The effect of exercise and training status on platelet activation: do cocoa polyphenols play a role?

Sedentary and trained men respond differently to the same intensity of exercise, this is probably related to their platelet reactivity and antioxidant capacity. There is growing interest in the utilization of antioxidant-rich plant extracts as dietary food supplements. The aim of this study was to investigate the effect of an acute bout of sub maximal exercise on platelet count and differential response of platelet activation in trained and sedentary subjects and to observe if cocoa polyphenols reverse the effect of exercise on platelet function. The practical significance of this study was that many sedentary people engage in occasional strenuous exercise that may predispose them to risk of heart disease. Fasting blood samples were collected from 16 male subjects, pre and post 1-h cycling exercise at 70% of maximal aerobic power (VO2max) before and after consumption of cocoa or placebo. Agonist stimulated citrated whole blood was utilized for measuring platelet aggregation, adenosine triphosphate (ATP) release and platelet activation. Baseline platelet count (221 ± 33 times 109/L) and ATP release (1.4 ± 0.6 nmol) increased significantly (P < 0.05) after exercise in all subjects. Baseline platelet numbers in the trained were higher (P < 0.05) than in the sedentary (235 ± 37 vs. 208 ± 34 times 109/L), where as platelet activation in trained was lower (P < 0.05) than sedentary (51 ± 6 vs. 59 ± 5%). Seven days of cocoa polyphenol supplementation had little effect on any of the parameters measured. We conclude that trained subjects show decreased activation of stimulated platelets when compared to the sedentary subjects and short-term cocoa polyphenol supplementation did not decrease platelet activity in response to exercise independent of prior training status.

Immune thrombocytopenic purpura (ITP) and breast cancer. Does adjuvant therapy for breast cancer improve platelet counts in ITP?

Although both breast cancer and immune thrombocytopenic purpura (ITP) are common conditions, the simultaneous coexistence of these two diseases is rare. ITP is an autoimmune disease in which the presence of autoantibodies against platelets results in splenic sequestration and thrombocytopenia that may be associated with lymphoid neoplasms [1]. Except for an observational case series of 10 patients [2], only a few individual case reports of ITP coinciding with breast cancer have been reported [3–8]. We are reporting two cases with simultaneous confirmed ITP and breast cancer. The platelet counts in both women have improved during adjuvant breast cancer chemotherapy.

Impact on hemostatic parameters of interrupting sitting with intermittent activity

Introduction: Excessive sitting has been associated with an elevated risk of vascular conditions, particularly venous thrombosis. Interrupting sitting time with intermittent physical activity can reduce venous stasis; however, impacts on other aspects of thrombogenesis are less understood. Purpose: To examine the effects of interrupting sitting time on blood coagulation and blood volume parameters in sedentary, middle-age, overweight/obese adults (11 men and 8 women; age = 53.8 T 4.9 yr, body mass index = 31.2 T 4.1 kgImj2; mean T SD). Methods: The randomized three-period, three-treatment acute crossover trial consisted of uninterrupted sitting and sitting interrupted by 2-min bouts of either light- or moderate-intensity treadmill walking every 20 min. In each trial condition, blood samples were collected at baseline before the consumption of a standardized meal (j2 h) and postintervention (5 h). Results: Plasma fibrinogen increased from baseline with uninterrupted sitting (0.24 gILj1, 95% confidence interval = 0.13–0.34, P G 0.001). Lightintensity but not moderate-intensity activity breaks attenuated the increase by 0.17 gILj1 (95% confidence interval = 0.01–0.32, P G 0.05). There were no between-condition differences in prothrombin time, activated partial thromboplastin time, von Willebrand
factor, D-dimer, or platelet count. Uninterrupted sitting reduced plasma volume and increased hematocrit, hemoglobin, and red blood cell count; effects attenuated by both light- and moderate-intensity breaks (P G 0.05). White blood cell count increased with uninterrupted sitting and further increased with moderate-intensity breaks. Mean platelet volume increased with moderate-intensity but not lightintensity breaks or uninterrupted sitting. Conclusion: Uninterrupted sitting increased fibrinogen and reduced plasma volume, with associated increases in hemoglobin and hematocrit. Activity breaks attenuated these responses, indicative of an ameliorating influence on the procoagulant effects of uninterrupted sitting.

