Photodynamic therapy generates a matrix barrier to invasive vascular cell migration

Photodynamic therapy (PDT) inhibits experimental intimal hyperplasia. PDT results in complete vascular wall cell eradication with subsequent adventitia but minimal media repopulation. This study was designed to test the hypothesis that PDT alters the vascular wall matrix thereby inhibiting invasive cell migration, and as such, provides an important barrier mechanism to favorably alter the vascular injury response. Untreated smooth muscle cells (SMCs) and fibroblasts were seeded on control and PDT-treated (100 J/cm(2); photosensitizer was chloroaluminum-sulfonated phthalocyanine, 5 microg/mL) 3-dimensional collagen matrix gels. Invasive cell migration was temporally quantified by calibrated microscopy. Zymography and ELISA assessed SMC matrix metalloproteinase levels. Molecular changes of gel proteins and their susceptibility to collagenase were analyzed by SDS-PAGE and Western blot. Limited pepsin digestion and histology were used to assess the in vivo relevance of the model, using an established rat carotid artery model at 1 and 4 weeks after balloon injury and PDT. PDT of 3-dimensional matrix of gels led to a 52% reduction of invasive SMCs and to a 59% reduction of fibroblast migration (P<0.001) but did not significantly affect secretion of matrix metalloproteinases. PDT induced collagen matrix changes, including cross-linking, which resulted in resistance to protease digestion. PDT led to a durable 45% reduction in pepsin digestion susceptibility of treated arteries (P<0.001) and inhibition of periadventitial cell migration into the media. These data suggest that PDT of matrix gels generates a barrier to invasive cellular migration. This newly identified effect on matrix proteins underscores its pleiotropic actions on the vessel wall, and as such, PDT may be of considerable potential therapeutic value to inhibit restenosis.