Polymorphism in the tissue factor region is associated with basal but not endotoxin-induced tissue factor-mRNA levels in leukocytes

Human Genetic Variation in F3 and Its Impact on Tissue Factor-Dependent Disease

Tissue factor (TF) is the primary initiator of blood coagulation in humans. As improper intravascular TF expression and procoagulant activity underlie numerous thrombotic disorders, there has been longstanding interest in the contribution of heritable genetic variation in F3, the gene encoding TF, to human disease. This review seeks to comprehensively and critically synthesize small case-control studies focused on candidate single nucleotide polymorphisms (SNPs), as well as modern genome-wide association studies (GWAS) seeking to discover novel associations between variants and clinical phenotypes. Where possible, correlative laboratory studies, expression quantitative trait loci, and protein quantitative trait loci are evaluated to glean potential mechanistic insights. Most disease associations implicated in historical case-control studies have proven difficult to replicate in large GWAS. Nevertheless, SNPs linked to F3, such as rs2022030, are associated with increased F3 mRNA expression, monocyte TF expression after endotoxin exposure, and circulating levels of the prothrombotic biomarker D-dimer, consistent with the central role of TF in the initiation of blood coagulation.

Genetic polymorphisms and plasma levels of tissue factor and tissue factor pathway inhibitor in venous thromboembolism

Tissue factor (TF) and tissue factor pathway inhibitor (TFPI) play important roles in coagulation. The aim of this study was to investigate the distributions of TF and TFPI polymorphisms in Koreans and to analyze the association of these genetic polymorphisms with plasma levels and development of venous thromboembolism (VTE). The polymorphisms TF 5466 A > G, TF -603 A > G, TFPI -287 T > C and TFPI -33 T > C were investigated in 40 Korean VTE patients and 40 age-matched and sex-matched controls by real-time PCR followed by melting curve analysis and DNA sequence analysis. Plasma levels of TF and TFPI were measured by enzyme-linked immunosorbent assay. The G allele of TF 5466 was not detected, and allelic frequencies of TF -603 G, TFPI -287 C and TFPI -33 C were 27.5, 67.5 and 16.2%, respectively. The distributions of TF and TFPI polymorphisms were not different between patients and controls. The presence of TF -603 G allele was correlated with low plasma TF levels (P = 0.029). Mean plasma TFPI levels were similar between TFPI genotypic groups. Although not statistically significant, plasma TF and TFPI levels were higher in patients than controls. The distributions of TF and TFPI polymorphisms in Koreans were considerably different from whites, suggesting ethnic variations. The TF -603 A > G polymorphism was significantly correlated with decreased plasma TF levels. Neither genetic polymorphisms in TF and TFPI nor their plasma levels seem to act as direct risk factors for VTE.

Arterial thrombus formation in cardiovascular disease

The pathogenesis of arterial thrombosis is complex and dynamic. Unlike venous thrombi, arterial thrombi typically form under conditions of high blood flow and are mainly composed of platelet aggregates, giving them the appearance of 'white clots'. Strong evidence suggests that arterial thrombi originate as a consequence of an injured atherosclerotic plaque, and that their formation involves the release of prothrombotic material (such as tissue factor), platelet aggregation, and platelet adhesion to the vascular wall. The initially labile platelet plaque is then stabilized by insoluble fibrin produced upon activation of the coagulation cascade. Inherited genetic factors (gene polymorphisms) and acquired predisposing conditions (such as the concentration and activity of clotting factors) can influence both the composition and the size of an arterial thrombus. Further research is needed to elucidate the functions of blood coagulation proteins and cellular elements that are critical to the pathogenesis of arterial thrombosis. This Review explains mechanisms of pathological arterial thrombus formation and discusses genetic and acquired risk factors of atherothrombosis.

Tissue factor gene polymorphisms and haplotypes and the risk of ischemic vascular events: four studies and a meta-analysis

OBJECTIVE

The exposure of tissue factor (TF) to blood flow is the initial step in the coagulation process and plays an important role in thrombogenesis. We investigated the role of genetic polymorphisms and haplotypes of the TF gene in the risk of ischemic vascular disease.

METHODS

Four hundred and twenty-two Italian patients with juvenile myocardial infarction (MI) and 434 controls, 808 US cases with MI and 1005 controls, 267 Italian cases with juvenile ischemic stroke and 209 controls and 148 German cases with juvenile ischemic stroke and 191 controls were studied. rs1361600, rs3917629 (rs3354 in the US population), rs1324214 and rs3917639 Tag single nucleotide polymorphisms were genotyped. Additionally, a meta-analysis of all previous studies on TF loci and the risk of ischemic coronary disease (ICD) was performed.

RESULTS

After multivariable analysis none of the SNPs, major SNP haplotypes or haplotype-pairs showed any consistent association with MI. Pooled meta-analysis of six studies also suggested that TF polymorphisms are not associated with CHD. A significant, independent association between SNP rs1324214 (C/T) and juvenile stroke was found in Italian and German populations (OR for TT homozygotes = 0.47, 95% CI 0.24-0.92, in combined analysis). Pooled analysis also showed a significant association for haplotype H3 (OR = 0.76, 95% CI 0.57-1.00) and haplotype-pair H3-H3 (OR = 0.43, 95% CI 0.20-0.92).

CONCLUSIONS

TF genetic variations were associated with the risk of ischemic stroke at young age, but did not affect ischemic coronary disease.

