Electronic cigarette liquid exposure induces flavor-dependent osteotoxicity and increases expression of a key bone marker, collagen type I

The Effects of Nicotine- and Cigarette-Related Products on Osteogenesis, Bone Formation, and Bone Mineralization: A Systematic Review

BACKGROUND

Many clinicians associate nicotine as the causative agent in the negative and deleterious effects of smoking on bone growth and spine fusion. Although nicotine is the primary driver of physiological addiction in smoking, isolated and controlled use of nicotine is one of the most effective adjuncts to quitting smoking.

OBJECTIVE

To explore the relationship between nicotine and noncombustion cigarette products on bone growth.

METHODS

One thousand five studies were identified, of which 501 studies were excluded, leaving 504 studies available for review. Of note, 52 studies were deemed to be irrelevant. Four hundred fifty-two studies remained for eligibility assessment. Of the remaining 452, 218 failed to assess study outcomes, 169 failed to assess bone biology, 13 assessed 5 patients or fewer, and 12 were deemed to be ineligible of the study criteria. Forty studies remained for inclusion within this systematic review.

RESULTS

Of the 40 studies identified for inclusion within the study, 30 studies were classified as "Animal Basic Science," whereas the remaining 10 were categorized as "Human Basic Science." Of the 40 studies, 11 noted decreased cell proliferation and boney growth, whereas 8 showed an increase. Four studies noted an increase in gene expression products, whereas 11 noted a significant decrease.

CONCLUSION

The results of this study demonstrate that nicotine has a variety of complex interactions on osteoblast and osteoclastic activities. Nicotine demonstrates dose-dependent effects on osteoblast proliferation, boney growth, and gene expression. Further study is warranted to extrapolate the effects of solitary nicotine on clinical outcomes.

The impact of e-cigarette exposure on different organ systems: A review of recent evidence and future perspectives

The use of electronic cigarettes (e-cigs) is rapidly increasing worldwide and is promoted as a smoking cessation tool. The impact of traditional cigs on human health has been well-defined in both animal and human studies. In contrast, little is known about the adverse effects of e-cigs exposure on human health. This review summarizes the impact of e-cigs exposure on different organ systems based on the rapidly expanding recent evidence from experimental and human studies. A number of growing studies have shown the adverse effects of e-cigs exposure on various organ systems. The summarized data in this review indicate that while e-cigs use causes less adverse effects on different organs compared to traditional cigs, its long-term exposure may lead to serious health effects. Data on short-term organ effects are limited and there is no sufficient evidence on long-term organ effects. Moreover, the adverse effects of secondhand and third hand e-cigs vapour exposure have not been thoroughly investigated in previous studies. Although some studies demonstrated e-cigs used as a smoking cessation tool, there is a lack of strong evidence to support it. While some researchers suggested e-cigs as a safer alternative to tobacco smoking, their long-term exposure health effects remain largely unknown. Therefore, more epidemiological and prospective studies including mechanistic studies are needed to address the potential adverse health effects of e-cigs to draw a firm conclusion about their safe use. A wide variation in e-cigs products and the lack of standardized testing methods are the major barriers to evaluating the existing data. Specific regulatory guidelines for both e-cigs components and the manufacturing process may be effective to protect consumer health.

Tobacco heating system has less impact on bone metabolism than cigarette smoke

Cigarette smoking promotes osteoclast activity, thus increasing the risk of secondary osteoporosis, leading to osteoporosis-associated fracture and impaired fracture healing. Heated tobacco products (HTP) are considered potential reduced-risk alternatives to cigarettes. However, their impact on bone metabolism remains to be elucidated. We developed an in vitro model that mimics in vivo bone cell interactions to comparatively evaluate the effects of HTPs and cigarette smoke on bone cell functionality and viability. We generated an in vitro coculture system with SCP-1 and THP-1 cells (1:8 ratio) cultured on a decellularized Saos-2 matrix with an optimized coculture medium. We found that, following acute or chronic exposure, particulate matter extract from the aerosol of an HTP, the Tobacco Heating System (THS), was less harmful to the bone coculture system than reference cigarette (1R6F) smoke extract. In the fracture healing model, cultures exposed to the THS extract maintained similar osteoclast activity and calcium deposits as control cultures. Conversely, smoke extract exposure promoted osteoclast activity, resulting in an osteoporotic environment, whose formation could be prevented by bisphosphonate coadministration. Thus, THS is potentially less harmful than cigarette smoke to bone cell differentiation and bone mineralization - both being crucial aspects during the reparative phase of fracture healing.

