Silica particles contribute to the procoagulant activity of DNA and polyphosphate isolated using commercial kits

Biocompatible aggregation-induced emission active polyphosphate-manganese nanosheets with glutamine synthetase-like activity in excitotoxic nerve cells

Glutamine synthetase (GS) is vital in maintaining ammonia and glutamate (Glu) homeostasis in living organisms. However, the natural enzyme relies on adenosine triphosphate (ATP) to activate Glu, resulting in impaired GS function during ATP-deficient neurotoxic events. To date, no reports demonstrate using artificial nanostructures to mimic GS function. In this study, we synthesize aggregation-induced emission active polyP-Mn nanosheets (STPE-PMNSs) based on end-labeled polyphosphate (polyP), exhibiting remarkable GS-like activity independent of ATP presence. Further investigation reveals polyP in STPE-PMNSs serves as phosphate source to activate Glu at low ATP levels. This self-feeding mechanism offers a significant advantage in regulating Glu homeostasis at reduced ATP levels in nerve cells during excitotoxic conditions. STPE-PMNSs can effectively promote the conversion of Glu to glutamine (Gln) in excitatory neurotoxic human neuroblastoma cells (SH-SY5Y) and alleviate Glu-induced neurotoxicity. Additionally, the fluorescence signal of nanosheets enables precise monitoring of the subcellular distribution of STPE-PMNSs. More importantly, the intracellular fluorescence signal is enhanced in a conversion-responsive manner, allowing real-time tracking of reaction progression. This study presents a self-sustaining strategy to address GS functional impairment caused by ATP deficiency in nerve cells during neurotoxic events. Furthermore, it offers a fresh perspective on the potential biological applications of polyP-based nanostructures.

Inhibitors of Polyphosphate and Neutrophil Extracellular Traps

The contact pathway of blood clotting has received intense interest in recent years as studies have linked it to thrombosis, inflammation, and innate immunity. Because the contact pathway plays little to no role in normal hemostasis, it has emerged as a potential target for safer thromboprotection, relative to currently approved antithrombotic drugs which all target the final common pathway of blood clotting. Research since the mid-2000s has identified polyphosphate, DNA, and RNA as important triggers of the contact pathway with roles in thrombosis, although these molecules also modulate blood clotting and inflammation via mechanisms other than the contact pathway of the clotting cascade. The most significant source of extracellular DNA in many disease settings is in the form of neutrophil extracellular traps (NETs), which have been shown to contribute to incidence and severity of thrombosis. This review summarizes known roles of extracellular polyphosphate and nucleic acids in thrombosis, with an emphasis on novel agents under current development that target the prothrombotic activities of polyphosphate and NETs.

Intrinsic coagulation pathway-mediated thrombin generation in mouse whole blood

Calibrated Automated Thrombography (CAT) is a versatile and sensitive method for analyzing coagulation reactions culminating in thrombin generation (TG). Here, we present a CAT method for analyzing TG in murine whole blood by adapting the CAT assay used for measuring TG in human plasma. The diagnostically used artificial and physiologic factor XII (FXII) contact activators kaolin, ellagic acid and polyphosphate (polyP) stimulated TG in murine blood in a dose-dependent manner resulting in a gradual increase in endogenous thrombin potential and peak thrombin, with shortened lag times and times to peak. The activated FXII inhibitor rHA-Infestin-4 and direct oral anticoagulants (DOACs) interfered with TG triggered by kaolin, ellagic acid and polyP and TG was completely attenuated in blood of FXII- (F12 -/-) and FXI-deficient (F11 -/-) mice. Moreover, reconstitution of blood from F12 -/- mice with human FXII restored impaired contact-stimulated TG. HEK293 cell-purified polyP also initiated FXII-driven TG in mouse whole blood and addition of the selective inhibitor PPX_Δ12 ablated natural polyP-stimulated TG. In conclusion, the data provide a method for analysis of contact activation-mediated TG in murine whole blood. As the FXII-driven intrinsic pathway of coagulation has emerged as novel target for antithrombotic agents that are validated in mouse thrombosis and bleeding models, our novel assay could expedite therapeutic drug development.

