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Biomedical subjects

A Houben

Publications and source records attributed to A Houben.

46 records · Page 3Linked to original sources
PubMed1985

Alteration of enzymes in ageing human fibroblasts in culture. III. Modification of superoxide dismutase as an environmental and reversible process.

The alteration of superoxide dismutase (SOD) defined as the change occurring in its thermostability and observed in ageing cells, concerned the cytoplasmic but not the mitochondrial enzymes. Altered SOD disappeared if it was incubated in a supernatant from the young cells whereas supernatants from the old cells induced the alteration. The alteration induced on purified SOD was found to be associated with the appearance of thermolabile tetramers. Cytoplasmic SOD tetramers were also observed in the supernatants of the old cells. The addition of NADPH into the incubation medium could reverse this alteration; also when cultivated in the presence of vincamine the alteration, normally present in the old cells, disappears. The alteration of SOD is therefore associated with the formation of tetramers; it is a reversible process influenced by the cytoplasmic composition of the old cells.

Aging↗
PubMed1980

Subcellular fractionation of WI-38 fibroblasts. Comparison between young and old cells.

WI-38 fibroblasts cultivated in vitro were homogenized and their subcellular organelles analysed by the techniques of differential centrifugation and isopycnic equilibration in density gradient. In these experiments, the assayed enzymes were known to be specifically associated with subcellular components in other cells types. In most cases, their behaviour and properties corresponded with observations made in earlier studies and we could consider them as being representative of the specific subcellular organelles. Some significant differences were observed between young and old fibroblasts. The specific activity of alkaline phosphodiesterase was lower in the old cells whereas for the other enzymes it was identical or higher, especially for the 5'-nucleotidase; also the particulate fractions obtained by differential centrifugation contained more material. After equilibration in density gradient, the average density of the 5'-nucleotidase, alkaline phosphodiesterase and N-acetyl-beta-D-glucosaminidase was less in the old than in the young cells, whereas that of the galactosyltransferase of Golgi apparatus was greater. For mitochondria, endoplasmic reticulum and peroxisomes, the differences observed were small.

Cell Fractionation↗
PubMedDate not supplied

Antibiotic resistance of Escherichia coli in fecal samples of healthy people in two different areas in an industrialized country.

Fecal samples of 310 healthy persons, from two populations from different areas in the Netherlands, were examined for the presence of Escherichia coli resistant to ampicillin, tetracycline, sulfamethoxazole, trimethoprim and nitrofurantoin. High prevalences of resistance were found in both populations, ranging from 28% for trimethoprim to 89% for ampicillin. The percentages of the fecal samples with a dominantly resistant E. coli flora (> 50% resistance) were distinctly lower, ranging from 1% for nitrofurantoin to 21% for tetracycline. No significant differences in the level of resistance were observed between these two comparable populations in two different areas. The susceptibilities to 11 antimicrobial agents of 456 at random isolated E. coli were determined. The percentages of resistance varied widely: from 80% for chloramphenicol to 9% for nitrofurantoin. Only 19% of the isolates were susceptible to all antibiotics tested and 14% were resistant to more than four of the agents tested. Great differences in resistance rates between the two populations examined were seen for chloramphenicol (80% to 41%) and trimethoprim (16% to 36%). The results of this study underscore the presence of a human reservoir of antibiotic resistant microorganisms.

Adolescent↗
PubMedDate not supplied

Alteration of enzymes in ageing human fibroblasts in culture. I. Conditions for the appearance of an alteration in glucose 6-phosphate dehydrogenase.

Glucose 6-phosphate dehydrogenase has been found to be altered in ageing human fibroblasts in culture. In this article, we have studied the effects of incubation conditions on glucose 6-phosphate dehydrogenase present in isolated cells or homogenates from young and old cells. We show that incubation at 4 degrees C and pH 7.4 induced the appearance of a heat-labile enzyme; this was not the case at pH 6.5. Also NADP+, when present, protects the enzyme from being modified. The kinetics of the modification indicates that the altered form of the enzyme is an intermediary stage between the active and inactive forms. We now have a model system in which the appearance of an altered enzyme can be induced in only a few hours; this model will be used in our next paper to study the mechanism of this alteration.

Cell Survival↗
PubMedDate not supplied

Alteration of enzymes in ageing human fibroblasts in culture. II. Conditions for the reversibility and the mechanism of the alteration of glucose 6-phosphate dehydrogenase.

The appearance of a heat-labile glucose 6-phosphate dehydrogenase fraction can be induced by incubation of human fibroblasts at 4 degrees C and pH 7.4. Using this system we first studied the effects of pH and NADP+ on the reversibility of the alteration. In young cells, the induced alteration of glucose 6-phosphate dehydrogenase disappeared if the pH of the medium was lowered to 6.5 or if NADP+ was added. In old cells, the disappearance of the natural heat-labile glucose 6-phosphate dehydrogenase was possible only if both pH 6.5 and NADP+ were present. Secondly, we studied the effects of the alteration and its reversibility on the equilibrium between the enzyme subunits; we showed that alteration and inactivation are linked to a dissociation of the enzyme subunits into inactive monomers. We also proposed a model where the heat-labile enzyme is a transient form between the active dimer and inactive monomer. Our results are in perfect agreement with the theories of post-translational modifications now proposed to explain the presence of the altered enzymes in old cells.

Cell Survival↗