Biomedical subjects

T F Huang

Publications and source records attributed to T F Huang.

At least 73 records · Page 4Linked to original sources

PubMed1994

In vivo antithrombotic effect of triflavin, an Arg-Gly-Asp containing peptide on platelet plug formation in mesenteric microvessels of mice.

Triflavin, an Arg-Gly-Asp-containing snake venom peptide, inhibits platelet aggregation through the blockade of fibrinogen binding to the activated platelets. In this study, platelet thrombus formation was induced by irradiation of the mesenteric venules with filtered light in mice pretreated intravenously with fluorescein sodium. Electron microscopy reveals moderately damaged endothelial cells, as well as aggregates consisting almost exclusively of platelets with pseudopod formation, and degranulated appearance. Triflavin (10-20 micrograms/g) significantly prolonged the lag period of inducing platelet plug formation in mesenteric venules when it was intravenously infused. Triflavin (20 micrograms/g) prolonged the occlusion time about 2-fold (from control 112 +/- 23 to 240 +/- 47 s). Furthermore, PGE1 briefly prolonged the occlusion time about 1.5-fold (from 105 +/- 21 to 168 +/- 20 s) when it was given by continuous infusion (40 micrograms/kg/min). On the other hand, triflavin was also effective in reducing the mortality of ADP-induced acute pulmonary thromboembolism in mice when administered intravenously at dose of 2-4 micrograms/g. Heparin (1.5 U/g) and indomethacin (200 micrograms/g) had no significant effect in prolonging the occlusion time or in reducing ADP-induced pulmonary embolism in mice. Therefore, triflavin is an effective antithrombotic agent in preventing the thromboembolism in these two in vivo models.

Acute Disease↗

PubMed1994

Effect of naloxone on platelet aggregation in rats.

The effect of naloxone on aggregation of blood platelets was investigated. Naloxone in millimolar concentrations dose-dependently inhibited collagen (20 mu g/ml)-induced platelet aggregation in rats PRP. For comparison with IC50 values on a molar basis, the ability of naloxone against platelet aggregation is similar to aspirin, but about 7-8 fold smaller than verapamil. In anesthetized spontaneously hypertensive rats (SHR), naloxone did not significantly alter the pressure response whereas administration of prazosin caused diminution of mean arterial pressure (MAP) related to dose. Naloxone did not interfere with the hematological parameters (i.e., WBC, RBC, PLT, HGB, HCT ... etc.) in Sprague-Dawley (SD) rats. The present study shows naloxone to be effective in obviating platelet aggregation, and seems to be reasonable in prevention of pulmonary platelet trapping (PPT), which is thought to play an important role in the pathogenesis of adult respiratory distress syndrome (ARDS).

Animals↗

PubMed1994

Triflavin, an antiplatelet peptide, inhibits tumor cell-extracellular matrix adhesion through an arginine-glycine-aspartic acid-dependent mechanism.

The interaction of tumor cells with extracellular matrix components such as laminin, fibronectin, and collagen has been shown to be mediated through a family of cell-surface receptors that specifically recognize an arginine-glycine-aspartic acid amino acid sequence within each protein. Triflavin, a 7.5 kDa cysteine-rich polypeptide purified from Trimeresurus flavoviridis snake venom, belongs to a family of arginine-glycine-aspartic acid-containing peptides termed disintegrins that have been isolated from the venoms of various vipers and shown to be potent inhibitors of platelet aggregation. In this study, we showed that triflavin inhibited adhesion of human hepatoma J-5 cells to extracellular matrices (fibronectin, vitronectin, fibrinogen, and collagen type I) in a dose-dependent manner. On the other hand, triflavin exerted a limited inhibitory effect on cell attachment to collagen type IV and laminin (< or = 40%). Triflavin is approximately 1000 times more potent than glycine-arginine-glycine-aspartic acid-serine at inhibiting cell adhesion. When immobilized on plate, triflavin promoted J-5 cell attachment; this attachment was inhibited by glycine-arginine-glycine-aspartic acid-serine. In addition, triflavin labeled with iodine 125 binds to J-5 cells in a saturable manner and its binding was also inhibited by glycine-arginine-glycine-aspartic acid-serine. Its Kd value was estimated to be 3.9 x 10(-7) mol/L and the number of binding sites was around 60,000 per cell. Furthermore, triflavin did not affect tritiated thymidine uptake during a 3-day incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗

PubMed1993

Frangulin B, an antagonist of collagen-induced platelet aggregation and adhesion, isolated from Rhamnus formosana.

