Object: The purpose of this study was to analyze the effect of single high-dose gamma irradiation at a cellular biological level on tissue cultures obtained in patients who underwent surgery for cerebral arteriovenous malformation (AVM).
Methods: The cell proliferation indices and changes in activation of p53, p21Waf-1, and mdm-2 were determined. Additionally, immunohistochemical investigations for vimentin, desmin, alpha-smooth muscle actin (alpha-SMA), glial fibrillary acidic protein, Factor VIII-related antigen (F-VIII), cytokeratin, S100, and transforming growth factor-beta (TGFbeta) were performed on cultured AVM cells after a single high-dose irradiation. Normal human brain microvessel endothelial (HBE) cells and aortic smooth muscle cells served as controls. The proliferation index decreased on the 5th day after irradiation and remained depressed over the observation period in the irradiated AVM cultures. The p53, p21Waf-1, and mdm-2 messenger RNA measurements showed considerable elevation both in AVM cultures and HBE cells after 15-Gy irradiation, which indicated apoptosis. Immunohistochemistry revealed strong vimentin positivity in the nonirradiated cultures, which gradually decreased in the irradiated cultures. Transforming growth factor-beta positivity was demonstrated in the irradiated specimens, indicating transformation of fibroblastic cells into activated myofibroblastic elements. This transformation was confirmed by demonstrating elevated SMA expression as well in the radiation-treated fibroblasts.
Conclusions: The presence of TGFbeta and alpha-SMA activity in the irradiated AVM cells suggests that along with the genetically confirmed apoptotic activity, fibroblast transformation into myofibroblasts might be one of the mechanisms leading to shrinkage and obliteration of AVMs after single high-dose gamma irradiation.