Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We wished to determine whether the metabolism of arachidonic acid, through lipoxygenase and cytochrome P-450 pathways, is involved in production of endothelium-derived relaxing factor(s) (EDRFs) in canine femoral veins. Veins were removed from anesthetized dogs and cut into rings. Endothelium was deliberately removed from some rings. In separate sets of experiments, rings were incubated with either AA861 (10(-5) M) or TMK777 (10(-6) M), inhibitors of 5-lipoxygenase, nordihydroguaiaretic acid (NDGA 3 x 10(-6) M), an inhibitor of lipoxygenase or proadifen (SKF 525A, 10(-6) M), an inhibitor of cytochrome P-450. In addition, some rings were incubated with a combination of indomethacin (10(-5) M) and NG-monomethyl-L-arginine (L-NMMA 10(-4) M) or, where appropriate, a solvent control. Concentration-response curves were obtained for acetylcholine, adenosine diphosphate, thrombin, A23187, and nitric oxide in rings contracted with a submaximal concentration of prostaglandin F2 alpha. AA861 and TMK777 did not alter endothelium-dependent relaxations to the agonists, whether with or without indomethacin and L-NMMA. However, indomethacin plus L-NMMA reduced endothelium-dependent relaxations to thrombin. These results suggest that metabolism of arachidonic acid, through lipoxygenase and cytochrome P-450 pathways, does not produce an EDRF in veins. However, thrombin receptor-activated relaxations are mediated in part by products of the cyclooxygenase pathway and nitric oxide.
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PMID:Role of lipoxygenase and cytochrome P-450 in production of endothelium-derived relaxing factors in canine femoral veins. 127 84

1. Peritoneal mast cells from rat were co-incubated in vitro in a platelet aggregometer cuvette with washed rabbit platelets. In response to stimulation with calcium ionophore (A23187; 1-5 microM), the mast cells released a substance which stimulated the platelets to aggregate. These concentrations of ionophore did not stimulate platelet aggregation in the absence of mast cells, nor affect the responsiveness of the platelets to aggregation induced by thrombin or PAF. Release of a PAF-like substance was also observed in response to stimulation of the mast cells with antigen. 2. This pro-aggregatory activity is attributable to the release of PAF by the mast cells, since the activity could be abolished by preincubating the platelets with a specific PAF receptor antagonist (WEB 2086; 10 microM). Furthermore, the platelet-aggregating factor co-migrated with PAF on thin-layer chromatographs and could be abolished by incubation with phospholipase A2 (20 micrograms ml-1) or a specific antibody directed against PAF. 3. The release of PAF by peritoneal mast cells could be inhibited, in a concentration-dependent manner, by PF-5901 (IC50 of 3.9 microM) or Wy-50,295 (IC50 of 1.2 microM), two structurally similar compounds with inhibitory effects on leukotriene synthesis, as well as leukotriene D4 (LTD4) receptor antagonist properties. 4. Inhibition of PAF synthesis was not observed when the mast cells were incubated with a structurally unrelated 5-lipoxygenase inhibitor (A-64077), a structurally dissimilar inhibitor of 5-lipoxygenase activating protein (MK-886) or with a structurally related LTD4 receptor antagonist (MK-571) which lacks inhibitory effects on leukotriene synthesis, each at concentrations of up to 100 microM.5. Neither PF-5901 nor Wy-50,295 (1 or 10 microM) significantly affected histamine release or prostaglandin D2 synthesis by peritoneal mast cells in response to calcium ionophore stimulation.6. These results demonstrate the ability of a class of quinoline-based compounds to inhibit PAF synthesis by peritoneal mast cells. This activity does not appear to be related to effects of these compounds on leukotriene synthesis or LTD4 receptors. The ability of these compounds to inhibit PAF synthesis may contribute to their anti-inflammatory properties.
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PMID:Platelet-activating factor synthesis by peritoneal mast cells and its inhibition by two quinoline-based compounds. 159 92

We have previously demonstrated that clotting of whole human blood in vitro not only triggers the production of thromboxane (TX) B2 but is also accompanied by formation of 5-lipoxygenase-derived cysteinyl-leukotrienes (LT). In order to further characterize the mechanisms leading to activation of the cysteinyl-LT production, we have now investigated the effects of thrombin on cysteinyl-LT as well as TXB2 formation in whole human blood. Addition of exogenous human alpha-thrombin (0.1 - 3.0 U/ml) to whole human blood incubated in vitro led to a concentration- and time-dependently increased release of TXB2 into the serum samples. The serum contents of cysteinyl-LT were, however, not significantly affected. Inactivation of endogenously generated thrombin by inhibitors such as recombinant hirudin (HBW 023, 0.43 - 1.43 microM) or the peptidyl chloromethyl ketone, D-Phe-Pro-Arg-CH2Cl (1.0 - 100 microM) concentration- and time-dependently inhibited the release of TXB2 into the serum or plasma samples. In contrast, however, serum contents of cysteinyl-LT remained unchanged. The identity of immunoreactive material was confirmed by thin-layer chromatography of immunoreactive TXB2 and by reversed phase HPLC of immunoreactive cysteinyl-LT. As expected, washed human platelets stimulated with alpha-thrombin were identified as the major source of TXB2 generation but purified monocytes were also found to release some TXB2 upon alpha-thrombin stimulation. Release of TXB2 by isolated human polymorphonuclear leukocytes (PMN) was negligible in the presence of this stimulus. None of the cells which are known to possess 5-lipoxygenase activity such as PMN or monocytes did release neither cysteinyl-LT nor LTB4 upon stimulation with human alpha-thrombin up to 10 U/ml. These data demonstrate that TXB2 production and cysteinyl-LT formation are differentially activated in spontaneously clotting whole human blood in vitro, the former being dependent on endogenously generated thrombin the latter being dependent on a stimulus yet to be identified.
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PMID:Thromboxane and cysteinyl-leukotriene formation are differentially activated in spontaneously clotting whole human blood in vitro. 186 9

