Aptamers influence the hemostatic system by activating the intrinsic coagulation pathway in an in vitro Chandler-Loop model

Effect of bivalirudin on coagulation in neonatal (cord) and adult human blood in vitro

INTRODUCTION

Bivalirudin is recommended as an alternative to heparin in cardiac surgery with cardiopulmonary bypass. Although it has been used in infants and children for this indication, there is a paucity of data on the pharmacologic effects of bivalirudin in neonates. Given the immaturity of the hemostatic system in neonates, we hypothesized that coagulation responses to bivalirudin in this population would be different than in adults.

METHODS

Blood samples were drawn from placenta-cord units and from healthy adult donors. The study was carried out in two steps. First, bivalirudin was added to cord and adult blood samples at concentrations of 0, 5, 10, 15, and 20 μg/mL. Activated clotting time and thromboelastographic variables were recorded. Next, we used a Chandler loop system to assess the efficacy of bivalirudin in a simple model of cardiopulmonary bypass. The loops were primed with cord or adult blood and were run until thrombus was detected. Plasma bivalirudin concentrations were measured at 1, 15, 30, 45, 60, and 75 min after initiating rotation of the loops using liquid chromatography/mass spectrometry.

RESULTS

Bivalirudin elicited a dose-dependent prolongation inhibition of coagulation in both cord and adult blood samples with greater potency in cord blood in comparison to adult blood (activated clotting time: 627 ± 50 vs. 452 ± 22 s at 15 μg/mL bivalirudin, p < .0001). This relative potency was also demonstrated in the Chandler loop system, but interestingly, cord blood appeared to inactivate bivalirudin more rapidly than adult blood with earlier clotting in loops containing cord blood.

CONCLUSIONS

This study demonstrates that bivalirudin has greater potency in cord blood in vitro than in adult blood. Plasma degradation appears to proceed more rapidly in cord blood than in adults. Both of these findings should be considered when planning dosing regimens in neonatal patients.

Aptamers as Therapeutic Agents: Has the Initial Euphoria Subsided?

Aptamers are synthetic DNA or RNA oligonucleotide ligands with great potential for therapeutic applications. A vast number of disease-related targets have been used to identify agonistic, antagonistic, or inhibitory aptamers, or aptamer-based targeting ligands. However, only a few aptamers have reached late-stage clinical trials so far and the commercial infrastructure is still far behind that of other therapeutic agents such as monoclonal antibodies. The desirable properties of aptamers such as selectivity, chemical flexibility, or cost-efficiency are faced by challenges, including a short half-life in vivo, immunogenicity, and entrapment in cellular organelles. Aptamer research is still in an early stage, and a deeper understanding of their structure, target interactions, and pharmacokinetics is necessary to catch up to the clinical market. In this review, we will discuss the benefits and limitations in the development of therapeutic aptamers, as well as the advances and future directions of aptamer research. The progress towards effective therapies seems to be slow, but it has not stopped and the best is yet to come.

The Kv1.3 channel-inhibitory toxin BF9 also displays anticoagulant activity via inhibition of factor XIa

The Kv1.3 channel plays potential roles in immune, inflammation and coagulation system. Many studies showed that Kv1.3 channel inhibitors have immunosuppressive and anti-inflammatory activities, but no Kv1.3 channel inhibitors have been found to have anticoagulation activities. Here, based on our previous work about Kv1.3 channel toxin peptide inhibitors, we first attempt to test anticoagulation activities of four known venom-derived Kv1.3 channel inhibitors with different structural folds: BmKTX with CSα/β structural fold, OmTx3 with CSα/α structural fold, BF9 with Kuntz-type structural fold, and SjAPI-2 with Ascaris-type structural fold. Our results showed that BmKTX and OmTx3 have no activities towards both intrinsic and extrinsic coagulation pathway, SjAPI-2 just has weak activity towards intrinsic coagulation pathway, and BF9 has potent activity towards intrinsic coagulation pathway with no apparent effect on extrinsic coagulation pathway. Enzyme and inhibitor reaction kinetics experiments further showed that BF9 inhibited intrinsic coagulation pathway-associated coagulation factor XIa, but have no apparent effects on common coagulation pathway coagulation factor IIa. Structure-activity relationship showed that Gly14, Asn17, Ala18 and Ile20 of BF9 are main residues involved in the inhibiting effect on factor XIa. To the best of our knowledge, BF9 is the first anticoagulant with Kv1.3 channel inhibitory activity. Together, our present studies found the first dual functional peptides with Kv1.3 channel and coagulation factor XIa inhibitory activities, and provided a new molecular template for the lead drug discovery towards immune and thrombosis-associated human diseases.

