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.

Recombinant human antithrombin expressed in the milk of non-transgenic goats exhibits high efficiency on rat DIC model.

Plasma-derived antithrombin (pAT) is often used for the treatments of disseminated intravascular coagulation (DIC) patients. In this paper, the recombinant adenovirus vector encoding human antithrombin (AT) cDNA was constructed and directly infused into the mammary gland of two goats. The recombinant human antithrombin (rhAT) was purified by heparin affinity chromatography from the goat milk, and then used in the treatment of thirty lipopolysaccharide (LPS) induced DIC rats. A high expression level of rhAT up to 2.8 g/l was obtained in the milk of goats. After purification, the recovery rate and the purity of the rhAT were up to 54.7 +/- 3.2% and 96.2 +/- 2.7%, respectively. In blood of the DIC rat model treated with rhAT, the levels of antithrombin and thrombin-antithrombin (TAT) were augmented significantly; meanwhile the consumption of fibrinogen and platelet was reduced significantly, and the increase of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) concentration was restrained modest and non-significant. For the above DIC indexes, there were no differences between pAT and rhAT (P > 0.05). Our results demonstrated that the way we established is a pragmatic tool for large-scale production of rhAT, and the rhAT produced with this method has potential as a substitute for pAT in the therapy of DIC patients.

Emerging technologies and quality assurance in hemostasis: a review of findings from the Royal College of Pathologists of Australasia Quality Assurance Program.

Regular multilaboratory surveys of laboratories by the Royal College of Pathologists of Australasia Quality Assurance Program (QAP) have been conducted to assess proficiency in tests of hemostasis for the last 40 years. This article focuses primarily on specialized assays of hemostasis, for which surveys have been conducted for some 10 years. For von Willebrand disease (vWD) evaluations, a total of 47 plasma samples have been dispatched to survey participants, including representative samples from normal individuals plus all of the major vWD subtypes (i.e., types 1, 2A, 2B, 2M, 2N, and 3). These surveys have focused partly on the issue of diagnostic interpretive error rates associated with different assays and test panels. In this context, considerable improvement is seen when laboratories incorporate the vWF:collagen-binding assay into the test panel. Thrombophilia-associated tests assessed by the program and discussed in this review include activated protein c resistance, lupus anticoagulant, and deficiencies of protein C, protein S, and antithrombin. Other tests briefly reviewed here include factor assays and inhibitors, D-dimer, and heparin/anti-Xa assays. Anticardiolipin antibody and anti-beta(2)-glycoprotein I antibody (aB(2)GPI) testing, assessed by the Immunology QAP, is also reviewed briefly, as are genetic tests associated with thrombophilic markers such as factor V Leiden and the prothrombin gene.

Recombinant human antithrombin expressed in Chinese hamster ovary cells shows in vivo efficacy on rat DIC model similarly to plasma-derived antithrombin regardless of different N-glycosylation.

Plasma-derived human antithrombin (pAT) is used for the treatments of disseminated intravascular coagulation (DIC) and hereditary antithrombin deficiencies. We expressed recombinant human antithrombin (rAT) in Chinese hamster ovary (CHO) cells. The purified rAT is composed of 55% alpha-isoform and 45% beta-isoform. The structure of the N-linked oligosaccharides of rAT is the same biantennary complex type as previously found in pAT with less sialylated on the non-reducing ends. Most of the oligosaccharides of rAT are fucosylated at the reducing ends of N-acetylglucosamine, while those of pAT are not fucosylated. Despite of the difference in sialylation and fucosylation of the oligosaccharide units, rAT and pAT showed indistinguishable heparin cofactor and progressive activities, and they bound to thrombin in a one-to-one stoichiometric manner. In lipopolysaccharide (LPS)-induced and thromboplastin-induced DIC rat models, rAT reduced fibrinogen and platelet consumption to a similar extent with pAT. In LPS-induced DIC model, both ATs similarly restrained the increase of alanine aminotransferase and aspartate aminotransferase activities. Finally, pharmacokinetic analysis showed that both ATs had similar half-lives in the circulation of normal rats. Together, the present study demonstrated that rAT prepared in CHO cells has potential for a substitute of pAT in therapeutic use.

