Effects of the oral, direct factor Xa inhibitor rivaroxaban on commonly used coagulation assays

INTRODUCTION

Rivaroxaban is an oral direct factor Xa inhibitor developed for prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary but the dose-dependent effects on common reagents and assay procedures are largely unknown.

OBJECTIVES

To investigate the effect of rivaroxaban on commonly used coagulation assays.

MATERIALS AND METHODS

Rivaroxaban was added to plasma from healthy subjects in the concentration range 0-1000 μg L(-1) and analyzed using different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, fibrinogen and activated protein C (APC) resistance assays.

RESULTS

At an expected peak concentration of rivaroxaban in clinical use, the APTTs were almost invariably prolonged but at lower concentrations the effect was weak. The concentration needed to double the APTT varied between 389 ± 106 and 617 ± 149 μg L(-1) for different reagents. The PT assays showed a marked degree of difference. In general, the Quick PT type assays were more sensitive compared with the Owren type PT assays. The results from antithrombin assays were dependent on the type of reagent, with the Xa-based assay being sensitive for rivaroxaban with an estimated increase of 0.09 IU mL(-1) per 100 μg L(-1) rivaroxaban. There were only minor effects on fibrinogen assays based on thrombin reagents. The APTT-based assay for APC resistance is affected in a dose-dependent manner whereas an assay based on the activation of coagulation at the prothrombinase level was unaffected.

CONCLUSIONS

Different assays, and even different reagents within an assay group, display variable effects by therapeutic concentrations of rivaroxaban.

Increased levels of an apoptotic product in the sera from women with pre-eclampsia

Pre-eclampsia is associated with both maternal and foetal complications. Several studies have shown increased trophoblast apoptosis in the placenta of women with this condition. The aim of this study was to investigate whether increased apoptosis can be detected as elevated levels of an apoptotic product in serum samples from women with pre-eclampsia. For this purpose, we used the M30-Apoptosense ELISA assay, which measures a neo-epitope of cytokeratin 18 that is exposed after cleavage by caspases during apoptosis of epithelial cells (M30 antigen). The M30-antigen concentrations were measured in the sera of 15 healthy pregnant women and 15 patients with pre-eclampsia (gestation weeks 24-34). Patients with pre-eclampsia had significantly higher serum M30-antigen concentrations, median 120 U/L, compared to 15 healthy pregnant women matched for pregnancy length, median 104 U/L (p = 0.01). This is consistent with previous findings of increased trophoblast apoptosis in women with pre-eclampsia and raises the possibility that M30-antigen can be used as a serum marker for the severeness of this condition for the mother and child.

The Role of Coagulation and Inflammation After Angioplasty in Patients with Peripheral Arterial Disease

PURPOSE

Restenosis remains a frequent complication after angioplasty in peripheral arterial disease. Inflammation plays a critical role in the vascular response to injury. Effective medical treatment to improve patency after angioplasty is still elusive. The aims of this prospective clinical study were to investigate changes in blood coagulation and inflammatory markers after angioplasty and their significance for restenosis.

METHODS

Thirty-four patients with peripheral arterial disease underwent angioplasty of the iliac and superficial femoral arteries. Ten patients undergoing diagnostic angiography were included in the study as controls. Plasma levels of tissue factor, prothrombin fragment 1 + 2, D-dimer, P-selectin, C-reactive protein (CRP), and fibrinogen were analyzed before and after angioplasty. Patients were followed up with angiography after 6 months to assess restenosis.

RESULTS

CRP was elevated the day after angioplasty (6.6 mg/l, p = 0.0001) and tended to peak after 1 week (11 mg/l, p = 0.09). There was a significant increase of D-dimer and P-selectin 1-4 hr after angioplasty (0.4 mg/l, p = 0.001 and 68 ng/ml, p = 0.05, respectively). None of the biochemical markers was a statistically significant predictor of restenosis.