Making difference count: a demographic study of overseas born teachers

This article reports on the findings of a demographic study which is part of an Australian Research Council funded case study. It seeks to better understand the experiences and challenges facing teachers who are overseas born and educated non-native speakers of English. The investigation has been carried out in Victorian government metropolitan, regional city and rural secondary schools. A statewide survey has provided data about this previously `invisible' population of teachers, their demographic location, their qualifications, backgrounds and the nature of their teaching experiences. The findings raise a number of concerns in relation to overseas born teachers of ethnic difference in rural schools where cultural and professional isolation may be of particular concern. We explore some of the implications for teacher education in the light of increasing numbers of overseas born students entering teacher education courses.

Understanding environmental influences on nutrition and physical activity behaviors: where should we look and what should we count?

Research interest in the influence of environmental factors on nutrition and physical activity behaviors has surged internationally in recent years. This is evident from a rapidly expanding literature and facilitated by advances in methodological and analytical approaches to assessing multiple levels of influence on health behaviors. However, a number of conceptual challenges complicate research endeavours in this field. The purpose of this paper is to provide a 'state of the science' overview of evidence regarding environmental influences on nutrition and physical activity behaviors. We focus particularly on a number of key conceptual and methodological issues, including: a consideration of how the environment is defined; the selection and operationalization of environmental exposures; and the importance of integrating existing understanding of individual influences on behavior with the emerging data on the role of the environment. We draw on examples from the published literature including our own research studies to illustrate these issues. We conclude by proposing a research agenda to progress understanding of the influences of the environment on population nutrition and physical activity behaviors.

Dietary flavanols and procyanidin oligomers from cocoa (Theobroma cacao) inhibit platelet function

BACKGROUND: Flavonoids may be partly responsible for some health benefits, including antiinflammatory action and a decreased tendency for the blood to clot. An acute dose of flavanols and oligomeric procyanidins from cocoa powder inhibits platelet activation and function over 6 h in humans. OBJECTIVE: This study sought to evaluate whether 28 d of supplementation with cocoa flavanols and related procyanidin oligomers would modulate human platelet reactivity and primary hemostasis and reduce oxidative markers in vivo. DESIGN: Thirty-two healthy subjects were assigned to consume active (234 mg cocoa flavanols and procyanidins/d) or placebo (< or = 6 mg cocoa flavanols and procyanidins/d) tablets in a blinded parallel-designed study. Platelet function was determined by measuring platelet aggregation, ATP release, and expression of activation-dependent platelet antigens by using flow cytometry. Plasma was analyzed for oxidation markers and antioxidant status. RESULTS: Plasma concentrations of epicatechin and catechin in the active group increased by 81% and 28%, respectively, during the intervention period. The active group had significantly lower P selectin expression and significantly lower ADP-induced aggregation and collagen-induced aggregation than did the placebo group. Plasma ascorbic acid concentrations were significantly higher in the active than in the placebo group (P < 0.05), whereas plasma oxidation markers and antioxidant status did not change in either group. CONCLUSIONS: Cocoa flavanol and procyanidin supplementation for 28 d significantly increased plasma epicatechin and catechin concentrations and significantly decreased platelet function. These data support the results of acute studies that used higher doses of cocoa flavanols and procyanidins.

