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Biomedical subjects

R Seifert

Publications and source records attributed to R Seifert.

At least 145 records · Page 8Linked to original sources
PubMed1987

Activation of protein kinase C by cis- and trans-octadecadienoic acids in intact human platelets and its potentiation by diacylglycerol.

Octadecadienoic acids (linoleic acid and linolelaidic acid) and the diacylglycerol, 1-oleoyl-2-acetyl-rac-glycerol (OAG) concentration-dependently induced activation of gel-filtered human platelets, i.e. aggregation and phosphorylation of 20 kDa and 47 kDa peptides. In contrast, octadecenoic acids (oleic and elaidic acid) and octadecanoic (stearic) acid were inactive. Octadecadienoic acid-induced platelet activation was suppressed by the protein kinase C inhibitor, polymyxin B, but not by the cyclooxygenase inhibitor, indomethacin. OAG-induced activation was potentiated by octadecadienoic acids present at non-stimulatory concentrations. Our data suggest that octadecadienoic acids and diacylglycerol synergistically induce platelet activation via protein kinase C. Furthermore, linolelaidic acid may provide a useful experimental tool to study fatty acid regulation of protein kinase C in intact cells.

Blood Platelets↗
PubMed1987

Reversible activation of NADPH oxidase in membranes of HL-60 human leukemic cells.

NADPH oxidase in membranes of undifferentiated and dimethylsulphoxide-differentiated HL-60 cells was activated by arachidonic acid (AA) in the presence of Mg2+ and a cytosolic cofactor (CF) found in differentiated HL-60 cells. Basal superoxide (O2-) formation was enhanced several-fold by addition of the stable GTP-analogue, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), prior to AA and was completely prevented by that of GDP. Basal and GTP gamma S-stimulated O2- formation was terminated by GDP. In the presence of Mg2+ or EDTA, basal O2- formation ceased after 25 or 10 min, respectively, and was reinitiated by GTP gamma S or GTP gamma S plus Mg2+. Albumin terminated O2- formation, which was reactivated by AA in the presence of GTP gamma S. Our results show that (1) activation of NADPH oxidase in HL-60 membranes is dependent on endogenous GTP, Mg2+, AA and CF, which is induced during myeloid differentiation, and that (2) NADPH oxidase activation is a reversible process modulated by exogenous guanine nucleotides at various stages of activity of NADPH oxidase. We suggest crucial roles of guanine nucleotide-binding proteins in the activation, deactivation and reactivation of the enzyme.

Cell Differentiation↗
PubMed1987

Fatty-acid-induced activation of NADPH oxidase in plasma membranes of human neutrophils depends on neutrophil cytosol and is potentiated by stable guanine nucleotides.

Both cis and trans unsaturated fatty acids and sodium dodecyl sulfate activated NADPH oxidase in plasma membranes of human neutrophils in the presence of neutrophil cytosol. In contrast, 5,8,11,14-icosatetraynoic acid, saturated fatty acids, esters, peroxides and 4 beta-phorbol 12-myristate 13-acetate, a potent activator of protein kinase C, were inactive. 5,8,11,14-icosatetraynoic acid inhibited superoxide formation elicited by fatty acids. Guanosine 5'[gamma-thio]triphosphate (GTP[gamma S]), a potent activator of guanine-nucleotide-binding proteins (N-proteins) enhanced superoxide formation elicited by fatty acids up to fourfold, supporting our previous suggestion that NADPH oxidase is regulated by an N-protein [Seifert, R. et al. (1986) FEBS Lett. 205, 161-165]. Cytosols from various tissues, soybean lipoxygenase and protein kinase C, purified from chicken stomach, did not substitute neutrophil cytosol. The activity of neutrophil cytosol was destroyed by heating at 95 degrees C. Superoxide formation was not affected by the inhibitor of protein kinase C 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7). Removal of cytosolic ATP by preincubation with hexokinase and glucose, dialysis of neutrophil cytosol or chelation of calcium with EGTA did not abolish the stimulatory effect of arachidonic acid and GTP[gamma S]. Thus, the cytosolic cofactor appears to be a neutrophil-specific and heat-labile protein, which is neither a lipoxygenase nor protein kinase C.

Cell Membrane↗
PubMed1987

Platelet monoamine oxidase activity and schizophrenia--a myth that refuses to die?