Systematic review on e-cigarette and its effects on weight gain and adipocytes

Smoking and obesity are leading causes of morbidity and mortality worldwide. E-cigarette which was first introduced in 2000s is perceived as an effective alternative to conventional tobacco smoking. Limited knowledge is available regarding the risks and benefits of e-cigarettes. This study systematically reviews the current literature on the effects of e-cigarettes on body weight changes and adipocytes. The search was performed using OVID Medline and Scopus databases and studies meeting the inclusion criteria were independently assessed. This review included all English language, empirical quantitative and qualitative papers that investigated the effects of e-cigarettes on bodyweight or lipid accumulation or adipocytes. Literature searches identified 4965 references. After removing duplicates and screening for eligibility, thirteen references which involve human, in vivo and in vitro studies were reviewed and appraised. High prevalence of e-cigarette was reported in majority of the cross sectional studies conducted among respondent who are obese or overweight. More conclusive findings were identified in in vivo studies with e-cigarette causing weight decrease. However, these observations were not supported by in vitro data. Hence, the effect of e-cigarette on body weight changes warrants further investigations. Well-designed population and molecular studies are needed to further elucidate the role of e-cigarettes in obesity.

E-cigarette vaping liquids and the flavoring chemical cinnamaldehyde perturb bone, cartilage and vascular development in zebrafish embryos

As electronic cigarettes (e-cigarettes) become increasingly popular smoking devices, there is an increased risk for unintended exposure to e-cigarette liquids through improper disposal resulting in leaching into the environment, third hand vapor exposure through air, or embryonic exposure through maternal vaping. Thus, the safety of e-cigarettes for wildlife and developing embryos need to be thoroughly investigated. We examined perturbations in zebrafish embryonic development after exposures to two cinnamon flavored vaping liquids (with 12 mg/ml nicotine and without nicotine) for e-cigarettes from two different vendors, as well as the flavoring chemical cinnamaldehyde. We focused on the effects of the vaping liquids on hatching success and bone, cartilage and blood vessel development in 3-4 days old transgenic zebrafish larvae. We found that exposures to both of the vaping liquids perturbed the development of the cleithrum and craniofacial cartilage. Exposure to the liquids further caused non-overlapping and partially or completely missing intersegmental vessels. Hatching success was also reduced. Exposure to pure cinnamaldehyde replicated the effects of the vaping liquids with a 50% effect concentration (EC₅₀) of 34-41 µM. Quantification of the amount of cinnamaldehyde in the vaping liquids by mass spectrometry revealed EC₅₀s around 10-40 times lower than for pure cinnamaldehyde, suggesting that additional compounds or metabolites present in the vaping liquids mediate toxicity. Presence of nicotine in one of the vaping liquids decreased its EC₅₀s about two fold compared to the liquid without nicotine. Exposure to the humectants propylene glycol and vegetable glycerin did not affect the vascular, cartilage or bone development in zebrafish embryos. In conclusion, our study shows that exposure to cinnamaldehyde containing vaping liquids causes severe tissue-specific defects in developing embryos.

The chemistry and toxicology of vaping

Vaping is the process of inhaling and exhaling an aerosol produced by an e-cigarette, vape pen, or personal aerosolizer. When the device contains nicotine, the Food and Drug Administration (FDA) lists the product as an electronic nicotine delivery system or ENDS device. Similar electronic devices can be used to vape cannabis extracts. Over the past decade, the vaping market has increased exponentially, raising health concerns over the number of people exposed and a nationwide outbreak of cases of severe, sometimes fatal, lung dysfunction that arose suddenly in otherwise healthy individuals. In this review, we discuss the various vaping technologies, which are remarkably diverse, and summarize the use prevalence in the U.S. over time by youths and adults. We examine the complex chemistry of vape carrier solvents, flavoring chemicals, and transformation products. We review the health effects from epidemiological and laboratory studies and, finally, discuss the proposed mechanisms underlying some of these health effects. We conclude that since much of the research in this area is recent and vaping technologies are dynamic, our understanding of the health effects is insufficient. With the rapid growth of ENDS use, consumers and regulatory bodies need a better understanding of constituent-dependent toxicity to guide product use and regulatory decisions.

