Transferrin confers neuroprotection in ex vivo and in vivo glaucoma rat models

Abstract

Purpose : Iron is essential for retinal metabolism, but excess iron can cause oxidative stress. In glaucoma eyes, progressive retinal ganglion cell (RGC) death has been associated with dysregulation of iron homeostasis. Transferrin (TF) is an endogenous iron transporter that controls iron ocular levels. Local administration of TF is neuroprotective in various models of retinal degeneration, controlling iron-induced oxidative stress without undesirable side-effects. Herein, we evaluated the protective effects of TF on RGCs in retinal explants exposed to various stresses and in a rat model of ocular hypertension (OHT).

Methods : Rat retinal explants (n = 6-10/stress condition) were subjected for 24 hours to 1mM FeSO₄, 100µM NMDA, or 100µM CoCl₂, and maintained in culture until 96 hours. TF (50 mg/mL) was added during the whole stress incubation period. Survival of Brn3a-immunolabeled RGCs was quantified at 96 hours. In vivo, OHT was induced by injection of magnetic microbeads into the anterior chamber of adult Brown Norway rats (n = 5/group). Animals then received four weekly intravitreal injections of TF or vehicle (BSS). Naïve rats served as normotensive internal controls. RBPMS-immunolabeling of flat-mounted retinas and PPD-stained optic nerve sections were used for, respectively, RGC and axon quantification at 4 weeks.

Results : All three stresses induced about 50% RGC cell loss in retinal explants. Incubation with TF significantly preserved RGCs against FeSO₄-induced toxicity (+49.5 %, p = 0.0354). Similarly, TF partly protected RGCs against NMDA-induced excitotoxicity (+42.2 %, p = 0.0027) or CoCl₂-induced RGC hypoxia (+54.4 %, p = 0.0053). In IOP rats, RGC density at 4 weeks was significantly decreased in BSS-treated animals in comparison to naïve animals (-49.7%) whereas RGC number was not statistically different from naïve animals in TF-treated rats (p = 0.2475). TF preserved RGCs by about 70% compared to BSS-treated animals with OHT (p = 0.0008). Similarly, the axon density at 4 weeks was not different from the naïve group in TF-treated rats (p = 0.2480), while preserving about 47% of the axons when compared to vehicle group (p = 0.0027).

Conclusions : These results indicate that TF can interfere with different cell death mechanisms involved in glaucoma pathogenesis and demonstrate the ability of TF to protect RGCs exposed to elevated IOP. Altogether these results suggest that TF could benefit glaucoma patients.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.