Cigarette Smoke Extract, but Not Electronic Cigarette Aerosol Extract, Inhibits Monoamine Oxidase in vitro and Produces Greater Acute Aversive/Anhedonic Effects Than Nicotine Alone on Intracranial Self-Stimulation in Rats

Evidence update on e-cigarette dependence: A systematic review and meta-analysis

INTRODUCTION

We conducted this review to examine the risk of e-cigarette dependence in different populations by updating the review on this topic by the National Academies of Science, Engineering, and Medicine.

METHODS

Six academic databases were searched for studies published between September 2017 and December 2023. We included peer-reviewed human, animal, cell/in vitro original studies examining associations of e-cigarette use and dependence but excluded qualitative studies. Three types of e-cigarette exposure were examined: acute, short-to-medium term, and long-term. Meta-analysis were conducted when possible. Different risk of bias tools were used for assessing quality of the included human studies.

RESULTS

We included 107 studies, of which 34 studies were included in the subgroup analysis. Meta-analyses showed that non-smoker current vapers had no statistically significant difference in level or prevalence of dependence compared to non-vaper current smokers and dual users. However, never smoker current vapers had a lower level of dependence (SMD -0.723, p < 0.01) compared to dual users, which was also supported by ANOVA test. Narrative review findings suggest that nicotine vapers had higher level of dependence than non-nicotine vapers and e-cigarette dependence is positively associated with nicotine concentration, frequency, and duration of use. No strong relationship was found between dependence and product types or features. Socio-demographic factor-based subgroup findings were inconclusive.

CONCLUSIONS

The level and prevalence of e-cigarette dependence is similar to cigarette dependence. There was high variability in the definitions and methods used for defining populations and assessing dependence. Further research and monitoring are crucial.

Effects of volatile organic compounds found in cigarette smoke on intracranial self-stimulation in rats

BACKGROUND

Understanding the role of non-nicotine constituents in tobacco use disorder (TUD) could inform the development of more effective treatments for TUD and tobacco control policies. Cigarette smoke contains considerable levels of various volatile organic compounds (VOCs) including acetaldehyde, toluene, and benzene. While acetaldehyde and toluene can have substance use disorder (SUD)-related effects and/or potentiate the TUD-related effects of nicotine in some preclinical models, their role in TUD is not fully understood, and effects of benzene have not been evaluated in any preclinical model of SUDs. This study evaluated the SUD-related effects of parenteral (s.c.) administration of these VOCs in an intracranial self-stimulation (ICSS) model in male and female rats. The ability of acetaldehyde and benzene to influence nicotine's effects on ICSS was also examined.

METHODS AND RESULTS

In Experiment 1, acetaldehyde (10-150mg/kg) did not lower ICSS thresholds, suggesting a lack of SUD-related effects. Rather, 100mg/kg acetaldehyde elevated ICSS thresholds, indicating aversive/anhedonic effects. Benzene (600-1500mg/kg) reduced ICSS thresholds, while toluene (100-1500mg/kg) did not affect ICSS. Nicotine (1.0mg/kg) and methamphetamine (0.3 or 0.56mg/kg) (positive controls) increased and decreased ICSS thresholds, respectively. In Experiment 2, acetaldehyde (60mg/kg) did not influence nicotine's (0.125-1.0mg/kg) effects on ICSS, whereas benzene (600mg/kg) produced a downward shift in the nicotine ICSS dose-response function in males but not in females.

CONCLUSIONS

Benzene, but not acetaldehyde or toluene, had SUD-related effects in an ICSS model. As such, benzene may contribute to the TUD-related effects of combusted tobacco products, particularly in males.

