Alterations in methylation status of immune response genes promoters in cell-free DNA during a hemodialysis procedure

Cell-free DNA: the role in pathophysiology and as a biomarker in kidney diseases

Cell-free DNA (cfDNA) is present in various body fluids and originates mostly from blood cells. In specific conditions, circulating cfDNA might be derived from tumours, donor organs after transplantation or from the foetus during pregnancy. The analysis of cfDNA is mainly used for genetic analyses of the source tissue -tumour, foetus or for the early detection of graft rejection. It might serve also as a nonspecific biomarker of tissue damage in critical care medicine. In kidney diseases, cfDNA increases during haemodialysis and indicates cell damage. In patients with renal cell carcinoma, cfDNA in plasma and its integrity is studied for monitoring of tumour growth, the effects of chemotherapy and for prognosis. Urinary cfDNA is highly fragmented, but the technical hurdles can now be overcome and urinary cfDNA is being evaluated as a potential biomarker of renal injury and urinary tract tumours. Beyond its diagnostic application, cfDNA might also be involved in the pathogenesis of diseases affecting the kidneys as shown for systemic lupus, sepsis and some pregnancy-related pathologies. Recent data suggest that increased cfDNA is associated with acute kidney injury. In this review, we discuss the biological characteristics, sources of cfDNA, its potential use as a biomarker as well as its role in the pathogenesis of renal and urinary diseases.

Circulatory mitochondrial DNA is a pro-inflammatory agent in maintenance hemodialysis patients

Chronic inflammation is highly prevalent in maintenance hemodialysis (MHD) patients, and it has been shown to be a strong predictor of morbidity and mortality. Mitochondrial DNA (mtDNA) released into circulation after cell damage can promote inflammation in patients and animal models. However, the role and mechanisms of circulatory mtDNA in chronic inflammation in MHD patients remain unknown. Sixty MHD patients and 20 health controls were enrolled in this study. The circulatory mtDNA was detected by quantitative real-time PCR assay. Plasma interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) were quantitated by ELISA assay. Dialysis systems in MHD patients and in vitro were used to evaluate the effect of different dialysis patterns on circulatory mtDNA. Circulatory mtDNA was elevated in MHD patients comparing to that of health control. Regression analysis demonstrated that plasma mtDNA was positively associated with TNF-α and the product of serum calcium and phosphorus, while negatively associated with hemoglobin and serum albumin in MHD patients. MtDNA induced the secretion of IL-6 and TNF-α in the THP-1 cells. Single high-flux hemodialysis (HF-HD) and on line hemodiafiltration (OL-HDF) but not low-flux hemodialysis (LF-HD) could partially reduce plasma mtDNA in MHD patients. In vitro, both HD and hemofiltration (HF) could fractional remove mtDNA. Collectively, circulatory mtDNA is elevated and its level is closely correlated with chronic inflammation in MHD patients. HF-HD and HDF can partially reduce circulatory mtDNA in MHD patients.

DNA methylation: hemodialysis versus hemodiafiltration

Aberrant DNA methylation is an emerging characteristic of chronic kidney disease including dialysis patients. It appears to be associated to inflammation. We compared the global DNA methylation status in 10 control subjects compared to 80 dialysis patients (N = 40 on-line hemodiafiltration, N = 40 high-flux hemodialysis) in relation to the dialysis technique and inflammation. Whole blood DNA methylation was assessed with a 5-mc DNA enzyme linked immunosorbent assay Kit. Global DNA methylation was higher in hemodialysis (HD) compared to on-line hemodiafiltration (HDF) patients (0.045 vs. 0.039; P < 0.0001) and controls (0.045 vs. 0.0284; P = 0.0002 for HD; 0.039 vs. 0.0284; P = 0.0254 for on-line HDF). To study the influence of the dialysis technique on DNA methylation we divided dialysis patients according to the median value of 5-mC. DNA methylation was highest in inflamed patients on hemodialysis. The dialysis technique was the only independent predictor of global DNA methylation in dialysis patients. On-line HDF could be associated with a favorable DNA methylation profile.

Methylation status of immune response genes promoters in cell-free DNA differs in hemodialyzed patients with diabetic nephropathy according to the intensity of anemia therapy

BACKGROUND

Anemia is a major complication of end-stage renal disease. Hemodialysis itself is regarded as a stimulus activating inflammation. Pro-inflammatory cytokines are able to suppress erythropoiesis. In this pilot study, we analyzed the changes in methylation status of promoters of immune response genes in cell-free DNA to detect the differences between diabetic subjects (n = 18) with different therapeutic doses of recombinant erythropoietin.

METHODS

The extent of promoter methylation of 24 genes in plasma cell-free DNA was examined before and after hemodialysis using EpiTect Methyl qPCR Array Inflammatory Response and Autoimmunity (Qiagen).

RESULTS

The patients with higher methylation status of gene sequences IL13RA1, IL15, EDG3 and INHA in interdialytic interval were significantly overrepresented in the group with none or mild anemia therapy.

CONCLUSION

The results are in agreement with the fact that IL13 and IL15 are known inhibitors of erythropoiesis and with considered immunomodulatory role of cell-free DNA.