Cigarette smoke augments asbestos-induced alveolar epithelial cell injury: role of free radicals.
Cigarette smoke augments asbestos-induced bronchogenic carcinoma by mechanisms that are not established. Alveolar epithelial cell (AEC) injury 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 production and DNA damage to cultured AEC and that phytic acid, an iron chelator, is protective. We hypothesized that whole cigarette smoke extracts (CSE) augment amosite asbestos-induced AEC injury by generating iron-induced free radicals that damage DNA and reduce cellular GSH and ATP levels. Asbestos or CSE each caused dose-dependent toxicity to AEC (WI-26 and rat alveolar type I-like cells) as assessed by 51chromium release. The combination of asbestos (5 microg/cm2) and CSE (0.O1-0.1%) caused synergistic injury whereas higher doses of each agent primarily had an additive toxic effect. Asbestos (5 microg/cm2) augmented CSE-induced (0.01-1.0%) AEC DNA damage over a 4 h exposure period as assessed by an alkaline unwinding, ethidium bromide fluorometric technique. These effects were synergistic in A549 cells and additive in WI-26 cells. Asbestos (5 microg/cm2) and CSE (0.5-1.0%) reduced A549 and WI-26 cell GSH levels as assessed spectrophotometrically and ATP levels as assessed by luciferin/luciferase chemiluminescence but a synergistic interaction was not detected. Phytic acid (500 microM) and catalase (100 microg/ml) each attenuated A549 cell DNA damage and depletion of ATP caused by asbestos and CSE. However, neither agent attenuated WI-26 cell 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-induced DNA damage in cultured alveolar epithelial cells. These data provide additional support that asbestos and cigarette smoke are genotoxic to relevant target cells in the lung and that iron-induced free radicals may in part cause these effects.
Kamp
D W
DW
Department of Medicine, Northwestern University Medical School, Veterans Affairs Chicago Health Care System, IL 60611, USA. d-kamp@nwu.edu
Greenberger
M J
MJ
Sbalchierro
J S
JS
Preusen
S E
SE
Weitzman
S A
SA
D000255:Adenosine Triphosphate / Q000378:metabolism; D000975:Antioxidants / Q000494:pharmacology; D017639:Asbestos, Amosite / Q000633:toxicity*; D002460:Cell Line; D004249:DNA Damage / Q000187:drug effects; D004848:Epithelium / Q000187:drug effects / Q000473:pathology; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D008175:Lung Neoplasms / Q000139:chemically induced; D010833:Phytic Acid / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000473:pathology; D012907:Smoking / Q000009:adverse effects; D013638:Tars / Q000494:pharmacology*
D000975:Antioxidants; D013638:Tars; C024746:tobacco tar; D017639:Asbestos, Amosite; D010833:Phytic Acid; D000255:Adenosine Triphosphate; D005978:Glutathione