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Biomedical subjects

G Müller

Publications and source records attributed to G Müller.

At least 19 recordsLinked to original sources
PubMed1992

Conformation/activity studies of rationally designed potent anti-adhesive RGD peptides.

The Arg-Gly-Asp (RGD) sequence is a universal cell-recognition site of various extracellular proteins that interact with integrin cell-surface receptors. In order to design low-molecular-mass RGD protein antagonists, the determination of the biologically active conformation is a prerequisite. We present a method that yields detailed insight into the steric factors which govern the binding of the ligands to their receptors by systematically scanning the conformational space accessible for the tripeptide sequence RGD. The investigation is based on the conformationally controlled design of homodetic cyclic oligopeptides and their structural determination, coupled with biological assays. For this purpose, a whole set of cyclic pentapeptides and hexapeptides has been synthesized and their three-dimensional structures in solution analyzed by modern two-dimensional NMR techniques in combination with restrained and free molecular dynamics simulations. Their biological activity was compared with that of linear GRGDS in inhibition assays of tumor cell adhesion to laminin P1 and vitronectin substrates. An up to 100-fold, and in part selective, increase in activity was observed for two cyclic pentapeptides. Most other peptides showed a decreased activity which, however, was useful to correlate activity with rather small variations in conformation. Detailed comparative studies of the systematically designed conformations and the corresponding anti-adhesive activities offer an access to lead structures for a rational indirect drug design of peptide and peptidomimetic pharmaceuticals with strong interfering activity for integrin-mediated cell-cell and cell-matrix interactions.

Amino Acid Sequence↗
PubMed1992

The cAMP-binding ectoprotein from Saccharomyces cerevisiae is membrane-anchored by glycosyl-phosphatidylinositol.

Saccharomyces cerevisiae contains an amphiphilic cAMP-binding glycoprotein at the outer face of the plasma membrane (M(r) = 54,000). It is converted to a hydrophilic form by treatment with glycosyl-phosphatidylinositol-specific phospholipases C and D (GPI-PLC/D), suggesting membrane anchorage by a covalently bound glycolipid. Determination of the constituents of the purified anchor by gas-liquid chromatography and amino acid analysis reveals the presence of glycerol, myo-inositol, glucosamine, galactose, mannose, ethanolamine, and asparagine (as the carboxyl-terminal amino acid of the Pronase-digested protein to which the anchor is attached). Complementary results are obtained by metabolic labeling, indicating that fatty acids and phosphorus are additional anchor constituents. The phosphorus is resistant to alkaline phosphatase, whereas approximately half is lost from the protein after treatment with GPI-PLD or nitrous acid, and all is removed by aqueous HF indicating the presence of two phosphodiester bonds. Inhibition of N-glycosylation by tunicamycin or removal of protein-bound glycan chains by N-glycanase or Pronase does not abolish radiolabeling of the anchor structure by any of the above compounds. Analysis of the products obtained after sequential enzymic and chemical degradation of the anchor agrees with the arrangement of constituents in GPIs from higher eucaryotes. Evidence for anchorage of the yeast cAMP-binding protein by a GPI anchor is strengthened additionally by the reactivity of the GPI-PLC-cleaved anchor with antibodies directed against the cross-reacting determinant of trypanosomal variant surface glycoproteins.

Amidohydrolases↗
PubMed1992

Functional roles of amino acid residues involved in forming the alpha-helix-turn-alpha-helix operator DNA binding motif of Tet repressor from Tn10.

