Antithrombin 3, antifactor Xa and heparin

Synthesis and Anticoagulant Properties of a Novel Heparinoid N-Sulfate-Bearing Vinylpolymer

A novel heparinoid polymer was prepared with an N-sulfate side chain group by sulfation of poly( N-vinylacetamide-co-vinylamine) [poly(NVA-co-VAm)] which was obtained by the partial hydrolysis of poly( N-vinylacetamide) [poly(NVA)]. The hydrolysis of poly(NVA) was controlled by reaction time and temperature and the sulfation of poly(NVA-co-VAm) was performed with chlorosulfonic acid. Poly( N-vinylacetamide-co-vinylamine-co-vinylsulfamic acid) [poly(NVA-co-VAm-co-VSA)] was confirmed by means of IR spectroscopy, and the degree of sulfation of poly(NVA-co-VAm-co-VSA) was estimated by elemental analysis. The anticoagulant properties of poly(NVA-co-VAm-co-VSA) were evaluated using the Lee-White clotting test and activated partial thromboplastin time (APTT) test. The human whole blood clotting time in the presence of poly(NVA-co-VAm-co-VSA) was prolonged compared with poly(NVA) and poly(NVA-co-VAm). The clotting time was prolonged with increased N-sulfate groups on the polymer. APTT tests of the polymer were also prolonged with N-sulfate increases. The results suggest that the N-sulfate components on the polymer can endow anticoagulant activity to synthetic polymers.

Activated F IX concentrate (FEIBA) used in the treatment of haemophilic patients with antibody to F VIII

Bleeding episodes in five haemophiliacs with antibody to F VIII were treated by activated F IX concentrate (FEIBA). Relief of pain and haemostasis in affected muscles and joints were recorded in each case. One patient developed a mild attack of disseminated intravascular coagulation with an uneventful recovery. A substantial rise in natural inhibitors of coagulation was seen in two patients, and all but one experienced a rise in F VIII antibody titer.

Mechanisms of antithrombin polymerisation and heparin activation probed by the insertion of synthetic reactive loop peptides

Incubation of antithrombin with a series of synthetic reactive loop peptides showed that 6-mer and 7-mer peptides, P14-P9 and P14-P8 of antithrombin respectively, induced loop-sheet polymerisation and binary complex formation. These peptides are likely to anneal to the upper part of the dominant A-sheet, favouring sheet opening and allowing insertion of a second reactive loop in the lower part of the A-sheet to form polymers. The insertion of longer peptides filled the A-sheet beyond the P7 position and prevented polymerisation. Heparinised antithrombin was more resistant to polymerisation and peptide insertion, indicating that heparin induces a conformational change that closes the A-sheet and expels the reactive loop.

In vivo evaluation of DX-9065a, a synthetic factor Xa inhibitor, in experimental vein graft

An in vivo effect of a novel synthetic Xa inhibitor, DX-9065a, was evaluated in a highly thrombogenic venous graft model. A woven Tetron tube graft was interposed in the inferior vena cava of rabbits. All the grafts were completely occluded within 5 hours after a bolus injection of heparin (50 U/kg) given just prior to the grafting. The following agents were continuously given to the respective group of rabbits for 2 h after the bolus injection of heparin; heparin (50 U/kg/h, UFH-group), DX-9065a (0.05 mg/kg/h, DX-group) and argatroban (32 microG/kg/h, MD-group). During a 5-h observation period, the anti-Xa activity in circulating blood between the UFH- and DX-group and the anti-thrombin activity between the UFH- and MD-group were not significantly different. The graft patency in the DX-group (4/4) and MD-group (4/4) was significantly better than that in the UFH-group (3/10). Ultrastructural analysis of the luminal surface of the harvested graft by scanning electron microscopy revealed the reduced formation of fibrin networks entrapping erythrocytes in the DX- and MD-group in comparison with the patent UFH-group. In conclusion, a novel synthetic Xa inhibitor DX-9065a exerts a potent in vivo antithrombotic effect, which was comparable with argatroban, a synthetic thrombin inhibitor.

