Unlocking Aspirin's Chemopreventive Activity: Role of Irreversibly Inhibiting Platelet Cyclooxygenase-1.

The mechanism by which aspirin consumption is linked to significant reductions in the incidence of multiple forms of cancer and metastatic spread to distant tissues, resulting in increased cancer patient survival is not well understood. In this study, using colon cancer as an example, we provide both in vitro (cell culture) and in vivo (chemically induced mouse model of colon cancer) evidence that this profound antineoplastic action may be associated with aspirin's ability to irreversibly inhibit COX-1-mediated platelet activation, thereby blocking platelet-cancer cell interactions, which promote cancer cell number and invasive potential. This process may be driven by platelet-induced epithelial-mesenchymal transition (EMT), as assessed using confocal microscopy, based upon changes in cell morphology, growth characteristics and fibronectin expression, and biochemical/molecular analysis by measuring changes in the expression of the EMT markers; vimentin, β-catenin, and SNAIL.

Single-molecule force measurements of the polymerizing dimeric subunit of von Willebrand factor.

Von Willebrand factor (VWF) multimers are large adhesive proteins that are essential to the initiation of hemostatic plugs at sites of vascular injury. The binding of VWF multimers to platelets, as well as VWF proteolysis, is regulated by shear stresses that alter VWF multimeric conformation. We used single molecule manipulation with atomic force microscopy (AFM) to investigate the effect of high fluid shear stress on soluble dimeric and multimeric forms of VWF.

Association between cell-derived microparticles and adverse events in patients with nonpulsatile left ventricular assist devices.

Background: Continuous-flow left ventricular assist devices (LVADs) expose blood cells to high shear stress, potentially resulting in the production of microparticles that express phosphatidylserine (PS+) and promote coagulation and inflammation. In this prospective study, we attempted to determine whether PS+ microparticle levels correlate with clinical outcomes in LVAD-supported patients.

Methods: We enrolled 20 patients undergoing implantation of the HeartMate II LVAD (Thoratec Corp, Pleasanton, CA) and 10 healthy controls who provided reference values for the microparticle assays.

Racial differences in human platelet PAR4 reactivity reflect expression of PCTP and miR-376c.

Racial differences in the pathophysiology of atherothrombosis are poorly understood. We explored the function and transcriptome of platelets in healthy black (n = 70) and white (n = 84) subjects. Platelet aggregation and calcium mobilization induced by the PAR4 thrombin receptor were significantly greater in black subjects.

Mechanical activation of a multimeric adhesive protein through domain conformational change.

The mechanical force-induced activation of the adhesive protein von Willebrand factor (VWF), which experiences high hydrodynamic forces, is essential in initiating platelet adhesion. The importance of the mechanical force-induced functional change is manifested in the multimeric VWF's crucial role in blood coagulation, when high fluid shear stress activates plasma VWF (PVWF) multimers to bind platelets. Here, we showed that a pathological level of high shear stress exposure of PVWF multimers results in domain conformational changes, and the subsequent shifts in the unfolding force allow us to use force as a marker to track the dynamic states of the multimeric VWF.

Proteomic analysis of resting and thrombin-stimulated platelets reveals the translocation and functional relevance of HIP-55 in platelets.

The platelet surface is a dynamic interface that changes rapidly in response to stimuli to co-ordinate the formation of thrombi at sites of vascular injury. Tight control is essential as loss of organisation may result in the inappropriate formation of thrombi (thrombosis) or excessive bleeding. In this paper we describe the comparative analysis of resting and thrombin-stimulated platelet membrane proteomes and associated proteins to identify proteins important to platelet function.

Differences in responses of platelets to fluid shear stress in patients with peripheral artery disease (PAD) and coronary artery disease (CAD).

Information on differences in platelet function between patients with peripheral arterial disease (PAD) and patients with coronary artery disease (CAD) is limited. We sought to examine the differences in the platelets response to shear stress in patients with PAD compared to those with CAD. Men with symptomatic PAD (ankle brachial index [ABI] < 0.

Correlation of CD34+ cells with tissue angiogenesis after traumatic brain injury in a rat model.

Increasing evidence suggests that circulating endothelial progenitor cells, which are a subpopulation of hematopoietic progenitor CD34(+) cells, play a critical role in neovascularization and tissue repair. We have tested the hypothesis that traumatic brain injury (TBI) could mobilize CD34(+) cells to peripheral blood and brain tissue, a process critical for vascular repair, in a rat model of TBI. Male Wistar rats were subjected to controlled fluid percussion.

Flow cytometric measurement of microparticles: pitfalls and protocol modifications.

Upon activation, many cells shed components of their plasma membranes as microparticles. Depending on the methods of preparation and analyses, microparticle counts may vary significantly between laboratories, making data analyses and clinical correlations challenging. To assess how variations in sample preparation affect microparticle measurements, blood samples from 13 healthy, adult volunteers were labeled with Annexin V, cell-specific antibodies, and antibodies against tissue factor (TF).

Increased platelet sensitivity among individuals with aspirin resistance - platelet aggregation to submaximal concentration of arachidonic acid predicts response to antiplatelet therapy.

Aspirin 'resistance' (AR) is a phenomenon of uncertain etiology describing decreased platelet inhibition by aspirin. We studied whether (i) platelets in AR demonstrate increased basal sensitivity to a lower degree of stimulation and (ii) platelet aggregation with submaximal stimulation could predict responses to aspirin. Serum thromboxane B(2) (TxB(2)) levels and platelet aggregation with light transmission aggregometry (LTA) were measured at baseline and 24 hours after 325 mg aspirin administration in 58 healthy subjects.

