The effect of a nitric oxide donor on endogenous endothelin-1 expression in renal ischemia/reperfusion injury

Scavenging reactive oxygen species using tempol in the acute phase of renal ischemia/reperfusion and its effects on kidney oxygenation and nitric oxide levels

Background

Renal ischemia/reperfusion (I/R) injury is commonly seen in kidney transplantation and affects the allograft survival rates. We aimed to test our hypothesis that scavenging reactive oxygen species (ROS) with tempol would protect renal oxygenation and nitric oxide (NO) levels in the acute phase of renal I/R.

Methods

Rats were randomly divided: (1) no I/R, no tempol; (2) no I/R, but with tempol; (3) I/R without tempol; and (4) I/R with tempol. I/R was induced by 30-min clamping of the renal artery. Tempol (200 μmol/kg/h/i.v) was administered 15 min prior to I/R.

Results

I/R without tempol led to a significant decrease in renal oxygen delivery and microvascular oxygenation. Tempol, however, protected renal oxygenation after I/R. At R90, the creatinine clearance rate was lower in the I/R-subjected group that did not receive tempol compared to that in the other groups. I/R injury without tempol treatment led to a significant increase in tissue malondialdehyde levels and a significant decrease in tissue NO levels. Tempol administration before I/R could prevent oxidative stress and altered tissue NO levels.

Conclusions

This underscores that unbalance between oxygen, NO, and ROS forms an important component of the pathogenesis of I/R-induced AKI and should therefore be taken into account when designing a prevention/treatment strategy for renal I/R injury in transplantation.

Effect of sildenafil in renal ischemia/reperfusion injury in rats

PURPOSE

To evaluate the effect of sildenafil, administered prior to renal ischemia/reperfusion (I/R), by scintigraphy and histopathological evaluation in rats.

METHODS

Twenty-four rats were divided randomly into two groups. They received 0.1 ml of 99mTechnetium-etilenodicisteine intravenous, and a baseline (initial) renal scintigraphy was performed. The rats underwent 60 minutes of ischemia by left renal artery clamping. The right kidney was not manipulated. The sildenafil group (n=12) received orally 1 mg/kg of sildenafil suspension 60 minutes before ischemia. Treatment with saline 0.9% in the control group (n=12). Half of the rats was assessed after 24 hours and half after seven days I/R, with new renal scintigraphy to study differential function. After euthanasia, kidneys were removed and subjected to histopathological examination. For statistical evaluation, Student t and Mann-Whitney tests were used.

RESULTS

In the control group rats, the left kidneys had significant functional deficit, seven days after I/R, whose scintigraphic pattern was consistent with acute tubular necrosis, compared with the initial scintigraphy (p<0.05). Sildenafil treatment resulted in better differential function of the left kidneys 24h after reperfusion, compared with controls. Histopathologically, the left kidney of control rats (24 hours after I/R) showed a higher degree of cellular necrosis when compared with the sildenafil treated rats (p<0.05).

CONCLUSION

Sildenafil had a protective effect in rat kidneys subjected to normothermic I/R, demonstrated by scintigraphy and histomorphometry.

Hypothermic machine perfusion after static cold storage does not improve the preservation condition in an experimental porcine kidney model

Background

Combining hypothermic techniques, as a more practical approach to preservation, may enhance the condition of kidneys donated after cardiac death.

Methods

Porcine kidneys were retrieved after 10 min in situ warm ischaemia, then preserved by either 18 h static cold storage (CS), hypothermic machine perfusion for 18 h (HMP) or 14 h static CS followed by 4 h HMP (4HMP). Kidneys were reperfused for 3 h with oxygenated autologous blood on an isolated organ perfusion system to assess renal function and injury.

