Search PubMed⌕ Search

Biomedical subjects

H Mett

Publications and source records attributed to H Mett.

53 records · Page 3Linked to original sources
PubMed1990

Remarks on the screening of antibiotics for antibacterial activity.

The general principles of screening antibiotics for antimicrobial activity are similar to those for screening for other pharmacological effects. The system should be adapted to the specific character of the test substance and the objectives of the program. In the screening of beta-lactams, standard tests, such as determination of the MICs, effects of inoculum size or activity against systemic infection in mice, should be supplemented by less conventional studies on for instance activity against dormant bacteria or, in the case of penems or carbapenems, stability in the presence of kidney and lung dehydropeptidases.

Animals↗
PubMed1989

Physiological studies of the regulation of beta-lactamase expression in Pseudomonas maltophilia.

The kinetics of beta-lactamase induction in Pseudomonas maltophilia IID1275/873 were investigated. Upon induction with beta-lactam antibiotics, a correlation was seen between the increase in specific beta-lactamase activity and the generation time, as well as the concentration of inducer in the medium. The specific beta-lactamase activity increased slowly within the first 0.5 generation and then more rapidly; it decreased regularly after about 2 generations of growth in the presence of inducer. This decrease could presumably be attributed to the continuous breakdown of inducer by beta-lactamases in the culture medium. In a chemostat culture with continuous supply of fresh inducer-containing medium, the specific beta-lactamase activity could be stabilized at a high level over several generations. Removal of the beta-lactam after a certain induction time showed that a short exposure of the bacteria to inducer caused induction kinetics comparable to those resulting from continuous exposure of the cells to inducer. The two beta-lactamases of P. maltophilia, L1 and L2, were induced simultaneously under various experimental conditions.

Enzyme Induction↗
PubMed1988

Rapid method for determining the beta-lactamase-inducing potency of drugs.

A rapid semiquantitative method for determining the beta-lactamase inducing potency of drugs was developed. Bacteria carrying a gene for inducible beta-lactamase expression were inoculated at a concentration of 10(8) CFU/ml into microtiter plates for determination of MICs, which were recorded after 4 h of incubation. A suitable chromogenic beta-lactamase substrate was then added, and after incubation for another 3 h colour changes were monitored.

Anti-Bacterial Agents↗
PubMed1988

Ultrasonic disintegration of bacteria may lead to irreversible inactivation of beta-lactamase.

When ultrasonic disintegration of bacteria was employed to liberate intracellular beta-lactamases there was rapid and irreversible inactivation of the type-Id beta-lactamase from Pseudomonas aeruginosa. Various type-V beta-lactamases (PSE-2, 3 and 4) from P. aeruginosa, as well as Enterobacter cloacae type-Ia beta-lactamase were much less affected by sonication. None of the beta-lactamases was inactivated by French Press disruption. We suggest that French Press disruption should be the method of choice for the release of beta-lactamases, unless the enzyme in question is known to be unaffected by ultrasonic treatment.

Chromatography, Gel↗
PubMed1987

Interaction of the novel penem CGP 31 608 and its enantiomer with type Id beta-lactamase and penicillin-binding proteins.

The novel penem CGP 31,608 (5R, 6S, 8R) and its enantiomer CGP 32,879 (5S, 6R, 8S) were shown to be essentially stable against hydrolysis by type Id beta-lactamase isolated from Pseudomonas aeruginosa 18S/H. CGP 31 608 was a potent progressive inhibitor of this enzyme (150 = 32 microM), which was only weakly inhibited by CGP 32,879 (150 = 460 microM). CGP 31,608 had the highest affinity for penicillin-binding protein (PBP) 4 from Escherichia coli K-12 (150 = 1 microgram/ml), followed by PBPs 2 (10 micrograms/ml) and 1A/1Bs (100 micrograms/ml); CGP 32,879 did not inhibit binding of 14C-benzylpenicillin to the PBPs. The steric configuration of the beta-lactam nucleus of penems appears to strongly influence their affinity for beta-lactamases and target PBPs. The balanced spectrum of CGP 31,608 may be explained by its beta-lactamase stability and affinity for several vital PBPs.

