March 2008

 

OPHTHALMOLOGY NEWS

 

Taurine ... protection from oxidative stress?


by Matt Young EyeWorld Contributing Editor

 

 

Research studies taurine’s role in glucose-induced cataract formation

Afraid of high-glucose induced cataract? Perhaps you should drink more Red Bull. The Journal of Nutritional Science and Vitaminology didn’t exactly recommend that prophylaxis, but researchers did suggest that taurine—which is a main Red Bull energy drink ingredient—could protect the lens from oxidative stress induced by a high level of glucose. “Taurine has an antioxidant capacity and its level in diabetic cataractous lens is markedly decreased,” wrote study co-author Young H. Kwon, M.D., Ph.D., Department of Food and Nutrition, Seoul National University, Korea.

Drink taurine for prevention?

Investigators tested whether pretreatment with taurine protects a lens against oxidative stress and cataract formation in glucose-induced cataract formation. Rat lenses tested were divided into four groups. The first group consisted of 13 lenses in a normal medium, which served as the control. The second group was composed of 12 lenses that were first incubated in a taurine medium for two days, then rested in a normal medium for six days. The third group was incubated in a normal medium for two days, then placed in a 55.6 mM glucose medium for six days. The fourth group was incubated in a taurine medium for two days, followed by a glucose medium for six days. “The antioxidative effect of 30 mM taurine … showed 34.8% inhibition,” Dr. Kwon noted. However, taurine apparently cannot reverse certain changes in cataract development, as demonstrated by wet weight analysis. Researchers knew that the wet weight of the lens increases with cataract progression. Indeed, the wet weight of lenses placed in the high glucose medium was significantly greater than control lenses. But taurine did not decrease the weight of the lenses subjected to the glucose medium.

Researchers found that taurine did not even interfere with the increase in opacity of the glucose-subjected lenses, as demonstrated by image analysis of the opacities. Using the Image-Pro Analysis (MediaCybernetics, Bethesda, Md. system (where an increase in the grade correlates directly with an increase in opacity), researchers found that the control group demonstrated grade II to III. High glucose without taurine revealed a grade of III to V. The level of opacity with taurine and glucose was II to V. “With the change of the lenticular weight, the opacity of the lens clearly increased with a high concentration of glucose, but taurine did not interfere with this increase of the opacity of the lens,” Dr. Kwon reported. What taurine did do was affect glutathione (GSH) levels. “The oxidative stress response of the lens is characterized by a diminishing level of GSH and reduced activity of antioxidant enzymes,” Dr. Kwon wrote. But with taurine-treated high glucose lenses, GSH increased significantly compared to glucose lenses without taurine. Levels of GSH were even similar to that of the control group. This demonstrated taurine is involved in GSH action. “In the present study, taurine reversed the levels of oxidative stress and kept the GSH level high, although the physiological characteristics of the cataracts were not changed by the addition of taurine,” Dr. Kwon wrote. “Therefore, taurine seems to act as an antioxidant with GSH in high glucose-induced cataracts.”

That makes sense, considering what is already known about taurine. “Taurine is involved in several physiological reactions such as bile acid conjugation, osmoregulation, calcium transport regulation, and cell membrane stabilization,” Dr. Kwon noted. “It is also known to protect tissues against oxidative damage by scavenging hypochlorous acid (HOCL).”

The researchers noted that taurine levels in diabetic cataractous lenses are notably decreased. While antioxidant action of taurine “remains unestablished,” this study gives new evidence that supports this link related to protection against diabetic cataract.

An antioxidant for glaucoma?

Even so, John D. Sheppard, M.D., professor of ophthalmology, microbiology and immunology, Eastern Virginia Medical School, Norfolk, Va., said the better intervention for preventing high-glucose induced cataract is tight glucose control. “Taurine is compensating for poor glucose control,” Dr. Sheppard said. Taurine is interesting, however, as an antioxidant, especially for its neuroprotection against glaucoma, Dr. Sheppard said. Gingko still may be even better in that regard, he said. “One thousand milligrams of taurine six times a day may not be specific enough to target tissue,” Dr. Sheppard said. “There is more support that gingko is effective in this regard.” Performing scientific studies to compare antioxidants for glaucoma are difficult, however, he said. “The costs of producing this kind of data in a chronic slowly progressive disease would be prohibitive,” Dr. Sheppard said. “Nobody is going to make money selling taurine or gingko.”

Editors’ note: Dr. Kwon has no financial interests related to this study. Dr. Sheppard has no financial interests related to his comments.

Contact Information

Kwon: hye0414@snu.ac.kr

Sheppard: 757-622-2200, docshep@hotmail.com

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