Bacterial polyphosphates induce CXCL4 and synergize with complement anaphylatoxin C5a in lung injury

Polyphosphates are linear polymers of inorganic phosphates that exist in all living cells and serve pleiotropic functions. Bacteria produce long-chain polyphosphates, which can interfere with host defense to infection. In contrast, short-chain polyphosphates are released from platelet dense granules and bind to the chemokine CXCL4. Here, we report that long-chain polyphosphates induced the release of CXCL4 from mouse bone marrow-derived macrophages and peritoneal macrophages in a dose-/time-dependent fashion resulting from an induction of CXCL4 mRNA. This polyphosphate effect was lost after pre-incubation with recombinant exopolyphosphatase (PPX) Fc fusion protein, demonstrating the potency of long chains over monophosphates and ambient cations. In detail, polyphosphate chains >70 inorganic phosphate residues were required to reliably induce CXCL4. Polyphosphates acted independently of the purinergic P2Y1 receptor and the MyD88/TRIF adaptors of Toll-like receptors. On the other hand, polyphosphates augmented LPS/MyD88-induced CXCL4 release, which was explained by intracellular signaling convergence on PI3K/Akt. Polyphosphates induced Akt phosphorylation at threonine-308. Pharmacologic blockade of PI3K (wortmannin, LY294002) antagonized polyphosphate-induced CXCL4 release from macrophages. Intratracheal polyphosphate administration to C57BL/6J mice caused histologic signs of lung injury, disruption of the endothelial-epithelial barrier, influx of Ly6G⁺ polymorphonuclear neutrophils, depletion of CD11c⁺SiglecF⁺ alveolar macrophages, and release of CXCL4. Long-chain polyphosphates synergized with the complement anaphylatoxin, C5a, which was partly explained by upregulation of C5aR1 on myeloid cells. C5aR1^-/- mice were protected from polyphosphate-induced lung injury. C5a generation occurred in the lungs and bronchoalveolar lavage fluid (BALF) of polyphosphate-treated C57BL/6J mice. In conclusion, we demonstrate that polyphosphates govern immunomodulation in macrophages and promote acute lung injury.

DNASE-MEDIATED DISSOLUTION OF NEUTROPHIL EXTRACELLULAR TRAPS ACCELERATES IN VITRO THROMBIN GENERATION KINETICS IN TRAUMA PATIENTS

ABSTRACT

Introduction: Neutrophil extracellular traps (NETs) trigger thrombin generation. We aimed to characterize the effects of deoxyribonuclease (DNAse) on NET components (cell-free DNA [cfDNA] and histones) and thrombin generation after trauma. Methods: Citrated plasma samples were collected from trauma patients and healthy volunteers. Thrombin generation (calibrated automated thrombogram) was measured as lag time (LT, in minutes), peak height (in nM), and time to peak thrombin generation (in minutes). Citrullinated histone 3 (CitH3) and 4 (CitH4) were measured by enzyme-linked immunosorbent assay; cfDNA by PicoGreen (all in nanograms per milliliter). Samples analyzed +/- DNAse (1,000 U/mL). Results expressed as median and quartiles [Q1, Q3], Wilcoxon testing, P < 0.05 significant. Results: We enrolled 46 patients (age, 48 [31, 67] years; 67% male) and 21 volunteers (age, 45 [28, 53] years; 43% male). Deoxyribonuclease treatment of trauma plasma led to shorter LT (3.11 [2.67, 3.52] min; 2.93 [2.67, 3.19] min), shorter time to peak thrombin generation (6.00 [5.30, 6.67] min; 5.48 [5.00, 6.00] min), greater peak height (273.7 [230.7, 300.5] nM; 288.7 [257.6, 319.2] nM), decreased cfDNA (576.9 [503.3, 803.1] ng/mL; 456.0 [393.5, 626.7] ng/mL), decreased CitH3 (4.54 [2.23, 10.01] ng/mL; 3.59 [1.93, 7.98] ng/mL), and increased H4 (1.30 [0.64, 6.36] ng/mL; 1.75 [0.83, 9.67] ng/mL), all P < 0.001. The effect of DNAse was greater on trauma patients as compared with volunteers for LT (ΔLT, -0.21 vs. -0.02 min, P = 0.007), cfDNA (ΔcfDNA -133.4 vs. -84.9 ng/mL, P < 0.001), and CitH3 (ΔCitH3, -0.65 vs. -0.11 ng/mL, P = 0.004). Conclusion: Deoxyribonuclease treatment accelerates thrombin generation kinetics in trauma patient samples as compared with healthy volunteers. These findings suggest that NETs may contribute to the hypercoagulable state observed in trauma patients.

