The Effect of DDAVP Infusion on Thrombin Generation in Platelet-rich Plasma of von Willebrand Type 1 and in Mild Haemophilia A Patients

In von Willebrand disease (vWD) type 1 and mild haemophilia A patients we studied the effect of an infusion of DDAVP (0.3 µg/kg body weight) on thrombin generation in platelet-rich plasma (PRP) and platelet-poor plasma (PPP). Baseline thrombin generation in PRP was diminished both in the haemophilia A and vWD patients. It was normal in vWD plasma when sufficient procoagulant phospholipids were present, either via adding phospholipid vesicles to PPP or via scrambling of the platelet membrane with ionomycin in PRP. In haemophilia A plasma, thrombin generation did not normalize by providing procoagulant phospholipids. Treatment with DDAVP temporarily restored thrombin generation in PRP to normal in both diseases.

To investigate the individual roles of von Willebrand factor (vWF) and factor VIII, we also studied the effect of factor VIII infusion on thrombin generation in a severe haemophilia patient. It appears that at a fixed normal vWF concentration, <25% factor VIII is sufficient for normal thrombin generation in PRP. At a sufficient factor VIII concentration, however, thrombin generation is still lower than normal in vWD patients; ∼40% of vWF is required for half-normal thrombin generation in PRP.

It thus appears that vWF is also a clotting factor, in the sense that it is required for normal thrombin generation. This underlines the importance of the interaction between coagulation and the platelets in normal haemostasis. Thrombin generation in PRP appears to be a suitable test to reflect the combined function.

Biomarkers for Prediction of Central Venous Catheter Related-Thrombosis in Patients With Hematological Malignancies

OBJECTIVE

In a prospective setting, we aimed to find associations between biomarkers of the hemostatic system and the occurrence of central venous catheter (CVC)-related thrombosis in patients with hematological malignancies undergoing intensive chemotherapy.

METHODS

The study was conducted between July 2006 and August 2010 at the University Hospital Maastricht, the Netherlands. Consecutive adult patients with hematological malignancies who were going to receive a CVC for intensive chemotherapy were included. The primary end points were (a) symptomatic CVC-related thrombosis and (b) CVC-related infections. Blood samples were taken directly after catheterization, and easy to determine biomarkers (platelet count, leukocyte count, and hemoglobin level) in combination with blood group, factor VIII (FVIII), plasminogen activator inhibitor 1 (PAI-1), activated protein C (APC) resistance, and free protein S antigen were determined.

RESULTS

Blood was collected and analyzed from 168 patients. The incidence of symptomatic CVC-related thrombosis was 9%. In univariate analysis, white blood cell count >10.6 × 10⁹/L, mean FVIII activity, and PAI-1 >12.2 IU/mL were found to be associated with the development of symptomatic CVC-related thrombosis.

CONCLUSION

Elevated leukocyte count, high PAI-1, and high FVIII were associated with an increased incidence of symptomatic CVC-related thrombosis. We hope in future that simple, easy to determine laboratory tests that reflect the hemostatic and fibrinolytic activity in combination with clinical parameters may help to identify hematological patients at highest risk of CVC-related thrombosis and help to tailor the management of thromboprophylaxis in hematological patients undergoing CVC placement.

Perioperative dilutional coagulopathy treated with fresh frozen plasma and fibrinogen concentrate: a prospective randomized intervention trial

BACKGROUND AND OBJECTIVES

  Treatment of dilutional coagulopathy by transfusing fresh frozen plasma (FFP) remains sub-optimal. We hypothesized that partial replacement of transfused FFP by fibrinogen concentrate results in improved coagulant activity and haemostasis. This was tested in a controlled clinical intervention trial with patients experiencing massive bleeding during major surgery.

METHODS

  Patients undergoing major elective surgery were treated according to current protocols. When transfusion with FFP was required, patients were randomized as follows: group A received 4 units FFP and group B received 2 units FFP plus 2 g fibrinogen concentrate. Blood samples were taken before and after the intervention. Analysts were blinded to the treatment type.

RESULTS

  Group A (B) consisted of 21 (22) patients, in 16 (17) of whom bleeding stopped after intervention. Plasma fibrinogen increased significantly more in group B (0·57 g/l) than in group A (0·05 g/l). However, levels of prothrombin and factors VIII, IX and X increased more in group A than in group B. Rotational thromboelastometry (ROTEM) of whole blood and plasma revealed improved fibrin clot formation in group B but not in group A. Thrombin generation [calibrated automated thrombogram (CAT)] in plasma increased more in group A. Principal parameters determining whole-blood thromboelastometry were the fibrinogen level and platelet count. In vitro addition of fibrinogen and prothrombin complex concentrate to pre-intervention samples restored both ROTEM and CAT parameters.

