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Biomedical subjects

A Stern

Publications and source records attributed to A Stern.

At least 19 recordsLinked to original sources
PubMed1992

Effects of ligands on reduction of oxygen by vanadium(IV) and vanadium(III).

V(IV) and V(III) reduce molecular oxygen with increasing rates as the pH is raised from 6.0 to 7.4. Under all conditions tested, V(IV) is the more efficient reductant. EDTA and ATP generally inhibit the reduction of oxygen by V(III) and V(IV). In contrast, desferrioxamine accelerates the reduction of oxygen by V(IV) but with decreasing effectiveness at pH 7.4 compared to pH 6.0, while desferrioxamine accelerates the reduction of oxygen by V(III) only at pH 6.0. Histidine enhances the reduction of oxygen by V(IV) at pH 7.0 and 7.4. The observed rates of oxygen reduction by V(III) and V(IV) imply that the intracellular distribution of vanadium among its redox states reflects not an equilibrium but a steady state.

Adenosine Triphosphate↗
PubMed1992

Binding of recombinant variants of human tissue-type plasminogen activator (t-PA) to human umbilical vein endothelial cells.

Endothelial cells synthesize and secrete hemostatic components like tissue-type plasminogen activator (t-PA) which is thought to be the major determinant of fibrinolytic activity in the blood. Most recently, a receptor protein for t-PA on human umbilical vein endothelial cells (HUVEC) in culture has been described (1); there are, however, in addition low affinity binding sites for t-PA on HUVEC. The sites of binding are of particular interest, because they are potential regulators of t-PA activity and clearance. We analysed the low affinity binding of recombinant t-PA (rt-PA) to normal diploid HUVEC and to the permanent human cell lines Jurkat, Daudi, HL 60 and K562 by flow cytometry applying t-PA specific monoclonal antibodies. Using this test system binding of both recombinant glycosylated human t-PA produced in Chinese hamster ovary cells (CHO-t-PA) and of nonglycosylated t-PA, produced in E. coli (BM 06.021) was investigated. Analysis of the binding pattern to HUVEC and other cell lines revealed that deglycosylation of full length rt-PA increases non-specific binding. Additionally, we investigated the binding properties of an unglycosylated t-PA deletion variant which comprises the kringle 2 and the protease domains (BM 06.022). Data obtained show that deletion of these domains most drastically reduces non-specific binding to HUVEC and other human cell lines.

Antibodies, Monoclonal↗
PubMed1992

Inhibition of hemin-induced hemolysis by desferrioxamine: binding of hemin to red cell membranes and the effects of alteration of membrane sulfhydryl groups.

Hemin binds to red cell membranes during hemin-induced hemolysis but the precise mechanism of hemolysis has not been characterized. Desferrioxamine (DFO), an iron chelator, inhibited hemin-induced hemolysis. DFO partially prevented hemin binding to red cell membranes and partially removed previously bound hemin. Glutathione, an intracellular sulfhydryl compound, also inhibited hemin-induced hemolysis but was only about one tenth as potent as DFO. Decrease of membrane sulfhydryl groups by treatment of cells with either N-ethylmaleimide (NEM) or diamide (azodicarboxylic acid bis [dimethylamide]) enhanced hemin-induced hemolysis. Enhancement of hemin-induced hemolysis by NEM and diamide and inhibition of hemolysis by DFO were independent with no evidence of synergism or interference between the two processes. Red cell membranes were saturated with hemin at approximately 75 nmol per mg protein. DFO decreased the hemin saturation level to 25 nmol per mg protein. In the presence of DFO, hemin was bound as the DFO-hemin complex since membranes preferentially removed DFO-hemin complexes from mixtures of complexed and free hemin while free DFO was not bound by the membranes. Access to the inner surface of the membrane was required for binding of the DFO-hemin complex since DFO completely prevented hemin binding in intact cells but not in cells undergoing hemolysis or red cell ghosts. Approximately 50 x 10(6) molecules of hemin were bound to the membrane of one red cell following hemin-induced hemolysis.

