Polyphosphate enhances fibrin clot structure

Abstract Polyphosphate, a linear polymer of inorganic phosphate, is present in platelet dense granules and is secreted on platelet activation. We recently reported that polyphosphate is a potent hemostatic regulator, serving to activate the contact pathway of blood clotting and accelerate factor V activation. Because polyphosphate did not alter thrombin clotting times, it appeared to exert all its procoagulant actions upstream of thrombin. We now report that polyphosphate enhances fibrin clot structure in a calcium-dependent manner. Fibrin clots formed in the presence of polyphosphate had up to 3-fold higher turbidity, had higher mass-length ratios, and exhibited thicker fibers in scanning electron micrographs. The ability of polyphosphate to enhance fibrin clot turbidity was independent of factor XIIIa activity. When plasmin or a combination of plasminogen and tissue plasminogen activators were included in clotting reactions, fibrin clots formed in the presence of polyphosphate exhibited prolonged clot lysis times. Release of polyphosphate from activated platelets or infectious microorganisms may play an important role in modulating fibrin clot structure and increasing its resistance to fibrinolysis. Polyphosphate may also be useful in enhancing the structure of surgical fibrin sealants.

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Short Polyphosphates Inhibit the Procoagulant Activities of Long-Chain Polyphosphate: A Novel Role for Platelet-Derived Pyrophosphate?.

Blood ◽

10.1182/blood.v116.21.1140.1140 ◽

2010 ◽

Vol 116 (21) ◽

pp. 1140-1140

Author(s):

Stephanie A. Smith ◽

James H. Morrissey

Keyword(s):

Factor Xa ◽

Fibrin Clot ◽

Short Chain ◽

Factor V ◽

Fibrin Polymerization ◽

Dense Granules ◽

Contact Pathway ◽

Clot Structure ◽

Long Chain ◽

Potent Inhibitory Activity

Abstract Abstract 1140 Introduction: Inorganic polyphosphates are negatively charged, linear phosphate polymers that influence hemostasis via accelerating factor V activation, triggering the contact pathway, and enhancing fibrin polymerization. The latter two effects require long-chain polyphosphates for optimal activity (>1000mers for activating the contact pathway and >250mers for enhancing fibrin polymerization). We explored whether short polyphosphates could inhibit the procoagulant effects of long polyphosphate polymers. Methods: Polyphosphate was size-fractionated by gel electrophoresis. “Long-chain polyphosphate” (LCP) was a heterogeneous polyphosphate preparation containing polymers ranging from 400 to several thousand phosphates long. Short-chain polyphosphate preparations were narrow fractions of homogeneous size. We also tested additional phosphate-containing molecules including ADP, ATP, monophosphate, pyrophosphate (PPi), and triphosphate. Clotting assays were performed using pooled normal plasma spiked with 0–20 μM LCP and 0–500 μM small (poly)phosphate; clotting was initiated by factor Xa plus CaCl2, or by CaCl2 alone (contact pathway). Fibrin was formed by clotting 2.6 mg/ml fibrinogen with 10 nM thrombin in the presence of 0–500 μM small (poly)phosphate plus 150 μM LCP and CaCl2. Results: Small polyphosphates (size range 23–83mer) reduced the ability of LCP to trigger the contact pathway of blood clotting, while monophosphate, PPi, triphosphate, ADP, and ATP all failed to influence the procoagulant activity of LCP. None of the small (poly)phosphates antagonized the ability of LCP to enhance factor V activation. Interestingly, monophosphate, PPi and triphosphate all inhibited the ability of LCP to enhance fibrin clot structure, with PPi being the most potent. Although ADP and ATP contain di- and tri-phosphates, they did not recapitulate the potent inhibitory activity of PPi. On the other hand, PPi had no measurable effect on the turbidity of fibrin clots formed in the absence of LCP. Conclusions: Short-chain polyphosphates inhibit the ability of LCP to initiate the contact pathway of coagulation. Platelet dense granules contain abundant PPi which is secreted in response to platelet agonists, although biological roles for platelet-secreted PPi are unclear. We propose that PPi is a novel modulator of fibrin clot structure, acting to regulate the effects of longer-chain polyphosphates on fibrin fibril formation. Disclosures: Smith: University of Illinois: Patents & Royalties. Morrissey:University of Illinois: Patents & Royalties.

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Polyphosphate Enhances Fibrin Clot Structure.