Emodin and its glycoside frangulin B were isolated from the plant Rhamnus formosana. Emodin inhibited the aggregation of rabbit platelets induced by arachidonic acid and collagen, without affecting that by ADP or PAF, while emodin acetate had no any antiplatelet effect. Frangulin B inhibited selectively and concentration-dependently collagen-induced aggregation and ATP release in rabbit platelets, without affecting those induced by arachidonic acid, ADP, PAF and thrombin. Frangulin B also inhibited the platelet aggregation induced by trimucytin which was reported to be a collagen receptor agonist isolated from Trimeresurus muscrosquamatus snake venom. The aggregability of platelets inhibited by frangulin B could be recovered after washing the platelets. Frangulin B also selectively suppressed the thromboxane B2 formation caused by collagen, but not those by arachidonic acid and thrombin. Similarly, the formation of inositol phosphate caused by collagen was also suppressed by frangulin B, while that of PAF or thrombin was not affected. In the presence of PGE1, frangulin B also decreased Mg(2+)-dependent platelet adhesion to collagen. It is concluded that frangulin B may be an antagonist of collagen receptor in platelet membrane.

Amino Acid Sequence↗

PubMed1993

Antiplatelet protease, kistomin, selectively cleaves human platelet glycoprotein Ib.

Kistomin, a metalloprotease purified from venom of Calloselasma rhodostoma, dose- and time-dependently prolonged the latent period of aggregation and inhibited ATP secretion of human washed platelets stimulated by thrombin. It inhibited aggregation induced by low concentrations of thrombin (< or = 0.2 U/ml) whereas it had only slight effect on aggregation induced by high concentrations of thrombin (> or = 0.5 U/ml). Meanwhile it also inhibited ristocetin-induced platelet aggregation in a dose- and time-dependent manner. It significantly inhibited cytosolic calcium rise of Quin 2--loaded platelets, completely blocked thromboxane B2 formation, and blocked [3H]inositol phosphates formation of [3H]myoinositol loaded platelets stimulated by 0.1 U/ml of thrombin. Kistomin inhibited significantly thromboxane but not [3H]inositol phosphates formation of platelets stimulated by a high concentration of thrombin (1 U/ml). Incubation of platelets with kistomin resulted in a selective cleavage of platelet membrane glycoprotein Ib as revealed by SDS/PAGE stained by periodic acid/Schiff reagent. These results suggested that thrombin activates platelets at least through two receptors/or effectors-mediated events. In addition to glycoprotein Ib, other surface membrane component(s) (e.g., the seven transmembrane domain thrombin receptor) may also be important in regulating the biochemical events of human platelets in response to thrombin. However, the extent and rate of platelet aggregation stimulated by low concentrations of thrombin ( < or = 0.2 U/ml) are closely related with the intactness of glycoprotein Ib.

Ancrod↗

PubMed1993

Vasoconstricting effect in rat aorta caused by thaliporphine isolated from the plant Neolitsea konishii K.

