MO900ENHANCED EXPRESSION OF THIOREDOXIN-INTERACTING PROTEIN (TXNIP) RESULTS IN REDUCED TRX ACTIVITY AND INCREASED OXIDATIVE DNA-DAMAGE IN PERITONEAL DIALYSIS PATIENTS*

Abstract

Abstract Background and Aims Peritoneal dialysis (PD) is an effective method of renal replacement therapy (RRT). The long-term use of PD as a RRT is limited due to adverse effects of high glucose-based PD solutions to the structure and function of the peritoneal membrane. PD patients show excessive oxidative stress compared to healthy controls. However, there are only scare information on pathophysiological mechanisms leading to oxidative DNA-damage in PD patients. Therefore, the aim of this study was to elucidate the mechanism leading to excessive oxidative stress in human samples of the peritoneal membrane. Method Human peritoneal biopsies of healthy controls, PD patients and patients with EPS were collected. Protein expression of TXNIP was analysed by ELISA using plasma samples and by immunohistochemistry of peritoneal biopsies using a Histo-Score. Protein expression of TRX was examined by immunohistochemistry. To measure TRX activity a kit based on the reduction of insulin by reduced TRX was used. The resulting oxidative DNA-damage was investigated by immunohistochemistry using a Histo-Score or by ELISA using plasma samples of patients. Results Biopsies from the peritoneum of 8 healthy controls, 11 uremic patients, 22 patients on PD < 12 months or 29 patients on PD > 12 months and of 13 patients with EPS were collected. The age of the uremic patients was higher (median 65.0 years, IQR: 49.0-75.0) than in the other subgroups (PD < 12 months: median 62.0 years, IQR: 52.25-68.25, PD > 12 months: median 60.0 years, IQR: 39.5-70.5 and EPS: median 51.00 years, IQR: 40.0-57.5). In general, there were more female participants in the control-group (75 %) compared to all other groups (uremic group: 27%, PD < 12 months: 18 %, PD >12 months: 41% and EPS group 33 %). Time on PD was longer in EPS patients (median 72.0 months) than in PD patients (PD <12 months: median 10.0 months and PD > 12 months: 39.0 months). The ELISA study of plasma samples showed that TXNIP is upregulated in all groups compared to healthy controls. Immunohistochemically studies of peritoneal biopsies showed also an upregulation of TXNIP upon exposure to high glucose-based dialysis fluids (PD and EPS group). Interestingly, a glucose-related change in protein expression of its interacting partner and cellular anti-oxidant TRX was only observed in EPS samples. TRX activity in uremic patients was almost unchanged compared to healthy controls except for one patient. However, enhanced TXNIP expression correlated with a reduced activity of TRX in samples of PD as well as EPS patients. Reduced TRX activity resulted in an increase of produced ROS. Therefore, the effect on the generation of oxidative damage was analysed by ELISA of plasma samples and by immunohistochemistry on peritoneal sections. Both analysis showed an increase in the oxidative DNA-damage marker 8-Hydroxydesoxyguanosin (8-OHdG) in all PD samples and samples of EPS patients compared to the control group. Conclusion Here, we show that high glucose-based peritoneal dialysis solutions lead to an upregulation of TXNIP expression in human peritoneal samples. This increase in TXNIP expression reduces the activity of its interacting partner an antioxidant TRX leading to an increase in ROS production and enhanced levels of DNA-damage. In this study, we elucidate for the first time a novel mechanism showing that glucose-dependent upregulation of TXNIP induces a perturbation of the intracellular redox equilibrium leading to alterations of the peritoneal membrane. Therefore, manipulation of TXNIP expression may be a promising therapeutic target to improve peritoneal membrane function.