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Biomedical subjects

I Kuhn

Publications and source records attributed to I Kuhn.

At least 19 recordsLinked to original sources
PubMed1992

Structure-function studies of the epidermal growth factor domains of human thrombomodulin.

Structure-function relationships in the 6 epidermal growth factor-like domains of human thrombomodulin (TME, residues 227-462) were studied by deletion mutagenesis. Purified and characterised proteins were used for kinetic studies. Deletion of EGF1, EGF2 and residues 310-332 in EGF3 had no effect on thrombin binding (Kd) or on kcat/KM for protein C activation by the thrombin-thrombomodulin complex. Deletion of the rest of EGF3 and the interdomain loop between EGF3 and EGF4 had no effect on Kd but decreased kcat/KM to 10% of TME. Deletion of residues 447-462 of EGF6 had no effect on kcat/KM but increased Kd for thrombin approximately 6-fold. Thus, the region 333-350 in EGF3-4 is critical for protein C activation by the thrombin-thrombomodulin complex and the region 447-462 in EGF6 is critical for thrombin binding.

Base Sequence↗
PubMed1992

Oxidation of a specific methionine in thrombomodulin by activated neutrophil products blocks cofactor activity. A potential rapid mechanism for modulation of coagulation.

Endothelial thrombomodulin (TM) plays a critical role in hemostasis as a cofactor for thrombin-dependent formation of activated protein C, a potent anticoagulant. Chloramine T, H2O2, or hypochlorous acid generated from H2O2 by myeloperoxidase rapidly destroy 75-90% of TM cofactor activity. Activated PMN, the primary in vivo source of biological oxidants, also rapidly inactivate TM. Oxidation of TM by PMN is inhibited by diphenylene iodonium, an inhibitor of NADPH oxidase. Both Met291 and Met388 in the six epidermal growth factor-like repeat domain are oxidized; however, only substitutions of Met388 lead to TM analogues that resist oxidative inactivation. We suggest that in inflamed tissues activated PMN may inactivate TM and demonstrate further evidence of the interaction between the inflammatory process and induction of thrombotic potential.

Adult↗
PubMed1992

Renal elimination of magnesium as a parameter of bioavailability of oral magnesium therapy.

Magnesium is an important cation in human physiology, especially in the regulation of membrane proteins, as a cofactor for various enzyme systems and in neuromuscular transmission. Magnesium deficiency leads to severe impairment in muscle function, particularly in cardiovascular diseases. Classical bioavailability studies with magnesium cannot be carried out for several reasons. As the magnesium concentration in plasma is extraordinarily well regulated, renal elimination proves to be the best method to determine the absorption of orally administered magnesium. Magnesium pools must first be filled, and the saturation phase of renal elimination then equals the degree of absorption. This parameter of bioavailability shows the percentage of eliminated magnesium in comparison to the administered dose. Eighteen healthy male volunteers were included in this study to compare 5 mg magnesium-DL-hydrogen aspartate with magnesium-L-hydrogen aspartate. After a saturation phase, the test substances were administered in random order. Blood samples for determination of magnesium concentrations were taken, but no typical pharmacokinetic concentration curves were obtained. The areas under the concentration-time curves were equal for both formulations (x = 40.22 [mval*h/l]). The bioavailability of both substances was determined from the renal elimination. No significant difference was found between both treatments. Bioavailability of 5 mg magnesium-DL-hydrogen aspartate was 44.5% and for magnesium-L-hydrogen aspartate 41.7%. It is evident that this method of magnesium determination is practical, comfortable for volunteers and gives reliable results in comparing the absorption of magnesium formulations.

Administration, Oral↗
PubMed1992

Gastric potential difference measurement as a quantification of gastrointestinal tolerability comparing a buffered acetylsalicylic acid formulation versus plain acetylsalicylic acid.

Two different acetylsalicylic acid (ASA, CAS 50-78-2) formulations (Aspirin) were compared regarding their gastric mucosal tolerability. After administration of plain ASA, buffered ASA and ASA placebo the decrease of gastric potential difference (GPD) was measured. Evaluation of the GPD parameters showed a better tolerability of buffered ASA than of plain ASA. It was therefore concluded that buffered ASA effects less gastric mucosal irritation than plain ASA.

Adult↗
PubMed1992

Dialysability of dimethindene maleate (Fenistil) from blood after intravenous injection.

Dimethindene, an antihistaminic drug, is the treatment of choice in dialysis patients suffering from skin itching. During hemodialysis procedures not only toxic metabolites, but also drugs are extracted from plasma. To answer the question if dimethindene is dialyzable from plasma, three healthy male volunteers received 4 mg of dimethindene solution intravenously. Ten minutes later 100 ml cubital vein blood was taken and 25,000 I.E. Liquemine was added. Plasma was separated and pumped through a cuprophan hollow fiber dialyzing module with an effective surface of 35 cm2. In periods of ten minutes samples of plasma and dialysate were taken to analyze their dimetindene concentrations. A mean clearance of 38 ml/min*m2, SD 10.2 and coefficient of variation [%] 26.8 was found. This is comparable to the well known clearance of theophylline, so it can be considered that dimethindene is eliminated from plasma during hemodialysis procedures.

Algorithms↗
PubMed1991

Iontophoresis--is there a future for clinical application?

