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Biomedical subjects

Y Yatomi

Publications and source records attributed to Y Yatomi.

At least 19 recordsLinked to original sources
PubMed2006

Inhibitory effects of ticlopidine on platelet function as assessed by three different methods.

The inhibitory effects of ticlopidine on platelet function were evaluated in 18 healthy male volunteers using three different platelet function tests. Three methods include the recently developed small collagen-beads method, which evaluates the platelet response in whole blood samples under shear stress conditions, the conventional platelet aggregometry and a cone-plate viscometer which measures shear-induced platelet aggregation (SIPA). The latter two methods use platelet-rich plasma as measurement samples instead of whole blood. SIPA was significantly inhibited by the oral intake of ticlopidine. The conventional platelet aggregometry detected significant inhibition of ticlopidine on ADP-induced platelet aggregation. In contrast, ticlopidine moderately inhibited platelet aggregation induced by low concentrations of collagen, but not by high concentrations of collagen. With the collagen-bead column method, ticlopidine significantly inhibited platelet retention rates when the retention rates exceeded 30% prior to ticlopidine uptake. On the other hand, there was no significant inhibition when the original retention rates prior to ticlopidine uptake were below 30%. The three methods all proved useful to evaluate the effect of ticlopidine on platelet function. However, taking into consideration easy procedures, lower costs and use of whole blood samples under shear stress conditions, we suggest the collagen-bead column can serve as an appropriate method for monitoring ticlopidine therapy.

Blood Platelets↗
PubMed2006

Aspirin resistance detected with aggregometry cannot be explained by cyclooxygenase activity: involvement of other signaling pathway(s) in cardiovascular events of aspirin-treated patients.

OBJECTIVES: Although the concept of aspirin resistance is extensively reported in medical literature, its precise mechanisms and clinical outcomes are largely unknown. In this study, we examined individual thromboxane biosynthesis and platelet aggregation in aspirin-treated patients, and whether the results of a platelet aggregation test influenced clinical outcomes. RESULTS: Subjects taking 81 mg of aspirin (n = 50) and controls (n = 38) were evaluated for platelet aggregation and platelet cyclooxygenase-1 (COX-1) activity by measuring collagen-induced thromboxane B2 production. For aggregometry, both light transmission (LT) and laser-light scattering methods were employed to quantitatively evaluate aggregate sizes and numbers. Aspirin treatment resulted in the inhibition of collagen-induced platelet aggregation, particularly the transition from small to large platelet aggregates. Although platelet COX-1 activity seemed to be uniformly inhibited in all patients, platelet aggregation studies showed great inter-individual differences; variation in platelet COX-1 activity only accounted for 6-20% of the individual aggregations. Factor analysis revealed the existence of a common factor (other than platelet COX-1) that explained 48.4% of the variations in platelet aggregation induced by collagen, adenosine diphosphate (ADP), and collagen-related peptide. We then prospectively enrolled 136 aspirin-treated patients in our study, and we found that being in the upper quartile level of LT, or with large aggregate formation induced by collagen, was an independent risk factor for developing cardiovascular events within 12 months [hazard ratio (HR) = 7.98, P = 0.008 for LT; HR = 7.76, P = 0.007 for large aggregates]. On the other hand, the existence of diabetes mellitus was an independent risk factor for overall outcomes (HR 1.30-11.9, P = 0.015-0.033). CONCLUSIONS: Aspirin resistance expressed as unsuppressed platelet COX-1 activity is a rare condition in an out-patient population. Other factor(s) affecting collagen-induced platelet aggregation may influence early outcomes in aspirin-treated patients.

Aged↗
PubMed2006

Sphingosine 1-phosphate in vascular biology: possible therapeutic strategies to control vascular diseases.

