Heparin Neutralization with Methylene Blue, Hexadimethrine, or Vancomycin After Cardiopulmonary Bypass

Engineered Protein Copolymers for Heparin Neutralization and Detection

Heparin is a widely applied anticoagulant agent. However, in clinical practice, it is of vital importance to reverse its anticoagulant effect to restore the blood-clotting cascade and circumvent side effects. Inspired by protein cages that can encapsulate and protect their cargo from surroundings, we utilize three designed protein copolymers to sequester heparin into inert nanoparticles. In our design, a silk-like sequence provides cooperativity between proteins, generating a multivalency effect that enhances the heparin-binding ability. Protein copolymers complex heparin into well-defined nanoparticles with diameters below 200 nm. We also develop a competitive fluorescent switch-on assay for heparin detection, with a detection limit of 0.01 IU mL^-1 in plasma that is significantly below the therapeutic range (0.2-8 IU mL^-1). Moreover, moderate cytocompatibility is demonstrated by in vitro cell studies. Therefore, such engineered protein copolymers present a promising alternative for neutralizing and sensing heparin, but further optimization is required for in vivo applications.

Monitoring of Anticoagulant Activity of Dabigatran and Rivaroxaban in the Presence of Heparins

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.

Serum Albumin-Peptide Conjugates for Simultaneous Heparin Binding and Detection

Heparin is a polysaccharide-based anticoagulant agent, which is widely used in surgery and blood transfusion. However, overdosage of heparin may cause severe side effects such as bleeding and low blood platelet count. Currently, there is only one clinically licensed antidote for heparin: protamine sulfate, which is known to provoke adverse effects. In this work, we present a stable and biocompatible alternative for protamine sulfate that is based on serum albumin, which is conjugated with a variable number of heparin-binding peptides. The heparin-binding efficiency of the conjugates was evaluated with methylene blue displacement assay, dynamic light scattering, and anti-Xa assay. We found that multivalency of the peptides played a key role in the observed heparin-binding affinity and complex formation. The conjugates had low cytotoxicity and low hemolytic activity, indicating excellent biocompatibility. Furthermore, a sensitive DNA competition assay for heparin detection was developed. The detection limit of heparin was 0.1 IU/mL, which is well below its therapeutic range (0.2-0.4 IU/mL). Such biomolecule-based systems are urgently needed for next-generation biocompatible materials capable of simultaneous heparin binding and sensing.

Self-assembled multivalent (SAMul) ligand systems with enhanced stability in the presence of human serum

Self-assembled cationic micelles are an attractive platform for binding biologically-relevant polyanions such as heparin. This has potential applications in coagulation control, where a synthetic heparin rescue agent could be a useful replacement for protamine, which is in current clinical use. However, micelles can have low stability in human serum and unacceptable toxicity profiles. This paper reports the optimisation of self-assembled multivalent (SAMul) arrays of amphiphilic ligands to bind heparin in competitive conditions. Specifically, modification of the hydrophobic unit kinetically stabilises the self-assembled nanostructures, preventing loss of binding ability in the presence of human serum - cholesterol hydrophobic units significantly outperform systems with a simple aliphatic chain. It is demonstrated that serum albumin disrupts the binding thermodynamics of the latter system. Molecular simulation shows aliphatic lipids can more easily be removed from the self-assembled nanostructures than the cholesterol analogues. This agrees with the experimental observation that the cholesterol-based systems undergo slower disassembly and subsequent degradation via ester hydrolysis. Furthermore, by stabilising the SAMul nanostructures, toxicity towards human cells is decreased and biocompatibility enhanced, with markedly improved survival of human hepatoblastoma cells in an MTT assay.

From fundamental supramolecular chemistry to self-assembled nanomaterials and medicines and back again – how Sam inspired SAMul

Personal inspiration led to the development of a programme of research targeting the use of self-assembled systems in nanomedicine, which in the process of approaching a range of applications has uncovered new fundamental concepts in supramolecular science.

