A weight of evidence evaluation of the mode of action of isoeugenol.

Isoeugenol is one of several phenylpropenoid compounds that is used as a fragrance, food flavoring agent and in aquaculture as a fish anesthetic. Carcinogenicity testing in rats and mice by NTP resulted in clear evidence of carcinogenicity (hepatic adenomas/carcinomas) in male mice only. A nongenotoxic threshold mode of action (MOA) is postulated for isoeugenol and is discussed considering the IPCS MOA and Human Relevance Framework. The weight of evidence indicates that isoeugenol is not genotoxic and that the carcinogenic outcome in male mice relates directly to the metabolism of individual compounds. Benchmark Dose (BMD) modeling was conducted to determine a Point of Departure (POD) and potential threshold of carcinogenicity. The results of the BMD evaluation for isoeugenol resulted in an estimated POD for carcinogenicity in the male mouse of 8 mg/kg with a lower limit of 4 mg/kg, representing a POD for the determination of an acceptable daily intake. With application of uncertainty factors, an ADI of 40 µg/kg is calculated. This daily dose in humans would be protective of human health, including carcinogenicity. A corresponding maximum residual level (MRL) of 3200 µg/kg fish is also estimated based on this POD that considers the threshold MOA.

The e-liquid flavoring cinnamaldehyde induces cellular stress responses in human proximal tubule (HK-2) kidney cells.

Flavored e-liquid use has become popular among e-cigarette users recently, but the effects of such products outside the lung are not well characterized. In this work, acute exposure to the popular flavoring cinnamaldehyde (CIN) was performed on human proximal tubule (HK-2) kidney cells. Cells were exposed to 0-100 µM CIN for 24-48 h and cellular stress responses were assessed. Mitochondrial viability via MTT assay was significantly decreased at 20 µM for 24 and 48 h exposure. Seahorse XFp analysis showed significantly decreased mitochondrial energy output at 20 µM by 24 h exposure, in addition to significantly reduced ATP Synthase expression. Seahorse analysis also revealed significantly decreased glycolytic function at 20 µM by 24 h exposure, suggesting inability of glycolytic processes to compensate for reduced mitochondrial energy output. Cleaved caspase-3 expression, a mediator of apoptosis, was significantly increased at the 24 h mark. C/EBP homologous protein (CHOP) expression, a mediator of ER-induced apoptosis, was induced by 48 h and subsequently lost at the highest concentration of 100 µM. This decrease was accompanied by a simultaneous decrease in its downstream target cleaved caspase-3 at the 48 h mark. The autophagy marker microtubule-associated protein 1 A/1B light chain 3 (LC3B-I and LC3B-II) expression was significantly increased at 100 µM by 24 h. Autophagy-related 7 (ATG7) protein and mitophagy-related proteins PTEN-induced putative kinase 1 (PINK1) and PARKIN expression were significantly reduced at 24 and 48 h exposure. These results indicate acute exposure to CIN in the kidney HK-2 model induces mitochondrial dysfunction and cellular stress responses.

The E-liquid flavoring vanillin alters energy and autophagic pathways in human proximal tubule (HK-2) epithelial cells.

The use of flavored e-liquids in electronic nicotine delivery systems (ENDS) has become very popular in recent years, but effects of these products have not been well characterized outside the lung. In this study, acute exposure to the popular flavoring vanillin (VAN) was performed on human proximal tubule (HK-2) kidney cells. Cells were exposed to 0-1000 µM VAN for 24 or 48 h and cellular stress responses were determined. Mitochondrial viability using MTT assay showed a significant decrease between the control and 1000 µM group by 48 h. Seahorse XFp analysis showed significantly increased basal respiration, ATP production, and proton leak after 24 h exposure. By 48 h exposure, these parameters remained significantly increased in addition to non-mitochondrial respiration and maximal respiration. Glycolytic activity after 24 h exposure showed significant decreases in glycolysis, glycolytic capacity, glycolytic reserve, and non-glycolytic acidification. The autophagy markers microtubule-associated protein 1A/1B light chain 3 (LC3B-I and LC3B-II) were probed via western blotting. The ratio of LC3B-II/LC3B-I was significantly increased after 24 h exposure to VAN, but by 48 h this ratio significantly decreased. The mitophagy marker PINK1 showed an increasing trend at 24 h, and its downstream target Parkin was significantly increased between the control and 750 µM group only. Finally, the oxidative stress marker 4-HNE was significantly decreased after 48 h exposure to VAN. These results indicate that acute exposure to VAN in the kidney HK-2 model can induce energy and autophagic changes within the cell.

