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R W Colman

Publications and source records attributed to R W Colman.

At least 145 records · Page 8Linked to original sources
PubMed1993

Thrombin- and cathepsin G-induced platelet aggregation: effect of protein kinase C inhibitors.

Two serine proteases, thrombin and cathepsin G, are potent agonists of human platelet activation. These pathophysiological proteases induce similar platelet responses, e.g., aggregation, shape change, and secretion of the dense granules. Maintenance of proteolytic function and the ability to bind to receptors on the platelet surface membrane are required for the responses elicited by both proteases. Protein kinase C (PKC) is a signal-transducing enzyme that is an important regulator of postreceptor intracellular changes following exposure of platelets to thrombin and cathepsin G. Inhibitors of purified PKC, e.g., staurosporine and calphostin C, have been frequently used to elucidate biochemical mechanisms mediated by the intracellular PKC following platelet activation by proteases. However, the effect of the PKC inhibitors on the amidolytic activity and on the ability of the two bioregulatory proteases to bind to cells has never been investigated. We found that staurosporine (1 and 1.5 microM), calphostin C (10 and 60 microM), and fisetin (200 and 220 microM), the three most commonly used and biochemically well-characterized inhibitors of purified PKC, completely inhibited thrombin-induced (2 nM) and cathepsin G-induced (0.85 microM) aggregation of washed human platelets, respectively. Each of the three PKC inhibitors completely blocked platelet shape change induced by thrombin (1 nM). Only fisetin inhibited platelet shape change induced by cathepsin G (0.5 microM). Only fisetin partially inhibited amidolytic activity of thrombin. The three PKC inhibitors had no inhibitory effect on the amidolytic activity of those concentrations of cathepsin G that cause maximum platelet aggregation and platelet shape change. The three PKC inhibitors completely blocked binding of 125I-thrombin to washed platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaloids↗
PubMed1993

Factor XII activation and inhibition in inflammation.

Biochemical observations during clinical sepsis using functional and immunological measurements of enzymes, cofactors and inhibitors of the kallikrein-kinin system indicate that activation of these proteases occur during hypotensive gram-negative septicemia and adult respiratory distress syndrome. Using animal models of septicemia, we demonstrated that protease inhibitors or neutralizing monoclonal antibodies to proteins of the contact system inhibit or prevent the formation of kallikrein and the decrease in kininogen. In addition, the irreversible phase of hypotension can be prevented and survival prolonged. Thus, bradykinin is one of the important mediators of hypotension. In contrast, the contact system plays little role in the associated DIC. In cardiopulmonary bypass, the formation of kallikrein leads to neutrophil degranulation and release of elastase. Selective inhibitors of kallikrein not only block its activation but play a predominant role in inhibiting elastase release.

Animals↗
PubMed1993

Tissue factor is expressed on monocytes during simulated extracorporeal circulation.

Certain forms of extracorporeal circulation exemplified by cardiopulmonary bypass require continuous high-dose anticoagulation to prevent thromboembolic complications. We hypothesized that monocytes may be stimulated to express tissue factor (TF) during prolonged simulated extracorporeal circulation. TF was identified both by flow cytometry by using three TF-specific monoclonal antibodies and functional assay of procoagulant activity (PCA). TF significantly increased between 2 and 6 hours of simulated extracorporeal circulation by both analyses. Relative fluorescence on monocytes increased from a control value of 100 to 313 +/- 79 on cells from the simulated extracorporeal circuit (p < 0.05). PCA increased from 21 +/- 8 to 775 +/- 326 pg TF/10(6) monocytes (p < 0.05) and was blocked 99.6% by preincubation of cells with a mixture of monoclonal antibodies to TF. By 6 hours, the number of leukocytes in the circuit was decreased by 43%. The cells were recovered from the oxygenator membrane by washing with EDTA. Compared with initial values, by 6 hours, both TF antigen at 378 +/- 90 (p < 0.05) and PCA at 1,357 +/- 280 pg TF/10(6) monocytes (p < 0.01) were highest in the recovered cells. Cells incubated for 6 hours and not subjected to simulated extracorporeal circulation did not increase TF. Examination of monocytes for the adhesive receptor CD11b/18 (Mac-1) paralleled TF expression, providing an additional putative receptor for the coagulant proteins, factor X and fibrinogen or fibrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigens, CD↗
PubMed1993

The contact system contributes to hypotension but not disseminated intravascular coagulation in lethal bacteremia. In vivo use of a monoclonal anti-factor XII antibody to block contact activation in baboons.