Myeloperoxidase has no effect on the low procoagulant activity of silica-free DNA

Blood coagulation and innate immunity are closely interrelated. At sites of inflammation, DNA and myeloperoxidase (MPO) are released from polymorphonuclear leukocytes (PMNs) as an integral component of neutrophil extracellular traps (NETs). NETs exert pleiotropic thrombogenic effects, with DNA-mediated contact activation of factor XII (FXII) likely playing a role. We have previously shown that MPO, a highly cationic protein, regulates coagulation through heteromolecular interactions with various negatively charged structures, including membrane phospholipids and low-molecular-weight heparin. The aims of our current study were to confirm that DNA activates coagulation and to investigate whether its procoagulant activity (PCA) is regulated by PMN-derived MPO. To this end, we used thrombin generation and FXIIa amidolytic activity assays to analyze the PCA of cell-free DNA isolated with silica membrane-based (cfDNA) or silica-free procedures (PaxDNA). cfDNA potently activated FXII and promoted thrombin generation in a concentration-dependent manner, but its PCA was largely attributable to contaminating silica particles. In contrast, pure, i.e. silica-free, PaxDNA was markedly less procoagulant. Although PaxDNA amplified thrombin generation in plasma, it was devoid of any direct FXII activating activity. MPO supershifted both cfDNA and PaxDNA in gel electrophoresis, but only silica-associated PCA of cfDNA was neutralized by MPO independently of its catalytic properties. Moreover, pretreatment with DNase I abolished silica-induced thrombin generation. In summary, we show that pure DNA has rather weak PCA, which is not further inhibited by heteromolecular complex formation with exogenous MPO. Our study thus provides novel mechanistic insights into the regulation of coagulation by extracellular DNA under inflammatory conditions.

Added Value of Blood Cells in Thrombin Generation Testing

The capacity of blood to form thrombin is a critical determinant of coagulability. Plasma thrombin generation (TG), a test that probes the capacity of plasma to form thrombin, has improved our knowledge of the coagulation system and shows promising utility in coagulation management. Although plasma TG gives comprehensive insights into the function of pro- and anticoagulation drivers, it does not measure the role of blood cells in TG. In this literature review, we discuss currently available continuous TG tests that can reflect the involvement of blood cells in coagulation, in particular the fluorogenic assays that allow continuous measurement in platelet-rich plasma and whole blood. We also provide an overview about the influence of blood cells on blood coagulation, with emphasis on the direct influence of blood cells on TG. Platelets accelerate the initiation and velocity of TG by phosphatidylserine exposure, granule content release and surface receptor interaction with coagulation proteins. Erythrocytes are also major providers of phosphatidylserine, and erythrocyte membranes trigger contact activation. Furthermore, leukocytes and cancer cells may be important players in cell-mediated coagulation because, under certain conditions, they express tissue factor, release procoagulant components and can induce platelet activation. We argue that testing TG in the presence of blood cells may be useful to distinguish blood cell-related coagulation disorders. However, it should also be noted that these blood cell-dependent TG assays are not clinically validated. Further standardization and validation studies are needed to explore their clinical usefulness.

