Co-activation of Gi and Gq proteins exerts synergistic effect on human platelet aggregation through activation of phospholipase C and Ca2+ signalling pathways

Our previous studies have shown that subthreshold concentrations of two platelet agonists exert synergistic effects on platelet aggregation. Here we studied the mechanism of synergistic interaction of 5-hydroxytryptamine (5-HT) and epinephrine mediated platelet aggregation. We show that 5-HT had no or little effect on aggregation but it did potentiate the aggregation response of epinephrine. The synergistic interaction of 5-HT (1-5 microM) and epinephrine (0.5-2 microM) was inhibited by alpha2-adrenoceptor blocker (yohimbine; IC50= 0.4 microM), calcium channel blockers (verapamil and diltiazem with IC50 of 10 and 48 mM, respectively), PLC inhibitor (U73122; IC50=6 microM) and nitric oxide (NO) donor, SNAP (IC50=1.6 microM)). The data suggest that synergistic effects of platelet agonists are receptor-mediated and occur through multiple signalling pathways including the activation PLC/Ca2+ signalling cascades.     

Inhibitory effects of phylligenin and quebrachitol isolated from Mitrephora vulpina on platelet activating factor receptor binding and platelet aggregation

Phylligenine, together with quebrachitol, stigmasterol and two aporphine alkaloids--oxoputerine and liriodenine--were isolated from the twigs of Mitrephora vulpina C.E.C. Fisch. They were evaluated for their ability to inhibit platelet activating factor (PAF) receptor binding to rabbit platelets using 3H-PAF as a ligand and their antiplatelet aggregation effect in human whole blood induced by arachidonic acid (AA), collagen and adenosine diphosphate (ADP). Of all the compounds tested, phylligenin and quebrachitol exhibited potent and concentration-dependent inhibitory effects on PAF receptor binding, with IC(50) values of 13.1 and 42.2 μM, respectively. The IC(50) value of phylligenin was comparable to that of cedrol (10.2 μM), a potent PAF antagonist. Phylligenin also showed strong dose-dependent inhibitory activity on platelet aggregation induced by AA and ADP.     

A novel class of platelet activating factor (PAF) antagonists. II. Modification of the 2-position of the glycerol backbone of PAF-sulfonamide isosteres.

In a continuing effort to obtain more potent platelet activating factor (PAF) antagonists, we tried to synthesize a series of PAF-sulfonamide isosteres in which the substituent at the 2-position was modified to an acetoxy equivalent other than the methoxy group. These modifications produced highly active PAF antagonists. Compound 3-[2-(5-methyl-2H-tetrazol-2-yl)-3-(octadecylcarbamoyloxy) propylaminosulfonyl]propylquinolinium iodide (52) showed the most potent activity in the in vitro inhibitory effect on PAF-induced platelet aggregation in rabbit platelet-rich plasma (IC50 = 125 nM) and also in the in vivo protective effect on PAF-induced lethality in mice, with prolonged duration of action. Optically active enantiomers of this compound were synthesized and the (S)-(-)-isomer (IC50 = 87 nM) was found to be three times more potent that the (R)-(+)-isomer (IC50 = 289 nM), clearly exemplifying the enantioselectivity in the PAF-antagonist action of this novel compound.     

Platelet aggregation inhibitors in hot water extract of green tea

The effect of hot water extract of green tea on the collagen-induced aggregation of washed rabbit platelets was examined. The extract lowered submaximal aggregation and prolonged the lag time in a dose-dependent manner. After fractionation of the extract, it was revealed that the tea catechins (tannins) are active principles for inhibition and that ester-type catechins are more effective than free-type catechins. One of the ester type catechins, epigallocatechin gallate (EGCG), suppressed the collagen-induced platelet aggregation completely at the concentration of 0.2 mg/ml (= 0.45 mM). Comparing IC50 values of EGCG and aspirin it was found that the potency of EGCG is comparable to that of aspirin. Thrombin- and platelet activating factor (PAF)-induced aggregation was also inhibited by EGCG. The elevation of cyclic adenosine 3',5'-monophosphate (cAMP) level was not observed in EGCG treated platelets.     

