Oxidative stress in chronic renal failure

Oxidative stress defines an imbalance between formation of reactive oxygen species (ROS) and antioxidative defence mechanisms. In view of the profound biological effects of ROS, in recent years numerous clinical and experimental studies focused on detection of signs of oxidative stress in renal patients. There is good evidence indicating that uraemia in general is associated with enhanced oxidative stress w1,2x, and treatment of uraemic patients with haemodialysis or peritoneal dialysis has been suggested to particularly contribute to oxidative stress and reduced antioxidant levels in these patients w3,4x. The latter may result from haemodialysis membrane-induced activation of macrophages on the surface of dialysis membranes during the dialysis session. Loss or deficiency of antioxidant activity (e.g. vitamin E deficiency) could also contribute to enhanced oxidative stress in uraemia. In this issue of Nephrology Dialysis Transplantation, Klemm et al. w5x investigate erythrocyte antioxidant capacity and formation of oxygen radicals in haemodialysis patients using the electron paramagnetic resonance method. Klemm et al. identified glutathione peroxidase as the prominent, highly effective radicaleliminating system in erythrocytes. As long as this system was intact, there was no difference between haemodialysis patients and controls; only when glutathione peroxidase was inhibited did erythrocytes of haemodialysis patients show a significant delay in the elimination of free radicals, indicating a defect in the antioxidant forces outside the glutathione peroxidase system. A series of reports over recent years demonstrated signs of increased oxidative stress in renal and haemodialysis patients. However, the significance of enhanced oxidative stress in renal patients remains to be further elucidated in clinical endpoint studies. The latter is of particular importance since in non-renal patients, studies using antioxidant treatments to prevent vascular and other diseases revealed equivocal effects w6–9x.