Diversification of polyphosphate end-labeling via bridging molecules

Investigation of the biological roles of inorganic polyphosphate has been facilitated by our previous development of a carbodiimide-based method for covalently coupling primary amine-containing molecules to the terminal phosphates of polyphosphate. We now extend that approach by optimizing the reaction conditions and using readily available “bridging molecules” containing a primary amine and an additional reactive moiety, including another primary amine, a thiol or a click chemistry reagent such as dibenzocyclooctyne. This two-step labeling method is used to covalently attach commercially available derivatives of biotin, peptide epitope tags, and fluorescent dyes to the terminal phosphates of polyphosphate. Additionally, we report three facile methods for purifying conjugated polyphosphate from excess reactants.

Bacterial polyphosphates interfere with the innate host defense to infection

Polyphosphates are linear polymers and ubiquitous metabolites. Bacterial polyphosphates are long chains of hundreds of phosphate units. Here, we report that mouse survival of peritoneal Escherichia coli sepsis is compromised by long-chain polyphosphates, and improves with bacterial polyphosphatekinase deficiency or neutralization using recombinant exopolyphosphatase. Polyphosphate activities are chain-length dependent, impair pathogen clearance, antagonize phagocyte recruitment, diminish phagocytosis and decrease production of iNOS and cytokines. Macrophages bind and internalize polyphosphates, in which their effects are independent of P2Y1 and RAGE receptors. The M1 polarization driven by E. coli derived LPS is misdirected by polyphosphates in favor of an M2 resembling phenotype. Long-chain polyphosphates modulate the expression of more than 1800 LPS/TLR4-regulated genes in macrophages. This interference includes suppression of hundreds of type I interferon-regulated genes due to lower interferon production and responsiveness, blunted STAT1 phosphorylation and reduced MHCII expression. In conclusion, prokaryotic polyphosphates disturb multiple macrophage functions for evading host immunity.

Polyphosphate, Zn2+ and high molecular weight kininogen modulate individual reactions of the contact pathway of blood clotting

BACKGROUND

Inorganic polyphosphate modulates the contact pathway of blood clotting, which is implicated in thrombosis and inflammation. Polyphosphate polymer lengths are highly variable, with shorter polymers (approximately 60-100 phosphates) secreted from human platelets, and longer polymers (up to thousands of phosphates) in microbes. We previously reported that optimal triggering of clotting via the contact pathway requires very long polyphosphates, although the impact of shorter polyphosphate polymers on individual proteolytic reactions of the contact pathway was not interrogated.

OBJECTIVES AND METHODS

We conducted in vitro measurements of enzyme kinetics to investigate the ability of varying polyphosphate sizes, together with high molecular weight kininogen and Zn2+ , to mediate four individual proteolytic reactions of the contact pathway: factor XII autoactivation, factor XII activation by kallikrein, prekallikrein activation by factor XIIa, and prekallikrein autoactivation.

RESULTS

The individual contact pathway reactions were differentially dependent on polyphosphate length. Very long-chain polyphosphate was required to support factor XII autoactivation, whereas platelet-size polyphosphate significantly accelerated the activation of factor XII by kallikrein, and the activation of prekallikrein by factor XIIa. Intriguingly, polyphosphate did not support prekallikrein autoactivation. We also report that high molecular weight kininogen was required only when kallikrein was the enzyme (ie, FXII activation by kallikrein), whereas Zn2+ was required only when FXII was the substrate (ie, FXII activation by either kallikrein or FXIIa). Activation of prekallikrein by FXIIa required neither Zn2+ nor high molecular weight kininogen.

CONCLUSIONS

Platelet polyphosphate and Zn2+ can promote subsets of the reactions of the contact pathway, with implications for a variety of disease states.