Emergence of highly-ordered hierarchical nanoscale aggregates on electrostatic binding of self-assembled multivalent (SAMul) cationic micelles with polyanionic heparin

Self assembled cationic micelles form well-defined structurally ordered hierarchical nanoscale aggregates on interaction with polyanionic heparin in solution.

A Nanoscale Tool for Photoacoustic-Based Measurements of Clotting Time and Therapeutic Drug Monitoring of Heparin

Heparin anticoagulation therapy is an indispensable feature of clinical care yet has a narrow therapeutic window and is the second most common intensive care unit (ICU) medication error. The active partial thromboplastin time (aPTT) monitors heparin but suffers from long turnaround times, a variable reference range, limited utility with low molecular weight heparin, and poor correlation to dose. Here, we describe a photoacoustic imaging technique to monitor heparin concentration using methylene blue as a simple and Federal Drug Administration-approved contrast agent. We found a strong correlation between heparin concentration and photoacoustic signal measured in phosphate buffered saline (PBS) and blood. Clinically relevant heparin concentrations were detected in blood in 32 s with a detection limit of 0.28 U/mL. We validated this imaging approach by correlation to the aPTT (Pearson's r = 0.86; p < 0.05) as well as with protamine sulfate treatment. This technique also has good utility with low molecular weight heparin (enoxaparin) including a blood detection limit of 72 μg/mL. We then used these findings to create a nanoparticle-based hybrid material that can immobilize methylene blue for potential applications as a wearable/implantable heparin sensor to maintain drug levels in the therapeutic window. To the best of our knowledge, this is the first use of photoacoustics to image anticoagulation therapy with significant potential implications to the cardiovascular and surgical community.

Nonclinical evaluation of novel cationically modified polysaccharide antidotes for unfractionated heparin

Protamine, the only registered antidote of unfractionated heparin (UFH), may produce a number of adverse effects, such as anaphylactic shock or serious hypotension. We aimed to develop an alternative UFH antidote as efficient as protamine, but safer and easier to produce. As a starting material, we have chosen generally non-toxic, biocompatible, widely available, inexpensive, and easy to functionalize polysaccharides. Our approach was to synthesize, purify and characterize cationic derivatives of dextran, hydroxypropylcellulose, pullulan and γ-cyclodextrin, then to screen them for potential heparin-reversal activity using an in vitro assay and finally examine efficacy and safety of the most active polymers in Wistar rat and BALB/c mouse models of experimentally induced arterial and venous thrombosis. Efficacy studies included the measurement of thrombus formation, activated partial thromboplastin time, bleeding time, and anti-factor Xa activity; safety studies included the measurement of hemodynamic, hematologic and immunologic parameters. Linear, high molecular weight dextran substituted with glycidyltrimethylammonium chloride groups at a ratio of 0.65 per glucose unit (Dex40-GTMAC3) is the most potent and the safest UFH inhibitor showing activity comparable to that of protamine while possessing lower immunogenicity. Cationic polysaccharides of various structures neutralize UFH. Dex40-GTMAC3 is a promising and potentially better UFH antidote than protamine.

Inactivation of heparin by cationically modified chitosan

This study was performed to evaluate the ability of N-(2-hydroxypropyl)-3-tri methylammonium chitosan chloride (HTCC), the cationically modified chitosan, to form biologically inactive complexes with unfractionated heparin and thereby blocking its anticoagulant activity. Experiments were carried out in rats in vivo and in vitro using the activated partial thromboplastin time (APTT) and prothrombin time (PT) tests for evaluation of heparin anticoagulant activity. For the first time we have found that HTCC effectively neutralizes anticoagulant action of heparin in rat blood in vitro as well as in rats in vivo. The effect of HTCC on suppression of heparin activity is dose-dependent and its efficacy can be comparable to that of protamine-the only agent used in clinic for heparin neutralization. HTCC administered i.v. alone had no direct effect on any of the coagulation tests used. The potential adverse effects of HTCC were further explored using rat experimental model of acute toxicity. When administered i.p. at high doses (250 and 500 mg/kg body weight), HTCC induced some significant dose-dependent structural abnormalities in the liver. However, when HTCC was administered at low doses, comparable to those used for neutralization of anticoagulant effect of heparin, no histopathological abnormalities in liver were observed.

