Exploring antithrombin: insights into its physiological features, clinical implications and analytical techniques.

Antithrombin is an essential protein that acts as a natural anticoagulant in the human body. It is synthesized by the liver and belongs to the serine protease inhibitors, which are commonly referred to as the SERPINS superfamily. The antithrombin molecule comprises 432 amino acids and has a molecular weight of approximately 58 200 D. It consists of three domains, including an amino-terminal domain, a carbohydrate-rich domain, and a carboxyl-terminal domain. The amino-terminal domain binds with heparin, whereas the carboxyl-terminal domain binds with serine protease. Antithrombin is a crucial natural anticoagulant that contributes approximately 60-80% of plasma anticoagulant activities in the human body. Moreover, antithrombin has anti-inflammatory effects that can be divided into coagulation-dependent and coagulation-independent effects. Furthermore, it exhibits antitumor activity and possesses a broad range of antiviral properties. Inherited type I antithrombin deficiency is a quantitative disorder that is characterized by low antithrombin activity due to low plasma levels. On the other hand, inherited type II antithrombin deficiency is a qualitative disorder that is characterized by defects in the antithrombin molecule. Acquired antithrombin deficiencies are more common than hereditary deficiencies and are associated with various clinical conditions due to reduced synthesis, increased loss, or enhanced consumption. The purpose of this review was to provide an update on the structure, functions, clinical implications, and methods of detection of antithrombin.

Antithrombin Therapy: Current State and Future Outlook.

Antithrombin (AT) is a natural anticoagulant pivotal in inactivating serine protease enzymes in the coagulation cascade, making it a potent inhibitor of blood clot formation. AT also possesses anti-inflammatory properties by influencing anticoagulation and directly interacting with endothelial cells. Hereditary AT deficiency is one of the most severe inherited thrombophilias, with up to 85% lifetime risk of venous thromboembolism. Acquired AT deficiency arises during heparin therapy or states of hypercoagulability like sepsis and premature infancy. Optimization of AT levels in individuals with AT deficiency is an important treatment consideration, particularly during high-risk situations such as surgery, trauma, pregnancy, and postpartum. Here, we integrate the existing evidence surrounding the approved uses of AT therapy, as well as potential additional patient populations where AT therapy has been considered by the medical community, including any available consensus statements and guidelines. We also describe current knowledge regarding cost-effectiveness of AT concentrate in different contexts. Future work should seek to identify specific patient populations for whom targeted AT therapy is likely to provide the strongest clinical benefit.

Management of Antithrombin Deficiency in Pregnancy.

Antithrombin (AT) deficiency is a high-risk thrombophilia and a rare condition. The risk of venous thromboembolism (VTE) is increased in AT-deficient women during pregnancy and the postpartum period and is especially high in women with a prior history of VTE. A thorough assessment of VTE risk is recommended in pregnant AT-deficient women, comprising the degree and type of AT deficiency, genetic mutations, personal and family history, and additional preexisting or pregnancy-specific risk factors. Due to a lack of adequate study data, there is limited guidance on the management of AT deficiency in pregnancy, including the need for prophylactic anticoagulation, the appropriate dose of low-molecular-weight heparin (LMWH), and the role of AT substitution. LMWH is the medication of choice for the pharmacological prophylaxis and treatment of VTE in pregnancy. Patients with a history of VTE should receive full-dose LMWH during pregnancy and the postpartum period. AT concentrates are a treatment option when anticoagulation is withheld in potentially high-risk events such as childbirth, bleeding, or surgery and in cases of acute VTE despite the use of therapeutic dose anticoagulation. Women with AT deficiency should be counseled at specialized centers for coagulation disorders or vascular medicine, and close cooperation between obstetricians and anesthesiologists is warranted before delivery and during the peripartum period.

Antithrombin Deficiency in Trauma and Surgical Critical Care.

