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Biomedical subjects

D K Galanakis

Publications and source records attributed to D K Galanakis.

34 records · Page 2Linked to original sources
PubMed1987

Albumin modulates lateral assembly of fibrin polymers: evidence of enhanced fine fibril formation and of unique synergism with fibrinogen.

We identified a new property of human albumin. It enhances formation of fine fibril (or leptofibril) structures during fibrin gelation, and by nephelometric and electron microscopic measurements, this property is independent of and synergistic with that of fibrinogen. We examined fibrin aggregation using physiologic temperatures and pH and albumin:fibrin concentration ratios below those at which the known accelerating effect on fibrin aggregation occurs. An albumin concentration dependent decrease in gel turbidity maxima was consistently demonstrable in buffers containing or lacking (2-5 mM) CaCl2. This decrease was shown to be induced by albumin preparations which had been exposed to 2 mM ethylene-diaminetetraacetate disodium salt (EDTA), dialyzed, and tested in EDTA-free buffer. A delay in the onset of aggregation was also shown in calcium-lacking buffers by use of either reaggregating fibrin or fibrinogen aggregated with low (0.01-0.05 unit/mL) thrombin concentrations. Rates of fibrin aggregation as well as those of fibrinopeptide release were not affected by albumin, and the decrease in gel absorbance was demonstrable when solubilized fibrin was reaggregated at all final fibrin concentrations (0.2-4 microM) examined. Computed from wavelength dependence turbidity measurements (1 microM fibrin, I = 0.20), albumin decreased the average mass:length ratio from 8.24 X 10(11) to 4.26 X 10(11) daltons/cm, or from that of an approximately six to a three protofibril-thick strand. It also decreased the mean fibril radius from 48.5 to 36.4 nm but had no effect on fibril density. Electron microscopic measurements of cross-sectional fibril widths, performed on sections of glutaraldehyde-fixed gels, disclosed differences between albumin-containing and control gels which were significant by chi 2 analysis (P greater than 0.001). Fibril groups of 7-20- and 21-40-nm width together comprised 77% of fibrils formed in the presence of albumin (n = 251) compared to 30% of controls (n = 309). Conversely, coarser fibrils of 41-60- and 61-97-nm width together comprised 23% of fibrils formed in the presence of albumin and 70% of controls. This albumin effect was demonstrable by use of different monomeric albumin preparations including defatted, undefatted (unexposed and exposed to 60 degrees C, 10 h), chromatographically [gel exclusion and (diethylaminoethyl)cellulose] pure, S-(carboxymethyl)albumin, and S-(N-ethylsuccinimidyl)albumin. Chromatographically isolated albumin oligomers lacked this property, suggesting that a specific site(s) on albumin was (were) required.(ABSTRACT TRUNCATED AT 400 WORDS)

Fibrin↗
PubMed1987

The synthetic RGDS peptide inhibits the binding of fibrinogen lacking intact alpha chain carboxyterminal sequences to human blood platelets.

The alpha chain 572-574 Arg-Gly-Asp sequence of fibrinogen appears to play only a minor role in platelet aggregation based on the ability of fibrinogen preparations lacking alpha chain carboxyterminal segments to support platelet aggregation, but synthetic Arg-Gly-Asp-Ser (RGDS) peptides are capable of inhibiting platelet aggregation and fibrinogen binding. The present study thus examined the ability of RGDS peptides to inhibit platelet interactions with a plasmic degradation product of fibrinogen (8D-50) that resembles an intermediate fragment X. Gel-filtered, human blood platelets suspended in 0.01 mol/L HEPES-buffered modified Tyrode's solution, pH 7.5, were stimulated with 20 mumol/L adenosine diphosphate and the binding of 125I-labeled 8D-50 or intact fibrinogen (0.01 to 0.6 mg/mL) assessed in the presence of 0 to 117 mumol/L RGDS. The data revealed that RGDS decreased the apparent affinity of 8D-50 and intact fibrinogen for platelets but did not affect the maximum number of binding sites. RGDS thus appears to be a competitive inhibitor not only of intact fibrinogen (Ki = 12 +/- 2 mumol/L) but also of 8D-50 (Ki = 15 +/- 3 mumol/L) (mean +/- SD, n = 3).

Amino Acid Sequence↗
PubMed1984

Dysfibrinogenemia. A current perspective.

At least 24 single amino acid substitution dysfibrinogens are currently known. Emerging evidence supports conclusions reached from studies on normal fibrinogen, which relate to the importance of release of A peptides to formation of a physiologically adequate fibrin clot; the existence of "D-D" or (b-b) polymerization sites; and the importance of the gamma chain carboxy terminal segment in fibrin assembly.

Afibrinogenemia↗
PubMed1983

Binding of fibrinogen to ADP-treated platelets. Comparison of plasma fibrinogen fractions and early plasmic fibrinogen derivatives.

