Plant food anthocyanins inhibit platelet granule secretion in hypercholesterolaemia: Involving the signalling pathway of PI3K-Akt.

Controlling platelet granule secretion has been considered an effective strategy to dampen thrombosis and prevent atherosclerosis. Anthocyanins are natural plant pigments and possess a wide range of biological activities, including cardiovascular protective activity. In the present study we explored the effects and the potential mechanisms of anthocyanins on platelet granule secretion in hypercholesterolemia. In a randomised, double-blind clinical trial, 150 hypercholesterolaemic individuals were treated with purified anthocyanins (320 mg/day) or placebo for 24 weeks. Anthocyanins consumption significantly reduced plasma levels of ß-thromboglobulin (ß-TG), soluble P-selectin, and of Regulated on Activation Normal T cell Expressed and Secreted (RANTES) as compared with the placebo. A minor reduction in platelet factor 4 (PF4) and transforming growth factor ß1 (TGF-ß1) levels were also observed. In in vitro experiments, we observed that puriÓ¿ed anthocyanin mixture, as well as its two main anthocyanin components, delphinidin-3-glucoside (Dp-3-g) and cyanidin-3-glucoside (Cy-3g) directly inhibited platelet á-granule, dense granule, and lysosome secretion evaluated by P-selectin, RANTES, ß-TG, PF4, TGF-ß1, serotonin, ATP, and CD63 release. Further, anthocyanins inhibited platelet PI3K/Akt activation and consequently attenuated eNOS phosphorylation and cGMP production, thus interrupting MAPK activation. LY294002, a PI3K inhibitor, did not cause additional inhibitory efficacy, indicating that anthocyanin-induced effects may be involved in inhibition of the PI3K/Akt signalling pathway. These results provide evidence that by inhibiting platelet granule secretion, anthocyanins may be a potent cardioprotective agent.

Platelets in thrombosis and hemostasis: old topic with new mechanisms.

Platelets are small anucleate cells generated from megakaryocytes in the bone marrow. After being released into the circulation, platelets play key roles in the surveillance of vascular injury, and can quickly adhere and aggregate at the site of injury, which are critical events for vascular repair and hemostasis. However, the same biological processes of platelet adhesion and aggregation may also cause thrombotic disorders. The formation of a platelet plug at sites of atherosclerotic lesion rupture is the most common mechanism leading to myocardial or cerebral infarction. Platelet-related deep vein thrombosis is also one of the leading causes of mortality worldwide. The contribution of several platelet receptors and their ligands has been highlighted in these processes. In platelet adhesion, particularly at high shear stress, GPIbα-von Willebrand factor (VWF) interaction may initiate this event, which is followed by GPVI signalling and firm platelet adhesion mediated by members of the integrin family, such as ß3 (αIIbß3) and ß1 (α2ß1, α5ß1) integrins. In platelet aggregation, although GPIbα-VWF, P selectin-sulfatides, and other molecules, may be involved, the process is mainly mediated by ß3 (αIIbß3) integrin and its ligands, such as fibrinogen and VWF. It is intriguing that platelet adhesion and aggregation still occur in mice lacking both fibrinogen and VWF, suggesting that other unforeseen molecule(s) may also be important in these processes. Identification and characterization of these molecules will enrich our knowledge in the basic science of hemostasis and thrombosis, and may lead to the development of new therapies against bleeding disorders and thrombotic diseases.

Plant food delphinidin-3-glucoside significantly inhibits platelet activation and thrombosis: novel protective roles against cardiovascular diseases.

Delphinidin-3-glucoside (Dp-3-g) is one of the predominant bioactive compounds of anthocyanins in many plant foods. Although several anthocyanin compounds have been reported to be protective against cardiovascular diseases (CVDs), the direct effect of anthocyanins on platelets, the key players in atherothrombosis, has not been studied. The roles of Dp-3-g in platelet function are completely unknown. The present study investigated the effects of Dp-3-g on platelet activation and several thrombosis models in vitro and in vivo. We found that Dp-3-g significantly inhibited human and murine platelet aggregation in both platelet-rich plasma and purified platelets. It also markedly reduced thrombus growth in human and murine blood in perfusion chambers at both low and high shear rates. Using intravital microscopy, we observed that Dp-3-g decreased platelet deposition, destabilized thrombi, and prolonged the time required for vessel occlusion. Dp-3-g also significantly inhibited thrombus growth in a carotid artery thrombosis model. To elucidate the mechanisms, we examined platelet activation markers via flow cytometry and found that Dp-3-g significantly inhibited the expression of P-selectin, CD63, CD40L, which reflect platelet α- and δ-granule release, and cytosol protein secretion, respectively. We further demonstrated that Dp-3-g downregulated the expression of active integrin αIIbß3 on platelets, and attenuated fibrinogen binding to platelets following agonist treatment, without interfering with the direct interaction between fibrinogen and integrin αIIbß3. We found that Dp-3-g reduced phosphorylation of adenosine monophosphate-activated protein kinase, which may contribute to the observed inhibitory effects on platelet activation. Thus, Dp-3-g significantly inhibits platelet activation and attenuates thrombus growth at both arterial and venous shear stresses, which likely contributes to its protective roles against thrombosis and CVDs.

