Effect of genetic variations in platelet glycoproteins Ibalpha and VI on the risk for coronary heart disease events in postmenopausal women taking hormone therapy

Estradiol cycling drives female obesogenic adipocyte hyperplasia

White adipose tissue (WAT) distribution is sex dependent. Adipocyte hyperplasia contributes to WAT distribution in mice driven by cues in the tissue microenvironment, with females displaying hyperplasia in subcutaneous and visceral WAT, while males and ovariectomized females have visceral WAT (VWAT)-specific hyperplasia. However, the mechanism underlying sex-specific hyperplasia remains elusive. Here, transcriptome analysis in female mice shows that high-fat diet (HFD) induces estrogen signaling in adipocyte precursor cells (APCs). Analysis of APCs throughout the estrous cycle demonstrates increased proliferation only when proestrus (high estrogen) coincides with the onset of HFD feeding. We further show that estrogen receptor α (ERα) is required for this proliferation and that estradiol treatment at the onset of HFD feeding is sufficient to drive it. This estrous influence on APC proliferation leads to increased obesity driven by adipocyte hyperplasia. These data indicate that estrogen drives ERα-dependent obesogenic adipocyte hyperplasia in females, exacerbating obesity and contributing to the differential fat distribution between the sexes.

Sex-Dependent Effect of Platelet Nitric Oxide: Production and Platelet Reactivity in Healthy Individuals

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Platelet reactivity is greater in healthy women compared with men.

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Following an oral nitrate load, platelet nitric oxide production increased disproportionately more in healthy women than healthy men with attenuated platelet reactivity in women and enhanced platelet reactivity in men.

A nitrate-rich diet has many cardiovascular benefits, but the mechanism behind this is unclear. We hypothesized that the ingestion of nitrate augments nitrate to nitrite reduction, leading to nitric oxide (NO) production, which may suppress platelet reactivity. In a randomized, double-blinded, placebo-controlled study involving healthy individuals, ingestion of nitrate augmented saliva and plasma nitrite/nitrate concentration and enhanced platelet NO production disproportionately in women compared with men. The response of elevated platelet NO in men was increased platelet reactivity and the response of markedly elevated platelet NO in women slightly inhibited platelet reactivity.

The Role of Epigenetics in the Regulation of Hemostatic Balance

Epigenetics, a term conventionally used to explain the intricate interplay between genes and the environment, is now regarded as the fundament of developmental biology. Several lines of evidence garnered over the past decades suggest that epigenetic alterations, mostly encompassing DNA methylation, histone tail modifications, and generation of microRNAs, play an important, though still incompletely explored, role in both primary and secondary hemostasis. Epigenetic variations may interplay with platelet functions and their responsiveness to antiplatelet drugs, and they may also exert a substantial contribution in modulating the production and release into the bloodstream of proteins involved in blood coagulation and fibrinolysis. This emerging evidence may have substantial biological and clinical implications. An enhanced understanding of posttranscriptional mechanisms would help to clarify some remaining enigmatic issues in primary and secondary hemostasis, which cannot be thoughtfully explained by genetics or biochemistry alone. Increased understanding would also pave the way to developing innovative tests for better assessment of individual risk of bleeding or thrombosis. The accurate recognition of key epigenetic mechanisms in hemostasis would then contribute to identify new putative therapeutic targets, and develop innovative agents that could be helpful for preventing or managing a vast array of hemostasis disturbances.

Sexual Dimorphism in Drug Metabolism and Pharmacokinetics

Background:

Sex and gender-based differences are observed well beyond the sex organs and affect several physiological and biochemical processes involved in the metabolism of drug molecules. It is essential to understand not only the sex and gender-based differences in the metabolism of the drug but also the molecular mechanisms involved in the regulation of drug metabolism for avoiding sex-related adverse effects of drugs in the human.

Method:

The articles on the sex and gender-based differences in the metabolism of drug molecules were retrieved from the Pub Med database. The articles were classified into the metabolism of the drug molecule, gene expression regulation of drug-metabolizing enzymes, the effect of sex hormones on the metabolism of drug, expression of drugmetabolizing enzymes, etc.

