Cell invasion, RAGE expression, and inflammation in oral squamous cell carcinoma (OSCC) cells exposed to e-cigarette flavoring

The Toxicological Effects of e-Cigarette Use in the Upper Airway: A Scoping Review

OBJECTIVE

While evidence continues to emerge on the negative health effects of electronic cigarettes (e-cigarettes) on the lungs, little is known regarding their deleterious effects on the upper airway. The purpose of this review is to summarize the toxicological effects of e-cigarettes, and their components, on the upper airway.

DATA SOURCES

PubMed, SCOPUS, EMBASE databases.

REVIEW METHODS

Systematic searches were performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines from 2003 to 2023. Studies were included if they investigated the toxicological effects of e-cigarette exposure on human or animal upper airway tissue. Two authors independently screened, reviewed, and appraised all included articles.

RESULTS

A total of 822 unique articles were identified, of which 53 met inclusion criteria and spanned subsites including the oral cavity (22/53 studies), nasal cavity/nasopharynx (13/53), multiple sites (10/53), larynx (5/53), trachea (2/53), and oropharynx (1/53). The most commonly observed consequences of e-cigarette use on the upper airway included: proinflammatory (15/53 studies), histological (13/53), cytotoxicity (11/53), genotoxicity (11/53), and procarcinogenic (6/53). E-cigarette humectants independently induced toxicity at multiple upper airway subsites, however, effects were generally amplified when flavoring(s) and/or nicotine were added. Across almost all studies, exposure to cigarette smoke exhibited increased toxicity in the upper airway compared with exposure to e-cigarette vapor.

CONCLUSION

Current data suggest that while e-cigarettes are generally less harmful than traditional cigarettes, they possess a distinct toxicological profile that is enhanced upon the addition of flavoring(s) and/or nicotine. Future investigations into underexamined subsites, such as the oropharynx and hypopharynx, are needed to comprehensively understand the effects of e-cigarettes on the upper airway.

Impact of Electronic Cigarettes on the Upper Aerodigestive Tract: A Comprehensive Review for Otolaryngology Providers

Objective

The use and effects of electronic (e)-cigarettes (e-cigs) are particularly relevant for otolaryngology providers as tobacco plays a major role in benign and malignant diseases of the upper aerodigestive tract. This review aims to (1) summarize the recent policies regarding e-cigs and important patterns of use and (2) serve as a comprehensive resource for clinical providers on the known biologic and clinical effects of e-cigs on the upper aerodigestive tract.

Data Sources

PubMed/MEDLINE.

Review Methods

We conducted a narrative review on (1) general information on e-cig use and informative findings in the lower respiratory system and a comprehensive review on (2) the effects of e-cigs on cell and animal models and the clinical implications of these products on human health as is relevant to otolaryngology.

Conclusions

Although e-cigs are likely less harmful than conventional cigarettes, preliminary research on e-cigs suggest several deleterious effects including in the upper aerodigestive tract. Due to this, there has been increased interest in restricting e-cig usage, particularly among the adolescent population, and caution in recommending e-cigs to current smokers.

Implications for Practice

Chronic e-cig use is likely to have clinical implications. It is critical for otolaryngology providers to be aware of the rapidly changing regulations and use patterns regarding e-cigs and how e-cigs influence human health, particularly with regards to the upper aerodigestive tract, to accurately council patients regarding potential risks and benefits of use.

Inflammation and Invasion in Oral Squamous Cell Carcinoma Cells Exposed to Electronic Cigarette Vapor Extract