The hypotension and disseminated intravascular coagulation (DIC) in bacteremia is thought to be mediated by the combined actions of cytokines, prostaglandins, and complement. The contact system, via the release of bradykinin and the activation of Factor XI, has been postulated to be contributing to the observed hypotension and DIC. Using a mAb to Factor XII (C6B7), we blocked the activation of the contact system in an established experimental baboon model in which Escherichia coli was infused to produce lethal bacteremia with hypotension. The untreated group (n = 5) displayed contact activation, manifested by a significant decrease in high molecular weight kininogen (HK) and a significant increase in alpha 2 macroglobulin-kallikrein complexes (alpha 2M-Kal). The C6B7-treated group (n = 5) showed an inactivation of Factor XII and the changes in HK and alpha 2M-Kal complexes were prevented. Both groups developed DIC manifested by a decrease in platelet, fibrinogen, and Factor V levels. The untreated group developed irreversible hypotension. The treated group experienced an initial hypotension that was reversed and extended the life of the animals. This study suggests that irreversible hypotension correlates with prolonged activation of the contact system, and specific antibody therapy can modulate both the pathophysiological and biochemical changes.

Animals↗
PubMed1993

Aprotinin inhibits the contact, neutrophil, and platelet activation systems during simulated extracorporeal perfusion.

Aprotinin reduces blood loss after cardiac operations and decreases the bleeding time. The mechanism of action of aprotinin that produces these effects is not clear. During simulated extracorporeal circulation the contact and complement systems, platelets, and neutrophils are activated. We investigated the effect of aprotinin on kallikrein-C1-inhibitor complex and C1-C1-inhibitor complex formation, neutrophil degranulation, and platelet release and aggregation during simulated extracorporeal circulation. Fresh heparinized human blood was recirculated at 37 degrees C for 2 hours in a spiral coil membrane oxygenator-roller pump perfusion circuit. Changes in platelet count, leukocyte count, platelet response to adenosine diphosphate, and plasma levels of beta-thromboglobulin, kallikrein-C1-inhibitor complexes, C1-C1-inhibitor complexes, and neutrophil elastase were measured before and at 5, 30, 60, and 120 minutes of recirculation at 0, 0.015, 0.03, 0.06, and 0.12 mg/ml doses of aprotinin. Platelet counts decreased to 36% +/- 12% of control values at 5 minutes and increased to 56% +/- 13% at 120 minutes without aprotinin. Aprotinin did not affect platelet counts, but it did prevent the decrease in sensitivity of platelets to adenosine diphosphate and it attenuated beta-thromboglobulin release. In the absence of aprotinin, kallikrein-C1-inhibitor and C1-C1-inhibitor complexes increased progressively to 0.53 +/- 0.14 U/ml and 2.38 +/- 0.33 U/ml, respectively, at 120 minutes. Kallikrein-C1-inhibitor complexes were completely inhibited and C1-C1-inhibitor complexes were partially inhibited at aprotinin concentrations of 0.03 mg/ml or greater. Release of neutrophil elastase was partially but not completely inhibited at the highest dose of aprotinin and was 50% inhibited at a dose of 0.03 mg/ml. Because activation of the fibrinolytic system does not occur in this system, the changes were independent of the inhibition of plasmin. We conclude that aprotinin in high doses completely inhibited kallikrein-induced activation of neutrophils and partially inhibited complement-induced activation. Aprotinin did not directly affect platelet adhesion or aggregation, but it indirectly preserved platelet sensitivity to agonists and also attenuated release of alpha-granule contents. The data indicate that in the presence of aprotinin platelet function was partially preserved, kallikrein production was totally inhibited, complement activation was partially inhibited, and neutrophil release was partially inhibited, thus attenuating the "whole body inflammatory response" associated with cardiopulmonary bypass.

