic treatment approaches will be needed to further extend our findings.

The CB1 Neutral Antagonist AM4113 Retains the Therapeutic Efficacy of the Inverse Agonist Rimonabant for Nicotine Dependence and Weight Loss with Better Psychiatric Tolerability

BACKGROUND

Multiple studies suggest a pivotal role of the endocannabinoid system in regulating the reinforcing effects of various substances of abuse. Rimonabant, a CB₁ inverse agonist found to be effective for smoking cessation, was associated with an increased risk of anxiety and depression. Here we evaluated the effects of the CB₁ neutral antagonist AM4113 on the abuse-related effects of nicotine and its effects on anxiety and depressive-like behavior in rats.

METHODS

Rats were trained to self-administer nicotine under a fixed-ratio 5 or progressive-ratio schedules of reinforcement. A control group was trained to self-administer food. The acute/chronic effects of AM4113 pretreatment were evaluated on nicotine taking, motivation for nicotine, and cue-, nicotine priming- and yohimbine-induced reinstatement of nicotine-seeking. The effects of AM4113 in the basal firing and bursting activity of midbrain dopamine neurons were evaluated in a separate group of animals treated with nicotine. Anxiety/depression-like effects of AM4113 and rimonabant were evaluated 24h after chronic (21 days) pretreatment (0, 1, 3, and 10mg/kg, 1/d).

RESULTS

AM4113 significantly attenuated nicotine taking, motivation for nicotine, as well as cue-, priming- and stress-induced reinstatement of nicotine-seeking behavior. These effects were accompanied by a decrease of the firing and burst rates in the ventral tegmental area dopamine neurons in response to nicotine. On the other hand, AM4113 pretreatment did not have effects on operant responding for food. Importantly, AM4113 did not have effects on anxiety and showed antidepressant-like effects.

CONCLUSION

Our results indicate that AM4113 could be a promising therapeutic option for the prevention of relapse to nicotine-seeking while lacking anxiety/depression-like side effects.

Moderators of Varenicline Treatment Effects in a Double-Blind, Placebo-Controlled Trial for Alcohol Dependence: An Exploratory Analysis

OBJECTIVES

To explore whether varenicline (Chantix) showed more efficacy in treating certain subgroups of patients. In a recent multisite trial, varenicline was shown to be effective in reducing drinking in alcohol-dependent patients, both smokers and nonsmokers. Given the heterogeneity among alcohol-dependent patients, secondary analyses were conducted to determine whether certain subgroups responded more favorably than others to treatment with varenicline.

METHODS

Data were drawn from a phase 2 randomized, double-blind, placebo-controlled multisite 13-week trial of varenicline in alcohol-dependent patients (Litten et al., 2013). Seventeen moderator variables were selected for exploratory testing on the basis of theoretical and scientific interest.

RESULTS

Of the 17 moderator variables assessed, 4 were statistically significant, including cigarettes per day reduction, treatment drinking goal, years drinking regularly, and age of the patient. Two other variables—the type of adverse events experienced by patients and the severity of alcohol-related consequences—seemed to moderate the varenicline treatment effect at borderline statistical significance. Individuals who reduced the number of cigarettes per day experienced a significant effect from varenicline in reducing drinking, whereas those who did not change or who increased their number of cigarettes observed no beneficial effect. Reviewing the moderators related to severity, varenicline seemed to have greater efficacy than placebo among less severely dependent patients.

CONCLUSIONS

Varenicline seems to be more efficacious in certain subgroups, particularly in those who reduced their smoking and in the "less severe" patient. Additional studies are warranted to confirm the results of these exploratory analyses.

Repeated administration of an acetylcholinesterase inhibitor attenuates nicotine taking in rats and smoking behavior in human smokers

Tobacco smoking remains the leading cause of preventable death worldwide and current smoking cessation medications have limited efficacy. Thus, there is a clear need for translational research focused on identifying novel pharmacotherapies for nicotine addiction. Our previous studies demonstrated that acute administration of an acetylcholinesterase inhibitor (AChEI) attenuates nicotine taking and seeking in rats and suggest that AChEIs could be repurposed for smoking cessation. Here, we expand upon these findings with experiments designed to determine the effects of repeated AChEI administration on voluntary nicotine taking in rats as well as smoking behavior in human smokers. Rats were trained to self-administer intravenous infusions of nicotine (0.03 mg kg(-1) per 0.59 ml) on a fixed-ratio-5 schedule of reinforcement. Once rats maintained stable nicotine taking, galantamine or donepezil was administered before 10 consecutive daily nicotine self-administration sessions. Repeated administration of 5.0 mg kg(-1) galantamine and 3.0 mg kg(-1) donepezil attenuated nicotine self-administration in rats. These effects were reinforcer-specific and not due to adverse malaise-like effects of drug treatment as repeated galantamine and donepezil administration had no effects on sucrose self-administration, ad libitum food intake and pica. The effects of repeated galantamine (versus placebo) on cigarette smoking were also tested in human treatment-seeking smokers. Two weeks of daily galantamine treatment (8.0 mg (week 1) and 16.0 mg (week 2)) significantly reduced smoking rate as well as smoking satisfaction and reward compared with placebo. This translational study indicates that repeated AChEI administration reduces nicotine reinforcement in rats and smoking behavior in humans at doses not associated with tolerance and/or adverse effects.

2012 Division of medicinal chemistry award address. Trekking the cannabinoid road: a personal perspective

My involvement with the field of cannabinoids spans close to 3 decades and covers a major part of my scientific career. It also reflects the robust progress in this initially largely unexplored area of biology. During this period of time, I have witnessed the growth of modern cannabinoid biology, starting from the discovery of its two receptors and followed by the characterization of its endogenous ligands and the identification of the enzyme systems involved in their biosynthesis and biotransformation. I was fortunate enough to start at the beginning of this new era and participate in a number of the new discoveries. It has been a very exciting journey. With coverage of some key aspects of my work during this period of "modern cannabinoid research," this Award Address, in part historical, intends to give an account of how the field grew, the key discoveries, and the most promising directions for the future.