An investigation into the effect of Trigonella foenum-graecum L. seed extract and derivative, Vicenin-2, on inflammatory responses of macrophage and endothelial cells

 Plant extracts are known to have beneficial effects in chronic inflammatory conditions such as diabetes. This study investigated the effects of Trigonella foenum-graecum L. (Fenugreek) seed extracts on inflammatory responses of macrophages. A cell-bioassay guided extraction identified a methanolic extract of fenugreek seeds (FME) with potent anti-inflammatory effects. This extract significantly reduced secretion of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) in THP-1 macrophages (dTHP-1) stimulated with glycated-BSA. The effect of FME on TNF-α was also reproduced in peripheral blood mononuclear cells (PBMCs) and when dTHP-1 cells were stimulated with LPS. The effect of FME on the polarization of dTHP-1 towards the M2 phenotype at the expense of the M1 phenotype was also confirmed through increased expression of IL-10 and Dectin-1. Although FME did not significantly enhance the gene expression of the M2 marker, IL-1Ra alone, FME acted synergistically in the presence of IL-4, increasing the expression of IL-10, Dectin-1 and IL-1Ra. A C-glycosidic flavonoid, Vicenin-2 (V-2), which was found to be present in FME, demonstrated similar actions to FME, by significantly suppressing proinflammatory cytokine release and upregulating M2 marker (IL-10). V-2 also increased Dectin-1 gene expression, synergistically, in the presence of IL-4. The regulatory mechanisms involved in the actions of FME and V-2 were explored using a gene reporter assay. Both FME and V-2 significantly (p<0.05) inhibited the activity of nuclear transcription factor, NF-κB. Also, FME significantly (p<0.05) increased the activity of PPAR-γ. V-2 effects appeared to be mediated through homodimerization of the p50 subunit of NF-κB and suppression of IκB-α phosphorylation. V-2 exerted anti-inflammatory effects in endothelial cells (HUVEC) by reducing TNF-α induced MCP-1 expression. V-2 also enhanced release of extracellular vesicles (EVs) from gBSA treated dTHP-1 cells. Additionally, the EVs derived from dTHP-1 cells down-regulated expression of inflammatory markers in HUVECs; ICAM-1 and VCAM-1 significantly, and MCP-1, non-significantly. In conclusion this study suggests a beneficial effect of FME and V-2 in regulating macrophage inflammatory responses. Further studies are required to clarify their role on EV expression, characterization and endothelial cell function.