Biomedical subjects

G Hecht

Publications and source records attributed to G Hecht.

At least 19 recordsLinked to original sources

PubMed2006

Respiratory symptoms and bronchial responsiveness among cleaning and disinfecting workers in the food industry.

OBJECTIVES: To measure the levels of exposure to nitrogen trichloride (NCl3) and aldehydes among cleaning and disinfecting workers in the atmosphere of food industry plants during cleaning and disinfecting operations, and to examine how they relate to irritant and chronic respiratory symptoms-which are indices of pulmonary function-and bronchial hyperresponsiveness (BHR) to methacholine. METHODS: 175 exposed workers (M = 149; F = 26) recruited from 17 enterprises of the food industry (8 cattle, pig, and ovine slaughterhouses, 8 fowl slaughterhouses, and 1 catering firm) and 70 non-exposed workers (M = 52; F = 18) were examined. Concentration levels of NCl3 and aldhehydes were measured by personal sampling. Symptoms were assessed by means of a questionnaire and the methacholine bronchial challenge (MBC) test using an abbreviated method. Subjects were labelled MBC+ if forced expiratory volume in one second (FEV1) fell by 20% or more. The linear dose-response slope (DRS) was calculated as the percentage fall in FEV1 at last dose divided by the total dose administered. RESULTS: 277 air samples were taken in the 17 food industry plants. For a given plant and in a given workshop, the actual concentrations of chloramines, aldehydes, and quaternary ammonium compounds were measured with personal samplers during the different steps of the procedures. For each cleaner, a total exposure index Sigma was calculated. A statistically significant concentration-response relationship was found between eye, nasal, and throat symptoms of irritation--but not chronic respiratory symptoms--and exposure levels or exposure duration. No relation was found between BHR and exposure. CONCLUSIONS: These data show that cleaning and disinfecting workers in the food industry are at risk of developing eye, nasal, and throat irritation symptoms. Although NCl3 exposure does not seem to carry a risk of developing permanent BHR, the possibility of transient BHR cannot be ruled out entirely.

Adult↗

PubMed2004

Simultaneous sampling of peroxyacetic acid and hydrogen peroxide in workplace atmospheres.

The use of peroxyacetic acid (PAA) in the disinfection processes in the food industry or for medical purposes is increasing. As it is the product of the reaction of acetic acid (AA) and hydrogen peroxide (HP) and coexists with them, and given the fact that the chemical properties of these two substances are not very different from PAA, the sampling and analysis of this substance in working atmospheres is difficult. A specific sampling device was developed. It is composed of: (i) a cassette with quartz fibre filters impregnated with titanium oxysulfate hydrate for the sampling of HP followed by; (ii) a tube filled with silica gel soaked with methyl p-tolylsulfoxide for the sampling of PAA. The analysis of this silica gel was performed by liquid chromatography with UV detection of the methyl p-sulfone generated by the sampling of PAA. The conservation of the sampling media (before and after sampling) and its efficiency were also checked. From the results of sampling campaigns performed in various workplaces, the relative contributions of PAA, AA and HP to an exposure index, taking into account the atmospheric concentrations and the threshold limit values, were established. This calculation shows that the simultaneous determination of PAA and HP, which the method presented in this paper allows, provides a fairly good estimation of the exposure.

Air Pollutants, Occupational↗

PubMed2003

Intestinal epithelial responses to enteric pathogens: effects on the tight junction barrier, ion transport, and inflammation.

The effects of pathogenic organisms on host intestinal epithelial cells are vast. Innumerable signalling pathways are triggered leading ultimately to drastic changes in physiological functions. Here, the ways in which enteric bacterial pathogens utilise and impact on the three major physiological functions of the intestinal epithelium are discussed: alterations in the structure and function of the tight junction barrier, induction of fluid and electrolyte secretion, and activation of the inflammatory cascade. This field of investigation, which was virtually non-existent a decade ago, has now exploded, thus rapidly expanding our understanding of bacterial pathogenesis. Through increased delineation of the ways in which microbes alter host physiology, we simultaneous gain insight into the normal regulatory mechanisms of the intestinal epithelium.

Bacterial Infections↗

PubMed2002

Generation of controlled atmospheres for the determination of the irritant potency of peroxyacetic acid.