Purification of silica-free DNA and characterization of its role in coagulation

BACKGROUND

Although extracellular DNA has been reported to activate coagulation, its direct effects and consequent interpretations have recently been questioned because of silica and polyphosphate (polyP) contaminations when DNA is isolated using common silica-based kits.

OBJECTIVES

To identify and characterize alternative methods of isolating DNA that is free of silica with functionally undetectable levels of polyP.

METHODS

DNA was isolated from the whole blood or buffy coat using three different DNA isolation kits: (a) the silica-based QIAGEN QIAMP DNA Blood mini kit (silica-DNA), (b) the non-silica-based QIAGEN PAXgene Blood DNA kit (PAX-DNA), and (c) the non-silica-based QuickGene DNA whole blood kit large (DBL-DNA). The procoagulant properties of DNA were assessed by thrombin generation and plasma clotting assays. A polyP detection assay was used to detect polyP contamination.

RESULTS AND CONCLUSIONS

Unlike the isolated DNA, commercially available calf thymus DNA contains thrombinlike amidolytic activity. The PAX-DNA and DBL-DNA did not contain silica nor functionally detectable polyP as contaminants. Both PAX- and DBL-DNA were procoagulant in a dose-dependent manner, which is neutralized with deoxyribonuclease I (DNase I). Thus, we recommend the use of PAX-DNA or DBL-DNA for functional studies to investigate the role of extracellular DNA.

Plasma levels of circulating DNA are associated with outcome, but not with activation of coagulation in decompensated cirrhosis and ACLF

Acute-on-chronic liver failure (ACLF) is a recently (re)defined syndrome of acute decompensation of cirrhosis that presents with extrahepatic organ failure(s) and poor outcome. Given the prominent role of inflammation and activation of coagulation in ACLF, we hypothesized that ACLF might be characterized by the generation of neutrophil extracellular traps (NETs), that could drive both activation of coagulation and progression of organ failure.

Methods

We measured markers of circulating DNA, activation of coagulation, inflammation, and oxidative stress in 52 patients with acute decompensation (AD) of cirrhosis and 57 patients with ACLF on admission, and compared levels with 40 healthy controls.

Results

All analytes were higher in patients compared to controls. Plasma levels of cell-free DNA, but not of the specific NET marker myeloperoxidase-DNA complexes were higher in patients with ACLF compared to AD cirrhosis. In addition, TAT complexes (coagulation), IL-6 (inflammation), and TBARS (oxidative stress) were higher in ACLF compared to AD. Markers for activation of coagulation were not associated with circulating DNA, IL-6, or TBARS. In contrast, levels of circulating DNA, IL-6, and TBARS were higher in patients with more severe disease, higher in patients with organ failure, and higher in patients that died within 30 days of admission. Importantly, myeloperoxidase-DNA levels did not differ between patients with complications and poor outcome.

Conclusions

Collectively, we show that cell-free DNA, inflammation, and oxidative stress are associated with outcomes in AD and ACLF, but not with activation of coagulation. Our data argue against a role of NETs in activation of coagulation and in progression of organ failure in patients with AD and ACLF.

Lay summary

Acute-on-chronic liver failure is a devastating syndrome that can follow acute decompensation of chronic liver disease. Herein, we demonstrate that these patients accumulate DNA released from dying cells in their blood, and that the quantity of this DNA is related to the outcome of disease. We also show that outcome of disease is not related to recently described neutrophil extracellular traps, which have been shown in animal models to play vital roles in the progression of liver diseases.

