A modified Arg-Asp-Val (RDV) peptide derived during the synthesis of Arg-Glu-Asp-Val (REDV), a tetrapeptide derived from an alternatively spliced site in fibronectin, inhibits the binding of fibrinogen, fibronectin, von Willebrand factor and vitronectin to activated platelets.

Characterization of a side-product obtained during the synthesis of Arg-Glu-Asp-Val (REDV) with inhibitory activity in thrombin-activated platelet aggregation was carried out. The semipreparative column fractionation of REDV peptide was rechromatographed on an analytical HPLC column and revealed two peaks which were re-tested for inhibitory activity. Using amino acid analysis with sequencing and fast atom bombardment mass spectrometry (FABMS), the first peak was determined to be REDV with molecular mass of 517 Da, and the second peak was determined to be a modified RDV with a mass of 608 Da. The modified RDV peptide inhibited thrombin-induced platelet aggregation with an IC50 of 200 microM, and complete inhibition occurred at 600 microM. However, the REDV peptide did not inhibit platelet aggregation up to 1 mM concentration. The modified RDV peptide eluted platelet glycoprotein IIb-IIIa complex that had been bound to GRGDSP-agarose. These studies show that the modified RDV peptide interacts with the platelet glycoprotein IIb-IIIa complex. Based on the collision-induced dissociation (CID) mass spectral data analysis, the modified RDV peptide has been characterized to contain an N-terminus blocking group on the Arg residue. The origin of this blocking group is presumed to have originated from decomposition products of the phenylacetamidomethyl (PAM) resin used in the solid-phase synthesis of the target peptide Arg-Glu-Asp-Val.     

Boophilus microplus: its saliva contains microphilin, a small thrombin inhibitor

Saliva of the cattle tick Boophilus microplus contains two thrombin inhibitors, BmAP and microphilin. This work presents the purification and characterization of microphilin. It was purified from the saliva by gel filtration, ultrafiltration through a 3 kDa cut-off membrane and affinity chromatography in a thrombin-Sepharose column. Analysis by mass spectrometry showed a molecular mass of 1770 Da. Microphilin is the smallest salivary thrombin inhibitor peptide known to date. It inhibits fibrinocoagulation and thrombin-induced platelet aggregation with an IC(50) of 5.5 microM, is temperature resistant and its inhibitory activity was abolished by protease K treatment. Microphilin did not inhibit the amidolytic activity of the enzyme upon a small chromogenic substrate, but inhibited the hydrolysis of a substrate that binds both catalytic site and exosite I. Therefore, we propose that microphilin blocks thrombin at exosite I.     

Antiplatelet property of Curcuma longa L. rhizome-derived ar-turmerone

The antiplatelet activities of Curcuma longa L. rhizome-derived materials were measured using a platelet aggregometer and compared with those of aspirin as antiplatelet agent. The active constituent from the rhizome of Curcuma longa L. was isolated and characterized as ar-turmerone by various spectral analyses. At 50% inhibitory concentration (IC50) value, ar-turmerone was effective in inhibiting platelet aggregation induced by collagen (IC50, 14.4 microM) and arachidonic acid (IC50, 43.6 microM). However, ar-turmerone had no effect on platelet activating factor or thrombin induced platelet aggregation. In comparison, ar-turmerone was significantly more potent platelet inhibitor than aspirin against platelet aggregation induced by collagen. These results suggested that ar-turmerone could be useful as a lead compound for inhibiting platelet aggregation induced by collagen and arachidonic acid.     

