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

miR-486-5p protects against rat ischemic kidney injury and prevents the transition to chronic kidney disease and vascular dysfunction

AIM

Acute kidney injury (AKI) increases the risk for progressive chronic kidney disease (CKD). MicroRNA (miR)-486-5p protects against kidney ischemia-reperfusion (IR) injury in mice, although its long-term effects on the vasculature and development of CKD are unknown. We studied whether miR-486-5p would prevent the AKI to CKD transition in rat, and affect vascular function.

METHODS

Adult male rats were subjected to bilateral kidney IR followed by i.v. injection of liposomal-packaged miR-486-5p (0.5 mg/kg). Kidney function and histologic injury were assessed after 24 h and 10 weeks. Kidney endothelial protein levels were measured by immunoblot and immunofluorescence, and mesenteric artery reactivity was determined by wire myography.

RESULTS

In rats with IR, miR-486-5p blocked kidney endothelial cell increases in intercellular adhesion molecule-1 (ICAM-1), reduced neutrophil infiltration and histologic injury, and normalized plasma creatinine (P<0.001). However, miR-486-5p attenuated IR-induced kidney endothelial nitric oxide synthase (eNOS) expression (P<0.05). At 10 weeks, kidneys from rats with IR alone had decreased peritubular capillary density and increased interstitial collagen deposition (P<0.0001), and mesenteric arteries showed impaired endothelium-dependent vasorelaxation (P<0.001). These changes were inhibited by miR-486-5p. Delayed miR-486-5p administration (96 h, 3 weeks after IR) had no impact on kidney fibrosis, capillary density, or endothelial function.

CONCLUSION

In rats, administration of miR-486-5p early after kidney IR prevents injury, and protects against CKD development and systemic endothelial dysfunction. These protective effects are associated with inhibition of endothelial ICAM-1 and occur despite reduction in eNOS. miR-486-5p holds promise for the prevention of ischemic AKI and its complications.

Polystyrene microplastic-induced extracellular vesicles cause kidney-related effects in the crosstalk between tubular cells and fibroblasts

Plastic waste accumulation and its degradation into microplastics (MPs) and nanoplastics (NPs) pose environmental concerns. Previous studies have indicated that polystyrene (PS)-MPs harm living animals. Extracellular vesicles (EVs) are associated with metabolic reprogramming and mitochondrial dysfunction in various kidney diseases. In this article, we evaluated how PS-MPs affected tubular cells and fibroblasts. The results demonstrated that PS-MPs increased EV production in human tubular cells and caused endoplasmic reticulum (ER) stress-related proteins without inducing inflammation-related proteins in human tubular cells. The uptake of PS-MPs and incubation with the conditioned medium of PS-MPs induced reactive oxygen species (ROS) production and ER stress-related proteins in fibroblast cells. The fibroblast cells treated with the conditioned medium of PS-MPs also increased the expression of fibrosis-related proteins. Our findings suggested that the expression of EV-related markers increased in tubular cells via Beclin 1 after PS-MP treatment. In addition, PS-MPs induced ROS production in vitro and in vivo. We found that PS-MPs also altered the expression of EV markers in urine, and CD63 expression was also increased in vitro and in vivo after PS-MP treatment. In conclusion, PS-MP-induced EVs lead to ER stress-related proteins, ROS production and fibrosis-related proteins in tubular cells and fibroblasts.

Characterization of the Oxidative Stress in Renal Ischemia/Reperfusion-Induced Cardiorenal Syndrome Type 3