Association between estrogen receptor alpha and beta gene polymorphisms and deep vein thrombosis.

BACKGROUND: Estrogen and the estrogen receptors alpha (ESR1) and beta (ESR2) play a role in regulating genes, including coagulation and fibrinolysis genes. OBJECTIVE: We investigated the association between ESR1 c.454-397T>C and c.454-351A>G and ESR2 1082A>G and 1730A>G polymorphisms and the risk of deep vein thrombosis (DVT), in 134 patients and 134 controls with acquired risk factors for thrombosis associated with estrogen alterations, such as pregnancy, puerperium, oral contraceptives (OC), and hormone replacement therapy (HRT). We also analysed 134 men with DVT. We investigated the relationship of these polymorphisms and the levels of fibrinogen, protein C (PC), protein S (PS), and antithrombin (AT) activity. METHODS: Gene polymorphisms were identified by using PCR and RFLP. Coagulation methods were used to measure PC, PS, and fibrinogen. Chromogenic methods were used to quantify AT. RESULTS AND CONCLUSIONS: The presence of the AA genotype of the 1730G>A polymorphism (OR=0.18; 95%CI=0.05-0.62) suggests a protective effect for DVT in women using OC. As the GG genotype of the 1730G>A polymorphism is associated with increased PS activity in all control women and women using OC, this suggested that a protective effect must occur by another pathway not related to PS. The AA and AG genotypes of the c.454-351A>G and GG genotype of the 1082G>A polymorphisms are associated with increased fibrinogen concentration in pregnant women. The GG haplotype in the ESR2 gene (P<0.001) was related to factor V Leiden or G20210A mutation in the prothrombin gene, or both, as predictive factors of DVT.

Biodistribution of covalent antithrombin-heparin complexes.

We have developed a covalent antithrombin-heparin (ATH) complex with advantages compared to non-covalent antithrombin:heparin (AT:H) mixtures. In addition to increased activity, ATH has a longer intravenous half-life that is partly due to reduced plasma protein binding. Given ATH's altered clearance, we investigated biodistribution of ATH in vivo. ATH made from either human plasma-derived AT (pATH) or recombinant human (produced in goats) AT (rhATH) was studied. 125I-ATH + unlabeled carrier was injected into rabbits at different doses. 131I-labeled albumin was administered just before sacrifice as a marker for trapped blood in tissues. Immediately after sacrifice, animal components were removed, weighed, and subsamples were counted for gamma-radioactivity. Percent recoveries of ATH in various organs/compartments at different time points were calculated, and kinetic distribution plots generated. At saturating doses, early disappearance of rhATH from the circulation was much faster than pATH. Co-incident with clearance, 26 +/- 3% of dose for rhATH was liver-associated compared to only 3.7 +/- 0.5% for pATH by 20 min. Also, at early time periods, >60% of all extravascular ATH was liver-associated. Analysis of the vena cava and aorta suggested that vessel wall binding might also account for initial plasma loss of rhATH. By 24 h, most of pATH and rhATH were present as urinary degradation products (51 +/- 3% and 63 +/- 8%, respectively). In summary, systemic elimination of ATH is greatly influenced by the form of AT in the complex, with liver uptake and degradation playing a major role.

Prothrombotic activity is associated with the anatomical as well as the functional severity of peripheral arterial occlusive disease.

