Clot Accumulation Characteristics of Plasminogen-bearing Liposomes in a Flow-system

In this study, the clot accumulation properties of liposome-coupled plasminogen were compared to those of free (non-liposomal) plasminogen in an in vitro, closed-loop, flow-system. After introduction of a clot into the closed system, double-radiolabelled plasminogen-liposomes were administered and the accumulation of radiolabel on the entire clot was measured.

Liposomal plasminogen showed improved accumulation over free plasminogen, on both a fibrin clot and a whole blood clot. Moreover, once liposomal plasminogen was fibrin associated, it could not be washed away with buffer, in contrast to free plasminogen. Liposomal plasminogen was able to compete successfully with an excess of free plasminogen. The plateau levels for the accumulated amount of plasminogen depended on the incubated amount of plasminogen and were influenced by partial degradation of the clot. Furthermore, it was shown that a threshold liposomal plasminogen surface-density was needed for optimum clot accumulation.

Longitudinal weight differences, gene expression and blood biomarkers in BMI-discordant identical twins

Background

BMI discordant monozygotic (MZ) twins allows an examination of the causes and consequences of adiposity in a genetically controlled design. Few studies have examined longitudinal BMI discordance in MZ pairs.

Objectives

To study the development over time of BMI discordance in adolescent and adult MZ twin pairs, and to examine lifestyle, metabolic, inflammatory, and gene expression differences associated with concurrent and long-term BMI discordance in MZ pairs.

Subjects/Methods

BMI data from 2775 MZ twin pairs, collected in eight longitudinal surveys and a biobank project between 1991 and 2011, were analyzed to characterize longitudinal discordance. Lifestyle characteristics were compared within discordant pairs (ΔBMI ≥ 3 kg/m²) and biomarkers (lipids, glucose, insulin, CRP, fibrinogen, IL-6, TNF-α and sIL-6R and liver enzymes AST, ALT and GGT) and gene expression were compared in peripheral blood from discordant pairs who participated in the NTR biobank project.

Results

The prevalence of discordance ranged from 3.2% in 1991 (mean age=17, SD=2.4) to 17.4% (N=202 pairs) in 2009 (mean age=35, SD=15), and was 16.5% (N=174) among pairs participating in the biobank project (mean age=35, SD=12). Of 699 MZ with BMI data from 3-5 time points, 17 pairs (2.4%) were long-term discordant (at all available time points; mean follow-up range=6.4 years). Concurrently discordant pairs showed significant differences in self-ratings of which twin eats most (p=2.3×10⁻¹³), but not in leisure time exercise activity (p=0.28) and smoking (p>0.05). Ten out of 14 biomarkers showed significantly more unfavorable levels in the heavier of twin of the discordant pairs (p-values < 0.001); most of these biomarker differences were largest in longitudinally discordant pairs. No significant gene expression differences were identified, although high ranking genes were enriched for Gene Ontology (GO) terms highlighting metabolic gene regulation and inflammation pathways.

Conclusions

BMI discordance is uncommon in adolescent identical pairs but increases with higher pair-mean of BMI at older ages, although long-term BMI discordance is rare. In discordant pairs, the heavier twin had a more unfavorable blood biomarker profile than the genetically matched leaner twin, in support of causal effects of obesity.

Consequences for the APTT due to direct action of factor XIa on factor X, resulting in bypassing factors VIII-IX

BACK GROUND

It has recently been reported that factor XIa can activate factor X directly and can bypass factors VIII-IX. We evaluated the consequences for factor analysis with the one-stage APTT.

METHODS

APTT was performed with the Actin FS reagent with ellagic acid as the standard. Silica, high lipid (PTT-A) or low lipid (PTT-LA) were also tested. Factor depleted and deficient plasma's were obtained from commercial sources.

RESULTS

The APTT clotting times in factor XII, XI, High Molecular Weight Kininogen, factor X and factor V deficient plasma's were all significantly longer (>100s) than the clotting times of factor VIII- and IX-depleted or deficient plasma's (<100s). That the shorter times for factor VIII and IX deficient plasmas were due to contact activation was supported by biphasic inhibition of the clotting times with addition of Corn Trypsin Inhibitor and Trasylol. The role of factor XI and the by-passing of factor VIII/IX was shown by the use of quenching antibodies towards factor XI and VIII. Enriching factor VIII or IX depleted plasma with purified factor XI and addition of factor XIa showed a strong dependence on factor XI level. Calibration curves for factor analysis were steeper for factors FXII, HMWK, FX and FV, compared to those of both factors VIII and IX. Curves for VIII/IX were found steeper by the use of APTT-A/silica-based, 50% diluted substrate plasma and low factor XI in the substrate plasma.

CONCLUSIONS

In factors VIII and IX deficient plasmas, the APTT shows an activity which can be attributed to contact activation of factor X by factor XIa. This direct activity is lower with silica reagent compared to ellagic acid, dilution of plasma and low factor XI in substrate plasma.