The Procoagulant Activity of Apoptotic Cells Is Mediated by Interaction with Factor XII

Apoptotic cells, by externalizing phosphatidylserine (PS) as a hallmark feature, are procoagulant. However, the mechanism by which apoptotic cells activate coagulation system remains unknown. Intrinsic coagulation pathway is initiated by coagulation factor XII (FXII) of contact activation system. The purpose of this study was to determine whether FXII is involved in procoagulant activity of apoptotic cells. Using western blotting and chromogenic substrate assay, we found that incubation with apoptotic cells, but not with viable cells, resulted in rapid cleavage and activation of FXII in the presence of prekallikrein and high molecular weight kininogen (HK), other two components of contact activation system. As detected by flow cytometry, FXII bound to apoptotic cells in a concentration-dependent manner, which was inhibited by annexin V and PS liposome. Direct association of FXII with PS was confirmed in a surface plasmon resonance assay. Clotting time of FXII-deficient plasma induced by apoptotic cells was significantly prolonged, which was fully reversed by replenishment with FXII. Corn trypsin inhibitor, a FXII inhibitor, completely prevented apoptotic cells-induced intrinsic tenase complex formation. Consistently, apoptotic cells significantly increased thrombin production in normal plasma, which was not affected by an inhibitory anti-tissue factor antibody. However, blocking of PS by annexin V, inhibition of FXII, or the deficiency of FXII suppressed apoptotic cells-induced thrombin generation. Addition of purified FXII to FXII-deficient plasma recovered thrombin generation to the normal plasma level. In conclusion, FXII binds to apoptotic cells via PS and becomes activated, thereby constituting a novel mechanism mediating the procoagulant activity of apoptotic cells.

Extracellular nucleic acids in immunity and cardiovascular responses: between alert and disease

Severe inflammatory complications are a potential consequence in patients with predetermined conditions of infections, pulmonary diseases, or cardiovascular disorders. Notably, the amplitude of the inflammatory response towards these complications can dictate the disease progression and outcome. During the recent years, evidence from basic research as well as from clinical studies has identified self-extracellular nucleic acids as important players in the crosstalk between immunity and cardiovascular diseases. These stress- or injury-induced endogenous polymeric macromolecules not only serve as "alarmins" or "Danger-associated molecular patterns" (DAMPs), but their functional repertoire goes far beyond such activities in innate immunity. In fact, (patho-) physiological functions of self-extracellular DNA and RNA are associated and in many cases causally related to arterial and venous thrombosis, atherosclerosis, ischemia-reperfusion injury or tumour progression. Yet, the underlying molecular mechanisms are far from being completely understood. Interestingly enough, however, novel antagonistic approaches in vitro and in vivo, particularly using natural endonucleases or synthetic nucleic acid binding polymers, appear to be promising and safe therapeutic options for future studies. The aim of this review article is to provide an overview of the current state of (patho-) physiological functions of self-extracellular nucleic acids with special emphasis on their role as beneficial / alerting or adverse / damaging factors in connection with immune responses, inflammation, thrombosis, and cardiovascular diseases.

