Energy metabolism and renal ischemia

Role of mitochondrial-derived oxidants in renal tubular cell cold-storage injury

Cold storage (CS) is regarded as a necessary procedure during donation of a deceased-donor kidney that helps to optimize organ viability. Increased oxidant generation during CS as well as during the reperfusion (or rewarming/CS.RW) phase has been suggested to be a major contributor to renal injury, although the source of and/or biochemical pathways involved in oxidant production remain unclear. The purpose of this study was to determine if renal tubular mitochondrial superoxide is capable of inducing oxidant production and mitochondrial damage in response to a CS.RW insult. To test the role of mitochondrial superoxide in CS.RW injury, we used rat renal proximal tubular (NRK) cells overexpressing manganese superoxide dismutase (MnSOD), the major mitochondrial antioxidant. Oxidant production, mitochondrial membrane potential, respiratory complex function, and cell death were all altered after exposure of NRK cells to CS.RW. MnSOD overexpression or inhibition of nitric oxide synthase provided significant protection against oxidant generation, respiratory complex inactivation, and cell death. These findings implicate mitochondrial superoxide, nitric oxide, and their reaction product, peroxynitrite, as key signaling molecules involved in CS.RW injury of renal tubular cells and suggest that therapeutic inhibition of these pathways may protect the donor kidney.

Linoleic acid epoxide promotes the maintenance of mitochondrial function and active Na+ transport following hypoxia

Low concentrations of arachidonic acid monoepoxides protect against ischemia/reperfusion injury. This study examined whether low concentrations of the linoleic acid monoepoxide, cis-12,13-epoxy-9-octadecenoic acid (12,13-EOA), protect renal cells against decreases in mitochondrial and transport functions induced by hypoxia/reoxygenation. Primary cultures of rabbit renal proximal tubular cells (RPTC) were pretreated with diluent or 1, 5, or 10 microM 12,13-EOA for 1 h and exposed to 2 h hypoxia/0.5 h reoxygenation in the absence of 12,13-EOA. Basal respiration, oligomycin-sensitive oxygen consumption (QO2), and ATP content decreased 31, 35 and 65%, respectively, following hypoxia/reoxygenation. Hypoxia/reoxygenation also increased mitochondrial membrane potential (DeltaPsi(m)). Pretreatment with 12,13-EOA prevented decreases in basal and oligomycin-sensitive QO2s and increases in DeltaPsi(m). Despite the protection against decreases in mitochondrial function, 12,13-EOA pretreatment did not prevent the initial decrease in intracellular ATP content following hypoxia. However, pretreatment did accelerate the recovery of intracellular ATP levels during reoxygenation. Pretreatment with 12,13-EOA also prevented hypoxia-induced decreases in active Na+ transport. Ouabain-sensitive QO2 (a marker of active Na+ transport) decreased 38% following hypoxia/reoxygenation but was maintained in RPTC pretreated with 1, 5 or 10 microM 12,13-EOA prior to hypoxia. Pretreatment of RPTC with the hydrolyzed product of 12,13-EOA, 12,13-dihydroxyoctadecenoic acid, did not have any protective effects against mitochondrial dysfunction and decreases in active Na+ transport. Thus, this is the first report demonstrating that preconditioning of RPTC with low concentrations of 12,13-EOA, but not its hydrolyzed product, maintains mitochondrial respiration, accelerates restoration of ATP levels, and prevents decreases in active Na+ transport following hypoxia/reoxygenation.

Carolina rinse solution minimizes kidney injury and improves graft function and survival after prolonged cold ischemia

BACKGROUND

Kidney damage caused by cold ischemia-reperfusion injury promotes adverse outcomes after renal transplantation. The purpose of this study was to determine whether Carolina rinse solution (CRS) used at the end of cold ischemic storage decreases kidney injury and improves graft function and survival.

METHODS

Inbred male Lewis rats were used as donors and recipients. Left kidneys were removed from donor rats, infused with cold University of Wisconsin solution, and stored for 24, 30, or 48 hr at 0-1 degrees C. Just before implantation, kidneys were flushed with either Ringer's solution or CRS at 35-37 degrees C or were not treated. Kidneys were then transplanted into recipient rats with removal of both native kidneys.

RESULTS

Survival and renal function were analyzed over a 14-day postoperative period. Among rats receiving kidneys after 24-hr cold storage, creatinine clearance was 75% greater in rats transplanted with kidneys flushed with CRS compared with Ringer's solution or nontreatment. In animals receiving kidneys after 30-hr cold storage, recipient survival after CRS was significantly higher than with Ringer's solution or without flushing (80% vs. 25% and 17%, respectively). However, CRS failed to prevent renal graft failure after 48 hr of cold storage (14% survival with CRS vs. 0% with Ringer's solution). In separate ex vivo studies, nonviable cell nuclei were labeled by trypan blue after cold preservation and brief warm reperfusion. CRS decreased podocyte and peritubular endothelial cell killing associated with cold ischemia-reperfusion injury.

CONCLUSION

Flushing renal explants with warm CRS before implantation diminishes cold ischemia-reperfusion injury and improves the function and survival of transplanted kidneys.

The effects of ischemia and reperfusion on mucosal respiratory function, adenosine triphosphate, electrolyte, and water content in the ascending colon of ponies

OBJECTIVE

The purpose of this study was to examine the effects of ischemia and reperfusion on the biochemical integrity of equine colonic mucosa to assess the relative roles of ischemic- and reperfusion-induced damage.

STUDY DESIGN

Two hours of no-flow ischemia experimentally induced by 720 degrees counterclockwise ascending colon volvulus followed by 2 hours reperfusion after derotation.

ANIMALS

Ten ponies.

METHODS

Ascending colon biopsies were obtained every hour for measurement of mucosal adenosine triphosphate (ATP), water, sodium, and potassium content. Additional samples were homogenized for assay of mitochondrial respiratory function.

RESULTS

ATP content diminished 92% after ischemia and recovered to only 44% of control levels (P < .001 versus controls) after 2 hours reperfusion. Reperfusion increased mucosal water and decreased sodium and potassium content for the duration of the experiment. Both NADH-(pyruvate) and FADH-linked (succinate) respiration decreased after ischemia and did not recover during reperfusion indicating electron transport chain dysfunction.

CONCLUSIONS

Two hours ischemia induced severe metabolic dysfunction in equine colon mucosa which persisted throughout reperfusion. Unequivocal evidence of injury specific to reperfusion was not observed in this study suggesting that much of the damage observed during reperfusion may be a continuation of injury induced during the ischemic period and not specific to reperfusion per se.

CLINICAL RELEVANCE

This study suggests that greater efforts to metabolically support ischemically injured mucosa may be an important aspect of obtaining improved survival of horses affected by ascending colon volvulus (ACV).