Anthocyanin extract from black rice significantly ameliorates platelet hyperactivity and hypertriglyceridemia in dyslipidemic rats induced by high fat diets.

Our previous studies have demonstrated that anthocyanin extract from black rice (AEBR) inhibits atherosclerosis. Whether dietary AEBR supplementation can affect platelet function, an important factor in the pathogenesis of cardiovascular diseases, remains unclear. The aim of the present study is to explore the effects and mechanisms of dietary AEBR supplementation on platelet function and lipid profile in dyslipidemic rats. We demonstrated herein that thromboxane A(2), the thrombogenic ratio of thromboxane A2 and prostacyclin, serum calmodulin, and soluble P-selectin were significantly decreased in rats fed a high fat diet supplemented with AEBR. AEBR supplementation also remarkably lowered serum triglyceride and raised hepatic CPT-1 mRNA expression. These findings suggest that dietary intake of AEBR reduces platelet hyperactivity, hypertriglyceridemia, and body weight gain, and facilitates in the maintenance of optimal platelet function in dyslipidemic rats induced by high fat diets.

Nramp1 promotes efficient macrophage recycling of iron following erythrophagocytosis in vivo.

Natural resistance-associated macrophage protein 1 (Nramp1) is a divalent metal transporter expressed exclusively in phagocytic cells. We hypothesized that macrophage Nramp1 may participate in the recycling of iron acquired from phagocytosed senescent erythrocytes. To evaluate the role of Nramp1 in vivo, the iron parameters of WT and KO mice were analyzed after acute and chronic induction of hemolytic anemia. We found that untreated KO mice exhibited greater serum transferrin saturation and splenic iron content with higher duodenal ferroportin (Fpn) and divalent metal transporter 1 (DMT1) expression. Furthermore, hepatocyte iron content and hepcidin mRNA levels were dramatically lower in KO mice, indicating that hepcidin levels can be regulated by low-hepatocyte iron stores despite increased transferrin saturation. After acute treatment with the hemolytic agent phenylhydrazine (Phz), KO mice experienced a significant decrease in transferrin saturation and hematocrit, whereas WT mice were relatively unaffected. After a month-long Phz regimen, KO mice retained markedly increased quantities of iron within the liver and spleen and exhibited more pronounced splenomegaly and reticulocytosis than WT mice. After injection of (59)Fe-labeled heat-damaged reticulocytes, KO animals accumulated erythrophagocytosed (59)Fe within their liver and spleen, whereas WT animals efficiently recycled phagocytosed (59)Fe to the marrow and erythrocytes. These data imply that without Nramp1, iron accumulates within the liver and spleen during erythrophagocytosis and hemolytic anemia, supporting our hypothesis that Nramp1 promotes efficient hemoglobin iron recycling in macrophages. Our observations suggest that mutations in Nramp1 could result in a novel form of human hereditary iron overload.

Atrial fibrillation.

In 2000, some 2.3 million Americans were affected by atrial fibrillation, and that number is expected to rise as our population ages. Atrial fibrillation is both a reflection of active physiologic stressors on the body and a marker of future cardiac disease progression. The disorganized atrial activity that characterizes atrial fibrillation affects cardiac function, metabolic demand, and quality of life. However, our understanding of the etiology and treatment of this condition continues to advance with the result of recent large-scale clinical trials. Diabetes, hypertension, congestive heart failure, valvular disease, and myocardial infarction are all risk factors in the development of atrial fibrillation. And the diagnosis confers a five-fold increase in the incidence of stroke. (Patients at increased risk for stroke include those with congestive heart failure, hypertension, age greater than 75, diabetes, and previous stroke.) Anticoagulation is a critical action in most cases of atrial fibrillation, as data show a 68% relative risk reduction of stroke when patients are treated with warfarin. Prior to recent trials, achieving sinus rhythm was thought to invariably improve symptoms, cardiac function, and mortality. The adverse effects of antiarrhythmic medications are now being recognized, and treatment strategies emphasizing ventricular rate control have been recommended in recent clinical practice guidelines. This shift in thinking is influencing both outpatient and emergency department management. Controlling the ventricular rate in atrial fibrillation increases cardiac output, decreases the metabolic demand of the heart, and avoids the potentially dangerous side effects of rhythm-control drugs. Rate-control agents should be selected based on the clinical profile of individual patients. A well-chosen subset of patients may benefit from either chemical or electrical cardioversion; this appears to be a reasonably safe procedure and can be accomplished on an outpatient basis. Understanding causal etiologies, managing risk for stroke (and need for anticoagulation), addressing rate, and assessing the risks of cardioversion are key elements in a comprehensive approach to atrial fibrillation.