Anticoagulant effects of a low molecular weight heparinoid (Org 10172) in human volunteers and haemodialysis patients

Org 10172, a low MW heparinoid derived from animal intestinal mucosal tissue, has a mean molecular weight of 6500 D and a specific activity of 8.0 anti-Xa U/mg. Its elimination half-life after i.v. administration is 18 hours. Six human volunteers received repeated single i.v. injections of 800 and 3200 anti-Xa units of Org 10172, 5000 IU heparin or placebo. Bleeding time, platelet count and plasma beta thromboglobulin were not affected by Org 10172 or heparin. Heparin stimulated ADP-induced platelet aggregation (0.2 uM; p less than 0.05) and inhibited thrombin induced aggregation (0.3 U/ml; p less than 0.05), while the heparinoid lacked these effects. Heparin increased plasma platelet factor 4, whereas Org 10172 had no effect. In contrast to heparin Org 10172 had only a minor effect on the activated partial thromboplastin time and thrombin time, while both compounds induced anti-Xa activity in plasma. In a crossover study in six haemodialysis patients, both heparin and Org 10172 (34.4 and 22.4 anti-Xa units/kg/body weight) successfully prevented clotting of the extracorporeal circuit. Microscopical analysis of the artificial kidney membranes showed that the 34.4 unit Org 10172 dosage was as effective as heparin in preventing fibrin deposition. The haemostatic and coagulation effects were as expected from those observed in the volunteers except that there was a slower elimination of the plasma anti-Xa response. In addition heparin and Org 10172 (34.4 anti-Xa units/kg) inhibited the Xa-induced platelet aggregation (0.5 U/ml; p less than 0.01 and p less than 0.001 respectively).     

Early clinical experience of a new heparinoid, Org 10172, in prevention of deep venous thrombosis

The potential antithrombotic effect of a new low molecular weight heparinoid, Org 10172, was examined in a randomized, double-blind, placebo-controlled, dose-ranging pilot study of the prevention of deep venous thrombosis (DVT) in 45 high-risk patients having major thoracic or abdominal surgery for cancer. Org 10172 was given in doses of 500, 750 or 1000 U bd subcutaneously. DVT occurred in 9 of 14 patients given placebo and in 4 of 11 patients given 500 U bd but in none of the 20 patients given 750 or 1000 U bd. Operative blood loss and post-operative bleeding were not significantly different between the groups but one patient given 1000 U bd had major post-operative bleeding. Average mid-interval and trough plasma anti-Xa levels reached 0.26 and 0.20 U/ml respectively following the highest dose. It is concluded that Org 10172 is a potentially useful antithrombotic agent and that the effective and safe dose appears to be between 500 and 1000 U bd for prevention of DVT in high-risk patients.     

Time courses of the antithrombotic effects, bleeding enhancing effects and interactions with factors Xa and thrombin after administration of low molecular weight heparinoid Org 10172 or heparin to rats

Time response curves of the anti-thrombotic effects, bleeding enhancing effects, effects on APTT, anti-Xa activities, anti-thrombin activities and thrombin generation inhibitory activities of the low molecular weight heparinoid Org 10172 and heparin have been compared in rats. The time courses of these effects were similar for heparin but quite different for Org 10172. Org 10172 induced anti-thrombotic and anti-Xa effects which lasted approximately 3 times longer than those at the same anti-Xa doses of heparin, whereas the bleeding enhancing effects and effects on APTT of Org 10172 were of shorter duration than those of heparin. The half-life of the anti-thrombin effect after Org 10172 seemed somewhat longer than after heparin administration. Thrombin generation inhibition by Org 10172 showed a slightly longer duration than by heparin. The similarities between the time courses of the anti-thrombotic effect and the anti-Xa activity after Org 10172 administration suggest that the most appropriate parameter to monitor Org 10172 treatment is the plasma anti-Xa level.     

