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

Abstract

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 pro-inflammatory 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.