Behavioural and pharmacological mechanisms of bupropion's anti-smoking effects: recent preclinical and clinical insights

The co-use of nicotine and prescription psychostimulants: A review of their behavioral and neuropharmacological interactions

BACKGROUND

Nicotine is commonly co-used with other psychostimulants. These high co-use rates have prompted much research on interactions between nicotine and psychostimulant drugs. These studies range from examination of illicitly used psychostimulants such as cocaine and methamphetamine to prescription psychostimulants used to treat attention deficit hyperactivity disorder (ADHD) such as methylphenidate (Ritalin™) and d-amphetamine (active ingredient of Adderall™). However, previous reviews largely focus on nicotine interactions with illicitly used psychostimulants with sparse mention of prescription psychostimulants. The currently available epidemiological and laboratory research, however, suggests high co-use between nicotine and prescription psychostimulants, and that these drugs interact to modulate use liability of either drug. The present review synthesizes epidemiological and experimental human and pre-clinical research assessing the behavioral and neuropharmacological interactions between nicotine and prescription psychostimulants that may contribute to high nicotine-prescription psychostimulant co-use.

METHODS

We searched databases for literature investigating acute and chronic nicotine and prescription psychostimulant interactions. Inclusion criteria were that participants/subjects had to experience nicotine and a prescription psychostimulant compound at least once in the study, in addition to assessment of their interaction.

RESULTS AND CONCLUSIONS

Nicotine clearly interacts with d-amphetamine and methylphenidate in a variety of behavioral tasks and neurochemical assays assessing co-use liability across preclinical, clinical, and epidemiological research. The currently available research suggests research gaps examining these interactions in women/female rodents, in consideration of ADHD symptoms, and how prescription psychostimulant exposure influences later nicotine-related outcomes. Nicotine has been less widely studied with alternative ADHD pharmacotherapy bupropion, but we also discuss this research.

Elucidating the reinforcing effects of nicotine: a tribute to Nadia Chaudhri

Nadia Chaudhri worked with us as a graduate student in the Center for Neuroscience at the University of Pittsburgh from 1999 until she earned her PhD in 2005, a time that coincided with the discovery in our lab of the dual reinforcing actions of nicotine, a concept that she played an important role in shaping. The research that was described in her doctoral thesis is among the foundational pillars of the now well-accepted notion that nicotine acts as both a primary reinforcer and an amplifier of other reinforcer stimuli. This reinforcement-enhancing action of nicotine is robust and likely to be a powerful driver of nicotine use. Below, we discuss the evidence that these two actions of nicotine - primary reinforcement and reinforcement enhancement - are distinct and dissociable, a finding that Nadia was closely associated with. We go on to address two other topics that greatly interested Nadia during that time, the generalizability of the reinforcement-enhancing action of nicotine to multiple classes of reinforcing stimuli and potential sex differences in the dual reinforcing actions of nicotine. The research has greatly expanded since Nadia's involvement, but the core ideas that she helped to develop remain central to the concept of the dual reinforcing actions of nicotine and its importance for understanding the drivers of nicotine use.

Characterization of the Stereoselective Disposition of Bupropion and Its Metabolites in Rat Plasma and Brain

BACKGROUND AND OBJECTIVES

Bupropion is an atypical antidepressant and smoking cessation aid; its use is associated with wide intersubject variability in efficacy and safety. Knowledge of the brain pharmacokinetics of bupropion and its pharmacologically active metabolites is considered important for understanding the cause-effect relationships driving this variability.

METHODS

Brain concentrations from rats administered a 10 mg/kg subcutaneous dose of racemic bupropion were analyzed using a stereoselective LC/MS-MS method. A 2 mg/kg dose of (S,S)-hydroxybupropion, which has comparable pharmacologic potency to bupropion, was administered to a separate group of rats. Plasma exposure and unbound concentrations in both matrices from companion equilibrium dialysis experiments were determined to assess potential carrier-mediated transport at the blood-brain barrier.

RESULTS

Exposures to unbound forms of bupropion enantiomers were similar in plasma; this was also true in brain. This trend held for reductive diastereomer metabolite pairs in the two matrices. Unbound (R,R)-hydroxybupropion exposure was 1.5-fold higher than (S,S)-hydroxybupropion exposure in plasma and brain following bupropion administration. Unbound concentration ratios (K_p,uu) of a given molecular form decreased over time: between 4 and 6 h, these were < 1 for the two bupropion enantiomers, and they were ~ 1 for metabolites that formed. Administration of preformed (S,S)-hydroxybupropion also demonstrated a declining K_p,uu.

CONCLUSIONS

The temporal shift in K_p,uu among the different molecular forms provides evidence regarding the operation of carrier-mediated transport and/or within-brain metabolism of bupropion, and, thereby, fresh insight regarding the causes of intersubject variability in the safety and efficacy of bupropion therapy.

