CIGARETTE-SMOKE AUGMENTS ASBESTOS-INDUCED ALVEOLAR EPITHELIAL-CELL INJURY - ROLE OF FREE-RADICALS

Cigarette smoke augments asbestos-induced bronchogenic carcinoma by me chanisms that are not established. Alveolar epithelial cell (AEC) inju ry due to oxidant-induced DNA damage and depletion of glutathione (GSH ) and adenosine triphosphate (ATP) may be one important mechanism. We previously showed that amosite asbestos-induces hydroxyl radical produ ction and DNA damage to cultured AEC and that phytic acid, an iron che lator, is protective. We hypothesized that whole cigarette smoke extra cts (CSE) augment amosite asbestos-induced AEC injury by generating ir on-induced free radicals that damage DNA and reduce cellular GSH and A TP levels. Asbestos or CSE each caused dose-dependent toxicity to AEC (WI-26 and rat alveolar type I-like cells) as assessed by (51)chromium release. The combination of asbestos (5 mu g/cm(2)) and CSE (0.01-0.1 %) caused synergistic injury whereas higher doses of each agent primar ily had an additive toxic effect. Asbestos (5 mu g/cm(2)) augmented CS E-induced (0.01-1.0%) AEC DNA damage over a 4 h exposure period as ass essed by an alkaline unwinding, ethidium bromide fluorometric techniqu e. These effects were synergistic in A549 cells and additive in WI-26 cells. Asbestos (5 mu g/cm(2)) and CSE (0.5-1.0%) reduced A549 and WI- 26 cell GSH levels as assessed spectrophotometrically and ATP levels a s assessed by luciferin/luciferase chemiluminescence but a synergistic interaction was not detected. Phytic acid (500 mu M) and catalase (10 0 mu g/ml) each attenuated A549 cell DNA damage and depletion of ATP c aused by asbestos and CSE. However, neither agent attenuated WI-26 cel l DNA damage nor the reductions in GSH levels in WI-26 and A549 cells exposed to asbestos and CSE. We conclude that CSE enhance asbestos-ind uced DNA damage in cultured alveolar epithelial cells. These data prov ide additional support that asbestos and cigarette smoke are genotoxic to relevant target cells in the lung and that iron-induced free radic als may in part cause these effects. (C) 1998 Elsevier Science Inc.