Neutralisation of Heparan Sulphate and Low Molecular Weight Heparin by Protamine

The Endothelial Glycocalyx in Pig-to-Baboon Cardiac Xenotransplantation-First Insights

Cardiac xenotransplantation has seen remarkable success in recent years and is emerging as the most promising alternative to human cardiac allotransplantation. Despite these achievements, acute vascular rejection still presents a challenge for long-term xenograft acceptance and new insights into innate and adaptive immune responses as well as detailed characterizations of signaling pathways are necessary. In allotransplantation, endothelial cells and their sugar-rich surface-the endothelial glycocalyx-are known to influence organ rejection. In xenotransplantation, however, only in vitro data exist on the role of the endothelial glycocalyx so far. Thus, in the current study, we analyzed the changes of the endothelial glycocalyx components hyaluronan, heparan sulfate and syndecan-1 after pig-to-baboon cardiac xenotransplantations in the perioperative (n = 4) and postoperative (n = 5) periods. These analyses provide first insights into changes of the endothelial glycocalyx after pig-to-baboon cardiac xenotransplantation and show that damage to the endothelial glycocalyx seems to be comparable or even less pronounced than in similar human settings when current strategies of cardiac xenotransplantation are applied. At the same time, data from the experiments where current strategies, like non-ischemic preservation, growth inhibition or porcine cytomegalovirus (a porcine roseolovirus (PCMV/PRV)) elimination could not be applied indicate that damage of the endothelial glycocalyx also plays an important role in cardiac xenotransplantation.

Endothelial glycocalyx during early reperfusion in patients undergoing cardiac surgery

Background

Experimental cardiac ischemia-reperfusion injury causes degradation of the glycocalyx and coronary washout of its components syndecan-1 and heparan sulfate. Systemic elevation of syndecan-1 and heparan sulfate is well described in cardiac surgery. Still, the events during immediate reperfusion after aortic declamping are unknown both in the systemic and in the coronary circulation.

Methods

In thirty patients undergoing aortic valve replacement, arterial concentrations of syndecan-1 and heparan sulfate were measured immediately before and at one, five and ten minutes after aortic declamping (reperfusion). Parallel blood samples were drawn from the coronary sinus to calculate trans-coronary gradients (coronary sinus–artery).

Results

Compared with immediately before aortic declamping, arterial syndecan-1 increased by 18% [253.8 (151.6–372.0) ng/ml vs. 299.1 (172.0–713.7) ng/ml, p < 0.001] but arterial heparan sulfate decreased by 14% [148.1 (135.7–161.7) ng/ml vs. 128.0 (119.0–138.2) ng/ml, p < 0.001] at one minute after aortic declamping. There was no coronary washout of syndecan-1 or heparan sulfate during reperfusion. On the contrary, trans-coronary sequestration of syndecan-1 occurred at five [-12.96 ng/ml (-36.38–5.15), p = 0.007] and at ten minutes [-12.37 ng/ml (-31.80–6.62), p = 0.049] after reperfusion.

Conclusions

Aortic declamping resulted in extracardiac syndecan-1 release and extracardiac heparan sulfate sequestration. Syndecan-1 was sequestered in the coronary circulation during early reperfusion. Glycocalyx has been shown to degrade during cardiac surgery. Besides degradation, glycocalyx has propensity for regeneration. The present results of syndecan-1 and heparan sulfate sequestration may reflect endogenous restoration of the damaged glycocalyx in open heart surgery.

Elucidating the Interactions Between Heparin/Heparan Sulfate and SARS-CoV-2-Related Proteins-An Important Strategy for Developing Novel Therapeutics for the COVID-19 Pandemic

Owing to the high mortality and the spread rate, the infectious disease caused by SARS-CoV-2 has become a major threat to public health and social economy, leading to over 70 million infections and 1. 6 million deaths to date. Since there are currently no effective therapeutic or widely available vaccines, it is of urgent need to look for new strategies for the treatment of SARS-CoV-2 infection diseases. Binding of a viral protein onto cell surface heparan sulfate (HS) is generally the first step in a cascade of interaction that is required for viral entry and the initiation of infection. Meanwhile, interactions of selectins and cytokines (e.g., IL-6 and TNF-α) with HS expressed on endothelial cells are crucial in controlling the recruitment of immune cells during inflammation. Thus, structurally defined heparin/HS and their mimetics might serve as potential drugs by competing with cell surface HS for the prevention of viral adhesion and modulation of inflammatory reaction. In this review, we will elaborate coronavirus invasion mechanisms and summarize the latest advances in HS-protein interactions, especially proteins relevant to the process of coronavirus infection and subsequent inflammation. Experimental and computational techniques involved will be emphasized.

