Abstract
Green tea extracts exhibit anti-oxidative and anti-inflammatory actions in different disease conditions. We hypothesized that green tea extract and its catechin constituents ameliorate sodium iodate-induced retinal degeneration in rats by counteracting oxidative stress. In this study, adult Sprague-Dawley rats were intravenously injected with a single dose of sodium iodate. Green tea extract (GTE; Theaphenon-E) or combinations of its catechin constituents, including (−)-epigallocatechin gallate (EGCG), were administered intra-gastrically before injection. Live imaging analysis using confocal scanning laser ophthalmoscopy and spectral-domain optical coherence tomography showed a progressive increase of degenerating profile across the retinal surface and decrease in thickness of outer nuclear layer (ONL) at Day-14 of post-injection. These lesions were significantly ameliorated by Theaphenon-E and catechin combinations with EGCG. Catechins with exclusion of EGCG did not show obvious protective effect. Histological analyses confirmed that Theaphenon-E and catechins containing EGCG protect the retina by reducing ONL disruption. Retinal protective effects were associated with reduced expression of superoxide dismutase, glutathione peroxidase and caspase-3, and suppression of 8-iso-Prostaglandin F2α generation in the retina. In summary, GTE and its catechin constituents are potent anti-oxidants that offer neuroprotection to the outer retinal degeneration after sodium iodate insult, among which EGCG is the most active constituent.
Highlights
In the retina for the groups pre-treated with GTE Theaphenon E, combination of its catechins containing epigallocatechin gallate (EGCG)
We have investigated the effects of GTE and its catechin constituents on retinal lesions generated by sodium iodate-induced oxidative stress in adult rat retina
Major findings include: i) in vivo imaging using confocal scanning laser ophthalmoscopy (cSLO) and SD-optical coherence tomography (OCT) shows that sodium iodate induces a progressive and consistent damage to the retina; ii) histological examinations reveal a loss of retinal pigment epithelium (RPE) and disruption of cellular arrangement in the cone and rod layer and the outer nuclear layer; iii) these damages are alleviated effectively by the GTE Theaphenon E, and by its catechin constituents containing EGCG; iv) GTE and its catechin constituents suppress significantly the increases in Sod[1], Gpx[3] and caspase 3, and reduce production of 8-iso-PGF2α after sodium iodate insult
Summary
In the retina for the groups pre-treated with GTE Theaphenon E, combination of its catechins containing EGCG. These increases were significantly suppressed by treatments with Theaphenon E, catechins with EGCG or EGCG alone, but was not obvious with catechin without EGCG. We hypothesized that GTE and its catechin constituents ameliorate sodium iodate-induced retinal degeneration in rats by counteracting oxidative stress induced by sodium iodate. To address this hypothesis, we determined the treatment effects of oral intake of GTE or combinations of catechins on progressive RPE and photoreceptor degeneration induced by sodium iodate in rats, using live imaging techniques including confocal scanning laser ophthalmoscopy (cSLO) and spectral-domain optical coherence tomography (OCT). The biochemical and histological effects of catechin treatments on the levels of oxidative stress markers were evaluated
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