Gambogic acid ameliorates high glucose– and palmitic acid–induced inflammatory response in ARPE-19 cells via activating Nrf2 signaling pathway: ex vivo

Diabetic retinopathy (DR) is a serious microvascular complication of diabetes. Gambogic acid has been reported to have anti-inflammatory effect. However, the effect of GA on inflammatory response of ARPE-19 cells remains unclear. In our study, ARPE-19 cells were stimulated by palmitic acid (PA) induction in the presence of 30 mM glucose and then treated with 0.5, 1, 2, 5, 10, or 20 μM GA. CCK-8 assay showed that cell viability was increased by GA treatment at doses of 0.5, 1, and 2 μM instead of higher doses. ELISA analysis found that GA dose-dependently reduced the production of pro-inflammatory mediators TNF-α and IL-1β. Western blot indicated that GA downregulated the expression of NLRP3 inflammasome components including TXNIP, NLRP3, ASC, cleaved-caspase-1, and cleaved-IL-1β in a dose-dependent manner. In addition, Western blot and immunofluorescence analysis suggested that GA effectively increased the protein level of nuclear factor E2-related factor-2 (Nrf2). RT-qPCR showed that GA significantly increased the mRNA levels of Heme oxygenase-1 (HO-1) and NADPH:quinone oxidoreductase1 (NQO1). Furthermore, Nrf2 siRNA transfection confirmed the above effects of GA. In total, subtoxic doses of GA significantly flattened the inflammatory response induced by HG and PA in ARPE-19 cells via modulating the Nrf2 signaling pathway.