Photodynamic therapy of arteries: preservation of mechanical integrity

Photodynamic therapy (PDT) of tumors, as a primary treatment or as an adjunctive intra- operative therapy, may expose major vascular structures to injury. PDT has also been proposed to prevent neointimal hyperplasia following angioplasty of stenotic arteries. This study aimed to determine the effect of PDT on the normal rabbit carotid artery, and to determine whether this injury resulted in weakening of the vessel wall. PDT of the carotid arteries of NZW rabbits, using either disulphonated aluminum phthalocyanine or 5- aminolaevulinic acid induced protoporphyrin IX as photosensitizers, was performed using a light dose of 100 J/cm2. Histological examination of the carotids treated with both drugs demonstrated full thickness loss of cellularity 3 days following photodynamic therapy. Treated vessels all remained patent and no inflammatory infiltrate was observed. Elastin van Gieson staining showed preservation of inner and medial elastic laminae and medial and adventitial collagen. Further rabbits were similarly treated with PDT to 1 cm segments of both common carotids and sacrificed at 3, 7, and 21 days. The carotids were exposed and control and treated segments subjected to intraluminal hydrostatic distension until the vessels ruptured. No reduction in the pressure required to rupture the vessels was evident in treated vessels compared with controls. It is concluded that in spite of full thickness cell death, PDT treated arteries are not at risk of thrombotic occlusion or hemorrhage.