CONCLUSIONS

  Partial replacement of transfused FFP by fibrinogen increases fibrin clot formation at the expense of less improved thrombin generation. Coagulation factors other than fibrinogen alone are required for full restoration of haemostasis.

The plasma kallikrein-kinin system and risk of cardiovascular disease in men

BACKGROUND

The plasma kallikrein-kinin system (PKKS) has been implicated in cardiovascular disease, but activation of the PKKS has not been directly probed in individuals at risk of coronary heart disease (CHD) or stroke.

OBJECTIVE

To determine the involvement of the PKKS, including factor XI, in cardiovascular disease occurring in a nested case-control study from the Second Northwick Park Heart Study (NPHS-II).

METHODS AND RESULTS

After a median follow-up of 10.7 years, 287 cases of CHD and stroke had been recorded and 542 age-matched controls were selected. When FXIIa-C1 esterase inhibitor (C1-inhibitor) concentrations were divided into tertiles (lowest tertile as reference), the odds ratios (ORs) at 95% CIs for CHD were 0.52 (0.34-0.80) in the middle tertile and 0.73 (0.49-1.09) in the highest tertile (P = 0.01 for the overall difference; P = 0.01 for CHD and stroke combined). For kallikrein-C1-inhibitor complexes, the ORs for stroke were 0.29 (0.12-0.72) and 0.67 (0.30-1.52) in the middle and high tertiles, respectively (P = 0.02). FXIIa-C1-inhibitor and kallikrein-C1-inhibitor complexes were negatively related to smoking and fibrinogen (P < 0.005). FXIa-inhibitor complexes correlated strongly with FXIIa-inhibitor complexes.

CONCLUSIONS

Lower levels of inhibitory complexes of the PKKS enzymes and particularly of FXIIa contribute to the risk of CHD and stroke in middle-aged men. This observation supports the involvement of the PKKS in atherothrombosis.

Soluble tissue factor is a candidate marker for progression of microvascular disease in patients with Type 2 diabetes

OBJECTIVE

To determine the relationship between abnormalities in blood coagulation and prevalent or incident cardiovascular complications in Type 2 diabetes.

DESIGN AND METHODS

Prospective cohort study of 128 patients with Type 2 diabetes in whom blood samples were collected at baseline and after 1 year of follow-up. All cardiovascular complications at baseline and follow-up were recorded. Forty-three healthy, age-matched subjects served as a control group.

RESULTS

Logistic analysis revealed an independent relationship between soluble tissue factor (TF) and microvascular disease [per pg mL(-1) TF: Exp(B) = 1.008; CI(95%)1.002-1.014], or neurogenic disease [Exp(B) = 1.006; CI(95%)1.001-1.011]. The highest levels of soluble TF were observed in patients with microvascular and neurogenic disease (P < 0.001). Patients with Type 2 diabetes having a soluble TF concentration >300 pg mL(-1) are at a 15-fold higher risk for the presence of microvascular disease and at a 10-fold higher risk for the presence of neurogenic disease compared with the patients with concentrations below 100 pg mL(-1). Soluble TF was correlated with tissue type plasminogen activator, von Willebrand factor antigen, systolic blood pressure and age. Levels of F1' + 2, D-dimer, FVIII activity, t-PA and vWFag were not different among patients with micro-, macro- or neurogenic complications compared with patients without those complications. Forty-eight new micro-, macro- and/or neurogenic complications were diagnosed after 1 year follow-up. With the exception of higher F1 + 2 levels after 1 year all other markers remained unchanged. A trend toward higher soluble TF levels was observed in patients with new microvascular events (P = 0.056).

CONCLUSIONS

Soluble TF is associated with existing microvascular and neurogenic complications in patients with Type 2 diabetes and is a candidate marker for progression of microvascular disease.

Non-pharmaceutical measures for prevention of post-thrombotic syndrome

BACKGROUND

Post-thrombotic syndrome (PTS) is a long-term complication of deep vein thrombosis (DVT) characterised by chronic pain, swelling and skin changes in the affected limb. One in every three patients with DVT will develop post-thrombotic complications within five years.

