Dynamics of phosphorothioate oligonucleotides in normal and laser photocoagulated retina

Aims-To investigate the distribution, persistence, and stability of fluores cently labelled phosphorothioate oligonucleotides (PS-ODNs) in normal and l aser photocoagulated retina following intravitreal injection in the rat. Methods-Fluorescently labelled PS-ODNs were injected intravitreally into pi gmented eyes at doses of 0.5-10.0 nmol in 2.0 mu l solution. The dynamics o f PS-ODNs was evaluated by fluorescent microscopy of cryosections and flat mounted retinal pigment epithelium (RPE)-choroid-sclera. Genescan analysis was used to assess the integrity of PS-ODNs in the retina after injection. The dynamics of PS-ODNs was also evaluated in the retina following krypton laser photocoagulation with a protocol producing choroidal neovascularisati on (CNV). Results-Following intravitreal injection the PS-ODNs demonstrated dose and time dependent distribution and persistence in the retina, where they acces sed all neural layers. However, they preferentially accumulated in the RPE layer, demonstrated as bright granules in the cytoplasm of the cells. Injec tions of 5.0 and 7.5 nmol of PS-ODNs exhibited strong fluorescence in the r etina for 6 weeks after injection. Genescan analysis demonstrated that the PS-ODNs remained almost completely intact for at least 12 weeks. Following laser treatment, the PS-ODNs were concentrated in the regions of laser phot ocoagulation and retained high intensity for at least 8 weeks after injecti on, particularly localised to macrophages, RPE, and the local choroidal tis sue. Conclusions-These results indicate that PS-ODNs are stable and accessible t o most neural layers of the retina, and they preferentially accumulate in t he RPE layer following intravitreal injection. The successful delivery of P S-ODNs into normal and laser photocoagulated retina suggests that PS-ODNs m ay have potential in the development of therapy for attenuating retinal deg enerations and CNV.