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Biomedical subjects

Y Yatomi

Publications and source records attributed to Y Yatomi.

At least 55 records · Page 3Linked to original sources
PubMed1999

Inhibitory effects of beraprost on platelet aggregation: comparative study utilizing two methods of aggregometry.

We evaluated the inhibitory effects of beraprost, a stable prostacyclin analogue, on platelet aggregation, assessed by two methods of platelet aggregometry. The conventional aggregometry detects changes in light transmission (LT) of a platelet suspension, and a recently developed aggregometry based upon a particle counting principle detects light scattering (LS) generated by platelet aggregates. Since LS is more sensitive than LT in detecting platelet aggregates of small size, the minimal concentrations of agonists (ADP, epinephrine, collagen, and U46619) to induce detectable aggregate formation were consistently lower with LS (1/2 to 1/6) than with LT. The effects of beraprost were evaluated on platelet aggregation induced by the optimal concentrations of agonists thus determined for each sample. The IC50 values of beraprost on platelet aggregation, as assessed by LS, were 1/2 to 1/10 of those assessed by LT. In suppressing platelet aggregation assessed by LS, beraprost was especially potent with IC50 of 0.2-0.5 nM when platelets were activated by U46619, a thromboxane A2 analogue, or low concentrations of collagen which activates platelets through thromboxane A2 production. The IC50 values were 2-5 nM with ADP and epinephrine, which induce the formation of small aggregates independently of thromboxane A2 production. These findings suggest that LS can detect inhibitory effects of lower concentrations of antiplatelet agents, since it detects the formation of small aggregates induced by agonists in the lower concentration range than LT. It is also suggested that beraprost potently inhibits thromboxane A2-elicited initial signal transduction pathway, reflected by the formation of small aggregates.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1999

Suppression of protein kinase C is associated with inhibition of PYK2 tyrosine phosphorylation and enhancement of PYK2 interaction with Src in thrombin-activated platelets.

Blood platelets have recently been shown to express PYK2, a nonreceptor tyrosine kinase belonging to the FAK gene family. In this study, we examined the involvement of protein kinase C (PKC) in PYK2-related responses in human platelets. While PYK2 tyrosine phosphorylation induced by thrombin was inhibited by preincubation of platelets with PKC inhibitors, staurosporine and Ro31-8220, PYK2 association with Src was markedly enhanced under the same conditions. Platelet intracellular Ca2+ mobilization induced by thrombin was hardly inhibited by these PKC inhibitors. p130Cas is a docking protein that associates with FAK or PYK2 through the SH3 domain. Although we identified p130Cas in platelets for the first time, this docking protein failed to interact with PYK2. These results suggest that PKC activation (but not Ca2+ mobilization) is involved in PYK2 tyrosine phosphorylation and that PYK2 associates with Src without PYK2 tyrosine phosphorylation or p130Cas involvement in platelets.

Enzyme Activation↗
PubMed1999

Signal transduction pathways mediated by glycoprotein Ia/IIa in human platelets: comparison with those of glycoprotein VI.

Human platelets were activated either by glycoprotein (GP) Ia/IIa agonist (rhodocytin) or by a GPVI agonist (collagen-related peptide, CRP), and the intracellular signal transduction pathways were compared in the presence of various inhibitors. Rhodocytin isolated from Calloselasma rhodostoma venom was verified as a GPIa/IIa agonist, based on the inhibitory effects of three mAbs directed against GPIa. Platelet activation mediated by GPIa/IIa led to overt platelet aggregation, elevation of intracellular Ca2+, and tyrosine phosphorylation of several proteins, similar to that of GPVI. p72(syk) and phospholipase Cgamma2 (PLCgamma2) tyrosine phosphorylation were also observed with GPIa/IIa-mediated platelet aggregation, although they peaked slightly later than that of GPVI. In contrast to GPVI-mediated platelet activation, most of these phenomena induced by GPIa/IIa activation were markedly suppressed by acetylsalicylic acid (ASA) or cytochalasin D. These findings suggest that the requirements for thromboxane A2 (TXA2) production and actin polymerization, which are the characteristics of collagen-induced platelet activation, are derived from the GPIa/IIa-mediated signal transduction, but not from that of GPVI.

Antibodies, Monoclonal↗
PubMed1999

The novel sphingosine 1-phosphate receptor AGR16 is coupled via pertussis toxin-sensitive and -insensitive G-proteins to multiple signalling pathways.