Fibrinogen supports platelet aggregation by binding to specific receptors. The importance of the fibrinogen A alpha chain in this hemostatic function is controversial. We found that fibrinogen derivatives, isolated from plasma or obtained after limited plasmin digestion, that lacked approximately 13,000 to 46,000 MW peptides from the carboxyterminal of their A alpha chains (I-6, I-9, I-9D88) displayed undiminished capacity to support ADP-induced platelet aggregation and to bind to gel-filtered platelets. Analysis of their binding disclosed upwardly concave Scatchard plots that could be resolved into high- and low-affinity binding components similar to those of intact fibrinogen. The dissociation constant for high-affinity binding of fractions I-6 and I-9, however, was slightly higher than that of intact fibrinogen, correlating with the slight decrease in the rate of platelet aggregation observed using these fractions. Low-affinity binding was unchanged. In contrast, fibrinogen derivative I-9D88, lacking as much as 2/3 from the carboxyterminal side of both A alpha chains, was indistinguishable from intact fibrinogen in its ability to bind to platelets and support aggregation. This suggested that the small differences in binding affinities noted with fractions I-6 and I-9 were most likely due to changes in molecular conformation rather than to losses of specific peptides. A more degraded derivative (I-9D50) lacking even larger A alpha segments (MW 46,000 to 48,000), as well as aminoterminal segments (B beta 1-56) from the B beta chains, possessed only 70% to 75% of the platelet aggregating activity of intact fibrinogen. Its binding to ADP-treated platelets was quantitatively similar to that of intact fibrinogen but its Scatchard plot was linear, with loss of low-affinity binding. These data indicate that (1) fibrinogen binding to platelet receptors does not require the carboxyterminal 2/3 of the A alpha chain and (2) low-affinity platelet fibrinogen interactions as revealed by Scatchard analysis reflect fibrinogen binding to platelets via an aminoterminal segment of the A alpha and/or B beta chains, the loss of which results in a slight but significant decrease in platelet aggregation support.

Adenosine Diphosphate↗
PubMed1978

Circulating thrombin time anticoagulant in a procainamide-induced syndrome.

Circulating anticoagulants are unusual in drug-induced syndromes. We evaluated the prolonged thrombin time of plasma from a patient with a procainamide-induced syndrome. This defect was shown to be due to a circulating anticoagulant that was not of fibrin or fibrinogen origin and that prolonged thrombin and reptilase clotting times of plasma. Subclinical doses of heparin sodium induced hemorrhagic manifestations in this patient. Following cessation of heparin therapy, the circulating anticoagulant persisted but the bleeding tendency abated. All clinical and laboratory manifestations of this syndrome abated gradually following cessation of procainamide therapy.

Aged↗
PubMed1978

Monoclonal IgG anticoagulants delaying fibrin aggregation in two patients with systemic lupus erythematosus (SLE).

There is paucity of information regarding the prolonged plasma thrombin time known to occur in some patients with systemic lupus erythematosus. Detailed investigations of plasma from two such patients disclosed that IgG accounted for this defect in each case. IgG isolated from plasma of either patient possessed the property of delaying fibrin aggregation and prolonging the clotting times of fibrinogen. Preincubation of IgG from either patient with anti-IgG or anti-Fab (rabbit) serum abolished this anticoagulant property. Moreover, the anticoagulant IgG from the first patient was neutralized with anit-k chain and anti-IgG3, that from the second patient with anti-lambda chain and anti-IgG1 serum. These anticoagulants were also dissimilar with respect to their interactions with fibrin(ogen). IgG from the first patient had no anticoagulant activity against fibrin(ogen) species lacking intact Aalpha chains. IgG from the second patient displayed undiminished anticoagulant effect on such fibrin(ogen) species. We conclude that each anticoagulant interacted with a distinct region(s) on the fibrinogen molecule and that these interactions affect or involve sites that participate in the fibrin self-assembly process.

Adolescent↗
PubMed1976

Evaluation of the role of in vivo proteolysis (fibrinogenolysis) in prolonging the thrombin time of human umbilical cord fibrinogen.

These studies have been directed at evaluating the role played by proteolysis (fibrinogenolysis) in vivo in prolonging the thrombin time of human umbilical cord ("fetal") fibrinogen. The aggregation rate of cord fibrin compared with that from adult plasma is always delayed when the reaction is carried out under conditions of relatively high ionic strength (e.g., 0.29); this difference is not apparent at relatively low ionic strength (e.g., 0.09). In addition, as assessed by turbidimetric techniques, the maximum absorbance attained by cord fibrin is considerably less than that attained by adult fibrin. Coagulable fibrinogen catabolites (i.e., fraction I-5) are present in cord plasma and, like their counterparts from adult plasma, lack various portions of the COOH-terminal region of the A alpha chain. However, their presence in plasma does not explain the behavioral differences between cord and adult fibrin. Moreover, differences revealed by turbidimetric comparison of cord and adult fibrin from plasma fraction I-2 persist in fibrin from fraction I-5; it therefore appears that the COOH-terminal region of the A alpha chain does not contain the structure(s) accounting for the unique behavior of "fetal" fibrinogen.

Female↗
PubMedDate not supplied

Evaluation of two new assays for determination of serum fibrinogen/fibrin degradation products.

Two new commercial assays for the detection of degradation products of fibrinogen/fibrin (FDP) were evaluated against two standard procedures. The first, a new hemagglutination inhibition (HAI) assay using glutaraldehyde-treated cells, was compared with the tanned red cell hemagglutination inhibition immunoassay (TRCHII). Analysis of 43 samples from patients with a variety of bleeding disorders and thrombotic conditions showed a high degree of correlation between methods (r = 0.934). The second new assay, a rapid slide test using antibody-coated latex particles, was compared with results obtained by electroimmunoassay. There were no significant differences in the results as assessed by two statistical parameters. It was concluded that both new tests are useful for routine use in clinical laboratories.

Evaluation Studies as Topic↗