Olga Dashevsky

Platelet-derived microparticles promote invasiveness of prostate cancer cells via upregulation of MMP-2 production

Prostate cancer commonly affects men in the Western world. A major factor of the life‐threatening course of this disease is the high rate of metastasis, predominantly to bones. Circulating tumor cells encounter platelets and may activate them, resulting in a production of microparticles (MPs). MPs are small platelet fragments expressing membrane receptors as well as cytoplasmic constituents. Here, we report that prostate cancer cells, Clone‐1 (Cl‐1), preincubated with platelet‐derived MPs (PMPs), demonstrate increased invasion through a gelatin‐coated (a denatured form of collagen) membrane of the Boyden chamber system. This effect was accompanied by an increased secretion of metalloproteinase‐2 (MMP‐2) as demonstrated by a gelatin zymography. Application of MMP‐2/9 inhibitor reversed the PMP‐induced tumor cell invasion. PMPs were shown to adhere to Cl‐1 cells, but direct contact between them may not be mandatory for MMP secretion because PMP lysate induced MMP‐2 production by Cl‐1 cells to the same extent as did intact PMPs. PMP‐induced MMP‐2 secretion was inhibited by neutralization of either PKC or total intracellular tyrosine phosphorylation, but was not affected by blocking major intraplatelet cytokines. Actinomycin D (a transcription inhibitor) did not modify this effect, whereas cycloheximide (an inhibitor of protein translation) abolished the MMP‐2 release. MMP‐2 secretion was accompanied by a rapid and transient increase in MMP‐2 mRNA level after a 2‐hr coincubation of prostate cancer cells with PMPs. Thus, PMPs promote tumor invasiveness, at least in part by stimulation of MMP‐2 production.

C-reactive protein promotes platelet adhesion to endothelial cells: a potential pathway in atherothrombosis.

C‐reactive protein (CRP) is a strong predictor for acute cardiovascular events. Several endothelial prothrombotic effects of CRP have been recently reported. This study examined the effect of CRP on bovine aortic endothelial cell (EC) activation and capacity to recruit human platelets under flow conditions using the cone and plate(let) analyser method. Human recombinant CRP promoted platelet adhesion in a dose‐ and time‐dependent manner, with a maximal effect at 20 μg/ml (increase of 174% over baseline, P < 0·01). Similar effects were observed following incubation of EC with sera of transgenic mice that express human CRP (10 μg/ml). Anti‐intercellular adhesion molecule‐1 neutralising monoclonal antibody and nitric oxide donor, sodium nitroprusside, blocked the effect of CRP, reducing adhesion from 202% to 128% (P < 0·05) and 114% (P = 0·02) respectively. The pro‐adhesive effect of CRP was abolished by calphostin C (a protein kinase C inhibitor), whereas the extracellular signal‐regulated kinase antagonist, PD98059, did not have any effect. CRP promoted P‐selectin expression on the EC surface and blockade of P‐selectin reversed CRP‐induced platelet adhesion. In conclusion, CRP promoted platelet adhesion to EC. Our results emphasise the possible role of CRP in linking inflammation and thrombosis and provide a potential mechanism for the high incidence of vascular events associated with high CRP levels.

Involvement of platelet derived microparticles in tumor metastasis and tissue regeneration

Platelets play a major role in hemostasis, but are also involved in vascular biology processes such as angiogenesis and tumor metastasis. Activated platelets release many proteins favoring wound healing and promoting angiogenesis. Microparticles (MP) are small plasma membrane vesicles shed from cells upon their activation or apoptosis. Platelet-derived microparticles (PMP) constitute the majority of the pool of MP circulating in the blood. PMP express and may transfer functional receptors, stimulate the release of cytokines, activate intracellular signaling pathways, promote angiogenesis, and are involved in tissue regeneration and cancer metastasis. We investigated the effect of PMP on cancer cells metastasis and their potential beneficial effect in an ischemic stroke model.

Platelet Microparticles Induce Angiogenesis and Neurogenesis after Cerebral Ischemia

Activated platelets shed microparticles, which contain a variety of growth factors central to angiogenesis and neurogenesis. The aim of this study was to explore whether platelet derived microparticles (PMP) can boost endogenous neural stem cells dependent repair mechanisms following stroke in a rat model. To examine the effects of PMP therapy in-vivo, we delivered PMP or vehicle via a biodegradable polymer to the brain surface after permanent middle cerebral artery occlusion (PMCAO) in rats. Rats were tested with the neurological severity score and infarct volumes were measured at 90 days post-ischemia. Immunohistochemistry was used to determine the fate of newborn cells and to count blood vessels in the ischemic brain. The results show that PMP led to a dose dependent increase in cell proliferation, neurogenesis and angiogenesis at the infarct boundary zone and significantly improved behavioral deficits.