Substance abuse and neurotransmission

The number of people who suffer from a substance abuse disorder has continued to rise over the last decade; particularly, the number of drug-related overdose deaths has sharply increased during the COVID-19 pandemic. Converging lines of clinical observations, supported by imaging and neuropsychological performance testing, have demonstrated that substance abuse-induced dysregulation of neurotransmissions in the brain is critical for development and expression of the addictive properties of abused substances. Recent scientific advances have allowed for better understanding of the neurobiological processes that mediates drugs of abuse and addiction. This chapter presents the past classic concepts and the recent advances in our knowledge about how cocaine, amphetamines, opioids, alcohol, and nicotine alter multiple neurotransmitter systems, which contribute to the behaviors associated with each drug. Additionally, we discuss the interactive effects of HIV-1 or COVID-19 and substance abuse on neurotransmission and neurobiological pathways. Finally, we introduce therapeutic strategies for development of pharmacotherapies for substance abuse disorders.

Bupropion for smoking cessation in adolescents

QUESTION

An adolescent who smokes regularly came to my clinic for help quitting. While I am aware that bupropion is a first-line medication for smoking cessation among adults, is it effective and safe for adolescents?

ANSWER

Most adolescent smokers in Canada would like to quit, but more than 90% of the attempts are unsuccessful. Bupropion appears to be more effective than other pharmacologic options in improving abstinence among adolescents who smoke in the short term; however, it is not approved by Health Canada for those younger than 18 years. Bupropion has not been associated with an increase in adverse events in smoking cessation trials. More research is needed on the long-term effectiveness and safety of bupropion in this population.

Drug testing complementary metal-oxide-semiconductor chip reveals drug modulation of transmitter release for potential therapeutic applications

Neurodegenerative diseases, such as Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease, are considered incurable and significantly reduce the quality of life of the patients. A variety of drugs that modulate neurotransmitter levels have been used for the treatment of the neurodegenerative diseases but with limited efficacy. In this work, an amperometric complementary metal‐oxide‐semiconductor (CMOS) chip is used for high‐throughput drug testing with respect to the modulation of transmitter release from single vesicles using chromaffin cells prepared from bovine adrenal glands as a model system. Single chromaffin cell amperometry was performed with high efficiency on the surface‐modified CMOS chip and follow‐up whole‐cell patch‐clamp experiments were performed to determine the readily releasable pool sizes. We show that the antidepressant drug bupropion significantly increases the amount of neurotransmitter released in individual quantal release events. The antidepressant drug citalopram accelerates rapid neurotransmitter release following stimulation and follow‐up patch‐clamp experiments reveal that this is because of the increase in the pool of readily releasable vesicles. These results shed light on the mechanisms by which bupropion and citalopram may be potentially effective in the treatment of neurodegenerative diseases. These results demonstrate that the CMOS amperometry chip technology is an excellent tool for drug testing to determine the specific mechanisms by which they modulate neurotransmitter release.

Nicotine-induced molecular alterations are modulated by GABAB receptor activity

It has been demonstrated that GABAB receptors modulate nicotine (NIC) reward effect; nevertheless, the mechanism implicated is not well known. In this regard, we evaluated the involvement of GABAB receptors on the behavioral, neurochemical, biochemical and molecular alterations associated with the rewarding effects induced by NIC in mice, from a pharmacological and genetic approach. NIC-induced rewarding properties (0.5 mg/kg, subcutaneously, sc) were evaluated by conditioned place preference (CPP) paradigm. CPP has three phases: preconditioning, conditioning and postconditioning. GABAB receptor antagonist 2-hydroxysaclofen (0.25, 0.5 and 1 mg/kg; intraperitoneally, ip) or the GABAB receptor agonist baclofen (3 mg/kg; ip) was injected before NIC during the conditioning phase. GABAB1 knockout (GABAB1 KO) mice received NIC during the conditioning phase. Vehicle and wild-type controls were employed. Neurochemical (dopamine, serotonin and their metabolites), biochemical (nicotinic receptor α4β2, α4β2nAChRs) and molecular (c-Fos) alterations induced by NIC were analyzed after the postconditioning phase by high-performance liquid chromatography (HPLC), receptor-ligand binding assays and immunohistochemistry, respectively, in nucleus accumbens (Acb), prefrontal cortex (PFC) and ventral tegmental area (VTA). NIC induced rewarding effects in the CPP paradigm and increased dopamine levels in Acb and PFC, α4β2nAChRs density in VTA and c-Fos expression in Acb shell (AcbSh), VTA and PFC. We showed that behavioral, neurochemical, biochemical and molecular alterations induced by NIC were prevented by baclofen. However, in 2-hydroxysaclofen pretreated and GABAB1 KO mice, these alterations were potentiated, suggesting that GABAB receptor activity is necessary to control alterations induced by NIC-induced rewarding effects. Therefore, the present findings provided important contributions to the mechanisms implicated in NIC-induced rewarding effects.

