Arachidonic Acid-induced Platelet Aggregation Research Articles

Long-term Effects of Erythropoietin on Platelet Serotonin Storage and Platelet Aggregation in Hemodialysis Patients with Reference to Ketanserin Treatment

Correction of uremic platelet serotonin (5-HT) storage pool deficiency is one of the very early hemostatic effects of erythropoietin (Epo) therapy. In this work, platelet 5-HT with relation to primary hemostasis was studied in 15 hemodialysis patients treated with Epo for 8 months. Moreover, effects of ketanserin, a blocker of platelet and vascular smooth muscle cell 5-HT 2A receptors, in these patients were followed. The parameters studied were compared with relevant values in healthy controls and in hemodialysis patients not treated with Epo, and remeasured in the long-term Epo patients after a 14-day oral ketanserin trial. Platelet 5-HT content in the eighth month of Epo therapy was not different from the one in untreated patients. Ristocetin- and collagen-induced platelet aggregation were enhanced in comparison with both control groups, as opposed to unaltered response to ADP and arachidonic acid. Fibrinogen concentration was lower than in the untreated group. An inverse correlation between ADP-induced platelet aggregation and the skin bleeding time ( r=−0.536, p<0.05) and a positive one between the former and platelet 5-HT ( r=0.644, p<0.01) were found. Platelet count correlated positively with both platelet 5-HT ( r=0.823, p<0.0002) and ADP-induced platelet aggregation ( r=0.596, p<0.02). Ketanserin produced a decrease in ristocetin-induced platelet aggregation, fibrinogen, and prolongation of the bleeding time. The first two of the changes correlated positively with their pre-ketanserin values ( r=0.923, p<0.00001 and r=0.839, p<0.0001, respectively). Post-ketanserin, positive correlations between depressed ristocetin- and arachidonic acid-induced platelet aggregation ( r=0.760, p<0.005), and between collagen- and corresponding values of arachidonic acid- ( r=0.622, p<0.02), ADP-induced platelet aggregation ( r=0.396, p<0.01), and platelet 5-HT ( r=0.654, p<0.05) were found.

A new antiplatelet diarylheptanoid from Alpinia blepharocalyx.

A new diarylheptanoid, 1,7-bis(4-hydroxyphenyl)-3-hydroxy-1,3-heptadien-5-one (1), along with seven other known compounds, were isolated from the seeds of Alpinia blepharocalyx. Of these, compounds 1 and 3 showed strong inhibition of collagen-induced, arachidonic acid-induced, and adenosine diphosphate-induced platelet aggregation of human whole blood. Compound 3 also strongly inhibited ristocetin-induced platelet aggregation. Structures of these compounds were elucidated by spectroscopic and chemical means.

The effects of varying dietary n-6 to n-3 fatty acid ratios on platelet reactivity, coagulation screening assays, and antithrombin III activity in dogs.

Thirty beagles were placed on diets containing ratios of n-6 to n-3 fatty acids ranging from 5:1 to 100:1 for 12 weeks to determine the effects of these diets on platelet reactivity, coagulation screening assays, and antithrombin III activity. Although small changes were observed in adenosine diphosphate (ADP)-, collagen-, and arachidonic acid-induced platelet aggregation and 14C-serotonin release, fibrinogen concentrations, and antithrombin III activities during the 12-week study, these changes were not of clinical significance and did not correlate with the varying ratios of n-6 to n-3 fatty acids.

Platelet membrane glycoprotein IV (CD36) is involved in arachidonic acid induced-platelet aggregation.

