Protective Effects Of Taurine On Retinopathy Of Diabetic Rats And Its Mechanisms

Taurine(named 2-aminoethane sulfonic acid), a β-amino acid in vivo, belongs to nonprotein amino acid and mainly distributes in excitable tissues such as nervous systems, muscle tissues, retinas, lymphocytic cells and blood platelets. Taurine is one of the important anti-disease factors as an endogenetic cell protectant, and thereby plays an essential physiological role in human body. In retina, taurine is the most abundant free amino acid, serving as an inhibitor of neuromodulator. This anti-neuromodulator function may explain its ability to quench the excitotoxic effect of glutamate demonstrated in most recent researches. Many investigations display that, in the early phase of diabetic retinopathy, dysfunctions of nervous and glial cell have taken place before capillary disorder, including increased expression of the intermediate filament glial fibrillary acidic protein (GFAP) in Müller cells, functional disturbance of glutamate transporters, activation of N-methyl-D-aspartate subtype of glutamate receptors(NR1)and etc; Along with the elongation of diabetic retina course, taurine contents gradually decrease. In the report, we investigated the effects of taurine on diabetic retina in STZ-induced diabetic rats so as to study the molecular mechanism of the effects of taurine on diabetic rat retina. Amino acid analyses were used to assay amino acid contents. Transmission electron microscope was used to observe effects of taurine on retina ultrastructural changes of diabetic rats. We observed effects of taurine on GFAP,glutamate transporters(GLAST),NR1,glutamate(Glu) and γ-aminobutyric acid(GABA). The results showed that: (1) Histopathological and ultrastructural changes are ameliorated apparently under 1.2% taurine. (2) In early stages of diabetic rat retina, the contents and immunoreactions of Glu and GABA were increased. However, decreases in the contents and molecule expression of Glu and GABA were detected with enhanced intake of taurine. (3) From the second to the third month, the mRNA and protein expression of GFAP have gradually increased. Taurine could down-regulate both expressions in this period. (4) In the first month, the mRNA expression of GLAST decreased and the mRNA expression of NR1 increased in diabetic rat retina. Taurine was able to up-regulate the former expression while down-regulate the latter in diabetic rat retina during this time period. The results above suggest that: (1) Taurine can effectively improve changes of histopathology and ultrastructure in diabetic rat retina. (2) Taurine is capable of decreasing the contents of Glu and GABA. (3) Taurine can restrain excitotoxicity of glutamate, up-regulate the mRNA expression of GLAST, down-regulate the mRNA and protein expression of GFAP, and the mRNA expression of NR1. These observations suggest that taurine may play a key role of nerve protection.