Postnatal Cardiovascular Consequences in the Offspring of Pregnant Rats Exposed to Smoking and Smoking Cessation Pharmacotherapies

Approximately 20% of pregnant women smoke despite intentions to quit. Smoking cessation drugs, such as nicotine replacement therapy (NRT) and bupropion, are recommended treatments. Adverse cardiovascular outcomes in offspring have raised concerns about NRT's safety during pregnancy. However, the effect of bupropion is unknown. Using a rat model, we determined whether NRT and bupropion interventions during pregnancy are safer than continued smoking on offspring's cardiovascular function. Male offspring of controls and dams exposed to cigarette smoke (1.6 packs/day, inhalation), nicotine (2 mg/kg/d subcutaneously), and bupropion (13 mg/kg twice daily orally) were assessed for fetoplacental weight, cardiac function, blood pressure, and vascular reactivity. Fetoplacental weights were decreased and spontaneous beating and intracellular calcium in neonatal cardiomyocytes were increased in smoking, nicotine, and bupropion offspring; however, these effects were more accentuated in smoking followed by nicotine and bupropion offspring. Increased heart rate and decreased cardiac output, stroke volume, and left ventricular percent posterior wall thickening were observed in smoking, nicotine, and bupropion offspring. The left ventricular mass was reduced in smoking and nicotine but not in bupropion offspring. Blood pressure was higher with decreased endothelium-dependent relaxation and exaggerated vascular contraction to angiotensin II in smoking and nicotine offspring, with more pronounced dysfunctions in smoking than nicotine offspring. Maternal bupropion did not impact offspring's blood pressure, endothelium-dependent relaxation, and vascular contraction. In conclusion, maternal nicotine intervention adversely affects offspring's cardiovascular outcomes, albeit less severely than continued smoking. However, bupropion causes cardiac derangement in offspring but does not adversely affect blood pressure and vascular function.

Bupropion-induced inhibition of α7 nicotinic acetylcholine receptors expressed in heterologous cells and neurons from dorsal raphe nucleus and hippocampus

The pharmacological activity of bupropion was compared between α7 nicotinic acetylcholine receptors expressed in heterologous cells and hippocampal and dorsal raphe nucleus neurons. The inhibitory activity of bupropion was studied on GH3-α7 cells by Ca2+ influx, as well as on neurons from the dorsal raphe nucleus and interneurons from the stratum radiatum of the hippocampal CA1 region by using a whole-cell voltage-clamp technique. In addition, the interaction of bupropion with the α7 nicotinic acetylcholine receptor was determined by [3H]imipramine competition binding assays and molecular docking. The fast component of acetylcholine- and choline-induced currents from both brain regions was inhibited by methyllycaconitine, indicating the participation of α7-containing nicotinic acetylcholine receptors. Choline-induced currents in hippocampal interneurons were partially inhibited by 10 µM bupropion, a concentration that could be reached in the brain during clinical administration. Additionally, both agonist-induced currents were reversibly inhibited by bupropion at concentrations that coincide with its inhibitory potency (IC50=54 µM) and binding affinity (Ki=63 µM) for α7 nicotinic acetylcholine receptors from heterologous cells. The [3H]imipramine competition binding and molecular docking results support a luminal location for the bupropion binding site(s). This study may help to understand the mechanisms of actions of bupropion at neuronal and molecular levels related with its therapeutic actions on depression and for smoking cessation.

Drug safety evaluation of naltrexone/bupropion for the treatment of obesity

INTRODUCTION

Obesity is a known health risk for the development of several preventable diseases. Obesity-related metabolic alterations negatively impact different physiological mechanisms, which supports the rationale for the use of combined drug therapy. Naltrexone is an opioid antagonist for the treatment of opioid and alcohol dependency, whereas bupropion is a norepinephrine/dopamine reuptake inhibitor used to treat depression and smoking cessation. Although not effective as individual monotherapies for obesity, naltrexone and bupropion in combination produce weight loss and a metabolic profile beneficial for the potential treatment of obesity.

AREAS COVERED

This review examines the safety and antiobesity effects of naltrexone and bupropion alone and in combination. It reviews the results of four Phase III clinical trials of a novel fixed dose of sustained-released naltrexone/bupropion.