Deferoxamine↗
PubMed1992

Pharmacokinetic and thrombolytic properties of unglycosylated recombinant tissue-type plasminogen activator (BM 06.021) produced in Escherichia coli.

Recombinant tissue-type plasminogen activator (rt-PA) was produced in Escherichia coli cells in order to obtain an unglycosylated rt-PA (BM 06.021) with increased thrombolytic potency due to altered pharmacokinetic properties. The pharmacokinetics were studied in rabbits upon intravenous infusion of 200 kU/kg over 30 min. The thrombolytic dose-response effects were evaluated in a rabbit model with 125I-labeled venous thrombi upon intravenous infusion over 4 h. The thrombolytic effects after intravenous bolus injection of 200 kU/kg BM 06.021 were investigated in a canine model of coronary artery thrombosis. All studies were performed comparing BM 06.021 with glycosylated rt-PA (alteplase). BM 06.021 demonstrated a longer (p less than 0.05) half-life (5.6 +/- 2.6 vs. 2.1 +/- 0.3 min) and a lower (p less than 0.05) clearance rate (7.5 +/- 0.8 vs. 22.2 +/- 3.1 ml.min-1.kg-1) than alteplase in rabbits upon intravenous infusion. The dose-response curve of BM 06.021 for thrombolysis in a rabbit model of jugular vein thrombosis was located to the left of that for alteplase with a 2.1-fold lower effective dose of 50% thrombolysis (ED50) of BM 06.021 (207 vs. 436 kU/kg). Intravenous bolus injection of 200 kU/kg BM 06.021 induced the same reperfusion rate (4/6) as intravenous infusion of 800 kU/kg alteplase over 90 min in a canine model of coronary artery thrombosis. The residual thrombus wet weight did not significantly differ between BM 06.021 and alteplase (5.7 +/- 1.8 vs. 6.3 +/- 1.1 mg). The results indicate that unglycosylated rt-PA (BM 06.021) has a higher in vivo thrombolytic potency than glycosylated rt-PA (alteplase).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

In vitro cytotoxicity of methylated phenylenediamines.

The acute cytotoxicities of methylated phenylenediamines (PDs) were evaluated with the neutral red assay, using BALB/c 3T3 mouse fibroblasts as the bioindicators. When the test agents were grouped according to their degree of methylation, good correlations were noted between their in vitro cytotoxicity and their in vivo myotoxicity to experimental animals, as well as to their in vitro autoxidation rates. For test agents of comparable methylation, the sequence of potency was ring-methylated p-PD > N-methylated p-PD >> N-methylated o-PD > N-methylated m-PD.

Animals↗
PubMed1992

Desferrioxamine enhances the reactivity of vanadium (IV) and vanadium (V) toward ferri- and ferrocytochrome c.

Ligands, especially desferrioxamine, affect the rate at which vanadium reduces or oxidizes cytochrome c. Whether reduction or oxidation occurs, and how fast, depends on the nature of the ligand, the state of reduction of the vanadium, the pH (6.0, 7.0, or 7.4), and the availability of oxygen. In general, oxidation of ferrocytochrome c was favored by (1) low pH, (2) an oxidized state of the vanadium, (3) the presence of oxygen, and (4) more strongly binding ligands (desferrioxamine much greater than histidine = ATP greater than EDTA greater than albumin greater than aquo). Thus, at pH 6.0, desferrioxamine accelerated the V(V)-catalyzed ferrocytochrome c oxidation 160-fold aerobically, and 3500-fold anaerobically. In general, strongly binding ligands slowed oxidations, especially at higher pH. Desferrioxamine was unique among the five ligands in that it not only accelerated oxidation of ferrocytochrome c at pH 6.0, but at pH 7.4 the redox balance shifted to the point where it paradoxically reduced ferricytochrome c. V(V) is an improbable electron donor, but desferrioxamine will reduce cytochrome c, and V(V) accelerates this process. Oxidation of cytochrome c by V(V):desferrioxamine was faster anaerobically, and reduction by V(IV):desferrioxamine was faster aerobically. Although V(V) did not oxidize ferrocytochrome c at pH 7.4, V(IV) did, provided oxygen and desferrioxamine were both present. V(IV):desferrioxamine almost completely reduced ferricytochrome c, and this reduction was followed by a slow, progressive oxidation. This latter oxidation of cytochrome c is mediated by active species generated in the reaction between V(IV):desferrioxamine and oxygen, because none of these reagents alone can induce oxidation at a comparable rate. The mediating species were transient, and generated in reactions with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)