Blood platelets are very unique in that they store sphingosine 1-phosphate (Sph-1-P) abundantly (possibly due to the existence of highly active sphingosine kinase and a lack of Sph-1-P lyase) and release this bioactive lipid extracellularly upon stimulation. Vascular endothelial cells (ECs) and smooth muscle cells (SMCs) respond dramatically to this platelet-derived bioactive lipid mainly through a family of G protein-coupled Sph-1-P receptors named S1P1, 2, 3, 4, and 5, originally referred to as EDG-1, 5, 3, 6, and 8, respectively. In fact, the importance of Sph-1-P in platelet-vascular cell interactions has been revealed in a number of recent reports. Through interaction with ECs, Sph-1-P can mediate physiological wound healing processes such as vascular repair, although this important bioactive lipid can become atherogenic and thrombogenic, and cause or aggravate cardiovascular diseases especially under certain pathological conditions. On the other hand, Sph-1-P induces vasoconstriction through interaction with SMCs. It is likely that regulation of Sph-1-P biological activities is important for the therapeutical purpose to control vascular disorders. Particularly, the development of specific S1P receptor agonists or antagonists seems a reasonable strategy to selectively regulate the bioactivity of Sph-1-P, considering that a great diversity of Sph-1-P actions has been reported and that this diversity depends mainly on the S1P receptor subtype involved. In this review, I will summarize recent findings on possible roles of Sph-1-P in vascular biology and its therapeutical implications.

Animals↗
PubMed2004

The intracellular action of sphingosine 1-phosphate in GPVI-mediated Ca2+ mobilization in platelets.

We analyzed the intracellular action of sphingosine 1-phosphate (Sph-1-P), formed from sphingosine (Sph) by sphingosine kinase (SPHK), in platelets. When sphingosine kinase activity was inhibited by N,N-dimethylsphingosine (DMS), Ca2+ mobilization induced by convulxin, an agonist of the collagen receptor glycoprotein VI (GPVI), was moderately but specifically abolished; that induced via G protein-coupled receptors was not affected. Under the same conditions, however, tyrosine phosphorylation of Syk and phospholipase Cgamma2, which is essential for the GPVI-mediated signaling, was not inhibited. Sphingosine kinase activity of the platelet membrane fraction increased specifically upon stimulation with convulxin or collagen. Our results suggest that intracellular sphingosine 1-phosphate is related to Ca2+ mobilization in GPVI-mediated signaling pathways.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2004

Cleavage of platelet endothelial cell adhesion molecule-1 (PECAM-1) in platelets exposed to high shear stress.

Platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) is a 130 kDa transmembrane glycoprotein that belongs to the immunoglobulin superfamily and is expressed on the surface of endothelial cells, platelets, and other blood cells. Although the importance of this adhesion molecule in various cell-cell interactions is established, its functional role in platelets remains to be elucidated. In this study, we examined whether PECAM-1 underwent changes in platelets exposed to high shear stress. Platelet PECAM-1 was cleaved under high shear stress and was released into the extracellular fluid as a fragment with an approximate molecular weight of 118 kDa. The cleavage was inhibited by an anti-VWF MoAb, but not by recombinant VWF A1 domains. These findings suggest that the GPIb-VWF interaction is involved in PECAM-1 cleavage under high shear stress, and that the cleavage is independent of GPIb clustering by VWF multimers. Furthermore, EGTA or calpeptin inhibited PECAM-1 cleavage. This finding provides evidence for the involvement of calpain in PECAM-1 cleavage. Flow-cytometric analysis revealed that PECAM-1 expression on the platelet surface was decreased under high shear stress. This reduction occurred exclusively in a specific population of platelets, which corresponded to platelet-derived microparticles (PMP). In conclusion, PECAM-1 cleavage under high shear stress is closely related to the activation of calpain and the process of PMP formation mediated by the GPIb-VWF interaction.

Blood Platelets↗
PubMed2001

Rac, a small guanosine triphosphate-binding protein, and p21-activated kinase are activated during platelet spreading on collagen-coated surfaces: roles of integrin alpha(2)beta(1).

