Purpose: To study the effect of systemic hypoxia-inducible factor prolyl hydroxylase inhibition (HIF PHDi) in the rat 50/10 oxygen-induced retinopathy (OIR) model.
Methods: Oxygen-induced retinopathy was created with the rat 50/10 OIR model. OIR animals received intraperitoneal injections of dimethyloxalylglycine (DMOG, 200 μg/g), an antagonist of α-ketoglutarate cofactor and inhibitor for HIF PHD, on postnatal day (P)3, P5, and P7. Control animals received intraperitoneal injections of PBS. On P14 and P21, animals were humanely killed and the effect on vascular obliteration, tortuosity, and neovascularization quantified. To analyze HIF and erythropoietin, rats at P5 were injected with DMOG (200 μg/g). Western blot or ELISA measured the levels of HIF-1 and Epo protein. Epo mRNA was measured by quantitative PCR.
Results: Alternating hyperoxia and hypoxia in untreated rats led to peripheral vascular obliteration on day P14 and P21. Rats that were treated with systemic DMOG by intraperitoneal injections had 3 times less ischemia and greater peripheral vascularity (P = 0.001) than control animals treated with PBS injections. Neovascularization similarly decreased by a factor of 3 (P = 0.0002). Intraperitoneal DMOG administration increased the levels of HIF and Epo in the liver and brain. Serum Epo also increased 6-fold (P = 0.0016). Systemic DMOG had no adverse effect on growth of rats treated with oxygen.
Conclusions: One of the many controversies in the study of retinopathy of prematurity is whether hyperoxia or alternating hyperoxia and hypoxia creates the disease phenotype in humans. We have previously demonstrated that PHDi prevents OIR in mice exposed to 5 days of sustained 75% oxygen followed by 5 days of 21% oxygen. The 50/10 rat experiments demonstrate that PHDi is also effective in a 24-hour alternating hyperoxia-hypoxia model. The rat OIR model further validates the therapeutic value of HIF PHDi to prevent retinopathy of prematurity because it reduces oxygen-induced vascular obliteration and retinovascular growth attenuation in prolonged and/or alternating hyperoxia.
Keywords: angiogenesis; erythropoietin; hypoxia-inducible factor; ischemia; prolyl hydroxylase inhibition; retina; retinopathy of prematurity.