Pioglitazone, a PPARγ agonist, reduces nicotine craving in humans, with marginal effects on abuse potential

New insights into the involvement of serotonin and BDNF-TrkB signalling in cannabidiol's antidepressant effect

Cannabidiol (CBD) is a phytocannabinoid devoid of psychostimulant properties and is currently under investigation as a potential antidepressant drug. However, the mechanisms underlying CBD's antidepressant effects are not yet well understood. CBD targets include a variety of receptors, enzymes, and transporters, with different binding-affinities. Neurochemical and pharmacological evidence indicates that both serotonin and BDNF-TrkB signalling in the prefrontal cortex are necessary for the antidepressant effects induced by CBD in animal models. Herein, we reviewed the current literature to dissect if these are independent mechanisms or if CBD-induced modulation of the serotonergic neurotransmission could mediate its neuroplastic effects through subsequent regulation of BDNF-TrkB signalling, thus culminating in rapid neuroplastic changes. It is hypothesized that: a) CBD interaction with serotonin receptors on neurons of the dorsal raphe nuclei and the resulting disinhibition of serotonergic neurons would promote rapid serotonin release in the PFC and hence its neuroplastic and antidepressant effects; b) CBD facilitates BDNF-TRKB signalling, especially in the PFC, which rapidly triggers neurochemical and neuroplastic effects. These hypotheses are discussed with perspectives for new drug development and clinical applications.

Substance Addiction Rehabilitation Drugs

The relapse rate of substance abusers is high, and addiction rehabilitation adjunct drugs need to be developed urgently. There have been numerous reports on blocking the formation of substance addiction, but studies on drugs that can alleviate withdrawal symptoms are very limited. Both the dopamine transporter (DAT) hypothesis and D3 dopamine receptor (D3R) hypothesis are proposed. DAT activators reduce the extracellular dopamine level, and D3R antagonists reduce the neuron's sensitivity to dopamine, both of which may exacerbate the withdrawal symptoms subsequently. The D3R partial agonist SK608 has biased signaling properties via the G-protein-dependent pathway but did not induce D3R desensitization and, thus, may be a promising drug for the withdrawal symptoms. Drugs for serotoninergic neurons or GABAergic neurons and anti-inflammatory drugs may have auxiliary effects to addiction treatments. Drugs that promote structural synaptic plasticity are also discussed.

PPARγ Modulators in Lung Cancer: Molecular Mechanisms, Clinical Prospects, and Challenges

Lung cancer is one of the most lethal malignancies worldwide. Peroxisome proliferator-activated receptor gamma (PPARγ, NR1C3) is a ligand-activated transcriptional factor that governs the expression of genes involved in glucolipid metabolism, energy homeostasis, cell differentiation, and inflammation. Multiple studies have demonstrated that PPARγ activation exerts anti-tumor effects in lung cancer through regulation of lipid metabolism, induction of apoptosis, and cell cycle arrest, as well as inhibition of invasion and migration. Interestingly, PPARγ activation may have pro-tumor effects on cells of the tumor microenvironment, especially myeloid cells. Recent clinical data has substantiated the potential of PPARγ agonists as therapeutic agents for lung cancer. Additionally, PPARγ agonists also show synergistic effects with traditional chemotherapy and radiotherapy. However, the clinical application of PPARγ agonists remains limited due to the presence of adverse side effects. Thus, further research and clinical trials are necessary to comprehensively explore the actions of PPARγ in both tumor and stromal cells and to evaluate the in vivo toxicity. This review aims to consolidate the molecular mechanism of PPARγ modulators and to discuss their clinical prospects and challenges in tackling lung cancer.

Cue-reactivity targeted smoking cessation intervention in individuals with tobacco use disorder: a scoping review

Objectives

Cue-reactivity is a critical step leading to the emergence of addictive psychology and the triggering of addictive behaviors within the framework of addiction theory and is considered a significant risk factor for addiction-related behaviors. However, the effect of cue-reactivity targeted smoking cessation intervention and the cue-reactivity paradigms used in the randomized controlled trials varies, which introduces more heterogeneity and makes a side-by-side comparison of cessation responses difficult. Therefore, the scoping review aims to integrate existing research and identify evidence gaps.

Methods

We searched databases in English (PubMed and Embase) and Chinese (CNKI and Wanfang) using terms synonymous with 'cue' and 'tobacco use disorder (TUD)' to April 2023, and via hand-searching and reference screening of included studies. Studies were included if they were randomized controlled trials taking cue-reactivity as an indicator for tobacco use disorder (TUD) defined by different kinds of criteria.

