Increased number of high sensitive platelets in hypercholesterolemia, cardiovascular diseases, and after incubation with cholesterol

Impacts of cigarette smoking on blood circulation: do we need a new approach to blood donor selection?

Smoking is a major public health problem and is considered the leading cause of preventable death worldwide. Gas-phase smoke carries bioactive substances and toxic compounds, affecting human health and reducing life spans. The negative effects of smoking on red blood cell (RBC) quality include destroying RBCs and increasing carboxy hemoglobin (COHb). Smoking increases the concentrations of heavy metals such as cadmium (Cd) and lead (Pb) in the blood. Moreover, tobacco smoking has been found to be associated with heightened platelet (PLT)-dependent thrombin level which will induce a prothrombotic state. Smoking may affect the blood circulation of donors, and subsequently the blood components, and ultimately the recipients of transfusion. Nevertheless, there are no restrictions on smoking for volunteer blood donor screenings currently. We reviewed the articles about the influence of smoking on smokers' blood circulation as well as the impact of donated blood products on transfusion when these smokers act as blood donors. We aim to attract blood collection centers' attention to strengthen the management of blood donors who smoke, avoiding their use in massive transfusion protocol and susceptible recipients, especially pediatric ones.

Understanding the molecular mechanisms of statin pleiotropic effects

Statins represent the cornerstone of pharmacotherapy for the prevention of atherosclerotic cardiovascular disease. These medications not only reduce low-density lipoprotein cholesterol (LDL-C) via inhibition of 3-hydroxy-3-methylglutarate attached to CoA reductase, the key rate-limiting step in the cholesterol biosynthetic pathway, but also upregulate expression of the low-density lipoprotein receptor, improving serum clearance. Given LDL-C is a causal risk factor for the development of atherosclerosis, these complementary mechanisms largely explain why statin therapy leads to reductions in major adverse cardiovascular events. However, decades of basic and clinical research have suggested that statins may exert other effects independent of LDL-C lowering, termed pleiotropic effects, which have become a topic of debate among the scientific community. While some literature suggests statins may improve plaque stability, reduce inflammation and thrombosis, decrease oxidative stress, and improve endothelial function and vascular tone, other studies have suggested potential harmful pleiotropic effects related to increased risk of muscle-related side effects, diabetes, hemorrhagic stroke, and cognitive decline. Furthermore, the introduction of newer, non-statin LDL-C lowering therapies, including ezetimibe, proprotein convertase subtilisin/Kexin Type 9, and bempedoic acid, have challenged the statin pleiotropy theory. This review aims to provide a historical background on the development of statins, explore the mechanistic underpinnings of statin pleiotropy, review the available literature, and provide up to date examples that suggest statins may exert effects outside of LDL-C lowering and the cardiovascular system.

Do statins reduce the mortality rate in stroke patients treated with systemic thrombolysis in a 5-year

The present study investigated the association between pre-treatment with a cholesterol-lowering drug (statin) or new setting hereon and the effect on the mortality rate in patients with acute ischemic stroke who received intravenous systemic thrombolysis. During a 5-year period (starting in October 2008), 542 consecutive stroke patients who received intravenous systemic thrombolysis with recombinant tissue plasminogen activator (rt-PA) at the Department of Neurology, University Hospital Schleswig-Holstein, Campus Lübeck, Germany, were included. Patients were characterized according to statins. The primary endpoint was mortality; it was assessed twice: in hospital and 3 months after discharge. The secondary outcome was the rate of symptomatic intracerebral hemorrhage. Of the 542 stroke patients examined (mean age 72 ± 13 years; 51% women, mean National Institutes of Health Stroke Scale (NIHSS) score 11), 138 patients (25.5%) had been pre-treated with statin, while in 190 patients (35.1%) statin therapy was initiated during their stay in hospital, whereas 193 (35.6%) never received statins. Patients pre-treated with statin were older and more frequently had previous illnesses (arterial hypertension, diabetes mellitus and previous cerebral infarctions), but were comparably similarly affected by the stroke (NIHSS 11 vs. 11; P = 0.76) compared to patients who were not on statin treatment at the time of cerebral infarction. Patients pretreated with statin did not differ in 3-month mortality from those newly treated to a statin (7.6% vs. 8%; P = 0.9). Interestingly, the group of patients pretreated with statin showed a lower rate of in hospital mortality (6.6% vs. 17.0; P = 0.005) and 3-month mortality (10.7% vs. 23.7%; P = 0.005) than the group of patients who had no statin treatment at all. The same effect was seen for patients newly adjusted to a statin during the hospital stay compared to patients who did not receive statins (3-month mortality: 7.1% vs. 23.7%; P < 0.001). With a good functional outcome (mRS ≤ 2), 60% of patients were discharged, the majority (69.6%; P < 0.001) of whom received a statin at discharge. The rate of symptomatic intracerebral hemorrhages in the course of cranial computed tomography was independent of whether the patients were pretreated with a statin or not (8.8% vs. 8.7%, P = 0.96). Pre-treatment with statin as well as new adjustment could reveal positive effect on prognosis of intravenous thrombolyzed stroke patients. Further investigations are required. The study was approved by the Ethic Committee of the University of Lübeck (approval No. 4-147).

Advances in Platelet Subpopulation Research

Although lacking a nucleus, platelets are increasingly recognized not only for their complexity, but also for their diversity. Some 50 years ago platelet subpopulations were characterized by size and density, and these characteristics were thought to reflect platelet aging. Since, our knowledge of platelet heterogeneity has grown to recognize that differences in platelet biochemistry and function exist. This includes the identification of vanguard and follower platelets, platelets with differing procoagulant ability including "COAT-platelets" which enhance procoagulant protein retention on their surface, and most recently, the identification of platelet subpopulations with a differential ability to generate and respond to nitric oxide. Hence, in this mini-review, we summarize the current knowledge of platelet subpopulation diversity focusing on their physical, biochemical, and functional heterogeneity. In addition, we review how platelet subpopulations may change between health and disease and how differences among platelets may influence response to anti-platelet therapy. Finally, we look forward and discuss some of the future directions and challenges for this growing field of platelet research.