Protein phosphatase 2A negatively regulates integrin alpha(IIb)beta(3) signaling.

Integrin alpha(IIb)beta(3) activation is critical for platelet physiology and is controlled by signal transduction through kinases and phosphatases. Compared with kinases, a role for phosphatases in platelet integrin alpha(IIb)beta(3) signaling is less understood. We report that the catalytic subunit of protein phosphatase 2A (PP2Ac) associates constitutively with the integrin alpha(IIb)beta(3) in resting platelets and in human embryonal kidney 293 cells expressing alpha(IIb)beta(3).

Magnesium maintains endothelial integrity, up-regulates proteolysis of ultra-large von Willebrand factor, and reduces platelet aggregation under flow conditions.

Mg (++) regulates endothelial functions and has anti-inflammatory effects. Its effects on thrombosis have been demonstrated, but the mechanism remains poorly understood. We investigated the roles of MgSO(4) in regulating the release and cleavage of the prothrombotic ultra-large (UL) von Willebrand factor (VWF) and VWF-mediated platelet adhesion and aggregation.

Changes in circulating human endothelial progenitor cells after brain injury.

Endothelial progenitor cells (EPCs) are mobilized from the bone marrow to blood circulation in response to tramatic or inflammatory stimulations. Once released, they actively seek and home to the sites of vascular injury to promote vascular repair. We monitored changes of EPC counts in peripheral blood of 29 patients with traumatic brain injury for up to 21 days.

Platelet reactivity among Asian Indians and Caucasians.

Asian Indians are reported to have higher mortality and morbidity from coronary artery disease (CAD) than other ethnic groups. This variation in events cannot be explained only by differences in conventional risk factors. Platelet activation is an important factor in the pathogenesis of CAD, however, there are limited data concerning platelet reactivity in Asian Indians.

Acquired ADAMTS-13 deficiency in pediatric patients with severe sepsis.

We studied the state of ultra-large von Willebrand factor (ULVWF) proteolysis in 21 pediatric patients with severe sepsis and found that the overall group of patients had moderately reduced ADAMTS-13 activity, but 31% had severe enzymatic deficiency. The severe deficiency correlated with greater adhesion activity of von Willebrand factor, severity of thrombocytopenia and plasma levels of interleukin-6. It also correlated clinically with severity of illness and organ dysfunction.

Enhanced platelet adhesion and aggregation by endothelial cell-derived unusually large multimers of von Willebrand factor.

Endothelial cells synthesize and secrete von Willebrand factor (VWF) multimers, including unusually large forms (ULVWF), which are usually cleaved into smaller multimers found in normal plasma (P-VWF). Thrombotic thrombocytopenic purpura (TTP) is a microangiopathic disorder characterized by systemic attachment of platelets to inadequately cleaved ULVWF multimers. We have compared ULVWF and P-VWF in their capacity to become immobilized onto surfaces in vitro and their ability to mediate platelet adhesion.

Aggregometry detects platelet hyperreactivity in healthy individuals.

Aggregometry is widely used to assess platelet function, but its use in identifying platelet hyperreactivity is poorly defined. We studied platelet aggregation in 359 healthy individuals using the agonists adenosine diphosphate (ADP), epinephrine, collagen, collagen-related peptide, and ristocetin. We also assessed the reproducibility of these assays in 27 subjects by studying them repeatedly on at least 4 separate occasions.

Heterogeneous effects of tissue inhibitors of matrix metalloproteinases on cardiac fibroblasts.

The balance between matrix metalloproteinases (MMPs) and their natural inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), plays a critical role in cardiac remodeling. Although a number of studies have characterized the pathophysiological role of MMPs in the heart, very little is known with respect to the role of TIMPs in the heart. To delineate the role of TIMPs in the heart we examined the effects of adenovirus-mediated overexpression of TIMP-1, -2, -3, and -4 in cardiac fibroblasts.

Effects of low temperature on shear-induced platelet aggregation and activation.

Background: Hemorrhage is a major complication of trauma and often becomes more severe in hypothermic patients. Although it has been known that platelets are activated in the cold, studies have been focused on platelet behavior at 4 degrees C, which is far below temperatures encountered in hypothermic trauma patients. In contrast, how platelets function at temperatures that are commonly found in hypothermic trauma patients (32-37 degrees C) remains largely unknown, especially when they are exposed to significant changes in fluid shear stress that could occur in trauma patients due to hemorrhage, vascular dilation/constriction, and fluid resuscitation.

Duration of exposure to high fluid shear stress is critical in shear-induced platelet activation-aggregation.

Platelet functions are increasingly measured under flow conditions to account for blood hydrodynamic effects. Typically, these studies involve exposing platelets to high shear stress for periods significantly longer than would occur in vivo. In the current study, we demonstrate that the platelet response to high shear depends on the duration of shear exposure.

Platelet aggregation and activation under complex patterns of shear stress.

Arterial stenosis results in a complex pattern of blood flow containing an extremely fast flow in the throat of stenosis and a post-stenosis low flow. The fast flow generates high shear stress that has been demonstrated in vitro to activate and aggregate platelets. One potential problem of these in vitro studies is that platelets are invariably exposed to a high shear stress for a period that is significantly longer than they would have experienced in vivo.