Relationship between platelet phospholipid FA and mean platelet volume in healthy men

Increased mean platelet volume (MPV) has been suggested as an independent risk factor for acute myocardial infarction and the increased reactivity of large platelets. The aim of this study was to investigate the correlation between platelet phospholipid (PL) PUFA composition and MPV in 139 free-living healthy men ages 20-55 yr (vegans, n = 18; ovolacto vegetarians, n = 43; moderate meat-eaters, n = 60; and high meateaters, n = 18). Each subject completed a semiquantitative Food Frequency Questionnaire and gave a blood sample. Platelet PL FA composition and MPV were determined by standard methods. MPV was significantly greater in the vegans than in the ovolacto vegetarian, moderate, or high meat-eater groups (P < 0.01). Both vegan and ovolacto vegetarian groups had significantly higher platelet PL 18:2n-6 and 22:4n-6, and lower 20:5n-3 and 22:6n-3 compared with the moderate and high meat-eater groups. The vegans demonstrated a significant reduction in 20:4n-6 and 22:5n-3 compared with the ovolacto vegetarian, high meat-eater, and moderate meat-eater groups. Bivariate analysis results showed that MPV was significantly positively correlated with platelet PL 18:2n-6 (P = 0.048) and negatively correlated with 20:3n-6 (P = 0.02), 20:5n-3 (P = 0.005), and 22:5n-3 (P< 0.0001), respectively. In a multiple linear regression analysis, after controlling for potential confounding factors such as dietary group, age, exercise, body mass index, and dietary polyunsaturated and saturated fat, cholesterol, carbohydrate, and fiber intake, the MPV was still strongly negatively correlated with platelet PL 20:3n-6 (P = 0.003) and 22:5n-3 (P = 0.001). The present data suggest that 22:5n-3 and 20:3n-6 may play a role in the structural function of the platelet membrane.

Short-term diets enriched in stearic or palmitic acids do not alter plasma lipids, platelet aggregation or platelet activation status

Objective: To determine whether healthy males who consumed increased amounts of dietary stearic acid compared with increased dietary palmitic acid through the consumption of commercially available foods, exhibited any changes in plasma lipids, platelet aggregation or platelet activation status.
Design: A randomised cross-over dietary intervention.
Subjects and interventions: Nine free-living healthy males consumed two experimental diets (stearic acid enriched, diet S, and palmitic acid enriched, diet P) for 3 weeks in a randomised cross-over design separated by a 3 week washout phase. The diets consisted of 30% of energy as fat (30% of which was derived from the treatment diets) providing 13 g=day as stearic acid and 17 g=day as palmitic acid on diet S and 7g=day as stearic acid and 22 g=day as palmitic acid on diet P. The dietary ratio of stearic to palmitic acids was 0.76 on diet S compared with 0.31 on diet P. Blood samples were collected on days 0 and 21 of each dietary period.
Results: LDL cholesterol levels and platelet aggregation response to the agonist ADP were significantly decreased (P <0.025) in subjects on diet S compared with day 0. Apart from that, there were no significant changes in plasma lipids, plateletaggregation, mean platelet volume and platelet reactivity between diets. There were no significant changes in stearic or palmitic acid levels in plasma phospholipid or triacylglycerol. There was a significant difference in palmitic acid levels in platelet phospholipids between the two diets.
Conclusions: Use of commonly available foods led to a 27% increase in stearic acid (diet S) and a 19% increase in palmitic acid (diet P), on diets S and P respectively, and no significant differences between the two diets in plasma lipoprotein concentrations, platelet aggregation or platelet activation status.

The influence of fish, meat and polyunsaturated fat intakes on platelet phopholipid polyunsaturated fatty acid in male Melbourne Chinese and Caucasian

Objective: The aims of this study were to investigate (1) platelet phospholipid (PL) polyunsaturated fatty acid (PUFA) composition in subjects who were the Melbourne Chinese migrants, compared with those who were the Melbourne Caucasians and (2) the relationship between platelet PL PUFA and intake of fish, meat and PUFA.

Design: Cross-sectional comparison of the Melbourne Chinese and Caucasians.

Setting: Free-living male subjects.

Subjects: Ninety-seven Melbourne Chinese migrants and 78 Melbourne Caucasians who were recruited in Melbourne.

Outcome measures: Dietary intake was assessed using a semi-quantitative food frequency questionnaire. The platelet PUFA was measured by gas-liquid chromatography.