In this study, the receptors and signals involved in collagen-induced platelet spreading were examined. It was found that platelet spreading on collagen (presenting a polygon shape with a number of filopodialike projections) was inhibited by the anti-integrin alpha(2) antibody, suggesting the involvement of integrin alpha(2)beta(1) in this process. Studies with a glutathione-S-transferase fusion protein that binds specifically to activated Rac and in vitro p21-activated kinase (PAK) kinase assays revealed that Rac and PAK were activated during this collagen-activated process. Platelet spreading on collagen-coated surfaces was inhibited strongly by PP1 (a Src family kinase inhibitor) or weakly by wortmannin (a phosphatidylinositol 3-kinase [PI3-kinase] inhibitor) but not at all by Y-27632 (a Rho kinase inhibitor). The surfaces coated with anti-integrin alpha(2)beta(1) antibodies also induced platelet spreading (presenting an almost complete round shape) and activation of Rac and PAK, although more slowly than collagen-coated surfaces. The antibody-induced responses were strongly inhibited by PP1 or wortmannin but not by Y-27632. The same concentration of Y-27632 inhibited collagen-induced shape change of platelets in suspension. These findings suggest that Rac and/or PAK activation, but not Rho, may play certain roles in platelet spreading via integrin alpha(2)beta(1) and that Src family kinases and PI3-kinase participate in these processes. Furthermore, the difference between spreading on collagen and the anti-integrin antibody suggests the involvement of other receptor(s) (in addition to the integrin alpha(2)beta(1)) for collagen-induced spreading, the most likely candidate being glycoprotein VI.

Amides↗
PubMed2001

Wheat germ agglutinin-induced platelet activation via platelet endothelial cell adhesion molecule-1: involvement of rapid phospholipase C gamma 2 activation by Src family kinases.

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is a 130K transmembrane glycoprotein that belongs to the immunoglobulin gene superfamily and is expressed on the surface of hematological or vascular cells, including platelets and endothelial cells. Although the importance of this adhesion molecule in various cell-cell interactions is established, its function in platelets remains ill-defined. In the process of clarifying the mechanism by which the lectin wheat germ agglutinin (WGA) activates platelets, we unexpectedly discovered that PECAM-1 is involved in signal transduction pathways elicited by this N-acetyl-D-glucosamine (NAGlu)-reactive lectin. WGA, which is a very potent platelet stimulator, elicited a rapid surge in Syk and phospholipase C (PLC)-gamma 2 tyrosine phosphorylation and the resultant intracellular Ca(2+) mobilization; collagen, as reported, induced these responses, but in a much slower and weaker manner. WGA strongly induced tyrosine phosphorylation of a 130-140K protein, which was confirmed to be PECAM-1 by immunoprecipitation and immunodepletion studies. WGA-induced PECAM-1 tyrosine phosphorylation occurred rapidly, strongly and in a manner independent of platelet aggregation or cell-cell contact; these characteristics of PECAM-1 phosphorylation were not mimicked at all by receptor-mediated platelet agonists. In addition, WGA was found to associate with PECAM-1 itself, and anti-PECAM-1 antibody, as well as NAGlu, specifically inhibited WGA-induced platelet aggregation. In PECAM-1 immunoprecipitates, Src family tyrosine kinases existed, and a kinase activity was detected, which increased upon WGA stimulation. Furthermore, the Src family kinase inhibitor PP2 inhibited WGA-induced platelet aggregation, Ca(2+) mobilization, and PLC-gamma 2 tyrosine phosphorylation. Finally, WGA induced PECAM-1 tyrosine phosphorylation and cytoskeletal reorganization in vascular endothelial cells. Our results suggest that (i) PECAM-1 is involved in WGA-induced platelet activation, (ii) PECAM-1 clustering by WGA activates unique and strong platelet signaling pathways, leading to a rapid PLC activation via Src family kinases, and (iii) WGA is a useful tool for elucidating PECAM-1-mediated signaling with wide implications not confined to platelets.

Acetylglucosamine↗
PubMed2001

Role of Fc receptor gamma-chain in platelet glycoprotein Ib-mediated signaling.

