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PubMed1994

Interaction of heparin with synthetic antithrombin III peptide analogues.

Heparin-binding proteins may contain specific patterns of basic amino acids, called consensus sequences, that interact with heparin. Small peptides were synthesized that contained consensus sequences (i.e. FAKLNCRLYRKANKSSK) or disrupted consensus sequences (i.e. K136-->A) based on the known sequence of antithrombin III (amino acid residues 123-139). These peptides were then examined in both competitive and non-competitive binding experiments using bioassays, fluorescence spectroscopy, affinity chromatography and n.m.r. spectroscopy. Both the consensus and disrupted-consensus peptide bound to heparin. Peptides with consensus sequences bound specifically to the pentasaccharide antithrombin III-binding site within heparin. In contrast, peptides with disrupted consensus sequences showed no specificity, binding to any sequence within heparin. Proton nuclear Overhauser enhancement spectroscopy demonstrated the proximity of leucine and tyrosine (within the consensus sequence) to the N-acetyl moiety found primarily within the pentasaccharide antithrombin III-binding site of heparin. This experiment confirmed the findings of the other techniques and helped to localize the binding sites in both peptides and heparin. A model is proposed for both specific and non-specific heparin interaction with consensus and disrupted-consensus peptides.

Amino Acid Sequence↗
PubMed1995

Effects of aging on the synthesis of antithrombin-binding sites on heparin chains and heparan sulphate chains in the rat.

[35S]Heparin proteoglycans were isolated from the skins and peritoneal mast cells of male rats aged 2 to 22 months. Their [35S]heparin chains were separated on antithrombin-agarose into fractions with high and low affinities for antithrombin. In skin, the proportion of 35S-labelled high-affinity heparin chains declined from 23% at 2 months to 8% at 12 months and did not change significantly between 12 and 22 months. In peritoneal mast cells, the proportion of 35S-labelled high-affinity heparin chains increased from 14% at 2 months to 21% at 4 months and then did not vary significantly until 15 months of age. By 21 months a consistent and significant decline to 8% occurred. The structures of high-affinity heparin proteoglycans did not change with age. Their decreased proportions, without change in their structure, may indicate that they are produced by a unique subset of mast cells, the proportion of which declines with age. [35S]heparan sulphate chains were isolated from skins and brains of rats in the same age range and fractionated on antithrombin-agarose. There were no significant variations in the proportions of 35S-labelled high-affinity heparan sulphate chains in skin (10%) or brain (24%) between 4 and 22 months of age.

Aging↗
PubMed2003

The long-term within- and between-laboratory variability for assay of antithrombin, and proteins C and S: results derived from the external quality assessment program for thrombophilia screening of the ECAT Foundation.

A stable laboratory performance is important for comparability and transferability of laboratory data both within and between laboratories. The lack of a reference system within hemostasis hampers laboratories in establishing their laboratory performance over a prolonged period of time. Therefore, based on data from an external quality assessment program, we evaluated the between laboratory variation (CVBETWEEN) and the long-term within-laboratory variation (LCVa) for antithrombin, and proteins C and S. We evaluated the CVBETWEEN for the period 1996-2001, including the results of 64-240 laboratories from 23 different surveys (protein S activity 15 surveys). We observed a quite high CVBETWEEN and a broad range for each analyte. The CVBETWEEN was significantly higher for antithrombin and protein S for samples with low levels similar to heterozygous deficiencies. We also evaluated the LCVa, including the results of 136 laboratories. The lowest LCVa[median and 95% content interval (CI)] was observed for antithrombin (7.6%; 3.6-35.5%), intermediate values for protein C activity and antigen (8.6%; 3.5-25.3% and 10.8%; 4.8-33.1%, respectively) and highest values for the protein S variables (13.4%; 6.4-50.6% for total protein S antigen, 14.1%; 6.5-79.1% for free protein S antigen and 17.2%; 7.2-84.3% for protein S activity). We concluded that the main reason for the high CVBETWEEN is the long-term within-laboratory variability. Application of linear regression on data of an external quality assessment program is a useful model to demonstrate per analyte per laboratory the long-term variability (LCVa). It is concluded that improvement of the long-term within-laboratory test performance is the first priority in hemostasis to yield important improvements in the comparability and transferability of laboratory data.

Antithrombin III↗
PubMed1999

Uptake of heparin cofactor II and antithrombin into the aorta wall after a deendothelializing injury in vivo: comparison with the behaviors of prothrombin and fibrinogen.

