Different responses by cultured aortic and venous smooth muscle cells to gamma radiation

Background. Stenosis of hemodialysis arteriovenous grafts is usually focal and caused by the proliferation of vascular smooth muscle cells (SMCs). External radiation of the graft is a potential strategy to prevent stenosis; however, the relative responsiveness of arterial and venous SMCs to radiation is unknown. Methods. Human aortic and saphenous vein SMCs were cultured in a medium containing growth factors and serum and treated with 0 to 50 Gy in a γ irradiator. At 2 to 20 days post-irradiation, cell counting, methylthiazoletetrazolium dye reduction, [³H]-thymidine uptake, and bromodeoxyuridine (BrdU) incorporation assays were performed. Results. All assays showed that 1 to 50 Gy inhibited the proliferation of both aortic and venous SMCs in a dose-dependent manner. Importantly, venous cells were less susceptible to radiation in all assays, compared to aortic cells. At day 10, 1 to 50 Gy of radiation inhibited the increase in the number of aortic cells by 24% to 66% and venous cells by 8% to 25% (P < 0.01) (aortic vs. venous). The differences between aortic and venous cells varied among different assays and were most pronounced in the BrdU assay. Conclusion. Inasmuch as myointimal hyperplasia occurs at both arterial and venous anastomoses, future strategies using radiation to prevent hemodialysis vascular access stenosis should take these differences into consideration.