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Biomedical subjects

L Martis

Publications and source records attributed to L Martis.

At least 37 records · Page 2Linked to original sources
PubMed1995

Functional properties of mesothelial cells after prolonged exposure to dialysate effluent.

The authors tested in vitro the effect of glucose-based and amino acid-based dialysate effluent on the function of human peritoneal mesothelial cells. After 9 days of exposure to the tested effluents with medium (1:1 v/v) or to a medium supplemented with 10% fetal calf serum (FCS) (control), several functional properties of the cells were studied. The synthesis of DNA measured by incorporation of 3H-methyl-thymidine was higher in mesothelial-cell monolayers exposed to the dialysates than in the controls. Synthesis of hyaluronic acid was similar in all three groups, but after stimulation with Il-1 the cells exposed to the dialysates produced more hyaluronic acid. Synthesis of tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) was higher in the control cells. However, after stimulation with IL-1, the cells exposed to the dialysate showed greater synthesis of PAI-1 than of t-PA. Also, procoagulant activity of the control cells was higher than that of the cells exposed to the dialysates. We have concluded that the functional properties of the mesothelial cells may be altered in vitro during prolonged exposure to the dialysate, something that may also occur in vivo.

Amino Acids↗
PubMed1994

Glycosaminoglycan chondroitin sulphate prevents loss of ultrafiltration during peritoneal dialysis in rats.

We evaluated the effect of 6 days of intraperitoneal saline infusion on peritoneal peroxidation and permeability in rats. Peroxidation of the peritoneum as measured by malondialdehyde concentration in the omentum was increased and there was a concomitant augmented membrane permeability to glucose and resulted in a loss of ultrafiltration. In vitro experiments with mesothelial cells showed that glycosaminoglycan chondroitin sulphate appears to act as a scavenger of free radicals and so protects the mesothelial cells against injury. Thus, in rats, supplementation of the infused saline with chondroitin sulphate reduces peroxidation of the peritoneum and prevents loss of ultrafiltration during peritoneal dialysis. These results suggest that chondroitin sulphate may be effective in preventing the deterioration of peritoneal permeability during chronic peritoneal dialysis. This beneficial effect probably derives from the scavenging of free radicals by chondroitin sulphate.

Animals↗
PubMed1994

Evaluation of short-chain polypeptides as an osmotic agent in continuous ambulatory peritoneal dialysis patients.

OBJECTIVES: To assess whether dialysate containing short-chain polypeptides is well tolerated in continuous ambulatory peritoneal dialysis (CAPD) patients and to determine its effect on fluid and solute transport, plasma amino acid levels, and biochemical parameters. DESIGN: Two-treatment, two-period cross-over design. SETTING: Renal Unit, Academic Medical Center, Amsterdam and Renal Unit, University Hospital, Gent. PATIENTS: Two groups of 10 stable CAPD patients. INTERVENTION: All patients received a trial solution (1.36% glucose and 1% peptides, 381 mOsm/kg) and a control solution (2.27% glucose, 404 mOsm/kg) in randomized order. The patients were examined on four consecutive days in which two dwell periods on days 1 and 3 of either 4 (Group I) or 8 hours (Group II) were performed. RESULTS: The peptide solution was well tolerated in all patients. In addition, no differences were found in the parameters for the effective peritoneal surface area and the intrinsic permeability, implying that no irritating effect of the peptide solution was present. Net ultrafiltration was not different in Group I: -43 +/- 125 versus 86 +/- 125 mL (mean +/- SEM) and marginally lower in Group II: -94 +/- 64 versus 51 +/- 64 mL, despite the lower osmolality of the trial solution compared to the control solution. Glucose absorption was higher than the peptide absorption in all patients: Group I: 66 +/- 10% versus 57 +/- 13% (p = 0.0003); Group II: 80 +/- 5% versus 72 +/- 11% (p = 0.006). No differences in plasma amino acid profiles could be detected. CONCLUSIONS: Short-chain polypeptides are absorbed less than glucose and can be used as an osmotic agent in CAPD patients. However, longer-term studies are needed to evaluate possible additional effects of peptides on the nutritional status of CAPD patients.

Adult↗
PubMed1994

In vitro influence of lactate on function of peritoneal fibroblasts.

