Plasma cholesterol levels were measured in the plasma collected from the rabbits before starting on the diet supplemented with cholesterol (0 week), at the time of denudation (1 week), at the time of photodynamic therapy (PDT) treatment (6 weeks), and 7 or 28 days after PDT treatment (7 or 10 weeks). Note that levels remain significantly elevated, despite a lowered maintenance diet of 0.05% dietary cholesterol at 28 days. *p < 0.001 compared with 0 weeks; +p < 0.001 compared with 1 week; @p < 0.01 compared with 6 weeks.

Fluorescent localization of Miravant photosensitizer compound after incubation at 0 (A), 4 (B), 8 (C), and 24 h (D). Note at 4 h there is evidence of photosensitizer in media (M) and plaque (P). At 8 and 24 h after injection, photosensitizer is present within plaque regions containing macrophages.

(A) The effects of Miravant photosensitizer compound incubation time on cell depletion throughout entire regional plaques. Note that maximum cell depletion is observed at 8 and 24 h after injection. Also note, in rabbits killed at 3 days after photodynamic therapy (PDT), evidence of significant plaque cell apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (black) staining (B) compared with contralateral untreated control (C).

Green bars are drug-only controls, whereas brown bars represent drug and light combination. Graphs A to D show the effects of photodynamic therapy (PDT) on plaque stenosis, plaque area, lumen area, and external elastic membrane area (n = 12 arteries/group). Note that by 28 days after treatment, PDT significantly reduced plaque percent stenosis (A), reduced plaque area (B), and increased lumen area (C) with no evidence of negative or expansive arterial remodeling (D). *p < 0.05; **p < 0.01.

Blue bars represent light-only controls, green bars are drug-only controls, and brown bars represent drug and light combination. Graph A shows initial (7 days) transient reduction in all atherogenic cells/mm² of plaque followed by plaque cell repopulation by 28 days (n = 12 arteries/group). Photomicrographs show hematoxylin and eosin staining of iliac arteries at 7 and 28 days after photodynamic therapy (PDT) (B and C) versus controls (D and E). Note the loss of "foam" cells at 28 days in panel C compared with controls. Magnification x200. ***p < 0.001.

Green bars are drug-only controls, whereas brown bars represent drug and light combination. Panel A shows that the area of plaque (mm²) occupied by macrophages is reduced by photodynamic therapy (PDT) at 7 days after treatment and that macrophage removal is sustained at 28 days after PDT regardless of elevated plasma cholesterol, an acute inflammatory stimulus (n = 12 arteries/group). Panel B shows transient loss of plaque smooth muscle cells/mm² of plaque at 7 days after PDT, followed by an increase in -actin area by 28 days, indicative of plaque repopulation with a stable plaque cell phenotype (n = 12 arteries/group). *p < 0.05; ***p < 0.001.

Photodynamic therapy (PDT) simultaneously reduced macrophages (A and F) and replaced existing plaque matrix with quiescent smooth muscle cells (B and G) in the non-G2 or S phases (C and H) as indicated by the Ki67 cell proliferation marker. After endothelial denudation of all rabbit arteries, staining with Factor VIII revealed the presence of endothelium in PDT-treated arteries and controls (D and J) indicative of arterial repair by 28 days. Panels E and K show the presence of the internal elastic membrane and external elastic membrane with Movat's stain. Note that plaque area is significantly less than controls at 28 days after PDT. Magnification x200.