Anti-Bacterial Agents↗
PubMed1984

Duodeno-pancreatic secretions enhance bactericidal activity of antimicrobial drugs.

We have studied the action of various antimicrobial agents in microbiological media and in human duodeno-pancreatic secretions. In the latter medium, clioquinol exhibited a rapid bactericidal effect on both growing and stationary bacteria at concentrations near its MIC. However, it was merely bacteriostatic in microbiological media, even at high concentrations. Phanquinone, chlorquinaldol, and, to a lesser extent, also chloramphenicol and trimethoprim likewise displayed enhanced bactericidal activity in duodeno-pancreatic secretions, but various other antibacterial agents did not. These findings suggest that duodeno-pancreatic secretions contain a factor augmenting the antibacterial activity of a number of drugs.

Adult↗
PubMed1983

Fimbria-specific antibodies detach Escherichia coli from human cells.

Antibodies obtained from rabbits immunized with purified adhesion-mediating fimbriae of Escherichia coli SS142 were specific for the fimbriae of the homologous strain; they did not cross-react with isolated fimbriae of three different E. coli strains or with protein extracts from nine other adhesive E. coli strains. The antibodies inhibited adhesion to Intestine 407 tissue culture cell monolayers and hemagglutinating activity of E. coli SS142 but not of several other E. coli strains. The antibodies were able not only to prevent but also to reverse the adhesion of E. coli SS142 to Intestine 407 cells or human erythrocytes. Analysis of the kinetics of inhibition suggested that the antibodies did not competitively inhibit adhesion. Such antibodies can be useful for distinguishing different mechanistic steps of bacterial adhesion. Their ability to reverse bacterial adhesion in vitro may be of clinical relevance.

Adhesiveness↗
PubMed1983

Properties of pili from Escherichia coli SS142 that mediate mannose-resistant adhesion to mammalian cells.

We isolated pili from Escherichia coli SS142. These pili had a diameter of 6 nm and an average length of 400 nm. They were composed of subunits with a molecular weight of 18,000. Their amino acid composition was determined; methionine and proline were not detected. The isolated pili retained mannose-resistant hemagglutinating activity. Proteolytic digestion and glutaraldehyde fixation led to partial or complete loss of the hemagglutinating activity of the pili without causing any detectable damage to their supramolecular structure, which was only disintegrated by treatment with hot sodium dodecyl sulfate. The hemagglutinating activity of E. coli SS142 was inhibited by the glycoproteins fetuin and Tamm-Horsfall protein, as well as by the glycolipids phytyl lactoside, dansyl-sphingosine lactoside, and digalactosyl diglyceride. Isolated pili inhibited the adhesion of the homologous strain E. coli SS142 to Intestine 407 cell monolayers, but did not inhibit the adhesion of E. coli strain B-413, B-506, or 2699. This indicates that E. coli SS142 binds to a receptor different from those recognized by the other strains and that mannose-resistant adhesion to tissue culture cells can be classified into different subtypes.

Adhesiveness↗
PubMed1982

Effects of low concentrations of antibiotics on Escherichia coli adhesion.

We have previously shown that subinhibitory concentrations of antibiotics may influence the adhesion of Escherichia coli SS142 to human epithelioid tissue culture cells. This report shows that these effects are not limited to E. coli SS142 or to our tissue culture system. Most of the 10 E. coli strains studied showed decreased adhesion to Intestine 407 tissue culture cells after growth in 25% of the minimum inhibitory concentration of streptomycin, tetracycline, trimethoprimsulfametrole, chloramphenicol, and clindamycin. Nalidixic acid at 25% of the minimum inhibitory concentration caused an increase of adhesion. The hemagglutinating activity of the five hemagglutinating strains and the adhesiveness of E. coli SS142 to human buccal cells were similarly affected by low concentrations of the above-mentioned antibiotics. We conclude that E. coli adhesion to human epithelioid tissue culture cells is a valid model of bacterial adhesion because of its high accuracy and reproducibility.

Anti-Bacterial Agents↗
PubMed1980

Soluble nascent peptidoglycan in growing Escherichia coli cells.