The initiation of a denuding injury to the vascular endothelium rapidly leads to a deposition of platelets and fibrin at the site of injury. We have measured previously the responses of rabbit fibrinogen, prothrombin, and antithrombin to a deendothelializing balloon-catheter injury to the rabbit aorta in vivo. In this study, rabbit iodine 125-labeled HCII and iodine 125-labeled AT were coinjected intravenously into anesthetized rabbits 5 minutes before deendothelialization of the thoracic aorta. The rabbit was exsanguinated at 5 to 60 minutes after injury, the aorta was excised, and the accumulation of each radiolabeled protein in each layer of aorta wall was determined relative to the concentration of the respective native protein in circulating blood at exsanguination. The maximum flux rates into the aorta wall (i.e., platelet layer and intima-media) in the first minute after injury were calculated from the uptake data; approximately 2.8 molecules of AT accumulated for each HCII molecule. By comparison with previous measurements, the maximum flux rate of AT was similar to that of prothrombin. Further, the molar ratio of accumulated prothrombin/AT + HCII) in the aorta wall was 0.75. Detergent extracts of the injured aorta intima-media contained unreacted HCII and HCII complexes; the uninjured aorta contained only unreacted HCII. By contrast, high molecular weight AT complexes and unreacted AT were extracted from the uninjured, and in greater quantity from the injured, aorta wall. We conclude that, of the plasma antithrombins, AT accumulated more rapidly than HCII in vivo and appeared to be the more active inhibitor at the site of vascular injury. HCII may play a relatively minor role as an antithrombin and possibly only after injury.

Animals↗
PubMed1983

Mutation of antitrypsin to antithrombin. alpha 1-antitrypsin Pittsburgh (358 Met leads to Arg), a fatal bleeding disorder.

Our previous studies predicted a functional relationship between the plasma proteins alpha 1-antitrypsin and antithrombin III. To elucidate this relationship we investigated the plasma of a 14-year-old boy who had died from an episodic bleeding disorder. A variant alpha 1-antitrypsin was identified in which the methionine at position 358 had been replaced by an arginine. This had converted the alpha 1-antitrypsin from its normal function as an inhibitor of elastase to that of an inhibitor of thrombin. This finding indicates that the reactive center of alpha 1-antitrypsin is methionine 358, which acts as a bait for elastase, just as the normal reactive center of antithrombin III is arginine 393, which acts as a bait for thrombin. The independence of the new thrombin inhibitor from heparin control explains the bleeding disorder; it also indicates that heparin normally acts directly on antithrombin III, revealing its inherent inhibitory activity. The episodic nature of the bleeding was a consequence of the mutant protein's being an acute-phase reactant, the level of which increased several-fold after trauma.

Adolescent↗
PubMed1980

Evidence for a 3-O-sulfated D-glucosamine residue in the antithrombin-binding sequence of heparin.

An octasaccharide with high affinity for antithrombin was isolated after partial deaminative cleavage of heparin with nitrous acid. After conversion of the 2,5-anhydro-D-mannose end group to anhydro[1-3H]mannitol, labeled pentasaccharide was released from the octasaccharide by periodate-alkali treatment. Incubation of the pentasaccharide with a recently discovered 3,O-sulfatase from human urine resulted in desulfation, suggesting the occurrence of a 3-sulfate group on the terminal glucosamine residue. The same glucosamine residue was recovered as a 2,5-anhydro[1-3H]mannitol derivative by a procedure involving deamination of the octasaccharide with nitrous acid, reduction of the products with sodium boro[3H]hydride, isolation of 3H-labeled tetrasaccharide by gel chromatography, and release of the labeled end-group by periodate-alkali treatment. Paper electrophoresis indicated disulfated anhydro[3H]mannitol, presumably sulfated at C3 and C6, as a major component, along with smaller amounts of monosulfated (presumably 3-sulfated) anhydro[3H]mannitol. Similar treatment of an analogous tetrasaccharide derived from heparin with low affinity for antithrombin failed to produce any disulfated anhydromannitol. These results suggest that 3-sulfated glucosamine is a unique component of high-affinity heparin, located at a specific position in the antithrombin-binding sequence of the molecule.

Animals↗
PubMed1984

Evaluation of critical groups required for the binding of heparin to antithrombin.

