MMP1 and osteoarthritis: One example is collagenase, which is classified as matrix metalloproteinase-1 (MMP-1) and was previously reported to be at elevated levels in synovial fluid and blood serum of rheumatoid arthritis (RA) (30 ± 2.9 nM_MMP-1 in synovial fluid [4]) and osteoarthritis (OS) patients (8.9 ± 1.7 nM MMP-1 in synovial fluid [4]), and correlated with inflammation in acute RA and chronic pathology of OS [4,5,6].