Conference Article| May 01 1996 Platelet membrane glycoprotein IV (CD36) is involved in arachidonic acid induced-platelet aggregation ASIM K. DUTTA-ROY; ASIM K. DUTTA-ROY 1Division of Biochemical Sciences, Rowett Research Institute, Aberdeen, AB2 9SB Search for other works by this author on: This Site PubMed Google Scholar LYNN C. CROSBIE; LYNN C. CROSBIE 1Division of Biochemical Sciences, Rowett Research Institute, Aberdeen, AB2 9SB Search for other works by this author on: This Site PubMed Google Scholar MARGARET J. GORDON; MARGARET J. GORDON 1Division of Biochemical Sciences, Rowett Research Institute, Aberdeen, AB2 9SB Search for other works by this author on: This Site PubMed Google Scholar FIONA. M. CAMPBELL FIONA. M. CAMPBELL 1Division of Biochemical Sciences, Rowett Research Institute, Aberdeen, AB2 9SB Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1996) 24 (2): 167S. https://doi.org/10.1042/bst024167s Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation ASIM K. DUTTA-ROY, LYNN C. CROSBIE, MARGARET J. GORDON, FIONA. M. CAMPBELL; Platelet membrane glycoprotein IV (CD36) is involved in arachidonic acid induced-platelet aggregation. Biochem Soc Trans 1 May 1996; 24 (2): 167S. doi: https://doi.org/10.1042/bst024167s Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1996 Biochemical Society1996 Article PDF first page preview Close Modal You do not currently have access to this content.

Platelet aggregation, sensitivity to prostaglandin E1 and thromboxane A2 release in recombinant hirudin- and heparin-anticoagulated blood.

Hirudin is the most potent known natural inhibitor of thrombin and is presently gaining popularity as an anticoagulant since recombinant forms have become available. The aim of the present study was to compare platelet aggregation, sensitivity to prostaglandin E1 and thromboxane A2 release in r-hirudinized and heparinized blood. Platelet aggregation was measured turbidimetrically using a dual channel aggregometer (Labor, Germany) in blood samples of healthy volunteers anticoagulated with r-hirudin W015 (Behring) and heparin (20 micrograms/ml blood each). Aggregation was induced by arachidonic acid (0.5, 1.0 and 2.0 mM) and adenosine diphosphate (1.0 microM). Prostaglandin E1 in concentrations 10, 20, 40 and 80 ng/ml was used. Plasma thromboxane B2 content was measured by gas chromatography/mass spectrometry. This study showed a significantly lower arachidonic acid induced platelet aggregation in r-hirudinized plasma. Three minutes after the aggregation induction by 0.5 mM arachidonic acid the plasma thromboxane B2 concentration was 23.0 ng/ml in blood anticoagulated with r-hirudin and 108.4 ng/ml in heparin-anticoagulated blood. The extent of the aggregation induced by adenosine diphosphate was nearly the same in hirudinized and heparinized plasma. Platelet sensitivity to prostaglandin E1 was significantly higher in r-hirudinized blood. Thus, platelet aggregation induced by arachidonic acid is significantly lower and sensitivity to prostaglandin E1 higher in r-hirudin-anticoagulated blood in comparison with heparin-anticoagulated blood.

In vitro study of the anti-aggregating activity of two nitroderivatives of acetylsalicylic acid.

The antiplatelet activity of two new nitrocompounds, chemically related to acetylsalicylic acid (NCX 4215 and NCX 4016), was studied in vitro to verify the hypothetical dual action of these drugs. Both drugs, in a dose-dependent way, inhibited arachidonic acid-induced platelet aggregation and thromboxane A2 production, measured as thromboxane B2 concentration in whole blood. These effects are likely to be related to cyclo-oxygenase inhibition. NCX 4215 and NCX 4016 in a dose-dependent way inhibited also thrombin-induced aggregation of platelets pretreated with acetylsalicylic acid. These inhibitory effects are related to nitric oxide release and cGMP increase and significantly reversed by oxyhaemoglobin and methylene blue. Either as a cyclo-oxygenase inhibitor or as a nitric oxide donor, NCX 4016 proved to be significantly more potent than NCX 4215.

Effects of cocaine on human platelet aggregation in vitro.