A novel class of platelet activating factor (PAF) antagonists. I. Synthesis and structure-activity studies on PAF-sulfonamide isosteres.

New platelet activating factor (PAF) antagonists, 3 were synthesized by replacing the charged phosphate and trimethylammonium moieties with sulfonamide and heterocyclic quaternary ammonium functionalities, respectively (PAF-sulfonamide isosteres). Darmstoff phosphatidic acid analogues of this class (Darmstoff-sulfonamide isosteres), 6 were also synthesized. The activity of these compounds as PAF antagonists was evaluated from their in vitro inhibitory effect on PAF-induced platelet aggregation in rabbit platelet-rich plasma. Among the compounds tested, some of the 2-methoxypropane derivatives with an octadecylcarbamoyloxy or octadecylcarbamoylthio side chain at the 1-position and a propylsulfonamide function bearing a terminal polar substituent such as a quaternary quinolinium or substituted quinolinium group at the 3-position were found to be the most potent (IC50 = 0.3-0.6 microM).     

Preparation of immunoaffinity mini-columns for the analysis of platelet activating factor (PAF) in biological samples.

Using an antibody to BN 52719, an analogue of platelet activating factor (PAF), immunoaffinity mini-columns for the separation of PAF from biological samples were prepared. Rabbits were immunized with BN 52719 and immunoglobulin G (IgG) from the antiserum was coupled with Sepharose 4B. The resulting suspension of the IgG-coated Sepharose 4B in 25 mM phosphate buffer (pH 6.9) was poured into a plastic mini-column (bed volume 2.0 x 0.8 cm). Stepwise elution of the column with methanol revealed that lyso-PAF is eluted with 20-30% methanol in water whereas PAF is eluted with 50-80% methanol. For the determination of PAF in biological samples, it is recommended that lipids are extracted from the samples and the extract, reconstituted in 20% methanol, is loaded on the column. The column is then washed with 50% methanol followed by elution of PAF with 80% methanol. A small amount of [3H]PAF is added to the samples for measurement of the recoveries of PAF during the procedures of extraction and elution. The PAF is then quantified by radioimmunoassay or bioassay. Employing the immunoaffinity mini-column and radioimmunoassay, the contents of PAF in macrophages and conditioned medium after stimulation with calcium ionophore A23187, or tumor promoters such as TPA and thapsigargin, were measured.     

Inhibitory effects of 2'-hydroxychalcones on rat lens aldose reductase and rat platelet aggregation

Inhibitory effects of synthetic 2'-hydroxychalcone derivatives on rat lens aldose reductase (RLAR) and on platelet aggregation were investigated for the prevention or the treatment of chronic diabetic complications. 5'-chloro-4,2'-dihydroxychalcone (8) and 5'-chloro-3,2'-dihydroxychalcone (27) exhibited a potent inhibitory effect on rat platelet aggregation induced by ADP (IC50=0.10 and 0.06 mg/ml, respectively) and collagen (IC50=44 and 16 microg/ml, respectively) but showed relatively weak inhibitory activities on RLAR.     

Biphenyls, a new class of compound that inhibits platelet-activating factors

Honokiol (1), a constituent of Magnoliae cortex, and related synthetic biphenyls inhibited the platelet aggregation induced by a few aggregating agents. In particular, compounds 3, 5, and 10 had an inhibitory effect on platelet activating factor (PAF), which provides a new class of PAF inhibitor.     

Calcium-influx increases SOD1 aggregates via nitric oxide in cultured motor neurons

Familial amyotrophic lateral sclerosis (fALS) is caused by mutations in Cu/Zn-superoxide dismutase (SOD1), and SOD1 aggregation and calcium toxicity are involved in neuronal death. However, the effect of altered calcium homeostasis on the SOD1 aggregation is unknown. To investigate whether calcium triggers mutant SOD1 aggregation in vitro, human mutant SOD1 (G93A) was transfected into motor neuronal cell line (VSC 4.1 cells). These cells were then treated with calcium ionophore A23187 or agents that induce intracellular calcium release like cyclic ADP ribose, ryanodine or thapsigargin. A23187 was found to increase mutant SOD1 aggregation and neuronal nitric oxide synthase (nNOS) expression. Moreover, the NOS inhibitor (L-NAME) and a NO-dependent cyclic GMP cascade inhibitor (ODQ) reduced SOD1 aggregation, whereas an exogenous NO donor (GSNO) increased mutant SOD1 aggregation, which was also prevented by NOS or cGMP cascade inhibitor. Our data demonstrate that calcium-influx increases SOD1 aggregation by upregulating NO in cultured motor neuronal cells.     