Thaliporphine (0.1-100 microM) produced sustained, concentration-dependent contraction in isolated rings of rat aorta. Thaliporphine (ED50 = 1.5 +/- 0.5 microM) was less potent than endothelin (ED50 = 3.9 +/- 0.4 nM), but was more potent than Bay K 8644 (ED50 = 5.5 +/- 0.6 microM). Thaliporphine also contracted guinea-pig trachea and ileum preparations, and increased the force of beating of rat left atria, but was less potent on these tissues than on rat aorta. Thaliporphine-induced contraction of rat aorta was not affected by prazosin (0.3 microM), atropine (1 microM), saralasin (10 microM) or ketanserin (10 microM). However, the contraction was slightly potentiated by the removal of endothelium. Preincubation of the rat aorta in Ca(2+)-free Krebs solution (containing 1 mM EGTA) for 15 min completely abolished thaliporphine-induced contractions, and the subsequent addition of 3 mM CaCl2 restored thaliporphine-induced contractions to the control level. In rat aorta, thaliporphine-induced contractions were significantly reduced by nifedipine (1-30 nM) or verapamil (0.01-0.3 microM), and significantly increased by Bay K 8644 (0.1 microM) or KCl (20 mM). The pA2 values for nifedipine and verapamil against thaliporphine-induced contractions were 9.4 +/- 0.1 and 8.4 +/- 0.2, respectively. The results indicate that thaliporphine exerts its vasoconstrictor effect on rat aorta mainly by promoting Ca2+ entry.

Animals↗

PubMed1993

Trimucytin: a collagen-like aggregating inducer isolated from Trimeresurus mucrosquamatus snake venom.

Trimucytin is a potent platelet aggregation inducer isolated from Trimeresurus mucrosquamatus snake venom. Similar to collagen, trimucytin has a run of (Gly-Pro-X) repeats at the N-terminal amino acids sequence. It induced platelet aggregation, ATP release and thromboxane formation in rabbit platelets in a concentration-dependent manner. The aggregation was not due to released ADP since it was not suppressed by creatine phosphate/creatine phosphokinase. It was not either due to thromboxane A2 formation because indomethacin and BW755C did not have any effect on the aggregation even thromboxane B2 formation was completely abolished by indomethacin. Platelet-activating factor (PAF) was not involved in the aggregation since a PAF antagonist, kadsurenone, did not affect. However, RGD-containing peptide triflavin inhibited the aggregation, but not the release of ATP, of platelets induced by trimucytin. Indomethacin, mepacrine, prostaglandin E1 and tetracaine inhibited the thromboxane B2 formation of platelets caused by collagen and trimucytin. Forskolin and sodium nitroprusside inhibited both platelet aggregation and ATP release, but not the shape change induced by trimucytin. In quin-2 loaded platelets, the rise of intracellular calcium concentration caused by trimucytin was decreased by 12-O-tetradecanoyl phorbol-13 acetate, imipramine, TMB-8 and indomethacin. In the absence of extracellular calcium, both collagen and trimucytin caused no thromboxane B2 formation, but still induced ATP release which was completely blocked by R 59022. Inositol phosphate formation in platelets was markedly enhanced by trimucytin and collagen. MAB1988, an antibody against platelet membrane glycoprotein Ia, inhibited trimucytin- and collagen-induced platelet aggregation and ATP release.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1993

CIS-19, a novel platelet activating factor receptor antagonist: in vitro and in vivo studies.

The effects of CIS-19 (cis-2-(3,4-dimethoxyphenyl)-6-isopropoxy-7-methoxyl-1-(N-methylforma mido)-1,2, 3,4-tetrahydronaphthalene) was determined in vitro in rabbit platelets and in vivo in rats and guinea-pigs. CIS-19 inhibited in a selective and concentration-dependent manner the aggregation and ATP release reaction of rabbit platelets induced by PAF (4 nM). The IC50 values of CIS-19 on PAF-induced aggregation of washed platelets and platelet-rich plasma were 11.3 +/- 2.7 and 16.8 +/- 3.0 microM respectively. BN52021 also inhibited PAF-induced aggregation of washed platelets with an IC50 value of 11.7 +/- 2.8 microM. CIS-19 inhibited [3H]PAF (4 nM) binding to washed rabbit platelets with an IC50 value of 1.5 +/- 0.2 microM. The concentration-response curve of PAF-induced aggregation of washed platelets was shifted rightwards by CIS-19 with pA2 and pA10 values of 7.1 (6.8-7.3 for 95% confidence limit) and 6.1 (5.8-6.2) respectively. The thromboxane B2 formation of washed platelets caused by AA, collagen or thrombin was not affected by CIS-19 of concentrations below 400 microM. CIS-19 (25 microM) completely blocked PAF-induced, but not collagen- or thrombin-induced [3H]inositol monophosphate formation of washed platelets. When CIS-19 (2.5 and 5 mg/kg) was injected i.v. into the femoral vein, it did not affect the blood pressure of rats, but antagonized PAF (2.5 micrograms/kg, i.v.)-induced hypotensive shock either preventively or curatively. CIS-19 (2.5 and 5 mg/kg) also blocked PAF (50 ng/kg)-induced, but not AA (50 micrograms/kg)-induced, bronchoconstriction in guinea-pigs. It is concluded that CIS-19 is an effective PAF receptor antagonist not only in vitro, but also in vivo.

