MMP1 and rheumatoid arthritis: Although apelin was connected with promotion of metalloproteinases production when administered in vitro to chondrocytes (mainly MMP-1, MMP-3, and MMP-9) and showed positive correlation with MMP-2 in patients with RA, therefore facilitating harmful effects on joint structure, its reduced levels in RA were predictors of development of atherosclerosis and plaque instability, leading to higher cardiovascular risk in this group of patients [9].