Hypercholesterolemia impairs the Glucagon-like peptide 1 action on platelets: Effects of a lipid-lowering treatment with simvastatin

BACKGROUND

The incretin hormone Glucagon-like peptide 1(GLP-1) plays a pivotal role in maintaining glucose homeostasis with effects also on the cardiovascular system. GLP-1 influences platelet functions by increasing the inhibitory action of nitric oxide (NO) and reducing oxidative stress. To date, the role of hypercholesterolemia (HyC) on platelet GLP-1 effects needs to be elucidated.

METHODS

Forty-five subjects with primary HyC and twenty normocholesterolemic controls (NoC) were enrolled. In platelets from all subjects, the native GLP-1 (7-36), the truncated GLP-1 (9-36) and the GLP-1 analogue Liraglutide were evaluated in their ability to interfere with the activation of NO/PKG/VASP, PI-3K/Akt e MAPK/ERK-1/2 pathways and oxidative stress. Furthermore, in HyC subjects the role of a lipid-lowering therapy with statin on GLP-1 related peptide effects on platelet function was evaluated.

RESULTS

Unlike in NoC, in platelets from HyC subjects the GLP-1 related peptides GLP-1 (7-36), GLP-1 (9-36) and Liraglutide all failed to: i) increase the antiaggregating effects of NO and the NO-induced VASP-ser239 phosphorylation, ii) decrease phosphorylation levels of Akt and ERK-2 and iii) reduce reactive oxygen species (ROS) generation. The treatment with simvastatin (40 mg/die) in HyC (n = 18) significantly reduced total and LDL cholesterol levels, platelet aggregability/activation, ROS production and NO action but did not modify platelet sensitivity to the GLP-1 effects.

CONCLUSION

Collectively, these results indicate that hypercholesterolemia per se is characterized by a resistance to GLP-1 effects on platelets and this impairment is not corrected by treatment with simvastatin.

Rosuvastatin Decreases Mean Platelet Volume in Patients With Diabetes Mellitus

Statins have multiple effects (also known as pleiotropic effects) on inflammation, plaque stabilization, endothelial function, and hemostasis. We evaluated the effects of rosuvastatin on mean platelet volume (MPV)--a marker for platelet activity--in patients with diabetes mellitus (DM) on rosuvastatin medication. Patients (n = 178) who were to be prescribed high-intensity rosuvastatin were retrospectively enrolled according to their medical records. Baseline and 6-month biochemical tests, automated blood count, cell-volume analysis, and their cardiovascular risk factors were recorded. Rosuvastatin significantly reduced the MPV and the lipid parameters including total cholesterol, triglyceride, and low-density lipoprotein cholesterol (LDL-C). However, there was no correlation between MPV and LDL-C before (r = -.66; P = .383) and after (r = -.112; P = .135) rosuvastatin treatment or between ΔMPV and ΔLDL-C after 40 mg rosuvastatin daily therapy (r = -.155; P = .073). Rosuvastatin significantly decreases the MPV as well as cholesterol levels. The antiplatelet activation properties of high-dose rosuvastatin treatment in patients with DM are not lipid dependent.

The antithrombotic effects of statins

Hypercholesterolemia is considered the primary risk factor for cardiovascular disease. An estimated 200 million prescriptions are issued per year for statins to treat hypercholesterolemia. Importantly, statins have additional beneficial effects independent of their effects on lipids. Recent studies have shown that statins reduce thrombosis via multiple pathways, including inhibiting platelet activation and reducing the pathologic expression of the procoagulant protein tissue factor. Many of the antithrombotic effects of statins are attributed to inhibiting prenylation of RhoA and effects on other intracellular signaling molecules such as NF-κB and KLF2. These antithrombotic activities of statins likely contribute to the ability of statins to reduce the incidence of cardiovascular death.

Alterations in the extracellular catabolism of nucleotides and platelet aggregation induced by high-fat diet in rats: effects of α-tocopherol

The aim of this study was to assess whether α-tocopherol administration prevented alterations in the ectonucleotidase activities and platelet aggregation induced by high-fat diet in rats. Thus, we examined four groups of male rats which received standard diet, high-fat diet (HFD), α-tocopherol (α-Toc), and high-fat diet plus α-tocopherol. HFD was administered ad libitum and α-Toc by gavage using a dose of 50 mg/kg. After 3 months of treatment, animals were submitted to euthanasia, and blood samples were collected for biochemical assays. Results demonstrate that NTPDase, ectonucleotide pyrophosphatase/phosphodiesterase, and 5'-nucleotidase activities were significantly decreased in platelets of HFD group, while that adenosine deaminase (ADA) activity was significantly increased in this group in comparison to the other groups (P < 0.05). When rats that received HFD were treated with α-Toc, the activities of these enzymes were similar to the control, but ADA activity was significantly increased in relation to the control and α-Toc group (P < 0.05). HFD group showed an increased in platelet aggregation in comparison to the other groups, and treatment with α-Toc significantly reduced platelet aggregation in this group. These findings demonstrated that HFD alters platelet aggregation and purinergic signaling in the platelets and that treatment with α-Toc was capable of modulating the adenine nucleotide hydrolysis in this experimental condition.

