Kaempferol (found especially in grapefruits) was shown to inhibit synovial fibroblast proliferation by suppressing inflammatory cytokines (inhibiting IL-1β), inhibiting the phosphorylation of ERK-1/2, p38, and JNK, inhibiting the activation of NF-κB, and reducing oxidative stress by inhibiting the production of MMPs, COX-2, and PGE2 in RA-derived synovial fibroblasts [178]. Here, MAPK3 is linked to rheumatoid arthritis.