Rocío González-Conejero

Biological assessment of aspirin efficacy on healthy individuals: Heterogeneous response or aspirin failure?

Background and Purpose— The widespread use of aspirin requires clarification of the aspirin resistance phenomenon. Most studies on this field are focused on patients which may affect the action of aspirin. Methods— We evaluated the biological efficacy of aspirin in healthy subjects. Results— Agonist–induced platelet aggregation was fully abrogated by 100 mg of aspirin in all individuals. By contrast, with the platelet function analyzer-100 device, 33.3% of the subjects displayed no response. This failure was overcome by 500 mg or by in vitro treatment of blood with 30 &mgr;mol/L acetylsalicylic acid. Intake of 100 mg of aspirin efficiently reduced by 75% the level of 11-dehydro thromboxane B2 (11-dTxB2) in all cases. However, variability on the pre-aspirin level (range 72.4 to 625.9 ng/mmol creatinine) led to substantial differences in the residual amount of the metabolite between subjects treated with aspirin (range 12.9 to 118.0 ng/mmol creatinine). Finally, there was no influence of platelet glycoprotein IIb/IIIa (Pro33Leu), platelet glycoprotein Ia/IIa, (C807T), and FXIII (Val34Leu) polymorphisms on the efficacy of aspirin. However, the cyclooxygenase (Cox)-1 50T allele associated with higher level of 11-dTxB2, both before and after aspirin. Moreover, the Cox-2 −765C variant displayed a slightly higher reduction in 11-dTxB2 level on treatment with aspirin. Conclusions— Our findings suggest that full resistance of healthy subjects to aspirin is rather unlikely. However, differences in aspirin absorption, or pharmacokinetic, or other unrecognized factors may lead to lack of effect of low dose of aspirin in some subjects when using tests like platelet function analyzer-100. Whether Cox polymorphisms are thrombotic risk factor for patients under aspirin will require further research.

The venous thrombosis risk factor 20210 A allele of the prothrombin gene is not a major risk factor for arterial thrombotic disease

A nucleotide change (G to A transition) at position 20210 has recently been demonstrated to be a risk factor for venous thrombosis. The relevance of this polymorphism to thrombotic disease was investigated by genotypic identification in three prospective case–control studies: 101 case patients with acute coronary heart disease (CHD), 104 patients with acute cerebrovascular disease (CVD), 82 patients with a confirmed diagnosis of deep venous thrombosis (DVT), and one control age‐ and sex‐matched for each patient. The prevalence of the genetic variation was significantly associated with the occurrence of DVT, but did not differ in patients with CHD or CVD from that in controls, suggesting that this allele should not be considered a major risk factor for arterial thrombotic disease.

Pharmacogenetic relevance of CYP4F2 V433M polymorphism on acenocoumarol therapy

VKORC1 and CYP2C9 polymorphisms are used to predict the safe dose of oral anticoagulant therapy. A new variant of CYP4F2 (V433M) has recently been related to the required warfarin dose. We evaluated its influence in earliest response to acenocoumarol in 100 selected men who started anticoagulation (3 mg for 3 consecutive days). V433M genotype exerted a gene dosage-dependent effect on the decrease of factors II, VII, IX, and X in the earliest response to acenocoumarol, with homozygous 433V subjects being the most sensitive. Similarly, after the initiation of therapy, international normalized ratio also experienced a gene dosage-dependent effect (P = .015), and 433V subjects needed 4 mg/week less than 433M carriers to achieve a steady anticoagulation (P = .043). Multivariate linear regression analysis revealed a significant contribution of V433M polymorphism to variability of both early international normalized ratio value (R(2) = 0.14) and dose requirements (R(2) = 0.19). Our data underline the relevant role of CYP4F2 V433M polymorphism in the pharmacogenetics of coumarin anticoagulants.