Withdrawal from repeated nicotine vapor exposure increases somatic signs of physical dependence, anxiety-like behavior, and brain reward thresholds in adult male rats

Nicotine vapor consumption via electronic nicotine delivery systems has increased over the last decade. While prior work has shed light on the health effects of nicotine vapor inhalation, its unique effects on the brain and behavior have not been thoroughly explored. In this study we assessed markers of withdrawal following 14 days of nicotine vapor exposure. For Experiment 1, 21 adult male rats were exposed to ambient air or 6, 12, or 24 mg/mL nicotine vapor for 14 consecutive days. Following exposure on day 14, rats were injected with the nicotinic receptor antagonist mecamylamine (3.0 mg/mL) and assessed for somatic withdrawal signs and anxiety-like behavior in the elevated plus maze. For Experiment 2, 12 adult male rats were tested for intracranial self-stimulation (ICSS) immediately following exposure to vehicle vapor (50%/50%, vegetable glycerin/propylene glycol) or 24 mg/mL nicotine vapor, for 14 consecutive days. ICSS behavior was assessed for an additional 14 days, following cessation of repeated vapor exposure. Results reveal that rats with repeated nicotine vapor exposure display an increase in behavioral indicators of withdrawal following injection of mecamylamine (precipitated withdrawal). Additionally, increases in ICSS stimulation thresholds, indicative of reduced brain reward sensitivity, persist following cessation of repeated nicotine vapor exposure (spontaneous withdrawal). These data suggest that repeated e-cigarette use leads to nicotine dependence and withdrawal that affects behavior and brain reward function. Further characterization of the health effects of nicotine vapor is necessary to improve treatment strategies for nicotine use disorder and public health policies related to novel nicotine delivery systems.

Chronic exposure to cigarette smoke extract increases nicotine withdrawal symptoms in adult and adolescent male rats

The aim of the current study was to determine whether non-nicotine constituents of cigarette smoke contribute to nicotine dependence in adolescent and adult male Sprague Dawley rats. For 10 days animals were given three times daily intravenous injections of nicotine (1.5 mg/kg/day) or cigarette smoke extract (CSE) containing an equivalent dose of nicotine. Both spontaneous and mecamylamine-precipitated withdrawal were then measured. Chronic treatment with CSE induced significantly greater somatic and affective withdrawal signs than nicotine in both adolescents and adults. Mecamylamine-precipitated somatic signs were similar at both ages. In contrast, animals spontaneously withdrawn from chronic drug treatment exhibited significant age differences: whereas adolescents chronically treated with nicotine did not show somatic signs, those treated with CSE showed similar physical withdrawal to those of adults. Mecamylamine did not precipitate anxiety-like behavior at either age. However, both adolescents and adults showed significant anxiety in a light-dark box test 18 h after spontaneous withdrawal. Anxiety-like behavior was still evident in an open field test 1 month after termination of drug treatment, with adolescents showing significantly greater affective symptoms than adults. Our findings indicate that non-nicotine constituents of cigarette smoke do contribute to dependence in both adolescents and adults and emphasize the importance of including smoke constituents with nicotine in animal models of tobacco dependence.

β-Carboline Alkaloids in Soy Sauce and Inhibition of Monoamine Oxidase (MAO)

Monoamine oxidase (MAO) oxidizes neurotransmitters and xenobiotic amines, including vasopressor and neurotoxic amines such as the MPTP neurotoxin. Its inhibitors are useful as antidepressants and neuroprotectants. This work shows that diluted soy sauce (1/3) and soy sauce extracts inhibited human MAO-A and -B isozymes in vitro, which were measured with a chromatographic assay to avoid interferences, and it suggests the presence of MAO inhibitors. Chromatographic and spectrometric studies showed the occurrence of the β-carboline alkaloids harman and norharman in soy sauce extracts inhibiting MAO-A. Harman was isolated from soy sauce, and it was a potent and competitive inhibitor of MAO-A (0.4 µM, 44 % inhibition). The concentrations of harman and norharman were determined in commercial soy sauces, reaching 243 and 52 μg/L, respectively. Subsequently, the alkaloids 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THCA) and 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA) were identified and analyzed in soy sauces reaching concentrations of 69 and 448 mg/L, respectively. The results show that MTCA was a precursor of harman under oxidative and heating conditions, and soy sauces increased the amount of harman under those conditions. This work shows that soy sauce contains bioactive β-carbolines and constitutes a dietary source of MAO-A and -B inhibitors.