Asbestos causes apoptosis in alveolar epithelial cells: role of iron-induced free radicals.
Asbestos causes asbestosis and malignancies by mechanisms that are not fully understood. Alveolar epithelial cell (AEC) injury by iron-induced reactive oxygen species (ROS) is one important mechanism. To determine whether asbestos causes apoptosis in AECs, we exposed WI-26 (human type I-like cells), A549 (human type II-like cells), and rat alveolar type II cells to amosite asbestos and assessed apoptosis by terminal deoxynucleotidyl transferase-mediated deoxyuridine-5'-triphosphate-biotin nick end labeling (TUNEL) staining, nuclear morphology, annexin V staining, DNA nucleosome formation, and caspase 3 activation. In contrast to control medium and TiO2, amosite asbestos and H2O2 each caused AEC apoptosis. A role for iron-catalyzed ROS was suggested by the finding that asbestos-induced AEC apoptosis and caspase 3 activation were each attenuated by either an iron chelator (phytic acid and deferoxamine) or a.OH scavenger (dimethyl-thiourea, salicylate, and sodium benzoate) but not by iron-loaded phytic acid. To determine whether asbestos causes apoptosis in vivo, rats received a single intratracheal instillation of amosite (5 mg) or normal saline solution, and apoptosis in epithelial cells in the bronchoalveolar duct regions was assessed by TUNEL staining. One week after exposure, amosite asbestos caused a 3-fold increase in the percentage of apoptotic cells in the bronchoalveolar duct regions as compared with control (control, 2.1% +/- 0.35%; asbestos, 7.61% +/- 0.15%; n = 3). However, by 4 weeks the number of apoptotic cells was similar to control. We conclude that asbestos-induced pulmonary toxicity may partly be caused by apoptosis in the lung epithelium that is mediated by iron-catalyzed ROS and caspase 3 activation.
Aljandali
A
A
Department of Medicine, Divisions of Pulmonary and Critical Care Medicine and Hematology-Oncology, Northwestern University Medical School and Veterans Administration Chicago Health Care System, Lakeside Division, IL, USA.
Pollack
H
H
Yeldandi
A
A
Li
Y
Y
Weitzman
S A
SA
Kamp
D W
DW
D000818:Animals; D017209:Apoptosis; D017639:Asbestos, Amosite / Q000008:administration & dosage / Q000633:toxicity*; D001980:Bronchi / Q000166:cytology / Q000187:drug effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002452:Cell Count; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000633:toxicity; D017665:Hydroxyl Radical / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D007322:Instillation, Drug; D007442:Intubation, Intratracheal; D007501:Iron / Q000378:metabolism; D007502:Iron Chelating Agents / Q000494:pharmacology; D010833:Phytic Acid / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D020160:Sodium Benzoate / Q000494:pharmacology
D016166:Free Radical Scavengers; D007502:Iron Chelating Agents; D017382:Reactive Oxygen Species; D017639:Asbestos, Amosite; D017665:Hydroxyl Radical; D010833:Phytic Acid; D006861:Hydrogen Peroxide; D007501:Iron; C505407:CASP3 protein, human; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D020160:Sodium Benzoate