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Biomedical subjects

J H Beer

Publications and source records attributed to J H Beer.

45 records · Page 3Linked to original sources
PubMed1993

[The wrong mushroom. Diagnosis and therapy of mushroom poisoning, especially of Amanita phalloides poisoning].

By far the most frequent deadly intoxication with mushrooms is caused by Amanita phalloides. The diagnosis is based upon the long latency phase, the typical clinical picture of which includes four periods (the asymptomatic latent phase, the gastroenteritis phase, the oligosymptomatic interval and the hepatorenal phase), analysis of the mushrooms by the expert and the sensitive radioimmunoassay for amanitin in blood, urine or gastric content. The therapy includes (1) stabilisation of the patient with the correction of hypoglycemia and electrolyte imbalance, substitution with coagulation factors (FFP) and red cells and the treatment of septic complications, (2) decontamination, which consists of gastric lavage, the administration of activated charcoal and laxatives as well as the forced diuresis, and (3) therapy with high doses of penicillin or ceftazidime and of silibinine. The pathophysiological mechanisms are discussed. The other important types of mushroom intoxications are summarized in Table 1.

Amanita↗
PubMed1992

[Platelet receptors: nomenclature--structure--function. 1].

Current knowledge on platelet receptors, their structure, function and interaction with their ligands, and the various nomenclatures, is summarized. The role of platelet receptors in thrombosis and hemostasis, and in cell adhesion and invasion, is discussed. Many of the receptors are members of large families of cell-adhesion molecules (such as the integrin family of cell-adhesion receptors) and have common subunits. While some receptors are exclusive to platelets and megakaryocytes (e.g. GP IIb/IIIa), others may be found on several other cell types (such as the receptors for epinephrine or vitronectin). In addition, the receptors for the most important platelet agonists and the platelet binding sites of factors of plasmatic coagulation and fibrinolysis are reviewed.

Binding Sites↗
PubMed1992

Immobilized Arg-Gly-Asp (RGD) peptides of varying lengths as structural probes of the platelet glycoprotein IIb/IIIa receptor.

The interactions between ligands containing the recognition sequence arginine-glycine-aspartic acid (RGD) and integrin receptors are important in many cell-cell and cell-protein interactions. The platelet contains five integrin receptors and they contribute significantly to platelet adhesion and aggregation. To investigate the RGD binding domains on platelet integrins, we immobilized a series of RGD peptides containing variable numbers of glycine residues [(G)n-RGDF] on polyacrylonitrile beads and evaluated the ability of the beads to interact with platelets. With native platelets, virtually no interaction occurred with G1-RGDF beads, but the interactions increased as the number of glycine residues increased, plateauing with the G9-RGDF and G11-RGDF beads. ADP pretreatment enhanced the interactions with all of the beads, whereas prostaglandin E1 pretreatment eliminated the interactions with the shortest peptide beads, but only partially inhibited interactions with the longer peptide beads. Monoclonal antibodies to glycoprotein (GP) IIb/IIIa were most effective in inhibiting the interactions, but antibodies to GPIIb/IIIa with similar inhibitory effects on fibrinogen binding varied dramatically in their ability to inhibit the interaction between platelets and immobilized RGD peptides. Our data indicate that the majority of RGD binding sites on GPIIb/IIIa can be reached by peptides that extend out approximately 11 to 32 A from the surface of the bead, and these results are in accord with the dimensions of integrin receptors deduced from electron microscopy. Activation of GPIIb/IIIa facilitates the interactions, but platelet inhibition fails to eliminate the interactions with the longer peptide beads, suggesting that access to the RGD binding site on at least a fraction of the GPIIb/IIIa receptors is always possible for preferred ligands. Finally, we found that the G3-RGDF peptide beads were uniquely sensitive to the activation state of the GPIIb/IIIa receptor.

Acrylic Resins↗
PubMed1992

Thromboerythrocytes. In vitro studies of a potential autologous, semi-artificial alternative to platelet transfusions.

