EXPLORING THE ROLE OF ANTITHROMBIN REPLACEMENT FOR THE TREATMENT OF PREECLAMPSIA

By:Dr. Indra

PPDS 1 Obstetry and GynaecologyMedical Faculty of Sebelas Maret University / dr. Moewardi Hospital Surakarta2015

CHAPTER IINTRODUCTION

Antithrombin III (henceforth referred to as antithrombin or AT) is a 58-kDa molecule belonging to the serine protease inhibitor (serpin) superfamily that plays a central role in anticoagulation and in regulating appropriate wound healing in mammalian circulation systems. It blocks our blood clotting mechanism by inactivating the major clotting protein thrombin. It is, therefore, called anti-thrombin. While antithrombin III was the original name given to this protein, the correct name now is just antithrombin, with the III dropped. Common names and abbreviations for the same protein are antithrombin, antithrombin III, AT, ATIII, and heparin cofactor I. As its name implies, antithrombin was first characterized as an inhibitor of thrombin. Antithrombin also affects other serine proteases of the coagulation cascade.[3, 4, 5, 6] A diagrammatic representation of the serine proteases with which antithrombin interacts is shown in the image below. Recent studies have shown that antithrombin also has anti-inflammatory actions that are independent of its effect on regulating coagulation.Antithrombin deficiency, which may be congenital or acquired, results in increased risk for venous thrombosis and, far less commonly, arterial thrombosis. Pre-eclampsia is a multisystem disorder that complicates 3%8% of pregnancies in Western countries and constitutes a major source of morbidity and mortality worldwide. The criteria that defne pre-eclampsia have not changed over the past decade. These are: onset at >20 weeks gestational age of 24-hour proteinuria 30 mg/day or, if not available, a protein concentration 30 mg (1+ on dipstick) in a minimum of two random urine samples collected at least 46 hours but no more than 7 days apart, a systolic blood pressure >140 mmHg or diastolic blood pressure 90 mmHg as measured twice, using an appropriate cuff, 46 hours and less than 7 days apart, and disappearance of all these abnormalities before the end of the 6th week postpartum. Nonetheless, some presentations of pregnancy-related hypertension combined with clinical or laboratory abnormalities or intrauterine growth restriction should also be considered as potential pre-eclampsia. Overall, 10%15% of maternal deaths are directly associated with pre-eclampsia and eclampsia. Some epidemiological fndings support the hypothesis of a genetic and immunological etiology. The risk of pre-eclampsia is 2-fold to 5-fold higher in pregnant women with a maternal history of this disorder. Depending on ethnicity, the incidence of pre-eclampsia ranges from 3% to 7% in healthy nulliparas and 1% to 3%. in multiparas. Moreover, nulliparity and a new partner have been shown to be important risk factors (Table 1). Other risk factors have been identified, including a medical history of chronic hypertension, kidney disease, diabetes, obesity, birthplace in Africa, age 35 years, and pregnancy characteristics, such as twin or molar pregnancy, previous pre-eclampsia, or fetal congenital abnormality. High altitude has also been shown to increase the incidence of pre-eclampsia, and is attributed to greater placental hypoxia, smaller uterine artery diameter, and lower uterine artery blood fow. Pre-eclampsia may be life-threatening for both mother and child, increasing both fetal and maternal morbidity and mortality. In the mother, pre-eclampsia may cause premature cardiovascular disease, such as chronic hypertension, ischemic heart disease, and stroke, later in life, while children born after pre-eclamptic pregnancies and who are relatively small at birth, have an increased risk of stroke, coronary heart disease, and metabolic syndrome in adult life. The sole curative treatment being delivery, management must continuously balance the riskbeneft ratio of induced preterm delivery and maternalfetal complications. Screening women at high risk and preventing recurrences are also key issues in the management of pre-eclampsia.