Adenosine Triphosphate↗

PubMed1993

Rhodostomin, an RGD-containing peptide expressed from a synthetic gene in Escherichia coli, facilitates the attachment of human hepatoma cells.

Rhodostomin (Rho) from snake venom, a potent inhibitor of platelet aggregation, contains 68 amino acids having an RGD sequence and 12 cysteine residues. A chemically synthesized Rho gene was cloned and expressed in Escherichia coli. The expression of Rho gene fused with the glutathione S-transferase (GST) gene was about 10-30% of total cell proteins. The Rho-fusion protein could be recognized by antibodies raised against either a native Rho peptide or a synthetic peptide. The purified GST-Rho coated on culture plates facilitated the attachment of human hepatoma cells, which was inhibitable by co-incubation with a synthetic hexapeptide GRGDSP but not with a related peptide of GRGESP, suggesting that the E. coli-expressed Rho-fusion protein was properly folded and biologically functional.

Amino Acid Sequence↗

PubMed1993

Triflavin, an Arg-Gly-Asp-containing peptide, inhibits tumor cell-induced platelet aggregation.

In this study, we examined the effect of triflavin, an Arg-Gly-Asp (RGD)-containing snake venom peptide, on human cervical carcinoma (HeLa) cell- and B16-F10 mouse melanoma cell-induced platelet aggregation (TCIPA) in heparinized platelet-rich plasma. TCIPA appears to play an important role in the development of certain experimental tumor metastases. Two ADP-scavenging agents, apyrase (10 U/ml) and creatine phosphate (CP) (5 mM)/creatine phosphokinase (CPK) (5 U/ml) completely inhibited B16-F10 TCIPA, but hirudin (5 U/ml) had no effect. In contrast, apyrase and CP/CPK did not inhibit HeLa TCIPA while hirudin completely inhibited it. Furthermore, HeLa cells initially induced platelet aggregation and then blood coagulation at a later stage. In addition, HeLa cells shortened, in a concentration-dependent manner, the recalcification time of normal as well as factor VIII- and IX-deficient human plasma, but did not affect the recalcification time of factor VII-deficient plasma. This suggests that HeLa TCIPA occurs via activation of the extrinsic pathway, probably owing to tumor cell expression of tissue factor-like activity. HeLa cell-induced thrombin generation was confirmed by detection of amidolytic activity towards a chromogenic substrate, S-2238 (H-D-Phe-Pip-Arg-p-NA). Triflavin and GRGDS inhibited, in a dose-dependent manner, TCIPA caused by either cell line. On a molar basis, triflavin was 10,000-30,000 times more potent than GRGDS in this regard. Moreover, monoclonal antibodies raised against glycoprotein (GP) IIb/IIIa complex (i.e., 7E3 and AP2) and against GP Ib (i.e., AP1) completely inhibited HeLa TCIPA. 7E3 and AP2 inhibited B16-F10 TCIPA by up to 80% whereas AP1 showed only 30% inhibition of B16-F10 TCIPA. In conclusion, the inhibitory effect of triflavin on HeLa and B16-F10 TCIPA may be mediated principally by the binding of triflavin to the fibrinogen receptor associated with GP IIb/IIIa complex on the platelet surface. However, GP Ib is also involved in HeLa TCIPA as thrombin formation is the key factor in triggering platelet aggregation caused by HeLa cells.

Animals↗

PubMed1992

A novel alpha-type fibrinogenase from Agkistrodon rhodostoma snake venom.

