EFFECTS OF INTRARENAL ADMINISTRATION OF THE CALCIUM ANTAGONIST NIMODIPINE DURING PORCINE AORTIC OCCLUSION-INDUCED ISCHEMIA/REPERFUSION INJURY

Testing Danegaptide Effects on Kidney Function after Ischemia/Reperfusion Injury in a New Porcine Two Week Model

INTRODUCTION

Ischemia/reperfusion injury (I/R-I) is a leading cause of acute kidney injury (AKI) and is associated with increased mortality. Danegaptide is a selective modifier of the gap junction protein connexion 43. It has cytoprotective as well as anti-arrhythmic properties and has been shown to reduce the size of myocardial infarct in pigs. The aim of this study was to investigate the ischemia-protective effect of Danegaptide in a porcine renal I/R-I model with two weeks follow up.

METHODS

Unilateral renal I/R-I was induced in pigs by clamping the left renal artery over a two hour period. The model allowed examination of renal blood flow by magnetic resonance imaging (MRI) and the measurement of single kidney GFR two weeks after injury. Eleven animals were randomized to Danegaptide-infusion while nine animals received placebo. Kidney histology and urinary neutrophil gelatinase-associated lipocalin (NGAL) excretion were included as markers of AKI.

RESULTS

Unilateral kidney I/R-I resulted in an immediate ~50% GFR reduction, associated with a four-fold increase in urinary NGAL-excretion. Fourteen days after I/R-I, the total GFR was ~75% of baseline with a significantly lower GFR in the injured left kidney compared to the right kidney. No differences in GFR were observed between the treated and non-treated animals immediately after I/R-I or at Day 14. Furthermore, no differences were observed in the urinary excretion of NGAL, renal blood flow or other markers of renal function.

CONCLUSIONS

As expected this porcine renal I/R-I model was associated with reduced GFR two weeks after injury. Danegaptide did not improve renal function after I/R-I.

Effects of intravenous sulfide during porcine aortic occlusion-induced kidney ischemia/reperfusion injury

In rodents, inhaled H2S and injection of H2S donors protected against kidney ischemia/reperfusion (I/R) injury. During porcine aortic occlusion, the H2S donor Na2S (sulfide) reduced energy expenditure and decreased the noradrenaline requirements needed to maintain hemodynamic targets during early reperfusion. Therefore, we tested the hypothesis whether sulfide pretreatment may also ameliorate organ function in porcine aortic occlusion-induced kidney I/R injury. Anesthetized, ventilated, and instrumented pigs randomly received either sulfide or vehicle and underwent 90 min of kidney ischemia using intraaortic balloon-occlusion, and 8 h of reperfusion. During reperfusion, noradrenaline was titrated to maintain blood pressure at baseline levels. Sulfide attenuated the fall in creatinine clearance and the rise in creatinine blood levels, whereas renal blood flow and fractional Na+ excretion were comparable. Sulfide also lowered the blood IL-6, IL-1β, and nitrite + nitrate concentrations, which coincided with reduced kidney oxidative DNA base damage and iNOS expression, and attenuated glomerular histological injury as assessed by the incidence of glomerular tubularization. While expression of heme oxygenase 1 and cleaved caspase 3 did not differ, sulfide reduced the expression Bcl-xL and increased the activation of nuclear transcription factor κB. During porcine aortic occlusion-induced kidney I/R injury, sulfide pretreatment attenuated tissue injury and organ dysfunction as a result of reduced inflammation and oxidative and nitrosative stress. The higher nuclear transcription factor κB activation was probably due to the drop in temperature.

Aortic cross-clamping and reperfusion in pigs reduces microvascular oxygenation by altered systemic and regional blood flow distribution

BACKGROUND

In this study, we tested the hypothesis that aortic cross-clamping (ACC) and reperfusion cause distributive alterations of oxygenation and perfusion in the microcirculation of the gut and kidneys despite normal systemic hemodynamics and oxygenation.

METHODS

Fifteen anesthetized pigs were randomized between an ACC group (n = 10), undergoing 45 minutes of aortic clamping above the superior mesenteric artery, and a time-matched sham surgery control group (n = 5). Systemic, intestinal, and renal hemodynamics and oxygenation variables were monitored during 4 hours of reperfusion. Microvascular oxygen partial pressure (microPo(2)) was measured in the intestinal serosa and mucosa and the renal cortex, using the Pd-porphyrin phosphorescence technique. Intestinal luminal Pco(2) was determined by air tonometry and the serosal microvascular flow by orthogonal polarization spectral imaging.

RESULTS

Organ blood flow and renal and intestinal microPo(2) decreased significantly during ACC, whereas the intestinal oxygen extraction and Pco(2) gap increased. The intestinal response to reperfusion after ACC was a sustained reactive hyperemia but no such effect was seen in the kidney. Despite a sustained high intestinal O(2) delivery, serosal microPo(2) (median [range], 49 mm Hg [41-67 mm Hg] versus 37 mm Hg [27-41 mm Hg]; P < 0.05 baseline versus 4 hours reperfusion) and the absolute number of perfused microvessels decreased along with an increased intestinal Pco(2) gap (17 mm Hg [10-19 mm Hg] versus 23 mm Hg [19-30 mm Hg]; P < 0.05). In contrast, the kidney showed a progressive O(2) delivery decrease accompanied by a decrease in renal cortex oxygenation (70 mm Hg [52-93 mm Hg] versus 57 mm Hg [33-64 mm Hg]; P < 0.05).

CONCLUSION

Increased systemic and regional blood flow and oxygen supply after ACC does not ensure adequate regional blood flow and microcirculatory oxygenation in all organs.

Emerging concepts in acute kidney injury following cardiac surgery

Acute kidney injury (AKI) remains a significant cause of morbidity and mortality following cardiac surgery. Through a more thorough understanding of perioperative genomics and the evolving role of early biomarkers of AKI, the authors seek to improve meaningful outcomes among cardiac surgery patients. In this review, the focus will be on advances in risk stratification, evolving definitions and improving early diagnosis of AKI, identification of effective individualized therapies, and future directions.