Results: The Melbourne Chinese had significantly higher proportions of platelet PL 20:5n-3 (P=0.006), 22:6n-3 (P<0.0001), total n-3 (P=0.027) and 22:5n-6 (P=0.0002), and a significantly higher intake of fish (P=0.012) and white meat (P=0.0045) compared with the Melbourne Caucasians. In addition, the Melbourne Chinese had significantly lower proportions of 20:3n-6 (P=0.023), 20:4n-6 (P<0.002), 22:4n-6 (P<0.0001), total n-6 (P=0.037), 22:5n-3 (P<0.0001) and ratio of n-6/n-3 (P=0.011), and a significantly lower intake of red and total meat (P<0.0001) than the Melbourne Caucasians. Fish consumption was significantly positively correlated with platelet PL 20:5n-3 and 22:6n-3, and significantly negatively correlated with 22:5n-3 (P<0.05). Meat consumption was significantly positively correlated with 22:5n-3 and significantly negatively correlated with 22:5n-6, 20:5n-3 and 22:6n-3 (P<0.05). Dietary PUFA intake was significantly positively correlated with 20:3n-6, 22:4n-6 and 22:5n-3, and significantly negatively correlated with 22:5n-6, 20:5n-3 and 22:6n-3 (P<0.05).

Conclusions: Compared with Caucasians, the Melbourne Chinese had a significantly higher level of platelet PL n-3 PUFA, which might contribute to the low CVD mortality in this population. Platelet PL 20:5n-3 and 22:6n-3 were significantly positively correlated with fish intake, and negatively significantly correlated with dietary intake of meat and PUFA, while 22:5n-3 was significantly positively correlated with dietary meat and PUFA intake, and significantly negatively correlated with fish intake. Dietary intake of PUFA and fish are potential confounding factors for assessing the effects of meat consumption on platelet PL individual PUFA. Dietary intake of PUFA and meat did not influence the incorporation of fish long chain n-3 PUFA to platelet PL in this study population.

Inhibition of platelet aggregation by omega-3 polyunsaturated fatty acids is gender specific — redefining platelet response to fish oils

Existence of gender differences in cardiovascular disease (CVD) following long-chain omega-3 polyunsaturated fatty acid (LCn-3 PUFA) supplementation have suggested that sex hormones play a role in cardio-protection. The objective of this study was to determine gender specific responses in the efficacy of LCn-3 PUFA to inhibit platelet aggregation in vitro. Blood was analyzed for collagen-induced platelet aggregation following pre-incubation with LCn-3 PUFA in healthy adults (n=42). Eicosapentaenoic acid (EPA) was significantly more effective in reducing platelet aggregation compared with docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). When grouped by gender, this differential pattern was followed in males only. In females, DHA, DPA and EPA were all equally effective. Between group analyses (LCn-3 PUFA vs. gender) showed that both DHA and DPA were significantly less effective in males compared with females. EPA was equally effective in reducing platelet aggregation in both groups. These findings show that significant gender differences exist in platelet aggregation in response to various LCn-3 PUFA treatments.

The platelet glycoprotein Ia/IIa gene polymorphism C807T/G873A: a novel risk factor for retinal vein occlusion

Retinal vein occlusion (RVO) is associated with hyperhomocysteinaemia and the antiphospholipid syndrome—disorders known to contribute to both arterial and venous thrombosis. In both of these conditions and RVO, platelet activation occurs. Aspirin, not warfarin, is the most effective antithrombotic agent in RVO and, taken together, these observations suggest an important role for platelets in this common ocular thrombotic condition. Platelet glycoprotein Ia/IIa (GpIa/IIa) is an adhesion molecule mediating platelet–collagen interactions and is key to the initiation of thrombosis. Recently, the cellular density of this molecule was shown to be determined by two silent, linked polymorphisms (C807T/G873A) within the GpIa/IIa gene. There is evidence that some of the resulting genotypes are associated with thrombo-embolic disease. This study therefore aimed to establish the prevalence of the GpIa/IIa polymorphisms and the three commonest hereditary thrombophilic disorders (prothrombin gene G20210A (PT) mutation, Factor V Leiden (FVL), and the thermolabile methylene tetrahydrofolate reductase C677T (MTHFR) mutation) in patients with RVO and normal controls. The GpIa/IIa polymorphisms and thrombophilic abnormalities were all identified using the polymerase chain reaction.