Results

Data were extracted on each study's country, population, methods, timeframes, outcomes, cue-reactivity paradigms, and so on. Of the 2,944 literature were retrieved, 201 studies met the criteria and were selected for full-text screening. Finally, 67 pieces of literature were selected for inclusion and data extraction. The results mainly revealed that non-invasive brain stimulation and exercise therapy showed a trend of greater possibility in reducing subjective craving compared to the remaining therapies, despite variations in the number of research studies conducted in each category. And cue-reactivity paradigms vary in materials and mainly fall into two main categories: behaviorally induced craving paradigm or visually induced craving paradigm.

Conclusion

The current studies are still inadequate in terms of comparability due to their heterogeneity, cue-reactivity can be conducted in the future by constructing a standard library of smoking cue materials. Causal analysis is suggested in order to adequately screen for causes of addiction persistence, and further explore the specific objective cue-reactivity-related indicators of TUD.

New medications development for smoking cessation

Diseases associated with nicotine dependence in the form of habitual tobacco use are a major cause of premature death in the United States. The majority of tobacco smokers will relapse within the first month of attempted abstinence. Smoking cessation agents increase the likelihood that smokers can achieve long-term abstinence. Nevertheless, currently available smoking cessation agents have limited utility and fail to prevent relapse in the majority of smokers. Pharmacotherapy is therefore an effective strategy to aid smoking cessation efforts but considerable risk of relapse persists even when the most efficacious medications currently available are used. The past decade has seen major breakthroughs in our understanding of the molecular, cellular, and systems-level actions of nicotine in the brain that contribute to the development and maintenance of habitual tobacco use. In parallel, large-scale human genetics studies have revealed allelic variants that influence vulnerability to tobacco use disorder. These advances have revealed targets for the development of novel smoking cessation agents. Here, we summarize current efforts to develop smoking cessation therapeutics and highlight opportunities for future efforts.

Cannabidiol and substance use disorder: Dream or reality

BACKGROUND

Cannabidiol (CBD) is one of the major constituents of Cannabis sativa L. that lacks psychotomimetic and rewarding properties and inhibits the rewarding and reinforcing effects of addictive drugs such as cocaine, methamphetamine (METH), and morphine. Additionally, CBD's safety profile and therapeutic potential are currently evaluated in several medical conditions, including pain, depression, movement disorders, epilepsy, multiple sclerosis, Alzheimer's disease, ischemia, and substance use disorder. There is no effective treatment for substance use disorders such as addiction, and this review aims to describe preclinical and clinical investigations into the effects of CBD in various models of opioid, psychostimulant, cannabis, alcohol, and nicotine abuse. Furthermore, the possible mechanisms underlying the therapeutic potential of CBD on drug abuse disorders are reviewed.

METHODS

The current review considers and summarizes the preclinical and clinical investigations into CBD's effects in various models of drug abuse include opioids, psychostimulants, cannabis, alcohol, and nicotine.

RESULTS

Several preclinical and clinical studies have proposed that CBD may be a reliable agent to inhibit the reinforcing and rewarding impact of drugs.

CONCLUSIONS

While the currently available evidence converges to suggest that CBD could effectively reduce the rewarding and reinforcing effects of addictive drugs, more preclinical and clinical studies are needed before CBD can be added to the therapeutic arsenal for treating addiction.

Repurposing Peroxisome Proliferator-Activated Receptor Agonists in Neurological and Psychiatric Disorders

Common pathophysiological mechanisms have emerged for different neurological and neuropsychiatric conditions. In particular, mechanisms of oxidative stress, immuno-inflammation, and altered metabolic pathways converge and cause neuronal and non-neuronal maladaptative phenomena, which underlie multifaceted brain disorders. The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors modulating, among others, anti-inflammatory and neuroprotective genes in diverse tissues. Both endogenous and synthetic PPAR agonists are approved treatments for metabolic and systemic disorders, such as diabetes, fatty liver disease, and dyslipidemia(s), showing high tolerability and safety profiles. Considering that some PPAR-acting drugs permeate through the blood-brain barrier, the possibility to extend their scope from the periphery to central nervous system has gained interest in recent years. Here, we review preclinical and clinical evidence that PPARs possibly exert a neuroprotective role, thereby providing a rationale for repurposing PPAR-targeting drugs to counteract several diseases affecting the central nervous system.

