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Biomedical subjects

M Livio

Publications and source records attributed to M Livio.

At least 37 records · Page 2Linked to original sources
PubMed1983

Salicylate fails to prevent the inhibitory effect of 5,8,11,14-eicosatetraynoic acid on human platelet cyclo-oxygenase and lipoxygenase activities.

Sodium salicylate is inactive both on cyclo-oxygenase and lipoxygenase prepared from human platelets. It prevents the inhibition of cyclo-oxygenase induced by aspirin, but does not counteract the inhibitory effect of 5,8,11,14-eicosatetraynoic acid on both enzymes. It also fails to interfere with the inhibitory activity of nordihydroguaiaretic acid on lipoxygenase. These data indicate that, unlike eicosatetraynoic acid, non-steroidal anti-inflammatory drugs interact with a site on cyclo-oxygenase distinct from the catalytic site, although related to it. Such a supplementary binding site is lacking on lipoxygenase.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1983

In vivo platelet activation with in vitro hyperaggregability to arachidonic acid in renal allograft recipients.

Renal allograft recipients were investigated to determine the extent and possible nature of in vivo platelet activation. In 92 allografted patients stable for more than 4 months' duration, intraplatelet serotonin in circulating platelets was depleted significantly. In a further 16 patients studied serially for 12 to 16 weeks following transplantation, intraplatelet serotonin fell abruptly within 4 days from transplantation to very low levels, and remained thus for 10 weeks, rising toward normal at about 12 weeks. Although some patients showed abrupt falls in intraplatelet serotonin coincident with acute rejection episodes, there was no difference in intraplatelet serotonin in seven patients whose grafts functioned well immediately and remained stable, and seven in whom repeated rejection led to graft loss within 3 months. Thus, these tests of platelet function do not permit diagnosis of rejection or prediction of graft outcome. Plasma platelet factor 4 (PF4) concentrations, in contrast, were normal in most patients during the first 6 weeks after grafting, then rose and remained abnormal up to 13 years following the allograft in the long-term stable graft recipients. This discrepancy suggests a different mode of platelet activation in the first few weeks after grafting from subsequent months. Despite universal depletion of intraplatelet amines and alpha-granule contents only four out of 14 early allograft recipients had an abnormal bleeding time, and platelet aggregation thresholds with adenosine-5'-diphosphate and collagen were not different from controls. However, thresholds for platelet aggregation with arachidonic acid were reduced significantly (P less than 0.01) and thromboxane B2 generation was increased in vitro. There was no correlation between depletion of intraplatelet serotonin and circulating platelet-agglutinating material, but nine of 17 biopsy specimens from rejecting allografts taken during the first 3 months showed extensive glomerular localization of platelet membrane antigens and PF4.

Adenosine Diphosphate↗
PubMed1983

Reduced platelet thromboxane formation in uremia. Evidence for a functional cyclooxygenase defect.

A qualitative platelet abnormality and a bleeding tendency are frequently associated with renal failure and uremia. We demonstrated previously that uremic patients display an abnormal platelet aggregation to arachidonic acid and reduced malondialdehyde production in response to thrombin and arachidonic acid. The objectives of this investigation were: (a) to compare platelet prostaglandin (PG) and thromboxane (TX) production in whole blood and in platelet-rich plasma (PRP) of 21 uremic patients and 22 healthy subjects; (b) to evaluate the concentration and activity of platelet PG- and TX-forming enzymes; (c) to assess the functional responsiveness of the platelet TXA(2)/PGH(2) receptor; (d) to explore the hemostatic consequences of partially reduced TXA(2) production.Platelet immunoreactive TXB(2) production during whole blood clotting was significantly reduced, by approximately 60%, in uremic patients as compared to age- and sex-matched controls. Exogenous thrombin (5-30 IU/ml) failed to restore normal TXB(2) production in uremic platelets. Uremic PRP produced comparable or slightly higher amounts of TXB(2) than normal PRP at arachidonate concentrations 0.25-1 mM. However, when exposed to substrate concentrations >2 mM, uremic PRP produced significantly less TXB(2) than normal PRP. To discriminate between reduced arachidonic acid oxygenation and altered endoperoxide metabolism, the time course of immunoreactive TXB(2) and PGE(2) production was measured during whole blood clotting. The synthesis and release of both cyclooxygenase-derived products was slower and significantly reduced, at all time intervals considered. Furthermore, PGI(2) production in whole blood, as reflected by serum immunoreactive 6-keto-PGF(1alpha) concentrations, was significantly reduced in uremic patients as compared with healthy subjects. PGH synthase levels, as determined by an immunoradiometric assay, were not significantly different in platelets from uremic patients as compared to control platelets. A single 40-mg dose of aspirin given to five healthy volunteers reduced their serum TXB(2) to levels found in uremic patients. This was associated with a significant increase of threshold aggregating concentrations of ADP and arachidonic acid and prolongation of bleeding time. Substantially similar threshold concentrations of U46619, a TXA(2) agonist, induced aggregation of normal and uremic platelets. Prostacyclin induced a significant elevation of uremic platelet cyclic AMP, which was suppressed by U46619, further suggesting normal responsiveness of the TXA(2)/PGH(2) receptor. WE CONCLUDE THAT: (a) an abnormality of platelet arachidonic acid metabolism exists in uremia, leading to a reduced TXA(2) production; (b) the characteristics of this abnormality are consistent with a functional cyclooxygenase defect; (c) reduced TXA(2) production may partially explain the previously described abnormality of platelet function in uremia.

