In vivo platelet activation is responsible for enhanced vascular endothelial growth factor levels in hypertensive patients

Relationship Between Change Rate of Tacrolimus Clearance During Continuous Intravenous Infusion and Recipient Recovery at an Early Stage After Living Donor Liver Transplantation

BACKGROUND AND OBJECTIVE

Tacrolimus clearance (CL) is significantly altered according to recovery of liver function at an early stage after living donor liver transplantation (LDLT). In this study, we aimed to examine the impact of the change rate from postoperative day (POD) 1 in CL (ΔCL) of tacrolimus during continuous intravenous infusion (CIVI) on recipient recovery.

METHODS

A tacrolimus population pharmacokinetic model on POD1 after LDLT was developed using Phoenix NLME 1.3. The CL_POD1 was calculated using the final model. The CL_POD4-7 was calculated by dividing total daily tacrolimus dose by the area under the concentration-time curve from 0 to 24 h.

RESULTS

Data were obtained from 57 LDLT recipients, along with 540 points (177 points on POD1, 363 points on POD4-7) of tacrolimus whole blood concentrations at CIVI. The median tacrolimus CL decreased from POD1 to POD4 (from 2.73 to 1.40 L/h) and was then stable until POD7. Stepwise Cox proportional hazards regression analyses showed that the graft volume (GV)/standard liver volume (SLV) ratio (GV/SLV) and the tacrolimus ΔCL_POD6 were independent factors predicting early discharge (within 64 days median value) of recipients after LDLT [hazard ratio (HR) = 1.041, P = 0.001 and HR = 1.023, P = 0.004].

CONCLUSIONS

The tacrolimus ΔCL during CIVI immediately after LDLT in each recipient was a useful indicator for evaluation of recovery at an early stage after LDLT.

Influence of Cardiometabolic Risk Factors on Platelet Function

Platelets are key players in the thrombotic processes. The alterations of platelet function due to the occurrence of metabolic disorders contribute to an increased trend to thrombus formation and arterial occlusion, thus playing a major role in the increased risk of atherothrombotic events in patients with cardiometabolic risk factors. Several lines of evidence strongly correlate metabolic disorders such as obesity, a classical condition of insulin resistance, dyslipidemia, and impaired glucose homeostasis with cardiovascular diseases. The presence of these clinical features together with hypertension and disturbed microhemorrheology are responsible for the prothrombotic tendency due, at least partially, to platelet hyperaggregability and hyperactivation. A number of clinical platelet markers are elevated in obese and type 2 diabetes (T2DM) patients, including the mean platelet volume, circulating levels of platelet microparticles, oxidation products, platelet-derived soluble P-selectin and CD40L, thus contributing to an intersection between obesity, inflammation, and thrombosis. In subjects with insulin resistance and T2DM some defects depend on a reduced sensitivity to mediators—such as nitric oxide and prostacyclin—playing a physiological role in the control of platelet aggregability. Furthermore, other alterations occur only in relation to hyperglycemia. In this review, the main cardiometabolic risk factors, all components of metabolic syndrome involved in the prothrombotic tendency, will be taken into account considering some of the mechanisms involved in the alterations of platelet function resulting in platelet hyperactivation.

Alterations to the contents of plasma membrane structural lipids are associated with structural changes and compartmentalization in platelets in hypertension

Arterial hypertension (HTN) can lead to serious organ damage. Several mechanisms have been implicated in the pathogenesis of HTN including constitutive activation of platelets, which increases the risk of aggregation and clot formation. We recently demonstrated the plasma membranes of platelets from patients with HTN exhibit modified structural and physicochemical properties; Raman and Fourier transform infrared by attenuated total reflectance (FTIR-ATR) spectroscopy also indicated lipid content and protein structure alterations. This study aimed to precisely quantify the constituents of the main structural phospholipids and cholesterol in the plasma membranes of platelets from patients with HTN and normotensive individuals. We also assessed the consequence of these alterations on platelet structure and function. Liquid chromatography coupled to triple quadrupole mass spectrometry revealed the plasma membranes of HTN platelets contained less cholesterol and phosphatidylcholine, more phosphatidylserine and phosphatidylethanolamine and had similar sphingosine contents. Atomic force microscopy revealed HTN platelets exhibited increased surface roughness and more pleats. Transmission electron microscopy revealed diminution of the internal membranous structures in HTN platelets. Our findings strongly suggest plasma membrane lipid content alterations-including cholesterol depletion-occur in HTN, and these alterations may induce morphological and physiological abnormalities that participate in the functional changes associated with hypertension.