The authors studied the effect of sodium lactate (NaLact) on the function of human peritoneal fibroblasts (F) in vitro. NaLact inhibits the proliferation of fibroblasts in a dose-dependent way: at a concentration of 40 mM, it decreases the growth of these cells by 34%. A similar effect was observed with other solutes (glucose, mannitol, sodium chloride) at identical concentrations, suggesting that the factor responsible for slower growth of the cells was hyperosmolality. When applied to fibroblast monolayers, NaLact (40 mM) increased the synthesis of total proteins by 10%. Exposure of the fibroblasts to NaLact did not increase noncollagen protein production, and the observed increase in total protein synthesis was due to the increased synthesis of collagen. We could not reproduce this effect of lactate on fibroblast collagen synthesis with other osmotic solutes. Our results suggest that dialysis fluid hyperosmolality may be one of the factors responsible for the decrease of the cellular components within the peritoneal interstitium; whereas NaLact is specifically responsible for the increased production of collagen by peritoneal fibroblasts, leading to the deposition of masses of collagen in the extracellular space.

Cell Division↗
PubMed1994

Effect of the dialysate effluent from CAPD patients on peritoneal mesothelial cells and fibroblasts.

The authors studied the in vitro effect of overnight "dwelled" dialysate obtained from 5 continuous ambulatory peritoneal dialysis (CAPD) patients on the growth of, and protein synthesis by, peritoneal mesothelial cells and fibroblasts. In each patient, an overnight exchange was performed with Dianeal 2.5% on day 1 and with a solution containing amino acids 1.1% on day 2. Both types of dialysate supported the proliferation of fibroblasts and mesothelial cells, but the amino acid dialysate had a stronger effect on the growth of mesothelial cells than the Dianeal dialysate did. In the presence of either dialysate, synthesis of noncollagen proteins by mesothelial cells and fibroblasts was low. By contrast, the synthesis of collagen was enhanced, and the Dianeal dialysate had a much stronger effect than the amino acid dialysate did. Present results show that, during its intraperitoneal dwell, dialysis fluid within the peritoneal cavity stimulates the generation of bioactive substances which affect the function of peritoneal cells. This reaction is influenced by the composition of the dialysis solution.

Cell Division↗
PubMed1994

In vitro study of the effect of osmotic solutes on the interactions between cells from the peritoneum and peritoneal cavity.

OBJECTIVE: To study how the presence of osmotic solutes in medium affects growth of the peritoneal mesothelial cells and fibroblasts and how osmotic solutes influence the production of factors regulating growth of these cells. DESIGN: The proliferation of mesothelial cells and fibroblasts was evaluated by measuring the incorporation of 3H-thymidine into the cells. Cells were exposed to osmotic solutes; the concentration of the latter in the medium was continuously lowered over the time of the experiment to simulate changes of their concentration in the dialysate. The synthesis of factors influencing the proliferation of the mesothelial cells or fibroblasts, by mesothelial cells or fibroblasts themselves, or by peritoneal leukocytes, was tested by the characteristics of the "conditioned" medium. The conditioned medium was produced by exposing standard medium to mesothelial or fibroblasts monolayer or to peritoneal leukocytes over 24 hours; following filtration it was applied to growing test cells for the study of growth factors. RESULTS: The effect of osmotic solutes on the growth of mesothelial cells is less inhibitory when their concentration is gradually lowered over the time of the study, compared to previous findings with a constant concentration. Peritoneal leukocytes produce growth factors for mesothelial cells and fibroblasts. Glucose and amino acids inhibit production of peritoneal leukocyte-derived growth factors for mesothelial cells, while glycerol increases synthesis of such growth factors for fibroblasts. Mesothelial cells produce factors stimulating the proliferation of mesothelial cells and fibroblasts. In the presence of glycerol or amino acids synthesis of mesothelium-derived growth factors for fibroblasts is augmented. Finally, fibroblasts produce factors that inhibit the proliferation of the mesothelial cells, and this effect is potentiated in the presence of amino acids. CONCLUSIONS: Cytotoxicity of the osmotic solutes measured by the inhibition of growth of the mesothelial cells or their increased damage is significantly reduced during in vitro kinetic study when the concentration of these solutes is gradually lowered. Presence of osmotic solutes in the medium affects synthesis of growth factors derived from mesothelium, fibroblasts, or peritoneal leukocytes, which affect the proliferation of mesothelial cells or fibroblasts.

Amino Acids↗
PubMed1993

Effect of phosphatidylcholine on the function of human mesothelial cells in vitro.

We tested the hypothesis that phosphatidylcholine (PC) molecules present in the dialysis solution may interact with the mesothelial cell membrane and modify its function. In vitro experiments were performed on human mesothelial cells (HMC) in culture. PC decreased proliferation of HMC when used at concentrations of 200 mg/l and higher. PC was also cytotoxic to HMC as measured by the release of lactate dehydrogenase from their cytosol. Cells exposed to PC had a diminished capacity for taking up 86Rb from medium. PC decreased the fibrinolytic properties of HMC and increased their procoagulant activity. Our results suggest that the positive short-term effect of the addition of PC to the dialysis solution (i.e., an increase in ultrafiltration) may be over-shadowed by its deleterious action on HMC membrane.

