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Biomedical subjects

A Shostak

Publications and source records attributed to A Shostak.

At least 19 recordsLinked to original sources
PubMed2005

A short review of experimental peritoneal sclerosis: from mice to men.

Peritoneal sclerosis has been induced in rodents in vivo by exposing the membrane to a variety of experimental interventions: asbestos, 0.1% chlorexidine, iron dextran, glucose degradation products, AGE deposits derived from uremia per se, sodium hypochlorite, lypopolysaccharide, low pH, pure water, silica or zymosan. With a few exceptions (pure water, chlorhexidine and low pH), the other substances mentioned operate setting out different degrees of oxidative stress. This short review describes several experimental interventions in rodents, aimed at acute exfoliation or long-term, sustained injury of the mesothelial monolayer performed by means of intraperitoneal injections of different oxidant agents. Acute exfoliation induced by deoxycholate resulted in a depopulated monolayer coincident with immediate alteration of the peritoneal permeability, evidenced by increased urea D/P ratio, higher glucose absorption rate, elevated albumin losses in the effluent and significant reduction of the ultrafiltration rate. In the long term (30 days), these manifestations of membrane failure persisted and coincided with substantial peritoneal sclerosis. Peritoneal sclerosis was also induced by IP injections of 0.125% trypsin and 6.6 mM/L solution of formaldehyde. Using the doughnut rat model of mesothelial regeneration, exposure to 4.25% glucose or 7.5% icodextrin solutions severely hampered repopulation of the monolayer, which was replaced by a thick sheet of fibrous tissue. It is concluded that peritoneal sclerosis derives mostly from sustained oxidative injury to the peritoneal membrane. Loss of the mesothelial monolayer is the first step in the chain of events leading to this complication.

Animals↗
PubMed2001

The winged helix transcription factor Foxc1a is essential for somitogenesis in zebrafish.

Previous studies identified zebrafish foxc1a and foxc1b as homologs of the mouse forkhead gene, Foxc1. Both genes are transcribed in the unsegmented presomitic mesoderm (PSM), newly formed somites, adaxial cells, and head mesoderm. Here, we show that inhibiting synthesis of Foxc1a (but not Foxc1b) protein with two different morpholino antisense oligonucleotides blocks formation of morphological somites, segment boundaries, and segmented expression of genes normally transcribed in anterior and posterior somites and expression of paraxis implicated in somite epithelialization. Patterning of the anterior PSM is also affected, as judged by the absence of mesp-b, ephrinB2, and ephA4 expression, and the down-regulation of notch5 and notch6. In contrast, the expression of other genes, including mesp-a and papc, in the anterior of somite primordia, and the oscillating expression of deltaC and deltaD in the PSM appear normal. Nevertheless, this expression is apparently insufficient for the maturation of the presumptive somites to proceed to the stage when boundary formation occurs or for the maintenance of anterior/posterior patterning. Mouse embryos that are compound null mutants for Foxc1 and the closely related Foxc2 have no morphological somites and show abnormal expression of Notch signaling pathway genes in the anterior PSM. Therefore, zebrafish foxc1a plays an essential and conserved role in somite formation, regulating both the expression of paraxis and the A/P patterning of somite primordia.

Amino Acid Sequence↗
PubMed2001

Protective effect of aminoguanidine upon capillary and submesothelial anionic sites.