A temporal relationship has been established between cocaine ingestion and myocardial infarction, and a cocaine-induced increase in platelet aggregation has been suggested as a possible explanation. However, the mechanisms of cocaine associated coronary thrombosis have yet to be completely elucidated. For this reason, we examined the in vitro effect of cocaine and its metabolites on platelet aggregation. Platelet aggregation was tested by obtaining platelet rich plasma from 42 healthy volunteers and incubating the platelet rich plasma in six concentrations of cocaine (ranging from 1.47 to 2940 nmol) for 10 minutes prior to aggregation with ADP 1 microM. The same procedure was used to test the effect of two cocaine metabolites, benzoylecgonine and ecgonine methyl ester, on platelet aggregation. Abnormal results were confirmed by inducing aggregation with ADP at higher concentrations (2.4 and 10 microM) and with arachidonic acid (624 microM). At increasing concentrations, cocaine progressively inhibited ADP and arachidonic acid induced platelet aggregation. No effect was seen with benzoyl ecgonine or ecgonine methyl ester as compared to saline. These data suggest that under certain conditions cocaine may negatively affect hemostasis by decreasing platelet aggregation.

Antiplatelet and Antithrombotic Effects of YM337, the Fab Fragment of a Humanized Anti-GPIIb/IIIa Monoclonal Antibody in Monkeys

The antiplatelet and antithrombotic effects of the Fab fragment of the humanized antiplatelet glycoprotein (GP) IIb/IIIa monoclonal antibody C4G1 (YM337) were investigated in monkeys. First, the relationship between the inhibition of platelet aggregation and the prolongation of bleeding time was studied in rhesus monkeys. YM337 dose-dependently inhibited ex vivo platelet aggregation, with complete inhibition at doses higher than 0.25 mg/kg intravenous injection or 1.5 micrograms/kg/min infusion. At 0.25 mg/kg bolus injection followed by 1.5 micrograms/kg/min infusion, YM337 immediately and continuously inhibited platelet aggregation during the 6-h infusion period with platelet aggregation rapidly returning to over 50% of baseline within 1 h after the cessation of infusion. Template-bleeding time was significantly prolonged during the period of complete inhibition of platelet aggregation. Second, the antithrombotic effects of YM337 were investigated in a photochemically-induced thrombosis model in squirrel monkeys. YM337 at a dose of 1 mg/kg intravenous injection followed by 6 micrograms/kg/min infusion for 60 min prevented occlusive thrombus formation in all 4 monkeys. In contrast, time to occlusive thrombus formation did not change on intravenous bolus injection of aspirin 17 mg/kg (11.3 +/- 5.2 min) or sodium ozagrel (9.4 +/- 3.0 min) compared with saline (13.3 +/- 4.0 min). YM337 but not aspirin or sodium ozagrel significantly inhibited ex vivo ADP-induced platelet aggregation, while all drugs completely inhibited arachidonic acid-induced platelet aggregation. However, while aspirin and sodium ozagrel inhibited the thromboxane B2 generation accompanying arachidonic acid-induced platelet aggregation, YM337 had no effect on this variable. Platelet counts and bleeding time showed no significant change in any group in this squirrel monkey model. These results indicate that YM337, with a short half-life, may be a useful therapeutic agent in patients with thrombotic disorders.

The Antiplatelet Effects of a New Nitroderivative of Acetylsalicylic Acid - An In Vitro Study of Inhibition on the Early Phase of Platelet Activation and on TXA2 Production

We studied in vitro the antiplatelet activity of a new nitroderivative chemically related to acetylsalicylic acid: 2 acetoxybenzoate 2-[1-nitroxy-methyl]-phenyl ester (NCX 4016), in order to identify any effects due to the release of nitric oxide and the blockade of cyclo-oxygenase. The effects of scalar doses of NCX 4016 on the early phase of platelet activation, platelet aggregation and thromboxane A2 production were investigated. We observed inhibitory effects of NCX 4016 on platelet adhesion (IC50 = 7.3 x 10(-5) M), platelet cytosolic calcium concentration, assayed by fluorescent probe Fura 2, and the expression of glycoprotein IIb/IIIa (CD41/alpha IIb beta 3) (IC50 = 3.4 x 10(-5) M) and P-selectin (CD62/GMP-140) (IC50 = 4.9 x 10(-5) M) measured by flow cytometry. NCX 4016 also prevented thrombin-induced platelet aggregation (IC50 = 3.9 x 10(-5) M). None of these parameters were affected by acetylsalicylic acid. These inhibitory activities of NCX 4016 were abolished by oxyhaemoglobin and methylene blue. Intracellular cyclic GMP observed during thrombin-induced aggregation was increased by incubation with NCX 4016. These results appear to be attributable to the release of nitric oxide, which activates soluble platelet guanylylcyclase and promotes intracellular cyclic GMP increase. NCX 4016 almost completely inhibited platelet thromboxane A2 production and arachidonic acid-induced platelet aggregation. This also occurred in the presence of oxyhaemoglobin and methylene blue, indicating that its antiplatelet activity can be attributed not only to nitric oxide release but also to cyclo-oxygenase inhibition.