Results

Intrarenal resistance was significantly higher in the 4HMP group than in the CS and HMP groups: mean(s.d.) area under the curve (AUC) 8·48(2·97), 3·41(1·80) and 3·78(1·68) mmHg/min.h respectively (P = 0·011). Creatinine clearance was lower after 4HMP and CS: AUC 2·3(0·6) and 2·2(1·7) ml per min per 100g.h respectively versus 9·8(7·3) ml per min per 100g.h in the HMP group (P = 0·022). Levels of endothelin 1 were higher in the 4HMP and CS groups: mean(s.d.) 21·6(4·0) and 24·2(2·3) pg/ml respectively versus 11·4(4·6) pg/ml in the HMP group (P = 0·002). Morphological damage was increased in the 4HMP group.

Conclusion

This porcine kidney study demonstrated no advantage to the addition of 4 h of HMP after CS.

[Ischemia-reperfusion syndrome and role of preservation graft technique after laparoscopic versus open nephrectomy in a experimental model of living donor kidney transplant]

INTRODUCTION

Delayed graft function alter living donor transplantation is a subject of debate. Delayed graft function can be partially explained by renal ischemia-reperfusion injury, when severe is associated with decreased graft survival. In this experimental living donor model study, we analyze the hemodynamic, histological and biochemical effects of laparoscopic nephrectomy. We also, analyze the effect of a pulsatile machine perfusion for kidney preservation during cold ischemia time.

MATERIAL AND METHODS

Twenty large-white pigs (average weight 40-45 kgrs) were divided in 4 experimental groups: Group A: Laparoscopic nephrectomy+ immediate graft perfusion in pulsatile vacuum pump+autotransplant Group B: Laparoscopic nephrectomy+ immediate graft perfusion by gravity+autotransplant Group C: Open nephrectomy+immediate graft perfusion in pulsatile vacuum pump+autotransplant Group D: Open nephrectomy+ immediate graft perfusion by gravity+autotransplant Both laparoscopic and open nephrectomy were completed transperitoneally according to standardized technique. Hypothermic perfusion was done in a system designed in our lab.

RESULTS

We observed a decreased renal artery flow in kidneys procured laparoscopically compared to open nephrectomy. We found an artery flow recovery during the first 60 minutes after revascularization. Renal machine perfusion during cold ischemia time seems to have no beneficial effect, but shows a deleterious effect on hemodynamic event for renal transplantation. Lower plasma nitric oxide level is observed in kidneys obtained by laparoscopy compared with open surgical technique. And finally, we also found higher histological damage in proximal tubular and endothelial cell, in kidneys obtained by laparoscopy compared with open surgery.

CONCLUSIONS

In our experience: Laparoscopic nephrectomy versus open nephrectomy produces, in a model of living donor transplant, a lower value or renal blood flow and a higher value of renal vascular resistanse. These hemodynamic findings tend to normalize by 60 min after the reperfusion. A lower blood concentration of nitric oxide after the transplant was detected in laparoscopic group Vs open surgery group.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.

Sildenafil improves immediate posttransplant parameters in warm-ischemic kidney transplants: experimental study

OBJECTIVE

To evaluate in an experimental model the effects of the PDE5 inhibitor sildenafil on kidney grafts autotransplanted after a period of 45 minutes of warm ischemia and 60 minutes of hypothermic pump perfusion.

METHODS

Nine laboratory large-white pigs were divided into two groups. Group A (n = 4): oral dose of 100 mg sildenafil was administered 1 hour before the surgery. Group B (n = 5): no sildenafil given. Right single nephrectomy was completed after a 45-minute period of warm ischemia by complete vascular clamping. Before the autotransplant, all kidneys were submitted to a 60-minute period of hypothermic pulsatile perfusion. Renal flow, arterial pressure, and renal vascular resistance were recorded in real time for 60 minutes after autotransplant. Nitric oxide levels were determined in blood samples of the renal vein at predefined intervals. Optical and electronic microscopy was performed on all organs at the end of the procedure.

RESULTS

Renal vascular flow was significantly higher and renal vascular resistance significantly lower in the sildenafil group compared with the non-sildenafil group. No significant differences were observed in systemic arterial pressure values between both groups. Nitric oxide levels were significantly higher for all periods in the sildenafil group. No differences were observed in histological studies.

