Antithrombin deficiency and its laboratory diagnosis

Molecular Mechanisms of the Impaired Heparin Pentasaccharide Interactions in 10 Antithrombin Heparin Binding Site Mutants Revealed by Enhanced Sampling Molecular Dynamics

Antithrombin (AT) is a critical regulator of the coagulation cascade by inhibiting multiple coagulation factors including thrombin and FXa. Binding of heparinoids to this serpin enhances the inhibition considerably. Mutations located in the heparin binding site of AT result in thrombophilia in affected individuals. Our aim was to study 10 antithrombin mutations known to affect their heparin binding in a heparin pentasaccharide bound state using two molecular dynamics (MD) based methods providing enhanced sampling, GaMD and LiGaMD2. The latter provides an additional boost to the ligand and the most important binding site residues. From our GaMD simulations we were able to identify four variants (three affecting amino acid Arg47 and one affecting Lys114) that have a particularly large effect on binding. The additional acceleration provided by LiGaMD2 allowed us to study the consequences of several other mutants including those affecting Arg13 and Arg129. We were able to identify several conformational types by cluster analysis. Analysis of the simulation trajectories revealed the causes of the impaired pentasaccharide binding including pentasaccharide subunit conformational changes and altered allosteric pathways in the AT protein. Our results provide insights into the effects of AT mutations interfering with heparin binding at an atomic level and can facilitate the design or interpretation of in vitro experiments.

Clinical and Molecular Characterization of Nine Novel Antithrombin Mutations

Antithrombin (AT) is the major plasma inhibitor of thrombin (FIIa) and activated factor X (FXa), and antithrombin deficiency (ATD) is one of the most severe thrombophilic disorders. In this study, we identified nine novel AT mutations and investigated their genotype-phenotype correlations. Clinical and laboratory data from patients were collected, and the nine mutant AT proteins (p.Arg14Lys, p.Cys32Tyr, p.Arg78Gly, p.Met121Arg, p.Leu245Pro, p.Leu270Argfs*14, p.Asn450Ile, p.Gly456delins_Ala_Thr and p.Pro461Thr) were expressed in HEK293 cells; then, Western blotting, N-Glycosidase F digestion, and ELISA were used to detect wild-type and mutant AT. RT-qPCR was performed to determine the expression of AT mRNA from the transfected cells. Functional studies (AT activity in the presence and in the absence of heparin and heparin-binding studies with the surface plasmon resonance method) were carried out. Mutations were also investigated by in silico methods. Type I ATD caused by altered protein synthesis (p.Cys32Tyr, p.Leu270Argfs*14, p.Asn450Ile) or secretion disorder (p.Met121Arg, p.Leu245Pro, p.Gly456delins_Ala_Thr) was proved in six mutants, while type II heparin-binding-site ATD (p.Arg78Gly) and pleiotropic-effect ATD (p.Pro461Thr) were suggested in two mutants. Finally, the pathogenic role of p.Arg14Lys was equivocal. We provided evidence to understand the pathogenic nature of novel SERPINC1 mutations through in vitro expression studies.

Thrombosis associated with mycoplasma pneumoniae infection (Review)

Mycoplasma pneumoniae is a common pathogen causing respiratory infections in children and adults. In addition to respiratory diseases, Mycoplasma pneumoniae is also involved in numerous extrapulmonary diseases. Thrombosis is an extrapulmonary manifestation associated with Mycoplasma pneumoniae infection. In recent years, an increasing number of case reports have been published identifying thrombosis secondary to Mycoplasma pneumoniae infection. In the present study, the available relevant literature in English available on PubMed, Medline and Web of Science was consulted. The results of the present study demonstrated that in patients with thrombosis caused by Mycoplasma pneumoniae infection, some of the factors causing thrombosis are transient and some are due to hereditary thrombophilia. Following timely treatment, the majority of patients recovered completely but some patients had a poor prognosis. The present review focuses on the pathogenesis, clinical features, treatment and prognosis of this crucial issue, which contributes toward the understanding of the disease.

