L-Arginine infusion after ischaemia-reperfusion of rat kidney enhances lipid peroxidation

Pericyte-mediated constriction of renal capillaries evokes no-reflow and kidney injury following ischaemia

Acute kidney injury is common, with ~13 million cases and 1.7 million deaths/year worldwide. A major cause is renal ischaemia, typically following cardiac surgery, renal transplant or severe haemorrhage. We examined the cause of the sustained reduction in renal blood flow ('no-reflow'), which exacerbates kidney injury even after an initial cause of compromised blood supply is removed. Adult male Sprague-Dawley rats, or NG2-dsRed male mice were used in this study. After 60 min kidney ischaemia and 30-60 min reperfusion, renal blood flow remained reduced, especially in the medulla, and kidney tubule damage was detected as Kim-1 expression. Constriction of the medullary descending vasa recta and cortical peritubular capillaries occurred near pericyte somata, and led to capillary blockages, yet glomerular arterioles and perfusion were unaffected, implying that the long-lasting decrease of renal blood flow contributing to kidney damage was generated by pericytes. Blocking Rho kinase to decrease pericyte contractility from the start of reperfusion increased the post-ischaemic diameter of the descending vasa recta capillaries at pericytes, reduced the percentage of capillaries that remained blocked, increased medullary blood flow and reduced kidney injury. Thus, post-ischaemic renal no-reflow, contributing to acute kidney injury, reflects pericytes constricting the descending vasa recta and peritubular capillaries. Pericytes are therefore an important therapeutic target for treating acute kidney injury.

A review of oxidative stress in acute kidney injury: protective role of medicinal plants-derived antioxidants

Acute kidney injury (AKI) is the common clinical syndrome which is associated with increased morbidity and mortality. The severity extends from less to more advanced spectrums which link to biological, physical and chemical agents. Oxidative stress (OS)-related AKI has demonstrated the increasing of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and the decreasing of endogenous antioxidants. Medicinal plants-derived antioxidants can be ameliorated oxidative stress-related AKI through reduction of lipid peroxidation (LPO) and enhancement of activities and levels of endogenous antioxidants. Therefore, medicinal plants are good sources of exogenous antioxidants which might be considered the important remedies to ameliorate pathological alterations in oxidative stress-related AKI.

NFAT5 is activated by hypoxia: role in ischemia and reperfusion in the rat kidney

The current hypothesis postulates that NFAT5 activation in the kidney's inner medulla is due to hypertonicity, resulting in cell protection. Additionally, the renal medulla is hypoxic (10–18 mmHg); however there is no information about the effect of hypoxia on NFAT5. Using in vivo and in vitro models, we evaluated the effect of reducing the partial pressure of oxygen (PO₂) on NFAT5 activity. We found that 1) Anoxia increased NFAT5 expression and nuclear translocation in primary cultures of IMCD cells from rat kidney. 2) Anoxia increased transcriptional activity and nuclear translocation of NFAT5 in HEK293 cells. 3) The dose-response curve demonstrated that HIF-1α peaked at 2.5% and NFAT5 at 1% of O₂. 4) At 2.5% of O₂, the time-course curve of hypoxia demonstrated earlier induction of HIF-1α gene expression than NFAT5. 5) siRNA knockdown of NFAT5 increased the hypoxia-induced cell death. 6) siRNA knockdown of HIF-1α did not affect the NFAT5 induction by hypoxia. Additionally, HIF-1α was still induced by hypoxia even when NFAT5 was knocked down. 7) NFAT5 and HIF-1α expression were increased in kidney (cortex and medulla) from rats subjected to an experimental model of ischemia and reperfusion (I/R). 7) Experimental I/R increased the NFAT5-target gene aldose reductase (AR). 8) NFAT5 activators (ATM and PI3K) were induced in vitro (HEK293 cells) and in vivo (I/R kidneys) with the same timing of NFAT5. 8) Wortmannin, which inhibits ATM and PI3K, reduces hypoxia-induced NFAT5 transcriptional activation in HEK293 cells. These results demonstrate for the first time that NFAT5 is induced by hypoxia and could be a protective factor against ischemic damage.