Figure 1 Algorithm for antihypertensive treatment of pre-eclampsia.Note: MBP = [systolic BP + 2 diastolic BP]/3. Abbreviations: MBP, mean blood pressure; Ci, contraindication; SBP, systolic blood pressure; DBP, diastolic blood pressure.Women with AT deficiency are at particularly high risk for developing clots during pregnancy and after delivery.The exact risk of developing blood clots during pregnancy is impossible to determine accurately. One study showed that only 3 % of pregnancies will be complicated by a blood clot if no concomitant prophylactic blood thinners are given. However, other studies have shown that blood clots occur in up to 50 % of pregnancies. Treatment with heparin injections underneath the skin (subcutaneously) during pregnancy should strongly be considered to prevent blood clots. However, no well designed clinical studies exist that allow strong recommendations as to how exactly to treat pregnant women (dose of heparin; treatment with antithrombin concentrate, etc.).Some physicians recommend antithrombin replacement therapy during delivery, when heparin may be contraindicated, since heparin might lead to an increased risk of bleeding. AT concentrate may also be given for a few days after delivery, together with heparin. Warfarin is not used during pregnancy because it may cause birth defects. However, for 6-12 weeks postpartum, warfarin should be considered, because there is a high risk for blood clots in the post-delivery period. A summary of 45 cases of pregnancy in women with AT deficiency with detailed information concerning prophylactic therapy with heparin and/or antithrombin has recently been published. However, no treatment guidelines can be derived from that publication, since many different regimens were used. Women with AT deficiency also have an increased risk for pregnancy loss, either early (miscarriage) or late (stillbirth) in the pregnancy. This is probably due to blood clots forming in the placenta, leading to blockage of blood flow and oxygen delivery to the fetus. Approximately 1 of 6 pregnancies in women with antithrombin deficiency (17 %) will end with an early fetal loss, and 1 in 40 pregnancies (2.3 %) will end with a stillbirth if no blood thinners are given. Therapy with heparin with or without antithrombin throughout the pregnancy likely decreases that risk.There have been limited case reports and studies using antithrombin replacement in the setting of preeclampsia. Buller administered a dose of 2,000 Units of antithrombin (plasma) concentrate to an antithrombin deficient patient with severe preeclampsia and found that the antithrombin infusion improved blood pressure, proteinuria and coagulation parameters. The patient had an uneventful Cesarean delivery. Terao et al (1989) considered that there was a 40% efcacy in the treated group vs 0% in the untreated group They also found a correlation between GI and antithrombin activity. Nakabayashi and colleagues evaluated antithrombin (plasma) replacement vs heparin in early onset severe preeclampsia with intrauterine fetal growth restriction under 32 weeks and concluded that antithrombin replacement therapy was useful for improving maternal hypertension and fetal weight in severe preeclampsia. Kobayashi and colleagues (2005) on a late Phase II study reported improved uteroplacental circulation found with administration of antithrombin replacement The optimal dose of antithrombin replacement was 3000 units/ day, which was efcacious and safe for both mother and fetus. Maki and colleagues (2000) performed that antithrombin replacement in addition to conventional therapy improved maternal symptoms, improved the biophysical profle score, prolonged pregnancy and decreased prevalence of very low birth weight infants Paternoster (2004) concluded that the Standard dose of antithrombin replacement corrects the hemostatic abnormality, while the High dose also corrects infammatory state In summary, there is preliminary evidence suggesting a beneft to antithrombin replacement in the setting of preeclampsia.

