3-Week Inhalation Exposure to Cigarette Smoke and/or Lipopolysaccharide in AKR/J Mice

Abstract

AKR/J mice were exposed to cigarette smoke (CS) and/or lipopolysaccharide (LPS) via inhalation for 3 wk and pulmonary responses were evaluated. The objective was to explore the feasibility of coexposing LPS with cigarette smoke under a subacute exposure, as a surrogate for viral or bacterial insults, that would mimic the pathogenesis of infection-related chronic obstructive pulmonary disease (COPD) exacerbations. The study was the first step in an effort to develop a rodent COPD model in which morphologic lesions of COPD develop in a shorter period of exposure and more closely simulate human COPD. Mice were exposed 6 h/day, 5 days/wk for 3 wk to one of the following: (1) sham control: filtered air; (2) CS: 250 μg/L wet total particulate matter (WTPM) for 5 h/day followed by 1 h/day air; (3) LPS: 0.5 μg/L LPS (055:B5 Escherichia coli; 3,000,000 EU/mg) for the last 1 h/day 2 day/wk (following 5 h/day of filtered air); and (4) CS/LPS: CS 5 h/day followed by air or LPS (2 days/wk) for 1 h/day. After the last exposure, animals were necropsied and subjected to bronchoalveolar lavage (BAL) or histopathology. The BAL neutrophil counts were highest in the LPS group, while macrophage counts were higher in the CS/LPS group than other exposed groups. The LPS group displayed the greatest increases in BAL cytokines, while KC (keratinocyte-derived chemokine) and TARC (thymus and activation-regulated chemokine) were highest in the CS group. The CS/LPS group had generally lower cytokine levels relative to the LPS or CS groups, except for the levels of RANTES and G-CSF (granulocyte-colony stimulating factor) comparable to the LPS group. At microscopic examination of lung sections, celluar inflammatory infiltrates were most notable in the CS/LPS group, which had a diffuse, predominantly macrophage infiltrate with fewer neutrophils. The LPS group had predominantly neutrophils in the pulmonary infiltrate and the CS group had a predominantly macrophage inifiltrate in alveolar ducts and adjacent alveoli. Apoptotic labeling of lung cells was highest with the CS/LPS group. In summary, the CS/LPS group displayed greater cellular infiltration and apoptotic responses in the lung with an indication of immunosuppressive effects (lower BAL cytokines) than the CS or LPS group, suggesting that the CS/LPS model shows promise to be further explored as an animal model for studying pathogenesis of COPD exacerbations. A longer term study with interim assessments is needed to confirm that the subacute responses observed in the CS/LPS group will result in greater severity of COPD-related pulmonary lesions following prolonged exposures.