CONCLUSION

Our experimental work suggested a positive effect of sildenafil on the immediate posttransplant outcome of warm-ischemic kidneys without systemic secondary effects.

Organ systems dependent on nitric oxide and the potential for nitric oxide-targeted therapies in related diseases

Nitric oxide (NO) is a universal messenger molecule that plays diverse and essential physiologic roles in multiple organ systems, including the vasculature, bone, muscle, heart, kidney, liver, and central nervous system. NO is produced by 3 known isoforms-endothelial, neuronal, and inducible NO synthase-each of which perform distinct functions. Impairment of NO bioactivity may be an important factor in the pathogenesis of a wide range of conditions, including preeclampsia, osteoporosis, nephropathy, liver disease, and neurodegenerative diseases. Although increased levels of NO synthase or NO bioactivity have been associated with some of these disease states, research increasingly suggests that preservation or promotion of normal NO bioactivity may be beneficial in reducing the risks and perhaps reversing the underlying pathophysiology. Based on this rationale, studies investigating the use of NO-donating or NO-promoting agents in some of these diseases have produced positive results, at least to some degree, in either animal or human studies. Further investigation of NO-targeted therapies in these diverse diseases is clearly mandated.

Oxidative stress and nitric oxide in kidney function

PURPOSE OF REVIEW

Nitric oxide is a potent, endogenous vasodilator that regulates systemic blood pressure and renal function, among other functions. The bioactivity of nitric oxide is reduced by superoxide, a major reactive oxygen species. Overproduction of superoxide and other related reactive oxygen species resulting in oxidative stress reduces the biological effects of nitric oxide. Though both of these highly reactive species have distinct roles in other pathways, their interaction is emerging as a major regulatory factor in normal and pathological renal function. The purpose of this review is to highlight the recent studies on oxidative stress and nitric oxide in the kidney, focusing on their interaction in normal and pathological conditions.

RECENT FINDINGS

Studies have focused on pro-oxidant pathways and nitric oxide defense systems in normal and pathological conditions. The oxidant potential of uncoupled nitric oxide synthases is gaining interest as a pro-oxidant system. Both animal and clinical studies have attempted to identify strategies to intervene at various stages of the oxidant-nitric oxide pathways to improve function during renal failure.

SUMMARY

Several new approaches and provocative findings have emerged over the last year. A regulatory role for nitric oxide in the control of the renal microcirculation and as a participant in tubule function is further described. New information of the cause and possible prevention of acute and chronic renal failure has also been produced in the last year. These advances demonstrate the value of research in the normal and pathological roles of oxidative stress and nitric oxide in the kidney.

Effects of sodium nitrite on ischemia-reperfusion injury in the rat kidney

Reactive oxygen and nitrogen species play a key role in the pathophysiology of renal ischemia-reperfusion (I/R) injury. Recent studies have shown that nitrite (NO2−) serves as an endogenous source of nitric oxide (NO), particularly in the presence of hypoxia and acidosis. Nanomolar concentrations of NO2−reduce injury following I/R in the liver and heart in vivo. The purpose of this study was to evaluate the role of NO2−in renal I/R injury. Male Sprague-Dawley rats underwent a unilateral nephrectomy followed by 45 min of ischemia of the contralateral kidney or sham surgery under isoflurane anesthesia. Animals received normal saline, sodium NO2−, or sodium nitrate (NO3−; 1.2 nmol/g body wt ip) at 22.5 min after induction of ischemia or 15 min before ischemia. A separate set of animals received saline, NO2−, or NO3−(0.12, 1.2, or 12 nmol/g body wt iv) 45 min before ischemia. Serum creatinine and blood urea nitrogen were increased following I/R injury but were not significantly different among treatment groups at 24 and 48 h after acute renal injury. Interestingly, NO3−administration appeared to worsen renal injury. Histological scoring for loss of brush border, tubular necrosis, and red blood cell extravasation showed no significant differences among the treatment groups. The results indicate that, contrary to the protective effects of NO2−in I/R injury of the liver and heart, NO2−does not provide protection in renal I/R injury and suggest a unique metabolism of NO2−in the kidney.