Can switching from cigarettes to heated tobacco products reduce consequences of pulmonary infection?

Abstract

Rationale: While tobacco industry data suggests that switching from combustible cigarettes to heated tobacco products (HTPs), like IQOS, may reduce the users' exposure to respiratory toxicants, it is not known if using HTPs impacts the outcomes of acute respiratory infections.

Objectives: Does switching from cigarettes to HTPs improve responses to pulmonary infection.

Methods: We conducted experiments in which 3 groups of mice were pre-exposed to cigarette smoke for 8 weeks, followed by 8-week exposure to (1) HTPs (tobacco product switching), (2) air (smoking cessation), or (3) continued exposure to cigarette smoke. Pulmonary bacterial clearance and surrogate markers of lung damage were assessed as study outcomes.

Main results: Significantly compromised clearance of bacteria from the lungs post-acute challenge occurred in both the switching group and in mice continuously exposed to cigarette smoke. Bacterial clearance, inflammatory T-cell infiltration into the lungs, and albumin leak improved at 12 h post-acute challenge in the switching group compared to mice continuously exposed to cigarette smoke. Bacterial clearance, total lung immune-cell infiltration, inflammatory T-cell infiltration into the lungs, the content of total proteins in the BAL, and albumin leak measured post-acute challenge were compromised in the switching group compared to mice in the cessation group. Switching from cigarettes to HTPs did not improve lung myeloperoxidase and neutrophil elastase levels (markers for lung inflammation and damage), which, however, were significantly reduced in the cessation group.

Conclusions: This study reveals only a modest improvement in respiratory infection outcomes after switching exposure from cigarettes to HTPs and significantly compromised outcomes compared to a complete cessation of exposure to all tobacco products.

Keywords: Combustible cigarettes; Heated tobacco products (HTPs); IQOS; NTHI; Respiratory infection; Smoking cessation; Tobacco product switching.

Fig. 1

Schema of exposures. The figure depicts the schema of exposures in animals to various aerosols in the study

Fig. 2

Lung-endothelial damage induced at the end of inhalation exposure. At the end of exposures, intratracheal instillations of FITC-dextran were given to mice and the levels of FITC-dextran leaking into plasma were quantified one hour later to measure the extent of lung-endothelial damage as described in detail in methods. Panel A represents data from males + females combined, while panel B represents data as males versus females. Difference between two groups is considered significant at p < 0.05 and statistical significance of the difference between two groups is indicated with symbols **p < 0.01; ***p < 0.001; ****p < 0.0001 after performing non-parametric Kruskal-Wallis test with false discovery rate (FDR) correction for multiple comparisons by GraphPad Prism V.9 software (GraphPad; La Jolla, CA, USA). In each experiment 10 males and 10 females per exposure group were used. Results are depicted as mean ± SE

Fig. 3

NTHI clearance from the lungs. Two days after exposures ended, all animals were challenged by intratracheal instillation of 1 million colony forming units of NTHI and euthanized at 0, 4, and 12 h after challenge. Lungs were harvested, tissue homogenates prepared, and various dilutions of the homogenate plated onto chocolate agar plates to grow and count NTHI colony forming units as described in detail in the supplemental methods. Data are presented as %NTHI clearance as a measure of lung bacterial burden. Difference between two groups was considered significant at p < 0.05 using Kruskal-Wallis test corrected for multiple comparisons by controlling the False Discovery Rate using Two-stage linear step-up procedure of Benjamini, Krieger and Yekuieli post-test by GraphPad Prism V.9 software (GraphPad; La Jolla, California, USA). Desired FDR was adjusted at Q = 0.1. * Statistically significant difference from continued exposure to cigarettes (blue). # Statistically significant difference from cessation (green). Numbers of mice used for: continued exposure to CS group (n = 8 mice at 0, n = 8 mice at 4 h and n = 6 mice at 12 h timepoint); for switching to HTP group (n = 12 mice at each 0, 4 and 12 h timepoints), and for cessation group (n = 10 mice at 0 h, n = 8 mice at 4 h and n = 6 mice at 12 h timepoint). Results are depicted as mean ± SE

