Comparative oxidative and inflammatory responses to heated tobacco aerosol and cigarette smoke extracts in human lung fibroblasts

Introduction Combustible cigarette smoke induces oxidative stress and inflammation in lung cells. Heated tobacco products (HTPs) have been proposed as alternatives with reduced toxicant emissions, but their cellular effects remain incompletely characterized. Methods MRC-5 human lung fibroblasts were exposed to aqueous cigarette smoke extract (CSE; 0.1–1.0 puffs/mL) or heated tobacco aerosol extract (HTE; 1.5–5.5 puffs/mL for viability, 3.0–5.5 puffs/mL for other endpoints). Concentrations were anchored to each product’s 24 h IC 50 (CSE 0.70 puffs/mL, 95% CI 0.63–0.77; HTE 4.76 puffs/mL, 95% CI 4.39–5.16). Cytotoxicity, oxidation-sensitive dihydroethidium (DHE) fluorescence, intracellular TNF-α and IL-6, and morphology were assessed. ATG5 protein was included as an exploratory endpoint. Results Both extracts increased DHE fluorescence and intracellular TNF-α and IL-6 in a concentration-dependent manner, with reduced viability and morphological changes. ATG5 findings were inconclusive, as no concentration differed from the untreated control. Nominal puff concentrations were not considered equivalent doses. In an exploratory comparison near each product’s 24 h IC 50 (CSE 0.7 and HTE 4.75 puffs/mL), CSE produced greater DHE fluorescence (3.17- versus 2.31-fold over vehicle) and greater intracellular IL-6 and TNF-α signals than HTE. Equivalent viability at the 90 min and 4 h endpoints was not established. Discussion Under these study-specific conditions, HTE elicited quantitatively smaller oxidative and inflammatory responses than CSE at the selected comparison concentrations.