Dark-Rearing (DR) precludes the initiating event in OIR and eliminates the pathology seen in the second phase of disease: Rationale for novel non-invasive treatment for ROP

Abstract

Purpose : The initiating event in ROP is delayed retinal vascularization as a consequence of required oxygen supplementation. We hypothesized neonates in high O2 environments should be reared in total darkness, creating a “metabolic sump” via continuous photoreceptor depolarization, eliminating the initiating event in the disease.

Methods : 4 groups of SD rats were examined at P14 & P18: 1) Room Air + normal light reared (NLR); 2) Room air + dark rearing (DR). 3) 50/10 OIR + normal light 4) 50/10 OIR + dark rearing. Retinae were examined for vascular density index (VDI), vaso-obliteration & neovascularization, hypoxyprobe-1, astrocyte ensheathment, ultrastructure via TEM and gene expression via qPCR. Electroretinograms (ERG) were recorded at P18 & P25 in OIR, & in long term DR rats (P30/60/90). Retinal O2 profiles were modeled for P14 at 60 & 75% inspired O2 in NLR & DR.

Results : Confirming our proof of principle, DR rats had a higher vascular density than NLR rats in room air (VDI=43±1.0 vs.38±1.1 p<0.05 - P7). DR protected vessels from vaso-obliteration (20.6% ± 4.9 v 39.0% ± 4.0 p<0.05). In the hypoxic 2nd phase of OIR, DR reduced pre-retinal neovascularization (4.1% ± 0.9 v 15.8% ± 1.3 p<0.05); tissue hypoxia as evidenced by reduced HP1; protected astrocytes & pericytes from hypoxic damage; and preserved retinal ultrastructure. DR prevented upregulation of HIF1a (65.5% ± 27.2 v -20.4 ± 4.6 p<0.05), VEGF164 (496.6% ± 11.1 v 291.2% ± 60.1 p<0.05) and AP1/Jun (179.8% ± 26.9 v -51.7 ± 16.7, p<0.05) in peripheral retina at P14. DR had no detrimental effects on retinal function as evidenced by ERG at P18 and P25 in OIR, & after long-term DR. O2 profile modeling under DR at 60% inspired O2 at P14 showed that inner retina maintains 'physiological hypoxia' in DR but not in NLR ,whilst 75% O2 overwhelms the protective effect of DR.

Conclusions : DR precludes the initiation of ROP by maintaining retinal vascularization during the 1st phase of OIR. As a consequence, when neonates are returned to RA, the retina is protected from hypoxia-induced vaso-proliferation in phase 2 of ROP and it’s associated damaging effects on retinal structure and function. This cost-effective, non-invasive intervention by reducing disease severity can supplement current therapies and, may negate the need for invasive therapies including laser and anti-VEGF. Show more