OBJECTIVES

To determine the relative effectiveness of, and the rate of complications using non-pharmaceutical interventions in patients with DVT in the prevention of PTS.

SEARCH STRATEGY

The reviewers searched the Cochrane Peripheral Vascular Diseases Group Specialised Trials Register (last searched January 2003), and the Cochrane Central Register of Controlled Trials (CENTRAL) (last searched Issue 4, 2002). In addition, hand searching of non-listed journals and personal communications with researchers was undertaken.

SELECTION CRITERIA

Randomised controlled trials (RCTs) of non-pharmaceutical interventions, such as bandaging and elastic stockings in patients with clinically confirmed DVT. The primary outcome was the occurrence of PTS. There was no restriction on date or language. One reviewer (DNK) identified and assessed titles and abstracts for relevance. This was verified independently by a second reviewer (RS).

DATA COLLECTION AND ANALYSIS

Data extraction was undertaken independently by two reviewers (DNK, RS), using data extraction sheets.

MAIN RESULTS

Three RCTs that evaluated compression therapy were identified. Two studies compared elastic compression stockings with a pressure of 30-40 mm Hg at the ankle with no intervention applied directly after an episode of DVT. The other small study compared elastic compression stockings (pressure 20-30 mm Hg) with stockings that were one to two sizes too large in patients one year after DVT. Overall, in the treatment group at two years, the use of elastic compression stockings was associated with a highly statistically significant reduction in the incidence of PTS with odds ratio (OR) 0.31 (95% confidence interval (CI) 0.20 to 0.48). In addition, the incidence of severe PTS was reduced from OR 0.39 (95% CI 0.20 to 0.76). In another RCT that considered the first nine days post DVT, no difference in the incidence of pulmonary embolism and size of thrombus in the femoral vein was found. A statistically significant reduction (p <0.05) was found in pain, swelling and clinical scores, favouring the compression group.

REVIEWER'S CONCLUSIONS

There is substantial evidence that elastic compression stockings reduce the occurrence of PTS after DVT. No serious adverse effects were mentioned in the studies. Hence, elastic compression stockings should be added to the treatment of DVT to prevent the development of post-thrombotic syndrome.

Tissue factor pathway inhibitor (TFPI) release after heparin stimulation is increased in Type 1 diabetic patients with albuminuria

AIMS

To study heparin-stimulated TFPI release in relation to complications in Type 1 diabetic patients.

SUBJECTS AND METHODS

Nineteen uncomplicated Type 1 diabetic patients (group I) were compared with 18 patients with retinopathy (group II), and nine patients with retinopathy and albuminuria (group III). Blood samples were taken before (basal) and till 30 min after 5000 IU of heparin i.v. (post-heparin). TFPI activity was measured chromogenically. Von Willebrand factor, tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and thrombomodulin were also measured.

RESULTS

Basal TFPI activity was higher in group III (121 +/- 10%) compared with group II (111 +/- 8%) or group I (110 +/- 13%) (P < 0.05), and strongly correlated with albuminuria (r = 0.66, P < 0.05). At all time points after heparin administration, TFPI activity in group III was significantly higher than in group I. TFPI activity was also higher in group III than in group II 5-30 min post-heparin. The increase in post-heparin TFPI activity, measured as the incremental area under the curve, was higher in group III compared with group I (65 +/- 7 vs. 59 +/- 4; P < 0.05). Of the other parameters, only thrombomodulin was higher in group III (44 +/- 24 vs. 26 +/- 7 (group II) and 28 +/- 9 ng/ml (group I); P < 0.01).

CONCLUSIONS

We conclude that basal and post-heparin TFPI activity is increased in albuminuric patients. The increase in heparin-stimulated TFPI release in patients with albuminuria is higher than in patients with retinopathy or without complications. This could be the result of altered endothelial glycosaminoglycan characteristics.

