Gamma Irradiation Modulates Vascular Smooth Muscle Cells and Extracellular Matrix Function: Implications for Neointimal Development

Objective: Migration of vascular smooth muscle cells (SMCs) into the subintimal space, and their proliferation and resultant deposition of extracellular matrix are key processes in the development of intimal hyperplasia, leading to vascular recurrent stenosis. The purpose of this study was to investigate the effects of clinically administered doses of -radiation on SMCs and extracellular matrix proteins in vitro, to better understand how it impinges on cellular and extracellular components of recurrent stenosis. Methods: The effects of -irradiation (10, 20 Gy) on SMC migration into three-dimensional collagen matrix gels was quantitated by calibrated light microscopy, and the release of metalloproteinases into conditioned media was investigated with an enzyme-linked immunosorbent assay and zymography. Collagen production was assayed with [3H]-proline incorporation, and SMC phenotype changes with confocal microscopy with a fluorescent -actin antibody. The effect of -irradiation on extracellular matrix was investigated by quantitating untreated SMC proliferation (3H-thymidine incorporation) on irradiated endothelial cell– derived matrix and by assessing structural collagen matrix changes with sodium dodecylsulfate polyacrylamide gel electrophoresis. All groups were compared with nonirradiated control groups. Results: SMC vertical migration was significantly decreased by -irradiation (48% and 55%, respectively; P < .0001). Irradiation did not generate measurable matrix protein crosslinks, nor did it alter the production of metalloproteinases or collagen synthesis. However, -irradiation decreased the ability of extracellular matrix to induce nonirradiated SMC proliferation (15% reduction; P .0028). Moreover, -irradiation reversed the secretory phenotype of cultured SMCs to a contractile type. Conclusions: The -irradiation–induced reduction of cellular migration, changes in SMC phenotype, and functional activity of matrix-bound factors, and no measurable effects on the production of extracellular matrix proteins, may in part explain the diverse effects of -irradiation on the restenotic response. (J Vasc Surg 2004;39:1097-1103.) Clinical Relevance. -Irradiation has found clinical application in the prevention of vascular recurrent stenosis. Although short-term results indicate reduction of recurrent stenosis, late results are not so promising. This in vitro study interrogated the biologic effects of -irradiation on vascular smooth muscle cells (SMCs) and their extracellular matrix, to enable understanding of how it affects recurrent stenosis. The results are mixed: -irradiation does not inhibit protein synthesis, but does inhibit SMC three-dimensional migration, enhances SMC transformation to a contractile phenotype, and reduces the functional activity of matrix-associated growth factors. This provides insight into how -irradiation alters the biologic response of arteries after intervention. Vascular recurrent stenosis is a post-interventional multifactorial process that involves the migration of smooth muscle cells (SMCs) and myofibroblasts into the subintimal space, and their proliferation and deposition of extracellular matrix proteins.1,2 Recurrent stenosis remains the major drawback to cardiovascular interventions, and therefore methods to prevent