EXPERT OPINION

Naltrexone/bupropion has a greater weight loss efficacy than two FDA-approved medications, orlistat and lorcaserin. Although the weight loss produced by phentermine/topiramate is superior to naltrexone/bupropion, the safety profile of naltrexone/bupropion has less severe adverse effects. In addition, naltrexone/bupropion is well tolerated, with nausea being the most reported adverse event. Unlike other centrally acting medications, lorcaserin and phentermine/topiramate, naltrexone/bupropion has no abuse potential.

Postnatal metabolic and reproductive consequences of fetal and neonatal exposure to the smoking cessation drug bupropion

INTRODUCTION

In all, 10% to 20% of all pregnant women smoke despite intentions to quit. Smoking cessation drugs such as nicotine replacement therapy (NRT) and bupropion are recommended for pregnant women. Our observation that developmental exposure to nicotine adversely affects metabolic and reproductive outcomes in rats has raised concerns about NRT's safety during pregnancy. Conversely, the effect of bupropion has not been reported.

OBJECTIVE

The goal of this study was to examine the effect of fetal and neonatal exposure to bupropion on postnatal metabolic and reproductive outcomes.

METHODS

Dams (N = 5/group) were exposed to saline or bupropion (5 or 10 mg/kg per d) for 2 weeks prior to mating until weaning. We assessed weight, adiposity, and glucose homeostasis in all offspring until 26 weeks of age. Onset of puberty, fertility, and pregnancy outcomes in the female offspring were also assessed.

RESULTS

Fetal and neonatal exposure to bupropion did not cause metabolic derangement in the offspring despite a significant decrease in birth weight in the offspring of dams treated with 10/mg/kg per d bupropion (5.9 ± 0.2 g vs control 6.7 ± 0.2 g; P = .02). Moreover, with the exception of accelerated pubertal onset in F1 and F2 offspring, bupropion administration to pregnant dams had no impact on fertility or pregnancy outcomes for either the dam or the female offspring.

CONCLUSION

Fetal and neonatal exposure to the smoking cessation drug bupropion, unlike NRT, does not appear to adversely affect metabolic outcomes or the fertility of the female offspring. However, bupropion does appear to alter pubertal onset through an as yet unknown mechanism.

Galantamine attenuates some of the subjective effects of intravenous nicotine and improves performance on a Go No-Go task in abstinent cigarette smokers: a preliminary report

RATIONALE

Galantamine (GAL), a reversible and competitive inhibitor of acetylcholinesterase, is used clinically in the treatment of Alzheimer's dementia. Some preclinical and clinical studies support the potential efficacy of cholinesterase inhibitors for smoking cessation, although their effects on the behavioral and physiological responses to nicotine have not been examined. The goal of this study was to characterize GAL's actions on multiple outcomes, including withdrawal severity and cognitive performance, as well as subjective and physiological responses to nicotine administered intravenously.

METHODS

A total of 12 smokers participated in a double-blind, placebo-controlled, crossover study. Smokers had two 4-day treatment periods, assigned in random sequence, to GAL (8 mg/day) or placebo treatment. On day 4 of each treatment phase, smokers had an experimental session in which they received an intravenous (IV) dose of saline or 1 mg/70 kg nicotine, 1 h apart, in a random order.

RESULTS

GAL attenuated the self-reported rating of "craving for cigarettes" and prevented decrements in performance in a Go/No-Go task. In response to IV nicotine, GAL treatment attenuated the self-report ratings of "like the drug effects," "good drug effects," "bad drug effects," and "stimulated."

CONCLUSIONS

These findings support the potential utility of GAL as a treatment for smoking cessation.

Effects of the combination of metyrapone and oxazepam on intravenous nicotine self-administration in rats

RATIONALE

Despite increased education regarding its dangers, cigarette smoking remains a significant public health concern due to serious associated health consequences such as cancer and respiratory and cardiovascular diseases. Most smokers fail in their attempts to quit smoking, and current pharmacological interventions have relatively low levels of efficacy and are associated with significant adverse events. We have previously reported that combinations of metyrapone and oxazepam, administered at doses that were ineffective when delivered singly, resulted in dose-related decreases in cocaine self-administration in rats while not affecting food-maintained responding during the same sessions.

OBJECTIVES

The current study was designed to test the effects of the administration of a metyrapone:oxazepam combination on nicotine self-administration in rats.

METHODS

Several dose combinations of metyrapone (12.5, 25 or 50 mg/kg) and oxazepam (5 or 10 mg/kg) were tested in rats trained to intravenously (IV) self-administer nicotine (0.03 mg/kg/infusion) during 1-h self-administration sessions using both fixed-ratio and progressive-ratio (PR) schedules of reinforcement.

RESULTS

The administration of low doses of metyrapone and oxazepam in combination significantly decreased IV nicotine self-administration in rats. At the lowest doses of 12.5 mg/kg of metyrapone and 5 mg/kg of oxazepam, the drugs alone did not decrease IV nicotine self-administration, but the combination was effective. Varenicline was also tested using the fixed-ratio schedule, and reductions in nicotine intake were similar to those seen with the moderate dose of the combination.