Potential capacity of aptamers to trigger immune activation in human blood

Target specific short single-stranded DNA (ssDNA) molecules, called aptamers, are auspicious ligands for numerous in vivo applications. However, aptamers are synthetic molecules, which might be recognized by the immune cells in vivo and induce an activation of the innate immune system. Thus, immune activation potential of synthetic ssDNA oligonucleotides (ODNs) was determined using a well established closed-loop circulation model. Fresh human blood was incubated at 37°C for 2 or 4 hours with ssDNA ODNs (SB_ODN) or CpG ODN as positive control. Transcriptional changes were determined by microarray analyses. Blood samples containing SB_ODN demonstrated after 4 hours a significant regulation of 295 transcripts. Amongst others, CCL8, CXCL10, CCL7 and CXCL11 were highest regulated genes. Gene Ontology terms and KEGG pathway analyses exhibited that the differentially expressed genes belong to the transcripts that are regulated during an immune and inflammatory response, and were overrepresented in TLR signaling pathway. This study shows for the first time the potential of aptamers to activate immune system after systemic application into the human blood. Thus, we highly recommend performing of these preclinical tests with potential aptamer-based therapeutics.

Hemocompatibility evaluation of different silver nanoparticle concentrations employing a modified Chandler-loop in vitro assay on human blood

Due to their antibacterial effects, the use of silver nanoparticles (AgNPs) in a great variety of medical applications like coatings of medical devices has increased markedly in the last few years. However, blood in contact with AgNPs may induce adverse effects, thereby altering hemostatic functions. The objective of this study was to investigate the hemocompatibility of AgNPs in whole blood. Human whole blood (n=6) was treated with different AgNPs concentrations (1, 3 and 30mgl(-1)) or with saline/blank solutions as controls before being circulated in an in vitro Chandler-loop model for 60min at 37°C. Before and after circulation, various hematologic markers were investigated. Based on the hematologic parameters measured, no profound changes were observed in the groups treated with AgNP concentrations of 1 or 3mgl(-1). AgNP concentrations of 30mgl(-1) induced hemolysis of erythrocytes and α-granule secretion in platelets, increased CD11b expression on granulocytes, increased coagulation markers thrombin-antithrombin-III complex, kallikrein-like and FXIIa-like activities as well as complementing cascade activation. Overall, we provide for the first time a comprehensive evaluation including all hematologic parameters required to reliably assess the hemocompatibility of AgNPs. We strongly recommend integrating these hemocompatibility tests to preclinical test procedures prior to in vivo application of new AgNP-based therapies.

Extracellular nucleic acids as novel alarm signals in the vascular system. Mediators of defence and disease

Upon vascular injury or tissue damage, the exposed intracellular material such as nucleic acids, histones and other macromolecules may come into contact with vessel wall cells and circulating blood cells and may thus, have an enduring influence on wound healing and body defence processes. This short review summarizes recent work related to extracellular DNA and RNA and their role as prominent alarm signals and inducers of different defence reactions related to innate immunity and thrombus formation. Of particular importance are DNA-histone complexes (nucleosome material) that, having been expelled during stimulation of the neutrophils, not only trap and eliminate bacteria but also promote thrombus formation in the arterial and venous system. Consequently therefore, the administration of DNase exhibits strong antithrombotic functions. Similarly, extracellular RNA provokes activation of the contact phase system of blood coagulation and, by interacting with specific proteins and cytokines, it promotes vascular permeability and oedema formation. The development of RNA-mediated thrombosis, vasogenic oedema or proinflammatory responses are counteracted by the administration of RNase1 in several pathogenetic animal models. Thus, extracellular nucleic acids appear not only to function as host alarm signals that serve to amplify the defence response, but they also provide important links to thrombus formation as part of the innate immune system.