Antithrombin and its inherited deficiencies

Human antithrombin is the major inhibitor of the coagulation serine proteases accounting for approximately 80% of the thrombin inhibitory activity of plasma. It is a member of the serpin family of serine protease inhibitors and in common with some other members of this family it undergoes a dramatic increase in its inhibitory activity in the presence of heparin and other sulphated glycosaminoglycans. Two functional domains in antithrombin are recognised, the reactive site domain which interacts with the active site serine residue of the protease and the heparin binding domain. The gene for antithrombin has been cloned and its entire nucleotide sequence determined. A deficiency or functional abnormality of antithrombin may result in an increased risk of thromboembolic disease. Such deficiencies are estimated to affect as many as 1:300 of the general population and 3 to 5% of patients with thrombotic disease. On the basis of functional and immunological antithrombin assays, antithrombin deficiency may be subdivided into Types I and II. Type I disease is due to a wide variety of heterogeneous DNA mutations whilst in Type II disease missense mutations leading to single amino acid substitutions have been identified in all cases. Clinically, Type I antithrombin deficiency is associated with recurrent thromboembolic disease whereas in Type II deficiency the risk of thrombosis is closely related to the position of the mutation within the protein. Thus, heterozygotes with mutations within the heparin binding domain of antithrombin have a relatively low risk of thrombosis compared to those with mutations at or close to the reactive site of the molecule.

Evaluation of hemostatic function following Norplant-2 rods removal

Women using the Norplant-2 rod system in Singapore have been shown to have a change in their hemostatic function. There is a decrease in vitamin K dependent factors II, VII and a tendency toward lowered fibrinolytic activity after use of Norplant-2 rods. There was also an increase in platelet number and accelerated-platelet aggregation. These changes are similar to those seen with the Norplant six-capsule system and it would appear that both systems do not activate the coagulation system or enhance a state of hypercoagulation. On removal of the Norplant-2 rods at the end of 5 years, the significant changes seen in hemoglobin function observed with Norplant-2 rod use remained.

Evaluation of hemostatic function following Norplant implant removal

Norplant implant use in Singapore showed a decrease in vitamin K-dependent Factors II, V, VII and reduction in fibrinolytic activity at the end of 5 years of use. Increased platelet numbers and accelerated platelet aggregation were also found throughout the 5 years of Norplant use. It thus appears that unlike the combined pill, prolonged Norplant use does not activate the coagulation system and does not enhance a state of hypercoagulation. On removal of the Norplant implants at the end of 5 years, the significant changes seen in hemostatic function observed with Norplant use remained.

Haemostatic abnormalities in African swine fever a comparison of two virus strains of different virulence (Dominican Republic '78 and Malta '78)

African swine fever (ASF) virus strains cause haemorrhage by producing a variety of defects, which vary in severity from strain to strain. To distinguish the main haemostatic defects leading to haemorrhage, two groups of pigs were infected with moderately virulent (Dominican Republic '78) and less virulent (Malta '78) ASF virus strains. Mortality rate and severity of clinical observations were greater in pigs infected with DR '78 virus compared with pigs infected with Malta '78 virus. The animals became febrile from day 3 to 4 onwards at a time when the viraemia was high (10(7) to 10(8) HAD50/ml). No difference was found during the period observed in their pattern of viraemia or pyrexia. Thrombocytopenia developed in both groups but with different kinetics, suggesting two different mechanisms of sequestration of platelets. When coagulation tests were performed, significant abnormalities were found, including evidence for disseminated intravascular coagulation. These abnormalities were much less pronounced in the group infected with Malta '78. Antithrombin III activity did not change significantly in either group. Decreased plasminogen activity was found in the early phase of disease in DR '78 infected pigs. These results indicate that when haemorrhage does occur in DR '78 infected pigs, it is a consequence of more pronounced degrees of haemostatic impairment probably due to a marked endothelial injury and/or generation of procoagulant activity.

Purification and characterization of an antithrombin III inactivating enzyme from the venom of the African night adder (Causus rhombeatus)

A serine proteinase was isolated from the venom of the night adder (Causus rhombeatus) by fast protein liquid chromatography (anion-exchange, gel filtration and hydrophobic interaction). The protein (termed CR-serpinase) had an estimated mol. wt of 45,500 as determined by SDS-PAGE, pI of 4.7 and a carbohydrate content of 18.9%. Incubation of CR-serpinase with purified human antithrombin III at a molar ratio of 1:66 resulted in a loss of more than 90% of the initial AT III activity within 10 min. The reaction was dependent on heparin. In SDS-PAGE inactivation of human antithrombin III was correlated with the occurrence of two cleavage products. The cleavage site in the antithrombin III molecule was determined to be Arg 393-Ser 394 by amino-terminal sequencing. CR-Serpinase had no thrombin-like activity since no fibrinogen conversion was induced and had no procoagulant activity. CR-Serpinase activity was not inhibited by antithrombin III-heparin and was not decreased by a 10-min preincubation in normal human plasma. Inactivation of antithrombin III by CR-serpinase appeared to be very specific.