Arachidonic acid uptake by human platelets is mediated by CD36

The involvement of glycoprotein (GP) IV (CD36) in arachidonic acid uptake by human platelets was investigated using an anti-CD36 monoclonal antibody (MAB). The binding of [(14)C]arachidonic acid to MAB-treated platelets was significantly reduced compared with untreated platelets. The MAB also inhibited arachidonic acid-induced platelet aggregation and thromboxane A(2) synthesis in a dose-dependent manner. Pre-incubation of gel-filtered platelets with the MAB (10mg/I) inhibited arachidonic acid-induced platelet aggregation by 50% and collagen-induced platelet aggregation by 7-8% and the lag time was increased by 200%. Although the mechanism of platelet aggregation is not fully understood yet, the inhibition of arachidonic acid-induced platelet aggregation by the MAB could be the result of a reduced uptake of exogeneously added arachidonic acid by the MAB-treated platelets. Our data clearly indicate that arachidonic acid uptake by platelets is mediated, at least in part, by CD36.

Mechanisms of satigrel (E5510), a new anti-platelet drug, in inhibiting human platelet aggregation. Selectivity and potency against prostaglandin H synthases isozyme activities and phosphodiesterase isoform activities.

Satigrel (E5510, 4-cyano-5,5-bis(4-methoxyphenyl)-4-pentenoic acid) is a potent inhibitor of platelet aggregation. Like cyclooxygenase/prostaglandin H synthase (PGHS) inhibitors such as aspirin, which suppress platelet aggregation by inhibiting thromboxane A2 production, satigrel inhibits collagen- and arachidonic acid-induced aggregation of human platelets. In contrast to other PGHS inhibitors, satigrel, like cyclic nucleotide phosphodiesterase (PDE) inhibitors such as cilostazol, shows inhibitory activity against thrombin-induced platelet aggregation. To investigate the mechanism of the anti-platelet activity of satigrel, we examined the selectivity and potency of satigrel against PGHS isozyme activities and PDE isoform activities. Two isozymes of PGHS are known; constitutive enzyme (PGHS1) and inducible enzyme (PGHS2). Satigrel showed inhibitory activity against PGHS1 (IC50: 0.081 microM) and PGHS2 (IC50: 5.9 microM), suggesting the selective inhibition of PGHS1. Indomethacin, which is a selective inhibitor of PGHS1, showed similar selectivity against PGHS isozymes (IC50: 0.12 microM and 1.4 microM, respectively). These results support that satigrel suppresses thromboxane A2 production by inhibiting PGHS1. It is known that three isozymes of PDE exist in human platelets: Type V, which specifically hydrolyzes guanosine 3',5'-cyclic monophosphate (cGMP), Type III, which mainly hydrolyzes cAMP, and Type II, which hydrolyzes both cGMP and cAMP. We separated these three isozymes from human platelets and examined the inhibitory activity of satigrel against each enzyme. Of the three isozymes, the inhibitory activity of satigrel was the most potent against Type III PDE (IC50: 15.7 microM). The IC50 value for Type III corresponded with that for thrombin-induced platelet aggregation. Type V and Type II were also inhibited by satigrel (IC50: 39.8 and 62.4 microM, respectively). In human platelets, satigrel increased both cAMP and cGMP levels in a dose-dependent manner (100, 300 microM). In conclusion, satigrel inhibits collagen- and arachidonic acid-induced platelet aggregation through preventing thromboxane A2 synthesis by selective inhibition of the target enzyme, PGHS1, which exists in platelets. The anti-aggregating activity of satigrel against thrombin-induced aggregation may be due to elevation of the cyclic nucleotide levels through the inhibition of PDE isozymes.

