The effects of inhaled flavors on intravenous nicotine

Pulsed nicotine infusions as a model for smoking: validating a tool to explore nicotine thresholds in humans

RATIONALE

No previous studies examined the discriminative stimulus effects of intravenous (IV) nicotine in humans.

OBJECTIVES

To evaluate a pulsed IV nicotine infusion procedure designed to mimic inhaled nicotine delivery and to identify a range of nicotine doses that may capture the threshold doses for the subjective and discriminative stimulus effects of nicotine. By determining these thresholds, we can gain valuable insights into the addictive threshold of nicotine.

METHODS

Eleven participants had 2 Test Sessions following overnight abstinence from smoking. Test Session 1 examined participants' ability to discriminate 0.1 mg nicotine/pulse nicotine from saline. Test Session 2 examined if participants can discriminate 0.05, 0.025, and 0.0125 mg nicotine/pulse of nicotine from saline. These nicotine doses were delivered as a cluster of 4 pulsed-nicotine infusions of 2-second duration with a 28-second interval between each pulse.

RESULTS

The lowest doses of nicotine that produced greater responses than saline for discrimination, subjective effects, and heart rate ranged from 0.05 to 0.1 mg nicotine/pulse.

CONCLUSIONS

These findings support the validity of our pulsed-infusion procedure as a model for nicotine delivery by smoking and its utility in examining factors that may impact the addictive threshold of nicotine.

The effect of e-cigarettes on cognitive function: a scoping review

AIM

Much research has been conducted on the acute effects of nicotine on human cognitive performance, demonstrating both enhancing and impairing cognitive effects. With the relatively recent introduction of electronic cigarettes ('e-cigarettes') as a smoking cessation device, little is known about the cognitive effects of e-cigarettes specifically, either as a nicotine replacement device or in the absence of nicotine. The purpose of this review was to present an overview of evidence from empirical studies on the effect of e-cigarettes on cognitive function.

APPROACH

Guided by Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews guidelines (PRISMA-ScR), SCOPUS, PubMed, and EBSCOhost were searched from 2006, the year e-cigarettes were introduced, to June 2023 for relevant papers, along with reference lists checked for additional papers.

KEY FINDINGS

Seven experimental and four cross-sectional survey studies were identified and included. The majority of the studies only include regular and current cigarette smokers and primarily assessed the acute cognitive effect of e-cigarettes relative to nicotine. While the findings primarily suggest either no or positive effect of e-cigarettes on cognition in cigarette smokers, associations between e-cigarettes and cognitive impairments in memory, concentration and decision making were reported in both cigarette smokers and never-smokers.

IMPLICATIONS AND CONCLUSIONS

The acute cognitive effect of e-cigarettes on regular cigarette smokers appears minimal. However, long-term cognitive effect and their effects on never-smokers are unclear. Given that the increased numbers of e-cigarette users are non-smokers and/or adolescents, research with those naïve to nicotine and a developmentally vulnerable adolescent population on its long-term effect is needed.

The Scientific Basis for the Regulation of Flavors in Tobacco Products

Effective tobacco policies are important for reducing the harm of tobacco use and can have a broad impact at the population level. This review provides an overview of how clinical science can inform tobacco policies with a focus on policies related to flavored tobacco products, using menthol cigarettes as an illustrative example. Specifically, this review summarizes the role of flavors in tobacco use and the history of regulation of flavored tobacco products by the US Food and Drug Administration (FDA), provides an overview of clinical research methods used to contribute to the scientific evidence to inform FDA tobacco policies, discusses key findings related to menthol tobacco products using these methods, and proposes future directions for clinical research. As the tobacco marketplace continues to evolve with new products and flavor chemicals, ongoing clinical science will be essential for establishing evidence-based policies to protect public health and reduce tobacco-related health disparities.

Effects of electronic cigarette e-liquid flavouring on cigarette craving

BACKGROUND

E-liquid flavour restrictions may discourage electronic cigarette (e-cigarette) uptake among youth. However, possible unintended consequences may include reduced appeal and effectiveness of e-cigarettes for smoking cessation. Non-tobacco flavours appear to be important for smoking cessation, but how and why are currently unclear.

METHODS

We conducted an experimental study in a UK sample of adult daily smokers using an independent groups design (N=84). Participants were randomised to use an e-cigarette with nicotine-containing fruit/sweet-flavoured e-liquid (blackcurrant, strawberry, vanilla, caramel) or unflavoured e-liquid for 1 week. The primary outcomes were average, peak and cue-elicited cigarette craving (the latter was assessed using a cue exposure task). The secondary outcomes were smoking lapse occurrence, enjoyment of the e-cigarette, ease of transitioning from smoking to using an e-cigarette, intentions to continue using an e-cigarette, intentions and motivation to quit smoking, return to smoking, and continuation of e-cigarette use.