Differentiating haemostasis from thrombosis for therapeutic benefit

The central role of platelets in the formation of the primary haemostatic plug as well as in the development of arterial thrombosis is well defined. In general, the molecular events underpinning these processes are broadly similar. Whilst it has long been known that disturbances in blood flow, changes in platelet reactivity and enhanced coagulation reactions facilitate pathological thrombus formation, the precise details underlying these events remain incompletely understood. Intravital microscopy studies have highlighted the dynamic and heterogeneous nature of thrombus development and demonstrated that there are considerable spatiotemporal differences in the activation states of platelets within a forming thrombus. In this review we will consider the factors regulating the activation state of platelets in a developing thrombus and discuss how specific prothrombotic factors may influence this process, leading to excessive thrombus propagation. We will also discuss some potentially novel therapeutic approaches that may reduce excess thrombus development whilst minimising bleeding risk.

Relationship between serum cholesterol and indices of erythrocytes and platelets in the US population

Whereas dyslipidemia has been associated with leukocytosis, the relationship between serum cholesterol and other hematopoietic lineages is poorly defined. Erythrocytes and platelets, anucleate cells relegated to nonspecific diffusional exchange of cholesterol with serum, have been proposed to have a distinct relationship to cholesterol from leukocytes. We examined the relationship between serum cholesterol and circulating erythrocyte/platelet indices in 4,469 adult participants of the National Health and Nutrition Examination Survey (NHANES) 2005-2006. In linear regression analyses, serum non-high density lipoprotein-cholesterol (non-HDL-C) was positively associated with mean erythrocyte number, hematocrit, hemoglobin concentration, platelet count, and platelet crit independently of age, gender, race/ethnicity, smoking, body mass index, serum folate, and C-reactive protein. The magnitude of the relationship was most marked for platelets, with lowest versus highest non-HDL-C quartile subjects having geometric mean platelet counts of 258,000/μl versus 281,000/μl, respectively (adjusted model, P < 0.001 for trend). These associations persisted in a sensitivity analysis excluding several conditions that affect erythrocyte/platelet and/or serum cholesterol levels, and were also noted in an independent analysis of 5,318 participants from NHANES 2007-2008. As non-HDL-C, erythrocytes, and platelets all impact cardiovascular disease risk, there is a need for advancing understanding of the underlying interactions that govern levels of these three blood components.

Cholesterol enrichment of rabbit platelets enhances the Ca(2+) entry pathway induced by platelet-derived secondary feedback agonists

AIMS

Hypersensitivity of platelets due to increased platelet cholesterol levels has been reported in hypercholesterolemia. However, the signaling pathways linking increased platelet reactivity and cholesterol contents are not fully understood. This study aims to determine the direct effect of cholesterol enrichment of platelets on the pathways including Ca(2+) mobilization and secondary feedback agonists such as adenosine diphosphate (ADP) and thromboxane A2 (TXA2).

MAIN METHODS

In vitro cholesterol enrichment of rabbit platelets was performed by incubation with cholesterol complexed with methyl-β-cyclodextrin. Ca(2+) mobilization was monitored using platelets loaded with fura-PE3/AM, a fluorescent calcium indicator. Released ATP and TXB2 from platelets were measured by a luciferin-luciferase ATP assay system and a TXB2 ELISA Kit, respectively.

KEY FINDINGS

Cholesterol enrichment of rabbit platelets significantly enhanced Ca(2+) mobilization induced by thrombin, accompanying an augmented Ca(2+) entry. The augmentation of Ca(2+) entry by cholesterol enrichment was significantly suppressed by treatment with inhibitors for secondary feedback agonists. In cholesterol-enriched platelets, the amount of released ATP or TXB2 induced by thrombin was not significantly altered in comparison with control platelets, whereas an increase in [Ca(2+)]i induced by ADP or U46619, a TXA2 mimetic, was significantly enhanced.

SIGNIFICANCE

These results suggest that cholesterol enrichment of rabbit platelets results in enhanced Ca(2+) mobilization via ADP/TXA2-dependent augmentation of the Ca(2+) entry pathway. The results reveal a novel mechanism by which platelet hypersensitivity is regulated by cholesterol contents.

An eicosanoid-centric view of atherothrombotic risk factors

Cardiovascular disease is the foremost cause of morbidity and mortality in the Western world. Atherosclerosis followed by thrombosis (atherothrombosis) is the pathological process underlying most myocardial, cerebral, and peripheral vascular events. Atherothrombosis is a complex and heterogeneous inflammatory process that involves interactions between many cell types (including vascular smooth muscle cells, endothelial cells, macrophages, and platelets) and processes (including migration, proliferation, and activation). Despite a wealth of knowledge from many recent studies using knockout mouse and human genetic studies (GWAS and candidate approach) identifying genes and proteins directly involved in these processes, traditional cardiovascular risk factors (hyperlipidemia, hypertension, smoking, diabetes mellitus, sex, and age) remain the most useful predictor of disease. Eicosanoids (20 carbon polyunsaturated fatty acid derivatives of arachidonic acid and other essential fatty acids) are emerging as important regulators of cardiovascular disease processes. Drugs indirectly modulating these signals, including COX-1/COX-2 inhibitors, have proven to play major roles in the atherothrombotic process. However, the complexity of their roles and regulation by opposing eicosanoid signaling, have contributed to the lack of therapies directed at the eicosanoid receptors themselves. This is likely to change, as our understanding of the structure, signaling, and function of the eicosanoid receptors improves. Indeed, a major advance is emerging from the characterization of dysfunctional naturally occurring mutations of the eicosanoid receptors. In light of the proven and continuing importance of risk factors, we have elected to focus on the relationship between eicosanoids and cardiovascular risk factors.