Reduced alcohol use in patients prescribed pioglitazone

BACKGROUND AND OBJECTIVES

Alcohol use disorder (AUD) is common and causes significant morbidity and mortality. Currently approved medications are moderately effective. Novel medications are needed to address AUD. Preliminary data suggests pioglitazone may reduce alcohol use.

METHODS

Veterans seen at the Minneapolis VA Health Care System, who were prescribed pioglitazone for diabetes between October 1, 2015 and September 30, 2016, were identified using a national VA database (N = 49). Further chart review was performed to identify all Alcohol Use Disorder Identification Test-Consumption (AUDIT-C) scores prior to starting pioglitazone. Hierarchical Linear models were used to compare all AUDIT-C scores on and off pioglitazone and compare the change in AUDIT-C scores over time before and during pioglitazone was prescribed. AUDIT-C scores were nested within subject with fixed effects for pioglitazone and random intercept and slope for time.

RESULTS

Forty-nine patients were prescribed pioglitazone and had AUDIT-C scores of 3 or more. The estimated mean AUDIT-C score prior to receiving pioglitazone was 3.98 (95% confidence interval [CI]: 3.51-4.44) and this was reduced to 2.89 (95% CI: 2.46-3.32), reflecting a significant change F(1, 323) = 43.3, p < .001 in the score. The primary reduction occurred within the first year of the pioglitazone prescription. This effect remained significant after controlling for age.

CONCLUSION AND SCIENTIFIC SIGNIFICANCE

This is the first study of pioglitazone used in a clinical sample focused on alcohol use outcome. The data show that pioglitazone may reduce alcohol use in patients with heavy drinking. Clinical trials of pioglitazone are warranted in patients with AUD.

The (Poly)Pharmacology of Cannabidiol in Neurological and Neuropsychiatric Disorders: Molecular Mechanisms and Targets

Cannabidiol (CBD), the major nonpsychoactive Cannabis constituent, has been proposed for the treatment of a wide panel of neurological and neuropsychiatric disorders, including anxiety, schizophrenia, epilepsy and drug addiction due to the ability of its versatile scaffold to interact with diverse molecular targets that are not restricted to the endocannabinoid system. Albeit the molecular mechanisms responsible for the therapeutic effects of CBD have yet to be fully elucidated, many efforts have been devoted in the last decades to shed light on its complex pharmacological profile. In particular, an ever-increasing number of molecular targets linked to those disorders have been identified for this phytocannabinoid, along with the modulatory effects of CBD on their cascade signaling. In this view, here we will try to provide a comprehensive and up-to-date overview of the molecular basis underlying the therapeutic effects of CBD involved in the treatment of neurological and neuropsychiatric disorders.

Variants and expression changes in PPAR-encoding genes display no significant association with schizophrenia

A few studies suggested the contribution of PPARs to the etiology of schizophrenia (SCZ). However, it is still not clear whether variants in PPAR-encoding genes have a direct association with SCZ. The potential linkage between SCZ and the variants within PPAR encoding genes (PPARA, PPARD, and PPARG) was tested in a large cohort genome-wide association study (GWAS). Then, a mega-analysis was conducted using 14 gene expression profiling experiments in various human brain regions. Finally, the expression levels of the three PPAR-encoding genes were quantified in early-onset SCZ patients. Only one PPARG polymorphisms, rs62242085, presented a minor frequency deviation in the SCZ cohort (P-value = 0.035). None of the PPAR-encoding genes presented significant expression change within the brain regions profiled in 14 datasets acquired from different populations (P-value > 0.14) or in the whole blood of early-onset overall SCZ patients (P-value > 0.22). However, compared with healthy female controls, female early-onset SCZ patients presented a moderate but significant decrease in the expression level of PPARD (LFC = −0.55; P-value = 0.02) and a strong, but non-significant decrease in expression of PPARG (LFC = −1.30; P-value = 0.13). Our results do not support a significant association between variants in PPAR-encoding genes and SCZ, but suggest a necessity to explore the role of PPARD and PPARG in early SCZ phenotypes, specifically in females.

