Polyphosphate, platelets, and coagulation

Nanoapatite-Loaded κ-Carrageenan/Poly(vinyl alcohol)-Based Injectable Cryogel for Hemostasis and Wound Healing

Immediate control of excessive bleeding and prevention of infections are of utmost importance in the management of wounds. Cryogels have emerged as promising materials for the rapid release of medication and achieving hemostasis. However, their quick release properties pose the challenge of exposing patients to high concentrations of drugs. In this study, hybrid nanocomposites were developed to address this issue by combining poly(vinyl alcohol) and κ-carrageenan with whitlockite nanoapatite (WNA) particles and ciprofloxacin, aiming to achieve rapid hemostasis and sustained antibacterial effects. A physically cross-linked cryogel was obtained by subjecting a blend of poly(vinyl alcohol) and κ-carrageenan to successive freezing-thawing cycles, followed by the addition of WNA. Furthermore, ciprofloxacin was introduced into the cryogel matrix for subsequent evaluation of its wound healing properties. The resulting gel system exhibited a 3D microporous structure and demonstrated excellent swelling, low cytotoxicity, and outstanding mechanical properties. These characteristics were evaluated through analytical and rheological experiments. The nanocomposite cryogel with 4% whitlockite showed extended drug release of 71.21 ± 3.5% over 21 days and antibacterial activity with a considerable growth inhibition zone (4.19 ± 3.55 cm). Experiments on a rat model demonstrated a rapid hemostasis property of cryogels within an average of 83 ± 4 s and accelerated the process of wound healing with 96.34% contraction compared to the standard, which exhibited only ∼78% after 14 days. The histopathological analysis revealed that the process of epidermal re-epithelialization took around 14 days following the skin incision. The cryogel loaded with WNAs and ciprofloxacin holds great potential for strategic utilization in wound management applications as an effective material for hemostasis and anti-infection purposes.

Factor XI/XIa inhibitors for the prevention and treatment of venous and arterial thromboembolism: A narrative review

During the past decade, direct oral anticoagulants (DOACs) have advanced and simplified the prevention and treatment of venous thromboembolism (VTE). However, there remains a high incidence of bleeds, which calls for agents that have a reduced risk of bleeding. Factor XI (FXI) deficiency is associated with lower rates of venous thrombosis and stroke compared to the general population with a lower risk of bleeding. In conjunction with this, phase 2 studies have demonstrated safety and the potential for reduced thrombotic events with FXI inhibitors as compared to currently available medications. The aim of this review is to summarize key data on the clinical pharmacology of FXI, the latest developments in clinical trials of FXI inhibitors, and to describe the efficacy and safety profiles of FXI inhibitors for the prevention of venous and arterial thromboembolism.

Smart thrombosis inhibitors without bleeding side effects via charge tunable ligand design

Current treatments to prevent thrombosis, namely anticoagulants and platelets antagonists, remain complicated by the persistent risk of bleeding. Improved therapeutic strategies that diminish this risk would have a huge clinical impact. Antithrombotic agents that neutralize and inhibit polyphosphate (polyP) can be a powerful approach towards such a goal. Here, we report a design concept towards polyP inhibition, termed macromolecular polyanion inhibitors (MPI), with high binding affinity and specificity. Lead antithrombotic candidates are identified through a library screening of molecules which possess low charge density at physiological pH but which increase their charge upon binding to polyP, providing a smart way to enhance their activity and selectivity. The lead MPI candidates demonstrates antithrombotic activity in mouse models of thrombosis, does not give rise to bleeding, and is well tolerated in mice even at very high doses. The developed inhibitor is anticipated to open avenues in thrombosis prevention without bleeding risk, a challenge not addressed by current therapies.

A keratin/chitosan sponge with excellent hemostatic performance for uncontrolled bleeding

Uncontrolled bleeding leads to a higher fatality rate in the situation of surgery, traffic accidents and warfare. Traditional hemostatic materials such as bandages are not ideal for uncontrolled or incompressible bleeding. Therefore, it is of great significance to develop a new medical biomaterial with excellent rapid hemostatic effect. Keratin is a natural, biocompatible and biodegradable protein which contains amino acid sequences that induce cell adhesion. As a potential biomedical material, keratin has been developed and paid attention in tissue engineering fields such as promoting wound healing and nerve repair. Herein, a keratin/chitosan (K/C) sponge was prepared to achieve rapid hemostasis. The characterizations of K/C sponge were investigated, including SEM, TGA, liquid absorption and porosity, showing that the high porosity up to 90.12 ± 2.17 % resulted in an excellent blood absorption. The cytotoxicity test and implantation experiment proved that the K/C sponge was biocompatible and biodegradable. Moreover, the prepared K/C sponge showed better hemostatic performance than chitosan sponge (CS) and the commercially available gelatin sponge in both rat tail amputation and liver trauma bleeding models. Further experiments showed that K/C sponge plays a hemostatic role through the endogenous coagulation pathway, thus shortening the activated partial thromboplastin time (APTT) effectively. Therefore, this study provided a K/C sponge which can be served as a promising biomedical hemostatic material.