The impact of E-cigarette vaping and vapour constituents on bone health

BACKGROUND

In contrast to cigarettes, electronic cigarette use (E-cigarettes) has grown substantially over the last decade. This is due to their promotion as both a safer alternative to cigarettes and as an aide to stop smoking. Critically, upon E-cigarette use, the user may be exposed to high doses of nicotine in addition to other compounds including flavouring chemicals, metal particulates and carbonyl compounds, particularly in highly vascularised tissues such as bone. However, there has been limited investigation into the impact of E-cigarette usage on bone physiology, particularly over extended time periods and there are no clinical recommendations regarding E-cigarette usage in relation to orthopaedic surgery. This literature review draws together data from studies that have investigated the impact of E-cigarette vapour and its major constituents on bone, detailing the models utilised and the relevant mechanistic and functional results.

MAIN BODY

Currently there is a lack of studies both in vivo and in vitro that have utilised E-cigarette vapour, necessary to account for changes in chemical composition of E-cigarette liquids upon vaping. There is however evidence that human bone and bone cells express nicotine receptors and exposure of both osteoblasts and osteoclasts to nicotine, in high concentrations may reduce their viability and impair function. Similarly, it appears that aldehydes and flavouring chemicals may also negatively impact osteoblast viability and their ability to form bone. However, such functional findings are predominantly the result of studies utilising bone cell lines such as MG-63 or Saos-2 cells, with limited use of human osteoblasts or osteoclasts. Additionally, there is limited consideration for a possible impact on mesenchymal stem cells, which can also play an import role in bone repair.

CONCLUSION

Understanding the function and mechanism of action of the various components of E-cigarette vapour in mediating human bone cell function, in addition to long term studies to determine the potential harm of chronic E-cigarette use on human bone will be important to inform users of potential risks, particularly regarding bone healing following orthopaedic surgery and injury.

Toxicology of flavoring- and cannabis-containing e-liquids used in electronic delivery systems

Electronic cigarettes (e-cigarettes) were introduced in the United States in 2007 and by 2014 they were the most popular tobacco product amongst youth and had overtaken use of regular tobacco cigarettes. E-cigarettes are used to aerosolize a liquid (e-liquid) that the user inhales. Flavorings in e-liquids is a primary reason for youth to initiate use of e-cigarettes. Evidence is growing in the scientific literature that inhalation of some flavorings is not without risk of harm. In this review, 67 original articles (primarily cellular in vitro) on the toxicity of flavored e-liquids were identified in the PubMed and Scopus databases and evaluated critically. At least 65 individual flavoring ingredients in e-liquids or aerosols from e-cigarettes induced toxicity in the respiratory tract, cardiovascular and circulatory systems, skeletal system, and skin. Cinnamaldehyde was most frequently reported to be cytotoxic, followed by vanillin, menthol, ethyl maltol, ethyl vanillin, benzaldehyde and linalool. Additionally, modern e-cigarettes can be modified to aerosolize cannabis as dried plant material or a concentrated extract. The U.S. experienced an outbreak of lung injuries, termed e-cigarette, or vaping, product use-associated lung injury (EVALI) that began in 2019; among 2,022 hospitalized patients who had data on substance use (as of January 14, 2020), 82% reported using a delta-9-tetrahydrocannabinol (main psychoactive component in cannabis) containing e-cigarette, or vaping, product. Our literature search identified 33 articles related to EVALI. Vitamin E acetate, a diluent and thickening agent in cannabis-based products, was strongly linked to the EVALI outbreak in epidemiologic and laboratory studies; however, e-liquid chemistry is highly complex, and more than one mechanism of lung injury, ingredient, or thermal breakdown product may be responsible for toxicity. More research is needed, particularly with regard to e-cigarettes (generation, power settings, etc.), e-liquids (composition, bulk or vaped form), modeled systems (cell type, culture type, and dosimetry metrics), biological monitoring, secondhand exposures and contact with residues that contain nicotine and flavorings, and causative agents and mechanisms of EVALI toxicity.