Mutations in the shutter region of antithrombin result in formation of disulfide-linked dimers and severe venous thrombosis

Summary.  Background: Missense mutations causing conformational alterations in serpins can be responsible for protein deficiency associated with human diseases. However, there are few data about conformational consequences of mutations affecting antithrombin, the main hemostatic serpin. Objectives: To investigate the conformational and clinical effect of mutations affecting the shutter region of antithrombin. Patients and methods: We identified two families with significant reduction of circulating antithrombin displaying early and severe venous thrombosis, frequently associated with pregnancy or infection. Mutations were determined by standard molecular methods. Biochemical studies were performed on plasma samples. One variant (P80S) was purified by heparin‐affinity chromatography and gel filtration, and evaluated by proteomic analysis. Finally, we modelled the structure of the mutant dimer. Results: We identified two missense mutations affecting the shutter region of antithrombin: P80S and G424R. Carriers of both mutations presented traces of a similar abnormal antithrombin, supporting inefficiently expressed rather than non‐expressed variants. The abnormal antithrombin purified from P80S carriers is an inactive disulfide‐linked dimer of mutant antithrombin whose properties are consistent with head‐to‐head insertion of the reactive loop. Conclusions: Our data support the conclusion that missense mutations affecting the shutter region of serpins have specific conformational effects resulting in the formation of mutant oligomers. The consequent inefficiency of secretion explains the accompanying deficiency and loss of function, but the severity of thrombosis associated with these mutations suggests that the oligomers also have new and undefined pathological properties that could be exacerbated by pregnancy or infection.

HPA-1 genotype in arterial thrombosis???role of HPA-1b polymorphism in platelet function

Recently, the HPA-1b (PlA2) polymorphism of the platelet glycoprotein IIIa has been suggested as a genetic risk factor for coronary artery disease. We conducted two case-control studies of 103 patients with ischaemic cerebrovascular disease (CVD) and 101 patients with ischaemic heart disease (IHD). The groups were matched for age, race and sex. No significant differences regarding selected risk factors (hypertension, diabetes mellitus, hypercholesterolaemia and smoking) were found between case patients and controls. Moreover, we investigated 286 normal individuals from the Mediterranean area. Genotyping of HPA-1 was performed by PCR-allelic specific restriction and single-strand conformation polymorphism analysis. The prevalence of HPA-1b was similar among case patients and controls (29.2% vs. 25.3% and 26.7% vs. 34.6% for CVD and IHD case-control studies, respectively). The HPA-1b allele was found in 36.4% of the normal population. Finally, the analysis of platelet function in nine controls with the three possible HPA-1 genotypes (three a/a, three a/b and three b/b) indicates that HPA-1b genotype does not modify either the in vitro platelet aggregation and activation profile, nor the GP IIb/IIIa interaction with fibrinogen or von Willebrand factor. Our results do not support the role of HPA-1b polymorphism as an inherited risk factor for arterial thrombotic disease.

The number of platelet glycoprotein Ia molecules is associated with the genetically linked 807 C/T and HPA-5 polymorphisms.

BACKGROUND: The neutral 807 C/T (Phe224) polymorphism (807 C/T polymorphism) of the glycoprotein (GP)Ia gene has been recently associated with the number of GPIa molecules on the platelet surface. The association of the number of GPIa molecules with other GPIa polymorphisms, such as HPA‐5 (Glu/Lys505) (HPA‐5 polymorphism), involved in alloimmune thrombocytopenias is unknown.

Genetic polymorphisms of factor Vii are not associated with arterial thrombosis

A high plasma concentration of factor VII procoagulant activity is considered an independent risk factor for coronary heart disease. Recently, two polymorphisms of factor VII gene (insertion of a decanucleotide at −323 [A2], and the variant Q353) have been associated with 20–25% lower levels of this protein in plasma. In this study, the prevalence of these two factor VII polymorphisms were evaluated in relation to the development of acute thromboembolic events. Thus, we conducted three case-control studies of patients diagnosed with acute coronary syndromes, acute cerebrovascular events and deep venous thrombosis (101, 104 and 97 cases, respectively). No significant differences were detected in the prevalence of these polymorphisms between patients and controls, suggesting that the A1/A2 or R/Q alleles do not play an important role in the development of thromboembolic episodes.