Antiplatelet of vasorelaxing actions of some benzylisoquinoline and phenanthrene alkaloids.

Members of a series of benzylisoquinoline and phenanthrene alkaloids were tested for their antiplatelet and vasorelaxing actions. Atherosperminine HClO4 (15) and atherosperminium I (16) showed strong inhibition of adenosine 5'-diphosphate-induced platelet aggregation. dl-N-Methylcoclaurine (1), dl-coclaurine (6), 15, 16, xylopine hydroxylamine (18), and atherosperminine N-oxide (19) showed strong inhibition of arachidonic acid-induced platelet aggregation. Compounds 1, 15, 16, dicentrine methine (17), 18, and 19 showed strong inhibition of collagen-induced platelet aggregation. d-(-)-Magnocurarine I (8), 15, and 16 showed strong inhibition of platelet-activating factor-induced platelet aggregation. Compounds 15, 17, and 19 showed vasorelaxing action in rat thoracic aorta.

Antiaggregating and vasodilatory effects of a new nitroderivative of acetylsalicylic acid

We studied in vitro the effects on platelet aggregation and vascular tone of a new nitrocompound (nitroxy-butyl-acetylsalicylate: NO-ASA). In order to elucidate any possible activity due to the release of nitric oxide or the inhibition of platelet cyclo-oxygenase we compared NO-ASA to acetylsalicylic acid. NO-ASA 1 mM inhibited arachidonic acid-induced platelet aggregation (basal 75.4 ± 2.35%; NO-ASA 22 ± 3.46%; M ± SEM; P<0.001; n=6), but proved less active than acetylsalicylic acid (complete inhibition at 2 × 10 −5 M). NO-ASA also significantly reduced thrombin-induced (0.04–0.08 U/ml) platelet aggregation in acetylsalicylic acid-treated platelets (basal 70.5 ± 1.7%; NO-ASA 35.4 ± 2.2%; P<0.001; n=10; IC 50 7 × 10 −5 M). Methylene blue reduced the effects of NO-ASA on thrombin-induced (NO-ASA 46.7 ± 5.25%; NO-ASA + MB 59.1 ± 4.3%; P<0.01; n=8), but not arachidonic acid-induced platelet aggregation. The inhibitory effects of NO-ASA on platelet aggregation were partially removed by oxyhaemoglobin. Platelet thromboxane A 2 production (TXB 2 concentration in the supernatant of the aggregate 35.38 ± 7.81 ng/ml; n=8), was totally abolished by acetylsalicylic acid (0.17 ± 0.04 ng/ml; P<0.001; n=8) and reduced by NO-ASA (8.3 ± 4.05 ng/ml; P<0.01; n=8). In vitro studies on isolated rat aortic rings showed NO-ASA 10 −3 M, but not ASA up to 10 −3 M, induce a dose dependent vasorelaxation (100% of epinephrine-induced contraction) both in intact and endothelium denuded arteries (IC 50 5 × 10 −5 M). Addition of methylene blue reversed this relaxation. In conclusion these data demonstrate that NO-ASA acts through a double mechanism: a) by inhibiting cyclo-oxygenase and b) by releasing NO active on guanylyn cyclase both in platelets and in vascular smooth muscle cells.

Whole-Blood Platelet Aggregation Predicts In Vitro and In Vivo Primary Hemostatic Function in the Elderly