Aprotinin↗
PubMed1993

Reocclusion after thrombolytic therapy: strategies for inhibiting thrombin-induced platelet aggregation.

The use of first generation plasminogen activators, urokinase, streptokinase and tissue plasminogen activator has revolutionized thrombolytic therapy for myocardial infarction and ischaemia, and potentially stroke. However, thrombolytic therapy employing these activators is limited by reocclusion of the very arteries being opened, which follows in a small but significant number of patients. The development of second generation plasminogen activators, e.g. staphylokinase and anisoylated plasminogen streptokinase activator complex, has not alleviated the problems encountered with classical plasminogen activators. It is now widely recognized that aberrant platelet aggregation induced primarily by thrombin, rather than plasmin, is one of the major causes of recurrent thrombosis following pharmacologic thrombolysis. Agents that (a) inhibit enzymatic and/or coagulant activity of thrombin, (b) block binding of thrombin to its receptor, and (c) interfere with the generation of thrombin by the prothrombinase complex may compromise haemostasis resulting in haemorrhage. We recently demonstrated that thrombin-induced platelet aggregation is accompanied by cleavage of aggregin, a putative ADP-receptor on the platelet surface, and that these events are indirectly mediated by intracellularly activated calpain expressed on the surface. In this review, we discuss the known mechanisms of thrombin-induced platelet aggregation and suggest relative advantages of potential pharmacological agents, being developed in our laboratory, over those that have been previously developed and tested. These inhibitors selectively prevent aggregation of platelets induced by thrombin by inhibiting calpain expressed on the surface. Moreover, one of these inhibitors which blocks thrombin-induced platelet aggregation does not interfere with other platelet responses mediated by thrombin or platelet aggregation induced by other agonists, such as, ADP, collagen, phorbol myristate acetate and thromboxane A2 mimetics. This selectivity could reduce the chances of perturbing the formation of a haemostatic plug.

Amino Acid Sequence↗
PubMed1993

Upregulation of Mac-1 surface expression on neutrophils during simulated extracorporeal circulation.

The leukocyte integrin Mac-1 (alpha m beta 2, CD11b/18 CR3, MO1), in addition to binding iC3b, has been shown to be the receptor for the coagulation proteins fibrinogen, factor X, and high molecular weight kininogen. Mac-1 is known to be upregulated by agonists that stimulate neutrophils or monocytes. Previous studies from this laboratory have documented neutrophil activation during cardiopulmonary bypass. We therefore used an experimental model for cardiopulmonary bypass, a simulated extracorporeal circulation, to study the surface expression of Mac-1 on peripheral blood leukocytes by immunofluorescence flow cytometry. The number of Mac-1 receptors in polymorphonuclear leukocytes had increased 2.2 times and 2.9 times baseline by 2 hours at 37 degrees C and 28 degrees C, respectively (p < 0.001). Neutrophil elastase-alpha 1-proteinase inhibitor complexes (a measure of neutrophil degranulation) increased more than sixfold from 41 micrograms/L to 256 micrograms/L after 2 hours at 28 degrees C. The number of Mac-1 receptors expressed on polymorphonuclear leukocytes correlated with polymorphonuclear leukocyte elastase complexes (r = 0.93). Mac-1--bearing lymphocytes did not display any change in receptor number in the simulated extracorporeal circulation. By 2 hours, monocytes at 37 degrees C showed only insignificant increase; at 28 degrees C they displayed a 1.6 times increase (p < 0.05). By maintaining a temperature-matched standing control samples, we could prove that, unlike the Mac-1 in polymorphonuclear leukocytes, this increase in monocyte Mac-1 is not from bypass but is rather an effect of temperature. These data suggest that a receptor for procoagulant proteins on circulating polymorphonuclear leukocytes (Mac-1) is upregulated during simulated extracorporeal circulation.

Adult↗
PubMed1992

Fibrinogen blocks the autoactivation and thrombin-mediated activation of factor XI on dextran sulfate.

