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There is a history for the use of in vitro bioassays to assess the toxicological properties of mainstream cigarette smoke (MSS). The results described in the literature were, for the most part, obtained with MSS collected under Federal Trade Commission (FTC) or International Organization for Standardization (ISO) conditions. However, numerous studies have shown that smokers smoke their cigarettes more intensely (e.g., they take larger puffs and/or more frequent puffs and/or partially occlude filter ventilation) than they are smoked on smoking machines operated under FTC (or ISO) conditions. It has also been reported that MSS composition changes with changes in smoking conditions. Furthermore, some governmental agencies have adopted regulations that specify more intensive protocols (i.e., Health Canada Intensive, HCI) for the collection of MSS for in vitro toxicological assays. Consequently, the performance of the Ames assay (TA98+S9, TA100+S9) and neutral red uptake assay under ISO and HCI protocols was studied with two blended (KR1R4F/KR2R4F, KR1R5F) and one flue-cured (CIM-7) reference cigarettes. The main outcome was when results were reported on a per milligram TPM (that portion of the mainstream smoke which is trapped in the smoke trap, expressed as milligrams per cigarette) basis generated under ISO conditions was more mutagenic and more cytotoxic than was TPM generated under HCI conditions. However, the decrease in biological activity could not be explained only by the increased in the water content of the TPM on going from ISO to HCI smoking conditions, and the results may be influenced by differences in smoke chemistry as a result of differing smoke collection systems.
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