RESULTS

E-liquid flavouring did not appear to have an effect on average cigarette craving (b 0.18, 95% CI -0.44 to 0.79, p=0.57), peak cigarette craving (b -0.12, 95% CI -0.59 to 0.35, p=0.62) or cue-elicited cigarette craving (b -0.21, 95% CI -3.86 to 3.43, p=0.91). We did not find evidence of a difference in secondary outcomes.

CONCLUSIONS

We did not find evidence to suggest that nicotine-containing fruit/sweet-flavoured and unflavoured e-liquids have different effects on cigarette cravings after 1 week of use. Further research is needed to establish if differences emerge over longer periods of exposure and extend to smoking cessation outcomes.

Neuromodulatory and neurotoxic effects of e-cigarette vapor using a realistic exposure method

The most direct effects of inhaled harmful constituents are the effects on the airways. However, inhaled compounds can be rapidly absorbed and subsequently result in systemic effects. For example, e-cigarette vapor has been shown to evoke local effects in the lung, although little is known about subsequent effects in secondary target organs such as the brain. Traditionally, such effects are tested using in vivo models. As an alternative, we have combined two in vitro systems, which are Air-Liquid-Interface (ALI) cultured alveolar cells (A549) and rat primary cortical cultures grown on multi-well microelectrode arrays. This allows us to assess the neurological effects of inhaled compounds. We have used exposure to e-cigarette vapor, containing nicotine, menthol, or vanillin to test the model. Our results show that ALI cultured A549 cells respond to the exposure with the production of cytokines (IL8 and GROalpha). Furthermore, nicotine, menthol, and vanillin were found on the basolateral side of the cell culture, which indicates their translocation. Upon transfer of the basolateral medium to the primary cortical culture, exposure-related changes in spontaneous electrical activity were observed correlating with the presence of e-liquid components in the medium. These clear neuromodulatory effects demonstrate the feasibility of combining continuous exposure of ALI cultured cells with subsequent exposure of neuronal cells to assess neurotoxicity. Although further optimization steps are needed, such a combination of methods is important to assess the neurotoxic effects of inhaled compounds realistically. As such, an approach like this could play a role in future mechanism-based risk assessment strategies.

Development of pulsed intravenous nicotine infusions as a model for inhaled nicotine in humans

RATIONALE

Although nicotine from cigarettes is delivered in puff-sized amounts, most preclinical and human intravenous (IV) nicotine studies have used bolus or continuous infusions.

OBJECTIVES

To determine the feasibility of a pulsed-nicotine infusion model in smokers.

METHODS

Following overnight abstinence, 12 adult smokers underwent 5 laboratory sessions. Using a crossover design, in each session, participants were assigned to 1 of 5 conditions: (1) high/fast: 1.0 mg nicotine delivered over 5 pulsed-infusions, then 15 saline infusions; (2) high/slow: 1.0 mg nicotine delivered over 20 pulsed-infusions; (3) low/fast: 0.2 mg nicotine delivered over 5 pulsed-infusions, then 15 saline infusions; (4) low/slow: 0.2 mg nicotine delivered over 20 pulsed-infusions; and (5) placebo: Saline delivered over 20 pulsed-infusions. Subjective drug effects, urges to smoke, nicotine withdrawal, and cognitive performance were measured in each session.

RESULTS

Both the high/fast and high/slow conditions were associated with greater "head rush" and "high" (p < 0.05). The high/fast condition also provided greater suppression of urges to smoke and nicotine withdrawal (p < 0.05), indexed by the Questionnaire of Urges to Smoke-Brief, and the Minnesota Nicotine Withdrawal Scale, respectively. The high/fast and high/slow conditions produced greater increases in heart rate (p < 0.01) than saline. Finally, there were no main effects of dosing conditions on cognitive performance, indexed by the continuous performance test.

CONCLUSIONS

These findings demonstrate the feasibility of pulsed-nicotine infusions to model nicotine delivery by smoking. This model could inform future studies testing novel smoking cessation therapies and tobacco regulatory studies testing the impact of nicotine reduction approaches.

The Role of Nicotine and Flavor in the Abuse Potential and Appeal of Electronic Cigarettes for Adult Current and Former Cigarette and Electronic Cigarette Users: A Systematic Review

INTRODUCTION

Many adult cigarette smokers use electronic cigarettes (e-cigarettes) to cut down on or quit smoking cigarettes. E-cigarettes with higher abuse potential and appeal might facilitate complete switching. E-liquid nicotine concentration and flavor are two of the characteristics that may affect the abuse potential and appeal of e-cigarettes. The objective of this systematic review was to compile results from survey, animal, human laboratory, and clinical studies to understand the possible effects of nicotine concentration and flavor on abuse potential and appeal of e-cigarettes in adult current and former cigarette and e-cigarette users.