Given the physical properties of peroxyacetic acid, which decomposes into acetic acid and hydrogen peroxide, the generation and analysis of controlled atmospheres used to test the irritant potency of this peracid in mice require specific developments. The sampling and analytical method was based on the simultaneous sampling on a titanyl sulphate-impregnated silica gel tube (allowing the determination of total peroxides, peroxyacetic acid and hydrogen peroxide) and in an impinger containing a methyl-p-tolyl sulphide solution (of which the analysis yields the concentration of total acids, peroxyacetic acid and acetic acid, and peroxyacetic alone). From these results the concentrations of the different products can be inferred without interference. A special device composed of inert materials was designed for the generation of the controlled atmosphere. Buffering the peroxyacetic solution at pH 7 with a phosphate buffer allowed the generation of peroxyacetic acid atmospheres with negligible concentrations of acetic acid and hydrogen peroxide.

Acetic Acid↗

PubMed2002

Measuring the emission rate of an aerosol source placed in a ventilated room using a tracer gas: influence of particle wall deposition.

A method to measure the emission rate of an airborne pollutant source using a tracer gas was tested in the case of an aerosol source. The influence of particle deposition on the walls of a test room of 72 m3 was studied. The deposition rate of an aerosol of MgCl2 was determined by means of two methods: one based on measuring the aerosol concentration decay inside the ventilated room, the other based on calculation of the material mass balance. The concentration decay was monitored by optical counting and the aerosol mass concentration determined by means of sampling on a filter and analysis of the mass deposited by atomic absorption spectrometry. Four series of measurements were carried out. The curve giving the deposition rate according to the particle aerodynamic diameter (d(ae)) was established and shows deposition rates higher than those predicted using the model of Corner. The decay method gives the best results. The study carried out has shown that the phenomenon of deposition has little effect on the measurement of the aerosol source emission rate using a tracer gas for particles of aerodynamic diameter < 5 microm (underestimation < 25%). For particles of a greater diameter, wall deposition is an extremely limiting factor for the method, the influence of which can, however, be limited by using a test booth of small volume and keeping the sampling duration as short as possible.

Aerosols↗

PubMed2001

Dynamics of IgG1 and IgG2 subclass response in dogs naturally and experimentally infected with Ehrlichia canis.

Immunoglobulin (Ig) G subclasses were measured in dogs naturally and experimentally infected with Ehrlichia canis using enzyme-linked immunosorbant assay (ELISA). In this study, a higher IgG2 subclass response was noticed to natural and experimental E. canis infection in dogs. Anti-E. canis-IgG2 optic density (OD) values were found to be significantly higher than anti-E. canis-IgG1 during the different phases of the disease, and no differences in the IgG subclass responses to E. canis infection were found between symptomatic and asymptomatic dogs. Doxycycline treatment, which eliminated the rickettsia in three of four persistently infected dogs, had no noticeable influence on the E. canis-IgG subclass OD values during the treatment period. In order to facilitate the study, an ELISA for the detection of anti-E. canis IgG was developed and was shown to be sensitive and specific for E. canis-IgG, and in a significant correlation with the indirect immunofluorescence antibody test.

Animals↗

PubMed2001

Enteropathogenic Escherichia coli activates ezrin, which participates in disruption of tight junction barrier function.

Enteropathogenic Escherichia coli (EPEC) is an important human intestinal pathogen, especially in infants. EPEC adherence to intestinal epithelial cells induces the accumulation of a number of cytoskeletal proteins beneath the bacteria, including the membrane-cytoskeleton linker ezrin. Evidence suggests that ezrin can participate in signal transduction. The aim of this study was to determine whether ezrin is activated following EPEC infection and if it is involved in the cross talk with host intestinal epithelial cells. We show here that following EPEC attachment to intestinal epithelial cells there was significant phosphorylation of ezrin, first on threonine and later on tyrosine residues. A significant increase in cytoskeleton-associated ezrin occurred following phosphorylation, suggesting activation of this molecule. Nonpathogenic E. coli and EPEC strains harboring mutations in type III secretion failed to elicit this response. Expression of dominant-negative ezrin significantly decreased the EPEC-elicited association of ezrin with the cytoskeleton and attenuated the disruption of intestinal epithelial tight junctions. These results suggest that ezrin is involved in transducing EPEC-initiated signals that ultimately affect host physiological functions.

