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Biomedical subjects

A Stern

Publications and source records attributed to A Stern.

At least 73 records · Page 4Linked to original sources
PubMed1997

Hemin-induced membrane sulfhydryl oxidation: possible involvement of thiyl radicals.

Sublytic levels (microM) of hemin destabilized RBC membrane as indicated by ghost fragmentation pattern using a laser viscodiffractometer. Furthermore, electron microscopic study shows that 5 microM of hemin induced echinocytic transformation whereas higher hemin concentration (40 microM) induced spherocytic transformation. In addition, hemin oxidized sulfhydryl groups in a dose dependent fashion and Electron Spin Resonance study suggests that such oxidation may involve a thiyl radical. Moreover, sulfhydryl compounds enhanced hemin-induced lipid peroxidation. Desferroxamine could prevent hemin-induced sulfhydryl oxidation as well as hemin-induced decrease in membrane stability. In contrast, vitamin E could effectively prevent hemin-induced lipid peroxidation but could not prevent hemin-mediated membrane destabilization.

Deferoxamine↗
PubMed1996

Redox modulation of tyrosine phosphorylation-dependent signal transduction pathways.

The main purpose of this review article is to provide a better understanding of the role of oxidants as modulators/mediators of tyrosine phosphorylation-dependent signal transduction pathways. It is generally accepted that reversible phosphorylation of protein tyrosine residues by polypeptide growth factor receptor protein tyrosine kinases (e.g., epidermal growth factor receptor, platelet derived growth factor receptor, insulin receptor) is a signalling mechanism implicated in cell proliferation, adhesion, differentiation, transformation, and apoptosis. It is controlled by the opposing actions of protein tyrosine kinases and protein tyrosine phosphatases. Nevertheless, increasing amounts of experimental data indicate that intracellular redox state plays a major role in the mechanisms underlying the actions of growth factors. Furthermore, redox active species mediate signalling processes on their own. Thus, in this article we attempted to discuss these points, presenting our published as well as unpublished contribution to the field.

Animals↗
PubMed1996

Effect of disulfide bonds on the structure, function, and stability of the trypsin/tPA inhibitor from Erythrina caffra: site-directed mutagenesis, expression, and physiochemical characterization.

Erythrina trypsin/tPA inhibitor (ETI) from the seeds of Erythrina caffra retains its native structure and inhibitory function after reducing its two disulfide bonds. In order to elucidate the specific role of these crosslinks, alanine residues were substituted for cysteines after cloning the gene in Escherichia coli. Expression of the recombinant inhibitor and the substitution mutants, C83A, CC39, 83AA, and CC132, 139AA, led to inclusion bodies. After solubilization in guanidinium-chloride (GdmCl)/dithiothreitol and oxidation in glutathione buffer, activity could be recovered at yields up to 80%. The mutant proteins exhibit full inhibitory function without detectable alterations of their native structure. However, their stability is reduced: at acid pH, where the oxidized natural inhibitor retains its native structure, the reduced wildtype protein and the mutants undergo at least partial denaturation, reflected by decreased pH ranges of stability: pH 5-7 for the reduced inhibitor, pH 2.5-8.5 for CC132, 139AA, and pH 3.5-8.5 for C83A and CC39, 83AA. Urea and GdmCl denaturation at pH 7 show hysteresis for both the oxidized inhibitor and the double mutant CC132, 139AA. In contrast, the reduced protein and the other mutants exhibit true equilibrium transitions at pH 7, with urea half-concentrations of 0.9 M and 1.9 M and GdmCl half-concentrations of 0.5 M and 1.0 M, respectively. The stability of Erythrina trypsin/tPA inhibitor follows the sequence: oxidized ETI > CC132, 139AA > CC39, 83AA and C83A > reduced ETI.

Amino Acid Sequence↗
PubMed1996

Comparison of the recombinant Escherichia coli-produced protease domain of tissue-type plasminogen activator with alteplase, reteplase and streptokinase in a canine model of coronary artery thrombolysis.

Recent in vitro studies have shown that although recombinant Escherichia coli-produced protease domain of tissue-type plasminogen activator (t-PA) has no appreciable fibrin binding and less plasminforming activity compared to the wild-type, it is nevertheless an effective fibrinolytic agent in a dynamic in vitro plasma clot lysis system. The purpose of the present study was to evaluate the pharmacological profile of the protease in a canine model of coronary artery thrombosis. The effects of a single i.v. bolus injection of 1 mg/kg protease were compared with those of alteplase, reteplase and streptokinase at clinically relevant doses and dosing regimens in eight dogs per group. The protease rapidly restored coronary blood flow at 12 +/- 1 min in all treated dogs with a significantly higher maximal coronary blood flow than in the reference groups, but was associated with short cycles of reocclusion in 4/8 animals. Overall, the coronary blood flow quality of the protease was not significantly different from that of the reference thrombolytics. Although fibrinogen was nearly completely degraded during protease treatment, the bleeding time was not significantly more prolonged than in reference groups. In conclusion, the protease domain is a rapidly acting, effective, bolus-injectable thrombolytic agent associated with a systemic lytic state and does not appear to cause significantly more bleeding than the reference thrombolytic agents.

