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Biomedical subjects

A Fontaine

Publications and source records attributed to A Fontaine.

At least 19 recordsLinked to original sources
PubMed1992

X-ray absorption spectroscopy of carbonyl basket handle Fe(II) porphyrins: the distortion of the tetrapyrrolic macrocycle.

The distortion of the tetrapyrrolic macrocycle, the Fe-C-O bond angle and the Fe local electronic structure of carbonyl basket-handle Fe2+ porphyrins as a function of the basket-handle chain length have been studied by X-ray absorption near edge structure (XANES) spectroscopy, both in the solid state and in toluene solution. The Fe-C-O bond angle has been found to be linear in all compounds while the increasing distortion of the macrocycle with shortening of the chain length is indicated by the multiple scattering resonance in the heme plane appearing at 22 eV in the XANES spectrum.

Iron↗
PubMed1992

Stenosis of the renal artery: assessment of slowed systole in the downstream circulation with Doppler sonography.

Slowing and dampening of systole in the arterial network distal to stenosis is a well-known Doppler sign of severe arterial stenosis. To determine whether this sign is present in boys and girls with such stenosis, intrarenal Doppler curves (acceleration index [AI] and resistive index [RI]) were compared with findings on renal arteriograms in 20 boys and girls; the AI was also measured in 10 boys and girls without renal disease. Statistical analysis of AI and RI measurements was performed. Eleven of 32 renal arteries were normal. The normal AI was 4.0-7.0; in arteries with greater than 75% stenosis, the AI was 0.7-1.7. In five arteries studied after angioplasty, the AI had changed from 0.7-1.5 to 4.0-5.6 at the first posttreatment examination (performed 28 hours to 1 week after angioplasty), and it remained normal during the 3-year follow-up period. In kidneys with stenotic arteries, the RIs were lower (0.43-0.54) than in healthy subjects (0.56-0.63). Regression and correlation coefficients of AI and RI measurements were statistically significant, and discrimination between normal arteries and those with greater than 75% stenosis was excellent.

Child↗
PubMed1992

[Causes and modalities of pediatric ambulatory care in ten hospitals in the Ile-de-France region].

BACKGROUND: The increasing shortage of financial resources requires optimal use of hospital care by patients. However, the studies carried out to date in France have been limited to patients who are hospitalized, and have not included those seen as out-patients. POPULATION AND METHODS: All patients seen as out-patients in 10 hospitals in the Paris district (3 pediatric hospitals and 7 pediatric departments located in hospitals for adults and children), during the week of 19-26 April 1989, were given a questionnaire on the age, sex, nationality, socio-cultural and economic features of the family, history of earlier medical visits or admissions, the existence of pediatrician or practitioner, and the means and time taken to get to the hospital. Medical diagnosis was established for each patient following the WHO International Classification of Diseases (9th edition). RESULTS: 2,365 out of 2,675 questionnaires were usable. The main features were: 50% of patients were less than 3 years old, 55% were of French origin; 78% belonged to families with relatively low socio-economic status. Both parents had professional activities in 49% of families, 7% of mothers did not speak or write French. The ratio of patients aged less than 3 years admitted to the emergency ward was higher than the average. The most frequent diseases presented by these patients were respiratory (23%), infectious (14%), gastro-intestinal (10%) and neurological (7%); 14% of the patients were seen for symptoms that could not be assigned to a specific disease. 39% of patients were seen in out-patient clinics and 61% in emergency wards. 40% were sent by a health professional to out-patient clinics and only 25% to emergency wards. CONCLUSIONS: Despite the fact that this study is subject to particular conditions, i.e., relative frequency of infectious diseases due to seasonal causes, it suggests that the hospital is becoming the primary source of health care with an increasing percentage of patients seen in "emergency", even though this emergency is often more apparent than real. Health care networks should be established.

Ambulatory Care↗
PubMed1991

OmpB (osmo-regulation) and icsA (cell-to-cell spread) mutants of Shigella flexneri: vaccine candidates and probes to study the pathogenesis of shigellosis.

Genetic and molecular data now available on the pathogenic properties of Shigella flexneri allow rational design of live attenuated vaccine strains. The genes required at given steps of the infection process can be selectively mutated to impair the bacterium's capacity to interact with intestinal epithelial cells and/or survive within intestinal tissues in general. We have tested two mutations in S. flexneri serotype 5a (M90T) which, alone or in combination, have yielded promising results when evaluated as vaccine prototypes in orally infected macaque monkeys. The first mutation, icsA, blocks intracellular and cell-to-cell spread of the micro-organism. This mutant (SC560) appeared reasonably well tolerated and elicited protection against homologous challenge. The second mutation, ompB, disconnects the bacterium from one of its major environmental regulatory factors, osmolarity. This mutant (SC433) still caused slight dysenteric symptoms in vaccinees. It was also perfectly protective. When these two mutations were combined, the double mutant (SC445), was perfectly tolerated but failed to protect one out of five animals. These studies bring interesting prospects of the possibility of immunizing against shigellosis. In addition to providing new possibilities for vaccine design, construction and evaluation of these mutants allowed substantial progress in understanding the pathogenesis of shigellosis.