Energy sensors in drug addiction: A potential therapeutic target

Addiction is defined as the repeated exposure and compulsive seek of psychotropic drugs that, despite the harmful effects, generate relapse after the abstinence period. The psychophysiological processes associated with drug addiction (acquisition/expression, withdrawal, and relapse) imply important alterations in neurotransmission and changes in presynaptic and postsynaptic plasticity and cellular structure (neuroadaptations) in neurons of the reward circuits (dopaminergic neuronal activity) and other corticolimbic regions. These neuroadaptation mechanisms imply important changes in neuronal energy balance and protein synthesis machinery. Scientific literature links drug-induced stimulation of dopaminergic and glutamatergic pathways along with presence of neurotrophic factors with alterations in synaptic plasticity and membrane excitability driven by metabolic sensors. Here, we provide current knowledge of the role of molecular targets that constitute true metabolic/energy sensors such as AMPK, mTOR, ERK, or K_ATP in the development of the different phases of addiction standing out the main brain regions (ventral tegmental area, nucleus accumbens, hippocampus, and amygdala) constituting the hubs in the development of addiction. Because the available treatments show very limited effectiveness, evaluating the drug efficacy of AMPK and mTOR specific modulators opens up the possibility of testing novel pharmacotherapies for an individualized approach in drug abuse.

Role of PPARs in Progression of Anxiety: Literature Analysis and Signaling Pathways Reconstruction

Peroxisome proliferator-activated receptor (PPAR) group includes three isoforms encoded by PPARG, PPARA, and PPARD genes. High concentrations of PPARs are found in parts of the brain linked to anxiety development, including hippocampus and amygdala. Among three PPAR isoforms, PPARG demonstrates the highest expression in CNS, where it can be found in neurons, astrocytes, and glial cells. Herein, the highest PPARG expression occurs in amygdala. However, little is known considering possible connections between PPARs and anxiety behavior. We reviewed possible connections between PPARs and anxiety. We used the Pathway Studio software (Elsevier). Signal pathways were created according to previously developed algorithms. SNEA was performed in Pathway Studio. Current study revealed 14 PPAR-regulated proteins linked to anxiety. Possible mechanism of PPAR involvement in neuroinflammation protection is proposed. Signal pathway reconstruction and reviewing aimed to reveal possible connection between PPARG and CCK-ergic system was conducted. Said analysis revealed that PPARG-dependent regulation of MME and ACE peptidase expression may affect levels of nonhydrolysed, i.e., active CCK-4. Impairments in PPARG regulation and following MME and ACE peptidase expression impairments in amygdala may be the possible mechanism leading to pathological anxiety development, with brain CCK-4 accumulation being a key link. Literature data analysis and signal pathway reconstruction and reviewing revealed two possible mechanisms of peroxisome proliferator-activated receptors involvement in pathological anxiety: (1) cytokine expression and neuroinflammation mechanism and (2) regulation of peptidases targeted to anxiety-associated neuropeptides, primarily CCK-4, mechanism.

The acute and repeated effects of cigarette smoking and smoking-related cues on impulsivity

INTRODUCTION AND AIMS

Impulsivity may be a risk factor that increases vulnerability to nicotine dependence. However, nicotine exposure itself may directly increase impulsivity. This is a secondary analysis of the first study in a controlled laboratory setting, which assessed the effects of nicotine administration (acute and repeated) and exposure to smoking cues on behavioural impulsivity in humans (ClinicalTrials.gov Identifier: NCT01395797).

DESIGN AND METHODS

Twenty-seven smokers completed three tasks to assess behavioural impulsivity (the Immediate Memory Task and the Delayed Memory Task assessing response initiation, and the GoStop Task assessing response inhibition) following: (i) 4 days of cigarette smoking (nicotinised or denicotinised cigarette); (ii) acute cigarette smoking (nicotinised); and (iii) exposure to smoking-related cues.

RESULTS

Four days of nicotinised cigarette smoking (vs. denicotinised) did not significantly increase Immediate Memory Task, Delayed Memory Task and GoStop scores. However, acute cigarette smoking increased GoStop impulsivity, but only following 4 days of smoking nicotinised cigarettes (P < 0.05). Exposure to smoking-related cues had no statistically significant effect on impulsivity.

DISCUSSION AND CONCLUSIONS

Our results suggest that repeated nicotine exposure may sensitise subsequent acute nicotine effects on behavioural impulsivity in heavy smokers.