Result:

Several drug molecules are known, which are metabolized differently in males and females. These differences in metabolism may be due to the genomic and non-genomic action of sex hormones. Several other drug molecules still require further evaluation at the molecular level regarding the sex and gender-based differences in their metabolism. Attention is also required at the effect of signaling cascades associated with the metabolism of drug molecules.

Conclusion:

Sex and gender-based differences in the metabolism of drugs exist at various levels and it may be due to the genomic and non-genomic action of sex hormones. Detailed understanding of the effect of sex and related condition on the metabolism of drug molecules will help clinicians to determine the effective therapeutic doses of drugs dependingon the condition of patient and disease.

Epigenetic modulation of glycoprotein VI gene expression by DNA methylation

AIMS

Glycoprotein VI (GPVI) is an important platelet membrane receptor. The expression of GPVI on platelet membranes is increased in patients with coronary heart disease (CHD). DNA methylation is one of the most common post-replication and pre-transcriptional modifications and plays a critical role in the regulation of gene expression. Here, we aimed to reveal how methylation regulates GPVI expression.

MAIN METHODS

Pyrosequencing was used to determine whether the GPVI promoter region in leukocytes from CHD patients is hypomethylated. The expressions of GPVI in CHD patients were detected using qRT-PCR and Western blot. The effect of methylation of the GPVI promoter region on regulating its transcriptional activity was analyzed using in vitro luciferase assay. The expression of P-selectin in platelet-like particles was determined using flow cytometry, and SYK phosphorylation was observed using Western blot.

KEY FINDINGS

We found that the GPVI promoter region in leukocytes from CHD patients was hypomethylated and the expression of GPVI at the mRNA and protein level was elevated in CHD patients. We also found that the hypermethylation of GPVI promoter region inhibited the expression of GPVI in the -322 to +75, -539 to +75, and -937 to +75 regions in Dami cells. Moreover, the data showed that the methylation or demethylation regulated the GPVI expression and platelet-like particle activation in Dami cells.

SIGNIFICANCE

Taken together, these results indicate that DNA methylation regulates GPVI expression and that CpG methylation levels in the promoter region of the GPVI gene may be a biomarker of CHD.

miR-15a-5p regulates expression of multiple proteins in the megakaryocyte GPVI signaling pathway

Essentials The action of microRNAs (miRs) in human megakaryocyte signaling is largely unknown. Cord blood-derived human megakaryocytes (MKs) were used to test the function of candidate miRs. miR-15a-5p negatively regulated MK GPVI-mediated αIIbβ3 activation and α-granule release. miR-15a-5p acts as a potential "master-miR" regulating genes in the MK GPVI signaling pathway. SUMMARY: Background Megakaryocytes (MKs) invest their progeny platelets with proteins and RNAs. MicroRNAs (miRs), which inhibit mRNA translation into protein, are abundantly expressed in MKs and platelets. Although platelet miRs have been associated with platelet reactivity and disease, there is a paucity of information on the function of miRs in human MKs. Objective To identify MK miRs that regulate the GPVI signaling pathway in the MK-platelet lineage. Methods Candidate miRs associated with GPVI-mediated platelet aggregation were tested for functionality in cultured MKs derived from cord blood. Results An unbiased, transcriptome-wide screen in 154 healthy donors identified platelet miR-15a-5p as significantly negatively associated with CRP-induced platelet aggregation. Platelet agonist dose-response curves demonstrated activation of αIIbβ3 in suspensions of cord blood-derived cultured MKs. Overexpression and knockdown of miR-15a-5p in these MKs reduced and enhanced, respectively, CRP-induced αIIbβ3 activation but did not alter thrombin or ADP stimulation. FYN, SRGN, FCER1G, MYLK. and PRKCQ, genes involved in GPVI signaling, were identified as miR-15a-5p targets and were inhibited or de-repressed in MKs with miR-15a-5p overexpression or inhibition, respectively. Lentiviral overexpression of miR-15a-5p also inhibited GPVI-FcRγ-mediated phosphorylation of Syk and PLCγ2, GPVI downstream signaling molecules, but effects of miR-15a-5p on αIIbβ3 activation did not extend to other ITAM-signaling receptors (FcγRIIa and CLEC-2). Conclusion Cord blood-derived MKs are a useful human system for studying the functional effects of candidate platelet genes. miR-15a-5p is a potential "master-miR" for specifically regulating GPVI-mediated MK-platelet signaling. Targeting miR-15a-5p may have therapeutic potential in hemostasis and thrombosis.