Inhibition of calpain blocks platelet secretion, aggregation, and spreading

Previous studies have indicated that the Ca(2+)-dependent protease, calpain, is activated in platelets within 30-60 s of thrombin stimulation, but specific roles of calpain in platelets remain to be identified. To directly test the functions of calpain during platelet activation, a novel strategy was developed for introducing calpain's specific biological inhibitor, calpastatin, into platelets prior to activation. This method involves treatment of platelets with a fusion peptide, calpastat, consisting of the cell-penetrating signal sequence from Kaposi's fibroblast growth factor connected to a calpain-inhibiting consensus sequence derived from calpastatin. Calpastat specifically inhibits thrombin peptide (SFLLR)-induced alpha-granule secretion (IC(50) = 20 microM) during the first 30 s of activation, thrombin-induced platelet aggregation (IC(50) = 50 microM), and platelet spreading on glass surfaces (IC(50) = 34 microM). Calpastat-Ala, a mutant peptide in which alanine is substituted at conserved calpastatin residues, lacks calpain inhibitory activity and fails to inhibit secretion, aggregation, or spreading. The peptidyl calpain inhibitors calpeptin, MDL 28,170 (MDL) and E64d also inhibit secretion, aggregation and spreading, but require 3-10-fold higher concentrations than calpastat for biological activity. Together, these findings demonstrate that calpain regulates platelet secretion, aggregation, and spreading and indicate that calpain plays an earlier role in platelet activation following thrombin receptor stimulation than had been previously detected.     

Inhibition of [3H]platelet activating factor (PAF) binding by Zn2+: a possible explanation for its specific PAF antiaggregating effects in human platelets

Zinc ions in the micromolar range exhibited a strong inhibitory activity toward platelet activating factor (PAF)-induced human washed platelet activation, if added prior to this lipid chemical mediator. The concentration of Zn2+ required for 50% inhibition of aggregation (IC50) was inversely proportional to the concentration of PAF present. The IC50 values (in microM) for Zn2+ were 8.8 +/- 3.9, 27 +/- 5.8, and 34 +/- 1.7 against 2, 5, and 10 nM PAF, respectively (n = 3-6). Zn2+ exhibited comparable inhibitory effects on [3H]serotonin secretion and the IC50 values (in microM) were 10 +/- 1.2, 18 +/- 3.5, and 35 +/- 0.0 against 2, 5, and 10 nM PAF, respectively (n = 3). Under the same experimental conditions, aggregation and serotonin secretion induced by ADP (5 microM), arachidonic acid (3.3 microM), or thrombin (0.05 U/ml) were not inhibited. Introduction of Zn2+ within 0-2 min after PAF addition not only blocked further platelet aggregation and [3H]serotonin secretion but also caused reversal of aggregation. Analysis of [3H]PAF binding to platelets showed that Zn2+ as well as unlabeled PAF prevented the specific binding of [3H]PAF. The inhibition of [3H]PAF specific binding was proportional to the concentration of Zn2+ and the IC50 value was 18 +/- 2 microM against 1 nM [3H]PAF (n = 3). Other cations, such as Cd2+, Cu2+, and La3+, were ineffective as inhibitors of PAF at concentrations where Zn2+ showed its maximal effects. However, Cd2+ and Cu2+ at high concentrations exhibited a significant inhibition of the aggregation induced by 10 nM PAF with IC50 values being five- and sevenfold higher, respectively, than the IC50 for Zn2+, and with the IC50 values for inhibition of binding of 1 nM [3H]PAF being 5 and 19 times higher, respectively, than the IC50 for Zn2+. The specific inhibition of PAF-induced platelet activation and PAF binding to platelets suggested strongly that Zn2+ interacted with the functional receptor site of PAF or at a contiguous site.     