The importance of prothrombotic activity in cardiovascular disease has been well established. However, limited data exist on the relationship between prothrombotic activity and the severity of peripheral arterial occlusive disease (PAD). The objective of the present study was to investigate the relationship between markers of haemostasis and the diagnostic measures of PAD: ankle-brachial-index (ABI), maximum treadmill walking distance and angiographic score. In a cross-sectional study of 127 patients (mean age 66 years; 64% males) with angiographically verified PAD, fasting blood samples were drawn, and citrated plasma was obtained for determination of selected haemostatic variables: von Willebrand factor (vWF), thrombomodulin (sTM), thrombin-antithrombin complex (TAT), soluble tissue factor (sTF), tPA antigen (tPAag) and D-dimer were all significantly correlated with the angiographic score (p < 0.05 for all). D-dimer, tPAag and fibrinogen were inversely correlated with the maximum treadmill walking distance, (p < 0.0001, p < 0.04 and p < 0.05, respectively), whereas fibrinogen was the only variable correlating to ABI (r = -0.223, p < 0.05). After adjustment for relevant covariates, D-dimer and TAT remained statistically significantly associated with the angiographic score (p < 0.001), and fibrinogen was, independent of other risk factors, inversely related with both the maximum treadmill walking distance and the ABI (p < 0.01 for both). This rather large study in patients with PAD showed that plasma levels of D-dimer, TAT and fibrinogen significantly predicted the extent of atherosclerosis, evaluated by angiographic score, maximum treadmill walking distance and ABI, respectively. These findings demonstrate a prothrombotic state in PAD patients, which might be of importance in future diagnosis and treatment of the disease.

Development of a fed-batch culture process for enhanced production of recombinant human antithrombin by Chinese hamster ovary cells.

Antithrombin is a serine protease inhibitor that inactivates several coagulation proteases, primarily thrombin and factor Xa. The Chinese hamster ovary (CHO) cell line transfected with a vector expressing recombinant human antithrombin (rAT) and a selectable marker, glutamine synthetase (GS), was cultivated in a 2-l fed-batch culture process using serum-free, glutamine-free medium. To maximize the rAT yield, effects of culture pH, balanced amino acid feeding, and an increased glutamate concentration on cell metabolism and rAT production were investigated. When cells were grown at pH values of 6.6, 6.8, 7.0, and 7.2, the maximum cell density and maximum lactate concentration decreased with decreasing pH. The highest production level of rAT was obtained at culture pH 6.8 due to the extended culture lifetime. Compared to the imbalanced amino acid feeding at culture pH 6.8, the balanced amino acid feeding increased the amount of rAT activity by 30% as a result of an increased viable cell number. A decrease in the specific glucose consumption rate (q(Glc)) with increasing culture time was observed in all the above-mentioned experiments, while the glucose concentration was maintained above 0.7 g l(-1). In addition, a decrease in the specific rAT production rate (q(rAT)) was observed after the depletion of lactate in the late cultivation stage. Taken together, these results suggest that the reduced availability of cellular energy caused by the decrease in q(Glc) and depletion of lactate led to the decrease in q(rAT). This decrease in q(rAT) was partially prevented by increasing the residual glutamate concentration from 1 mM to 7 mM, thus resulting in an additional 30% increase in the amount of rAT activity. The optimized fed-batch culture process yielded 1.0 g l(-1) rAT at 287 h of cultivation.

Production of recombinant human antithrombin by Pichia pastoris.

This paper deals with the production of recombinant human antithrombin (rAT) by the methylotrophic yeast Pichia pastoris. In preliminary methanol-limited fed-batch fermentation, the rAT concentration reached 324 mg/l at 192 h of cultivation, but the specific heparin cofactor (HC) activity of rAT in the culture supernatant was 10% of that of plasma-derived antithrombin (pAT). To improve the specific HC activity of rAT, effort was first focused on the optimization of culture pH and media composition, resulting in protection of rAT against pH-dependent instability and proteolytic degradation. However, even in the optimized methanol-limited fed-batch fermentation, the specific HC activity of rAT in the culture supernatant was still 20% that of pAT. To investigate the unknown mechanisms involved in the decreased specific HC activity of rAT, the culture supernatant of mock-transfected cells was prepared by methanol-limited fed-batch fermentation. When pAT was added to this supernatant, a rapid decrease in HC activity was observed; the residual HC activity was 26% after 24 h of incubation at 25 degrees C. The loss of pAT activity was prevented by addition of a formaldehyde scavenger, amino urea, to the supernatant. In addition, alcohol oxidase activity was observed in the supernatant, resulting in the accumulation of formaldehyde in the culture broth. These results suggest that the formaldehyde produced by methanol oxidation in the culture broth of P. pastoris might decrease the HC activity of rAT during fermentation. Replacing the methanol with glycerol as the carbon source improved the specific HC activity of rAT from 20% to above 40% of that of pAT. In the glycerol-limited fed-batch fermentation, rAT is expressed at 100 mg/l under the control of the truncated mutated AOX2 promoter.