Pharmacological actions of statins: a critical appraisal in the management of cancer

Statins, among the most commonly prescribed drugs worldwide, are cholesterol-lowering agents used to manage and prevent cardiovascular and coronary heart diseases. Recently, a multifaceted action in different physiological and pathological conditions has been also proposed for statins, beyond anti-inflammation and neuroprotection. Statins have been shown to act through cholesterol-dependent and -independent mechanisms and are able to affect several tissue functions and modulate specific signal transduction pathways that could account for statin pleiotropic effects. Typically, statins are prescribed in middle-aged or elderly patients in a therapeutic regimen covering a long life span during which metabolic processes, aging, and concomitant novel diseases, including cancer, could occur. In this context, safety, toxicity, interaction with other drugs, and the state of health have to be taken into account in subjects treated with statins. Some evidence has shown a dichotomous effect of statins with either cancer-inhibiting or -promoting effects. To date, clinical trials failed to demonstrate a reduced cancer occurrence in statin users and no sufficient data are available to define the long-term effects of statin use over a period of 10 years. Moreover, results from clinical trials performed to evaluate the therapeutic efficacy of statins in cancer did not suggest statin use as chemotherapeutic or adjuvant agents. Here, we reviewed the pharmacology of the statins, providing a comprehensive update of the current knowledge of their effects on tissues, biological processes, and pathological conditions, and we dissected the disappointing evidence on the possible future use of statin-based drugs in cancer therapy.

Arterial thrombosis--insidious, unpredictable and deadly

The formation of blood clots--thrombosis--at sites of atherosclerotic plaque rupture is a major clinical problem despite ongoing improvements in antithrombotic therapy. Progress in identifying the pathogenic mechanisms regulating arterial thrombosis has led to the development of newer therapeutics, and there is general anticipation that these treatments will have greater efficacy and improved safety. However, major advances in this field require the identification of specific risk factors for arterial thrombosis in affected individuals and a rethink of the 'one size fits all' approach to antithrombotic therapy.

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.

Pleiotropic effects of statins. - Basic research and clinical perspectives -

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, which are widely used to lower serum cholesterol levels in the primary and secondary prevention of cardiovascular disease. Recent experimental and clinical evidence suggests that the beneficial effects of statins may extend beyond their cholesterol-lowering effects, to include so-called pleiotropic effects. These cholesterol-independent effects include improving endothelial function, attenuating vascular and myocardial remodeling, inhibiting vascular inflammation and oxidation, and stabilizing atherosclerotic plaques. The mechanism underlying some of these pleiotropic effects is the inhibition of isoprenoid synthesis by statins, which leads to the inhibition of intracellular signaling molecules Rho, Rac and Cdc42. In particular, inhibition of Rho and one of its downstream targets, Rho kinase, may be a predominant mechanism contributing to the pleiotropic effects of statins. The aim of the present review is to provide an update on the non-cholesterol-dependent statin effects in the cardiovascular system and highlight some of the recent findings from bench to bedside to support the concept of statin pleiotropy.

Stroke pharmacogenomics

Circulatory disease accounts for fifteen million deaths each year, of which stroke accounts for four and a half million- with an estimated nine million stroke survivors annually. The overall incidence rate of stroke is 2 to 2.5 per thousand adults with an approximate prevalence of 5 per thousand and an estimated 5-year risk of stroke recurrence of 15 to 40 percent. Conventional risk factors for stroke include: increasing age, hypertension, diabetes mellitus, smoking, increased body mass index, ischemic heart disease, heart failure, atrial fibrillation and lack of physical activity. Age is the strongest risk factor for both ischemic and haemorrhagic stroke with its incidence doubling for each successive decade after the age of fifty-five years. However, there is a substantial portion of patients with significant cerebrovascular disease who do not have any of these stroke risk-factors, leading to the speculation that there are other factors that have not been identified yet So as to improve diagnosis and treatment strategies, as well as to reduce the related public health burden, it could be helpful to successfully identify its extremely complex genetic determinants (polygenic, multiple genes play a role). Pharmacogenetics is the field of pharmacology that deals with the influence of genetic variation on drug response by correlating gene expression and gene variants with the efficacy or toxicity of drugs. The principle drugs in stroke medicine are antithrombotics. The aim of this paper was to review the most commonly used drugs for stroke such as rtPA in the acute phase as well as antiplatelets and wafarin for secondary prophylaxis.

Impact of surface electric properties of carbon-based thin films on platelets activation for nano-medical and nano-sensing applications

Electric surface properties of biomaterials, playing key role to various biointerfacial interactions, were related to hemocompatibility and biosensing phenomena. In this study, the examination of surface electric properties of amorphous hydrogenated carbon thin films (a-C:H) was carried out by means of electrostatic force microscope (EFM) and observation of differences in spatial charge distribution on the surface of the examined films during platelets adhesion was made. The thrombogenic potential of a-C:H thin films developed by magnetron sputtering with ~42% sp³ content and hydrogen partial pressure during deposition was evaluated, by in situ observation with atomic force microscope (AFM) of platelets’ activation and their subsequent adhesion. Platelet-rich plasma drawn from healthy donors was used and semi-contact mode of AFM was applied. Platelets behavior and their correlation with the electric surface properties of the examined a-C:H films by EFM was made for hemocompatibility enhancement and sensing platelets that are less electrical negatively charged and with higher tendency to aggregate and form thrombus. The results are discussed in view of the effect of different deposition conditions of hydrogenated carbon films on their structural and morphological characteristics, surface roughness and electrical properties attributing to different hemocompatibility and sensing aspects.