Phenolic chemical composition of Petroselinum crispum extract and its effect on haemostasis

From the aqueous extract (Pc) of Petroselinum crispum (Mill) flat leaves specimens were isolated and identified the flavonoids apigenin (1), apigenin-7-O-glucoside or cosmosiin (2), apigenin-7-O-apiosyl-(1 --> 2)-O-glucoside or apiin (3) and the coumarin 2",3"-dihydroxyfuranocoumarin or oxypeucedanin hydrate (4). The inhibitory activity toward clotting formation and platelet aggregation was assessed for Pc flavonoids (1) and (2), and the coumarin (4). Pc showed no inhibition on clotting activity when compared with the control. On the other hand, a strong antiplatelet aggregation activity was observed for Pc (IC50 = 1.81 mg/mL), apigenin (IC50 = 0.036 mg/mL) and cosmosiin (IC50 = 0.18 mg/mL). In all cases ADP was used as inductor of platelet aggregation. Our results showed that Pc, apigenin and cosmosiin interfere on haemostasis inhibiting platelet aggregation. To the best of our knowledge this is the first report for the cosmosiin antiplatelet aggregation in vitro activity.     

Effects of protopine on blood platelet aggregation. III. Effect of protopine on the metabolic system of arachidonic acid in platelets

The mode of action of protopine on blood platelet aggregation was investigated in the metabolic system of arachidonic acid and in liberation of platelet activating factor using in vitro experimental models. Protopine inhibited the releases of arachidonic acid and platelet activating factor from platelet membrane phospholipids. Protopine also inhibited the conversion of prostaglandin G2 to thromboxane A2, as well as carboxyheptyl imidazole, a thromboxane synthetase inhibitor. These results indicated that protopine functions both as a phospholipase inhibitor and a thromboxane synthetase inhibitor. It is expected that protopine can be applied for treatment of thrombosis as an antiplatelet drug.     

川芎嗪衍生物的设计、合成及抗血小板凝集活性研究

分别以川芎嗪(TMP)和邻苯二胺为起始原料,经KMn O4氧化、酯缩合、环化、还原等步骤合成了7个新型的川芎嗪衍生物,其结构经1H NMR、13C NMR及HRMS确证。并采用Born比浊法初步测试了化合物的体外抗血小板凝集活性。结果表明,化合物3和7对二磷酸腺苷(ADP)诱导的血小板凝集抑制率IC50分别为0.23mmol/L和0.27mmol/L,优于母体化合物川芎嗪(0.42mmol/L)。     

Platelet aggregation inhibitors from Populus sieboldii Miquel.

The water extract of Populus sieboldii Miquel (Salicaceae) inhibited arachidonic acid-induced platelet aggregation. Pyrocatechol and salicyl alcohol were isolated as active constituents. Pyrocatechol showed an inhibitory effect on platelet aggregation induced by arachidonic acid with IC100 value of 4 microM, which was 25 times more potent than aspirin.     