Molecular docking study of frequently used food additives for selected targets depending on the chromosomal abnormalities they cause.

Food additives (FAs) (flavor enhancers, sweeteners, etc.) protect foods during storage and transportation, making them attractive to consumers. Today, while the desire to access natural foods is increasing, the chemicals added to foods have started to be questioned. In this respect, genotoxicity tests have gained importance. Studies show that some food additives may have genotoxic risks. Previous studies carried out in our laboratory also revealed genotoxic effects of Monopotassium glutamate (MPG), Monosodium glutamate (MSG), Magnesium diglutamate (MDG) as flavor enhancers; Potassium benzoate (PB), Potassium sorbate (PS), Sodium benzoate (SB), Sodium sorbate (SS) as preservatives; Acesulfame potassium (ACE-K), Xylitol (XYL) as sweeteners. In this study, we determined the interactions of these food additives with ATM and p53 proteins, which are activated in the cell due to genotoxic effects, and with DNA by employing the molecular docking method for the first time. Among the food additives, SB (-4.307) for ATM, XYL (-4.629) for p53, and XYL (-4.927) for DNA showed the highest affinity. Therefore, flexible docking (IFD) scores were determined for SB, XYL, and MDG from flavor enhancers. The potential binding modes of the food additives to target molecules' possible inhibition mechanisms were determined by molecular docking. Thus, new information was obtained to show how these additives cause chromosomal abnormalities.

Sex Differences in E-Cigarette Use and Related Health Effects.

BACKGROUND: Electronic cigarettes (e-cigarettes) comprise a variety of products designed to deliver nicotine, flavorings, and other substances. To date, multiple epidemiological and experimental studies have reported a variety of health issues associated with their use, including respiratory toxicity, exacerbation of respiratory conditions, and behavioral and physiological effects. While some of these effects appear to be sex- and/or gender-related, only a portion of the research has been conducted considering these variables. In this review, we sought to summarize the available literature on sex-specific effects and sex and gender differences, including predictors and risk factors, effects on organ systems, and behavioral effects. METHODS: We searched and selected articles from 2018-2023 that included sex as a variable or reported sex differences on e-cigarette-associated effects. RESULTS: We found 115 relevant studies published since 2018 that reported sex differences in a variety of outcomes. The main differences reported were related to reasons for initiation, including smoking history, types of devices and flavoring, polysubstance use, physiological responses to nicotine and toxicants in e-liquids, exacerbation of lung disease, and behavioral factors such as anxiety, depression, sexuality, and bullying. CONCLUSIONS: The available literature supports the notion that both sex and gender influence the susceptibility to the negative effects of e-cigarette use. Future research needs to consider sex and gender variables when addressing e-cigarette toxicity and other health-related consequences.

Occurrence of Perillaldehyde and Other (Suspected) Genotoxic Flavoring Substances in Water-Based Beverages Consumed by Belgian Children.

Despite the extensive use of flavoring substances in food, their monitoring for regulatory purposes is currently limited. This raises public health issues, especially as some compounds are prohibited due to (geno)toxicity. A solvent-assisted flavor evaporation (SAFE) method coupled with GC/MS (SIM) was validated here for diverse water-based beverages. Thirty flavoring substances out of the 38 targeted were validated, showing good analytical performances and confirming the versatility of the SAFE technique. The method was then applied to 94 samples, including fruit juices, iced teas, lemonades, colas, and sports beverages. Overall, seven different flavoring substances of interest were detected in the samples. Perillaldehyde and furan-2(5H)-one, two genotoxic flavoring substances, were found at concentrations up to 153 and 143 µg·kg-1, respectively. Perillaldehyde levels were significantly higher in commercial citrus juices than in freshly squeezed juices. Food control laboratories could use the developed method to face the current growing need to improve flavoring substance monitoring and conduct risk assessments.

Toxicological assessment of E-cigarette flavored E-liquids aerosols using Calu-3 cells: A 3D lung model approach.