High Preoperative Serum Syndecan-1, a Marker of Endothelial Glycocalyx Degradation, and Severe Acute Kidney Injury after Valvular Heart Surgery

Degradation of endothelial glycocalyx (EG) is associated with inflammation and endothelial dysfunction, which may contribute to the development of acute kidney injury (AKI). We investigated the association between a marker of EG degradation and AKI after valvular heart surgery. Serum syndecan-1 concentrations were measured at induction of anesthesia and discontinuation of cardiopulmonary bypass in 250 patients. Severe AKI was defined as Kidney Disease: Improving Global Outcomes Criteria Stage 2 or 3. Severe AKI occurred in 13 patients (5%). Receiver operating characteristic analysis of preoperative syndecan-1 to predict severe AKI showed area under curve of 0.714 (95% confidence interval (CI), 0.575–0.853; p = 0.009). The optimal cut-off value was 90 ng/mL, with a sensitivity of 61.5% and specificity of 78.5%. In multivariable analysis, both preoperative syndecan-1 ≥ 90 ng/mL and Cleveland Clinic Foundation score independently predicted severe AKI. Severe tricuspid regurgitation was more frequent (42.4% vs. 17.8%, p < 0.001), and baseline right ventricular systolic pressure (41 (33–51) mmHg vs. 33 (27–43) mmHg, p = 0.001) and TNF-α (1.85 (1.37–2.43) pg/mL vs. 1.45 (1.14–1.92) pg/mL, p <0.001) were higher in patients with high preoperative syndecan-1. Patients with high preoperative syndecan-1 had longer hospital stay (16 (12–24) days vs. 13 (11–17) days, p = 0.001). In conclusion, a high preoperative syndecan-1 concentration greater than 90 ng/mL was able to predict severe AKI after valvular heart surgery and was associated with prolonged hospitalization.

The neutralization of heparan sulfate by heparin-binding copolymer as a potential therapeutic target

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.

The neutralization of heparan sulfate (HS) by a heparin-binding copolymer (HBC) could be a promising treating option for bacterial or viral infections or bleeding related to overproduction of HS in cancer or other diseases.

Binding, internalization, and membrane incorporation of human immunodeficiency virus-1 at the blood-brain barrier is differentially regulated

Human immunodeficiency virus (HIV)-1 within the CNS induces neuro-acquired immunodeficiency syndrome and acts as a reservoir for reinfection of peripheral tissues. HIV-1 crosses the blood-brain barrier (BBB) within infected immune cells and as cell-free virus by a CD4-independent mechanism. Which proteins control free virus transport across the BBB are unknown, but work with wheatgerm agglutinin (WGA) and heparin suggests that heparan sulfate proteoglycans, sialic acid, and N-acetyl-beta-D-glucosaminyl acid bind HIV-1. Here, we found that an HIV-1 T-tropic virus was taken up by mouse brain endothelial cells in vitro and crossed the BBB in vivo and could be effluxed as intact virus. Uptake was stimulated by WGA and protamine sulfate (PS) and inhibited by heparin. BBB uptake of virus involved four distinguishable binding sites: i) reversible cell surface binding involving gp120 and sensitive to PS/heparin but insensitive to WGA; internalization with a ii) WGA-sensitive site binding gp120 and iii) a PS/heparin-sensitive site not involving gp120; iv) membrane incorporation not affected by WGA, heparin, or PS. In conclusion, binding, internalization, and membrane incorporation are separately regulated steps likely determining whether HIV-1 is incorporated into brain endothelial cells, transported across them, or returned to the circulation.

