Glucose degradation products increase apoptosis of human mesothelial cells

The heat sterilization of glucose solutions for peritoneal dialysis (PDS) induces the formation of glucose degradation products (GDPs), a phenomenon amplified by lactate and neutral pH. In the new three-compartment bag (3CB) PDS, a glucose solution at pH 3 is kept apart from the buffer until use, and the final solution delivers glucose concentrations that are similar to traditional PDS (TPD), with pH 6 and a lower content of GDPs. As GDPs have oxidant activity that may favour apoptosis, we investigated mesothelial cell apoptosis modulation by 12 h cultures in media supplemented with: (i) two relevant GDPs, methylglyoxal (MGly) and formaldehyde (For) in time and dose-dependence assays, (ii) GDPs at concentrations detected in TPD and 3CB, and (iii) commercial TPD and 3CB PDS, both with 1.36% glucose.

Apoptosis was evaluated by terminal 3' uridine labelling. Key proteins involved in the apoptotic pathway were investigated by reverse transcription polymerase chain reaction (RT-PCR) mRNA expression and immunoperoxidase staining (caspase 9, tumour suppressor protein p53, inducible cyclooxygenase COX-2).

The apoptotic effects of MGly and For were dose and time dependent. GPDs at concentrations detected in TPD induced greater transcription and translation of apoptotic pathway proteins (caspase 9, p53 and COX-2) than GPDs in 3CB. This resulted in a higher apoptotic rate, which was not influenced by addition of sterile glucose. A similar enhancement of apoptosis was detected when mesothelial cells were incubated with TPD, whereas incubation in 3CB PDS resulted in less enhanced apoptosis. The 12 h incubation effect of PDS on cultured mesothelial cells was not related to advanced glycosylated end-product formation.

As the rate of mesothelial cell apoptosis is lower in 3CB than in TPD solutions, the 3CB appears to provide improved biocompatibility.