CHAPTER IIANTITHROMBIN

Antithrombin is a complex glycoprotein with multiple pharmacologically important activities in both the coagulation and infammatory cascades Normal serum AT levels range between 12 5 15 mg/dL (Murano et al 1980) It is the most critical modulator of coagulation (Figure 1) and has potent anti-infammatory properties (Figure 2) independent of its efects on coagulation (reviewed in Roemisch et al 2002)

Antithrombin (AT) concentrates can be therapeutically useful in cases of primary and acquired AT deficiency; their use, to be reserved to clinical conditions in which low levels of functional AT are associated with a thrombotic imbalance in haemostasis, has yet to be supported by clear scientific evidence.A. Notions of physiologyAT is a glycoprotein synthesised by the liver. Its molecular weight is 58,000 Da and it circulates in the plasma at a concentration of 150 mg/mL. Belonging to the family of serpins or inhibitors of serine proteases, it inhibits proteases. AT is the most potent naturally occurring inhibitor of coagulation and plays a fundamental role in maintaining haemostatic balance. Furthermore, it has anti-inflammatory and anti-aggregant properties mediated through the release of prostacyclins from endothelial cells. Normal values of AT activity in the plasma range from 80% to 120%. In normal conditions its biological half-life is 1.5-2.5 days; in conditions of acquired deficiency and in the presence of heparin, the half- life of AT can be notably shorter, being reduced to even a few hours.B. Preparations of ATAT concentrates, like all other plasma derivates, are prepared from pools of human plasma, made from at least 1,000 different donors. Various companies have been licensed to manufacture this product for clinical use. AT preparations undergo microbial inactivation by pasteurisation, sometimes followed by nanofiltration. Vials containing 500, 1,000, 1,500 and 2,000 UI are available.C. Mechanism of actionAT is used as replacement therapy in conditions of acquired or inherited deficiency, in particular circumstances. Its anticoagulant activity is mainly due to the inhibition of thrombin, activated factor X (FXa) and, to a lesser degree, also other activated clotting factors (FIXa, FXIa, FXIIa). The rate of formation of the thrombin-antithrombin complex is very greatly increased by heparan sulphate, present on the surface of endothelial cells. Subjects lacking AT have an increased risk of thrombosis, particularly in the presence of other thrombophilic conditions.D. Congenital AT deficiencyThe estimated prevalence is 1/2,000-5,000 in the general population and 2-3% in a selected population of patients with thrombotic event. There are two different types of congenital deficiency of AT, which are inherited in an autosomal dominant manner:- TYPE I (quantitative defect), in which there are proportional decreases in the concentration and, therefore, functional activity of the AT.- TYPE II (qualitative defect), characterised by normal levels of protein, but a reduction in its functional activity.E. Acquired AT deficiencyVarious clinical conditions are associated with acquired AT deficiency:1) Reduced production: - acute and chronic liver disorders;- premature neonates;- treatment with L-asparaginase.2) Increased excretion/loss:- protein-losing enteropathy;- nephrotic syndrome;- burns.3) Dilution:- massive transfusion;- plasma exchange;- extracorporeal circulation.4) Increased consumption:- disseminated intravascular coagulation (DIC);- major surgery;- heparin infusion;- multiple trauma;- severe sepsis/septic shock;- severe thromboembolism;- haemolytic-uraemic syndrome;- pre-eclampsia.F. IndicationsThe use of AT concentrates, to be reserved to clinical conditions in which low levels of functional AT are associated with a thrombotic imbalance in haemostasis, has yet to be supported by clear scientificevidence.1. Patients with congenital AT deficiencyIn the absence of symptoms or risk factors, congenital AT deficiency is not an indication for replacement therapy with AT concentrates, which should be reserved, on a temporary basis and in association with heparin therapy, to the following circumstances (Grade of Recommendation: 2C):- prophylaxis of deep vein thrombosis and thromboembolism in high-risk conditions: major surgery, obstetric procedures (such as delivery or abortion), trauma, immobilisation;- treatment of ongoing thrombosis, until the indicated level of oral anticoagulation is reached.Patients with congenital AT deficiency and repeated episodes of thromboembolism must receive life-long oral anticoagulant therapy (Grade of Recommendation: 2C+) (Table I).2. Patients with acquired AT deficiencyThere is little evidence concerning treatment with AT in conditions of acquired deficiency; replacement therapy with AT may be useful, although the levels of evidence are not high, in DIC associated with severe sepsis, in which the use of high doses, not associated with heparin, could improve the survival of patients (Grade of Recommendation: 2C+).Further studies are needed on the use of AT concentrates in the case of:- DIC associated with trauma, burns, pregnancy;- neonates of mothers with AT deficiency or a family history of severe venous thromboembolism;- ongoing thrombosis with low levels of AT and resistance to heparin;- acute thromboembolism during treatment with L-asparaginase;- extracorporeal circulation;- thrombosis of the hepatic artery following orthotopic liver transplantation;- veno-occlusive disease following bone marrow transplantation;Furthermore, the use of AT is not generally indicated (given the lack of proof of clinical efficacy), even when AT levels are considerably below normal, in the following conditions of chronic, not decompensated deficiency: acute or chronic liver disease, nephrotic syndrome, protein-losing enteropathy, pre-eclampsia, neonatal respiratory distress syndrome, multiple trauma and post-operatively in the absence of DIC (Table I).G. Calculation of the dose of AT to administerThere is no evidence that higher than normal levels of AT provide greater protection than physiological levels, just as an overdose does not imply an increased risk of bleeding. Before starting replacement therapy with a specific concentrate, it is advisable to assay AT functional activity. Given that the administration of 1UI/kg of body weight increases plasma AT activity by 1.5%, the dose to administered is calculated as follows: units of AT = body weight (kg) x [desired level assayed activity(%)]/1.5.For example:60 kg x (100 38%)/1.5 = 2,480 UI.The dose and timing of subsequent administrations are based on the results of monitoring plasma AT activity every 12-48 h. H. Monitoring indices for clinical auditingUse of AT treatment in the following conditions: - congenital AT deficiency in the absence of symptoms or risk factors and/or with AT values >70%.I. Side effects and adverse reactionsAT infusions are generally well tolerated; allergic-type reactions are, however, possible. The use of AT concentrates contemporaneously with heparin increases the risk of bleeding and careful clinical and laboratory monitoring is, therefore, necessary, particularly in patients at high haemorrhagic risk.J. RecommendationsIt is recommended that all the details of the product infused, including its batch number, are recorded in the clinical records.

