Pilar Medina

Influence of the 4600A/G and 4678G/C polymorphisms in the endothelial protein C receptor (EPCR) gene on the risk of venous thromboembolism in carriers of factor V Leiden

Two polymorphisms in the endothelial protein C receptor (EPCR) gene, 4600A/G and 4678G/C, have been reported to influence the risk of venous thromboembolism (VTE). The objective of this study was to assess whether these polymorphisms modify the risk of VTE in carriers of factor V (FV) Leiden. We genotyped 295 carriers of FV Leiden for these polymorphisms: 100 unrelated patients with a history of VTE (propositi) and 195 relatives (14 of them symptomatic) of 81 of the propositi. Spontaneous VTE events occurred in 71% of propositi carrying the 4678GG genotype, 65% carrying the GC, and 43% with the CC genotype. The mean age at the first onset was significantly higher in propositi carrying the 4678CC than in those with the GC or GG genotype (p = 0.046). Among the 276 carriers of FV Leiden from the 81 families studied, the 95 symptomatic members had similar 4600G allele and 4600AG genotype frequencies but significantly lower 4678C allele (p = 0.002) and 4678CC genotype (p = 0.004) frequencies than the 181 asymptomatic members. The probability of being free of thrombosis at age 40 was significantly higher in the 66 carriers of the 4678CC genotype (94%) than in the 138 carrying the GC (72%) or in the 72 with the 4678GG genotype (60%) (p < 0.001). Multivariate analysis showed that the 4678CC genotype reduced the risk of thrombosis in carriers of FV Leiden (OR = 0.31;95% CI = 0.16-0.83). The incidence of VTE was higher in the 195 relatives with FV Leiden than in the 133 without FV Leiden (OR = 4.7; CI = 1.3-7.2). These results show that carriers of FV Leiden with the 4678CC genotype have a significantly reduced risk of VTE compared with those carrying the 4678GG or GC genotype, probably due to the higherAPC levels previously observed in individuals carrying the 4678CC genotype.

Activated protein C levels in Behçet's disease and risk of venous thrombosis

Behçets disease is a multi‐systemic inflammatory disorder of unknown cause. Most abnormalities have been associated with endothelial injury caused by vasculitis. Thrombosis occurs in about 25% of patients, although the mechanism is unknown. The objective of this study was to evaluate the protein C activation system in Behçets disease and its correlation with venous thromboembolism (VTE). Thirty‐nine patients (12 with VTE) and 78 age‐ and sex‐matched controls were included in the study, and levels of protein C, protein S, activated protein C (APC), protein C inhibitor (PCI), soluble thrombomodulin (TM), antithrombin (AT), α1‐antitrypsin, fibrinogen, factor VIII, von Willebrand factor (VWF) and C‐reactive protein (CRP) were measured. APC and TM levels were significantly lower in patients than in controls, whereas protein S, AT, α1‐antitrypsin, fibrinogen, factor VIII, VWF and CRP levels were significantly higher in patients than in controls. APC, PCI and TM levels were lower in patients with VTE (0·65 ± 0·19 ng/ml, 86% ± 22% and 15·5 ± 7·1 ng/ml respectively) than in those without VTE (0·78 ± 0·17 ng/ml, 100% ± 15% and 22·1 ± 15·3 ng/ml) (P < 0·05). In patients, APC levels below 0·75 ng/ml (10th percentile of the control group) increased the risk of VTE about fivefold (odds ratio = 5·1; 95% confidence interval = 1·1–23·4). These results show that reduced APC levels are associated with the high incidence of VTE in Behçets disease.

Haplotypes of the EPCR gene, prothrombin levels, and the risk of venous thrombosis in carriers of the prothrombin G20210A mutation

Background Haplotypes A1 and A3 in the endothelial protein C receptor (EPCR) gene are tagged by 4678G/C and 4600A/G respectively. We assessed whether these haplotypes modify the risk of venous thromboembolism in carriers of the prothrombin 20210A allele. Design and Methods We genotyped 4678G/C and 4600A/G in 246 20210A carriers: 84 venous thromboembolism propositi and 162 relatives (13 symptomatic), and in 140 relatives not carrying the 20210A variant. Prothrombin and soluble EPCR (sEPCR) levels were also measured. Results Among propositi, the mean age at first onset was lower in carriers (35±8 years) than non-carriers of the 4600G allele (44±14 years) (p=0.004). The probability of being free of thrombosis at age 40 was lower in 20210A carriers with the EPCR 4600G allele (p=0.015). The frequency of the 4600G allele (p=0.002) and the levels of prothrombin antigen (p=0.002) and sEPCR (p<0.001) were higher in the propositi than in their asymptomatic relatives. Multivariate analyses showed that the presence of the 4600G allele (OR=2.5, 95% confidence interval 1.3–5.0), sEPCR >147 ng/mL (2.8, 1.5–5.2) and prothrombin >129% (3.8, 1.8–8.3) all increased the thrombotic risk. In bivariate analysis, including the 4600G allele and sEPCR>147 ng/mL, only the latter remained associated with risk. Conclusions These results show that in 20210A carriers the venous thromboembolism risk is influenced both by the actual prothrombin levels and by the EPCR A3 haplotype, via its effect on sEPCR levels.