Copy number variants implicate cardiac function and development pathways in earthquake-induced stress cardiomyopathy

The pathophysiology of stress cardiomyopathy (SCM), also known as takotsubo syndrome, is poorly understood. SCM usually occurs sporadically, often in association with a stressful event, but clusters of cases are reported after major natural disasters. There is some evidence that this is a familial condition. We have examined three possible models for an underlying genetic predisposition to SCM. Our primary study cohort consists of 28 women who suffered SCM as a result of two devastating earthquakes that struck the city of Christchurch, New Zealand, in 2010 and 2011. To seek possible underlying genetic factors we carried out exome analysis, genotyping array analysis, and array comparative genomic hybridization on these subjects. The most striking finding was the observation of a markedly elevated rate of rare, heterogeneous copy number variants (CNV) of uncertain clinical significance (in 12/28 subjects). Several of these CNVs impacted on genes of cardiac relevance including RBFOX1, GPC5, KCNRG, CHODL, and GPBP1L1. There is no physical overlap between the CNVs, and the genes they impact do not appear to be functionally related. The recognition that SCM predisposition may be associated with a high rate of rare CNVs offers a novel perspective on this enigmatic condition.

Focusing on plasma glycoprotein VI

New methods for analysing both platelet and plasma forms of the platelet-specific collagen receptor, glycoprotein VI (GPVI) in experimental models or human clinical samples, and the development of the first therapeutic compounds based on dimeric soluble GPVI-Fc or anti-GPVI antibody-based constructs, coincide with increased understanding of the potential pathophysiological role of GPVI ligand binding and shedding. Platelet GPVI not only mediates platelet activation at the site of vascular injury where collagen is exposed, but is also implicated in the pathogenesis of other diseases, such as atherosclerosis and coagulopathy, rheumatoid arthritis and tumour metastasis. Here, we describe some of the critical mechanisms for generating soluble GPVI from platelets, and future avenues for exploiting this unique platelet-specific receptor for diagnosis and/or disease prevention.

Plasma-derived Extracellular Vesicles Contain Predictive Biomarkers and Potential Therapeutic Targets for Myocardial Ischemic (MI) Injury

Myocardial infarction (MI) triggers a potent inflammatory response via the release of circulatory mediators, including extracellular vesicles (EVs) by damaged cardiac cells, necessary for myocardial healing. Timely repression of inflammatory response are critical to prevent and minimize cardiac tissue injuries, nonetheless, progression in this aspect remains challenging. The ability of EVs to trigger a functional response upon delivery of carried bioactive cargos, have made them clinically attractive diagnostic biomarkers and vectors for therapeutic interventions. Using label-free quantitative proteomics approach, we compared the protein cargo of plasma EVs between patients with MI and from patients with stable angina (NMI). We report, for the first time, the proteomics profiling on 252 EV proteins that were modulated with >1.2-fold after MI. We identified six up-regulated biomarkers with potential for clinical applications; these reflected post-infarct pathways of complement activation (Complement C1q subcomponent subunit A (C1QA), 3.23-fold change, p = 0.012; Complement C5 (C5), 1.27-fold change, p = 0.087), lipoprotein metabolism (Apoliporotein D (APOD), 1.86-fold change, p = 0.033; Apolipoprotein C-III (APOCC3), 2.63-fold change, p = 0.029) and platelet activation (Platelet glycoprotein Ib alpha chain (GP1BA), 9.18-fold change, p < 0.0001; Platelet basic protein (PPBP), 4.72-fold change, p = 0.027). The data have been deposited to the ProteomeXchange with identifier PXD002950. This novel biomarker panel was validated in 43 patients using antibody-based assays (C1QA (p = 0.005); C5 (p = 0.0047), APOD (p = 0.0267); APOC3 (p = 0.0064); GP1BA (p = 0.0031); PPBP (p = 0.0465)). We further present that EV-derived fibrinogen components were paradoxically down-regulated in MI, suggesting that a compensatory mechanism may suppress post-infarct coagulation pathways, indicating potential for therapeutic targeting of this mechanism in MI. Taken together, these data demonstrated that plasma EVs contain novel diagnostic biomarkers and therapeutic targets that can be further developed for clinical use to benefit patients with coronary artery diseases (CADs).

