Inhibition of ADP-triggered blood platelet aggregation by diadenosine polyphosphate analogues

The synthesis and biological evaluation of new diadenosine polyphosphate analogues on blood platelet aggregation are reported. The most active are compounds with a sulfur atom replacing one or both non-bridging oxygens at phosphorus bound to adenosyl residues and hydroxymethyl groups of bis(hydroxymethyl)phosphinic acid.     

Experimental basis of platelet aggregation inhibition by acetylsalicylic acid

The difference in the effectiveness of aspirin for the prevention of stroke and secondary prevention of myocardial infarction was discussed on the basis of inhibition of platelet aggregation.     

Oxygen-radical-mediated lipid peroxidation and inhibition of ADP-induced platelet aggregation

The effects of lipid peroxidation on ADP-induced aggregation of washed rat platelets were examined using a oxygen-radical-generating system consisting of H2O2 and ferrous ion. Lipid peroxidation was assessed by measurement of thiobarbituric acid-reactive substances (TBARS). Incubation of the platelets with various concentrations of H2O2 (2-10 mM) in the presence of 10 microM Fe2+ resulted in a decrease of the aggregating capacity and an increase of TBARS value, depending on the concentrations of H2O2. Addition of catalase (0.1 mg/ml) to the incubation medium containing 10 microM Fe2+ and 10 mM H2O2 effectively protected the aggregating capacity, but superoxide dismutase (0.1 mg/ml) did not protect H2O2/Fe(2+)-induced inhibition of the platelet aggregation. The results of kinetic studies on the platelet aggregation with varying ADP and Ca2+ concentrations suggested that treatment of the platelets with H2O2/Fe2+ causes decreases in the binding affinities of ADP and Ca2+ for the platelets. On the basis of these results, change in the aggregating capacity of the platelets by treatment with H2O2/Fe2+ is discussed in relation to lipid peroxidation.     

The effects of some salicylate analogues on human blood platelets. 2. The role of platelet acetylation in the inhibition of platelet aggregation

Aspirin, 2,3-diacetoxybenzoic acid, 2,6-diacetoxybenzoic acid and 2-propoxybenzoic acid were incubated in human platelet-rich plasma at 37°C for 5 and 10 min and the effects upon collagen induced platelet aggregation and the uptake by platelets of radioactive acetate and propionate groups from 14C-labelled analogues were studied to determine if a correlation existed between acylation of the platelet and inhibition of aggregation. Inhibition of aggregation and the uptake of radioactive label were both concentration-dependent and both increased with the time of incubation. Potency re inhibitors of aggregation was, in decreasing order, aspirin, 2,propoxybenzoic acid, 2,3-diacetoxybenzoic acid and 2,6-diacetoxybenzoic acid. Uptake of radioactive label however, was greatest with aspirin, intermediate with 2,3- and 2,6-diacetoxybenzoic acid, and lowest with 2-propoxybenzoic acid. Platelets exposed to a metabolic inhibitor (oligomycin, 10^?5M for 15 min) showed reduced uptake of labelled acetate and propionate and the degree of uptake did not correlate with the degree of inhibitory activity of the analogues on platelet aggregation. Platelet fragments produced by sonification did not take up radioactive label and chloroform: methanol extraction removed about 50% of the label from intact platelets. The results do not support the hypothesis that acetylation of platelets by aspirin is solely responsible for its inhibitory effects on aggregation but do not conflict with the suggestion that acetylation of platelets may be responsible for the persistent $\text{in}$$\text{vivo}$ effects of aspirin.     

QSAR studies on biological activity of piritrexim analogues against pc DHFR

Quantitative structure-activity relationship (QSAR) studies for 2,6-substituted 2,4-diaminopyrido[3,2-d] pyrimidine analogues of piritrexim (PTX) as inhibitors of dihydrofolate reductase (DHFR) are now made using topological indices. The results have shown that best models are obtained by multiparametric analysis. The predictive potential of the model is discussed on the basis of a cross-validation method.     

Prostaglandin synthesis inhibition reduces platelet aggregation in diabetes mellitus

Platelet aggregation, platelet prostaglandin precursor fatty acids, glycaemia and lipid levels were studied in a group of insulin dependent diabetics whilst taking Aspirin (900 mg daily) and Dipyridamole (300 mg daily) and again two months after discontinuing this treatment.     

Mechanism of inhibition of thrombin-induced platelet aggregation by pyridoxal phosphate

Thrombin and ADP-induced platelet aggregation are reversibly inhibited by pyridoxal phosphate. Sodium borohydride converts Schiff bases formed between pyridoxal phosphate and amino groups to covalent bonds. When platelets treated with sodium borohydride and pyridoxal phosphate are resuspended in fresh platelet-poor plasma, they recover their response to thrombin, but not to ADP. Thus Schiff base formation between pyridoxal phosphate and platelet surface amino groups does not block thrombin aggregation. The loss of thrombin potency as an aggregating agent is due to interaction between pyridoxal phosphate and thrombin. This is evidenced by spectrophometric determination of adduct formation and loss of hydrolytic action on p-tosyl-L-arginine methyl ester.     

