Platelet glycoprotein Ia gene dimorphism alpha2-807 in malignant arrhythmia in coronary artery disease

Preparation and Characterization of the Sulfobutylether-β-Cyclodextrin Inclusion Complex of Amiodarone Hydrochloride with Enhanced Oral Bioavailability in Fasted State

Amiodarone hydrochloride (AMD) is used in the treatment of a wide range of cardiac tachyarrhythmias, including both ventricular fibrillation (VF) and hemodynamically unstable ventricular tachycardia (VT). The objectives of this study were to improve the solubility and bioavailability in fasted state and to reduce the food effect of AMD by producing its inclusion complex with sulfobutylether-β-cyclodextrin (SBE-β-CD). The complex was prepared through a saturated water solution combined with the freeze-drying method and then characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. The solubilities of AMD and its complex were 0.35 and 68.62 mg/mL, respectively, and the value of the inclusion complex was significantly improved by 196-fold compared with the solubility of free AMD. The dissolution of the AMD-SBE-β-CD inclusion complex in four different dissolution media was larger than that of the commercial product. The cumulative dissolution was more than 85% in water, pH 4.5 NaAc-HAC buffer, and pH 1.2 HCl aqueous solution. Moreover, the pharmacokinetic study found that the C _max, AUC_(0-t), and AUC_(0-∞) of the AMI-SBE-β-CD inclusion complex had no significant difference in fasted and fed state, which indicated that the absorption of the AMI-SBE-β-CD inclusion complex in fasted state was increased and not affected by food.

Genetic regulation of platelet receptor expression and function: application in clinical practice and drug development

Understanding genetic contributions to platelet function could have profound clinical ramifications for personalizing platelet-directed pharmacotherapy, by providing insight into the risks and possible benefits associated with specific genotypes. This article represents an integrated summary of presentations related to genetic regulation of platelet receptor expression and function given at the Fifth Annual Platelet Colloquium in January 2010. It is supplemented with additional highlights from the literature covering (1) approaches to determining and evidence for the associations of genetic variants with platelet hypo- and hyperresponsive phenotypes, (2) the ramifications of these polymorphisms with regard to clinical responses to antiplatelet therapies, and (3) the role of platelet function/genetic testing in guiding antiplatelet therapy.

Genetics of sudden cardiac arrest

Sudden cardiac arrest (SCA) due to ventricular arrhythmias is a major cause of mortality in western populations with up to 450,000 deaths in the United States each year. Although environmental factors clearly contribute to the determinants of SCA, familial aggregation studies and advances in the molecular genetics of inherited arrhythmias suggest that genetic factors confer susceptibility to SCA in the general population. Research in this area typically has focused on association of common genetic variants with intermediate phenotypes that predispose to SCA risk, such as QT interval, but few studies have examined genetic risk factors for SCA. We review the evidence for genetic susceptibility to SCA in the general population and focus on the studies published to date that have explored genetic risk factors.

Lack of association between the platelet glycoprotein Ia C807T gene polymorphism and coronary artery disease: a meta-analysis

BACKGROUND

The platelet-collagen receptor, glycoprotein (GP) la/lla plays a crucial role in the adhesion of platelets to fibrillar collagen, an event contributing to the pathogenesis of thrombosis. The C807T polymorphism of the GPla gene is considered a genetic marker of the platelet GPla/lla density. The importance of the GPla gene C807T polymorphism as a genetic risk factor for coronary artery disease (CAD) remains controversial. To assess this association, we performed a meta-analysis of published data.

METHODS

A comprehensive meta-analysis of 19 studies, with a total sample of 13835 subjects using random effects models.

RESULTS

The C versus T allele contrast gave an OR of 0.998 with 95% Cl 0.937-1.064. Similarly, comparing the C homozygotes with the T homozygotes, the CC genotype versus the others and the TT genotype versus the rest, no evidence of any gene-disease association was obtained. Furthermore, the meta-regression analysis did not disclose any variable that could modify the role of this polymorphism in the development of CAD.