Animals↗

PubMed2001

Microbes and microbial toxins: paradigms for microbial-mucosal interactions. VII. Enteropathogenic Escherichia coli: physiological alterations from an extracellular position.

Enteropathogenic Escherichia coli (EPEC) is primarily associated with infantile diarrhea in developing countries. This intriguing pathogen exerts numerous physiological effects on its host target tissue, the intestinal epithelium, all from an extracellular location. Expression of a type III secretory apparatus allows this organism to transfer bacterial effector molecules directly into host cells. As a result of EPEC attachment to and/or translocation of proteins into intestinal epithelial cells, many signaling cascades are activated. Ultimately, host functions are perturbed, including alteration of ion transport, disruption of the tight junction barrier, and activation of the inflammatory response.

Diarrhea↗

PubMed2001

EPEC-activated ERK1/2 participate in inflammatory response but not tight junction barrier disruption.

Enteropathogenic Escherichia coli (EPEC) alters many functions of the host intestinal epithelia. Inflammation is initiated by activation of nuclear factor (NF)-kappaB, and paracellular permeability is enhanced via a Ca2+- and myosin light-chain kinase (MLCK)-dependent pathway. The aims of this study were to identify signaling pathways by which EPEC triggers inflammation and to determine whether these pathways parallel or diverge from those that alter permeability. EPEC-induced phosphorylation and degradation of the primary inhibitor of NF-kappaB (IkappaBalpha) were tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta independent. In contrast to Salmonella typhimurium, EPEC-stimulated IkappaBalpha degradation and IL-8 expression did not require Ca2+. Instead, extracellular signal-regulated kinase (ERK)-1/2 was significantly and rapidly activated. ERK1/2 inhibitors attenuated IkappaBalpha degradation and IL-8 expression. Although ERK1/2 can activate MLCK, its inhibition had no impact on EPEC disruption of the tight junction barrier. In conclusion, EPEC-induced inflammation 1) is TNF-alpha and IL-1beta receptor independent, 2) utilizes pathways differently from S. typhimurium, 3) requires ERK1/2, and 4) employs signals that are distinct from those that alter permeability. This is the first time that EPEC-activated signaling cascades have been linked to independent functional consequences.

Calcium↗

PubMed2001

Translocated EspF protein from enteropathogenic Escherichia coli disrupts host intestinal barrier function.

The mechanisms by which enteropathogenic Escherichia coli (EPEC), an important cause of diarrhea among infants in developing countries, induce symptoms are not defined. EPEC have a type III secretion system required for characteristic attaching and effacing changes that modify the cytoskeleton and apical surface of host cells. Infection of polarized intestinal epithelial cell monolayers by EPEC leads to a loss of transepithelial electrical resistance, which also requires the type III secretion system. We demonstrate here that EspF, a protein that is secreted by EPEC via the type III secretion system, is not required for quantitatively and qualitatively typical attaching and effacing lesion formation in intestinal epithelial cells. However, EspF is required in a dose-dependent fashion for the loss of transepithelial electrical resistance, for increased monolayer permeability, and for redistribution of the tight junction-associated protein occludin. Furthermore, the analysis of EPEC strains expressing EspF-adenylate cyclase fusion proteins indicates that EspF is translocated via the type III secretion system to the cytoplasm of host cells, a result confirmed by immunofluorescence microscopy. These studies suggest a novel role for EspF as an effector protein that disrupts intestinal barrier function without involvement in attaching and effacing lesion formation.

Bacterial Adhesion↗

PubMed2000

Galanin-1 receptor up-regulation mediates the excess colonic fluid production caused by infection with enteric pathogens.

Galanin is widely distributed in enteric nerve terminals lining the gastrointestinal tract. We previously showed that pathogenic Escherichia coli, but not normal commensal organisms, increase galanin-1 receptor expression by epithelial cells lining the colon (i.e., colonocytes). When present, galanin-1 receptor activation by ligand causes colonocyte Cl- secretion. We herein demonstrate that disparate pathogens including Salmonella typhimurium and Shigella flexerii also increase colonocyte galanin-1 receptor expression, whose activation is responsible for a principal component of the increased colonic fluid secretion observed. Although eliminating the GAL1R gene by homologous recombination does not alter basal colonic fluid secretion, removal of one or both alleles completely attenuates the increase in fluid secretion due to infection with enteric pathogens. Galanin-1 receptor up-regulation therefore represents a novel mechanism accounting for the increased colonic fluid secretion observed in infectious diarrhea due to several different pathogens.

