Are aldehydes in heat-sterilized peritoneal dialysis fluids toxic in vitro?

OBJECTIVE

Chemical analysis of several brands of peritoneal dialysis fluids (PD fluids) has revealed the presence of 2-furaldehyde, 5-HMF (5-hydroxymethylfuraldehyde), acetaldehyde, formaldehyde, glyoxal, and methylglyoxal. The aim of this study was to investigate if the in vitro side effects caused by glucose degradation products, mainly formed during heat sterilization, are due to any of these recently identified aldehydes.

DESIGN

Cell growth media or sterile filtered PD fluids were spiked with different concentrations of thealdehydes.

MEASUREMENTS

In vitro side effects were determined as the inhibition of cell growth of cultured mouse fibroblasts or stimulated superoxide radical release from human peritoneal cells.

RESULTS

Our results demonstrate that the occurrences of 2-furaldehyde, 5-HMF, acetaldehyde, formaldehyde, glyoxal, or methylglyoxal in heat-sterilized PD fluids are probably not the direct cause of in vitro side effects. In order to induce the same magnitude of cell growth inhibition as the heat-sterilized PD fluids, the concentrations of 2-furaldehyde, glyoxal, and 5-HMF had to be 50 to 350 times higher than those quantified in the PD fluids. The concentrations of acetaldehyde, formaldehyde, and methylglyoxal observed in the heat-sterilized PD fluids were closer to the cytotoxic concentrations although still 3 to 7 times lower.

CONCLUSION

Since none of these aldehydes caused in vitro toxicity at the tested concentrations, the toxicity found in PD fluids is likely to be due to another glucose degradation product, not yet identified. However, it is possible that these aldehydes may still have adverse effects for patients on peritoneal dialysis.

Heat sterilized PD-fluids impair growth and inflammatory responses of cultured cell lines and human leukocytes

We have recently demonstrated that commercial PD-fluids inhibit the growth of a cultured mouse fibroblast cell line. Toxic substances produced during heat sterilization were believed to be the probable cause of the growth inhibition. The aim of the present study was to investigate if heat sterilized PD-fluids affect other cell types and other cellular functions than the growth of fibroblasts. The effect of three commercially and one laboratory made PD-fluid on cell growth of a mouse macrophage cell line (RAW) and a human neuroblastoma cell line (SH-SY5Y) was examined. The influence on stimulated release of tumour necrosis factor alpha (TNF alpha) from the macrophage cell line and stimulated superoxide generation from freshly prepared human leukocytes were also investigated. Compared to the filter sterilized PD-fluid, we found that heat treated PD-fluids significantly inhibited the growth of the two cell lines and impaired the stimulated release of TNF alpha and superoxide radicals. These results demonstrate that heat sterilization of PD-fluids produces substances that are cytotoxic regardless of the cell species, the cell type or the cell function tested.

In vitro toxicity of biomaterials determined with cell density, total protein, cell cycle distribution and adenine nucleotides

Inhibition of cell growth is the most commonly used endpoint for in vitro toxicity of biomaterials. The use of several different endpoints might however generate more information concerning the nature of the toxicity. Thus, we examined the toxicity of two biomaterials, Polyvinylchloride (PVC) and Polyoximethene (POM), with different selected endpoints. The influence of cell growth on these endpoints was also investigated. Water extracts from the polymeric materials were tested on the continuous cell line L-929. Cell density, total protein, total protein per cell, fraction of cells in G0/G1- or S-phase, the concentration of ATP, ADP and AMP were used as endpoints. The PVC material did not significantly influence any of these endpoints until after 72 hours of exposure and the main part of the toxicity at 72 hours was related to higher proliferation rate in control cultures. After the cells had been incubated for 8 hour with POM the main toxic effect was on the energy parameters. In conclusion the PVC material was less toxic than the POM material. Our results also implies that the choice of endpoint will influence the evaluation of cytotoxicity.

Toxicity of peritoneal dialysis fluids on cultured fibroblasts, L-929

Peritoneal dialysis (PD) fluids are known to suppress the reactions of inflammatory cells in vitro. PD-fluids have also been shown to have cytotoxic influence on mesothelial cells. The combinations of these factors may have a detrimental effect on the peritoneum or may impair cellular defence against bacterial peritonitis. Some authors have discussed the relevance of heat sterilization to both so-called peritoneal side-effects and to chemical decomposition of fluids. Four commercial PD-fluids and one laboratory-made PD-fluid were tested for cytotoxicity on a cultured fibroblast cell line, L-929. Cytotoxicity was determined as an inhibition of cell growth by quantification of total protein. The laboratory-made PD-fluid was sterilized either by filtration or by filtration and heat. The commercial and the heat-sterilized laboratory made PD-fluids caused significant inhibition of cell growth (53 to 76%) in contrast to saline and the filter-sterilized laboratory-made PD-fluid. Since the pH values of all the testsolutions were neutral, low pH was not the cause of toxicity. Our results regarding the L-929 cells indicate that the cytotoxicity of PD-fluids is of a general nature. Furthermore, the results indicate that the heat sterilization process might be partially responsible for causing toxicity in PD-fluids.

The effect of sodium chloride on the extraction of DNA fragments during Feulgen acid hydrolysis

Feulgen acid hydrolysis was performed on ascites tumour cells labelled with radioactive DNA-precursors. The development of fragments of apurinic acid and the extraction of purines were studied by monitoring the variations in the extraction rate during the hydrolysis when sodium chloride was either present or absent from the hydrolysis solution. The changes in the rate of extraction of purines and the alterations in the initial retardation of the apurinic acid extracting process followed approximately the same pattern. The extractability of apurinic acid fragments during hydrolysis in 0.3 M HCl was found to be a maximum when the sodium chloride concentration was about 1 M. Sudden exchange experiments, in which acid was substituted for sodium chloride after various times of hydrolysis, revealed a successive shortening of the extractable fragments during the low acid concentration hydrolysis. The results strengthen the view that, during hydrolysis, apurinic acid is lost from the cells through a reaction whose form is determined, first, by an initial retardation of the depolymerization, second, by the maximum length at which fragments developed through the depolymerization become soluble and are lost by diffusion, and last, at low acid concentrations, by a mechanism whose influence is equivalent to the presence of bonds between the fragments and an unextractable stable structure.

Temperature and acid concentration in the search for optimum Feulgen hydrolysis conditions

Exposure and removal of aldehyde groups during Feulgen acid hydrolysis were studied at a wide range of temperature and acid concentrations. Temperatures between 9 and 75degreesC were found to influence only the rate of the hydrolysis reaction over the entire range from high (6 M) to low (0.05 M) HCl concentrations. The temperature dependence was high, and around +5degreesC was sufficient to double the reaction rate. The influence of acid concentrations between 0.02 and 6 M was studied, and the extraction rates that determine the peak values of the Feulgen hydrolysis curve were found to depend in the same way on the (H+) concentration. A diagram is given that makes it possible to determine the time to reach the point during hydrolysis where the maximum amount of aldehyde groups are developed for a wide range of temperatures and acid concentrations. Temperatures slightly above room temperature in combination with high acid concentration is recommended for Feulgen hydrolysis.