CONCLUSIONS

The results of this study suggest a potential utility of the combination of metyrapone and oxazepam for smoking cessation in humans.

Bupropion and its main metabolite reverse nicotine chronic tolerance in the mouse

INTRODUCTION

Although the antidepressant bupropion is prescribed to aid in smoking cessation, little is known concerning its mechanisms of action in this regard. One factor that might influence quit success is nicotine tolerance, which could promote high levels of nicotine intake in order to maintain nicotine's subjective effects (thereby making attempts to reduce smoking more difficult).

METHODS

To explore whether bupropion and its active hydroxymetabolite modulate nicotine tolerance, mice were injected for 14 days with saline or nicotine. On Day 14, animals received saline, (2S,3S)-hydroxybupropion, or bupropion at different doses. On Day 15, mice were assayed on test day for nicotine-induced analgesia and hypothermia.

RESULTS

Animals chronically injected with saline + nicotine developed tolerance to nicotine's effects in both assays. Administration of bupropion and (2S,3S)-hydroxybupropion dose-dependently reversed chronic nicotine tolerance.

CONCLUSIONS

These results indicate that bupropion's ability to promote smoking cessation may be partly due to its attenuation of nicotine tolerance since both measured responses of nicotine (antinociception and hypothermia) are mediated to a large extent by neuronal α4β2* nicotine receptors.

Genetic variants in the serotonin transporter influence the efficacy of bupropion and nortriptyline in smoking cessation

AIMS

We investigated whether variants in the serotonin transporter gene (SLC6A4) influence smoking cessation rates using antidepressant therapy (i.e. bupropion and nortriptyline).

DESIGN

Pharmacogenetic (secondary) analysis of a randomized, placebo-controlled efficacy trial of bupropion and nortriptyline for smoking cessation.

SETTING

Single-centre study, Maastricht University, the Netherlands.

PARTICIPANTS

A total of 214 of 255 (84%) current daily smokers participating in a randomized controlled efficacy trial.

MEASUREMENTS

Subjects were genotyped for three functional variants in SLC6A4 (5-HTTLPR, STin2, rs25531). Primary outcome measures were prolonged abstinence from weeks 4-12, 4-26 and 4-52. Secondary outcome measures included 7-day point prevalence abstinence at weeks 4, 12, 26 and 52.

FINDINGS

Carriers of the 5-HTTLPR high-activity L-variant had higher prolonged cessation rates with bupropion than placebo [odds ratio (OR) = 1.44, 95% confidence interval (CI) = 1.01-2.05, P = 0.04]. Combining the three variants resulted in increased prolonged cessation rates for both bupropion and nortriptyline among carriers of four to five high-activity variants (bupropion: OR = 2.00, 95% CI =1.21-3.29, P = 0.01; nortriptyline: OR = 1.91, 95% CI = 1.02-3.56, P = 0.04). Similar results were found for point prevalence abstinence.

CONCLUSIONS

Bupropion and nortriptyline seem to be more effective in smoking cessation among SLC6A4 high-activity variant carriers, probably by blocking the increased serotonin transporter activity, thereby increasing serotonin levels. Prospective studies have to assess if this can improve cessation rates when treatment is targeted at individuals based on their genotypes.

Pharmacotherapy for smoking cessation: current advances and research topics

Promoting smoking cessation is among the key medical interventions aimed at reducing worldwide morbidity and mortality in this century. Both behavioural counselling and pharmacotherapy have been shown to significantly increase long-term abstinence rates, and combining the two treatment modalities is recommended. This article provides an update on pharmacotherapy for smoking cessation in the general population. Current first-line agents used to support quit attempts are nicotine replacement therapy (NRT), bupropion and varenicline. Research suggests that abstinence rates can be increased by combining different forms of NRT or simultaneously administering NRT and non-nicotine medications. New treatments targeting the nicotinic acetylcholine receptor as well as other pathophysiological pathways involved in nicotine addiction are being developed, with nicotine vaccines now being tested in phase III clinical trials. Among the numerous research topics currently addressed, pharmacogenetics and tailoring therapy to specific groups of smokers look most promising. However, substantial progress is unlikely to be made unless social gradients impeding effective treatment of all smokers are overcome. In addition, public smoking bans and reimbursement of medication costs are crucial in reducing the future burden of disease caused by smoking on a global level.