Fruitflow®: the first European Food Safety Authority-approved natural cardio-protective functional ingredient

Hyperactive platelets, in addition to their roles in thrombosis, are also important mediators of atherogenesis. Antiplatelet drugs are not suitable for use where risk of a cardiovascular event is relatively low. It is therefore important to find alternative safe antiplatelet inhibitors for the vulnerable population who has hyperactive platelets in order to reduce the risk of cardiovascular disease. Potent antiplatelet factors were identified in water-soluble tomato extract (Fruitflow^®), which significantly inhibited platelet aggregation. Human volunteer studies demonstrated the potency and bioavailability of active compounds in Fruitflow^®. Fruitflow^® became the first product in Europe to obtain an approved, proprietary health claim under Article 13(5) of the European Health Claims Regulation 1924/2006 on nutrition and health claims made on foods. Fruitflow^® is now commercially available in different countries worldwide. In addition to its reduction in platelet reactivity, Fruitflow^® contains anti-angiotensin-converting enzyme and anti-inflammatory factors, making it an effective and natural cardio-protective functional food.

Alterations in plasma membrane promote overexpression and increase of sodium influx through epithelial sodium channel in hypertensive platelets

Platelets are small, anucleated cell fragments that activate in response to a wide variety of stimuli, triggering a complex series of intracellular pathways leading to a hemostatic thrombus formation at vascular injury sites. However, in essential hypertension, platelet activation contributes to causing myocardial infarction and ischemic stroke. Reported abnormalities in platelet functions, such as platelet hyperactivity and hyperaggregability to several agonists, contribute to the pathogenesis and complications of thrombotic events associated with hypertension. Platelet membrane lipid composition and fluidity are determining for protein site accessibility, structural arrangement of platelet surface, and response to appropriate stimuli. The present study aimed to demonstrate whether structural and biochemical abnormalities in lipid membrane composition and fluidity characteristic of platelets from hypertensive patients influence the expression of the Epithelial Sodium Channel (ENaC), fundamental for sodium influx during collagen activation. Wb, cytometry and quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR) assays demonstrated ENaC overexpression in platelets from hypertensive subjects and in relation to control subjects. Additionally, our results strongly suggest a key role of β-dystroglycan as a scaffold for the organization of ENaC and associated proteins. Understanding of the mechanisms of platelet alterations in hypertension should provide valuable information for the pathophysiology of hypertension.

Inhibitory effects of kiwifruit extract on human platelet aggregation and plasma angiotensin-converting enzyme activity

Previous human studies suggest that supplementation with kiwifruits lowers several cardiovascular risk factors such as platelet hyperactivity, blood pressure and plasma lipids. The cardiovascular health benefit of fruit and vegetables is usually attributed to the complex mixture of phytochemicals therein; however, kiwifruit's cardioprotective factors are not well studied. In this study, we investigated the effects of kiwifruit extract on human blood platelet aggregation and plasma angiotensin-converting enzyme (ACE) activity. A sugar-free, heat-stable aqueous extract with molecular mass less than 1000 Da was prepared from kiwifruits. Typically, 100 g kiwifruits produced 66.3 ± 5.8 mg (1.2 ± 0.1 mg CE) of sugar-free kiwifruit extract (KFE). KFE inhibited both human platelet aggregation and plasma ACE activity in a dose-dependent manner. KFE inhibited platelet aggregation in response to ADP, collagen and arachidonic acid, and inhibitory action was mediated in part by reducing TxA2 synthesis. The IC50 for ADP-induced platelet aggregation was 1.6 ± 0.2 mg/ml (29.0 ± 3.0 μg CE/ml), whereas IC50 for serum ACE was 0.6 ± 0.1 mg/ml (11.0 ± 1.2 μg CE/ml). Consuming 500 mg of KFE (9.0 mg CE) in 10 g margarine inhibited ex vivo platelet aggregation by 12.7%, 2 h after consumption by healthy volunteers (n = 9). All these data indicate that kiwifruit contains very potent antiplatelet and anti-ACE components. Consuming kiwifruits might be beneficial as both preventive and therapeutic regime in cardiovascular disease.