By means of CM-Sephadex C-50 column chromatography, gel-filtration on sephadex G-75 and Sephacryl S-200 columns, a purified fibrinogenase, kistomin, was obtained from venom of Agkistrodon rhodostoma. It was a single peptide-chain with a molecular mass of about 21,800 Da containing about 202 amino-acid residues as revealed by amino acid analysis. Kistomin preferentially cleaved A alpha- and subsequently the gamma-chain of fibrinogen, leaving the B beta-chain unaffected. Its fibrinogenolytic activity was estimated to be 36.6 +/- 4.5 mg/min per mg protein and was inhibited by the pretreatment of EDTA, suggesting that it is a metalloproteinase. Its fibrinogenolytic activity in platelet-poor plasma is much less potent as compared to that in purified fibrinogen solution. It inhibited ristocetin-induced aggregation of human platelets in a dose-dependent manner in the presence of von Willebrand factor.

Amino Acids↗

PubMed1992

Triflavin, an RGD-containing antiplatelet peptide, binds to GpIIIa of ADP-stimulated platelets.

Triflavin, an Arg-Gly-Asp-containing snake venom peptide, inhibits platelet aggregation through the blockade of fibrinogen binding to the activated platelets. It binds to fibrinogen receptors associated with the glycoprotein IIb/IIIa complex with a Kd value of 7 x 10(-8) M. In this report, a chemical cross-linking approach was used to further characterize the binding components of triflavin on platelet membrane. 125I-triflavin binding was performed with the aid of a chemical cross-linking reagent, DTSSP. Analysis of the cross-linked products by SDS-PAGE (7.5% gel) and subsequent autoradiogram revealed that 125I-triflavin was cross-linked specifically to a protein with an apparent molecular weight of 1.1 x 10(5), and this reaction was inhibited by GRGDS and excess of non-labeled triflavin. This 110 KDa component was identified to be GpIIIa, recognized by AP3, a mAb against GpIIIa, by immunoblotting technique. These results indicate that the triflavin-binding sites on platelets reside at a site in close proximity to GpIIIa.

Adenosine Diphosphate↗

PubMed1992

Vasorelaxation of rat thoracic aorta caused by osthole isolated from Angelica pubescens.

The pharmacological effects of osthole on isolated rat thoracic aorta were examined. Osthole inhibited norepinephrine (NE, 3 microM)-induced phasic and tonic contractions in rat thoracic aorta in a concentration-dependent manner (40-200 microM). The tonic contraction elicited by NE was also relaxed by the addition of osthole. This relaxing effect of osthole was not affected by indomethacin (20 microM) and was still observed in endothelium-denuded rat aorta. Methylene blue (50 microM) partially antagonized this relaxing effect of osthole. In high-K+ medium (80 mM), the Ca2+ (0.03-3 mM)-induced vasocontraction was inhibited concentration dependently by osthole (20-100 microM). Addition of osthole (100 microM) at the plateau of the K+ (80 mM)-induced contraction caused relaxation. Methylene blue (50 microM) did not antagonize this relaxation. In Ca(2+)-free medium, the caffeine (10 mM)-induced phasic contraction was also suppressed by osthole in a concentration-dependent manner. Although the cAMP level was not changed by osthole, the cGMP level of rat aorta was increased by osthole in a concentration-dependent manner. The increase in cGMP level caused by osthole was completely blocked by methylene blue. [3H]Inositol monophosphate formation caused by NE was not affected by osthole at a concentration of 200 microM. The 45Ca2+ influx elicited by either NE or high K+ was inhibited by osthole in a concentration-dependent manner. It is concluded that osthole relaxes rat thoracic aorta by virtue of its Ca(2+)-channel blocking properties and by elevating cGMP levels in vascular smooth muscle.

Animals↗

PubMed1992

PAF antagonism in vitro and in vivo by aglafoline from Aglaia elliptifolia Merr.