Catalase↗
PubMed1992

Biochemical properties of the kringle 2 and protease domains are maintained in the refolded t-PA deletion variant BM 06.022.

BM 06.022 is a t-PA deletion variant which comprises the kringle 2 and the protease domain. Production of BM 06.022 in Escherichia coli leads to the formation of inactive inclusion bodies, which have to be refolded by an in vitro refolding process to achieve activity and proper structure of the domains. We analysed the biochemical properties of BM 06.022 to obtain some information about the structure of kringle 2 and the protease as compared with the structure of these domains in the intact t-PA molecule. The kinetic analysis of the amidolytic activity of BM 06.022 and CHO-t-PA yielded similar values for kcat (13.9 s-1 and 11.4 s-1 for the single chain forms and 33.9 s-1 and 27.1 s-1 for the two chain forms of BM 06.022 and CHO-t-PA, respectively) and for Km (2.5 mM and 2.1 mM for the single chains forms and 0.5 mM and 0.3 mM for the two chain forms of BM 06.022 and CHO-t-PA, respectively). BM 06.022 and CHO-t-PA have the same plasminogenolytic activity in the absence of CNBr fragments of fibrinogen. However, BM 06.022 has a lower plasminogenolytic activity in the presence of CNBr fragments of fibrinogen and a lower affinity to fibrin as compared with CHO-t-PA. The affinity of BM 06.022 for fibrin is completely suppressed by 0.3 mM epsilon-aminocaproic acid, while the intact t-PA has a residual affinity of approximately 30%. The dissociation constants for the interaction with the lysine analogue epsilon-aminocaproic acid are 0.10 mM and 0.09 mM for BM 06.022 and the intact t-PA, respectively. Furthermore, BM 06.022 and CHO-t-PA are inhibited by PAI-1 in a similar manner.

Amidohydrolases↗
PubMed1992

Granulocyte-macrophage colony-stimulating factor (GM-CSF) treatment of clozapine-induced agranulocytosis: a case report.

BACKGROUND: Granulocytopenia and agranulocytosis are severe side effects of clozapine therapy. Even if these side effects are detected early and if clozapine is discontinued, patients suffering from agranulocytosis are extremely endangered by infectious diseases for up to 3 to 4 weeks until hematologic recovery. Therefore, any treatment that reduces this critical time span would decrease the risks of clozapine treatment. METHOD: The case of a patient in whom severe agranulocytosis developed after 7 weeks of clozapine treatment is presented. RESULTS: After clozapine discontinuation, treatment with granulocyte-macrophage colony-stimulating factor (GM-CSF), a glycoprotein that has been shown to stimulate the proliferation of precursor cells in the bone marrow and their differentiation into granulocytes and macrophages, was initiated. Under GM-CSF treatment, total granulocyte count rose from 63/cu mm to a value greater than 1500/cu mm within 5 days without complications or major side effects. CONCLUSION: This case report suggests that treatment with GM-CSF may lower the risks associated with clozapine-induced agranulocytosis and therefore may indirectly improve the safety of clozapine therapy.

Adult↗
PubMed1991

The class 3 outer membrane protein (PorB) of Neisseria meningitidis: gene sequence and homology to the gonococcal porin PIA.