Investigation of the Differences in Antithrombin to Heparin Binding among Antithrombin Budapest 3, Basel, and Padua Mutations by Biochemical and In Silico Methods

Antithrombin (AT) is a serine protease inhibitor, its activity is highly accelerated by heparin. Mutations at the heparin-binding region lead to functional defect, type II heparin-binding site (IIHBS) AT deficiency. The aim of this study was to investigate and compare the molecular background of AT Budapest 3 (p.Leu131Phe, ATBp3), AT Basel (p.Pro73Leu), and AT Padua (p.Arg79His) mutations. Advanced in silico methods and heparin-binding studies of recombinant AT proteins using surface plasmon resonance method were used. Crossed immunoelectrophoresis and Differential Scanning Fluorimetry (NanoDSF) were performed in plasma samples. Heparin affinity of AT Padua was the lowest (KD = 1.08 × 10^-6 M) and had the most severe consequences affecting the allosteric pathways of activation, moreover significant destabilizing effects on AT were also observed. KD values for AT Basel, ATBp3 and wild-type AT were 7.64 × 10^-7 M, 2.15 × 10^-8 M and 6.4 × 10^-10 M, respectively. Heparin-binding of AT Basel was slower, however once the complex was formed the mutation had only minor effect on the secondary and tertiary structures. Allosteric activation of ATBp3 was altered, moreover decreased thermostability in ATBp3 homozygous plasma and increased fluctuations in multiple regions of ATBp3 were observed by in silico methods suggesting the presence of a quantitative component in the pathogenicity of this mutation due to molecular instability.

Age and Origin of the Founder Antithrombin Budapest 3 (p.Leu131Phe) Mutation; Its High Prevalence in the Roma Population and Its Association With Cardiovascular Diseases

Background: Antithrombin (AT) is one of the most important regulator of hemostasis. AT Budapest 3 (ATBp3) is a prevalent type II heparin-binding site (IIHBS) deficiency due to founder effect. Thrombosis is a complex disease including arterial (ATE) and venous thrombotic events (VTE) and the Roma population, the largest ethnic minority in Europe has increased susceptibility to these diseases partly due to their unfavorable genetic load. We aimed to calculate the age and origin of ATBp3 and to explore whether the frequency of it is higher in the Roma population as compared with the general population from the corresponding geographical area. We investigated the association of ATBp3 with thrombotic events in well-defined patients' populations in order to refine the recommendation when testing for ATBp3 is useful.

Methods and Results: Prevalence of ATBp3, investigated in large samples (n = 1,000 and 1,185 for general Hungarian and Roma populations, respectively) was considerably high, almost 3%, among Roma and the founder effect was confirmed in their samples, while it was absent in the Hungarian general population. Age of ATBp3—as calculated by analysis of 8 short tandem repeat sequences surrounding SERPINC1—was dated back to XVII Century, when Roma migration in Central and Eastern Europe occurred. In our IIHBS cohort (n = 230), VTE was registered in almost all ATBp3 homozygotes (93%) and in 44% of heterozygotes. ATE occurred with lower frequency in ATBp3 (around 6%); it was rather associated with AT Basel (44%). All patients with ATE were young at the time of diagnosis. Upon investigating consecutive young (<40 years) patients with ATE (n = 92) and VTE (n = 110), the presence of ATBp3 was remarkable.

Conclusions: ATBp3, a 400-year-old founder mutation is prevalent in Roma population and its Roma origin can reasonably be assumed. By the demonstration of the presence of ATBp3 in ATE patients, we draw the attention to consider type IIHBS AT deficiency in the background of not only VTE but also ATE, especially in selected populations as young patients without advanced atherosclerosis. We recommend including the investigation of ATBp3 as part of thrombosis risk assessment and stratification in Roma individuals.

The Effect of Direct Oral Anticoagulants on Antithrombin Activity Testing Is Abolished by DOAC-Stop in Venous Thromboembolism Patients

CONTEXT.—

Direct oral anticoagulants (DOACs) may cause false negative results of antithrombin (AT) deficiency screening.

OBJECTIVE.—

To evaluate the impact of DOAC-Stop, an agent reversing in vitro effects of DOACs, on AT testing in anticoagulated patients.

DESIGN.—

We assessed 130 venous thromboembolism patients aged 46.7 ± 13.5 years. Blood samples were collected 2 to 27 hours after DOAC intake from 49 patients on rivaroxaban, 54 on apixaban, and 27 on dabigatran. Antithrombin activity was assessed using the activated factor X (FXa)-based and the activated factor II (FIIa)-based method twice, before and after DOAC-Stop treatment, together with plasma DOAC levels using coagulometric assays.