Statins and cardiovascular diseases: from cholesterol lowering to pleiotropy

Statins are 3-hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase inhibitors, which are prescribed extensively for cholesterol lowering in the primary and secondary prevention of cardiovascular disease. Recent compelling evidence suggests that the beneficial effects of statins may not only be due to their cholesterol lowering effects, but also, to their cholesterol-independent or pleiotropic effects. Through these so-called pleiotropic effects, statins are directly involved in restoring or improving endothelial function, attenuating vascular remodeling, inhibiting vascular inflammatory response, and perhaps, stabilizing atherosclerotic plaques. These cholesterol-independent effects of statins are predominantly due to their ability to inhibit isoprenoid synthesis, the products of which are important lipid attachments for intracellular signaling molecules, such as Rho, Rac and Cdc42. In particular, inhibition of Rho and its downstream target, Rho-associated coiled-coil containing protein kinase (ROCK), has emerged as the principle mechanisms underlying the pleiotropic effects of statins. This review provides an update of statin-mediated vascular effects beyond cholesterol lowering and highlights recent findings from bench to bedside to support the concept of statin pleiotropy.

Increased platelet cholesterol and decreased percentage volume of platelets as a secondary risk factor for coronary artery disease

Platelet hyperactivity is likely to contribute to the progression of atherogenesis and organized thrombus formation on vascular surfaces. The purpose of this study was to examine the effect of hypercholesterolemia on the cholesterol content of platelets, on platelet responsiveness and other platelet indices using platelets from 5 groups of age-matched subjects (n = 30 each), which includes healthy controls. All groups except controls had a high plasma lipid profile. While subjects in group I had only hyperlipidemia, those in groups II and III had hyperlipidemia in conjunction with diabetes mellitus and hypertension, respectively. The fourth group consisted of patients with confirmed coronary artery disease (CAD). The parameters studied include packed cell volume of platelets (platelet crit), platelet distribution width (PDW), platelet cholesterol and platelet aggregation in response to adenosine diphosphate and collagen. All the patient groups showed increased platelet aggregation (p < 0.05) and low platelet crit compared with controls (p < 0.05). In addition, platelet cholesterol was increased in patients with coronary disease, hyperlipidemia and diabetes mellitus (p < 0.05) but not in patients with hypertension (p > 0.05); PDW was high only in CAD (p < 0.05). A higher PDW indicated a prothrombotic tendency in CAD patients. Our data suggest that hyperlipidemia increases the lipid content in platelets and enhances their reactivity. Hyperactive platelets with increased platelet cholesterol may contribute to accelerated atherogenesis associated with CAD.

Study of V1a vasopressin receptor gene single nucleotide polymorphisms in platelet vasopressin responsiveness

There is a significant heterogeneity among individuals in terms of platelet aggregation response to arginine vasopressin (AVP). The aim of this study was to evaluate whether four single nucleotide polymorphisms (SNPs) in the promoter region of vasopressin V1a receptor gene (V1aR) could be used as genetic markers for divergent platelet aggregation response to AVP. Seventeen of 33 subjects showed more than 60% of maximum platelet aggregation and were classified as responders. Sixteen were classified as nonresponders because they had less than 30% aggregation. In a preliminary study, V1aR gene sequences were determined in two responders and two nonresponders. We found four SNPs in the promoter region of the V1aR gene: -6951G/A, -4112A/T, -3860T/C, and -242C/T. In all 33 subjects the genotypes of four SNPs were determined using either polymerase chain reaction (PCR) with allele-specific primers or PCR followed by restriction-fragment length polymorphism (RFLP). There were no differences in the AVP-induced aggregation between the subjects with and without variant alleles of each four SNPs. The genotype frequencies of four SNPs of V1aR were almost identical between AVP responders and nonresponders. These results suggest that the four SNPs in the promoter region of the V1aR gene may not be useful as genetic markers for platelet aggregation heterogeneity.

Effects of statins on 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibition beyond low-density lipoprotein cholesterol

Statins are potent inhibitors of cholesterol biosynthesis and exert beneficial effects in the primary and secondary prevention of coronary artery disease. However, the overall benefits observed with statins appear to occur much earlier and to be greater than what might be expected from changes in lipid levels alone, suggesting effects beyond cholesterol lowering. Indeed, recent studies indicate that some of the cholesterol-independent or "pleiotropic" effects of statins involve improving endothelial function, enhancing the stability of atherosclerotic plaques, decreasing oxidative stress and inflammation, and inhibiting the thrombogenic response. Many of these pleiotropic effects are mediated by inhibition of isoprenoids, which serve as lipid attachments for intracellular signaling molecules. In particular, inhibition of the small guanosine triphosphate-binding proteins Rho, Ras, and Rac, whose proper membrane localization and function are dependent on isoprenylation, may play an important role in mediating the pleiotropic effects of statins.

Pleiotropic effects of statins

Statins are potent inhibitors of cholesterol biosynthesis. In clinical trials, statins are beneficial in the primary and secondary prevention of coronary heart disease. However, the overall benefits observed with statins appear to be greater than what might be expected from changes in lipid levels alone, suggesting effects beyond cholesterol lowering. Indeed, recent studies indicate that some of the cholesterol-independent or "pleiotropic" effects of statins involve improving endothelial function, enhancing the stability of atherosclerotic plaques, decreasing oxidative stress and inflammation, and inhibiting the thrombogenic response. Furthermore, statins have beneficial extrahepatic effects on the immune system, CNS, and bone. Many of these pleiotropic effects are mediated by inhibition of isoprenoids, which serve as lipid attachments for intracellular signaling molecules. In particular, inhibition of small GTP-binding proteins, Rho, Ras, and Rac, whose proper membrane localization and function are dependent on isoprenylation, may play an important role in mediating the pleiotropic effects of statins.