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Levels of circulating DNA, IL6, and TBARS are higher in patients with ACLF than in patients with AD

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Circulating DNA, IL6, and TBARS are higher in patients with organ failure and those who died

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Circulating DNA, IL6, and TBARS are not correlated with markers of activation of coagulation

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The neutrophil extracellular trap marker MPO-DNA was not related to coagulation or outcome

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DNA- or NET-related coagulation does not appear to drive ACLF progression

Polyphosphate Chain Length Determination in the Range of Two to Several Hundred P-Subunits with a New Enzyme Assay and 31P NMR

Currently, ³¹P NMR is the only analytical method that quantitatively determines the average chain length of long inorganic polyphosphate (>80 P-subunits). In this study, an enzyme assay is presented that determines the average chain length of polyphosphate in the range of two to several hundred P-subunits. In the enzyme assay, the average polyP chain length is calculated by dividing the total polyphosphate concentration by the concentration of the polyphosphate chains. The total polyphosphate is determined by enzymatic polyphosphate hydrolysis with Saccharomyces cerevisiae exopolyphosphatase 1 and S. cerevisiae inorganic pyrophosphatase 1, followed by colorimetric orthophosphate detection. Because the exopolyphosphatase leaves one pyrophosphate per polyphosphate chain, the polyphosphate chain concentration is assayed by coupling the enzymes exopolyphosphatase (polyP into pyrophosphate), ATP sulfurylase (pyrophosphate into ATP), hexokinase (ATP into glucose 6-phosphate), and glucose 6-phosphate dehydrogenase (glucose 6-phosphate into NADPH), followed by fluorometric NADPH detection. The ability of ³¹P NMR and the enzyme assay to size polyP was demonstrated with polyP lengths in the range from 2 to ca. 280 P-subunits (no polyP with a longer chain length was available). The small deviation between methods (-4 ± 4%) indicated that the new enzyme assay performed accurately. The limitations of ³¹P NMR (i.e., low throughput, high sample concentration, expensive instrument) are overcome by the enzyme assay that is presented here, which allows for high sample throughput and requires only a commonly available plate reader and micromole per liter concentrations of polyphosphate.

Neutrophils: back in the thrombosis spotlight

Reactive and clonal neutrophil expansion has been associated with thrombosis, suggesting that neutrophils play a role in this process. However, although there is no doubt that activated monocytes trigger coagulation in a tissue factor-dependent manner, it remains uncertain whether stimulated neutrophils can also directly activate coagulation. After more than a decade of debate, it is now largely accepted that normal human neutrophils do not synthetize tissue factor, the initiator of the extrinsic pathway of coagulation. However, neutrophils may passively acquire tissue factor from monocytes. Recently, the contact system, which initiates coagulation via the intrinsic pathway, has been implicated in the pathogenesis of thrombosis. After the recent description of neutrophil extracellular trap (NET) release by activated neutrophils, some animal models of thrombosis have demonstrated that coagulation may be enhanced by direct NET-dependent activation of the contact system. However, there is currently no consensus on how to assess or quantify NETosis in vivo, and other experimental animal models have failed to demonstrate a role for neutrophils in thrombogenesis. Nevertheless, it is likely that NETs can serve to localize other circulating coagulation components and can also promote vessel occlusion independent of fibrin formation. This article provides a critical appraisal of the possible roles of neutrophils in thrombosis and highlights some existing knowledge gaps regarding the procoagulant activities of neutrophil-derived extracellular chromatin and its molecular components. A better understanding of these mechanisms could guide future approaches to prevent and/or treat thrombosis.

