**5. Conclusions**

The data presented in this study indicate that AST could protect photoreceptor cells from apoptosis secondary to high glucose-induced oxidative stress. In addition, we have demonstrated that the protective effects of AST are mediated by upregulated Nrf2 and that increased expression of downstream Phase II enzymes results from activation of the PI3K/Akt pathway. Thus, AST should be considered as a nutritional supplement that could benefit patients with diabetes, especially in view of preventing the visual loss in DR.

**Author Contributions:** Conceptualization, C.-M.Y. and C.-H.Y.; methodology, T.-T.L. and C.-H.Y.; software, T.-T.L. and C.-H.Y.; validation, C.-M.Y. and C.-H.Y.; formal analysis, T.-T.L. and C.-H.Y.; investigation, T.-T.L., C.-M.Y., and C.-H.Y.; resources, C.-H.Y.; data curation, T.-T.L., C.-M.Y., and C.-H.Y.; writing—original draft preparation, T.-T.L.; writing—review and editing, C.-M.Y. and C.-H.Y.; visualization, T.-T.L.; supervision, C.-M.Y. and C.-H.Y.; funding acquisition, C.-M.Y. and C.-H.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We thank Zi-Yun Weng for the technical support.

**Conflicts of Interest:** The authors declare no conflict of interest.