Current Perspectives on Characteristics, Compositions, and Toxicological Effects of E-Cigarettes Containing Tobacco and Menthol/Mint Flavors

Electronic nicotine delivery systems/devices (ENDS) such as electronic cigarettes (e-cigarettes) have been made available globally, with the intent to reduce tobacco smoking. To make these products more appealing to young adults, many brands have added flavoring agents. However, these flavoring agents are shown to progressively result in lung toxicity when inhaled via e-cigarettes. While recent federal regulations have banned the sale of flavored e-cigarettes other than tobacco or menthol flavors, concerns have been raised about the health effects of even these flavors. In this review, we evaluate the current toxicological data with regard to effects upon exposure in animal models and in vitro cell culture for these popular flavorants. We have tabulated the current e-cigarette products containing these most common flavors (menthol, mint, and tobacco) in the market. We have also indicated the prevalence of tobacco and menthol-flavor use among e-cigarette users and highlighted the possible challenges and benefits that will result from new federal regulations.

The flavoring and not the nicotine content is a decisive factor for the effects of refill liquids of electronic cigarette on the redox status of endothelial cells

•

The pattern of the effect on Ea.hy926 redox status differs among flavored e-liquids.

•

Tobacco flavored e-liquids increase ROS generation with concomitant increase in TBARS.

•

Vanilla flavored e-liquids profile depends on the nicotine content.

•

Apple/mint flavored e-liquids activate the cellular antioxidant defense.

•

Flavorings and not the nicotine content play a key role in free radical generation.

Electronic cigarettes are constantly gaining ground as they are considered less harmful than conventional cigarettes, and there is also the perception that they may serve as a potential smoking cessation tool. Although the acute effects of electronic cigarette use have been extensively studied, the long-term potential adverse effects on human health remain largely unknown. It has been well-established that oxidative stress is involved in the development of various pathological conditions. So far, most studies on e-cigarettes concern the effects on the respiratory system while fewer have focused on the vascular system. In the present study, we attempted to reveal the effects of electronic cigarette refill liquids on the redox state of human endothelial cells (EA.hy926 cell line). For this purpose, the cytotoxic effect of three e-liquids with different flavors (tobacco, vanilla, apple/mint) and nicotine concentrations (0, 6, 12, 18 mg/ml) were initially examined for their impact on cell viability of EA.hy926 cells. Then, five redox biomarkers [reduced form of glutathione (GSH), reactive oxygen species (ROS), total antioxidant capacity (TAC), thiobarbituric acid reactive substances (TBARS) and protein carbonyls (CARBS)] were measured. The results showed a disturbance in the redox balance in favor of free radicals in tobacco flavored e-liquids while vanilla flavored e-liquids exhibited a more complex profile depending on the nicotine content. The most interesting finding of the present study concerns the apple/mint flavored e-liquids that seemed to activate the cellular antioxidant defense and, thus, to protect the cells from the adverse effects of free radicals. Conclusively, it appears that the flavorings and not the nicotine content play a key role in the oxidative stress-induced toxicity of the e-liquids.

3D Bioprinted Osteogenic Tissue Models for In Vitro Drug Screening

Metabolic bone disease affects hundreds of millions of people worldwide, and as a result, in vitro models of bone tissue have become essential tools to help analyze bone pathogenesis, develop drug screening, and test potential therapeutic strategies. Drugs that either promote or impair bone formation are in high demand for the treatment of metabolic bone diseases. These drugs work by targeting numerous signaling pathways responsible for regulating osteogenesis such as Hedgehog, Wnt/β-catenin, and PI3K-AKT. In this study, differentiated bone marrow-derived mesenchymal stem cell (BM-MSC) scaffold-free 3D bioprinted constructs and 2D monolayer cultures were utilized to screen four drugs predicted to either promote (Icariin and Purmorphamine) or impair osteogenesis (PD98059 and U0126). Osteogenic differentiation capacity was analyzed over a four week culture period by evaluating mineralization, alkaline phosphatase (ALP) activity, and osteogenesis related gene expression. Responses to drug treatment were observed in both 3D differentiated constructs and 2D monolayer cultures. After four weeks in culture, 3D differentiated constructs and 2D monolayer cultures treated with Icariin or Purmorphamine showed increased mineralization, ALP activity, and the gene expression of bone formation markers (BGLAP, SSP1, and COL1A1), signaling molecules (MAPK1, WNT1, and AKT1), and transcription factors (RUNX2 and GLI1) that regulate osteogenic differentiation relative to untreated. 3D differentiated constructs and 2D monolayer cultures treated with PD98059 or U0126 showed decreased mineralization, ALP activity, and the expression of the aforementioned genes BGLAP, SPP1, COL1A1, MAPK1, AKT1, RUNX2, and GLI1 relative to untreated. Differences in ALP activity and osteogenesis related gene expression relative to untreated cells cultured in a 2D monolayer were greater in 3D constructs compared to 2D monolayer cultures. These findings suggest that our bioprinted bone model system offers a more sensitive, biologically relevant drug screening platform than traditional 2D monolayer in vitro testing platforms.