Scientific progress and ethical considerations are increasingly shifting the toxicological focus from in vivo animal models to in vitro studies utilizing physiologically relevant cell cultures. Consequently, we evaluated and validated a three-dimensional (3D) model of the human lung using Calu-3 cells cultured at an air-liquid interface (ALI) for 28 days. Assessment of seven essential genes of differentiation and transepithelial electrical resistance (TEER) measurements, in conjunction with mucin (MUC5AC) staining, validated the model. We observed a time-dependent increase in TEER, genetic markers of mucus-producing cells (muc5ac, muc5b), basal cells (trp63), ciliated cells (foxj1), and tight junctions (tjp1). A decrease in basal cell marker krt5 levels was observed. Subsequently, we utilized this validated ALI-cultured Calu-3 model to investigate the adversity of the aerosols generated from three flavored electronic cigarette (EC) e-liquids: cinnamon, vanilla tobacco, and hazelnut. These aerosols were compared against traditional cigarette smoke (3R4F) to assess their relative toxicity. The aerosols generated from PG/VG vehicle control, hazelnut and cinnamon e-liquids, but not vanilla tobacco, significantly decreased TEER and increased lactate dehydrogenase (LDH) release compared to the incubator and air-only controls. Compared to 3R4F, there were no significant differences in TEER or LDH with the tested flavored EC aerosols other than vanilla tobacco. This starkly contrasted our expectations, given the common perception of e-liquids as a safer alternative to cigarettes. Our study suggests that these results depend on flavor type. Therefore, we strongly advocate for further research, increased user awareness regarding flavors in ECs, and rigorous regulatory scrutiny to protect public health.

In Vitro high-throughput toxicological assessment of E-cigarette flavors on human bronchial epithelial cells and the potential involvement of TRPA1 in cinnamon flavor-induced toxicity.

Electronic cigarettes (ECs) are considered a less hazardous alternative to tobacco smoking but are not harmless. Growing concerns about the safety profiles of flavors in e-liquids underpin the need for this study. Here, we screened 53 nicotine-free flavored e-liquids (across 15 flavor categories) across a 3-point concentration range (0.25%, 0.5%, and 1% v/v) in a high-throughput fashion in human bronchial epithelial (HBEC-3KT) submerged cell cultures to identify 'toxic hits' using in vitro endpoint assays comprising cell count, cell viability, and lactate dehydrogenase (LDH). We observed significant, dose-dependent adverse effects only with cinnamon, vanilla tobacco, and hazelnut e-liquids compared to media-only and PG/VG vehicle controls. Hence, we further analyzed these three flavors for their effects on HBEC-3KT proliferation, mitochondrial health, and oxidative stress. A significant decrease in cell proliferation after 36 h was observed for each e-liquid toxic hit compared to media-only and PG/VG controls. Hazelnut (at all concentrations) and vanilla tobacco (1%) increased cytoplasmic reactive oxygen species generation compared to media-only and PG/VG controls. Conversely, all three flavors at 0.5% and 1% significantly decreased mitochondrial membrane potential compared to PG/VG and media-only controls. Chemical analysis revealed that all three flavors contained volatile organic compounds. We hypothesized that the cytotoxicity of cinnamon might be mediated via TRPA1; however, TRPA1 antagonist AP-18 (10 µM) did not mitigate these effects, and cinnamon significantly increased TRPA1 transcript levels. Therefore, pathways mediating cinnamon's cytotoxicity warrant further investigations. This study could inform public health authorities on the relative health risks assessment following exposure to EC flavor ingredients.

Oral nicotine pouches with an aftertaste? Part 1: screening and initial toxicological assessment of flavorings and other ingredients.

Nicotine pouches are oral products that deliver nicotine without containing tobacco. Previous studies mainly focused on the determination of known tobacco toxicants, while yet no untargeted analysis has been published on unknown constituents, possibly contributing to toxicity. Furthermore, additives might enhance product attractiveness. We therefore performed an aroma screening with 48 different nicotine-containing and two nicotine-free pouches using gas chromatography coupled to mass spectrometry, following acidic and basic liquid-liquid extraction. For toxicological assessment of identified substances, European and international classifications for chemical and food safety were consulted. Further, ingredients listed on product packages were counted and grouped by function. Most abundant ingredients comprised sweeteners, aroma substances, humectants, fillers, and acidity regulators. 186 substances were identified. For some substances, acceptable daily intake limits set by European Food Safety Agency (EFSA) and Joint FAO/WHO Expert Committee on Food Additives are likely exceeded by moderate pouch consumption. Eight hazardous substances are classified according to the European CLP regulation. Thirteen substances were not authorized as food flavorings by EFSA, among them impurities such as myosmine and ledol. Three substances were classified by International Agency for Research on Cancer as possibly carcinogenic to humans. The two nicotine-free pouches contain pharmacologically active ingredients such as ashwagandha extract and caffeine. The presence of potentially harmful substances may point to the need for regulation of additives in nicotine-containing and nicotine-free pouches that could be based on provisions for food additives. For sure, additives may not pretend positive health effects in case the product is used.