Translational research in addiction: toward a framework for the development of novel therapeutics

The development of novel substance use disorder (SUD) therapeutics is insufficient to meet the medical needs of a growing SUD patient population. The identification of translatable SUD models and tests is a crucial step in establishing a framework for SUD therapeutic development programs. The present review begins by identifying the clinical features of SUDs and highlights the narrow regulatory end-point required for approval of a novel SUD therapeutic. A conceptual overview of dependence is provided, followed by identification of potential intervention targets in the addiction cycle. The main components of the addiction cycle provide the framework for a discussion of preclinical models and their clinical analogs, all of which are focused on isolated behavioral end-points thought to be relevant to the persistence of compulsive drug use. Thus, the greatest obstacle to successful development is the gap between the multiplicity of preclinical and early clinical end-points and the regulatory end-point of sustained abstinence. This review proposes two pathways to bridging this gap: further development and validation of the preclinical extended access self-administration model; inclusion of secondary end-points comprising all of the measures highlighted in the present discussion in Phase 3 trials. Further, completion of the postdictive validation of analogous preclinical and clinical assays is of high priority. Ultimately, demonstration of the relevance and validity of a variety of end-points to the ultimate goal of abstinence will allow researchers to identify truly relevant therapeutic mechanisms and intervention targets, and establish a framework for SUD therapeutic development that allows optimal decision-making and resource allocation.

Pharmacological treatment for depression during opioid agonist treatment for opioid dependence

BACKGROUND

Lifetime prevalence of depression in subjects with opioid dependence is higher than in the general population (44-54% versus 16%) and represents a risk factor for morbidity and mortality. For patients on opioid agonist treatment, current prevalence rates of depression ranges between 10 and 30%, influencing negatively the outcome of the treatment.

OBJECTIVES

To evaluate the efficacy and the acceptability of antidepressants for the treatment of depressed opioid dependents treated with opioid agonists.

SEARCH STRATEGY

We searched Pubmed, EMBASE, CINAHL (to October 2009), CENTRAL (The Cochrane Library Cochrane Drug and Alcohol Group Specialised Register, issue 4, 2009), main electronic sources of ongoing trials, specific trial databases and reference lists of all relevant papers.

SELECTION CRITERIA

Randomised and controlled clinical trials examining the efficacy of any antidepressant medication to treat depressed opioid dependents in treatment with opioid agonists.

DATA COLLECTION AND ANALYSIS

Two authors independently screened and extracted data from studies.

MAIN RESULTS

Seven studies, 482 participants, met the inclusion criteria.- Comparing antidepressant with placebo, no statistically significant results for dropouts. Selecting studies with low risk of bias, 325 participants, results favour placebo, RR 1.40 (Cl 95% 1.00 to 1.96). For severity of depression, results from two studies, 183 participants, favour antidepressants utilising Clinical Global Impression Scale RR 1.92 (CI 95% 1.26 to 2.94), while another study, 95 participants, utilising the Hamilton Depression Rating Scale, did not find a statistically significant difference RR 0.96 (CI 95% 0.54 to 1.71). For adverse events, result favour placebo, four studies, 311 participants, RR 2.90 (Cl 95% 1.23 to 6.86). For drug use, three studies, 211 participants, it was not possible to pool data because outcomes' measures were not comparable. Looking at singular studies, no statistically significant difference was seen.- Comparing different classes of antidepressants, the results favour tricyclics for severity of depression, two studies, 183 participants, RR 1.92 (Cl 95% 1.26 to 2.94) and favour placebo for adverse events, two studies, 172 participants, RR 3.11 (Cl 95% 1.06 to 9.12).

AUTHORS' CONCLUSIONS

There is low evidence, at the present, supporting the clinical use of antidepressants for the treatment of depressed opioid addicts in treatment with opioid agonists. There is a need of larger randomised studies investigating relevant outcomes, safety issues and reporting data to allow comparison of results.

Double target concept for smoking cessation

Tobacco use is estimated to be the largest single cause of premature death in the world. Nicotine is the major addictive substance in tobacco products. After cigarette smoking, nicotine quickly acts on its target, nicotinic acetylcholine receptors (nAChRs), which are widely distributed throughout the mammalian central nervous system and are expressed as diverse subtypes on cell bodies, dendrites and/or nerve terminals. Through the nAChRs in brain reward circuits, nicotine alters dopaminergic (DA) neuronal function in the ventral tegmental area (VTA) and increases dopamine release from VTA to nuclear accumbens (NA), which leads to nicotine reward, tolerance and dependence. After quitting smoking, smokers experience withdrawal symptoms, including depression, irritability, difficulty concentrating or sleeping, headache, and tiredness. Recently, evidence has been accumulated to reveal the molecular and cellular mechanisms of nicotine reward, tolerance and dependence. The outcomes of these investigations provide pharmacological basis for smoking cessation. Here, I briefly summarize recent advancements of our understanding of nicotine reward, tolerance and dependence. Based on these understandings, I propose a double target hypothesis, in which nAChRs and dopamine release process are two important targets for smoking cessation. Dysfunction of nAChRs (antagonism or desensitization) is crucial to abolish nicotine dependence and the maintenance of an appropriate level of extracellular dopamine eliminates nicotine withdrawal syndromes. Therefore, the medications simultaneously act on these two targets should have the desired effect for smoking cessation. I discuss how to use this double target concept to interpret recent therapies and to develop new candidate compounds for smoking cessation.