The Impact of "Vaping" Electronic Cigarettes on Spine Health

“Vaping” or the use of electronic cigarettes (e-cigarettes) has greatly increased within the past decade, with growing popularity among adolescents. E-cigarettes have many harmful effects on multiple organ systems, but more research is needed to fully understand the extent of possible risks. Our narrative literature review aims to provide comprehensive insight into the impact of e-cigarette use on spinal health with a specific focus on intervertebral disc (IVD) health, bone health, and spinal fusion. There are many metallic compounds and chemical flavoring additives within e-cigarette liquids that are associated with human toxicity. These chemical toxins have been linked to increased oxidative stress leading to systemic inflammation. E-cigarette carcinogens have shown to have a toxic effect on osteoblast cells, and long-term use may decrease bone mineral density and increase the future risk for osteoporosis. Additionally, nicotine in e-liquids negatively impacts IVD health by creating hypoxic environments that degenerate the IVD vasculature and cellular matrix. While studies have demonstrated the inhibitory effects of nicotine use on spinal fusions in animal models, the impact of e-cigarette use on spinal fusion operations in human patients is currently lacking. Future research should focus on the influence of e-cigarette use on spinal health, particularly in adolescents with long-term follow-up, as childhood is a critical time for bone growth and development. Additionally, studies exploring the effects of e-cigarettes on spinal surgery outcomes, such as spinal fusions, are sparse in the literature. Further prospective research studies with a focus on the variety of e-cigarette chemical toxins and flavoring agents is needed to assess the impact on spinal health.

Cytotoxic and genotoxic effects of e-liquids and their potential associations with nicotine, menthol and phthalate esters

In this study, we determined DNA damage and chromosome breakage (indicators of genotoxicity) and cell viability (an indicator of cytotoxicity) in human lymphoblastoid TK6 and Chinese hamster ovary (CHO) cells treated with 33 e-liquids using in vitro single cell gel (comet), micronucleus (MN), and trypan blue assays, respectively. We also measured the contents of nicotine, five phthalate esters, and DL-menthol in the e-liquids to examine their effects on DNA damage, chromosome breakage, and cell viability. Our chemical analyses showed that: (1) six e-liquids had nicotine ≥2-fold higher than the manufacture's label claim (2-3.5 mg); (2) both dimethyl- and dibutyl-phthalate levels were >0.1 μg/g, i.e., their threshold limits as additives in cosmetics; and (3) the DL-menthol contents ranged from 0.0003 to 85757.2 μg/g, with those of two e-liquids being >1 mg/g, the threshold limit for trigging sensory irritation. Though all the e-liquids induced DNA damage in TK6 cells, 20 resulted in cell viabilities ≤75%, indicating cytotoxicity, yet the inverse relationship between cell viability and DNA damage (r = -0.628, p = 0.003) might reflect their role as pro-apoptotic and DNA damage inducers. Fifteen e-liquids induced MN% in TK6 cells ≥3-fold that of untreated cells. Some of the increase in %MN might be false due to high cytotoxicity, yet six brands showed acceptable cell viabilities (59-71%), indicating chromosome damage. DNA damage and %MN increased when the TK6 cells were exposed to metabolic activation. The CHO cells were less sensitive to the genotoxic effects of the e-liquids than the TK6 cells. DL-menthol was found to be associated with decreased cell viability and increased DNA damage, even at low levels. We cannot dismiss the presence of other ingredients in e-liquids with cytotoxic/genotoxic properties since out of the 63 different flavors, 47 induced DNA damage (≥3-folds), and 26 reduced cell viability (≤75%) in TK6 cells.

