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ChAdOx1 nCoV-19 adenoviral vector vaccine (ChAd) against coronavirus disease 2019 has been associated with vaccine-induced thrombosis and thrombocytopenia (VITT), especially in young women who have presented with unusual localized thrombosis after receiving the vaccine. The pathogenesis of VITT remains incompletely understood. We tried to provide new insights into mechanisms underlying this phenomenon in the model of arterial thrombosis electrically induced in the carotid artery of female rats. At 28 days post-vaccination, ChAd induced SARS-CoV-2-specific neutralizing antibody responses in all animals. The analysis of the blood vessel/thrombus area showed slight luminal narrowing of the carotid artery with extravasation of blood in vaccinated rats. These small changes were not accompanied by differences in thrombus weight and composition. The vaccinated animals presented a slight increase (by around 14-24%) in platelet aggregation. ChAd did not significantly affect blood coagulation, platelet counts, and their activation markers. Unaffected thrombus formation, the lack of thrombocytopenia and all the measured blood and hemostasis parameters that predominantly stayed unchanged, indicate that the ChAd does not increase the risk of arterial thrombosis development in female rats.

The methods used in preclinical studies should minimize the suffering and the number of animals but still provide precise and consistent results enabling the introduction of drug candidates into the phase of clinical trials. Thus, we aimed to develop a method allowing us to perform preliminary safety and toxicity studies of candidates for human medicines, while reducing the number of animals. We have devised a method based on a combination of two devices: Plugsys (Transonics System Inc., Ithaca, NY, USA) and PhysioSuite (Kent Scientific Corporation, Torrington, CT, USA), which allow simultaneous registration of nine circulatory and respiratory parameters, and body temperature. Vehicle and adrenaline, or nitroglycerin, as reference substances were administered into the right femoral vein of Wistar rats. Physiological conditions were registered over 60 min after drug administration by measuring systolic, diastolic and mean blood pressure, heart rate (HR), blood perfusion of paw vessels, blood oxygen saturation, respiratory rate, average and peak exhaled CO2, and body temperature. Blood pressure was measured by cannula placed in the left common carotid artery and connected to the pressure transducer (Plugsys). The other parameters were measured by the PhysioSuite. Adrenaline-induced immediate dose-related hypertension and nitroglycerin hypotension were correlated with the change in blood perfusion. They both increased HR. Adrenaline decreased blood oxygen saturation and slightly affected respiratory parameters, while nitroglycerin caused a progressive increase in respiratory rate and a decrease in the peak of exhaled CO2. Our method may become an inseparable part of the preliminary safety and toxicity studies of tested drugs, while being an important step towards improving animal welfare.

Uncontrolled bleeding after enoxaparin (ENX) is rare but may be life-threatening. The only registered antidote for ENX, protamine sulfate (PS), has 60% efficacy and can cause severe adverse side effects. We developed a diblock copolymer, heparin-binding copolymer (HBC), that reverses intravenously administered heparins. Here, we focused on the HBC inhibitory activity against subcutaneously administered ENX in healthy mice. BALB/c mice were subcutaneously injected with ENX at the dose of 5 mg/kg. After 110 min, vehicle, HBC (6.25 and 12.5 mg/kg), or PS (5 and 10 mg/kg) were administered into the tail vein. The blood was collected after 3, 10, 60, 120, 360, and 600 min after vehicle, HBC, or PS administration. The activities of antifactors Xa and IIa and biochemical parameters were measured. The main organs were collected for histological analysis. HBC at the lower dose reversed the effect of ENX on antifactor Xa activity for 10 min after antidote administration, whereas at the higher dose, HBC reversed the effect on antifactor Xa activity throughout the course of the experiment. Both doses of HBC completely reversed the effect of ENX on antifactor IIa activity. PS did not reverse antifactor Xa activity and partially reversed antifactor IIa activity. HBC modulated biochemical parameters. Histopathological analysis showed changes in the liver, lungs, and spleen of mice treated with HBC and in the lungs and heart of mice treated with PS. HBC administered in an appropriate dose might be an efficient substitute for PS to reverse significantly increased anticoagulant activity that may be connected with major bleeding in patients receiving ENX subcutaneously.