A novel anti-thrombotic heparinoid (ORG 10172) devoid of bleeding inducing capacity: A survey of its pharmacological properties in experimental animal models

The pharmacological profile of Org 10172, a mixture of sulphated glycosaminoglycorunans derived from hog intestinal mucosa, has been assessed in experimental thrombosis and bleeding models in rats and compared with heparin USP. Org 10172 inhibited thrombus formation in arterio-venous shunts dose dependently, the dose required for 50% inhibition (ID₅₀) of thrombus formation was 40 anti-X_a units/kg i.v. The ID₅₀ for heparin USP was 70 anti-X_a units/kg i.v. Org 10172 hardly increased bleeding in doses upto 1600 anti-X_a units/kg i.v., whereas heparin USP dose dependently increased bleeding from 90 anti-X_a units/kg i.v. onwards. The benefit (anti-thrombotic)/risk (bleeding) ratio of Org 10172 was therefore considerably better than that of heparin USP. The improved profile of Org 10172 towards bleeding might be caused by differences in the interaction with blood platelets in comparison with heparin USP. Org 10172 had less effect on the platelet content in thrombi than heparin USP. Org 10172 did not inhibit collagen induced release of serotonin in contrast to heparin USP. Org 10172 inhibited factor X_a induced aggregation of rabbit platelets but only at anti-X_a levels which were fifteen times higher than for heparin USP. In contrast to heparin USP Org 10172 had only a very weak effect on the activated partial thromboplastin time (APTT) ex vivo.     

The anticoagulant effect of heparinoid Org 10172 during haemodialysis: an objective assessment

The heparinoid of natural origin Org 10172 has anti-factor Xa activity but minimal anti-thrombin activity, and little effect upon broad spectrum assays such as the KCCT in vitro. Its anticoagulant effects have been compared to those of commercial heparin in 7 patients undergoing haemodialysis for chronic renal failure. Commercial heparin was administered in a dose (5,000 iu bolus + 1,500 iu/hour continuous iv infusion) previously shown to inhibit fibrin formation during haemodialysis. This produced mean anti-factor Xa levels in plasma between 0.7-1.0 iu/ml and largely suppressed fibrin formation for 5 h dialysis measured as mean FPA levels in plasma. Administration of Org 10172 as a bolus of 1,350 anti-factor Xa u or 2,000-2,400 anti-factor Xa u produced plasma anti-factor Xa levels of less than 0.5 u/ml and allowed fibrin clot and FPA generation during dialysis. Org 10172 administered as a bolus dose of 4,000-4,800 anti-factor Xa u produced mean anti-factor Xa levels of greater than 0.5 u/ml, allowed dialysis of 6 patients for 5 h and appreciably suppressed FPA generation during dialysis, with little effect on the KCCT. It is concluded that the anti-factor Xa activity of Org 10172 may reflect its ability to inhibit fibrin during dialysis and that single bolus injection of Org 10172 may be a useful alternative method of achieving anticoagulation.     

Placental transfer of Org 10172, a low-molecular weight heparinoid, in the awake late-pregnant guinea pig

The placental transfer of Org 10172, a low-molecular weight heparinoid, was determined in 12 awake late-pregnant guinea pigs. Nine animals receiving placebo served as controls. After 5 days i.v. treatment with Org 10172 (2 x 300 anti-Xa U/kg/day), anti-Xa activity in fetal plasma amounted to 2.4% of the maternal concentration. The Org 10172 transfer across the placenta was also evaluated with 3H-labelled Org 10172. One hour after the administration of the latter compound, fetal Org 10172-bound 3H-activity had reached 1.5% of the maternal value. The associated extremely low placental Org 10172 transfer indicates that the Org 10172 transport across the placenta of the guinea pig is membrane-limited and that the placental permeability is negligibly low. Since the hemochorial placenta of the guinea pig closely resembles that of the human, it is likely that similar transplacental transfer properties of Org 10172 apply to man.     