A simple new competition assay for heparin binding in serum applied to multivalent PAMAM dendrimers

We report a competition assay using our recently reported dye Mallard Blue, which allows us to identify synthetic heparin binders in competitive media, including human serum - using this we gain insight into the ability of PAMAM dendrimers to bind heparin, with the interesting result that low-generation G2-PAMAM is the preferred heparin binder.

Use of an Automated Coagulation Analyzer to Perform Heparin Neutralization With Polybrene in Blood Samples for Routine Coagulation Testing: Practical, Rapid, and Inexpensive

Context.—Heparin contamination in blood samples may cause false prolongation of activated partial thromboplastin time (aPTT) and prothrombin time results. Polybrene can neutralize heparin, but it affects coagulation by itself.

Objectives.——To determine the optimal concentration of polybrene to neutralize heparin, to determine the suitable sequence of reagents for the neutralization method performed on the analyzer at the same time as prothrombin time and aPTT testing, and to detect the heparin contamination in blood samples for coagulation tests in our hospital using this method.

Design.—Various concentrations of heparin were added to 10 normal and 76 abnormal plasma samples to study the efficacy of polybrene. Two programs of reagent sequencing for aPTT with polybrene performed on the analyzer were tested. Samples suspected of heparin contamination according to our criteria were selected for neutralization during a 3-month period.

Results.——The optimal final concentration of polybrene was 25 μg/mL. Polybrene should be added after the aPTT reagent to minimize its interference effect. Even though results of prothrombin time and aPTT after neutralization did not equal those before the spike of heparin, the differences might not be clinically significant. Eighty-one of 4921 samples (1.6%) were selected for aPTT with the neutralization method, and the detection rate of heparin contamination was 84% (68 of 81), giving an overall incidence of 1.4% (68 of 4921).

Conclusions.—This method is inexpensive and can be performed rapidly with prothrombin time and aPTT on the automated analyzer, which makes it easy to practice with no need for extra plasma volumes.

Mallard blue: a high-affinity selective heparin sensor that operates in highly competitive media

We report the simple synthesis and full investigation of a novel heparin binding dye, mallard blue, an arginine-functionalized thionine. This dye binds heparin in highly competitive media, including water with high levels of competitive electrolyte, buffered aqueous solution and human serum. The dye reports on heparin levels by a significant change in its UV-vis spectroscopic profile. Molecular dynamics modeling provides detailed insight into the binding mode. Heparin binding is shown to be selective over other glycosaminoglycans, such as hyaluronic acid and chondroitin sulfate. Importantly, we demonstrate that, in the most competitive conditions, mallard blue outperforms standard dyes used for heparin sensing such as azure A.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.

Neutralization of heparin activity

Heparin is the mainstay in the treatment and prevention of thrombosis in such diverse clinical settings as venous thromboembolism, acute coronary syndrome, cardiopulmonary bypass, and hemodialysis. However, the major complication of heparin - like that of all anticoagulants - is bleeding. Heparin may need to be reversed in the following settings: clinically significant bleeding; prior to an invasive procedure; at the conclusion of a procedure involving extracorporeal circulation (e.g., cardiopulmonary bypass, dialysis). This chapter discusses protamine sulfate, as well as several other agents that are able to neutralize heparin, including their pharmacological properties, indications, dosing, and efficacy.