This study evaluates albuminuria and peritoneal permeability to albumin in control and diabetic rats, as well as in diabetic animals treated with subcutaneously injected aminoguanidine hydrochloride (Ag) (5 mg/100 g/day), during a follow-up period of 6 months. Aminoguanidine effectively prevented albuminuria and albumin extravasation in the mesenteric interstitial tissue (control, 0.43 +/- 0.11 microg EB/100 g of dry tissue, Ag, 0.60 +/- 0.44; untreated diabetic animals, 1.22 +/- 0.73; control and Ag group vs untreated diabetic rats, P < 0.001). Albumin D/P ratio of the aminoguanidine-exposed rats (0.017 +/- 0.011) was higher than that of controls (0.008 +/- 0.002), but significantly lower (P < 0.001) than values observed in the untreated group of animals (0.046 +/- 0.003). Administration of aminoguanidine preserved both submesothelial and subendothelial electronegative charges. For capillary basement membrane (BM), control at zero time, 32 +/- 4 AS/microm BM; control at 6 months, 33.4; aminoguanidine-treated rats, 35 +/- 2. For submesothelial BM, control at zero time, 33 +/- 3; control at 6 months, 32 +/- 3; aminoguanidine-treated rats, 35 +/- 3. Splitting and thickening of both basement membranes were not prevented by the therapeutic intervention. We conclude that the shielding effect of aminoguanidine upon the permselectivity capabilities of the endothelial and mesothelial monolayers appears to be connected, basically to the preservation of anionic fixed charges.

Albuminuria↗
PubMed2000

High glucose accelerates the life cycle of the in vivo exposed mesothelium.

BACKGROUND: Mouse mesothelium exposed in vivo for 30 days to high glucose solutions develop morphological changes that characterize a population of cells near the end of their life span. METHODS: The present study was designed to explore, in mesothelial cell imprints, whether these changes could derive from an early acceleration of the cell population life cycle in mice exposed for periods of up to 30 days to a 4.25% glucose fluid (236 mmol/L/L) prepared in Hank's balanced salt solution (HBSS). Three critical points of the cell's life cycle were evaluated: the G1 checkpoint [proliferating cell nuclear antigen (PCNA) expression], DNA synthesis ((3)H-thymidine incorporation), and the prevalence of mitosis. RESULTS: Cell populations exposed to a high glucose concentration showed an initial acceleration of their life cycle, as sustained by a peak of mitosis at two hours, an early increase of DNA incorporation sustained during the first 24 hours, as well as a top level of PCNA expression after three to four hours. These significantly higher values, compared with the control animals treated with HBSS, collapsed after 24 hours and were nil after 30 days of exposure. CONCLUSIONS: Exposure to a high glucose concentration induced an early and short-lived acceleration of the mesothelial cell cycle, and with a longer exposure this was followed by a depletion of the growth capabilities of the exposed monolayer.

Animals↗
PubMed2000

Protective effect of pyruvate upon cultured mesothelial cells exposed to 2 mM hydrogen peroxide.

Rat peritoneal mesothelial cells in culture have the capability of generating hydrogen peroxide. Exposure of these cells to glucose-enriched, lactated-buffered fluids for peritoneal dialysis significantly increases the production of H(2)O(2). Increased liberation of oxygen radicals also involves the risk of damaging the peritoneal membrane. Pyruvate being a natural oxidant scavenger abundantly present in mammalian cells, we hypothesized that its protective effects facing H(2)O(2) can eventually be of relevance for the mesothelial monolayer of patients on long-term peritoneal dialysis. So far, we designed an experimental study in which rat peritoneal mesothelial cells in culture were exposed to 2 mM H(2)O(2). Cell damage was estimated in terms of decreased capability of the mitochondrial dehydrogenases to reduce MTT. Addition of 2 mM sodium pyruvate to the medium prevented the negative effect of hydrogen peroxide. The MTT/protein values for the control group were 0.00357 +/- 0.00075. The ratio after exposure to 2 mM H(2)O(2) was 0. 00217 +/- 0.00028, whereas that detected in cells incubated in H(2)O(2) plus pyruvate was 0.00325 +/- 0.0082 (p < 0.05). These results indicate that pyruvate protected rat peritoneal mesothelial cells in culture against oxidant injury. These data are one more piece of evidence pointing at pyruvate as a potentially useful buffer for peritoneal dialysis solutions.

Animals↗
PubMed1999

Effect of hyperosmolality upon the mesothelial monolayer exposed in vivo and in situ to a mannitol-enriched dialysis solution.