Role of medullary blood flow in the pathogenesis of renal ischemia-reperfusion injury

PURPOSE OF REVIEW

Renal ischemia-reperfusion injury (IRI) is a common cause of acute kidney injury (AKI). Alterations in renal medullary blood flow (MBF) contribute to the pathogenesis of renal IRI. Here we review recent insights into the mechanisms of altered MBF in the pathogenesis of IRI.

RECENT FINDINGS

Although cortical blood flow fully recovers following 30-45  min of bilateral IRI, recent studies have indicated that there is a prolonged secondary fall in MBF that is associated with a long-term decline in renal function. Recent findings indicate that angiopoietin-1, atrial natriuretic peptide, heme oxygenase-1, and the gasotransmitters CO and H(2)S, may limit the severity of IRI by preserving MBF. Additional studies have also suggested a role for cytochrome P450-derived 20-HETE in the postischemic fall in MBF.

SUMMARY

Impaired MBF contributes to the pathogenesis of renal IRI. Measurement of renal MBF provides valuable insight into the underlying mechanisms of many renoprotective pathways. Identification of molecules that preserve renal MBF in IRI may lead to new therapies for AKI.

The antioxidant role of oral administration of garlic oil on renal ischemia-reperfusion injury

AIM

In this study we examined the effect of oral application of garlic form [garlic oil (GO)] on rats after renal ischemia-reperfusion (I/R) injury.

MATERIALS AND METHODS

Forty male Wistar albino rats were divided into four groups: control, sham-operated, I/R, and I/R+GO. GO was diluted in water and administered by oral intubation three times each week for 6 weeks. All rats except sham-operated underwent 45 min of bilateral renal ischemia followed by 6 hr of reperfusion. Blood samples and kidney tissues were harvested from the rats, and then rats were killed. Serum urea, creatinine, and cystatin C levels were determined. Total antioxidant capacity (TAC), catalase (CAT), total oxidant status (TOS), oxidative stress index (OSI), myeloperoxidase (MPO), nitrite oxide (NO), and protein carbonyl (PC) levels in kidney tissue and blood were measured. In addition, kidney tissue histopathology was evaluated.

RESULTS

The serum urea, creatinine, and cystatin C levels were significantly higher in I/R group compared to I/R+GO group (p<0.01). The serum and tissue antioxidant markers (TAC, CAT) were significantly lower in I/R group than I/R+GO group (p<0.01). The serum oxidant markers (TOS, MPO, NO, and PC) were significantly higher in I/R group than I/R+GO group (p<0.01). Also oral application of GO was effective in decreasing of tubular necrosis score.

CONCLUSION

Based on the present data, we conclude that increased antioxidants and decreased oxidants modulated by oral application of GO attenuated the renal I/R injury.

Cardiovascular consequences when nitric oxide and lipid signaling converge

The identification of nitric oxide ((*)NO) as an endogenously produced free radical mediator of endothelial-dependent relaxation and host defense has fundamentally changed concepts of cell signal transduction. Ligand-receptor oriented paradigms of cell signaling were originally centered on the concept of a high affinity and specific interaction between a ligand and its receptor, resulting in the activation of secondary signaling events such as gene expression or modulation of catalytic protein function. While (*)NO ligation of the heme iron of soluble guanylate cyclase is consistent with this perspective, the readily diffusible and broadly reactive (*)NO is increasingly appreciated to react with a vast array of target molecules that mediate paracrine vasodilator actions, inhibition of thrombosis and neointimal proliferation, and both pro- and antiinflammatory signaling reactions that are not affected by inhibitors of soluble guanylate cyclase. There is an expanding array of functionally significant "off target" collateral reactions mediated by (*)NO that are guanylate cyclase-independent and rather are dictated by anatomic distribution and the formation of secondary (*)NO-derived species. These reactions are a critical element of redox-regulated signaling and are addressed herein in the context of the oxidation of unsaturated fatty acids to vascular and inflammatory signaling mediators. Because of their abundance and the intrinsic reactivity of unsaturated lipid intermediates and eicosanoid metabolism enzymes with (*)NO and other oxides of nitrogen, lipid signaling mechanisms are a significant target for regulation by (*)NO in the vascular compartment. This convergence of (*)NO and lipid signaling pathways thus adds another level of regulation to physiological responses such as vasodilation, thrombosis, and inflammation. Herein, interactions between (*)NO and lipid signaling events are placed in the context of cardiovascular regulation.

