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Biomedical subjects

G Hecht

Publications and source records attributed to G Hecht.

52 records · Page 3Linked to original sources
PubMed1993

Phorbol ester sequentially downregulates cAMP-regulated basolateral and apical Cl- transport pathways in T84 cells.

The effect of phorbol esters on adenosine 3',5'-cyclic monophosphate (cAMP)-regulated epithelial Cl- transport was studied in T84 cells, a human colonic cell line that serves as a model for electrogenic Cl- secretion. Preincubation of T84 cell monolayers with phorbol 12-myristate 13-acetate (PMA) caused a time- and dose-dependent inhibition of the net transepithelial secretory response to 10 microM forskolin (half-maximal inhibition at a concentration of approximately 10 nM PMA and a time of 45 min). Similar inhibition was observed with phorbol 12,13-dibutyrate but not the inactive phorbol ester phorbol 12,13-diacetate. Na(+)-K(+)-2Cl- cotransporter activity, assessed by bumetanide-sensitive 86Rb+ uptake, and K+ conductance, assessed by 86Rb+ efflux, were both found to be markedly reduced by PMA with a time course that paralleled the loss of the cAMP-regulated Cl- secretory response. One- and four-hour treatment of T84 cells with 100 nM PMA caused a sustained increase in the membrane-bound fraction of protein kinase C (PKC) but a decrease in total cellular PKC. Although, at these time points, the Na(+)-K(+)-2Cl- cotransporter and K+ efflux pathways were markedly inhibited (associated with inhibition of the forskolin-stimulated transepithelial Cl- secretory response), the activity of the cAMP-regulated Cl- efflux pathway, assessed by 125I-labeled efflux, remained unaffected. With prolonged exposure to PMA (up to 10), the cAMP-regulated Cl- efflux pathway was also eventually inhibited, and transepithelial electrical resistance progressively declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗
PubMed1992

Clostridium difficile toxin B disrupts the barrier function of T84 monolayers.

The contribution of toxin B to Clostridium difficile-associated infection is undefined. Toxin B induces dramatic phenotypic alterations (cytotoxic effects) in cultured mesenchymal and nonintestinal epithelial cells, yet its effects on intestinal epithelial cells are not clearly understood. The alterations induced by toxin B in nonintestinal cells appear to be secondary to toxin-induced redistribution of filamentous actin. It has not been determined whether toxin B exerts similar effects on cultured intestinal epithelial cells or whether such phenotypic alterations are of any physiological consequence. To address these questions, we examined the effect of C. difficile toxin B on the phenotype and barrier function of T84 cell monolayers. Our studies show that the cytotoxic effects of toxin B, i.e., cell rounding, do extend to cultured intestinal epithelial cells (T84). In addition, toxin B dramatically reduces the barrier function of T84 monolayers grown on collagen-coated filters. Toxin B-induced redistribution of filamentous actin appears to be responsible for the alterations in both intestinal epithelial cell phenotype and barrier function. Specifically, filamentous actin comprising the perijunctional actomyosin ring, known to be important in regulating tight junction permeability, is condensed into discrete plaques. Flux studies confirm that the permeability defect is at the level of the tight junction. We conclude that toxin-induced changes in actin distribution perturb intercellular junctional contacts and thereby ablate epithelial barrier function. There was no evidence of cell death as determined by lactate dehydrogenase release assays.

Actins↗
PubMed1992

Exposure to sulphuric acid and sulphur dioxide in the manufacturing of titanium dioxide.

An assessment of exposure to sulphuric acid and sulphur dioxide was performed in the French titanium dioxide manufacturing industry. The three plants use the sulphuric acid process, with potential exposure mainly to sulphur dioxide and sulphuric acid. The exposures found were below the French limit values, except for some employees using the Moore filtration process in one plant. For sulphuric acid sampling, a comparison was made between thoracic particulate mass and inhalable particulate mass, from samples taken with a Marple cascade impactor. This comparison shows that the suggested new limit value (0.1 mg m-3 in thoracic particulate mass) would be much more severe than the present one (1.0 mg m-3 with no restriction as to the droplet size).

Chemical Industry↗
PubMed1991

Stabilization of F-actin prevents cAMP-elicited Cl- secretion in T84 cells.