Antithrombin deficiency (ATD) was described in 1965 by Olav Egeberg as the first known inherited form of thrombophilia. Today, it is understood that ATDs can be congenital or acquired, leading to qualitative, quantitative, or mixed abnormalities in antithrombin (AT). All ATDs ultimately hinder AT's ability to serve as an endogenous anticoagulant and antiinflammatory agent. As a result, ATD patients possess higher risk for thromboembolism and can develop recurrent venous and arterial thromboses. Because heparin relies on AT to augment its physiologic function, patients with ATD often exhibit profound heparin resistance. Although rare as a genetic disorder, acquired forms of ATD are seen with surprising frequency in critically ill patients. This review discusses ATD in the context of surgical critical care with specific relevance to trauma, thermal burns, cardiothoracic surgery, and sepsis.

Management of antithrombin deficiency: an update for clinicians.

Introduction. Antithrombin is a serpin that inhibits multiple procoagulant serine proteases and acts as an endogenous anticoagulant. Thus, congenital antithrombin deficiency constitutes a major thrombophilic state, the most severe so far. Areas covered. In the present work, we globally review the biology, genetics, diagnosis, and management of congenital antithrombin deficiency, and also discuss puzzling questions and future perspectives regarding this severe inherited thrombophilia. Expert opinion. Although this disorder exerts high clinical heterogeneity, many carriers will need careful and long-term anticoagulation and/or thromboprophylaxis, especially in high-risk situations, such as surgery and pregnancy. Notably, antithrombin concentrates constitute a considerable arsenal for both treatment and prevention of acute venous thrombosis in subjects with antithrombin deficiency. Current evidences are based almost exclusively on retrospective case series, so an integrated functional, biochemical and molecular characterization will be of clinical relevance and guide hematologists' personalized decisions.

Capped antithrombin III dosing is cost effective in the management of asparaginase-associated thrombosis.

Asparaginase therapy induces a transient antithrombin III (ATIII) deficiency, which contributes to the risk of asparaginase-induced thrombosis. At Cincinnati Children's Hospital Medical Center, management of asparaginase-induced thrombosis includes ATIII supplementation during therapeutic anticoagulation with enoxaparin. Due to the expense associated with ATIII, a capped dosing approach for ATIII was evaluated in this population. Peak ATIII levels were obtained following capped doses to evaluate response. In this pilot evaluation, 11 patients received a total of 138 capped doses for a total cost savings of $803 782. This pilot evaluation represents the first reported analysis of capped ATIII dosing in oncology patients.

Double-Blind, Randomized, Placebo-Controlled Trial Comparing the Effects of Antithrombin Versus Placebo on the Coagulation System in Infants with Low Antithrombin Undergoing Congenital Cardiac Surgery.

OBJECTIVES: To determine whether precardiopulmonary bypass (CPB) normalization of antithrombin levels in infants to 100% improves heparin sensitivity and anticoagulation during CPB and has beneficial effects into the postoperative period. DESIGN: Randomized, double-blinded, placebo-controlled prospective study. SETTING: Multicenter study performed in 2 academic hospitals. PARTICIPANTS: The study comprised 40 infants younger than 7 months with preoperative antithrombin levels <70% undergoing CPB surgery. INTERVENTIONS: Antithrombin levels were increased with exogenous antithrombin to 100% functional level intraoperatively before surgical incision. MEASUREMENTS AND MAIN RESULTS: Demographics, clinical variables, and blood samples were collected up to postoperative day 4. Higher first post-heparin activated clotting times (sec) were observed in the antithrombin group despite similar initial heparin dosing. There was an increase in heparin sensitivity in the antithrombin group. There was significantly lower 24-hour chest tube output (mL/kg) in the antithrombin group and lower overall blood product unit exposures in the antithrombin group as a whole. Functional antithrombin levels (%) were significantly higher in the treatment group versus placebo group until postoperative day 2. D-dimer was significantly lower in the antithrombin group than in the placebo group on postoperative day 4. CONCLUSION: Supplementation of antithrombin in infants with low antithrombin levels improves heparin sensitivity and anticoagulation during CPB without increased rates of bleeding or adverse events. Beneficial effects may be seen into the postoperative period, reflected by significantly less postoperative bleeding and exposure to blood products and reduced generation of D-dimers.

