ApoTransferrin preserves photoreceptors from death

Abstract

Purpose: Iron has a dual role. Essential for cellular functions, it enhances oxidative stress when it is in excess and under a labile form. Iron accumulation is observed in outer retina of patients with Age-Related Macular Degeneration and in animal models of retinal degeneration. We have previously shown that apotransferrin (apoTf, iron free), protects photoreceptors in models of retinal degenerations due to genetic mutations (rd10 mice and RCS rats). Here, we analyze the protective role of apoTf on a model of photoreceptors degeneration induced by intense white light.

Methods: To follow apoTf distribution in retina after intreavitreal injection, ApoTf (apoTfH) isolated from human plasma and coupled with fluorochrom Alexa488 was injected into anesthetized rats and eyes were collected 2 hours later. Retinal degeneration was induced in 8-week-old Wistar rats by intense white light-emitting diodes providing 6,000 lux during 24 hours. To assess time-dependent effect, apoTfH was injected before or after dark adaptation. In vivo explorations were done by Optical Coherence Tomography and Electroretinography (ERG; scotopic and photophic recordings) 10 days after the end of light exposure. Then eyes were collected and retinal sections were realized to evaluate outer nuclear layer thickness. Eyes were also collected at different time points after the end of illumination to stain iron metabolism proteins and analyze cell death markers.

Results: After injection, apoTfH is present rapidly through the entire retina, especially in Müller glial cells and photoreceptors segments. Intravitreal injection of apoTfH before dark adaptation period has no protective effect. But, if apoTfH is injected just before light exposure, cones and rods histology was preserved against the deleterious effects of light. ERG demonstrate a preservation of electrical responses of photoreceptors in rats treated with apoTfH. Immunostainings show a modification of iron-regulating proteins expression (ferritins and Tf receptor) and a decrease of cell death markers in rats treated with apoTfH.

Conclusions: ApoTfH has high therapeutic potential on neurodenegerative processes implicating oxidative stress.

Keywords: 615 neuroprotection • 648 photoreceptors • 634 oxidation/oxidative or free radical damage