Functional interactions between cannabinoids, omega-3 fatty acids, and peroxisome proliferator-activated receptors: Implications for mental health pharmacotherapies

Cannabis contains a plethora of phytochemical constituents with diverse neurobiological effects. Cannabidiol (CBD) is the main non-psychotropic component found in cannabis that is capable of modulating mesocorticolimbic DA transmission and may possess therapeutic potential for several neuropsychiatric disorders. Emerging evidence also suggests that, similar to CBD, omega-3 polyunsaturated fatty acids may regulate DA transmission and possess therapeutic potential for similar neuropsychiatric disorders. Although progress has been made to elucidate the mechanisms underlying the therapeutic properties of CBD and omega-3s, it remains unclear through which receptor mechanisms they may produce their purported effects. Peroxisome proliferator-activated receptors are a group of nuclear transcription factors with multiple isoforms. PPARγ is an isoform activated by both CBD and omega-3, whereas the PPARα isoform is activated by omega-3. Interestingly, the activation of PPARγ and PPARα with selective agonists has been shown to decrease mesocorticolimbic DA activity and block neuropsychiatric symptoms similar to CBD and omega-3s, raising the possibility that CBD and omega-3s produce their effects through PPAR signaling. This review will examine the relationship between CBD, omega-3s, and PPARs and how they may be implicated in the modulation of mesocorticolimbic DAergic abnormalities and associated neuropsychiatric symptoms.

Advances in smoking cessation pharmacotherapy: Non-nicotinic approaches in animal models

The landscape of worldwide tobacco use is changing, with a decrease in traditional smoking and an exponential rise in electronic cigarette use. No new nicotine cessation pharmacotherapies have come to market in the last 10 years. The current therapies that have been approved by the United States Food and Drug Administration for nicotine cessation include nicotine replacement therapy, varenicline, a nicotinic acetylcholine receptor partial agonist, and the atypical antidepressant bupropion. Nicotine replacement therapy and varenicline both act on nicotinic acetylcholine receptors. Bupropion inhibits the dopamine transporter, the norepinephrine transporter, and the nicotinic acetylcholine receptors to inhibit smoking behavior. Notwithstanding these treatments, rates of successful nicotine cessation in clinical trials remain low. Recent pharmacological approaches to improve nicotine cessation rates in animal models have turned their focus away from activating nicotinic acetylcholine receptors. The present review focuses on such pharmacological approaches, including nicotine vaccines, anti-nicotine antibodies, nicotine-degrading enzymes, cannabinoids, and metformin. Both immunopharmacological and enzymatic approaches rely on restricting and degrading nicotine within the periphery, thus preventing psychoactive effects of nicotine on the central nervous system. In contrast, pharmacologic inhibition of the enzymes which degrade nicotine could affect smoking behavior. Cannabinoid receptor agonists and antagonists interact with the dopamine reward pathway and show efficacy in reducing nicotine addiction-like behaviors in preclinical studies. Metformin is currently approved by the Food and Drug Administration for the treatment of diabetes. It activates specific intracellular kinases that may protect against the lower metabolism, higher oxidation, and inflammation that are associated with nicotine withdrawal. Further studies are needed to investigate non-nicotinic targets to improve the treatment of tobacco use disorder. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Potential of Glial Cell Modulators in the Management of Substance Use Disorders

The pervasive and devastating nature of substance use disorders underlies the need for the continued development of novel pharmacotherapies. We now know that glia play a much greater role in neuronal processes than once believed.  The various types of glial cells (e.g., astrocytes, microglial, oligodendrocytes) participate in numerous functions that are crucial to healthy central nervous system function. Drugs of abuse have been shown to interact with glia in ways that directly contribute to the pharmacodynamic effects responsible for their abuse potential. Through their effect upon glia, drugs of abuse also alter brain function resulting in behavioral changes associated with substance use disorders. Therefore, drug-induced changes in glia and inflammation within the central nervous system (neuroinflammation) have been investigated to treat various aspects of drug abuse and dependence. This article presents a brief overview of the effects of each of the major classes of addictive drugs on glia. Next, the paper reviews the pre-clinical and clinical studies assessing the effects that glial modulators have on abuse-related behavioral effects, such as pleasure, withdrawal, and motivation. There is a strong body of pre-clinical literature demonstrating the general effectiveness of several glia-modulating drugs in models of reward and relapse. Clinical studies have also yielded promising results, though not as robust. There is still much to disentangle regarding the integration between addictive drugs and glial cells. Improved understanding of the relationship between glia and the pathophysiology of drug abuse should allow for more precise exploration in the development and testing of glial-directed treatments for substance use disorders.

