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.

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.

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.

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.

Interactions of cells from peritoneal dialysate with mesothelial cells and fibroblasts in culture.

Peritoneal mesothelial cells and fibroblasts were co-cultured in vitro with peritoneal white blood cells (PWBC) obtained from CAPD patients, after an overnight exchange with 0.5% Dianeal or 2.5% Dianeal. Unstimulated PWBC inhibited proliferation of mesothelial cells and fibroblasts. Upon stimulation with lipoposaccharides (LPS), PWBC from the 0.5% dextrose exchange, enhanced the growth of mesothelial cells and fibroblasts, whereas when stimulated with LPS, PBWC from the 2.5% dextrose exchange increased only proliferation of fibroblasts.

Amino acid solutions for CAPD: rationale and clinical experience.

Protein-calorie malnutrition is present in a sizable proportion of dialysis patients. In CAPD patients, constant glucose absorption from dialysate may displace other calorie sources, such as protein, and may suppress the appetite, thus contributing to malnutrition. Use of amino acids in place of glucose as the osmotic agent has been studied extensively. Ultrafiltration and small-molecule clearance similar to that with glucose can be achieved with amino acid solutions, but nitrogenous waste produced by amino acids limits the extent to which they can replace hypertonic glucose. Side effects of CAPD with amino acids appear to be minor and easily manageable. Most studies have found at least some nutritional benefit of amino acid solutions in addition to that of lowering the glucose load. Short-term studies of amino acid solutions for dialysis indicate that they may improve protein nutrition in malnourished CAPD patients.

Comparison of patient and technique survival in continuous ambulatory peritoneal dialysis (CAPD) and hemodialysis: a multicenter study.

Patient and technique survival were compared in adult patients new to continuous ambulatory peritoneal dialysis (CAPD) or (primarily) center hemodialysis (HD) in the time period 1981 to 1983, and followed-up in March 1985. Risk factors were identified at entrance into the study, and results were analyzed using Cox's proportional hazards model. For nondiabetic patients, the difference in survival which favored CAPD (relative risk = 0.62) was not significant at the 5% level (p = 0.08). Age was a significant risk factor in both groups. The average number of hospital visits was the same; however, CAPD showed a small but significant increase in average annual hospital days per year (10.14 vs. 9.18). For diabetic patients, there was no significant difference in survival between CAPD and HD. The CAPD group showed a significant increase in hospital visits (relative risk 1.81 vs. 1.40) and average hospital days per year (19.43 vs. 13.41). Both CAPD groups showed significantly higher treatment changeover rates.

Calcium carbonate as a phosphate binder: is there a need to adjust peritoneal dialysate calcium concentrations for patients using CaCO3?

The widespread use of calcium carbonate as a phosphate binder is limited by its tendency to develop hypercalcemia in some patients using effective dosages needed to control hyperphosphatemia. Most common continuous ambulatory peritoneal dialysis (CAPD) regimens using dialysis solutions containing 3.5 mEq/L of calcium result in net absorption of calcium from the dialysis solution and, hence limit the amount of oral calcium that can be administered. Peritoneal dialysis solutions with reduced calcium levels are needed for effective use of CaCO3 to control hyperphosphatemia in some dialysis patients.

Impact of regulations on artificial organs research.

From a research perspective, some of the primary problems created by the FDA regulations include: the amount of time necessary to comply with the regulations and to obtain FDA and IRB review of the studies. The cost of such delays may be great in terms of statistical death. Lack of understanding of the regulations on the part of investigators. Escalated costs and extra restrictions on the use of animals. Benefits of the regulations appear to be: better preclinical testing performed prior to initiating clinical trials, and improved testing protocols, both of which may result in lower risks to patients.

In vivo strain measurements of a prosthetic aortic valve.

Up to the present, stress forces on prosthetic heart valves have been studied primarily in an in vitro state and have been derived with a fair amount of estimation. Because of the practical and clinical implications, such as forces that may cause fabric wear or material deterioration, we felt that in vivo determination would be worthy of investigation. A microminiature strain gauge was secured to each leg of a non-cloth-covered prosthetic aortic valve and connected to a dual-beam oscilloscope. Strain measurements were first determined in a pulse duplicator with a blood analogue solution and physiological pressures and flow. The valve was also implanted into a dog in the subcoronary position and strain again measured. In vivo strain was found to be approximately 57 per cent of strain on a prosthetic aortic valve, in vitro, under the conditions of this experiment. This represents the first time that strain and force on a prosthetic aortic valve have been determined directly in the intact animal.