Ikuo Koyama

Reactivity of Taurine with Aldehydes and Its Physiological Role.

The chemical reactions of the amino group of taurine with aldehydes were investigated. Glucose, acetaldehyde, and malondialdehyde were used as aldehydes. After taurine had reacted, the amounts of remaining taurine and aldehydes were measured, and the reactivity was evaluated. Amino acids such as glycine, alpha-alanine, and beta-alanine were compared because of their structural resemblance to each other. Taurine showed a high reactivity with each one of the aldehydes tested. It is known that protein is altered through reactions of the amino group with various aldehydes. Low density lipoprotein (LDL) was used as a model protein and the inhibiting effect of taurine against the modification of LDL by malondialdehyde was examined. It was shown that the inhibiting effects of taurine correlated with the reactivity of malondialdehyde with amino acids. Further, the taurine-glucose reaction product showed an antioxidative effect on the peroxidation of liposomes made of yolk phosphatidylcholine as a biomembrane model. The results suggest the possibility of an inhibiting effect of taurine against the modification of protein, as well as an antioxidative effect through the reactions of taurine with aldehydes in vivo.

Reactivity of taurine with aldehydes and its physiological role.

The chemical reactions of the amino group of taurine with aldehydes were investigated. Glucose, acetaldehyde, and malondialdehyde were used as aldehydes. After taurine had reacted, the amounts of remaining taurine and aldehydes were measured, and the reactivity was evaluated. Amino acids such as glycine, alpha-alanine, and beta-alanine were compared because of their structural resemblance to each other. Taurine showed a high reactivity with each one of the aldehydes tested. It is known that protein is altered through reactions of the amino group with various aldehydes. Low density lipoprotein (LDL) was used as a model protein and the inhibiting effect of taurine against the modification of LDL by malondialdehyde was examined. It was shown that the inhibiting effects of taurine correlated with the reactivity of malondialdehyde with amino acids. Further, the taurine-glucose reaction product showed an antioxidative effect on the peroxidation of liposomes made of yolk phosphatidylcholine as a biomembrane model. The results suggest the possibility of an inhibiting effect of taurine against the modification of protein, as well as an antioxidative effect through the reactions of taurine with aldehydes in vivo.

THE REACTIVITY OF TAURINE WITH HYPOCHLOROUS ACID AND ITS APPLICATION FOR EYE DROPS

The ability of taurine to protect biomembranes attacked by HOCl was examined using canine erythrocytes which had been pre-treated with HOCl. Of the amino acids tested, taurine was the most effective in inhibiting attack by HOCl, followed by glycine, alpha-alanine and beta-alanine. During the incubation of HOCl-treated erythrocytes with taurine, an appreciable amount of monochlorotaurine (TauNHCl) was detected in the supernatant. This suggests that taurine may remove the oxidized chlorine from HOCl-treated erythrocytes, resulting in the production of TauNHCl. The effect of taurine on the removal of Cl+ moiety was examined using Sepharose gel with amino groups. Taurine removed Cl+ from HOCl-treated Sepharose gel. The yield of TauNHCl depended on the concentration of taurine. The effectiveness of taurine in preventing ocular surface damage caused by HOCl was investigated in albino rabbits. The activity of lactate dehydrogenase (LDH) released from ocular tissues into tears during eye irritation was used as an index of ocular surface damage. Taurine effectively protected ocular surface tissues from damage induced by HOCl, and arrested the progression of tissue damage that had already been initiated by HOCl. These finding suggest that taurine may be clinically useful in the treatment of ocular surface damage caused by oxidants such as HOCl.