Innovative approaches to the preservation of the peritoneal membrane: from bench to bedside

The Association Between Glucose Exposure and the Risk of Peritonitis in Peritoneal Dialysis Patients

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BACKGROUND AND OBJECTIVE

Little or no clinical evidence is available on the association between glucose exposure and peritoneal host defense in peritoneal dialysis (PD) patients. The objective of the present study was to quantify the exposure to glucose during the first year on PD and investigate the association with subsequent peritonitis. ♦

METHODS

We analyzed prospectively collected demographic and peritonitis data from incident adult PD patients between 1990 and 2010. For the present study, we conducted a review of both in- and outpatient medical records of all patients to obtain their day-to-day dialysis schemes during the first year on PD. From these data, the average exposure to glucose was quantified. The exposure was stratified into low- and high-glucose groups based on the median, analyzed per standard deviation and in quartiles. Cox proportional hazard models were used to calculate crude and adjusted hazard ratios (HRs) and 95% confidence intervals for the association between glucose exposure and peritonitis. Adjustments were made for age, sex, primary kidney disease, diabetes mellitus, Davies comorbidity score and the treatment period. ♦

RESULTS

In total, 230 patients were included in the study of whom 151 (66%) experienced a first peritonitis episode. The median follow-up time was 2.6 years (interquartile range [IQR]: 1.9 - 3.8) in the low-glucose group and 3.1 (IQR: 2.1 - 4.2) in the high-glucose group. After adjustment for confounding factors, no association between high glucose exposure and the risk of peritonitis was found (HR: 0.81; 0.55 - 1.17). No association was present when glucose exposure was analyzed per standard deviation (SD) (HR: 0.98; 0.79 - 1.21) or patient quartiles were applied. No association was identified between glucose exposure and severe peritonitis, Staphylococcus aureus peritonitis, or a peritonitis episode that lasted more than 14 days. ♦

CONCLUSIONS

Exposure to glucose is not associated with an increased risk of peritonitis. The equilibrium between glycemic harm to peritoneal host defense and detrimental effects of glucose on invading microorganisms may determine the susceptibility to peritoneal infection.

Peritoneal dialysis: from bench to bedside

Peritoneal dialysis was first employed in patients with acute renal failure in the 1940s and since the 1960s for those with end-stage renal disease. Its popularity increased enormously after the introduction of continuous ambulatory peritoneal dialysis in the end of 1970s. This stimulated both clinical and basic research. In an ideal situation, this should lead to cross-fertilization between the two. The present review describes two examples of interactions: one where it worked out very well and another where basic science missed the link with clinical findings. Those on fluid transport are examples of how old physiological findings on absorption of saline and glucose solutions were adopted in peritoneal dialysis by the use of glucose as an osmotic agent. The mechanism behind this in patients was first solved mathematically by the assumption of ultrasmall intracellular pores allowing water transport only. At the same time, basic science discovered the water channel aquaporin-1 (AQP-1), and a few years later, studies in transgenic mice confirmed that AQP-1 was the ultrasmall pore. In clinical medicine, this led to its assessment in patients and the notion of its impairment. Drugs for treatment have been developed. Research on biocompatibility is not a success story. Basic science has focussed on dialysis solutions with a low pH and lactate, and effects of glucose degradation products, although the first is irrelevant in patients and effects of continuous exposure to high glucose concentrations were largely neglected. Industry believed the bench more than the bedside, resulting in 'biocompatible' dialysis solutions. These solutions have some beneficial effects, but are evidently not the final answer.

HSP induction in mesothelial cells by peritoneal dialysis fluid depends on biocompatibility test system

BACKGROUND

We have previously shown that exposure of mesothelial cells (MC) to peritoneal dialysis fluids (PDF) not only caused toxic injury, but also induced cytoprotective heat shock proteins (HSP). This study was performed in order to compare HSP expression in MC upon PDF exposure in three currently used biocompatibility test systems.

METHODS

Omentum-derived human peritoneal MC underwent 3 modalities of exposure to heat- or filter-sterilized PDF: (A) pure PDF for 60 minutes followed by a recovery-period in pure culture medium for 24 hours; (B) 1:1 mixture of PDF and culture medium for 24 hours or (C) pure PDF for 60 minutes followed by a recovery-period in a 1:1 mixture of PDF and culture medium for 24 hours. Biocompatibility was assessed by LDH-release into the supernatant and HSP-72 expression in MC lysates.

RESULTS

Short-term exposure of MC to pure PDF (Modality A) resulted in concordant LDH release and upregulation of HSP-72, regardless of heat or filter sterilization. In contrast, both test systems that exposed MC to heat-sterilized PDF during the recovery period (Modalities B and C) resulted in severe cellular lethality but low HSP-72 expression.

CONCLUSIONS

This study clearly shows that HSP expression in MC upon PDF exposure depends on the biocompatibility test system. The presence of heat-sterilized PDF during recovery resulted in significant downregulation of Hsp-72 despite severe cell injury. Therefore, Hsp-72 expression reflects adequate cellular stress responses rather than PDF cytotoxicity.

Peritoneal dialysis fluids can alter HSP expression in human peritoneal mesothelial cells

BACKGROUND

Acute exposure of mesothelial cells to peritoneal dialysis fluid (PDF) has been shown not only to result in injury but also to induce cytoprotective heat shock proteins (HSP). The aim of the present study was to evaluate the expression of HSP in a more chronic in vitro PDF exposure system, searching for a role of glucose degradation products (GDP).

METHODS

Human peritoneal mesothelial cells (HPMC) were chronically incubated in filter- or heat-sterilized PDF (mixed 1:1 with cell culture medium), or in control cell culture medium. After incubation periods of 1, 3 and 10 days, cell extract was assessed for Ezrin, Hsp27 and Hsp72, and supernatant for IL-6 and IL-8. After 24-h exposure to the GDP 3.4-di-deoxyglucosone-3-ene (3.4-DGE), HPMC were assessed for expression of Hsp27 and Hsp72, and for release of LDH, IL-6 and IL-8.

RESULTS

In vitro PDF exposure for more than 1 day resulted in reduced cell mass, lower expression of the epithelial marker Ezrin and depressed cellular levels of both HSP, associated with increased IL-6 and IL-8 release. These effects occurred earlier and stronger with heat-sterilized than with filter-sterilized PDF. Exposure of HPMC to 3.4-DGE resulted in suppression of HSP, and increased release of LDH, IL-6 and IL-8.

CONCLUSION

Our data show that GDP (dys)regulate the mesothelial cell stress response. This was associated with reduced cell mass, loss of the epithelial phenotype and sterile cellular inflammation following extended exposure to heat-sterilized PDF. Toxic effects of PDF might thus be extended to reduced mesothelial cell stress responses.