Polymorphisms of P‐selectin glycoprotein ligand‐1 are associated with neutrophil–platelet adhesion and with ischaemic cerebrovascular disease

P‐selectin glycoprotein ligand (PSGL‐1) shares common features with platelet glycoprotein Ibα. A recently described polymorphism in this receptor that results in a variable number of tandem repeats (VNTR) sequence present either 16, 15 or 14 times (alleles A, B or C) could, similar to GPIbα, be functionally relevant. The allelic frequency of this polymorphism was investigated in 469 individuals from the south of Spain, and was similar to that previously described in other Caucasian populations: 85% A, 14% B and 1% C alleles. We identified two new polymorphisms genetically linked to the C isoform, resulting in the Ser273Phe and Met274Val changes. To assess the functional consequence of the polymorphisms in the receptor, we performed flow cytometric analysis of P‐selectin dependent neutrophil–platelet interaction. Neutrophils carrying the shortest C allele and the amino acid variations in residues 273 and 274 exhibited a significantly lower capacity to bind activated platelets than A/B and A/A samples (mean fluorescence intensity of CD42b+ neutrophils 262 versus 303 and 319 respectively, P < 0·05). The distribution of the VNTR was analysed in three case–control studies including 104 cerebrovascular (CVD), 101 coronary heart disease (CHD) and 150 deep venous thrombosis (DVT) patients. The results showed that smaller (B and C) alleles seem to be associated with a lower risk of developing CVD (P = 0·008) but not to be related to CHD or DVT. In conclusion, polymorphisms of the PSGL‐1 receptor may influence the neutrophil–platelet binding, and represent a risk factor for CVD.

Protein Z/Z‐dependent protease inhibitor (PZ/ZPI) anticoagulant system and thrombosis

A new anticoagulant system involving a serpin has been recently characterised. The protein Z/Z‐dependent protease inhibitor (PZ/ZPI) system inhibits activated factors X, XI and IX by different mechanisms. By homology with other anticoagulant systems (antithrombin or the protein C/protein S), deficiency of the serpin (ZPI) or its cofactor (PZ) might imbalance the haemostatic system with thrombotic consequences. Evidence supports the in vivo anticoagulant role of this complex and the thrombotic consequences of its deficiency. Non‐sense variations of the ZPI (W303X and R67X) have been associated with increased risk of venous thrombosis. Moreover, PZ deficient mice carrying the FV Leiden have a thrombotic phenotype. Finally, some reports suggest that PZ deficiency might increase the risk of thrombosis. However, other studies question the thrombotic relevance of both ZPI and PZ deficiencies. This system could play a redundant role in haemostasis that explains the conflicting results on its thrombotic potential, which might be exacerbated in combination with other prothrombotic factors.

Role of Fibrinogen Levels and Factor XIII V34L Polymorphism in Thrombolytic Therapy in Stroke Patients

Background and Purpose— The identification of genetic and environmental factors that could improve the benefit/risk ratio of thrombolytic therapy in patients with ischemic stroke is crucial. Methods— We studied the role in the efficacy and side-adverse effects of thrombolytic therapy in stroke of 2 factors involved in the structure and stability of fibrin clot: fibrinogen levels and factor XIII (FXIII) V34L, a common and functional polymorphism. Our study enrolled 200 consecutive patients with stroke who received intravenous recombinant tissue plasminogen activator. Results— Patients with FXIII V/V genotype and low fibrinogen (<3.6 g/L) displayed the best clinical outcome. In contrast, carriers of the L34 variant and high fibrinogen levels showed almost no clinical response. Moreover, patients with high fibrinogen levels at admission displayed higher mortality than patients with lower fibrinogen levels (22.6% versus 9.7%, P=0.027; OR=2.72). The FXIII V34L polymorphism also associated with mortality: 20.0% of L34 carriers but 9.1% of patients with V/V genotype died after thrombolytic therapy (P=0.034; OR=2.50). The deleterious effect of this variant seemed to be exacerbated by high levels of fibrinogen, supporting the role of fibrinogen levels in determining the hemostatic consequences of the FXIII polymorphism. Conclusions— Our study identifies 2 markers involved in fibrin formation associated with the efficacy of thrombolytic therapy and early mortality rates in patients with ischemic stroke. These markers could be useful to identify patients with stroke suitable for a safe thrombolytic therapy.