Transferrin Non-Viral Gene Therapy for Treatment of Retinal Degeneration

Abstract

Dysregulation of iron metabolism is observed in animal models of retinitis pigmentosa (RP) and in patients with age-related macular degeneration (AMD), possibly contributing to oxidative damage of the retina. Transferrin (TF), an endogenous iron chelator, was proposed as a therapeutic candidate. Here, the efficacy of TF non-viral gene therapy based on the electrotransfection of pEYS611, a plasmid encoding human TF, into the ciliary muscle was evaluated in several rat models of retinal degeneration. pEYS611 administration allowed for the sustained intraocular production of TF for at least 3 and 6 months in rats and rabbits, respectively. In the photo-oxidative damage model, pEYS611 protected both retinal structure and function more efficiently than carnosic acid, a natural antioxidant, reduced microglial infiltration in the outer retina and preserved the integrity of the outer retinal barrier. pEYS611 also protected photoreceptors from N-methyl-N-nitrosourea-induced apoptosis. Finally, pEYS611 delayed structural and functional degeneration in the RCS rat model of RP while malondialdehyde (MDA) ocular content, a biomarker of oxidative stress, was decreased. The neuroprotective benefits of TF non-viral gene delivery in retinal degenerative disease models further validates iron overload as a therapeutic target and supports the continued development of pEY611 for treatment of RP and dry AMD.

Ocular Barriers and Their Influence on Gene Therapy Products Delivery

“…Plasmid DNA on the other hand can be delivered to cells in the anterior segment of the eye using physical methods such as current, laser, light, ultrasound, guns, or chemical methods, but it still needs to bypass the corneal barriers [ 40 ]. Naked plasmid DNA, injected in the ciliary muscle, has been efficiently transduced in ciliary muscle cells using a disposable electrotransfer device, allowing the sustained intraocular production of therapeutic proteins in the ocular media for more than 6 months [ 41 , 42 , 43 , 44 , 45 ].…”

Insights into the Roles of the Sideroflexins/SLC56 Family in Iron Homeostasis and Iron-Sulfur Biogenesis

“…Human transferrin electrotransfection in rodents was shown to protect retinal structure and function, reducing microglial infiltration and preserving the integrity of the outer retinal barrier in a photo-oxidative model. Transferrin, a natural iron chelator, delayed also the retina degeneration and decreased oxidative stress [ 119 ]. This work validates iron overload as a therapeutic target for pathologies as retinitis pigmentosa or age-related macular degeneration.…”

MERTK-Mediated LC3-Associated Phagocytosis (LAP) of Apoptotic Substrates in Blood-Separated Tissues: Retina, Testis, Ovarian Follicles

“…The degradation of transferrin results in the liberation of iron ions which accumulate in debris zone. This triggers oxidative stress [75], which contributes to the apoptotis of photoreceptors [69,76]. Intravitreal injections or non-viral delivery of transferrin in its iron-free form (apotransferrin) to chelate unbound iron, or antioxidant biomolecules, delay retinal degeneration in RCS rats, supporting the consistency of such a scenario [75][76][77].…”

“…This triggers oxidative stress [75], which contributes to the apoptotis of photoreceptors [69,76]. Intravitreal injections or non-viral delivery of transferrin in its iron-free form (apotransferrin) to chelate unbound iron, or antioxidant biomolecules, delay retinal degeneration in RCS rats, supporting the consistency of such a scenario [75][76][77]. In 2000, two independent research groups concurrently identified a single gene defect, the Mer tyrosine kinase (Mertk) [78][79][80].…”