Preincubation in the Prothrombinase-induced Clotting Time test (PiCT) is necessary for in vitro evaluation of fondaparinux and to be avoided for the reversible, direct factor Xa inhibitor, rivaroxaban

INTRODUCTION

There is no clear consensus about tests in vitro that are suitable for evaluating various factor Xa inhibitors. The availability of reversible and irreversible inhibitors further complicates the application of available assays.

METHODS

We evaluated the suitability of the prothrombinase-induced clotting test (PiCT) for fondaparinux and rivaroxaban, as representatives for irreversible and reversible inhibition of factor Xa, with specific attention to preincubation times prior to re-calcification, in the context of automate program limitations.

RESULTS

We demonstrate that the PiCT assay requires a preincubation step to allow inhibitory activity by fondaparinux. Without this step, inhibition in the test is minimal and lacking sufficient dynamic range. In contrast, to measure the reversible inhibition by rivaroxaban, we found any preincubation introduced an artifact in inhibition as exemplified by a biphasic pattern and only the test without a preincubation phase gave informative results.

CONCLUSION

It is concluded that PiCT in its format with two steps is suitable for fondaparinux evaluation, while its format without preincubation (the one-addition format) is suitable for reversible inhibitors such as rivaroxaban. Unfortunately, both types of inhibitors cannot be compared in vitro in a single assay format.

Biological variation in inflammatory and hemostatic markers

BACKGROUND

Concentrations of inflammatory and hemostatic variables are influenced by biological variation, which is the natural within-subject variation over time.

OBJECTIVES

The aim of this study was to determine fibrinogen, C-reactive protein (CRP), platelet aggregation, thrombin generation and prothrombin time (PT): (i) the number of repeated measurements needed to obtain the true habitual concentration of an individual; (ii) the recommended analytical imprecision for diagnosis and monitoring; (iii) the recommended analytical bias; (iv) the contribution of analytical imprecision to test result variability; (v) the index of individuality; (vi) the reference change value; and (vii) the seasonal variation.

SUBJECTS AND METHODS

We collected 520 blood samples over a 1-year period from 40 healthy individuals, and determined the between-subject, within-subject and seasonal variation in fibrinogen, CRP, platelet aggregation, thrombin generation and PT.

RESULTS

One or two repeated measurements were sufficient to establish the true habitual concentration, except for platelet aggregation and peak thrombin generation, where at least four and nine repeated measurements were needed, respectively. For diagnosis, the maximal recommended coefficient of analytical variation (CV) was 4%-27%, except for CRP (77.7%). For monitoring, these CVs were on average 3% lower. Recommended analytical bias varied between 1.7% and 33.2%. Finally, seasonal variation was observed in concentrations of fibrinogen and thrombin generation, which could explain approximately 11% of their total variation.

CONCLUSION

This study provides insights into the biological variability of selected inflammatory and hemostatic markers, which can be used for sample size calculations and to determine the analytical quality specifications for their respective assays.

Effects of hormone treatment on hemostasis variables

A survey was made of the changes in hemostasis and related inflammatory biomarkers for hormone treatments (HT) of women. Treatments included were oral and non-oral estrogens combined or not with progestogens, raloxifene, tamoxifene, tibolone and ethinylestradiol in oral contraceptives with non-androgenic progestogens. Special attention was given to dosages lower than the present standard dose and we explored how treatment variants approached a situation of minimal changes in biomarkers. For oral unopposed estrogens, dose reduction effectively reduced the changes in some hemostasis markers, but not in a specific set of anticoagulant variables (antithrombin, protein S, tissue factor pathway inhibitor, and the endogenous thrombin potential assay for resistance to activated protein C). Inflammation markers from the liver showed a dose-dependent reduction but effects were not nullified at the lowest dose tested. It was concluded that adequate reduction of estrogen dose for these effects will coincide with the dose-range of efficacy. Androgenic progestogens may be suitable for further reducing the impact of estrogens on some of the anticoagulant variables; reductions of estrogen-induced C-reactive protein increases appear possible with specific progestogens (medroxyprogesterone actate, nomegestrol acetate). For non-oral unopposed estrogens, all variables except inflammation biomarkers from the vascular wall showed minimal changes. Reduction in vascular inflammatory biomarkers, considered to mark anti-inflammatory effects, is augmented by medroxyprogesterone actate or norethisterone acetate. It was concluded that unopposed, non-oral estrogen treatment is the present best available option approaching minimal effects of treatment on biomarkers. Progestogen selection requires more data. We postulated that minimal effects on all cardiovascular biomarkers should define the HT with maximal safety for venous and arterial vascular events. The survey has identified specific biomarkers sensitive to low-dose unopposed and opposed estrogen which can be used to characterize future preparations for HT.