Electronic cigarettes (eCig) represent a new avenue of tobacco exposure that involves heating oil-based liquids and the delivery of aerosolized flavors with or without nicotine, yet little is known about their overall health impact. The oral cavity is an anatomic gateway for exposure that can be compromised by activating myriad of signaling networks. Oral squamous cell carcinoma (OSSC) is a common malignancy affecting 30,000 people in the United States each year. Our objective was to determine the impact of eCig and nicotine on gingival OSSC invasion and their secretion of pro-inflammatory molecules. Gingiva-derived Ca9-22 cells and tongue-derived Cal27 cells were exposed to eCig vapor extract (EVE) generated from Red Hot or Green Apple (Apple) flavored eCig solution +/- nicotine for 6 hours. Isolation of protein lysates and collection conditioned media was done after treatment. Real-time cellular invasion was assessed using a RTCA DP instrument. Protein expression was determined using western blot. Compared to controls, we observed: elevated NF-kB, TNF-α, ERK, JNK, MMP-13 and cell invasion by Ca9-22 treated with Apple EVE; increased TNF-α and JNK by Ca9-22 treated with Red Hot EVE; and increased TNF-α and JNK by Cal27 cells treated with both Apple and Red Hot EVE. We conclude that eCig flavoring and nicotine orchestrated differential cell invasion and inflammatory effects. This study provides an important initial step in dissecting mechanisms of cancerous invasion and molecular avenues employed by OSCC.

The anti-tumor effects of evodiamine on oral squamous cell carcinoma (OSCC) through regulating advanced glycation end products (AGE) / receptor for advanced glycation end products (RAGE) pathway

Evodiamine (EVO) is emerging as a novel anti-tumor drug, which is involved in the inhibition of cell proliferation and apoptosis. High-Mobility Group Box 1 (HMGB1)/RAGE is involved in invasive behavior of OSCC cells and angiogenesis. In this study, we evaluated the potential of EVO in OSCC in vitro and in vivo. We found that RAGE silencing suppressed HSC-4 cell proliferation and invasion, and tube formation of HUVEC. EVO showed marked inhibitory effects on the malignant behaviors of HSC-4 cells in a dose-dependent manner. Further experiments revealed that the RAGE overexpression was able to markedly block the effects of EVO on cell proliferation and invasion, and tube formation. By analyzing the expression of High-Mobility Group Box 1 (HMGB1) and RAGE in HSC-4 cells, the result showed that EVO slightly reduced HMBG1 levels and dramatically decreased RAGE levels, while RAGE overexpression did have no marked influences on HMBG1 levels. The anti-tumor effects of EVO were further confirmed in mouse oral squamous cell carcinoma xenograft models. Remarkable anti-tumor effects of EVO were also demonstrated, as presented by reduced tumor size and levels of HMBG1 and RAGE in tumor tissue of mouse oral squamous cell carcinoma xenograft models. The results demonstrated that EVO has a direct binding effect on HMGB1, but it may be involved in degrading the protein. More importantly, it can reduce the activity of RAGE pathway by affecting the binding between HMBG1 and RAGE. To conclude, EVO inhibited proliferation, invasion and angiogenesis of OSCC through affecting the downstream signal transduction system of AGE/RAGE by targeting RAGE.

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.

Cell invasion, RAGE expression, and inflammation in oral squamous cell carcinoma (OSCC) cells exposed to e-cigarette flavoring

Objective

Electronic cigarettes have given rise to a new, largely unregulated market within the smoking industry. While generally supposed to be less harmful than traditional tobacco smoke, awareness of the biological effects of electronic cigarette liquid is still scarce. Our objective was to determine the impact of electronic cigarette flavoring and nicotine on gingival squamous cell carcinoma invasion, RAGE expression, and the elaboration of pro‐inflammatory molecules.

Methods and Materials

Gingival and tongue squamous cell carcinoma cells were exposed to Red Hot or Green Apple flavored electronic cigarette flavoring with or without nicotine. Immunofluorescence determined RAGE expression. Real‐time cellular invasion was assessed using a RTCA DP instrument. Culture medium was assayed for cytokine secretion.

Results

Compared to controls we observed: increased cell invasion in gingival cells with Red Hot electronic cigarette flavoring and decreased cell invasion with Green Apple; decreased cell invasion in tongue cells treated with Red Hot electronic cigarette flavoring and no differences in invasion with Green Apple; flavor and nicotine dependent increases in RAGE expression; and differential expression of IL‐1α, IL‐8, and MMP‐13.

Conclusion

We conclude that electronic cigarette flavoring and nicotine orchestrate differential regulation of oral squamous cell carcinoma (OSCC) cell invasion and inflammatory effects. This study provides an important initial step in dissecting RAGE‐mediated mechanisms of cancerous invasion and molecular avenues employed by OSCC.