Acetylenic analog of arachidonate that acts like aspirin on platelets

The effect of 5,8,11,14-eicosatetraynoic acid on endothelial cell gene expression

The endothelium plays a key role in inflammation, hemostasis and organ rejection. We report here that a synthetic polyunsaturated fatty acid, 5,8,11,14-eicosatetraynoic acid (ETYA), selectively inhibits the up-regulation of several genes on endothelial cells. ETYA suppresses endothelial cell activation by inhibiting the up-regulation of adhesion molecules like E-selectin. A runoff assay for E-selectin demonstrated that the suppression is at the level of transcription. The fact that ETYA inhibits E-selectin upon stimulation with a diverse group of stimuli like lipopolysaccharide, tumor necrosis factor-alpha or phorbol 12-myristate 13-acetate, suggests that ETYA does not exert its effect by modifying membrane-bound receptors. The messenger RNA for interleukin-8 and glyceraldehyde phosphate dehydrogenase are not affected. Pre-treatment of endothelial cells with ETYA also prevents the adherence of monocytes to tumor necrosis factor-alpha-stimulated cells.

Failure of platelets to enhance aggregation of temperature-stabilized neutrophils: effects of warming and of drugs

Polymorphonuclear leukocytes (PMNs) were isolated on a Ficoll-Hypaque gradient, suspended in modified Hank's buffer, and aggregated alone or in the presence of washed platelets (4 or 8/PMN). Platelets had no effect on formyl-methionyl-leucyl-phenylalanine (FMLP)-induced aggregation of PMNs that had been allowed to equilibrate at 37 degrees C for 5 min after storage at room temperature. Pretreatment of platelets with an inhibitor of cyclooxygenase (ASA) or lipoxygenase (nordihydroguaiaretic acid, NDGA) produced no significant effect whereas pretreatment with an inhibitor of both enzymes (eicosatetraynoic acid) or of phospholipase (methylprednisolone sodium succinate) caused a modest but statistically-significant inhibition of PMN aggregation which appeared to be a direct effect on PMNs rather than through platelets. The warming of PMNs from 0 degrees C or 22 degrees C to 37 degrees C produced a spontaneous, reversible aggregation within 2 or 3 min, the extent of which was dependent on the degree of temperature change. This aggregation was enhanced by the presence of platelets in a 'dose' (count) dependent fashion. This enhancement was not decreased by any of the aforementioned drugs, in fact, the aggregation was augmented by all drugs, the difference being statistically significant for NDGA. Thus different mechanisms appear to be involved in spontaneous vs FMLP-induced aggregation. The role of platelets in PMN aggregation remains to be elucidated but the importance of controlling for the effects of temperature changes in such studies is self-evident.

Opsonized-zymosan induces a respiratory burst in human blood platelets

Opsonized-zymosan-stimulated polymorphonuclear cells show a cyanide-insensitive oxygen consumption. We have investigated whether opsonized-zymosan could induce similar metabolic change in human blood platelets. Preparation of intact human blood platelets, obtained by separation through a Ficoll layer (23% w/v) were challenged with opsonized-zymosan. The polymorphonuclear cell contamination was less than 1/10(8) platelets. The opsonized-zymosan-stimulated platelets showed an increase of oxygen consumption. The mean of oxygen burst measured by a polarographic method with a Clark electrode was 11 nmole/10(9) platelets/min (S.E.M. 4; n = 15). The duration of the burst was 2 min. Unstimulated platelets did not show the oxygen burst. The inhibitors of respiratory chain and prostaglandin synthesis completely abolished the oxygen consumption by opsonized-zymosan-stimulated platelets. The simultaneous addition of NADH (1 mM) and opsonized-zymosan induced a burst of oxygen consumption, which occurred after a variable lag phase (10-12 min) from the stimulation, also in the presence of inhibitors. This burst, which lasted about 1 min, amounted to 10 nmole/10(9) platelets/min (S.E.M. 2; n = 15) and it was higher in the presence of NAN3, a catalase inhibitor. Zymosan treated with hydrazine or heated plasma (56 degrees C) did not cause increased oxygen consumption. Inulin or inulin-treated serum did not stimulate platelets. In these experimental conditions some NADH disappeared, as shown by isotachophoresis. The results demonstrated that an immunological stimulus may activate a membrane-linked cyanide-insensitive oxygen metabolizing system.