Blood ◽

10.1182/blood.v110.11.403.403 ◽

2007 ◽

Vol 110 (11) ◽

pp. 403-403

Author(s):

Stephanie A. Smith ◽

James H. Morrissey

Keyword(s):

High Energy ◽

Fibrin Clot ◽

Clot Formation ◽

Length Ratio ◽

Factor Xiiia ◽

Clot Lysis ◽

Cross Linking ◽

Inorganic Polyphosphate ◽

Calcium Dependent ◽

Clot Structure

Abstract Introduction: Inorganic polyphosphate (polyP) is a negatively charged polymer of phosphate units linked by high energy phosphoanhydride bonds. Dense granules of human platelets contain polyP which is released in response to thrombin stimulation. We recently reported that polyphosphate is a potent hemostatic regulator, accelerating blood clotting by activating the contact pathway and promoting the activation of factor V. Our previous studies found that polyP did not affect the time to clot formation when plasma was clotted with thrombin, however, suggesting that polyP exerts its procoagulant actions upstream of thrombin. We now report that polyP enhances fibrin clot structure. Methods: Purified fibrinogen and polyP were preincubated for 15 min in multiwell plates in buffer containing CaCl2, after which clotting was initiated by adding 0.1 to 8 nM thrombin and fibrin clot formation was evaluated by quantifying the change in turbidity (A405). Mass-length ratios were calculated from scans of A400 to A800. The effect of polyP on fibrinolysis was examined by adding 8 nM plasmin to the reaction mixtures immediately prior to thrombin. Scanning electron microscopy (SEM) was employed to visualize clot structure, and time courses of covalent fibrin cross-linking were assessed by SDS-PAGE. Results: PolyP had no effect on time to clot formation, but clots formed in the presence of polyP had markedly (up to threefold) higher turbidity than clots formed in the absence of polyP (see figure), irrespective of thrombin concentration. The increased turbidity in the presence of polyP was calcium-dependent and was enhanced when fibrinogen, CaCl2, and polyP were preincubated for up to 15 min prior to initiation of clotting with thrombin. PolyP increased the mass-length ratio of fibrin, and SEM confirmed that fibers formed with polyP were thicker than those formed without polyP. The ability of polyP to enhance fibrin clot turbidity was independent of factor XIIIa activity, and polyP did not alter the rate or extent of covalent fibrin cross-linking by factor XIIIa. When plasmin was included in clotting reactions containing polyP, mean times to 50% clot lysis were 28.5 ± 0.8 min for clots without polyP but 120.4 ± 5.6 min for clots with polyP. Conclusions: PolyP alters polymerization of fibrin, resulting in fibers of higher mass-length ratio that are lysed more slowly. This effect is calcium-dependent and is enhanced by preincubation of fibrinogen with calcium and polyP. Release of polyP from activated platelets or infectious microorganisms may therefore enhance fibrin clot structure. Figure Figure

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Polyphosphate exerts differential effects on blood clotting, depending on polymer size

Blood ◽

10.1182/blood-2010-01-266791 ◽

2010 ◽

Vol 116 (20) ◽

pp. 4353-4359 ◽

Cited By ~ 186

Author(s):

Stephanie A. Smith ◽

Sharon H. Choi ◽

Rebecca Davis-Harrison ◽

Jillian Huyck ◽

John Boettcher ◽

...

Keyword(s):

Blood Clotting ◽

Fibrin Clot ◽

Host Responses ◽

Coagulation Cascade ◽

Factor V ◽

Differential Effects ◽

Activated Platelets ◽

Contact Pathway ◽

Anticoagulant Function ◽

Clot Structure

AbstractPolyphosphate, a linear polymer of inorganic phosphate, is secreted by activated platelets and accumulates in many infectious microorganisms. We recently showed that polyphosphate modulates the blood coagulation cascade at 3 steps: it triggers the contact pathway, it accelerates factor V activation, and it enhances fibrin polymerization. We now report that polyphosphate exerts differential effects on blood clotting, depending on polymer length. Very long polymers (≥ 500mers, such as those present in microorganisms) were required for optimal activation of the contact pathway, while shorter polymers (∼ 100mers, similar to the polymer lengths released by platelets) were sufficient to accelerate factor V activation and abrogate the anticoagulant function of the tissue factor pathway inhibitor. Optimal enhancement of fibrin clot turbidity by polyphosphate required ≥ 250mers. Pyrophosphate, which is also secreted by activated platelets, potently blocked polyphosphate-mediated enhancement of fibrin clot structure, suggesting that pyrophosphate is a novel regulator of fibrin function. In conclusion, polyphosphate of the size secreted by platelets is very efficient at accelerating blood clotting reactions but is less efficient at initiating them or at modulating clot structure. Microbial polyphosphate, which is highly procoagulant, may function in host responses to pathogens.

