Photodynamic therapy induces apoptosis in intimal hyperplastic arteries

Photodynamic therapy (PDT) generates free radicals through the absorption o f light by photosensitizers. PDT shows promise in the treatment of intimal hyperplasia, which contributes to restenosis, by completely eradicating cel ls in the vessel wall. This study investigates the mechanisms of PDT-induce d cell death. PDT, using the photosensitizer chloroaluminum-sulfonated phth alocyanine (1 mg/kg) and laser light (lambda = 675 nm) 100 J/cm(2) was admi nistered to rat carotid arteries after balloon injury-induced intimal hyper plasia. Apoptosis was determined by cell morphology with light microscopy a nd transmission electron microscopy, DNA cleavage by terminal dUTP nick-end labeling staining, and nucleosomal fragmentation (ladder pattern) by DNA a garose gel electrophoresis. Four hours after PDT, apoptosis was observed in vascular cells, as evidenced by terminal dUTP nick-end labeling staining a nd transmission electron microscopy. Within 24 hours no cells were present in the neointima and media. Immunofluorescence using an cu-smooth muscle ce ll actin antibody confirmed the disappearance of all neointimal and medial cells within 24 hours. No inflammatory cell infiltrate was observed during this time frame. Apoptosis was sharply confined to the PDT treatment held. These data demonstrate that vascular PDT induces apoptosis as a mechanism o f rapid, complete, and precise cell eradication in the artery wall. These f indings and the lack of inflammatory reaction provide the basis for underst anding and developing PDT for a successful clinical application in the trea tment of hyperplastic conditions such as restenosis.