Dextran sulfate included in factor Xa assay reagent overestimates heparin activity in patients after heparin reversal by protamine

A lack of correlation between activated partial thromboplastin time (aPTT), thrombin time (TT) and anti-factor Xa (AXa) activity was observed in patients after cardiac surgery with cardiopulmonary bypass (CBP). Indeed, AXa activity measured by the chromogenic assay, Coamatic Heparin, was higher than expected with regard to results obtained in coagulation assays. To account for this discrepancy, another AXa chromogenic assay was tested. First, AXa activity was measured with two chromogenic assays (Coamatic Heparin and Rotachrom Heparin) in plasma samples of 25 patients undergoing cardiac surgery at two time points after heparin reversal by protamine. AXa activity was significantly higher when measured with Coamatic Heparin than with Rotachrom Heparin in samples collected just after protamine infusion (p<0.01). Next, since Coamatic( Heparin contains dextran sulfate (DXS) to reduce the influence of heparin antagonists such as platelet factor 4 (PF4), whereas Rotachrom Heparin does not, we hypothesized that the dextran sulfate contained in the reagent might explain this discrepancy. We therefore performed in vitro studies consisting in neutralizing unfractionated heparin (UFH) with protamine and measuring AXa activity with the two chromogenic assays. An AXa activity was still measurable with Coamatic Heparin after neutralization, thus strongly suggesting that dextran sulfate dissociates protamine/heparin complexes. We conclude that Coamatic Heparin assays should be avoided when measuring AXa activity in plasma samples immediately after protamine infusion, as inaccurate results may lead to inadequate management of heparin reversal.

Mechanisms responsible for the failure of protamine to inactivate low-molecular-weight heparin

Protamine is unable to completely reverse the anticoagulant effect of the low-molecular-weight heparins (LMWH), a fact of clinical importance given the rapid increase in use of LMWH in clinical practice. This investigation sought to determine the mechanism by which LMWH were able to resist protamine-mediated inactivation. Affinity fractionation of LMWH by passage through a protamine column, with subsequent determination of molecular mass and sulphate charge density, demonstrated that the protamine-resistant fraction in LMWH is an ultra-low-molecular-weight fraction with low sulphate charge density. This group of molecules was not found in unfractionated heparin, even when species of similar molecular mass were compared. We then determined that different commercially available LMWH varied in their ability to be neutralized by protamine, and that this variability correlated with the total sulphate content of the LMWH. We conclude that reduced sulphate charge, not molecular mass, is the principle reason that protamine is unable to fully inactivate LMWH. Furthermore, different LMWH vary in their ability to be neutralized by protamine, suggesting that product-specific recommendations for neutralization might be developed.

Iduronic acid-containing glycosaminoglycans on target cells are required for efficient respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is an important human respiratory pathogen, particularly in infants. Glycosaminoglycans (GAGs) have been implicated in the initiation of RSV infection of cultured cells, but it is not clear what type of GAGs and GAG components are involved, whether the important GAGs are on the virus or the cell, or what the magnitude is of their contribution to infection. We constructed and rescued a recombinant green fluorescent protein (GFP)-expressing RSV (rgRSV) and used this virus to develop a sensitive system to assess and quantify infection by flow cytometry. Evaluation of a panel of mutant Chinese hamster ovary cell lines that are genetically deficient in various aspects of GAG synthesis showed that infection was reduced up to 80% depending on the type of GAG deficiency. Enzymatic removal of heparan sulfate and/or chondroitin sulfate from the surface of HEp-2 cells also reduced infection, and the removal of both reduced infection even further. Blocking experiments in which RSV was preincubated with various soluble GAGs revealed the relative blocking order of: heparin > heparan sulfate > chondroitin sulfate B. Iduronic acid is a component common to these GAGs. GAGs that do not contain iduronic acid, namely, chondroitin sulfate A and C and hyaluronic acid, did not inhibit infection. A role for iduronic acid-containing GAGs in RSV infection was confirmed by the ability of basic fibroblast growth factor to block infection, because basic fibroblast growth factor binds to GAGs containing iduronic acid. Pretreatment of cells with protamine sulfate, which binds and blocks GAGs, also reduced infection. In these examples, infection was reduced by pretreatment of the virus with soluble GAGs, pretreatment of the cells with GAG-binding molecules, pretreatment of the cells with GAG-destroying enzymes or in cells genetically deficient in GAGs. These results establish that the GAGs involved in RSV infection are present on the cell rather than on the virus particle. Thus, the presence of cell surface GAGs containing iduronic acid, like heparan sulfate and chondroitin sulfate B, is required for efficient RSV infection in cell culture.