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Polyphosphate: an ancient molecule that links platelets, coagulation, and inflammation

Blood ◽

10.1182/blood-2012-03-306605 ◽

2012 ◽

Vol 119 (25) ◽

pp. 5972-5979 ◽

Cited By ~ 217

Author(s):

James H. Morrissey ◽

Sharon H. Choi ◽

Stephanie A. Smith

Keyword(s):

Blood Clotting ◽

Molecular Mechanisms ◽

Fibrin Clot ◽

Human Platelets ◽

Factor V ◽

Inorganic Polyphosphate ◽

Contact Pathway ◽

Anticoagulant Function ◽

Clot Structure

AbstractInorganic polyphosphate is widespread in biology and exhibits striking prohemostatic, prothrombotic, and proinflammatory effects in vivo. Long-chain polyphosphate (of the size present in infectious microorganisms) is a potent, natural pathophysiologic activator of the contact pathway of blood clotting. Medium-chain polyphosphate (of the size secreted from activated human platelets) accelerates factor V activation, completely abrogates the anticoagulant function of tissue factor pathway inhibitor, enhances fibrin clot structure, and greatly accelerates factor XI activation by thrombin. Polyphosphate may have utility as a hemostatic agent, whereas antagonists of polyphosphate may function as novel antithrombotic/anti-inflammatory agents. The detailed molecular mechanisms by which polyphosphate modulates blood clotting reactions remain to be elucidated.

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Aβ delays fibrin clot lysis by altering fibrin structure and attenuating plasminogen binding to fibrin

Blood ◽

10.1182/blood-2011-11-389668 ◽

2012 ◽

Vol 119 (14) ◽

pp. 3342-3351 ◽

Cited By ~ 58

Author(s):

Daria Zamolodchikov ◽

Sidney Strickland

Keyword(s):

Structural Changes ◽

Fibrin Clot ◽

Brain Parenchyma ◽

Amyloid Peptide ◽

Clot Lysis ◽

Fibrin Network ◽

Β Amyloid Peptide ◽

Clot Structure ◽

The Brain ◽

Fibrin Clots

Abstract Alzheimer disease is characterized by the presence of increased levels of the β-amyloid peptide (Aβ) in the brain parenchyma and cerebral blood vessels. This accumulated Aβ can bind to fibrin(ogen) and render fibrin clots more resistant to degradation. Here, we demonstrate that Aβ42 specifically binds to fibrin and induces a tighter fibrin network characterized by thinner fibers and increased resistance to lysis. However, Aβ42-induced structural changes cannot be the sole mechanism of delayed lysis because Aβ overlaid on normal preformed clots also binds to fibrin and delays lysis without altering clot structure. In this regard, we show that Aβ interferes with the binding of plasminogen to fibrin, which could impair plasmin generation and fibrin degradation. Indeed, plasmin generation by tissue plasminogen activator (tPA), but not streptokinase, is slowed in fibrin clots containing Aβ42, and clot lysis by plasmin, but not trypsin, is delayed. Notably, plasmin and tPA activities, as well as tPA-dependent generation of plasmin in solution, are not decreased in the presence of Aβ42. Our results indicate the existence of 2 mechanisms of Aβ42 involvement in delayed fibrinolysis: (1) through the induction of a tighter fibrin network composed of thinner fibers, and (2) through inhibition of plasmin(ogen)–fibrin binding.