Heparin-associated thrombocytopenia: the antibody is not heparin specific.

In this study the hypothesis was assessed whether heparin-associated thrombocytopenia (HAT) may be caused by an antibody dependent on polysulfated oligosaccharide epitopes, present not only on heparin but also on different polysulfated substances such as dextran sulfate and pentosan polysulfate. We found that the major factor for eliciting platelet activation with sera of HAT type II patients is neither the structure nor the AT III binding capacity of an oligosaccharide, but rather its grade of sulfation. This was shown by in vitro crossreactivity studies with 40 sera of HAT type II patients using unfractionated heparins, LMW heparins (Fragmin, Fraxiparin), enoxaparin, LMW heparinoid (Org 10172 and its subfractions), de-N-sulfated heparin, dermatan sulfate, dextran sulfate, pentosan polysulfate and dextran. Platelet activation was measured by the heparin induced platelet activation (HIPA) assay and the serotonin release assay (SRA). The platelet activating factor was isolated with the IgG fraction, but did not bind to heparin and dextran sulfate fixed to a solid phase. By isoimmune fixation electrophoresis a monoclonal gammopathy was ruled out in the three sera assessed. The in vivo effect of different LMW heparins and the heparinoid Org 10172 was observed in 10 patients with HAT type II. In a prospective study, a compatible heparin-like anticoagulant was selected for 10 HAT patients for whom further parenteral anticoagulation was required. The only substance that showed no crossreactivity in vitro was the LMW heparinoid Org 10172, which differs from heparin and LMW heparins by its low-grade sulfation. Upon treatment with the heparinoid, all 10 patients had a good clinical outcome, even if they had previously developed thromboembolic complications under LMW heparin administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of heparin and a low molecular weight heparinoid on specific endogenous and exogenous fibrinolytic factors during rest and exercise.

The effects of heparin (5,000 IU i.v.) and the low molecular weight heparinoid Org 10172 (Orgaran) (3,250 anti-Xa units i.v.) on components of the fibrinolytic system were studied in two double-blind, randomised, placebo-controlled, cross-over trials using healthy subjects. In study A (n = 6) the effects were studied during rest and standardized exercise and in study B (n = 6) during a low dose infusion of recombinant tissue-type plasminogen activator (rt-PA; 80 micrograms over 16 min). At rest, heparin and Org 10172 did not influence the plasma concentrations of endogenous t-PA antigen and activity, urokinase-type PA (u-PA) antigen, plasmin activatable pro-urokinase (scu-PA), active urokinase (tcu-PA) and plasminogen activator inhibitor-1 (PAI-1) antigen. Recombinant t-PA antigen and activity during rt-PA infusion were also not affected. During exercise, neither heparin nor Org 10172 influenced the area under the curve (AUC) of t-PA and u-PA antigen and t-PA activity when compared with placebo. Unexpectedly, after heparin the AUC of t-PA activity was 49% larger (range +19 to +245%) than after Org 10172 (p < 0.05). The last difference was considered spurious, scu-PA, tcu-PA and PAI-1 antigen levels at 2 min after termination of exercise were unaffected by both compounds (p > 0.05). Sulphated polysaccharides do not increase fibrinolytic activity of the plasma by changing the concentrations of the components of the fibrinolytic system.     

Randomized double-blind, placebo controlled safety study of a low molecular weight heparinoid in patients undergoing transurethral resection of the prostate

In preparation for an efficacy study, the effect of the low molecular weight heparinoid Org 10172 on postoperative blood loss was assessed in a randomized double-blind, placebo controlled study in patients undergoing transurethral resection of the prostate (TURP). Org 10172 and placebo were given twice daily as i.v. injection for three postoperative days starting one hour preoperatively. Three doses of Org 10172 (800, 1600, and 2400 anti-Xa units b.d.) were evaluated against placebo in three consecutive patient blocks respectively. Each block consisted of 20 patients, 15 receiving Org 10172 and 5 patients placebo. The study was discontinued after 9 patients of the third block had completed the protocol because of excessive urinary blood loss. Data analysis showed a dose-dependent increase in postoperative haemoglobin loss, this was not significant for the 800 anti-Xa units b.d. dosage but was significant in those patients treated with 1600 (p less than 0.05) and 2400 anti-Xa units b.d. (p less than 0.01). It was concluded that the heparinoid Org 10172 caused a dose dependent increase in urinary blood loss following TURP.     