Effect of Norplant-2 rods on haemostatic function

A longitudinal study on one-hundred Singaporean women using Norplant-2 rod implant for contraception and their effects on the haemostatic function was carried out. There was a decrease in vitamin K-dependent Factors II, VII and a tendency towards lowered fibrinolytic activity after prolong use of Norplant-2 rods. The results indicate that the Norplant-2 rod implant system does not contribute towards hypercoagulable state but increased platelets and accelerated platelet aggregation observed will require further study to ascertain whether there is a concomitant increase in platelet activation.

Effect of long-term use of Norplant implants on haemostatic function

This study describes the effects of Norplant on haemostatic function after 5 years of use in 97 women. There was a decrease in vitamin-K dependent Factors II, V, VII and reduction in fibrinolytic activity at 2 and 4 years of use. Increased platelet numbers and accelerated platelet aggregation were found throughout the 5 years of Norplant use, whilst raised alpha 2-Macroglobulin (a2-M) and antithrombin III (ATIII) antigen level were observed for up to 4 years of use. Prolonged Norplant use does not appear to activate the coagulation system and does not enhance a state of hypercoagulation.

Oral contraceptives and antithrombin III: variations by dosage and ABO blood group

A randomized clinical trial of oral contraceptives evaluated 67 women on a regimen of 50 micrograms ethinyl estradiol and 1.0 mg norethindrone, 61 women on a regimen of 35 micrograms ethinyl estradiol and 1.0 mg norethindrone, and 64 women on a regimen of 35 micrograms ethinyl estradiol and 0.5 mg norethindrone. ABO blood group type was determined in all women. At baseline and at 3, 6, and 9 months, plasma antithrombin III levels, by both an immunologic and an activity method, and selected plasma levels of the contraceptive steroids were measured. Antithrombin III levels for all oral contraceptive groups combined decreased from baseline by 19.7% and 28.8% for the immunologic and activity methods, respectively. Analysis of interrelationships among antithrombin III by activity method, oral contraceptive type, and ABO blood group showed larger declines in antithrombin III for type O women using the highest estrogen dose preparation (31.6%) and for non-type O women using the lowest progestin dose preparation (38.9%). Plasma levels of contraceptive steroids also were related to changes in the most extreme levels of antithrombin III.

Thrombocytopenia and leptospirosis

The present study has intended to contribute to the elucidation of the pathogenic mechanisms, involved in the thrombocytopenia and in the bleeding diathesis seen in the course of Leptospirosis. The group of cases included in the present prospective study consisted of 30 patients with Leptospirosis, admitted to the Infectious and Parasitic Diseases Ward, Hospital das Clínicas, Faculty of Medicine, University of São Paulo. The following possible mechanisms of thrombocytopenia have been considered and therefore investigated: platelet consumption, due to disseminated intravascular coagulation; immune-mediated platelet destruction, due to platelet-associated antibodies and an inhibited platelet production in the bone marrow. Thrombocytopenia occurred in 86.6% of 30 patients and did not seem to be immune-mediated by platelet-associated antibodies. Furthermore it did not seem to be due to a disseminated intravascular coagulation consumption. Although there was a statistically-significant correlation between bone marrow platelet production and platelet counts we think that the static microscopic examination of a bone marrow aspirate cannot accurately depict the dynamic mechanisms of platelet production when these cells are being consumed in peripheral blood. Vasculitis should be considered as the most important factor for the pathogenesis of the bleeding disturbances in Leptospirosis. However, we believe that thrombocytopenia, uremia and coagulation disorders, individually or as a group, should be included among the contributing factors that lead to and worsen bleeding episodes, which represent the leading cause of death in this disease.