Antioxidant and protective effects of silymarin on ischemia and reperfusion injury in the kidney tissues of rats

BACKGROUND

Renal ischemia/reperfusion (I/R) injury is a major cause of acute renal failure. Silymarin is extracted from Silybum marianum and Cynara cardunculus seeds and fruits. The aim of this study is to investigate whether silymarin administration prevents the damage induced by I/R in rat kidneys.

MATERIALS AND METHODS

Thirty male Wistar rats were randomly divided into five experimental groups (n = 6, each) as follows; control group, sham-operated group, I/R group, silymarin group, and I/R + silymarin group. In the I/R and I/R + silymarin groups, both renal arteries were occluded using nontraumatic microvascular clamps for 45 min. Then, at the end of 24 h of reperfusion, the animals were killed. Kidney function tests, the serum and tissue antioxidant enzymes and oxidant products were determined.

RESULTS

Animals that were subjected to I/R exhibited significant increase in serum urea, creatinine, and cystatin C levels compared with the rats treated with silymarin prior to the I/R process (P < 0.001). The serum enzymatic activities of superoxide dismutase and glutathione peroxidase significantly decreased in the I/R group; however, this reduction was significantly improved by the treatment with silymarin (P < 0.001 and P < 0.05, respectively). Renal I/R produced a significant increase in serum and tissue malondialdehyde, nitric oxide, and protein carbonyl as compared with controls. Treatment with silymarin resulted in significant reduction in these markers (P < 0.001).

CONCLUSION

Based on our findings, silymarin protects the kidneys against I/R injury. This finding may provide a basis for the development of novel therapeutic strategies for protection against the damages caused by I/R.

Oral beta-glucan protects kidney against ischemia/reperfusion injury in rats

BACKGROUND

Ischemia-reperfusion (I/R) injury is one of the leading causes of acute renal failure. Beta-(1-->3)-glucans are glucose polymers with a variety of stimulatory effects on the immune system. We designed this study to determine the possible protective effect of the orally administered soluble beta-glucan against I/R injury.

METHODS

30 rats were randomly divided into 5 experimental groups (control, sham operated, beta-glucan, I/R and I/R+beta-glucan groups, n = 6 each). Beta-glucan was administered orally to 6 rats of the beta-glucan and I/R+beta-glucan groups. The rats were subjected to bilateral renal ischemia followed by reperfusion in the I/R and I/R+beta-glucan groups. All of the rats were then sacrificed and kidney function tests, serum and tissue oxidants and antioxidants were evaluated.

RESULTS

The serum urea and cystatin C levels were significantly higher in the I/R group compared to the I/R+beta-glucan group (p < 0.01). The serum and tissue antioxidant markers (SOD, GSH-Px) were significantly lower in the I/R group than the I/R+beta-glucan group (p < 0.01). The serum oxidant markers (NO and PC) were significantly higher in the I/R group than the I/R+beta-glucan group (p < 0.01).

CONCLUSION

Based on the present data, we conclude that increased antioxidants and decreased oxidants modulated by beta-glucan attenuated the renal I/R injury.