Low-molecular-weight heparins and heparinoids and their use in acute or progressing ischemic stroke.

Thrombotic or thromboembolic occlusion of a cerebral artery is the most common pathophysiologic mechanism of acute ischemic stroke. An antithrombotic agent would therefore appear to be an ideal medication for treatment of this condition. Heparin is an effective anticoagulant, but it has poor bioavailability and effects on thrombin and platelets that predispose it to life-threatening complications such as hemorrhage and thrombocytopenia. Low-molecular-weight (LMW) heparins have better bioavailability, a higher anti-Xa:anti-IIa ratio, and less effect on platelets than heparin; yet their heterogeneity has hampered their proper investigation in clinical trials and it has not yet been proven that they exhibit less tendency toward hemorrhage and thrombocytopenia than conventional heparin. The LMW heparinoid, Org 10172, is superior to standard heparin in terms of its bioavailability, anti-Xa:anti-IIa ratio, and lack of effect on platelets. It is less likely than heparin and many LMW heparins to induce thrombocytopenia. Like the various heparins, Org 10172 exhibits dose-dependent hemorrhagic tendencies, yet preliminary studies have found doses that are safe for use in patients with acute ischemic stroke. These studies also suggest that Org 10172 may improve outcome and lessen mortality in this population. A prospective, randomized, double-blind, controlled trial is needed to establish the potential efficacy of Org 10172 in patients who suffer acute or progressing ischemic stroke.     

The influence of Org 10172, an antithrombotic heparinoid, on urinary blood loss after transurethral prostatectomy

We have measured the effects of Org 10172 (a mixture of naturally occurring glycosaminoglycans derived from hog intestinal mucosa) on blood loss after transurethral prostatectomy (TURP), using doses which are likely to prevent postoperative venous thrombosis (VT). 48 patients entered a double-blind randomised pilot study: 18 were given subcutaneous (sc) injections of a placebo and 30 received sc Org 10172 (750 anti-Xa units/day, 500 units twice daily (bid), or 750 units bid, starting just before TURP and continued until discharge; 10 patients per group). No Org 10172 regimen increased peroperative blood loss but all caused a similar trend towards increased urinary bleeding after surgery. Since there was no apparent dose effect gradient, it was decided to pool the data from all three dosing blocks: this analysis showed that Org 10172 increased geometric mean blood loss during the first 2 days after surgery from 10.4 gm hemoglobin (Hgb; range = 3.2-71) to 20.5 gm Hgb (range = 1.9-147) (p = .005), an effect which retained its significance after allowing for two other major determinants of postoperative bleeding, the weight of prostate resected and the length of surgery, and also when pooling was restricted to the twice daily Org 10172 injection groups and their corresponding controls. Bleeding was not severe, but our results indicate a need for caution when considering the use of Org 10172 in this setting.     

Interaction study between Org 10172, a low molecular weight heparinoid, and acetylsalicylic acid in healthy male volunteers.