Mechanism of heparin action

Heparin catalysis of clotting proteinase inactivation occurs most efficiently through the reaction of the proteinase with the antithrombin-heparin complex. The efficiency of a heparin molecule in this reaction depends on the presence of a specific pentasaccharide sequence in it, and its molecular weight. The mechanism by which such high affinity heparin acts when antithrombin III is the inhibitor is promotion of the formation of an intermediate proteinase-heparin-antithrombin complex. Heparin promotion of thrombin inactivation by heparin cofactor II may occur by a similar mechanism. The requirement for a specific oligosaccharide sequence within the heparin molecule does not, however, exist for heparin cofactor II. Binding of heparin to both thrombin and antithrombin III interferes with thrombin inactivation. This binding is very dependent on the ionic strength of the reaction mixture and may explain some of the discordant results and interpretations from early studies on the mechanism of heparin action. Low ionic strength in in vitro reactions also results in cleavage of antithrombin III by thrombin in the presence of heparin and effectively converts antithrombin III from an inhibitor to a substrate.

A three-year evaluation of hemostatic function in Singaporean Norplant-2 rod acceptors

A longitudinal study of hemostatic function was carried out on 100 Singaporean acceptors using Norplant-2 rods for contraception. The results at the end of three years indicate a possible increased predisposition to thrombosis, as evidenced by significant increases in platelet count and aggregability. The prothrombin time (PT) and activated partial thromboplastin time (APTT) continued to remain shortened at the end of three years of use. There was also a general fall in most of the vitamin K coagulation factors. There is thus still an indication of a possible enhanced potential for hypercoagulation at the end of three years of Norplant-2 rod use.

Antithrombin-III assay without influence of heparin cofactor II

A new biological method for the assay of plasma antithrombin-III (AT-III) activity was developed without influence from heparin cofactor II (HC-II). AT-III deficient plasma is used as a substrate and diluted prothrombin time reagent as a reaction trigger for the specific assay of AT-III. The AT-III deficient plasma is prepared by passage of plasma through a heparin-agarose column. In the presence of heparin, AT-III in the sample shows concentration dependent anticoagulant activity and calibration curve is linear on semi-logarithmic graph paper. The results of reproducibility, recoveries and correlation studies with a chromogenic assay indicate that this biological method is reliable and suitable for routine use in clinical laboratories. Influence of HC-II is minimal. The method provides several advantages over those of chromogenic substrate and fibrinogen.

A three-year evaluation of hemostatic function in Singaporean Norplant acceptors

In a longitudinal study involving 100 Singaporean women, results indicate that the acceptors persist in having a possibly increased predisposition to thrombosis, as evidenced by a significant increase in platelet count and aggregability. Furthermore, the shortened prothrombin time and activated partial thromboplastin time, together with changes in vitamin K factors, still indicate the possible enhanced potential for hypercoagulation.

Effects of three types of combined O.C. pills on blood coagulation, fibrinolysis and platelet function

The results of a prospective longitudinal controlled study comparing the coagulation effects of a standard low-dose combined oral contraceptive (Microgynon 30), a desogestrel-containing pill (Marvelon) and a triphasic preparation (Triquilar) after one year's treatment in ethnic Chinese women is presented in this paper. In general the changes in coagulation parameters are similar to those seen in Caucasian women. The rise in Factor VII levels seen at 6 and 12 months in Marvelon users was not present to a significant degree in the other pill users. Antithrombin III levels remained unchanged in Microgynon and Marvelon users but with Triquilar there was a significant fall at 6 and 12 months of use. Whether these differences have any clinical relevance in the local Chinese population with low incidence of thromboembolism remains to be seen.

Two-year follow-up of changes in clinical chemistry in Singaporean Norplant acceptors: haemostatic changes

A longitudinal study of coagulation parameters was carried out on 100 Singaporean acceptors using Norplant for contraceptive purposes. At the end of 2 years of use, results from this ongoing study indicate that these acceptors continue to have an increased predisposition to thrombosis as evidenced by significant increases in platelet count and aggregability. The shortened but stable prothrombin time and activated partial thromboplastin time and increase in certain coagulation factors indicate that Norplant acceptors still have a possible potential for hypercoagulation at the end of two years of use.

Two-year follow-up of changes in clinical chemistry in Singaporean Norplant-2 rod acceptors: haemostatic changes

A longitudinal study of coagulation parameters was carried out on 100 Singaporean acceptors using Norplant-2 rods for contraceptive purposes. At the end of 2 years of use, results from this study show a return of platelet count to preinsertion level while platelet aggregation remained significantly enhanced. Thus the net effect of these two changes on an increased tendency for thrombosis needs further evaluation. The PT and APTT continued to remain persistently shortened during the period of use. There was also a general fall in fibrinogen and most other coagulation factors during the two years of use. Thus, again, the net effect of these two changes on the exposed potential for hypercoagulation at the end of the first year needs further evaluation throughout the five years of Norplant-2 use.

