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Biomedical subjects

Michel Simonet

Publications and source records attributed to Michel Simonet.

16 recordsLinked to original sources
PubMed2006

NODs in defence: from vulnerable antimicrobial peptides to chronic inflammation.

Defensins and cathelicidins are prevalent and essential gastrointestinal cationic antimicrobial peptides (CAPs). However, these defensive peptides are not infallible because certain enteropathogens can overcome their protective function. Furthermore, impaired defensin synthesis has been linked to the occurrence of Crohn's disease (CD), a chronic inflammatory bowel disease. Recently, defective bacterial sensing through NOD1 and NOD2 has been related to reduced defensin production, CD predisposition and susceptibility to enteric infection. Hence, we propose that microbial sensors at the gut interface monitor the levels of these effector peptides, which might function as "danger" signals to confer tolerance and alert immunocytes. Further work is required to clarify how gastrointestinal CAPs are regulated and to assess their role in maintaining epithelial homeostasis and triggering adaptive immunity.

Amino Acid Sequence↗
PubMed2006

High intra-abdominal pressure enhances the penetration and antitumor effect of intraperitoneal cisplatin on experimental peritoneal carcinomatosis.

OBJECTIVE: To investigate the role of increased intra-abdominal pressure (IAP) on the intratumoral accumulation and the antitumor effect of intraperitoneal cisplatin in rats with advanced peritoneal carcinomatosis. To evaluate the tolerance of IAP in pigs, as it is a large animal with a body size equivalent to humans. SUMMARY BACKGROUND DATA: To investigate if an active convection, driven by a positive IAP, increases cisplatin penetration and antitumor effectiveness in a model of advanced peritoneal carcinomatosis in rats. EXPERIMENTAL DESIGN: BDIX rats with macroscopic peritoneal tumors received cisplatin administered as intravenous injection (IV), conventional intraperitoneal injection (IP), or sustained intraperitoneal injection of cisplatin given in a large volume of solvent for maintaining IAP for 1 hour. Platinum tissue concentration was measured by atomic absorption spectroscopy (AAS), and platinum distribution into the tumor nodules was assessed by the particular-induced x-ray emission (PIXE) method. The antitumor effect was assessed in a survival experiment. The hemodynamic, local, and systemic tolerance of IAP, with or without cisplatin, was evaluated in Large White pigs. RESULTS: The maximum tolerated IAP was 22 mm Hg for 1 hour in nonventilated rats. IAP, in comparison with IV or conventional IP injections, resulted in the increased concentration and depth of diffusion of platinum into diaphragm and peritoneal tumor nodules. Consequently, IAP treatment induced an extended survival of rats treated at an advanced stage of carcinomatosis. In 7 50- to 70-kg ventilated pigs, a 40-mm Hg IAP was well tolerated when maintained stable for 2 hours. Renal failure occurred in pigs receiving a total dose of 200 and 400 mg of cisplatin with IAP, but a dose of 100 mg was well tolerated. CONCLUSIONS: Intraperitoneal chemotherapy with increased IAP, in comparison with conventional IP or IV chemotherapy, improved the tumor accumulation and the antitumor effect of cisplatin in rats bearing advanced peritoneal carcinomatosis. In preclinical conditions, the tolerance of sustained IAP was manageable in ventilated pigs.

Abdomen↗
PubMed2005

A Multi-Source Information System via the Internet for End-Stage Renal Disease: Scalability and Data Quality.

A Multi-Source Information System (MSIS), has been designed for the Renal Epidemiology and Information Network (REIN) dedicated to End-Stage Renal Disease (ESRD). MSIS aims at providing reliable follow-up data for ESRD patients. It is based on an n-tier architecture, made out of a universal client, a dynamic Web server connected to a production database and to a data warehouse. MSIS is operational since 2002 and progressively deployed in 9 regions in France. It includes 11,500 patients. MSIS facilitates documenting medical events which occur during the course of ESRD patient' health care and provides means to control the quality of each patient's record and reconstruct the patient trajectory of care. Consolidated data are made available to a data warehouse and to a geographic information system for analysis and data representation in support of public-health decision making.