We have examined the quantitative importance of various monosaccharide residues of an octasaccharide domain of heparin that are responsible for the binding of this oligosaccharide to antithrombin. Different fragments of the octasaccharide were prepared by enzymatic digestion and the avidities of these oligosaccharides for antithrombin were determined by equilibrium dialysis. The data show that the non-reducing-end and the reducing-end tetrasaccharides contribute equally to the binding energy of the octasaccharide. The O6-sulfate group of the N-acetyl glucosamine moiety within the nonreducing-end tetrasaccharide is responsible for approximately equal to 45% of the binding energy of the octasaccharide. Neither the two non-sulfated uronic acid groups that flank this residue nor the N-sulfated glucosamine residue on the reducing end of this tetrasaccharide sequence that bears the unique O3-sulfate substituent contribute significantly to the binding energy of the octasaccharide. We suggest that the lack of sulfation of the two uronic acid moieties within the nonreducing-end tetrasaccharide may be required to permit the N-acetyl glucosamine O6-sulfate group to interact with a specific region on the antithrombin molecule. However, we cannot exclude the possibility that the O3-sulfate group plays an important role in orienting this O6-sulfate group within the nonreducing-end tetrasaccharide.

Animals↗
PubMed1988

Interruption of acute platelet-dependent thrombosis by the synthetic antithrombin D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone.

Since the antithrombin action of heparin fails to interrupt arterial thrombosis, a mediating role for thrombin (EC 3.4.21.5) in the formation of high-shear platelet-dependent thrombus has been unproven. To determine whether thrombin is important in acute arterial thrombus formation and to assess the therapeutic potential of inhibiting its action, the effects of the synthetic covalent antithrombin D-phenylalanyl-L-prolyl-L-arginyl chloromethyl ketone (FPRCH2Cl) on arterial-flow vascular graft thrombosis and occlusion have been studied in a nonhuman primate model. Continuous intravenous infusion of FPRCH2Cl (100 nmol/kg per min) into vascular graft-bearing baboons (Papio anubis) abolished (i) vascular graft 111In-platelet deposition, (ii) vascular graft occlusion, (iii) thrombus-associated in vivo release of platelet-specific proteins and fibrinopeptides, (iv) platelet hemostatic plug formation, (v) thrombin-induced platelet aggregation ex vivo, and (vi) thrombin-induced blood clotting. The effects of FPRCH2Cl largely disappeared within 15 min after the infusion had been discontinued. FPRCH2Cl produced no detectable cardiovascular or other acute side effects. In contrast, sustained comparably anticoagulating levels of heparin had no effect upon 111In-platelet graft deposition, graft occlusion, platelet function as measured by the bleeding time, platelet aggregation ex vivo, or release of platelet-specific proteins in vivo. We conclude that thrombin is the principal mediator of platelet-dependent hemostatic plug formation and of the formation of platelet-dependent high-flow acute graft thrombosis and occlusion. Moreover, FPRCH2Cl or other synthetic antithrombins may provide effective antithrombotic therapy for both arterial and venous thrombosis by simultaneously inhibiting platelet activation and fibrin formation.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Exosites 1 and 2 are essential for protection of fibrin-bound thrombin from heparin-catalyzed inhibition by antithrombin and heparin cofactor II.

Assembly of ternary thrombin-heparin-fibrin complexes, formed when fibrin binds to exosite 1 on thrombin and fibrin-bound heparin binds to exosite 2, produces a 58- and 247-fold reduction in the heparin-catalyzed rate of thrombin inhibition by antithrombin and heparin cofactor II, respectively. The greater reduction for heparin cofactor II reflects its requirement for access to exosite 1 during the inhibitory process. Protection from inhibition by antithrombin and heparin cofactor II requires ligation of both exosites 1 and 2 because minimal protection is seen when exosite 1 variants (gamma-thrombin and thrombin Quick 1) or an exosite 2 variant (Arg93 --> Ala, Arg97 --> Ala, and Arg101 --> Ala thrombin) is substituted for thrombin. Likewise, the rate of thrombin inhibition by the heparin-independent inhibitor, alpha1-antitrypsin Met358 --> Arg, is decreased less than 2-fold in the presence of soluble fibrin and heparin. In contrast, thrombin is protected from inhibition by a covalent antithrombin-heparin complex, suggesting that access of heparin to exosite 2 of thrombin is hampered when ternary complex formation occurs. These results reveal the importance of exosites 1 and 2 of thrombin in assembly of the ternary complex and the subsequent protection of thrombin from inhibition by heparin-catalyzed inhibitors.

Anticoagulants↗
PubMed2004

Significance of antithrombin III, protein C and protein S in acute mesenteric ischemia patients.