We examined the mechanism of the neutrophil (PMN)-dependent increase in pulmonary vascular permeability to protein after thrombin-induced pulmonary microembolism. Humoral factors that activate PMNs after thrombin-induced pulmonary microembolism were characterized in pulmonary lymph obtained from unanesthetized sheep challenged with intravenous infusion of alpha-thrombin. Time-dependent increases in PMN migration, aggregation, and superoxide anion (O2-) generation were induced by the pulmonary lymph obtained within 20 minutes after thrombin infusion. The pulmonary lymph neutrophil activating factors present in ether extracts of lymph had retention times of leukotriene B4 (LTB4) and monohydroxyeicosatetraenoic acids (HETEs) by high-performance liquid chromatography. The postthrombin lymph samples containing the LTB4 and HETEs increased PMN O2- generation and endothelial monolayer permeability to 125I-albumin in the presence of PMNs layered on the endothelial monolayers. Control lymph samples replete with LTB4, 5-HETE, and 15-HETE induced increases in PMN O2- generation and endothelial monolayer permeability to 125I-albumin in the presence of PMNs layered on the endothelial monolayers. Maximal increases in PMN O2- production and endothelial permeability occurred when LTB4, 5-HETE, and 15-HETE were coincubated with PMNs, indicating a synergistic action of these mediators in inducing PMN activation. Endothelial monolayer permeability to 125I-albumin did not increase with postthrombin lymph samples obtained after pretreatment with the 5-lipoxygenase inhibitor, L-651,392. The results indicate that lipoxygenase products generated in the lungs after thrombin-induced microembolism contribute to increased endothelial permeability secondary to PMN activation.
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PMID:Lipoxygenase products induce neutrophil activation and increase endothelial permeability after thrombin-induced pulmonary microembolism. 249 95

The effect of dilazep (tetrahydro-1H-1,4-diazepine-1,4(5H)-dipropanolbis(3,4, 5-trimethoxy-benzoate)dihydrochloride monohydrate, Comelian), a coronary and cerebral vasodilator and an anti-platelet agent, on endogenous and exogenous arachidonic acid (AA) metabolism by human neutrophils and platelet/neutrophil interactions was studied in vitro. Neutrophils preincubated with dilazep (up to 300 mumol/l) were incubated with the Ca ionophore A23187 in the absence or presence of AA. Platelet/neutrophil mixtures preincubated with dilazep (up to 100 mumol/l) were incubated with thrombin plus N-formylmethionylleucylphenylalanine (FMLP), FMLP plus AA, and platelet-activating factor (PAF) plus AA. AA metabolites including leukotriene B4 (LTB4), 5-hydroxyeicosatetraenoic acid (5-HETE) and 5S,12S-dihydroxyeicosatetraenoic acid (5S,12S-DiHETE) were analyzed and quantitated by reversed-phase high-performance liquid chromatography. The formation of LTB4 and 5-HETE from endogenous AA by neutrophils was inhibited by dilazep, whereas their production from exogenous AA was enhanced. LTB4 synthesis from endogenous AA by platelet/neutrophil interactions was inhibited by dilazep, while 5S,12S-DiHETE production was increased. The production of 5-lipoxygenase metabolites from exogenous AA by these interactions was increased by this drug. Thus, dilazep inhibits endogenous AA metabolism by neutrophils and by platelet/neutrophil interactions, whereas it stimulates exogenous AA metabolism by these blood cells and their interactions.
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PMID:Effects of dilazep on arachidonic acid metabolism by neutrophils and platelet/neutrophil interactions. 251 Jul 45

