Characterization of mainstream cigarette smoke-induced biomarker responses in ICR and C57Bl/6 mice

Pulmonary emphysema is a major component of the morbidity and mortality of chronic obstructive pulmonary disease (COPD). Currently there are no predictive biomarkers for COPD. Initial steps toward identifying potentially predictive biomarkers involve utilizing well-characterized mainstream smoke (MS) exposure conditions (dose-response) to identify changes in biomarkers of effect (inflammation, tissue injury, oxidative stress) in emphysema-susceptible and -resistant mouse strains. C57Bl/6 mice have been reported to develop emphysema when exposed chronically to cigarette smoke, while similarly exposed ICR mice do not. Male C57Bl/6 and ICR mice were exposed 2 h/day for 7 consecutive days to MS from a standard reference cigarette (2R4F) at 75, 250, and 600 microg total particulate matter (TPM)/L or filtered air. To confirm exposure, blood samples were collected toward the end of the last exposure and analyzed for carboxyhemoglobin, nicotine, and cotinine. Bronchoalveolar lavage (BAL) fluid samples were collected 2 or 12 h postexposure and analyzed for biomarkers of effect. MS dose differed slightly between strains. More necrosis was observed in nasal epithelium of exposed C57Bl/6 mice. Exposure concentration-dependent increases in apoptosis, chemokines, and neutrophil counts were greater in ICR mice. Similar increases in thymus and activated-regulated chemokine were only observed in C57Bl/6 mice. BAL fluid cells of C57Bl/6 mice appear to undergo necrosis, while the BAL fluid cells of ICR mice appear to undergo apoptosis following MS exposure. Utilizing two strains of mice we identified MS-responsive biomarkers of effect that may be predictive of COPD pathology. Chronic MS exposures are needed to link these biomarkers with emphysema.