Data Accuracy↗
PubMed2004

Yersinia pseudotuberculosis anti-inflammatory components reduce trinitrobenzene sulfonic acid-induced colitis in the mouse.

Rectal instillation of trinitrobenzene sulfonic acid (TNBS) induces acute colitis in the mouse. We tested the efficacy of Yersinia pseudotuberculosis anti-inflammatory components in preventing TNBS-triggered colitis. Animals were orally inoculated with virulence-attenuated Yersinia cells (a phoP mutant) prior to TNBS administration. Under these experimental conditions, colonic lesions and tumor necrosis factor alpha mRNA levels were significantly reduced.

Animals↗
PubMed2004

YAPI, a new Yersinia pseudotuberculosis pathogenicity island.

Pathogenicity islands (PAIs) are chromosomal clusters of pathogen-specific virulence genes often found at tRNA loci. In the Yersinia pseudotuberculosis 32777 chromosome, we characterized a 98-kb segment that has all of the characteristic features of a PAI, including insertion in a (phenylalanine) tRNA gene, the presence of a bacteriophage-like integrase-encoding gene, and direct repeats at the integration sites. The G+C content of the segment ranges from 31 to 60%, reflecting a genetic mosaic: this is consistent with the notion that the sequences were horizontally acquired. The PAI, termed YAPI (for Yersinia adhesion pathogenicity island), carries 95 open reading frames and includes (i) the previously described pil operon, encoding a type IV pilus that contributes to pathogenicity (F. Collyn et al., Infect. Immun. 70:6196-6205, 2002); (ii) a block of genes potentially involved in general metabolism; (iii) a gene cluster for a restriction-modification system; and (iv) a large number of mobile genetic elements. Furthermore, the PAI can excise itself from the chromosome at low frequency and in a precise manner, and deletion does not result in a significant decrease of bacterial virulence compared to inactivation of the fimbrial gene cluster alone. The prevalence and size of the PAI vary from one Y. pseudotuberculosis strain to another, and it can be found integrated into either of the two phe tRNA loci present on the species' chromosome. YAPI was not detected in the genome of the genetically closely related species Y. pestis, whereas a homologous PAI is harbored by the Y. enterocolitica chromosome.

Animals↗
PubMed2004

The response regulator PhoP of Yersinia pseudotuberculosis is important for replication in macrophages and for virulence.

Yersinia pestis and Yersinia pseudotuberculosis are closely related facultative intracellular pathogens. The response regulator PhoP was previously shown to be important for Y. pestis survival in macrophages and for virulence in a murine bubonic plague infection assay. Here the importance of PhoP for Y. pseudotuberculosis pathogenesis was investigated. Y. pseudotuberculosis phoP mutants were unable to replicate in low-Mg(2+) medium or in macrophages. phoP(+) Y. pseudotuberculosis strains initiated replication in macrophages after a lag period of approximately 5 h, as shown by fluorescence microscopy and viable count assays. Y. pseudotuberculosis phoP mutants died at a low rate in macrophages; there was no decrease in viability over the first 5 h of infection, and there was a 10-fold decrease in viability between 5 and 24 h of infection. Trafficking of phagosomes containing phoP(+) or phoP mutant Y. pseudotuberculosis was studied by using immunofluorescence microscopy and cathepsin D as a marker for lysosomes. Phagosomes containing phoP mutant Y. pseudotuberculosis acquired cathepsin D at a higher rate than phagosomes containing phoP(+) bacteria. However, the increased rate of marker acquisition for phagosomes containing mutant bacteria was only evident approximately 5 h after infection, suggesting that phoP mutants are able to retard phagosome maturation during the lag phase of intracellular growth. The results obtained with a Y. pestis phoP mutant were similar to those described above, except that the rates of intracellular killing and trafficking to cathepsin D-positive vacuoles were significantly higher. A Y. pseudotuberculosis phoP mutant was 100-fold less virulent than the wild-type strain in a murine intestinal infection model, suggesting that survival and replication in macrophages are important for Y. pseudotuberculosis pathogenesis.