It is well established that a condition of hypercoagulation due to deficiencies of antithrombin III, protein C and protein S may result in thrombo-embolism. To evaluate the possibility of hypercoagulation in acute mesenteric ischemia (AMI); clinical features, ECG changes, drug history, the length of intestine remaining after the resection and mortality of 15 consecutive patients were recorded and plasma levels of antithrombin III, Protein C and protein S were measured. Antihypertensive, antidiabetic and digitalis were the main drugs used by the patients. Atrial fibrillation was the main ECG finding (60%). AMI was attributed to thrombo-embolic phenomena because of atrial fibrillation in these patients. Levels of antithrombin III and protein S were lower in patients without atrial fibrillation compared to those with the condition (mean values 16.18 vs. 18.04 and 87.33 vs. 94.22 respectively) but the difference was not statistically significant. Levels of Protein C were lower and the length of intestine remaining after resection was shorter in patients without, compared to those with, atrial fibrillation (mean values 77.00 vs. 88.66, and 52.5 cm vs. 86.11 cm respectively). The difference was statistically significant (p < 0.05). Postoperative mortality rate was 33.3% (5 patients) and the length of intestine remaining after resection was the main determining factor in the prognosis of the patients. We conclude that a condition of hypercoagulation due to a deficiency of protein C has a significant role in the pathogenesis of AMI especially in patients without atrial fibrillation.

Acute Disease↗
PubMed1988

Antithrombin III and protein C in stable angina pectoris--influence of dietary supplementation with polyunsaturated fatty acids.

The effect on plasma antithrombin III (AT III) and protein C on a supplement with polyunsaturated fatty acids (PUFA's) was investigated in a double-blind study in 36 patients with stable angina pectoris. All participants were given a supplement to their normal diets of vegetable oil (4.8 g n-6 PUFA's) for 4 weeks and were then randomized to the same oil or to fish oil (4.8 g n-3 PUFA's) for 12 weeks. Both oil supplements resulted in a statistically significant decrease in AT III activity, but there were no differences between the two different types of PUFA's. Antithrombin III antigen, protein C antigen or activity did not change significantly after either oil supplement. The background and significance for the decrease in antithrombin III activity induced by n-3 and n-6 PUFA's in patients with ischaemic heart disease is unknown.

Aged↗
PubMed1998

Thrombin-antithrombin III and D-dimer plasma levels in patients with benign or malignant ovarian tumours.

In 50 patients with benign ovarian tumours, 39 malignant ovarian carcinoma patients and 39 age-matched healthy women, plasma levels of thrombin-antithrombin III complex and D-dimer were determined as well as CA 125. The coagulation activation marker thrombin-antithrombin III complex and D-dimer levels were elevated in the malignant group compared to the benign and control groups. The results suggest that coagulation and fibrinolysis must play a prominent role in ovarian cancer. Moreover, D-dimer and thrombin-antithrombin III were equally useful as CA 125 for the discrimination of patients with benign or malignant ovarian tumours as evidenced by receiver operating and likelihood ratio calculations.

Adenocarcinoma↗
PubMed2004

Comparison of mechanisms after post-hoc analyses of the drotrecogin alfa (activated) and antithrombin III trials in severe sepsis.

Severe sepsis is a heterogeneous syndrome in a heterogeneous population. The current scheme of classification does not enable distinction between systemic inflammatory response syndrome, sepsis and severe sepsis on the basis of the underlying biochemical, immunological and abnormal coagulation features. Planning, implementation and assessment of results of intervention studies on severe sepsis thus present enormous challenges. Two such studies were published in the year 2001. The study investigating the drug drotrecogin alfa (activated) was positive in the day-28 mortality endpoint; however, post-hoc analyses have raised controversies regarding the manner in which the study was carried out, the consistency of results presented, and the suggested mechanism of action. On the other hand, the KyberSept study that investigated antithrombin III reported negative results for the day-28 mortality endpoint, despite correct performance of the study. This, however, was not interpreted to mean proof of therapeutic inefficacy of administering antithrombin III and post-hoc analyses raise the suspicion of an undesirable drug interaction between antithrombin III and heparin. Apparently, neither of the sepsis studies meets the criteria which lie at the basis of critical assessment of the success or failure of clinical trials that could more significantly affect clinical treatment decisions.

Antithrombin III↗
PubMed1983

The behavior of antithrombin III, alpha 2 macroglobulin, and alpha 1 antitrypsin during cardiopulmonary bypass.

