Proinsulin formulated in PLGA microspheres delays vision loss and activates survival pathways in the rd10 mouse model of retinitis pigmentosa.

Abstract

Purpose: Retinitis pigmentosa (RP) is a heterogeneous group of inherited conditions that lead to blindness. Apoptosis of photoreceptors and retinal disorganization are common features in animal models of the disease. We have previously shown that systemic administration of proinsulin delays vision loss in rd10 mouse and P23H rat models of RP. To test the feasibility and efficacy of a local treatment based on proinsulin, we further assessed the potential of intravitreal delivery in the rd10 mouse.

Methods: In vivo studies: methionylated human recombinant proinsulin (rhPI-Met) was formulated in poly-lactic-co-glycolic acid (PLGA) microspheres that were administered by intravitreal injection in rd10 mice at postnatal day 15 (P15). In vitro studies: wild-type and rd10 retinas at P22 were placed in organotipic culture and treated with 10 nM rhPI-Met for different periods of time. Visual function was evaluated by ERG; photoreceptor cell death by TUNEL staining of whole-mount retinas; and retinal structure by immunohistochemistry in cryosections. Proinsulin content was determined by ELISA. Proinsulin signaling was studied by immunoblot.

Results: Delivery of proinsulin by microspheres in rd10 mice attenuated photoreceptor cell loss and prolonged the visual function. Proinsulin also prevented photoreceptor cell death in vitro. Proinsulin addition to the culture media led to insulin phosphorylation of receptor-type A and AKT.

Conclusions: PLGA microspheres are a feasible rhPI-Met delivery system. The released rhPI-Met is biologically active and has a therapeutic effect on the rd10 mouse model of retinitis pigmentosa. Proinsulin triggers insulin receptor signaling pathway.