Effects of E-Cigarette Aerosol Extracts on Human Neutrophil Viability and Inflammatory Responses to Streptococcus mutans

Background/Objective: The increasing use of electronic cigarettes (e-cigarettes) has raised concerns about their possible effects on oral immune responses. Neutrophils are essential for host defense against cariogenic bacteria such as Streptococcus mutans (S. mutans), and impaired neutrophil function may facilitate the progression of oral diseases. This study aims to investigate whether exposure to vaping aerosols alters neutrophil viability, oxidative responses, and proinflammatory cytokine production in response to the cariogenic bacterium S. mutans. Methods: Human neutrophils isolated from healthy donors were exposed to e-cigarette aerosol extracts produced from flavored and unflavored e-liquids, with and without nicotine. Cytotoxicity was determined by measuring lactate dehydrogenase (LDH) release. Intracellular reactive oxygen species (ROS) generation following S. mutans exposure was used as an indirect measure of neutrophil phagocytic activity. Pro-inflammatory cytokines (interleukin-1 beta (IL-1β) and interleukin-8 (IL-8)) were measured using an enzyme-linked immunosorbent assay (ELISA). Results: Under the tested conditions, e-cigarette aerosol extracts did not cause significant cytotoxicity. However, in neutrophils stimulated with S. mutans, certain flavorings (particularly tobacco and dessert-related flavors) significantly reduced ROS generation, suggesting impaired antimicrobial responses. In contrast, fruit and mint flavors had little impact. Minor flavor-dependent differences were observed for IL-1β and IL-8. The presence of nicotine did not significantly affect the levels of these cytokines. Conclusions: Aerosol extracts from e-cigarettes altered neutrophil oxidative responses in a flavor-dependent manner but did not cause significant cytotoxicity. These findings suggest mild immunological modulation rather than a direct inflammation effect and indicate that e-cigarette aerosols may alter antimicrobial responses despite having minimal effects on IL-1β and IL-8.