Reconsidering anhedonia in depression: lessons from translational neuroscience

Anhedonia is a core symptom of major depressive disorder (MDD), the neurobiological mechanisms of which remain poorly understood. Despite decades of speculation regarding the role of dopamine (DA) in anhedonic symptoms, empirical evidence has remained elusive, with frequent reports of contradictory findings. In the present review, we argue that this has resulted from an underspecified definition of anhedonia, which has failed to dissociate between consummatory and motivational aspects of reward behavior. Given substantial preclinical evidence that DA is involved primarily in motivational aspects of reward, we suggest that a refined definition of anhedonia that distinguishes between deficits in pleasure and motivation is essential for the purposes of identifying its neurobiological substrates. Moreover, bridging the gap between preclinical and clinical models of anhedonia may require moving away from the conceptualization of anhedonia as a steady-state, mood-like phenomena. Consequently, we introduce the term "decisional anhedonia" to address the influence of anhedonia on reward decision-making. These proposed modifications to the theoretical definition of anhedonia have implications for research, assessment and treatment of MDD.

Effects of hydroxymetabolites of bupropion on nicotine dependence behavior in mice

Bupropion is an atypical antidepressant that also has utility as a smoking cessation aid. Hydroxybupropions are major metabolites of bupropion and are believed to contribute to antidepressant and perhaps smoking cessation activities. Because bupropion metabolism is more similar in humans and mice than in humans and rats, the present study investigated effects of hydroxybupropion enantiomers in mouse behavioral models measuring various aspects of nicotine dependence. Bupropion and (2S,3S)-hydroxybupropion, but not (2R,3R)-hydroxybupropion, significantly decreased the development of nicotine reward as measured in the conditioned place preference and withdrawal paradigm in mice. Bupropion and both of its metabolites reversed affective and somatic withdrawal signs in nicotine-dependent mice, but the (2S,3S)-hydroxymetabolite had higher potency. Bupropion and (2S,3S)-, but not (2R,3R)-hydroxybupropion, produced partial substitution for nicotine in drug discrimination tests. Our findings support the hypothesis that the effects of bupropion on measures of nicotine dependence reflect actions of bupropion itself, its hydroxymetabolites, or a combination and suggest that the (2S,3S)-hydroxy isomer is the most active principle, making it a potentially better drug candidate for smoking cessation than bupropion.

Effect of the selective kappa-opioid receptor antagonist JDTic on nicotine antinociception, reward, and withdrawal in the mouse

RATIONALE

Several lines of evidence support a role for the endogenous opioid system in mediating behaviors associated with drug dependence. Specifically, recent findings suggest that the kappa-opioid receptor (KOR) may play a role in aspects of nicotine dependence, which contribute to relapse and continued tobacco smoking.

OBJECTIVE

The objective of this study is to determine the involvement of the KOR in the initial behavioral responses of nicotine, nicotine reward, and nicotine withdrawal using the highly selective KOR antagonist JDTic. JDTic doses of 1, 4, 8, or 16 mg/kg were administered subcutaneously (s.c.) 18 h prior to nicotine treatment.

RESULTS

JDTic dose-dependently blocked acute nicotine-induced antinociception in the tail-flick but not the hot-plate test and did not significantly attenuate morphine's antinociceptive effect in either the tail-flick or hot-plate test. Furthermore, JDTic (8 and 16 mg/kg, s.c.) failed to block the expression of nicotine reward as measured by the conditioned place preference model. In contrast, JDTic and the KOR antagonist norBNI attenuated the expression of both the physical (somatic signs and hyperalgesia) and affective (anxiety-related behavior and conditioned place aversion) nicotine withdrawal signs.

CONCLUSIONS

Our findings clearly show that the KOR is involved in mediating the withdrawal aspects of nicotine dependence. The results from this study suggest that blockade of the KOR by selective KOR antagonists may be useful smoking cessation pharmacotherapies.