Increased prevalence of factor V Leiden in patients with retinal vein occlusion and under 60 years of age.

Retinal vein occlusion (RVO) is a multifactorial disease involving vessel damage, stasis, viscosity and thrombosis. Conflicting findings on hereditary thrombophilic risk factors have been reported and their impact on RVO features remains to be defined. The aim of the present study was to evaluate the prevalence of hereditary thrombophilic risk factors (HTRF) and characteristics of RVO in patients with or without HTRF. The design of the study was a prospective, observational case series. Two hundred and thirty-four patients with RVO were included consecutively. A French healthy population of the same region was studied as control group. The HTRF studied were protein C (PC), protein S (PS) and antithrombin (AT) deficiencies, factor V Leiden (FVL) and factor II 20210A polymorphisms. Chi-Square was used for comparison with the healthy subjects and between RVO patient with and without HTRF according to localisation (branch vs. central), type of RVO (ischemic or non-ischemic), recurrence, age at first event and classical vascular risk factors. Twenty-two patients had HTRF (12 FV Leiden heterozygotes, 9 FII 20210A heterozygotes and 1 PS deficiency). No AT or PC deficiency was detected. Frequencies of PS deficiency, FVL and FII 20210A allele were similar to the reference population as well as to published data in the general caucasian population. Eighty-six patients experienced their first episode before the age of 60 years. Systemic hypertension, glaucoma and angina were significantly less frequent in patients with RVO before 60 years. Fourteen of the 22 patients with one HTRF (64%) experienced their first episode of RVO before the age of 60 years compared to 72 of 212 without HTRF (34%) (p = 0.006). Heterozygote status for FV Leiden was significantly more frequent in patients who had experienced their first episode of RVO before 60 years (p = 0.027). In conclusion, this study suggests a role of FV Leiden in the occurrence of RVO in patients younger than 60 years who exhibit fewer acquired vascular risk factors than in older patients.

Lipoprotein (a) and other prothrombotic risk factors in Caucasian women with unexplained recurrent miscarriage. Results of a multicentre case-control study.

From 1998 to 2003, 133 Caucasian women aged 17-40 years (median 29 years) suffering from unexplained recurrent miscarriage (uRM) were consecutively enrolled. In patients and 133 age-matched healthy controls prothrombotic risk factors (factor V (FV) G1691A, factor II (FII) G20210A, MTHFR T677T, 4G/5G plasminogen activator inhibitor (PAI)-1, lipoprotein (Lp) (a), protein C (PC), protein S (PS), antithrombin (AT), antiphospholipid/anticardiolipin (APA/ACA) antibodies) as well as associated environmental conditions (smoking and obesity) were investigated. 70 (52.6%) of the patients had at least one prothrombotic risk factor compared with 26 control women (19.5%; p<0.0001). Body mass index (BMI; p=0.78) and smoking habits (p=0.44) did not differ significantly between the groups investigated. Upon univariate analysis the heterozygous FV mutation, Lp(a) > 30 mg/dL, increased APA/ACA and BMI > 25 kg/m(2) in combination with a prothrombotic risk factor were found to be significantly associated with uRM. In multivariate analysis, increased Lp(a) (odds ratio (OR): 4.7/95% confidence interval (CI): 2.0-10.7), the FV mutation (OR:3.8/CI:1.4-10.7), and increased APA/ACA (OR: 4.5/CI: 1.1-17.7) had independent associations with uRM.