In the present study, we determined the agonist specificity and the signalling mechanisms of a putative sphingosine 1-phosphate (S1P) receptor, AGR16. In CHO cells transiently transfected with an AGR16 expression vector, but not in cells transfected with an empty vector, the addition of a low concentration of S1P (1 nM) caused an increase in the intracellular free Ca2+ concentration ([Ca2+]i) by mobilization of Ca2+ from both intra- and extra-cellular pools. To determine the spectrum of agonists for AGR16, we employed K562 cells, which in the naive state do not respond at all to either S1P or structurally related lipids with an increase in [Ca2+]i. In K562 cells stably expressing AGR16, S1P and sphingosylphosphorylcholine (SPC) dose-dependently increased [Ca2+]i with half-maximal values of 3 nM and 100 nM respectively. In CHO cells stably expressing AGR16 (CHO-AGR16), but not in parental CHO cells, we observed specific binding of [32P]S1P, which was displaced by unlabelled S1P and SPC. In CHO-AGR16 cells, but not in parental CHO cells, S1P stimulated the production of inositol phosphates and Ca2+ mobilization which was only 30% inhibited by pertussis toxin (PTX), different from the case of the recently identified S1P receptor EDG1. Also in CHO-AGR16 cells, but not in CHO cells, S1P at higher concentrations activated mitogen-activated protein kinase (MAPK) in a PTX-sensitive and Ras-dependent manner. S1P also induced the activation of two stress-activated MAPKs, c-Jun N-terminal kinase and p38, in a manner that was totally insensitive to PTX. In CHO-AGR16 cells, S1P induced stress-fibre formation, with an increase in myosin light chain phosphorylation, in a PTX-insensitive and Rho-dependent manner. S1P also induced an increase in the cellular cAMP content in CHO-AGR16 cells, which contrasts sharply with the case of EDG1. These results establish that the S1P receptor AGR16 is coupled via both PTX-sensitive and -insensitive G-proteins to multiple effector pathways.

Animals↗
PubMed1999

Metabolism and functional effects of sphingolipids in blood cells.

We examined the sphingolipid metabolism of peripheral blood cells, i. e. platelets, erythrocytes, neutrophils and mononuclear cells. A distinguishing characteristic of sphingolipid metabolism in these highly differentiated cells was their high sphingosine (Sph) kinase activity. The occurrence of [3H]sphingosine 1-phosphate (Sph-1-P) from [3H]Sph (actively incorporated from the outside) in the blood cells was strong, long-lasting, and independent of cell activation. Hence, the possibility of Sph-1-P playing a second messenger role is remote in these cells. About 40% of platelet Sph-1-P could be released extracellularly by 12-O-tetradecanoylphorbol 13-acetate, possibly through mediation by protein kinase C. On the other hand, in erythrocytes, neutrophils and mononuclear cells a significant percentage of Sph-1-P formed inside the cell was discharged without stimulation, whereas the stimulation-dependent release was marginal. In contrast to active [3H]Sph conversion to [3H]Sph-1-P, formation of [3H]sphingomyelin was barely detectable in the blood cells; this was especially true for anucleate platelets and erythrocytes. The Sph --> Sph-1-P pathway may become predominant over the Sph --> Cer --> sphingomyelin pathway during late-stage differentiation into platelets or erythrocytes. Sph and its methylated derivative, N, N-dimethylsphingosine, induced apoptosis not only in neutrophils but also in mononuclear cells, whereas Sph-1-P elicited Ca2+ mobilization in platelets. Our results suggest that all blood cells may remove plasma Sph, which is harmful or suppressive to cellular functions, and change it into Sph-1-P, acting as the source of plasma Sph-1-P, which may play a variety of important roles in blood vessels.

Apoptosis↗
PubMed1999

Primary gastric T-cell lymphomas: report of two cases and a review of the literature.