Platelet Microparticles Promote Neural Stem Cell Proliferation, Survival and Differentiation

Platelet microparticles (PMP) are small subcellular fragments, shed upon platelet activation. PMP host a variety of cytokines and growth factor that were previously shown to affect angiogenesis and postischemic tissue regeneration. This study attempted to explore the effect of PMP on neural stem cell (NSC) proliferation, survival and differentiation. Cells were grown as neurospheres and treated with PMP, or relevant growth factors, sphere size and cell fates were evaluated. PMP treatment led to larger neurospheres with increased cell survival. PMP treatment was comparable with the effect of acceptable single growth factors such as fibroblastic growth factor (FGF), vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF). PMP treatment also increased the differentiation potential of NSC to glia and neurons. Specific growth factor inhibitors only partly blocked these effects, which were associated with increments in ERK and Akt phosphorylation. In this study, we show that various growth factors contained within the PMP promote neuronal cell proliferation, survival and differentiation. The results suggest a role for platelet microparticles in augmenting endogenous neural progenitor and stem cells angiogenesis and neurogenesis that might be utilized for treatment following brain injury.

Platelet lysates stimulate angiogenesis, neurogenesis and neuroprotection after stroke

Platelets contain chemo-attractants and mitogens that have a major role in tissue repair. Therefore we hypothesised that tissue regeneration secondary to activation of endogenous neural stem cells (eNSC) can be enhanced by delivering platelets to the ischaemic brain. To examine these potential therapeutic effects we injected platelet-poor plasma (PPP), fibroblast growth factor (FGF2) and platelet lysate (PLT) to the lateral ventricles after permanent middle cerebral artery occlusion (PMCAO) in rats. The animals were tested with the neurological severity score, and infarct volumes were measured at 90 days post-PMCAO. Immunohistochemistry was used to determine the fate of newborn cells and to count blood vessels in the ischaemic brain. Platelets significantly increased eNSC proliferation and angiogenesis in the subventricular zone (SVZ) and in the peri-lesion cortex. Functional outcome was significantly improved and injury size was significantly reduced in rats treated with PLT suggesting additional neuroprotective effects. In conclusion, local delivery of PLT to the lateral ventricles induces angiogenesis, neurogenesis and neuroprotection and reduces behavioural deficits after brain ischaemia.

Allicin Inhibits Blood Vessel Growth and Downregulates Akt Phosphorylation and Actin Polymerization

INTRODUCTION Angiogenesis is a multistep cellular process in which new vessels emerge from preexisting endothelial vasculature in the presence of various growth factors and extracellular matrix (ECM) proteins (1). This process includes movement of endothelial cells (EC) to the site of future vessel development, proliferation, and formation of tubule-like structures followed by recruitment of pericytes and smooth muscle cells, that is, vessel maturation (1). Evidently, initial stages of vessel growth are dependent on the integrity of cellular cytoskeleton in ECs and the ability of intracellular monomeric actin to polymerize (2). Angiogenesis underlies a wide spectrum of both physiologic and pathologic processes including primary tumor growth, invasion, and metastases (3,4). In addition, inflammation and angiogenesis are linked together (5), and blood vessel growth constitutes an essential part in the pathogenesis of a number of inflammatory-mediated diseases including inflammatory bowel disease and rheumatoid arthritis (6,7). Therefore, inhibition of angiogenesis is a challenge that modern biology faces, and the development of novel antiangiogenic agents is highly important. Allicin (diallyl-thiosulfinate) is a major ingredient of fresh garlic extract. It is produced during the crushing of garlic cloves

Normal Wound Healing and Tumor Angiogenesis as a Game of Competitive Inhibition

Both normal wound healing and tumor angiogenesis are mitigated by the sequential, carefully orchestrated release of growth stimulators and inhibitors. These regulators are released from platelet clots formed at the sites of activated endothelium in a temporally and spatially controlled manner, and the order of their release depends on their affinity to glycosaminoglycans (GAG) such as heparan sulfate (HS) within the extracellular matrix, and platelet open canallicular system. The formation of vessel sprouts, triggered by angiogenesis regulating factors with lowest affinities for heparan sulfate (e.g. VEGF), is followed by vessel-stabilizing PDGF-B or bFGF with medium affinity for HS, and by inhibitors such as PF-4 and TSP-1 with the highest affinities for HS. The invasive wound-like edge of growing tumors has an overabundance of angiogenesis stimulators, and we propose that their abundance out-competes angiogenesis inhibitors, effectively preventing inhibition of angiogenesis and vessel maturation. We evaluate this hypothesis using an experimentally motivated agent-based model, and propose a general theoretical framework for understanding mechanistic similarities and differences between the processes of normal wound healing and pathological angiogenesis from the point of view of competitive inhibition.