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Biomedical subjects

R W Colman

Publications and source records attributed to R W Colman.

At least 19 recordsLinked to original sources
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

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↗
PubMed1992

Role of kinins in pain and hyperalgesia: psychophysical studies in a patient with kininogen deficiency.

1. Bradykinin is considered to be an important mediator of pain and hyperalgesia associated with injury and inflammation. Psychophysical studies were conducted in a patient with complete kininogen deficiency to determine whether the absence of bradykinin was associated with abnormalities in pain sensibility. Pain evoked by heat stimuli to the thenar eminence was tested before and after a localized burn, which has been shown to cause hyperalgesia in normal subjects. In addition, pain evoked by intradermal administration of bradykinin (0.1-10 micrograms) to the forearm and the effects of bradykinin on pain induced by heat stimuli were studied. The patient rated the intensity of pain evoked by all heat stimuli relative to the pain induced by a 3 s 45 degrees C stimulus. 2. The patient's heat pain threshold (45 degrees C) in the glabrous skin was similar to that of age-matched control subjects (n = 5) and to that previously observed in younger control subjects. 3. The burn resulted in a decrease in pain threshold and an increase in pain induced by suprathreshold stimuli. The magnitude of hyperalgesia was within the range observed in the age-matched control subjects and in younger control subjects. Thus, kinins are not essential for the development of hyperalgesia after heat injury. 4. In control subjects, intradermal injections of bradykinin produced pain and hyperalgesia to heat stimuli. In the patient, intradermal bradykinin injections induced minimal pain and no hyperalgesia to heat stimuli. Thus, congenital absence of kininogens may be associated with a deficiency in bradykinin receptors.

Aged↗
PubMed1992

Disseminated intravascular coagulation. Approach to treatment.

Disseminated intravascular coagulation (DIC) is a syndrome caused by the systemic generation of thrombin. Most cases are due to pathological activation of the intrinsic coagulation systems (e.g. in sepsis), and/or the extrinsic system (e.g. in malignancy and head trauma). Diagnosis is made by finding abnormalities in at least 3 of 4 laboratory values, namely prothrombin time, platelet count, fibrinogen and fibrinogen/fibrin degradation products. The most common clinical manifestation of DIC is bleeding, with thrombosis in less than 10% of acute cases but more frequently encountered in chronic DIC associated with malignancy. Acute DIC must first be treated by specific therapy of the underlying disease and general support measures. If serial clinical and laboratory monitoring improves, no further treatment is required. If severe or life-threatening haemorrhage occurs or a thrombotic event ensues, heparin anticoagulation followed by aggressive replacement with platelets, fresh plasma and possibly cryoprecipitate is indicated. Heparin doses should be 'therapeutic' (i.e. adequate to overcome the coagulant forces that may have produced a relative heparin-resistant state in the blood). Chronic DIC with haemorrhage, or more usually thrombosis, should also be treated with heparin; warfarin is ineffective. If DIC persists because, for example, a tumour does not regress, long term outpatient subcutaneous heparin therapy may be required.

Disseminated Intravascular Coagulation↗
PubMed1992

Activation of the contact system in lethal hypotensive bacteremia in a baboon model.

The hypotension in septicemia is believed to be mediated by the combined action of many mediators including cytokines, prostaglandins, and complement components. To evaluate the contribution of the contact/kinin-forming system to hypotension, the authors used an established experimental baboon model of bacteremia in which two concentrations of Escherichia Coli (E. coli) were used to produce lethal and nonlethal hypotension. The lethal group (n = 5) developed irreversible hypotension that significantly correlated with the decline in levels of high molecular weight kininogen (HK) and an increase in alpha 2 macroglobulin-kallikrein complexes (alpha 2M-kal). The nonlethal group (n = 9) experienced reversible hypotension, a less striking decline in HK, and only slight elevation in alpha 2M-kal. No significant changes were found in levels of factor XII, prekallikrein, and factor XI in either group. A significant change in the contact system, which reflects the fatal outcome, is the rise in alpha 2M-kal. This study suggests that irreversible hypotension correlates with prolonged activation of the contact system.

Animals↗
PubMed1992

The contribution of factor V to the coagulant property of pleural fluid.

Intrapleural fibrin deposition commonly accompanies pleural injury and may contribute to the organization of exudative pleural effusions, which leads to lung entrapment. Previous investigators have observed an increase in procoagulant proteins in pleural effusions but very little thrombin formation. FVa is the protein cofactor in the prothrombinase complex that dramatically enhances the generation of thrombin from prothrombin by the serine protease fXa. The presence of fVa within the pleural space could influence fibrin formation and pleural scarification. We examined pleural fluids obtained from patients who had lung cancer, CHF, and empyema for the presence of fV/fVa. The fV antigen was increased in exudative pleural fluids, in comparison with transudates. However, the specific activity of fV antigen present in exudates was significantly less than that observed for the lower concentration of antigen present in transudate and could not be activated to the same degree by thrombin. Immunoblots of fV antigen in exudates indicated that fV was partially cleaved and inactivated by unidentified proteases. We conclude that although fV is present in pleural fluid, it may be present in a degraded form, which may partially account for a lack of thrombin-generating capacity in these pleural fluids. The presence of fV does not necessarily correlate with pleural loculation.

Blood Coagulation Factors↗
PubMed1979

Effects of prostaglandin E1 on platelet loss during in vivo and in vitro extracorporeal circulation with a bubble oxygenator.

Temporary inhibition of platelet function with prostaglandin E1 (PGE1) prevents platelets loss and functional alterations during extracorporeal circulation with a membrane oxygenator. This study evaluated the ability of PGE1 to prevent platelet injury in circuits containing a bubble oxygenator. During in vitro recirculation of human blood, the circulating platelet count, expressed as a percent of initial levels, decreased to 29%; platelets became insensitive to adenosine diphosphate (ADP) and to epinephrine; and plasma levels of low-affinity platelet factor 4 (LA-PF4) progressively rose to 7.4 microgram per milliliter. With PGE1 (1.2 micron), platelet counts remained stable at 92%; platelet reactivity remained normal for 1 hour; and plasma levels of LA-PF4 rose to only 3.3 microgram per milliliter. In rhesus monkeys that underwent cardiopulmonary bypass using a bubble oxygenator without PGE1, platelet counts, expressed as a percent of the prebypass platelet count, declined to 38%; platelets became insensitive to ADP; plasma levels of LA-PF4 progressively rose to 8.4 microgram per milliliter; and the mean postoperative bleeding time was 4.6 minutes. In monkeys that received PGE1, platelet counts declined to only 65%; platelets remained threefold more sensitive to ADP; platelets demonstrated delayed release of LA-PF4 and the mean postoperative bleeding time was 2.7 minutes. This report demonstrates that in a bubble oxygenator system, PGE1 reduces platelet loss, mitigates platelet injury, and shortens postoperative bleeding times following extracorporeal circulation.

Animals↗
PubMed1979

Prekallikrein activation by Hageman factor: potentiation by proteins in the absence of high molecular weight kininogen.

Proteins which potentiate the conversion of prekallikrein to kallikrein by Hageman factor fragments are present in cryoprecipitate prepared from the plasma of an individual lacking HMW kininogen as well as in purified von Willebrand's factor preparations. However, the potentiator activity could be separated from the von Willebrand's antigen and ristocetin cofactor activity by chromatography on QAE-Sephadex. Moreover, it was present in plasma from an individual lacking von Willebrand's factor. These observations indicate that von Willebrand's factor is not responsible for the potentiator activity in cryoprecipitate.

Blood Coagulation↗