Animals↗

PubMed2000

Enteropathogenic Escherichia coli dephosphorylates and dissociates occludin from intestinal epithelial tight junctions.

Enteropathogenic Escherichia coli (EPEC) increases tight junction permeability in part by phosphorylating the 20 kDa myosin light chain (MLC20) that induces cytoskeletal contraction. The impact of this enteric pathogen on specific tight junction (TJ) proteins has not been investigated. We examined the effect of EPEC infection on occludin localization and phosphorylation in intestinal epithelial cells. After infection by EPEC, a progressive shift of occludin from a primarily TJ-associated domain to an intracellular compartment occurred, as demonstrated by immunofluorescent staining. A reverse in the ratio of phosphorylated to dephosphorylated occludin accompanied this morphological change. Eradication of EPEC with gentamicin resulted in the normalization of occludin localization and phosphorylation. The serine/threonine phosphatase inhibitor, calyculin A, prevented these events. The EPEC-associated decrease in transepithelial electrical resistance, a measure of TJ barrier function, returned to baseline after gentamicin treatment. Non-pathogenic E. coli, K-12, did not induce these changes. Transformation of K-12 with the pathogenicity island of EPEC, however, conferred the phenotype of wild-type EPEC. Deletion of specific EPEC genes encoding proteins involved in EPEC type III secretion markedly attenuated these effects. These findings suggest that EPEC-induced alterations in occludin contribute to the pathophysiology associated with this infection.

Anti-Bacterial Agents↗

PubMed2000

Innate immunity and the gut.

The intestinal epithelium encounters a unique environment consisting of microbes, both commensals and pathogens, as well as dietary nutrients and antigens. This complex composition necessitates the presence of a dynamic system of defense to contain both pathogenic and commensal bacteria within the lumen yet allow for nutrient absorption. Tight junctions provide protection of the intercellular spaces while other surface molecules, such as intestinal trefoil factor, help to maintain the structural integrity of the epithelium. Other more active processes, including upregulated expression and activation of antimicrobial peptides and enhanced fluid secretion, provide a second level of innate defense. Despite providing the interface between an exuberant immune system and a highly antigenic lumenal environment, the intestinal epithelium must remain quiescent. As such, several novel antiinflammatory mechanisms were recently identified. Studies that elaborate the various aspects of these pathways are discussed in this review.

Journal Article↗

PubMed2000

Dextran sulfate sodium-induced murine colitis activates NF-kappaB and increases galanin-1 receptor expression.

Galanin is widely distributed in enteric nerve terminals and acts to modulate intestinal motility by altering smooth muscle contraction. This ligand causes Cl(-) secretion when colonic epithelial cells express the galanin-1 receptor (Gal1-R) subtype. Because Gal1-R expression by colonic epithelia is upregulated by the transcription factor nuclear factor-kappaB (NF-kappaB), increasingly appreciated as critical in the pathophysiology of inflammatory bowel disease, we wondered whether the diarrhea associated with this condition could be due to NF-kappaB-mediated increases in Gal1-R expression. To test this hypothesis, we provided oral dextran sulfate sodium (DSS) to C57BL/6J mice. Although Gal1-R are not normally expressed by epithelial cells lining the mouse colon, DSS treatment resulted in increased NF-kappaB activation and Gal1-R expression. Whereas galanin had no effect on murine colonic tissues studied ex vivo, it progressively increased short-circuit current and colonic fluid secretion in DSS-treated mice. Concomitant parenteral administration of the NF-kappaB inhibitor dexamethasone attenuated the activation of this transcription factor by DSS, inhibiting the increase in Gal1-R expression. Although Gal1-R-specific antagonists do not exist, intracolonic administration of commercially available galanin antibody diminished the DSS-induced increase in colonic fluid accumulation. Overall, these data demonstrate that a significant component of the excessive fluid secretion observed in DSS-treated mice is due to increased Gal1-R expression.