MM-129 is a novel inhibitor targeting BTK/PI3K/AKT/mTOR and PD-L1, as it possesses antitumor activity against colon cancer. To evaluate the safety profile of MM-129, we conducted a toxicity study using the zebrafish and rodent model. MM-129 was also assessed for pharmacokinetics features through an in vivo study on Wistar rats. The results revealed that MM-129 exhibited favorable pharmacokinetics with quick absorption and 68.6% of bioavailability after intraperitoneal administration. No serious adverse events were reported for the use of MM-129, confirming a favorable safety profile for this compound. It was not fatal and toxic to mice at an anticancer effective dose of 10 μmol/kg. At the end of 14 days of administering hematological and biochemical parameters, liver and renal functions were all at normal levels. No sublethal effects were either detected in zebrafish embryos treated with a concentration of 10 μM. MM-129 has the potential as a safe and well-tolerated anticancer formulation for future treatment of patients with colon cancer.

The routine monitoring of direct oral anticoagulants (DOACs) may be considered in patients with renal impairment, patients who are heavily obese, or patients requiring elective surgery. Using the heparin-binding copolymer (HBC) and polybrene, we aimed to develop a solution for monitoring the anticoagulant activity of DOACs in human plasma in the interfering presence of unfractionated heparin (UFH) and enoxaparin. The thrombin time (TT) and anti-factor Xa activity were monitored in pooled plasma from healthy volunteers. In these tests, plasma with dabigatran or rivaroxaban was mixed with UFH or enoxaparin and then incubated with HBC or polybrene, respectively. HBC and polybrene neutralized heparins and enabled monitoring of anticoagulant activity of dabigatran in the TT test. Both agents allowed for accurate measurement of anti-factor Xa activity in the plasma containing rivaroxaban and heparins in the concentration range reached in patients’ blood. Here, we present diagnostic tools that may improve the control of anticoagulation by eliminating the contamination of blood samples with heparins and enabling the monitoring of DOACs’ activity.

Bleeding resulting from the application of low-molecular-weight heparins (LMWHs) may be treated with protamine sulfate, but this treatment lacks efficiency; its action against antifactor Xa activity is limited to ∼60%. Moreover, protamine sulfate can cause life-threatening hypersensitivity reactions. We developed diblock heparin-binding copolymer (HBC), which can neutralize the anticoagulant activity of parenteral anticoagulants. In the present study, we explored the safety profile of HBC and its potential to reverse enoxaparin, nadroparin, dalteparin, and tinzaparin in human plasma and at in vivo conditions. HBC-LMWH complexes were characterized using zeta potential, isothermal titration calorimetry, and dynamic light scattering. The rat cardiomyocytes and human endothelial cells were used for the assessment of in vitro toxicity. Male Wistar rats were observed for up to 4 days after HBC administration for clinical evaluation, gross necropsy, and biochemistry and histopathological analysis. Rats were treated with LMWHs alone or followed by short-time intravenous infusion of HBC, and bleeding time and antifactor Xa activity were measured. HBC completely reversed antifactor Xa activity prolonged in vitro by all LMWHs with an optimal weight ratio of 2.5:1. The complexes of HBC-LMWHs were below 5 µm. We observed no effects on the viability of cardiovascular cells treated with HBC at concentrations up to 0.05 mg/ml. Single doses up to 20 mg/kg of HBC were well tolerated by rats. HBC completely reversed the effects of LMWHs on bleeding time and antifactor Xa activity in vivo after 20 minutes and retained ∼80% and ∼60% of reversal activity after 1 and 2 hours, respectively. Well-documented efficacy and safety of HBC both in vitro and in vivo make this polymer a promising candidate for LMWHs reversal. SIGNIFICANCE STATEMENT: Over the last decade, there has been significant progress in developing antidotes for the reversal of anticoagulants. Until now, there has been no effective and safe treatment for patients with severe bleeding under low-molecular-weight heparin therapy. Based on our in vitro and in vivo studies, heparin-binding copolymer seems to be a promising candidate for neutralizing all clinically relevant low-molecular-weight heparins.

