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Biomedical subjects

J M Gerrard

Publications and source records attributed to J M Gerrard.

At least 127 records · Page 7Linked to original sources
PubMed1981

Interactions of zinc and arachidonic acid.

To probe the interaction of zinc with polyunsaturated fatty acids we have studied the effect of zinc on the cooxygenation of ferrous iron and arachidonic acid. Zinc inhibited the process of cooxygenation in a concentration dependent fashion. Further evaluation of the interaction of zinc and arachidonic acid gave spectroscopic evidence that zinc, oxygen and arachidonic acid can form an unstable hydroperoxide-like complex similar to that postulated earlier for iron, oxygen and arachidonic acid. However, in the case of zinc the complex will not proceed further to form stable peroxides and the unstable complex falls apart to give zinc and arachidonic acid intact. The findings have implications for the role of zinc in enzyme reactions and for antioxidant reactions of zinc within the cell. The influence of zinc on platelet aggregation was also evaluated. Zinc was found to inhibit cell-cell aggregation. However, in contrast to the known ability of zinc to inhibit prostaglandin synthesis in a broken cell preparation, zinc did not inhibit prostaglandin or thromboxane synthesis in the intact platelet. Inhibition of platelet aggregation by zinc must result from some other action of this cation.

Arachidonic Acids↗
PubMed1981

The endogenous lectin of human platelets is an alpha-granule component.

Platelets from patients with several bleeding disorders (congenital afibrinogenemia, Glanzmann's thrombasthenia, gray platelet syndrome, and Hermansky-Pudlak syndrome) were evaluated for both platelet-bound and platelet-free hemagglutination activities. Thrombin and A23187 activated afibrinogenemic, Hermansky-Pudlak, and thrombasthenic platelets had normal platelet-bound hemagglutination activity. Gray platelets activated by the same agents had deficient platelet-bound hemagglutination activity. In contrast, thrombin-activated afibrinogenemic, gray, and thrombasthenic platelets lacked platelet-free hemagglutination activity. Only thrombin-activated Hermansky-Pudlak platelets had a normal level of platelet-free hemagglutination activity. On the basis of these results and the distinguishing characteristics of the defective platelets, it is concluded that the alpha-granules are the origin of the enhanced hemagglutination activity. Furthermore, it is suggested that the insufficiency of the platelet-bound agglutinin may be the cause of the inability of gray platelets to aggregate normally in response to thrombin.

Blood Coagulation Disorders↗
PubMed1981

Clot retraction facilitates clot lysis.

Platelet facilitation of clot lysis was studied using the dilute clot lysis assay, a standardized assay for fibrinolysis shown to correlate with the development of postoperative deep vein thrombosis. Clots prepared from dilute platelet poor plasma showed prolonged clot lysis when compared with clots prepared in a similar fashion from dilute platelet rich plasma. Since in the presence of platelets clot retraction or contraction occurred, we evaluated a possible direct contribution of retraction to clot lysis. Dilute platelet poor plasma clots were compacted by centrifugation, to a similar extent as that achieved during clot retraction in dilute platelet rich plasma. These clots now lysed at a rate that approached that seen with dilute platelet rich plasma clots. Using an alternate alternate approach, dilute platelet rich plasma clots were treated with cytochalasin B to prevent clot retraction. Such clots now showed prolonged lysis similar to that seen with dilute platelet poor plasma. The prolonged lysis of cytochalasin B treated dilute platelet rich plasma clots was corrected by artificial compaction of the clots. The results suggest that clot retraction markedly facilitates clot lysis, and shows that a major role of platelets to facilitate clot lysis is the effect of these cells to cause clot retraction.

Blood Platelets↗
PubMed1980

Effects of 2,2'-dipyridyl and related compounds on platelet prostaglandin synthesis and platelet function.

2,2'-dipyridyl, a chelator of ferrous iron and inhibitor of platelet aggregation, was studied together with several similar compounds to determine the mechanism of their effects on platelets. All of these compounds were more potent inhibitors of arachidonic-acid-mediated aggregation (IC50, 0.17-1.8 mM) than of ADP-mediated aggregation (IC50, 7.6-19.7 mM). At low concentrations required to inhibit arachidonic-acid-mediated aggregation, 2,2'-dipyridyl, 4,4'-dipyridyl and 2-chloropyridine specifically inhibited the platelet cyclo-oxygenase. The mechanism of inhibition of ADP-induced aggregation was investigated, but was not explained. At concentrations needed to inhibit ADP-induced aggregation, 2,2'-dipyridyl did not alter cell ultrastructure, serotonin or nucleotide content or interfere with release of [14C]arachidonic acid or calcium movements. Therefore, our results indicate that 2,2'-dipyridyl and related compounds have two effects on platelets, both due to the unprotonated form. The inhibition of cyclo-oxygenase by low concentrations of these compounds is not due to bidentate iron chelation, since 4,4'-dipyridyl was almost as effective as 2,2'-dipyridyl, but is compatible with binding of these inhibitors to the iron in the heme of the cyclo-oxygenase.