CONCLUSION

We have observed a much more prolonged inflammatory response than previously noted, but only minor changes in coagulation activity after angioplasty. The biochemical markers, before and after angioplasty, were not related to restenosis. Further studies are needed to delineate the molecular mechanisms behind these observations and their involvement in thrombosis and restenosis. If these pathways are further defined, improved treatment strategies, including antithrombotic treatments and statins, could be tailored to modulate postprocedural inflammation.

Evaluation of low PAI-1 activity as a risk factor for hemorrhagic diathesis

BACKGROUND

Prospective studies of the epidemiology and clinical significance of low plasminogen activator inhibitor type 1 (PAI-1) activity are lacking.

OBJECTIVE

To evaluate the prevalence of low PAI-1 activity in patients with a bleeding tendency in comparison with a normal population.

METHODS

In 586 consecutive patients, referred because of bleeding symptoms, we added analyses of PAI-1 activity and tissue plasminogen activator complex with PAI-1 (t-PA-PAI-1) to the routine investigation, consisting of platelet count, bleeding time, prothrombin time, activated partial thromboplastin time, fibrinogen, factor VIII, von Willebrand factor activity, and antigen. Controls were 100 blood donors and 100 age- and sex-matched healthy individuals. The latter were also evaluated regarding the previous bleeding episodes. The bleeding history was classified as clinically significant or not, and the criteria were fulfilled in 75% of the patients and 18% of the healthy controls.

RESULTS

The routine laboratory investigation of the patients was negative in 57%. Low PAI-1 activity, defined as <1.0 U mL(-1), was found in 23% of the patients and in 13% and 10% of the blood donors and healthy controls, respectively (odds ratio and 95% CI, 2.04; 1.11-3.77 and 2.75; 1.39-5.42, respectively). The difference remained statistically significant after the adjustment for body mass index, use of estrogens, sex and age (odds ratio for patients vs. healthy controls 3.23; 95% CI, 1.22-8.56, P = 0.019). The distribution of the 4G/5G genotypes in the patients was not different from that of two control populations. No specific symptom predicted for low PAI-1, which did not aggravate the clinical picture in association with the other hemostatic defects. Low tPA-PAI-1 was not associated with the increased bleeding tendency.

CONCLUSION

Low PAI-1 activity is common in patients with a bleeding diathesis, but it is a risk factor of minor clinical importance and not associated with specific bleeding manifestations.

Low levels of endostatin in the urine from patients with malignant disease

Endostatin, a C-terminal subfragment of collagen XVIII, and angiostatin, a family of fragments originating from the NH(2)-terminal portion of plasminogen, have been described as potent inhibitors of angiogenesis and malignant growth. We have earlier reported the presence of angiostatin fragments in urine from cancer patients. In this study, we investigated the occurrence of endostatin and the correlation between the amounts of endostatin and angiostatin in urine collected from 104 patients with different types of malignancies and in 16 controls. The amounts of endostatin were measured with a commercial immunoassay. Angiostatin fragments were quantitated by Western blot analysis. Only small amounts of endostatin were observed, both in patients and controls, and there was no significant difference in the amount of endostatin between the patients and the controls. Both endostatin and angiostatin concentrations in the urine showed a strong dependence on impaired kidney function, especially tubulus function, measured as the amount of urine alpha(1)-microglobulin. Interestingly, there was no significant correlation between endostatin and angiostatin concentrations in the patients with impaired kidney function (elevated urine albumin or urine alpha(1)-microglobulin), suggesting a possible difference in circulating concentrations of these inhibitors.

