Celastrol Ameliorates Inflammation in Human Retinal Pigment Epithelial Cells by Suppressing NF-κB Signaling

Celastrol is a triterpenoid quinine methide that exerts important biological effects on a variety of disease models. In this study, we aim to assess the ability of celastrol to inhibit lipopolysaccharide (LPS)-induced inflammation in retinal pigment epithelial (RPE) cells.

Primary cultures of human RPE (HRPE) cells and ARPE-19 cell lines were treated with celastrol alone or in combination with LPS. The cytotoxic effect of celastrol on RPE cells was determined by the CCK-8 assay. Protein and mRNA levels of inflammatory cytokines, including IL-6, IL-8, and MCP-1, were detected by flow cytometry or by real-time fluorescent quantitative PCR, respectively. The levels of phosphorylated intermediates in the NF-κB signaling pathway (such as IκBα/β and p65) and MAPK signaling pathway (p38MAPK, SAPK/JNK, and p42/p44MAPK) were detected by western blotting.

Celastrol significantly inhibited LPS-induced expression of protein and mRNA expression levels encoding the proinflammatory cytokines, IL-6, IL-8, and MCP-1, in both HRPE and ARPE-19 cells. Cell viability and apoptosis assays revealed that celastrol had no apparent cytotoxic effect and it inhibited apoptosis of RPE cells at concentrations of less than 1 μM. Mechanistically, RPE cells that were pretreated with celastrol exhibited a substantial decrease in phosphorylation of the NF-κB pathway regulators, IKKα/β and IκBα, and subsequently inactivated P65, suggesting that celastrol ameliorates LPS-induced inflammation by suppressing the NF-κB signaling pathway.

Our results provide evidence that celastrol is a potent anti-inflammatory agent in RPE cells and it may have potential applications in prevention and treatment of age-related macular degeneration.