Pulmonary immune response regulation, genotoxicity, and metabolic reprogramming by menthol- and tobacco-flavored e-cigarette exposures in mice.

Menthol and tobacco flavors are available for almost all tobacco products, including electronic cigarettes (e-cigs). These flavors are a mixture of chemicals with overlapping constituents. There are no comparative toxicity studies of these flavors produced by different manufacturers. We hypothesized that acute exposure to menthol and tobacco-flavored e-cig aerosols induces inflammatory, genotoxicity, and metabolic responses in mouse lungs. We compared two brands, A and B, of e-cig flavors (PG/VG, menthol, and tobacco) with and without nicotine for their inflammatory response, genotoxic markers, and altered genes and proteins in the context of metabolism by exposing mouse strains, C57BL/6J (Th1-mediated) and BALB/cJ (Th2-mediated). Brand A nicotine-free menthol exposure caused increased neutrophils and differential T-lymphocyte influx in bronchoalveolar lavage fluid and induced significant immunosuppression, while brand A tobacco with nicotine elicited an allergic inflammatory response with increased Eotaxin, IL-6, and RANTES levels. Brand B elicited a similar inflammatory response in menthol flavor exposure. Upon e-cig exposure, genotoxicity markers significantly increased in lung tissue. These inflammatory and genotoxicity responses were associated with altered NLRP3 inflammasome and TRPA1 induction by menthol flavor. Nicotine decreased surfactant protein D and increased PAI-1 by menthol and tobacco flavors, respectively. Integration of inflammatory and metabolic pathway gene expression analysis showed immunometabolic regulation in T cells via PI3K/Akt/p70S6k-mTOR axis associated with suppressed immunity/allergic immune response. Overall, this study showed the comparative toxicity of flavored e-cig aerosols, unraveling potential signaling pathways of nicotine and flavor-mediated pulmonary toxicological responses, and emphasized the need for standardized toxicity testing for appropriate premarket authorization of e-cigarette products.

FEMA GRAS assessment of natural flavor complexes: Lemongrass oil, chamomile oils, citronella oil and related flavoring ingredients.

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavor ingredients. This publication, eleventh in the series, evaluates the safety of NFCs characterized by primary alcohol, aldehyde, carboxylic acid, ester and lactone constituents derived from terpenoid biosynthetic pathways and/or lipid metabolism. The scientific-based evaluation procedure published in 2005 and updated in 2018 that relies on a complete constituent characterization of the NFC and organization of the constituents into congeneric groups. The safety of the NFCs is evaluated using the threshold of toxicological concern (TTC) concept in addition to data on estimated intake, metabolism and toxicology of members of the congeneric groups and for the NFC under evaluation. The scope of the safety evaluation does not include added use in dietary supplements or any products other than food. Twenty-three NFCs, derived from the Hibiscus, Melissa, Ricinus, Anthemis, Matricaria, Cymbopogon, Saussurea, Spartium, Pelargonium, Levisticum, Rosa, Santalum, Viola, Cryptocarya and Litsea genera were affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

A contextualised e-cigarette testing strategy shows flavourings do not impact lung toxicity in vitro.

Vaping has the potential to reduce the individual health risks associated with smoking and e-cigarette flavours have been reported to help smokers' transition from cigarettes. In this manuscript, we provide evidence to support the reduced risk potential of e-cigarette aerosols and flavours by assessing commercially available e-liquids (Vuse ePod - Manufactured by British American Tobacco) in a 2D in vitro screening approach. We also analysed selected flavours using a more physiologically relevant 3D (MucilAir) whole aerosol exposure model, measuring toxicity and functional endpoints such as Trans Epithelial Electrical Resistance, Cilia Beat Frequency and Active Area. To contextualise responses, we have compared e-cigarette aerosol to cigarette smoke (1R6F research cigarette) and calculated the percentage reduction using a point of departure approach. We show that aerosolised flavoured e-liquids, (appropriately stewarded) do not increase the overall measured aerosol toxicity when compared to cigarette smoke. In fact, we demonstrate that the measured in vitro cellular toxicity of flavoured e-cigarette products remains > 95% reduced when compared to cigarette smoke toxicity, using point of departure (IC80) approach. These data indicate that the overall product toxicity is not increased in a flavour dependent manner and that flavoured e-cigarette products can potentially play a role in tobacco harm reduction.