A preliminary investigation of mesoionic xanthine analogues as inhibitors of platelet aggregation

A series of mesoionic xanthines (e.g. mesoionic thiazolopyrimidines, 3, and thiadiazolopyrimidines, 5) and related analogues were examined as inhibitors of human platelet aggregation. Appropriately substituted compounds were found to fully inhibit platelet aggregation, and anhydro-(6-ethyl-8-isopentyl-7-oxo-5-hydroxy-1,3,4-thiadiazolo[3,2 -a]pyrimidinium hydroxide) (5b) was 40 times more potent than the structurally related xanthine theophylline (1). Gel filtration studies suggest that compound 5b irreversibly inhibits aggregation and this might be due to its ability to act as a latent acylation agent.     

Sildenafil potentiates nitric oxide mediated inhibition of human platelet aggregation

Nitric oxide (NO) inhibits platelet aggregation primarily via a cyclic 3'5'-guanosine monophosphate (cGMP)-dependent process. Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor that potentiates NO action by reducing cGMP breakdown. We hypothesised that sildenafil would augment the inhibitory effects of NO on in vitro platelet aggregation. After incubation with sildenafil or the soluble guanylate cyclase inhibitor H-(1,2,4)oxadiazolo(4,3-a)quinoxallin-1-one (ODQ), collagen-mediated human platelet aggregation was assessed in the presence of two NO donors, the cGMP-dependent sodium nitroprusside (SNP) and the cGMP-independent diethylamine diazeniumdiolate (DEA/NO). SNP and DEA/NO caused a concentration-dependent inhibition of platelet aggregation. ODQ inhibited and sildenafil augmented the effect of SNP, and to a lesser extent the effect of DEA/NO. We conclude that sildenafil potentiates NO-mediated inhibition of platelet aggregation through blockade of cGMP metabolism and that PDE5 inhibitors may have important antiplatelet actions relevant to the prevention of cardiovascular disease.     

In vitro inhibition of rat platelet aggregation by ochratoxin A

The mycotoxin ochratoxin A (OA) consists of 5-chloro-3-methyl-3,4-dihydro-8-hydroxyisocoumarin moiety linked by an amide bond to β-L-phenylalanine. When added to washed rat platelets in vitro, OA caused a dose-dependent inhibition of aggregation induced by agonists such as adenosine diphosphate (ADP) or thrombin. The aggregatory response induced by prior addition of an agonist was also reversed in a dose-dependent manner by OA. Inhibition of aggregation appeared to be irreversible since exposure of platelets to OA followed by several washings removed most of the mycotoxin associated with the platelets but did not diminish the inhibitory response. Serotonin secretion from dense granules and arachidonic acid release from membrane phospholipid (especially phosphatidylcholine) as well as its further metabolism were also inhibited by OA. These results suggest that a disruption of the platelet plasma membrane structure by OA is probably responsible for inhibition of the primary and secondary phases of aggregation.     

Piperazinyl-glutamate-pyrimidines as potent P2Y12 antagonists for inhibition of platelet aggregation

Piperazinyl-glutamate-pyrimidines were prepared with oxygen, nitrogen, and sulfur substitution at the 4-position of the pyrimidine leading to highly potent P2Y₁₂ antagonists. In particular, 4-substituted piperidine-4-pyrimidines provided compounds with exceptional potency. Pharmacokinetic and physicochemical properties were fine-tuned through modifications at the 4-position of the piperidine ring leading to compounds with good human PRP potency, selectivity, clearance and oral bioavailability.     

Adenosine analogues as inhibitors of P2Y12 receptor mediated platelet aggregation

Modified adenosine derivatives may lead to the development of P2Y(12) antagonists that are potent, selective, and bind reversibly to the receptor. Analogues of 2',3'-trans-styryl acetal-N6-ureido-adenosine monophosphate were prepared by modification of the 5'-position. The resulting analogues were tested for P2Y(12) antagonism in a platelet aggregation assay.     

In vitro inhibition of rat platelet aggregation by ochratoxin A.

The mycotoxin ochratoxin A (OA) consists of 5-chloro-3-methyl-3,4-dihydro-8-hydroxyisocoumarin moiety linked by an amide bond to beta-L-phenylalanine. When added to washed rat platelets in vitro, OA caused a dose-dependent inhibition of aggregation induced by agonists such as adenosine diphosphate (ADP) or thrombin. The aggregatory response induced by prior addition of an agonist was also reversed in a dose-dependent manner by OA. Inhibition of aggregation appeared to be irreversible since exposure of platelets to OA followed by several washings removed most of the mycotoxin associated with the platelets but did not diminish the inhibitory response. Serotonin secretion from dense granules and arachidonic acid release from membrane phospholipid (especially phosphatidylcholine) as well as its further metabolism were also inhibited by OA. These results suggest that a disruption of the platelet plasma membrane structure by OA is probably responsible for inhibition of the primary and secondary phases of aggregation.     