CONCLUSION

Our findings support the view that C807T polymorphism of the GPla gene is not a significant risk factor for CAD, either alone or in combination with other major cardiovascular risk factors.

Influence of human platelet antigen match on the success of stem cell transplantation after myeloablative conditioning

Mismatches between donor and recipient for human platelet antigens (HPA) may affect the success of transplantation due to: (a) serving as minor histocompa-tibility antigens and therefore render recipients at risk for graft-versus-host disease (GvHD), (b) inhibition of thrombopoiesis due to platelet antibodies. We therefore evaluated the occurrence of GvHD and need of platelet support by prospective analysis of donor-recipient pairs (n=53) for HPA-1, -2, -3, and -5 allotypes and screening for platelet antibodies prior to transplantation and in weekly intervals until day 100 after transplantation. Neither the incidence of GvHD nor the onset of thrombopoiesis, nor the CCI after platelet transfusions, nor the frequency of platelet transfusions was affected by HPA mismatches. Settings of homozygous donors vs heterozygous recipients or homozygous recipients vs heterozygous donors were not associated with any adverse effects on the outcome of the transplantation. Thus, the HPA-match does not affect the success of transplantation.

Platelet receptors and their role in diseases

The absence or deficiency of specific platelet glycoprotein receptors has a well-defined role in causing several rare bleeding disorders such as Bernard-Soulier syndrome or Glanzmann's thrombasthenia. Several new rare disorders caused by defects in other receptors or their signalling pathways have recently been described. Platelet receptors are also often targets for antibodies in pathological conditions. The roles of platelet receptors or their polymorphism variants in diseases such as cardiovascular disorders have started to be intensively investigated over the last 5 years. Many of these findings still remain controversial. Recent evidence points to a fundamental role for platelets and their receptors in the origins of atherosclerosis. Studies on the role of platelet receptors in diseases such as asthma, diabetes and HIV are still at an early stage.

Increased platelet-collagen interaction associated with double homozygosity for receptor polymorphisms of platelet GPIa and GPIIIa

OBJECTIVE

There is considerable controversy regarding the clinical role of the single-nucleotide polymorphisms (SNPs) of the platelet glycoprotein receptor GPIa C807T and the Pl(A1/A2) of GPIIIa as cardiovascular risk factors. We hypothesized that two combined SNPs in their homozygous prothrombotic forms could clarify their pathophysiological impact.

METHODS AND RESULTS

We identified a family with a striking history of premature cardiovascular events and a high frequency of the prothrombotic form of the two SNPs. From this family, the platelets of a healthy, 27-year-old propositus with this double homozygosity were compared with three matched male neutral gene variant controls. The propositus had shortened PFA-100 closure times and an increased platelet aggregation response to collagen. Platelet deposition to collagen was augmented under the blood flow conditions of a high shear rate model (1600 s(-1)). Platelet adhesion on collagen monomers was induced in a static system, leading to the promotion of subsequent procoagulant activity.

CONCLUSIONS

The combined homozygous prothrombotic SNPs of GPIa and GPIIIa are associated with an increased platelet-collagen interaction and procoagulant activity that can be readily demonstrated in several independent systems. Our patient may serve as a useful model for the functional consequences of two combined, potentially procoagulant, platelet SNPs.

Platelet collagen receptor GPIa (C807T/HPA-5) haplotype is not associated with an increased risk of fatal coronary events in middle-aged men

Platelet GPIa/IIa receptors play key roles in the adhesion of platelets to collagen during the formation of coronary thrombosis. The C807T and HPA-5 polymorphisms of the gene for GPIa define three distinct alleles of GPIa which are associated with the surface expression of the protein in an allele-dependent fashion. Significance of these polymorphisms in victims of sudden cardiac death (SCD) was studied in Helsinki Sudden Death Study (HSDS) comprising 700 autopsied middle-aged Caucasian Finnish men with 288 SCD victims and 84 men with fatal acute myocardial infarction (AMI). The high-expression A1 allele was found in 36.6% of control men as opposed to 38.0% of all SCD victims and 36.9% of men with fatal AMI (P>0.4). The high-expression A1A1 genotype was found in 11.9% of men with fatal AMI and 10.0% of controls as opposed to the low-expression A2A2 genotype which was found in 29.8% of men with fatal AMI and in 31.2% of controls (OR 1.2, P>0.3). Age group (under/over 55) had no effect on the results. Our results do not support an effect of the GPIa haplotype on fatal coronary events among middle-aged men.

