Mechanism of Photodynamic Occlusion Using Liposomal Zn(II)-Phtalocyanine

Abstract

Purpose: To evaluate the potential of liposomal Zinc(II)-phthalocyanine (ZnPc) to selectively target subretinal vasculature. Methods: Photodynamic therapy (PDT) with liposomal Zinc(II)-phtalocyanine was used to induce choroidal occlusion in eyes of pigmented rabbits. Drug doses of 0.16, 0.24, 0.32, and 0.4 mg/kg body weight were administered. Photosensitization was performed at a wavelength of 671 nm and an irradiance of 100 mW/cm² applying fluences of 5, 10, 20, and 50 J/cm². Results: Using liposomal ZnPc, occlusion of choroidal vessels was achieved without damage to the overlying neurosensory retina. A tight dose correlation was found with a drug dose of 0.32 mg/kg and a light dose of 10 J/cm² inducing a selective thrombosis of the subretinal capillary layer. Histology revealed a selective intravascular alteration of the endothelial cells. Conclusions: PDT using liposomal ZnPc allows occlusion of subretinal vasculature with maintenance of neuroretina and RPE. The destructive effect on choroidal vascular endothelium is intensive.

KEYWORDS:

• choroidal vasculature
• liposomes
• photodynamic therapy
• zinc(II)-phtalocyanine