Evidence that heparin binding autocrine factors modulate testosterone production by the adult rat Leydig cell

Androgen production by adult rat Leydig cells is stimulated by pituitary LH but can also be modulated in vitro by paracrine stimulatory and inhibitory factors, many of which belong to growth factor families. Their actions are mediated through cell surface or extracellular matrix proteoglycans and the aim of this study was to determine the role of cell surface heparan sulfate proteoglycans in the regulation of testosterone secretion by adult rat Leydig cells. The presence of sodium chlorate (25 mM) and protamine sulfate (10 micrograms/ml) inhibited testosterone production by LH stimulated cells by over 50%, but had no effect on unstimulated cells. The LH responsiveness and testosterone production returned to normal after these agents were removed from the culture media. No significant difference in LH receptor numbers at the end of the culture period was seen between sodium chlorate treated and untreated cells. Testosterone production by dibutryl-cAMP stimulated Leydig cells was also inhibited by sodium chlorate. The addition of heparin inhibited testosterone production by LH stimulated cells in a dose-dependent manner, however, in unstimulated Leydig cells heparin stimulated testosterone production to up to 50% of that seen in LH stimulated cells. These data suggest that cell surface heparan sulfate proteoglycans modulate testosterone production by adult Leydig cells in vitro, and that this may involve the autocrine actions of heparin binding growth factors on the Leydig cells.

Low-molecular-weight heparin

Low molecular weight heparins (LMWHs) are mixtures of heparin molecules in the range of 3000 to 10,000 daltons. As LMWHs of various manufacturers are all produced differently, they are not comparable to each other and are therefore considered to be individual products with different pharmacologic and clinical properties. All these agents have some common characteristics, however, such as a higher availability after subcutaneous administration and a longer biologic half-life. Numerous clinical trials have demonstrated that LMWHs are highly effective and safe for postsurgical prophylaxis of deep vein thrombosis (DVT); therefore, the LMWHs that are commercially available so far, are mainly approved in this indication. LMWHs are also effective in the prophylaxis of DVT in medical indications, as well as for the treatment of established DVT.

Neutralization of the antithrombotic effects of heparin and Fraxiparin by protamine sulfate

In general, the in vitro anti Xa activity of low molecular weight heparins is neutralized to a lesser degree than the anti Xa activity of unfractionated heparin. To determine whether these differences occur in vivo, a rabbit stasis thrombosis model and a rat laser-induced thrombosis model were utilized. In the laser model, a similar degree of neutralization of the antithrombotic activity of heparin and Fraxiparin was obtained. However, in the stasis thrombosis model, significant antithrombotic activity of Fraxiparin remained after equigravimetric protamine administration. Ex vivo APTT, thrombin time, Heptest, amidolytic anti Xa and anti IIa assays were performed. A coefficient (r = .806) was obtained for the correlation of Heptest activity to antithrombotic effect in the stasis thrombosis model, while the coefficients obtained for the other tests ranged from .152-.570. However, after neutralization by protamine, the thrombin time exhibited the highest correlation coefficient (r = .685) between ex vivo activity and residual antithrombotic effect. Since Fraxiparin retains antithrombotic activity after protamine administration, clinical benefit may be observed for this low molecular weight heparin as compared to unfractionated heparin after neutralization.

Study on neutralization of low molecular weight heparin (LHG) by protamine sulfate and its neutralization characteristics

The neutralizing effects of protamine sulfate (PS) on anticoagulant activities of low molecular weight heparin (LHG) and conventional sodium heparin (Heparin) were investigated. The in vitro anti-factor Xa and APTT-prolonging activities of Heparin were almost completely neutralized by PS, whereas the activities of LHG remained partially intact in the presence of PS. Crossed immunoelectrophoresis of antithrombin III (AT III) and affinity chromatography of LHG- and Heparin-cellulose showed that AT III was substantially less dissociated from its binding to LHG than to Heparin in the presence of PS. As in vitro, the in vivo anticoagulant activities of Heparin administered i.v. to rabbits were almost completely neutralized by PS, while the anti-factor Xa and APTT-prolonging activities of LHG remained partially intact in the presence of PS. The thrombin time-prolonging activity of LHG, however, was completely inhibited by PS. Since the bleeding effect of Heparin or LHG is considered mainly due to its anti-thrombin activity, PS may be used as an agent to neutralize LHG, as in the case of Heparin, when bleeding happens to occur during LHG treatment.