Adult↗
PubMed1982

Non-steroidal anti-inflammatory drugs react with two sites on platelet cyclo-oxygenase. Evidence from "in vivo" drug interaction studies in rats.

Non-steroidal anti-inflammatory drugs inhibit platelet cyclo-oxygenase activity. This study shows that salicylate, diflunisal, sulphinpyrazone and indomethacin prevention vivo aspirin inhibitory effect on cyclo-oxygenase activity as measured by the formation of malondialdehyde and thromboxane B2, two products of platelet arachidonic acid metabolism. Salicylate also prevents the inhibitory effect of indomethacin. All these drugs therefore appear to interact with the same site on platelet cyclo-oxygenase. Since salicylate is inactive by itself on this platelet enzyme and diflunisal and sulphinpyrazone were used at ineffective doses, it is suggested that their interaction with aspirin (or indomethacin) occurs at the level of a supplementary binding site, rather than directly on the substrate active site. Interaction with this putative supplementary site is necessary but not sufficient for the efficacy of these drugs on cyclo-oxygenase inhibitors. Acetylation by aspirin of the active site appears to be a phenomenon secondary to the binding of salicylate moiety to the supplementary site.

Animals↗
PubMed1982

Indomethacin prevents the long-lasting inhibitory effect of aspirin on human platelet cyclo-oxygenase activity.

Aspirin and indomethacin do interact with the same site on cyclo-oxygenase. This suggestion is based on in vitro studies on ram seminal vesicles and in vivo drug interaction studies on rat platelets. The purpose of the present study was to ascertain whether the same interaction also occurred after administration of both drugs to human volunteers. Platelet aggregation induced by sodium arachidonate or by collagen, and formation of platelet MDA and TxB2 were measured before, two and 48 hours after ingestion of either indomethacin (50 mg) or aspirin (500 mg) or of both drugs (30 minutes apart). While the inhibitory effect of indomethacin on these parameters was short lasting, that of aspirin persisted for at least 48 hours. However, when both drugs were given concurrently, the long-lasting effect of aspirin was no longer detectable. Since competition at levels other than platelets was unlikely, this study indicates that indomethacin and aspirin inhibit human platelet cyclo-oxygenase by the same basic mechanism. Acetylation of the enzyme appears to be a secondary mechanism which makes the inhibitory effect of aspirin persistent.

Adult↗
PubMed1982

Platelet function in patients on maintenance hemodialysis: depressed or enhanced?

Uremic patients on long-term hemodialysis show a paradoxical association of hemorrhages on the one hand and thrombotic complications or atherosclerosis on the other. Platelet function has been found to be depressed in some cases but enhanced in others. In 19 patients, both platelet aggregation and prostaglandin formation appeared to be significantly enhanced in response to low concentrations of arachidonic acid but significantly reduced with high concentrations. It is suggested that this double functional abnormality of uremic platelets may contribute to the complex vascular disturbances of hemodialyzed patients.

Arachidonic Acids↗
PubMed1981

Differential effects of itanoxone--a new hypolipidemic and hypouricemic drug--on platelet and vascular prostaglandin generation in rats.

Itanoxone ((chloro-2'-diphenyl)-4-oxo-4 methylene 2-butyric acid), a newly developed, hypolipidemic and hypouricemic compound with moderate anti-inflammatory activity, showed a short-lived, dose-dependent (20--200 mg/kg, orally), apparently competitive inhibition of platelet malondialdehyde (MDA), stimulated by either thrombin or arachidonic acid. Repeated doses did not result in any cumulative effect. At doses which completely blocked MDA production, itanoxone also inhibited thrombin-stimulated thromboxane B2 production in platelets but had no measurable effect on vascular prostacyclin generation. Pretreatment with itanoxone partially prevented the inhibitory effect of aspirin on both platelet and vascular prostaglandin synthesis. This suggests that itanoxone--like aspirin--acts at the level of cyclo-oxygenase but with greater selectivity on the platelet enzyme. This pharmacological activity is of great theoretical interest for the potential use of this compound as an antithrombic drug.

