Morphologic changes in tubular cells from in situ kidneys following experimental hypothermia and rewarming

Effects of rewarming with extracorporeal membrane oxygenation to restore oxygen transport and organ blood flow after hypothermic cardiac arrest in a porcine model

We recently documented that cardiopulmonary resuscitation (CPR) generates the same level of cardiac output (CO) and mean arterial pressure (MAP) during both normothermia (38 °C) and hypothermia (27 °C). Furthermore, continuous CPR at 27 °C provides O₂ delivery (ḊO₂) to support aerobic metabolism throughout a 3-h period. The aim of the present study was to investigate the effects of extracorporeal membrane oxygenation (ECMO) rewarming to restore ḊO₂ and organ blood flow after prolonged hypothermic cardiac arrest. Eight male pigs were anesthetized and immersion cooled to 27 °C. After induction of hypothermic cardiac arrest, CPR was started and continued for a 3-h period. Thereafter, the animals were rewarmed with ECMO. Organ blood flow was measured using microspheres. After cooling with spontaneous circulation to 27 °C, MAP and CO were initially reduced to 66 and 44% of baseline, respectively. By 15 min after the onset of CPR, there was a further reduction in MAP and CO to 42 and 25% of baseline, respectively, which remained unchanged throughout the rest of 3-h CPR. During CPR, ḊO₂ and O₂ uptake (V̇O₂) fell to critical low levels, but the simultaneous small increase in lactate and a modest reduction in pH, indicated the presence of maintained aerobic metabolism. Rewarming with ECMO restored MAP, CO, ḊO₂, and blood flow to the heart and to parts of the brain, whereas flow to kidneys, stomach, liver and spleen remained significantly reduced. CPR for 3-h at 27 °C with sustained lower levels of CO and MAP maintained aerobic metabolism sufficient to support ḊO₂. Rewarming with ECMO restores blood flow to the heart and brain, and creates a "shockable" cardiac rhythm. Thus, like continuous CPR, ECMO rewarming plays a crucial role in "the chain of survival" when resuscitating victims of hypothermic cardiac arrest.

Comparison Between Two Pharmacologic Strategies to Alleviate Rewarming Shock: Vasodilation vs. Inodilation

Rewarming from hypothermia is often challenged by coexisting cardiac dysfunction, depressed organ blood flow (OBF), and increased systemic vascular resistance. Previous research shows cardiovascular inotropic support and vasodilation during rewarming to elevate cardiac output (CO). The present study aims to compare the effects of inodilatation by levosimendan (LS) and vasodilation by nitroprusside (SNP) on OBF and global oxygen transport during rewarming from hypothermia. We used an in vivo experimental rat model of 4 h 15°C hypothermia and rewarming. A stable isotope-labeled microsphere technique was used to determine OBF. Cardiac and arterial pressures were monitored with fluid-filled pressure catheters, and CO was measured by thermodilution. Two groups were treated with either LS (n = 7) or SNP (n = 7) during the last hour of hypothermia and throughout rewarming. Two groups served as hypothermic (n = 7) and normothermic (n = 6) controls. All hypothermia groups had significantly reduced CO, oxygen delivery, and OBF after rewarming compared to their baseline values. After rewarming, LS had elevated CO significantly more than SNP (66.57 ± 5.6/+30% vs. 54.48 ± 5.2/+14%) compared to the control group (47.22 ± 3.9), but their ability to cause elevation of brain blood flow (BBF) was the same (0.554 ± 0.180/+81 vs. 0.535 ± 0.208/+75%) compared to the control group (0.305 ± 0.101). We interpret the vasodilator properties of LS and SNP to be the primary source to increase organ blood flow, superior to the increase in CO.