The class 3 protein (PorB) is an important component of the meningococcal outer membrane. The structural gene (porB) encoding the class 3 protein has been cloned using primers suitable for the amplification of the corresponding chromosomal fragment by the polymerase chain reaction (PCR). The complete nucleotide sequence was determined and predicts a mature protein of 310 amino acids, preceded by a signal peptide of 19 residues. The predicted protein sequence of the class 3 protein exhibits essential structural homology to the gonococcal porin PIA. The class 3 protein encoding gene was expressed in Escherichia coli under the control of an inducible promoter.

Amino Acid Sequence↗
PubMed1991

Oxidation of NADH by vanadium: kinetics, effects of ligands and role of H2O2 or O2.

The mechanism of oxidation of NADH by either vanadium(V) or vanadium(IV) was examined in the presence of reducing agents, complexing agents, and hydrogen peroxide. Reducing agents that stimulate the oxidation of NADH by V(V) include: a variety of cysteine analogues, glutathione, beta-mercaptoethanol, dithiothreitol, and ascorbate. Complexing agents which stimulate NADH oxidation by V(V) include cystine, glutathione disulfide, and dehydroascorbate. Vanadium(IV)-dependent systems which oxidize NADH include combinations of V(IV) with cysteine or air alone. Combination of either V(V) or V(IV) with hydrogen peroxide leads to NADH oxidation. Based on kinetic analysis and the use of the diagnostic inhibitors--superoxide dismutase, catalase, albumin, mannitol, ethanol, and anaerobic conditions--we have assigned two major mechanisms of NADH oxidation. One is the previously reported mechanism which involves V(V)-superoxide as the NADH oxidant. This reaction is inhibited by superoxide dismutase and anaerobic conditions but not by catalase or ethanol. This reaction is observed for V(V) in the presence of reducing agents and complexing agents. The second reaction mechanism operates when V(IV) comes in contact with hydrogen peroxide and involves V(III)-superoxide as the NADH oxidant. This reaction is inhibited by catalase (if unligated hydrogen peroxide is an intermediate) and superoxide dismutase but not anaerobic conditions or ethanol. This mechanism is observed for reactions of V(IV) with air or hydrogen peroxide.

Albumins↗
PubMed1991

Thrombolysis with an Escherichia coli-produced recombinant plasminogen activator (BM 06.022) in the rabbit model of jugular vein thrombosis.

The recombinant plasminogen activator BM 06.022 consists of the kringle 2 and the protease domains of human t-PA and is unglycosylated because of the expression in Escherichia coli. The thrombolytic and pharmacokinetic properties as well as the hemostasis effects of BM 06.022 were investigated in the rabbit model of jugular vein thrombosis. The thrombi were 125I-fibrin labeled. Intravenous bolus injection of 50, 100, 200, and 400 kU/kg BM 06.022 or 400, 800, and 1600 kU/kg alteplase over 15 s to six rabbits/dose produced a dose-dependent increase of thrombolysis determined 2 h post injection. The dose-response curve of BM 06.022 was located left compared with that of alteplase. The effective dose of 50% thrombolysis (ED50) obtained by half-logarithmic regression analysis was 163 kU/kg (= 0.28 mg/kg) for BM 06.022 and 871 kU/kg (= 1.09 mg/kg) for alteplase. At equipotent doses (50% thrombolysis), the residual concentration of fibrinogen was 74.2% and 76.5%, that of plasminogen 66.7% and 69.4%, and that of alpha 2-antiplasmin 47.3% and 46% for BM 06.022 and alteplase, respectively. Pharmacokinetic analysis for plasma activity at a dose of 400 kU/kg revealed a half-life of 18.9 +/- 1.5 min for BM 06.022, whereas alteplase was distributed with a half-life of 2.1 +/- 0.1 min, accounting for 86.7 +/- 1.9% of the total AUC, followed by a beta-phase with a half-life of 13.8 +/- 0.9 min. Plasma clearance of BM 06.022 was 4.7 +/- 0.7 ml min-1 kg-1 compared with 20 +/- 1.2 ml min-1 kg-1 for alteplase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Pharmacokinetic properties of an Escherichia-coli-produced recombinant plasminogen activator (BM 06.022) in rabbits.

