Analysis of Cigarette Smoke Deposition Within an In Vitro Exposure System for Simulating Exposure in the Human Respiratory Tract

For the risk assessment of airborne chemicals, a variety of in vitro direct exposure systems have been developed to replicate airborne chemical exposure in vivo. Since cells at the air-liquid interface are exposed to cigarette smoke as an aerosol in direct exposure systems, it is possible to reproduce the situation of cigarette smoke exposure in the human respiratory system using this device. However it is difficult to know whether the exposed cigarette smoke in this system is consistent with the smoke retained in the human respiratory tract. The purpose of this study is to clarify this point using the CULTEX^® RFS module which is a recently developed direct exposure system. For this purpose, solanesol and acetaldehyde were respectively chosen as the particulate and gas/vapor phase representatives of smoke constituents, and their deposition and balance per unit area of cell culture surface of the RFS module were measured (dosimetry). We also conducted human retention studies to compare with the dosimetry data. By comparing inhaled smoke and exhaled smoke under three inhalation conditions, we estimated the regional retention and balance of each representative per unit surface area of the respiratory tract (mouth, bronchi, and alveoli separately). The deposition of solanesol and acetaldehyde per unit area of cell culture surface in the RFS module decreased dependent on the dilution flow rate and ranged from 0.26-0.0076%/cm² in our experimental conditions. The ratio of deposited acetaldehyde to deposited solanesol ranged from 0.96-1.96 in the RFS module. The retention of solanesol and acetaldehyde per unit surface area in the mouth and the bronchi ranged from 0.095-0.0083%/cm2 in this study. The retention per unit surface area of alveoli was far lower than in the other two regions (0.0000063%/cm²). The ratio of retained acetaldehyde to retained solanesol ranged from 0.54-1.97. From these results, we concluded that the CULTEX^® RFS module can simulate in vivo cigarette smoke exposure in terms of the exposed particulate and gas/vapor phase chemical balance. We also found that the exposure in this module could replicate the retention in the mouth and the bronchi.