Nitric oxide and platelet energy metabolism

This study was undertaken to determine whether nitric oxide (NO) can affect platelet responses through the inhibition of energy production. It was found that NO donors: S-nitroso-N-acetylpenicyllamine, SNAP, (5-50 microM) and sodium nitroprusside, SNP, (5-100 microM) inhibited collagen- and ADP-induced aggregation of porcine platelets. The corresponding IC50 values for SNAP and SNP varied from 5 to 30 microM and from 9 to 75 microM, respectively. Collagen- and thrombin-induced platelet secretion was inhibited by SNAP (IC50 = 50 microM) and by SNP (IC50 = 100 microM). SNAP (20-100 microM), SNP (10-200 microM) and collagen (20 microg/ml) stimulated glycolysis in intact platelets. The degree of glycolysis stimulation exerted by NO donors was similar to that produced by respiratory chain inhibitors (cyanide and antimycin A) or uncouplers (2,4-dinitrophenol). Neither the NO donors nor the respiratory chain blockers affected glycolysis in platelet homogenate. SNAP (20-100 microM) and SNP (50-200 microM) inhibited oxygen consumption by platelets. The effect of SNP and SNAP on glycolysis and respiration was not reduced by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, a selective inhibitor of NO-stimulated guanylate cyclase. SNAP (5-100 microM) and SNP (10-300 microM) inhibited the activity of platelet cytochrome oxidase and had no effect on NADH:ubiquinone oxidoreductase and succinate dehydrogenase. Blocking of the mitochondrial energy production by antimycin A slightly affected collagen-evoked aggregation and strongly inhibited platelet secretion. The results indicate that: 1) in porcine platelets NO is able to diminish mitochondrial energy production through the inhibition of cytochrome oxidase, 2) the inhibitory effect of NO on platelet secretion (but not aggregation) can be attributed to the reduction of mitochondrial energy production.     

Alpha-bulnesene, a novel PAF receptor antagonist isolated from Pogostemon cablin

Alpha-bulnesene is a sesquiterpenoid isolated from the water extract of Pogostemon cablin. It showed a potent and concentration-dependent inhibitory effect on platelet-activating factor (PAF) and arachidonic acid (AA) induced rabbit platelet aggregation. In a radioligand binding assay for the PAF receptor, alpha-bulnesene competitively inhibited [(3)H]PAF binding to the PAF receptor with an IC(50) value of 17.62+/-5.68microM. alpha-Bulnesene also dose-dependently inhibited PAF-induced intracellular Ca(2+) increase in fluo-3/AM-loaded platelets (IC(50) values of 19.62+/-1.32microM). Furthermore, alpha-bulnesene inhibited AA-induced thromboxane B(2) (TXB(2)) formation and prostaglandin E(2) (PGE(2)) formation. These results indicate that the inhibitory effect of alpha-bulnesene on platelet aggregation was due to a dual activity; specifically the chemical blocked PAF-induced intracellular signal transduction and interfered with cyclooxygenase activity, which resulted in a decrease in thromboxane formation. This study is the first to demonstrate that alpha-bulnesene is a PAF receptor antagonist as well as an anti-platelet aggregation agent.     

Complete amino acid sequence of kaouthiagin, a novel cobra venom metalloproteinase with two disintegrin-like sequences

The primary structure of kaouthiagin, a metalloproteinase from the venom of the cobra snake Naja kaouthia which specifically cleaves human von Willebrand factor (VWF), was determined by amino acid sequencing. Kaouthiagin is composed of 401 amino acid residues and one Asn-linked sugar chain. The sequence is highly similar to those of high-molecular mass snake venom metalloproteinases from viperid and crotalid venoms comprised of metalloproteinase, disintegrin-like, and Cys-rich domains. The metalloproteinase domain had a zinc-binding motif (HEXXHXXGXXH), which is highly conserved in the metzincin family. Kaouthiagin had an HDCD sequence in the disintegrin-like domain and uniquely had an RGD sequence in the Cys-rich domain. Metalloproteinase-inactivated kaouthiagin had no effect on VWF-induced platelet aggregation but still had an inhibitory effect on the collagen-induced platelet aggregation with an IC(50) of 0.2 microM, suggesting the presence of disintegrin-like activity in kaouthiagin. To examine the effects of these HDCD and RGD sequences, we prepared synthetic peptides cyclized by an S-S linkage. Both the synthetic cyclized peptides from the disintegrin-like domain and from the Cys-rich domain) had an inhibitory effect on collagen-induced platelet aggregation with IC(50) values of approximately 90 and approximately 4.5 microM, respectively. The linear peptide (RAAKHDCDLPELC) and the cyclized peptide had little effect on collagen-induced platelet aggregation. These results suggest that kaouthiagin not only inhibits VWF-induced platelet aggregation by cleaving VWF but also disturbs the agonist-induced platelet aggregation by both the disintegrin-like domain and the RGD sequence in the Cys-rich domain. Furthermore, our results imply that the corresponding part of the Cys-rich domain in other snake venom metalloproteinases also has a synergistic disturbing effect on platelet aggregation, serving as a second disintegrin-like domain. This is the first report of an elapid venom metalloproteinase with two disintegrin-like sequences.     

