Salt intake, oxidative stress, and renal expression of NADPH oxidase and superoxide dismutase

The hypothesis that a high salt (HS) intake increases oxidative stress was investigated and was related to renal cortical expression of NAD(P)H oxidase and superoxide dismutase (SOD). 8-Isoprostane PGF(2alpha) and malonyldialdehyde were measured in groups (n = 6 to 8) of conscious rats during low-salt, normal-salt, or HS diets. NADPH- and NADH-stimulated superoxide anion (O-2(-)) generation was assessed by chemiluminescence, and expression of NAD(P)H oxidase and SOD were assessed with real-time PCR. Excretion of 8-iso-prostane and malonyldialdehyde increased incrementally two-to threefold with salt intake (P < 0.001), whereas prostaglandin E-2 was unchanged. Renal cortical NADH- and NADPH- stimulable O-2(-) generation increased (P < 0.05) 30 to 40% with salt intake. Compared with low-salt diet, HS significantly (P < 0.005) increased renal cortical mRNA expression of gp91(phox) and P47(phox) and decreased expression of intracellular CuZn (IC)-SOD and mitochondrial (Mn)-SOD. Despite suppression of the renin-angiotensin system, salt loading enhances oxidative stress. This is accompanied by increased renal cortical NADH and NADPH oxidase activity and increased expression of gp91(phox) and P47(phox) and decreased IC- and Mn-SOD. Thus, salt intake enhances generation of O-2(-) accompanied by enhanced renal expression and activity of NAD(P)H oxidase with diminished renal expression of IC- and Mn-SOD.