The intrinsic pathway of blood coagulation is activated when factor XIa, one of the three contact-system enzymes, is generated and then activates factor IX. Factor XI has been shown to be efficiently activated in vitro by surface-bound factor XIIa after factor XI is transported to the surface by its cofactor, high molecular weight kininogen (HK). However, individuals lacking any of the three contact-system proteins--namely, factor XII, prekallikrein, and HK--do not suffer from bleeding abnormalities. This mystery has led several investigators to search for an "alternate" activation pathway for factor XI. Recently, factor XI has been reported to be autoactivated on the soluble "surface" dextran sulfate, and thrombin was shown to accelerate the autoactivation. However, it was also reported that HK, the cofactor for factor XIIa-mediated activation of factor XI, actually diminishes the thrombin-catalyzed activation rate of factor XI. Nonetheless, it was suggested that thrombin was a more efficient activator than factor XIIa. In this report we investigated the effect of fibrinogen, the major coagulation protein in plasma, on the activation rate of factor XI. Fibrinogen, the preferred substrate for thrombin in plasma, virtually prevented autoactivation of factor XI as well as the thrombin-mediated activation of factor XI, while having no effect on factor XIIa-catalyzed activation. HK dramatically curtailed the autoactivation of factor XI in addition to the thrombin-mediated activation. These data indicate that factor XI would not be autoactivated in a plasma environment, and thrombin would, therefore, be unlikely to potentiate the activation. We believe that the "missing pathway" for factor XI activation remains an enigma that warrants further investigation.

Dextran Sulfate↗
PubMed1992

Human factor XII (Hageman factor) autoactivation by dextran sulfate. Circular dichroism, fluorescence, and ultraviolet difference spectroscopic studies.

The first event leading to the activation of the plasma kallikrein-kinin system is the surface-dependent conversion of factor XII to an active enzyme. Factor XII autoactivation was investigated using dextran sulfate as a soluble activating surface, and the significance of aggregation and the nature of the conformational change were examined by ultraviolet difference spectroscopy, fluorescence and circular dichroism. Results indicate that DS500 (500-kDa dextran sulfate) induces aggregation of factor XII. Analysis of the binding data suggests that 165-192 factor XII molecules can bind to one DS500 chain, while a 1:1 stoichiometry is observed with 5-kDa dextran sulfate. The interaction of factor XII and dextran sulfate is a biphasic process. It is initiated by a fast contraction of the molecule upon binding, as revealed by an apparent increase in organized secondary structures, and then followed by a slow relaxation process during cleavage and subsequent activation. Overall, the results are consistent with a model in which factor XII undergoes conformational changes upon binding to the activating surface. The rapidity of autoactivation in the presence of DS500, as opposed to 5-kDa dextran sulfate, implies that aggregation provides a special mechanism whereby proteolytic cleavage is accomplished efficiently when factor XII molecules are bound side by side on the DS500 molecule.

Circular Dichroism↗
PubMed1992

Bacterial expression of biologically active high molecular weight kininogen light chain.

Human high molecular weight kininogen (HK), a single chain plasma glycoprotein, serves as a cofactor in the contact system of blood coagulation. After cleavage by human plasma kallikrein, the nonapeptide bradykinin is released. The HK light chain (LC) contains coagulant activity, which requires both the ability to bind the contact system zymogens, prekallikrein and factor XI, and the ability to interact with negatively charged surfaces. Since bacterial expression might not be successful if carbohydrate was required for activity, we evaluated that possibility by incubating plasma HK with endoglycosydase F. Although the procedure removed detectable N-linked carbohydrate, no change in specific activity occurred. We then developed a bacterial expression system to produce recombinant HK LC. The cDNA coding for the HK LC was prepared by polymerase chain reaction (PCR), digested with restriction enzymes EcoRI and PstI, and introduced into the bacterial expression vector pKK223-3. E. coli harboring this recombinant plasmid (pSK1) expressed HK LC upon induction with isopropylthio-galactoside (IPTG). The recombinant protein (27 kDa), when transferred onto a PVDF membrane, was recognized by monospecific polyclonal anti-HK LC-antibodies. The recombinant HK LC was purified by heparin agarose affinity chromatography to homogeneity and found to have a specific activity of 28 coagulant units per mg protein, similar to the specific activity of the LC derived by proteolytic digestion of human plasma HK. We conclude: 1) The HK LC synthesized in bacteria is biologically active, and 2) the 40% carbohydrate content of the HK LC is not required for its cofactor activity.