Differential inhibitory effects of the arachidonic acid analog ETYA on rat mast cell exocytosis evoked by secretagogues utilizing cellular or extracellular calcium

ETYA (5,8,11,14-eicosatetraynoic acid; 50-100 microM), which inhibits both cyclo-oxygenase and lipoxidase, inhibited histamine release evoked by secretagogues dependent on extracellular calcium (antigen, dextran, and concanavalin A) but failed to inhibit secretion elicited by secretagogues capable of mobilizing calcium from intracellular sites (48/80, polymyxin B, protamine sulfate and poly-L-lysine). Responses to these latter secretagogues were inhibited only by higher concentrations of ETYA (100-200 microM) that were cytotoxic. Secretion evoked by the calcium ionophore A23187 (0.1 microgram/ml) was inhibited at much lower concentrations of ETYA (1-10 microM) but this inhibition could not be overcome by increasing the concentration of calcium. Responses to higher concentrations of ionophore were not inhibited by ETYA except in amounts affecting cell viability. Like ETYA, each of several fatty acids, including arachidonic acid, were inhibitory towards histamine release evoked by A23187 or 48/80. The results indicate that EYTA acts at some early stage of stimulus-secretion coupling rather than on the final, common, calcium-activated steps of exocytosis. Moreover, this action may be unrelated to inhibition of lipoxidase or cyclooxygenase.

Role of arachidonic acid in stimulation of hexose transport by human polymorphonuclear leukocytes

Whereas insulin does not stimulate hexose transport in polymorphonuclear leukocytes, we recently reported that C5a causes the leukocytes to take up 2-[(3)H]deoxyglucose. We now find that fMet-Leu-Phe, in a concentration-related manner with an EC(50) (concentration producing 50% of stimulatory activity) of 1.2 nM, causes a 5.5-fold stimulation of deoxyglucose uptake. Moreover, arachidonic acid (5,8,11,14-eicosatetraenoic acid) similarly stimulated deoxyglucose uptake with an EC(50) of 0.6 muM. Stimulation by arachidonic acid exhibited structural specificity; five structural analogues of arachidonic acid, including arachidonyl alcohol, 8,11,14-eicosatrienoic acid, 11,14,17-eicosatrienoic acid, 5,8,11,14-eicosatetraynoic acid, and arachidic acid, did not stimulate deoxyglucose uptake. Release and metabolism of arachidonic acid may also be involved in the stimulation of deoxyglucose uptake by fMet-Leu-Phe. Inhibitors of arachidonic acid metabolism (5,8,11,14-eicosatetraynoic acid, nordihydroguaiaretic acid, indomethacin, aspirin, and benzylimidazole) caused parallel changes in the responses to both arachidonic acid and fMet-Leu-Phe. Stimulation of deoxyglucose uptake of polymorphonuclear leukocytes by chemotactic factors or arachidonic acid had the characteristics of carrier-facilitated hexose transport. The response was saturable with increasing concentrations of stimulant or substrate (deoxyglucose). It was stereospecific (inhibited by D-glucose but not by L-glucose) and was inhibited in resting and stimulated cells by 5 mug of cytochalasin B per ml. It was separable from the stimulation of oxidative metabolism; it occurred normally in polymorphonuclear leukocytes from a patient with chronic granulomatous disease (these are incapable of an oxidative metabolic response to membrane stimuli). Thus, stimulation of polymorphonuclear leukocytes is associated with enhanced hexose transport. Moreover, carrier-facilitated hexose transport and arachidonic acid metabolism may be linked, at least in these leukocytes: arachidonic acid mimies the stimulatory effects of chemotactic factors, and blockade of arachidonic acid metabolism inhibits the stimulation of hexose transport by these agents.