Human platelets were incubated alone or in whole blood with specific agonists such as thrombin or collagen, and 12-hydroxy-heptadecatrienoic (HHT) and 12-hydroxy-eicosatetraenoic (12-HETE) acids were measured by HPLC as indices of platelet cyclooxygenase and lipoxygenase activities, respectively. We found that both arachidonic acid metabolites are significantly formed at concentrations of thrombin insufficient to provoke platelet aggregation. The ratio HHT/12-HETE varied with increasing concentrations of thrombin, with an increase in the absence and a decrease in the presence of albumin in the incubation. When platelets were stimulated in whole blood, this ratio favoured HHT and the addition of albumin to isolated platelets had the same effect. The formation of oxygenated products of 12-HETE by leukocyte LTB w-hydroxylase and 5-lipoxygenase in unstimulated and stimulated leukocytes, respectively, was also investigated. We failed to detect any significant amounts of these products in whole blood incubated with relatively high concentrations of collagen in the presence or absence of the chemotactic peptide FMLP. We conclude that, although 12-HETE is a good substrate for leukocyte oxygenases when incubated at high concentration with the cells alone, its oxygenation is unlikely to occur in whole blood, making 12-HETE and/or HHT potential markers of platelet activation in vivo, provided they are not substantially degraded during passage of the blood through various organs.
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PMID:Metabolism of endogenous arachidonic acid in weakly activated platelets. Absence of leukocyte cooperative products in whole blood. 251 43

Using radioimmunoassay techniques we studied the formation of the 5-lipoxygenase-derived cysteinyl-leukotrienes (LT) in comparison to the cyclooxygenase product thromboxane (TX) B2 in whole human blood allowed to clot at 37 degrees C in vitro. Spontaneous clotting resulted in a time-dependent release of smaller amounts of cysteinyl-LT as well as release of large amounts of TXB2 into the serum. Cysteinyl-LT were characterized by their immunoreactive behaviour and their biological activity in the guinea pig ileum bioassay, an effect which could be antagonized by the SRS-A antagonist FPL 55712 (0.38 microM). By reversed phase HPLC cysteinyl-LT in the serum were identified as a mixture of LTC4, LTD4 and LTE4. At 90 and 120 min part of the immunoreactive material consisted of the omega-oxidized metabolite 20-OH-LTE4. Almost complete inhibition of cyclooxygenase activity by indomethacin (2.8 microM) did not affect cysteinyl-LT formation by clotting whole human blood in vitro nor did activation of platelets by compounds such as the TX mimetic U 46619 (10 microM), platelet-activating factor (PAF, 1 microM) or thrombin (3 IU/ml). In contrast, the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 microM), the Ca2+-chelating anticoagulants trisodium citrate (10 microM) and edetate disodium (EDTA, 5.4 mM) as well as the functionally unrelated heparin (20 IU/ml) significantly inhibited the formation of cysteinyl-LT as well as of TXB2. Thus, an event related to the process of clotting of whole human blood appears to be able to induce cysteinyl-LT formation in amounts which might be functionally relevant during thromboembolic events.
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PMID:Clotting of whole human blood induces cysteinyl-leukotriene formation. 254 55

Heat shock has a profound influence on the metabolism and behavior of eukaryotic cells. We have examined the effects of heat shock on the release from cells of arachidonic acid and its bioactive eicosanoid metabolites, the prostaglandins and leukotrienes. Heat shock (42-45 degrees) increased the rate of arachidonic acid release from human, rat, murine, and hamster cells. Arachidonate accumulation appeared to be due, at least partially, to stimulation of a phospholipase A2 activity by heat shock and was accompanied by the accumulation of lysophosphatidyl-inositol and lysophosphatidylcholine in membranes. Induction of arachidonate release by heat did not appear to be mediated by an increase in cell Ca++. Stimulation of arachidonate release by heat shock in hamster fibroblasts was quantitatively similar to the receptor-mediated effects of alpha thrombin and bradykinin. The effects of heat shock and alpha thrombin on arachidonate release were inhibited by glucocorticoids. Increased arachidonate release in heat-shocked cells was accompanied by the accelerated accumulation of cyclooxygenase products prostaglandin E2 and prostaglandin F2 alpha and by 5-lipoxygenase metabolite leukotriene B4. Elevated concentrations of arachidonic acid and metabolites may be involved in the cytotoxic effects of hyperthermia, in homeostatic responses to heat shock, and in vascular and inflammatory reactions to stress.
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PMID:Heat shock stimulates the release of arachidonic acid and the synthesis of prostaglandins and leukotriene B4 in mammalian cells. 255 53

Thrombin, a highly specific coagulation factor, can rapidly trigger lysozyme release from human neutrophils without concomitant activation of the 5-lipoxygenase pathway. This activation was not dependent on the presence of extracellular calcium. Since thrombin also induces the release of hemostatic and inflammatory metabolites from platelets and mast cells, it is proposed that it plays a significant role in amplification of the inflammatory response.
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PMID:Thrombin-induced calcium-independent degranulation of human neutrophils. 309 81

Opsonized zymosan is able to induce polymorphonuclear leucocyte activation as reflected by lysosomal degranulation and light emission. However this stimulus is a weak inducer of arachidonic acid metabolism in these cells. We have studied the effects of co-incubation of polymorphonuclear leucocytes and platelets, each of them exposed with its specific stimulus (i.e. opsonized zymosan and thrombin). The granule constituent release was enhanced in the presence of activated platelets, but not the chemiluminescence. The same results were found in time-course experiments. Another important effect of this co-incubation was the potentiation of the synthesis of 5-lipoxygenase metabolites of arachidonic acid by activated platelets. The in vitro study of cellular cooperation may be of great interest in evaluating the role of the messenger processes occurring from one cell to another.
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PMID:Activated platelets stimulate human neutrophils functions. 405 48


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