Polymorphisms in the endothelial protein C receptor gene and thrombophilia

The protein C anticoagulant pathway plays a crucial role as a regulator of the blood clotting cascade. Protein C is activated on the vascular endothelial cell membrane by the thrombin-thrombomodulin complex. Once formed, activated protein C (APC) down-regulates thrombin formation by inactivating factors (F)Va and FVIIIa. Endothelial protein C receptor (EPCR) is able to bind protein C and increase the rate of protein C activation. Normal APC generation depends on the precise assemblage, on the surface of endothelial cells, of thrombin, thrombomodulin, protein C and EPCR. Therefore, any change in the efficiency of this assemblage may cause reduced/increased APC generation and modify the risk of thrombosis. This review highlights the different mutations/polymorphisms reported in the EPCR gene and their association with the risk of thrombosis.

Endothelial protein C receptor polymorphisms and risk of myocardial infarction

Haplotypes A1 and A3 in the endothelial protein C receptor gene are tagged by the 4678G/C and 4600A/G polymorphisms, respectively, and have been reported to influence the risk of venous thromboembolism. This study shows that A1 and A3 haplotype carriers have a reduced risk of myocardial infarction. Background Haplotypes A1 and A3 in the endothelial protein C receptor gene are tagged by the 4678G/C and 4600A/G polymorphisms, respectively, and have been reported to influence the risk of venous thromboembolism. We assessed whether these haplotypes modify the risk of premature myocardial infarction. Design and Methods We genotyped these polymorphisms in 689 patients with premature myocardial infarction and 697 control subjects. Activated protein C and soluble endothelial protein C receptor levels were also measured. Results After adjustment for other cardiovascular risk factors, A1 and A3 haplotypes protected against premature myocardial infarction (odds ratio 0.7, 95% CI 0.4–0.8, p=0.044 and 0.5, 0.3–0.6, p<0.001, respectively). Moreover, the protective role of these haplotypes seemed to be additive, as carriers of both the A1 and A3 haplotypes had adjusted odds ratios of 0.3 (0.2–0.5, p<0.001) and 0.4 (0.2–0.8, p=0.006) compared to those carrying only the A1 or A3 haplotype, respectively. The presence of the A1 haplotype was associated with increased levels of activated protein C whereas individuals carrying the A3 haplotype showed the highest soluble endothelial protein C receptor levels. Conclusions These results show that A1 haplotype carriers have a reduced risk of premature myocardial infarction via the association of this haplotype with increased activated protein C plasma levels. The study also shows that carriers of the A3 haplotype have a reduced risk of myocardial infarction, only in part due to increased soluble endothelial protein C levels.

Prostate–Specific Antigen Complexed to α1–Antichymotrypsin in the Early Detection of Prostate Cancer

Objectives: To study the usefulness of the complexed–to–total (C:T) prostate–specific antigen (PSA) ratio in the early detection of prostate cancer in patients with a total PSA value <4.0 ng/ml.Patients and Methods: Total PSA and PSA complexed to α1–antichymotrypsin were measured in plasma from 193 men with benign prostatic hyperplasia (BPH) and 34 with prostate cancer. The diagnosis was confirmed in 28 BPH and 16 prostate cancer patients by biopsy and in 165 BPH and 18 prostate cancer patients by histological study following transurethral prostatectomy or open prostatectomy.Results: The area under the receiver operating characteristic (ROC) curve was significantly greater for the C:T PSA ratio (0.908) than for total PSA (0.692) (p<0.001). Using a cut–off point of 0.83 for the C:T PSA ratio and regardless of the digital rectal examination (DRE) finding, 20 of the 34 prostate cancer patients would have been given a correct diagnosis (59% sensitivity) and in only 8 of the 193 BPH patients would a biopsy have been necessary (96% specificity). With a cut–off of 0.79, the sensitivity increased to 85% with a specificity of 92%. When the analysis was restricted to the 44 patients with abnormal DRE, the area under the ROC curve for the C:T PSA ratio was 0.919, and a cut–off point of 0.78 gave a sensitivity of 87% and a specificity of 93%. Using a cut–off of 0.63, all prostate cancers were detected (100% sensitivity) and 54% of the negative biopsies would have been eliminated. For the 183 patients diagnosed following surgery, a cut–off of 0.82 gave a sensitivity of 72% and a specificity of 94%.Conclusion: Our results show that the C:T PSA ratio significantly improves the clinical utility of the PSA assay for detecting prostate cancer in patients with total PSA <4 ng/ml, increasing the sensitivity without significantly increasing the number of biopsies.