Influence of nitric oxide on microcirculation in pancreatic ischemia/reperfusion injury: an intravital microscopic study

Recently, protective effects of nitric oxide donors in pancreatic ischemia/reperfusion (IRI) injury have been described. Their role in post-ischemic microcirculation was previously not investigated. Ischemia reperfusion was induced in an isolated pancreatic tail segment in situ. Animals were randomized to four experimental groups (n=7 animals/group), the control group (CO) received saline as placebo. Treatment groups received either sodium nitroprusside (SN) 5 min before until 2 h after reperfusion, L-arginine (LA) 30 min before reperfusion until 2 h after reperfusion or sodium nitroprusside and L-arginine (SNLA) together. After induction of ischemia (2 h) post-ischemic microcirculation was observed for 2 h by intravital-fluorescence microscopy. Functional-capillary density (FCD), leukocyte adherence in post-capillary venules (LAV) and histological damage were analysed. After reperfusion FCD decreased in all groups (P<0.05). FCD was significantly restored in all groups with administration of nitric oxide donors after reperfusion (P<0.05) as compared to CO without significant difference between the individual nitric oxide donor groups. Leukocyte adherence was significantly increased 1 h and 2 h after reperfusion (P<0.001) as compared to baseline, which was lower in all nitric oxide donor groups. Histological damage in the pancreatic tail-segment was significantly reduced in nitric oxide donor groups (P<0.01). Administration of nitric oxide donors might be useful in ischemia-reperfusion injury of the pancreas by its protective effect on microcirculation and inflammatory reaction.

L-Arginine counteracts nitric oxide deficiency and improves the recovery phase of ischemic acute renal failure in rats

BACKGROUND

In ischemic acute renal failure (ARF), nitric oxide-dependent regulation of renal hemodynamics and glomerular function is disturbed. Previous studies indicate that the nitric oxide precursor l-arginine (l-Arg) has beneficial effects on renal function. Here we further analyzed the impact of l-Arg on functional and biochemical parameters of nitric oxide signaling during the course of ischemic ARF.

METHODS

Ischemic ARF was induced in rats by bilateral clamping of renal arteries for 45 minutes. l-Arg was applied intraperitoneally during clamping, and orally during 14 days of follow-up. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured, and biochemical parameters analyzed by protein immunoblots.

RESULTS

Clamping resulted in 70% to 90% reduction of GFR and RPF, with a gradual recovery by day 14. Using an in situ assay with the oxidative fluorescent dye hydroethidine, increased tubular generation of O2- was detected in the early course of ischemic ARF, indicating enhanced oxidative stress. These findings were accompanied by up-regulation of the nitric oxide receptor, soluble guanylate cyclase, and by significant regulatory changes of inducible nitric oxide synthase (iNOS) and endothelial NOS expression. l-Arg had a beneficial effect on GFR and RPF, decreased O2- production, diminished up-regulation of soluble guanylate cyclase, and prevented up-regulation of iNOS.

CONCLUSION

Ischemic ARF is accompanied by marked alterations in the expression of key enzymes of the nitric oxide pathway, indicative for deficiency of constitutive NOS activity. l-Arg supplementation reduces O2- generation and significantly improves the expression of nitric oxide signaling proteins as well as the recovery phase of ischemic ARF.

Acute renal failure: is nitric oxide the bad guy?

Nephrotoxicity is a major side effect in clinical practice, frequently leading to acute renal failure (ARF). Many physiological mechanisms have been implicated in drug-induced renal injury. Currently, nitric oxide (NO) is considered to be an important regulator of renal vascular tone and a modulator of glomerular function under both basal and physiopathological conditions. Historically, NO has been implicated in ARF and, after its discovery, several publications have suggested that changes in NO production could play an important role in the hemodynamic alterations observed in ARF. In this review, we evaluate the participation of NO in ARF and summarize many of the findings in this research area in an attempt to elucidate the role of NO in ARF.

