Uptake of hematoporphyrin derivative by atheromatous plaques: Studies in human in vitro and rabbit in vivo

Hematoporphyrin derivative, a photosensitive material used to identify and treat neoplastic tissue in humans, has been found to localize in atheromatous plaques in animals and has recently been found in postmortem human atherosclerotic plaques. It is not known whether human plaques take up hematoporphyrin derivative in vivo. In five patients undergoing surgical vascular procedures, specimens containing atheromatous plaques were removed and immediately incubated in autologous oxygenated blood at 37°C with hematoporphyrin derivative at a clinically relevant concentration for 2 hours. On exposure to ultraviolet light, porphyrin fluorescence was noted throughout each plaque, whereas adjacent plaque-free tissue showed no fluorescence. To compare in vitro with in vivo hematoporphyrin derivative uptake by plaques, the fluorescence of three types of arterial lesions (induced by a high cholesterol diet, catheters or balloon injury) was studied in 16 New Zealand White rabbits. Each lesion fluoresced selectively with the same intensity whether hematoporphyrin derivative exposure was performed in vitro or in vivo. Fluorescence microscopy did not show a difference in the pattern of hematoporphyrin derivative fluorescence between in vitro and in vivo specimens. The results suggest that human atheromatous plaques should take up hematoporphyrin derivative in vivo and are, therefore, potentially suitable for photochemical treatment as a new therapeutic approach to atherosclerosis.