The Tn10 derived Tet repressor contains an amino acid segment with high homology to the alpha-helix-turn-alpha-helix motif (HTH) of other DNA binding proteins. The five most conserved amino acids in HTH are probably involved in structural formation of the motif. Their functional role was probed by saturation mutagenesis yielding 95 single amino acid replacement mutants of Tet repressor. Their binding efficiencies to tet operator were quantitatively determined in vivo. All functional mutants contain amino acid substitutions consistent with their proposed role in a HTH. In particular, only the two smallest amino acids (serine, glycine) can substitute a conserved alanine in the proposed first alpha-helix without loss of activity. The last position of the first alpha-helix, the second position in the turn, and the fourth position in the second alpha-helix require mostly hydrophobic residues. The proposed C-terminus of the first alpha-helix is supported by a more active asparagine compared to glutamine replacement mutant of the wt leucine residue. The turn is located close to the protein surface as indicated by functional lysine and arginine replacements for valine. A glycine residue at the first position in the turn can be replaced by any amino acid yielding mutants with at least residual tet operator affinity. A structural model of the HTH of Tet repressor is presented.

Amino Acid Sequence↗
PubMed1992

Concentrations of tetrachloroethene in blood and trichloroacetic acid in urine in workers and neighbours of dry-cleaning shops.

Tetrachloroethene concentrations in blood and trichloroacetic acid concentrations in urine were determined--primarily over the course of a week--for 29 persons living in the vicinity of dry-cleaning shops. The mean levels of tetrachloroethene increased during the week. In some neighbours concentrations were exceeding the German biological threshold limit value for tetrachloroethene (1000 micrograms/l blood), persisting over the whole week in one case. The concentrations of tetrachloroethene in blood depended on the floor and the construction type of the building where these people were living, but not of the type of system used in the dry-cleaning shops. 5 of 12 dry-cleaners were found to have tetrachloroethene levels exceeding the German biological threshold limit value, some of them by a considerable amount.

Environmental Exposure↗
PubMed1992

Investigations of the frequency of DNA strand breakage and cross-linking and of sister chromatid exchange frequency in the lymphocytes of female workers exposed to benzene and toluene.

Peripheral lymphocyte DNA damage as measured by the method of alkaline filter elution and the frequency of sister chromatid exchange (SCE) in lymphocytes was investigated for a group of 20 female workers of a shoemaking plant who were exposed to benzene and toluene, primarily below the German threshold limit value of 5 and 100 p.p.m. respectively; the results were compared with those from a control group. In the female workers significantly raised (P less than 0.05) SCE values were found. The relative DNA elution rate through polycarbonate filters was significantly increased (P less than 0.001). The elution rate through polyvinylidene fluoride (HVLP) filters showed a tendency to increase (P = 0.052), which must be interpreted as indicating increased DNA strand breakage. The SCE rates of the female workers were significantly correlated (P less than 0.01) with the relative DNA elution rate through HVLP filters. There was no correlation with the actual benzene and toluene uptake measured by personal air monitoring. Four months after cessation of work, DNA strand breakage decreased significantly (P less than 0.05) in blood samples of six reinvestigated female workers.

Adult↗
PubMed1992

Pituitary factors in blood plasma are necessary for smooth muscle cell proliferation in response to injury in vivo.

Intimal thickening in response to vascular injury is inhibited in animals previously subjected to hypophysectomy. We have investigated the nature and cell kinetics of this effect in a balloon catheter model of injury to the rat carotid artery. The ability of injury to stimulate [3H]thymidine labeling 48 hours after injury was almost completely eliminated in hypophysectomized (hypox) compared with control animals (0.1% versus 32.1%). Total DNA content of the developing neointima 14 days after injury was only 30% of the values found in ballooned carotid arteries of normal rats. If hypox rats were treated with recombinant human growth hormone, the proliferative response was not restored. There are two possible general explanations for the reduction of proliferative response in hypox animals: 1) that smooth muscle cells in the hypox animals have lost the ability to respond to the stimulus of injury or 2) that the ability of the smooth muscle cells to respond has not been reduced by prior hypophysectomy, but that the response itself requires the presence of pituitary-dependent factors. Transplantation experiments were performed in vivo to distinguish between these possibilities. Carotid arteries in inbred Lewis rats were excised 1 hour after balloon injury to give platelets the opportunity to adhere. These vessels were then transplanted from hypox into control animals and vice versa. At 48 hours, proliferation of smooth muscle cells in "control-to-hypox" transplants was 0.3% compared with 14.3% in "control-to-control" transplants, whereas vessels from hypox rats increased their indices to 4.8% if transplanted into control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

A new device for long-term continuous enteral nutrition of rats by elementary diet via gastrostomy, following extensive oesophageal or lower gastrointestinal surgery.