Studies done using the in vivo mouse model of population analysis of mesothelium showed that dialysis solutions containing high concentrations of glucose induced the development of a hypertrophic phenotype. Since these changes were neither related to the low pH nor to the presence of lactate buffer, we hypothesized that the presence of glucose was at the origin of the observed alterations. Theoretical analysis of the problem points to three possible mechanisms: hyperosmolality; metabolic changes derived from the high-glucose concentration itself, and/or the presence of products derived from the nonenzymatic degradation of glucose. The present study was designed to demonstrate or rule out the eventual effect of hyperosmolality upon the monolayer, applying the in vivo mouse model of population analysis of mesothelium. For this purpose, morphometric observations made in mice injected once a day during 30 consecutive days with a filter-sterilized 4.25% solution of mannitol (233.29 mM) were compared with those seen in intact mice and in a previously reported group of animals exposed to heat-sterilized fluid, having an equimolar concentration of glucose (235.9 mM), and the same osmolality (486 mosm/l) and electrolyte concentrations. The main findings observed in the mannitol-treated mice during the period of exposure included increased cell size and cytoplasmic surface area, as well as decreased cell viability. The regenerative capabilities of the exposed mesothelium remained intact. After a recovery period of 7 days, the aforementioned parameters reverted to normal values. This pattern is significantly different from the hypertrophic, senescent and low regenerative phenotype observed in mice treated with the high-glucose concentration solution. We conclude that, at least in the in vivo and in situ setup, the detrimental effects of hyperosmolality alone upon the exposed mesothelium are quite limited and fully reversible within a recovery period of 7 days.

Animals↗
PubMed1999

High glucose induces a hypertrophic, senescent mesothelial cell phenotype after long in vivo exposure.

Previous studies, done using our mouse model for population analysis of the mesothelium, showed evidence indicating that in vivo, long-term exposure (up to 30 days) of the peritoneum to high-glucose (4.25% D-glucose) concentration dialysis solutions resulted in a hypertrophic mesothelial phenotype characterized by increased cell surface area, multinucleation, low proliferative capabilities, reduced cell viability, and enhanced enzymatic activity. These elements that define a senescent population of cells were not related to the pH of the fluid and its osmolality, or to the presence of buffer lactate. The present study was designed to explore the adverse effects of a lactate-free, filter-sterilized, high-D-glucose concentration solution (4.25%) at normal pH and prepared in Hanks' buffered salt solution after 2 h, 15 and 30 days of once a day intraperitoneal injection. Analysis of our observations indicate that in vivo exposure of the mesothelium to a high-glucose concentration induced a decreased density of the cell population, made up by larger and multinucleated cells, the viability of which was significantly lower than that observed in intact unexposed mice. The prevalence of mitosis showed an early and short-lived acceleration (up to 3 days), followed by values near zero during the rest of the follow-up period. So far, the main effect of the high-glucose concentration appears to result not from a mechanism of cytotoxicity, but from a substantial change in the life cycle of the exposed cell population, leading to their premature senescence and death in apoptosis. We hypothesize that this outcome may well be mediated by sustained oxidative stress derived from both a reduced production of scavengers, as well as the increased generation of oxygen-reactive species.

Animals↗
PubMed1998

Experimental use of raffinose as an osmotic agent for peritoneal dialysis.

Conventional glucose-based solutions for peritoneal dialysis fluids have been shown to raise problems of biocompatibility. We therefore evaluated the ultrafiltration capabilities of raffinose as an alternative osmotic agent in a non-uremic rat model. Animals were divided into four groups and injected intraperitoneally with solutions containing raffinose (4.5%, 345 mOsm/kg; 16.7%, 518 mOsm/kg) or glucose (1.5%, 346 mOsm/kg; 4.25%, 489 mOsm/kg). Data obtained from animals exposed to 16.7% raffinose were excluded because of precipitation of the osmotic agent. Low-osmolality raffinose solution induced higher ultrafiltered volume than the low-osmolality glucose-enriched fluid at 120 minutes of dwelling time. No significant differences were observed in effluent sodium and potassium concentration and protein dialysate-to-plasma (D/P) ratio. The D/P ratio of phosphate was higher in the low-osmolality raffinose-based fluid than in the low-osmolality glucose solution. The osmolality of the solutions was significantly decreased after a dwelling time of 120 minutes. We conclude that 4.5% raffinose is an effective osmotic agent. Total or partial replacement of glucose by raffinose for clinical peritoneal dialysis could be eventually considered after appropriate evaluation of its biocompatibility and general side effects.