Individual propensity for thrombosis: comparison of venous and arterial circulations

INTRODUCTION

The pathogenesis of venous thrombosis has been attributed to complex interaction between environmental and inherited variables. A basal predisposition for venous thrombophilia independent of environmental variables has not been previously defined experimentally. Both to address the existence of an individual propensity to venous thrombosis and to establish an animal model in which variables governing this propensity could be tested, we provoked venous thrombi in a cohort of pigs of uniform size and age. We furthermore sought to determine whether the thrombotic propensity in the venous circulation is associated with similar propensity for arterial thrombosis.

MATERIALS AND METHODS

Bilateral iliac venous stents were deployed and 2 h later, thrombi were harvested and weighed. The thrombotic response was compared to carotid arterial thrombi generated by crush injury within the same pig. Venous and arterial thrombus platelet deposition were measured by scintillation detection of autologous (111)In-platelet content.

RESULTS

In a cohort of 27 pigs, venous thrombus weights and platelet content varied over greater trrhan 10-fold range from least to greatest responders. There was strong intra-individual correlation of thrombus platelet deposition (r=0.86; p=0.008) and thrombus weights (r=0.68; p=0.015) between stented iliac vein pairs. Venous thrombosis correlated with whole blood platelet counts but not carotid platelet-rich thrombus formation.

CONCLUSIONS

The wide variation in venous thrombotic response to a standardized injury appears to represent an intrinsic propensity of the individual. The poor correlation with arterial thrombosis implies unique mechanisms responsible for this propensity in arteries and veins.

Daptomycin does not exert immunomodulatory effects in an experimental endotoxin model of human whole blood

BACKGROUND

Recent studies have shown that distinct classes of antimicrobial agents might exert immunomodulatory effects in experimental settings. Daptomycin is the first member of the class of cyclic lipopeptide antibiotics, which exert their antimicrobial activity via a unique mode of action on the bacterial cytoplasmic membrane. Thus, we tested its ability to influence pro-inflammatory cytokines by use of an established experimental model of human endotoxemia.

METHODS

A controlled experimental study design with 4 parallel groups was used. Whole blood from 10 healthy male volunteers was incubated either with saline (negative control), daptomycin (40 microg/ml, control), lipopolysaccharide (LPS; 50 pg/ml, positive control), or the combination of daptomycin plus LPS for 4 h. Real-time polymerase chain reaction was utilized for the measurement of selected pro-inflammatory cytokines, namely IL-1 beta, IL-6 (high sensitivity) and TNF-alpha on the mRNA level. Protein concentrations of these respective cytokines were measured in the supernatant using a commercially available ELISA.

RESULTS

Incubation of whole blood with LPS significantly increased protein and mRNA levels of cytokines compared to baseline (p < 0.05). However, the combination of daptomycin plus LPS did not exert any significant effect on mRNA and protein levels of IL-1 beta, IL-6 (high sensitivity) and TNF-alpha after 2 and 4 h of incubation compared to LPS incubation alone.

CONCLUSION

Daptomycin does not affect pro-inflammatory cytokines in the early phase of endotoxemia. This is most likely due to the unique mode of action of daptomycin, its low potential to penetrate into human cells and its high affinity to bacterial cytoplasmic membranes.

The tumor necrosis factor alpha -308 G/A polymorphism does not influence inflammation and coagulation response in human endotoxemia

Tumor necrosis factor (TNF)-alpha plays a major role in the immune system. Release of proinflammatory cytokines, such as TNF-alpha and interleukin 6, by macrophages and other cells occurs in response to bacterial products. It has been reported that the TNF-alpha -308 G/A polymorphism in the TNF-alpha gene determines basal TNF-alpha levels. We hypothesized that it may also be associated with the degree of inflammatory response in a well-standardized model of systemic inflammation. Eighty-seven young men (age range, 19-35 years) received 2 ng/kg i.v. endotoxin (lipopolysaccharide [LPS]). The TNF-alpha promoter genotype was analyzed on a TaqMan genomic analyzer. Inflammation markers (interleukin 6, TNF-alpha), temperature, and coagulation markers (prothrombin fragment F1+2, D-dimer) were measured at 0, 2, 6, and 24 h after LPS infusion. Tumor necrosis factor-alpha plasma concentrations increased from a baseline 1.3 ng/L (range, 0.8-3.1 ng/L) before LPS infusion to a peak of 57.5 ng/L (range, 10.8-131.4 ng/L) at 2 h after LPS and then decreased continually to 10.8 ng/L (range, 4.7-16.5 ng/L) after 6 h and returned to baseline values after 24 h (1.9 ng/L [range, 1.1-3.9 ng/L]). We observed no significant differences in TNF-alpha baseline levels or in response to LPS after stratification of the data according to TNF-alpha genotype. Basal and peak values of selected inflammatory and coagulation markers were not different between wild-type TNF-alpha -308 individuals (GG) and carriers of the TNF-alpha -308 mutant allele (GA and AA). The TNF-alpha -308 G/A polymorphism does not contribute significantly to the individual variability of systemic TNF-alpha plasma concentrations after endotoxin challenge. Thus, if any, the impact of the TNF-alpha -308 G/A polymorphism on systemic endotoxin-triggered inflammation seems to be limited.

Coagulation interventions in experimental human endotoxemia

Recognition of the link between coagulation activation and inflammation has led to the hypothesis that anticoagulants may be effective in the treatment of septic patients by altering the inflammatory response. However, only limited methodologies exist that can be used in human volunteers to mimic the physiologic alterations observed in critically ill patients. The human endotoxemia model represents a model of inflammation-induced tissue factor triggered coagulation activation. As it permits elucidation of a key player in this proinflammatory and procoagulant response, it serves as a useful tool to investigate novel therapeutics in a standardized setting. The aim of this review is to focus on coagulation interventions in the human endotoxemia model.