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Biomedical subjects

J Nicolas

Publications and source records attributed to J Nicolas.

At least 37 records · Page 2Linked to original sources
PubMed2000

Purification and some properties of catalase from wheat germ (Triticum aestivum L.).

Two isoforms of catalase, CAT-1 and CAT-2, were purified from wheat germ after extraction, ammonium sulfate precipitations, hydrophobic chromatography, and two ionic-exchange chromatographies. The global yields and the purification factors were close to 3% and 50 for CAT-1 and close to 6% and 100 for CAT-2. Both isoforms exhibit an optimum activity at pH 7. When pH was decreased from 7 to 5.6, CAT-1 showed a decreasing affinity for its substrate, whereas the opposite was found for CAT-2. Both isoforms were irreversibly denaturated when exposed to acidic pH, CAT-1 being more sensitive than CAT-2. Conversely, CAT-2 appeared to be more sensitive to inhibitors. The rate as well as the extent of denaturation during incubation with 3-amino-1,2,4-triazole (AT) were higher with CAT-2 than with CAT-1. Guaiacol is a competitive inhibitor more potent with respect to CAT-2. The difference in affinity for hydrogen peroxide as well as the poor stability of CAT-1 in acidic medium suggests that this isoform could be less effective during dough mixing.

Catalase↗
PubMed2000

Hybrid tool for quickly estimating the radiated acoustic power from a vibrating structure in a multiple-source environment

This paper presents a new hybrid method for predicting overestimating and underestimating indicators of the acoustic power radiated by a vibrating surface even in the presence of other surrounding acoustic sources. This method is applicable to plates or low curvature surfaces radiating in open acoustic fields. The method is hybrid in the sense that the vibration field is measured and the parietal pressure field is predicted considering two extreme academic cases "baffled" and "unbaffled." Many simplifications are made and justified in order to save running time. The method is successfully validated in comparison with experimental results on both laboratory and real life structures. This method has led to a quick tool, allowing one to obtain a good approximation of the radiated power in a few minutes. It provides a natural extension of a classical analyzer for vibroacoustics engineering.

Journal Article↗
PubMed1999

A symbolic-numeric approach to find patterns in genomes. Application to the translation initiation sites of E. coli.

DNA sequence data provided by genome sequencing programs open new research prospects. In this respect, computational investigations are of major importance to discover new 'functional/structural patterns' and to improve biological process knowledge. For example, even though the principal steps of translation initiation in prokaryotes are known, it is difficult to point out the exact pattern of the mRNA that is recognized by the ribosome. In this study, we have carried out a systematic context analysis of the complete genome of E. coli, around codons in competition for translation initiation. Using a combinatorial approach, we first show that it is possible to accurately define the initiation site by looking for the localization of patterns representing various combinations of trinucleotides. We have combined this approach with a statistical analysis based on the frequencies of these patterns. This leads to a decision tree, able to discriminate true and false starts with a recognition level near 90%. Our method may help to precisely localize the beginning of open reading frames, and point to likely mistakes for some genes in the database. The method may be included as a component of a gene recognition system, is not restricted to a particular genome or a two-classes discrimination, and may be applied to a broader class of biological patterns.

Base Sequence↗
PubMed1997

[Evaluation of the quality of life in pediatrics: how to collect the point of view of children].

There are very few available child quality of life questionnaires. We describe here a French questionnaire (AUQUEI) which consists of a structured format scale (26 items). The first part of the questionnaire studies child satisfaction. Response levels are measured by checking faces expressing different emotional states. The validation is satisfactory, and the questionnaire is able to differentiate healthy children from sick children (HIV positive). A second part of the questionnaire focuses on the child's own quality of life, and is based upon open-ended questions. This second approach allows to broaden the structured format scale and improves the understanding of the child's quality of life. It constitutes a necessary complement to the first part as it avoids using mechanically adult-specific concepts for children. We also found it to be sensitive enough to distinguish sick children from healthy ones. The AUQUEI questionnaire with its two complementary parts appears to be a potentially valuable tool to better understand the experience of sick children, in the various aspects of their life, and to follow their evolution.

Age Factors↗
PubMed1996

Evaluation of life quality for children infected by HIV: validation of a method and preliminary results.

The authors discuss a method developed for the evaluation of quality of life (QoL) of children infected by HIV. The method consists of several questionnaires intended for different evaluators (doctor, nurse, psychologist, and parents), and for the infected child. The protocol was administered to 47 families (interviewed in five centers in the south of France). A descriptive overview of this population notes the state of health and autonomy of the children and parents, and reveals important social difficulties within and beyond the family unit for 75% of the families. The results obtained furnish points to consider in the planning of psychosocial support systems. The reactions of the evaluators to the questionnaires as well as other elements of validation are presented: level of responses (acceptance), internal consistency, agreement between evaluators, and reliability and definition of the main indicators for QoL for the children. Questionnaires were simplified for a second survey so as to test the sensitivity of the method to time variations, improve acceptability, and test validity for the evaluation of QoL. The authors hope their method will interest specialized teams in the fields of therapeutic research and/or psychosocial support.

Adaptation, Psychological↗
PubMed1993

New spectrophotometric assay for polyphenol oxidase activity.

We describe a convenient and sensitive assay of polyphenol oxidase (PPO, EC 1.14.18.1) consisting of spectrophotometry at 300 nm based on the stoichiometric reaction of cysteine with o-quinones produced during the enzymatic oxidation of phenols. The adduct formed exhibited spectral properties different from those of the parent phenol. PPO activities extracted from apple, pear, and mushroom were assayed. The assay cannot be used with hydroxycinnamoyl derivatives since the cysteinyl adduct compounds exhibited spectral properties similar to those of their parent phenolic substrates. However, the cysteine-coupled method presents several advantages over the measurement of oxygen uptake by polarography or the direct estimation of o-quinone by spectrophotometry. The duration of the linear period was increased, allowing a better estimation of its value. The zone of proportionality between rates and enzyme quantities was enlarged. The difference in molar extinction coefficients between adduct and phenol at 300 nm ranged between 2000 and 2800 M-1.cm-1, i.e., two times higher than those of the corresponding o-quinones. Therefore, this assay improves the sensitivity of polyphenol oxidase detection over that of the direct spectrophotometric assay of quinone formation.