Potential interactions between Org 10172 (Lomoparan, i.v. bolus injection of 3,250 anti-Xa units followed by 750 units twice daily s.c. for 8 days) and acetylsalicylic acid (ASA) (500 mg orally 14 and 2 h before i.v. Org 10172 administration) were studied in eight healthy male volunteers using an open, randomised three-way cross-over design. Except for moderate bruising at venepuncture and s.c. injection sites which were equally distributed over all three treatments (Org 10172 alone, ASA alone, Org 10172 and ASA combined), no side effects were observed. The effects of the separate drugs on several haemostatic parameters were as expected, although the prolongations in bleeding time after ASA were highly variable and tended to be somewhat more pronounced after the combination (p greater than 0.05). Org 10172 did not influence the inhibiting effects of ASA on platelet function nor the functional recovery afterwards, as evaluated by thromboxane A2 (TXA2) generation and collagen-induced platelet aggregation. Furthermore, no important interactions were observed with regard to the coagulation tests and plasma anti-Xa activity. Although this study did not entirely exclude small interactions between Org 10172 and ASA in this relatively small group of subjects, these effects are probably without clinical significance.     

Bleeding times in rats treated with heparin, heparin fragments of high and low anticoagulant activity and chemically modified heparin fragments of low anticoagulant activity

A template bleeding time study in the rat was undertaken to see if it is possible to correlate bleeding times with the molecular weight, anticoagulant activity or chemical composition of heparin or heparin-derived compounds. Heparin from porcine intestinal mucosa (PM-heparin) and from bovine lung (BL-heparin) as well as heparin fragments from these sources were compared. Heparin fragments of low anticoagulant activity were prepared by affinity chromatography on immobilized antithrombin as well as by chemical modification. A heparin fragment of high affinity for antithrombin (HA-fragment) caused a marked and dose-dependent increase in bleeding time while the corresponding heparin fragment with low affinity for antithrombin (LA-fragment) had a marginal and non-dose dependent effect on the bleeding time. Similar results were also obtained with PM-heparin with high and low affinity for antithrombin. A high anti-FXa activity was not always correlated with a marked bleeding tendency. Provided that a fragment was devoid of activated partial thromboplastin time (APTT) activity, it was not possible to provoke a bleeding time of 20 min or longer, although the compound was administered at a dose of 1,088 U/kg (anti-FXa activity). On the other hand, a N-acetylated chemically oversulphated heparin fragment, with a very low anti-FXa activity (1 U/mg) and with an APTT activity of 34 U/mg, caused a bleeding time of 20 min or longer in 70% of the animals after injection of the same number of APTT units, 1,088 U/kg. These data indicate that the APTT activity is a better and more sensitive indicator of the bleeding than is the anti-FXa activity.     

Parenteral anticoagulation with the heparinoid Lomoparan (Org 10172) in patients with heparin induced thrombocytopenia and thrombosis.

Progressive thrombocytopenia may develop in as many as 5% of patients receiving heparin anticoagulation. In these patients, the risk of thromboembolic complications as well as continued thrombocytopenia necessitates discontinuation of heparin and initiation of an alternative anticoagulant when indicated. The heparinoid Lomoparan (Org 10172) is a mixture of several non-heparin low molecular weight glycosaminoglycans with proven anticoagulant efficacy that is generally non-reactive with platelets in the presence of plasma from patients with heparin induced thrombocytopenia, whereas standard heparin will induce platelet aggregation. We evaluated the role of heparinoid as a potential alternative anticoagulant in patients with heparin induced thrombocytopenia. During a 6 month period, we identified six patients with heparin induced thrombocytopenia who required an alternative parenteral anticoagulant, four as primary treatment for specific medical problem, and two as anticoagulation during a necessary surgical procedure. Heparinoid was used successfully in both medical and surgical patients requiring parenteral anticoagulation. In no case was there an exacerbation of the thrombocytopenia nor thromboembolic complications while on heparinoid therapy. Three of our patients sustained hemorrhagic complications, predominantly in the post-surgical setting in association with elevated anti-factor Xa levels and additional anticoagulant agents. We feel that these results confirm the utility of heparinoid anticoagulation in a select subset of patients with heparin induced thrombocytopenia who require continued parenteral anticoagulation.     

