Summary
Matrix metalloproteinases (MMPs) play an important role in many biological and pathological
processes including tissue remodeling, wound healing, inflammation, atherosclerosis,
and cancer. Numerous publications have supported the concept that activated MMP-2
enhances agonist-induced platelet aggregation and activated MMP-9 inhibits platelet
aggregation. In this study, we demonstrated that the organomercurial compound, 4-aminophenyl
mercuric acetate (APMA), which is routinely employed to activate latent MMPs at a
concentration of 1000 μ M, induces platelet aggregation at low concentration (5 μ
M) and inhibits agonist-induced platelet aggregation at concentrations ≥ 50 μ M. Activated
MMP-2, MMP-1, and MMP-9, following removal of APMA by ultrafiltration through an anisotropic
membrane, exert no independent effect on platelet aggregation. Acetylsalicylic acid
and BAPTA inhibited APMA-induced platelet aggregation indicating that the APMA mediated
pathway of platelet activation is dependent upon thromboxane and calcium signaling.
Zinc chelation with 1,10-phenanthroline, which inhibits zincdependent proteins including
metalloproteinases, also abrogated platelet functional responses to APMA. Additional
studies will be required to clarify the mechanism of the biphasic effect of APMA on
platelet aggregation.
Keywords Matrix metalloproteinases (MMP) - platelet aggregation - 4-aminophenylmercuric acetate
(APMA)