Investigating the Impact of Environmental Exposures on Oral Cancer Development: A Focus on E-Cigarette Use as a Risk Factor

Abstract

Oral squamous cell carcinoma (OSCC) represents a major global health concern, with rising incidence partly attributed to emerging lifestyle and environmental exposures. Among these, electronic cigarettes (e-cigarettes) have gained widespread popularity, particularly among youth, despite limited understanding of their long-term health consequences. This dissertation investigates the impact of e-cigarette exposure on oral carcinogenesis, with emphasis on epidemiological, cytotoxic, immunological, and phenotypic changes in oral epithelial cells. A comprehensive literature review outlines the histological structure of the oral mucosa and highlights key risk factors for OSCC, including tobacco, alcohol, betel quid, infectious agents, and socioeconomic determinants. Special emphasis is placed on the evolving regulatory landscape of e-cigarettes and their chemical composition, which includes nicotine, aldehydes, volatile organic compounds, and heavy metals substances capable of inducing oxidative stress, inflammation, and DNA damage. A scoping review was conducted to synthesise findings from in vitro and in vivo studies evaluating the biological effects of e-cigarette. Common findings included increased epithelial cell apoptosis, disruption of microbial balance, and upregulation of inflammatory cytokines such as IL-6 and IL-8. To further investigate these effects, lab-based experiments were performed using immortalised human oral keratinocytes (OKF6), following initial optimisation work with primary oral keratinocytes (SLC002). Exposure to e-liquids was assessed through assays including cell viability, colony formation, flow cytometry, and immunofluorescence staining. Flow cytometry analysis revealed that OKF6 cells retained a predominantly epithelial phenotype following 48-hour exposure to 1% e-liquid, with or without nicotine, and did not show a significant increase in mesenchymal or transitional markers. In conclusion, the scoping review confirmed biological and epidemiological evidence of risks associated with e-cigarette exposure, while lab-based experiments demonstrated cytotoxic and morphological changes without significant induction of EMT. These findings suggest early cellular stress responses but no evidence of malignant transformation under the tested conditions, highlighting the need for long-term studies to assess oral cancer risk.