On the usefulness of fibrinolysis variables in the characterization of a risk group for myocardial reinfarction

In a prospective study selected fibrinolysis variables were assessed in plasma samples from 29 consecutive patients recovering a first instance of acute myocardial infarction and the results were correlated with reinfarction during the next four years. Nine patients suffered a reinfarction leaving a group of 20 patients without evidence of relapse. The reinfarction group was characterized by lower tissue plasminogen activator activities in plasma euglobulins (p less than 0.05), significantly higher plasma concentrations of tissue plasminogen activator antigen (p less than 0.002) and a tendency to a higher plasma level of plasminogen activator inhibition capacity. There were no significant differences between the groups in plasma concentrations of plasminogen, histidine-rich glycoprotein, plasminogen kringle-4-binding-protein, and alpha 2-antiplasmin.

Estrogen receptor 1 haplotype does not regulate oral contraceptive-induced changes in haemostasis and inflammation risk factors for venous and arterial thrombosis

BACKGROUND

Administration of oral contraceptives (OCs) has profound effects on the plasma levels of haemostasis and inflammation variables, resulting in an increased thrombosis risk. Individuals show large differences in the response of these variables to OCs. Polymorphism in the estrogen receptor-1 (ER1) gene may explain part of this inter-individual response.

METHODS

We investigated the relationship between variants (c.454-397T>C and c.454-351A>G polymorphisms and the combined haplotype) in the ER1 gene in relation to changes in haemostasis and inflammation variables that are known risk factors for thrombosis in 507 healthy, nonsmoking, nulliparous women receiving six cycles of monophasic OCs with 20, 30 or 50 microg/day estrogen.

RESULTS

A significant relationship was observed between the ER1 haplotype and changes in tissue-type plasminogen activator activity (P = 0.006), but no clear interaction pattern between the genotypes or between the estrogen doses was seen. No relationships were observed for the other variables, neither in the haplotype nor in the single polymorphism analysis.

CONCLUSION

The ER1 haplotype does not have a strong effect on the estrogen-induced changes in haemostasis and inflammation risk markers for arterial and venous thrombosis.

The Harmonization of Quantitative Test Results of Different D-Dimer Methods

Nowadays D-dimer testing is frequently applied in the diagnosis of venous thromboembolism. However, the test results of different quantitative D-dimer tests can differ significantly. The background of this variability, which is mainly caused by the variety of fibrin degradation products in plasma, the specificity of D-dimer assays, and the calibrators used in the test, is summarized here. Because D-dimer is not a single entity in plasma but a mixture of heterogeneous fibrin degradation products, method standardization is in principle impossible. Efforts undertaken in the past to standardize D-dimer methods are summarized. All these projects failed and it was concluded that only harmonization of D-dimer test results seems to be feasible. The results of a large field study on which a new approach to the harmonization of quantitative D-dimer methods will be based is summarized in this article. This approach seems to be an adequate solution for overcoming the practical problem of variation of test outcome in different D-dimer assays.

Report on the Dutch consensus development meeting for implementation and further development of population screening for colorectal cancer based on FOBT

A consensus development meeting was held to evaluate whether or not in the Netherlands all requirements were fulfilled for implementation of population screening with FOBT for colorectal cancer, or whether consensus was present that fulfilment by additional research or organisational actions could be obtained within 2-3 years. There was consensus that all classical Wilson and Jungner (1968) criteria, and six additional ones added more recently, had already been fulfilled or could be fulfilled within 2-3 years. Consequently, it was concluded that a national population screening for colorectal cancer should be implemented and carried out in the Netherlands in line with current national and European cancer screening programmes. A list of organisational actions to be taken was established. Research that is needed before the actual national launch of the screening within 2-3 years has been defined. Priorities have to be set for research and organisational actions for the coming 2-3 years for the implementation of population screening. In addition, research suggestions have been defined for the next 10-15 years for evaluation and/or improvement of implemented FOBT screening, and for future screening methodology. It was considered essential that infrastructure for future research would be embedded in the screening programme. A project group to arrange this should be formed.

The fibrinolytic system and thrombotic tendency

The deposition of the insoluble protein matrix, fibrin is temporary. The mainly known mechanism of proteolytic removal is orchestrated by a cascade type of proteolytic process involving ultimately the formation from plasminogen of the active degradation enzyme plasmin. The occurrence of plasminogen deficiency without a massive deposition of fibrin and thrombotic events indicates the occurrence of alternate routes of fibrin degradation. In the literature, data have been reported about the direct fibrinolytic activity of various other enzymes including leucocytal elastase and cathepsin G and three metalloproteinases (MMP-3,MMP-7, MT1-MMP). The importance of each of these pathways and the possible differences in importance in various diseases, in acute situations and at different locations in the circulation, in tissues and organs is not known in detail. It is suggested that multiple combined knock-outs be created to evaluate the situation for various well-defined phenotypes. It is concluded that fibrin removal is an important biological process with various buffering mechanisms and only combinations of abnormalities in the various mechanisms and special situations will lead to fibrin accumulation and thrombotic events.