Zinc delays clot lysis by attenuating plasminogen activation and plasmin-mediated fibrin degradation

Abstract

Zinc circulates free in plasma at a concentration of 0.1-2 µM, but its levels increase locally when it is released from activated platelets. Although zinc influences many processes in haemostasis, its effect on fibrinolysis has not been thoroughly investigated. Using a fluorescent zinc-binding probe, we demonstrated that zinc binds tissue-type plasminogen activator (tPA) and plasmin with high affinity (Kd values of 0.2 µM), and surface plasmon resonance studies revealed that zinc binds fibrin with a Kd of 12.8 µM. Zinc had no effect on the affinity of plasminogen or plasmin for fibrin, but increased the affinity of tPA by two-fold. In the presence of 5 µM zinc, the catalytic efficiency of plasminogen activation by tPA was reduced by approximately two-fold, both in the absence or presence of fibrin. Zinc attenuated plasmin-mediated degradation of the fibrinogen alpha-chain by 43 %, but had no effect on trypsin degradation. tPA-mediated fibrin clot lysis was prolonged 2.5-fold by zinc in a concentration-dependent fashion, and tPA-mediated plasma clot lysis was attenuated by 1.5-fold. Therefore, our data indicate that zinc modulates fibrinolysis by attenuating tPA-mediated plasminogen activation and plasmin-induced fibrin degradation. These findings suggest that local release of zinc by platelets attenuates fibrinolysis.

Functional Regulation of the Plasma Protein Histidine-Rich Glycoprotein by Zn2+ in Settings of Tissue Injury

“…Primarily using mouse models, Shannon et al [63] showed that HRG interacts with fibrin filaments at the wound site in order to capture and prevent the escape of invading bacteria systemically. Notably, this interaction of HRG with fibrin is Zn 2+ -dependent, which acts as the cofactor between these binding partners [27,61,63]. In addition, an infection model of S. pyogenes (AP1 strain) in HRG -/- mice resulted in a marked reduction in survival rate, when compared to wild type.…”

“…Alternatively, the acidic pH and/or Zn 2+ may simply be regulating plasmin activity. The latter has been suggested, as a recent study demonstrates that Zn 2+ is capable of interacting with plasmin, t-PA and u-PA to reduce their activities and subsequently attenuate clot dissolution [27]. In addition, an acidic milieu has been shown to almost completely inhibit plasmin activity [50].…”

“…In addition, an acidic milieu has been shown to almost completely inhibit plasmin activity [50]. This therefore suggests that the acidic wound milieu and the transition element Zn 2+ inhibits plasmin activity, rather than a protective mechanism of HRG HRR becoming positively charged through Zn 2+ coordination or protonation of the histidines via acidic pH [27,50]. …”

“…Although since Zn 2+ is elevated during the initial stages of wound healing (inflammation and proliferation stages), complement activation still perseveres [6,24,27,85,93,94]. Therefore, taking into account the effects of Zn 2+ on HRG, particularly enhancing HRG affinity towards certain IgG subclasses, it could be assumed that Zn 2+ may actually favor complement activation [92].…”

“…Therefore, considering HRG is constitutively expressed from liver parenchymal cells and maintained at a plasma concentration of 100–150 µg/mL [1,2], it will be rapidly available at the wound site when inflammatory events begin the formation of the hemostatic plug through platelet adherence, in order to provide a temporary extracellular matrix (ECM) scaffold for cell migratory processes [20]. In addition, these processes also generate the necessary environment for the release of Zn 2+ through platelet degranulation and mechanical cell stress that in combination can elevate the serum concentrations above normal homeostatic values of free Zn 2+ from 0.2–2.0 μM to 19–50 μM [4,21,22,23,24,25,26,27]. This supports the growing evidence that a large proportion of the aforementioned immunological and vascular functions of HRG are dependent on the presence of Zn 2+ , with the pH potentially providing an additional layer of control by regulating metal coordination and overall net-charge.…”