Therapeutic Potential of Peroxisome Proliferator-Activated Receptor (PPAR) Agonists in Substance Use Disorders: A Synthesis of Preclinical and Human Evidence

Targeting peroxisome proliferator-activated receptors (PPARs) has received increasing interest as a potential strategy to treat substance use disorders due to the localization of PPARs in addiction-related brain regions and the ability of PPAR ligands to modulate dopamine neurotransmission. Robust evidence from animal models suggests that agonists at both the PPAR-α and PPAR-γ isoforms can reduce both positive and negative reinforcing properties of ethanol, nicotine, opioids, and possibly psychostimulants. A reduction in the voluntary consumption of ethanol following treatment with PPAR agonists seems to be the most consistent finding. However, the human evidence is limited in scope and has so far been less promising. There have been no published human trials of PPAR agonists for treatment of alcohol use disorder, despite the compelling preclinical evidence. Two trials of PPAR-α agonists as potential smoking cessation drugs found no effect on nicotine-related outcomes. The PPAR-γ agonist pioglitazone showed some promise in reducing heroin, nicotine, and cocaine craving in two human laboratory studies and one pilot trial, yet other outcomes were unaffected. Potential explanations for the discordance between the animal and human evidence, such as the potency and selectivity of PPAR ligands and sex-related variability in PPAR physiology, are discussed.

Dietary supplementation with pioglitazone hydrochloride improves intramuscular fat, fatty acid profile, and antioxidant ability of thigh muscle in yellow-feathered chickens

BACKGROUND

Muscle fat content and fatty acid composition play an important role in poultry flavor and taste. To investigate the effects of pioglitazone hydrochloride (PGZ) on growth performance and thigh muscle quality in yellow-feathered chickens, 360 female chickens were randomly divided into three groups and treated with three doses of PGZ (0, 7.5, and 15 mg kg^-1 ) for 28 days. Each group had six replicates of 20 chickens.

RESULTS

The results showed that dietary supplementation with 15 mg kg^-1 PGZ increased average daily feed intake (ADFI) and the average daily gain (ADG) from 0 to 14 days. Furthermore, the triglyceride (TG) level was decreased by 15 mg kg^-1 PGZ, whereas the eviscerated yield was increased. The relative weight of the heart and kidneys showed a linear increase with dietary PGZ supplementation, and the drip loss of the thigh muscle was significantly decreased by 15 mg kg^-1 PGZ supplementation. Moreover, a* value, intramuscular fat (IMF), and polyunsaturated fatty acids (PUFAs) showed a linear increase, and pH_{24 h} and drip loss showed a quadratic influence with the levels of PGZ supplementation. In particular, the PUFA proportion was increased by 7.63% and 9.14% in the 7.5 mg kg^-1 PGZ and 15 mg kg^-1 PGZ groups, respectively. Additionally, 15 mg kg^-1 of PGZ increased the total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-P_X ) activity.

CONCLUSION

In summary, 15 mg kg^-1 PGZ has substantial effects on growth performance and meat quality, particularly by decreasing drip loss and increasing IMF content, PUFA proportions, and antioxidant ability. © 2019 Society of Chemical Industry.

Cholinergic Receptors and Addiction

Human behavior can be controlled by physical or psychological dependencies associated with addiction. One of the most insidious addictions in our society is the use of tobacco products which contain nicotine. This addiction can be associated with specific receptors in the brain that respond to the natural neurotransmitter acetylcholine. These nicotinic acetylcholine receptors (nAChR) are ligand-gated ion channels formed by the assembly of one or multiple types of nAChR receptor subunits. In this paper, we review the structure and diversity of nAChR subunits and our understanding for how different nAChR subtypes play specific roles in the phenomenon of nicotine addiction. We focus on receptors containing β2 and/or α6 subunits and the special significance of α5-containing receptors. These subtypes all have roles in regulating dopamine-mediated neurotransmission in the mesolimbic reward pathways of the brain. We also discuss the unique roles of homomeric α7 nAChR in behavioral responses to nicotine and how our knowledge of nAChR functional diversity may help guide pharmacotherapeutic approaches for treating nicotine addiction. While nicotine addiction is a truly global problem, the use of areca nut (betel) products is also a serious addiction associated with public health issues across most of South Asia, impacting as many as 600 million people. We discuss how cholinergic receptors of the brain are also involved with areca addiction and the unique challenges for dealing with addiction to this substance.