To understand more fully the clinicopathological features of primary gastric T-cell lymphomas (PGTL), we report two cases of PGTL and review the literature. The present cases were not associated with human T-cell leukemia virus type 1 (HTLV-1) and were at clinical stage IIE. In both cases, T-cell origin of the lymphoma cells was diagnosed immunohistochemically. The clinical courses of these two cases were different: one followed a very aggressive clinical course and the patient died 6 months after the diagnosis, whereas the other patient survived more than 2 years without adjuvant chemotherapy. Clinicopathological features of 23 patients with PGTL are summarized with regard to their differences from primary small intestinal T-cell lymphomas (PSITL) and by association with HTLV-1. The median age at onset of PGTL was 58 years. The gender ratio was male-dominant (M:F = 2.3:1). About two-thirds (10 of 17) of PGTL cases had evidence of HTLV-1 infection. The most common presenting symptom for PGTL was upper abdominal discomfort and/or pain (76%), whereas that in PSITL was weight loss (61%) and diarrhea (42%). Typical lesions for PGTL were large ulcerations at the corpus to antrum. Neoplastic cells had no typical morphological characteristics for PGTL including HTLV-1-associated cases. CD3+4+8- was the most frequently observed surface phenotype of PGTL cells. Laboratory findings at diagnosis were not informative. Most patients were treated by gastrectomy with or without chemotherapy. PGTL, excluding that with HTLV-1, showed better prognosis than PSITL, although PGTL with HTLV-1 had a poorer prognosis.

Adult↗
PubMed1999

Sphingosine 1-phosphate formation and intracellular Ca2+ mobilization in human platelets: evaluation with sphingosine kinase inhibitors.

Sphingosine 1-phosphate (Sph-1-P) is considered to play a dual role in cellular signaling, acting intercellularly as well as intracellularly. In this study, we examined the role of Sph-1-P as a signaling molecule in human platelets, using DL-threo-dihydrosphingosine (DHS) and N,N-dimethylsphingosine (DMS), inhibitors of Sph kinase and protein kinase C. Both DMS and DL-threo-DHS were confirmed to be competitive inhibitors of Sph kinase obtained from platelet cytoplasmic fractions. In intact platelets labeled with [3H]Sph, stimulation with 12-O-tetradecanoylphorbol 13-acetate or thrombin did not affect [3H]-Sph-1-P formation. While both DMS and DL-threo-DHS inhibited not only [3H]Sph-1-P formation but also protein kinase C-dependent platelet aggregation, staurosporine, a potent protein kinase inhibitor, only inhibited the protein kinase C-dependent reaction. Hence, it is unlikely that Sph kinase activation and the resultant Sph-1-P formation are mediated by protein kinase C in platelets. Furthermore, Ca2+ mobilization induced by platelet agonists that act on G protein-coupled receptor was not affected by DMS or DL-threo-DHS. Our results suggest that Sph-1-P does not mediate intracellular signaling, including Ca2+ mobilization, in platelets.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1999

[Biological inter- and intra-individual variations of serum immunochemical constituents and their allowable limits of analytical error].

The biological inter- and intra-individual variations of serum immunochemical constituents were estimated by the analysis of variance. Twelve samples taken at weekly intervals were analyzed for 22 healthy individuals. As for immunoglobulin (Ig) G, IgA, IgM, IgE, C-reactive protein, anti-streptolysin O, alpha-fetoprotein, complement component 3 and 4, and ferritin, the intra-individual variations (with coefficient of variations (CVs) ranging from 4.8% to 51.7%) were smaller than the inter-individual variations (with CVs ranging from 14.6% to 107.6%). The values for carcinoembryonic antigen (with CVs of inter- and intra-individual variation being 31.6% and 39.6%, respectively) and beta 2-microglobulin (with CVs of inter- and intra-individual variation being 14.4% and 13.1%, respectively) were similar. The biological variations of serum immunochemical constituents, examined in this study, were larger than those of serum chemical constituents. Based on our data, we propose allowable limits of analytical error, which is less than one-half of the average intra-individual variation for evaluation of imprecision and is less than one-quarter of the inter- plus intra-individual variation for evaluation of inaccuracy.

Analysis of Variance↗
PubMed1998

EDG1 is a functional sphingosine-1-phosphate receptor that is linked via a Gi/o to multiple signaling pathways, including phospholipase C activation, Ca2+ mobilization, Ras-mitogen-activated protein kinase activation, and adenylate cyclase inhibition.

