Enhanced Oxidative DNA-Damage in Peritoneal Dialysis Patients via the TXNIP/TRX Axis

Peritoneal dialysis (PD) is an effective method of renal replacement therapy, providing a high level of patient autonomy. Nevertheless, the long-term use of PD is limited due to deleterious effects of PD fluids to the structure and function of the peritoneal membrane leading to loss of dialysis efficacy. PD patients show excessive oxidative stress compared to controls or chronic kidney disease (CKD) patients not on dialysis. Therefore, defense systems against detrimental events play a pivotal role in the integrity of the peritoneal membrane. The thioredoxin-interacting-protein (TXNIP)/thioredoxin (TRX) system also plays a major role in maintaining the redox homeostasis. We hypothesized that the upregulation of TXNIP negatively influences TRX activity, resulting in enhanced oxidative DNA-damage in PD patients. Therefore, we collected plasma samples and human peritoneal biopsies of healthy controls and PD patients as well. Using ELISA-analysis and immunohistochemistry, we showed that PD patients had elevated TXNIP levels compared to healthy controls. Furthermore, we demonstrated that PD patients had a reduced TRX activity, thereby leading to increased oxidative DNA-damage. Hence, targeting the TXNIP/TRX system as well as the use of oxidative stress scavengers could become promising therapeutic approaches potentially applicable in clinical practice in order to sustain and improve peritoneal membrane function.

The Expression Patterns of Peritoneal Defensins

Background

Local defense mechanisms are important for the integrity of the peritoneum, but few details are known about the expression patterns of antimicrobial proteins such as human defensin in normal and damaged peritoneum.

Methods

Part A: The expression of different defensins in normal ( n = 12), inflamed ( n = 5), and metastatic peritoneum ( n = 4) and in cultured human peritoneal mesothelial cells was analyzed using mRNA and immunohistochemistry. Part B: Using immunohistochemistry the expression of different defensins was analyzed in different subgroups: healthy controls ( n = 25), patients with chronic appendicitis ( n = 25) or acute appendicitis ( n = 10), and end-stage renal disease patients ( n = 25, with 15 on peritoneal dialysis).

Results

Part A: Human neutrophil peptides (HNP) 1 and 3 and human β-defensins (HBD) 1 to 3 mRNA were detected in peritoneal specimens. In addition, HNP1,3, HBD1, HBD2, and HBD3 proteins were detected using immunohistochemistry. Part B: HBD1 showed a constitutive expression in mesothelium, while HBD2 and HNP1,3 were associated with inflammation. Decreased expressions of HNP1,3 were observed in end-stage renal disease patients and in patients on peritoneal dialysis.

Conclusions

For the first time, the expression patterns of defensins in normal and damaged peritoneum have been described. The reduced expression of some defensins in end-stage renal disease is of potential clinical interest against the background of the frequent infective complications seen in peritoneal dialysis.

Aberrant function and differentiation of monocytes in end stage renal disease

Patients with end stage renal disease (ESRD) suffer from many disturbances of the immune system. These immunopathologies are related to the higher failure of vaccination, and increased prevalence of infections and neoplasms. In the presented article, we review the current data regarding the role of monocytes in immune dysfunctions which are observed in terminal renal failure. As monocytes play a pivotal role in regulating the function of the immune system, their dysfunction can have a profound effect on the immune system and may lead to accelerated arteriosclerosis and deteriorating overall health conditions. More specifically, we suggest that peripheral blood monocytes in patients with ESRD are chronically activated, and their functional and phenotypical features resemble those of inflammatory macrophages. This state of chronic inflammation is unfavorable for dendritic cells and consequently, the prevalence of dendritic cells is reduced. As these effects are consistent across different modes of dialysis, they are probably mediated by the uremia itself.

The effects of chronic kidney disease and renal replacement therapy on circulating dendritic cells

BACKGROUND

The mechanisms underlying the immunodeficiency of chronic kidney disease (CKD) are incompletely understood. Recently, we described decreased numbers of myeloid (m) and plasmacytoid (p) dendritic cells (DCs), considered the most important antigen-presenting cells, in peripheral blood of patients on chronic intermittent haemodialysis (CIHD). In this study, we analysed whether this reduction resulted from CKD or from renal replacement therapy (RRT).

METHODS

Using flowcytometry, we quantified mDCs and pDCs in peripheral blood of patients maintained on CIHD (n = 37), continuous ambulatory peritoneal dialysis (CAPD; n = 29), and patients with CKD not receiving RRT (n = 37). Twenty-nine healthy volunteers served as controls.

RESULTS

Patients with CKD (n = 103) had lower pDC and mDC counts compared with volunteers: 4.2 vs 8.3 and 10.0 vs 13.8 x 10(6) cells/l, respectively (P < or = 0.001). Within the CKD group, pDC counts did not differ between patients on CIHD, CAPD and those not receiving RRT (3.6 vs 5.0 vs 4.9 x 10(6) cells/l, respectively). In the latter group, pDC numbers correlated with the glomerular filtration rate (GFR; Spearman's r = 0.49; P<0.01). In contrast, mDC counts of patients on CIHD were lower compared with patients on CAPD (7.5 vs 10.1 x 10(6) cells/l; P = 0.039) and patients not receiving RRT (13.7 x 10(6) cells/l; P<0.001). Among non-dialyzing patients, no correlation existed between GFR and mDC numbers, which were comparable to those of volunteers, even when only non-dialyzing patients with a GFR below 15 ml/min were analysed.

CONCLUSIONS

Circulating DC counts are decreased in patients with CKD; for pDCs, this reduction is primarily related to the loss of GFR, whereas the dialysis treatment appears to affect mDC numbers.