CKD-506, an HDAC6 inhibitor, Reduced the production of IL-6 and TNF-α by activated PBMCs from RA patients; inhibited the production of IL-8, IL-6, MMP-1, and MMP-3 by activated FLS; inhibited the severity of arthritis in a murine model of AIA.456 Interestingly, these studies could not show an association between the use of these HDAC inhibitors and the deacetylation of H3 and H4. Here, MMP1 is linked to rheumatoid arthritis.