Two homologous strains of Escherichia coli, one of which completely lacked the cell envelope Braun's lipoprotein, were compared with respect to their peptidoglycan synthesis and assembly. Both strains were auxotrophic for diaminopimelic acid and their uptake of radiolabeled diaminopimelic acid was comparable. Analysis of subcellular fractions obtained after mechanical disruption of the cells in a French pressure cell and sedimentation of the cell envelopes showed the existence of a soluble, chromatographically immobile macromolecular peptidoglycan. This labeled peptidoglycan contained a reduced degree of peptide side chain cross-linkages (19 mol % of labeled residues as compared to that present in the insoluble cell sacculus, 27 mol %). In addition, approximately 20% of its peptide side chains terminated in pentapeptide structures versus 1 to 4% in the sacculus. Furthermore, the soluble peptidoglycan of the parent strain also contained covalently bound lipoprotein (4.6%). Extraction of the cell envelope fraction with detergents afforded an additional amount of soluble peptidoglycan. This material was quite similar, in its degree of cross-linkage and amount of covalently bound lipoprotein, to the peptidoglycan present in the detergent-insoluble sacculus. These results indicate that peptidoglycan strands which are, in part, covalently linked to lipoprotein are late stage synthesis intermediates which subsequently become covalently attached to the preexisting sacculus.

Ampicillin↗
PubMed1980

Two different species of murein transglycosylase in Escherichia coli.

We demonstrated that Escherichia coli murein transglycosylase exists in two forms. After mechanical disruption of the cells, one form was found in the soluble fraction and the other, in the cell envelope. The two enzymes differed with respect to molecular weight, isoelectric point, solubility in aqueous buffers, and to some extent in their requirements for maximal catalytic activity. The molecular weight of the membrane-bound transglycosylase (35,000) was half that of the soluble enzyme. Whether the high-molecular-weight soluble protein is a precursor of the membrane-bound enzyme species remains to be elucidated.

Cell Membrane↗
PubMedDate not supplied

Inhibitors of protein kinases: CGP 41251, a protein kinase inhibitor with potential as an anticancer agent.

CGP 41251 was originally identified as an inhibitor of protein kinase C (PKC), inhibiting mainly the conventional PKC subtypes, and subsequently shown to inhibit the vascular endothelial growth factor (VEGF) receptor kinase insert domain-containing receptor, which is involved in angiogenesis. CGP 41251 inhibits reversibly intracellular PKC activity, induction of c-fos and the corresponding activation of the mitogen-activated protein kinase induced by either tumor promoting phorbol esters, platelet-derived growth factor, or basic fibroblast growth factor, but not by the epidermal growth factor. CGP 41251 inhibited the ligand-induced autophosphorylation of the receptors for platelet-derived growth factor, stem cell factor, and VEGF (kinase insert domain-containing receptor) that correlated with the inhibition of the mitogen-activated protein kinase activation, but did not affect the ligand-induced autophosphorylation of the receptors for insulin, insulin-like growth factor-I, or epidermal growth factor. CGP 41251 showed broad antiproliferative activity against various tumor and normal cell lines in vitro, and is able to reverse the p-glycoprotein-mediated multidrug resistance of tumor cells in vitro. CGP 41251 showed in vivo antitumor activity as single agent and inhibited angiogenesis in vivo. Thus, CGP 41251 may suppress tumor growth by inhibiting tumor angiogenesis (via its effects on the VEGF receptor tyrosine kinases) in addition to directly inhibiting tumor cell proliferation (via its effects on PKCs).

Antineoplastic Agents↗
PubMedDate not supplied

Outer membrane permeability and beta-lactamase content in Pseudomonas maltophilia clinical isolates and laboratory mutants.

Low outer-membrane permeability appears to be responsible for the generally high degree of antibiotic resistance of Pseudomonas maltophilia. Constitutive overproduction of beta-lactamases affects the sensitivity of these bacteria only to those beta-lactam antibiotics that are hydrolyzed by strain-specific beta-lactamases and that do not efficiently induce these enzymes in inducible strains.

Anti-Bacterial Agents↗
PubMedDate not supplied

Sequence specific antisense oligonucleotide analog interference with spermidine/spermine N1-acetyltransferase gene expression.

