PHOTODYNAMIC THERAPY OF NORMAL AND BALLOON-INJURED RAT CAROTID ARTERIES USING 5-AMINO-LEVULINIC ACID

Background Although the management of atherosclerotic disease by the u se of balloon angioplasty is widespread, the treatment is limited by r estenosis in 30% to 50% of cases. Fibrocellular intimal hyperplasia, t he main cause of restenosis,. arises from proliferation and migration of medial smooth muscle cells (SMC) into the intimal layer. Factors le ading to intimal hyperplasia are incompletely understood, and drugs ha ve universally failed to influence clinical restenosis. Photodynamic t herapy (PDT), the light activation of photosensitizing drugs to genera te cytotoxic mediators, may have potential as prophylaxis for intimal hyperplasia. 5-Amino-levulinic acid-induced protoporphyrin IX (ALA-PPI X), a naturally occurring porphyrin precursor, and its product, -PPIX, offers a novel method of sensitization for PDT. We have investigated the pharmacokinetics of ALA in arteries and the effects of ALA-PPIX-se nsitized PDT on normal and balloon-injured arteries. Methods and Resul ts ALA (20 to 200 mg/kg) was injected into healthy rats, and PPIX fluo rescence was measured in the carotid arteries. In a second group of ra ts, the exposed carotid artery was laser illuminated (50 J/cm(2), 630 nm) 30 to 90 minutes after sensitization. Three and 14 days after PDT, histological sections from treated arteries were analyzed by light mi croscopy. Subsequently, two new groups of rats underwent PDT (ALA, 100 mg/kg; laser, 50 J/cm(2), 630 nm [at 60 to 90 minutes]). The left car otid arteries underwent balloon angioplasty by intraluminal passage of a Fogarty FG2 catheter immediately before irradiation. These rats wer e killed at 14 and 28 days together with laser-only, ALA-only, and unt reated control rats. The arteries were perfusion-fixed in five. ALA-PP IX induced arterial media fluorescence in a dose-dependent manner. In the normal arteries, PDT produced a dose-dependent cellular depletion in the treated arterial segment at 3 days, and this was complete with 100 and 200 mg/kg of ALA. At 14 days, the media remained acellular, al though the endothelial lining had regenerated. In the balloon-injured arteries, PDT produced complete inhibition of intimal hyperplasia at b oth 14 and 28 days (0%). This was significantly greater than that prod uced by any of the control rats (34% to 69% and 37% to 66% at the two times, respectively). Significance was at 99% using ANOVA and Fisher's PLSD test. No hemorrhage, thrombosis, or aneurysm formation was seen. Conclusions AZA-PPIX-sensitized PDT applied at the time of angioplast y effectively inhibits experimental intimal hyperplasia development in rats. This may offer a new approach to the management of angioplasty restenosis in patients.