Notoginsenoside R1 protects human keratinocytes HaCaT from LPS-induced inflammatory injury by downregulation of Myd88

Burn injury is a gigantic challenge in public health which brings multiple negative effects to patients both in physical and spiritual aspects. Inflammation plays vital roles in the progression of burn injury, and our study investigated whether notoginsenoside R1 (NGR1) alleviated lipopolysaccharide (LPS)-induced human keratinocyte HaCaT cell inflammatory injury. Inflammatory injury was induced by LPS in HaCaT cells. Stimulated cells were then treated by NGR1 in different concentrations. Cell viability and cell apoptosis were detected by Cell Counting Kit-8 and flow cytometry, respectively. The concentration of tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) was measured by enzyme-linked immunosorbent assay (ELISA). The accumulated levels of apoptosis-related proteins (caspase-3 and caspase-9), nuclear factor κB (NF-κB), p38 mitogen-activated protein kinase (p38MAPK) signal pathways–related proteins (p65, IκBα, and p38MAPK), and myeloid differentiation primary response 88 (MyD88) were examined by western blot. Transfection was used to alter the expression of MyD88. We found that LPS stimulated HaCaT cells and induced cell inflammation, evidenced by decreasing cell viability, increasing cell apoptosis, and elevating TNF-α and IL-6 expressions. Then, we found that NGR1 reversed the results by enhancing cell viability, inhibiting cell apoptosis, and reducing TNF-α and IL-6 expressions. In addition, NGR1 decreased the phosphorylation of p65, IκBα, and p38MAPK, which increased by LPS. Moreover, NGR1 negatively regulated the expression of MyD88, and transfection with pMyD88 led to the opposite results with what showed by NGR1 in LPS-stimulated HaCaT cells. To sum up, NGR1 alleviates LPS-induced HaCaT cell inflammatory injury by downregulation of MyD88, as well as inactivation of NF-κB and p38MAPK signal pathways.