Ddp1 Cooperates with Ppx1 to Counter a Stress Response Initiated by Nonvacuolar Polyphosphate

In diverse cells from bacterial to mammalian species, inorganic phosphate is stored in long chains called polyphosphate (polyP). These nearly universal polymers, ranging from three to thousands of phosphate moieties in length, are associated with molecular functions, including energy homeostasis, protein folding, and cell signaling. In many cell types, polyphosphate is concentrated in subcellular compartments or organelles. In the budding yeast Saccharomyces cerevisiae, polyP synthesis by the membrane-bound vacuolar transporter chaperone (VTC) complex is coupled to its translocation into the lumen of the vacuole, a lysosome-like organelle, where it is stored at high concentrations. In contrast, the ectopic expression of the bacterial polyphosphate kinase (PPK) results in the toxic accumulation of polyP outside the vacuole. In this study, we used label-free mass spectrometry to investigate the mechanisms underlying this toxicity. We find that PPK expression results in the activation of a stress response mediated in part by the Hog1 and Yak1 kinases and the Msn2/Msn4 transcription factors as well as by changes in protein kinase A (PKA) activity. This response is countered by the combined action of the Ddp1 and Ppx1 polyphosphatases that function together to counter polyP accumulation and downstream toxicity. In contrast, the ectopic expression of previously proposed mammalian polyphosphatases did not impact PPK-mediated toxicity in this model, suggesting either that these enzymes do not function directly as polyphosphatases in vivo or that they require cofactors unique to higher eukaryotes. Our work provides insight into why polyP accumulation outside lysosome-like organelles is toxic. Furthermore, it serves as a resource for exploring how polyP may impact conserved biological processes at a molecular level.

Effects of SARS‑CoV‑2 mRNA vaccines on platelet polyphosphate levels and inflammation: A pilot study

Platelets function as immune cells in conjunction with white blood cells, targeting invading pathogens and inducing immune reactions. Intercellular communications among these immune cells are partly mediated by platelet polyphosphate (polyP), which was originally recognized as a thrombotic and hemostatic biomolecule. To determine the involvement of polyP in SARS-CoV-2-mRNA vaccine-induced immune responses, specifically in inflammatory responses, the effects of mRNA vaccines on platelet polyP levels were examined. Before and after vaccination with the COVID-19 vaccine (BNT162b2), blood samples were obtained from healthy, non-smoking individuals who did not have any systemic diseases. Test group demographics skewed somewhat towards either older males (first vaccination, n=6; second vaccination, n=8) or younger females (first vaccination, n=14; second vaccination, n=23). polyP levels in washed platelets from the blood samples were determined using the fluorometric method with DAPI. The side-effects of vaccination were recorded as scores. In the female group, platelet polyP levels decreased after the first vaccination, and the side-effect score increased after the second vaccination. Moderate correlation coefficients were observed between the reduction in polyP levels and the side-effect scores and pre-vaccination polyP levels. Despite the small sample size, this pilot study suggests that platelet polyP may suppress the side effects induced by the mRNA vaccines after the first vaccination, but not the second vaccination in younger female subjects, who generally have higher immune responsiveness than their male counterparts.

Inorganic Polyphosphate, Mitochondria, and Neurodegeneration

With an aging population, the presence of aging-associated pathologies is expected to increase within the next decades. Regrettably, we still do not have any valid pharmacological or non-pharmacological tools to prevent, revert, or cure these pathologies. The absence of therapeutical approaches against aging-associated pathologies can be at least partially explained by the relatively lack of knowledge that we still have regarding the molecular mechanisms underlying them, as well as by the complexity of their etiopathology. In fact, a complex number of changes in the physiological function of the cell has been described in all these aging-associated pathologies, including neurodegenerative disorders. Based on multiple scientific manuscripts produced by us and others, it seems clear that mitochondria are dysfunctional in many of these aging-associated pathologies. For example, mitochondrial dysfunction is an early event in the etiopathology of all the main neurodegenerative disorders, and it could be a trigger of many of the other deleterious changes which are present at the cellular level in these pathologies. While mitochondria are complex organelles and their regulation is still not yet entirely understood, inorganic polyphosphate (polyP) could play a crucial role in the regulation of some mitochondrial processes, which are dysfunctional in neurodegeneration. PolyP is a well-preserved biopolymer; it has been identified in every organism that has been studied. It is constituted by a series of orthophosphates connected by highly energetic phosphoanhydride bonds, comparable to those found in ATP. The literature suggests that the role of polyP in maintaining mitochondrial physiology might be related, at least partially, to its effects as a key regulator of cellular bioenergetics. However, further research needs to be conducted to fully elucidate the molecular mechanisms underlying the effects of polyP in the regulation of mitochondrial physiology in aging-associated pathologies, including neurodegenerative disorders. With a significant lack of therapeutic options for the prevention and/or treatment of neurodegeneration, the search for new pharmacological tools against these conditions has been continuous in past decades, even though very few therapeutic approaches have shown potential in treating these pathologies. Therefore, increasing our knowledge about the molecular mechanisms underlying the effects of polyP in mitochondrial physiology as well as its metabolism could place this polymer as a promising and innovative pharmacological target not only in neurodegeneration, but also in a wide range of aging-associated pathologies and conditions where mitochondrial dysfunction has been described as a crucial component of its etiopathology, such as diabetes, musculoskeletal disorders, and cardiovascular disorders.

Polyphosphate degradation by Nudt3-Zn2+ mediates oxidative stress response

Polyphosphate (polyP) is a polymer of hundreds of phosphate residues present in all organisms. In mammals, polyP is involved in crucial physiological processes, including coagulation, inflammation, and stress response. However, after decades of research, the metabolic enzymes are still unknown. Here, we purify and identify Nudt3, a NUDIX family member, as the enzyme responsible for polyP phosphatase activity in mammalian cells. We show that Nudt3 shifts its substrate specificity depending on the cation; specifically, Nudt3 is active on polyP when Zn²⁺ is present. Nudt3 has in vivo polyP phosphatase activity in human cells, and importantly, we show that cells with altered polyP levels by modifying Nudt3 protein amount present reduced viability upon oxidative stress and increased DNA damage, suggesting that polyP and Nudt3 play a role in oxidative stress protection. Finally, we show that Nudt3 is involved in the early stages of embryo development in zebrafish.