The recombinant plasminogen activator BM 06.022 consists of the kringle 2 and the protease domains of human t-PA and is unglycosylated because of its expression in Escherichia coli. The pharmacokinetic properties of BM 06.022 following intravenous injection over 1 min were characterized in anesthetized male New Zealand white rabbits. BM 06.022 was injected at doses of 50, 100, 200, and 400 kU/kg bw (n = 5-6/dose). Activity concentrations in plasma were determined using an indirect spectrophotometric assay. The maximum plasma concentration and the area under the plasma concentration vs. time curve (AUC0-00) of BM 06.022 increased linearly with dose. The systemic clearance ranged from 2.5 to 3.0 ml.min-1.kg-1 and did not show dose-dependency, in contrast to alteplase which was studied at doses of 200, 400, 800, and 1600 kU/kg. A direct comparison of clearance rates of BM 06.022 and alteplase at doses of 200 and 400 kU/kg each revealed a 8.5-fold slower clearance rate of BM 06.022. The majority (18/23) of rabbits with BM 06.022 injection showed a pharmacokinetic profile which was best characterized by a one-compartment model in contrast to alteplase (10/23). The dose-groups of BM 06.022 showed an average dominant half-life ranging from 11.6 to 15.4 min, which was about five-times longer than the dominant half-life values of alteplase (2.3 to 4.5 min). Assuming a two-compartment model in the remaining animals, the initial alpha-phase of BM 06.022 accounted for 40.1 +/- 13.2% (n = 5) of the total AUC, whereas the alpha-phase of alteplase accounted for 82.7 +/- 3% (n = 13) of the total AUC.

Animals↗
PubMed1991

[Vascular injuries in children].

Vascular trauma in children differs in some respects from that in adults. In infants and children the total blood volume is smaller, and despite effective compensatory mechanisms, critical blood loss is also smaller. Gentle and meticulous technical skill is needed to correct injuries of minute vessels and allow adequate blood flow. The use of synthetic tubes and materials is not recommended, as they do not lengthen as the child grows. Ischemia is a major factor influencing limb growth and function. 3 different types of vascular injuries operated on in the past year are presented.

Blood Vessels↗
PubMed1991

[Emergency therapy with granulocyte-macrophage colony-stimulating factor (GM-CSF)].

Granulocyte-macrophage colony stimulating factor (GM-CSF) has been tested for tolerability and efficacy on a compassionate need case basis in 17 patients (5 females, 12 males aged 4-72 years, median 35 years). GM-CSF was given at the rate of 3.5-32 micrograms/kg for 2-64 days as a continuous infusion for the following indications: impending rejection following bone marrow transplantation (5 patients), severe neutropenia secondary to chemotherapy in tumor patients (5), severe aplastic anemia (3), immune granulocytopenia (2) and accidental overdose with cytostatic agents (2 patients). Tolerance of GM-CSF was good in regard to doses of up to 16 micrograms/kg. Fever, myalgia and eosinophilia were the most frequent side effects. The patient treated with 32 micrograms/kg developed thrombosis of the vena cava. Efficacy is more difficult to assess in this heterogenous population, but 11 of 17 patients showed increased granulocyte counts and 3 patients clearly recovered from severe neutropenia. The role of GM-CSF in this recovery, however, cannot be proven. The results further indicate that GM-CSF cannot reverse ongoing rejection following allogenic BMT and cannot correct immune neutropenia. The value of GM-CSF therapy in patients with severe aplastic anemia and in the context of chemotherapy still needs to be defined. It is certainly indicated in patients with an accidental overdose of chemotherapeutic agents.

Adolescent↗