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Biomedical subjects

W R Bell

Publications and source records attributed to W R Bell.

At least 55 records · Page 3Linked to original sources
PubMed1990

Fibrinolytic agents in the treatment of thrombotic disorders.

The oncology patient is often at increased risk of bleeding when thrombolytics are administered. Fortunately, the factors placing the patient at risk are easily identified and include intracranial disease, vascular defects produced by surgery, instrumentation or tumor invasion, underlying coagulopathy, and severe thrombocytopenia. Unfortunately, new clot-specific agents have not eliminated the problem of undesirable bleeding; in fact, they may cause more bleeding by more efficiently dissolving both pathological thrombi and hemostatic plugs. The development of a means of delivering thrombolytics solely to the target clot is desirable and should be performed when possible. Despite the need for caution, thrombolytics are remarkably effective in treating both venous and arterial thrombi, and it is a disservice to the patient not to carefully consider their use.

Arterial Occlusive Diseases↗
PubMed1989

Fibrinogen Baltimore IV: congenital dysfibrinogenemia with a gamma 275 (Arg----Cys) substitution.

The major functional characteristics of fibrinogen Baltimore IV include delayed fibrin monomer polymerization which is not corrected by the addition of calcium, inhibition of normal plasma coagulation upon mixing, and a biphasic polymerization profile in which the abnormal fibrin monomers appear to polymerize at about 2% of the normal rate (Ebert & Bell, Thromb. Res. 38:121-128, 1985). We now report the detection of an abnormal peptide in a comparative peptide map from a cyanogen bromide digest of fibrinogen Baltimore IV. The sequence of this peptide corresponds to the fibrinogen sequence gamma 265-310, except that Arg275 is replaced by Cys. Amino acid analyses of carboxymethylated peptides from control vs. fibrinogen Baltimore IV confirmed the sequencing data. Both the propositus and his affected daughter were heterozygous for the trait.

Amino Acid Sequence↗
PubMed1989

Fibrinogen sialic acid residues are low affinity calcium-binding sites that influence fibrin assembly.

Calcium ions occupy low (n congruent to 10; Kd congruent to 1 mM) and high (n = 3; Kd congruent to 1 microM) affinity sites on fibrinogen and facilitate fibrin monomer polymerization. We have previously localized two of the three high affinity Ca2+ sites to gamma 311-gamma 336. However, optimal enhancement of fibrin monomer polymerization occurs only at physiological millimolar Ca2+ concentrations which are two orders of magnitude higher than the concentration required for occupancy of the high affinity Ca2+-binding sites. In this study, we show that removal of fibrinogen sialic acid residues results in loss of low affinity Ca2+-binding sites. Clotting of asialofibrinogen appears to be Ca2+-independent and results in fiber bundles thicker in diameter than normal fibrin bundles as determined by turbidometry and scanning and transmission electron microscopy. By using a Ca2+-sensitive electrode, free sialic acid is shown to bind Ca2+ (Kd congruent to 1 mM). These observations suggest that the high affinity fibrinogen D-domain Ca2+-binding sites may play a role in the tertiary structure of the D-domain, whereas, sialic acid residues are low affinity sites whose occupancy by Ca2+ at physiological calcium concentration facilitates fibrin polymerization.

Asialoglycoproteins↗
PubMed1989

Oral contraceptives and lipids and lipoproteins: Part II--Relationship to plasma steroid levels and outlier status.

A randomized clinical trial of oral contraceptives evaluated 67 women on 50 ug ethinyl estradiol (EE) and 1.0 mg norethindrone (NE), 61 women on 35 ug EE and 1.0 mg NE, and 64 women on 35 ug EE and 0.5 mg NE. At baseline, three, six and nine months, lipids and lipoproteins were measured as well as selected plasma determinations of the contraceptive steroids. Data was related to change in outlier status for lipids/lipoproteins (less than 10th percentile for high-density lipoprotein cholesterol and apolipoprotein A-1, greater than 90th percentile for all others). Women on the lowest dose preparation had the smallest trend towards outlier status for high-density lipoprotein cholesterol and apolipoprotein A-1. An increase over the time period of the study in the initial slope (one hour level minus zero hour level over time) of NE and a decrease in the initial slope of EE was associated with a shift to outlier status for low-density lipoprotein cholesterol. A number of other relationships were also shown. Use of the techniques described might assist in identifying sub-groups of women at risk for adverse cardiovascular sequelae associated with oral contraceptive use.

