Abstract.Retinal pigmented epithelial cell (RPE) oxidative stress is known to have a vital role in the etiology of age-related macular degeneration (AMD). The present study aimed to investigate whether allicin, a natural product with antioxidant activity, was able to protect RPEs (ARPE-19) from hydrogen peroxide (H 2 O 2 )-induced damage, and to determine the underlying mechanisms. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay was used to determine cellular viability, and reactive oxygen species (ROS) were detected using a ROS Assay kit. The results demonstrated that allicin was able to protect ARPE-19 cells from H 2 O 2 -induced damage in a dose-dependent manner. In addition, allicin attenuated oxidative stress by reducing the levels of intracellular ROS and malondialdehyde (MDA), and enhancing the glutathione/glutathione disulfide (GSSG) ratio. With regards to the underlying mechanism, allicin was able to markedly modulate the expression levels of ROS-associated enzymes, including superoxide dismutase, NADPH oxidase 4 and NAD(P)H dehydrogenase quinone 1, and elevate the activity of nuclear factor erythroid 2-related factor 2 in the H 2 O 2 -stimulated ARPE-19 cells. These results suggested that allicin may exert protective effects against H 2 O 2 -induced cytotoxicity in RPEs via ROS regulation.

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Abstract.It has been previously demonstrated that there are interactions between sirtuin 1 (SirT1) and signal transducer and activator of transcription 3 (STAT3), which have versatile roles in various microenvironments. However, whether or not there is crosstalk between these two molecules during oxidative stress, and what mechanism of crosstalk occurs in retinal pigmented epithelium cells (RPEs), the protection of which may delay the process of age-related macular degeneration (AMD), has required further elucidation. The present study aimed to investigate the interactions between SirT1 and STAT3 in RPEs, following exposure to oxidative stress. The rates of proliferation and apoptosis, levels of intracellular reactive oxygen species and cell senescence of RPEs, induced by oxidants [H 2 O 2 and oxidized low density lipoprotein (oxLDL)], were evaluated. The results revealed a downregulation of SirT1 expression, and an upregulation of STAT3 expression during oxidative stress. Further investigation indicated that SirT1 protected RPEs from oxidative stress-induced damage. Furthermore, gain-and loss-of-function experiments indicated that SirT1 had negative effects on the regulation of STAT3 expression in RPEs during oxidative stress. Notably, STAT3 directly protected the cells from oxidative stress, rather than depending on SirT1. Additionally, the protective effects of STAT3 had no association with the modulation of cell senescence during oxidative stress. In conclusion, SirT1 had negative effects on the regulation of STAT3 expression during oxidative stress. However, SirT1 and STAT3 demonstrated protective roles against oxidative stress in RPEs. These results therefore suggested that there was an equilibrium mechanism between SirT1 and STAT3 against oxidative stress, meaning that an equilibrium mechanism is required to be considered when combined application of STAT3 and SirT1 were performed to treat AMD.