Inhalation exposure to heat-not-burn tobacco aerosol versus combustible cigarette smoke: comparative assessment of respiratory and systemic toxicity in an experimental rat model

Objective: Heat-not-burn tobacco products (IQOS) have emerged as potentially reduced-risk alternatives to combustible cigarettes (CSs), yet their inhalation toxicity profile remains incompletely characterized. Materials and Methods: This study evaluated the comparative respiratory and systemic effects of IQOS aerosol vs. CS smoke through whole-body inhalation exposure in an experimental rat model. Twenty-one male Wistar albino rats (8–10 weeks, 250–300 g) were randomly assigned to three groups (n = 7): control (ambient air), CS exposure (10 mg nicotine/day, ∼6 cigarettes/session), and IQOS exposure (equivalent nicotine dose, ∼8 HeatSticks/session). A custom-designed whole-body inhalation exposure system, developed in collaboration with Istanbul Technical University, delivered standardized aerosols following Health Canada Intense puffing parameters (55 mL puff volume, 27.5 mL/s flow rate, 2-s puff duration, 30-s inter-puff interval) during daily 1.5-h sessions over 21 consecutive days. Peripheral blood samples were collected on Days 7, 14, and 21 for assessment of plasma inflammatory markers (IL-1β, IL-6, TNF-α, and hs-CRP), oxidative stress parameters (total oxidant status [TOS], total antioxidant status, oxidative stress index), and DNA damage in isolated mononuclear leukocytes using the alkaline comet assay. Plasma cotinine was quantified as the primary biomarker of systemic nicotine absorption. Terminal lung tissue analysis on Day 21 evaluated local respiratory oxidative stress, inflammatory cytokine concentrations, and tissue cotinine deposition. Results: Plasma TOS increased progressively in both exposure groups (CS: 9.2 ± 1.82 to 14.71 ± 1.65 µmol H2O2 Eq/L; IQOS: 6.81 ± 1.25 to 11.49 ± 1.30 µmol H2O2 Eq/L), with CS demonstrating significantly higher oxidative burden. DNA damage in circulating cells escalated markedly (CS: 21.74 ± 2.51% to 47.76 ± 3.67% tail DNA; IQOS: 16.22 ± 1.87% to 33.44 ± 2.41% tail DNA). Lung tissue analysis revealed significant ‘elevation of inflammatory markers and oxidative stress parameters’ in both exposure groups. While IQOS inhalation induced less severe toxicity than CS smoke, it produced significant respiratory and systemic adverse effects including oxidative stress, inflammatory responses, and DNA damage. Discussion and Conclusion: These findings challenge claims of substantially reduced harm for heat-not-burn products and support continued regulatory oversight of inhaled tobacco delivery systems.