2,2'-Dipyridyl↗
PubMed1980

Effect of cholesterol on production of thromboxane b2 by platelets in vitro.

We altered platelet cholesterol by incubating the cells with either "cholesterol-rich" or "cholesterol-poor" liposomes. These platelets were then used to study the influence of cholesterol content on the metabolism of arachidonic acid, a fatty acid that serves as the critical precursor in the platelet for formation of the potent aggregating agent thromboxane A2. After addition of the aggregating agent thrombin, cholesterol-enriched platelets released 18.1 +/- 0.6 per cent (mean +/- 1 S.E.M.) [14C]arachidonic acid from prelabeled platelet phospholipids. This value was higher (P less than 0.001) than that for cholesterol-depleted platelets (14.6 +/- 1.0 per cent). Conversion of released arachidonic acid to platelet thromboxane B2 (the stable end product of thromboxane A2) was also higher in cholesterol-rich platelets (22.6 +/- 3.9 per cent) than in cholesterol-depleted platelets (13.8 +/- 2.7 per cent). These studies show that changes in the cholesterol content of human platelets in vitro have a significant effect on platelt metabolism of arachidonic acid. N Engl J Med 302:6-10, 1980).

Arachidonic Acids↗
PubMed1980

Reduction of ferric heme to ferrous by lipid peroxides: possible relevance to the role of peroxide tone in the regulation of prostaglandin synthesis.

In a recent hypothesis, ferrous heme is viewed as interacting with arachidonic acid to convert it to prostaglandin G2. If this hypothesis is correct it must be possible to explain how the ferric heme in hemoglobin which is usually added to the cyclo-oxygenase enzyme to restore activity is reduced. In the present paper we explore the possibility that reduction of the heme is accomplished by lipid peroxides, to see whether such an affect could explain the regulation of cyclo-oxygenase activity by "peroxide tone." Lipid peroxides formed by auto-oxidation or arachidonic acid were found to reduce ferric heme to ferrous heme. The amount of reduction of heme was proportional to the concentration of peroxide. A result of this finding is the expansion of the earlier hypothesis to understand how functional regulation of the cyclo-oxygenase activity may be achieved.

Arachidonic Acids↗
PubMed1980

1-arachidonyl-monoglyceride causes platelet aggregation: indirect evidence for an acylglycerol acylhydrolase involvement in the release of arachidonic acid for prostaglandin synthesis.

Phosphatidylcholine liposomes containing 1-arachidonyl-monoglyceride were found to cause aggregation of human platelets. In contrast, addition of phosphatidylcholine liposomes, 1-arachidonyl-monoglyceride, or phosphatidylcholine liposomes containing I-oleoyl-monoglyceride to a similar platelet preparation had no effect. Aggregation stimulated by 1-arachidonyl-monoglyceride was inhibited by 100 microM aspirin or 1 microM indomethacin, suggesting that the arachidonic acid is first released by; a platelet acylglycerol acylhydrolase and then converted to PGG2 and thromboxane A2 which initiate the platelet aggregation. Changes in platelet morphology in response to 1-arachidonyl-monoglyceride were similar to those reported previously to occur following stimulation of platelets by arachidonic acid or PGG2 providing further support for this concept. EDTA inhibited aggregation of platelets but no shape change or granule centralization in response to 1-arach-idonyl-monoglyceride. PGE1 and theophylline inhibited both aggregation and morphological changes. These results with inhibitors are similar to the effects of these inhibitors on PGG2 and provide further evidence for similarity between the action of 1-arachidonyl-monoglyceride and PGG2. The results provide important evidence to support the concept that an acylglycerol acylhydrolase may be involved in arachidonic acid release and platelet aggregation.

Arachidonic Acids↗
PubMed1980

Epinephrine and other activators of prostaglandin endoperoxide synthetase can reduce Fe3+-heme to Fe2+-heme.