Strategy for Cardiovascular Surgery in Patients with Antithrombin III Deficiency.

Antithrombin III (ATIII) deficiency is a rare disorder in which thrombosis can be induced by stimuli that do not usually lead to thrombus formation, including minor injuries and surgery. Therefore, patients with ATIII deficiency undergoing cardiovascular surgery that involves heparinization require careful perioperative management. We experienced five patients with ATIII deficiency who underwent cardiovascular surgery and were managed with ATIII replacement. By administration of ATIII concentrate, preoperative ATIII activity was maintained at ≥120% and postoperative ATIII activity at ≥80%. All five patients were treated successfully without postoperative complications such as hemorrhage or thrombosis. In patients with ATIII deficiency undergoing cardiac surgery, it is important to perform ATIII replacement to achieve preoperative ATIII activity ≥120% and postoperative ATIII activity ≥80%, while the activated clotting time (ACT) is maintained at >400 seconds during cardiopulmonary bypass. In addition, long-term postoperative anticoagulant therapy is necessary in hereditary ATIII deficiency patients with a history of thrombosis.

The Successful Prevention of Thromboembolism Using Rivaroxaban in a Patient with Antithrombin Deficiency during the Perioperative Period.

Antithrombin (AT) deficiency, a rare disorder of the coagulation system, is a serious risk factor for thromboembolism. Approximately 50-90% of patients with AT deficiency develop thromboembolism during their lifetime. In addition, surgery is a major risk factor for thromboembolism in these patients. We herein report the case of a 90-year-old woman with AT deficiency who was safely and successfully managed using rivaroxaban (a direct oral factor Xa inhibitor) during the perioperative period of surgery for right femur fracture. The present case illustrates the effectiveness of rivaroxaban in preventing thromboembolisms due to surgery, even in very elderly patients with antithrombin deficiency. Further investigations are needed to determine the optimal dosage of rivaroxaban.

Issues in the Diagnosis and Management of Hereditary Antithrombin Deficiency.

OBJECTIVE: To review insights gained in the past several years about hereditary antithrombin (AT) deficiency and to outline approaches to the management of patients with AT deficiency in the acute and chronic settings. DATA SOURCES: An extensive literature search of Scopus (January 2008-April 2016) was performed for the terms congenital antithrombin deficiency, inherited antithrombin deficiency, or hereditary antithrombin deficiency Additional references were identified by reviewing literature citations. STUDY SELECTION: All relevant English-language case reports, reviews, clinical studies, meeting abstracts, and book chapters assessing hereditary AT deficiency were included. DATA SYNTHESIS: AT deficiency significantly increases the risk of venous thromboembolism (VTE). The risk of VTE is particularly high during pregnancy, the postpartum period, and following major surgery. Effective clinical management includes determination of the appropriate type and duration of antithrombotic therapy (ie, AT replacement for acute situations) while minimizing the risk of bleeding. For persons newly diagnosed with AT deficiency, age, lifestyle, concurrent medical conditions, family history, and personal treatment preferences can be used to individualize patient management. Patients should be informed of the risks associated with hormonal therapy, pregnancy, surgical procedures, and immobility, which further increase the risk of VTE in patients with AT deficiency. CONCLUSION: AT deficiency poses the highest risk for VTE among the hereditary thrombophilias, often requiring long-term anticoagulation. Undertaking an evaluation for hereditary thrombophilia is controversial; however, a diagnosis of VTE in association with AT deficiency can have management implications. An important treatment option for patients with this disorder in high-risk situations is AT concentrate.

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.