Increased platelet aggregation is associated with higher coronary artery disease mortality. Enhanced platelet aggregation in platelet-rich plasma has also been described in the elderly. To define age-related changes in primary hemostasis, we studied 37 elderly and 31 young blood donors. There were no significant age-related differences in whole-blood platelet aggregation, platelet adherence and thrombus formation on human umbilical artery segments, or bleeding time. Plasma fibrinogen was significantly higher in elderly men and women, whereas activated factor VII was elevated only in elderly women. Collagen-induced platelet aggregation was significantly correlated with platelet adherence to the subendothelium in elderly (r = .488, P = .002) but not in young donors. Accordingly, collagen-induced platelet aggregation showed a significant inverse correlation with bleeding time only in the elderly (r = -.401, P = .014). Arachidonic acid-induced platelet aggregation was significantly associated with platelet adherence to the subendothelium (r = .658, P = .003) and bleeding time (r = -.540, P = .021) only in elderly men. In young donors, ADP-induced platelet aggregation was significantly correlated with platelet adherence to the thrombogenic adventitial surface (r = .395, P = .031); in the elderly this association only approached significance (r = .315, P = .058). Whole-blood platelet aggregation in response to collagen and arachidonic acid may be more useful in predicting primary hemostatic function in the elderly than in the young. Furthermore, in the elderly, the correlation between platelet aggregation in whole blood and platelet-arterial wall interactions in vitro and in vivo may contribute to the ability of this test to predict coronary risk.

Peripheral benzodiazepine ligands inhibit aggregation and thromboxane synthesis induced by arachidonic acid in rabbit platelets in vitro

Seven compounds having varying affinities for peripheral benzodiazepine (p sites) were evaluated in vitro as inhibitors of arachidonic acid-induced rabbit platelet aggregation and thromboxane B 2 (TXB 2) synthesis. With the exception of flumazenil, all compounds inhibited both parameters with IC 50 values ranging from 0.19 to 3.5 μM, with a significant correlation between the inhibition of aggregation and the synthesis of thromboxane B 2. The antiaggregatory effect was stereoselective, and inhibition was increased when cellular penetration was favoured by increasing the volume of the organic solvent. The order of potency of these compounds is consistent with an effect at intracellular p sites (Ro5-4864 > PK14067 > PK11195 ⪢ PK14068 ≥ clonazepam ≥ diazepam ⋙ flumazenil). However, the correlation between the aggregation inhibition and the synthesis of TXB 2 suggests that microsomal cyclooxygenase may be the intracellular target of these ligands. We therefore propose that this enzyme possesses a site for benzodiazepine ligands which may share certain characteristics with the peripheral benzodiazepine receptor.

Sex Differences in Platelet Adherence to Subendothelium: Relationship to Platelet Function Tests and Hematologic Variables

Men have significantly more atherosclerotic disease than women. Platelet-mediated thrombosis plays a role in the initiation of myocardial infarction and stroke. Citrated whole blood from male and female donors was perfused through an annular system over everted human umbilical artery segments. Comparisons were made between platelet adherence and thrombus formation on subendothelium, platelet aggregation in citrated whole blood, hematologic variables, and the bleeding time. Platelet spreading and adherence were approximately 22% greater with male blood (P < 0.001), whereas thrombus formation on subendothelium and collagen- and arachidonic acid-induced platelet aggregation did not show sex-related differences. Platelet aggregation with adenosine diphosphate was greater in women, related to their lower hematocrit values. By contrast, in women hematocrit values showed a slight but significant positive correlation with platelet adherence on subendothelium. Fibrinogen was significantly correlated with collagen- and adenosine-diphosphate-induced platelet aggregation and with platelet adherence, spreading, and thrombus formation on subendothelium. The mean bleeding time was slightly longer in women than in men (P = 0.118). Platelet aggregation was not associated with the bleeding time except for collagen-induced platelet aggregation in males; the latter was significantly correlated with platelet adherence and spreading in both sexes, while arachidonic acid-induced platelet aggregation predicted platelet adherence and spreading in males. Male blood shows enhanced primary hemostatic activity; this may predispose men to atherosclerosis.