3D QSAR studies on GSK-3 inhibition by aloisines

GSK-3 is involved in various physiological processes and its inhibitors have been evaluated as promising drug candidates for a lot of unmet pathologies. In this paper, inhibition of GSK-3 by aloisines is investigated by 3D QSAR studies. Two alignment rules were applied to check the influence of spatial alignment of the compounds. Both the CoMFA and CoMSIA techniques were carried out and ASS procedure was applied for CoMFA to find a satisfactory model. The best QSAR model obtained is a CoMSIA model characterized with r(2) of 0.938 and q(2) of 0.673 including steric, electrostatic and hydrophobic fields, possessing good predicting ability. To get a better understanding of the relationship between chemical structure and biological activity, a complex structure of aloisine with GSK-3 was obtained by superimposing GSK-3 into the known cocrystal structure of aloisine-CDK2, and then factors that affect the inhibition activity were investigated further, combining the QSAR study with the complex structure, the results of which are in good accordance and complementary to each other.     

Ajoene inhibition of platelet aggregation: possible mediation by a hemoprotein

Ajoene, an organosulfur compound derived from garlic, was found by spectral measurements, to interact, cooperatively, with a purified hemoprotein implicated, previously, in platelet activation. It modified the binding interactions of the protein with ligands, deemed to be physiologically relevant as effectors. The characteristics of the modifications were found to parallel those of ajoene induced modifications of agonist-induced aggregation kinetics of gel-filtered calf platelets.     

The effects of some salicylate analogues on human blood platelets. 1. Structure activity relationships and the inhibition of platelet aggregation

Utilizing a turbidometric technique and human platelet-rich plasma (PRP) at 37°C, aspirin, 2-propionyloxybenzoic acid, 2,3-diacetoxybenzoic acid, sodium salicylate and 4-aminosalicylic acid, at suitable final concentrations and without prior incubation in PRP, prevented adenosine diphosphate (ADP)-induced second phase platelet aggregation and inhibited collagen-induced aggregation. The minimum concentrations of the latter four compounds which inhibited second-phase ADP aggregation were respectively, 15, 43, 60 and 100 times the minimum inhibitory concentration of aspirin. Without prior incubation, 2,6-diacetoxybenzoic acid and 3-propionyloxybenzoic acid potentiated the second phase of ADP aggregation while 3-acetoxybenzoic acid, 4-acetoxybenzoic acid and 2,4-diacetoxybenzoic acid had no effects.Aspirin, 2,3-diacetoxybenzoic acid, 2,6-diacetoxybenzoic acid and 2-propionyloxybenzoic acid, incubated in PRP at 37°C for 5 and 10 min, inhibited collagen-induced platelet aggregation in a concentration dependent manner. Aspirin was most potent, followed by 2-propionyloxybenzoic acid, 2,3-diacetoxybenzoic acid and 2,6-diacetoxybenzoic acid. Inhibition increased with the time of incubation in all cases. The results indicate that structural specificity (the presence of an acyl group in the 2 position of the benzene ring) is important for the aggregation inhibiting activity of aspirin, but do not support the contention that such inhibition is dependent upon the availability of an acetyl radical.     

A novel, simple bioactivity assay for relaxin based on inhibition of platelet aggregation

In humans, the relaxin hormone family includes H1, H2 and H3 isoforms and insulin-like peptides 3 to 6. The ever-increasing interest in relaxin as potential new drug requires reliable methods to compare bioactivity of different relaxins. The existing bioassays include in vivo or ex vivo methods evaluating the organ-specific responses to relaxin and in vitro methods based on measurement of cAMP increase in relaxin receptor-bearing cells. We previously demonstrated that relaxin dose-dependently inhibits platelet aggregation. On this basis, we have developed a simple, reliable bioassay for relaxin used to compare purified porcine relaxin, assumed as reference standard, with two recombinant human H2 relaxins, H3 relaxin, insulin-like peptides 3 and 5. Pre-incubation of platelets with relaxins (3, 10, 30,100, 300 ng/ml; 10 min.) caused the inhibition of ADP-induced platelet aggregation. Within the 10-100 ng/ml range, porcine relaxin showed the highest effects and a nearly linear dose-response correlation. Lower peptide concentrations were ineffective, as were insulin-like peptides 3 and 5 at any concentration assayed. Platelet inhibition was mediated by specific RXFP1 relaxin receptor and cGMP, whose intracellular levels dose-dependently increased upon relaxin. For comparison, we stimulated THP-1 cells, a relaxin receptor-bearing cell line, with porcine relaxin, human H2 and H3 relaxins at the above concentrations (15 min.). We observed a dose-related increase of intracellular cAMP similar to the trend of platelet inhibition. Insulin like peptide 5 was ineffective. In conclusion, this study shows that inhibition of platelet aggregation may be used to assess bioactivity of relaxin preparations for experimental and clinical purposes.