In Chinese hamster ovary (CHO) cells transiently transfected with an expression vector for EDG1, but not an empty vector, sphingosine-1-phosphate (SP) at a concentration as low as 10(-10) M caused an increase in the intracellular free Ca2+ concentration ([Ca2+]i) as a result of mobilization of Ca2+ from both intracellular and extracellular pools. In a CHO clone stably expressing EDG1 receptor (CHO-EDG1 cells), SP induced increases in the production of inositol phosphates and the [Ca2+]i and inhibited forskolin-induced increase in the cellular cAMP content, all in a manner sensitive to pertussis toxin. SP also activated mitogen-activated protein kinase in CHO-EDG1 cells in pertussis toxin-sensitive and Ras-dependent manners. To evaluate the spectrum of agonists for EDG1, we used human erythroleukemia (HEL) cells, which at naive state do not respond to SP or structurally related lipids with an increase in the [Ca2+]i. In HEL cells stably expressing EDG1 receptor (HEL-EDG1 cells), SP dose-dependently increased the [Ca2+]i with half-maximal and maximal concentration values of 10(-9) and 3 x 10(-7) M, respectively; sphingosylphosphorylcholine at exclusively high concentrations, but not sphingosine at all, also increased the [Ca2+]i. HEL-EDG1 cells bound 32P-labeled SP, which was displaced dose dependently by unlabeled SP. These results indicate that EDG1, a member of the EDG family G protein-coupled receptors, is a specific, high-affinity SP receptor.

Adenylate Cyclase Toxin↗
PubMed1998

Effects of lysophosphatidic acid on proliferation of stellate cells and hepatocytes in culture.

Lysophosphatidic acid (LPA) is a growth factor-like mediator for fibroblasts or smooth muscle cells produced and released by activated platelets. Platelet activation occurs with hepatic necrosis and subsequent liver regeneration and fibrosis. In the fibrosis, hepatic stellate cells proliferate with phenotypic transformation to myofibroblasts. Thus, effects of LPA on proliferation of hepatocytes and stellate cells were investigated. In cultured rat stellate cells, LPA increased DNA synthesis with enhanced MAP kinase activity. Pertussis toxin (PTX) attenuated this mitogenic action. In contrast, LPA decreased DNA synthesis by cultured rat hepatocytes induced by hepatocyte growth factor (HGF) or epidermal growth factor (EGF) without affecting protein synthesis. Enhanced MAP kinase activity by HGF or EGF was not changed by LPA. This anti-mitogenic action was attenuated by PTX. TGFbeta level in the medium was less than the level effective for inhibiting the DNA synthesis in the presence of LPA. Our results suggest that LPA might affect proliferation of hepatocytes and stellate cells in liver diseases complicating platelet activation.

Animals↗
PubMed1998

Quantification of sphingosine derivatives in human platelets: inducible formation of free sphingosine.

To elucidate the physiologic role of sphingolipid-derived products as signaling molecules, we analyzed the levels of endogenous sphingosine (Sph) derivatives in human platelets. When the platelets were stimulated with thrombin or 12-O-tetradecanoylphorbol 13-acetate, neither ceramide formation nor sphingomyelin hydrolysis was observed, which suggests that the sphingomyelin cycle may not be an essential part of the signaling pathway under these conditions. In contrast, Sph was found to increase in platelets upon stimulation. The level of Sph 1-phosphate, which is formed from Sph by the action of Sph kinase, was not affected under our conditions. Although it has been established that Sph inhibits protein kinase C, which regulates the functional responses of the platelets, Sph levels which exert an inhibitory effect on protein kinase C cannot be attained under physiological conditions (without exogenous Sph). Considering the stimulation of the synthesis of Sph by the physiological agonist thrombin, we speculate that Sph is a signaling molecule of physiological importance in platelets, but protein kinase C may not be its target.

Adult↗
PubMed1998

[Influence of nitric oxide synthetase inhibitor on the blood pressure action of clonidine in rats].

We are investigating the influence of NO synthetase inhibitor on the clonidine-induced cardiovascular actions in urethane-anesthetized rats. The systemic blood pressure was measured from right femoral artery, heart rate from the pressure pulse under inhalation of O2. Nw-nitro-L-arginine-methylester (L-NAME, 5 mg/kg), NO synthetase inhibitor, administered intravenously increased blood pressure slightly, although decreased heart rate. The responses to L-NAME were stable about 10 min after the injection. Clonidine (5 mg/kg) administered intravenously indicated the transient increase blood pressure and following continuous decrease of blood pressure. The early transient hypertension of clonidine was potentiated by pretreatment with L-NAME and later continuous hypotension was markedly inhibited. While, the early transient hypertension of clonidine was inhibited by pretreatment with L-arginine and later continuous hypotension was potentiated. The hypertension and tachycardia of intravenous tyramine was enhanced by L-NAME. Clonidine administered into the cerebroventricle did not indicate the early transient hypertension, though produced the later continuous hypotension. These results suggest that L-NAME modifies the cardiovascular responses to clonidine and NO may participate in the modulation.

