Scanning Electron Microscopic Analysis of Acute Photodynamic Therapy for Atherosclerotic Plaques of Rabbit Aorta By Using a Pheophorbide Derivative

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Abstract
The aim of this study was to demonstrate acute efficacy of photodynamic therapy on atheromas by using a pheophorbide derivative, PH-1126. Cholesterol-fed atherosclerotic rabbits were injected intravenously with 1 mg/kg of PH-1126. Twenty-four hours later, PH-1126 selectively accumulated in atherosclerotic plaques. Then, atherosclerotic lesions in the upper thoracic aorta were treated by irradiation with a krypton ion laser at a wave-length of 647 nm. At 6 h after photodynamic therapy, the treated aorta was examined by scanning electron microscopy. Numerous teardrop-shaped cells were observed on the endothelial surface of the plaque irradiated at a total energy of 100 J/cm2. These cells were larger than monocytes and macrophages, and resembled foam cells in size and shape. The body of the teardrop-shaped cell resembled pumice stone, mainly because of the presence of globular elements in the cytoplasm. A part of the cell appeared to remain in the subendothelial space. These findings suggest that the cells may be foam cells from the intimal layer of atherosclerotic plaque that were expelled into the aortic lumen. It may become possible to flatten atheroma in a long-term period after photodynamic therapy using PH-1126 as a potent photosensitizer.