High urea and NaCl carbonylate proteins in renal cells in culture andin vivo, and high urea causes 8-oxoguanine lesions in their DNA

Urea and NaCl are elevated in the renal inner medulla. We now find that a high concentration of urea or NaCl increases reactive oxygen species (ROS) in mouse renal inner medullary (mIMCD3) cells in culture. Previously, high NaCl, but not high urea, was found to cause DNA double-strand breaks. We now tested whether high urea or NaCl causes oxidative damage to DNA or cellular proteins. We find that high urea increases mIMCD3 cell DNA single-strand breaks and 8-oxoguanine lesions. High NaCl does not cause detectable 8-oxoguanine lesions. High urea or NaCl also greatly increases carbonylation of proteins in mIMCD3 cells. Carbonylation occurs within 5 min and with as little as 5 mM urea, a normal plasma level. It increases as urea is raised over the range in uremia. A high raffinose level increases ROS and carbonylation. High sorbitol and glycerol levels do not increase ROS or carbonylation. Carbonyl content is high in mouse renal inner medullas where interstitial NaCl and urea concentrations are normally high. There, numerous proteins are carbonylated, and carbonylation occurs in both collecting ducts and thin limbs.