AP9 had some inhibitory effect on the secretion of pro-MMP9 (control, 33.7 ± 18.5%; RA, 31.8 ± 16.2), MMP-9 (control, 41.9 ± 5.8%; RA, 43.8 ± 5.1%) and MMP-2 (control, 100%; RA, 63.9 ± 6.2%) in the co-culture of human monocytes and fibroblasts in both the normal control and RA groups (Fig. 4c). Here, MMP2 is linked to rheumatoid arthritis.