Impaired wound healing after local soft x-ray irradiation in rat skin: time course study of pathology, proliferation, cell cycle, and apoptosis.
BACKGROUND
Soft x-ray irradiation is usually used to treat skin-related disease in the clinic, but its effect on wound healing has not been well elucidated. The purpose of our study was to develop a wound-healing model of local soft x-ray irradiation on rats and to clarify the possible cellular mechanisms through which radiation may influence healing.


METHODS
Full-thickness, 2-cm-diameter, dorsal cutaneous tissue was excised after local irradiation in rats. The dose-effect curve was recorded, and five animals irradiated with doses of 521 rad were killed at postwound days 3, 6, 9, and 15 and five were healed for histologic examination (hematoxylin and eosin staining), cell proliferation (5-bromo-2'-deoxyuridine [BrdU] incorporation), apoptosis (and terminal deoxynucleotidyl transferase biotin-dUTP nick end-labeling [TUNEL] method), and the cell cycle (flow cytometry).


RESULTS
Soft x-ray irradiation delayed wound-healing time with an S-like curve, and the wounds that received doses in excess of 700 rad failed to heal within 40 days. This dose-effect range is far below that of gamma and hard x-ray irradiation. Relative to control wounds, which contained prominent BrdU-positive labeling at days 3 through 9 and minimal TUNEL-positive labeling during the entire healing, the irradiated wounds had less BrdU-positive labeling and significant TUNEL-positive labeling at days 3 through 9 but more BrdU-positive labeling and similar TUNEL-positive labeling at day 15. Flow cytometry studies found a higher proportion of G0/G1 phase cells (days 3-9), a lower (days 3-9) then higher (days 13-22) proportion of S phase cells, and a persistent lower proportion of G2/M phase cells (during the entire healing process) in the irradiated wounds compared with the controls.


CONCLUSIONS
Local soft x-ray irradiation could delay wound healing in a dose-dependent manner and shows a more effective biological effect than that of gamma and hard x-ray irradiation. Radiation-induced inactive cell proliferation, active cell apoptosis, and arrested cell cycle at days 3 through 9 may be one of the cellular mechanism responsible for delayed wound healing.
Liu
Xia
X
Molecular Biologic Center, Research Institute of Surgery, Third Military Medical University, Chongqing, China.
Liu
Jian-Zhong
JZ
Zhang
En
E
Li
Ping
P
Zhou
Ping
P
Cheng
Tian-Min
TM
Zhou
Yuan-Guo
YG
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D002453:Cell Cycle / Q000528:radiation effects; D049109:Cell Proliferation / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012871:Skin Diseases / Q000532:radiotherapy*; D014945:Wound Healing / Q000528:radiation effects*; D014947:Wounds and Injuries / Q000473:pathology