Animals↗
PubMed1995

Nitric oxide stimulates tyrosine phosphorylation in murine fibroblasts in the absence and presence of epidermal growth factor.

In the present study, utilizing anti-phosphotyrosine monoclonal antibodies, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) as sources of NO and murine fibroblasts expressing the human epidermal growth factor (EGF) receptor (HER14 cells), we showed that tyrosine phosphorylation of a set of proteins (126, 56 and 43 kDa) was stimulated when cells were incubated with either SNP or SNAP and abolished by Methylene Blue and oxyhaemoglobin. Inhibition by Methylene Blue suggested an involvement of cyclic GMP in the process, which was evidenced by the effects of 8-bromo cyclic GMP. This analogue of cyclic GMP stimulated tyrosine phosphorylation of the same set of proteins phosphorylated after incubation with the NO source. Tyrosine phosphorylation of the same set of proteins was stimulated when cells were incubated simultaneously with SNP and EGF, showing that NO also potentiates EGF-evoked tyrosine kinase activity in HER14 cells. However, stimulation of the autophosphorylation of the EGF receptor, above the levels obtained for EGF alone, was not observed under those conditions. Additionally, we investigated the effects of NO on EGF-receptor tyrosine phosphatase activities in HER14 cells. Increasing concentrations of NO correlate with a gradual inhibition of these activities in HER14 cells, either in intact cells or in cell lysates. Taken together, these observations suggest that NO modulates tyrosine phosphorylation in HER14 cells.

Animals↗
PubMed1995

Identification and characterization of specific sequences encoding pathogenicity associated proteins in the genome of commensal Neisseria species.

The distribution of distinct sequences in pathogenic and commensal Neisseria species was investigated systematically by dot blot analysis. Probes representing the genes of Rmp, pilin and IgA1 protease were found to hybridize exclusively to the chromosomal DNA of the pathogenic species, Neisseria gonorrhoeae and/or Neisseria meningitidis. In contrast, specific sequences for the genes of the porin protein Por and the opacity protein (Opa) were also detected in a panel of commensal Neisseria species such as N. lactamica, N. subflava, N. flava, N. mucosa and N. sicca. Using opa-specific oligonucleotides as probes in chromosomal blots, the genomes of the commensal Neisseria species show a totally reduced repertoire of cross-hybridizing loci compared to the complex opa gene family of N. gonorrhoeae. DNA sequence analysis of one opa-related gene derived from N. flava and N. sicca, respectively, revealed a large degree of homology with previously described gonococcal and meningococcal genes, e.g., a typical repetitive sequence in the leader peptide and the distribution of the hypervariable and conserved regions. This observation, together with the finding, that the gene is constitutively transcribed, leads to the assumption that some of the commensal Neisseria species may have the potential for the expression of a protein harboring similar functions as the Opa proteins in pathogenic Neisseriae.

Amino Acid Sequence↗
PubMed1995

Severe anaphylactic reaction to bovine serum albumin at the first attempt of artificial insemination.

A 33-year-old woman without history of previous atopic diseases or drug allergies developed a severe anaphylactic reaction with asthma, vomiting, itching, generalized urticaria, and angioedema during artificial insemination with her husband's sperm. The sperm-processing medium contained bovine serum albumin (BSA). Skin prick test and RAST demonstrated an IgE-mediated hypersensitivity to BSA as well as a polyvalent atopic sensitization to pollens, animal danders, cow's milk, beef, pork, and mutton. SDS-PAGE studies indicated serum albumin to be the appropriate allergen with a high degree of cross-reactivity between serum albumin from different animal species. Artificial insemination with fluid containing potential allergens can, therefore, represent an unnecessary risk for atopic females, even in the absence of prior clinical symptoms of allergic diseases. Preoperative testing with the medium is recommended.

Adult↗
PubMed1995

Is allergy screening of blood donors necessary? A comparison between questionnaire answers and the presence of circulating IgE antibodies.

We investigated 477 consecutive blood donors on order to find the predictive value of a questionnaire as a screening method for preventing passive transfer of IgE antibodies to common allergens that might cause transfusion reactions. Of the 477 donors, 119 (24.9%) claimed to be allergic and 358 (75.1%) recorded no allergic complaints. Serological examination with Phadiatop and a multi-allergen mix for food (fx5) detected IgE antibodies in only 54.5% of the allegedly allergic blood donors. Among the allegedly asymptomatic donors, 12.3% showed positive results in these tests. Subsequently, radioallergosorbent test analyses with common inhalant and food allergens were performed to specify the IgE responses obtained. Our results demonstrate a remarkable difference between the questionnaire answers and the serological measurements of IgE antibodies and raise the question of whether - and if so, what kind of - allergy screening is warranted among presumptive blood donors.

Adolescent↗