The effects of Norplant-2 rods on clinical chemistry in Singaporean acceptors after 1 year of use: haemostatic changes

A longitudinal study of coagulation parameters was carried out on 100 Singapore acceptors using the levonorgestrel subdermal implants Norplant-2 rods for contraceptive purposes. At the end of 1 year of use, results from this on-going study indicates that these acceptors have an enhanced potential for hypercoagulation with a significant shortening of their prothrombin time and activated partial thromboplastin time. They also have an increased predisposition to thrombosis as evidenced by significant increases in platelet count and aggregability. A number of other parameters achieved statistically significant differences by the end of one year but since the results were within the normal accepted range, they were therefore unlikely to be of much clinical importance.

The effects of Norplant on clinical chemistry in Singaporean acceptors after 1 year of use: I. Haemostatic changes

A longitudinal study of coagulation parameters was carried out on 100 Singaporean acceptors using the levonorgestrel subdermal implants NORPLANT for contraceptive purposes. At the end of 1 year of use, results from this on-going study indicate that these subjects may have an increased predisposition to thrombosis as evidenced by significant increase in platelet count and aggregability. The results also show that NORPLANT acceptors may have an enhanced potential for hypercoagulation - with a significant shortening of their Prothrombin Time and Activated Partial Thromboplastin Time and increases in Factors V and X. As previously documented, mean values for haemoglobin and haematocrit were significantly elevated by the end of 1 year. A number of other parameters achieved statistically significant differences by the end of 1 year but these were probably due to the large sample size involved and were therefore not likely to be of much clinical importance.

Restenosis after arterial angioplasty: a hemorrheologic response to injury

Restenosis after arterial angioplasty appears to be a response to deep arterial injury, which is much more thrombogenic than superficial injury (endothelial denudation). Deep arterial injury exposes collagen, elastin and smooth muscle cells to circulating blood, releases tissue thromboplastin and causes immediate platelet-thrombus deposition as a result of activation of platelets and the clotting system, both of which mutually facilitate activation of the other. Regrowth of endothelium also is protective against platelet deposition. Platelet adherence to collagen, and thus to the arterial wall that is deeply injured, increases with shear rate (related inversely to the fourth power of luminal cross-sectional area and directly to blood flow); thus, the effect of shear rate increases the importance of adequate dilatation at the time of the procedure. Therapy that will reduce acute platelet-thrombus deposition appears to be an important factor for reduction of restenosis. Vasoconstriction occurs experimentally after arterial angioplasty in arterial segments proximal and distal to the dilated segment where there has been no necrosis of smooth muscle cells. The vasoconstriction is directly related to the severity of platelet deposition, can be reduced by reducing platelet deposition with low dose aspirin (1 mg/kg daily) and is probably mediated by vasoconstrictor substances from platelets (thromboxane A2, serotonin and other substances). Platelet-membrane receptor inhibitors to these substances reduce the vasoconstriction but do not reduce platelet deposition. Therapeutic intervention should probably involve both anticoagulation and platelet inhibition. Platelet-membrane receptor inhibition to the fibrinogen receptor, factor VIII-von Willebrand factor or both may be necessary acutely to sufficiently reduce acute platelet-thrombus deposition.

Tissue factor activity in leukemia cells. Special reference to disseminated intravascular coagulation

Tissue factor activity (TFA) of 10(8) leukemia cells was measured in 82 patients with acute nonlymphoid leukemia by the clotting method. The TFA bore a significant correlation to the development of disseminated intravascular coagulation (DIC) in these cases. Mean TFA value with standard deviation (SD) was 8.3 +/- 6.3 U in 48 cases with DIC, which was significantly higher than 0.3 +/- 4.2 U in 34 cases without DIC. Whereas Mean TFA in non-M3 was 0.9 +/- 6.3 U which was significantly lower than 37.2 +/- 2.3 U in M3, some non-M3 showed TFA as high as M3 and were complicated by DIC. In heparin treatment, dosage of heparin could not be controlled by either APTT or AcCT but was controlled by the extent of TFA of leukemia cells. Retrospective analysis of clinical features revealed that 97000X + 9000 units/day (X = logarithm value of TFA) of heparin is an adequate dosage for the successful treatment of DIC when TFA of leukemia cells is 0.8 U or more.