Fibrinogen binding to the integrin alpha(IIb)beta(3) modulates store-mediated calcium entry in human platelets

Effects of the occupation of integrin alpha(IIb)beta(3) by fibrinogen on Ca(++) signaling in fura-2-loaded human platelets were investigated. Adding fibrinogen to washed platelet suspensions inhibited increases in cytosolic [Ca(++)] concentrations ([Ca(++)](i)) evoked by adenosine diphosphate (ADP) and thrombin in a concentration-dependent manner in the presence of external Ca(++) but not in the absence of external Ca(++) or in the presence of the nonselective cation channel blocker SKF96365, indicating selective inhibition of Ca(++) entry. Fibrinogen also inhibited store-mediated Ca(++) entry (SMCE) activated after Ca(++) store depletion using thapsigargin. The inhibitory effect of fibrinogen was reversed if fibrinogen binding to alpha(IIb)beta(3) was blocked using RDGS or abciximab and was absent in platelets from patients homozygous for Glanzmann thrombasthenia. Fibrinogen was without effect on SMCE once activated. Activation of SMCE in platelets occurs through conformational coupling between the intracellular stores and the plasma membrane and requires remodeling of the actin cytoskeleton. Fibrinogen inhibited actin polymerization evoked by ADP or thapsigargin in control cells and in cells loaded with the Ca(++) chelator dimethyl BAPTA. It also inhibited the translocation of the tyrosine kinase p60(src) to the cytoskeleton. These results indicate that the binding of fibrinogen to integrin alpha(IIb)beta(3) inhibits the activation of SMCE in platelets by a mechanism that may involve modulation of the reorganization of the actin cytoskeleton and the cytoskeletal association of p60(src). This action may be important in intrinsic negative feedback to prevent the further activation of platelets subjected.

The effect of DDAVP infusion on thrombin generation in platelet-rich plasma of von Willebrand type 1 and in mild haemophilia A patients

In von Willebrand disease (vWD) type 1 and mild haemophilia A patients we studied the effect of an infusion of DDAVP (0.3 microg/kg body weight) on thrombin generation in platelet-rich plasma (PRP) and platelet-poor plasma (PPP). Baseline thrombin generation in PRP was diminished both in the haemophilia A and vWD patients. It was normal in vWD plasma when sufficient procoagulant phospholipids were present, either via adding phospholipid vesicles to PPP or via scrambling of the platelet membrane with ionomycin in PRP. In haemophilia A plasma, thrombin generation did not normalize by providing procoagulant phospholipids. Treatment with DDAVP temporarily restored thrombin generation in PRP to normal in both diseases. To investigate the individual roles of von Willebrand factor (vWF) and factor VIII, we also studied the effect of factor VIII infusion on thrombin generation in a severe haemophilia patient. It appears that at a fixed normal vWF concentration, <25% factor VIII is sufficient for normal thrombin generation in PRP. At a sufficient factor VIII concentration, however, thrombin generation is still lower than normal in vWD patients; approximately 40% of vWF is required for half-normal thrombin generation in PRP. It thus appears that vWF is also a clotting factor, in the sense that it is required for normal thrombin generation. This underlines the importance of the interaction between coagulation and the platelets in normal haemostasis. Thrombin generation in PRP appears to be a suitable test to reflect the combined function.

Endothelium-dependent vasodilatation, plasma markers of endothelial function, and adrenergic vasoconstrictor responses in type 1 diabetes under near-normoglycemic conditions

It is unknown whether and to what extent changes in various endothelial functions and adrenergic responsiveness are related to the development of microvascular complications in type 1 diabetes. Therefore, endothelium-dependent and endothelium-independent vasodilatation, endothelium-dependent hemostatic factors, and one and two adrenergic vasoconstrictor responses were determined in type 1 patients with and without microvascular complications. A total of 34 patients with type 1 diabetes were studied under euglycemic conditions on two occasions (11 without microangiopathy, 10 with proliferative and preproliferative retinopathy previously treated by laser coagulation, 13 with microalbuminuria, and 12 healthy volunteers also were studied). Forearm vascular responses to brachial artery infusions of N(G)-monomethyl-L-arginine (L-NMMA), sodium nitroprusside, acetylcholine (ACh), clonidine, and phenylephrine were determined. The ACh infusions were repeated during coinfusion of L-arginine. Furthermore, plasminogen activator inhibitor type 1 (PAI-1) activity, tissue plasminogen activator antigen levels, von Willebrand factor antigen levels, tissue factor pathway inhibitor (TFPI) activity, and endothelin-1 levels were measured. No differences in endothelium-dependent or endothelium-independent vasodilatation or adrenergic constriction were observed between the diabetic patients and the healthy volunteers. In comparison to the first ACh infusion, the maximal response to repeated ACh during L-arginine administration was reduced in the diabetic patients, except in the patients with proliferative and preproliferative retinopathy previously treated by laser coagulation. In these patients, the combined infusion of L-arginine and ACh resulted in an enhanced response. TFPI activity was elevated, and PAI-1 activity was reduced in the type 1 diabetic patients. Furthermore, PAI-1 activity was positively correlated with urinary albumin excretion (r = 0.48, P < 0.01) and inversely correlated with the vasodilatory response to the highest ACh dose (r = -0.37, P < 0.05). The response to the highest ACh and L-NMMA dose were positively correlated with mean arterial blood pressure (r = 0.32, P < 0.01; r = 0.41, P < 0.01, respectively). Forearm endothelium-dependent and endothelium-independent vasodilatation and adrenergic responsiveness were unaltered in type 1 diabetic patients with and without microvascular complications. Relative to healthy control subjects, endothelium-dependent vasodilatation was depressed during a repeated ACh challenge (with L-arginine coinfusion) in the diabetic patients without complications or with microalbuminuria. In contrast, this vasodilatation was enhanced in the patients with retinopathy. Elevation of TFPI was the most consistent marker of endothelial damage of all the endothelial markers measured.