AIMS AND METHODS

A comprehensive literature search was conducted in Ovid Medline and PsycINFO followed by citation tracking in Web of Science Core Collection. Peer-reviewed studies published in English between 2007 and August 2020 were selected that analyzed differences between e-liquid nicotine concentration and/or flavors, had outcome measures related to abuse potential and/or appeal, and included adult humans (18+) or animals. A total of 1624 studies were identified and screened. A qualitative synthesis of results was performed.

RESULTS

Results from 104 studies included in this review suggest that higher nicotine concentration and access to a variety of flavors are likely to be associated with higher abuse potential and appeal of e-cigarettes for adult current and former cigarette and e-cigarette users.

CONCLUSIONS

Higher nicotine concentrations and the availability of a variety of flavors in e-cigarettes might facilitate complete substitution for cigarettes. Future e-cigarette regulations should take into account their impact on smokers, for whom e-cigarettes may be a cessation tool or reduced-harm alternative.

IMPLICATIONS

E-cigarettes may provide a reduced-harm alternative to cigarettes for smokers unwilling/unable to quit or serve as a path for quitting all nicotine products. Higher nicotine concentrations and flavor variety are associated with higher abuse potential and appeal of e-cigarettes. Higher abuse potential and appeal products may help facilitate complete switching from cigarettes to e-cigarettes. Regulation of nicotine concentration and flavors aimed at decreasing naïve uptake may inadvertently decrease uptake and complete switching among smokers, reducing the harm reduction potential of e-cigarettes. Evidence-based effects of regulating nicotine concentration and flavors must be considered for the population as a whole, including smokers.

Impact of delivery rate on the acute response to intravenous nicotine: A human laboratory study with implications for regulatory science

Faster delivery rate enhances the abuse potential of drugs of abuse, yet systematic studies on the impact of delivery rate on the acute effects of nicotine in humans are lacking. Using an intravenous (IV) nicotine infusion procedure that allows precise control of rate of delivery, we examined the impact of nicotine delivery rate on the positive subjective drug effects, smoking urges, withdrawal, heart rate, blood pressure and attention function in smokers. Twenty-four male and female (ages 21-35) dependent smokers attended five experimental sessions, following overnight abstinence from smoking. Using a crossover design, participants attended five sessions, where they were assigned to a random sequence of saline infusion or 1 mg nicotine delivered over 1, 2.5, 5 or 10 min at rates of 1, 0.4, 0.2 or 0.1 mg/min, respectively. The positive subjective effects of nicotine were most robust under the two faster delivery rate conditions, 1- and 0.4-mg nicotine/min. In contrast, all nicotine delivery rates were equally more effective than saline in alleviating urges to smoke. Likewise, nicotine-induced heart rate increases did not vary with the rate of nicotine delivery. Lastly, the cognitive enhancing effects of nicotine were observed only under the two slowest delivery rate conditions-0.1- and 0.2-mg nicotine/min. Collectively, these findings support the critical role of delivery rate in optimizing nicotine's abuse potential versus potential therapeutic effects and have timely implications for developing novel therapeutics for nicotine dependence, as well as for tobacco regulatory science.

Acute effects of inhaled menthol on cognitive effects of intravenous nicotine among young adult cigarette smokers

Basic science studies indicate that menthol can enhance the cognitive effects of nicotine to increase nicotine dependence; however, the effect of menthol and nicotine on cognitive functioning among humans has been understudied. This double-blind, placebo-controlled study examined the dose-dependent effects of inhaled menthol flavoring and intravenous nicotine on cognitive task performance. Twenty menthol (MS) and 18 non-menthol (NMS) cigarette preferring, young-adult smokers (21% female; 7.9% Hispanic, 44.7% Non-Hispanic/White, 47.4% Non-Hispanic/Black) completed three sessions with randomized order of menthol flavoring (between-sessions: 0.0%/tobacco control, 0.5%/low, 3.2%/high) and intravenous nicotine (within-session: 0.0 mg/saline control, 0.25 mg/low, 0.5 mg/high). After each administration, participants completed three cognitive tasks: Continuous Performance Task (CPT), Mathematical Processing Task (MPT), and Stroop Task. Mixed effects models were used to examine interactive effects of cigarette type preference and menthol and nicotine doses. MS vs. NMS had decreased accuracy on CPT and MPT and efficiency during Stroop. No significant effects of cigarette type preference by menthol or nicotine were found for any task. Significant effects of nicotine by menthol were found during Stroop, where participants had greater accuracy for high nicotine compared to saline during the low menthol session. Significant effects of menthol by timepoint were seen during Stroop, where participants improved across timepoints during the low menthol session. Findings did not support significant effects of inhaled menthol, alone or with nicotine, on cognitive performance. Further research clarifying the impact of varying menthol and nicotine levels in nicotine products may help to elucidate menthol's role in smoking sustainment.