Assays of Matrix Metalloproteinases (MMPs) and MMP Inhibitors: Bioassays and Immunoassays Applicable to Cell Culture Medium, Serum, and Synovial Fluid

The metalloproteinases (MMPs) are a diverse family of enzymes that, together, are capable of degrading all the constituents of the extracellular matrix (ECM). They are required for normal development and for general turnover of the ECM, but are elevated in many pathological conditions including inflammatory disease such as arthritis and many cancers (1 ). These enzymes are tightly regulated at three main points, transcription, activation, and inhibition. All MMPs are secreted in a proform, which requires initial activation by another proteinase, and once activated, there are at least four specific MMP inhibitors (tissue inhibitors of metalloproteinases, or TIMPs) which can bind irreversibly (2 ). MMPs such as MMP-1 (collagenase 1) are also susceptible to proteolytic cleavage (this can be autologus cleavage) in the hinge region producing N and C terminal fragments which lose there ability to degrade specific substrates, i.e., cleaved MMP-1 can no longer cut triple helical collagen. MMPs often have overlapping substrate specificities: there are at least five commonly found collagenases, MMP-1, MMP-2, MMP-8, MMP-13, and MMP-14 (MMP-18 is also a collagenase but has only been found so far in xenopus) which will all degrade triple helical collagen in a bioassay (see Subheading 3.1. ).