Vtc5 Is Localized to the Vacuole Membrane by the Conserved AP-3 Complex to Regulate Polyphosphate Synthesis in Budding Yeast

Polyphosphates (polyP) are energy-rich polymers of inorganic phosphates assembled into chains ranging from 3 residues to thousands of residues in length. They are thought to exist in all cells on earth and play roles in an eclectic mix of functions ranging from phosphate homeostasis to cell signaling, infection control, and blood clotting. In the budding yeast Saccharomyces cerevisiae, polyP chains are synthesized by the vacuole-bound vacuolar transporter chaperone (VTC) complex, which synthesizes polyP while simultaneously translocating it into the vacuole lumen, where it is stored at high concentrations. VTC’s activity is promoted by an accessory subunit called Vtc5. In this work, we found that the conserved AP-3 complex is required for proper Vtc5 localization to the vacuole membrane. In human cells, previous work has demonstrated that mutation of AP-3 subunits gives rise to Hermansky-Pudlak syndrome, a rare disease with molecular phenotypes that include decreased polyP accumulation in platelet dense granules. In yeast AP-3 mutants, we found that Vtc5 is rerouted to the vacuole lumen by the endosomal sorting complex required for transport (ESCRT), where it is degraded by the vacuolar protease Pep4. Cells lacking functional AP-3 have decreased levels of polyP, demonstrating that membrane localization of Vtc5 is required for its VTC stimulatory activity in vivo. Our work provides insight into the molecular trafficking of a critical regulator of polyP metabolism in yeast. We speculate that AP-3 may also be responsible for the delivery of polyP regulatory proteins to platelet dense granules in higher eukaryotes.

Metformin inhibits polyphosphate-induced hyper-permeability and inflammation

Circulating inflammatory factor inorganic polyphosphate (polyP) released from activated platelets could enhance factor XII and bradykinin resulted in increased capillary leakage and vascular permeability. PolyP induce inflammatory responses through mTOR pathway in endothelial cells, which is being reported in several diseases including atherosclerosis, thrombosis, sepsis, and cancer. Systems and molecular biology approaches were used to explore the regulatory role of the AMPK activator, metformin, on polyP-induced hyper-permeability in different organs in three different models of polyP-induced hyper-permeability including local, systemic short- and systemic long-term approaches in murine models. Our results showed that polyP disrupts endothelial barrier integrity in skin, liver, kidney, brain, heart, and lung in all three study models and metformin abrogates the disruptive effect of polyP. We also showed that activation of AMPK signaling pathway, regulation of oxidant/anti-oxidant balance, as well as decrease in inflammatory cell infiltration constitute a set of molecular mechanisms through which metformin elicits it's protective responses against polyP-induced hyper-permeability. These results support the clinical values of AMPK activators including the FDA-approved metformin in attenuating vascular damage in polyP-associated inflammatory diseases.

The promises of lysine polyphosphorylation as a regulatory modification in mammals are tempered by conceptual and technical challenges

Polyphosphate (polyP) is a ubiquitous biomolecule thought to be present in all cells on Earth. PolyP is deceivingly simple, consisting of repeated units of inorganic phosphates polymerized in long energy-rich chains. PolyP is involved in diverse functions in mammalian systems-from cell signaling to blood clotting. One exciting avenue of research is a new nonenzymatic post-translational modification, termed lysine polyphosphorylation, wherein polyP chains are covalently attached to lysine residues of target proteins. While the modification was first characterized in budding yeast, recent work has now identified the first human targets. There is significant promise in this area of biomedical research, but a number of technical issues and knowledge gaps present challenges to rapid progress. In this review, the current state of the field is summarized and existing roadblocks related to the study of lysine polyphosphorylation in higher eukaryotes are introduced. It is discussed how limited methods to identify targets of polyphosphorylation are further impacted by low concentration, unknown regulatory enzymes, and sequestration of polyP into compartments in mammalian systems. Furthermore, suggestions on how these obstacles could be addressed or what their physiological relevance may be within mammalian cells are presented.

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.

The therapeutic potential of inorganic polyphosphate: A versatile physiological polymer to control coronavirus disease (COVID-19)

Rationale: The pandemic caused by the novel coronavirus SARS-CoV-2 is advancing rapidly. In particular, the number of severe courses of the disease is still dramatically high. An efficient drug therapy that helps to improve significantly the fatal combination of damages in the airway epithelia, in the extensive pulmonary microvascularization and finally multiorgan failure, is missing. The physiological, inorganic polymer, polyphosphate (polyP) is a molecule which could prevent the initial phase of the virus life cycle, the attachment of the virus to the target cells, and improve the epithelial integrity as well as the mucus barrier. Results: Surprisingly, polyP matches perfectly with the cationic groove on the RBD. Subsequent binding studies disclosed that polyP, with a physiological chain length of 40 phosphate residues, abolishes the binding propensity of the RBD to the ACE2 receptor. In addition to this first mode of action of polyP, this polymer causes in epithelial cells an increased gene expression of the major mucins in the airways, of MUC5AC and MUC1, as well as a subsequent glycoprotein production. MUC5AC forms a gel-like mucus layer trapping inhaled particles which are then transported out of the airways, while MUC1 constitutes the periciliary liquid layer and supports ciliary beating. As a third mode of action, polyP undergoes enzymatic hydrolysis of the anhydride bonds in the airway system by alkaline phosphatase, releasing metabolic energy. Conclusions: This review summarizes the state of the art of the biotherapeutic potential of the polymer polyP and the findings from basic research and outlines future biomedical applications.

