Platelet and leukocyte derived matrix metalloproteinases (MMP) 1, -2 in humans undergoing cardiopulmonary bypass mediate increased formation of platelet-leukocyte aggregates and platelet dysfunction

Abstract

Aims: Matrixmetalloproteinases (MMP) are important in remodeling of extracellular matrix. Recent evidence suggests that the expression and activation of MMP-1 and -2 in activated platelets play an important role in modulating their aggregatory response and in formation of platelet-leukocyte aggregates (PLA). We investigated MMP activity in resting and activated platelets in humans and their promoting effects on PLA formation. Methods: Platelets (pl) and leukocytes (leu) from 41 patients undergoing CPB for myocardial revascularization were isolated. MMP activity was measured in releasates by zymography. Membrane surface MMP 1, -2 were measured by flow cytometry using human MoAbs. PLA formation was determined by dual color flow cytometry in platelet-leukocyte incubates. Results: Activation of platelets and leukocytes incubates resulted in enhanced gelatinolytic activity of MMP-1 (arbitrary units, resting Pl-Leu: 80±20, activated: 1150±70, p<0.0001) and MMP-2 (resting: 100±30, activated: 3050±50, p<0.0001. This resulted in increased expression of PLA formation (10x-9/L; before pump: 0.2±0.08; post pump: 0.4±0.03, p<0.001) and reduction of the aggregatory response of platelets in response to 10x-5g/ml of collagen (Impedance; pre-pump: 100; post-pump: 55, p<0.001). Control experiments with Pl-Leu suspension resulted in significant increase in PLA formation only when recombinant MMP-1, -2 was added (MMP-1: 75% increase light transmission; MMP-2: 50% increase in light transmission but not to thrombin given alone). Conclusions: The present data provide evidence for a direct effect of MMP-1,-2 in promoting PLA formation and platelet dysfunction. This is clinically important since PLA formation is required for extravasation of inflammatory cells in tissues, subsequenttly resulting in systemic inflammation.