The results of the study from researchers based at the Chinese University of Hong Kong and the Hong Kong Eye Hospital were published in the Journal of Agricultural and Food Chemistry and indicate that green tea consumption could benefit the eye against oxidative stress.
The scientists analyzed eye tissue from rats that drank green tea and found that the lens, retina and other tissues absorbed significant amounts of green tea catechins.
Although many antioxidants have been studied in the eye, the authors claim that theirs is the first paper to show distribution of individual catechins after ingestion of green tea extract and to evaluate their in vivo antioxidative effects in various parts of the eye.
The authors said that oxidative stress causes biological disturbances such as DNA damage and activation of proteolytic enzymes that can lead to tissue cell damage or dysfunction and eventually many ophthalmic diseases.
“Photooxidative stress can inactivate catalase in the lens to initiate cataract formation, while long-term effects of reactive oxygen intermediates could damage retinal tissue cells retinal pigment epithelium, and choriocapillaries . Oxidation is also associated with primary open angle glaucoma (POAG),” they said.
Green tea benefits
Other reported benefits for green tea have been risk reduction in terms of educing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, as well as aiding in weight management.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, and the four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate ECG), and epicatechin (EC).
The success has translated into a booming extract market, valued at a around $44m (€29.7m), according to recent report from Frost & Sullivan, and they predict the market is will grow by more than 13 per cent over the next seven years.
Key players include DSM, Taiyo, and Tate & Lyle.
Green tea extract (GTE) in tablet form was suspended in 0.5 mL of water, said the authors.
A dosage of 550 mg/kg of GTE was fed to the rats and the authors added that the doses of catechins were comparable to most published reports: 178 mg/kg epigallocatechin gallate - EGCG, 82.7 mg/kg, epicatechin gallate - ECG, 80.7 mg/kg gallocatechin gallate - GCG, 72.0 mg/kg epicatechin - EC, 58.7 mg/kg epigallocatechin - EGC, 56.7 mg/kg gallocatechin - GC, and 24 mg/kg catechin - C.
The rats, said the researchers, were sacrificed at different time intervals. And the eyes of the animals were then dissected into cornea, lens, retina, choroid-sclera, vitreous humor, and aqueous humor for analysis of catechins and 8-epi-isoprostane by HPLC-ECD and GC-NCI-MS, respectively.
Analysis of eye tissues demonstrated that eye structures absorbed significant amounts of individual catechins, said the researchers.
And the time of maximum concentration of the catechins varied from 30 minutes to around 12 hours, they continued.
The authors found that catechins were differentially distributed in eye tissues - the retina absorbed the highest levels of gallocatechin, while the aqueous humor tended to absorb epigallocatechin.
Significant reductions in 8-epi-isoprostane levels were found in the compartments except the choroid-sclera or plasma, indicating antioxidative activities of catechins in these tissues, concluded the team.
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print: DOI: 10.1021/jf9032602
Title: Green Tea Catechins and Their Oxidative Protection in the Rat Eye
Authors: C. Pui Pang et al