Fibrinolysis in patients with acute promyelocytic leukemia and disseminated intravascular coagulation during heparin therapy

Two patients diagnosed as having acute promyelocytic leukemia (APL) and disseminated intravascular coagulation (DIC) were closely followed by serial fibrinolysis and coagulation studies from the day of admission until completion of the first course of chemotherapy. One patient was treated with intravenous heparin and Trasylol (Bayer AG, West Germany) and the other received heparin therapy without Trasylol. In Patient 1, hyperfibrinolytic activity, not observed during the administration of Trasylol, developed with its discontinuance. In Patient 2, hyperfibrinolysis was observed coincidentally with a decrease in APL cells due to chemotherapy. These results indicate that hyperfibrinolysis in APL is not associated with DIC.

The significance of the fibrin/fibrinogen degradation product in serum of carcinoma patients with hematogenous metastasis

Fibrin/fibrinogen degradation product (FDP) was measured in 270 cases with various carcinomas. An elevation of FDP (5 micrograms/ml or more) was observed in 68 cases (25%). Of the 68 elevated FDP cases, 5 (82%) were inoperable or received nonradical resection. Forty of those 56 cases (71%) showed hematogenous metastasis. FDP in those cases which showed hematogenous metastasis was found to be due to fibrinolysis accompanied by consumption coagulopathy.

A pasteurized antithrombin III concentrate for clinical use

A method for large-scale production of a pasteurized antithrombin III (AT III) concentrate for therapeutic use has been adapted from published methods. It includes the following steps: (1) batchwise adsorption onto heparin-Sepharose from plasma depleted of cryoprecipitate and prothrombin complex; (2) chromatographic elution at high salt concentration; (3) pasteurization for 10 h at 60 degrees C in the presence of added citrate ion; (4) desalting on Sephadex G-25, and (5) sterile filtration and freeze-drying. Seven batches prepared in this manner gave a mean yield of 269 U AT III/kg plasma. The product passed all the usual animal safety and pyrogenicity tests and has been used successfully in several courses of treatment of congenital deficiencies.

Oral contraceptives and surgery: reduced antithrombin and antifactor Xa levels without postoperative venous thrombosis in low-risk patients

The effect of preoperative treatment with an estrogen containing oral contraceptive on the incidence of postoperative thrombosis (detected with 125I-fibrinogen leg scanning) was examined in 221 patients aged 18-49 years who had elective or emergency general intra-abdominal or gynecologic surgery, 99 of whom were taking an oral contraceptive before their operation. Eighty-five percent of the contraceptive treated patients had taken their preparation until 1-7 days before surgery and the rest until within a month of surgery; 81% were taking preparations containing 30 or 50 micrograms estrogen. Postoperative thrombosis developed in 1 of the 122 patients who were not taking a contraceptive and in none of the 99 contraceptive treated patients. As the 95% confidence limits for the 0% thrombosis rate observed in the contraceptive treated patients are 0-3.7%, the added risk of postoperative thrombosis attributable to oral contraceptive treatment before surgery is very small in young women who are otherwise at low risk of thrombosis. Plasma antithrombin level (by immunoassay), antithrombin activity (by chromogenic substrate assay), and antifactor Xa activity (by clotting assay), were measured before surgery in 81 patients, 42 of whom had been taking an oral contraceptive. Contraceptive treatment significantly reduced all 3 assay results. Its most marked effect was on antifactor Xa activity, which was reduced by contraceptive treatment from 103 +/- 24% (range 68 - 172%) to 81 +/- 27% (range 24 - 155%; with less than 80% activity in 54%, and less than 50% activity in 15% of patients). These results suggest that reduced preoperative antifactor Xa activity has a low specificity for thrombosis after moderately extensive surgery in young, otherwise fit, oral contraceptive treated women. This test is therefore unlikely to be a clinically useful predictor for postoperative thrombosis in this group of patients.