Animals↗
PubMed1990

The two-component regulatory system ompR-envZ controls the virulence of Shigella flexneri.

In Shigella flexneri, the ompB locus (containing the ompR and envZ genes) was found to modulate expression of the vir genes, which are responsible for invasion of epithelial cells. vir gene expression was markedly enhanced under conditions of high osmolarity (300 mosM), similar to that encountered in tissues both extra- and intracellularly. Two ompB mutants were constructed and tested for virulence and for osmotic regulation of vir genes. An envZ::Tn10 mutant remained invasive, although its virulence was significantly decreased as a result of its inability to survive intracellularly. By using a vir::lac operon fusion, this mutation was shown to decrease beta-galactosidase expression both in low- and high-osmolarity conditions but did not affect vir expression in response to changes in osmolarity. A delta ompB deletion mutant was also constructed via allelic exchange with an in vitro-mutagenized ompB locus of Escherichia coli. This mutation severely impaired virulence and abolished expression of the vir::lac fusion in both low- and high-osmolarity conditions. Therefore, a two-component regulatory system modulates virulence according to environmental conditions. In addition, the mutation affecting a spontaneous avirulent variant of S. flexneri serotype 5, M90T, has been mapped at the ompB locus and was complemented by the cloned E. coli ompB locus. Introduction of the vir::lac fusion into this mutant did not result in the expression of beta-galactosidase (Lac-).

Cloning, Molecular↗
PubMed1989

Biosynthesis of a repressor/nuclease hybrid protein.

The phage T7 endonuclease gene was fused to the 3' end of the lac repressor gene. The hybrid protein exhibits repressor and nuclease functions in a manner dependent on the conformation of the DNA. With supercoiled DNA, nuclease activity is directed to the major cruciform, whereas with linear DNA, the enzyme cleaves preferentially restriction fragments carrying the operator. These properties render the hybrid protein a unique probe of DNA conformation in vitro and in vivo.

DNA, Superhelical↗
PubMed1988

Role of Shiga toxin in the pathogenesis of bacillary dysentery, studied by using a Tox- mutant of Shigella dysenteriae 1.

A Tox- mutant of Shigella dysenteriae 1, SC501, was genetically engineered by cloning the Shiga toxin operon, inserting a cassette into the A subunit gene, and exchanging this in vitro-mutagenized sequence with the wild-type gene. SC501 produced a low amount of residual cytotoxicity which was not neutralized by a rabbit immune serum directed against Shiga toxin. Invasion of cultured cells demonstrated that Shiga toxin had no effect on the rate of intracellular growth of bacteria or on the rapid killing of invaded host cells. On the other hand, several significant differences were observed in macaque monkeys infected intragastrically with either the wild-type strain or its mutant. The production of Shiga toxin by the invading strain was correlated with the presence of blood within stools, a sharp drop in blood polymorphonuclear cells, and histopathological alterations, such as the destruction of capillary vessels within the connective tissue of the colonic mucosa, severe inflammatory vasculitis of the peritoneal mesothelium, and major efflux of inflammatory cells to the intestinal lumen. It is proposed that Shiga toxin influences the severity of bacillary dysentery by inducing colonic vascular damage, which accounts for bloody stools, intestinal ischemia, and inflation of a polymorphonuclear intestinal compartment during the infectious process.

Animals↗
PubMed1988

Pyocolon: an unusual manifestation of colon ischemia.

An unusual manifestation of a large bowel ischemia was observed in two patients. Both had a left flank tubular fluid collection demonstrated respectively by computed tomography (CT) and ultrasonography (US). At surgery, pyocolon (i.e. ischemic, dilated large bowel segments filled with pus) was discovered and resected. Pyocolon should be suspected in patients with ischemic colitis and sepsis. US, although useful, may be misleading; CT is the investigation of choice to establish the diagnosis.

Aged↗
PubMed1987

Stabilization of iron in a ferrous form by ferritin. A study using dispersive and conventional x-ray absorption spectroscopy.