Statine zur Behandlung von Erkrankungen des zentralen Nervensystems

3-Hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase inhibitors, "statins," are widely used oral cholesterol-lowering drugs. Statins competitively inhibit HMG-CoA reductase, the enzyme that catalyzes conversion of HMG-CoA to L-mevalonate, a key intermediate in cholesterol synthesis. Certain metabolites of L-mevalonate are also involved in posttranslational modifications of specific proteins with cell proliferation and differentiation properties. Thus, statins have important biologic effects beyond their cholesterol-reducing properties. Here we discuss recent experimental and clinical data that may support a potential role for statins in the treatment of three central nervous system (CNS) neurological diseases: Multiple sclerosis (MS), Alzheimer's disease (AD), and ischemic stroke. Despite their considerable pathogenic differences, in animal models of these disorders statins have shown beneficial effects. In both stroke and AD cohort studies suggest a beneficial treatment effect in humans; in MS, results from small open-label studies look encouraging. Multicenter, randomized, placebo-controlled clinical trials are in the planning or recruiting stage to evaluate the therapeutic effects of statins in all three disorders.

HMG-CoA reductase inhibitor attenuates platelet adhesion in intestinal venules of hypercholesterolemic mice

Whereas the anti-inflammatory properties of statins have been extensively studied, less attention has been devoted to the antithrombogenic effects of these drugs. We evaluated the effect of short-term (18 h) treatment with pravastatin (1 mg/kg) on hypercholesterolemia-induced platelet-endothelial (P/E) cell adhesion in intestinal venules. Mice were placed on either a normal diet (ND) or cholesterol-enriched diet (HCD) for 2 wk. Wild-type mice fed a HCD exhibited significantly elevated blood serum cholesterol levels, which were unaltered by pravastatin treatment. ND or HCD platelets were isolated, fluorescently labeled, and administered to either ND or HCD recipients. Intravital videomicroscopy was used to quantify transient (saltation) and firm adhesion of platelets. HCD mice receiving platelets from either ND or HCD mice exhibited increased P/E cell interactions compared with ND mice receiving platelets from ND or HCD mice. P/E adhesion was dramatically reduced when platelets from donor mice, recipient mice, or both were treated with pravastatin. The protective effect of pravastatin in hypercholesterolemia-induced P/E cell adhesion was abolished in NG-nitro-l-arginine methyl ester-treated mice. These results indicate that 1) hypercholesterolemia-induced P/E cell adhesion is mediated by changes in the vascular wall rather than circulating platelets; 2) pravastatin treatment inhibits the prothrombogenic effects of hypercholesterolemia via an action on both endothelial cells and platelets; and 3) the protective effect of pravastatin is nitric oxide dependent.

The role of statins in vascular disease

BACKGROUND

Recent publications have highlighted the benefits of statins in non-cardiac occlusive disease but also the failure of vascular surgeons to recognise and treat the risk factors for atherosclerosis, in particular hypercholesterolaemia. The aim of this review is to clarify the current experimental and clinical evidence for the use of statins in vascular disease.

METHODS

Literature compiled from an extensive search of Medline and the Cochrane database has been used for the basis of this review.

RESULTS

Experimental and clinical evidence consistently reports that statins improve endothelial dysfunction, are anti-inflammatory, anti-proliferative, anti-thrombogenic and anti-proteolytic. These effects are known to inhibit atherogenesis and improve plaque stability. Independent groups support the use of statins in the prevention of both primary and secondary cardiac events. The National Stroke association recommends their use to reduce strokes following myocardial infarction and the Heart Protection Study reports benefits in patients with non-cardiac occlusive disease.

CONCLUSIONS

There is substantial evidence advocating the use of statins in patients with clinically significant vascular disease. In the future this may evolve to include those patients at risk from neointimal hyperplasia, aneurysmal disease and ischaemia reperfusion injury.

The lipid and non-lipid effects of statins

The 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors, more commonly known as statins, are a class of drug widely used for the treatment of hypercholesterolaemia in patients with established cardiovascular disease as well as those at high risk of developing atherosclerosis. Their predominant action is to reduce circulating levels of low-density lipoprotein (LDL) cholesterol; to a smaller degree, they also increase high-density lipoprotein (HDL) cholesterol and reduce triglyceride concentrations. In recent years, however, there has been an increasing body of evidence that their effects on lipid profile cannot fully account for their cardiovascular protective actions: their beneficial effects are too rapid to be easily explained by their relatively slow effects on atherogenesis and too large to be accounted for by their relatively small effects on plaque regression. Experimental models have revealed that statins exert a variety of other cardiovascular effects, which would be predicted to be of clinical benefit: they possess anti-inflammatory properties, as evidenced by their ability to reduce the accumulation of inflammatory cells in atherosclerotic plaques; they inhibit vascular smooth muscle cell proliferation, a key event in atherogenesis; they inhibit platelet function, thereby limiting both atherosclerosis and superadded thrombosis; and they improve vascular endothelial function, largely through augmentation of nitric oxide (NO) generation. The relative importance of the lipid- and non-lipid-related effects of the statins in the clinical situation remains the subject of much continuing research.

Hypercholesterolemia promotes P-selectin-dependent platelet-endothelial cell adhesion in postcapillary venules

OBJECTIVE

The objectives of this study were to determine whether hypercholesterolemia promotes platelet-endothelial cell (P/E) adhesion in murine postcapillary venules and define the contributions of endothelial or platelet associated P-selection to hypercholesterolemia-induced P/E interactions.