Harmful chemicals emitted from electronic cigarettes and potential deleterious effects in the oral cavity

Use of electronic nicotine delivery systems (ENDS), such as electronic cigarettes (e-cigs), is increasing across the US population and is particularly troubling due to their adoption by adolescents, teens, and young adults. The industry’s marketing approach for these instruments of addiction has been to promote them as a safer alternative to tobacco, a behavioral choice supporting smoking cessation, and as the ‘cool’ appearance of vaping with flavored products (e.g. tutti frutti, bubble gum, and buttered popcorn etc.). Thus, there is a clear need to better document the health outcomes of e-cig use in the oral cavity of the addicted chronic user. There appears to be an array of environmental toxins in the vapors, including reactive aldehydes and carbonyls resulting from the heating elements action on fluid components, as well as from the composition of chemical flavoring agents. The chemistry of these systems shows that the released vapors from the e-cigs frequently contain levels of environmental toxins that considerably exceed federal occupational exposure limits. Additionally, the toxicants in the vapors appear to be retained in the host fluids/tissues at levels often approximating 90% of the levels in the e-cig vapors. These water-soluble reactive toxins can challenge the oral cavity constituents, potentially contributing to alterations in the autochthonous microbiome and host cells critical for maintaining oral homeostasis. This review updates the existing chemistry/environmental aspects of e-cigs, as well as providing an overview of the somewhat limited data on potential oral health effects that could occur across the lifetime of daily e-cig users.

E-vapor aerosols do not compromise bone integrity relative to cigarette smoke after 6-month inhalation in an ApoE-/- mouse model

Cigarette smoke (CS) exposure is one of the leading risk factors for human health. Nicotine-containing inhalable products, such as e-cigarettes, can effectively support tobacco harm reduction approaches. However, there are limited comparative data on the effects of the aerosols generated from electronic vapor products (e-vapor) and CS on bone. Here, we report the effects of e-vapor aerosols and CS on bone morphology, structure, and strength in a 6-month inhalation study. Eight-week-old ApoE^-/- mice were exposed to aerosols from three different e-vapor formulations-CARRIER (propylene glycol and vegetable glycerol), BASE (CARRIER and nicotine), TEST (BASE and flavor)-to CS from 3R4F reference cigarettes at matched nicotine concentrations (35 µg/L) or to fresh air (Sham) (N = 10 per group). Tibiae were analyzed for bone morphology by µCT imaging, biomechanics by three-point bending, and by histological analysis. CS inhalation caused a significant decrease in cortical and total bone volume fraction and bone density relative to e-vapor aerosols. Additionally, CS exposure caused a decrease in ultimate load and stiffness. In contrast, bone structural and biomechanical parameters were not significantly affected by e-vapor aerosol or Sham exposure. At the dissection time point, there was no significant difference in body weight or tibia bone weight or length among the groups. Histological findings revealed microcracks in cortical bone areas among all exposed groups compared to Sham control. In conclusion, because of the bone-preserving effect of e-vapor aerosols relative to CS exposure, e-vapor products could potentially constitute less harmful alternatives to cigarettes in situations in which bone health is of importance.

Neurotoxicity of e-cigarettes

It appears that electronic cigarettes (EC) are a less harmful alternative to conventional cigarette (CC) smoking, as they generate substantially lower levels of harmful carcinogens and other toxic compounds. Thus, switching from CC to EC may be beneficial for smokers. However, recent accounts of EC- or vaping-associated lung injury (EVALI) has raised concerns regarding their adverse health effects. Additionally, the increasing popularity of EC among vulnerable populations, such as adolescents and pregnant women, calls for further EC safety evaluation. In this state-of-the-art review, we provide an update on recent findings regarding the neurological effects induced by EC exposure. Moreover, we discuss possible neurotoxic effects of nicotine and numerous other chemicals which are inherent both to e-liquids and EC aerosols. We conclude that in recognizing pertinent issues associated with EC usage, both government and scientific researchers must address this public health issue with utmost urgency.

