, 2008).

In the present study, the VITROCELL® 24 air–liquid exposure system (VITROCELL® Systems GmbH, Waldkirch, Germany) was investigated in combination with the comet assay to assess DNA damage in 2 human lung cell lines, human lung adenocarcinoma cells (A549) and human bronchial epithelial cells (BEAS-2B), after exposure to WS. While similar WS exposure systems have been successfully used with human bronchial epithelial cell lines (Fukano et al., 2006, Massey et al., 1998 and Wolz et al., 2002) the VITROCELL® 24 has the added advantage of enabling exposure to multiple doses of WS within the same plate in a single run because it uses 24-well plates. Results showed a repeatable and reproducible dose–response relationship between DNA learn more damage and increased WS dose in both cell lines, demonstrating that the combination of the comet assay with the VITROCELL® 24 is a valuable new in vitro test system to screen and assess DNA damage in human lung cells exposed to cigarette smoke. Human lung cell lines A549 and BEAS-2B were exposed to diluted WS from the Reference Cigarette 3R4F in the VITROCELL® 24 and DNA damage was evaluated using the comet assay. Five

independent biological assay replicates were performed per cell line: 3 assays on the same day and 2 assays on 2 different days. The cells from 4 wells per dilution, per plate, were run in triplicate (cells split on 3 slides) for each independent assay and both intra-day and inter-day variability were assessed. An overview of the study design is presented in Fig. 1. A549. Lapatinib concentration cells and BEAS-2B cells (American Type Culture Collection, Manassas, VA, USA; number CCL-185™ and CRL-9609™, respectively) were cultured in Dulbecco’s modified Eagle medium containing 10% fetal bovine serum at 37 °C in a humidified incubator with 5% CO2 in air and 85% relative humidity. Cultures were screened for the presence of mycoplasma contamination using the Myco Alert Mycoplasma Detection Kit

(Lonza, Rockland, ME, USA). Cigarettes (University of Kentucky Reference Cigarette 3R4F; total particulate matter yield approximately 10 mg/cig) were smoked on the VC 10 smoking robot (Fig. 2A) in conformity with the International Organization for Standardization 5-Fluoracil concentration (ISO) smoking regimen (ISO, 2000). Two subsequent runs of 5 cigarettes were performed for each exposure, the smoking run was stopped after 7 puffs, and the overall exposure time was 14 min. Fresh WS (5 puffs per minute × 35 ml = 175 ml/min) from 5 cigarettes was passed puff-wise through the dilution system (Fig. 2B) and diluted with at least 5 different velocities of humidified synthetic air (SA; 85% nitrogen and 15% oxygen; Praxair, Düsseldorf, Germany). Dilution velocities ranged from 4 l/min to 0.2 l/min (from low to high smoke concentrations; Table 1).