3,4-DGE is present in conventional PD fluids at a concentration between 9 and 22 micromol/L, and is the most biologically active of all GDPs identified to date. Thus, it is the main candidate to be held responsible for the clinical bioincompatibility caused by conventionally manufactured PD fluids.

Objective Glucose degradation products (GDPs) in peritoneal dialysis (PD) fluids are cytotoxic and affect the survival of the peritoneal membrane. One of the most reactive GDPs in PD fluids is 3,4-dideoxyglucosone-3-ene (3,4-DGE). 3,4-DGE has been reported as an intermediate between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl furaldehyde (5-HMF) during degradation of glucose. In PD fluids, 3,4-DGE exists in a temperature-dependent equilibrium with a pool of unidentified substances. The aim of this study was to explore this equilibrium and its temperature dependence during the first months of storage after the sterilization procedure. Methods GDPs and inhibition of cell growth (ICG) were measured directly after sterilization of the PD fluid and during storage at different temperatures for 60 days. The following GDPs were analyzed: 3-DG, 3,4-DGE, 5-HMF, formaldehyde, acetaldehyde, glyoxal, and methylglyoxal. Results Immediately after sterilization, the concentration of 3,4-DGE was 125 μmol/L. During the first weeks of storage, it decreased by about 80%. At the same time, the 3-DG concentration increased. None of the other GDPs were significantly affected. Cytotoxicity correlated well with the concentration of 3,4-DGE. When pure 3,4-DGE was substituted for the lost amount of 3,4-DGE after 30 days of storage, the initial ICG was almost completely regained. Conclusions Heat sterilization of PD fluids promotes the formation of large quantities of 3,4-DGE, rendering the fluid highly cytotoxic. During storage, the main part of 3,4-DGE is reversibly converted in a temperature-dependent manner to a less cytotoxic pool, consisting mainly of 3-DG. Cytotoxicity seems to be dependent exclusively on 3,4-DGE. In order to avoid higher levels of 3,4-DGE concentrations, PD fluids should not be used too soon after sterilization and should not be stored at temperatures above room temperature.

Objective The formation of glucose degradation products (GDPs) during sterilization of peritoneal dialysis fluids (PDFs) is one of the most important aspects of biocompatibility of glucose-containing PDFs. Producers of PDFs are thus trying to minimize the level of GDPs in their products. 3,4-Dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most bioreactive GDP in PDFs. It exists in a temperature-dependent equilibrium with a pool of 3-deoxyglucosone (3-DG) and is a precursor in the irreversible formation of 5-hydroxymethyl furaldehyde (5-HMF). The aim of the present study was to investigate how to minimize GDPs in PDFs and how different manufacturers have succeeded in doing so. Design Glucose solutions at different pHs and concentrations were heat sterilized and 3-DG, 3,4-DGE, 5-HMF, formaldehyde, and acetaldehyde were analyzed. Conventional as well as biocompatible fluids from different manufacturers were analyzed in parallel for GDP concentrations. Results The concentrations of 3-DG and 3,4-DGE produced during heat sterilization decreased when pH was reduced to about 2. Concentration of 5-HMF decreased when pH was reduced to 2.6. After further decrease to a pH of 2.0, concentration of 5-HMF increased slightly, and below a pH of 2.0 it increased considerably, together with formaldehyde; 3-DG continued to drop and 3,4-DGE remained constant. Inhibition of cell growth was paralleled by 3,4-DGE concentration at pH 2.0 – 6.0. A high glucose concentration lowered concentrations of 3,4-DGE and 3-DG at pH 5.5 and of 5-HMF at pH 1. At pH 2.2 and 3.2, glucose concentration had a minor effect on the formation of GDPs. All conventional PDFs contained high levels of 3,4-DGE and 3-DG. Concentrations were considerably lower in the biocompatible fluids. However, the concentration of 5-HMF was slightly higher in all the biocompatible fluids. Conclusion The best way to avoid reactive GDPs is to have a pH between 2.0 and 2.6 during sterilization. If pHs outside this range are used, it becomes more important to have high glucose concentration during the sterilization process. There are large variations in GDPs, both within and between biocompatible and conventionally manufactured PDFs.

Objective Bioincompatible glucose degradation products (GDPs) develop during heat sterilization of peritoneal dialysis (PD) fluids. However, degradation may also take place during storage. Consequently, storage may add to the bioincompatibility caused by heat sterilization. The aim of the present study was to investigate how different factors such as the sterilization procedure, pH, glucose concentration, and temperature influence GDP production during storage. Design Degradation in glucose solutions was followed by pH and UV absorbance at 228 nm and 284 nm over 2 years of storage. Different sterilization times, storage temperatures, pH, and glucose concentrations were included in the study. Peritoneal dialysis fluids were also used in the experiment. Bioincompatibility was estimated through inhibition of cell growth in L-929 fibroblasts, and GDPs through UV absorption and liquid chromatography. Results The most important factor determining the rate of GDP production during storage was temperature. The GDPs created by heat sterilization promoted further degradation of glucose during subsequent storage. A pH of around 3.2 protected glucose from degradation during both heat sterilization and storage. At a storage temperature of 20°C and a pH of 3.2, degradation was almost negligible. Heat sterilization produced considerable amounts of GDPs absorbing at 228 nm. During initial storage, these 228 nm-absorbing GDPs almost disappeared. After reaching a nadir, absorbance at 228 nm again started to increase. Contrary to this, absorbance at 284 nm [caused mainly by 5-hydroxymethyl-2-furaldehyde (5-HMF)] increased during the whole storage period. After 2 years at 40°C, the concentrations of GDPs produced during storage were of the same magnitude as those caused by heat sterilization. Inhibition of cell growth of L-929 fibroblasts correlated well with the part of the absorbance at 228 nm not caused by 5-HMF in glucose solutions that were heat sterilized under a wide range of conditions. This part of 228 nm absorbance (denoted 228corr) was caused almost entirely by 3,4-dideoxyglucosone-3-ene (3,4-DGE). Conclusions Temperature is the single most important factor for glucose degradation during storage. The concentrations of bioincompatible GDPs produced may, under improper conditions, be as high as those produced during sterilization. High concentrations of glucose and low pH protect glucose from being degraded during both sterilization and storage. A good estimate of 3,4-DGE concentration in the fluids can be obtained correcting the UV absorbance at 228 nm for the influence from 5-HMF (and, when appropriate, for lactate). The 228corr may thus be used as a simple quality control for the fluids.

In the fermentation of lignocellulose hydrolysates to ethanol, two major problems are encountered: the fermentation of the pentose sugar xylose, and the presence of microbial inhibitors. Xylose can be directly fermented with yeasts, such as Pachysolen tannophilus, Candida shehatae, and Pichia stipis, or by isomerization of xylose to xylulose with the enzyme glucose (xylose) isomerase (XI; EC 5.3.1.5), and subsequent fermentation with bakers' yeast, Saccharomyces cerevisiae. The direct fermentation requires low, carefully controlled oxygenation, as well as the removal of inhibitors. Also, the xylose-fermenting yeasts have a limited ethanol tolerance. The combined isomerization and fermentation with XI and S. cerevisiae gives yields and productivities comparable to those obtained in hexose fermentations without oxygenation and removal of inhibitors. However, the enzyme is not very stable in a lignocellulose hydrolysate, and S. cerevisiae has a poorly developed pentose phosphate shunt. Different strategies involving strain adaptation, and protein and genetic engineering adopted to overcome these different obstacles, are discussed.