Acquired APC resistance and oral contraceptives: differences between two functional tests

Resistance to activated protein C (APC) is often associated with a mutation in factor V (factor VLeiden). Individuals without factor VLeiden who exhibit a response in functional APC-resistance tests similar to that of carriers of factor VLeiden are considered to be acquired APC resistant. This phenomenon is particularly observed in women using oral contraceptives (OC). In the present study we compared the response to APC in plasma from normal individuals, carriers of factor VLeiden and women who use OC using functional tests that either quantify the effect of APC on the endogenous thrombin potential (ETP) or on the activated partial thromboplastin time (aPTT). Both tests discriminated equally well between individuals with and without factor VLeiden who were not using OC. In contrast to the aPTT-based test, the ETP-based assay yielded significant differences in sensitivity to APC between non-OC users and OC users and between users of second and third generation OC. Since there was no correlation between APC-sensitivity determined with both assays in non-carriers of factor VLeiden and in women who use OC and a poor correlation in carriers of factor VLeiden, we propose that other plasma components differentially modulate the response to APC in the aPTT- and ETP-based APC-resistance tests and that OC change the level of plasma protein(s) that modulate the effect of APC on thrombin formation initiated via the extrinsic coagulation pathway.

The prevalence of factor V Leiden mutation in patients with leg ulcers and venous insufficiency

OBJECTIVES

To study the prevalence of factor V Leiden mutation in patients with chronic venous insufficiency and venous leg ulcers, compared with a control group, and to find out whether factor V Leiden mutation is more frequent in patients with chronic venous insufficiency and a history of deep venous thrombosis.

DESIGN

A case control study.

SETTING

Three outpatient dermatological clinics.

PATIENTS

Ninety-two patients (37 men, 55 women) with venous leg ulcers and 53 control patients (23 men, 30 women).

MAIN OUTCOME MEASURE

Factor V Leiden mutation.

RESULTS

Factor V Leiden mutation was significantly more frequent in patients with chronic venous insufficiency and venous leg ulcers than in the control group (23% vs 7.5%; P=.03), and the patients with factor V Leiden mutation were more likely to have a history of venous thromboembolism (91% vs 48%, P=.002). Also, recurrent deep venous thrombosis (38% vs 14%) and recurrent leg ulcerations (9 episodes or more) occurred more frequently in the patients with factor V Leiden mutation (43% vs 19%, P=.01). No difference was observed in venous refill time or in the presence of dermatoliposclerosis and atrophie blanche.

CONCLUSIONS

Factor V Leiden mutation is more frequent in patients with venous leg ulceration than in the control group and the general population. Patients with factor V Leiden mutation have an increased risk of developing deep venous thrombosis and recurrent leg ulceration.

Acquired haemophilia A in women postpartum: management of bleeding episodes and natural history of the factor VIII inhibitor

The present study reports on the treatment of bleeding episodes and the natural history of factor VIII inhibitors in 4 patients with acquired haemophilia A postpartum. Low titre type II factor VIII inhibitors in 3 patients and high titre type I inhibitor in 1 patient became apparent immediately to 7 months after delivery. High dose human factor VIII concentrate substitution was effective in controlling bleeding episodes in two cases of factor VIII inhibitor type II, but ineffective in 1 patient with high titre type I factor VIII inhibitor. High dose gammaglobulin intravenously in 1 patient with type II factor VIII inhibitor induced a partial correction of factor VIIIc levels for 2 wk. Immunosuppressive treatment in all 4 patients with acquired haemophilia A postpartum did not reduce the potency of the factor VIII inhibitors. The low titre type II inhibitors spontaneously disappeared in all 3 patients within a few months to 1 yr after discontinuation of the immunosuppressive treatment. The high titre type I factor VIII inhibitor persisted for more than 24 yr. We conclude that immunosuppression in 4 women with acquired haemophilia A postpartum did not significantly affect the factor VIII inhibitor titre.