RESULTS.—

The use of DOAC-Stop did not influence AT activity measured using the FIIa-based assay, whereas there was a marked decrease in AT activity determined using the FXa-based assay (ΔAT = 16.9%; 95% CI, 12.9%-19.1%). The AT-FIIa assay revealed decreased AT level (<79%) in all 10 (7.7%) genetically confirmed AT-deficient patients treated with rivaroxaban or apixaban (n = 5 each), whereas the AT-FXa assay showed decreased AT activity (<83%) in 2 subjects on rivaroxaban and 1 on apixaban with low plasma DOAC concentrations (<90 ng/mL). After DOAC-Stop median AT-FXa activity lowered from 83.5% (interquartile range, 66%-143%) to 65.5% (interquartile range, 57%-75%; P = .005; ΔAT = 18%) in AT-deficient patients, without any false negative results. The ΔAT in the FXa-based assay correlated with rivaroxaban and apixaban concentrations in the AT-deficient patients (r = 0.99, P < .001).

CONCLUSIONS.—

Application of DOAC-Stop enables reliable evaluation of AT deficiency screening in patients taking rivaroxaban or apixaban and tested using the FXa-based method.

Analysis of protein missense alterations by combining sequence- and structure-based methods

BACKGROUND

Different types of in silico approaches can be used to predict the phenotypic consequence of missense variants. Such algorithms are often categorized as sequence based or structure based, when they necessitate 3D structural information. In addition, many other in silico tools, not dedicated to the analysis of variants, can be used to gain additional insights about the possible mechanisms at play.

METHODS

Here we applied different computational approaches to a set of 20 known missense variants present on different proteins (CYP, complement factor B, antithrombin and blood coagulation factor VIII). The tools that were used include fast computational approaches and web servers such as PolyPhen-2, PopMusic, DUET, MaestroWeb, SAAFEC, Missense3D, VarSite, FlexPred, PredyFlexy, Clustal Omega, meta-PPISP, FTMap, ClusPro, pyDock, PPM, RING, Cytoscape, and ChannelsDB.

RESULTS

We observe some conflicting results among the methods but, most of the time, the combination of several engines helped to clarify the potential impacts of the amino acid substitutions.

CONCLUSION

Combining different computational approaches including some that were not developed to investigate missense variants help to predict the possible impact of the amino acid substitutions. Yet, when the modified residues are involved in a salt-bridge, the tools tend to fail, even when the analysis is performed in 3D. Thus, interactive structural analysis with molecular graphics packages such as Chimera or PyMol or others are still needed to clarify automatic prediction.

Aptamer-modified FXa generation assays to investigate hypercoagulability in plasma from patients with ischemic heart disease

BACKGROUND

High plasma levels of activated Factor VII-Antithrombin complex (FVIIa-AT) have been associated with an increased risk of cardiovascular mortality in patients with stable coronary artery disease (CAD).

OBJECTIVES

To investigate if FVIIa-AT levels are associated with activated factor X generation (FXaG) in modified assays.

PATIENTS/METHODS

Forty CAD patients were characterized for FVIIa-AT levels by ELISA and for FXaG in plasma. Novel fluorogenic FXaG assays, based on aptamers inhibiting thrombin and/or tissue factor pathway inhibitor (TFPI), were set up.

RESULTS

FXaG correlated with FVIIa-AT levels (R_AUC = 0.393, P = 0.012). The combination of thrombin inhibition and FXaG potentiation by using anti-thrombin and anti-TFPI aptamers, respectively, favors the study of time parameters. The progressive decrease in lag time from the lowest to the highest FVIIa-AT quartile was magnified by combining TFPI and thrombin inhibitory aptamers, thus supporting increased FXaG activity in the coagulation initiation phase. By exploring FXaG rates across FVIIa-AT quartiles, the largest relative differences were detectable at the early times (the highest versus the lowest quartile; 5.0-fold, P = 0.005 at 45 s; 3.5-fold, P = 0.001 at 55 s), and progressively decreased over time (2.3-fold, P = 0.002 at 75 s; 1.8-fold, P = 0.008 at 95 s; 1.6-fold, P = 0.022 at 115 s). Association between high FVIIa-AT levels and increased FXaG was independent of F7 -323 A1/A2 polymorphism influencing FVIIa-AT levels.

CONCLUSIONS

High FVIIa-AT plasma levels were associated with increased FXaG. Hypercoagulability features were specifically detectable in the coagulation initiation phase, which may have implications for cardiovascular risk prediction by either FVIIa-AT complex measurement or modified FXaG assays.