The Evolving Landscape of e-Cigarettes: A Systematic Review of Recent Evidence

Smoking continues to be a burden to economies and health-care systems across the world. One proposed solution to the problem has been e-cigarettes; however, because they are a relatively new product in the market, little is known about their potential health impacts. Furthermore, e-cigarettes continue to evolve at a rapid rate, making it necessary to regularly review and summarize available studies. Although e-cigarettes are marketed as a smoking cessation tool by some manufacturers, the reality is that many nonsmokers, including youth, are using them. This review focuses on two major demographic groups (smokers and nonsmokers) and evaluates the most recent data (early 2017 to mid 2019) regarding the potential health effects of e-cigarettes. We assessed peer-reviewed studies on the health impacts of e-cigarettes, with a particular focus on common questions asked by policy makers, clinicians, and scientists: (1) What are the effects of e-cigarettes compared with air/not smoking?; (2) Is there any direct evidence of harm or benefit to humans?; (3) Is there a risk from secondhand exposure?; (4) What are the risks and/or benefits of e-cigarettes compared with tobacco cigarette use?; (5) Are there risks or benefits to specific populations (eg, people with COPD or asthma, pregnant women [and their offspring])?; (6) What are the effects of flavoring chemicals?; (7) What are the effects of including nicotine in e-liquids?; (8) How often is nicotine concentration labeling incorrect?; and (9) What are the risks when e-cigarettes explode?

A Summary of In Vitro and In Vivo Studies Evaluating the Impact of E-Cigarette Exposure on Living Organisms and the Environment

Worldwide use of electronic cigarettes has been rapidly expanding over recent years, but the long-term effect of e-cigarette vapor exposure on human health and environment is not well established; however, its mechanism of action entails the production of reactive oxygen species and trace metals, and the exacerbation of inflammation, which are associated with potential cytotoxicity and genotoxicity. The present study examines the effects of selected liquid chemicals used in e-cigarettes, such as propylene glycol/vegetable glycerin, nicotine and flavorings, on living organisms; the data collected indicates that exposure to e-cigarette liquid has potentially detrimental effects on cells in vitro, and on animals and humans in vivo. While e-liquid exposure can adversely influence the physiology of living organisms, vaping is recommended as an alternative for tobacco smoking. The study also compares the impact of e-cigarette liquid exposure and traditional cigarette smoke on organisms and the environmental impact. The environmental influence of e-cigarette use is closely connected with the emission of airborne particulate matter, suggesting the possibility of passive smoking. The obtained data provides an insight into the impact of nicotine delivery systems on living organisms and the environment.

Cinnamon-flavored electronic cigarette liquids and aerosols induce oxidative stress in human osteoblast-like MG-63 cells

As noncombustible nicotine delivery devices, electronic cigarettes (e-cigarettes) are the most popular tobacco product among youth. The widespread popularity of e-cigarettes combined with possible health consequences suggest a need to further research health hazards associated with e-cigarette use. Since conventional tobacco use is a risk factor for osteoporosis, this study investigates the impact of nicotine-free, cinnamon-flavored e-cigarette liquid (e-liquid) on bone-forming osteoblasts compared to flavorless e-liquid. Human tumor-derived osteoblast-like MG-63 cells were exposed for 24 h or 48 h to 0.0.4 %, 0.04 %, 0.4 % or 1 % of unvaped e-liquid or 0.0025 %, 0.025 %, 0.25 %, 1 % or 2.5 % of aerosol condensate in addition to a culture medium only control. Changes in cell viability were assessed by MTT assay, and the expression of a key bone protein, collagen type I, was analyzed by immunofluorescence. Production of reactive oxygen species (ROS) was detected by fluorometry to assess oxidative stress. Cell viability decreased in a dose-dependent manner, and ROS production increased, which was most pronounced with cinnamon-flavored e-liquids. There were no detectable changes in collagen type I protein following exposure to any of the aerosol condensates. This study demonstrates osteoblast-like cells are sensitive to both e-liquids and aerosol condensates and suggests the cytotoxicity of cinnamon-flavored e-liquids might be associated with oxidative stress rather than changes in collagen type I protein expression. This in vitro study provides insight into the potential impacts of e-cigarette use on bone cells.