Fig. 4

Impact of exposures on pulmonary immune-cell infiltration. Total number of leucocytes (A), CD11b⁺Ly6G⁺ neutrophils (B), CD11b⁺CD68⁺ macrophages (C), CD4⁺IL17A⁺ T-cells (D) and CD4⁺RORγt⁺ inflammatory T-cells (E) in the lungs of exposed-mice infected with NTHI for 0, 4, and 12 h were determined by flow cytometry using specific markers and following a gating strategy as described previously (9, 22, 19) and shown in supplemental figure E1. Difference between two groups is considered significant at p < 0.05 using the Kruskal-Wallis test corrected for multiple comparisons by controlling the False Discovery Rate using Two-stage linear step-up procedure of Benjamini, Krieger and Yekuieli post-test. Desired FDR was adjusted at Q = 0.1. * Statistically significant difference from continued exposure to cigarettes (blue). # Statistically significant difference from cessation (green). * Statistically significant difference from continued exposure to cigarettes (blue). # Statistically significant difference from cessation (green). Numbers of mice used for: continued exposure to CS group (n = 8 mice at 0, n = 11 mice at 4 h and n = 8 mice at 12 h timepoint); for switching to HTP group (n = 12 mice at each 0, 4 and 12 h timepoints), and for cessation group (n = 10 mice at 0 h, n = 12 mice at 4 h and n = 8 mice at 12 h timepoint). Results are depicted as mean ± SE

Fig. 5

Markers of lung epithelial damage induced after inhalation exposure were quantified. Levels of (A) total proteins and (B) albumin in the BAL of exposed-mice infected with NTHI for 0, 4, and 12 h were quantified as described in the Materials and Methods section. Difference between groups is considered significant at p < 0.05 using the Kruskal-Wallis test corrected for multiple comparisons by controlling the False Discovery Rate using Two-stage linear step-up procedure of Benjamini, Krieger and Yekuieli post-test. Desired FDR was adjusted at Q = 0.1. * Statistically significant difference from continued exposure to cigarettes (blue). # Statistically significant difference from cessation (green). * Statistically significant difference from continued exposure to cigarettes (blue). # Statistically significant difference from cessation (green). Numbers of mice used for: continued exposure to CS group (n = 8 mice at 0, n = 11 mice at 4 h and n = 8 mice at 12 h timepoint); for switching to HTP group (n = 12 mice at each 0, 4 and 12 h timepoints), and for cessation group (n = 10 mice at 0 h, n = 12 mice at 4 h and n = 8 mice at 12 h timepoint). Results are depicted as mean ± SE

Fig. 6

Measurement of MPO activity and NE levels in lung lysates prepared from the lungs of exposed-mice infected with NTHI for 0, 4, and 12 h. Switching from cigarettes to HTP did not modulate MPO activity whereas cessation was beneficial (A) and switching augmented lung NE levels (B). Difference between groups is considered significant at p < 0.05 using the Kruskal-Wallis test corrected for multiple comparisons by controlling the False Discovery Rate using Two-stage linear step-up procedure of Benjamini, Krieger and Yekuieli post-test. Desired FDR was adjusted at Q = 0.1. *Statistically significant difference from continued exposure to cigarettes (blue). # Statistically significant difference from cessation (green). Numbers of mice used for MPO assay: continued exposure to CS group (n = 8 mice at 0, n = 8 mice at 4 h and n = 7 mice at 12 h timepoint); for switching to HTP group (n = 8 mice at each 0, 4 and 12 h timepoints), and for cessation group (n = 8 mice at each 0, 4 and 12 h timepoints). Numbers of mice used for NE assay: continued exposure to CS group (n = 8 mice at 0, n = 10 mice at 4 h and n = 8 mice at 12 h timepoint); for switching to HTP group (n = 10 mice at each 0, 4 and 12 h timepoints), and for cessation group (n = 8 mice at 0, n = 10 mice at 4 h and n = 8 mice at 12 h timepoint). Results are depicted as mean ± SE