The mechanism of high affinity pentasaccharide binding to antithrombin, insights from Gaussian accelerated molecular dynamics simulations

The activity of antithrombin (AT), a serpin protease inhibitor, is enhanced by heparin and heparin analogs against its target proteases, mainly thrombin, factors Xa and IXa. Considerable amount of information is available on the multistep mechanism of the heparin pentasaccharide binding and conformational activation. However, much of the details were inferred from 'static' structures obtained by X-ray diffraction. Moreover, limited information is available for the early steps of binding mechanism other than kinetic studies with various ligands. To gain insights into these processes, we performed enhanced sampling molecular dynamics (MD) simulations using the Gaussian Accelerated Molecular Dynamics (GAMD) method, applied previously in drug binding studies. We were able to observe the binding of the pentasaccharide idraparinux to a 'non-activated' AT conformation in two separate trajectories with low root mean square deviation (RMSD) values compared to X-ray structures of the bound state. These trajectories along with further simulations of the AT-pentasaccharide complex provided insights into the mechanisms of multiple conformational transitions, including the expulsion of the hinge region, the extension of helix D and the conformational behavior of the reactive center loop (RCL). We could also confirm the high stability of helix P in non-activated AT conformations, such states might play an important role in heparin binding. 'Generalized correlation' matrices revealed possible paths of allosteric signal propagation to the binding sites for the target proteases, factors Xa and IXa. Enhanced MD simulations of ligand binding to AT may assist the design of new anticoagulant drugs.Communicated by Ramaswamy H. Sarma.

Clinical and laboratory characteristics of antithrombin deficiencies: A large cohort study from a single diagnostic center

INTRODUCTION

Inherited antithrombin (AT) deficiency is a heterogeneous disease. Due to low prevalence, only a few studies are available concerning genotype-phenotype associations. The aim was to describe the clinical, laboratory and genetic characteristics of AT deficiency in a large cohort including children and to add further laboratory data on the different sensitivity of functional AT assays.

PATIENTS AND METHODS

Non-related AT deficient patients (n=156) and their family members (total n=246) were recruited. Clinical and laboratory data were collected, the mutation spectrum of SERPINC1 was described. Three different AT functional assays were explored.

RESULTS

Thirty-one SERPINC1 mutations including 11 novel ones and high mutation detection rate (98%) were detected. Heparin binding site deficiency (type IIHBS) was the most frequent (75.6%) including AT Budapest3 (ATBp3), AT Padua I and AT Basel (86%, 9% and 4% of type IIHBS, respectively). Clinical and laboratory phenotypes of IIHBS were heterogeneous and dependent on the specific mutation. Arterial thrombosis and pregnancy complications were the most frequent in AT Basel and AT Padua I, respectively. Median age at the time of thrombosis was the lowest in ATBp3 homozygotes. The functional assay with high heparin concentration and pH7.4 as assay conditions had low (44%) sensitivity for ATBp3 and it was insensitive for AT Basel and Padua I.

CONCLUSION

Type IIHBS deficiencies behave differently in clinical and laboratory phenotypes from each other and from other AT deficiencies. Heparin concentration and pH seem to be the key factors influencing the sensitivity of AT functional assays to IIHBS.

Early onset of abdominal venous thrombosis in a newborn with homozygous type II heparin-binding site antithrombin deficiency

: The overall incidence of thromboembolic events in the neonatal period is 5 per 100 000 births, wherein more than 40% of all such manifestations are symptomatic renal vein thromboses. We describe the case of a newborn female who developed extensive thrombosis, which filled the inferior vena cava and renal vein and was diagnosed in the first weeks of life. A homozygous type II heparin-binding site antithrombin deficiency (c. 391C>T, p. Leu131Phe) was detected in the background. Despite the timely diagnosis and appropriate treatment, clinical signs of renal insufficiency, because of left kidney atrophy and arterial hypertension, were observed. Our case demonstrates the seriousness of the consequences arising after early onset of venous thrombosis caused by homozygous type II heparin-binding site antithrombin deficiency. In addition to prompt diagnosis, of huge importance is the determination of inherited thrombophilia, as it significantly affects therapeutic treatment and indicates that long-term follow-up is mandatory.