Our results show that the frequency of the GpIa/IIa polymorphisms was similar in our normal control population to previously published series. Patients with RVO, however, had only a 10% (4/40) frequency of the lowest risk subtype (CC/GG) compared to 37.5% (15/40) in the control group—P 0.0039. The incidence of the PT, FVL, and MTHFR thrombophilic mutations was not different between the two groups, but interestingly none of the 7/40 RVO cases with a PT, FVL, or MTHFR mutation had the low-risk GpIa/IIa genotype while all but one of the controls did—P<0.05. Thus, 17.5% of RVO patients harboured more than one prothrombotic abnormality. The principal difference between the RVO and control group was the very high incidence of the intermediate-risk GpIa/IIa subtype (CT/GA)—82.5 vs 50%, P<0.05.

These results suggest a major role for GpIa/IIa polymorphisms in the pathogenesis of RVO.

A microfluidics device to monitor platelet aggregation dynamics in response to strain rate micro-gradients in flowing blood

This paper reports the development of a platform technology for measuring platelet function and aggregation based on localized strain rate micro-gradients. Recent experimental findings within our laboratories have identified a key role for strain rate micro-gradients in focally triggering initial recruitment and subsequent aggregation of discoid platelets at sites of blood vessel injury. We present the design justification, hydrodynamic characterization and experimental validation of a microfluidic device incorporating contraction–expansion geometries that generate strain rate conditions mimicking the effects of pathological changes in blood vessel geometry. Blood perfusion through this device supports our published findings of both in vivo and in vitro platelet aggregation and confirms a critical requirement for the coupling of blood flow acceleration to downstream deceleration for the initiation and stabilization of platelet aggregation, in the absence of soluble platelet agonists. The microfluidics platform presented will facilitate the detailed analysis of the effects of hemodynamic parameters on the rate and extent of platelet aggregation and will be a useful tool to elucidate the hemodynamic and platelet mechano-transduction mechanisms, underlying this shear-dependent process.

Gender-specific inhibition of platelet aggregation following omega-3 fatty acid supplementation

Background and Aims : Increased platelet aggregation is a major risk factor for heart attacks, stroke and thrombosis. Long chain omega-3 polyunsaturated fatty acids (LCn-3PUFA; eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA) reduce platelet aggregation; however studies in the published literature involving EPA and/or DHA supplementation have yielded equivocal results. Recent in vitro studies have demonstrated that inhibition of platelet aggregation by LCn-3PUFA is gender specific. We examined the acute effects of dietary supplementation with EPA or DHA rich oils on platelet aggregation in healthy male and females.

Methods and Results : A blinded placebo controlled trial involving 15 male and 15 female subjects. Platelet aggregation was measured at 0, 2, 5 and 24 h post-supplementation with a single dose of either a placebo or EPA or DHA rich oil capsules. The relationship between LCn-3PUFA and platelet activity at each time point was examined according to gender vs. treatment. EPA was significantly the most effective in reducing platelet aggregation in males at 2, 5 and 24 h post-supplementation (−11%, −10.6%, −20.5% respectively) whereas DHA was not effective relative to placebo. In contrast, in females, DHA significantly reduced platelet aggregation at 24 h (−13.7%) while EPA was not effective. An inverse relationship between testosterone levels and platelet aggregation following EPA supplementation was observed.

Conclusion : Interactions between sex hormones and omega-3 fatty acids exist to differentially reduce platelet aggregation. For healthy individuals, males may benefit more from EPA supplementation while females are more responsive to DHA.