Analytical aspects regarding the measurement of metalloproteinases and their inhibitors in blood

Objective: Both in vitro and in vivo investigations have shown that the balance between matrix metalloproteinases (MMP) and the tissue inhibitors of metalloproteinases (TIMP) seems to be important in physiological and pathological processes which involve tissue remodeling and repair. Design and Methods: In order to investigate the analytical reliability of new commercial ELISA tests, BIOTRAK(TM) test kits (Amersham Int.) were used for the determination of metalloproteinase-1 (MMP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1), and the MMP-1/TIMP-1 complex in blood. Results: The detection limits and the precision data were in the usual ranges of ELISA tests so that concentrations found in blood could be determined reliably. Since all three analytes were lower in heparin plasma than in serum or EDTA plasma, heparin plasma was selected as the specimen of choice. Measurement of diluted samples gave higher values than those of undiluted native plasma samples because the inhibitory effects of specific/unspecific inhibitors or other matrix components were apparently reduced. To obtain comparable data from different laboratories, the predilution of samples must be defined. We recommend to use diluted plasma samples of 1:5, 1:21, and 1:11 for the determination of MMP-1, TIMP-1, and the complex MMP-1/TIMP-1, respectively. The preliminary upper 95% reference limits measured under these conditions in healthy subjects (40 females. 40 males) were 14.4 mu g/L for MMP-1 in females, 20 mu g/L for MMP-1 in males, 1668 mu g/L for TIMP-1 and 116 mu g/L for the complex MMP-1/TIMP-1. Conclusion: The study has shown that the BIOTRAK(TM) test combinations for MMP-1, TIMP-1, and MMP-1/TIMP-1 complex allow a reliable measurement of the analyte concentrations in heparin plasma. In order to avoid preanalytical misinterpretations only heparin plasma samples in defined dilutions should be used.