Tetrahydrocurcumin Attenuates NaIO3-Induced Retinal Oxidative Injury via Suppression of NOX2-Derived ROS-Mediated Apoptosis

Oxidative stress is a major contributor to the development of age-related macular degeneration (AMD), and excessive oxidative stress can induce retinal pigment epithelium (RPE) dysfunction, apoptosis, and retinal degeneration. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) is a major enzymatic source of reactive oxygen species (ROS); however, its mechanistic role in sodium iodate (NaIO3)-induced oxidative injury remains unclear. Tetrahydrocurcumin (THC), the major metabolite of curcumin, exhibits potent antioxidant and cytoprotective activities, but its protective effects against AMD-associated retinal degeneration have not been fully elucidated. In the present study, we investigated whether THC protects against NaIO3-induced ROS-mediated apoptosis in RPE cells through regulation of NOX2 signaling. In vitro, THC significantly attenuated NaIO3-induced cytotoxicity and prevented apoptosis by suppressing hydrogen peroxide (H2O2) production and intracellular ROS accumulation in ARPE-19 cells. THC also preserved mitochondrial membrane potential by inhibiting the Src/p47phox/NOX2 signaling pathway and subsequently attenuated mitochondria-mediated apoptotic signaling. Furthermore, THC markedly reduced the expression of apoptotic proteins, including Bax, cleaved caspase-3, and cleaved PARP, concomitantly with suppression of Ras/Raf/MEK/ERK signaling. Mechanistically, treatment with the selective NOX2 inhibitor GSK2795039 significantly attenuated NaIO3-induced ROS accumulation and mitochondrial depolarization, while co-treatment with THC further enhanced these protective effects. In vivo, THC ameliorated NaIO3-induced retinal structural abnormalities by preserving the outer nuclear layer (ONL), reducing caspase-3 expression, and improving pupillary light responses in mice. Collectively, these findings demonstrate that THC protects against NaIO3-induced retinal degeneration through suppressing NOX2-dependent oxidative stress and downstream Ras/Raf/MEK/ERK-mediated apoptotic signaling, highlighting its potential as a therapeutic candidate for AMD and other oxidative stress-related retinal disorders.