Influence of platelet collagen receptor polymorphisms on risk for arterial thrombosis

CONTEXT

Collagens are major components of the vascular subendothelium, and the interaction of platelets with collagens initiates normal hemostasis or pathologic arteriothrombosis. Genetic factors that affect the interaction of platelets with collagens could represent risk factors for either arteriothrombosis or excessive hemorrhage. In this regard, we first found that platelet levels of one of the major platelet collagen receptors, integrin alpha(2)beta(1), vary up to 10-fold in normal healthy individuals and that the higher-level phenotype is associated with allele 1 (807T) of the integrin alpha(2) gene. More recently, we found that there is roughly a fivefold range in platelet glycoprotein VI content among normal individuals, which may also influence risk for thromboembolism.

OBJECTIVE

To determine if genetic polymorphisms of platelet glycoproteins involved in collagen-related function are associated with higher risk for thrombotic disorders, such as coronary heart disease, myocardial infarction, or stroke.

METHODS

We examined the genetic mechanisms responsible for variation in expression levels of the collagen receptor integrin alpha(2)beta(1) and the potential influence of this variation on risk for thrombotic diseases.

RESULTS

We found that patients with arteriothrombotic diseases have a higher frequency of alpha(2) allele 1 (associated with higher levels of platelet integrin alpha(2)beta(1)). We further found that platelet glycoprotein VI content directly correlates with platelet prothrombinase activity, suggesting that a higher phenotype of platelet glycoprotein VI also may contribute to increased risk of arteriothrombotic diseases.

CONCLUSION

Genetic polymorphisms that influence the level or function of platelet collagen receptors need to be seriously considered as genetic risk factors for arteriothrombotic diseases.

The influence of genomics on outcome after cardiovascular surgery

Recent findings in molecular research suggest that the outcome of cardiovascular surgery is at least partly determined by the individual patient's genetic predisposition to react to surgical trauma and extracorporal circulation. The activation of cellular as well as humoral cascades occurs in the perioperative period, and influences the extent of pro- and anticoagulation and pro- and anti-inflammation. These events contribute to the incidence and severity of perioperative ischaemia or organ dysfunction, and thus determine adverse outcomes in patients undergoing cardiac surgery. Candidate genes that are possibly involved in the development of adverse outcomes not only consist of genes relevant to the field of coagulation and inflammation, but also genes functioning in lipid metabolism, ion channels, membrane integrity and others. Genomic variations may prove to serve as future diagnostic tools for the risk stratification of patients undergoing cardiovascular surgery.

The influence of platelet collagen receptor polymorphisms in hemostasis and thrombotic disease

Extracellular collagens modulate the rate of platelet activation and thereby markedly influence hemostasis and thrombosis. Platelet receptors for collagens, such as the integrin alpha(2)beta(1), platelet glycoprotein (GP) VI or, indirectly, the GPIb complex, are unexploited targets of pharmacological control, and polymorphisms of these receptors have recently become factored into the genetic risk for thrombosis. Seemingly contradictory findings already exist with regard to the contribution of GPIbalpha and integrin alpha(2) polymorphisms, but these discrepancies will be resolved once there is better standardization of clinical studies. There is already substantial evidence that GPIbalpha VNTR A or B alleles, the GPIbalpha-5C allele, and integrin alpha(2) allele 1 (T(807)) each contribute to increased risk for morbidity in thrombotic disease. However, larger, prospective genetic and epidemiological studies are needed to clarify the role of each of these polymorphisms, the contribution of other platelet receptor polymorphisms, and the synergistic effects of combinations of these factors. In addition, in vitro studies that establish the functional relevance of these polymorphisms will provide sound biological explanations for the results of clinical correlation studies.