A novel disintegrin, jerdonatin, inhibits platelet aggregation and sperm-egg binding

A novel disintegrin, jerdonatin, was purified to homogeneity from Trimeresurus jerdonii venom by gel filtration and reversed-phase high-pressure liquid chromatography. We isolated the cDNA encoding jerdonatin from the snake venom gland. Jerdonatin cDNA precursor encoded pre-peptide, metalloprotease and disintegrin domain. Jerdonatin is composed of 72 amino acid residues including 12 cysteines and the tripeptide sequence Arg-Gly-Asp (RGD), a well-known characteristic of the disintegrin family. Molecular mass of jerdonatin was determined to be 8011 Da by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Jerdonatin inhibited ADP- and collagen-induced human platelet aggregation with IC50 of 123 and 135 nM, respectively. We also investigated the effect of jerdonatin on the binding of B6D2F1 hybrid mice spermatozoa to mice zona-free eggs and their subsequent fusion. Jerdonatin significantly inhibited sperm-egg binding in a concentration-dependent manner, but had no effect on the fusion of sperm-egg. These results indicate that integrins on the egg play a role in mammalian fertilization.     

Selective inhibition of platelet lipoxygenase by esculetin

The effects of coumarin and its derivatives on rat platelet lipoxygenase and cyclooxygenase activities were studied. Esculetin (6,7-dihydroxycoumarin) was found to inhibit the lipoxygenase more strongly than the cyclooxygenase; its concentration for 50% inhibition (IC50) was 0.65 microM for platelet lipoxygenase and 0.45 mM for platelet cyclooxygenase. Esculin (the 6-glucoside of esculetin) and umbelliferone (7-hydroxy-coumarin) also selectively inhibited the lipoxygenase, though less strongly (IC50 = 290 and 500 microM, respectively). 4-Hydroxycoumarin and coumarin had no inhibitory effect on either enzyme at concentrations up to 1 mM. The mechanism of the lipoxygenase inhibition by esculetin was non-competitive. Other antioxidants (hydroquinone, gallic acid and ascorbic acid) were less inhibitory to both enzymes and showed little selectivity.     

The evaluation and structure-activity relationships of 2-benzoylaminobenzoic esters and their analogues as anti-inflammatory and anti-platelet aggregation agents

Forty-seven 2-benzoylaminobenzoic esters were synthesized and evaluated in anti-platelet aggregation, inhibition of superoxide anion generation, and inhibition of neutrophil elastase release assays. Most 2-benzoylamino-4-chlorobenzoic acid derivatives showed selective inhibitory effects on arachidonic acid (AA)-induced platelet aggregation. Among them, compounds 6b and 7b exhibited more potent inhibitory effects (ca. 200-fold) than aspirin. Additionally, compounds 1a and 5a showed strong inhibitory effects on neutrophil superoxide generation with IC(50) values of 0.65 and 0.17 microM, respectively. However, compounds 6d and 6e exhibited dual inhibitory effects on platelet aggregation and neutrophil elastase (NE) release; therefore, these two compounds may be new leads for development as anti-inflammatory and anti-platelet aggregatory agents.     

Second messengers in platelet aggregation evoked by serotonin and A23187, a calcium ionophore.