Prognostic importance of the uPa/PAI-1 complex in breast cancer

The complex between urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1 (plasminogen activator inhibitor 1) has been prognostically evaluated in patients with breast cancer. The concentrations of uPA antigen, PAI-1 antigen and the uPA/PAI-1 complex were analysed in extracts from breast cancer tumours from 233 patients (median follow-up of patients: 71months). The uPA/PAI-1 complex typically constituted about 5% of the uPA antigen (total uPA). The concentration of complex was found to correlate more strongly to the concentration of PAI-1 (r = 0.72; p < 0.0001) than to the concentration of uPA (r = 0.55: p < 0.0001). Interestingly, in this material the uPA/PAI-1 complex (using an optimised cutoff level of 0.22 ng microg(-1) DNA) had a stronger prognostic value than optimised cut-off valuesfor uPA or PAI-1. The data suggest that activation of prourokinase within the tumour, which is a prerequisite for the formation of the uPA/PAI-1 complex, is of better prognostic value than the production of prourokinase or PAI-1 in the breast cancer tumour.

Primary habitual abortions are associated with high frequency of factor V Leiden mutation

OBJECTIVE

To analyze the prevalence of the mutation G1691A in factor V gene (Leiden mutation), of mutation C677T in the methylenetetrahydrofolate reductase (MTHFR) gene, and of polymorphism in G20210A in the prothrombin gene in women with recurrent abortions; further, to identify a subgroup at higher risk of being carriers of these mutations.

DESIGN

Prospective case control evaluation.

SETTING

University clinic.

PATIENT(S)

Eighty-four women with 3 or more consecutive miscarriages were compared with 69 controls.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Polymerase chain reactions were performed to identify the mutations G1691A in factor V and C677T in MTHFR genes and the polymorphism G20210A in the prothrombin gene.

RESULT(S)

In women with primary habitual abortions, 27.8% carried the Leiden mutation. No difference was observed in the prevalence of mutation C677T in the MTHFR gene or in polymorphism G20210A in the prothrombin gene.

CONCLUSION(S)

The Leiden mutation may play a considerable role for women having primary recurrent abortions.

ERK signalling in metastatic human MDA-MB-231 breast carcinoma cells is adapted to obtain high urokinase expression and rapid cell proliferation

Increased urokinase plasminogen activator (u-PA) production is associated with tumor invasion and metastasis in several malignancies, including breast cancer. The mechanisms underlying constitutive u-PA expression are not well understood. We examined the relationship between the signal strength of the ERK pathway and the level of u-PA expression in the metastatic human breast cancer cell line MDA-MB-231. Treatment with the MEK1 inhibitor PD98059 resulted in decreased ERK1/2 phosphorylation and decreased u-PA mRNA and protein expression. Inhibition of ERK1/2 activity also led to decreased cell proliferation and to decreased cyclin D1 expression. Less than 5% of total ERK1/2 was phosphorylated in exponentially growing MDA-MB-231 cells, and ERK1/2 activity could be stimulated by okadaic acid. Okadaic acid did not stimulate u-PA expression, but induced strong expression of the cdk-inhibitor p21Cip1. These findings suggest that ERK1/2 signaling is tuned to a level which results in high u-PA expression and rapid cell proliferation.

Angiostatin fragments in urine from patients with malignant disease

Angiostatin, a family of fragments originating from the NH2-terminal portion of plasminogen, has been described as a potent inhibitor of angiogenesis. In order to examine to what extent angiostatin can be detected in cancer patients, urine was collected from 117 patients with different types of malignancies and subjected to Western blot analysis, utilizing antibodies raised against "kringles" 1-3 in plasminogen. A heterogeneous mixture of fragments was observed, with patterns that also varied between patients. Angiostatin fragments were quantified by densitometric scanning. The concentrations were 27 +/- 75 (SD) micrograms L-1 (range, 1-565 micrograms L-1) in urine from cancer patients, as compared to 3 +/- 2 (SD) micrograms L-1 (range, 1-10 micrograms L-1) in urine from healthy individuals. Thirty-three patients (28%) had elevated levels using a cut off level at 15 micrograms L-1 (clearly above the highest level obtained among control subjects). NH2-terminal amino acid sequence analysis of purified angiostatin fragments from one patient showed a heterogeneous pattern, but were consistent with the region between the preactivation peptide in plasminogen and "kringle" 1, as expected. Several of the patients with urinary angiostatin showed signs of poor kidney function. We conclude that angiostatin can be detected in urine from cancer patients, but at present, the clinical significance of this finding is unclear.