Involvement of bivalent cations and arachidonic acid in neutrophil aggregation

Chemotactic factors and arachidonic acid aggregate neutrophils; indomethacin and 5,8,11,14-eicosatetraynoic acid, two blockers of cellular arachidonate metabolism, inhibit these responses. Additionally, A23187, an ionophore which specifically transports bivalent cations into cells, also aggregates the neutrophils, and this response, as well as the response to chemotactic factors, requires the presence of extracellular calcium and magnesium. In this report these relationships were further studied. It was found that human neutrophil aggregation stimulated by arachidonic acid required calcium and magnesium. Furthermore, cells preincubated with arachidonate for 4 min before exposure to the bivalent cations did not aggregate before or after this exposure and, following this exposure, were refractory to subsequent stimulation by more arachidonate, a chemotactic tripeptide (formylmethionylleucylphenylalanine), or A23187, i.e., these cells had become nonselectively desensitized to the aggregating agents. Finally, indomethacin and 5,8,11,14-eicoasatetraynoic acid inhibited the aggregation response stimulated by A23187 and their potency in doing so paralleled their potency in inhibiting the responses induced by arachidonate or the chemotactic tripeptide. Thus, the neutrophil aggregation responses induced by arachidonate, chemotactic factor, and A23187 were similarly influenced by preincubating the cells with arachidonate, had similar requirements for calcium and magnesium, and were similarly inhibited by blockers of arachidonate metabolism. It appears that bivalent cations and arachidonic acid play essential and, perhaps, interacting roles in the aggregation response to diverse stimuli.

Prostaglandins, platelets, and atherosclerosis

Metabolism of arachidonic acid (AA) in blood platelets and in vascular endothelium does not lead to prostaglandins, but thromboxane A2 and prostacyclin are generated. These labile metabolites of AA antagonize each other: thromboxane A2 is a vasoconstrictor and proaggregatory agent, whereas prostacyclin dilates arteries, prevents platelets from aggregation, and dissipates the preformed platelet clumps. Prostacyclin is a powerful stimulator of adenylate cyclase in platelets and therefore its antiplatelet action is potentiated by phosphodiesterase inhibitors such as theophylline or dipyridamole. Cyclo-oxygenase of AA is inhibited by aspirin, thromboxane synthetase by analogues of prostaglandin endoperoxides, and prostacyclin synthetase by linear lipid peroxides. A hypothesis is put forward that atherosclerosis develops because of pathological, nonenzymic lipid peroxides. A hypothesis is put forward that atherosclerosis develops because of pathological, nonenzymic lipid peroxydation in the body and the subsequent molecular damage to prostacyclin synthetase in the rheologically determined areas of arterial walls. Endothelium deprived of prostacyclin is the basis for microthrombi formation, and follows a sequence of events described by Rokitansky and later by Ross. Prostacyclin is also a circulating hormone which is generated by the lungs. Thereby a damage of this "endocrine gland" by respiratory disorders, air pollution, or tobacco smoking are likely to contribute to pathogenesis of atherosclerosis, myocardial infarction, and arterial thromboembolism. Pharmacological treatment and prevention of these diseases should logically include antioxydants, prostacyclin and its analogues, thromboxane synthetase inhibitors and perhaps cyclooxygenase inhibitors (aspirin ?). Prostacyclin was already infused intravenously to men and its powerful antiaggregatory and deaggregatory actions were demonstrated. These properties of prostacyclin along with its vasodilator and positive inotropic actions destine this hormone to be a new type of antithrombotic drug in acute myocardial infarction.

Arachidonic acid aggregates neutrophils

Arachidonic acid, but not several structurally similar fatty acids, stimulated neutrophils in suspension to aggregate; this effect was blocked by 5, 8, 11, 14-eicosatetraynoic acid, an inhibitor of arachidonic acid metabolism. Analagous to platelets, arachidonate may be a precursor of active metabolites which mediate neutrophil responses.

Role of arachidonic acid derivatives in neutrophil aggregation: a hypothesis

Chemotactic substances stimulate neutrophils in suspension to aggregate. Arachidonic acid (but not several structurally related fatty acids) induces a similar neutrophil response. We now report that two blockers of arachidonic acid metabolism, indomethacin and 5,8,11,14-eicosatetraynoic acid, inhibit this arachidonic acid-mediated response. Moreover, both blockers also inhibit aggregation stimulated by a synthetic chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine, and their potency in doing so parallels their potency in inhibiting the response to arachidonic acid. These results suggest that metabolites of arachidonic acid may stimulate certain neutrophil functions and be involved in cellular responses to at least some chemotactic substances.