Oral contraceptives and venous thrombosis: different sensitivities to activated protein C in women using second- and third-generation oral contraceptives

Epidemiological studies have shown that women who use third-generation oral contraceptives (OC) containing desogestrel, gestodene or norgestimate have a higher risk of venous thrombosis than women who use second-generation OC containing levonorgestrel. It is also known that a mutation in factor V (factor V(Leiden)), which results in resistance to activated protein C (APC) and which is the most common cause of hereditary thrombophilia, potentiates the prothrombotic effect of OC. Effects of APC on thrombin generation in the plasma of women using OC were compared to the response to APC in non-OC users and in individuals that were heterozygous or homozygous for factor V(Leiden). The response towards APC was evaluated on basis of the ratio (APC-sr) of the time integrals of thrombin formation determined in the presence and absence of APC. Compared with women not using OC, women who used OC exhibited a significantly decreased sensitivity to APC (P<0.001), independent of the kind of OC used. Women who used third-generation monophasic OC were significantly less sensitive to APC than women using second-generation OC (P<0.001) and had APC-sr that did not significantly differ from heterozygous female carriers of factor V(Leiden) who did not use OC. Women who were heterozygous for factor V(Leiden) and used OC had APC-sr in the range of homozygous carriers of factor V(Leiden). Two women who started OC therapy had significantly elevated APC-sr within 3 d. Acquired APC resistance may explain the epidemiological observation of increased risk for venous thrombosis in OC users, especially in women using third-generation OC.

Increased tissue factor pathway inhibitor (TFPI) and coagulation in patients with insulin-dependent diabetes mellitus

Recently, we found an increase in tissue factor pathway inhibitor (TFPI) activity in patients with insulin-dependent diabetes mellitus (IDDM). This increase in TFPI activity could be the result of increased thrombin formation and/or altered binding of TFPI to glycosaminoglycans. We studied TFPI activity (chromogenic assay) in relation to prothrombin F1 + 2 fragments and endogenous thrombin potential (ETP), in 46 IDDM patients, and 18 age and sex-matched healthy controls. Prothrombin, antithrombin and thrombomodulin were also determined. In IDDM patients, TFPI activity and F1 + 2 levels were significantly higher, while ETP, prothrombin antigen levels, and antithrombin activity were lower as compared to the controls. In IDDM patients with microalbuminuria, a manifestation of generalized angiopathy, TFPI activity, F1 + 2 and thrombomodulin levels were higher than in patients with only retinopathy or patients without complications. No correlation between TFPI activity, F1 + 2 levels and thrombomodulin was found, while TFPI activity was negatively correlated with ETP (r = -0.27). Microalbuminuria was significantly correlated with TFPI activity (r = 0.46), F1 + 2 (r = 0.56), and thrombomodulin (r = 0.52). In TFPI-depleted plasma, ETP increased, indicating that ETP is affected by TFPI. In conclusion, the increase in TFPI activity in IDDM patients may not be considered to be a reaction on a procoagulant state. It is hypothesized that vascular damage, leading to alterations in glycosaminoglycans, is in part responsible for the changes in TFPI activity, F1 + 2 levels and ETP.