Ischaemic preconditioning ameliorates functional disturbance and impaired renal perfusion in rat ischaemia-reperfused kidneys

1. The effects of ischaemic preconditioning (IP) on renal function, haemodynamics and lipid peroxidation in the rat ischaemia-reperfused kidney model were examined. 2. In Wistar male rats, application of a single or three periods of 5 min bilateral renal ischaemia was performed prior to 30 min bilateral ischaemia and 90 min reperfusion (IR). The glomerular filtration rate (GFR) was estimated in terms of inulin clearance. Fractional excretion of sodium (FE(Na)) and lithium (FE(Li)), indicating total and proximal tubular sodium handling, respectively, was also measured and renal blood flow was monitored throughout the experiment. In addition, renal lipid peroxidation (LPO) levels in reperfused kidneys were evaluated. 3. A 2.8-fold increase in recovery of GFR (P < 0.005), a 50% reduction in FE(Na) (P < 0.005) and a 40% decrease in FE(Li) (P < 0.05) after IR resulted from the single period of 5 min IP. Renal blood flow was also higher than that in the control group (P < 0.01). No change of LPO levels was observed. 4. We conclude that IP may have an ability to ameliorate reperfused renal function and haemodynamics with a suitable period of preconditioned ischaemia, although this effect is independent of LPO.

Biphasic role for nitric oxide in experimental renal warm ischaemia-reperfusion injury

BACKGROUND

Whilst nitric oxide has a clearly defined role in renal haemostasis, debate continues over its pathophysiology. This study investigated the function of nitric oxide in a model of renal warm ischaemia-reperfusion injury.

METHODS

Rats underwent bilateral renal warm ischaemia (45 min) after pretreatment with nitric oxide donors, nitric oxide synthase (NOS) inhibitors or saline (control). Following reperfusion (20 min) a unilateral nephrectomy was performed to measure renal nitric oxide (as nitroxides) and oxidative DNA and protein damage. Renal function was measured on days 2 and 7 before terminal nephrectomy for analysis and morphology.

RESULTS

The increase in renal nitric oxide level seen early in reperfusion (20 min) (P < 0.01) was prevented by inhibition of constitutive (cNOS) but not inducible (iNOS) NOS. The increase in oxidative damage (P < 0.01) was exacerbated by nitric oxide donors (P < 0.01) but ameliorated by NOS inhibition (P < 0.01). Control nitric oxide remained increased through to day 7 (P < 0.01) but was reduced by nitric oxide donors and cNOS inhibitors (P < 0.05). Oxidative damage returned towards normal in the control group, whereas both DNA and protein damage persisted following NOS inhibition (P < 0.01).

CONCLUSION

Inhibition of the postischaemic increase in the level of nitric oxide was associated with an early decrease in, but eventual exacerbation of, oxidative damage. This suggests the prolonged increase in renal nitric oxide concentration was cytoprotective overall.

4-Hydroxynonenal as a biological signal: molecular basis and pathophysiological implications

Reactive oxygen intermediates (ROI) and other pro-oxidant agents are known to elicit, in vivo and in vitro, oxidative decomposition of omega-3 and omega-6 polyunsaturated fatty acids of membrane phospholipids (i.e, lipid peroxidation). This leads to the formation of a complex mixture of aldehydic end-products, including malonyldialdehyde (MDA), 4-hydroxy-2,3-nonenal (HNE), and other 4-hydroxy-2,3-alkenals (HAKs) of different chain length. These aldehydic molecules have been considered originally as ultimate mediators of toxic effects elicited by oxidative stress occurring in biological material. Experimental and clinical evidence coming from different laboratories now suggests that HNE and HAKs can also act as bioactive molecules in either physiological and pathological conditions. These aldehydic compounds can affect and modulate, at very low and nontoxic concentrations, several cell functions, including signal transduction, gene expression, cell proliferation, and, more generally, the response of the target cell(s). In this review article, we would like to offer an up-to-date review on this particular aspect of oxidative stress--dependent modulation of cellular functions-as well as to offer comments on the related pathophysiological implications, with special reference to human conditions of disease.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).