Interaction between von Willebrand factor (vWF) and glycoprotein Ib (GPIb) stimulates tyrosine kinases and subsequent tyrosine phosphorylation events in human platelets. This study found that the combination of vWF and botrocetin, by interacting with GPIb, induced tyrosine phosphorylation of Fc receptor gamma-chain (FcR gamma-chain), Syk, linker for activation of T cells (LAT), and phospholipase C gamma2 (PLCgamma2). Pretreatment of platelets with 10 microM PP1 completely inhibited these tyrosine phosphorylation events. On GPIb stimulation, Src and Lyn formed a complex with FcR gamma-chain and Syk, suggesting that Src and Lyn are involved in FcR gamma-chain tyrosine phosphorylation and downstream signals. In spite of the PLCgamma2 tyrosine phosphorylation, however, there was no intracellular calcium release and inositol 1,4,5-trisphosphate production. In Brij 35 lysates, FcR gamma-chain was found to constitutively associate with GPIb. The number of GPIb expressed on FcR gamma-chain-deficient platelets was comparable to that of the wild-type, as assessed by flow cytometry. However, tyrosine phosphorylation of Syk, LAT, and PLCgamma2 in response to vWF plus botrocetin was significantly suppressed, suggesting that FcR gamma-chain mediates activation signals related to GPIb. Compared with the aggregation response of wild-type platelets, that of FcR gamma-chain-deficient platelets in response to vWF plus botrocetin was impaired, implying that FcR gamma-chain is required for the full activation of platelets mediated by GPIb. (Blood. 2001;97:3836-3845)

Adaptor Proteins, Signal Transducing↗
PubMed2001

Potentiation of ibudilast inhibition of platelet aggregation in the presence of endothelial cells.

Although communications between platelets and endothelial cells or other blood cells are important in in vivo thrombus formation, laboratory platelet function tests are usually performed in isolation from these surrounding cells. In this study, we evaluated the effect of an antiplatelet drug, ibudilast (3-isobutyryl-2-isopropylpyrazolo[1,5-a]pyridine), on platelet aggregation in the presence and absence of human umbilical vein endothelial cells (HUVECs) and with the use of platelet-rich plasma (PRP) or whole blood as platelet samples. Stimulation-dependent platelet aggregation was weakened in the presence of HUVECs, which was especially prominent when the thrombin receptor-activating peptide SFLL (compared with ADP and epinephrine) was used as an aggregating agent. Ibudilast hardly affected SFLL-induced platelet aggregation (in PRP), while this antiplatelet agent was found to clearly inhibit this SFLL-induced response in a concentration-dependent manner, in the presence of HUVECs. Ibudilast tended to inhibit ADP- or epinephrine-induced platelet aggregation in the presence of HUVECs, but the effects were not statistically significant. Enhanced inhibition by ibudilast of SFLL-induced platelet aggregation (in the presence of HUVECs) was reproduced with the use of whole blood samples when a screen filtration pressure method was employed. It is suggested that the platelet aggregation studies in the presence of endothelial cells and/or other blood cells provide us with valuable information on platelet reactivity in vivo and improvement of antiplatelet therapy.

Blood Platelets↗
PubMed2001

Involvement of Hic-5 in platelet activation: integrin alphaIIbbeta3-dependent tyrosine phosphorylation and association with proline-rich tyrosine kinase 2.

Hic-5 and paxillin, members of the LIM protein family, have been shown to be localized in focal adhesion and to have a role in integrin-mediated signalling. In the present study we examined the involvement of Hic-5 in human platelet activation: platelets express Hic-5 but not paxillin, whereas human umbilical-vein vascular endothelial cells and MEG-01 cells express mainly paxillin. When platelets were stimulated with thrombin, collagen or the stable thromboxane A(2) analogue U46619, Hic-5 was markedly tyrosine-phosphorylated, in a manner dependent on integrin alphaIIbbeta3-mediated aggregation. In addition, direct activation of protein kinase C with PMA resulted in tyrosine phosphorylation of Hic-5 only when platelets were fully aggregated with the exogenous addition of fibrinogen. Furthermore, PMA-induced Hic-5 tyrosine phosphorylation was also observed when platelets adhered to immobilized fibrinogen. In studies on immunoprecipitation and immunodepletion, Hic-5 seemed to associate with proline-rich tyrosine kinase 2 (Pyk2) but only marginally with focal adhesion kinase. When platelets were stimulated with thrombin, both Hic-5 and Pyk2 translocated to the cytoskeleton from the cytosol and membrane fractions in a manner dependent on alphaIIbbeta3-mediated aggregation. Finally, on stimulation with PMA, Hic-5, as well as Pyk2, translocated to the cell periphery, where a meshwork of actin filaments assembled after adhesion to immobilized fibrinogen. Our results suggest that Hic-5 might be important in platelet aggregation and adhesion, in a manner dependent on alphaIIbbeta3-mediated outside-in signalling, through association with Pyk2.