Gender Differences in Cardiovascular Drugs

The different responses of women and men to cardiovascular drugs reflect gender -specific variances in pharmacokinetic profiles and drug sensitivities coupled to inherent differences in the underlying physiology of each sex. Thus, many common cardiovascular drugs exhibit gender -specific therapeutic and adverse effects. For example, the QT interval of the electrocardiogram is longer in women compared to men, and accordingly, drugs that prolong the QT interval are more likely to cause lethal ventricular arrhythmias in female than male patients. As more clinical drug trials include women subjects, our improved knowledge base for assessing the risk/benefit ratio for cardiovascular drugs in women will enable us to consider gender as one factor in prescribing drugs and adjusting drug loading and maintenance dosages. This short review will present evidence for gender- related differences in the responses to common cardiovascular drugs including statins, antiplatelet and antithrombotic agents, β-blockers, digoxin, vasodilator therapies, and drugs associated with the Long QT Syndrome.

Pharmacogenomics, pharmacokinetics and pharmacodynamics: interaction with biological differences between men and women

Pharmacological response depends on multiple factors and one of them is sex-gender. Data on the specific effects of sex-gender on pharmacokinetics, as well as the safety and efficacy of numerous medications, are beginning to emerge. Nevertheless, the recruitment of women for clinical research is inadequate, especially during the first phases. In general, pharmacokinetic differences between males and females are more numerous and consistent than disparities in pharmacodynamics. However, sex-gender pharmacodynamic differences are now increasingly being identified at the molecular level. It is now even becoming apparent that sex-gender influences pharmacogenomics and pharmacogenetics. Sex-related differences have been reported for several parameters, and it is consistently shown that women have a worse safety profile, with drug adverse reactions being more frequent and severe in women than in men. Overall, the pharmacological status of women is less well studied than that of men and deserves much more attention. The design of clinical and preclinical studies should have a sex-gender-based approach with the aim of tailoring therapies to an individual's needs and concerns.

The frequencies of six important thrombophilic mutations in a population of the Czech Republic

The primary aim was to determine frequencies of mutations related to risk of venous thrombosis in healthy Caucasians in Central Bohemia. In a cohort of 1527 healthy individuals the frequency of risk alleles for the mutations FV Leiden and FII 20210G>A was 4.5% and 1.3%, respectively. Frequency of 4G PAI-1 allele was 55.5%. Genotype frequencies were: GG 91.03%, GA 8.91%, and AA 0.07% for FV Leiden; GG 97.45%, GA 2.49%, and AA 0.07% for FII 20210G>A; 4G/4G 30.26%, 4G/5G 50.56%, and 5G/5G 19.19% for PAI-1. Frequency of the risk allele A in polymorphism SERPINC1 (IVS +141G >A) was 11.3%, and frequencies of genotypes were as follows: GG 78.36%, GA 20.66%, and AA 0.98%. Frequency of the risk allele T for polymorphism GP6 13254T>C was 87.7%, and frequencies of genotypes were as follows: TT 77.14%, TC 21.15%, and CC 1.70%. Frequency of the risk allele A in polymorphism CYP4V2 (Lys259Gln) was 65.2%, and frequencies of genotypes were: CC 12.25%, CA 45.12 %, and AA 42.63%. All observed genotypes and alleles frequencies were without gender differences. Their occurrences confirm a relatively high prevalence of hereditary thrombophilia predisposition in the Czech Republic.