Catechol Oxidase↗
PubMed1991

[Fetal curarization by umbilical cord puncture during pregnancy].

Two cases of foetal neuromuscular blockade carried out to obtain foetal immobility during long procedures (in utero foetal exchange transfusion, foetal imaging) are reported. The blockade was carried out in the operating theatre, the mother being awake. Foetal weight had been estimated according to usual echographic parameters. After a long needle had been inserted in the umbilical vein under the guidance of ultrasonography, 0.1 mg.kg-1 vecuronium was injected. Muscle paralysis lasted for about 2 hours in both cases, foetal movements returning spontaneously. There were no side effects due to this technique, a transient foetal bradycardia excepted. Foetal neuromuscular blockade by direct cord injection of muscle relaxants seems to be a simpler, and perhaps safer, technique than obtaining foetal immobility by maternal anaesthesia.

Blood Transfusion, Intrauterine↗
PubMed1991

Collective human food poisonings by clenbuterol residues in veal liver.

Twenty-two patients were reported to complain of tremor, headaches, tachycardia and dizziness 1-3 h after eating veal liver. As clinical symptoms were not suggestive of an infectious cause, the presence of veterinary drug residues was suspected. Clenbuterol, a beta 2-agonist, was being illegally used in cattle because of its anabolizing properties and may explain the observed effects. Assays of clenbuterol in samples of veal liver showed concentrations of 0.375 and 0.500 micrograms/g. To our knowledge, this is one of the first reports of clinical symptoms in humans associated with the consumption of veterinary drug residue-containing food.

Animals↗
PubMed1988

[The value of measuring membrane potentials of urothelial cells using cytofluorometry in the study of tumors of the bladder. Preliminary analysis].

In the context of investigation of a prognostic marker applicable to bladder tumours, the authors propose the cytofluorometric study of the membrane potential of malignant urothelial cells using a molecular probe, 3,3' dihexyloxacarbocyanine. This preliminary study demonstrated a significant increase in the membrane potential of malignant urothelial cells in comparison with normal cells, which leads the authors to propose this cellular parameter as a new tool in the prognostic evaluation of bladder tumours.

Biomarkers, Tumor↗
PubMed1986

Pluripotent hemopoietic stem cells give rise to osteoclasts.

Osteopetrosis in the ia (incisors absent) rat is the result of reduced bone resorption due to abnormal osteoclasts. The mutant osteoclasts lack a ruffled border--the membrane specialization involved in osteolysis. Studies in the ia mutant have shown that when pluripotent hemopoietic stem cells from normal littermates are transplanted into ia recipients, normal osteoclasts are formed and the skeletal sclerosis is eventually cured. The present study was conducted to provide evidence for the mechanism of the cure. Do the transplanted stem cells provide a helper function, i.e. secrete soluble factor(s) which transform pre-existing osteoclasts, or do they fuse with each other or pre-existing osteoclasts, or do they fuse with each other or pre-existing osteoclasts to form functional osteoclasts? Using the procedures described by Gold-schneider and co-workers, and fluorescence-activated cell sorting (FACS), pluripotent hemopoietic stem cells were isolated from normal rat bone marrow, labeled with saturated FITC, and injected intravenously into irradiated ia rats. After 48 hr, the recipients' long bones were removed and split longitudinally, and the endosteal surface was scraped. The resulting cellular suspension containing osteoclasts was examined by phase contrast and fluorescence microscopy. Fluorescing mononuclear cells of donor origin that had homed to the bone marrow demonstrated moderate cytoplasmic fluorescence. Approximately 30% of the osteoclasts observed demonstrated light cytoplasmic fluorescence. When cellular pools incapable of curing osteopetrosis (thymocytes) were labeled and injected into ia recipients, no labeled osteoclasts were observed. These studies indicated that pluripotent hemopoietic stem cells, when transplanted into ia hosts, fuse with each other and differentiate into osteoclasts or fuse with pre-existing osteoclasts.

Animals↗
PubMed1983

Effect of whole-body irradiation on phagocytic activity of rat alveolar macrophages.

The phagocytic activity of rat alveolar macrophages was studied in vitro for up to six weeks after whole-body gamma irradiation (7.5 Gy). Ingestion of fluorescent latex microspheres was evaluated using both microscopic examination and flow cytometric quantitation. After a transient decrease on first day post-irradiation, a slight increase in the phagocytic ability was observed from day 14 to day 28, with a maximum on day 21. From day 35 onwards, phagocytic capacities returned approximately to those of the controls. The percentage of phagocytic cells (cells having ingested one microsphere or more) increased by 75 per cent on day 21 after irradiation and the phagocytic index (percentage of phagocytic cells X the average number of ingested microspheres per cell) increased by 250 per cent while at the same time, the number of recovered alveolar cells decreased by 37 per cent. The augmentation of phagocytic capacities after irradiation was particularly characterized by an increase in the percentage of cells ingesting more than five microspheres. Flow cytometric studies showed a significant increase in mean cell size on day 21 post-irradiation. The augmentation of the phagocytic activity was not found when macrophages from control rats were incubated with serum or alveolar lavage fluid from an irradiated donor. Augmentation of phagocytic capacity was also observed after 8.5 Gy but no effect could be observed after 6.5 Gy.

Animals↗