A prothrombinase-based assay for detection of resistance to activated protein C

In this paper we present a new method for the detection of resistance to activated protein C (APC) that is based on direct measurement of the effect of APC on the cofactor activity of plasma factor Va. The factor V present in a diluted plasma sample was activated with thrombin and its sensitivity towards APC was subsequently determined by incubation with phospholipids and APC. The loss of factor Va cofactor activity was quantified in a prothrombinase system containing purified prothrombin, factor Xa and phospholipid vesicles and using a chromogenic assay for quantitation of thrombin formation. The reaction conditions were optimized in order to distinguish normal, heterozygous and homozygous APC-resistant plasmas. Maximal differences in the response of these plasmas towards APC were observed when factor Va was inactivated by APC in the absence of protein S and when the cofactor activity of factor Va was determined at a low factor Xa concentration (0.3 nM). Addition of 0.2 nM APC and 20 microM phospholipid vesicles to a 1000-fold diluted sample of thrombin-activated normal plasma resulted in loss of more than 85% of the cofactor activity factor Va within 6 min. Under the same conditions, APC inactivated approximately 60% and approximately 20% of the factor Va present in plasma samples from APC-resistant individuals that were heterozygous or homozygous for the mutation Arg506-->Gln in factor V, respectively. Discrimination between the plasma samples from normal and heterozygous and homozygous APC-resistant individuals was facilitated by introduction of the so-called APC-sensitivity ratio (APC-sr). The APC-sr was defined as the ratio of the factor Va cofactor activities determined in thrombin-activated plasma samples after 6 min incubation with or without 0.2 nM APC and was multiplied by 100 to obtain integers (APC-sr = ¿factor Va+APC square root of factor Va-APC¿ x 100). Clear differences were observed between the APC-sr of plasmas from normal healthy volunteers (APC-sr: 8-20, n = 33) and from individuals that were heterozygous (APC-sr: 35-50, n = 17) or homozygous APC resistant (APC-sr: 82-88, n = 7). There was no mutual overlap between the APC-sr of normal plasmas and plasmas from heterozygous or homozygous APC resistant individuals (p < 0.0001). In all cases our test gave the same result at the DNA-based assay. Since the test is performed on a highly diluted plasma sample there is no interference by conditions that affect APC resistance tests that are based on clotting time determinations (e.g. coagulation factor deficiencies, oral anticoagulation, heparin treatment, the presence of lupus anticoagulants, pregnancy or the use of oral contraceptives). Furthermore, we show that part of the factor Va assay can be performed on an autoanalyzer which increases the number of plasma samples that can be handled simultaneously.

Tissue factor pathway inhibitor activity in patients with IDDM

Until now, several endothelium-dependent hemostatic parameters have been proposed as markers of vascular endothelial dysfunction in diabetes. We studied tissue factor pathway inhibitor (TFPI) activity in insulin-dependent diabetes mellitus (IDDM) patients without macro-or microvascular complications, before and after intravenous administration of heparin, in comparison with age-matched control subjects. We also examined the effect of acute hyperglycemia on TFPI activity in healthy men. A clotting and a chromogenic assay were used for determining TFPI activity. In the clotting assay, the COOH-terminus of TFPI is essential, but in the chromogenic assay, it is of minor importance. When the chromogenic assay was used, TFPI activity before heparin injection was significantly higher in the IDDM patients (92 +/- 24 vs. 112 +/- 23%, P < 0.01). The postheparin increase in TFPI activity, measured with both assays, was significantly higher in the diabetic subjects (area under the curve: clotting assay 64 +/- 14 vs. 81 +/- 24, P < 0.05; chromogenic assay 82 +/- 26 vs. 121 +/- 35, P < 0.0001). A positive correlation between TFPI activity and glycated hemoglobin was demonstrated. Acute hyperglycemia did not alter TFPI activity. It can be concluded that TFPI activity, especially after stimulation with heparin, is affected by chronic hyperglycemia in diabetic subjects without vascular complications. Alterations in TFPI activity may therefore reflect early endothelial dysfunction.

Increased plasma activity of plasminogen activator inhibitor 1 (PAI-1) in two patients with Klinefelter's syndrome complicated by leg ulcers

Klinefelter's syndrome is the most frequent major abnormality of sexual differentiation in men with two or more X-chromosomes, and affects one in 500 males. The syndrome is characterized by eunuchoid body proportions, scanty facial and body hair, gynaecomastia, and small firm testes. Leg ulcers, especially in combination with hyperpigmentation, have been reported in association with Klinefelter's syndrome. Thromboembolic processes are also frequently observed. The leg ulcers in patients with Klinefelter's syndrome are usually attributed to venous insufficiency. We describe two patients with Klinefelter's syndrome associated with recurrent ulcers and hyperpigmentation on both legs, in whom no venous or other underlying cause could be found. The patients were not taking any drugs, in particular no supplemental androgen therapy. Both had normal plasma testosterone values. We detected increased activity of plasminogen activator inhibitor 1 (PAI-1), with only a partial decrease upon venous occlusion. A possible role for this inhibitor of fibrinolysis in the pathogenesis of ulceration is discussed.