Does an allergy to fish pre-empt an adverse protamine reaction? A case report and a literature review

The operating theatre exposes patients to myriad potential agents which could result in a life-threatening anaphylactic reaction. Anaesthetic drugs, blood products, and latex are only some of the possible allergens. Reactions are deemed to be anaphylactic when immediate sensitivity is combined with cardiovascular collapse. A patient who had a known allergy to shellfish presented for first time cardiopulmonary bypass. The perfusion team were concerned that there was a realistic possibility that an adverse reaction to protamine could occur. Anaphylactic reactions to protamine in patients allergic to fish have been reported. The anaesthetic team were informed and the necessary precautions taken. We report on the outcome for our patient and also discuss other risk factors and the types of reactions that can result when an adverse reaction to protamine occurs.

Heparin and Low-Molecular-Weight Heparin

This article about unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a pentasaccharide, catalyzing the inactivation of thrombin and other clotting factors. UFH also binds endothelial cells, platelet factor 4, and platelets, leading to rather unpredictable pharmacokinetic and pharmacodynamic properties. Variability in activated partial thromboplastin time (aPTT) reagents necessitates site-specific validation of the aPTT therapeutic range in order to properly monitor UFH therapy. Lack of validation has been an oversight in many clinical trials comparing UFH to LMWH. In patients with apparent heparin resistance, anti-factor Xa monitoring may be superior to measurement of aPTT. LMWHs lack the nonspecific binding affinities of UFH, and, as a result, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties. LMWHs have replaced UFH for most clinical indications for the following reasons: (1) these properties allow LMWHs to be administered subcutaneously, once daily without laboratory monitoring; and (2) the evidence from clinical trials that LMWH is as least as effective as and is safer than UFH. Several clinical issues regarding the use of LMWHs remain unanswered. These relate to the need for monitoring with an anti-factor Xa assay in patients with severe obesity or renal insufficiency. The therapeutic range for anti-factor Xa activity depends on the dosing interval. Anti-factor Xa monitoring is prudent when administering weight-based doses of LMWH to patients who weigh > 150 kg. It has been determined that UFH infusion is preferable to LMWH injection in patients with creatinine clearance of < 25 mL/min, until further data on therapeutic dosing of LMWHs in renal failure have been published. However, when administered in low doses prophylactically, LMWH is safe for therapy in patients with renal failure. Protamine may help to reverse bleeding related to LWMH, although anti-factor Xa activity is not fully normalized by protamine. The synthetic pentasaccharide fondaparinux is a promising new antithrombotic agent for the prevention and treatment of venous thromboembolism.

Intracellular redox status affects transplasma membrane electron transport in pulmonary arterial endothelial cells

Pulmonary arterial endothelial cells possess transplasma membrane electron transport (TPMET) systems that transfer intracellular reducing equivalents to extracellular electron acceptors. As one aspect of determining cellular mechanisms involved in one such TPMET system in pulmonary arterial endothelial cells in culture, glycolysis was inhibited by treatment with iodoacetate (IOA) or by replacing the glucose in the cell medium with 2-deoxy-D-glucose (2-DG). TPMET activity was measured as the rate of reduction of the extracellular electron acceptor polymer toluidine blue O polyacrylamide. Intracellular concentrations of NADH, NAD(+), NADPH, and NADP(+) were determined by high-performance liquid chromatography of KOH cell extracts. IOA decreased TPMET activity to 47% of control activity concomitant with a decrease in the NADH/NAD(+) ratio to 34% of the control level, without a significant change in the NADPH/NADP(+) ratio. 2-DG decreased TPMET activity to 53% of control and decreased both NADH/NAD(+) and NADPH/NADP(+) ratios to 51% and 55%, respectively, of control levels. When lactate was included in the medium along with the inhibitors, the effects of IOA and 2-DG on both TPMET activity and the NADPH/NADP(+) ratios were prevented. The results suggest that cellular redox status is a determinant of pulmonary arterial endothelial cell TPMET activity, with TPMET activity more highly correlated with the poise of the NADH/NAD(+) redox pair.