Transdermal application of drugs is a field of great importance in medical therapy. The application is painless and may be controlled at any time. Iontophoresis is one method for transdermal application of substances, especially for larger or charged molecules which cannot be administered by a simple transdermal route. The problems arise from the complex equipment and the electrical properties of the skin. A better understanding of skin structure and electric transmission through human skin has led to renewed interest in iontophoresis as an administration mode. Iontophoresis is the method of choice in administration of certain local anesthetics and has had its greatest success in therapy of hyperhidrosis. New applications are to be expected, particularly in administration of peptide and protein drugs.

Administration, Cutaneous↗
PubMed1990

Vaccination against polyoma virus (PyV) tumors using vaccinia-PyV recombinants: a major tumor-specific transplantation antigen (TSTA) epitope resides within the C-terminal segment of middle-T protein.

We previously reported that inoculation of rats with live vaccinia virus (VV) recombinants VVpyMT, VVpyLT expressing either the middle-T (MT) or large-T (LT) proteins of polyomavirus (PyV) can elicit immunity to challenge with syngeneic PyV-tumor cells. We now report the results of cross-vaccination studies. VVpyMT was ineffective against cells expressing LT protein but prevented development of MT-expressing cells. Conversely, the VVpyLT was ineffective against MT-expressing cells. In the two experiments performed, tumor growth enhancement rather than retardation was observed in VVpyLT-vaccinated animals receiving PyV-LT (FRLTI) challenge tumor cells. To determine the location of the major TSTA within MT, a further VV recombinant (VVpyMT/Cfr) was constructed that expresses only the unique C-terminal segment of MT. VVpyMT-Cfr and VVpyMT were equally effective in eliciting tumor immunity, indicating the presence of a major TSTA epitope within the unique C-terminal region of MT.

Amino Acid Sequence↗
PubMed1988

Characterization of a surface antigen of Eimeria tenella sporozoites and synthesis from a cloned cDNA in Escherichia coli.

An antigenic surface protein of Eimeria tenella sporozoites has been identified that is the target of two neutralizing monoclonal antibodies Ptn 7.2A4/4 and Ptn 9.9D12. The antigen as isolated from the parasite is composed of a 17 kDa polypeptide and a 8 kDa polypeptide linked by a disulfide bridge. De novo synthesis of the antigen does not begin until approximately 16-20 h after the initiation of oocyst sporulation. A cDNA library was constructed using mRNA from sporulated oocysts and a clone encoding the antigen was isolated. The Ta4 gene encodes a single polypeptide of 25 kDa which contains the 17 and 8 kDa polypeptides. The protein has been synthesized in Escherichia coli either directly or as part of a beta-galactosidase fusion protein. The products synthesized in E. coli are single polypeptides and are not cleaved to two polypeptides as is seen in the parasite. The products accumulate in bacteria in an insoluble form which can be solubilized and renatured to an immunoreactive form.

Amino Acid Sequence↗
PubMed1986

Positive-selection vectors utilizing lethality of the EcoRI endonuclease.

The construction and use of a series of positive-selection vectors are described. These plasmids encode EcoRI endonuclease, the synthesis of which is under the control of the lacUV5 promoter. The pKG2 plasmid encodes a wild-type EcoRI endonuclease. In the absence of EcoRI methylase, the endonuclease is lethal. Cloning into any of the unique restriction sites within the endonuclease-coding gene allows survival of the transformed EcoRI-methylase-less host. The pKGW and pKGS plasmids encode an altered EcoRI endonuclease which, when repressed in a lacIQ host, allows survival in the absence of the methylase. Induction with IPTG, however, results in cell death as a result of high-level EcoRI synthesis. Cloning into any of the unique restriction sites within the EcoRI gene of pKGW or pKGS allows survival of derepressed transformed cells. These vectors strongly select for cloning events which inactivate the endonuclease gene.

Chromosome Mapping↗
PubMed1986

Arbovirological survey in Silica plateau area, Roznava District, Czechoslovakia.

The serosurveys conducted in the Silica plateau area of the Slovak karst region revealed the presence of specific neutralizing antibody against tick-borne encephalitis (TBE) virus in 18% of local inhabitants (33 examined, mostly goats and sheep farmers), 54% of goats (26 examined), 18% of sheep (120 examined) and 13% of cattle (60 examined), against Lipovník (LIP) virus in 30% of inhabitants, 88% of goats, 55% of sheep and 45% of cattle, and against Bhanja (BHA) virus in 27% of inhabitants, 46% of goats, 29% of sheep and 23% of cattle. The results of hemagglutination-inhibition tests with TBE and BHA antigens were analogous. A detailed analysis of these serologic data points to a recent enhancement of the circulation of LIP and BHA viruses and to a very low TBE virus activity in this natural focus of arboviral infections. The immunological surveys of the 32 former "Roznava disease" patients, conducted 25 years after an extensive epidemic of a TBE virus infection that originated in Roznava in 1951, revealed the presence of neutralizing (and also hemagglutination-inhibiting) antibodies against TBE virus in as many as 78% of cases. Antibodies against LIP and BHA viruses were also detectable in the sera of 16% and 9%, respectively, of these individuals. Populations of the ectoparasites examined for the presence of arbovirus comprised 231 Ixodes ricinus, 806 Dermacentor marginatus and 204 Haemaphysalis punctata ticks and 117 specimens of the louse-flies Melophagus ovinus. Two strains of arbivirus that were antigenically related to Lipovník and Tribec viruses belonging to a group of Kemerovo viruses were isolated from male and female I. ricinus ticks collected from cattle.

Adolescent↗