Localization of lipoprotein-delivered benzoporphyrin derivative in the rabbit eye

Photodynamic therapy (PDT) using the photosensitizer Benzoporphyrin derivative monoacid (BPD-MA or verteporfin) is currently under investigation for the treatment of choroidal neovascularization. We investigated the localization of this photosensitizer using fluorescence microscopy and quantified its presence in ocular tissues after porphyrin extraction using fluorescence spectroscopy.

Albino rabbits were administered 2mg/kg BPD-MA pre-complexed with low density lipoprotein (LDL) intravenously, or given no treatment. The eyes were enucleated at intervals between 5 minutes and 24 hours after dye injection and were studied with light and fluorescence microscopy, or dissected for porphyrin extraction.

At 5 minutes after dye injection, there was bright fluorescence from the choroid and retinal pigment epithelium (RPE) with trace retinal outer segment fluorescence. After 20 minutes, there was increased photoreceptor outer segment and RPE fluorescence but decreased choroidal fluorescence. By 2 hours no fluorescence remained in either the choroid or the photoreceptors and there was diminished fluorescence of the RPE. Trace RPE fluorescence was still visible at 24 hours. Fluorescence localization of liposomal BPD (2mg/kg) at the earliest (5 minutes) time point was indistinguishable from that of the BPD-LDL complex. Using spectrofluorimetry, the highest BPD-MA levels from the eye were measured in the retina/RPE/uvea complex with lower levels measured from the sclera and other tissues.

BPD-MA with LDL rapidly accumulates in the choroid, RPE, and photoreceptors after intravenous injection. Future studies of PDT with BPD-MA for the treatment of fundus disorders may need to address the relationship between dye localization and photodynamically-mediated injury.