Adolescent↗
PubMed1989

Oral contraceptives and lipids and lipoproteins: Part I--Variations in mean levels by oral contraceptive type.

A randomized clinical trial of oral contraceptives evaluated 67 women on 50 micrograms ethinyl estradiol (EE) and 1.0 mg norethindrone (NE), 61 women on 35 micrograms EE and 1.0 mg NE, and 64 women on 35 micrograms EE and 0.5 mg NE. Fasting lipids and lipoproteins were measured at baseline, three, six and nine months. All groups showed an increase in plasma total cholesterol, triglycerides, low-density lipoprotein/apolipoprotein B and apolipoprotein A-1. The group taking the preparation with 0.5 mg of NE was the only one to result in an elevation of high-density lipoprotein cholesterol; the other two groups showed declines in the mean levels of this lipoprotein over the study time period. Mean changes in lipid/lipoprotein levels associated with oral contraceptive use appear to be at least partially related to the doses of the contraceptive steroids.

Adolescent↗
PubMed1989

Stimulation of fibrinogen synthesis in cultured rat hepatocytes by fibrinogen degradation product fragment D.

The direct stimulation of fibrinogen biosynthesis by fibrinogen degradation produces (FDPs) was studied in rat hepatocyte cultures. Pure rat FDP fragment D (FDP-D) (Mr 90,000) and FDP fragment E (FDP-E) (Mr 40,000) and mixtures of the two (FDP-DE) were added to rat hepatocytes cultured in serum-free hormonally defined medium. Hydrocortisone (20 microM) significantly increased synthesis of fibrinogen, as determined by incorporation of [35S]methionine. FDP-D and FDP-E did not increase fibrinogen synthesis in the presence of hydrocortisone. However, hepatocytes cultured without hydrocortisone displayed increased fibrinogen synthesis (2.0- to 2.8-fold) with FDP-D (2.6-6.7 microM) but not with FDP-E (5.7 microM). At these FDP concentrations the synthesis of albumin, haptoglobin, and transferrin was not increased. FDP-D-induced fibrinogen synthesis was inhibited (greater than 90%) by actinomycin D and cycloheximide, indicating that the increase in [35S]methionine incorporation was from de novo protein synthesis. The role of FDP-D was further substantiated by showing that FDP-D, but not FDP-E, bound to the hepatocytes. These data indicate that FDP-D, but not FDP-E, directly and specifically stimulates fibrinogen synthesis in rat hepatocytes; this stimulation does not require any additional serum or protein cofactors.

Animals↗
PubMed1989

Acute-phase behavior of factor VIII procoagulant and other acute-phase reactants in rabbits.

We measured the plasma concentrations of factor VIII procoagulant (FVIII:C) in rabbits in two laboratory models of inflammation and after injections of purified homologous interleukin 1 (IL-1). The mean FVIII:C activities 2-4 days following the intramuscular injection of turpentine were significantly elevated, as were the concentrations of fibrinogen and C-reactive protein (CRP). By contrast, rabbits given 50 ng of bacterial lipopolysaccharide intravenously developed increased levels of FVIII:C but not of fibrinogen or CRP. We then studied plasma levels of FVIII:C, fibrinogen, and CRP after injections of either form of purified rabbit IL-1. If the rabbits' temperatures were monitored, FVIII:C levels increased in a log dose-related manner. This effect was not seen unless the rabbits were restrained and was seen in restrained rabbits even if the temperatures were not monitored. Fibrinogen and CRP levels did not change after IL-1 injections. These findings demonstrate that FVIII:C is an acute-phase reactant as judged by its response to turpentine inflammation or endotoxin injections, and to injections of IL-1 in restrained rabbits. FVIII:C appears to be a more sensitive acute-phase reactant than either fibrinogen or CRP. Neither of the latter proteins responded to low-dose endotoxin injections nor to either form of purified homologous IL-1. The doses of IL-1 given did cause fever, neutrophil leukocytosis, and hypoferremia.

