Effect of sex difference on platelet aggregation using an optical method in healthy subjects

Sex-Related Differences in Platelet Aggregation: A Literature Review Supplemented with Local Data from a Group of Generally Healthy Individuals

The process of platelet aggregation is often influenced by several factors including sex and age. A literature review confirmed the existence of sex-related differences in platelet aggregation. Although 68 out of 78 papers found such differences, there are still some controversies regarding these differences, which can be due to multiple factors (age, trigger, concomitant disease, sample handling, etc.). These outcomes are discussed in line with novel results obtained from a local study, in which blood samples from a total of 53 overall healthy women and men with ages ranging from 20 to 66 years were collected. Aggregation was induced with seven different triggers (ristocetin, thrombin receptor activating peptide 6 [TRAP-6], arachidonic acid [AA], platelet-activating factor 16 [PAF-16], ADP, collagen, or thromboxane A₂ analog U-46619) ex vivo. In addition, three FDA-approved antiplatelet drugs (vorapaxar, ticagrelor, or acetylsalicylic acid [ASA]) were also tested. In general, women had higher aggregation responses to some agonists (ADP, TRAP), as well as lower benefit from inhibitors (ASA, vorapaxar). The aggregatory responses to AA and TRAP decreased with age in both sexes, while responses to ADP, U-46619, and PAF were affected by age only in women. In conclusion, more studies are needed to decipher the biological importance of sex-related differences in platelet aggregation in part to enable personalized antiplatelet treatment.

Platelet Responses in Cardiovascular Disease: Sex-Related Differences in Nutritional and Pharmacological Interventions

Cardiovascular diseases (CVD) represent one of the biggest causes of death globally, and their prevalence, aetiology, and outcome are related to genetic, metabolic, and environmental factors, among which sex- and age-dependent differences may play a key role. Among CVD risk factors, platelet hyperactivity deserves particular mention, as it is involved in the pathophysiology of main cardiovascular events (including stroke, myocardial infarction, and peripheral vascular injury) and is closely related to sex/age differences. Several determinants (e.g., hormonal status and traditional cardiovascular risk factors), together with platelet-related factors (e.g., plasma membrane composition, receptor signaling, and platelet-derived microparticles) can elucidate sex-related disparity in platelet functionality and CVD onset and outcome, especially in relation to efficacy of current primary and secondary interventional strategies. Here, we examined the state of the art concerning sex differences in platelet biology and their relationship with specific cardiovascular events and responses to common antiplatelet therapies. Moreover, as healthy nutrition is widely recognized to play a key role in CVD, we also focused our attention on specific dietary components (especially polyunsaturated fatty acids and flavonoids) and patterns (such as Mediterranean diet), which also emerged to impact platelet functions in a sex-dependent manner. These results highlight that full understanding of gender-related differences will be useful for designing personalized strategies, in order to prevent and/or treat platelet-mediated vascular damage.

The Effects of Andrographis paniculata on Platelet Activity in Healthy Thai Volunteers

Background. Andrographis paniculata (AP) has been used in Thai traditional medicine to treat various infections, including the common cold and fever. Its bioactive compound, andrographolide, has shown antiplatelet activities in an in vitro study model. Since clinical studies of the effects of AP on the human platelet function have never been reported, we investigated its effect on platelet activity in ten healthy volunteers. Methods. Two grams of AP was taken 3 times within one day. The blood was withdrawn by venipuncture before and 2 and 24 hours after the AP administration to analyze the effects of AP on platelet aggregation, the expression of enzyme cyclooxygenase (COX) mRNA and protein, and TXB₂, including P-selectin. Result. Even though there was no significant change in the studied parameters, this study exhibited patient-to-patient variability in platelet function. It was found that ADP-induced platelet aggregation tended to decrease after AP administration, while epinephrine-induced platelet aggregation in females tended to be higher than that in males for the entire study period. Moreover, COX-1 mRNA levels tended to decrease while P-selectin levels tended to rise after AP administration. Conclusion. These controversial results are possibly due to the multifactorial mechanisms of platelet aggregation as well as the multichemical composition of AP. Further study, probably at the molecular level, is needed to unveil the underlying mechanisms of action of AP.

Standardization and reference ranges for whole blood platelet function measurements using a flow cytometric platelet activation test

Introduction

Platelet function testing with flow cytometry has additional value to existing platelet function testing for diagnosing bleeding disorders, monitoring anti-platelet therapy, transfusion medicine and prediction of thrombosis. The major challenge is to use this technique as a diagnostic test. The aim of this study is to standardize preparation, optimization and validation of the test kit and to determine reference values in a population of 129 healthy individuals.

Methods

Platelet function tests with 3 agonists and antibodies against P-selectin, activated αIIbβ3 and glycoprotein Ib (GPIb), were prepared and stored at -20°C until used. Diluted whole blood was added and platelet activation was quantified by the density of activation markers, using flow cytometry. Anti-mouse Ig κ particles were included to validate stability of the test and to standardize results. Reference intervals were determined.

Results

Blood stored at room temperature (RT) for up to 4h after blood donation and preheated/tested at 37°C resulted in stable results (%CV<10%), in contrast to measuring at RT. The intra-assay %CV was <5%. Incubation of anti-mouse Ig κ particles with antibodies stored for up to 12 months proved to give a stable fluorescence. The inter-individual variation measured in the 129 individuals varied between 23% and 37% for P-selectin expression and αIIbβ3 activation, respectively.

Conclusions

The current study contributes to the translation of flow cytometry based platelet function testing from a scientific tool to a diagnostic test. Platelet function measurements, using prepared and stored platelet activation kits, are reproducible if executed at 37°C. The reference ranges can be validated in clinical laboratories and ongoing studies are investigating if reduced platelet reactivity in patients with bleeding complications can be detected.