The role of platelet collagen receptor (glycoprotein Ia/IIa; integrin alpha2 beta1) polymorphisms in thrombotic disease

Differences in rates of platelet activation induced by extracellular matrix components such as collagens markedly influence normal hemostasis and the pathologic outcome of thrombosis. Thus, platelet collagen receptors, the integrin alpha2beta1, glycoprotein VI, and the glycoprotein Ib complex, represent unexploited targets of pharmacologic control. Polymorphisms of these receptors are now understood as factors that potentially contribute to thrombotic risk. There is substantial evidence that the GPIbalpha variable number of tandem repeats A or B alleles, the -5C allele of GPIbalpha, and the integrin alpha2 allele 1 (T807) each contribute to risk for and morbidity from thrombotic disease. The extent of their individual contributions is disputed. More well-designed, large, prospective, genetic and epidemiologic studies are needed to clarify the role of these and other platelet receptor polymorphisms, and additional in vitro studies are needed to provide a sound biologic explanation for the outcomes of clinical correlations.

Platelet glycoprotein gene polymorphisms and risk of thrombosis: facts and fancies

Over the past several years, platelet glycoprotein gene polymorphisms have received increasing attention as possible inherited determinants of prothrombotic tendency. However, their role in genetic susceptibility to thrombotic disease remains controversial. The glycoprotein IIIa Leu33Pro amino acid substitution appears to be associated with a subtle effect on platelet thrombogenicity in vitro, but is not a major risk factor for arterial thrombotic disease among the general population. Evidence suggests that the glycoprotein IIIa Pro33 allele may be associated with increased risk of thrombotic events following coronary re-vascularization and possibly among younger subjects with atherosclerosis. The nucleotide 807T variant of glycoprotein Ia is associated with increased platelet glycoprotein Ia/IIa receptor density, collagen-induced platelet adhesion and an increased risk of early onset myocardial infarction and stroke. Evaluation of the roles of the glycoprotein Ibalpha Thr145Met and variable number of tandem repeat polymorphisms has been complicated by their lack of well-defined effects on platelet adhesive function and the strong linkage disequilibrium between the two sites. Future epidemiologic studies of platelet glycoprotein gene polymorphisms will require larger sample sizes and family based approaches to further elucidate clinically important associations with thrombotic disease, including gene-environment and gene-gene interactions. Other polymorphisms of potential functional significance within genes encoding platelet membrane proteins will undoubtedly be discovered. The challenge will be to integrate advances in platelet biology with molecular and genetic epidemiology to enhance our understanding of the genetic determinants of common, but etiologically complex thrombotic diseases.

Platelet glycoproteins and their role in diseases

The role of platelet glycoprotein receptors in disorders caused by their absence or defects such as in Bernard-Soulier syndrome or Glanzmann's thrombasthenia has been known for many decades now. Their function as targets for pathological antibodies is also well established. The possible roles of platelet receptors or their polymorphism variants in the origins of diseases such as cardiovascular disorders are less well studied. Investigation of this area began about five years ago and many findings still remain controversial. The involvement of platelet receptors in other diseases like asthma, diabetes and HIV are only starting to be studied.

Platelet polymorphisms in thrombotic disorders

Plaque rupture and/or endothelial damage lead to exposure of von Willebrand factor (VWF) and collagen which facilitate the adhesion of circulating platelets via glycoprotein (GP) GPIb-IX-V and integrin alpha2 beta1, respectively, to the damaged vessel wall. This process activates the platelets and leads to a conformational change of a second integrin alphaIIb beta3 that facilitates fibrinogen binding and platelet aggregation. Thrombin generated at the blood-plaque interface converts fibrinogen to fibrin, which stabilizes thrombus growth. Therefore, any genetic differences that might alter surface expression or activity of these receptors could influence the risk for adverse outcome as a result of the hemostatic process. In the last five years, there has been a rapid accumulation of literature concerning the relationship between genetic variations in platelet glycoproteins and risk for coronary heart disease. In this study, we have presented a comprehensive review of the impact of platelet receptor polymorphisms and thrombotic risk.