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Elevated prothrombin results in clots with an altered fiber structure: a possible mechanism of the increased thrombotic risk

Blood ◽

10.1182/blood-2002-08-2527 ◽

2003 ◽

Vol 101 (8) ◽

pp. 3008-3013 ◽

Cited By ~ 113

Author(s):

Alisa S. Wolberg ◽

Dougald M. Monroe ◽

Harold R. Roberts ◽

Maureane Hoffman

Keyword(s):

Plasma Levels ◽

Thrombin Generation ◽

Fibrin Clot ◽

Length Ratio ◽

Dependent Manner ◽

Thrombotic Risk ◽

Increased Risk ◽

Clot Structure ◽

Dose Dependent ◽

Fibrin Clots

AbstractIndividuals with elevated prothrombin levels are at increased risk of venous thrombosis. To understand the mechanism behind this observation, we studied the effect of prothrombin concentration on thrombin generation and fibrin clot structure. The pattern of thrombin generation was directly related to the prothrombin level at all concentrations tested. From 0% to 300% of normal plasma levels of prothrombin, increasing the prothrombin concentration increased the initial rate, peak, and total amount of thrombin generated. Importantly, fibrin clot structure was also affected by the prothrombin concentration. Fibrin clots made from prothrombin concentrations less than 10% of plasma levels were weak and poorly formed. Fibrin clots made at 10% to 100% of plasma levels of prothrombin had similar fiber structures (mass-to-length ratio; μ). However, the fiber mass-to-length ratio decreased with increasing prothrombin levels more than 100% of plasma levels, in a dose-dependent manner. These results suggest that increased levels of prothrombin alter thrombin generation and clot structure. Specifically, elevated prothrombin levels produce clots with reduced fibrin mass-to-length ratios compared with normal clots. We hypothesize that this alteration in fibrin clot structure is an important determinant of the risk of thrombosis.

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3309Complement activation leads to C3 and C5 dependent prothrombotic alterations of fibrin clots

European Heart Journal ◽

10.1093/eurheartj/ehz745.0073 ◽

2019 ◽

Vol 40 (Supplement_1) ◽

Author(s):

K A Schutt ◽

S Maxeiner ◽

K Lysaja ◽

M Berger ◽

S Ruetten ◽

...

Keyword(s):

Electron Microscopy ◽

Complement Activation ◽

Fibrin Clot ◽

Complement C3 ◽

Clot Lysis ◽

Lysis Time ◽

Patients With Diabetes ◽

Clot Structure ◽

Clot Lysis Time ◽

Fibrin Clots

Abstract Background and aims Alterations of clot structure with thin fibres, small pores and prolonged fibrinolysis are associated with an increased cardiovascular risk. We previously demonstrated complement C3 to be incorporated into fibrin clots resulting in prolongation of fibrinolysis, an effect which was exaggerated in patients with diabetes. Patients with diabetes are known to display higher levels of complement activation. However, the role of complement activation in particular activation of C3 and C5 on clot lysis time remains unexplored. Thus, the present study seeks to determine whether activation of complement C3 and C5 by cobra venom factor (CVF) has an impact on fibrin clot structure and clot lysis. Materials and methods Fibrin clot structure and lysis were determined in a plasma pool of healthy controls in the presence and absence of the complement C3 and C5 activator CVF using a validated turbidimetric assay and scanning electron microscopy. C3 activation was inhibited by the addition of the small 14-AA-peptide Cp40, while C5 activation was blocked by the addition of the FDA approved monoclonal antibody eculizumab (Emab). Results Complement activation with CVF leads to a prothrombotic clot structure with thinner fibres (Co 0.20±0.001 au, CVF 0.13±0.001 au; p<0.0001) and prolongation of clot lysis time (Co 864±32 sec, CVF 1665±17 sec; p<0.0001), which was confirmed by electron microscopy (Co 94.7±1.44 nm, CVF 60.7±0.96 nm; p<0.0001). Inhibition of C3 activation by Cp40 improved clot structure resulting in thicker fibres (Co 0.20±0.001 au, CVF 0.13±0.001 au, CP40 0.20±0.002 au; p<0.0001) and shorter clot lysis time (Co 100%, CVF 181±8.9%, CP40 139±7.8%; p<0.0001), while scrambled protein had no effect on either clot structure or lysis time. As CVF can also activate C5 convertase we next investigated the inhibition of complement C5 activation with eculizumab. The latter improved both fibre thickness (Co 0.20±0.002 au, CVF 0.13±0.003 au, Emab 0.16±0.006 au; p<0.0001) and clot lysis time (Co 100%, CVF 192±12%, Emab 140±11%; p<0.001). The combined inhibition of C3 and C5 activation using both, Cp40 and eculizumab in combination optimized clot structure (Co 0.22±0.001 au, CVF 0.13±0.0006 au, Cp40/Emab 0.21±0.001 au; Co vs. Cp40/Emab p=0.003) and restored clot lysis time (Co 100%, CVF 226±6%, CP40/Emab 104±1%; Co vs. Cp40/Emap p=0.8). The results were confirmed by electron microscopy (fibre thickness: Co 93±1.4 nm, CVF 68±1.3 nm, Cp40 83±1.4 nm, Emab 78±1.7 nm, CP40/Emap 95±1.6 nm). Conclusions Complement activation at the level of complement C3 and C5 has a detrimental impact on clot properties. Blocking C3 and C5 activation can restore both clot density and prolongation of clot lysis time. Further studies are needed to determine the underlying binding sites on fibrin(ogen) to pave the way for molecules improving clot properties without affecting immune responses. Acknowledgement/Funding KS is supported by the German Research Foundation (DFG) (SFB/TRR219 C-07; HE 5666/1-2 to KS (née Hess)]