Cardiovascular and thrombophilic risk factors for idiopathic sudden sensorineural hearing loss.

BACKGROUND: In recent years there has been a significant increase in the diagnosis of sudden sensorineural hearing loss (SSHL) in western, countries with an incidence of 20 of 100,000 people affected every year. No clear causes for this disease have been found thus far, but cochlear ischemia has been hypothesized in patients in whom an infectious episode or acoustic neurinoma have been excluded. OBJECTIVES: The aim of this case-control study was to investigate a number of acquired and inherited thrombophilic risk factors [antithrombin, protein C and S; factor V (FV) Leiden, FII polymorphism; lupus anticoagulant (LA); anticardiolipin (aCL) antibodies; fasting homocysteine (Hcy); lipoprotein(a) (Lp(a)); plasminogen activator inhibitor-1 (PAI-1)] in addition to cardiovascular risk factors in patients with idiopathic SSHL (ISSHL). PATIENTS AND METHODS: We investigated 155 patients (67 male/88 female; age: 55 (range 19-79 years) with a diagnosis of ISSHL within 30 days from the onset of symptoms, and 155 controls (67 male/88 female; age 54 (range 19-78 years). Fasting Hcy levels were significantly higher in patients than in controls [11.6 (6.7-60) micromol/L vs. 8.7 (5.0-24) micromol/L] as well as PAI-1 levels [19 (2-95) mg/dL vs. 14.5 (4.0-87) mg/dL]. Lupus anticoagulant was present in 13 of 155 (8.4%) patients; 20 patients (12.9%) had positivity of aCL (four IgM and 16 IgG). In no patient was a deficiency of physiological clotting inhibitors antithrombin, protein C and protein S found. No significant differences between patients and controls were observed for Lp(a) plasma levels [111 (1-1146) mg/L vs. 103 (11-695) mg/L] and for the presence of FV Leiden (4.5% vs. 4.5%) and FII variant G20210A (3.8% vs. 3.2%). RESULTS AND CONCLUSIONS: Independent risk factors for ISSHL at the multivariate analysis (adjusted for age, sex and the traditional cardiovascular risk factors) were the positivity of aCL: OR 5.6 (95% CI 2.0-15.3); cholesterol levels within the second and third tertiles (with respect to the first tertile): T2 = OR 4.8 (95% CI 1.9-12.6)/T3 = OR 19 (95% CI 7-50.1); PAI-1 and Hcy levels within the third tertile (with respect to the first tertile): OR 20 (95% CI 7.8-78) and OR 4.0 (95% CI 2.0-8.1), respectively. These preliminary data suggest that hypercholesterolemia, hyperhomocysteinemia, elevated PAI-1 levels and anticardiolipin antibodies are associated with ISSHL, so indirectly supporting the hypothesis of a vascular occlusion in the pathogenesis of the disease.

Effect of genetic background on glycosylation heterogeneity in human antithrombin produced in the mammary gland of transgenic goats.

Glycosylation is involved in the correct folding, targeting, bioactivity and clearance of therapeutic glycoproteins. With the development of transgenic animals as expression systems it is important to understand the impact of different genetic backgrounds and lactations on glycosylation. We have evaluated the glycosylation of recombinant antithrombin produced in several transgenic goat lines, from cloned animals and from different types of lactation including induced lactations. Our results show glycosylation patterns from the protein expressed in animals, derived from the same founder goat, are mostly comparable. Furthermore, the protein expressed in two cloned goats had highly consistent oligosaccharide profiles and similar carbohydrate composition. However, there were significantly different oligosaccharide profiles from the proteins derived from different founder goats. Artificial induction of lactation did not have significant effects on overall carbohydrate structures when compared to natural lactation. The only major difference was that recombinant antithrombin from induced lactations contained a slightly higher ratio of N-acetylneuraminic acid to N-glycolylneuraminic acid and less amount of oligosaccharides containing N-glycolylneuraminic acid. The oligosaccharides from all animals were a mixture of high mannose-, hybrid- and complex-type oligosaccharides. Sialic acid was present as alpha-2,6-linkage and no alpha-1,3-linked galactose was observed. These results indicate that transgenic animals with closely related genetic backgrounds express recombinant protein with comparable glycosylation.