In kidney disease (KD), several factors released into the bloodstream can induce a series of changes in the heart, leading to a wide variety of clinical situations called cardiorenal syndrome (CRS). Reactive oxygen species (ROS) play an important role in the signaling and progression of systemic inflammatory conditions, as observed in KD. The aim of the present study was to characterize the redox balance in renal ischemia/reperfusion-induced cardiac remodeling. C57BL/6 male mice were subjected to occlusion of the left renal pedicle, unilateral, for 60 min, followed by reperfusion for 8 and 15 days, respectively. The following redox balance components were evaluated: catalase (CAT), superoxide dismutase (SOD), total antioxidant capacity (FRAP), NADPH oxidase (NOX), nitric oxide synthase (NOS), hydrogen peroxide (H₂O₂), and the tissue bioavailability of nitric oxide (NO) such as S-nitrosothiol (RSNO) and nitrite (NO₂⁻). The results indicated a process of renoprotection in both kidneys, indicated by the reduction of cellular damage and some oxidant agents. We also observed an increase in the activity of antioxidant enzymes, such as SOD, and an increase in NO bioavailability. In the heart, we noticed an increase in the activity of NOX and NOS, together with increased cell damage on day 8, followed by a reduction in protein damage on day 15. The present study concludes that the kidneys and heart undergo distinct processes of damage and repair at the analyzed times, since the heart is a secondary target of ischemic kidney injury. These results are important for a better understanding of the cellular mechanisms involved in CRS.

l-NIL prevents the ischemia and reperfusion injury involving TLR-4, GST, clusterin, and NFAT-5 in mice

On renal ischemia-reperfusion (I/R) injury, recruitment of neutrophils during the inflammatory process promotes local generation of oxygen and nitrogen reactive species, which, in turn, are likely to exacerbate tissue damage. The mechanism by which inducible nitric oxide synthase (iNOS) is involved in I/R has not been elucidated. In this work, the selective iNOS inhibitor l- N6-(1-iminoethyl)lysine (l-NIL) and the NOS substrate l-arginine were employed to understand the role of NOS activity on the expression of particular target genes and the oxidative stress elicited after a 30-min of bilateral renal ischemia, followed by 48-h reperfusion in Balb/c mice. The main findings of the present study were that pharmacological inhibition of iNOS with l-NIL during an I/R challenge of mice kidney decreased renal injury, prevented tissue loss of integrity, and improved renal function. Several novel findings regarding the molecular mechanism by which iNOS inhibition led to these protective effects are as follows: 1) a prevention of the I/R-related increase in expression of Toll-like receptor 4 (TLR-4), and its downstream target, IL-1β; 2) reduced oxidative stress following the I/R challenge; noteworthy, this study shows the first evidence of glutathione S-transferase (GST) inactivation following kidney I/R, a phenomenon fully prevented by iNOS inhibition; 3) increased expression of clusterin, a survival autophagy component; and 4) increased expression of nuclear factor of activated T cells 5 (NFAT-5) and its target gene aquaporin-1. In conclusion, prevention of renal damage following I/R by the pharmacological inhibition of iNOS with l-NIL was associated with the inactivation of proinflammatory pathway triggered by TLR-4, oxidative stress, renoprotection (autophagy inactivation), and NFAT-5 signaling pathway.

Sex Difference in Gentamicin-induced Nephrotoxicity: Influence of L-arginine in Rat Model

Background:

L-arginine is an important precursor for the formation of nitric oxide (NO). According to previous studies, NO function is related to gender. Likewise, chronic renal diseases have lower prevalence in female. Gentamicin (GM) is an aminoglycoside antibiotic. According to some studies, males are more sensitive to GM renal nephrotoxicity. This study attempts to find protective effects of L-arginine on GM nephrotoxicity in male and female rats.

Methods:

Male and female rats were divided into eight groups: Rats were randomly assigned to 8 groups each including both male and female rats. The first and second groups received vehicle (saline), the third and fourth groups received gentamicin (80 mg/kg), the fifth and sixth groups received L-arginine (150 mg/kg), and finally, seventh and eighth groups received gentamicin+ L- arginine. Next, 9 days after administering drugs, blood samples were collected from the heart. After making sacrifices, the level of blood urea, creatinine (Cr), nitrite, and malondialdehyde (MDA) was measured in serums. Likewise, nitrite and MDA were measured in the homogenized kidney tissue.

Results:

GM significantly increased serum level of urea and Cr in male and female rats (P < 0.05). However, co-administration of GM + L-arginine significantly did not decrease urea and Cr level in male rats, whereas, in female rats, they significantly reduced (P < 0.05). In response to GM, renal MDA level increased in male and female rats (P < 0.05), and in the presence of GM + L-arginine, the level of MDA significantly decreased in both genders (P < 0.05).