Di- and triblock copolymers with low dispersity of molecular weight were synthesized using radical addition-fragmentation chain transfer polymerization. The copolymers contained anionic poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPS) block as an anticoagulant component. The block added to lower the toxicity was either poly(ethylene glycol) (PEG) or poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC). The polymers prolonged clotting times both in vitro and in vivo. The influence of the polymer architecture and composition on the efficacy of anticoagulation and safety parameters was evaluated. The polymer with the optimal safety/efficacy profile was PEG47- b-PAMPS108, i.e., a block copolymer with the degrees of polymerization of PEG and PAMPS blocks equal to 47 and 108, respectively. The anticoagulant action of copolymers is probably mediated by antithrombin, but it differs from that of unfractionated heparin. PEG47- b-PAMPS108 also inhibited platelet aggregation in vitro and increased the prostacyclin production but had no antiplatelet properties in vivo. PEG47- b-PAMPS108 anticoagulant activity can be efficiently reversed with a copolymer of PEG and poly((3-(methacryloylamino)propyl)trimethylammonium chloride) (PMAPTAC) (PEG41- b-PMAPTAC53, HBC), which may be attributed to the formation of polyelectrolyte complexes with PEG shells without anticoagulant properties.

Protamine is widely used to neutralize the anticoagulant effects of unfractionated heparin, particularly after cardiac surgery. Recent reports suggest that some patients undergoing cardiopulmonary bypass exposed to heparin and protamine may develop thrombocytopenia. Multimolecular protamine-heparin complexes lead to immunization and production of immunoglobulin G class antibodies that may activate platelets through FcγIIa receptors. Some patients injected with protamine during cardiopulmonary bypass have increased the risk of early thromboembolic events due to the presence of these antibodies in the blood. In the present review, we will focus on studies investigating the mechanism of platelet activation by anti-protamine-heparin antibodies. We will compare antibodies that are associated with immune heparin-induced thrombocytopenia. In addition, we will describe the clinical consequences of protamine-induced thrombocytopenia, risk factors and general guidelines for management of thromboembolic complications in the post-cardiac surgery patients.

Protamine sulfate (PS) is a polycationic protein drug obtained from the sperm of fish, and is used to reverse the anticoagulant effect of unfractionated heparin (UFH). However, the interactions between PS, UFH, and platelets are still not clear. We measured the platelet numbers and collagen-induced aggregation, P-selectin, platelet factor 4, &beta, thromboglobulin, prostacyclin metabolite, D-dimers, activated partial thromboplastin time, prothrombin time, anti-factor Xa, fibrinogen, thrombus weight and megakaryocytopoiesis in blood collected from mice and rats in different time points.. All of the groups were treated intravenously with vehicle, UFH, PS, or UFH with PS. We found a short-term antiplatelet activity of PS in mice and rats, and long-term platelet-independent antithrombotic activity in rats with electrically-induced thrombosis. The antiplatelet and antithrombotic potential of PS may contribute to bleeding risk in PS-overdosed patients. The inhibitory effect of PS on the platelets was attenuated by UFH without inducing thrombocytopenia. Treatment with UFH and PS did not affect the formation, number, or activation of platelets, or the thrombosis development in rodents.

Besides regulating ligand–receptor and cell–cell interactions, heparan sulfate (HS) may participate in the development of many diseases, such as cancer, bacterial or viral infections, and their complications, like bleeding or inflammation. In these cases, the neutralization of HS could be a potential therapeutic target. The heparin-binding copolymer (HBC, PEG41-PMAPTAC53) was previously reported by us as a fully synthetic compound for efficient and safe neutralization of heparins and synthetic anticoagulants. In a search for molecular antagonists of HS, we examined the activity of HBC as an HS inhibitor both in vitro and in vivo and characterized HBC/HS complexes. Using a colorimetric Azure A method, isothermal titration calorimetry and dynamic light scattering techniques we found that HBC binds HS by forming complexes below 200 nm with less than 1 : 1 stoichiometry. We confirmed the HBC inhibitory effect in rats by measuring activated partial thromboplastin time, prothrombin time, anti-factor Xa activity, anti-factor IIa activity, and platelet aggregation. HBC reversed the enhancement of all tested parameters caused by HS demonstrating that cationic synthetic block copolymers may have a therapeutic value in various disorders involving overproduction of HS.