Amino Acid Sequence↗
PubMed2003

A dynamic Web application within an n-tier architecture: a Multi-Source Information System for end-stage renal disease.

A Multi-Source Information System (MSIS) has been designed for the Renal Epidemiology and Information Network (REIN) dedicated to End-Stage Renal Disease. Interoperability has been considered at 4 levels: semantics, network, formats and contents. An n-tier architecture has been chosen at the network level. It is made out of a universal client, a dynamic Web server connected to a production database and to a data warehouse. The MSIS is patient-oriented, based on a regional organization. Its implementation in the context of a regional experimentation is presented with insights on the design and underlying technologies. The n-tier architecture is a robust model and flexible enough to aggregate multiple information sources and integrate modular developments. The data warehouse is dedicated to support health care decision-making.

Data Display↗
PubMed2002

[SIMS REIN: a multi-source information system for end-stage renal disease].

In France, the prevalence of End-Stage Renal Disease (ESRD) is not precisely known. The sources of information are scattered and not coordinated. Consequently, care is ill adapted to meet the demand. The Multi-Source Information System is the basis of the Renal Epidemiology and Information Network (REIN). It is dedicated to improve and organise our medical and epidemiological knowledge of ESRD and to aid public health decision-making in this area. The proposed approach is based on the datawarehouses. This model allows a unified vision of scattered data into distinct databases, for a better management, be it particular (patient follow-up) or global (regional follow-up), with a finality of aid in decision-making. Several categories of problems were considered: the global conception of the information system, the organisation of the datawarehouse, which offers different viewpoints of the data, the integration of heterogeneous data coming from different sources, data exchange and definition of a specific ontology.

Computer Communication Networks↗
PubMed2002

The Yersinia pseudotuberculosis Yut protein, a new type of urea transporter homologous to eukaryotic channels and functionally interchangeable in vitro with the Helicobacter pylori UreI protein.

Urea uptake in eukaryotes and prokaryotes occurs via diffusion or active transport across the cell membrane. Facilitated diffusion of urea in both types of organisms requires a single-component channel. In bacteria, these transport systems allow rapid access of urease to its substrate, resulting in ammonia production, which is needed either for resistance to acidity or as a nitrogen source. In Yersinia pseudotuberculosis, a ureolytic enteropathogenic bacterium, a gene of unknown function (yut) located near the urease locus was found to encode a putative membrane protein with weak homology to single-component eukaryotic urea transporters. When expressed in Xenopus oocytes, Yut greatly increases cellular permeability to urea. Inactivation of yut in Y. pseudotuberculosis results in diminished apparent urease activity and reduced resistance to acidity in vitro when urea is present in the medium. In the mouse model, bacterial colonization of the intestine mucosa is delayed with the Yut-deficient mutant. Although structurally unrelated, Yut and the Helicobacter pylori UreI urea channel were shown to be functionally interchangeable in vitro and are sufficient to allow urea uptake in both bacteria, thereby confirming their function in the respective parent organisms. Homologues of Yut were found in other yersiniae, Actinobacillus pleuropneumoniae, Brucella melitensis, Pseudomonas aeruginosa and Staphylococcus aureus. The Y. pseudotuberculosis Yut protein is therefore the first member of a novel class of bacterial urea permeases related to eukaryotic transporters.

Amino Acid Sequence↗
PubMed2002

Yersinia pseudotuberculosis harbors a type IV pilus gene cluster that contributes to pathogenicity.

Fimbriae have been shown to play an essential role in the adhesion of pathogenic gram-negative bacteria to host cells. In the enteroinvasive bacterium Yersinia pseudotuberculosis, we characterized a previously unknown 11-kb chromosomal locus involved in the synthesis of type IV pili. The locus consists of 11 open reading frames forming a polycistronic unit and encoding putative Pil proteins, PilLMNOPQRSUVW. When introduced into Escherichia coli, the Y. pseudotuberculosis operon reconstituted bundles of filaments at a pole on the bacterial surface, demonstrating that the pil locus was functional in a heterogenous genetic background. Environmental factors regulated transcription of the Y. pseudotuberculosis operon; in particular, temperature, osmolarity, and oxygen tension were critical cues. Deletion of the type IV pilus gene cluster was associated with a reduction of Y. pseudotuberculosis pathogenicity for mice infected orally. Forty-one percent of Y. pseudotuberculosis strains isolated from human or animal sources harbored the type IV pilus locus. Therefore, the pil locus of Y. pseudotuberculosis might constitute an "adaptation island," permitting the microorganism to colonize a vast reservoir.