Arterial antithrombotic effects of aspirin, heparin, enoxaparin and clopidogrel alone, or in combination, in the rat

INTRODUCTION: Many antithrombotic drugs may have a deleterious effect on normal haemostasis leading to bleeding complications. The aim of this study was to determine if sub-therapeutic (low) doses of antithrombotic agents, when administered in combination, have enhanced efficacy without augmentation of bleeding time. MATERIALS AND METHODS: The antithrombotic effects of i.v. aspirin (4-30 mg/kg), heparin (100-500 U/kg), enoxaparin (4-30 mg/kg) and clopidogrel (10-20 mg/kg) were studied in a rat Folts-like preparation of carotid arterial thrombosis. The frequency of cyclic flow reductions (CFRs; indicating occlusive thrombus formation) and bleeding time were measured. Drug doses that were singly ineffective at preventing occlusive thrombus formation were tested in the following combinations: aspirin (10 mg/kg) with heparin (250 U/kg); aspirin (4 mg/kg) with enoxaparin (4 mg/kg); and aspirin (10 mg/kg) with clopidogrel (10 mg/kg). RESULTS: Control period (pretreatment) CFRs were not significantly different between groups; average 7.0+/-0.3 CFRs/30 min (n=64). Tail bleeding time before drug(s) was 3.1+/-0.1 min (n=86). When administered alone, aspirin (4-30 mg/kg), heparin (250 U/kg) or enoxaparin (4 mg/kg) had no effect on CFRs or bleeding time. Heparin (500 U/kg), enoxaparin (10 and 30 mg/kg) and clopidogrel (20 mg/kg) significantly decreased CFRs. Single administration of heparin (500 U/kg) or enoxaparin (30 mg/kg) increased bleeding time by 4- or 11-fold. When co-administered, aspirin 10 mg/kg and heparin 250 U/kg decreased CFRs, but also increased bleeding time by 11-fold. However, combination of aspirin and enoxaparin (4 mg/kg each), or aspirin and clopidogrel (10 mg/kg each), decreased CFRs with no effect on bleeding. CONCLUSIONS: In a preparation of arterial thrombosis in the rat, combinations of sub-efficacious (low) doses of aspirin with enoxaparin or clopidogrel inhibited thrombus formation without augmenting bleeding time. However, low-dose aspirin combined with heparin, whilst inhibiting thrombus formation, exacerbated bleeding time. If these findings translate into the clinic, the use of effective low-dose combinations may have therapeutic advantages.     

Anticoagulant effects of two types of low molecular weight heparin administered subcutaneously

Two types of LMW heparin were prepared by gel filtration of standard heparin (LMW fraction) and by degradation of heparin by nitrous acid (LMW fragment), respectively. The effects on factor Xa inhibition (XaI), APTT, platelet aggregation and AT III level of these preparations were studied after subcutaneous administration to humans and compared with those of standard heparin. At a dose of 5000 IU (XaI) the LMW fraction and LMW fragment induced peak plasma XaI activity of 0.32 IU/ml and 0.41 IU/ml respectively, compared to 0.07 IU/ml for heparin. Still 11.5 h after administration both LMW preparations gave higher activities than heparin ever induced. Following administration of 10,000 IU (XaI) of the LMW fragment the plasma peak XaI activity was 0.81 IU/ml. This prolonged the APTT from 36 sec to 46 sec only. The half-lives of the XaI activity in plasma were between 3 and 4 hours. No effect on platelet aggregation or AT-III level was demonstrated.     

A rapid and sensitive test for diagnosing heparin-associated thrombocytopenia.

Heparin-associated thrombocytopenia (HAT) is a severe complication of heparin therapy. Its diagnosis is difficult. Conventional assays employ platelet aggregometry (PAA) and/or 14C-serotonin release (SRA) which are either insensitive (PAA) or require radioactive tracers (SRA). We here describe a newly developed sensitive and rapid assay based on visual evaluation of heparin-induced platelet activation (HIPA) in microtiter wells. Using sera of 34 patients with clinically suspected HAT we found the HIPA assay to be as sensitive as the SRA and superior to PAA. The HIPA assay allows investigation of crossreactivity with different types of heparins, low molecular weight (LMW) heparins and heparinoids. Three patients who required further parenteral anticoagulation and in whom the HIPA assay was negative before treatment with the LMW heparinoid Org 10172, were treated with this new heparinoid without adverse reactions. We conclude that the HIPA assay may be a useful tool for differential diagnosis and therapy in patients with HAT.     