Association of platelet collagen receptor polymorphisms with premature acute myocardial infarction

The impact of platelet collagen receptor polymorphisms in the pathogenesis of myocardial infarction at young age remains unknown. To determine whether either of the two platelet collagen receptor polymorphisms (GP VI T13254C and GP Ia C807T) was associated with premature acute myocardial infarction. One hundred patients with premature acute myocardial infarction and 100 age-matched controls with normal coronary angiograms were studied. Genotyping was done using PCR followed by restriction fragment length polymorphism (RFLP). GP Ia C807T polymorphism was more frequent in the patient group (65%) than in the control group (53%). However, there was no association between this polymorphism and premature acute myocardial infarction (P = 0.08). The prevalence of T13254C polymorphism did not differ between patients (38%) and controls (33%), and this polymorphism was not associated with premature acute myocardial infarction (P = 0.46). Logistic regression analysis also indicated no association between these polymorphisms and premature acute myocardial infarction (C807T with P = 0.51 and T13254C with P = 0.20). There is no association between GP VI T13254C or GP Ia C807T polymorphisms and premature acute myocardial infarction.

Platelet biology and response to antiplatelet therapy in women: implications for the development and use of antiplatelet pharmacotherapies for cardiovascular disease

Women are underrepresented in cardiovascular studies, even as their preponderance in the aging population steadily increases. Although concerns have been raised about the differential benefit of antiplatelet medications for women, the propensity for increased bleeding among women has also been recognized. A better understanding of the factors contributing to the observed sex-related differences in platelet biology is warranted. These factors include differences in the frequency and expression of genetic polymorphisms affecting platelet responsiveness to agonists (with and without antiplatelet therapies), which might be obtained through population-based studies and in large controlled clinical trials; inflammatory marker levels and their influence on atherothrombotic risk, and the role of specific hormones in mediating platelet activation and function. Knowledge gained about these mechanistic factors might inform the development of sex-specific antithrombotic treatment regimens that confer optimized safety and efficacy.

Platelet signaling

This chapter summarizes current ideas about the intracellular signaling that drives platelet responses to vascular injury. After a brief overview of platelet activation intended to place the signaling pathways into context, the first section considers the early events of platelet activation leading up to integrin activation and platelet aggregation. The focus is on the G protein-mediated events utilized by agonists such as thrombin and ADP, and the tyrosine kinase-based signaling triggered by collagen. The second section considers the events that occur after integrin engagement, some of which are dependent on close physical contact between platelets. A third section addresses the regulatory events that help to avoid unprovoked or excessive platelet activation, after which the final section briefly considers individual variations in platelet reactivity and the role of platelet signaling in the innate immune response and embryonic development.

Variability of platelet indices and function: acquired and genetic factors

Each individual has an inherent variable risk of bleeding linked to genetic or acquired abnormal platelet number or platelet dysfunction. In contrast, it is less obvious that the variability of platelet phenotypes (number, mean platelet volume, function) may contribute to the variable individual risk of thrombosis. Interindividual variability of platelet indices or function may be either due to acquired factors, such as age, sex, metabolic variables, smoke, dietary habits, and ongoing inflammation, or due to genetic factors. Acquired variables explain a small portion of the heterogeneity of platelet parameters. Genetic factors, instead, appear to play a major role, although a consistent portion of such a genetic variance has not yet been attributed to any specific genetic factor, possibly due to the high number of DNA loci potentially involved and to the limited effect size of each individual SNP. A portion of variance remains thus unexplained, also due to variability of test performance. A major contradiction in present platelet knowledge is, indeed, the difficulty to reconcile the universally accepted importance of platelet indices or function and the lack of reliable platelet parameters in cardiovascular risk prediction models. Trials on antiplatelet drugs were generally designed to select a homogeneous sample, whose results could be applied to an "average subject," tending to exclude the deviation/extreme values. As the current indications for antiplatelet treatment in primary or secondary prevention of ischemic vascular disease still derive from the results of such clinical trials where platelet function and its variability was not investigated, we cannot at present rely upon any current platelet test to either initiate, or monitor, or modify or stop treatment with any antiplatelet drug. Evidence is, however, increasing that traditional platelet aggregometry and other more recently developed platelet function assays could be useful to optimize antiplatelet therapy and to predict major adverse cardiac events.The observation of interindividual differences in platelet response to antiplatelet drugs has enlarged the spectrum and the possible clinical relevance of the variability of platelet indices or function. The development of "personalized medicine" will benefit from the concepts discussed in this chapter.