Proposed metabolic dysfunctions in diabetic microthromboses and microangiopathy

This report describes, at least in part, the role of prostaglandin and cyclic nucleotide metabolism in the etiology of the vascular disease associated with diabetes mellitus. Alterations in this metabolism seem associated with induction of platelet aggregation leads to microthromboses leads to microangiopathy sequences that are subtle but inexorable over a long period of time. Prostaglandins are generally elevated in blood from patients having frank signs of diabetic retinopathy when compared with nondiabetic subjects. Prostaglandin concentration remained elevated in diabetic retinopathy patients receiving indomethacin. We formed, therefore, the working hypothesis--yet to be fully tested either in patients or animal models with and without indomethacin treatment--that the increased prostacyclin (synthesized by endothelial microsomes) and cyclic-AMP production, both of which favor prevention of platelet aggregation, accompany the increased concentration of one or more of the prostaglandin E and F compounds. Concurrently, there may be an accompanying reduction of thromboxane A2 (synthesized by platelet microsomes) and cyclic-GMP (both of which favor platelet aggregation) production in the diabetic patients. The elevated prostaglandin in the diabetic patients not receiving indomethacin could possibly be directed toward slowing but not preventing the progression of the complex disease process in diabetes.

The effect of 5,8,11,14-eicosatetraynoic acid on lipid metabolism

The purpose of this presentation is to review the current state of knowledge regarding 5,8,11,14-eicosatetraynoic acid (ETYA, Ro 3-1428) and its effects on lipid metabolism. Accordingly, the topics discussed include hypocholesterolemic and dermatological studies involving ETYA in both animals and man, as well as the effects of ETYA on desaturase enzymes. Metabolic studies involving ETYA are also noted. Primary interest is focused on the effects of ETYA on selected processes of arachidonate metabolism, and the effect of ETYA on inflammation, platelet aggregation and tumor growth are discussed, keeping in mind the relevance of arachidonate metabolism to these processes.

Synthesis of thromboxane A2 by non-aggregating dog platelets challenged with arachidonic acid or with prostaglandin H2

Dog platelets challenged with arachidonic acid fail to aggregate but synthesize a substance which aggregates rabbit and human platelets, this aggregation being suppressed by dibutyryl cyclic AMP. The aggregating substance contracts strips of rabbit aorta and of coeliac and mesenteric arteries, is soluble in diethyl ether, has a half-life of about 40 seconds at 37 degrees C and of 100 seconds at 22 degrees C. Its generation is blocked by various inhibitors of prostaglandin biosynthesis. The thromboxane A2 synthetase inhibitor imidazole and its analogue benzimidazolamine also suppress generation of vessel contracting activity in incubates of dog platelets and prostaglandin H2. Since dog platelets also transform prostaglandin H2 into thromboxane A2 their failure to aggregate, when stimulated by arachidonic acid or by prostaglandin H2, is not due to lack of thromboxane synthesizing ability.

Acute anti-inflammatory effects of aspirin and dexamethasone in rats deprived of endogenous prostaglandin precursors

Paw oedema, induced by carrageenan, was potentiated in normal rats by arachidonic acid and bishomo-gamma-linoleic acid, but not by 5,8,11-eicosatrienoic acid. The latter is not an endogenous prostaglandin precursor, but replaces the other two in essential fatty acid deficient (EFAD) rats. Carrageenan oedema was partially suppressed in these EFAD rats. Aspirin exhibited equal suppression of carrageenan oedema in both normal and EFAD rats, despite the fact that, in the latter, prostaglandins are of negligible importance. The anti-inflammatory effect of dexamethasone was also identical in both normal and EFAD rats. The view that interference with the prostaglandin-system explains the acute anti-inflammatory effects of the two drugs, is discussed, in relation to the present results.

Adenine nucleotide metabolism of blood platelets. IX. Time course of secretion and changes in energy metabolism in thrombin-treated platelets

