Indicators of fibrinolysis during cardiopulmonary bypass after exogenous antithrombin-III administration for acquired antithrombin III deficiency

Native and activated antithrombin inhibits TMPRSS2 activity and SARS-CoV-2 infection

Host cell proteases such as TMPRSS2 are critical determinants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) tropism and pathogenesis. Here, we show that antithrombin (AT), an endogenous serine protease inhibitor regulating coagulation, is a broad-spectrum inhibitor of coronavirus infection. Molecular docking and enzyme activity assays demonstrate that AT binds and inhibits TMPRSS2, a serine protease that primes the Spike proteins of coronaviruses for subsequent fusion. Consequently, AT blocks entry driven by the Spikes of SARS-CoV, MERS-CoV, hCoV-229E, SARS-CoV-2 and its variants of concern including Omicron, and suppresses lung cell infection with genuine SARS-CoV-2. Thus, AT is an endogenous inhibitor of SARS-CoV-2 that may be involved in COVID-19 pathogenesis. We further demonstrate that activation of AT by anticoagulants, such as heparin or fondaparinux, increases the anti-TMPRSS2 and anti-SARS-CoV-2 activity of AT, suggesting that repurposing of native and activated AT for COVID-19 treatment should be explored.

Antithrombin: anti-inflammatory properties and clinical applications

Many humoral and cellular components participate in bidirectional communication between the coagulation and inflammation pathways. Natural anticoagulant proteins, including antithrombin (AT), tissue factor pathway inhibitor, and protein C, suppress proinflammatory mediators. Conversely, inflammation blunts anticoagulant activity and, when uncontrolled, promotes systemic inflammation-induced coagulation, such as those that occur in disseminated intravascular coagulation and severe sepsis. This review discusses the mechanisms of action and clinical use of AT concentrate in critically ill patients and in the settings of perioperative anticoagulation management for surgery and obstetrics. AT is a serine protease inhibitor with broad anticoagulant activity and potent anti-inflammatory properties. In clinical conditions associated with hereditary or acquired AT deficiency, administration of AT concentrate has been shown to restore proper haemostasis and attenuate inflammation. Of note, AT modulates inflammatory responses not only by inhibiting thrombin and other clotting factors that induce cytokine activity and leukocyte-endothelial cell interaction, but also by coagulation-independent effects, including direct interaction with cellular mediators of inflammation. An increasing body of evidence suggests that AT concentrate may be a potential therapeutic agent in certain clinical settings associated with inflammation. In addition to the well-known anticoagulation properties of AT for the treatment of hereditary AT deficiency, AT also possesses noteworthy anti-inflammatory properties that could be valuable in treating acquired AT deficiency, which often result in thrombotic states associated with an inflammatory component.

Bivalirudin as an adjunctive anticoagulant to heparin in the treatment of heparin resistance during cardiopulmonary bypass-assisted cardiac surgery

Heparin resistance (unresponsiveness to heparin) is characterized by the inability to reach acceptable activated clotting time values following a calculated dose of heparin. Up to 20% of the patients undergoing cardiothoracic surgery with cardiopulmonary bypass using unfractionated heparin (UFH) for anticoagulation experience heparin resistance. Although UFH has been the "gold standard" for anticoagulation, it is not without its limitations. It is contraindicated in patients with confirmed heparin-induced thrombocytopenia (HIT) and heparin or protamine allergy. The safety and efficacy of the use of the direct thrombin inhibitor bivalirudin for anticoagulation during cardiac surgery has been reported. However, there have been no reports on the treatment of heparin resistance with bivalirudin during CPB. In this review, we report the favorable outcome of our single-center experience with the alternative use of bivalirudin in the management of anticoagulation of heparin unresponsive patients undergoing coronary artery bypass graft surgery.

Review article: heparin sensitivity and resistance: management during cardiopulmonary bypass

Heparin resistance during cardiac surgery is defined as the inability of an adequate heparin dose to increase the activated clotting time (ACT) to the desired level. Failure to attain the target ACT raises concerns that the patient is not fully anticoagulated and initiating cardiopulmonary bypass may result in excessive activation of the hemostatic system. Although antithrombin deficiency has generally been thought to be the primary mechanism of heparin resistance, the reasons for heparin resistance are both complex and multifactorial. Furthermore, the ACT is not specific to heparin's anticoagulant effect and is affected by multiple variables that are commonly present during cardiac surgery. Due to these many variables, it remains unclear whether decreased heparin responsiveness as measured by the ACT represents inadequate anticoagulation. Nevertheless, many clinicians choose a target ACT to assess anticoagulation, and interventions aimed at achieving the target ACT are routinely performed in the setting of heparin resistance. Treatments for heparin resistance/alterations in heparin responsiveness include additional heparin or antithrombin supplementation. In this review, we discuss the variability of heparin potency, heparin responsiveness as measured by the ACT, and the current management of heparin resistance.

2011 update to the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists blood conservation clinical practice guidelines

BACKGROUND

Practice guidelines reflect published literature. Because of the ever changing literature base, it is necessary to update and revise guideline recommendations from time to time. The Society of Thoracic Surgeons recommends review and possible update of previously published guidelines at least every three years. This summary is an update of the blood conservation guideline published in 2007.

METHODS

The search methods used in the current version differ compared to the previously published guideline. Literature searches were conducted using standardized MeSH terms from the National Library of Medicine PUBMED database list of search terms. The following terms comprised the standard baseline search terms for all topics and were connected with the logical 'OR' connector--Extracorporeal circulation (MeSH number E04.292), cardiovascular surgical procedures (MeSH number E04.100), and vascular diseases (MeSH number C14.907). Use of these broad search terms allowed specific topics to be added to the search with the logical 'AND' connector.