Activation of PPARγ Attenuates the Expression of Physical and Affective Nicotine Withdrawal Symptoms through Mechanisms Involving Amygdala and Hippocampus Neurotransmission

An isoform of peroxisome proliferator-activated receptors (PPARs), PPARγ, is the receptor for the thiazolidinedione class of anti-diabetic medications including pioglitazone. Neuroanatomical data indicate PPARγ localization in brain areas involved in drug addiction. Preclinical and clinical data have shown that pioglitazone reduces alcohol and opioid self-administration, relapse to drug seeking, and plays a role in emotional responses. Here, we investigated the behavioral effect of PPARγ manipulation on nicotine withdrawal in male Wistar rats and in male mice with neuron-specific PPARγ deletion (PPARγ^(-/-)) and their littermate wild-type (PPARγ^(+/+)) controls. Real-time quantitative RT-PCR and RNAscope in situ hybridization assays were used for assessing the levels of expression and cell-type localization of PPARγ during nicotine withdrawal. Brain site-specific microinjections of the PPARγ agonist pioglitazone were performed to explore the role of this system on nicotine withdrawal at a neurocircuitry level. Results showed that activation of PPARγ by pioglitazone abolished the expression of somatic and affective nicotine withdrawal signs in rats and in (PPARγ^(+/+)) mice. This effect was blocked by the PPARγ antagonist GW9662. During early withdrawal and protracted abstinence, the expression of PPARγ increased in GABAergic and glutamatergic cells of the amygdala and hippocampus, respectively. Hippocampal microinjections of pioglitazone reduced the expression of the physical signs of withdrawal, whereas excessive anxiety associated with protracted abstinence was prevented by pioglitazone microinjection into the amygdala. Our results demonstrate the implication of the neuronal PPARγ in nicotine withdrawal and indicates that activation of PPARγ may offer an interesting strategy for smoking cessation.SIGNIFICANCE STATEMENT Smoking cessation leads the occurrence of physical and affective withdrawal symptoms representing a major burden to quit tobacco use. Here, we show that activation of PPARγ prevents the expression of both somatic and affective signs of nicotine withdrawal. At molecular levels results show that PPARγ expression increases in GABAergic cells in the hippocampus and in GABA- and glutamate-positive cells in the basolateral amygdala. Hippocampal microinjections of pioglitazone reduce the insurgence of the physical withdrawal signs, whereas anxiety linked to protracted abstinence is attenuated by pioglitazone injected into the amygdala. Our results demonstrate the implication of neuronal PPARγ in nicotine withdrawal and suggest that PPARγ agonism may represent a promising treatment to aid smoking cessation.

Exploration and Development of PPAR Modulators in Health and Disease: An Update of Clinical Evidence

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that govern the expression of genes responsible for energy metabolism, cellular development, and differentiation. Their crucial biological roles dictate the significance of PPAR-targeting synthetic ligands in medical research and drug discovery. Clinical implications of PPAR agonists span across a wide range of health conditions, including metabolic diseases, chronic inflammatory diseases, infections, autoimmune diseases, neurological and psychiatric disorders, and malignancies. In this review we aim to consolidate existing clinical evidence of PPAR modulators, highlighting their clinical prospects and challenges. Findings from clinical trials revealed that different agonists of the same PPAR subtype could present different safety profiles and clinical outcomes in a disease-dependent manner. Pemafibrate, due to its high selectivity, is likely to replace other PPARα agonists for dyslipidemia and cardiovascular diseases. PPARγ agonist pioglitazone showed tremendous promises in many non-metabolic disorders like chronic kidney disease, depression, inflammation, and autoimmune diseases. The clinical niche of PPARβ/δ agonists is less well-explored. Interestingly, dual- or pan-PPAR agonists, namely chiglitazar, saroglitazar, elafibranor, and lanifibranor, are gaining momentum with their optimistic outcomes in many diseases including type 2 diabetes, dyslipidemia, non-alcoholic fatty liver disease, and primary biliary cholangitis. Notably, the preclinical and clinical development for PPAR antagonists remains unacceptably deficient. We anticipate the future design of better PPAR modulators with minimal off-target effects, high selectivity, superior bioavailability, and pharmacokinetics. This will open new possibilities for PPAR ligands in medicine.

Cigarette smoking, type 2 diabetes mellitus, and glucagon-like peptide-1 receptor agonists as a potential treatment for smokers with diabetes: An integrative review

Tobacco use disorder (TUD), in particular cigarette smoking, contributes significantly to the macro- and micro-vascular complications of type 2 diabetes mellitus (DM). Persons with DM who regularly use tobacco products are twice as likely to experience mortality and negative health outcomes. Despite these risks, TUD remains prevalent in persons with DM. The objective of this integrative review is to summarize the relationship between TUD and DM based on epidemiological and preclinical biological evidence. We conclude with a review of the literature on the glucagon-like peptide-1 (GLP-1) as a potential treatment target for addressing comorbid TUD in smokers with DM.