T84 cells, a human intestinal epithelial cell line, serve as a model of electrogenic Cl- secretion. We find that cAMP-elicited Cl- secretion in T84 cells is accompanied by a marked redistribution of F-actin in the basolateral portion of the cell. To prevent this F-actin redistribution and thereby assess its importance to Cl- secretion, we have defined simple conditions under which this model epithelium can be loaded with nitrobenzoxadiazole (NBD)-phallicidin. This reagent binds F-actin with high affinity thus stabilizing the F-actin cytoskeleton by preventing depolymerization, an event necessary for dynamic reordering of actin microfilaments. NBD-phallicidin loading is not cytotoxic as assessed by lactic dehydrogenase release, protein synthesis, transepithelial resistance, and the ability of the loaded cells to pump Na+ in an absorptive direction in response to the apical addition of a Na+ ionophore. However, cAMP-elicited redistribution of F-actin and the cAMP-elicited Cl- secretory response are both markedly impaired in NBD-phallicidin preloaded T84 cells. In contrast, the carbachol-elicited Cl- secretory response (Ca++ mediated) is not attenuated by NBD-phallicidin preloading nor is it accompanied by redistribution of F-actin. These findings suggest that the cAMP-elicited cytoskeletal redistribution we describe is an integral part of cAMP-elicited Cl- secretion in T84 cells.

Actins↗
PubMed1988

Clostridium difficile toxin A perturbs cytoskeletal structure and tight junction permeability of cultured human intestinal epithelial monolayers.

Toxin A of Clostridium difficile causes severe inflammatory enterocolitis in man and animals that appears to be mediated in part by acute inflammatory cells that migrate into the toxin A-exposed mucosa. To determine the direct effects of toxin A on intestinal epithelial permeability and structure in the absence of other modulating factors, we used cultured monolayers of a human intestinal epithelial cell line (T84). A toxin A concentration of 7 x 10(-1) micrograms/ml (3 x 10(-9) M) nearly abolished monolayer transepithelial resistance within 6-8 h. This marked permeability defect occurred while the monolayers were still confluent. Dual sodium-mannitol flux studies localized the permeability defect to the intercellular tight junction. Cytotoxicity assays and morphological evaluation using Nomarski optics and electron microscopy failed to demonstrate any evidence of cell damage at the time the maximum resistance response was observed. Fluorescent staining for F actin, however, revealed a marked decrease in fluorescent intensity in toxin-treated monolayers versus controls. These data show that toxin A can directly affect the barrier function of this model intestinal epithelium and initially does so by selectively enhancing tight junction permeability. Furthermore, cytoskeletal structure is markedly altered over the same time course, although the integrity of individual cells is maintained. Because the cytoskeleton of intestinal epithelial cells is known to be capable of regulating tight junction permeability, we speculate that the above effects of toxin A on epithelial barrier function result from alterations of the cytoskeleton.

Animals↗
PubMed1987

Bioequivalence and pharmacokinetic profile of promethazine hydrochloride suppositories in humans.

A bioequivalence study of promethazine hydrochloride (10-[2-(dimethylamino)propyl]-phenothiazine monohydrochloride) was conducted in 20 male human subjects with the purpose of comparing, under blind condition, the human serum levels of promethazine in three different formulations. The formulations tested were a 50-mg promethazine hydrochloride polyethylene glycol suppository, a 50-mg promethazine hydrochloride cocoa butter-white wax suppository, and a 50-mg oral dose of promethazine hydrochloride syrup. Each subject received single doses of each of the three formulations on each of three different days on a crossover basis. From the measured serum levels, estimates of the bioavailability parameters (area under the serum concentration versus time curve, time-to-peak serum concentration, and peak serum concentration) were obtained by least-squares digital computer fitting. Also, a one-compartment pharmacokinetic open model with two consecutive first-order input steps is proposed. Statistical analysis of the results was performed by using a linear multiple regression approach for the analysis of variance. No significant differences between the syrup and the polyethylene glycol suppositories were obtained (p greater than 0.05) for the above three bioavailability parameters. However, the polyethylene glycol suppositories provided statistically higher peak serum concentration, shorter time-to-peak serum concentration, and larger area under the serum concentration versus time curve than the cocoa butter-white wax suppositories.

Adult↗
PubMedDate not supplied

Comparison of the sensory irritation response in mice to chlorine and nitrogen trichloride.

The expiratory bradypnoea indicative of upper airway irritation in mice was evaluated during a 60-min oronasal exposure to increasing concentrations of chlorine and nitrogen trichloride. The airborne concentration resulting in a 50% decrease in the respiratory rate of mice (RD50) was calculated for each chemical. Chlorine and nitrogen trichloride showed dissimilar concentration-response curves. While the maximal response of nitrogen trichloride was reached in 10 min, the maximal response of chlorine was reached between 45 and 60 min of exposure. The results showed both chemicals to have an irritant potency of the same order of magnitude. The RD50 values of chlorine and nitrogen trichloride were 3.5 and 2.5 ppm, respectively. On the basis of a TLV-STEL (threshold limit value for short-term exposure limit) equal to 0.1 RD50 and a TLV-TWA (time-weighted average) equal to 0.03 RD50, the current TLVs for chlorine seem too high (1 and 0.5 ppm, respectively) and should be reduced to 0.5 and 0.1 ppm, respectively. For nitrogen trichloride, 0.3 ppm and 0.1 ppm are proposed as TLV-STEL and TLV-TWA, respectively.