METHODS AND RESULTS

Wild-type (WT) or P-selectin deficient (P-sel-/-) platelets were isolated and labeled with the fluorochrome CFSE and administered to either WT or P-sel-/- mice placed on a normal diet (ND) or high cholesterol diet (HCD). Intravital videomicroscopy was used to quantify platelet saltation and firm adhesion. HCD-WT mice exhibited a time-dependent increase in P/E cell interactions (relative to ND-WT). Flow cytometry revealed an increased expression of P-selectin on circulating platelets of HCD-WT mice at 2 weeks compared with ND-WT mice. When WT platelets were monitored in HCD-P-sel-/- mice, P/E adhesion was dramatically reduced. However, when P-sel-/- platelets were monitored in HCD-WT recipients, P/E adhesive interactions were reduced even further, comparable to ND-WT mice.

CONCLUSIONS

These results indicate that elevated cholesterol levels promote P/E adhesion in postcapillary venules and that whereas both endothelial and platelet P-selectin contribute to hypercholesterolemia-induced recruitment of platelets, platelet-associated P-selectin seems to play a more important role in producing the prothrombogenic phenotype in venules.

Platelet sialic acid as a potential pathogenic factor in coronary heart disease

It was previously reported that, compared to healthy individuals, patients with coronary heart disease (CHD) exhibit a higher proportion of platelets with lower densities and higher propensity to aggregate. Reasons for this increased tendency to aggregate were unknown but appeared to be independent of the patient's age, gender, or smoking habits. Sialic acid (N-acetyl-neuraminic acid), a negatively charged sugar and constituent of many glycoproteins and gangliosides, is known to confer the bulk of negative charges to mammalian cell surfaces. These negatively charged surfaces can help cells of the bloodstream to maintain a relative distance from each other due to repulsion of the same (negative) charges. In this study, we examined whether differences in platelet sialic acid are a potential pathogenic factor in patients with coronary heart disease. Upon isolating platelets, we found a significantly higher (p < 0.05) proportion of low density platelets in patients compared to healthy controls, which is in accordance with previously published data. We found significantly less (p < 0.05) sialic acid in platelets from patients compared to the control. Most of the platelet total sialic acid was susceptible to cleavage by neuraminidase, demonstrating sialic acid to be preferably localized at the outer platelet surface. We conclude that the lower sialic acid content found in platelets from CHD patients could represent a contributing factor for the observed higher aggregability of platelets from these patients. Due to the lower sialic acid content and resulting lower negative surface charge, less repulsion between the platelets could facilitate aggregation.

Pleiotropic effects of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors or statins are potent inhibitors of cholesterol biosynthesis. Several large clinical trials have demonstrated the beneficial effects of statins in the primary and secondary prevention of coronary heart disease. However, the overall clinical benefits observed with statin therapy appear to be greater than what might be expected from changes in lipid profile alone, suggesting that the beneficial effects of statins may extend beyond their effects on serum cholesterol levels. Indeed, recent experimental and clinical evidence indicates that some of the cholesterol-independent or "pleiotropic" effects of statins involve improving or restoring endothelial function, enhancing the stability of atherosclerotic plaques, and decreasing oxidative stress and vascular inflammation. Many of these pleiotropic effects of statins are mediated by their ability to block the synthesis of important isoprenoid intermediates, which serve as lipid attachments for a variety of intracellular signaling molecules. In particular, the inhibition of small GTP-binding proteins, Rho, Ras, and Rac, whose proper membrane localization and function are dependent on isoprenylation, may play an important role in mediating the direct cellular effects of statins on the vascular wall.

Genetic and environmental contributions to platelet aggregation: the Framingham heart study

BACKGROUND

Platelet aggregation plays an important role in arterial thrombosis in coronary heart disease, stroke, and peripheral arterial disease. However, the contribution of genetic versus environmental influences on interindividual variation in platelet aggregability is poorly characterized.

METHODS AND RESULTS

We studied the heritability of platelet aggregation responses in 2413 participants in the Framingham Heart Study. The threshold concentrations of epinephrine and ADP required to produce biphasic platelet aggregation and collagen lag time were determined. Mixed-model linear regression was used to calculate correlation coefficients within sibships and within spouse pairs. Variance and covariance component methods were used to estimate the proportion of platelet aggregation attributable to measured covariates versus additive genetic effects. After accounting for environmental covariates, the adjusted sibling correlations for epinephrine, ADP, and collagen lag time were 0.24, 0.22, and 0.31, respectively (P=0.0001 for each). In contrast, adjusted correlations for spouse-pairs were -0.01, 0.05, and -0.02, respectively (all P>0.30). The estimated heritabilities were 0.48, 0.44, and 0.62, respectively. Measured covariates accounted for only 4% to 7% of the overall variance in platelet aggregation, and heritable factors accounted for 20% to 30%. The platelet glycoprotein IIIa Pl(A2) polymorphism and the fibrinogen Hind III beta-148 polymorphism contributed <1% to the overall variance.

CONCLUSIONS

In our large, population-based sample, heritable factors play a major role in determining platelet aggregation, and measured covariates play a lesser role. Future studies are warranted to identify the key genetic variants that regulate platelet function and to lay the groundwork for rational pharmacogenetic approaches.

Collagen-stimulated unidirectional translocation of cholesterol in human platelet membranes

When human platelets are stimulated with collagen or thrombin, the asymmetric distribution of membrane lipids is disrupted as phosphatidylserine and phosphatidylethanolamine translocate from the inner monolayer to the outer monolayer. Coincident with the stimulus-dependent rearrangement of membrane phospholipids is a rapid redistribution of cholesterol from the outer to the inner membrane monolayer. This redistribution of cholesterol was observed when the stimulus was collagen or ADP. The data presented here show that epinephrine stimulation does not promote cholesterol translocation but does potentiate collagen-promoted movement of cholesterol. To investigate the process of cholesterol translocation, experiments were performed to determine whether collagen stimulated reverse cholesterol movement; i.e. from the inner to the outer monolayer. For this study, the fluorescent sterol cholestatrienol (C-3) was incorporated into platelet membranes by exchange from cholesterol-containing phosphatidylcholine small unilamellar vesicles. C-3 was then removed selectively from the outer monolayer by treatment of the platelets with bovine serum albumin (BSA). During the subsequent incubation of BSA-treated platelets, C-3 moved spontaneously into the outer from the inner monolayer. This translocation had an apparent half-time of approximately 25 min and was unaltered by the presence of collagen. These results suggest that collagen treatment of platelets selectively facilitates the inward movement of the sterol. We have hypothesized that cholesterol translocation may be thermodynamically driven as a result of an unfavorable entropy, resulting in cholesterol translocation out of an environment becoming enriched in phosphatidylethanolamine. The unidirectional nature of collagen-promoted cholesterol movement from the phosphatidylethanolamine-rich outer monolayer is consistent with this interpretation.