CHAPTER IIIPREECLAMPSIA

Preeclampsia is most commonly defned by new-onset proteinuria and, potentially, other end-organ dysfunction. Hypertension and proteinuria are discussed above under Diagnosis of Hypertension and Management of Proteinuria. Women with preeclampsia may have a diminished, or no, nocturnal BP decrease. Maternal end-organ dysfunction and fetal manifestations of preeclampsia illustrated in the Figure are all non-specifc. In this model of its origins we describe preeclampsia that arises primarily through imperfect placentation (early-onset or placental preeclampsia [pink]) or through either a lowered maternal threshold or excessive physiological placentation (late-onset or maternal preeclampsia [blue]). Some aspects of the preeclampsia process are specifc to it, while others are shared with normotensive IUGR. A lowered maternal threshold may also infuence the development of early-onset preeclampsia through direct endothelial cell activation. The consequences of endothelial cell activation that appear consistent between all women with preeclampsia include a variable impact on multiple vulnerable organ systems. Disease severity generally correlates with the degree and number of organ dysfunctions. Fetal manifestations may occur before, with, or in the absence of maternal manifestations.Table below outlines the end-organ dysfunctions of preeclampsia: adverse conditions and severe complications. Adverse conditions consist of maternal symptoms, signs, and abnormal laboratory results, and abnormal fetal monitoring results that may herald the development of severe maternal or fetal complications (including stillbirth). The adverse conditions are those that we wait for and respond to (e.g., low oxygen saturation) in an effort to avoid entirely the severe complications (e.g., pulmonary edema). That response could be more intensive maternal or fetal monitoring, specifc treatment, or delivery. Severe maternal complications of preeclampsia warrant delivery.The adverse conditions are manifestations of preeclampsia that increase the risk of adverse maternal or perinatal outcomes. Table 3 lists the adverse conditions by maternal organ system. Of particular importance are preterm preeclampsia, chest pain or dyspnea, and abnormality of one or more of oxygen saturation by pulse oximetry, platelet count, serum creatinine, or aspartate transaminase. Proteinuria predicts neither short-term adverse outcomes nor long-term maternal renal prognosis. HELLP syndrome is represented by its component parts (hemolysis, elevated liver enzymes, and low platelets), to which we react to by initiating delivery.