A device for intragastric nutrition of unsedated and minimally restrained rats under complete alimentary abstinence has been developed. The cannulation system consists of an infusion pump, modified glass syringe as flow swivel, rat-harness and a silicone-tube-gastrostomy. The animals were kept in special cages and coprophagy was prevented by an own model of faecal collection cup. Methionine and Ca-glycerophosphate had to be added to a commercial elementary diet. The rats were allowed to move freely during intragastric infusion, which was applied for 14 to 28 days in 118 Wistar-rats (350-400 g). They maintained weight on an energy supply of 86.4 kcal/day.

Animals↗
PubMed1992

Subcellular distribution of amebapain, the major cysteine proteinase of Entamoeba histolytica.

Amebapain, the major cysteine proteinase of E. histolytica, appears to be important both for digestion and as a cytotoxic factor. By immunocytology we established that amebapain was bound to matrix-like structures both on the cell surface and within subcellular vesicles; the amebapain co-localized with pinocytized iron oxide, suggesting that the enzyme recycles between plasma membrane and pinocytic vesicles. We conclude from these data that (i) the pinocytic vesicles in E. histolytica perform functions that in higher eukaryotes are taken over by specialized organelles such as lysosomes and cytotoxic granules, and (ii) the vesicles contain a matrix that helps retain the protease upon exocytosis of vesicle contents.

Animals↗
PubMed1992

[Experiences with alkaline filter elution for the detection of DNA damage by genotoxic compounds].

In biological effect monitoring the alkaline filter elution is a suitable method to detect DNA strand breakage and cross-linking in peripheral blood lymphocytes. We applied this method to three groups of workers occupationally exposed to carcinogens: n = 39 welders with exposure to chromium and nickel, n = 20 female shoemakers with exposure to benzene and n = 25 disinfectors in hospitals with exposure to ethylene oxide. In comparison to standardised control groups our results must be interpreted as indicating an increased rate of DNA cross-linking in welders and disinfectors whereas the female shoemakers showed an increased rate of DNA strand breakage. The differences between the results of the exposed groups and the stratified control groups were significant in most cases. We could reexamine 6 shoemakers 4 months after cessation of exposure to benzene; at this moment the results were indicating a clear decrease of the DNA strand breakage. Therefore the method of alkaline filter elution seems to be a valuable tool in biological effect monitoring of groups occupationally or environmentally exposed to carcinogens, especially if the exposure is low, but persistent over a long period.

Benzene↗
PubMed1992

[Diagnostic potential of biochemical and cytological parameters in bronchoalveolar lavage fluid in healthy calves and calves with pneumonia].

Bronchoalveolar lavage fluid (LF) was obtained from cranial as well as from caudal regions of the bovine lung in healthy and pneumonic calves. LF was investigated biochemically, cytologically, and bacteriologically. In healthy lungs free of pneumonic lesions, no differences due to the different parts of the lung were established. An increase in both protein content and number of cells and a marked influx of neutrophils were found to be the most important alterations caused by pneumonic lesions. The diagnostic potential of lactate dehydrogenase, alkaline phosphatase and the size of alveolar macrophages in LF was validated.

Alkaline Phosphatase↗
PubMed1992

Influence of HDL on the formation of 6-keto-PGF1 alpha and TXB2 in vitro: the importance of the source of HDL.

