Immunomodulatory Effect of Dioscorea esculenta L. on NF-κB, TLR-4, TNF-α, and IL-10 Expressions in LPS-stimulated RAW 264.7 Mouse Macrophages

BACKGROUND: Gene expressions of toll-like receptor 4 (TLR)-4, nuclear factor-kappaB (NF-κB), tumor necrosis factor (TNF)-α, and interleukin (IL)-10 are known to have roles in the inflammatory process and affect the regulation of the immune system. A preliminary study showed that Dioscorea esculenta L. tuber has immunomodulatory activity against macrophage phagocytosis activity and lymphocyte proliferation. However, the immunomodulatory activity of aqueous extract (AE), polysaccharide fraction (PF), and non-polysaccharide fraction (NPF) of D. esculenta L. tubers on these gene expressions have not been elucidated well. Therefore, this study was performed to determine its immunomodulatory activity by utilizing RAW 264.7 cell culture induced by lipopolysaccharide (LPS).METHODS: RAW 264.7 cells were stimulated with LPS at a concentration of 1 µg/mL for 30 minutes before incubation with non-toxic concentrations of AE, PF, NPF, positive control, and inulin at 25 and 50 µg/mL. TNF-α, IL-10, TLR-4, NF-κB, and β-actin expressions were evaluated using reverse transcription-polymerase chain reaction (RT-PCR) and were normalized with β-actin as an internal control. Triplicate experiments were performed throughout this study.RESULTS: Treatment with 25 µg/mL NPF significantly decreased the expression of NF-κB, TLR-4, and TNF-α (p<0.05). In contrast, treatment of 25 and 50 µg/mL PF significantly decreased the NF-κB expression (p<0.05). Moreover, only treatment with 50 µg/mL AE exhibited a significant increase in IL-10 expression (p<0.05).CONCLUSION: Treatment with D. esculenta L. tuber stimulated macrophage RAW 264.7 cells via NF-κB, TLR-4, TNF-α, and IL-10 expressions. NPF at 25 µg/mL has stronger immunomodulatory activity in reducing the expression of genes involved in the inflammatory process that plays a role in regulating the immune system.KEYWORDS: Dioscorea esculenta L., Immunomodulator, IL-10, NF-κB, TLR-4, TNF-α, RAW 264.7 cell