The protective effect of 17 beta-estradiol on oxygen-induced retinopathy and its relation with the changes of malondialdehyde

Evaluating the neuroprotective effect of 17β-estradiol in rodent models of oxidative retinopathies

PURPOSE

To determine the neuroprotective effect of estrogen on the structure and function of the retina exposed to an oxidative stress.

METHODS

Male Sprague-Dawley rat pups were exposed to either hyperoxia (O₂E: from P8 to P14) or bright light (LE: from P14 to P28) with or without 17 β-estradiol (βE₂) treatment. Retinal structure (histology) and function (ERG) were assessed at selected time points.

RESULTS

In the O₂E model, βE₂ injections caused a significant reduction of the ERG and a significantly thinner OPL compared to untreated oxygen-exposed group (O₂-exposed) rats. In contrast, in the LE model βE₂, treatment was beneficial to the retinal structure (thicker ONL) and function (better preserved ERG amplitudes) compared to untreated light-exposed group (light-exposed rats).

CONCLUSION

Our results show that in conditions where the primary target of the oxidative stress is the outer retina (i.e., the photoreceptors) estrogen can protect the retina, while in situations where the inner retina (or retinal vasculature) is the main site of oxidative damage, estrogen may potentiate the detrimental effect of oxidative stress on the retina.

The progress of prophylactic treatment in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a retinal vascular disorder frequently found in premature infants. Different therapeutic strategies have been developed to treat ROP. However, there are still many children with ROP suffering by severe limitations in vision or even blindness. Recently, ROP has been suggested to be caused by abnormal development of the retinal vasculature, but not simply resulted by retinal neovascularization which takes about 4 to 6wk after birth in premature infants. Thus, instead of focusing on how to reduce retinal neovascularization, understanding the pathological changes and mechanisms that occur prior to retinal neovascularization is meaningful, which may lead to identify novel target(s) for the development of novel strategy to promote the healthy growth of retinal blood vessels rather than passively waiting for the appearance of retinal neovascularization and removing it by force. In this review, we discussed recent studies about, 1) the pathogenesis prior to retinal neovascularization in oxygen-induced retinopathy (OIR; a ROP in animal model) and in premature infants with ROP; 2) the preclinical and clinical research on preventive treatment of early OIR and ROP. We will not only highlight the importance of the mechanisms and signalling pathways in regulating early stage of ROP but also will provide guidance for actively exploring novel mechanisms and discovering novel treatments for early phase OIR and ROP prior to retinal neovascularization in the future.

17β-estradiol ameliorates oxygen-induced retinopathy in the early hyperoxic phase

Retinopathy of prematurity (ROP) is a major and leading cause of blindness in premature infants. It has been realized that early treatment for ROP is important. However, all the early treatments of ROP are focusing on peripheral retinal ablation which does not surmount the limit of extinguishing retinal neovascularization and protecting the retinas of children with ROP from the injury of ablation. In this study, we investigated the morphological changes of retina and oxidative stress alterations in the early phase of oxygen-induced retinopathy (OIR) and tested the effects of 17β-estradiol (17β-E2), a nonselective estrogen receptor (ER) agonist, on early phase OIR development. We found that large central capillary-free areas were induced in the retinas of pups exposed to hyperoxia on postnatal day 9 (P9), whereas vascularization was almost complete in the retinas of pups exposed to normoxia at the same age. The concentrations of malondiadehyde (MDA), an end-product of oxidative stress, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a major enzyme producing free radicals, as well as the activity of NADPH oxidase were significantly elevated in the retinas of pups exposed to hyperoxia on P9 and postnatal day 13 (P13) compared to those in age matched pups exposed to normoxia. Treatment with 17β-E2 decreased not only the percentage of the central capillary-free area to total retina area but also the concentrations of MDA and NADPH oxidase as well as the activity of NADPH oxidase in a dose-dependent manner in pups exposed to hyperoxia on p9 and P13. The concentration of VEGF was significantly decreased on P9 but increased on P14 in the retinas of pups exposed to hyperoxia, whereas it was significantly elevated on P9 but decreased on P14 in the retinas of pups treated with 17β-E2. The effect of 17β-E2 could be reversed by the co-treatment with ICI182780, a high affinity estrogen receptor antagonist, which suggested that 17β-E2 might exert its effect on early hyperoxic phase of OIR through estrogen receptor. Our results suggest that treatment with antioxidant drugs at early hyperoxic phase of ROP even before the appearance of retinal neovascularization may be more effective than their application to ROP at late phase, which may abolish the deleterious factors that contribute to retinal neovascularization and promote retinal blood vessels to develop healthily.