Amino Acid Sequence↗
PubMed2002

The superantigen gene ypm is located in an unstable chromosomal locus of Yersinia pseudotuberculosis.

Yersinia pseudotuberculosis produces YPM (Y. pseudotuberculosis-derived mitogen), a superantigenic toxin that exacerbates the virulence of the bacterium in vivo. To date, three alleles of the superantigen gene (ypmA, ypmB, and ypmC) have been described. These genes are not found in all Y. pseudotuberculosis strains and have a low GC content, suggesting their location on mobile genetic elements. To elucidate this question, the genetic environment of the superantigen-encoding genes was characterized and 11 open reading frames (ORFs) were defined. Sequence analysis revealed that the ypm genes were not associated with plasmids, phages, transposons, or pathogenicity islands and that the superantigen genes were always located in the chromosome between ORF3 and ORF4. Nonsuperantigenic strains exhibited the same genetic organization of the locus but lacked the ypm gene between ORF3 and ORF4. A new insertion sequence, designated IS1398, which displays features of the Tn3 family, was characterized downstream of the ypmA and ypmC genes. A 13.3-kb region containing the ypm genes was not found in the genome of Y. pestis (CO92 and KIM 5 strains). We experimentally induced deletion of the ypm gene from a superantigen-expressing Y. pseudotuberculosis: using the association of aph(3')-IIIa and sacB genes, we demonstrated that when these reporter genes were present in the ypm locus, deletion of these genes was about 250 times more frequent than when they were located in another region of the Y. pseudotuberculosis chromosome. These results indicate that unlike other superantigenic toxin genes, the Yersinia ypm genes are not associated with mobile genetic elements but are inserted in an unstable locus of the genome.

Alleles↗
PubMed2002

Genes encoding specific nickel transport systems flank the chromosomal urease locus of pathogenic yersiniae.

The transition metal nickel is an essential cofactor for a number of bacterial enzymes, one of which is urease. Prior to its incorporation into metalloenzyme active sites, nickel must be imported into the cell. Here, we report identification of two loci corresponding to nickel-specific transport systems in the gram-negative, ureolytic bacterium Yersinia pseudotuberculosis. The loci are located on each side of the chromosomal urease gene cluster ureABCEFGD and have the same orientation as the latter. The yntABCDE locus upstream of the ure genes encodes five predicted products with sequence homology to ATP-binding cassette nickel permeases present in several gram-negative bacteria. The ureH gene, located downstream of ure, encodes a single-component carrier which displays homology to polypeptides of the nickel-cobalt transporter family. Transporters with homology to these two classes are also present (again in proximity to the urease locus) in the other two pathogenic yersiniae, Y. pestis and Y. enterocolitica. An Escherichia coli nikA insertion mutant recovered nickel uptake ability following heterologous complementation with either the ynt or the ureH plasmid-borne gene of Y. pseudotuberculosis, demonstrating that each carrier is necessary and sufficient for nickel transport. Deletion of ynt in Y. pseudotuberculosis almost completely abolished bacterial urease activity, whereas deletion of ureH had no effect. Nevertheless, rates of nickel transport were significantly altered in both ynt and ureH mutants. Furthermore, the ynt ureH double mutant was totally devoid of nickel uptake ability, thus indicating that Ynt and UreH constitute the only routes for nickel entry. Both Ynt and UreH show selectivity for Ni(2+) ions. This is the first reported identification of genes coding for both kinds of nickel-specific permeases situated adjacent to the urease gene cluster in the genome of a microorganism.

ATP-Binding Cassette Transporters↗