Induction of the polyamine acetylating enzyme, spermidine/spermine N1-acetyltransferase (SSAT), is one of several biochemical effects associated with the antiproliferative action of polyamine analogs such as N1, N11 diethylnorspermine (DENSPM). Findings to date indicate that this complex and extremely potent gene response involves increased gene transcription, stabilization of mRNA, enhanced translation and protein stabilization. In this study, SSAT-directed antisense oligonucleotide analogs (AOs) were studied for their ability to prevent enzyme induction by DENSPM. Nine 18-mer fully phosphorothioate modified AOs targeting the start codon, exon 6, stop codon and polyadenylation regions of the human SSAT mRNA were synthesized and evaluated in MALME-3M human melanoma cells prior to and during a 6 hr treatment with 10 microM DENSPM. The most effective AOs were those targeting sequences in the stop codon region. Of these, AO-82 suppressed DENSPM induction of SSAT activity, enzyme protein and mRNA by 70-80%. The quantitative similarity of these effects suggests AO interference with mRNA stabilization, a property apparently mediated by sequences located in the stop codon region. Growth inhibition by DENSPM in the presence of the terminally phophorothioated analogs of AO-82 remained similar to that produced by DENSPM alone. While it is possible that SSAT induction may not be involved in analog-mediated antiproliferative activity, a more likely interpretation is that the approximately 50% suppression of the enzyme response achieved in growth studies is not sufficient to abrogate growth inhibition.

Acetyltransferases↗
PubMedDate not supplied

Design and synthesis of novel tyrosine kinase inhibitors using a pharmacophore model of the ATP-binding site of the EGF-R.

One of the most promising targets for the rational design of anti-cancer drugs is the family of the EGF-receptor protein tyrosine kinases. Despite the high sequence homology within the ATP-binding region of protein tyrosine and/or serine threonine kinases, ATP-competitive compounds have the potential to be selective inhibitors of protein kinases. Dianilino-phthalimides CGP 52 411 and CGP 53,353 have been identified as potent and ATP-competitive inhibitors of the EGF-R tyrosine kinase with no or only minor activity against a panel of tyrosine and serine/threonine kinases. Using a calculated 3-D computer model of the catalytic domain of the EGF-R-tyrosine kinase together with CGP 52 411 as example of an ATP-competitive inhibitor, a pharmacophore model for ATP-competitive inhibitors in the active site of the EGF-R PTK was developed. With the help of this model, 4-phenylamino-7H-pyrrolo[2,3-d]pyrimidines were then identified as new potent EGF-R PTK inhibitors. In an interactive process, the class of the 4-phenylamino-pyrrolo-pyrimidines was optimized and structure-activity-relationship of a series of derivatives thereof are discussed. In vitro, the most active compounds (CGP 59 326, CGP 60 261, CGP 62 706) inhibited the EGF-R tyrosine kinase with IC50 value between 6-30 nM. High selectivity towards a panel of non-receptor tyrosine kinases (c-SRC, v-Abl) and serine/threonine kinases (PKC alpha, PKA) was observed. Kinetic analysis revealed competitive type kinetics relative to ATP. In cells, EGF-stimulated cellular tyrosine phosphorylation was inhibited by these compounds at IC50 values between 0.1-0.3 microM, whereas the ligand-induced receptor autophosphorylation of the PDGR-R was not effected by concentrations up to 100 microM. Furthermore, CGP 59 326, CGP 60 261, CGP 62 706 were able to selectively inhibit c-fos mRNA expression in EGF-dependent cell lines with (IC50) approx. 0.1-1 microM) but not in EGF-independent cell systems (IC50 > 100 microM). Proliferation of the EGF-dependent MK cell line was inhibited with similar IC50 values. In addition, CGP 59 326 and CGP 62 706 showed good in vivo efficacy at low doses after oral or subcutaneous administration in nude mice tumor models using xenografts of the EGF-dependent A431 cell lines. The ED50 values were between 1.5-2 mg/kg. Phenylamino-pyrrolo-pyrimidines therefore represent a new series of tyrosine kinase inhibitors which preferentially inhibit the EGF-mediated signal transduction pathway and have the characteristics for further evaluation as anticancer agents.

Adenosine Triphosphate↗