Polyphosphate in thrombosis, hemostasis, and inflammation

This illustrated review focuses on polyphosphate as a potent modulator of the plasma clotting cascade, with possible roles in hemostasis, thrombosis, and inflammation. Polyphosphates are highly anionic, linear polymers of inorganic phosphates that are widespread throughout biology. Infectious microorganisms accumulate polyphosphates with widely varying polymer lengths (from a few phosphates to over a thousand phosphates long), while activated human platelets secrete polyphosphate with a very narrow size distribution (about 60-100 phosphates long). Work from our lab and others has shown that long-chain polyphosphate is a potent trigger of clotting via the contact pathway, while polyphosphate of the size secreted by platelets accelerates factor V activation, blocks the anticoagulant activity of tissue factor pathway inhibitor, promotes factor XI activation by thrombin, and makes fibrin fibrils thicker and more resistant to fibrinolysis. Polyphosphate also modulates inflammation by triggering bradykinin release, inhibiting the complement system, and modulating endothelial function. Polyphosphate and nucleic acids have similar physical properties and both will trigger the contact pathway-although polyphosphate is orders of magnitude more procoagulant than either DNA or RNA. Important caveats in these studies include observations that nucleic acids and polyphosphate may co-purify, and that these preparations can be contaminated with highly procoagulant microparticles if silica-based purification methods are employed. Polyphosphate has received attention as a possible therapeutic, with some recent studies exploring the use of polyphosphate in a variety of formulations to control bleeding. Other studies are investigating treatments that block polyphosphate function as novel antithrombotics with the possibility of reduced bleeding side effects.

Elevated Plasma Levels of Cell-Free DNA During Liver Transplantation Are Associated With Activation of Coagulation

Patients undergoing liver transplantation have complex changes in their hemostatic system, and the net effect of these changes appears to be a "rebalanced" hemostatic profile. Recently, a process called NETosis in which a neutrophil expels DNA and proteins that form a weblike structure, has been described as a mechanism of pathogen entrapment. Increasing evidence suggests a pivotal role for neutrophil extracellular traps (NETs) and their main component, cell-free DNA (cfDNA), in activation of coagulation. Because liver transplantation is associated with substantial (hepatocyte) cell death and intrahepatic neutrophil accumulation, NETs might play an important role in the hemostatic balance during liver transplantation. Here, we determined markers for NETs in the plasma of patients undergoing a liver transplantation and examined their association with activation of coagulation. Markers for NETs and markers for activation of coagulation were determined in serial plasma samples taken from patients undergoing a liver transplantation (n = 21) and compared with plasma levels in healthy controls. We found perioperative increases of markers for NETs with levels of cfDNA and nucleosomes that peaked after reperfusion and myeloperoxidase (MPO)-DNA complexes that peaked during the anhepatic phase. CfDNA and nucleosome levels, but not MPO-DNA levels, correlated with prothrombin fragment 1+2 and thrombin-antithrombin complex levels, which are established markers for activation of coagulation. Neutrophils undergoing NETosis were observed by immunostainings in postreperfusion biopsies. In conclusion, although NETosis occurs during liver transplantation, the majority of circulating DNA appears to be derived from cell death within the graft. The perioperative increases in cfDNA and nucleosomes might contribute to the complex hemostatic rebalance during liver transplantation.

Polyphosphate Stabilizes Protein Unfolding Intermediates as Soluble Amyloid-like Oligomers

Inorganic polyphosphate (polyP) constitutes one of the most conserved and ubiquitous molecules in biology. Recent work in bacteria demonstrated that polyP increases oxidative stress resistance by preventing stress-induced protein aggregation and promotes biofilm formation by stimulating functional amyloid formation. To gain insights into these two seemingly contradictory functions of polyP, we investigated the effects of polyP on the folding model lactate dehydrogenase. We discovered that the presence of polyP during the thermal unfolding process stabilizes folding intermediates of lactate dehydrogenase as soluble micro-β-aggregates with amyloid-like properties. Size and heterogeneity of the oligomers formed in this process were dependent on the polyP chain length, with longer chains forming smaller, more homogenous complexes. This ability of polyP to stabilize thermally unfolded proteins even upon exposure to extreme temperatures appears to contribute to the observed resistance of uropathogenic Escherichia coli toward severe heat shock treatment. These results suggest that the working mechanism of polyP is the same for both soluble and amyloidogenic proteins, with the ultimate outcome likely being determined by a combination of polyP chain length and the client protein itself. They help to explain how polyP can simultaneously function as general stress-protective chaperone and instigator of amyloidogenic processes in vivo.