Acute-Phase Proteins↗
PubMed1989

Abrupt reversal of gestational autoimmune thrombocytopenia after delivery. A case report.

Autoimmune thrombocytopenia purpura frequently is first noted during pregnancy. The severity of the disorder varies, but when the patient presents with active bleeding from any site, therapy is mandatory. Treatment generally consists of corticosteroids and/or splenectomy. A woman developed severe autoimmune thrombocytopenia purpura during pregnancy that proved refractory to corticosteroids and splenectomy. Six days after delivery her platelet count returned to normal. The etiology of autoimmune thrombocytopenia purpura remains unknown, but this experience suggests that in this patient the thrombocytopenia was related to her pregnancy.

Adrenal Cortex Hormones↗
PubMed1989

Control of bleeding in patients with immune and nonimmune thrombocytopenia with aminocaproic acid.

Patients with thrombocytopenia have an increased risk of bleeding. We have used 18 courses of aminocaproic acid in 17 patients with either immune or nonimmune thrombocytopenia to successfully control hemorrhage associated with reduced platelet counts. The types of hemorrhage controlled included the following: vaginal, gastrointestinal, intracerebral, cutaneous, mucous membrane, subconjunctival, and renal, as well as that associated with dental extractions, tracheostomy, and sites of Penrose drains. The number of platelet and red blood cell transfusions administered decreased substantially following institution of aminocaproic acid therapy. We conclude that therapy with aminocaproic acid is safe and useful in the management of bleeding in patients with both immune and nonimmune thrombocytopenia.

Adult↗
PubMed1988

Deglycosylation of fibrinogen accelerates polymerization and increases lateral aggregation of fibrin fibers.

Fibrinogen, the major structural precursor of blood clots, was deglycosylated by peptide-N-(N-acetyl-beta-glucosaminyl)asparagine amidase without denaturation of the polypeptide chains. Deglycosylated fibrinogen behaved normally in clinical coagulation assays, although it is less soluble than normal fibrinogen. However, the turbidity of clots formed from deglycosylated fibrinogen always rose faster and higher than that of clots from normal fibrinogen. Scanning and transmission electron microscopy demonstrated that fibrin made from clots of deglycosylated fibrinogen consisted of thicker, less-branched fiber bundles in a more porous network. Moreover, the degree of lateral aggregation was directly related to clot turbidity and inversely related to branching. Deglycosylation promoted turbidity development, lateral aggregation, and porosity of clots under all conditions tested. All other steps in the coagulation pathways appeared to be unaffected by the absence of carbohydrate. These results suggest that carbohydrate constitutively affects the behavior of deglycosylated fibrinogens by 1) contributing a repulsive force that promotes fibrinogen solubility and limits fibrin assembly and 2) sensitizing fibrin to conditions that influence assembly and clot structure.

Factor XII↗
PubMed1988

Fibrinogen Baltimore III: congenital dysfibrinogenemia with a shortened gamma-subunit.

An abnormal fibrinogen has been found in an asymptomatic Negro female. Clinical laboratory findings were normal, except for a prolonged thrombin time which was corrected by addition of calcium. Fibrinopeptide release by thrombin and crosslinking by factor XIII also occurred normally, but fibrin monomer polymerization was delayed. Sodium dodecylsulfate-polyacrylamide gel electrophoresis disclosed that 50% of the gamma-subunits migrated with an apparent Mr of 45,500, approximately 1,500 Da smaller than normal. The evidence suggests that an internal sequence of 10-15 residues is missing from the gamma-subunit of the abnormal fibrinogen.