Association of the Thrombomodulin Gene c.1418C>T Polymorphism With Thrombomodulin Levels and With Venous Thrombosis Risk

Objective—To investigate the association of the THBD c.1418C>T polymorphism, which encodes for the replacement of Ala455 by Val in thrombomodulin (TM), with venous thromboembolism (VTE), plasma soluble TM, and activated protein C levels. In addition, human umbilical vein endothelial cells (HUVEC) isolated from 100 umbilical cords were used to analyze the relation between this polymorphism and THBD mRNA and TM protein expression. Approach and Results—The THBD c.1418C>T polymorphism was genotyped in 1173 patients with VTE and 1262 control subjects. Levels of soluble TM and activated protein C were measured in 414 patients with VTE (not on oral anticoagulants) and 451 controls. HUVECs were genotyped for the polymorphism and analyzed for THBD mRNA and TM protein expression and for the ability to enhance protein C activation by thrombin. The 1418T allele frequency was lower in patients than in controls (P<0.001), and its presence was associated with a reduced VTE risk, reduced soluble TM levels, and increased circulating activated protein C levels (P<0.001). In cultured HUVEC, the 1418T allele did not influence THBD expression but was associated with increased TM in cell lysates, increased rate of protein C activation, and reduced soluble TM levels in conditioned medium. Conclusions—The THBD 1418T allele is associated with lower soluble TM, both in plasma and in HUVEC-conditioned medium, and with an increase in functional membrane–bound TM in HUVEC, which could explain the increased activated protein C levels and the reduced VTE risk observed in individuals carrying this allele.

Activated protein C levels in obesity and weight loss influence

Obesity is associated with a high risk of cardiovascular events. Several haemostatic disturbances which could contribute to this increased risk have been described in obesity; nevertheless, the state of coagulation inhibitors has been scarcely studied in these patients. The aim of the present study was to compare activated protein C levels in obese patients and in a control group, and to evaluate the effect of weight loss. In 67 severe or morbid obese patients, an evaluation was performed at baseline and 3 months after diet. The same determinations were performed in 67 healthy volunteers with normal body weight. We also quantified the levels of protein C and prothrombin fragment 1+2. Obese patients showed significantly higher levels of activated protein C, protein C and fragment 1+2. No correlation was found between activated protein C and fragment 1+2 levels in obese patients. After three months of diet, a significant decrease in activated protein C and fragment 1+2 was observed. In conclusion, activated protein C levels are increased in obese patients, but only a minor fraction of this increase may be explained by the higher thrombin generation and C protein levels. Activated protein C levels decrease with weight loss, due in part to a thrombin generation reduction.

The endothelial cell protein C receptor: Its role in thrombosis

The protein C anticoagulant pathway plays a crucial role as a regulator of the blood clotting cascade. Protein C is activated on the vascular endothelial cell membrane by the thrombin-thrombomodulin complex. The endothelial protein C receptor binds protein C and further enhances protein C activation. Once formed, activated protein C down-regulates thrombin formation by inactivating factors Va and VIIIa and exerts cytoprotective effects through endothelial protein C receptor binding. An adequate generation of activated protein C depends on the precise assembly, on the surface of the endothelial cells, of thrombin, thrombomodulin, protein C, and endothelial protein C receptor. Therefore, any change in the efficiency of this assembly may cause a reduction or increase in activated protein C generation and modulate the risk of thrombosis. This review highlights the role of the endothelial protein C receptor in disease and discusses the association of its mutations with the risk of thrombosis.

Inherited Abnormalities in the protein C Activation Pathway

The protein C (PC) anticoagulant pathway plays a crucial role in the regulation of fibrin formation via proteolytic degradation of the procoagulant cofactors factor Va and VIIIa by activated PC (APC). PC circulates in plasma as a zymogen, which is activated, on the surface of endothelial cells by the thrombin-thrombomodulin complex. Another endothelial cell-specific protein, the endothelial cell PC/APC receptor (EPCR), binds PC on the endothelial cell surface and further enhances the rate of PC activation. Normal APC generation depends on the precise assemblage, on the surface of endothelial cells, of at least four proteins: thrombin, thrombomodulin (TM), PC and EPCR. Therefore, any change in the efficiency of this assemblage may cause reduced APC generation and an increase in the risk of thrombosis. In the last years, several reports have suggested the association between mutations in TM and EPCR genes and venous and arterial thrombosis. Surprisingly, no studies have been reported linking mutations with levels of circulating APC, the final product of the interaction between thrombin, TM, PC and EPCR. Here, we describe the previously reported mutations in the TM and EPCR genes, and present the design and evaluation of a new strategy to investigate TM, EPCR, PC and prothrombin gene mutations in arterial and venous thrombosis.