Biomedical Applications of Bacteria-Derived Polymers

Plastics have found widespread use in the fields of cosmetic, engineering, and medical sciences due to their wide-ranging mechanical and physical properties, as well as suitability in biomedical applications. However, in the light of the environmental cost of further upscaling current methods of synthesizing many plastics, work has recently focused on the manufacture of these polymers using biological methods (often bacterial fermentation), which brings with them the advantages of both low temperature synthesis and a reduced reliance on potentially toxic and non-eco-friendly compounds. This can be seen as a boon in the biomaterials industry, where there is a need for highly bespoke, biocompatible, processable polymers with unique biological properties, for the regeneration and replacement of a large number of tissue types, following disease. However, barriers still remain to the mass-production of some of these polymers, necessitating new research. This review attempts a critical analysis of the contemporary literature concerning the use of a number of bacteria-derived polymers in the context of biomedical applications, including the biosynthetic pathways and organisms involved, as well as the challenges surrounding their mass production. This review will also consider the unique properties of these bacteria-derived polymers, contributing to bioactivity, including antibacterial properties, oxygen permittivity, and properties pertaining to cell adhesion, proliferation, and differentiation. Finally, the review will select notable examples in literature to indicate future directions, should the aforementioned barriers be addressed, as well as improvements to current bacterial fermentation methods that could help to address these barriers.

Impact of g force and timing on the characteristics of platelet-rich fibrin matrices

Recently, new centrifugation protocols for the preparation of platelet-rich fibrin (PRF) have been introduced in an attempt to further improve the beneficial impact of these 2nd generation platelet concentrate membranes. This in-vitro study aimed to compare the biological and physical characteristics of three types of PRF membranes using two different centrifuges with adapted relative centrifugal forces (RCF): leucocyte- and platelet-rich fibrin, advanced platelet-rich fibrin, and advanced platelet-rich fibrin⁺. Release of growth factors, macroscopic dimensions, cellular content and mechanical properties of the respective membranes, prepared from blood of the same individual were explored. Furthermore, the impact of timing (blood draw-centrifugation and centrifugation-membrane preparation) was assessed morphologically as well as by electron microscopy scanning. No statistically significant differences amongst the three PRF modifications could be observed, neither in their release of growth factors or the cellular content, nor in clot/membrane dimensions. The difference between both centrifuges were negligible when the same g-force was used. A lower g-force, however, reduced membrane tensile strength. Timing in the preparation process had a significant impact. Adaptation of RCF only had a minimal impact on the final characteristics of PRF membranes.

Inorganic Polyphosphate in Host and Microbe Biology

Inorganic polyphosphate (polyP) is produced by both bacteria and their eukaryotic hosts, and it appears to play multiple important roles in the interactions between those organisms. However, the detailed mechanisms of how polyP synthesis is regulated in bacteria, and how it influences both bacterial and host biology, remain largely unexplored. In this review, we examine recent developments in the understanding of how bacteria regulate the synthesis of polyP, what roles polyP plays in controlling virulence in pathogenic bacteria, and the effects of polyP on the mammalian immune system, as well as progress on developing drugs that may be able to target bacterial polyP synthesis as novel means of treating infectious disease.

In vitro flow-based assay: From simple toward more sophisticated models for mimicking hemostasis and thrombosis

In vitro flow-based assays are widely used to investigate the role of platelets and coagulation in hemostasis and thrombosis. Their main advantage over other assays relies on the fact that they integrate blood flow that regulates many aspects of platelet function, including adhesion, activation, and aggregation. Blood flow is also central in the regulation of coagulation through its ability to modulate the local concentrations of coagulation factors within and around thrombi. The most broadly used assay to study thrombus formation consists in perfusing whole blood over immobilized fibrillar collagen through a single channel, which helps to reproduce thrombus formation as it occurs in vivo after vascular injury, with platelets adhering, becoming activated, and forming a mural thrombus. This process can also be studied under conditions of thrombin generation, notably by recalcifying blood collected in sodium citrate. In this manuscript, we briefly discuss the advantages and limits of this broadly used "in vitro thrombus formation model." The main emphasis is on the description of the most recent developments regarding design of new flow models and new techniques, and how these may advance the landscape of in vitro studies into the formation of physiological or pathophysiological thrombi. Challenges linked to mimicking the formation of a hemostatic plug in a healthy vessel or a thrombus in diseased arteries and the complexity of reproducing the various aspects of venous thrombosis are discussed. Future directions are proposed to improve the physiological or pathophysiological relevance of current flow-based assays.

Fluorescent Cytochemical Detection of Polyphosphates Associated with Human Platelets

Polyphosphate (polyP) is released from activated platelets and activates the intrinsic coagulation pathway. However, polyP may also be involved in various pathophysiological functions related to platelets. To clarify these functions, we established a cytochemical method to reproducibly visualize polyP in platelets. Platelets obtained from healthy non-smoking donors were suspended in phosphate-buffered saline and quickly immobilized on glass slides using a Cytospin. After fixation and membrane permeabilization, platelets were treated with 4′,6- diamidino-2-phenylindole (DAPI) and examined using a fluorescence microscope with a blue-violet excitation filter block (BV-2A). Fixed platelets were also subjected to immunocytochemical examination to visualize serotonin distribution. Under the optimized conditions for polyP visualization, immobilized platelets were fixed with 10% neutral-buffered formalin for 4 h or longer and treated with DAPI at a concentration of 10 µg/mL in 0.02% saponin- or 0.1% Tween-20-containing Hanks balanced salt solution as a permeabilization buffer for 30 min at room temperature (22–25 °C). Based on the results obtained by using activated platelets, treatment with alkaline phosphatases, and serotonin release, the DAPI⁺ targets were identified as polyP. Therefore, this cytochemical method is useful for determining the amount and distribution of polyP in platelets.