Animals↗
PubMed1998

Increased mesenteric, diaphragmatic, and pancreatic interstitial albumin content in rats with acute abdominal sepsis.

This study was designed to evaluate the decreased permselectivity of the capillary wall and the resultant higher permeability to macromolecular anionic albumin in septic rats, by quantitative estimation of Evans blue-albumin complexes in interstitial tissue. Septic peritonitis was induced by intraperitoneal injection of Escherichia coli-O6 KS H16. Twenty-four hours after induction of septic peritonitis, intact (healthy, noninoculated animals) and septic rats were perfused with 5 mL/Kg of a solution of Evans blue in normal saline (20 mg/mL in .9% NaCl). In septic rats, the interstitial concentration of Evans blue in mesentery, pancreas, and diaphragmatic muscle was significantly higher than that observed in intact animals. The present observations were made in the same experimental model of abdominal sepsis that showed a substantial reduction in the endothelial negative charge of the mesenteric, pancreatic, and diaphragmatic capillary beds. The evidence obtained from this experiment confirms that the loss of the permselective properties of capillary wall for macromolecular anionic albumin derives from a drastic reduction of its normally present and regularly distributed fixed electronegative charges.

Abdomen↗
PubMed1998

Correction of uremic iron deficiency anemia in hemodialyzed patients: a prospective study.

This prospective study was designed to evaluate the eventual correction of anemia and iron status in 39 iron-deficient uremics starting hemodialysis. Nine patients (control group) had no iron supplementation, 10 had oral ferrous iron, and 20 were treated with intravenous iron gluconate. Follow-up periods were 12 months for the control group and 26 months for patients treated with oral or intravenous iron. No patient was treated with erythropoietin. At zero time, all patients were anemic (Hb <78 g/l) and showed signs of severe iron deficiency, diagnosed on the basis of depleted bone marrow iron stores, reduced hemoglobin iron, and transferrin saturation <21%. The hemoglobin levels, observed in patients of the control and the oral iron groups at the end of the follow-up periods, were not significantly different from those detected at zero time. In contradistinction, patients treated with intravenous iron showed after 26 months of follow-up a significant increase of blood hemoglobin values, reaching a mean value of 126 g/l. So far, this evidence supports both the concept that iron absorption is compromised in chronic uremics and that the parenteral way is the more effective route for iron replacement in this specific group of patients.

Adult↗
PubMed1998

Biocompatibility of a glucose-free, acidic lactated solution for peritoneal dialysis evaluated by population analysis of mesothelium.

Glucose-enriched, racemic lactate buffered solutions for peritoneal dialysis induce a significant reduction of cell viability as well as a hypertrophic, senescent phenotype of the exposed monolayer. The present study was designed to verify whether the aforementioned changes resulted form the buffer, from the osmotic agent, or from a combined effect of both. Mice were acutely (2 h) and long-term (15 and 30 days) exposed to daily intraperitoneal injections of a racemic lactate, heat-sterilized, low-pH (5.2), glucose-free solution. Imprints of the monolayer were taken at the end of each time interval. The glucose-free lactated buffer used in the present study did not induce significant changes in density distribution, mean cell size, mean cytoplasmic surface area, prevalence of large cells, multinucleation, proportion of observed cells in mitosis, and cell viability. So far, the previously mentioned hypertrophic phenotype appears to derive from substantial alterations in the cell cycle of mesothelium exposed to high concentrations of glucose and/or advanced glycosylation end products and unrelated to lactate.

Acids↗
PubMed1996

Increased peritoneal permeability to albumin in streptozotocin diabetic rats.