Platelet monoamine oxidase (MAO) activity was determined using kynuramine as a substrate in a group of schizophrenic patients (n = 107), a group of healthy individuals (n = 100), and a group of psychiatric patients who were neither schizophrenics nor alcoholics (n = 110). No significant difference emerged between the schizophrenics and the other two groups, while a significant reduction in platelet MAO activity in a group of alcoholics (n = 60) was confirmed. Breaking down the schizophrenic group according to course of illness, phenomenology (paranoid-hallucinatory or not) and drug use did not lead to a significant deviation in platelet MAO activity in any of these subgroups. It can also be demonstrated from the literature that the results reached by most research teams question the usefulness of platelet MAO activity as a genetic marker for psychiatric illness.

Adult↗
PubMed1986

Guanine nucleotides stimulate NADPH oxidase in membranes of human neutrophils.

In the chain of events by which chemotactic peptides stimulate NADPH oxidase-catalyzed superoxide formation in human neutrophils, the involvements of a pertussis toxin-sensitive guanine nucleotide-binding protein (N-protein), mobilization of intracellular calcium and protein kinase C stimulation have been proposed. Superoxide formation was studied in membranes from human neutrophils; NADPH oxidase was stimulated by arachidonic acid in the presence of neutrophil cytosol. Fluoride and stable GTP analogues, such as GTP gamma S and GppNHp, which all activate N-proteins, enhanced NADPH oxidase activity up to 4-fold. GDP beta S inhibited the effect of GTP gamma S. These data suggest that NADPH oxidase is regulated by an N-protein, independent of an elevation of the cytoplasmic calcium concentration.

Cell Membrane↗
PubMed1986

[Combined therapy with high-dosage cisplatin and radiation in advanced ENT tumors (a phase-II study)].

The most promising method to obtain at least a palliative effect in advanced ORL tumors seems to be a combination of chemotherapy and radiotherapy. We made an attempt to reach a higher remission rate (n = 28) by means of an extraordinary high dose of cis-platinum and the usual maximum radiation dose of 60 Gy: The method had to be abandoned because the rates of success (CR and PR) decreased from 79% to 46% in eight months, the side effects, however, were beyond a tolerable degree. We are of the opinion that the same results can be obtained by less radical methods, too.

Adult↗
PubMed1986

Heparin kinetics during hemodialysis: variation in sensitivity, distribution volume, and dosage.

A method to assess heparin kinetics and individualize dosages was examined in 27 patients during chronic hemodialysis. Pretreatment heparin sensitivities were determined to establish the relationship between heparin concentration and activated clotting times (ACTs). Distribution volume was calculated by dividing the heparin loading dose by the 5-min heparin concentration. Assessments were made during three different dialysis periods. There was a 10-fold range in pretreatment heparin sensitivities. Intrapatient heparin sensitivity remained relatively consistent between dialysis periods. The degree of heparin sensitivity was significantly correlated to baseline ACT. Patients post-splenectomy were more sensitive to heparin. Large intra- and interpatient variation in distribution volume was also observed. Men, patients less than 60 years old, and patients post-splenectomy represented variables that contributed to higher heparin dose requirements.

Adolescent↗
PubMed1985

Monoclonal antibodies to bovine alpha-crystallin.

Monoclonal antibodies to bovine alpha-crystallin have been produced using hybridoma technology. Five selected hybridoma clones were maintained as ascites tumours in mice and gram quantities of the antibodies were purified from the ascites fluids by affinity chromatography on alpha m-crystallin covalently bound to Sepharose CL-2B. Preliminary characterization studies suggest that the antibodies are pure and monospecific. The antibodies could be divided into two groups on the basis of their reactivities towards iodinated alpha-crystallin, their ability to bind to Protein A-Sepharose, their immunoglobulin subclass, their immunoelectrophoretic patterns and their abilities to react with chicken and opossum alpha-crystallin. The availability of these monoclonal antibodies will greatly facilitate studies on the surface topography of alpha-crystallin.

Amino Acids↗
PubMed1984

Nicotinamide methylation. Tissue distribution, developmental and neoplastic changes.

The distribution of cytosolic activity of nicotinamide:S-adenosylmethionine methyltransferase (nicotinamide methylase, EC 2.1.1.1) in normal tissues from adult rat and mouse and in tumors and the change in the enzyme activity during the development of rat tissues were studied. (1) Rat liver exhibited the highest nicotinamide methylase activity among all adult tissues tested; other rat tissues, like adrenal, pancreas, kidney, brain and mouse tissues, had only less than 15% of the adult rat liver activity. (2) 3 days before birth, fetal liver showed a very low nicotinamide methylase activity (2% of adult rat liver), which, however, increased already 1 day before birth and reached the adult level on the day 28 after birth. (3) In a variety of hepatomas and ascites tumors, an inverse correlation, with some exceptions, between tumor growth rate and nicotinamide methylase activity could be seen. In all hepatomas, with the exception of Morris hepatoma 5123tc, nicotinamide methylase activity was significantly decreased in comparison to normal adult rat liver. The highly malignant Zajdela hepatoma, Yoshida sarcoma, sarcoma 180 and Ehrlich ascites tumor methylated nicotinamide only at a negligibly low rate. (4) Cultured RLC cells (an established rat liver cell line) from the stationary growth phase or G1-arrested RLC cells had about half of the adult rat liver activity, yet the activity was 70% higher than that of the logarithmically growing RLC cells.