14-3-3ζ-Mediated Stimulation of Oxidative Phosphorylation Exacerbates Oxidative Damage Under Hypothermic Oxygenated Conditions in Human Renal Tubular Cells (HK-2)

Cellular survival and death are at least partially regulated by the phosphorylation of proteins. A chaperon protein, 14-3-3ζ, regulates the activity of many proteins by covering the phosphorylation site within a 14-3-3 binding motif. Therefore, regulation of 14-3-3ζ activity may affect the fate of cells subjected to cold preservation and/or hypothermic oxygenated conditions. The present study assessed whether 14-3-3ζ protects cells from hypothermic oxygenation-induced injury and clarified its role in mitochondrial functions. Human renal tubular cell line HK-2 or 14-3-3ζ-overexpressed HK-2 (ζHK-2) cells were subjected to 72 hours of normoxic cold preservation in UW solution with or without antioxidants and hydroperoxides. Cellular death, adenosine triphosphate (ATP) content, and MTT catabolism were evaluated. Deferoxamine treatment reduced cellular death and augmented ATP content in both cell types. These indices were higher in ζHK-2, regardless of deferoxamine treatment. Exposure to hydroperoxides did not affect cellular death in either cell type, whereas hydroperoxide supplementation significantly reduced ATP content, except for low-dose hydrogen peroxide in HK-2 cells. MTT assay at normal state showed higher values in ζHK-2 cells, whereas it was impaired by hydroperoxides in both cell types. These results suggest that accumulation of hydroperoxides as a byproduct of the augmented oxidative phosphorylation by 14-3-3ζ overexpression causes mitochondrial dysfunction. In conclusion, despite possessing many potentially protective functions, 14-3-3ζ exacerbates cellular injury under hypothermic oxygenated conditions. 14-3-3ζ accelerates mitochondrial functions together with iron-dependent oxidative damage. Although further investigations are necessary, upregulation of 14-3-3ζ could be a method to maintain mitochondrial function under hypothermic oxygenated conditions, as shown in hypothermic machine preservation of renal grafts, when appropriate antioxidant treatment is administered.

Ischemia-reperfusion: From cell biology to acute kidney injury

Ischemia reperfusion injury occurs in the kidney when blood supply is interrupted in clinical settings such as kidney transplantation or nephron sparing surgery for renal tumors. These lesions lead to acute kidney injury (AKI) a detrimental situation associated with impaired short-term allograft function (delayed graft function or primary non function) but also long-term transplant survival through the onset of chronic allograft nephropathy. The present review details the cellular and molecular consequences of ischemia reperfusion in a native kidney as well as in a kidney graft after cold ischemia time, giving a comprehensive description of biological pathways involved during the phase of ischemia and during the reperfusion period where the rapid return to normoxia leads to a large burst of reactive oxygen species along with a dramatic reduction in antioxidant defenses. This work also focuses on the distinct susceptibilities of kidney cells to ischemia (endothelial vs epithelial) and the outcome of acute kidney injury.

Prognostic factors and a prognostic index for cats with acute kidney injury

BACKGROUND

The clinical manifestations of acute kidney injury (AKI) range from mild to fatal in cats; however, prognosis factors have been rarely studied.

HYPOTHESIS/OBJECTIVES

To find the clinical factors significantly correlated with the outcome among cats with AKI and to develop a simple prognostic index.

ANIMALS

Seventy cats with AKI were recruited.

METHODS

Demographic and clinicopathological data obtained from 70 cats with AKI were retrospectively collected. Student's t-test or Mann-Whitney U-test and Pearson chi-square test or Fisher's exact were applied to determine the factors associated with survival in cats with AKI. Using logistic regression, the statistically significant factors associated with prognosis were identified and a new prediction model was generated.

RESULTS

The overall case fatality rate was 64% (45/70). The results showed that nonsurviving cats had significantly lower levels of PCV, WBC, RBC, LDH and albumin, a lower albumin/globulin ratio, lower blood glucose, and a reduced body temperature, as well as being older. Serum urea and creatinine concentrations were not statistically significant as prognostic factors, but a decrease in these 2 variables in 3 days was significantly related to a reduction in death. A summary prognostic index including body temperature and LDH and albumin concentrations had area under the receiver-operating characteristic curve (AUROC) for predicting death of 0.86 (P < .05) and a cut-off value of 0.82, a sensitivity of 77% and a specificity of 90%.

CONCLUSIONS

The prognosis in cats with AKI is quite different from that found for human and dogs.

Impact of normothermic preservation with extracellular type solution containing trehalose on rat kidney grafting from a cardiac death donor

Background

The aim of this study was to investigate factors that may improve the condition of a marginal kidney preserved with a normothermic solution following cardiac death (CD) in a model of rat kidney transplantation (RTx).