In view of recent evidence that activation of prostaglandin endoperoxide synthetase by lipid peroxides may relate to the ability of such peroxides to reduce heme, we tested other activators of this enzyme. Epinephrine, norepinephrine, ascorbic acid and tryptophan were all found to reduce Fe3+-heme to Fe2+-heme, though tryptophan was considerably weaker than the others. We suggest that reduction of heme by these compounds might account for their ability to reduce the lag phase on addition of substrate to the enzyme. Epinephrine was assessed for its effects on the lag phase in activation of soybean lipoxygenase and was found to cause a similar reduction of the lag phase of this related enzyme. These findings support the concept that reduction of Fe3+-heme to Fe2+-heme is critical to activation of both the prostaglandin endoperoxide synthetase and soybean lipoxygenase enzymes, and that mechanisms involved in regulation of the valence of iron are important for regulating enzyme activity.

Ascorbic Acid↗
PubMed1980

A hypothesis for a role for unsaturated fatty acids in electron transport and its potential application to understanding the mitochondrial respiratory chain.

Unsaturated fatty acids are required for mitochondrial oxidative phosphorylation and electron transport, though their role has not been determined. We have considered the possibility that unsaturated fatty acids might facilitate electron transfer from non-heme iron to heme iron. Unsaturated fatty acids markedly enhanced the reduction of ferric cytochrome c by ferrous iron. Neither stearic acid nor methyl arachidonic acid were effective suggesting that both a double bond and the carboxylic acid group were essential. Thus unsaturated fatty acids can directly facilitate electron transfer from non-heme iron to heme iron. We hypothesize that unsaturated fatty acids may play a similar critical role in mitochondrial oxidative phosphorylation and other biological processes where rapid electron transfer occurs.

Animals↗
PubMed1980

Biochemical studies of two patients with the gray platelet syndrome. Selective deficiency of platelet alpha granules.

The biochemistry of platelets from two unrelated patients with the gray platelet syndrome, a deficiency of platelet alpha-granules, has been evaluated. Ultrastructural studies of their platelets revealed the number of alpha-granules to be less than 15% of normal, whereas the number of dense bodies was within normal limits. Platelets from both patients had severe deficiencies of platelet factor 4 and beta-thromboglobulin (less than 10% of normal). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a marked deficiency of thrombin-sensitive protein in both patients. Analysis of the platelet-derived growth factor in one patient showed it was also markedly reduced. Levels of lysosomal enzymes, adenine nucleotides, serotonin, and catalase, and conversion of arachidonic acid by the lipoxygenase and cyclo-oxygenase enzymes, were within normal limits. The results provide important evidence to define the contents of alpha-granules and to differentiate these contents from the contents of lysosomal granules, dense bodies, and peroxisomes. Functional studies of these platelets showed deficiencies in ADP, thrombin, and collagen aggregation. The results suggest that alpha-granules or their contents make a contribution to normal platelet aggregation.

Acid Phosphatase↗
PubMed1980

Alteration in the balance of prostaglandin and thromboxane synthesis in diabetic rats.

An evaluation of platelet and vascular (aortic) arachidonic acid metabolism was performed in Lewis male rats rendered diabetic by injection of streptozotocin, and the results were compared to those in matched controls. Parameters evaluated included the release of this fatty acid from prelabeled platelets and aortas and conversion of labeled fatty acid to thromboxane B2 and 6-keto-PGF1 alpha in platelets and aortas, respectively. Diabetic rat platelets showed markedly increased release of arachidonic acid with thrombin used as the aggregating stimulus. Conversion of arachidonic acid to thromboxane B2 was slightly, but not significantly, higher in the diabetic rats. In the vessel, thrombin-stimulated release of arachidonic acid was slightly, but not significantly, increased in the diabetic animals when compared to controls. This finding was associated with a decrease in vascular production of 6-keto-PGF1 alpha both in vascular tissues incubated with arachidonic acid alone and in vascular tissues incubated with thrombin. The changes observed both in platelet and vascular metabolism of arachidonic acid were corrected by islet issue transplantation, suggesting a disease-specific effect. The changes observed in arachidonic acid metabolism suggest a significant imbalance in thromboxane A2 and PGI2 production in diabetic rats. Such changes might promote the development of the microvascular changes seen in diabetes mellitus.

Animals↗
PubMed1980

The influence of albumin and calcium on human platelet arachidonic acid metabolism.

The effects of in vitro changes in calcium and albumin on human platelet arachidonic acid metabolism were evaluated. Hypoalbuminemia enhanced the conversion of released 14C-arachidonic acid from prelabeled platelet phospholipids to the metabolites of the platelet cyclooxygenase and lipoxygenase pathways. This effect was, however, associated with a decreased release of arachidonic acid in the presence of hypoalbuminemia, such that the overall conversion of released 14C-arachidonic acid to platelet thromboxane B2 was similar in the presence of physiologic albumin concentration (3.5 g/dl) or at decreased albumin concentrations of 0.7 and 0.0 g/dl. External calcium was shown to be important for optimal platelet arachidonic acid release, with maximal release occurring at 1 mM calcium.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1980

Selective deficiency in collagen-induced platelet aggregation during L-asparaginase therapy.