Aging↗
PubMed1983

Application of the peroxidase anti-peroxidase system as an universal reagent for the two-site binding enzyme immunoassay.

An indirect two-site binding enzyme immunoassay (EIA) is described, in which horse-radish peroxidase (HRP) is bound immunologically to anti-HRP IgG in the form of peroxidase anti-peroxidase complexes (PAP-complex). In this EIA both purified HRP and crude HRP had the same sensitivity due to the selective reaction of the monospecific anti-HRP IgG with the highly active HRP isoenzymes in both preparations. To obtain similar results the amount of crude HRP needed is 18 times higher than that of purified HRP. A comparison of differently composed PAP-complexes showed that only those formed in an excess of HRP yielded a highly sensitive EIA. Urea splitting of the PAP-complexes did not raise the specific activity of the enzyme. The PAP-complexes were used in an assay for quantification of the pregnancy-associated alpha 2-glycoprotein and compared with an indirect two-site binding EIA, in which purified HRP was covalently bound to IgG. Both test variants resulted in the same sensitivity and showed similar precision.

Animals↗
PubMed1983

Use of anticholinergics in the nursing home: an empirical study and review.

The Medicare Utilization Review Committee conducted a survey to determine the use of drugs with anticholinergic effects in confused elderly nursing home patients. Twenty-nine patients (34.5 percent) were receiving anticholinergic drugs, predominantly from the antidepressant and antipsychotic class. Thioridazine (Mellaril) was the most frequently used antipsychotic. No patients received higher than the equivalent recommended daily dose of atropine when calculated in terms of relative anticholinergic potency. No statistically significant correlation could be found between the presence of confusion and the amount of anticholinergics administered. Confusion and cognitive deterioration frequently are encountered when caring for aged patients. Clinical experience and recent studies suggest that anticholinergics may increase the risk of or exacerbate existing confusion, and this possible effect of anticholinergic activity should be considered when prescribing for elderly patients.

Aged↗
PubMed1983

[Clinical experience with blood vessel ligation in uncontrollable nosebleed].

Between 1978 and 1980 in the ENT clinics of Mannheim 19 patients with severe epistaxis have been treated surgically. Nearly always epistaxis was due to hypertonus or arteriosclerosis. Before ligation of maxillary or ethmoid arteries Bellocq's nasal packing was used. Ligation was always successful. After one year in three cases we observed a recidive of epistaxis, not due to bad surgical treatment but rich anastomoses of the maxillary artery. It is strange, that artery ligation is recommended, when posterior nasal packing fails, although its complications are more severe and frequent than those of chirurgical treatment including the anesthesiological risk. Ligation in severe epistaxis is effective and of low risk. It is an alternative to posterior nasal packing.

Epistaxis↗
PubMed1983

Heparin-associated thrombocytopenia: a prospective evaluation of 211 patients.

Two hundred eleven consecutive patients treated for acute thromboembolic disease were evaluated prospectively for the incidence of thrombocytopenia while receiving heparin treatment. One hundred patients received beef lung heparin and 111 patients received porcine intestinal mucosal heparin. All patients received a minimum of 4 consecutive days of continuous intravenous heparin, and platelet counts were determined prior to, at least twice weekly, and at the cessation of heparin therapy. Heparin-associated thrombocytopenia was defined as a decline from a normal platelet count (100,000-400,000/mm3) to less than 100,000/mm3 with a return to above 100,000/mm3 after the discontinuation of heparin. Heparin-associated thrombocytopenia developed in 11 patients (5.2% incidence). Ten of the thrombocytopenic patients had received beef lung heparin and one received porcine mucosal heparin. Chi-square analysis of these data was significant (p = 0.007). Plasma from seven of nine thrombocytopenic patients demonstrated a plasma factor compatible with a heparin-sensitive antiplatelet antibody. Heparin-associated thrombocytopenia appeared on days 2 to 10 of therapy. Cessation of heparin resulted in remission of thrombocytopenia within 4 days in all patients. Serial quantitative platelet count determinations are indicated in all patients receiving therapeutic heparinization for the early recognition and resolution of heparin-associated thrombocytopenia.

Adolescent↗