Protamine sulfate (PS) is the only available option to reverse the anticoagulant activity of unfractionated heparin (UFH), however it can cause cardiovascular and respiratory complications. We explored the toxicity of PS and its complexes with UFH in zebrafish, rats, and mice. The involvement of nitric oxide (NO) in the above effects was investigated. Concentration–dependent lethality, morphological defects, and decrease in heart rate (HR) were observed in zebrafish larvae. PS affected HR, blood pressure, respiratory rate, peak exhaled CO2, and blood oxygen saturation in rats. We observed hypotension, increase of HR, perfusion of paw vessels, and enhanced respiratory disturbances with increases doses of PS. We found no effects of PS on human hERG channels or signs of heart damage in mice. The hypotension in rats and bradycardia in zebrafish were partially attenuated by the inhibitor of endothelial NO synthase. The disturbances in cardiovascular and respiratory parameters were reduced or delayed when PS was administered together with UFH. The cardiorespiratory toxicity of PS seems to be charge–dependent and involves enhanced release of NO. PS administered at appropriate doses and ratios with UFH should not cause permanent damage of heart tissue, although careful monitoring of cardiorespiratory parameters is necessary.

Unfractionated heparin is a strongly anionic anticoagulant used extensively in medicine to prevent blood clotting. In the case of an emergency bleeding in response to heparin, the protamine sulfate is administered. Despite its extensive clinical use, protamine may produce life-threatening side effects such as systemic hypotension, catastrophic pulmonary vasoconstriction or allergic reactions. Recent studies have demonstrated new organ-specific complications of the heparin reversal with protamine.Past and present knowledge of the mechanisms responsible for the toxicity of protamine and the most promising potential replacements of protamine in the different phases of development.Despite of the low therapeutic index, protamine is the only registered antidote of heparins. The toxicology of protamine depends on a complex interaction of the high molecular weight, a cationic peptide with the surfaces of the vasculature and blood cells. The mechanisms involve membrane receptors and ion channels targeted by different vasoactive compounds, such as nitric oxide, bradykinin or histamine. Unacceptable side effects of protamine have led to a search for new alternatives: UHRA, LMWP, and Dex40-GTMAC3 are in the preclinical stage; the two other agents (andexanet alfa and PER977) are already in the advanced clinical phases.

The parenteral anticoagulants may cause uncontrolled and life-threatening bleeding. Protamine, the only registered heparin antidote, is partially effective against low-molecular weight heparins, completely ineffective against fondaparinux and may cause unacceptable toxicity. Therefore, we aimed to develop a synthetic compound for safe and efficient neutralization of all parenteral anticoagulants. We synthesized pegylated PMAPTAC block copolymers, and then, we selected a lead heparin-binding copolymer (HBC). We assessed the effectiveness of HBC in the model of arterial thrombosis electrically induced in the carotid artery of rats by measuring thrombus weight, bleeding time, activated partial thromboplastin time, activated clotting time, and anti-factor Xa activity. The intravital tissue distribution, the cardiorespiratory, and organ toxicity were monitored. HBC diminished antithrombotic and anticoagulant effects of unfractionated heparin. Moreover, it stopped bleeding and completely reversed the enhancement of clotting times and anti-factor Xa activity caused by enoxaparin or fondaparinux. We observed slight pulmonary congestion and cell infiltration, but the cardiorespiratory parameters remained unchanged. We found a strong signal of fluorescently-labeled HBC in the urine, and a weaker in the liver and in the kidney. No signs of hepatic or nephrotoxicity were observed in the blood biochemistry or histopathologic examination. We developed a copolymer efficiently neutralizing effects of heparins in the living organism, which shows a very promising efficacy/safety profile and may help in the management of uncontrolled bleeding resulting from an anticoagulant injection. HBC could enable the safe replacement of unfractionated heparin with low-molecular weight heparins in patients undergoing cardiac surgery and complex vascular procedures.