Blood Platelets↗
PubMed2001

Rhodocytin induces platelet aggregation by interacting with glycoprotein Ia/IIa (GPIa/IIa, Integrin alpha 2beta 1). Involvement of GPIa/IIa-associated src and protein tyrosine phosphorylation.

Although glycoprotein Ia/IIa (GPIa/IIa, integrin alpha(2)beta(1)) has established its role as a collagen receptor, it remains unclear whether GPIa/IIa mediates activation signals. In this study, we show that rhodocytin, purified from the Calloselasma rhodostoma venom, induces platelet aggregation, which can be blocked by anti-GPIa monoclonal antibodies. Studies with rhodocytin-coupled beads and liposomes loaded with recombinant GPIa/IIa demonstrated that rhodocytin directly binds to GPIa/IIa independently of divalent cations. In vitro kinase assays and Western blotting of GPIa immunoprecipitates revealed that Src and Lyn constitutively associate with GPIa/IIa and that Src activity increases transiently after rhodocytin stimulation. Src specifically associates with p130 Crk-associated substrate (Cas) in a manner dependent upon Cas phosphorylation, suggesting that Src is responsible for Cas tyrosine phosphorylation. While all these phenomena occur early after rhodocytin stimulation in a cAMP-resistant manner, tyrosine phosphorylation of Syk and phospholipase Cgamma2, intracellular Ca(2+) mobilization, and platelet aggregation occur later in a cAMP-sensitive manner. Cytochalasin D, which interferes with actin polymerization and blocks receptor clustering, inhibits all the rhodocytin-mediated signals we examined in this study. We suggest that rhodocytin, by clustering GPIa/IIa, activates GPIa/IIa-associated Src, which then mediates downstream activation signals.

Animals↗
PubMed2001

Sphingosine 1-phosphate: synthesis and release.

Sphingosine 1-phosphate (Sph-1-P) is a bioactive sphingolipid, acting both as an intracellular second messenger and extracellular mediator, in mammalian cells. In cell types where Sph-1-P acts as an intracellular messenger, stimulation-dependent synthesis of Sph-1-P, possibly resulting from sphingosine (Sph) kinase activation, is essential. Since this important kinase has recently been cloned, precise regulation of intracellular Sph-1-P synthesis will be clarified in the near future. As an intercellular mediator, elucidation of sources for extracellular Sph-1-P is important, in addition to identification of the cell surface receptors for this phospholipid. Blood platelets are very unique in that they store Sph-1-P abundantly (possibly due to the existence of highly active Sph kinase and a lack of Sph-1-P lyase) and release this bioactive lipid extracellularly upon stimulation. It is likely that platelets are an important source for extracellular Sph-1-P, especially for plasma and serum Sph-1-P. Platelet-derived Sph-1-P seems to play an important role in vascular biology.

Animals↗
PubMed2001

[New laboratory tests for detecting platelet abnormalities].

Platelets play important roles in thrombosis and hemostasis, and their abnormalities lead to hemostatic disorders or thrombotic diseases. The development of new tests for assessing platelet disorders is awaited. In this article, the measurement of blood thrombopoietin levels and detection of platelet aggregates with a particle counting method using light scattering are described as candidates for new laboratory tests for detecting platelet abnormalities.

Animals↗