We investigated the combined effect of 5-hydroxytryptamine (5-HT, serotonin) and calcium ionophore (A23187) on human platelet aggregation. Aggregation, monitored at 37 degrees C using a Dual-channel Lumi-aggregometer, was recorded for 5 min after challenge by a change in light transmission as a function of time. 5-HT (2-200 microM) alone did not cause platelet aggregation, but markedly potentiated A23187 (low dose) induced aggregation. Inhibitory concentration (IC50) values for a number of compounds were calculated as means +/- SEM from dose-response determinations. Synergism between 5-HT (2-5 microM) and A23187 (0.5-2 microM) was inhibited by 5-HT receptor blockers, methysergide (IC50 = 18 microM) and cyproheptadine (IC50 = 20 microM), and calcium channel blockers (verapamil and diltiazem, IC50 = 20 microM and 40 microM respectively). Interpretation of the effects of these blockers is complicated by their lack of specificity. Similarly, U73122, an inhibitor of phospholipase C (PLC), blocked the synergistic effect at an IC50 value of 9.2 microM. Wortmannin, a phosphatidylinositide 3-kinase (PI 3-K) inhibitor, also blocked the response (IC50 = 2.6 microM). However, neither genistein, a tyrosine-specific protein kinase inhibitor, nor chelerythrine, a protein kinase C inhibitor, affected aggregation at concentrations up to 10 microM. We conclude that the synergistic interaction between 5-HT and ionophore may be mediated by activation of PLC/Ca2+ and PI 3-kinase signalling pathways, but definitive proof will require other enzyme inhibitors with greater specificity.     

SQ-27986 inhibition of platelet aggregation is mediated through activation of platelet prostaglandin D2 receptors

SQ-27986, a oxabicycloheptane derivative, potently inhibits ADP-, collagen- and arachidonic acid-induced platelet aggregation in human platelet-rich plasma. Human platelet aggregation induced by ADP is inhibited by SQ-27986 (EC50 = 22nM), and the inhibitory action of SQ-27986 can be prevented with N-0164, a PGD2 antagonist. By comparison, ADP-induced rat platelet aggregation is unaffected by SQ-27986 (IC50 greater than 80 microM). Washed human platelets treated with SQ-27986 exhibit elevated cAMP levels and activated cAMP-dependent protein kinase. Elevation of platelet cAMP levels (greater than 4 fold basal) and activation of the cAMP-dependent protein kinase (greater than 4 fold) are observed with SQ-27986 concentrations above 100 nM. The SQ-27986-induced elevation of cAMP can be prevented by N-0164. Lysed platelets treated with SQ-27986 showed stimulated adenylate cyclase activity. SQ-27986 competes with [3H]prostaglandin D2 binding to isolated platelet membranes (EC50 for SQ-27986 is 20 nM, which was more potent than cold PGD2 itself). Radiolabeled Iloprost binding is virtually unaffected by SQ-27986 (EC50 greater than 100 microM), indicating that SQ-27986 does not interact with platelet prostacyclin receptors. These studies indicate that SQ-27986 inhibits platelet aggregation by activating platelet adenylate cyclase via stimulation of platelet PGD2 receptors.     

Effects of a novel non-carboxylic thromboxane A2 receptor antagonist (BM-531) derived from torasemide on platelet function

In this study we examined the thromboxane A(2)(TXA(2)) receptor antagonist property of BM-531 (N-tert -butyl- N'-[(2-cyclohexylamino-5-nitrobenzene)sulfonyl]urea), a torasemide derivative, on platelet function. The drug affinity for human washed platelet TXA(2)receptors labelled with [(3)H]SQ-29,548 has been determined (IC50: 0.0078 microM) and demonstrated to be higher than sulotroban (IC50: 0.93 microM) and SQ-29,548 (IC50: 0.021 microM). The antiaggregatory potency has been confirmed since we demonstrated that BM-531 prevented platelet aggregation in human citrated platelet-rich plasma induced by arachidonic acid (600 microM) (ED100: 0.125 microM), U-46619, a stable TXA(2)agonist (1 microM) (ED50: 0.482 microM) and collagen (1 microg mL(-1)) (% of inhibition: 42.9% at 10 microM) and inhibited the second wave of ADP (2 microM). Moreover, when BM-531 was incubated in whole blood from healthy donors, the closure time measured by the recently developed platelet function analyser (PFA-100(trade mark)) was significantly prolonged. These results suggest that BM-531 can be regarded as a novel non-carboxylic TXA(2)antagonist with a powerful antiplatelet potency.     