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 Dublin (p.Val30Glu): a relatively common variant with moderate thrombosis risk of causing transient antithrombin deficiency

The key haemostatic role of antithrombin and the risk of thrombosis associated with its deficiency support that the low incidence of antithrombin deficiency among patients with thrombosis might be explained by underestimation of this disorder. It was our aim to identify mutations in SERPINC1 causing transient antithrombin deficiency. SERPINC1 was sequenced in 214 cases with a positive test for antithrombin deficiency, including 67 with no deficiency in the sample delivered to our laboratory. The p.Val30Glu mutation (Antithrombin Dublin) was identified in five out of these 67 cases, as well as in three out of 127 cases with other SERPINC1 mutations. Genotyping in 1593 patients with venous thrombosis and 2592 controls from two populations, revealed a low prevalent polymorphism (0.3 %) that moderately increased the risk of venous thrombosis (OR: 2.9; 95 % CI: 1.07-8.09; p= 0.03) and identified one homozygous patient with an early thrombotic event. Carriers had normal anti-FXa activity, and plasma antithrombin was not sensitive to heat stress or proteolytic cleavage. Analysis of one sample with transient deficit revealed a type I deficiency, without aberrant or increased latent forms. The recombinant variant, which lacked the two amino-terminal residues, had reduced secretion from HEK-EBNA cells, formed hyperstable disulphide-linked polymers, and had negligible activity. In conclusion, p.Val30Glu by affecting the cleavage of antithrombin's signal peptide, results in a mature protein lacking the N-terminal dipeptide with no functional consequences in normal conditions, but that increases the sensitivity to be folded intracellularly into polymers, facilitating transient antithrombin deficiency and the subsequent risk of thrombosis.

Founder effect is responsible for the p.Leu131Phe heparin-binding-site antithrombin mutation common in Hungary: phenotype analysis in a large cohort

BACKGROUND

Antithrombin (AT) is a key regulator of the coagulation. In type II deficiency, the heparin-binding-site defect (type II HBS) is considered to be relatively low thrombosis risk.

OBJECTIVES

Our aims were to search for SERPINC1 mutation(s) and to describe the clinical and laboratory phenotype of a large number of AT Budapest3 (ATBp3, p.Leu131Phe) carriers and confirm the presence of a founder effect.

PATIENTS/METHODS

AT-deficient patients were recruited and carriers of ATBp3, n = 102 (63 families) were selected. To investigate the founder effect, eight intragenic single nucleotide polymorphisms, a 5'-length dimorphism, and five microsatellite markers were detected. Clinical and laboratory data of the patients were collected and analyzed.

RESULTS

In AT deficiency, 16 different causative mutations were found, and the great majority of patients were of type II HBS subtype. Most of them (n = 102/118, 86.5%) carried the ATBp3 mutation. The ATBp3 mutant allele was associated with one single haplotype, while different haplotypes were detected in the case of normal allele. The anti-factor Xa-based AT activity assay that we used could detect all ATBp3 patients with high sensitivity in our cohort. ATBp3 homozygosity (n = 26) was associated with thrombosis at a young age and conferred a high thrombotic risk. Half of the heterozygotes (n = 41/76, 53.9%) also had venous and/or arterial thrombosis, and pregnancy complications were also recorded.

CONCLUSION

In Hungary, the founder mutation, ATBp3, is the most common AT deficiency. Our study is the first in which the clinical characterization of ATBp3 mutation was executed in a large population.

Dynamic properties of the native free antithrombin from molecular dynamics simulations: computational evidence for solvent- exposed Arg393 side chain

While antithrombin (AT) has small basal inhibitory activity, it reaches its full inhibitory potential against activated blood coagulation factors, FXa, FIXa, and FIIa (thrombin), via an allosteric and/or template (bridging) mechanism by the action of heparin, heparan sulfate, or heparin-mimetic pentasaccharides (PS). From the numerous X-ray structures available for different conformational states of AT, only indirect and incomplete conclusions can be drawn on the inherently dynamic properties of AT. As a typical example, the basal inhibitory activity of AT cannot be interpreted on the basis of "non-activated" free antithrombin X-ray structures since the Arg393 side chain, playing crucial role in antithrombin-proteinase interaction, is not exposed. In order to reveal the intrinsic dynamic properties and the reason of basal inhibitory activity of antithrombin, 2 μs molecular dynamics simulations were carried out on its native free-forms. It was shown from the simulation trajectories that the reactive center loop which is functioning as "bait" for proteases, even without any biasing potential can populate conformational state in which the Arg393 side chain is solvent exposed. It is revealed from the trajectory analysis that the peptide sequences correspond to the helix D extension, and new helix P formation can be featured with especially large root-mean-square fluctuations. Mutual information analyses of the trajectory showed remarkable (generalized) correlation between those regions of antithrombin which changed their conformations as the consequence of AT-PS complex formation. This suggests that allosteric information propagation pathways are present even in the non-activated native form of AT.