Neutralization of low molecular weight heparin by polybrene prevents thromboxane release and severe pulmonary hypertension in awake sheep

Protamine reversal of heparin anticoagulation in patients is occasionally associated with life-threatening acute pulmonary hypertension. In a sheep model, we evaluated the effect on this adverse cardiopulmonary reaction of modifying the type of heparin (low molecular weight heparin compared with unfractionated heparin) and the type of heparin antagonist (polybrene compared with protamine). Protamine reversal of low molecular weight heparin (LMWH) and polybrene reversal of unfractionated heparin induced more than a 10-fold increase of plasma thromboxane B2 levels, a threefold increase of pulmonary vascular resistance and pulmonary artery pressure, and a 25% decrease of PaO2. A similar adverse reaction followed protamine reversal of conventional unfractionated heparin. However, with polybrene (1 mg/kg) reversal of LMWH (1 mg/kg), we measured neither pulmonary hypertension (pulmonary artery pressure was 22.6 +/- 3.6 mm Hg at 1 minute after polybrene reversal of LMWH compared with 47.9 +/- 4.2 mm Hg after protamine reversal of unfractionated heparin, p less than 0.005 groups differ), hypoxemia (PaO2 was unchanged 2 minutes after polybrene compared with a decrease of 26 mm Hg 2 minutes after protamine, p less than 0.05), nor acute release of thromboxane into arterial plasma (thromboxane B2 was 0.2 +/- 0.1 at 1 minute after polybrene compared with 3.7 +/- 1.7 ng/ml at 1 minute after protamine, p less than 0.005). The hemodynamic effects and mediator release were also benign after neutralization of larger doses of LMWH (3 mg/kg) by polybrene (3 mg/kg). The increases of activated clotting time and activated partial thromboplastin time due to both types of heparin were completely reversed with polybrene. Anti-Xa activity increased to more than 3 IU/ml 4 minutes after LMWH anticoagulation (p less than 0.01) but was only partially neutralized by polybrene. Various polyanion-polycation complexes that are formed when heparin anticoagulation is reversed induce thromboxane release and acute pulmonary vasoconstriction in awake sheep. Reversal of LMWH anticoagulation with polybrene does not elicit this adverse reaction.

Heparin-like anticoagulant associated with systemic candidiasis

A 15 year old girl with aplastic anemia developed a heparin-like anticoagulant during the course of systemic candidiasis. This was initially detected in the laboratory by an elevation of the thrombin clotting time which corrected with toluidine blue but not by mixing with normal plasma. In vivo and in vitro the anticoagulant was remarkably resistant to neutralization by protamine sulfate. Nevertheless, its heparin-like nature was confirmed by its sensitivity to heparinase and its dependence on antithrombin III.

Comparison between a low molecular weight and standard heparin for anticoagulation during extracorporeal CO2 removal in the dog

Anticoagulant properties towards an artificial surface of a chemically depolymerized low molecular weight heparin (LMWH) have been compared to those of a standard heparin (SH). The experimental model consisted in a seven hours extracorporeal veno-venous bypass for CO2 removal (EC-CO2R) using a membrane lung. Four animals received 150 anti-FXa U/kg followed by 40 anti-FXa U/kg/h of LMWH or 300 IU/kg followed by 100 IU/kg/h of SH. Mean Factor Xa inhibition was 49% in LMWH group and 28.5% in SH group. Mean Factor IIa inhibition was 31% and 49% respectively. After three hours of bypass fibrin deposition occurred in the reservoir in three out of four dogs receiving LMWH while none was observed under SH. No statistically significant difference between the two groups was found for any of the coagulation parameters tested (fibrinogen, factor V, antithrombin III, plasminogen, alpha 2-antiplasmin, platelet counts). At the end of bypass 5000 U protamine abolished both anti-FXa and anti-FIIa activities in the SH group but failed to neutralize more than half of the anti-FXa activity in the LMWH group. These results suggest that high anti-FIIa activities are required to prevent fibrin formation induced by artificial surfaces and that equivalent amounts of anti-FXa activities are ineffective for this purpose. In addition the use of LMWH may raise problems when emergency neutralization procedures are required.

Interaction of a new low molecular weight heparin (OP/LMWH) with human platelets

In vitro platelet proaggregating effect of unfractionated heparin (H) and OP/LMWH were studied with human platelets. OP/LMWH produced a significant less potentiation of ADP and PAF induced aggregation and slightly counteracted the antiaggregating effect of PGI2, in comparison with H. The proaggregating effect of both heparins was neutralized by equal contemporaneous amount of protamine sulfate.