In an attempt to overcome the limitations and drawbacks of using fresh platelets for transfusion therapy of thrombocytopenic patients, we have performed in vitro experiments on an autologous, semi-artificial alternative to platelet transfusions. Based on our previous studies of the interactions of unactivated and activated platelets with beads coated with peptides of various lengths, all of which contained the arginine-glycine-aspartic acid (RGD) cell recognition sequence, the peptide Ac-CGGRGDF-NH2 was chosen for covalent coupling to erythrocytes. A heterobifunctional crosslinking reagent (N-maleimido-6-aminocaproyl ester of 1-hydroxy-2-nitrobenzene-4-sulfonic acid) was used to crosslink via the peptide's free sulfhydryl group and the erythrocyte's surface amino groups. Approximately 0.5-1.5 x 10(6) peptide molecules bound per erythrocyte after 2 h of incubation, and most of the peptides appeared to crosslink to glycophorin A. The resulting cells, termed thromboerythrocytes, interacted selectively with activated platelets to form mixed aggregates. Studies with fluid phase RGD peptides and monoclonal antibodies indicated that the RGD peptides on the thromboerythrocytes interacted with the GPIIb/IIIa receptors on activated platelets. Thromboerythrocytes could also bind to platelets adherent to collagen. There was minimal erythrocyte hemolysis during the formation of thromboerythrocytes and studies of thromboerythrocyte osmotic fragility and cellular deformability showed no significant changes from control erythrocytes. Whereas there is a 20:1 ratio of erythrocytes to platelets in the circulation of normal individuals, the erythrocytes from as little as 50 ml of blood could be transformed into the equivalent of 2 U of platelets by numbers (equivalent to 18 U of platelets by mass), and reinfused into the same individual within several hours. These data encourage us to proceed to in vivo studies to assess the hemostatic efficacy of thromboerythrocytes in thrombocytopenic animals.

Amino Acid Sequence↗
PubMed1992

[Prevention of venous thromboembolism in internal medicine patients].

In the entirety of medical patients, mechanical prophylactic measures and subcutaneous application of heparin have a documented efficiency and few side effects. With them the hospital mortality can be lowered by about 30%. When analysing the risks for patients of internal medicine, immobilisation respectively absence of the muscle pump play a central role in the list of risk factors. Possibilities for improving prophylaxis comprise an individual adjustment of heparin dosing (the improved efficiency in comparison with fixed dosing is not yet proven, but probable on the basis of experience made with surgical patients), the combination with mechanical/physical measures and the more consistent realisation in patients at risk. For achieving this the dosing only once per day with low molecular heparin is favourable, the latter being at least equally efficient.

Early Ambulation↗
PubMed1989

Collagen-platelet interactions: evidence for a direct interaction of collagen with platelet GPIa/IIa and an indirect interaction with platelet GPIIb/IIIa mediated by adhesive proteins.

Using intact human platelets as the immunogen and a functional, collagen-coated bead agglutination assay, we have produced a murine monoclonal antibody (6F1) that blocks the interaction between platelets and collagen in the presence of Mg++. 6F1 affinity-purified the platelet glycoprotein Ia/IIa complex, and approximately 800 molecules of 6F1 bound per platelet at saturation. 6F1 nearly completely inhibited collagen-induced platelet aggregation and inhibited platelet adhesion to collagen by greater than 95% when plasma proteins were absent. Antibody 10E5, which blocks the binding of adhesive glycoproteins to GPIIb/IIIa, produced only minor inhibition (approximately 25%) of adhesion under the same circumstances. In contrast, when tested in platelet-rich plasma (PRP), 6F1 had only a minor effect on collagen-induced platelet aggregation, prolonging the lag phase but not the slope or maximum aggregation. Similarly, when collagen was precoated with plasma, 6F1 caused less inhibition of platelet adhesion (53%) than without the precoating (greater than 95%). Antibody 10E5 inhibited this adhesion by 32%, and the combination of 6F1 and 10E5 was more effective than either alone, inhibiting it by 90%. Time course studies of platelet agglutination of collagen-coated beads using PRP containing physiologic concentrations of divalent cations showed early inhibition by 6F1, indicating that the GPIa/IIa receptor operates in this environment. With more prolonged incubation, however, 6F1 was less effective; this later agglutination could be partially prevented by adding 10E5 or PGE1 to the 6F1. These data support a model wherein collagen can directly interact with GPIa/IIa and can indirectly interact with GPIIb/IIIa via intermediary adhesive proteins. The physiological significance of these interactions, and potential interactions with other receptors, remains to be established.

Antibodies, Monoclonal↗
PubMedDate not supplied

Evaluation of back pain secondary to spinal epidural hematoma associated with aspirin intake and a partial platelet glycoprotein Ia/IIa deficiency.

We report a case of spontaneous spinal epidural hemorrhage with three unusual features: (1) the hemorrhage was associated with aspirin ingestion and a reduced level of platelet glycoprotein Ia/IIa; (2) the patient presented with typical severe back pain but without neurologic dysfunction; and (3) the patient initially recovered without surgical decompression but suffered from recurrent epidural hematoma.

Adult↗
PubMedDate not supplied

Effect of methylene blue on the disposition of ethanol.

The effect of methylene blue on the disposition of ethanol was studied in rats and humans. Methylene blue increased the metabolism of [(14)C]ethanol to (14)CO(2) in isolated hepatocytes and in intact rats by 75% and 30%, respectively. In healthy volunteers, methylene blue did not affect the pharmacokinetics of ethanol and did not alleviate the ethanol-induced NAD redox changes as reflected by the increase in the [lactate]/[pyruvate] ratio.

Adult↗