Changes in the energy metabolism of washed human platelets were compared with the kinetics of secretion induced by thrombin (5 units/ml). A 50% decrease in the level of metabolic ATP (3H-labelled), which was essentially complete in 30s, was matched in rate by adenine nucleotide secretion from storage in dense granules. Incubation of platelets with antimycin before thrombin addition increased the rate of fall in metabolic ATP, but did not affect the rate of adenine nucleotide secretion. beta-N-Acetylglucosaminidase secretion, which was slower than adenine nucleotide secretion in control platelets, was noticeably inhibited by antimycin, confirming previous reports that different regulatory mechanisms exist for dense and alpha-granule secretion. The rates of rephosphorylation of metabolic ADP to ATP via glycolysis and oxidative phosphorylation were estimated by measuring lactate production and O2 consumption in resting and thrombin-stimulated platelets and compared to the level of metabolic ATP (9-10 nmol/mg of platelet protein in the resting state). The rate of ATP production was stimulated at least two fold from 12 nmol to 24 nmol/min/mg within seconds of thrombin addition. This increased rate was maintained over the observed period of 5 min although the level of metabolic ATP had decreased to 4-5 nmol/mg within 30 s; the turnover of the remaining metabolic ATP thus increased four fold over the resting state although the actual stimulation of energy production was only two fold.

Inhibition of prostaglandin biosynthesis by triynoic acids

Prostaglandin biosynthesis from eicosa-8,11,14-trienoic acid in microsomes from bovine seminal vesicles is inhibited by acetylenic acids. Octadeca-6,9,12-triynoic acid and eicosa-8,11,14-triynoic acid are the most potent inhibitors. These acids both contain an omega-8 methylene group. Within the 20-carbon acetylenic acid series, inhibition decreases in the sequence eicosa-8,11,14-triynoic acid greater than eicosa-7,10,13-triynoic acid greater than eicosa-5,8,11-triynoic acid. Furthermore, eicosa-8,11,14-triynoic acid is a more potent inhibitor of arachidonic acid induced platelet aggregation than either eicosa-7,10,13-triynoic acid or eicosa-5,8,11-triynoic acid. The omega-8 methylene group is not the only determinent of inhibitory potency since docosa-10,13,16-triynoic acid is less potent than its 18 and 20 carbon analogs and all of these acids have an omega-8 methylene group.

Alpha-tocopherol: its inhibition on human platelet aggregation

Alpha-tocopherol inhibits human platelet aggregation induced by arachidonate sodium, collagen, epinephrine, adenosine diphosphate or thrombin - arachidonate sodium being the most susceptible. The second phase of the biphasic platelet aggregation induced by epinephrine or adenosine diphosphate is preferentially inhibited.

Effect of eicosa-5, 8, 11, 14-tetraynoic acid on fatty acid composition of selected organs in the rat

Eicosa-5, 8, 11, 14-tetraynoic acid or archidonic acid or no supplement (controls) was given orally to rats maintained on a fat free diet and the fatty acid composition of total lipids of several organs determined. No changes were noted in the total fatty acid concentrations of the organs examined in the various groups. A decrease in the amount of arachidonic acid, 22:4omega6 and 22:5omega 6 (as percent of total fatty acids), and an increase in the amount of 20:3omega6 and linoleate were observed in total lipids of several organs. In the group receiving the arachidonate supplement, there was less linoleate and 20:3omega 6 and more archidonate than in the controls. Both eicosa-5, 8, 11, 14-tetraynoic acid and arachidonate supplements resulted in a decrease in 20:3omega9 in most organs studied. Generally, the most marked changes were seen in liver but, of the other organs examined (heart, kidney, testis, brain, and adrenals), only the adrenals failed to show any significant differences between the controls and each of the two supplemented groups. Although the experimental conditions preclude conclusive interpretation of the changes observed, it is suggested that eicosa-5, 8, 11, 14-tetraynoic acid was effective in inhibiting the conversion of linoleate to archidonate and the conversion of arachidonate to 22:4 and 22:5.

Prostaglandin E2 potentiation of platelet aggregation induced by LASS endoperoxide: absent in storage pool disease, normal after aspirin ingestion

Patients with storage pool disease and normal subjects who ingest aspirin show diminished collagen-induced platelet aggregation and an absent second wave of aggregation with ADP or adrenaline. These 'second-phase' aggregation responses are thought to be mediated by cyclic endoperoxide ('labile aggregation stimulating substance', LASS) that is derived from arachidonic acid and is the precursor of prostaglandin E2 (PGE2) and PGE2alpha. Furthermore, although PGE2 does not directly aggregate platelets, it markedly potentiates LASS-induced aggregation. The platelets of six patients with storage pool disease were capable of converting arachidonic acid to LASS, but the potentiation of LASS-induced aggregation by PGE2 was markedly diminished. In contrast, PGE2-potentiation of LASS aggregation was not reduced after aspirin ingestion. The effects of aspirin can be attributed entirely to its ability to block the enzymatic conversion of arachidonic acid to LASS and PGE2. These findings explain why a mutual correction of the aggregation defects is often seen when aspirin-treated platelets are mixed with storage pool-deficient platelets. This is because 'aspirin platelets' aggregate to the mixture of LASS and PGE2 produced by the storage pool-deficient platelets, which are themselves unresponsive. The findings in storage pool disease support previous conclusions that prostaglandin sensitization of platelets to the pro-aggregatory effects of LASS is an important factor in irreversible aggregation, and could be clinically important.