Stabilization of iron in a bioavailable form is the function of ferritin, a protein of 24 subunits forming a coat around a core of less than or equal to 4500 hydrated iron atoms. The core of ferritin isolated from tissues contains Fe3+, but Fe2+ is required for experimental core formation in protein coats; reduction of Fe3+ to Fe2+ facilitates iron removal from protein coats. Using the differences in x-ray absorption spectra (x-ray absorption near edge structure) between Fe2+ and Fe3+ to monitor reconstitution of ferritin from Fe2+ and protein coats, we observed stabilization of Fe2+, apparently inside the coat. Mixtures of Fe2+ and Fe3+ persisted for greater than or equal to 16 h in air indicating that, in vivo, some iron in ferritin could be stored as Fe2+ and with Fe3+ could yield magnetite.

Animals↗
PubMed1987

Linear Fe-C-O configuration in carbonyl 1-methylimidazole iron(II) porphyrin detected by XANES in dispersive mode.

The linear Fe-C-O configuration has been determined in the carbonyl 1-methylimidazole hindered iron(II) porphyrin derived from 'basket handle' complexes in which there are no constraints on the proximal imidazole. The structure at the iron site has been determined in toluene solution by fast measurements of XANES spectra, using the dispersive X-ray absorption method.

Carbon↗
PubMed1987

A native cruciform DNA structure probed in bacteria by recombinant T7 endonuclease.

T7 endonuclease preferentially cleaves purified supercoiled pBR322 and colE1 plasmids at the single-stranded regions exposed when palindromic sequences assume cruciform structures (Panayotatos, N., and Wells, R.D. (1981) Nature 289, 466-470). In vivo, however, induction of nuclease synthesis off a cloned gene caused complete degradation of the bacterial DNA but not of the plasmid vector; presumably, single-stranded regions (cruciforms?) on the genome effectively complete for the nuclease with similar sites on the plasmid (Panayotatos, N., and Fontaine, A. (1985) J. Biol. Chem. 260, 3173-3177). To overcome this competition, we introduced on the plasmid the naturally occurring colE1 palindrome which forms a more stable cruciform in vitro. In addition, we increased the target size (and the T7 endonuclease gene dosage) by raising the copy number of the plasmid 5-fold. Induction of the endonuclease encoded by this new plasmid (pLAT75) resulted not only in degradation of genomic DNA but also in intracellular nicking and linearization of the plasmid. The cleavage site in vivo was mapped at the colE1 palindrome and coincided with the site cleaved specifically in vitro by either T7 or S1 endonuclease only when this palindrome assumes the cruciform structure. These results indicate that cruciform structures exist intracellularly and demonstrate the usefulness of endonucleases as probes of DNA topology in vivo.

DNA Restriction Enzymes↗
PubMed1986

[Reception of adolescents at an intersector dispensary. Retrospective study of 5 years of operation].

The study of some characteristics (clinical and sociodemographic) of a population of adolescent clients and the modes of reception and therapeutic modalities which have been proposed for them introduces a discussion on: the contributions and the limits of so-called informal modes of reception and assigning to treatment, as well as the value of taking into consideration the ways the adolescents relate to their environment; the necessity for rapid agreement and the diversity of the observed evolutions which justify both the need for adequate identification of immediate movement and for a dynamic perspective; and, after considering the adequacy of the gathered information for our way of thinking and practicing, the pertinence of an epidemiological evaluation and its utility for clinicians.

Adolescent↗
PubMed1985

An endonuclease specific for single-stranded DNA selectively damages the genomic DNA and induces the SOS response.

A plasmid carrying the bacteriophage T7.3 endonuclease gene under the control of the lacUV5 promoter could be maintained in the transcriptionally active state only in recA+ strains. In recA- strains, endonuclease induction resulted in extensive degradation of the genomic DNA and cell death. In sharp contrast, the plasmid DNA remained intact in the supercoiled form. In recA+ strains, the recA protein levels were increased and the SOS functions of the host were activated, as shown by measurements of recA protein synthesis and prophage induction. These results indicate that in normal undisrupted and non-irradiated cells, enzymatic nucleolytic damage can induce the SOS response and can be controlled by the DNA repair system of the host. In addition, the higher sensitivity of the genomic DNA to the single-strand-specific endonuclease relative to the plasmid suggests that the two molecules differ in their physiological states and most likely in their degree of single-stranded content.

Cell Survival↗
PubMed1978

Vulnerability of keto bile acids to alkaline hydrolysis.

Rigorous alkaline hydrolysis of the two primary (cholic and chenodeoxycholic) and of the two preponderant secondary (deoxycholic and lithocholic) bile acids found in bile led to excellent recoveries. Such was not the case with 11 different keto bile acid standards. Recoveries for a number of standards were unacceptably low and a variety of artefactural products were tentatively identified by gas-liquid chromatography. Keto bile acids bearing a keto gropu on C-3 were particularly vulnerable. In view of thee findings, quantitative and qualitative data reported on biological specimens submitted to saponification in ethanol, methanol, or even in water are of questionable significance.

Bile Acids and Salts↗