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Effects of actin filaments on fibrin clot structure and lysis

Blood ◽

10.1182/blood.v80.4.928.928 ◽

1992 ◽

Vol 80 (4) ◽

pp. 928-936 ◽

Cited By ~ 23

Author(s):

PA Janmey ◽

JA Lamb ◽

RM Ezzell ◽

S Hvidt ◽

SE Lind

Keyword(s):

Actin Filaments ◽

Fibrin Clot ◽

Actin Binding ◽

Clot Lysis ◽

Plasma Gelsolin ◽

Fibrin Network ◽

Viscoelastic Effects ◽

Rheologic Properties ◽

Clot Structure ◽

Fibrin Clots

Abstract The muscle and cytoskeletal protein actin is released from cells as a consequence of cell death and interacts with components of the hemostatic and fibrinolytic systems, including platelets, plasmin, and fibrin. We report here that incorporation of actin filaments into fibrin clots changes their viscoelastic properties by increasing their shear modulus at low deforming stresses and by nearly eliminating their tendency to become more rigid with increasing deformation (ie, exhibit strain-hardening). The viscoelastic effects depended on the length of the actin filaments as shown by the effects of the plasma filament- severing protein, gelsolin. Binding of actin to fibrin clots also varied with actin filament length. The plasma actin-binding proteins gelsolin and vitamin D-binding protein reduced, but did not eliminate, the incorporation of actin in the clot. Fluorescence microscopy showed a direct association of rhodamine-labeled actin filaments with the fibrin network. Incubation of clots containing long actin filaments in solutions containing physiologic concentrations of gelsolin (2 mumol/L) released 60% of the actin trapped in the clot. Reduction of the actin content of a fibrin clot by incubation in a gelsolin-containing solution resulted in an increased rate of clot lysis. The ability of plasma gelsolin to shorten actin filaments may therefore be of physiologic and potentially of therapeutic importance insofar as gelsolin-mediated diffusion of actin from the clot may restore the clot's rheologic properties and render it more sensitive to the lytic action of plasmin.

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Effects of actin filaments on fibrin clot structure and lysis

Blood ◽

10.1182/blood.v80.4.928.bloodjournal804928 ◽

1992 ◽

Vol 80 (4) ◽

pp. 928-936

Author(s):

PA Janmey ◽

JA Lamb ◽

RM Ezzell ◽

S Hvidt ◽

SE Lind

Keyword(s):

Actin Filaments ◽

Fibrin Clot ◽

Actin Binding ◽

Clot Lysis ◽

Plasma Gelsolin ◽

Fibrin Network ◽

Viscoelastic Effects ◽

Rheologic Properties ◽

Clot Structure ◽

Fibrin Clots

The muscle and cytoskeletal protein actin is released from cells as a consequence of cell death and interacts with components of the hemostatic and fibrinolytic systems, including platelets, plasmin, and fibrin. We report here that incorporation of actin filaments into fibrin clots changes their viscoelastic properties by increasing their shear modulus at low deforming stresses and by nearly eliminating their tendency to become more rigid with increasing deformation (ie, exhibit strain-hardening). The viscoelastic effects depended on the length of the actin filaments as shown by the effects of the plasma filament- severing protein, gelsolin. Binding of actin to fibrin clots also varied with actin filament length. The plasma actin-binding proteins gelsolin and vitamin D-binding protein reduced, but did not eliminate, the incorporation of actin in the clot. Fluorescence microscopy showed a direct association of rhodamine-labeled actin filaments with the fibrin network. Incubation of clots containing long actin filaments in solutions containing physiologic concentrations of gelsolin (2 mumol/L) released 60% of the actin trapped in the clot. Reduction of the actin content of a fibrin clot by incubation in a gelsolin-containing solution resulted in an increased rate of clot lysis. The ability of plasma gelsolin to shorten actin filaments may therefore be of physiologic and potentially of therapeutic importance insofar as gelsolin-mediated diffusion of actin from the clot may restore the clot's rheologic properties and render it more sensitive to the lytic action of plasmin.