The risk of recurrent venous thromboembolism in carriers and non-carriers of the G1691A allele in the coagulation factor V gene and the G20210A allele in the prothrombin gene. DURAC Trial Study Group. Duration of Anticoagulation

The results concerning the risk of recurrent venous thromboembolism (VTE) in carriers of the G1691A mutation in the coagulation factor V gene are not consistent and this risk in carriers of the G20210A polymorphism in the prothrombin gene has hitherto not been reported. We followed 534 patients for 48 months after their first episode of objectively documented VTE. The prevalence of the G1691A allele in 467 (87.5%) of the patients and in 207 controls was 25.3% and 8.2%, respectively, in heterozygote form and 2.4% and 0.5%, respectively, in homozygote form. The adjusted odds ratio (OR) for the first VTE was 4.4 (95% CI 2.6-7.8). The risk of recurrent VTE in heterozygotes was not statistically different from non-carriers (17.8% vs 17.6%), with 85% power to detect a hazard ratio of 2.35. Homozygotes had a significantly increased risk (p = 0.036) of recurrent VTE. The prevalence of the G20210A allele in 456 patients and 207 controls was 6.1% and 1.4%, respectively. The adjusted OR was 4.6 (95% CI 1.6-19.3) for the first VTE in 28 carriers of this polymorphism. The risk of recurrent VTE for these was not statistically different from non-carriers with an OR of 0.9 (95% CI 0.2-2.9).

Increased expression of alpha-enolase in c-jun transformed rat fibroblasts without increased activation of plasminogen

Two-dimensional gel electrophoresis was used to identify polypeptides differentially expressed between normal and c-jun transformed rat fibroblasts. The level of a 49 kDa polypeptide was 3-fold elevated in c-jun transformed cells. Sequence analysis by ion trap mass spectrometry identified the polypeptide as rat alpha-enolase. Enolase functions as a cell surface receptor for plasminogen, suggesting that upregulation may increase plasminogen activation and cell surface proteolysis important for tumor growth. However, no difference was observed between normal and transformed cells in formation of plasmin, suggesting that upregulation of alpha-enolase may contribute to an increased metabolic capacity, but not to increased plasminogen activation.

Thrombotic risk factors and oral contraception

Eighty-one women with a history of thrombosis were classified into three groups: group I (n = 29), women in whom thrombosis developed during oral contraception; group II (n = 33), those who used oral contraceptives (OC) without complications but experienced vascular occlusion in other risk situations; group III (n = 19), women who never used OC. The level of antibodies to anionic phospholipids (PLa), a response to activated protein C (APC), and the presence for the mutation in the coagulation factor V gene causing APC resistance were studied. In the studied groups, APC resistance was present in 14% to 42% of patients. PLa were elevated in about half of APC-resistant patients. The incidence of APC resistance correlated with the recurrency of the thrombotic events within the groups. In most cases it was tightly connected to the mutation in the factor V gene. Women in whom thrombosis developed while they were taking OC (group I) differed from the others, having a remarkable disagreement between the lowest incidence of APC resistance and a relatively increased number of the mutation (14% vs 38%, p < 0.025). This finding suggested that the APC response is flexible. An influence of OC that predisposes a reduction in APC response is discussed.

Studies on phospholipid antibodies, APC-resistance and associated mutation in the coagulation factor V gene

