Mitochondrial-derived ROS Contribute to the Development of Hypertensive-Diabetic Kidney Injury.

Hypertension (HTN) is common in diabetes mellitus (DM) and substantially increases the risk for diabetic nephropathy. Current therapies only slow the progression to end-stage renal disease (ESRD) in hypertensive-diabetic patients rather than halt it. Thus, new insights into the mechanisms of this disease are needed. To investigate the mechanisms by which HTN and DM interact to promote renal injury, we developed a model combining streptozotocin (STZ)-induced type 1 DM and inter-renal aorta constriction (AC)-induced HTN in male Wistar rats. In this model (Wistar-DM+AC), both kidneys are exposed to the same levels of hyperglycemia, circulating hormones, and neural influences, but the left kidney below the AC has normal to slightly reduced blood pressure (BP), while the right kidney above the AC is exposed to elevated BP. To assess the roles of mitochondrial-derived reactive oxygen species (ROS) and mitochondrial dysfunction in causing kidney injury, Wistar-DM+AC rats were also treated with saline vehicle or mito-TEMPO, a mitochondrial-targeted antioxidant, for 6 weeks starting 2 weeks after AC surgery (0.4mg/kg/day, osmotic mini-pump). Eight weeks after AC or sham surgery, glomerular filtration rate (GFR) and urinary albumin excretion (UAE) in left and right kidneys were measured separately by collecting urine from each kidney to evaluate the change of renal function. Mitochondrial oxygen consumption rate and superoxide generation from the cortex of left and right kidneys were measured simultaneously by Oroboros high-resolution respirometry. Kidneys exposed to DM or HTN alone had only mild glomerular injury and slightly increased UAE. In contrast, right kidneys from Wistar-DM+AC rats which had been exposed to DM plus HTN for 8 weeks had much greater increases in UAE (3.4±0.7 vs1.9±1.3 μg/min), significantly reduced GFR (0.5±0.1 vs 0.7±0.1 ml/min/g of kidney weight) as well as reduced mitochondrial oxygen consumption rate and increased mitochondrial ROS generation compared to left kidneys of Wistar-DM+AC rats. In Wistar-DM+AC rats that received mitoTEMPO treatment, the right kidneys exposed to the same levels of elevated BP and blood glucose had lower albumin excretion (1.7±0.3 μg/min), higher GFR (1.3±0.2 ml/min/g of kidney weight), and preserved mitochondrial oxygen consumption with reduced mitochondrial-derived ROS compared to the right kidneys of vehicle-treated Wistar-DM+AC rats. These results suggest that mitochondrial-derived ROS may contribute to kidney injury when HTN is superimposed on DM. Pharmacological inhibition of mitochondrial ROS generation attenuates kidney injury and may be a potential therapeutic strategy for diabetic nephropathy.