Rhodocetin, a novel platelet aggregation inhibitor from the venom of Calloselasma rhodostoma (Malayan pit viper): synergistic and noncovalent interaction between its subunits.

A novel platelet aggregation inhibitor, rhodocetin, was purified from the crude venom of Calloselasma rhodostoma. It inhibited collagen-induced platelet aggregation in a dose-dependent manner, with an IC50 of 41 nM. Rhodocetin has a heterodimeric structure with alpha and beta subunits, which could be separated on a nonreducing denaturing gel or reverse-phase HPLC column. Individually neither subunit inhibited platelet aggregation even at 2.0 microM concentration. Titration and reconstitution experiments showed that, when these subunits are mixed to give a 1:1 complex, most of its biological activity was recovered. The reconstituted complex inhibited platelet aggregation with an IC50 of 112 nM, about 3-fold less effective than the native molecule. Circular dichroism analysis revealed that the reconstituted complex had a spectrum similar to that of the native protein. By using surface plasmon resonance studies, we established that the stoichiometry of binding between the two subunits is 1:1 and the subunits interact with a Kd of 0.14 +/- 0.04 microM. The complete amino acid sequences of the alpha (15956.16 Da, 133 residues) and beta (15185.10 Da, 129 residues) subunits show a high degree of homology with each other (49%) and with the Ca2+-dependent lectin-related proteins (CLPs) (typically 29-48%) isolated from other snake venoms. Unlike the other members of the family in which the subunits are held together by an interchain disulfide bond, rhodocetin subunits are held together only through noncovalent interactions. The cysteinyl residues forming the intersubunit disulfide bridge in all other known CLPs are replaced by Ser-79 and Arg-75 in the alpha and beta subunits of rhodocetin, respectively. These studies support the noncovalent and synergistic interactions between the two subunits of rhodocetin. This is the first reported CLP dimer with such a novel heterodimeric structure.     

Design of new potent and selective secretory phospholipase A2 inhibitors. Part 5: synthesis and biological activity of 1-alkyl-4-[4,5-dihydro-1,2,4-[4H]-oxadiazol-5-one-3-ylmethylbenz-4'-yl(oyl)] piperazines

Among the different PLA(2)s identified to date, the group IIA secretory PLA(2) (sPLA(2) GIIA) is implied in diverse pathological conditions. In this work we describe the synthesis, inhibitory activities, and structure-activity relationships (SAR) of a new class of substituted piperazine derivatives. The in vitro fluorimetric assay using two groups of enzymes, GIB and GIIA, revealed several compounds as highly potent inhibitors (IC(50)=0.1 microM). The in vivo activity assessed by ip or per os administration in a carrageenan-induced edema test in rats showed that two compounds proved to be as potent as indomethacin (10 mg/kg).     

Synthesis, antiproliferative, and antiplatelet activities of oxime- and amide-containing quinolin-2(1H)-one derivatives

Certain oxime- and amide-containing quinolin-2(1H)-one derivatives were synthesized and evaluated for their antiproliferative and antiplatelet activities. These compounds were synthesized via alkylation of hydroxyl precursors followed by the reaction with NH(2)OH or NaN(3) (Schmidt reaction). The preliminary assays indicated that amide derivatives are either weakly active or inactive while the oxime counterparts exhibited potent inhibitory activities against platelet aggregation induced by collagen, AA (arachidonic acid), and U46619 (the stable thromboxan A(2) receptor agonist). Among them, (Z)-6-[2-(4-methoxyphenyl)-2-hydroxyiminoethoxy]quinolin-2(1H)-one (7c) was the most active against AA induced platelet aggregation with an IC(50) of 0.58microM and was inactive against cell proliferation. For the inhibition of U46619 induced aggregation, 7a and 8a-c exhibited very potent activities with IC(50) values in a range between 0.54 and 0.74microM. For the antiproliferative evaluation, N-(biphenyl-4-yl)-2-(2-oxo-1,2-dihydroquinolin-7-yloxy)acetamide (11d) was the most potent with GI(50) values of <10, 10.8, and <10microM against the growth of MT-2, NCI-H661, and NPC-Tw01, respectively, and possessed only a weak antiplatelet activity. Further evaluation of 11d as a potential anticancer agent is on-going.     