A study of platelet functions, some hemostatic and fibrinolytic parameters in relation to serotonin in hemodialyzed patients under erythropoietin therapy

Erythropoietin corrects anemia and improves hemostasis, but on the other hand bears a risk of thrombotic complications. Therefore in the present study an attempt has been made to evaluate bleeding time, platelet functions and some hemostatic and fibrinolytic parameters in relation to blood and platelet serotonin before and after 1, 2, 4, 8 and 12 weeks of treatment. 22 chronically hemodialyzed patients were administered with human recombinant erythropoietin (rHuEPO) in a dose of 2000 IU s.c. 3 times a week. Bleeding time was shortened significantly as early as after 1 week of the therapy, whereas hematocrit and hemoglobin increased after 2 weeks. These changes lasted throughout the study. Only a transient rise in platelet count, collagen-induced platelet aggregation, β-thromboglobulin and VIII:C activity were observed during therapy relative to baseline values. ADP- and arachidonic acid-induced platelet aggregation seemed to be unaffected by rHuEPO treatment, whereas a gradual and progressive enhancement in platelet aggregation in response to ristocetin was found, starting from the 2nd week of the therapy. It lasted throughout the study and correlated inversely with the bleeding time and positively with a rise in both blood and platelet serotonin. rHuEPO did not alter plasminogen, fibrinogen, platelet factor 4, α 2macroglobulin levels, protein C activity and euglobulin clot lysis time. A decline in protein C and S concentrations and antithrombin III activity observed during the therapy were counterbalanced by a fall in the activity of α 2 antiplasmin, C1 esterase inhibitor and plasminogen activator inhibitor. It is concluded that rHuEPO may improve platelet/vessel wall interactions possibly by means of serotonergic mechanisms. A lowered activity of inhibitors of fibrinolysis may be regarded as a protection against a general tendency to thrombosis during rHuEPO therapy.

Synthesis and antiplatelet activity of 2-amino-4,5-diphenylthiazole derivatives

A series of 4,5-diphenylthiazoles containing morpholinoalkyl amino groups at the 2 position was synthesized and their anti-platelet activities were evaluated. The inhibitory effects of the compounds in which phenyl groups at the 4 position were substituted by methoxy groups were more potent than those of aspirin and ibuprofen on the collagen-induced rabbit platelet aggregation. These compounds were also shown to have potent efficacies on the arachidonic acid-induced platelet aggregation. On the other hand, these compounds did not affect the ADP-induced platelet aggregation similarly to non-steroidal anti-inflammatory agents. Moreover, their efficacies on the inhibition of prostaglandin synthesis were more potent than that of ibuprofen. Therefore, we thought that 2-(morpholinoalkyl)amino-4,5-diphenylthiazoles, in spite of their basic properties, inhibited the platelet aggregation based on cyclooxygenase.

Application of chemical cytochrome P-450 model systems to studies on drug metabolism—VIII. Novel metabolism of carboxylic acids via oxidative decarboxylation

The oxidative decarboxylation of carboxylic acids by the chemical cytochrome P-450 model and rat liver microsomal systems was investigated. In the chemical system using meso-tetrakis(pentafluorophenyl)porphyrin iron chloride [Fe(TPFPP)Cl] with iodosylbenzene (PhIO), α-arylcarboxylic acids and α,α,α-trisubstituted acetic acids are converted to the corresponding one-carbon-reduced alcohol ( I) and carbonyl derivatives ( II) via oxidative decarboxylation. These products were then used as standards to identify the metabolites in vivo and in vitro. Biliary excretion of I a and II a in bile duct-cannulated rats after oral administration of ketoprofen amounted to 0.22 and 0.03% of the dose, respectively. In the case of indomethacin, I b and II b were detected as metabolites in the rat liver microsomal system, in yields of 2.8 and 0.29%, respectively. Further, the yields of I b and II b were decreased in the presence of SKF-525A. Thus, these metabolites were formed by cytochrome P-450-dependent reactions. Metabolites I a , I b, II a and II b had moderate to strong inhibitory activities on arachidonic acid-induced platelet aggregation and cyclooxygenase activity in vitro, comparable to those of the parent compounds.

Platelet antiaggregant methoxyphenylthienyl ketoxime ethers: synthesis and structure-activity relationships.

Some new oximinoalkanoic (n = 2,3,4) esters and acids derived from methoxyphenylthienyl ketones have been synthesized and evaluated in vitro for their inhibitory effects on arachidonic acid-induced human platelet aggregation. Of the eighteen oximinoethers tested the most active derivatives, which were four times more active as aspirin, belonged to the para methoxy series with Z configuration and n = 2 or 3.