Cell Division↗
PubMed1993

Toxicity of free radicals to mesothelial cells and peritoneal membrane.

We studied the toxicity of free radicals to human mesothelial cells in vitro and to the peritoneal membrane of rats during peritoneal dialysis. Free radicals cause damage to mesothelial cells as measured by release of cytosolic markers such as 86Rb and lactate dehydrogenase. Vitamin E neutralized the toxic effect of free radicals in vitro. Human mesothelial cells exposed over 6 h to a mixture of essential and nonessential amino acids in medium are more vulnerable to the cytotoxic effect of free radicals than control cells exposed to medium alone. Cells exposed previously to glucose or glycerol are less vulnerable than controls. In rats free radicals generated intraperitoneally by a xanthine-xanthine oxidase system induce changes in peritoneal permeability similar to those observed during peritonitis: loss of ultrafiltration, increased glucose absorption from the dialysate and augmented transperitoneal loss of albumin. In addition lipids in the peritoneum became peroxidated. The addition of vitamin E to the peritoneal fluid with xanthine-xanthine oxidase prevents peroxidation of lipids and the subsequent loss of ultrafiltration. Our results show that free radicals may exert a potentially toxic effect on the peritoneal membrane during peritonitis. In such circumstances the addition of free radical scavenger to the dialysis fluid may preserve intact structure and function of peritoneum.

Animals↗
PubMed1993

Enhancement of viability of human peritoneal mesothelial cells with glutathione precursor: L-2-oxothiazolidine-4-carboxylate.

This study tested the effect of L-2-oxothiazolidine-4-carboxylate (procysteine), a precursor of the intracellular cysteine, on the function of human mesothelial cells (HMCs) in in vitro culture. Procysteine stimulated the proliferation of HMCs and decreased the spontaneous death rate of these cells. HMCs pretreated with procysteine were resistant to injury by free radicals. Procysteine also reversed the cytotoxic effects of a mixture of essential and nonessential amino acids on HMCs, such as increased susceptibility to injury by free radicals and inhibition of proliferation.

Amino Acids↗
PubMed1993

In vitro study of the mechanism of potassium transport into human mesothelial cells. I: Effect of hyperosmolality.

OBJECTIVE: To study the mechanism(s) of potassium transport into human mesothelial cells (HMC) exposed to osmotic solutes. DESIGN: Using potassium analog 86Rb, we evaluated its intracellular transport through three pathways: 1. blocked by ouabain; 2. blocked by furosemide but not by ouabain; 3. blocked by neither furosemide nor ouabain. Experiments were performed in a normotonic medium (control) or in a medium supplemented with osmotic solutes (glucose, glycerol, mannitol). Both the acute and chronic effects of osmotic solutes on potassium transport were studied. RESULTS: The acute exposure of mesothelial cells to osmotic solutes modifies the intracellular transport of potassium through all studied channels, and the effect is specific for every solute. In mesothelial cells exposed over 7 days to glucose (90 mM), the intracellular transport via ouabain- and furosemide-blocked channels is decreased, whereas it is increased through the third pathway. Total intracellular accumulation of 86Rb (potassium) ions in mesothelial cells cultured in a medium supplemented with various concentrations of glucose is decreased, and this effect is proportional to the concentration of glucose in the medium. CONCLUSIONS: The intracellular transport of potassium in mesothelial cells is regulated through at least three independent mechanisms. Acute or chronic exposure of mesothelial cells to a hypertonic medium affects the intracellular accumulation of potassium, and this effect is specific for the various osmotic solutes.

Biological Transport↗
PubMed1993

Experimental peritoneal dialysis solutions.

A survey of the literature suggests continued interest in modifying the composition of peritoneal dialysis solutions. Osmotic agents such as glucose polymers and short-chain polypeptides may find a role in peritoneal dialysis fluids as partial substitutes for dextrose. New solutions containing amino acids should serve as more than sinks for uremic toxins by providing nutritional support and by ameliorating uremic lipid abnormalities. Increasing emphasis is being paid to biocompatibility during the development of new peritoneal dialysis fluids.

Amino Acids↗
PubMed1992

Chondroitin sulphate and peritoneal permeability.

We studied the effect of chronic intraperitoneal (ip) infusion of saline supplemented with the glycosaminoglycan-chondroitin sulphate 0.1% on the permeability and peroxidation of the peritoneal membrane in rats and compared this with the effect of saline infusion alone. Animals treated with chondroitin sulphate had a higher net ultrafiltration (uf), a slower glucose absorption from the dialysate and less trans-peritoneal loss of proteins. Chronic ip infusion of chondroitin sulphate reduced peroxidation of the peritoneum. These observations suggest that chondroitin may effect the peritoneal interstitium-an important barrier of fluid and solutes transport.

Animals↗