Effects of Thrombin on the Neurovascular Unit in Cerebral Ischemia

Cerebral ischemia is a cerebrovascular disease with high morbidity and mortality that poses a significant burden on society and the economy. About 60% of cerebral ischemia is caused by thrombus, and the formation of thrombus proceeds from insoluble fibrin, following its transformation from liquid fibrinogen. In thrombus-induced ischemia, increased permeability of the blood-brain barrier (BBB), followed by the extravasation of blood components into the brain results in an altered brain microenvironment. Changes in the brain microenvironment affect brain function and the neurovascular unit (NVU), the working unit of the brain. Recent studies have reported that coagulation factors interact with the NVU and its components, but the specific function of this interaction is highly speculative and warrants further investigations. In this article, we reviewed the role of coagulation factors in cerebral ischemia and the role of coagulation factors in thrombosis. Additionally, the influence of thrombin on the NVU is introduced, as well as in the function of NVU, which may help to explore part of brain injury mechanism during ischemia. Lastly, we propose some novel therapeutic approaches on ischemic stroke by reducing the risk of coagulation.

Is there a link between inorganic polyphosphate (polyP), mitochondria, and neurodegeneration?

Mitochondrial dysfunction - including increased apoptosis, calcium and protein dyshomeostasis within the organelle, and dysfunctional bioenergetics and oxidative status - is a common, early feature in all the major neurodegenerative diseases, including Alzheimer's Disease (AD) and Parkinson's Disease (PD). However, the exact molecular mechanisms that drive the organelle to dysfunction and ultimately to failure in these conditions are still not well described. Different authors have shown that inorganic polyphosphate (polyP), an ancient and well-conserved molecule, plays a key role in the regulation of mitochondrial physiology under basal conditions. PolyP, which is present in all studied organisms, is composed of chains of orthophosphates linked together by highly energetic phosphoanhydride bonds, similar to those found in ATP. This polymer shows a ubiquitous distribution, even if a high co-localization with mitochondria has been reported. It has been proposed that polyP might be an alternative to ATP for cellular energy storage in different organisms, as well as the implication of polyP in the regulation of many of the mitochondrial processes affected in AD and PD, including protein and calcium homeostasis. Here, we conduct a comprehensive review and discussion of the bibliography available regarding the role of polyP in the mitochondrial dysfunction present in AD and PD. Taking into account the data presented in this review, we postulate that polyP could be a valid, innovative and, plausible pharmacological target against mitochondrial dysfunction in AD and PD. However, further research should be conducted to better understand the exact role of polyP in neurodegeneration, as well as the metabolism of the polymer, and the effect of different lengths of polyP on cellular and mitochondrial physiology.

Platelet adhesion on commercially pure titanium plates in vitro III: effects of calcium phosphate-blasting on titanium plate biocompatibility

BACKGROUND

Platelet-rich plasma (PRP) is often used to improve surface biocompatibility. We previously found that platelets rapidly adhere to plain commercially pure titanium (cp-Ti) plates in the absence, but not in the presence, of plasma proteins. To further expand on these findings, in the present study, we switched titanium plates from a plain surface to a rough surface that is blasted with calcium phosphate (CaP) powder and then examined platelet adhesion and activation.

METHODS

Elemental distribution in CaP-blasted cp-Ti plates was analyzed using energy-dispersive X-ray spectroscopy. PRP samples prepared from anticoagulated blood samples of six healthy, non-smoking adult male donors were loaded on CaP-blasted cp-Ti plates for 1 h and fixed for examination of platelet morphology and visualization of PDGF-B and platelet surface markers (CD62P, CD63) using scanning electron microscopy and fluorescence microscopy. Plain SUS316L stainless steel plates used in injection needles were also examined for comparison.

RESULTS

Significant amounts of calcium and phosphate were detected on the CaP-blasted cp-Ti surface. Platelets rapidly adhered to this surface, leading to higher activation. Platelets also adhered to the plain stainless surface; however, the levels of adhesion and activation were much lower than those observed on the CaP-blasted cp-Ti plate.

CONCLUSIONS

The CaP-blasted cp-Ti surface efficiently entraps and activates platelets. Biomolecules released from the activated platelets could be retained by the fibrin matrix on the surface to facilitate regeneration of the surrounding tissues. Thus, PRP immersion could not only eliminate surface air bubbles but also improve the biocompatibility of the implant surface.

Immunothrombosis and thromboinflammation in host defense and disease

Platelets are increasingly being recognized for playing roles beyond thrombosis and hemostasis. Today we know that they mediate inflammation by direct interactions with innate immune cells or secretion of cytokines/chemokines. Here we review their interactions with neutrophils and monocytes/macrophages in infection and sepsis, stroke, myocardial infarction and venous thromboembolism. We discuss new roles for platelet surface receptors like GPVI or GPIb and also look at platelet contributions to the formation of neutrophil extracellular traps (NETs) as well as to deep vein thrombosis during infection, e.g. in COVID-19 patients.