Antithrombin III (AT III) Padua2: a "new" congenital abnormality with defective heparin co-factor activities but no thrombotic disease

A "new" antithrombin III (AT III) abnormality is described in five members of the same family. None of the affected members showed thrombotic manifestations and no consanguinity was present in the family. The main laboratory features were: normal routine clotting tests, slightly decreased AT III activities in all assays carried out in the presence of heparin. In the absence of heparin, antithrombin III activities were instead within normal limitis. Progressive AT III activity and AT III antigen were also normal. Crossed immunoelectrophoresis in the absence of heparin showed a normal pattern both in plasma and serum. In the presence of heparin, the propositi's plasma showed a major, less anodal, abnormal peak and a smaller normal peak. Three peaks were present in the propositi's serum as compared with the two normal ones. This AT III abnormality is different from AT III Padua previously described by us and we propose the toponym of Antithrombin Padua-2 to define this condition.

Properties of antithrombin-thrombin complex formed in the presence and in the absence of heparin

Purification of antithrombin-thrombin complex by ion-exchange chromatography on DEAE-agarose resulted in predominantly monomeric complex, whereas purification on matrix-linked heparin produced large amounts of aggregated complex. Monomeric antithrombin-thrombin complexes formed in the presence and in the absence of heparin had similar conformations and heparin affinities. Moreover, the first-order dissociation rate constants, measured by thrombin release, of these complexes were similar, 2.3 X 10(-6)-3.4 X 10(-6)S-1, regardless of whether newly formed or purified complex was analysed. Similar dissociation rate constants were also obtained for purified complex formed with or without heparin, from analyses by dodecyl sulphate/polyacrylamide-gel electrophoresis of the release of modified antithrombin, cleaved at the reactive-site bond. No dissociation of intact antithrombin from the complex was detected by activity measurements or by gel electrophoresis. Aggregation of the complex was found to be accompanied by a decrease in apparent dissociation rate. The similar properties of antithrombin-thrombin complexes formed with or without heparin support the concept of a catalytic role for the polysaccharide in the antithrombin-thrombin reaction. Furthermore, the results indicate that the reaction between enzyme and inhibitor involves the rapid formation of an irreversible, kinetically stable, complex that dissociates into active thrombin and modified, inactive, antithrombin by a first-order process with a half-life of about 3 days. The inhibition thus resembles a normal proteolytic reaction, one intermediate step of which is very slow.

Antithrombin III and anti-activated factor X activity in patients with acute promyelocytic leukemia and disseminated intravascular coagulation treated with heparin

Two patients diagnosed as having acute promyelocytic leukemia (APL) and disseminated intravascular coagulation (DIC) were closely followed from the day of admission until completion of the first course of chemotherapy with serial coagulation studies including plasma levels of functional antithrombin III activity (AT III) by fluorometric analysis and anti-activated Factor X activity (anti-Xa) by coagulation assay. Both patients were treated with intravenous heparin and the presence of heparin in plasma was followed by the thrombin time. Consistently normal levels of AT III (greater than 80%) were found despite evidence of intravascular coagulation. However, plasma levels of anti-Xa were often low (less than 70%) and increased only in the presence of heparin. The significance of these results in relationship to heparin therapy for disseminated intravascular coagulation of APL is discussed.

Purification and characterization of guinea pig antithrombin III

Antithrombin III (AT III) is a serine esterase inhibitor which regulates the activity of a number of coagulation factors. In this report, a three-step procedure for the purification of guinea pig AT III is described. This method, which involves affinity chromatography with heparin-Sepharose, ion exchange chromatography using DEAE-Sepharose, and Sephadex G-100 gel chromatography, results in purified, functionally active AT III with a 39% yield. The potential role of this molecule in the regulation of lymphocyte activation is discussed.

Antithrombin III and anti-activated factor X activity in patients with acute promyelocytic leukemia and disseminated intravascular coagulation treated with heparin

Two patients diagnosed as having acute promyelocytic leukemia (APL) and disseminated intravascular coagulation (DIC) were closely followed from the day of admission until completion of the first course of chemotherapy with serial coagulation studies including plasma levels of functional antithrombin III activity (AT III) by fluorometric analysis and anti-activated Factor X activity (anti-Xa) by coagulation assay. Both patients were treated with intravenous heparin and the presence of heparin in plasma was followed by the thrombin time. Consistently normal levels of AT III (greater than 80%) were found despite evidence of intravascular coagulation. However, plasma levels of anti-Xa were often low (less than 70%) and increased only in the presence of heparin. The significance of these results in relationship to heparin therapy for disseminated intravascular coagulation of APL is discussed.

