Degradation in peritoneal dialysis fluids may be avoided by using low pH and high glucose concentration

OBJECTIVE

When glucose is present in a medical fluid, the heat applied during sterilization leads to degradation. The glucose degradation products (GDPs) give rise to bioincompatible reactions in peritoneal dialysis patients. The extent of the degradation depends on a number of factors, such as heating time, temperature, pH, glucose concentration, and catalyzing substances. In the present work, we investigated the influence of pH and concentration in order to determine how to decrease the amounts of GDPs produced.

DESIGN

Glucose solutions (1%-60% glucose; pH 1-8) were heat sterilized at 121 degrees C. Ultraviolet (UV) absorption, aldehydes, pH, and inhibition of cell growth (ICG) were used as measures of degradation.

RESULTS

Glucose degradation was minimum at an initial pH (prior to sterilization) of around 3.5 and at a high concentration of glucose. There was considerable development of acid degradation products during the sterilization process when the initial pH was high. Two different patterns of development of UV-absorbing degradation products were seen: one below pH 3.5, dominated by the formation of 5-hydroxy-methyl-2-furaldehyde (5-HMF); and one above, dominated by degradation products absorbing at 228 nm. 3-Deoxyglucosone (3-DG) concentration and the portion of 228 nm UV absorbance not caused by 5-HMF were found to relate to the in vitro bioincompatibility measured as ICG; there was no relation between 5-HMF or absorbance at 284 nm and bioincompatibility.

CONCLUSION

In order to minimize the development of bioincompatible GDPs in peritoneal dialysis fluids during heat sterilization, pH should be kept around 3.2 and the concentration of glucose should be high. 5-HMF and 284 nm UV absorbance are not reliable as quality measures. 3-DG and the portion of UV absorbance at 228 nm caused by degradation products other than 5-HMF seem to be reliable indicators of bioincompatibility.

Toxicity of 20 Chemicals from the MEIC Programme Determined by Growth Inhibition of L-929 Fibroblast-like Cells

The Multicentre Evaluation of In vitro Cytotoxicity (MEIC) programme is an international project aimed at evaluating the relevance of in vitro tests in predicting human toxicity. We have screened 20 chemicals (MEIC codes 31-50) from the programme, by using a cytotoxicity test based on growth inhibition of the mouse fibroblast-like L-929 cell line. Inhibition of cell growth was determined by the neutral red uptake method, which is well established and is used for screening the cytotoxicity of chemicals and plastics for pharmaceuticals and medical devices. The concentrations causing 50% inhibition of cell growth after a 72-hour exposure period varied from 3.1μM for hexachlorophene, to 1.4mM for caffeine. This is within the same range as results recently obtained with five other cell models. However, with some chemicals (chloroform, carbon tetrachloride and dichloromethane), no reliable results were obtained. These substances could not be dissolved in a reproducible way in any of the solvents used and, furthermore, they were highly volatile, which led to difficulties in maintaining the concentrations.

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.

Toxicity of heat sterilized peritoneal dialysis fluids is derived from degradation of glucose

Heat sterilization makes peritoneal dialysis (PD) solutions cytotoxic. Two compounds in the solutions, lactate and glucose, can be degraded by heat. This study's goal was to discover which of the compounds was responsible for the cytotoxicity. The influence of sterilization temperature on degradation of the compounds was also subjected to investigation. Solutions of glucose and lactate and a mixture of lactate and glucose were prepared. These were sterilized in glass ampules in an oil bath at different temperatures for varying times. Toxicity was determined as inhibition of cell growth with a fibroblast cell line (L929), and ultraviolet (UV) absorbance was measured at 284 nm. Lactate solutions did not show cytotoxicity after heat sterilization. Glucose solutions that were heat sterilized showed an increase in UV absorbance at 284 nm and were cytotoxic. The mixture of lactate and glucose exhibited the same cytotoxicity as glucose alone. Lower sterilization temperatures lead to increased cytotoxicity and an increase in UV absorbance at 284 nm. Results indicate that the toxic products formed during heat sterilization of PD fluids are derived from glucose.