Asbestos-induced alveolar epithelial cell apoptosis: role of mitochondrial dysfunction caused by iron-derived free radicals.
Asbestos causes asbestosis and malignancies by mechanisms that are not fully understood. Alveolar epithelial cell (AEC) injury by iron-derived reactive oxygen species (ROS) is one important mechanism implicated. We previously showed that iron-catalyzed ROS in part mediate asbestos-inducedAEC DNA damage and apoptosis. Mitochondria have a critical role in regulating apoptosis after exposure to agents causing DNA damage but their role in regulating asbestos-induced apoptosis is unknown. To determine whether asbestos causes AEC mitochondrial dysfunction, we exposed A549 cells to amosite asbestos and assessed mitochondrial membrane potential changes (delta(psi)m) using a fluorometric technique involving tetremethylrhodamine ethyl ester (TMRE) and mitotracker green. We show that amosite asbestos, but not an inert particulate, titanium dioxide, reduces delta(psi)m after a 4 h exposure period. Further, the delta(psi)m after 4 h was inversely proportional to the levels of apoptosis noted at 24 h as assessed by nuclear morphology as well as by DNA nucleosome formation. A role for iron-derived ROS was suggested by the finding that phytic acid, an iron chelator, blocked asbestos-induced reductions in A549 cell delta(psi)m and attenuated apoptosis. Finally, overexpression of Bcl-xl, an anti-apoptotic protein that localizes to the mitochondria, prevented asbestos-induced decreases in A549 cell delta(psi)m after 4 h and diminished apoptosis. We conclude that asbestos alters AEC mitochondrial function in part by generating iron-derived ROS, which in turn can result in apoptosis. This suggests that the mitochondrial death pathway is important in regulating pulmonary toxicity from asbestos.
Kamp
David W
DW
Veterans Administration Chicago Health Care System: Lakeside Division, Northwestern University Medical School, IL, USA.
Panduri
Vij ayalakshmi
Va
Weitzman
Sigmund A
SA
Chandel
Navdeep
N
D017209:Apoptosis / Q000187:drug effects*; D001194:Asbestos / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000633:toxicity; D002460:Cell Line; D005609:Free Radicals / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects; D007501:Iron / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D010833:Phytic Acid / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000473:pathology*; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; D005609:Free Radicals; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D001194:Asbestos; D010833:Phytic Acid; D007501:Iron