Gender, race and diet affect platelet function tests in normal subjects, contributing to a high rate of abnormal results

To assess sources of variability in platelet function tests in normal subjects, 64 healthy young adults were tested on 2-6 occasions at 2 week intervals using four methods: platelet aggregation (AGG) in platelet-rich plasma (PRP) in the Bio/Data PAP-4 Aggregometer (BD) and Chrono-Log Lumi-Aggregometer (CL); and AGG in whole blood (WB) in the CL and Multiplate Platelet Function Analyser (MP), with ATP release (REL) in CL-PRP and CL-WB. Food and medication exposures were recorded prospectively for 2 weeks prior to each blood draw. At least one AGG abnormality was seen in 21% of 81 drug-free specimens with CL-PRP, 15% with CL-WB, 13% with BD-PRP and 6% with MP-WB, increasing with inclusion of REL to 28% for CL-PRP and 30% for CL-WB. Epinephrine AGG and REL were significantly reduced in males (P < 0·0001). Ristocetin AGG and collagen and thrombin REL were significantly reduced in Blacks (P < 0·0001). One-third of specimens drawn following flavonoid-rich food exposures had aberrant results, compared to 8·5% of specimens without such exposures (P = 0·0035). PRP tests had less intra-individual variation than WB tests. Gender, race, diet and test system affected results of platelet function testing in healthy subjects, suggesting caution when interpreting the results of platelet function testing in patients.

Reference intervals for platelet aggregation assessed by multiple electrode platelet aggregometry

INTRODUCTION

Analyses of platelet aggregation in hirudin whole blood using Multiplate® was validated. Reference intervals for the most commonly used agonists were established, and the association between platelet aggregation, age, gender and haematological values was analysed.

MATERIAL AND METHODS

We included 121 healthy individuals to establish reference intervals and six healthy individuals for evaluation of the day-to-day variation. Platelet aggregation was evaluated on hirudin whole blood employing Multiplate® induced by arachidonic acid, ADP, collagen and ristocetin (RISTOlow and RISTOhigh). Measurements of haematological values were performed employing Sysmex K-4500.

RESULTS

We found no association between platelet aggregation and age (p>0.57 for all agonists, except RISTOlow: p=0.05). Platelet aggregation was significantly higher in women compared to men for all agonists (p<0.0003), except RISTOlow (p=0.05). A reference interval is presented as 95% confidence interval suitable for any age and both sex. Day-to-day variation was <11% for all agonists except for RISTOlow. No association was found between platelet aggregation and haematocrit or red blood cell count after adjusting for age and gender except for RISTOhigh. A positive significant association was found between platelet count and platelet aggregation (p<0.04). Finally, a significant positive association was found between platelet aggregation and white blood cell count for all agonists (p<0.05) except RISTOlow and RISTOhigh (p>0.05).

CONCLUSION

Reference intervals for platelet aggregation in healthy individuals (age: 17 to 66 years) were established in hirudin whole blood measured by Multiplate® employing the most commonly used agonists.

Gender differences in platelet aggregation in healthy individuals

This study evaluated gender variability in platelet aggregation in response to common agonists. Platelet aggregation was measured in 36 healthy men and women free of any antiplatelet medication, aged 22-36 years, of Caucasian (White not of Hispanic origin), Hispanic, and African-American not of Hispanic origin. In this ex-vivo study, we investigated platelet aggregation in response to adenosine-5'-diphosphate (ADP), epinephrine (EPI), arachidonic acid (AA) and collagen (COL), using a platelet ionized calcium aggregometer (Chrono-Log Co.). Platelet aggregation response to all tested agonists was higher in females than in males regardless of ethnicity. The most significant differences were observed with collagen (P < 0.01). Among the ethnic groups, Caucasian women were most prone to platelet aggregation. Gender is a determinant of agonist effects on platelet aggregability in healthy subjects.

The effect of menstrual cycle on platelet aggregation in reproductive-age women

Our aim was to assess the change in platelet activity along the menstrual cycle. We conducted a prospective observational study. The study group included 16 healthy women with regular menstrual cycles, which were compared to a control group of 14 healthy males. Exclusion criteria were age <18 years or >45 years, use of oral contraceptives or any other forms of hormonal therapy and medical disorders or medications that might affect platelet aggregation. Blood samples were taken from each of the women at four different phases of the menstrual cycle: day 1 +/- 1, day 7 +/- 1, day 14 +/- 1, and day 21 +/- 1. A single blood sample was taken from the males. Platelet aggregation was assessed in whole blood samples using the Multiplate analyzer with three different agonists (ADP, arachidonic acid (AA), and thrombin-receptor activating peptide (TRAP)). Platelet aggregation for each of the women at each of the phases of the menstrual cycle was expressed as the percentage change from the day 1 +/- 1 value. A total of 390 aggregation assays were performed. The mean aggregation activity was significantly higher in females compared with males, irrespective of the agonist used. For the TRAP and the ADP agonists, the relative platelet activity decreased along the menstrual cycle from day 1 towards day 21 and from day 7 towards day 21, respectively, although differences reached statistical significance only for day 21 (-12.4% +/- 3.2%, P < 0.05 for TRAP, and -9.5% +/- 3.9%, P < 0.05 for ADP). When using AA to induce platelet aggregation, the relative platelet activity was highest around the time of ovulation (11.0% +/- 4.7%) and was significantly lower on day 21 (-8.5% +/- 6.7%, P < 0.05). In conclusion, platelet aggregation activity is higher in females compared with males. The association between the phase of the menstrual cycle and platelet activity appears to vary with the type of agonist, but platelet aggregation is consistently lowest in the mid-luteal phase irrespective of the agonist used.