Aglafoline, isolated from Aglaia elliptifolia Merr, inhibited in a selective and concentration-dependent manner the aggregation and ATP release reaction induced in washed rabbit platelets by PAF (platelet-activating factor). The IC50 values of aglafoline, BN52021 and kadsurenone on PAF (3.6 nM)-induced platelet aggregation were about 50, 12 and 18 microM, respectively. Aglafoline also inhibited [3H]PAF (3.6 nM) binding to washed rabbit platelets with an IC50 value of 17.8 +/- 2.6 microM. The concentration-response curve of PAF-induced platelet aggregation was shifted to the right by aglafoline with pA2 and pA10 values of 5.97 and 5.04, respectively. Although thromboxane B2 formation caused by collagen and thrombin was partially suppressed by aglafoline, thromboxane B2 formation caused by ionophore A23187 and arachidonic acid was not affected. Aglafoline inhibited the [3H]inositol monophosphate formation caused by PAF but not that caused by collagen or thrombin in the presence of indomethacin (20 microM). The cAMP content of washed rabbit platelets was not affected by aglafoline. Rat femoral intravenous administration of aglafoline (10 mg/kg) did not affect blood pressure. However, aglafoline (10 mg/kg) both prophylactically and therapeutically antagonized PAF (2.5 micrograms/kg)-induced hypotensive shock in rats. Intravenous PAF (30 ng/kg) caused severe bronchoconstriction in guinea pigs. This effect was completely blocked by aglafoline. This implies aglafoline is an effective PAF antagonist not only in vitro, but also in vivo.

Adenosine Triphosphate↗

PubMed1992

Triflavin, an Arg-Gly-Asp containing snake venom peptide, inhibits aggregation of human platelets induced by human hepatoma cell line.

Triflavin, an Arg-Gly-Asp (RGD)-containing peptide, purified from snake venom of Trimeresurus flavoviridis, inhibits human platelet aggregation through the blockade of fibrinogen binding to fibrinogen receptors associated with glycoprotein IIb/IIIa complex. In this report, we examined the effect of triflavin on tumor cells (human hepatoma J-5)-induced platelet aggregation (TCIPA) of heparinized platelet-rich plasma (PRP). ADP-scavenger agents, apyrase (10 U/ml) and creatine phosphate (5 mM)/creatine phosphokinase (5 U/ml) did not inhibit TCIPA while hirudin (5 U/ml) completely inhibited it. J-5 cells initially induced platelet aggregation, then blood coagulation occurred. J-5 cells concentration-dependently shortened the recalcification time of normal as well as Factor VIII, IX-deficient human plasmas, while it was inactive at shortening the recalcification time of Factor VII-deficient plasma, suggesting J-5 cells induced platelet aggregation through activation of extrinsic pathway, leading to thrombin formation as evidenced by the amidolytic activity on s-2238 by expressing tissue factor-like activity. Triflavin inhibited TCIPA in a dose-dependent manner (IC50, 0.02 microM). When compared on molar ratio, triflavin was approximately 30,000 times more potent than GRGDS (IC50, 0.58 mM). On the other hand, GRGES showed no significant effect on TCIPA, even its concentration was raised to 4 mM. Additionally, the monoclonal antibodies, raised against glycoprotein IIb/IIIa complex (i.e., 7E3 and 10 E5) inhibited J-5 TCIPA. In conclusion, we suggest the inhibitory effect of triflavin on J-5 TCIPA may be chiefly mediated by the binding of triflavin to the fibrinogen receptor associated with glycoprotein IIb/IIIa complex on platelet surface membrane.

Amino Acid Sequence↗

PubMed1992

Antiplatelet actions of some coumarin compounds isolated from plant sources.