Activated platelets correlate with mobilization of naïve CD34(+) cells and generation of CD34(+) /KDR(+) cells in the circulation. A meta-regression analysis

BACKGROUND

Bone marrow-derived circulating CD34(+) progenitor cells participate in remodeling and repair of the vasculature. Coexpression of the kinase-insert domain-containing receptor (KDR) has been proposed to identify the regenerative capacity. Recently, we provided evidence that the major fraction of circulating CD34(+) /KDR(+) cells is not mobilized from bone marrow, but is generated at sites of vascular injury through interaction with platelets.

OBJECTIVES

To determine the relationship between platelet activation, the recruitment of naïve CD34(+) cells and the generation of CD34(+) /KDR(+) progenitor cells in a broad range of (patho)physiologic conditions, a detailed meta-regression analysis was conducted.

METHODS/RESULTS

Twenty-eight conditions were found in which the numbers of CD34(+) and/or CD34(+) /KDR(+) cells and the levels of soluble P-selectin, as a marker for in vivo platelet activation, were documented. To combine heterogeneous data from 214 selected articles, results were standardized to a uniform scale by calculating standardized mean differences (SMDs) obtained from patient and control cohorts. Subsequently, a random-effects meta-regression analysis was performed on pooled SMDs.

CONCLUSIONS

Our systemic survey supports a model in which activated platelets are a determinant for mobilization of CD34(+) cells from the bone marrow and the generation of CD34(+) /KDR(+) cells in the circulation.

Chlorthalidone Decreases Platelet Aggregation and Vascular Permeability and Promotes Angiogenesis

Variations in diuretic-mediated inhibition of carbonic anhydrase-dependent chloride transport in platelets and vascular smooth muscle could account for the contrasting efficacy of the thiazide and thiazide-like diuretics in reducing cardiovascular morbidity in patients with hypertension. We assessed platelet carbonic anhydrase activity and catecholamine-induced platelet aggregation in the presence of a thiazide and a “thiazide-like” inhibitor of the sodium-chloride cotransporter. Individual variation in platelet carbonic anhydrase activity correlated with contrasting sensitivity to epinephrine-mediated platelet aggregation. Both chlorthalidone, which potently inhibits platelet carbonic anhydrase, and bendroflumethiazide, which has much less effect on this enzyme, increased the amount of epinephrine needed to induce platelet aggregation when compared with the absence of a diuretic. However, chlorthalidone was significantly more effective than bendroflumethiazide in reducing epinephrine-mediated platelet aggregation. Chlorthalidone also induced marked changes in the number of gene transcripts for two proteins that mediate angiogenesis and vascular permeability, vascular endothelial growth factor C and transforming growth factor-β3; chlorthalidone and bendroflumethiazide had contrasting effects on the expression of vascular endothelial growth factor C. Chlorthalidone and bendroflumethiazide reduced vascular permeability to albumin, but only chlorthalidone increased angiogenesis. Thiazides and thiazide-like diuretics can comparably reduce blood pressure, but the drugs in this class are not all alike. It can be suggested from our findings that thiazide and thiazide-like diuretics vary in their pleiotropic effects on platelets and in the vasculature, and these differences could explain the contrasting ability of these drugs to reduce cardiovascular morbidity despite comparable reduction in blood pressure.