Polymorphisms in the platelet-specific collagen receptor GP6 are associated with risk of nonfatal myocardial infarction in Caucasians

BACKGROUND AND AIMS

Glycoprotein 6 (GP6) is a platelet-specific collagen receptor implicated in the thrombotic pathway to acute myocardial infarction (AMI), but a possible genetic relationship between GP6 and AMI is poorly understood. We tested for the genetic association between AMI and single nucleotide polymorphisms (SNPs) in 24 loci, including GP6.

METHODS AND RESULTS

We conducted a case-control study of AMI and GP6 in a community-based population (n = 652 cases, 625 controls). We also examined men and women separately and stratified the latter by use of hormone replacement therapy (HRT). Among both sexes, the strongest association was for a protective missense polymorphism (rs1163662) in the GP6 gene (OR = 0.70; Bonferroni-adjusted p < 0.05). SNPs in GP6 were also strongly associated with AMI among women who reported ever taking HRT, but not among women who never took HRT. Haplotype analyses were consistent with the single-SNP findings.

CONCLUSIONS

In this sample of white non-Hispanic men and women, several SNPs in GP6 were significantly related to risk of AMI. Development of pharmacologic therapy directed towards platelet activity and thrombosis may reduce the incidence of AMI among at-risk groups.

Hypercoagulable state, pathophysiology, classification and epidemiology

Hypercoagulable state is not a uniform disease. It is a complex condition with an abnormal propensity for thrombosis that may or may not lead to thrombosis, depending on complex gene-gene and gene-environment interactions. The prevalence of the hypercoagulable state depends on the ethnicity and clinical history of the population being studied. The consequences of a hypercoagulable state due to thrombosis of veins and arteries are the most important cause of sickness and death in developed countries at present. Primary hypercoagulable state is an inherited condition caused by the reduced level of natural anticoagulants due to a qualitative defect or quantitative deficiency of an antithrombotic protein, or increased concentrations or function of coagulation factors. Most of the inherited abnormalities recognized to date have little or no effect on arterial thrombosis and are associated primarily with venous thromboembolism. Arterial thrombosis usually develops as a complication of atherosclerosis and patients usually have more than one traditional risk factor. Secondary hypercoagulable states generally occur as a result of a large number of transient or permanent acquired conditions that increase the tendency for formation of blood clots. New epidemiological data and clinical trials suggest that many acquired risk factors in the pathophysiology of arterial and venous thrombosis overlap and coexist for both disorders.

The minor allele of GP6 T13254C is associated with decreased platelet activation and a reduced risk of recurrent cardiovascular events and mortality: results from the SMILE-Platelets project

BACKGROUND

Contradictory results have been published on the effects of T13254C (rs1613662), which distinguishes the two major isoforms of GP6, the gene encoding the platelet receptor glycoprotein VI, on platelet function and the risk of cardiovascular disease.

METHODS

We performed a population-based case-control study, the Study of Myocardial Infarctions in Leiden, among 547 male patients with a first myocardial infarction (MI) and 646 control subjects, as well as a prospective cohort study in which the same MI patients were followed for recurrent events (fatal and non-fatal MI and unstable angina) and mortality (median follow-up of 12 years). P-selectin expression by platelets induced by crosslinked collagen-related peptide (CRP-XL) was measured by whole blood flow cytometry in 274 MI patients.