We serially measured concentrations of three protease inhibitors, antithrombin III, alpha 2 macroglobulin, and alpha 1 antitrypsin in patients with coronary artery and valvular heart disease during extracorporeal circulation. Assays for immunoreactive antiproteases and for functional antithrombin III were performed on plasma samples obtained at selected intervals before, during, and after cardiopulmonary bypass. Significant reductions of all protease inhibitors occurred at some time during cardiopulmonary bypass, although patterns of change were dissimilar for the two patient groups. A return toward preoperative levels was observed after cardiopulmonary bypass was discontinued, but antithrombin III remained diminished in the patients with coronary artery disease. The acute serial changes in this group of alpha globulins is evidence of their participation during the dynamic stress of extracorporeal circulation. Their timely intervention as serine protease antagonists deters sustained thrombogenesis and fibrinolysis during cardiopulmonary bypass.

Adult↗
PubMed1982

Cloning and expression of the cDNA for human antithrombin III.

A partial cDNA clone for human antithrombin III (ATIII) was obtained by screening a cDNA library prepared from size fractionated liver RNA with a pool of eight 16-base long synthetic DNA fragments whose sequence was determined from protein sequence data. A fragment of the partial cDNA clone was used to enrich RNA for ATIII messages, and cDNA clones encoding the entire ATIII structural gene were identified. The complete nucleotide and predicted amino acid sequences of human ATIII and its 32 residue signal peptide are reported, and provide further opportunity to compare the ATIII primary structure with corresponding regions from homologous proteins, alpha 1-antitrypsin and ovalbumin. Plasmids in which the structural genes for mature and pre-ATIII were linked to the E. coli trp promoter-operator support the synthesis of human antithrombin III and pre-antithrombin III in bacteria.

Amino Acid Sequence↗
PubMed1990

Hemostatic variables in Japanese and Caucasian men. Tissue plasminogen activator, antithrombin III, and protein C and their relations to coronary risk factors.

Mortality rates of coronary heart disease are much lower in Japan than in the United States. The authors' previous report on coagulation factors showed that population levels of plasma fibrinogen and factor VII activity parallel this mortality difference. To investigate other hemostatic variables, the authors assessed indicators of fibrinolytic activity (tissue plasminogen activator antigen) and coagulation inhibition (antithrombin III activity and protein C) in 136 men aged 34-55 years in four different samples: rural Japanese, urban Japanese, Japanese Americans, and Caucasian Americans. Mean tissue plasminogen activator antigen was higher in Caucasians and Japanese Americans than in rural and urban Japanese (p less than 0.01), while a contrasting trend in mean antithrombin III activity was suggested (p = 0.10). No significant differences were observed in mean levels of protein C. After controlling for known coronary risk factors, mean levels of tissue plasminogen activator antigen remained significantly different across the four samples (p less than 0.01); mean antithrombin III activity was not different (p = 0.23). Population differences in tissue plasminogen activator antigen parallel the coronary heart disease mortality difference between Japan and the United States. Although no definite evidence is available showing that tissue plasminogen activator antigen is a risk factor for coronary heart disease, the present study suggests a positive ecologic association between this hemostatic factor and coronary heart disease mortality.

Adult↗
PubMed1990

Generation of affinity for antithrombin III by supplemental sulfation of heparin species with low affinity for the protein.

The tributylammonium salt of a porcine heparin subfraction with low affinity for antithrombin III (Mr 7,500-18,000; anti-clotting activity, 7 USP units/mg), having degrees of sulfate substitution at D-glucosamine and L-iduronic acid residues of GlcNS 0.786, GlcN6s 0.628, and IdoA2s 0.682 mol, was reacted with 10 or 20 mol of pyridine-sulfur trioxide per mol equiv. of available hydroxyl groups in N,N-dimethylformamide at -10 degrees C for 1 h. Both chemical and NMR spectroscopic analyses revealed that sulfation proceeded exclusively at HO-6 in D-glucosamine and HO-2 in L-iduronic acid residues, according to the amount of the sulfating reagent used (GlcNS: 0.825, 0.830; GlcN6s: 0.872, 0.928; IdoA2s: 0.687, 0.749 mol, respectively). Affinity chromatography of the sulfated products on antithrombin III-Sepharose gel indicated that the polysaccharide acquired some affinity for the protein following the sulfation, as shown by the increase in the proportion of the high-affinity heparin fraction (%) from 1.1 to 6.7. Biological examination of these products indicated that sulfation at natural positions along with the polysaccharide chain resulted in significant increases in all the activities (blood anti-clotting, anti-Factor IIa, and anti-Factor Xa), and in the strength of intrinsic fluorescence of antithrombin III.

Animals↗