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Size Matters: Differential Effects of RNA and Polyphosphate on Blood Clotting

Blood ◽

10.1182/blood.v112.11.3074.3074 ◽

2008 ◽

Vol 112 (11) ◽

pp. 3074-3074

Author(s):

Stephanie A. Smith ◽

James H. Morrissey

Keyword(s):

Metal Ion ◽

Blood Clotting ◽

Factor Xa ◽

Fibrin Clot ◽

Factor V ◽

Clotting Time ◽

Yeast Trna ◽

Clotting Cascade ◽

Contact Pathway ◽

Clot Structure

Abstract Introduction: Recently, both inorganic polyphosphate (Smith et al., PNAS103:903-8, 2006) and RNA (Kannemeier et al., PNAS104:6388–93, 2007) have been proposed as (patho)physiologic activators of the contact pathway in blood clotting. We also recently showed that polyphosphate of the size secreted by human platelets (approximately 75-mer) acts at two other points in the blood clotting cascade: it accelerates factor V activation and it enhances fibrin clot structure (Smith & Morrissey, Blood, in press). We now compare the ability of RNA and polyphosphate of varying chain lengths to modulate the blood clotting cascade at these three critical points: initiation, factor V activation, and fibrin polymerization. Methods: Polyphosphate was size-fractionated and its procoagulant activities were compared to those of polyinosinic acid, a synthetic singlestranded RNA (ssRNA); polyinosinic acid:polycytidylic acid, a synthetic double-stranded RNA (dsRNA); yeast tRNA or kaolin. Clotting assays were performed using purified fibrinogen, pooled normal plasma, or factor V-deficient plasma to which factor Va was added. Clotting was initiated by CaCl2 (contact pathway), factor Xa, or thrombin. Results: Long-chain polyphosphate (100-mer to 800-mer) triggered the contact pathway with a potency similar to kaolin and was about 30-fold more potent than ssRNA and some 3000- fold more potent than dsRNA or tRNA. Medium-chain polyphosphate (20-mer to 100-mer) and ssRNA both shortened factor Xa clotting times with similar potency, but dsRNA and yeast tRNA were without effect. Replacing plasma factor V with Va blocked the ability of either polyphosphate or ssRNA to shorten factor Xa clotting times, suggesting that both polymers accelerate factor V activation. And finally, when purified fibrinogen was clotted with thrombin, adding either ssRNA or polyphosphate yielded fibrin clots that were about threefold more turbid, indicating that both polymers enhance fibrin clot formation, while dsRNA and yeast tRNA were without effect. (We previously documented that polyphosphate enhances fibrin turbidity by dramatically increasing fibril diameter.) Interestingly, ssRNA significantly shortened the thrombin clotting time of purified fibrinogen, while polyphosphate had no effect on thrombin clotting times. Furthermore, the ability of polyphosphate to enhance fibrin clot structure was calcium-dependent, while ssRNA enhancement of fibrin clotting by thrombin was metal ion-independent. Conclusions: This study shows that RNA modulates critical downstream clotting functions in addition to its previously identified role in triggering the contact pathway. Long-chain polyphosphate (i.e., the size that accumulate in microorganisms, but not the size secreted by platelets) is substantially more potent than RNA in triggering the contact pathway of blood clotting. We therefore propose that polyphosphate may play an important role in host responses to pathogens by triggering the contact pathway. Polyphosphate of the size secreted by platelets had similar potency to ssRNA in accelerating factor V activation. And finally, polyphosphate of the size secreted by platelets had similar potency to RNA in enhancing fibrin clot structure, although the metal ion-dependencies of the two differed, as did their effects on thrombin clotting time. In general, ssRNA was far more potent than dsRNA or tRNA in modulating the blood clotting system.

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