Hematoporphyrin uptake in atherosclerotic plaques: therapeutic potentials

Atherosclerotic plaques were induced in abdominal aortas of rabbits. At 8 weeks, 5 mg of dihematoporphyrin ether (Photofrin II) per kg was injected intravenously followed by sacrifice of the animal, fluorescence microscopy, and quantitative assay of porphyrin in the plaque-containing aortas at 1, 12, 24, 48, and 72 hours. Photofrin II was taken up preferentially by the plaque, with the highest plaque to normal wall ratio occurring at 48 hours. Phototherapy was carried out in 13 animals in each of which two plaques had been induced. With a 630-nm light source 48 hours after the infusion of Photofrin, one of the pair of plaques was treated while the other served as a control. Animals were killed at 2, 4, and 6 weeks. The 6-week specimens showed the most dramatic reduction in plaque in comparison to controls. Photodynamic therapy may provide an alternate strategy in dealing with focal atherosclerosis.