Neuroinflammation in addiction: A review of neuroimaging studies and potential immunotherapies

Addiction is a worldwide public health problem and this article reviews scientific advances in identifying the role of neuroinflammation in the genesis, maintenance, and treatment of substance use disorders. With an emphasis on neuroimaging techniques, this review examines human studies of addiction using positron emission tomography to identify binding of translocator protein (TSPO), which is upregulated in reactive glial cells and activated microglia during pathological states. High TSPO levels have been shown in methamphetamine use but exhibits variable patterns in cocaine use. Alcohol and nicotine use, however, are associated with lower TSPO levels. We discuss how mechanistic differences at the neurotransmitter and circuit level in the neural effects of these agents and subsequent immune response may explain these observations. Finally, we review the potential of anti-inflammatory drugs, including ibudilast, minocycline, and pioglitazone, to ameliorate the behavioral and cognitive consequences of addiction.

Assessment of pioglitazone and proinflammatory cytokines during buprenorphine taper in patients with opioid use disorder

BACKGROUND

Preliminary evidence suggested that the PPARγ agonist pioglitazone reduces opioid-withdrawal symptoms, possibly by inhibiting increases in proinflammatory cytokines.

METHODS

A randomized, placebo-controlled clinical trial was conducted utilizing two different study designs (entirely outpatient, and a combination of inpatient and outpatient) to evaluate the safety and efficacy of pioglitazone as an adjunct medication for people with opioid physical dependence undergoing a buprenorphine taper. Participants were stabilized on buprenorphine/naloxone (sublingual, up to 16/4 mg/day), then randomized to receive oral pioglitazone (up to 45 mg/day) or placebo before, during, and after buprenorphine taper. Outcome measures included the Subjective Opiate Withdrawal Scale (SOWS) and Clinical Opiate Withdrawal Scale, use of rescue medications to alleviate opioid withdrawal symptoms, and opioid-positive urine specimens. Cerebrospinal fluid (CSF) and plasma were collected during the taper in a subset of participants for measurement of proinflammatory cytokines.

RESULTS

The clinical trial was prematurely terminated due to slow enrollment; 40 participants per group were required for adequate statistical power to test study hypotheses. Twenty-four participants enrolled; 17 received at least one dose of study medication (6 pioglitazone, 11 placebo). SOWS scores were higher in the pioglitazone arm than in the placebo arm after adjusting for use of rescue medications; participants in the pioglitazone arm needed more rescue medications than the placebo arm during the post-taper phase. SOWS scores were positively correlated with monocyte chemoattractant protein-1 (MCP-1) in CSF (r = 0.70, p = 0.038) and plasma (r = 0.77, p = 0.015). Participants having higher levels of plasma MCP-1 reported higher SOWS, most notably after the buprenorphine taper ended.

CONCLUSIONS

Results from this study provide no evidence that pioglitazone reduces opioid withdrawal symptoms during buprenorphine taper. High correlations between MCP-1 and opioid withdrawal symptoms support a role of proinflammatory processes in opioid withdrawal.

TRIAL REGISTRATION

clinicaltrials.gov identifier: NCT01517165.

The PPARγ Agonist Pioglitazone Fails to Alter the Abuse Potential of Heroin, But Does Reduce Heroin Craving and Anxiety

Possibly through its effects on glia, the peroxisome proliferator-activated gamma receptor (PPARγ) agonist pioglitazone (PIO) has been shown to alter the effects of heroin in preclinical models. Until now, these results have not been assessed in humans. Heroin-dependent participants were randomized to either active (45 mg, n = 14) or placebo (0 mg, n = 16) PIO maintenance for the duration of the three-week study. After stabilization on buprenorphine (8 mg), participants began a two-week testing period. On the first to fourth test days, participants could self-administer drug or money by making verbal choices for either option. On the fifth day, active heroin and money were administered and participants could work to receive heroin or money using a progressive ratio choice procedure. Test days 6-10 were identical to test days 1-5 with the exception that, during one of the test weeks, placebo was available on the first four days, and during the other week heroin was available. PIO failed to alter the reinforcing or positive subjective effects of heroin, but it did reduce heroin craving and overall anxiety. Although we were unable to replicate the robust effects found in preclinical models, these data provide an indication of drug effects that deserves further exploration.