Contact Pathway Function During Human Whole Blood Clotting on Procoagulant Surfaces

Microfluidic thrombosis assays allow the control of anticoagulation, hemodynamics, pharmacology, and procoagulant surfaces containing collagen ± tissue factor (TF). With corn trypsin inhibitor (CTI) ranging from low (1–4 μg/mL) to high levels (40–60 μg/mL), the function of Factor XIIa (FXIIa) can be modulated in the presence of low or high surface TF. With high CTI and no collagen/TF in the assay, no thrombin is generated during 15-min microfluidic perfusion. At low CTI (no TF), the generation of FXIa leads to fibrin polymerization at ~300 s after the initiation of flow over collagen, an onset time shortened at zero CTI and prolonged at high CTI. The engagement of FXIa was difficult to observe for clotting on high TF surfaces due to the dominance of the extrinsic pathway. Low TF surfaces allowed observable crosstalk between extrinsic pathway generation of thrombin and thrombin-mediated activation of FXIa, a feedback detected at >5 min and attenuated with polyphosphate inhibitor. From thrombin-antithrombin immunoassay of the effluent of blood flowing over collagen/TF, the majority of thrombin was found captured on intrathrombus fibrin. Additionally, extreme shear rates (>10,000 s⁻¹) can generate massive von Willebrand Factor fibers that capture FXIIa and FXIa to drive fibrin generation, an event that facilitates VWF fiber dissolution under fibrinolytic conditions. Finally, we found that occlusive sterile thrombi subjected to pressure drops >70 mm-Hg/mm-clots have interstitial stresses sufficient to drive NETosis. These microfluidic studies highlight the interaction of contact pathway factors with the extrinsic pathway, platelet polyphosphate, VWF fibers, and potentially shear-induced NETs.

Ability of Polyphosphate and Nucleic Acids to Trigger Blood Clotting: Some Observations and Caveats

Polyphosphate plays several roles in coagulation and inflammation, while extracellular DNA and RNA are implicated in thrombosis and as disease biomarkers. We sought to compare the procoagulant activities of polyphosphate versus DNA or RNA isolated from mammalian cells. In a recent study, we found that much of the procoagulant activity of DNA isolated from mammalian cells using Qiagen kits resisted digestion with nuclease or polyphosphatase, and even resisted boiling in acid. These kits employ spin columns packed with silica, which is highly procoagulant. Indeed, much of the apparent procoagulant activity of cellular DNA isolated with such kits was attributable to silica particles shed by the spin columns. Therefore, silica-based methods for isolating nucleic acids or polyphosphate from mammalian cells are not suitable for studying their procoagulant activities. We now report that polyphosphate readily co-purified with DNA and RNA using several popular isolation methods, including phenol/chloroform extraction. Thus, cell-derived nucleic acids are also subject to contamination with traces of cellular polyphosphate, which can be eliminated by alkaline phosphatase digestion. We further report that long-chain polyphosphate was orders of magnitude more potent than cell-derived DNA (purified via phenol/chloroform extraction) or RNA at triggering clotting. Additional experiments using RNA homopolymers found that polyG and polyI have procoagulant activity similar to polyphosphate, while polyA and polyC are not procoagulant. Thus, the procoagulant activity of RNA is rather highly dependent on base composition.

Platelet-neutrophil interactions as drivers of inflammatory and thrombotic disease

Neutrophils are well known for their role in infection and inflammatory disease and are first responders at sites of infection or injury. Platelets have an established role in hemostasis and thrombosis and are first responders at sites of vascular damage. However, neutrophils are increasingly recognized for their role in thrombosis, while the immunemodulatory properties of platelets are being increasingly studied. Platelets and neutrophils interact during infection, inflammation and thrombosis and modulate each other’s functions. This review will discuss the consequences of platelet–neutrophil interactions in infection, thrombosis, atherosclerosis and tissue injury and repair.