Congenital Antithrombin Deficiency in a Pregnant Woman with Right Atrium Thrombosis.

BACKGROUND: One of the rare causes of venous thromboembolism in pregnancy is antithrombin III deficiency. Antithrombin III deficiency is estimated to carry a 30% risk of venous thrombotic complication during each pregnancy and postpartum. CASE DETAILS: We present thea case of a A 21-year-old pregnant woman (Para 1+) with a history of large atrial septal defect repair at our hospital (Imam Ali Hospital, 2 May 2014). The patient, with unknown history of antithrombin III deficiency, was admitted at our emergency center with dyspnea and chest pain for the rule out of tamponade. She presented with a right atrial thrombosis in the second trimester of pregnancy despite the use of therapeutic doses of heparin and warfarin in the postoperative period as thromboembolic prophylaxis. The risk of warfarin emberyopaty led to termination of pregnancy, and successful redo-cardiac surgery outcome was achieved with the combined use of therapeutic anticoagulation and regular plasma-derived antithrombin concentrate infusions to normalize her antithrombin levels. CONCLUSION: She recovered from the operation uneventfully, and wad discharged in the 12(th) postoperative day. In the 6(th) month of follow-up, antithrombin III increased to 70% in more stable level and transethoracic echocardiography showed no recurrence of right atrial thrombus formation. This case leads to further debate regarding whether full anticoagulation should be a worthy preventive measure for venous thromboembolic prophylaxis after an open heart surgery complicated by pregnancy in a women with inherited antithrombin III deficiency. This point may become more relevant as further experience is gained with the use of recombinant human antithrombin in known cases during open cardiac surgery.

Pharmacokinetics of recombinant human antithrombin in delivery and surgery patients with hereditary antithrombin deficiency.

Population pharmacokinetic (PK) analyses were conducted to refine dosing recommendations for recombinant human anti-thrombin therapy in surgery and delivery patients with hereditary antithrombin deficiency (HD). Single-dose PK data from patients with HD and nonlinear mixed-effects modeling were used to devise a dosing regimen to target antithrombin (AT) activity levels between 80% and 120% of normal. External validation with data from a phase 3 trial confirmed the correctness of a covariate-free model for surgery patients, but dosing adjustment was necessary for delivery patients. After different covariates were tested, the model was updated to incorporate the influential covariate, delivery. Simulations were used to develop a therapeutic drug-monitoring scenario that results in steady state AT activity levels within the target range as quickly as practically feasible. Data from a second clinical trial provided additional external validation and confirmed the accuracy of the dosing model for both groups of patients.

[Perioperative anticoagulant therapy in a patient with congenital antithrombin III deficiency undergoing posterior spinal fusion].

A 22-year-old female was scheduled to undergo posterior thoracolumbar spinal fusion. She had been diagnosed with congenital antithrombin III (AT-III) deficiency by the onset of pulmonary embolism and deep vein thrombosis after the first operation at the age of 18. Thereafter she had taken warfarin, 5 mg daily, until 4 days before the surgery. Preoperatively, we administered AT-III products to regulate AT-III activity. The posterior spinal fusion was performed successfully without surgical complications. Postoperatively, we continued administration of AT-III products to maintain AT-III activity above 75%. We also used low dose unfractionated heparin with AT-III by continuous intravenous infusion. Heparin was administered with dose adjustment to achieve a target activated partial thromboplastin time of 45 to 60 seconds. After the activated partial thromboplastin time was stabilized in the target range, we started warfarin therapy (target international normalized ratio, 1.5 to 2.5) on postoperative day 16 and stopped administration of heparin on postoperative day 19. There was no thrombosis complications during the perioperative period. Good anticoagulant management was achieved in a patient with congenital AT-III deficiency undergoing posterior spinal fusion.

[Role of antithrombin iii in cardiac surgery]. / Papel de la antitrombina iii en cirugía cardiaca.

