Anti-inflammatory effects of rhaponticin on LPS-induced human endothelial cells through inhibition of MAPK/NF-κβ signaling pathways

Abstract

The untreated systemic chronic inflammation leads to autoimmune diseases, hyperglycemia, cardiovascular diseases, type 2 diabetes, hypertension, osteoporosis, and so on. Phytochemicals effectively inhibit the inflammation, and numerous studies have proved that the phytocomponents possess anti-inflammatory property via inhibiting the cyclooxygenase and lipoxygenase signaling pathways. Rhaponticin is one such phytochemical obtained from the perennial plant Rheum rhaponticum L. belonging to Polygonaceae family. We assessed the anti-inflammatory potency of rhaponticin in endothelial cells induced with lipopolysaccharides (LPS). Four different endothelial cells induced with LPS were treated with rhaponticin and assessed for the nitric oxide generation. The cytotoxic potency of rhaponticin was evaluated in endothelial cells using the 3-(4,5-dimethylthizaol-2yl)-2,5-diphenyl tetrazolium bromide assay. The tumor necrosis factor-α (TNF-α) synthesis was quantified using the commercially available assay kit. The inflammatory signaling protein gene expression of TNF-α, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and interleukin-1β (IL-1β) was analyzed with quantitative polymerase chain reaction (PCR) analysis. The gene expression of NADPH oxidase (NOX) cytoplasmic catalytic subunits gp91^phox , p47^phox , and p22^phox was assessed with real-time PCR analysis. Finally, to confirm the anti-inflammatory potency of rhaponticin, the nuclear factor kappa B (NFκB) and mitogen-activated protein kinase (MAPK) signaling protein expression was analyzed with immunoblotting analysis. Rhaponticin treatment significantly decreased the levels of nitric oxide and TNF-α synthesis in LPS-induced endothelial cells. It significantly decreased the gene expression of inflammatory proteins and NOX signaling protein. The protein expression of NFκB and MAPK signaling proteins was drastically decreased in rhaponticin-treated endothelial cells induced with LPS. Overall, our results confirm that rhaponticin effectively inhibited the inflammation triggered by LPS in endothelial cells via downregulating iNOS, COX2, and NFκB and MAPK signaling pathways.

Keywords: NFκB and MAPK signaling; endothelial cells; inflammation; lipopolysaccharides; rhaponticin.