Temporal onset of hypoxia and oxidative stress after pulmonary irradiation.
OBJECTIVE
To investigate the temporal onset of hypoxia following irradiation, and to show how it relates to pulmonary vascular damage, macrophage accumulation, and the production of reactive oxygen species and cytokines. Our previous studies showed that tissue hypoxia in the lung after irradiation contributed to radiation-induced injury.


METHODS
Female Fisher 344 rats were irradiated to the right hemithorax with a single dose of 28 Gy. Serial studies were performed up to 20 weeks following irradiation. Radionuclide lung-perfusion studies were performed to detect changes in pulmonary vasculature. Immunohistochemical studies were conducted to study macrophages, tissue hypoxia (carbonic anhydrase-9 marker), oxidative stress (8-hydroxy-2'-deoxyguanosine), and the expression of profibrogenic (transforming growth factor-beta [TGF-beta]) and proangiogenic (vascular endothelial growth factor [VEGF]) cytokines.


RESULTS
Significant changes in lung perfusion along with tissue hypoxia were observed 3 days after irradiation. Significant oxidative stress was detected 1 week after radiation, whereas macrophages started to accumulate at 4 weeks. A significant increase in TGF-beta expression was seen within 1 day after radiation, and for VEGF at 2 weeks after radiation. Levels of hypoxia, oxidative stress, and both cytokines continued to rise with time after irradiation. The steepest increase correlated with vast macrophage accumulation.


CONCLUSIONS
Early changes in lung perfusion, among other factors initiate, the development of hypoxia and chronic oxidative stress after irradiation. Tissue hypoxia is associated with a significant increase in the activation of macrophages and their continuous production of reactive oxygen species, stimulating the production of fibrogenic and angiogenic cytokines, and maintaining the development of chronic radiation-induced lung injury.
Fleckenstein
Katharina
K
Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA.
Zgonjanin
Larisa
L
Chen
Liguang
L
Rabbani
Zahid
Z
Jackson
Isabel L
IL
Thrasher
Bradley
B
Kirkpatrick
John
J
Foster
W Michael
WM
Vujaskovic
Zeljko
Z
D000818:Animals; D002256:Carbonic Anhydrases / Q000378:metabolism; D015687:Cell Hypoxia; D003839:Deoxyadenosines / Q000378:metabolism; D005260:Female; D008168:Lung / Q000098:blood supply / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008262:Macrophage Activation / Q000502:physiology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D009929:Organ Size / Q000528:radiation effects; D018384:Oxidative Stress; D011832:Radiation Injuries / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D011877:Radionuclide Imaging; D051381:Rats; D011916:Rats, Inbred F344; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
C436623:8-hydroxy-2'-deoxyadenosine; D003839:Deoxyadenosines; D017382:Reactive Oxygen Species; D016212:Transforming Growth Factor beta; D042461:Vascular Endothelial Growth Factor A; D002256:Carbonic Anhydrases