The influence of HDL, isolated from normolipidemic human blood and blood of normo- and hyperlipidemic rabbits, on in vitro 6-keto-PGF1 alpha synthesis by rabbit aorta and on TXB2 synthesis by platelets of clotting human and rabbit blood was tested. The HDL fraction from normolipidemic subjects, when incubated with blood from normolipidemic humans or rabbits, inhibited TXB2 formation. The same fraction stimulated the formation of 6-keto-PGF1 alpha after incubation with rabbit aorta taken from normolipidemic animals. HDL taken from hyperlipidemic rabbits inhibited 6-keto-PGF1 alpha formation in rabbits and had no influence on TXB2 formation. These results support the hypothesis that not only is the absolute amount of HDL important for its influence on prostanoid formation, but also the origin and the composition of the HDL fraction.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

[Mucoviscidosis screening with immunoreactive trypsin].

Up to now 49,116 immunoreactive trypsin (IRT) measurements have been carried out in Austrian newborns in the first week of life. Related to provisionally chosen cut-off points, 301 newborns (0.61%) showed an elevated IRT value; 253 of them were successfully recalled. According to a direct strategy, sweat tests were done without a second IRT measurement in 101 infants; eleven of them were identified as cystic fibrosis (CF) patients. In accordance with a 2-step strategy, 152 infants were reinvestigated by a second IRT determination. Twenty-eight of them again showed an elevated IRT value, as based on provisional, age-dependent reference values; seven were subsequently identified as CF patients by sweat testing. So far two false-negative findings were obtained on IRT screening: one child was later identified as having CF on the basis of typical clinical symptoms and a positive sweat test, the other patient presenting with meconium ileus showed a normal IRT value after surgery, but was subjected to a sweat test in view of the underlying condition. These preliminary results suggest a CF incidence of 1 to 2460 newborns in Austria. Hence, IRT screening appears to be a reliable method for identifying CF patients in the newborn period, thereby facilitating early treatment and genetic counselling.

Austria↗
PubMed1992

[Laser in surgery of vascular anastomoses].

The disadvantages of present-day microvascular suturing techniques include suture-induced foreign-body granulomas, stenoses and aneurysms. In comparison, argon laser-assisted anastomoses show a more favorable histomorphology and a low rate of stenoses and aneurysms. Laser-assisted anastomoses pass through the same familiar healing phases seen in common wound-healing.

Anastomosis, Surgical↗
PubMed1992

[Lowering peripheral vascular resistance by distal arteriovenous fistula surgery. Clinical and experimental studies].

Vascular run off has an important influence on patency rates of infrapopliteal bypasses especially when prosthetic grafts are used. Construction of a distal arteriovenous fistula can improve volume and velocity of graft flow. 39 patients, 14 of them diabetic, had femoro-crural PTFE-bypasses. A distal arteriovenous fistula in common ostium technique was established in 20 cases. The patency rate (early occlusions) was improved, especially diabetic patients seemed to profit by lowering the peripheral outflow resistance, which was measured intraoperatively. The influence of arteriovenous fistulas of different calibre on bypass flow and perfusion was analysed in a circulation model.

Arteriovenous Shunt, Surgical↗
PubMed1992

[Acquired antithrombin III deficiency].

Acquired antithrombin III (AT III) deficiency is based on either decreased activity or synthesis, increased loss or increased consumption. The activity of AT III is decreased in metabolic acidosis, hyperlipoproteinemias and by lipid peroxides. Chronic liver diseases especially liver cirrhosis are associated with very low levels of AT III due to insufficient hepatic synthesis, reduced transcapillary flux ratios, diffuse intravascular coagulation and loss in the ascites. Gastrointestinal loss of AT III may occur in patients with active inflammatory bowel diseases. AT III deficiency is observed in nephrotic syndrome when urinary loss of protein exceeds 5 g/d. During hemodialysis we have not found low AT III levels. Disseminated intravascular coagulation is characterized by activation of the coagulation system and increased consumption of AT III. AT III complexes with activated coagulation factors are subsequently cleared by the reticuloendothelial system.

Antithrombin III↗