The mechanism behind the increased peritoneal permeability to albumin in diabetics is still unclear. In this study, streptozotocin diabetic rats developed albuminuria and significantly increased D/P of albumin after the fourth week of disease, reaching peak levels at the end of the 24 week period of follow-up. Coincidentally, extravasation of albumin to the interstitial tissue was evaluated with the Evans-blue method. Age-matched control rats showed Evans-blue concentrations of 0.023 +/- 0.013 micrograms/100 mg of dry tissue, whereas in diabetics the numbers were 1.22 +/- 0.719 micrograms (P < 0.001). Perfusion with Ruthenium-Red (RR) done in control at zero time, and in age-matched intact as well as in diabetic rats after 24 weeks of disease showed that the density distribution of capillary subendothelial anionic sites was significantly lower for diabetics (13 +/- 3/microns basement membrane vs. 31 +/- 3 and 34 +/- 4 in control groups; P < 0.001). Similar findings were made on the mesenteric submesothelial basement membrane. Mean density of RR decorated anionic sites was 12 +/- 2/microns basement membrane in diabetics, whereas those observed in both control groups were 31 +/- 2 and 31 +/- 3/microns (P < 0.001). Therefore, this reduced density of microvascular and submesothelial negative charges, equivalent to that induced by diabetes in other capillary beds, appears to be at the origin of the decreased permselectivity of the diabetic peritoneum for anionic serum albumin.

Albumins↗
PubMed1996

Daily short exposure of cultured mesothelial cells to lactated, high-glucose, low-pH peritoneal dialysis fluid induces a low-profile regenerative steady state.

This study was designed to evaluate cytotoxic effects and influence upon cell growth of cultured mesothelial cells exposed to modified 4.25% Dianeal dialysate fluid (M-199 in Dianeal solution, glucose 4.25 g, pH 5.2) (Expr. group), 60 min a day for a total period of follow-up of 13 consecutive days, compared with that observed in a control group (C). Beginning on day 7, the cell counts in group C were significantly higher than those observed at zero time (P < 0.05). Cell counts in the experimental group showed no significant differences between the first day of culture and each one of the 13 consecutive days of follow-up. Thymidine incorporation into DNA observed on the first day in C, was significantly higher (P < 0.01) beginning on the 10th day. Values observed in the experimental group were low during the whole period of follow-up. LDH mean values at each time interval, were significantly higher (P < 0.01 and < 0.001) for cells exposed to the dialysis solution. Repeated exposure of the mesothelium to 40 mMol/l lactate and high glucose concentrations induced severe cell injury and death, decreased cell growth and, consequently, a reduced rate of regeneration which is extended as long as the repeated exposure is maintained.

Animals↗
PubMed1996

Population analysis of mesothelium in situ and in vivo exposed to bicarbonate-buffered peritoneal dialysis fluid.

Population analysis of mesothelium (PAM) done using the in vivo and almost in situ technique of mesothelial cell imprints revealed that lactate-buffered solutions had detrimental effects upon cell viability, that high glucose concentration affected cytokinesis, whereas the association of both components led to a decreased density population of cells showing a larger surface area. In the present study, PAM was done on mesothelium of mice exposed to bicarbonate-buffered peritoneal dialysis fluid (BBF) with glucose concentrations of 1.5 and 4.25%, for periods of time of 2 h, 15 and 30 days, as well as after recovery intervals of 7 and 30 days, BBF did not affect mesothelial cell viability. However, the increased incidence of multinucleated cells observed with both glucose concentrations, more marked with the 4.25% solution, suggests a detrimental effect upon the mechanism of cytokinesis. Furthermore, the higher the glucose concentration, the higher the mean-cell cytoplasmic surface area and the proportion of large cells, both resulting most probably from the regulatory volume increase developed by cells continuously exposed to hyperosmolar fluids. So far, evidence presented in this study suggests once more that BBF is remarkably more compatible with a higher quality of adaptation and survival of the exposed mesothelium than the lactated fluid. The question of whether the alterations induced by the high concentration of glucose result from a specific effect of glucose, by the coincidental hyperosmolarity, or by both still remains unanswered.

Animals↗