Reoxygenation following ischemia causes tissue oxidative stress. We studied the role of oxidative stress caused by kidney ischemia/reperfusion (I/R) on the mitochondria of renal tissue slices. I/R caused the mitochondria to be swollen, fragmented, and have lower membrane potential. The mitochondria generated more reactive oxygen species (ROS) and nitric oxide (NO) in situ as measured by fluorescence of ROS- and NO-sensitive probes. Infusion of lithium ion, an inhibitor of glycogen kinase synthase-3, caused phosphorylation of its Ser-9 and restored the membrane potential and decreased ROS production of the mitochondrial fraction. Ischemic kidney and hypoxic rat preconditioning improved mitochondrial membrane potential and lowered ROS production caused by subsequent I/R similar to lithium ion infusion. Preconditioning normalized NO production in mitochondria as well. The drop in the mitochondrial membrane potential was prevented by NO synthase inhibition, demonstrating a strong contribution of NO to changes in mitochondrial energy metabolism during the I/R transition. Mitochondria in the I/R-stressed kidney contained less cytochrome c and more pro-apoptotic Bax, consistent with apoptotic degradation.

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Chronic renal insufficiency was modeled in rats by unilateral nephrectomy and electrocoagulation of both poles of the remaining kidney; acute renal failure was induced by 90-min clamping of the vascular pedicle of the only kidney. Injection of unfractionated culture of human fetal kidney cells or bone marrow mesenchymal stem cells into damaged kidney restored its function in rats with chronic renal insufficiency (observation period up to 2 months). After 2.5 months a relapse of chronic renal insufficiency was observed in 1 of 3 rats receiving human fetal kidney cells and in 1 of 2 animals receiving bone marrow mesenchymal stem cell culture. Injection of bone marrow mesenchymal stem cell culture to rats with acute renal failure improved recovery of renal function and prevented the death from uremia, while injection of total culture of human fetal kidney cells had virtually no effect on the course of acute renal failure.

Laser confocal microscopy showed that fluorescence of tetramethylrhodamine ethyl ether probe specifically accumulating in energized mitochondria significantly decreased in renal tubular epithelium after 40-min thermal ischemia, while fluorescence of dichlorodihydrofluorescein and diaminofluorescein probes in the same structures increased under these conditions, which attests to increased generation of ROS and NO, respectively. These forms were generated predominantly in mitochondria of tubular epitheliocytes. Hypoxic preconditioning (a series of sessions of breathing hypoxic mixture) preserved functional activity of mitochondria and prevented activation of ROS and NO generation. Ischemic preconditioning of the kidney consisting of three preliminary episodes of vascular clamping (5 min with 5 min reperfusion periods) also increased the percentage of functionally active mitochondria and prevented activation of NO synthesis without appreciably modifying ROS production. Both protective methods significantly reduced the severity of postischemic dysfunction of the kidney.

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