Pharmacologic agents for smoking cessation: a clinical review

Tobacco use has been clearly demonstrated to have negative health consequences. Smoking cigarettes is the predominant method of tobacco use. The tar contained within cigarettes and other similar products is also harmful. Other tarless tobacco containing products do exist but carry no significantly decreased risk. While nicotine is considered to be principally responsible for tobacco addiction, other chemicals in the cigarette smoke including acetaldehyde may contribute to the addictive properties of tobacco products. The adverse health consequences of tobacco use have been well documented. Studies have shown that a combined behavioral and pharmacological approach is more effective in smoking cessation than either approach alone. Pharmacotherapy can achieve 50% reduction in smoking. With pharmacotherapy the estimated 6-month abstinence rate is about 20%, whereas it is about 10% without pharmacotherapy. The first-line of drugs for smoking cessation are varenicline, bupropion sustained release, and nicotine replacement drugs, which are approved for use in adults. Data are insufficient to recommend their use in adolescents. This article reviews the use of pharmacological agents used for smoking cessation. A brief overview of epidemiology, chemistry, and adverse health effects of smoking is provided.

Effects of bupropion on simulated demand for cigarettes and the subjective effects of smoking

INTRODUCTION

The biobehavioral mechanism(s) mediating bupropion's efficacy are not well understood. Behavioral economic measures such as demand curves have proven useful in investigations of the reinforcing effects of drugs of abuse. Behavioral economic measures may also be used to measure the effect of pharmacotherapies on the reinforcing effects of drugs of abuse.

METHODS

The effects of bupropion on simulated demand for cigarettes were investigated in a placebo-controlled double-blind clinical trial. Participants reported the number of cigarettes they would purchase and consume in a single day at a range of prices. The effects of medication on the subjective effects of smoking were also explored.

RESULTS

Demand for cigarettes was well described by an exponential demand equation. Bupropion did not significantly decrease the maximum number of cigarettes that participants said they would smoke in a single day nor did it significantly alter the relation between price per cigarette and demand. Baseline demand elasticity did not predict smoking cessation, but changes in elasticity following 1 week of treatment did. Medication group had no effect on any subjective effects of smoking.

DISCUSSION

Bupropion had no significant effects on demand for cigarettes. The exponential demand equation, recently introduced in behavioral economics, proved amenable to human simulated demand and might be usefully employed in other pharmacotherapy studies as it provides a potentially useful measure of changes in the essential value of the drug as a reinforcer. Such changes may be useful in predicting the efficacy of medications designed to reduce drug consumption.

Acute effect of the anti-addiction drug bupropion on extracellular dopamine concentrations in the human striatum: an [11C]raclopride PET study

Bupropion is an effective medication in treating addiction and is widely used as an aid to smoking cessation. Bupropion inhibits striatal dopamine reuptake via dopamine transporter blockade, but it is unknown whether this leads to increased extracellular dopamine levels at clinical doses in man. The effects of bupropion on extracellular dopamine levels in the striatum were investigated using [(11)C]raclopride positron emission tomography (PET) imaging in rats administered saline, 11 or 25 mg/kg bupropion i.p. and in healthy human volunteers administered either placebo or 150 mg bupropion (Zyban Sustained-Release). A cognitive task was used to stimulate dopamine release in the human study. In rats, bupropion significantly decreased [(11)C]raclopride specific binding in the striatum, consistent with increases in extracellular dopamine concentrations. In man, no significant decreases in striatal [(11)C]raclopride specific binding were observed. Levels of dopamine transporter occupancy in the rat at 11 and 25 mg/kg bupropion i.p. were higher than predicted to occur in man at the dose used. Thus, these data indicate that, at the low levels of dopamine transporter occupancy achieved in man at clinical doses, bupropion does not increase extracellular dopamine levels. These findings have important implications for understanding the mechanism of action underlying bupropions' therapeutic efficacy and for the development of novel treatments for addiction and depression.

The neuropharmacological substrates of nicotine reward: reinforcing versus reinforcement-enhancing effects of nicotine

Compulsive nicotine use is thought to be maintained by the acute reinforcing effects of nicotine and the reinforcement-enhancing effects of nicotine, in addition to the negative consequences of nicotine abstinence. Nicotine self-administration and nicotine-induced enhancement of non-nicotine reinforcers such as intracranial self-stimulation provide measures of these dual rewarding properties of nicotine. First, pharmacological manipulations that modulate the reinforcing and reinforcement-enhancing effects of nicotine are identified and discussed. Second, the interpretation and implications of data that identified shared and specific pharmacological substrates underlying the dual rewarding effects of nicotine are discussed, including implications for the preclinical testing of putative antismoking medications. In conclusion, reinforcement-related behaviors that are mediated by central reinforcement processes are likely to, and generally do, exhibit a number of common pharmacological substrates. Interestingly, however, a few pharmacological classes of compounds seem to exert selective effects on components of the dual nicotine reward mechanisms, indicating differences in the pharmacological substrates of the reinforcing and reinforcement-enhancing effects of nicotine. Further characterization of such compounds may ultimately lead to the identification of novel medications for nicotine dependence in humans.