Platelet aggregation studies were performed on 10 pediatric patients with acute lymphoblastic leukemia (ALL) receiving induction therapy with vincristine, prednisone, and L-asparaginase. An isolated abnormality in platelet aggregation in response to collagen was found in all patients during the course of therapy. Platelet aggregation in response to collagen normalized following the discontinuation of L-asparaginase, while patients were still on vincristine and prednisone. In contrast to the abnormal collagen response, platelet aggregation induced by epinephrine, arachidonic acid, adenosine diphosphate (ADP), and thrombin were normal both during and following therapy. In the one patient with a normal platelet count before therapy, aggregation induced by all agents was normal. This selective abnormality in collagen aggregation therefore appears to result from therapy, with the use of L-asparaginase in particular being implicated.

Asparaginase↗
PubMed1980

The influence of vitamin E quinone on platelet structure, function, and biochemistry.

Although the effects of vitamin E on platelet function have been investigated in vivo and in vitro, vitamin E quinone, a natural metabolite of vitamin E, has been virtually overlooked. This oxidized form of vitamin E inhibits platelet aggregation and secretion induced by various aggregating agents more effectively than vitamin E by a magnitude of 5-10-fold. Vitamin E and vitamin E quinone do not alter platelet ultrastructure or cellular concentrations of serotonin and adenine nucleotides, including cAMP. Inhibition of aggregation by vitamin E quinone occurs in the absence of detectable reduction of vitamin E quinone or oxidation of vitamin E and is readily reversed by washing the platelet. Only vitamin E quinone prevents arachidonic acid release and slightly inhibits cyclooxygenase, whereas both agents partially prevent calcium release from a platelet subcellular organelle. Vitamin E quinone also inhibited synthesis of prostacyclin by endothelial cells with basal synthesis in the presence of external arachidonic acid being less affected than thrombin-stimulated PGI2 production. The greater potency of vitamin E quinone in suppressing platelet function compared to vitamin E suggests that this quinone metabolite may be the better antithrombotic agent and possibly responsible for in vivo effects previously attributed to vitamin E.

Arachidonic Acids↗
PubMed1980

Effect of low dose prostacyclin infusion on blood flow in acutely ischemic canine myocardium.

The effect of low dose prostacyclin (PGI2) infusion (0.025 to 0.035 microgram/kg per min) on regional blood flow distribution in acutely ischemic left ventricular myocardium was studied in nine open-chest anesthetized dogs. Blood flow was measured using left atrial injection of "15" micron radioactive microspheres 30 minutes following ligation of one to four branches of the left anterior descending coronary artery and again 7 to 9 minutes later during continuous PGI2 infusion when mean aortic pressure was reduced by 11 mmHg (P < 0.005). Heart rate, cardiac output, left atrial and pulmonary artery pressures and coronary sinus PO2 were unchanged during PGI2 administration. PGI2 had no effect on transmural flow in either ischemic (0.32 +/- 0.05 (SE) ml/min per g) or non-ischemic (0.82 +/- 0.06 ml/min per g) myocardium. The regional distribution of blood flow in ischemic and non-ischemic myocardium was also unchanged during PGI2 administration. Specifically, ischemic tissue subendocardial flow (0.21 +/- 0.05 ml/min per g) was not increased (0.20 +/- 0.06 ml/min per g). We conclude that low dose PGI2 infusion reduces systemic pressure but has no effect on either the transumral or regional distribution of blood flow in acutely ischemic canine myocardium.

Animals↗
PubMed1980

Lysophosphatidic acids: III. Enhancement of neutrophil chemotaxis.

1-Palmitoyl-lysophosphatidic acid (LPA) was studied for its influence on the chemotaxis and ultrastructure of human neutrophils. By itself, LPA had no effect on the indices of chemotaxis or random migration of neutrophils. However, LPA on either the cellular or attractant side of Boyden chambers significantly enhanced the chemotactic responses of neutrophils to suboptimal concentrations of formyl-methionyl-phenylalanine. The enhancement of chemotaxis was achieved with concentrations of LPA (120-240 microM) that had no effect alone on neutrophil ultrastructure. The results, taken together with recent advances in knowledge of the role of the phosphatidylinositol turnover response in mediating effects of stimulating agents on cells, may provide a novel concept for understanding neutrophil chemotaxis.

Chemotactic Factors↗