Base Sequence↗
PubMed1992

Aggregation of washed platelets by plasminogen and plasminogen activators is mediated by plasmin and is inhibited by a synthetic peptide disulfide.

Plasmin is known to activate platelets. However, it is not clear whether plasminogen activators as used in thrombolytic therapy can aggregate platelets and how this relates to the ability of each activator to convert plasminogen to plasmin. Urokinase (UK) and streptokinase (SK) activated purified plasminogen (2 microM) in a concentration-dependent manner. The rates of aggregation of washed platelets by the above plasminogen activators and plasminogen were similar to the extent of activation of plasminogen to plasmin in the absence of platelets. UK or SK (0.2 microM) and plasminogen (2 microM) aggregated platelets modified by an ADP affinity analog, 5'-p-fluorosulfonylbenzoyladenosine (FSBA), and cleaved aggregin, a putative ADP receptor, in [3H]FSBA-modified platelets. These results suggest that the effect was independent of ADP. In contrast, incubation mixtures containing only plasminogen (2 microM) and single chain tissue plasminogen activator (sc-tPA) (less than or equal to 0.12 microM) neither activated the zymogen to an appreciable extent nor aggregated platelets. But, in the presence of fibrin(ogen) fragments (tPA-stimulator), a mixture of plasminogen and sc-tPA aggregated unmodified and FSBA-modified platelets, and cleaved aggregin. The results imply that platelets, in the presence of t-PA stimulator, potentiate activation of plasminogen to plasmin by t-PA, as previously reported. P1, Phe-Gln-Val-Val-Cys-(NpyS)-Gly-NH2, (NpyS = 3-nitro-2-thiopyridine), a synthetic hexapeptide capable of binding to and inhibiting calpain, has been shown to inhibit platelet aggregation induced by purified plasmin. P1 inhibited platelet aggregation by plasminogen and any of the three plasminogen activators. Our results show that at plasma concentrations of plasminogen and at levels of UK and SK attained after infusion of these agents during thrombolysis, these mixtures can cause maximum aggregation which may contribute to reocclusion and stenosis following infarct therapy. P1 can effectively inhibit platelet aggregation under such conditions.

Amino Acid Sequence↗
PubMed1992

Immunovisualization of high (HK) and low (LK) molecular weight kininogens on isolated human neutrophils.

An immunocytochemical study was performed to examine the cellular localization and the subcellular distribution of kininogens in human blood cells. Kininogens were visualised using the immunogold-silver staining method and confocal scanning laser microscopy. We confirmed the existence of high molecular weight kininogen in human neutrophils and describe for the first time the presence of low molecular weight kininogen on these cells. Both high and low molecular weight kininogens were restricted to the neutrophils where they localized as clusters of immunogold particles on the cell membrane. No labeling was observed intracellularly in organelles such as mitochondria, endoplasmic reticulum, and azurophilic or specific granules after permeabilization of the neutrophils with Triton X-100, a procedure that permitted the visualization of elastase in the azurophilic granules. Clusters of high molecular weight kininogen molecules attached to the neutrophil surface could serve as receptors for plasma kallikrein and/or be the source of substrate for a discrete and circumscribed formation of kinins that may in turn facilitate the local diapedesis of neutrophils and the transudation of plasma constituents during acute inflammation.

Antibodies, Monoclonal↗
PubMed1992

Cellular and molecular regulation of factor V expression in human megakaryocytes.