Administration, Inhalation↗
PubMedDate not supplied

Field study of subjective assessment of negative pressure half-masks. Influence of the work conditions on comfort and efficiency.

The aim of this study was to assess the effects of work conditions on the acceptability and efficiency of respiratory protective devices (RPD). The subjective evaluation of comfort, protection, respiratory and visual constraint, and the acceptable duration of wear of six RPDs against dust was achieved by 30 workers during their actual work. Metabolic rate was evaluated for each worker, and dry and wet air temperatures measured in the work area. RPDs objective protection factor was measured during each of the 180 test periods. In the conditions of this study, the acceptable duration of wear was about 1 h. This duration and the comfort parameters were reduced when the air temperature increased. The younger workers and/or smokers were less sensitive to mask discomfort. Objective protection factors of the RPDs are reduced under warmer conditions, and when the metabolic rate is low. Finally, the results of this study also show the poor capacity of standardized leakage tests to assess the objective respiratory protection of workers in the field. Some hypotheses which can explain this fact are discussed.

Adult↗
PubMedDate not supplied

Effects of acute mental stress on serum lipids: mediating effects of plasma volume.

The present study assessed the acute effects of mental stress (mental arithmetic) on serum cholesterol, triglycerides, high-density lipoprotein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL-C), and the extent to which stress-induced changes are attributable to decreases in plasma volume. Total cholesterol, triglycerides, HDL-C, and LDL-C were assessed in 18 healthy men (35 +/- 7 years) during a resting baseline (30 minutes), challenging mental arithmetic (math; 10 minutes), and recovery (30 minutes). Five additional subjects served as controls receiving no stress intervention. An indirect estimation of the change in plasma volume was computed from hematocrit and hemoglobin at each time point. Results indicated significant (p < .001) increases in cholesterol, triglycerides, LDL-C, and HDL-C levels during mental arithmetic. Changes in lipid levels during stress were not related to plasma epinephrine levels or changes. Significant (p < .002) increases in hematocrit and hemoglobin levels reflected a 9.23% decrease in plasma volume during mental arithmetic. Correcting for this decreased plasma volume, changes in cholesterol, triglycerides, HDL-C, and LDL-C levels during math were no longer significant (p > .16, p > .23, p > .27, and p > .42, respectively). These results indicate that acute psychological stress can cause a rapid and substantial decrease in plasma volume, producing hemoconcentration. Thus, stress-mediated increases in circulating lipid concentrations are a secondary result of decreased plasma volume, perhaps due to vascular fluid shifts. Methodologically, stress-induced hemoconcentration during mental stress suggests that acute plasma volume decreases may need to be evaluated in studies of the biochemical effects of stress on high molecular weight substances.

Adult↗
PubMedDate not supplied

Prothrombotic effects of environmental stress: changes in platelet function, hematocrit, and total plasma protein.

Mental stress can affect a range of variables relevant to hemostasis and thrombosis. However, research has not clarified whether these effects occur as part of a generalized sympathoadrenal response or whether stress-induced increases in catecholamines and blood pressure have selective and independent effects on hematologic variables. This study assessed the effects of mental and cold pressor stress on platelet activation, hematocrit, and total plasma protein and the relationship of these changes to sympathoadrenal and hemodynamic mechanisms. Platelet factor 4, beta-thromboglobulin, total plasma protein, hematocrit values, and hemoglobin were measured in 22 healthy men (32 +/- 7 years) during rest, mental arithmetic, and cold pressor task. A no-stress control group of five male subjects was used to rule out the possible effects of blood withdrawal in producing these changes. Significant increases to mental arithmetic and cold pressor (p < .001) were observed in platelet factor 4 and beta-thromboglobulin. Increases (p < .002) in hematocrit values and total plasma protein also occurred with mental arithmetic and cold pressor. Correlational analyses revealed that changes in hematocrit and total plasma protein concentrations were related to increased mean arterial pressure during stress, and platelet activation correlated positively with norepinephrine and negatively with epinephrine. The present results indicate that acute psychologic and cold stress cause concurrent changes in several hemostatic factors (increased platelet activation, hematocrit, and total plasma protein) that may play key roles in thrombosis and ischemia. The relationships of hematocrit and total plasma protein to blood pressure increases and the associations between platelet activation and catecholamines support the notion that stress-induced increases in catecholamines and blood pressure have selective effects on specific hemostatic variables.

Adult↗