Involvement of phosphatidylinositol 3-kinase and insulin-like growth factor-I in YXLST-mediated neuroprotection.

In the present study, we examine the neuroprotective role of the external Qi of YXLST in cultured retinal neurons. Primary retinal neuronal cultures were grown from retinas of 0-2-day-old Sprague-Dawley rats. Cultures were treated directly with external Qi of YXLST 30 min prior to H(2)O(2) exposure in most experiments. Cell viability was measured by 3,(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide (MTT) assay. Apoptotic cell death was evaluated by the TdT-mediated digoxigenin-dUTP nick-end labeling TUNEL assay, and by DNA laddering analysis. Northern blot analysis was performed to examine the level of insulin-like growth factor-I (IGF-I) gene expression. Phosphatidylinositol 3-kinase (PI3K) assay was performed to study the PI3K activity. The results showed that treatment of external Qi of YXLST significantly attenuated neuronal death that was induced by 24-h exposure to hydrogen peroxide, and greatly inhibited hydrogen peroxide-induced apoptosis. External Qi of YXLST also upregulated IGF-I gene expression and increased PI3K activity. These observations indicate that external Qi-mediated IGF-I expression and PI3K signaling could be one of the mechanisms in neuroprotection by YXLST.