具有四氢苯并[4,5]咪唑并[1,2-a]吡嗪骨架凝血酶抑制剂的设计合成及生物活性研究

以具有四氢苯并[4,5]咪唑并[1,2-a]吡嗪新骨架的凝血酶抑制剂1为先导化合物,设计合成了14个氨基甲酸酯衍生物(2a~6a,2b~6b和7~10).同时,在化合物1结构的基础上,引入具有抗血栓活性的川芎醇(HTMP),设计合成了新型结构的化合物11.目标化合物的结构均经1H NMR,13C NMR和HRMS确证.生物活性测试结果显示,所有目标化合物对凝血酶诱导的血小板聚集均有一定的抑制活性,其中化合物4b的抑制活性[IC50=(0.11±0.08)μmol/L]强于对照药达比加群酯[IC50=(0.60±0.05)μmol/L].在体内抗血栓活性测试中,化合物4b能以剂量依赖的方式减少大鼠静脉血栓的形成.化合物11对凝血酶诱导的血小板聚集的抑制活性较弱,但其抑制大鼠静脉血栓形成的作用与达比加群酯相当,这可能是由于化合物11在体内水解为川芎醇和化合物1,两者协同产生抗血栓作用所致.     

Anti-plasmin inhibitor. VI. Structure of phlorofucofuroeckol A, a novel phlorotannin with both dibenzo-1,4-dioxin and dibenzofuran elements, from Ecklonia kurome Okamura

Phlorofucofuroeckol A (1), a novel phlorotannin with both dibenzo-1,4-dioxin and dibenzofuran elements, has been isolated from the brown alga Ecklonia kurome OKAMURA as a potent anti-plasmin inhibitor. Its structure has been elucidated to be 1,11-di(3,5-dihydroxyphenoxy)- benzofuro[3,2-a]dibenzo[b,e][1,4]dioxin-2,4,8,10,14-pentaol on the basis of the spectral data, in particular, by means of negative nuclear Overhauser effect (NOE) and long-range carbon-proton couplings (2JCH and 3JCH). Phlorofucofuroeckol A inhibited the action of alpha 2-macroglobulin (IC50 = 1.0 micrograms/ml) and alpha 2-plasmin inhibitor (IC50 = 0.3 micrograms/ml), the main plasmin inhibitors in plasma.     

Calcium is involved in photomovement of cyanobacterium Synechocystis sp. PCC 6803

The unicellular cyanobacterium Synechocystis sp. PCC 6803 (Syn6803) exhibits photomovement through gliding motility. For a better understanding of photomovement in Syn6803, we examined the effects of Ca2+ on photoorientation and motility using a computer-assisted videomicroscope motion analysis system. When calcium ion was chelated from the basic motility medium by adding 0.5 mM ethylene glycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), the photoorientation was completely inhibited, whereas the gliding motility remained approximately 70% of the control. Photoorientation impaired by EGTA was nearly recovered within 30 min upon addition of 1 mM Ca2+. The recovery of photoorientation by Ca2+ was mimicked by either Mn2+ or Mg2+ but not by Ba2+ or Sr2+. Lanthanum ion at 10 microM completely inhibited both phototactic orientation and gliding motility of Syn6803. Furthermore, pimozide (voltage-gated L-type calcium channel inhibitor), orthovanadate (calcium efflux blocker) and A23187 (calcium ionophore) partially inhibited phototactic orientation and gliding motility. Interestingly, photoorientation was prevented with increasing concentrations of calmodulin antagonist such as trifluoperazine (TFP) and chlorpromazine, but gliding motility was inhibited in proportion to the concentration of TFP. The results we present strongly indicate that Ca2+ plays a significant role in regulating the photomovement of Syn6803.     

Lactone and cyclic ether analogues of platelet-activating factor. Synthesis and biological activities

Six-membered lactone and tetrahydropyran analogues of platelet-activating factor (PAF), 4-11, and related antagonistic derivatives 41-46 were synthesized. None of the delta-lactones 4-7 showed PAF-like activities, while the corresponding cyclic ethers 8, 9 and 11 were slightly active. Some of the cyclic antagonists showed more potent inhibitory activities than the open chain antagonist CV-3988 against platelet aggregation (rabbit platelet-rich plasma, IC50) and hypotension (rat, ID50) induced by C16-PAF: e.g. dl-3-[6-[O-(trans-3-heptadecylcarbamoyloxytetrahydropyran-2- yl)methyl]phosphonoxy]hexylthiazolium (inner salt) (41d) (IC50 5.5 x 10(-7) M, ID50 0.046 mg/kg, i.v.); dl-3-[5-[O-(cis-3-heptadecylcarbamoylthiotetrahydropyran-2- yl)methyl]phosphonoxy]pentylthiazolium (inner salt) (43c) (IC50 5.7 x 10(-7) M, ID50 0.076 mg/kg, i.v.).     