Characterization and molecular cloning of a glutathione S-transferase from the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae)

Glutathione S-transferases (GST) catalyzing the conjugation of reduced glutathione to a vast range of xenobiotics including insecticides were characterized in the whitefly Bemisia tabaci. GST activities were determined in susceptible and resistant strains of B. tabaci towards artificial substrates, i.e. 1-chloro-2,4-dinitrobenzene (CDNB) in a photometric microplate assay and monochlorobimane (MCB) in a fluoroemtric microplate assay and characterized by their Michaelis-Menten kinetics. The inhibitory potential of ethacrynic acid was very effective with IC50-values between 0.9 and 5.8 microM depending on substrate and strain. The inhibitory effect of dicumarol was 10 times lower. Glutathione-affinity chromatography purified GST enzymes of two different B. tabaci strains appeared as a single band on SDS-PAGE and had a molecular mass of 23.5 kDa determined by MALDI mass spectrometry. The N-terminus of the purified enzyme was sequenced by Edman degradation. The nearly full-length cDNA of the enzyme was isolated by RT-PCR using a degenerate primer derived from the N-terminal amino acid sequence and contained an open reading frame encoding a 194-amino-acid protein. Comparison of the deduced amino acid sequence with GSTs from other species revealed that the enzyme is closely related to insect class sigma GSTs.     

Direct evidence for the interaction between papaverine and alpha 2-adrenergic receptors in canine platelets

The effects of papaverine on specific [3H]-yohimbine binding to canine platelet alpha 2-adrenergic receptors and on the platelet aggregation were assessed and compared with those of verapamil. Both compounds concentration-dependently inhibited [3H]-yohimbine binding with KI values for respective compounds of 0.39 +/- 0.05 microM (n = 3) and 15 +/- 0.19 microM (n = 3). In the presence of either compound KD values in Scatchard analysis of the equilibrium ligand binding increased in concentration-dependent manner, whereas Bmax did not change, indicating competitive inhibition of the ligand binding by these compounds. (-)-Epinephrine (3 microM) potentiation of adenosine diphosphate (ADP, 0.1 microM) aggregation was inhibited by papaverine with IC50 of 11 +/- 3.6 microM (n = 4). In the same experiments verapamil inhibited the platelet aggregation with lower IC50 (3.1 +/- 0.87 microM, n = 4) in comparison with that for papaverine. These results suggest that papaverine, like verapamil, inhibits physiological response of canine platelets through alpha-adrenergic receptor stimulation by direct interaction with the receptors.     

Isolation and characterization of a novel platelet aggregation inhibitory peptide from the medicinal mushroom, Inonotus obliquus

This study describes the extraction and characterization of a platelet aggregation inhibitory peptide from Inonotus obliquus. Ethanol extract from I. obliquus ASI 74006 mycelia showed the highest platelet aggregation inhibitory activity (81.2%). The maximum platelet aggregation inhibitory activity was found when the mycelia of I. obliquus ASI 74006 was extracted with ethanol at 80 degrees C for 12 h. The platelet aggregation inhibitor was purified by systematic solvent fractionation, ultrafiltration, Sephadex G-10 column chromatography, and reverse-phase HPLC. The purified platelet aggregation inhibitor is a novel tripeptide with a molecular mass of 365 Da, having a sequence of Trp-Gly-Cys. The purified platelet aggregation inhibitor also showed high platelet aggregation inhibitory activity in Institute of Cancer Research (ICR) mice.