Green tea catechins are able to penetrate eye tissue, which may help protect against glaucoma and other eye diseases, according to Hong Kong researchers.
In the introduction to their article published online on January 19, 2010 in the Journal of Agricultural and Food Chemistry, Chi Pui Pang of the Chinese University of Hong Kong and associates explain that oxidative stress causes DNA damage and activation of proteolytic enzymes which lead to the tissue damage observed in the development of eye diseases such as cataract and glaucoma. The antioxidant properties of polyphenols contained in green tea make the widely-consumed beverage a good candidate for eye protection, yet the delivery of green tea catechins to various areas of the eye had not previously been evaluated.
Using 9 week old rats, Dr Pang and colleagues orally administered a green tea extract that provided the following beneficial catechin compounds: epigallocatechin gallate (EGCG), epicatechin gallate (ECG), gallocatechin gallate (GCG), epicatechin (EC), epigallocatechin (EGC), gallocatechin (GC) and catechin. Catechin and 8-epi-isoprostane (a marker of oxidative stress) levels were measured in the animals' eye tissues at varying time points up to 20 hours following green tea extract administration.
The team found varying distribution of catechins throughout the animals' cornea, lens, retina, choroid-sclera, vitreous humor, and aqueous humor. Gallocatechin was present at the highest concentration in the retina, and EGC in aqueous humor. Maximum catechin concentration varied from one half to 12.2 hours. Although many studies have focused on ECGC, eye tissue levels of other catechins were found to be higher in the current investigation. A significant reduction in 8-epi-isoprostane rapidly followed green tea administration and was well maintained in all tissue and fluid examined with the exception of the choroid-sclera, demonstrating the antioxidant activity of catechins absorbed by these areas.
"To the best of our knowledge this 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 mammalian eye," the authors announce. "Our dosage reduced oxidative stress in some eye tissues for up to 20 hours. Our results indicate that green tea consumption could benefit the eye against oxidative stress," they conclude.
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The inability to efficiently extricate the fluid from the eye causes an increase in intraocular pressure (IOP). The tiny, delicate nerve fibers that make up the optic nerve at the back of the eye are slowly destroyed. Because the optic nerve relays visual messages from the eye to the brain, where seeing actually takes place, the health of this nerve is essential to sight. Restricting the free flow of aqueous humor, as seen by narrowing, hardening, or constriction of the exit channels, can be a purveyor of glaucoma.
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