Analysis of GTP-binding proteins, phosphoproteins, and cytosolic calcium in functional heterogeneous human blood platelet subpopulations

The biochemical basis for the functional heterogeneity of human blood platelets was investigated in terms of protein phosphorylation, cytoplasmic calcium ([Ca2+]i), the ratio of 46 and 50 kDa vasodilator-stimulated protein (VASP), and GTP-binding proteins (G-proteins). Platelets were fractionated by density. Comparing resting low-density platelets (LDP) to high-density platelets (HDP) revealed higher phosphorylation of proteins in the 47, 31, and 24 kDa ranges. A higher phosphorylation of the 20 kDa protein in LDP compared to HDP was related to an enhanced [Ca2+]i, an increased ADP-ribosylation of the inhibitory G-protein (G(i alpha1-3)) and rhoA, and a decreased ADP-ribosylation of the stimulatory G-protein (G(s alpha)). The differences in the ribosylation patterns of the subpopulations were not influenced by thrombin stimulation or exposure to prostaglandin E1 (PGE1). An 18 kDa phosphoprotein was more highly phosphorylated in resting HDP than in LDP. Thrombin exposure caused dephosphorylation of the 18 kDa phosphoprotein in the HDP, but generally increased phosphorylation of both HDP and LDP in the 47, 31, 24, and 20 kDa bands. Preincubation with prostaglandin E1 or sodium nitroprusside diminished the subsequent thrombin-induced increase in phosphorylation, particularly in HDP. In unstimulated HDP, the 50 kDa VASP phospho form was enhanced, whereas in unstimulated LDP the 46 kDa VASP dephospho form was increased. Our findings suggest that the functional heterogeneity of platelets is partly derived from differences in signal transduction mechanisms reflected in varying phosphoprotein patterns and G-protein properties of platelet stimulatory and inhibitory pathways.

Large versus small unilamellar vesicles mediate reverse cholesterol transport in vivo into two distinct hepatic metabolic pools. Implications for the treatment of atherosclerosis

Phospholipid liposomes are synthetic mediators of "reverse" cholesterol transport from peripheral tissue to liver in vivo and can shrink atherosclerotic lesions in animals. Hepatic disposal of this cholesterol, however, has not been examined. We compared hepatic effects of large (approximately equal to 120-nm) and small (approximately equal to 35-nm) unilamellar vesicles (LUVs and SUVs), both of which mediate reverse cholesterol transport in vivo but were previously shown to be targeted to different cell types within the liver. On days 1, 3, and 5, rabbits were intravenously injected with 300 mg phosphatidylcholine (LUVs or SUVs) per kilogram body weight or with the equivalent volume of saline. After each injection, LUV- and SUV-injected animals showed large increases in plasma concentrations of unesterified cholesterol, indicating mobilization of tissue stores. After hepatic uptake of this cholesterol, however, SUV-treated animals developed persistently elevated plasma LDL concentrations, which by day 6 had increased to more than four times the values in saline-treated controls. In contrast, LUV-treated animals showed normal LDL levels. By RNase protection assay, SUVs suppressed hepatic LDL receptor mRNA at day 6 (to 61 +/- 4% of control, mean +/- SEM), whereas LUVs caused a statistically insignificant stimulation. Hepatic HMG-CoA reductase message was also significantly suppressed with SUV, but not LUV treatment, and hepatic 7 alpha-hydroxylase message showed a similar trend. These data on hepatic mRNA levels indicate that SUVs, but not LUVs, substantially perturbed liver cholesterol homeostasis. We conclude that LUVs and SUVs mobilize peripheral tissue cholesterol and deliver it to the liver, but to distinct metabolic pools that exert different regulatory effects. The effects of one of these artificial particles, SUVs, suggest that reverse cholesterol transport may not always be benign. In contrast, LUVs may be a suitable therapeutic agent, because they mobilize peripheral cholesterol to the liver without suppressing hepatic LDL receptor mRNA and without provoking a subsequent rise in plasma LDL levels.

Involvement of guanylate cyclase and phosphodiesterases in the functional heterogeneity of human blood platelet subpopulations

Cyclic nucleotides are involved in the regulation of platelet activation, shape change, and aggregation. In this study we have investigated the role of guanylate cyclase and phosphodiesterase in three functional heterogeneous human blood platelet subpopulations separated according to density. In low-density platelets aggregation was enhanced and inhibited less when cyclic GMP was increased by sodium nitroprusside, compared to high-density platelets. Low-density platelets possessed a lower basal level of cyclic GMP and exhibited a small increase in cyclic GMP after stimulation with sodium nitroprusside. Cyclic GMP-dependent phosphodiesterase activity was similar in high, low, and intermediate-density platelets. In contrast, the activity of the cyclic AMP-dependent phosphodiesterase was higher in low-density compared to high and intermediate-density platelets. These results suggest that regulation of cyclic GMP and cyclic AMP levels plays an important role in the functional heterogeneity of human blood platelets.