The effect of fulvic acid (FA) on homocysteine-induced phosphorylation of MAPKs signal pathways in human monocyte. Human primary monocytes and U937 cells were kept as CL or stimulated with 200 μg/mL homocysteine for 4 h (A) or 8 h (B). Before being kept as CL or stimulated with homocysteine, cells were pretreated with PD98059 (PD), SP600125 (SP), or SB203580 (SB) individually for 1 h. (A) All bar graphs represent folds of CL monocytes and normalized to 18S rRNA. (B) PGE2 secretion was determined by ELISA assay. The results are shown as mean ± SEM of three individual experiments. *P < 0.05 versus CL. #P < 0.05 versus vehicle control (DMSO) with homocysteine stimulation. (C) U937 cells were kept as CL or stimulated with homocysteine for times indicated. (D) U937 monocytes were pre-treated with FA (0–10 μg/mL) for 4 h, and then stimulated with homocysteine for 0.5 h. The phosphorylation of ERK and JNK was determined by Western blotting. The results shown are representative of three independent experiments with similar results.