How maternal adverse conditions may predict fetal or neonatal outcomes in preeclampsia is unclear. The perinatal literature suggests that abnormal fetal monitoring of various types may identify increased fetal risk. The biophysical profle has unproven utility in high risk women, and may falsely reassure with early-onset IUGR or preeclampsia. Currently, there is no single fetal monitoring test to accurately predict fetal compromise in women with preeclampsia. Most experts suggest a combination of tests, with emphasis on umbilical artery Doppler when there is IUGR. Other non-specifc risk factors for severe complications of preeclampsia are immigrant status, young maternal age, nulliparity, lower maternal weight, and in the index pregnancy, multiple pregnancy and early-onset preeclampsia.Defnitions of severe preeclampsia vary, but most include multi-organ involvement. We modifed our defnition of severe preeclampsia to preeclampsia associated with one or more severe complications. Severe preeclampsia now warrants delivery regardless of gestational age. Our defnition excludes heavy proteinuria and HELLP syndrome, which are not absolute indications for delivery, and includes stroke and pulmonary edema, which are leading causes of maternal death in preeclampsia.

A transient hypertensive effect is not associated with an increased risk of adverse outcomes. White-coat effect in early pregnancy (~30%) is common. Forty percent of women progress to persistent hypertension at 20 weeks (i.e., gestational hypertension) and 8% to preeclampsia. Women with white-coat effect have risks (e.g., severe hypertension, preterm delivery, and NICU admission) intermediate between normotension and either pre-existing or gestational hypertension.Masked hypertension in early pregnancy (~30%) is also common, but associated perinatal risks are unknown. Outcomes with masked hypertension at 20 weeks (~10%) equate to those of gestational hypertension. Masked hypertension could be considered (and ambulatory or home BP monitoring performed) if there are unexplained maternal or perinatal complications typically associated with the HDPs.

CHAPTER IVEXPLORING THE ROLE OF ANTITHROMBIN REPLACEMENT FOR THE TREATMENT OF PREECLAMPSIA

From the medical research described in the literature, it is clear that preeclampsia is a multifactorial disorder that involves both the cardiovascular and infammatory systems Due to its pleiotropic nature as an anticoagulant and anti-infammatory agent, AT has been suggested as a potential treatment to ameliorate this disorder. Antithrombin (AT) replacement has been described in patients with hereditary AT deciency undergoing delivery; however, the kinetics of AT replacement in preeclampsia is not adequately understood. If one considers the various features of the preeclamptic state and the potential impact that AT treatment might provide on these features (Table 1), it is clear that the anti-infammatory properties of AT would most likely provide the most beneft in this disorder However, one cannot underestimate the damage that thrombin and microthrombi play in placental damage and maternal cardiovascular damage.