RESULTS

T13254C was not associated with a first MI, but seemed to be associated with a reduced incidence of recurrent events [per-allele hazard ratio 0.77, 95% confidence interval (CI) 0.56-1.06] and mortality (hazard ratio 0.57, 95% CI 0.37-0.89). Pooling with the Heart and Estrogen/Progestin Replacement Study revealed hazard ratios of 0.81 (95% CI 0.66-0.99) and 0.73 (95% CI 0.55-0.96). The minor C-allele was also strongly associated with a reduced percentage of P-selectin-expressing platelets. The reduction per C-allele was 23% (95% CI 18-28%). In an independent study of 219 healthy volunteers, the per-allele reduction of CRP-XL-induced aggregation was 10% (95% CI 2-18%).

CONCLUSION

The minor allele of GP6 T13254C that reduced platelet activation and aggregation also seemed to be associated with a reduced incidence of recurrent cardiovascular events and mortality, but was not associated with first MI.

Platelet pharmacogenomics

Platelet responsiveness to conventional antiplatelet therapy underlies a high interindividual variability influenced by various factors. For instance, antiplatelet therapy does not curtail the expected effects in a relevant number of patients as demonstrated by the occurrence of repeated cardiovascular events including stent thrombosis and/or by inadequate platelet inhibition measured by in vitro platelet function assays. Besides non-genetic factors such as age, gender, liver and renal function and co-medication, considerable variation of antiplatelet drug responsiveness can be attributed to genetic factors including polymorphisms and genetic variants of platelet surface proteins and drug metabolizing enzymes. Nowadays, platelet pharmacogenomics has started a new field with the goal to link genetic information of various drug targets to interindividual variability of drug response. Evolving data from large cohort studies suggest a promising role for pharmacogenomics in the context of antiplatelet therapy. Additionally, with the revolution of low cost and high-throughput genotyping techniques, genetic testing has become affordable for clinical application and individualization of therapy. However, a key issue to define the future role of pharmacogenomics will rely on the benefit and the timeliness of implementing the genetic information into therapeutic decision. Hence, it warrants further investigations to document the prognostic effects of therapeutic alterations in distinct genotypes. Concerning the safety profile of emerging antiplatelet and antithrombotic drugs in certain risk groups it would be fatal to individualize treatment barely on behalf of an atherothrombotic genotype. In contrast, individual risk assessment combining non-genetic information and pharmacogenetic analysis represents a reasonable concept. Here, we provide a review on current data describing the role of pharmacogenomics in the field of antiplatelet drug treatment in cardiovascular patients with future directions.

[Relationship between polymorphism of platelet membrane glycoprotein IIIa and coronary heart disease with blood-stasis syndrome in Chinese Han population]

OBJECTIVE

To investigate the genotype distributions of PLA1/PLA2 polymorphism in Chinese Han population from Beijing and Hebei Province and to study the correlation between the platelet membrane glycoprotein IIIa polymorphism and coronary heart disease (CHD) or CHD with blood-stasis syndrome.

METHODS

A total of 110 CHD patients with blood-stasis syndrome and 102 CHD patients with non-blood stasis syndrome were enrolled in the case-control study. Thirty-nine healthy volunteers were included as normal control. Syndrome differentiation in traditional Chinese medicine was performed in all of the patients. The genomic DNA was isolated from the whole blood and the locus typing of PLA was determined by TaqMan probe technology.

RESULTS

The locus typing of PLA1/PLA2 gene polymorphism was exclusively PLA1/PLA1 (TT) in healthy people, CHD patients and CHD patients with blood-stasis syndrome, while GPIIIa PLA1/PLA2 (TC) and PLA2/PLA2 (CC) were not found in all the selected objects. Statistical analysis of locus typing for other PLA1/PLA1 polymorphisms was not made in the study.

