Study On Mechanism Of γ-irradiation For Management Of Urethral Stenosis Resulting From Scar

BACKGROUND Recurrent urethral stenosis resulting from hypertrophic scar often needs repetitive transurethral manipulations, which brings patients great pain and expenses. Transurethral manipulations only have limited curative effect. In 1998, inspired by experience of radiation therapy for keloid and hypertrophic scar, Sun Yinghao and his colleagues took the lead in treating recurrent urethral stenosis resulting from hypertrophic scar by intraluminal γ-irradiation brachytherapy following transurethral incision or transurethral resection and gained satisfying curative effect. Many factors are involed in the pathogenesis of hypertrophic scar, of which abnormal balance between proliferation and apoptosis of fibroblasts is one of the most important. Several lines of evidence suggest thatγ-irradiation can lead to apoptosis and inhibition of proliferation of fibroblasts. But there are not systemic studies onγ-irradiation on fibroblasts derived from urethral hypertrophic scar. In view of this the cellular and molecular bases of γ-irradiation brachytherapy for the management of urethral stenosis resulting from hypertrophic scar are studied.PURPUSE To further explore the effect of γ-irradiation on fibroblasts that play an essential role in the pathogenesis ofhypertrophic scar, we isolated fibroblasts from urethral scar tissue and examined the balance between cell proliferation and apoptosis after γ- irradiation confining to doses of clinical application.METHODS Fibroblasts were primarily cultured from urethral scar tissue. MTT method and clonogenecity experiment were employed to obtain parameters of proliferation of fibroblasts after various doses of γ-irradiation ( 0, 5, 15Gy) from 60Co radiation generator. At the same time DNA contents, cell cycle distribution and change of cellular membrane were analyzed by flow cytometry. Morphological changes were evaluated by electron microscope technique. RESULTS γ-irradiation resulted in significant G0-G1 phase arrest and inhibition of fibroblast proliferation. Features of cell apoptosis ( e.g. apoptotic bodies, hypodiploid DNA peak and loss of plasma membrane) were shown in irradiated groups. The groups irradiated by 5Gy for 3 times at intervals of 24 hours shows no significant difference in cell cycle distribution and apoptosis from the ones treated with 15Gy in a lump.CONCLUSIONS γ-irradiation confining to doses of clinical application can induce proliferative inhibition and apoptosis of fibroblasts derived from urethral hypertrophic scar, which results in decreased number of fibroblasts in the pathogenesis of hypertrophic scar, hence prevents scar hypertrophy. It is reasonable to select low-dose-intermitent radiation for the management of urethral stenosis resulting from scar, which is probably able to avoidunnecessary injury of the tissue near the scar. The study provides some experimental base for the application of γ-irradiation in the management of urethral stenosis resulting from scar.