Abstract 099: Role Of Nox-induced Oxidative Stress In Mitochondrial Bioenergetic Dysfunction In The Kidney Cortex And Outer Medulla Of Dahl Salt-sensitive Rats During The Development Of Hypertension

Abstract

Background: Although renal mitochondrial dysfunction has been observed in various models of hypertension, the events leading to this dysfunction remain unclear. The present study focused on the role of salt (NaCl) intake upon renal mitochondrial bioenergetic function in Dahl salt-sensitive (SS) rats hypothesizing that a high salt (HS) diet would impair mitochondrial bioenergetics via stimulation of NOX-induced oxidative stress. Method: The HS induced progressive alteration of oxidative phosphorylation (OxPhos) and ATP synthesis in mitochondria obtained from renal cortex and outer medulla (OM) of male SS rats were compared to those of SS rats with dual knockout of NOX4 and p67 phox subunit of NOX2 (NOX DKO). Mitochondria were isolated from the cortex and OM of groups of age matched rats fed a 0.4% NaCl (LS) diet since weaning and at days 3, 7, 14 & 21 of a 4.0% NaCl (HS) diet feeding. ADP-induced (state 3) O 2 consumption rates (OCR) were measured in mitochondria energized with pyruvate and malate as substrates using an Oroboros Oxygraph-2k Instrument. Results: In SS rats, a biphasic pattern in state 3 OCR was observed with progressive uncoupling of OxPhos occurring in both cortex and OM. In the early phase of hypertension (days 3 & 7), state 3 OCR was increased (155 ± 8.2 to 190 ± 12.2 to 203.4 ± 12.1 nmol/min/mg in cortex and 101.4 ± 5.1 to 121.8 ± 7.3 to 112.8 ± 6.8 nmol/min/mg in OM; n = 5). In the established phase of hypertension (days 14 & 21), this increase was not sustained as state 3 OCR was reduced to 153 ± 7.65 and 132 ± 6.6 nmol/min/mg in cortex and 105 ± 7.3 and 63.3 ± 6.5 nmol/min/mg in OM. In contrast, SS NOX DKO rats fed a HS diet showed no significant differences in state 3 OCR in both cortex and OM, as was also observed in a control group of age matched NOX DKO rats maintained on a LS diet throughout the study. Conclusions: In SS rats, a HS diet causes initial increase in the efficiency of OxPhos for ATP production followed by a progressive decrease in the efficiency of OxPhos for ATP production in the established phase of hypertension. This biphasic pattern with ultimate reduction in the efficiency of OxPhos for energy production was not observed in SS NOX DKO rats demonstrating the important causal role of NOX-induced oxidative stress in the renal mitochondrial bioenergetic dysfunction.