CONCLUSION

The PLA1/PLA2 polymorphism of membrane glycoprotein IIIa is not a risk factor for CHD patients or CHD patients with blood-stasis syndrome in Chinese Han population, and the related genes may be some other gene polymorphisms.

Estrogen, inflammation, and platelet phenotype

BACKGROUND

Although exogenous estrogenic therapies increase the risk of thrombosis, the effects of estrogen on formed elements of blood are uncertain.

OBJECTIVE

This article examines the genomic and nongenomic actions of estrogen on platelet phenotype that may contribute to increased thrombotic risk.

METHODS

To determine aggregation, secretion, protein expression, and thrombin generation, platelets were collected from experimental animals of varying hormonal status and from women enrolled in the Kronos Early Estrogen Prevention Study.

RESULTS

Estrogen receptor beta predominates in circulating platelets. Estrogenic treatment in ovariectomized animals decreased platelet aggregation and adenosine triphosphate (ATP) secretion. However, acute exposure to 17beta-estradiol did not reverse decreases in platelet ATP secretion invoked by lipopolysaccharide. Thrombin generation was positively correlated to the number of circulating microvesicles expressing phosphatidylserine.

CONCLUSION

Assessing the effect of estrogen treatments on blood platelets may lead to new ways of identifying women at risk for adverse thrombotic events with such therapies.

Post-menopausal hormone therapy and cardiovascular events: a new paradigm based on pharmacogenetics?

The risk of coronary heart disease (CHD) events increases in women after menopause and it was thought that hormone therapy (HT) would decrease this risk. However, numerous large randomized clinical trials have not demonstrated decreased risk in secondary prevention and some have actually shown increased risk of cardiovascular events with HT in primary prevention. Platelets are involved in CHD events and platelet glycoprotein single-nucleotide polymorphisms may help to identify risk and treatment efficacy. It may become a plausible strategy in the future for clinicians to identify, by genotyping, high-risk patients who would benefit from HT to reduce CHD risk as well as to identify patients with neutral risk for whom HT could be harmful.

Platelet glycoprotein VI-related clinical defects

Human patients with defects associated with the platelet collagen receptor, glycoprotein (GP)VI, are rare and usually described as having a mild bleeding disorder. However, here we review clinical profiles of patients with familial or acquired GPVI defects, revealing the bleeding defect is often severe and associated with immune dysfunction. GPVI is a member of the immunoreceptor family, and co-expressed on platelets with Fc receptor gamma-chain (FcRgamma). Ligand binding to GPVI leads to activation of platelet integrins, in particular alpha(IIb)beta(3) that mediates platelet aggregation; and activation of endogenous platelet metalloproteinases resulting in ectodomain shedding and release of a soluble GPVI fragment. Increasing evidence supports the functional importance of GPVI/FcRgamma in thrombus formation at arterial shear rates, and expression levels of platelet GPVI may be a marker of thrombotic risk. Over the past 20 years, patients have been reported with GPVI-related defects involving: (i) an acquired deficiency, resulting from (a) anti-GPVI autoantibodies or (b) other causes; or (ii) a congenital deficiency, where (c) GPVI is not expressed or (d) is expressed in a dysfunctional form with defective signalling to alpha(IIb)beta(3). Clinical consequences of GPVI-related defects may be uniquely informative about the role of platelet GPVI in health and disease.

Platelet reactivity and genetics down on the pharm

It is widely accepted that there is marked inter-individual variation in platelet function, although this has not been formally studied in large numbers of subjects. We have recruited and studied three large populations: one to characterize platelet variation and the factors responsible for it; a second to estimate heritabilities of the variation in platelet function; and a third to test for interactions between platelet genes and hormone therapy in postmenopausal women. We find that platelet variability is substantial, inherited and can be reproducibly detected. We genotyped 2145 women in the Heart and Estrogen/progestin Replacement Study followed for coronary heart disease (CHD) events for 6 years and found that common combinations of polymorphisms in the genes for GPIbalpha and GPVI were associated with hormone therapy harm, benefit or no effect. If corroborated in future studies, platelet genotyping could be used to predict postmenopausal hormone safety.