Animals↗
PubMed1981

Salicylate-aspirin interaction in the rat. Evidence that salicylate accumulating during aspirin administration may protect vascular prostacyclin from aspirin-induced inhibition.

Aspirin inhibits cyclooxygenase, thus preventing thromboxane A2 production in blood platelets and prostacyclin in vascular cells. Aspirin is rapidly hydrolyzed to salicylate in the circulation. The objectives of this study were (a) to evaluate whether administration of salicylate, though ineffective by itself, prevents the inhibitory effect of aspirin on platelet and/or vascular cyclooxygenase activity; (b) to verify whether salicylate accumulating in blood after aspirin administration interferes with the pharmacological activity of further doses of aspirin. Pretreatment of rats with sodium salicylate (25-100 mg/kg i.p.) resulted in dose-related prevention of the effect of a subsequent dose of aspirin (2.5-10 mg/kg i.v.) on both platelet and vascular cells. Sodium salicylate appeared to amplify the greater response of platelets to aspirin compared with vessel wall. Pretreatment of rats with repeated high doses of aspirin (200 mg/kg) resulted after 24 h in blood salicylate levels (150-200 microgram/ml) that significantly prevented the inhibitory effect of a subsequent dose of aspirin on newly synthesized vascular prostacyclin. Blood salicylate levels obtained after 36 or 48 h (less than 50 microgram/ml) were too low to blunt aspirin's effect. The interference with aspirin of its major endogenous metabolite should be borne in mind when interpreting results obtained with high dose aspirin or during repeated administration of this drug.

Animals↗
PubMed1980

Malondialdehyde formation in rat platelet-rich plasma. I.A kinetic approach.

Malondialdehyde (MDA) is a stable produce of arachidonic acid metabolism, catalyzed by the enzyme cyclo-oxygenase. The experimental conditions for measuring the kinetics of MDA formation in rat citrated platelet-rich plasma were defined. Platelets were stimulated with either arachidonic acid, the substrate of MDA, or thrombin, an enzyme which induces release of free arachidonic acid from platelet membrane phospholipids. MDA formation was almost linear for a limited period of time (between 0 and 2 min with arachidonic acid and between 1 and 3 min with thrombin) and was concentration-dependent with saturation kinetics. The hyperbolic curves obtained could be recast in linear plots (according to Woolf transformation S/V versus S) when arachidonic acid was used. With thrombin, in contrast, the highest concentration at which no MDA production could be detected (3 NIH u/ml) had to be subtracted from each concentration of the enzyme used to obtain Woolf plots. The apparent Km value of arachidonic acid was 0.49 /+- 0.09 mM and Vmax was 1.44 /+- 0.06 nmoles MDA/1.4 Z 10(9) platelets/min. The corresponding values in experiments with thrombin were 6.5 /+- 1.5 NIH u/ml and 0.233 /+- 0.012 nmoles MDA/1.4 X 10(9) platelets/min.

Animals↗
PubMed1980

Malondialdehyde formation in rat platelet-rich plasma. II. Modification of the reaction kinetics by aspirin and indomethacin in vitro.

The type of inhibition and the relative potency of aspirin and indomethacin on rat platelet malondialdehyde (MDA) formation were investigated in an in vitro system. Both drugs inhibited the production of MDA after platelet stimulation with either thrombin (10 or 25 NIH u/ml) or sodium arachidonate (0.5-2.25 mM). Inhibition by both drugs was concentration-dependent, was partially removed when platelet-rich plasma was diluted with platelet-poor plasma, was much stronger when either drug was preincubated with platelets for 10 minutes than for 1 minute and was apparently competitive when analysed by Dixon plots (1/V versus inhibitor concentrations). It is suggested that both aspirin and indomethacin may inhibit in vitro cyclo-oxygenase activity in citrated platelet-rich plasma by a similar, if not identical, partially reversible mechanism, not involving - in a first step - covalent binding of either drug to enzyme. A scheme of the interaction of both drugs with cyclo-oxygenase is presented which also takes into account the irreversible acetylation of the enzyme occurring after longer incubation times with aspirin.

Animals↗