Coagulation of blood is of multidisciplinary interest. Cardiac surgery produces major changes in the delicate balance between pro-and anti-coagulant serum factors. The role of antithrombin iii has been analysed after finding evidence that associated decreased levels of protein activity to postoperative morbidity and mortality. Supplementing exogenous antithrombin is considered with the aim of optimising outcomes. Its intrinsic anticoagulant and anti-inflammatory properties have stimulated a growing interest, and suggests new lines of research.

Surgical treatment of atrial septal defect in a patient with familial antithrombin-III deficiency.

PURPOSE: A 41-year-old woman with familial antithrombin-III deficiency was admitted to our hospital for patch closure of an atrial septal defect. Antithrombin-III activity was 43% and its antigen level was 12.2 mg/dl, was diagnosed so type I antithrombin-III deficiency was diagnosed. METHODS: A dose of 2500 U of antithrombin-III concentrate was administered at 1 day before surgery, 1 hour before surgery, and 1 day after surgery. Heparinazation was performed at 200 IU/kg and the activated clotting time increased from a baseline of 140s to 622s. After establishing cardiopulmonary bypass and cardioplegic arrest, closure of the septal defect was done with a pericardial patch. RESULTS: The activated clotting time was maintained at more than 400s during cardiopulmonary bypass. There were no intraoperative complications and the postoperative course was uneventful. CONCLUSION: In patients with familial antithrombin-III deficiency, administration of antithrombin-III concentrate is effective when cardiopulmonary bypass is required.

Acquired antithrombin type IIb deficiency after liver transplantation: a case report.

A 3-year-old girl with multifocal hepatoblastoma was referred to our clinic for living-donor liver transplantation, the patient's father being the donor. Pretransplant evaluation revealed that the father presented partial asymptomatic antithrombin (AT) deficiency, with no inherited AT deficiency found in the girl. The genetic testing showed an AT type IIb deficiency responsible for a defect in the heparin-binding region of AT which is less thrombogenic but more common than the other AT qualitative defects. Her mother was ABO incompatible. Despite the thrombophilia on the father's side, transplantation was successfully performed under replacement therapy with intravenous AT concentrate and low-molecular-weight heparin thromboprophylaxis given to both the recipient and the donor. No thrombotic complications occurred. In the posttransplantation course, acquired partial AT deficiency was detected in the recipient, who received adjuvant chemotherapy without thrombotic complications. This case report highlights the relevance of full thrombophilic work-up before liver transplantation from a living donor, while illustrating that the procedure can be successfully performed in the case of AT deficiency on the donor's side provided that appropriate AT supplementation and thromboprophylaxis are administered to both the recipient and the donor.

Pharmacology and clinical applications of human recombinant antithrombin.

IMPORTANCE OF THE FIELD: Antithrombin therapy (AT) has been tested in various medical applications. With advances in genetics and biotechnology, large-scale production of human recombinant antithrombin (rhAT) is now feasible. The prospect of administering a recombinant protein rather than a pooled blood component, has rekindled interest in antithrombin therapy. However, many known properties of human pooled antithrombin (hpAT) still need to be investigated and established for rhAT. AREAS COVERED IN THIS REVIEW: The manufacture and clinical pharmacology of antithrombin. The literature, evidence and our own views about the future of this drug and its potential clinical applications. WHAT THE READER WILL GAIN: The reader will appreciate the biological rationale underpinning antithrombin administration in various clinical settings. The potential benefits and harms of the intervention are addressed. Novel future applications of recombinant antithrombin are broached. TAKE HOME MESSAGE: rhAT has been approved for its use in congenital antithrombin deficiency. rhAT has also been used off-label to treat heparin-resistance in cardiac surgery and sepsis. It is a promising adjuvant for immunosuppression in organ transplantation, and may have role as an anti-angiogenic, anti-tumor and anti-viral agent. rhAT has clear safety advantages over phAT, such as the avoidance of infection transmission.