The antipyretic effect of indomethacin

1. Several possible mechanisms of the antipyretic action of indomethacin administered cat. 2. Indomethacin did not decrease bacterial endotoxin-induced release of endogenous pyrogen in vivo. 3. Indomethacin (5-40 mug/kg) inhibited the pyrogenic effect of peripherally or centrally administered leucocytic progen. A dose of 10 mug/kg caused a parallel shift to the right of the log dose-response curve for I.V. leucocytic pyrogen and reduced the potency of the pyrogen at least 50%. 4. Incubation of leucocytic pyrogen with indomethacin did not alter its pyrogenic potency. 5. Indomethacin exerted only a slight non-dose-related hypothermic effect in afebrile animals. 6. Indomethacin (up to 1 mg/kg) did not diminish the hyperthermic response to intraventricular administration of prostaglandin E1. 7. This pattern of activity indicates that indomethacin acts centrally to inhibit an effect of leucocytic pyrogen.

Stimulus-secretion coupling in platelets. Effects of drugs on secretion on adenosine 5'-triphosphate

The mechanism of stimulus-secretion coupling in platelets was investigated by observing the effects of drugs on the kinetics on ATP secretion induced by either thrombin or the divalent cation ionophore A23187. The actual secretion is the same with either of these agents, since the rate constants and activation energies of secretion are the same and since drugs that affect the final, enzyme-independent steps of thrombin-induced secretion have the same effect on ionophore-induced secretion. Drugs that affect early steps of thrombin-induced secretion have no effect on ionophore-induced secretion. Drugs that act through cAMP (PGE1, theophylline, dibutyryl-cAMP) slow an early step in the mechanism of thrombin-induced secretion and completely block at higher levels, with the required concentration of inhibitor dependent on thrombin concentration. The inhibition of rate appears to be all-or-none, with no intermediate rates observed. By replacing thrombin with trypsin, which makes it possible to observe a complete change in rate-determining step from an enzyme-dependent to an enzyme-independent platelet step, it was found that these drugs slow the rate only when the enzyme-independent step is rate determining. These drugs have no effect on A23187-induced secretion. It was concluded that cAMP inhibits at a step after the enzyme step but before the final step by interfering with transmission of the stimulus-secretion coupling signal. Disruption of microfilament function by cytochalasin B (10 muM) accelerates the rate of secretion induced by either thrombin or ionophore. The microtubule agents colchicine, vinblastine, and vincristine had effects only at concentrations above those usually considered necessary for the specific inhibition of microtubule function. Drugs that inhibit prostaglandin synthesis (aspirin, indomethacin, eicosatetraynoic acid), drugs that block ATP production (antimycin A, deoxyglucose), or several other drugs previously reported to inhibit platelet function had no effect on secretion.

Prophylactic administrations of aspirin for the prevention of thrombo-embolic complications in postoperative reactive thrombocytosis

Hyperfunctioning platelets in the thrombocytotic patients after major surgery were satisfactorily controlled by a small dose of aspirin ingestion. Since aspirin is well documented as a potent inhibitor of platelet aggregation, a small dose of prophylactic administration of aspirin appeared to be a legitimate approach to a possible life-threatening thrombo-embolic complication after surgery, particularly when the platelets are excessively produced and hyperfunctioning.

An enzymatic mechanism for the antithrombotic and antihemostatic actions of aspirin

Aspirin-type drugs may inhibit irreversible clumping of human blood platelets by blocking the enzymatic conversion of arachidonic acid to a hitherto undiscovered factor, labile aggregation-stimulating substance, which triggers aggregation and to prostaglandin E(2), which sensitizes the platelets to its aggregatory effects.