Animals↗

PubMed2000

Infection by bacterial pathogens expressing type III secretion decreases luciferase activity: ramifications for reporter gene studies.

Pathogenic microbes influence gene regulation in eukaryotic hosts. Reporter gene studies can define the roles of promoter regulatory sequences. The effect of pathogenic bacteria on reporter genes has not been examined. The aim of this study was to identify which reporter genes are reliable in studies concerning host gene regulation by bacterial pathogens expressing type III secretory systems. Human intestinal epithelial cells, T84, Caco-2 and HT-29, were transfected with plasmids containing luciferase (luc), chloramphenicol acetyltransferase (CAT) or beta-galactosidase (beta-gal) as reporter genes driven by the inducible interleukin-8 (IL-8) or constitutively active simian virus 40 (SV40) promoter. Cells were infected with enteropathogenic E. coli or Salmonella typhimurium, and the reporter activity was assessed. Luc activity significantly decreased following infection, regardless of the promoter. The activity of recombinant luc was nearly ablated by incubation with either EPEC or Salmonella in a cell-free system. Activity was partially preserved by protease inhibitors, and immunoblot analysis showed a decreased amount and molecular weight of recombinant luc, suggesting protein degradation. Neither beta-gal nor CAT activity was altered by infection. Disruption of type III secretion prevented the loss of luc activity. We conclude that CAT or beta-gal, but not luc, can be used as reliable reporter genes to assess the impact of pathogenic microbes, especially those expressing type III secretion on host cell gene regulation.

Cell Line↗

PubMed1999

Workplace monitoring of hydrogen peroxide using titanyl-coated sorbents.

The current methods of sampling hydrogen peroxide, based on bubbling in acid solutions (titanium tetrachloride or titanium oxysulfate), are unsuitable for personal sampling. An alternative medium has been developed: silica gel coated with titanium oxysulfate. Sample tubes of this new sampling medium are suitable for personal sampling. The sampling performance is the same as that of the methods based on bubbling, but the tubes must be desorbed as soon as possible, even if the spectrophotometric analysis can be postponed. Special emphasis has been placed on the possible interference by peracetic acid, which is currently used in conjunction with hydrogen peroxide in the food industry.

Absorption↗

PubMed1999

Innate mechanisms of epithelial host defense: spotlight on intestine.

The single layer of epithelial cells lining the intestinal tract is charged with a most difficult task: protecting the underlying biological compartments from both the normal commensal flora that reside within the intestinal lumen as well as the uninvited pathogens. To such an end, the intestinal epithelial cells are equipped with a panoply of defense mechanisms, both constitutive and inducible. This review focuses only on those defense mechanisms that are initiated and executed by the intestinal epithelial cell. Fitting these strict criteria are three major categories of epithelial host defense: enhanced salt and water secretion, expression of antimicrobial proteins and peptides, and production of intestinal mucins. Each of these areas is discussed in this review.

Animals↗

PubMed1999

Myosin regulation of NKCC1: effects on cAMP-mediated Cl- secretion in intestinal epithelia.

The basally located actin cytoskeleton has been demonstrated previously to regulate Cl- secretion from intestinal epithelia via its effects on the Na+-K+-2Cl- cotransporter (NKCC1). In nontransporting epithelia, inhibition of myosin light chain kinase (MLCK) prevents cell-shrinkage-induced activation of NKCC1. The aim of this study was to investigate the role of myosin in the regulation of secretagogue-stimulated Cl- secretion in intestinal epithelia. The human intestinal epithelial cell line T84 was used for these studies. Prevention of myosin light chain phosphorylation with the MLCK inhibitor ML-9 or ML-7 and inhibition of myosin ATPase with butanedione monoxime (BDM) attenuated cAMP but not Ca2+-mediated Cl- secretion. Both ML-9 and BDM diminished cAMP activation of NKCC1. Neither apical Cl- channel activity, basolateral K+ channel activity, nor Na+-K+-ATPase were affected by these agents. Cytochalasin D prevented such attenuation. cAMP-induced rearrangement of basal actin microfilaments was prevented by both ML-9 and BDM. The phosphorylation of mosin light chain and subsequent contraction of basal actin-myosin bundles are crucial to the cAMP-driven activation of NKCC1 and subsequent apical Cl- efflux.

Actins↗