UC Davis

Quantifying the clearance and retention of inhaled particles in the respiratory tract is critical for understanding their toxicity and overall health impacts. While previous studies have focused on the clearance of monodisperse nanoparticles in animal models, limited research exists on the clearance kinetics of tobacco smoke particles. Even fewer studies provide lobe-specific clearance data, which hampers our understanding of smoke particle accumulation following long-term exposure. This gap highlights the need for further research, particularly involving little cigars given their popularity among youth. In this study, we investigated the lobar clearance of smoke particles in rat lungs following exposure to combusted Swisher Sweets regular-flavored little cigars. Twelve-week-old female Sprague-Dawley rats were exposed to smoke particles at a concentration of 80 mg/m3 for 4 h. Lung lobes were collected and analyzed for particle retention on Days 0, 1, 7, and 21 post-exposure. Inductively Coupled Plasma Mass Spectrometry was used to quantify chromium concentrations in each lobe, serving as a tracer for smoke particles. Our results revealed a two-phase clearance of little cigar smoke particles across all lung lobes, with an overall half-life of 5.7 days for the fast phase and 25.0 days for the slow phase. While no statistically significant differences in particle retention among lobes were observed after 21 days, the majority of retained particles were found in the left lobe and right caudal lobe. When comparing the half-life of smoke particles in this study to previously reported data for nanoparticles, we found the results to be comparable. Our findings demonstrate that the clearance of smoke particles follows a similar pattern across different lung lobes in rats, with a two-phase clearance mechanism indicating that the chromium in the smoke particles likely exists in the Cr (III) oxidation state. These insights provide valuable information for estimating the clearance and retention of little cigar smoke particles, contributing to toxicity research in the context of long-term exposure.