Acute Effects of Photodynamic Treatment on Elastic Fibre Network in Atherosclerotic Plaques of Rabbit Aorta

Our objective was to demonstrate the acute effects of photodynamic treatment on the elastic framework in the atherosclerotic plaque. The photosensitiser, mono-l-aspartyl chlorin 5₆ (NP5₆), was administered intravenously, at a dose of 5 mg/kg of body weight, to cholesterol-fed, atherosclerotic rabbits. Six hours later, visible atherosclerotic lesions of the abdominal aorta were irradiated with a diode laser, wavelength 664 nm. The energy administered ranged from 50 J/cm² to 200 J/cm². The abdominal aorta was then excised and digested by a modified hot alkaline method. Scanning electron microscopy revealed the destruction of the architecture of the elastic fibre network in the atherosclerotic plaque, whereas no change was seen in the non-atheromatous aortic wall. Damage to the elastic fibre network was more obvious in plaque that was exposed to higher energy levels. No significant changes were observed in laser-treated plaques in animals that did not receive the NP5₆ pretreatment. Findings suggest that atherosclerotic plaques of the abdominal aorta can be selectively degraded by laser irradiation following pretreatment with the photosensitiser, NP5₆. Received for publication 23 July 1997; accepted following revision 20 January 1998.