The mechanisms responsible for regulating FV expression in normal human megakaryocytes are unknown. To test the hypothesis that they are related to cell maturation events, we correlated human megakaryocyte FV antigen content with several putative maturation markers including cell size, morphologic stage of development, and ploidy level. Mature megakaryocytes were isolated from normal marrow by counterflow centrifugal elutriation. The cells were immunofluorescently labeled with a monoclonal antibody probe (B10) directed against the FV connecting peptide (150 kDa) and then reacted with Chromomycin A3 to allow for simultaneous DNA quantitation in the same cell. After processing, individual cells were stages and sized. FV antigen and nuclear DNA levels (ploidy) were measured by microphotometric measurements of total cytoplasmic or nuclear fluorescence. A total of 1,006 cells were examined, of which 12% were stage I, 8% were stage II, 35% were stage III, and 45% were stage IV. The geometric mean diameter (+/- SD) of cells in these stages was 48.3 +/- 11.8 microns2, 54.9 +/- 14.4 microns2, 61.7 +/- 20.02 microns2, and 56.7 +/- 13.2 microns2, respectively. Respective ploidy values in arbitrary fluorescence units, where 2 N = 5%, were 28.2 +/- 18.2%, 31.4 +/- 19.3%, 54.3 +/- 26.6%, and 33.2 +/- 22.7%. Calculated correlation coefficients (r) and coefficient of determination (r2) values suggested that FV antigen levels varied independently of any of the maturation markers studied. However, FV antigen levels could be upregulated by 24 h exposure to 8 nM phorbol myristate acetate (PMA). Presence of FV mRNA in a pure population of megakaryocytes was demonstrated by in situ hybridization and the polymerase chain reaction. Relative levels of megakaryocyte FV mRNA, as assessed by in situ hybridization, failed to reveal a detectable change after PMA exposure in spite of an increase in detectable protein. These data suggest that FV synthesis may be regulated at the post-transcriptional level and that it is subject to regulatory influences which are not coordinately linked to development of other terminal maturation markers.

Antibodies, Monoclonal↗
PubMed1992

The sequence HGLGHGHEQQHGLGHGH in the light chain of high molecular weight kininogen serves as a primary structural feature for zinc-dependent binding to an anionic surface.

The histidine-glycine-rich region of the light chain of cleaved high molecular weight kininogen (HK) is thought to be responsible for binding to negatively charged surfaces and initiation of the intrinsic coagulation, fibrinolytic, and kinin-forming systems. However, the specifically required amino acid sequences have not been delineated. An IgG fraction of a monoclonal antibody (MAb) C11C1 to the HK light chain was shown to inhibit by 66% the coagulant activity and by 57% the binding of HK to the anionic surface of kaolin at a concentration of 1.5 microM and 27 microM, respectively. Proteolytic fragments of HK were produced by successive digestion with human plasma kallikrein and factor XIa (FXIa). Those polypeptides that bound tightly (Kd = 0.77 nM) to a C11C1 affinity column were eluted at pH 3.0 and purified by membrane filtration. On 15% SDS polyacrylamide electrophoresis, the approximate M(r) was 7.3 kDa (range 6.2-8.1 kDa). Based on N-terminal sequencing, this polypeptide (1(2)), which extends from the histidine residue 459 to a lysine at position 505, 509, 511, 512, 515, or 520, inhibits by 50% the coagulant activity expressed by HK at a concentration of 22 microM. The synthetic peptide HGLGHGH representing the N-terminal of the 1(2)) fragment was synthesized, tested, and found at 4 mM to inhibit the procoagulant activity of HK 50%. A synthetic heptadecapeptide, HGLGHGHEQQHGLGHGH (residues 459-475) included within the 1(2) fragment, and with the ability to bind zinc, inhibited 50% of the HK coagulant activity at a concentration of 325 microM in the absence and presence of added Zn2+ (30 microM). The specific binding of 125I-HK to a negatively charged surface (kaolin) was inhibited 50% by unlabeled HK (5 microM). HGLGHGH, at a concentration of 7.0 mM, inhibited the binding to kaolin by 50%. The heptadecapeptide inhibited the specific binding of 125I-HK to kaolin by 50%, at a concentration of 2.3 mM, in the absence of Zn2+. In contrast, when Zn2+ was added, the concentration to achieve 50% inhibition decreased to 630 microM, indicating that Zn2+ was required to attain a favorable conformation for binding. Moreover, the 1(2) fragment was found to inhibit 50% of the 125I-HK binding to kaolin at a concentration of 380 microM. These results suggest that residues contained within the 1(2) fragment, notably HGLGHGHEQQHGLGHGH, serves as a primary structural feature for binding to a negatively charged surface.

Amino Acid Sequence↗