Cytotoxic effects of p-cresol in renal epithelial tubular cells

Background: The uremic syndrome is characterized by a deterioration of kidney function due to the accumulation of uremic toxins. Currently, 100 different uremic toxins have been identified. Uremic toxins are particularly difficult to remove by conventional dialysis treatments and are the major causes of mortality in patients with chronic kidney disease (CKD). p-Cresol is a well-known uremic toxin which accumulates in uremic serum. Our aim was to evaluate the in vitro effect of p-cresol on apoptosis and necrosis in renal tubular cells (RTCs) to better understand the pathophysiological effect of this toxin on the kidney. Methods: We studied apoptosis and necrosis in RTCs, which were incubated for 24 h with increasing concentrations of p-cresol. A DNA ladder was noted in treated cells as a qualitative marker of the apoptotic process. Furthermore, we performed quantitative analysis of cell viability using a flow cytometer and assessed caspase-3 activity. Results: Incubation with p-cresol for 24 h resulted in a significant reduction in RTC viability. DNA isolated from RTCs incubated with increasing p-cresol concentrations for 24 h showed a 'ladder' pattern of apoptosis at p-cresol concentrations of 10, 5 and 2.5 mg/l. However, we did not observe any significant changes in apoptosis levels detected by annexin V and caspase-3 compared with untreated cells. Cytofluorimetric analysis of necrosis highlighted significantly higher cell death rates in RTCs incubated with the higher p-cresol concentrations (range 40-10 mg/l) compared with other concentrations (5-2.5 mg/l) and untreated cells (p < 0.05). Necrosis induction was stronger at higher p-cresol concentrations. Conclusion: It is necessary to develop new therapeutic and dialytic strategies to manage p-cresol concentrations in CKD.