High extracellular phosphate increases platelet polyphosphate content

Platelet-derived extracellular polyphosphate (PolyP) is a major mediator of thrombosis. PolyP is a linear chain of inorganic phosphate (P_i) and is stored in platelet dense granules. P_i enters cells from the extracellular fluid through phosphate transporters and may be stored as PolyP. Here we show that high extracellular P_i concentration in vitro increases platelet PolyP content, in a manner dependent on phosphate transporters, IP6K and V-type ATPases. The increased PolyP also enhanced PolyP-dependent coagulation in platelet-rich plasma. These data suggest a mechanistic link between hyperphosphatemia, PolyP and enhanced coagulation, which may be important in pathologies such as chronic kidney disease.

Protease activity in single-chain prekallikrein

Prekallikrein (PK) is the precursor of the trypsin-like plasma protease kallikrein (PKa), which cleaves kininogens to release bradykinin and converts the protease precursor factor XII (FXII) to the enzyme FXIIa. PK and FXII undergo reciprocal conversion to their active forms (PKa and FXIIa) by a process that is accelerated by a variety of biological and artificial surfaces. The surface-mediated process is referred to as contact activation. Previously, we showed that FXII expresses a low level of proteolytic activity (independently of FXIIa) that may initiate reciprocal activation with PK. The current study was undertaken to determine whether PK expresses similar activity. Recombinant PK that cannot be converted to PKa was prepared by replacing Arg371 with alanine at the activation cleavage site (PK-R371A, or single-chain PK). Despite being constrained to the single-chain precursor form, PK-R371A cleaves high-molecular-weight kininogen (HK) to release bradykinin with a catalytic efficiency ∼1500-fold lower than that of kallikrein cleavage of HK. In the presence of a surface, PK-R371A converts FXII to FXIIa with a specific activity ∼4 orders of magnitude lower than for PKa cleavage of FXII. These results support the notion that activity intrinsic to PK and FXII can initiate reciprocal activation of FXII and PK in solution or on a surface. The findings are consistent with the hypothesis that the putative zymogens of many trypsin-like proteases are actually active proteases, explaining their capacity to undergo processes such as autoactivation and to initiate enzyme cascades.

Transferrin plays a central role in coagulation balance by interacting with clotting factors

Coagulation balance is maintained through fine-tuned interactions among clotting factors, whose physiological concentrations vary substantially. In particular, the concentrations of coagulation proteases (pM to nM) are much lower than their natural inactivator antithrombin (AT, ~ 3 μM), suggesting the existence of other coordinators. In the current study, we found that transferrin (normal plasma concentration ~40 μM) interacts with fibrinogen, thrombin, factor XIIa (FXIIa), and AT with different affinity to maintain coagulation balance. Normally, transferrin is sequestered by binding with fibrinogen (normal plasma concentration ~10 μM) at a molar ratio of 4:1. In atherosclerosis, abnormally up-regulated transferrin interacts with and potentiates thrombin/FXIIa and blocks AT's inactivation effect on coagulation proteases by binding to AT, thus inducing hypercoagulability. In the mouse model, transferrin overexpression aggravated atherosclerosis, whereas transferrin inhibition via shRNA knockdown or treatment with anti-transferrin antibody or designed peptides interfering with transferrin-thrombin/FXIIa interactions alleviated atherosclerosis. Collectively, these findings identify that transferrin is an important clotting regulator and an adjuster in the maintenance of coagulation balance and modifies the coagulation cascade.

Inorganic Polyphosphates As Storage for and Generator of Metabolic Energy in the Extracellular Matrix

Inorganic polyphosphates (polyP) consist of linear chains of orthophosphate residues, linked by high-energy phosphoanhydride bonds. They are evolutionarily old biopolymers that are present from bacteria to man. No other molecule concentrates as much (bio)chemically usable energy as polyP. However, the function and metabolism of this long-neglected polymer are scarcely known, especially in higher eukaryotes. In recent years, interest in polyP experienced a renaissance, beginning with the discovery of polyP as phosphate source in bone mineralization. Later, two discoveries placed polyP into the focus of regenerative medicine applications. First, polyP shows morphogenetic activity, i.e., induces cell differentiation via gene induction, and, second, acts as an energy storage and donor in the extracellular space. Studies on acidocalcisomes and mitochondria provided first insights into the enzymatic basis of eukaryotic polyP formation. In addition, a concerted action of alkaline phosphatase and adenylate kinase proved crucial for ADP/ATP generation from polyP. PolyP added extracellularly to mammalian cells resulted in a 3-fold increase of ATP. The importance and mechanism of this phosphotransfer reaction for energy-consuming processes in the extracellular matrix are discussed. This review aims to give a critical overview about the formation and function of this unique polymer that is capable of storing (bio)chemically useful energy.

Mechanisms for Reducing Neuropathic Pain

Injury typically results in the development of neuropathic pain, but the pain normally decreases and disappears in paralleled with wound healing. The pain results from cells resident at, and recruited to, the injury site releasing pro-inflammatory cytokines and other mediators leading to the development of pro-inflammatory environment and causing nociceptive neurons to develop chronic ectopic electrical activity, which underlies neuropathic pain. The pain decreases as some of the cells that induce pro-inflammation, changing their phenotype leading to the blocking the release of pro-inflammatory mediators while releasing anti-inflammatory mediators, and blocking nociceptive neuron chronic spontaneous electrical activity. Often, despite apparent wound healing, the neuropathic pain becomes chronic. This raises the question of how chronic pain can be eliminated. While many of the cells and mediators contributing to the development and maintenance of neuropathic pain are known, a better understanding is required of how the injury site environment can be controlled to permanently eliminate the pro-inflammatory environment and silence the chronically electrically active nociceptive neurons. This paper examines how methods that can promote the transition of the pro-inflammatory injury site to an anti-inflammatory state, by changing the composition of local cell types, modifying the activity of pro- and anti-inflammatory receptors, inducing the release of anti-inflammatory mediators, and silencing the chronically electrically active nociceptive neurons. It also examines the hypothesis that factors released from platelet-rich plasma applied to chronic pain sites can permanently eliminate chronic inflammation and its associated chronic pain.