Xanthyletin, xanthoxyletin, suberosin (all from Citrus grandis), aurapten (from Severinia huxifolia) and poncitrin (from Poncirus trifoliata) were isolated and their chemical structures were characterized to be coumarin compounds. All these coumarin compounds except xanthyletin inhibited the aggregation and ATP release of rabbit platelets induced by arachidonic acid, collagen, ADP, platelet-activating factor (PAF) or U46619 (a thromboxane A2 analog). Thrombin-induced ATP release, but not the aggregation, was also inhibited by these compounds. Xanthyletin inhibited only platelet aggregation induced by arachidonic acid and collagen, while poncitrin inhibited that caused by PAF more markedly than other coumarin compounds. The thromboxane B2 formation in washed platelets caused by arachidonic acid and collagen was suppressed by these coumarin compounds. The phosphoinositide breakdown caused by collagen and PAF was also inhibited by these compounds. They did not affect fibrinogen-induced aggregation of elastase-treated platelets. These antiplatelet actions were immediate, reversible by washout and independent on the incubation time (except suberosin). Antiaggregating effect was also studied by an electrical impedance method and the inhibitory effect of coumarin compounds on the whole blood and platelet-rich plasma was much less than that of platelet suspension in the aggregation induced by collagen, PAF and ADP. It is concluded that the antiplatelet actions of these coumarin compounds are due to the inhibition on thromboxane A2 formation and phosphoinositides breakdown.

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

PubMed1992

HA-29: an inhibitor of thromboxane A2 formation with antagonism of thromboxane A2/prostaglandin endoperoxide receptor in rabbit platelets.

HA-29, 2-[(3-methoxyphenyl)methyl]-pyrano[2,3-c]pyrazol-6(1H)-one, was investigated for its inhibitory mechanism of action in washed rabbit platelets. This compound inhibited the aggregation and ATP release of rabbit platelets induced by arachidonic acid and collagen in a concentration-dependent manner, without affecting those induced by ADP, PAF and thrombin. Prolongation of the incubation time of HA-29 with platelets did not cause further inhibition and the aggregability of the agent-treated platelets could be restored after washing of platelets. The concentration-response curve of U-46619-induced platelet aggregation was shifted to the right by HA-29 in a concentration-dependent manner, but the maximal aggregation was suppressed by HA-29. The pA2 and pA10 values of HA-29 on U-46619-induced platelet aggregation were 4.26 and 3.58, respectively, with a slope value of -1.4. The U-46619-induced aggregation was markedly disaggregated by HA-29 even it was added 5 min after U-46619. HA-29 inhibited the secondary aggregation and ATP release, but not the primary aggregation of human platelet-rich plasma induced by ADP and epinephrine. Thromboxane B2 formation caused by arachidonic acid, collagen and thrombin was markedly suppressed by HA-29. HA-29 also inhibited the formation of prostaglandin D2 caused by arachidonic acid. HA-29 inhibited almost completely the formation of inositol monophosphate caused by U-46619, but not that by collagen or thrombin. HA-29 did not affect U-46619-induced contraction of rat aorta. It is concluded that the antiplatelet effect of HA-29 is due to the inhibition of thromboxane A2 formation and blockade of thromboxane A2/prostaglandin endoperoxide receptor.

Adenosine Triphosphate↗

PubMed1992

Dicentrine, a novel antiplatelet agent inhibiting thromboxane formation and increasing the cyclic AMP level of rabbit platelets.

Dicentrine is an antiplatelet agent isolated from the Chinese herb Lindera megaphylla. We examined the in vitro effects of dicentrine on various aspects of platelet reactivity. Dicentrine inhibited the aggregation and ATP release of washed rabbit platelets induced by arachidonic acid (AA), collagen, ADP, platelet-activating factor (PAF), thrombin and U46619. Dicentrine also inhibited the thromboxane B2 formation caused by AA, collagen and thrombin in washed intact platelets or that induced by AA in lysed platelet homogenate, while prostaglandin D2 formation caused by AA was not increased. The generation of inositol monophosphates (in the presence of indomethacin) caused by thrombin, collagen and PAF was not suppressed significantly, nor did dicentrine suppress fibrinogen-induced aggregation of elastase-treated platelets. Dicentrine inhibited the intracellular Ca2+ increase in quin-2/AM-loaded platelets caused by thrombin, PAF, collagen and AA. The cyclic AMP level was elevated by dicentrine in a concentration-dependent manner. These data indicate that the inhibitory effect of dicentrine on platelet aggregation and ATP release was due to the inhibition of thromboxane formation and the elevation of the level of cyclic AMP.

Adenosine Triphosphate↗