FEMA GRAS assessment of natural flavor complexes: Allspice, anise, fennel-derived and related flavoring ingredients.

The FEMA Expert Panel program to re-evaluate the safety of natural flavor complexes (NFCs) used as flavoring ingredients in food has resulted in the publication of an updated constituent-based procedure as well as publications on the safety evaluation of many botanical-derived NFCs. This publication, ninth in the series and related to the ninth publication, describes the affirmation of the generally recognized as safe (GRAS) status for NFCs with propenylhydroxybenzene and allylalkoxybenzene constituents under their conditions of intended use as flavoring ingredients added to food. The Panel's procedure applies the threshold of toxicological concern (TTC) concept and evaluates relevant data on absorption, metabolism, genotoxic potential and toxicology for the NFCs themselves and their respective constituent congeneric groups. For NFCs containing allylalkoxybenzene constituent(s) with suspected genotoxic potential, the estimated intake of the individual constituent is compared to the TTC for compounds with structural alerts for genotoxicity and if exceeded, a margin of exposure is calculated using BMDL10 values derived from benchmark dose analyses using Bayesian model averaging, as presented in the tenth article of the series. Safety evaluations for NFCs derived from allspice, anise seed, star anise, sweet fennel seed and pimento leaves were conducted and their GRAS status was affirmed for use as flavoring ingredients. The scope of the safety evaluation contained herein does not include added use in dietary supplements or any products other than food.

In vitro and in vivo acute toxicity of an artificial butter flavoring.

Flavorings used in cookies, electronic cigarettes, popcorn, and breads contain approximately 30 chemical compounds, which makes it difficult to determine and correlate signs and symptoms of acute, subacute or chronic toxicity. The aim of this study was to characterize a butter flavoring chemically and subsequently examine the in vitro and in vivo toxicological profile using cellular techniques, invertebrates, and lab mammals. For the first time, the ethyl butanoate was found as the main compound of a butter flavoring (97.75%) and 24 h-toxicity assay employing Artemia salina larvae revealed a linear effect and LC50 value of 14.7 (13.7-15.7) mg/ml (R2 = 0.9448). Previous reports about higher oral doses of ethyl butanoate were not found. Observational screening with doses between 150-1000 mg/kg by gavage displayed increased amount of defecation, palpebral ptosis, and grip strength reduction, predominantly at higher doses. The flavoring also produced clinical signs of toxicity and diazepam-like behavioral changes in mice, including loss of motor coordination, muscle relaxation, increase of locomotor activity and intestinal motility, and induction of diarrhea, with deaths occurring after 48 h exposure. This substance fits into category 3 of the Globally Harmonized System. Data demonstrated that butter flavoring altered the emotional state in Swiss mice and disrupted intestinal motility, which may be a result of neurochemical changes or direct lesions in the central/peripheral nervous systems.

FEMA GRAS assessment of derivatives of basil, nutmeg, parsley, tarragon and related allylalkoxybenzene-containing natural flavor complexes.

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavoring ingredients in food. In this publication, tenth in the series, NFCs containing a high percentage of at least one naturally occurring allylalkoxybenzene constituent with a suspected concern for genotoxicity and/or carcinogenicity are evaluated. In a related paper, ninth in the series, NFCs containing anethole and/or eugenol and relatively low percentages of these allylalkoxybenzenes are evaluated. The Panel applies the threshold of toxicological concern (TTC) concept and evaluates relevant toxicology data on the NFCs and their respective constituent congeneric groups. For NFCs containing allylalkoxybenzene constituent(s), the estimated intake of the constituent is compared to the TTC for compounds with structural alerts for genotoxicity and when exceeded, a margin of exposure (MOE) is calculated. BMDL10 values are derived from benchmark dose analyses using Bayesian model averaging for safrole, estragole and methyl eugenol using EPA's BMDS software version 3.2. BMDL10 values for myristicin, elemicin and parsley apiole were estimated by read-across using relative potency factors. Margins of safety for each constituent congeneric group and MOEs for each allylalkoxybenzene constituent for each NFC were determined that indicate no safety concern. The scope of the safety evaluation contained herein does not include added use in dietary supplements or any products other than food. Ten NFCs, derived from basil, estragon (tarragon), mace, nutmeg, parsley and Canadian snakeroot were determined or affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

FEMA GRAS assessment of natural flavor complexes: Asafetida oil, garlic oil and onion oil.

The Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) applies its procedure for the safety evaluation of natural flavor complexes (NFCs) to re-evaluate the safety of Asafetida Oil (Ferula assa-foetida L.) FEMA 2108, Garlic Oil (Allium sativum L.) FEMA 2503 and Onion Oil (Allium cepa L.) FEMA 2817 for use as flavoring in food. This safety evaluation is part of a series of evaluations of NFCs for use as flavoring ingredients conducted by the Expert Panel that applies a scientific procedure published in 2005 and updated in 2018. Using a group approach that relies on a complete chemical characterization of the NFC intended for commerce, the constituents of each NFC are organized into well-defined congeneric groups and the estimated intake of each constituent congeneric group is evaluated using the conservative threshold of toxicological concern (TTC) concept. Data on the metabolism, genotoxic potential and toxicology for each constituent congeneric group are reviewed as well as studies on each NFC. Based on the safety evaluation, Asafetida Oil (Ferula assa-foetida L.), Garlic Oil (Allium sativum L.) and Onion Oil (Allium cepa L.) were affirmed as generally recognized as safe (GRASa) under their conditions of intended use as flavor ingredients.

Menthol flavoring in e-cigarette condensate causes pulmonary dysfunction and cytotoxicity in precision cut lung slices.

E-cigarette consumption is under scrutiny by regulatory authorities due to concerns about product toxicity, lack of manufacturing standards, and increasing reports of e-cigarette- or vaping-associated acute lung injury. In vitro studies have demonstrated cytotoxicity, mitochondrial dysfunction, and oxidative stress induced by unflavored e-cigarette aerosols and flavoring additives. However, e-cigarette effects on the complex lung parenchyma remain unclear. Herein, the impact of e-cigarette condensates with or without menthol flavoring on functional, structural, and cellular responses was investigated using mouse precision cut lung slices (PCLS). PCLS were exposed to e-cigarette condensates prepared from aerosolized vehicle, nicotine, nicotine + menthol, and menthol e-fluids at doses from 50 to 500 mM. Doses were normalized to the glycerin content of vehicle. Video-microscopy of PCLS revealed impaired contractile responsiveness of airways to methacholine and dampened ciliary beating following exposure to menthol-containing condensates at concentrations greater than 300 mM. Following 500 mM menthol-containing condensate exposure, epithelial exfoliation in intrabronchial airways was identified in histological sections of PCLS. Measurement of lactate dehydrogenase release, mitochondrial water-soluble-tetrazolium salt-1 conversion, and glutathione content supported earlier findings of nicotine or nicotine + menthol e-cigarette-induced dose-dependent cytotoxicity and oxidative stress responses. Evaluation of PCLS metabolic activity revealed dose-related impairment of mitochondrial oxidative phosphorylation and glycolysis after exposure to menthol-containing condensates. Taken together, these data demonstrate prominent menthol-induced pulmonary toxicity and impairment of essential physiological functions in the lung, which warrants concerns about e-cigarette consumer safety and emphasizes the need for further investigations of molecular mechanisms of toxicity and menthol effects in an experimental model of disease.

Pulmonary effects of e-liquid flavors: a systematic review.

Electronic cigarettes (ECs) are purported to be tobacco harm-reduction products whose degree of harm has been highly debated. EC use is considered less hazardous than smoking but is not expected to be harmless. Following the banning of e-liquid flavors in countries such as the US, Finland, Ukraine, and Hungary, there are growing concerns regarding the safety profile of e-liquid flavors used in ECs. While these are employed extensively in the food industry and are generally regarded as safe (GRAS) when ingested, GRAS status after inhalation is unclear. The aim of this review was to assess evidence from 38 reports on the adverse effects of flavored e-liquids on the respiratory system in both in vitro and in vivo studies published between 2006 and 2021. Data collected demonstrated greater detrimental effects in vitro with cinnamon (9 articles), strawberry (5 articles), and menthol (10 articles), flavors than other flavors. The most reported effects among these investigations were perturbations of pro-inflammatory biomarkers and enhanced cytotoxicity. There is sufficient evidence to support the toxicological impacts of diacetyl- and cinnamaldehyde-containing e-liquids following human inhalation; however, safety profiles on other flavors are elusive. The latter may result from inconsistencies between experimental approaches and uncertainties due to the contributions from other e-liquid constituents. Further, the relevance of the concentration ranges to human exposure levels is uncertain. Evidence indicates that an adequately controlled and consistent, systematic toxicological investigation of a broad spectrum of e-liquid flavors may be required at biologically relevant concentrations to better inform public health authorities on the risk assessment following exposure to EC flavor ingredients.