吡嗪类化合物的合成及其抗血小板凝集活性测试

为提高川芎嗪的抗血小板凝集活性,分别以不同的二胺、2,3-丁二酮和硫辛酸为起始原料,采用溴代、水解、环化、氧化、氢化、取代等反应,通过四条路线合成了7个川芎嗪衍生物,其结构经1H NMR、13C NMR及ESI-MS确证。采用Born比浊法初步测试了化合物的体外抗血小板凝集活性,结果显示,化合物1(IC50=0. 26mmol/L)、2(IC50=0. 27mmol/L)和7(IC50=0. 21mmol/L)对由二磷酸腺苷(ADP)诱导的血小板凝集具有一定的抑制活性,优于先导化合物川芎嗪(IC50=0. 49mmol/L)。因此,在不改变川芎嗪药效团的前提下对其进行不同程度的环化,能明显提高川芎嗪的抗血小板凝集活性,此研究为后期化合物的结构修饰提供了一定的参考价值。     

Inhibitory effects of acetylmelodorinol, chrysin and polycarpol from Mitrella kentii on prostaglandin E₂ and Thromboxane B₂ production and platelet activating factor receptor binding

Acetylmelodorinol, chrysin and polycarpol, together with benzoic acid, benzoquinone and stigmasterol were isolated from the leaves of Mitrella kentii (Bl.) Miq. The compounds were evaluated for their ability to inhibit prostaglandin E? (PGE?) and thromboxane B? (TXB?) production in human whole blood using a radioimmunoassay technique. Their inhibitory effect on platelet activating factor (PAF) receptor binding to rabbit platelet was determined using 3H-PAF as a ligand. Among the compounds tested, chrysin showed a strong dose-dependent inhibitory activity on PGE(2) production (IC?? value of 25.5 μM), which might be due to direct inhibition of cyclooxygenase-2 (COX-2) enzymatic activity. Polycarpol, acetylmelodorinol and stigmasterol exhibited significant and concentration-dependent inhibitory effects on TXB? production with IC?? values of 15.6, 19.1 and 19.4 μM, respectively, suggesting that they strongly inhibited COX-1 activity. Polycarpol and acetylmelodorinol showed strong dose-dependent inhibitory effects on PAF receptor binding with IC?? values of 24.3 and 24.5 μM, respectively.     

Synthesis and antitumor activity of new alkylphospholipids containing modifications of the phosphocholine moiety

New antitumor alkylglycerophospholipids, in which primarily the phosphocholine moiety of the platelet activating factor (PAF) molecule was modified, were synthesized from 1-alkyl-2-substituted glycerols by introducing polar head phosphoryl groups having methylene bridges of various lengths (from 2 to 14 carbons). They were tested for PAF agonistic activity and antitumor properties. In a series of 1-octadecyl-2-acetoacetylglycerophospholipids (1a-f), an increase in the length of the methylene bridge separating the phosphate and trimethylammonio group in the polar head side chain at position 3 of the glycerol backbone resulted in a progressive decrease in PAF agonistic activity and a characteristic change in antitumor activity against human promyelocytic leukemia cells (HL-60). Maximal potency was obtained with the compound having a decamethylene bridge (1e, IC50 value = 1.5 microgram/ml). Thus, alkylphospholipids possessing a decamethylene bridge and a variety of substituents at position 2 (1g-n) were synthesized. They showed potent inhibitory activity with IC50 values ranging from 0.4 to 1.9 micrograms/ml, depending on the nature of the 2-substituent in the phospholipid molecule. In in vivo tests of the present series of alkylglycerophospholipids (1a--n), using mice bearing sarcoma 180 and mice with mammary carcinoma MM46 (both cells and compounds were given i.p.), 1-octadecyl-2-acetoacetyl-3-glyceryl omega-trimethylammoniodecyl phosphate (1e) showed the most potent life-prolonging effect. The structure-activity relationships are discussed.