The influence of antibodies against phospholipids (PLa) on APC response was investigated in 155 women with a history of thromboembolism and/or repeated foetal losses. PLa were determined as antibodies against cardiolipin (CLa) and phosphatidyl serine (PSa) and as lupus anticoagulant (LA) tested by dilute Russell's Viper Venom time and by the Textarin/Ecarin ratio. APC-response was studied by a clotting (aPTT-based) and by an amidolytic (factor IXa-X-based) assay. A reduced response to APC (APC-resistance) was found in 49% of 65 PLa-positive and in 13% of 90 PLa-negative samples (chi 2 = 23.9; p < 0.5 x 10(-4)). It was more common in the samples with LA, as compared to CLa+PSa positive (58% vs. 30%, not significant). The presence of the mutation causing Arg506-Gln substitution in coagulation factor V was investigated in 84 samples. The occurrence of the mutation in APC-resistant patients with CLa+PSa or with LA in one of the two assays was similar to those without PLa (84% and 100%, respectively). In the absence of APC resistance, the occurrence of the mutation was similar in the samples with and without PLa (14% vs. 11%). Samples with LA, determined by both tests used, comprised a special group where the frequency of the mutation in the APC resistant samples was significantly reduced (p < 0.01). In the latter samples, the pathogenic mechanism of APC resistance may be connected with the influence on phospholipid membranes.

DNA polymorphisms in the human tyrosine hydroxylase/insulin/insulin-like growth factor II chromosomal region in relation to glucose and insulin responses

The feasibility of disease association studies using polymorphic DNA markers in the tyrosine hydroxylase/insulin/insulin-like growth factor II chromosomal region was indicated by a high degree of linkage disequilibrium found in haplotypes. Haplotypes were resolved in the parents from Scandinavian nuclear families by studying the segregation of eight DNA polymorphisms. Comparison of observed vs expected frequencies of haplotypes, as well as pairwise measures of linkage disequilibrium, indicated a high degree of linkage disequilibrium. Five restriction fragment length polymorphisms linked to the tyrosine hydroxylase/insulin/insulin growth factor II region of chromosome 11 were investigated in relation to Type 2 (non-insulin-dependent) diabetes mellitus, and to glucose and insulin responses to glucose infusion in healthy subjects. No significant differences in genotype frequencies between Type 2 diabetic (n = 53) and healthy subjects (n = 106) were found. A significant association (p < 0.001) was initially found between genotypes defined by a PstI polymorphism located 5' of the tyrosine hydroxylase gene and the early glucose response to a standardized glucose infusion test in healthy subjects. However, a follow-up study of 112 healthy individuals failed to confirm this finding.

DNA haplotype analysis suggests linkage disequilibrium in the human insulin receptor gene

Haplotypes of the insulin receptor gene were resolved in parents from Scandinavian nuclear families by studying the segregation of seven restriction fragment length polymorphisms (RFLPs). Of 97 unrelated parents, 41 had non-insulin-dependent diabetes mellitus (NIDDM). Considerable linkage disequilibrium in the region of the insulin receptor gene was found. Pairwise non-random associations were found between proximate RFLP sites, indicating the absence of recombinational hot spots between these sites. Thus, association studies between DNA polymorphisms at this locus and disease susceptibility genes could well be feasible in this population. Differences in the distribution of insulin receptor haplotypes were examined between NIDDM patients and healthy subjects. However, the differences observed were not statistically significant.

Screening for insulin receptor gene DNA polymorphisms associated with glucose intolerance in a Scandinavian population

The significance of insulin receptor gene variants in the aetiology of Type 2 (non-insulin-dependent) diabetes mellitus has been investigated by analysis of restriction fragment length polymorphisms in a genetically homogeneous Swedish population. Seven polymorphisms were analysed, spanning functionally important regions of the insulin receptor locus. Four of these polymorphisms were mapped more accurately within the gene compared to previous studies. The genotype distribution was compared in 76 Type 2 diabetic patients and 84 healthy control subjects. No significant differences were found in the distribution of genotypes between diabetic and control subjects at the p less than 0.01 level. In order to study the possible association between quantitative measures of glucose metabolism and these DNA polymorphisms, the fasting glucose and insulin concentrations were compared in the different genotype groups of control subjects and mildly diabetic patients treated with diet. No differences in fasting glucose or insulin concentrations were found at the p less than 0.005 level of significance. In conclusion, no significant associations were found between insulin receptor gene DNA polymorphisms and glucose intolerance.