Methods

Post-euthanasia, Lewis (LEW) donor rats were left for 1 h in a 23°C room. These critical kidney grafts were preserved in University of Wisconsin (UW), lactate Ringer's (LR), or extracellular-trehalose-Kyoto (ETK) solution, followed by intracellular-trehalose-Kyoto (ITK) solution at 4, 23, or 37°C for another 1 h, and finally transplanted into bilaterally nephrectomized LEW recipient rats (n = 4–6). Grafts of rats surviving to day 14 after RTx were evaluated by histopathological examination. The energy activity of these marginal rat kidneys was measured by high-performance liquid chromatography (HPLC; n = 4 per group) and fluorescence intensity assay (n = 6 per group) after preservation with UW or ETK solutions at each temperature. Finally, the transplanted kidney was assessed by an in vivo luciferase imaging system (n = 2).

Results

Using the 1-h normothermic preservation of post-CD kidneys, five out of six recipients in the ETK group survived until 14 days, in contrast to zero out of six in the UW group (p<0.01). Preservation with ITK rather than ETK at 23°C tended to have an inferior effect on recipient survival (p = 0.12). Energy activities of the fresh donor kidneys decreased in a temperature-dependent manner, while those of post-CD kidneys remained at the lower level. ETK was superior to UW in protecting against edema of the post-CD kidneys at the higher temperature. Luminescence intensity of successful grafts recovered within 1 h, while the intensity of grafts of deceased recipients did not change at 1 h post-reperfusion.

Conclusions

Normothermic storage with extracellular-type solution containing trehalose might prevent reperfusion injury due to temperature-dependent tissue edema.

Altered brain myelin sheath morphology after rewarming in situ

In this study cerebral ultrastructure was examined in an in vivo rat model, after rewarming from profound hypothermia (15-13 degrees C). Animals held at 37 degrees C served as controls. After rewarming, brains were examined by electron microscope. Micrographs were taken randomly, analyzed anonymously, and quantified by morphometry. Serum analysis of the stress marker S-100beta was carried out in identical groups. The most striking findings in rewarmed animals, when compared to controls, were alterations of myelin sheaths (p<.008) and elevated S-100beta (p<.0001). This indicates that cells in the central nervous system are susceptible to injury in an experimental model of accidental hypothermia and rewarming.

Ischemia/reperfusion injury in kidney transplantation: mechanisms and prevention

Ischemia has been an inevitable event accompanying kidney transplantation. Ischemic changes start with brain death, which is associated with severe hemodynamic disturbances: increasing intracranial pressure results in bradycardia and decreased cardiac output; the Cushing reflex causes tachycardia and increased blood pressure; and after a short period of stabilization, systemic vascular resistance declines with hypotension leading to cardiac arrest. Free radical-mediated injury releases proinflammatory cytokines and activates innate immunity. It has been suggested that all of these changes-the early innate response and the ischemic tissue damage-play roles in the development of adaptive responses, which in turn may lead to an acute font of kidney rejection. Hypothermic kidney storage of various durations before transplantation add to ischemic tissue damage. The final stage of ischemic injury occurs during reperfusion. Reperfusion injury, the effector phase of ischemic injury, develops hours or days after the initial insult. Repair and regeneration processes occur together with cellular apoptosis, autophagy, and necrosis; the fate of the organ depends on whether cell death or regeneration prevails. The whole process has been described as the ischemia-reperfusion (I-R) injury. It has a profound influence on not only the early but also the late function of a transplanted kidney. Prevention of I-R injury should be started before organ recovery by donor pretreatment. The organ shortage has become one of the most important factors limiting extension of deceased donor kidney transplantation worldwide. It has caused increasing use of suboptimal deceased donors (high risk, extended criteria [ECD], marginal donors) and uncontrolled non-heart-beating (NHBD) donors. Kidneys from such donors are exposed to much greater ischemic damage before recovery and show reduced chances for proper early as well as long-term function. Storage of kidneys, especially those recovered from ECD (or NHBD) donors, should use machine perfusion.