Animals↗
PubMed1998

Sphingosine 1-phosphate is a blood constituent released from activated platelets, possibly playing a variety of physiological and pathophysiological roles.

We have found that sphingosine 1-phosphate (Sph-1-P) acts as an autocrine stimulator of platelets, being abundantly stored in platelets and released extracellularly, and that its exogenous addition induces platelet activation (Yatomi et al., Blood 1995, 86, 193-202) through a specific receptor on the platelet surface (Yatomi et al., J. Biol. Chem. 1997, 272, 5291-5297). Very recently, we identified Sph-1-P as a normal constituent of human plasma and serum. Sph-1-P levels in plasma and serum were 191+/-79 and 484+/-82 pmol/ml (mean +/- S.D., n = 8), respectively. Platelets are most likely the source of Sph-1-P discharged during blood clotting, since they abundantly store Sph-1-P as compared with other blood cells, and release considerable amounts of stored Sph-1-P extracellularly upon stimulation. The Sph-1-P released from activated platelets may be involved in a variety of physiological processes, including thrombosis, atherosclerosis, and wound healing. Moreover, we often observed that Sph-1-P injection into mice (iv., 10 mg/kg) caused immediate rigor and death. This may be related to the recent observations from an other laboratory that nanomolar concentrations of Sph-1-P affected atrial myocyte K+ channel. These observations taken together strongly suggest pathophysiological roles of the released Sph-1-P in the blood. As one example, we found that Sph-1-P content in the plasma of platelet concentrates correlated with poor platelet increments after transfusion and with the occurrence of transfusion reactions in patients.

Animals↗
PubMed1997

Glycoprotein Ib-von Willebrand factor interactions activate tyrosine kinases in human platelets.

von Willebrand factor (vWF ) in the presence of botrocetin induces p72(syk) activation, assessed as its autophosphorylated level and in vitro kinase assays, the transient association of p72(syk) with p60(c-src), and the translocation of p60(c-src) and p54/58(lyn) to cytoskeletal fractions. Jararaca glycoprotein Ib-binding protein (GPIb-BP), which specifically binds to GPIb, abolished these phenomena, suggesting that they are mediated by the vWF-GPIb interaction. These tyrosine kinase-related events were not inhibited by GRGDS peptide (plus EGTA), indicating that GPIIb/IIIa is not involved in the observed responses. Shc, an adaptor protein, was also tyrosine phosphorylated by the botrocetin-vWF activation. When GPIb was immunoprecipitated with nonfunctional monoclonal antibodies (MoAbs) directed against GPIb, a kinase activity was found to associate with GPIb upon botrocetin-vWF activation. On the other hand, anti-GPIb MoAbs that inhibit the vWF-GPIb interaction did not coprecipitate a kinase activity. Because the recovery of GPIb did not differ significantly, it is suggested that the excessive presence of inhibitory anti-GPIb MoAb dissociated a kinase activity from GPIb. Phosphoamino acid analysis showed that the kinase activity was that of a tyrosine kinase. The identity of the tyrosine kinase and the mode of interaction with the cytoplasmic region of GPIb await to be determined. Our findings suggest that the tyrosine kinase associated with GPIb serves at a most proximal step in the signal transduction pathway involved in the vWF-GPIb-induced platelet activation, which leads to other tyrosine kinase-related intracellular signals.

Blood Platelets↗
PubMed1997

N,N-dimethylsphingosine 1-phosphate activates human platelets.

We recently reported that N,N-dimethylsphingosine 1-phosphate (DMS-1-P) can be formed from N,N-dimethylsphingosine (DMS) in activated platelets [Y. Yatomi et al., Biochem. Biophys. Res. Commun. 231 (1997) 848-851]. In this study, we synthesized, for the first time, DMS-1-P and examined the functional effects of DMS-1-P and its related sphingolipids on platelets. Although exogenous DMS was inactive, its phosphorylated derivative, DMS-1-P, induced platelet intracellular Ca2+ mobilization and shape change, but not aggregation or release reactions. Since sphingosine 1-phosphate (Sph-1-P) is structurally related to DMS-1-P and activates platelets more strongly than DMS-1-P, a competitive binding experiment for [3H]Sph-1-P was performed using DMS-1-P. DMS-1-P reduced the binding of [3H]Sph-1-P to platelets almost as much as unlabeled Sph-1-P did. These results suggest that DMS-1-P activates platelets via an interaction with a platelet surface receptor for Sph-1-P.

Blood Platelets↗