Women with AT deficiency are at particularly high risk for developing clots during pregnancy and after delivery.The exact risk of developing blood clots during pregnancy is impossible to determine accurately. One study showed that only 3 % of pregnancies will be complicated by a blood clot if no concomitant prophylactic blood thinners are given. However, other studies have shown that blood clots occur in up to 50 % of pregnancies. Treatment with heparin injections underneath the skin (subcutaneously) during pregnancy should strongly be considered to prevent blood clots. However, no well designed clinical studies exist that allow strong recommendations as to how exactly to treat pregnant women (dose of heparin; treatment with antithrombin concentrate, etc.).Some physicians recommend antithrombin replacement therapy during delivery, when heparin may be contraindicated, since heparin might lead to an increased risk of bleeding. AT concentrate may also be given for a few days after delivery, together with heparin. Warfarin is not used during pregnancy because it may cause birth defects. However, for 6-12 weeks postpartum, warfarin should be considered, because there is a high risk for blood clots in the post-delivery period. A summary of 45 cases of pregnancy in women with AT deficiency with detailed information concerning prophylactic therapy with heparin and/or antithrombin has recently been published. However, no treatment guidelines can be derived from that publication, since many different regimens were used. Women with AT deficiency also have an increased risk for pregnancy loss, either early (miscarriage) or late (stillbirth) in the pregnancy. This is probably due to blood clots forming in the placenta, leading to blockage of blood flow and oxygen delivery to the fetus. Approximately 1 of 6 pregnancies in women with antithrombin deficiency (17 %) will end with an early fetal loss, and 1 in 40 pregnancies (2.3 %) will end with a stillbirth if no blood thinners are given. Therapy with heparin with or without antithrombin throughout the pregnancy likely decreases that risk.Hallmarks of preeclampsia include aberrant trophoblast invasion, endothelial cell dysfunction, and activation of the coagulation cascade; decreased AT levels have also been noted. Weiner et al. measured AT levels near term in hypertensive patients (i.e., those with chronic hypertensive preeclampsia or chronic hypertension with superimposed preeclampsia) and reported that mean S.E. AT activity level was 60 15% in preeclamptic patients, 68 16% in patients with superimposed preeclampsia, and 85 15%in control patients.With a cutoff of 70%, the negative predictive value for preeclampsia was 89%, andwith a cutoff of 80% of normal. If plasma antithrombin III concentration at 12 hours 80% of normal. Maintenance dosage: Determine preinfusion (trough) and peak postinfusion antithrombin III concentrations and administer additional doses of antithrombin III at appropriate intervals (e.g., every 24 hours) until peak and trough concentrations are maintained within therapeutic range (i.e., steady state), generally 80120% of normal. In general, approximately 60% of initial loading dose every 24 hours required to maintain steady-state plasma antithrombin III concentrations within 80120% of normal. (See Laboratory Monitoring under Cautions.)Continue therapy for 28 days following thromboembolism or surgical or obstetric procedure, depending on clinical situation. (See General under Dosage and Administration.)

CHAPTER VSUMMARY

Pre-eclampsia is a rare pregnancy-related disease with an unpredictable course that can have serious consequences for both the mother and the fetus. The treatment is simple, ie, delivery. Nonetheless, induced preterm delivery requires careful weighing of both maternal and fetal risk-beneft. Accordingly, identifying delivery criteria in case of pre-eclampsia is crucial to optimal management. Current research focuses on the prediction of onset of pre-eclampsia or even severe pre-eclampsia so as to allow early management and improve the morbidity and mortality associated with this disease. Specifc tools for secondary prevention must also be developed for recurrent pre-eclampsia.In summary, it is clear that AT, in addition to its central role in the coagulation cascade, has potent anti-infammatory activities Since the anti-infammatory properties of AT are mediated through its interaction with heparin-like receptors such as syndecan-4, located on endothelial surfaces and leukocytes, supra-physiological doses are necessary to achieve a signifcant efect.A signifcant body of research, both non-clinical and clinical, has demonstrated the signifcant anticoagulant and potent anti-infammatory properties of antithrombin More limited non-clinical and clinical studies have shown the potential for AT therapeutic treatment of women with preeclampsia As suggested in a number of the clinical studies cited above, the next step is the use of antithrombin in a well-controlled, randomized clinical study in women with preeclampsia.The published studies do suggest a beneft to antithrombin replacement in preeclampsia. A high quality trial is needed to address the many questions raised by these provocative preliminary studies.

REFERENCES