Adult↗
PubMed1988

Heparin requirement for the quantitation of fibrinogen production by primary hepatocyte cultures.

We have reported a rapid method for the quantitation of proteins secreted in culture media (F.M. LaDuca, C.V. Dang, and W.R. Bell (1986) Anal. Biochem. 158, 262-267). Using the same method, we observe that serum-free rat hepatocyte cultures exhibited a 100% increase in detectable secreted fibrinogen-antigen in the presence of 1 unit/ml heparin or greater at 24 h of culture. The amount of transferrin, haptoglobin, and albumin detected was unaltered by the presence of heparin. Since heparin is known to affect certain cellular functions, the fates of [35S]methonine-labeled fibrinogen in cell extracts and culture media were examined employing pulse-chase experiments. Labeled intracellular fibrinogen disappeared at similar rates and was initially released into the media in similar amounts in the presence or absence of heparin. At 8 h during the chase, there was a 40-50% reduction in fibrinogen-antigen in spent culture medium lacking heparin. The presence of heparin did not alter the proteolytic degradation of secreted fibrinogen as determined by immunoblotting of spent culture media proteins separated by polyacrylamide gel electrophoresis. In vitro experiments indicate that clotting of fibrinogen by thrombin reduces the amount of immunodetectable fibrinogen. The results indicate that heparin increases the amount of detectable fibrinogen secreted by cultured hepatocytes by preventing clotting and not by stimulating synthesis or secretion or by inhibiting degradation. Hence, it is critically important to include heparin when secreted fibrinogen is quantitated by the method that we have developed.

Animals↗
PubMed1988

Thrombolysis in Myocardial Infarction (TIMI) Trial--phase I: hemorrhagic manifestations and changes in plasma fibrinogen and the fibrinolytic system in patients treated with recombinant tissue plasminogen activator and streptokinase.

Two hundred ninety patients with acute myocardial infarction were treated according to random assignment with an intravenous infusion of either 80 mg of recombinant tissue plasminogen activator (rt-PA) over 3 h or 1.5 million units of streptokinase over 1 h. Patients received an intravenous bolus of heparin (5,000 U [USP]) before pretreatment coronary angiography and a continuous infusion (1,000 U/h) starting 3 h later. The frequency of major and minor hemorrhagic events (33% rt-PA, 31% streptokinase) and associated transfusions (22% rt-PA, 20% streptokinase) were comparable in both groups. More than 70% of bleeding episodes in each group occurred at catheterization or vascular puncture sites. Precipitable fibrinogen levels, measured in plasma samples collected in the presence of a protease inhibitor (aprotinin), declined in rt-PA and streptokinase groups by averages of 26 and 57% at 3 h and by 33 and 58% at 5 h, respectively (rt-PA versus streptokinase, p less than 0.001). At 5 h the plasma plasminogen declined by 57% (rt-PA) and 82% (streptokinase) (p less than 0.001); plasma fibrin(ogen) degradation products were higher in streptokinase-treated patients (244 +/- 12 micrograms/ml, mean +/- SE) than in rt-PA-treated patients (97 +/- 9 micrograms/ml, p less than 0.001). At 27 h, plasma fibrinogen and plasminogen levels were lower and fibrin(ogen) degradation products higher than pretreatment levels in both groups. The frequency of hemorrhagic events was higher in patients with greater changes in plasma factors at 5 h; within treatment groups the levels of fibrin(ogen) degradation products correlated with bleeding complications (p less than 0.005). Thus, in the doses administered, rt-PA induces systemic fibrinogenolysis that is substantially less intense than that induced by streptokinase. The high frequency of bleeding encountered is related to the protocol used, including vigorous anticoagulation, arterial punctures and thrombolytic therapy. These findings emphasize the need for avoidance of invasive procedures and for meticulous care in the selection and management of patients subjected to thrombolytic therapy.

Clinical Trials as Topic↗