Prevention of deep vein thrombosis following total hip replacement by low molecular weight heparinoid.

We assessed the safety and efficacy of the novel low molecular weight heparinoid Lomoparan (Org 10172) for the prevention of deep-vein thrombosis in patients undergoing elective total hip replacement in a randomized, placebo-controlled, double-blind trial in 197 consecutive patients. The heparinoid (750 anti-factor Xa-units, s.c., b.i.d.) was administered to 97 patients and 99 patients received placebo. Study medication was started preoperatively and continued for 10 days. Efficacy was assessed by bilateral phlebography at day 10, postoperatively. The incidence of deep-vein thrombosis was 56.6% and 15.5% respectively in the placebo and heparinoid treated patients (incidence reduction: 74%; P less than 0.001). This reduction was observed both for proximal-vein thrombosis (25% to 8%; P less than 0.005) and isolated calf-vein thrombosis (31% to 7%; P less than 0.001). No major hemorrhage was observed. The number of red-cell units transfused and drain-fluid loss were comparable for the two study groups. Six patients in the heparinoid group and none in the control group developed minor wound hematomas (P less than 0.05). During an 8-week post-discharge follow-up period three patients with a normal venogram at day 10 developed clinically apparent venous thromboembolism, which was confirmed by objective testing. All three patients belonged to the heparinoid-treated group. We conclude that 750 anti-factor Xa units Org 10172 s.c. twice daily starting preoperatively is safe and effectively reduces early deep-vein thrombosis following elective total hip replacement. Further studies on the incidence of post-discharge thromboembolism are required.     

On the mechanism of heparin-induced potentiation of platelet aggregation

The role of antithrombin III (AT III) in heparin-induced potentiation of platelet aggregation was investigated using purified AT III and AT III depleted plasma. When ADP or epinephrine was added to citrated platelet rich plasma (PRP) one minute after addition of heparin, marked enhancement of platelet aggregation was observed, compared with the degree of platelet aggregation in the absence of heparin. However, heparin exhibited no potentiating effect on ADP- or epinephrine-induced platelet aggregation when platelets were resuspended in AT III depleted plasma prepared by immunosorption using matrix-bound antibodies to AT III. When purified AT III was added to AT III depleted plasma at a concentration of 20 μg/ml, potentiation of platelet aggregation by heparin was clearly demonstrated. These results suggest that the effect of heparin on platelet aggregation is also mediated by AT III.     

Antithrombin III Toyama: a hereditary abnormal antithrombin III of a patient with recurrent thrombophlebitis

A familial abnormal antithrombin III (AT-III) is reported. The characteristic of the abnormality in this family is low heparin cofactor activity with normal progressive antithrombin activity and normal or rather increased level of AT-III antigen. The patient is a 23-year-old female who had suffered from recurrent thrombophlebitis involving her lower extremities. Her plasma AT-III antigen concentration was 54 mg/dl and progressive antithrombin and factor Xa inhibitory activities were of normal level. However, the heparin cofactor activity of her plasma was as low as 26% of normal control. On crossed immunoelectrophoresis (CIE) containing heparin in the first dimension agarose, patient's AT-III showed no increase in electrophoretic mobility compared to that in the absence of heparin, suggesting that the patient's AT-III has no affinity for heparin. From CIE pattern in the presence of heparin, the patient was found to be a homozygote, and parents and one of her younger sisters were heterozygotes. Thus, the mode of inheritance is proposed to be autosomal dominant.