Heparin with low affinity to antithrombin III inhibits the activation of prothrombin in normal plasma

Standard unfractionated heparin is known to have two actions on blood clotting. Unfractionated heparin enhances the rates at which antithrombin III inactivates activated clotting factors, and inhibits the activation of both Factor X and prothrombin by disrupting the calcium and phospholipid dependent assembly of the Factor X and prothrombin activator complexes. This latter inhibitory action of heparin occurs independently of antithrombin III. A heparin fraction with low affinity to antithrombin III was prepared from standard heparin by affinity chromatography on antithrombin-III-Sepharose and its properties compared with unfractionated heparin. The low affinity heparin fraction and the unfractionated heparin had equivalent inhibitory effects on prothrombin activation in antithrombin III depleted plasma. In normal plasma, the low affinity fraction inhibited the activation of prothrombin. Unlike the unfractionated heparin, however, the fraction of heparin with low affinity to antithrombin III did not enhance the inactivation of either Factor Xa or thrombin. This antithrombin III independent inhibition of the activation of prothrombin was also evident when activated platelets were used as the source of the procoagulant phospholipids. The antithrombin III independent effect of heparin is unlikely to be important therapeutically, however, if this property of heparin is shared by other naturally occurring glycosaminoglycans, it could be important in maintaining the fluidity of blood under physiological conditions.

Further observations on the effects of dietary fatty acid composition on platelet reactivity and blood coagulation in man and the influence of methodology on findings

Eight human subjects were fed diets enriched in saturated fat (SF), or polyunsaturated fat (PUF) and after each dietary regimen the plasma heparinthrombin clotting time (HTCT) was determined. The HTCT of citrated plasma indicated reduced heparin-neutralizing activity (HNA) after PUF feeding compared with SF feeding. Platelet factor 4 (PF4) levels in the citrated plasma samples demonstrated an inverse correlation with the HTCT (r = 0.62). Experiments with purified PF4 indicated that the PF4 present in citrated plasma could only account for approximately 10% of the HNA. Plasma prepared in a manner which minimized in vitro release of platelet constituents contained significantly less PF4 after PUF feeding and indicated that most of the PF4 found in citrated plasma resulted from in vitro release. The factor Xa inhibitory activity of citrated plasma was not significantly altered by either of the dietary regimens.

A novel semi-synthetic sulphated polysaccharide with potent antithrombin activity

A mucopolysaccharide was isolated from mussel broth. After sulphation, an electrophoretically homogenous product was obtained with a molecular weight of approximately 40 000 daltons and a sulphur content of about 12%. The sulphated polysaccharide (S-Lim) displayed an anticoagulant activity in a thrombin test system with human plasma. Unlike heparin, the anticoagulant effect of S-Lim was observed also in a thrombin-fibrinogen clotting system in the absence of AT III. Complete inhibition of the effect of 1.0 mg S-Lim was achieved with 1.5 mg protamine. In an activated partial thromboplastin time test system the anticoagulant activity of 1.0 mg S-Lim corresponded to about 40 iu of heparin. S-Lim was also found to inhibit thrombin-induced platelet aggregation. Furthermore, S-Lim inhibited the thrombin-dependent activation of factor XIII in human plasma. S-Lim did not affect various tests systems measuring factor Xa activity. It is concluded that this new sulphated mucopolysaccharide acts as a pure antithrombin with a potency corresponding to 40--50 iu heparin/mg S-Lim. In contrast to heparin and other heparinoids it does not require the presence of AT III.

Comparison of antithrombin III assays using biological and chromogenic substrates

Antithrombin III (At III) levels in plasma samples were determined by incubation of diluted plasma with thrombin, either with or without heparin. Followed by measurement of residual thrombin using clotting and amidolytic methods. All assays were of multidose bioassay design suitable for parallel line analysis. Assays without heparin showed only a small difference between amidolytic and clotting methods, which was not significant at the 95% level. Assays with heparin showed a much larger difference between clotting and amidolytic methods which is shown to be attributable to the heat defibrination step used in the clotting assay. Heat defibrination and ancrod defibrination methods are compared using the amidolytic heparin cofactor assay and it is shown that heat defibrination can cause the loss of nearly 50% of the functional At III in a reconstituted freeze-dried plasma which was used as a standard. No loss occurs when ancrod is used for defibrination. It is an advantage of the amidolytic heparin cofactor assay that defibrination is not required.