Noncardiogenic pulmonary edema associated with protamine administration during coronary artery bypass graft surgery

Protamine sulfate is the only agent approved to reverse heparin-induced anticoagulation. As with any other drug, protamine has the potential to cause adverse effects that range from mild hypotension to potentially fatal events, such as noncardiogenic pulmonary edema (NCPE) and catastrophic pulmonary vasoconstriction. We report a case of NCPE after the administration of protamine to a patient undergoing coronary artery bypass graft surgery and discuss the diagnosis and management of this severe adverse event.

Noncardiogenic pulmonary edema immediately following rapid protamine administration

OBJECTIVE

To report the case of a rare, potentially preventable, immediate noncardiogenic pulmonary edema reaction to the rapid administration of protamine during coronary artery bypass graft (CABG) surgery.

CASE SUMMARY

A 74-year-old white man was administered a 250-mg bolus of protamine sulfate toward the end of CABG surgery to reverse the heparin anticoagulation. Immediately following the administration of protamine, oxygen saturation declined, pink frothy sputum was suctioned from the trachea, and 1500 mL of serous fluid was removed from the airway. The patient was stabilized, but the surgeons were unable to close his chest because of the profound edema. Chest closure occurred on hospital day 6, with discharge from the intensive care unit on hospital day 28.

DISCUSSION

Noncardiogenic pulmonary edema is a rare adverse event that occurs in 0.2% of cardiopulmonary bypass patients, with mortality rates approaching 30%. Complement activation or direct pharmacologic release of histamine by high concentrations of protamine is the suspected cause. High concentrations of protamine in the lungs may directly release histamine, with significant vasodilating effects.

CONCLUSIONS

Immediate reversal of heparin anticoagulation with protamine is necessary to control bleeding; however, rapid protamine injection can be associated with life-threatening pulmonary edema. Slower, cautious administration and accurate calculation of protamine doses may prevent such an event.

Recent experiences with hexadimethrine for neutralizing heparin after cardiopulmonary bypass

Hexadimethrine bromide was used for the neutralization of heparin during cardiac surgery in the late 1950s. For some years, this institution has used it for patients who may be allergic to protamine. In view of the recent renewal of interest in hexadimethrine, we present four cases outlining its use during cardiac procedures in such patients. Other drugs for reversing the action of heparin such as heparinase or platelet factor IV are not yet widely available.

Protamine reversal of heparin affects platelet aggregation and activated clotting time after cardiopulmonary bypass

Bleeding after cardiopulmonary bypass (CPB) is related to multiple factors. Excess protamine weakens clot structure and decreases platelet function; therefore, an increased activated clotting time (ACT) after protamine reversal of heparin may be misinterpreted as residual heparin anticoagulation. We evaluated the effects of protamine, recombinant platelet factor 4 (rPF4), and hexadimethrine on ACT in blood obtained after CPB. In addition, we examined the effect of protamine on in vitro platelet aggregation. Incremental doses of protamine, rPF4, and hexadimethrine were added to heparinized blood from CPB, and ACTs were performed. Incremental concentrations of protamine were added to heparinized platelet-rich plasma, and aggregometry was induced by adenosine diphosphate (ADP) and collagen. The mean heparin concentration at the end of CPB was 3.3 U/mL. Protamine to heparin ratios >1.3:1 produced a significant prolongation of the ACT that was not seen with rPF4 and was observed only with 5:1 hexadimethrine to heparin ratios. ADP-induced platelet aggregation was reduced with protamine administration > or =1.3:1. Excessive protamine reversal of heparin prolongs ACT and alters ADP-induced platelet aggregation in a dose-dependent manner in vitro. Additional protamine administered to treat a prolonged ACT may further increase clotting time, reduce platelet aggregation, and potentially contribute to excess bleeding after CPB.

IMPLICATIONS

We found that excess protamine prolonged the activated clotting time and altered platelet function after cardiopulmonary bypass, whereas heparin antagonists, such as recombinant platelet factor 4 and hexadimethrine, exhibited a wider therapeutic range without adversely affecting the activated clotting time. Approaches to avoid excess protamine or use of alternative heparin antagonists after cardiopulmonary bypass may be beneficial.