Injury-Induced Effectors of Neuropathic Pain

Injuries typically result in the development of neuropathic pain, which decreases in parallel with wound healing. However, the pain may remain after the injury appears to have healed, which is generally associated with an ongoing underlying pro-inflammatory state. Injury induces many cells to release factors that contribute to the development of a pro-inflammatory state, which is considered an essential first step towards wound healing. However, pain elimination requires a transition of the injury site from pro- to anti-inflammatory. Therefore, developing techniques that eliminate chronic pain require an understanding of the cells resident at and recruited to injury sites, the factors they release, that promote a pro-inflammatory state, and promote the subsequent transition of that site to be anti-inflammatory. Although a relatively large number of cells, factors, and gene expression changes are involved in these processes, it may be possible to control a relatively small number of them leading to the reduction and elimination of chronic neuropathic pain. This first of two papers examines the roles of the most salient cells and mediators associated with the development and maintenance of chronic neuropathic pain. The following paper examines the cells and mediators involved in reducing and eliminating chronic neuropathic pain.

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.

Progress and Applications of Polyphosphate in Bone and Cartilage Regeneration

Patients with bone and cartilage defects due to infection, tumors, and trauma are quite common. Repairing bone and cartilage defects is thus a major problem for clinicians. Autologous and artificial bone transplantations are associated with many challenges, such as limited materials and immune rejection. Bone and cartilage regeneration has become a popular research topic. Inorganic polyphosphate (polyP) is a widely occurring biopolymer with high-energy phosphoanhydride bonds that exists in organisms from bacteria to mammals. Much data indicate that polyP acts as a regulator of gene expression in bone and cartilage tissues and exerts morphogenetic effects on cells involved in bone and cartilage formation. Exposure of these cells to polyP leads to the increase of cytokines that promote the differentiation of mesenchymal stem cells into osteoblasts, accelerates the osteoblast mineralization process, and inhibits the differentiation of osteoclast precursors to functionally active osteoclasts. PolyP-based materials have been widely reported in in vivo and in vitro studies. This paper reviews the current cellular mechanisms and material applications of polyP in bone and cartilage regeneration.

Polyphosphates and Complement Activation

To sustain life in environments that are fraught with risks of life-threatening injury, organisms have developed innate protective strategies such that the response to wounds is rapid and localized, with the simultaneous recruitment of molecular, biochemical, and cellular pathways that limit bleeding and eliminate pathogens and damaged host cells, while promoting effective healing. These pathways are both coordinated and tightly regulated, as their over- or under-activation may lead to inadequate healing, disease, and/or demise of the host. Recent advances in our understanding of coagulation and complement, a key component of innate immunity, have revealed an intriguing linkage of the two systems. Cell-secreted polyphosphate promotes coagulation, while dampening complement activation, discoveries that are providing insights into disease mechanisms and suggesting novel therapeutic strategies.

Transformation of Amorphous Polyphosphate Nanoparticles into Coacervate Complexes: An Approach for the Encapsulation of Mesenchymal Stem Cells

Inorganic polyphosphate [polyP] has proven to be a promising physiological biopolymer for potential use in regenerative medicine because of its morphogenetic activity and function as an extracellular energy-donating system. Amorphous Ca²⁺ -polyP nanoparticles [Ca-polyP-NPs] are characterized by a high zeta potential with -34 mV (at pH 7.4). This should contribute to the stability of suspensions of the spherical nanoparticles (radius 94 nm), but make them less biocompatible. The zeta potential decreases to near zero after exposure of the Ca-polyP-NPs to protein/peptide-containing serum or medium plus serum. Electron microscopy analysis reveals that the particles rapidly change into a coacervate phase. Those mats are amorphous, but less stable than the likewise amorphous Ca-polyP-NPs and are morphogenetically active. Mesenchymal stem cells grown onto the polyP coacervate show enhanced growth/proliferation and become embedded in the coacervate. These results suggest that the Ca-polyP coacervate, formed from Ca-polyP-NPs in the presence of protein, can act as an adaptable framework that mimics a niche and provides metabolic energy in bone/cartilage engineering.

Apoptotic vesicles: deathly players in cancer-associated coagulation

Although cancer is associated with coagulation disorders, it is still unclear how the combination of tumor cell and host factors enhance the hypercoagulable state of cancer patients. Emerging evidence points to a central role for tumor endosomal and plasma membrane-derived vesicular components in the pathogenesis of cancer-related thrombosis. In particular, tumor cell membranes and extracellular vesicles (EV) harbor lipids and proteinaceous coagulation factors able to initiate multiple points within the coagulation matrix. The impact of chemotherapy upon a host already burdened with a hypercoagulable state increases the risk of pathological coagulation. We argue that chemotherapy-induced EV harbor the most active components for cancer related thrombosis and discuss how membrane components of the host and tumor act to initiate coagulation to enhance thrombotic risk in cancer patients.