Structural requirements for the procoagulant activity of nucleic acids

Nucleic acids, especially extracellular RNA, are exposed following tissue- or vessel damage and have previously been shown to activate the intrinsic blood coagulation pathway in vitro and in vivo. Yet, no information on structural requirements for the procoagulant activity of nucleic acids is available. A comparison of linear and hairpin-forming RNA- and DNA-oligomers revealed that all tested oligomers forming a stable hairpin structure were protected from degradation in human plasma. In contrast to linear nucleic acids, hairpin forming compounds demonstrated highest procoagulant activities based on the analysis of clotting time in human plasma and in a prekallikrein activation assay. Moreover, the procoagulant activities of the DNA-oligomers correlated well with their binding affinity to high molecular weight kininogen, whereas the binding affinity of all tested oligomers to prekallikrein was low. Furthermore, four DNA-aptamers directed against thrombin, activated protein C, vascular endothelial growth factor and nucleolin as well as the naturally occurring small nucleolar RNA U6snRNA were identified as effective cofactors for prekallikrein auto-activation. Together, we conclude that hairpin-forming nucleic acids are most effective in promoting procoagulant activities, largely mediated by their specific binding to kininogen. Thus, in vivo application of therapeutic nucleic acids like aptamers might have undesired prothrombotic or proinflammatory side effects.

DEHP and its active metabolites: leaching from different tubing types, impact on proinflammatory cytokines and adhesion molecule expression. Is there a subsumable context?

Introduction: Di(2-ethylhexyl)phthalate (DEHP) is suspected to be toxic for several reasons. During contact with a lipophilic medium, DEHP leaks from polyvinylchloride (PVC), but its influence on inflammatory reactions remains unknown. We examined specific DEHP leaching out of different tubing types, the possibly modulated liberation of proinflammatory cytokines and the induction of adhesion molecule expression in primary endothelial cells.

Materials and Methods: Blood samples were circulated in traditional PVC, nodioctyl phthalate (DOP) PVC and heparin-coated PVC tubing within a Chandler loop model. The blood was tested for the concentration of DEHP and its active metabolites as well as the liberation of the proinflammatory cytokines TNFα and IL1ß. Furthermore, we exposed human endothelial cells to circulated blood and analysed them for the expression of the adhesion molecules ICAM-1, VCAM-1 and E-selectin.

Results: In contrast to the other tubing, PVC tubing showed significantly elevated DEHP levels, but no alteration was observed concerning a potential up-regulation of the cytokines or activation of the endothelial adhesion molecule receptors.

Conclusions: Our data conclude that there is no correlation between DEHP leaching and the inflammatory response after ECC support, but this study showed that even DEHP-free material is leaching DEHP and its toxic metabolites.

Biological rationale for new drugs in the bleeding disorders pipeline

Since the introduction of replacement coagulation factor infusions for the treatment of hemophilia in the 1970s and subsequent improvements in the safety profile of available factor VIII (FVIII) and factor IX (FIX) concentrates, mortality among patients with hemophilia has improved considerably and now parallels that of the noncoagulopathic population in developed countries. Substantial morbidity, however, continues from the development of inhibitory antibodies, a recognized complication of clotting factor replacement; from infections and thrombosis complicating placement of central venous catheters, which are required in children with hemophilia due to frequent prophylactic infusions of coagulation factors with defined half-lives; and from disabling joint disease in individuals without access to costly prophylaxis regimens. In response to the need for long-acting, more potent, less immunogenic, and more easily administered therapies, an impressive array of novel agents is nearly ready for use in the clinical setting. These therapeutics derive from rational bioengineering of recombinant coagulation factors or from the discovery of nonpeptide molecules that have the potential to support hemostasis through alternative pathways. The number of novel agents in clinical trials is increasing, and many of the initial results are promising. In addition to advancing treatment of bleeding episodes or enabling adherence to prophylactic infusions of clotting factor concentrate, newer therapeutics may also lead to improvements in joint health, quality of life, and tolerability of iatrogenic or comorbidity-associated bleeding challenges.