Toward a bioengineered heparin: challenges and strategies for metabolic engineering of mammalian cells

Heparin is the most widely used pharmaceutical to control blood coagulation in modern medicine. A health crisis that took place in 2008 led to a demand for production of heparin from non-animal sources. Since Chinese hamster ovary (CHO) cells are capable of producing heparan sulfate (HS), a related polysaccharide naturally, and heparin and HS share the same biosynthetic pathway, we hypothesized that heparin could be produced in CHO cells by metabolic engineering. We developed stable human N-deacetylase/N-sulfotransferase (NDST2) and mouse heparan sulfate 3-O-sulfotransferase 1 (Hs3st1) expressing cell lines based on the expression of endogenous enzymes in the HS/heparin pathways of CHO-S cells. Both activity assay and disaccharide analysis showed that engineered HS attained heparin-like characteristics but not identical to pharmaceutical heparin, suggesting that further balancing the expression of transgenes with the expression levels of endogenous enzymes involved in HS/heparin biosynthesis might be necessary.

Metabolic engineering of Chinese hamster ovary cells: towards a bioengineered heparin

Heparin is the most widely used pharmaceutical to control blood coagulation in modern medicine. A health crisis that took place in 2008 led to a demand for production of heparin from non-animal sources. Chinese hamster ovary (CHO) cells, commonly used mammalian host cells for production of foreign pharmaceutical proteins in the biopharmaceutical industry, are capable of producing heparan sulfate (HS), a related polysaccharide naturally. Since heparin and HS share the same biosynthetic pathway, we hypothesized that heparin could be produced in CHO cells by metabolic engineering. Based on the expression of endogenous enzymes in the HS/heparin pathways of CHO-S cells, human N-deacetylase/N-sulfotransferase (NDST2) and mouse heparan sulfate 3-O-sulfotransferase 1 (Hs3st1) genes were transfected sequentially into CHO host cells growing in suspension culture. Transfectants were screened using quantitative RT-PCR and Western blotting. Out of 120 clones expressing NDST2 and Hs3st1, 2 clones, Dual-3 and Dual-29, were selected for further analysis. An antithrombin III (ATIII) binding assay using flow cytometry, designed to recognize a key sugar structure characteristic of heparin, indicated that Hs3st1 transfection was capable of increasing ATIII binding. An anti-factor Xa assay, which affords a measure of anticoagulant activity, showed a significant increase in activity in the dual-expressing cell lines. Disaccharide analysis of the engineered HS showed a substantial increase in N-sulfo groups, but did not show a pattern consistent with pharmacological heparin, suggesting that further balancing the expression of transgenes with the expression levels of endogenous enzymes involved in HS/heparin biosynthesis might be necessary.

Thrombin as a multi-functional enzyme. Focus on in vitro and in vivo effects

Thrombin is the central protease in the coagulation cascade and one of the most extensively studied of all enzymes. In addition to its recognised role in the coagulation cascade and haemostasis, thrombin is known to have multiple pleiotropic effects, which mostly have been shown only in in vitro studies: it plays a role in inflammation and cellular proliferation and displays a mitogen activity on smooth muscle cells and endothelial cells, predominantly by activation of angiogenesis. In vivo , thrombin effects were examined in animal models of intravenous or intraarterial thrombin infusion. An extensive literature search regarding in vivo data showed that i) thrombin administered as a bolus causes microembolism, ii) thrombin infused slowly at steady-state conditions (up to 1.6 U/kg/min) leads to bleeds but not to intravascular clotting, iii) large quantity of thrombin infused at low rates (0.05 U/kg/min) does not have any measurable effect, and iv) thrombin increases vascular permeability leading to tissue damage. Although several decades of research on thrombin functions have provided a framework for understanding the biology of thrombin, animal and human studies with use of newer laboratory techniques are still needed to confirm the pleiotropic thrombin functions shown in in vitro studies.

Ultra-performance ion-pairing liquid chromatography with on-line electrospray ion trap mass spectrometry for heparin disaccharide analysis

A high-resolution method for the separation and analysis of disaccharides prepared from heparin and heparan sulfate (HS) using heparin lyases is described. Ultra-performance liquid chromatography in a reverse-phase ion-pairing mode efficiently separates eight heparin/HS disaccharides. The disaccharides can then be detected and quantified using electrospray ionization mass spectrometry. This method is particularly useful in the analysis of small amounts of biological samples, including cells, tissues, and biological fluids, because it provides high sensitivity without being subject to interference from proteins, peptides, and other sample impurities.