The Role of Inflammation in Venous Thromboembolism

Venous thromboembolism (VTE), comprising deep vein thrombosis (DVT), and pulmonary embolism (PE), is becoming increasingly recognized as a cause of morbidity and mortality in pediatrics, particularly among hospitalized children. Furthermore, evidence is accumulating that suggests the inflammatory response may be a cause, as well as consequence, of VTE, but current anticoagulation treatment regimens are not designed to inhibit inflammation. In fact, many established clinical VTE risk factors such as surgery, obesity, cystic fibrosis, sepsis, systemic infection, cancer, inflammatory bowel disease, and lupus likely modulate thrombosis through inflammatory mediators. Unlike other traumatic mechanisms of thrombosis involving vascular transection and subsequent exposure of subendothelial collagen and other procoagulant extracellular matrix materials, inflammation of the vessel wall may initiate thrombosis on an intact vein. Activation of endothelial cells, platelets, and leukocytes with subsequent formation of microparticles can trigger the coagulation system through the induction of tissue factor (TF). Identification of biomarkers to evaluate VTE risk could be of great use to the clinician caring for a patient with inflammatory disease to guide decisions regarding the risk:benefit ratio of various types of potential thromboprophylaxis strategies, or suggest a role for anti-inflammatory therapy. Unfortunately, no such validated inflammatory scoring system yet exists, though research in this area is ongoing. Elevation of C-reactive protein, IL-6, IL-8, and TNF-alpha during a response to systemic inflammation have been associated with increased VTE risk. Consequent platelet activation enhances the prothrombotic state, leading to VTE development, particularly in patients with other risk factors, most notably central venous catheters.

Inorganic polyphosphate: a key modulator of inflammation

Inorganic polyphosphate (PolyP) is a molecule with prothrombotic and proinflammatory properties in blood. PolyP activates the NF-κB signaling pathway, increases the expression of cell surface adhesion molecules and disrupts the vascular barrier integrity of endothelial cells. PolyP-induced NF-κB activation and vascular hyperpermeability are regulated by the mammalian target of rapamycin complex-1 (mTORC1) and mTORC2 pathways, respectively. Through interaction with receptor for advanced glycation end products (RAGE) and P2Y1 receptors, PolyP dramatically amplifies the proinflammatory responses of nuclear proteins. Moreover, PolyP-mediated activation of the contact pathway results in activation of the kallikrein-kinin system, which either directly or in cross-talk with the complement system induces inflammation in both cellular and animal systems. Thus, polyP is a novel therapeutic target for the treatment of metabolic and acute/chronic proinflammatory diseases, including severe sepsis, diabetes, cardiovascular disease and cancer. In this review, we discuss recent findings on the inflammatory properties of polyP and propose a model to explain the molecular mechanism of proinflammatory effects of this molecule in different systems.

Polyphosphate is a novel cofactor for regulation of complement by a serpin, C1 inhibitor

The complement system plays a key role in innate immunity, inflammation, and coagulation. The system is delicately balanced by negative regulatory mechanisms that modulate the host response to pathogen invasion and injury. The serpin, C1-esterase inhibitor (C1-INH), is the only known plasma inhibitor of C1s, the initiating serine protease of the classical pathway of complement. Like other serpin-protease partners, C1-INH interaction with C1s is accelerated by polyanions such as heparin. Polyphosphate (polyP) is a naturally occurring polyanion with effects on coagulation and complement. We recently found that polyP binds to C1-INH, prompting us to consider whether polyP acts as a cofactor for C1-INH interactions with its target proteases. We show that polyP dampens C1s-mediated activation of the classical pathway in a polymer length- and concentration-dependent manner by accelerating C1-INH neutralization of C1s cleavage of C4 and C2. PolyP significantly increases the rate of interaction between C1s and C1-INH, to an extent comparable to heparin, with an exosite on the serine protease domain of the enzyme playing a major role in this interaction. In a serum-based cell culture system, polyP significantly suppressed C4d deposition on endothelial cells, generated via the classical and lectin pathways. Moreover, polyP and C1-INH colocalize in activated platelets, suggesting that their interactions are physiologically relevant. In summary, like heparin, polyP is a naturally occurring cofactor for the C1s:C1-INH interaction and thus an important regulator of complement activation. The findings may provide novel insights into mechanisms underlying inflammatory diseases and the development of new therapies.

The role of extracellular histones in haematological disorders

Over the past decades, chromosomal alterations have been extensively investigated for their pathophysiological relevance in haematological malignancies. In particular, epigenetic modifications of intra-nuclear histones are now known as key regulators of healthy cell cycles that have also evolved into novel therapeutic targets for certain blood cancers. Thus, for most haematologists, histones are DNA-chained proteins that are buried deep within chromatin. However, the plot has deepened with recent revelations on the function of histones when unchained and released extracellularly upon cell death or from activated neutrophils as part of neutrophil extracellular traps (NETs). Extracellular histones and NETs are increasingly recognized for profound cytotoxicity and pro-coagulant effects. This article highlights the importance of recognizing this new paradigm of extracellular histones as a key player in host defence through its damage-associated molecular patterns, which could translate into novel diagnostic and therapeutic biomarkers in various haematological and critical disorders.

HUS and the case for complement

Hemolytic-uremic syndrome (HUS) is a thrombotic microangiopathy that is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. Excess complement activation underlies atypical HUS and is evident in Shiga toxin-induced HUS (STEC-HUS). This Spotlight focuses on new knowledge of the role of Escherichia coli-derived toxins and polyphosphate in modulating complement and coagulation, and how they affect disease progression and response to treatment. Such new insights may impact on current and future choices of therapies for STEC-HUS.