Silicate Increases the Release of MMP-9 Forms in Peripheral Blood: Why Gelatin Zymography Differs Significantly in Citrate Plasma and Serum Obtained with or without Clot Activators

Whether serum or plasma is the best specimen for determination of matrix metalloproteinases (MMPs) is a matter of debate, as are the influences of sample collection and processing on MMP concentrations (1)(2)(3). MMP-2 concentrations do not differ significantly in plasma and serum, whereas MMP-9 concentrations are significantly higher in serum than in plasma, and in plasma differently affected by anticoagulants(2)(3). Furthermore, both unexpected protein peaks and increased MMP-9 concentrations occur in serum samples collected in tubes coated with clot accelerators such as kaolin or silica gel(2)(4).To find an explanation of the differences in MMP-9 concentrations among citrate plasma, serum, and serum with clot accelerators (Sca), we analyzed the effects of silicate on MMP in whole blood (WB), plasma, serum, and buffy coat (BC), as well as in culture media of U-937 myelomonocytic leukemia cells (SF U937).We obtained peripheral blood (PB) and BC samples from 30 healthy volunteers age 23–55 years (median 36 years). Samples were collected into plastic tubes (Vacutainer® from Becton Dickinson). After centrifugation at 500 g for 15 min at …