Summary Diabetic cataract is an ocular disease represented as blindness by lens opacification. Oxidative as well as osmotic stress caused by accumulation of polyols within the lens has been shown to be associated with glucose-induced cataractogenesis. Taurine has an antioxidant capacity and its level in diabetic cataractous lens is markedly decreased. Therefore, we investigated whether taurine is a part of antioxidative defense mechanism involved in protecting the lens against high glucose-induced oxidative stress and tissue damage. Lenses were isolated from male Sprague-Dawley rats weighing about 180-200 g and cultured in high glucose medium (55.6 m M ) for 6 d as a model of high glucose-induced cataractogenesis. To investigate the antioxidative effect of taurine, 30 m M taurine was added in normal medium for 2 d before the addition of high glucose. The culture of lenses in high glucose medium increased the weight and opacity of lenses of and the carbonylated protein level, and decreased glutathione (GSH) content. Although there were no significant effects of taurine on the weight or opacity of lenses, pretreatment of lenses with 30 m M taurine significantly reversed the level of protein carbonylation and GSH to those of controls. Therefore, taurine might spare GSH and protect the lens from oxidative stress induced by a high concentration of glucose. Key Words cataract, oxidative stress, glucose, taurine, GSH Diabetic cataract, one of the secondary complications of diabetes, is the major cause of blindness due to the opacification of the lens. The lens is the only transparent organ in the body and focuses light on the retina. The main components of the lens are about 63% of water and 35% of protein which is composed of over 90% of crystallins ( 1 ). Because the turnover rate of crystallins is very slow compared to many other organs, the reversal of protein modification by several factors is slow and it can be thought to induce cataract ( 2 ). The mechanism of cataractogenesis is not clear, but the osmotic stress and the oxidative stress have been thought of as the major causes of cataractogenesis ( 3 ). The osmotic stress by excessive accumulation of sorbitol formed from elevated glucose has been reported as the main mechanism of diabetic cataract. But several studies indicated that oxidative stress may be the major contributor to a sugar-induced cataractogenesis, which can be prevented or attenuated by antioxidants such as vitamin E ( 4 ), glutathione (GSH) ( 5 ), vitamin C ( 6 ), and Nacetylcysteine ( 7 ). It is shown that levels of major antioxidants were reduced in cataractogenesis by osmotic compensation against sorbitol accumulation ( 8 , 9 ). Along with the loss of antioxidants, the increase of glucose concentration in the lens would result in higher free radical generation and nonenzymatic glycation ( 10 , 11 ).Taurine (2-aminoethanesulfonic acid) has a sulphonic acid group, which is not found in other amino acids. Because this amino acid is not used for the synthesis of protein, it is abundant as a fre...

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