Neutralizing blood-borne polyphosphate in vivo provides safe thromboprotection

Abstract

Polyphosphate is an inorganic procoagulant polymer. Here we develop specific inhibitors of polyphosphate and show that this strategy confers thromboprotection in a factor XII-dependent manner. Recombinant Escherichia coli exopolyphosphatase (PPX) specifically degrades polyphosphate, while a PPX variant lacking domains 1 and 2 (PPX_Δ12) binds to the polymer without degrading it. Both PPX and PPX_Δ12 interfere with polyphosphate- but not tissue factor- or nucleic acid-driven thrombin formation. Targeting polyphosphate abolishes procoagulant platelet activity in a factor XII-dependent manner, reduces fibrin accumulation and impedes thrombus formation in blood under flow. PPX and PPX_Δ12 infusions in wild-type mice interfere with arterial thrombosis and protect animals from activated platelet-induced venous thromboembolism without increasing bleeding from injury sites. In contrast, targeting polyphosphate does not provide additional protection from thrombosis in factor XII-deficient animals. Our data provide a proof-of-concept approach for combating thrombotic diseases without increased bleeding risk, indicating that polyphosphate drives thrombosis via factor XII.

Processing of Factor XII during Inflammatory Reactions

“…The contact system has attracted strong scientific attention as a result of its contribution to pathological thrombus formation and the potential it holds for developing safe antithrombotic strategies without an associated bleeding risk (12). However, this system has also been repeatedly implicated in acute inflammatory and allergic reactions, as well as chronic inflammatory disease, often without a clear link to the coagulation system.…”

Single-chain factor XII: a new form of activated factor XII

“…A number of biologic substances, including polymers of orthophosphate (polyphosphate) [14–16], DNA [17,18], RNA [19], collagen [20] and misfolded protein aggregates [21] induce contact activation, and may represent physiologic or pathologic cofactors for the KKS in vivo . It has been proposed that the KKS contributes to the innate host response to invading microorganisms [5*,22–25].…”

Platelet polyphosphate: the long and the short of it

“…Of note, previous studies from this group showed that defective secretion from either a or dense granules alone did not affect intracerebral hemostasis during stroke, although it still reduced brain infarct sizes. 8,9 Molecules from both a and dense granules thus contribute to cerebral hemostasis in stroke, and release of either type could maintain cerebral vascular integrity. The latter might be the case when blocking initial platelet adhesion, for example by inhibiting the GPIb-VWF interaction, given that this strategy reduces brain injury without bleeding in experimental stroke.…”