Abstract
Retinal ischemia-reperfusion (rI/R) generates an oxidative condition causing the death of neuronal cells. Epigallocatechin 3-gallate (EGCG) has antioxidant and anti-inflammatory properties. Nonetheless, its correlation with the pathway of nuclear factor erythroid 2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) for the protection of the retina is unknown. We aimed to evaluate the neuroprotective efficacy of single-doses of EGCG in rI/R and its association with Nrf2/Ho-1 expression. In albino rabbits, rI/R was induced and single-doses of EGCG in saline (0–30 mg/kg) were intravenously administered to select an optimal EGCG concentration that protects from retina damage. To reach this goal, retinal structural changes, gliosis by glial fibrillary acidic protein (GFAP) immunostaining, and lipid peroxidation level by TBARS (thiobarbituric acid reactive substance) assay were determined. EGCG in a dose of 15 mg/kg (E15) presented the lowest levels of histological damage, gliosis, and oxidative stress in the studied groups. To determine the neuroprotective efficacy of E15 in a timeline (6, 24, and 48 h after rI/R), and its association with the Nrf2/HO-1 pathway, the following assays were done by immunofluorescence: apoptosis (TUNEL assay), necrosis (high-mobility group box-1; HMGB1), Nrf2, and HO-1. In addition, the Ho-1 mRNA (qPCR) and lipid peroxidation levels were evaluated. E15 showed a protective effect during the first 6 h, compared to 24 and 48 h after rI/R, as revealed by a decrease in the levels of all damage markers. Nuclear translocation Nrf2 and HO-1 staining were increased, including Ho-1 mRNA levels. In conclusion, a single dose of E15 decreases the death of neuronal cells induced by oxidative stress during the first 6 h after rI/R. This protective effect is associated with the nuclear translocation of Nrf2 and with an elevation of Ho-1 expression.
Highlights
Retinal ischemia/reperfusion occurs in acute angle-closure glaucoma, retinal vascular occlusion, diabetic retinopathy, and retinopathy of prematurity, causing irreversible neuronal damage due to increased levels of reactive oxygen species (ROS)
Under an oxidative stimulus, nuclear factor E2-related factor 2 (Nrf2) is translocated to the nucleus where it interacts with small proteins, and binds to ARE to activate the transcription of antioxidant genes such as the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex: quinone oxidoreductase 1, glutathione S-transferases (GSTs), gamma-glutamylcysteine ligase, and heme oxygenase 1 (HO-1) [3]
It can be observed that the inner nuclear layer (INL) has cellular loss characterized by pinocytic nuclei, vacuolization, edema, and disorganization between the INL and the outer nuclear layer (ONL) in the vehicle treated group
Summary
Retinal ischemia/reperfusion (rI/R) occurs in acute angle-closure glaucoma, retinal vascular occlusion, diabetic retinopathy, and retinopathy of prematurity, causing irreversible neuronal damage due to increased levels of reactive oxygen species (ROS). Under an oxidative stimulus, Nrf is translocated to the nucleus where it interacts with small proteins, and binds to ARE to activate the transcription of antioxidant genes such as the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex: quinone oxidoreductase 1, glutathione S-transferases (GSTs), gamma-glutamylcysteine ligase, and heme oxygenase 1 (HO-1) [3]. Epigallocatechin 3-gallate (EGCG) is a flavonoid present in large amounts in the plant Camellia sinensis (green tea) and, due to its antioxidative and anti-inflammatory properties, it has been proposed as a protective agent in damaged retinas by several kinds of oxidative insults [9,10,11,12]. EGCG increases Nrf2/HO-1 activity in a dose-dependent manner. High concentrations and long-term use could favor a pro-oxidant environment on retinas, rendering the determination of the optimal dose necessary [13]
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