A review of the clinical and diagnostic utility of laboratory tests for the detection of congenital thrombophilia.

Laboratory tests to detect congenital thrombophilia are frequently requested by clinicians. This review attempts to define (1) whether and to what extent laboratory testing may help clinicians make decisions on patient management, (2) the types of conditions to be investigated, and (3) the types of testing to be performed for each condition.

[Antithrombogenicity of human endothelial cells]. / Antithrombogenität humaner Endothelzellen.

UNLABELLED: In the preceeding decades, our understanding of the complexity in our haemostaseologic system has been evolutionized from a purely ex vivo standpoint to an increasingly in vivo oriented approach, by more and more respecting the immense metabolic interactions of our vascular endothelium, mainly thrombin, the central serine protease in our coagulatory system. So far, investigations concerning human endothelium only relied on experiments with embryonic human endothelial cells, derived from umbilical cord veins. The underlying investigation confronts the justified question about the transferability of such embryonic results to the adult vascular system. MATERIAL, METHODS: Micro- and macrovascular endothelial cells were isolated, purified and propagated in pure cultures. Integrated into an established filtration model, their potential to mediate antithrombogenicity was investigated. RESULTS, CONCLUSION: Surprisingly, immense differences in thrombin-induced antithrombogenicity were demonstrated. This justifies doubts concerning the transferability of HUVEC-based results to the whole human vascular system.

Association between the severity of sepsis and the changes in hemostatic molecular markers and vascular endothelial damage markers.

It is well known that disorders of coagulation and fibrinolysis play a major role in the development of organ dysfunction during sepsis. Furthermore, the importance of the early initiation of anticoagulation therapy for severe cases has been emphasized based on the success of recent clinical trials. The purpose of this study is to search for useful markers for predicting organ dysfunction. Plasma samples were prospectively collected from 78 patients within 48 h after the onset of sepsis. Hemostatic markers and endothelial damage markers were compared between the patients with and without organ dysfunction. The WBC and platelet counts were not different between the groups. In contrast, fibrin/fibrinogen degradation products, D-dimer, thrombin-antithrombin complex, plasmin alpha2-antiplasmin complex, soluble fibrin, and total plasminogen activator inhibitor-1 were significantly higher, and the antithrombin activity and protein C levels were lower in the patients with organ dysfunction. Thus, the changes in the hemostatic molecular markers were associated with organ dysfunction from an early stage of sepsis, and antithrombin and protein C activities were found to be the most reliable markers.

Systemic coagulation reactivation in recurrence of colorectal cancer.

At time of diagnosis, most cancer patients present with laboratory evidence of systemic coagulation activation. After treatment with curative intent, these hemostatic alterations seemingly disappear as seen in colorectal cancer with regard to prothrombin fragment 1+2 (F1+2), thrombin-antithrombin complex (TAT), and soluble fibrin (SF). The aim of this study was to investigate whether coagulation activation recurs with cancer recurrence and to study whether preoperative coagulation tests have any prognostic value in colorectal cancer. Plasma F1+2, TAT, and SF levels were prospectively recorded from 113 patients followed after curative resection of colorectal cancer. The patients were seen in clinic after 3, 6, 12, and 18 months, and after 2, 3, 4, and 5 years. Coagulation reactivation was observed at the time of recurrence, as demonstrated by significantly increased plasma TAT and SF, along with a non-significant increase (P = 0.09) in F1+2. Preoperative values of F1+2, TAT, and SF did not show association with prognosis.