RESULTS

In this 2011 guideline update, areas of major revision include: 1) management of dual anti-platelet therapy before operation, 2) use of drugs that augment red blood cell volume or limit blood loss, 3) use of blood derivatives including fresh frozen plasma, Factor XIII, leukoreduced red blood cells, platelet plasmapheresis, recombinant Factor VII, antithrombin III, and Factor IX concentrates, 4) changes in management of blood salvage, 5) use of minimally invasive procedures to limit perioperative bleeding and blood transfusion, 6) recommendations for blood conservation related to extracorporeal membrane oxygenation and cardiopulmonary perfusion, 7) use of topical hemostatic agents, and 8) new insights into the value of team interventions in blood management.

CONCLUSIONS

Much has changed since the previously published 2007 STS blood management guidelines and this document contains new and revised recommendations.

Antithrombin reduces monocyte and neutrophil CD11b up regulation in addition to blocking platelet activation during extracorporeal circulation

BACKGROUND

Patients undergoing cardiac surgery requiring cardiopulmonary bypass develop a systemic inflammatory reaction. Antithrombin III (AT) has anticoagulant effects but also shows evidence of anti-inflammatory activity. The aim of this study was to examine whether exogenous AT could reduce white blood cell activation (CD11b up regulation or elastase release), in addition to inhibiting platelet (PLT) activation and fibrin generation, during simulated cardiopulmonary bypass (sCPB), undertaken in the absence of endothelium.

STUDY DESIGN AND METHODS

sCPB was carried out with minimally heparinized (2 U/mL) human blood for 90 minutes in controls and with supplementation by low-dose (1 U/mL) and high-dose (5 U/mL) AT.

RESULTS

High-dose AT blunted thrombin generation during sCPB (prothrombin fragment 1.2); both doses significantly inhibited thrombin activity (fibrinopeptide A). Complement activation (C3a and C5b-9) was unaffected by AT. High-dose AT inhibited PLT activation (P-selectin expression and P-selectin-dependent monocyte-PLT conjugate formation). AT supplementation at the higher dose significantly abrogated monocyte and neutrophil CD11b up regulation and neutrophil elastase release.

CONCLUSION

In addition to anticoagulant and anti-PLT effects, pharmacologic AT doses significantly blunted monocyte and neutrophil CD11b up regulation and neutrophil elastase release during sCPB, independent of endothelial effects. These data provide evidence for the direct anti-inflammatory activity of AT that has clinical relevance for CPB complications.

Familial antithrombin-III deficiency during cardiopulmonary bypass: a case report

The serine protease inhibitor antithrombin-III (AT-III) is the principal in vivo inhibitor of blood coagulation, inactivating mainly thrombin, but also other serine proteases. Binding of AT-III to heparin dramatically increases its inhibitory effect. AT-III deficiency during cardiopulmonary bypass (CPB) can lead to insufficient anticoagulation which cannot be treated by higher doses of heparin. A 60-year-old male with familial AT-III deficiency was admitted to our hospital for coronary artery bypass surgery and aortic valve replacement. Four days before the operation, acenocoumarol was stopped and anti-Xa nadroparincalcium (Fraxiparine) was started. AT-III activity at that time was 56%. Two hours before the operation, a single dose of 4500 IU AT-III concentrate was administered. Heparinization was performed with 400 IU/kg of porcine mucosal heparin, increasing the activated coagulation time (ACT) from a baseline of 115 to 549 s. AT-III activity at that time was above 100% and the plasma D-dimer concentration was 230 ng/l. ACTs during CPB remained above 999 s, whereas the AT-III activity dropped to 54% and the D-dimer increased up to 500 ng/l at the end of CPB. CPB was terminated uneventfully. Heparin was reversed with 3 mg/kg protamine chloride, decreasing the ACT to 155 s. In the intensive care unit (ICU), the patientreceived prophylactic Fraxiparine and 1500 IU AT-III, increasing the AT-III activity to 84%. Postoperatively, there was continued blood loss, which necessitated the administration of whole blood and eventually re-exploration. The case presented illustrates an uneventful treatment of a patient with a hereditary AT-III deficiency undergoing CPB. In spite of an uneventful treatment with AT-III pre-CPB, administration of prophylactic AT-III concentrate after surgery should be considered with caution, as this might increase the postoperative morbidity.

A randomized trial of antithrombin concentrate for treatment of heparin resistance

BACKGROUND

Heparin resistance is an important clinical problem traditionally treated with additional heparin or fresh frozen plasma. We undertook a randomized clinical trial to determine if treatment with antithrombin (AT) concentrate is effective for treating this condition.

METHODS

Patients requiring cardiopulmonary bypass who were considered to be heparin resistant (activated clotting time < 480 seconds after > 450 IU/kg heparin) were randomized to receive either 1000 U AT or additional heparin.

RESULTS

AT concentrate was effective in 42 of 44 patients (96%) for immediately obtaining a therapeutic activated clotting time. This compared favorably to 28 of 41 patients (68%) treated with additional heparin (p = 0.001). All patients who failed heparin therapy were successfully treated with AT. The patients receiving AT required less time to obtain an adequate ACT but there was no difference in clinical outcomes among the groups. Study patients had deficient AT activity at baseline (56%+/-25%), which improved in those given AT concentrate (75%+/-31% versus 50%+/-23%, p < 0.0005).

CONCLUSIONS

Heparin resistance is frequently associated with AT deficiency. Treating this deficiency with AT concentrate is more effective and faster for obtaining adequate anticoagulation than using additional heparin.