Conclusions:

L-arginine demonstrated some protective effects in female rats but did not protect against GM nephrotoxicity in male rats for unknown reasons, probably related to the effects of sex hormones which needs further studies to be confirmed.

Inhibition of heparanase protects against chronic kidney dysfunction following ischemia/reperfusion injury

Renal ischemia/reperfusion (I/R) injury occurs in patients undergoing renal transplantation and with acute kidney injury and is responsible for the development of chronic allograft dysfunction as characterized by parenchymal alteration and fibrosis. Heparanase (HPSE), an endoglycosidase that regulates EMT and macrophage polarization, is an active player in the biological response triggered by ischemia/reperfusion (I/R) injury. I/R was induced in vivo by clamping left renal artery for 30 min in wt C57BL/6J mice. Animals were daily treated and untreated with Roneparstat (an inhibitor of HPSE) and sacrificed after 8 weeks. HPSE, fibrosis, EMT-markers, inflammation and oxidative stress were evaluated by biomolecular and histological methodologies together with the evaluation of renal histology and measurement of renal function parameters. 8 weeks after I/R HPSE was upregulated both in renal parenchyma and plasma and tissue specimens showed clear evidence of renal injury and fibrosis. The inhibition of HPSE with Roneparstat-restored histology and fibrosis level comparable with that of control. I/R-injured mice showed a significant increase of EMT, inflammation and oxidative stress markers but they were significantly reduced by treatment with Roneparstat. Finally, the inhibition of HPSE in vivo almost restored renal function as measured by BUN, plasma creatinine and albuminuria. The present study points out that HPSE is actively involved in the mechanisms that regulate the development of renal fibrosis arising in the transplanted organ as a consequence of ischemia/reperfusion damage. HPSE inhibition would therefore constitute a new pharmacological strategy to reduce acute kidney injury and to prevent the chronic pro-fibrotic damage induced by I/R.

The Renal Safety of L-Carnitine, L-Arginine, and Glutamine in Athletes and Bodybuilders

One of the major concerns about taking amino acid supplements is their potential adverse effects on the kidney as a major organ involved in the metabolism and excretion of exogenous substances. The aim of this study is to review available data about renal safety of the most prominent amino acid supplements including L-arginine, glutamine and also L-carnitine as well as creatine (as amino acid derivatives) in athletes and bodybuilders. The literature was searched by keywords such as "L-carnitine", "L-arginine", "glutamine", and "kidney injury" in databases such as Scopus, Medline, Embase, and ISI Web of Knowledge. Articles published from 1950 to December 2017 were included. Among 3171, 5740, and 1608 records after primary search in the relevant databases, 8, 7, and 5 studies have been finally included, respectively, for L-carnitine, L-arginine, and glutamine in this review. Arginine appears to have both beneficial and detrimental effects on kidney function. However, adverse effects are unlikely to occur with the routine doses (from 3 to >100 g/day). The risks and benefits of L-carnitine on the athletes' and bodybuilders' kidney have not been evaluated yet. However, L-carnitine up to 6000 mg/day is generally considered to be a safe supplement at least in healthy adults. Both short-term (20-30 g within a few hours) and long-term (0.1 g/kg four times daily for 2 weeks) glutamine supplementation in healthy athletes were associated with no significant adverse effects, but it can cause glomerulosclerosis and serum creatinine level elevation in the setting of diabetic nephropathy. Creatine supplementation (ranged from 5 to 30 g/day) also appears to have no detrimental effects on kidney function of individuals without underlying renal diseases. More clinical data are warranted to determine the optimal daily dose and intake duration of common supplemental amino acids associated with the lowest renal adverse effects in sportsmen and sports women.

Novel microspheres reduce the formation of deep venous thrombosis and repair the vascular wall in a rat model

L-Arginine (L-arg), widely known as a substrate for endogenous nitric oxide synthesis, can improve endothelial function associated with the vasculature, inhibit platelet aggregation, and alter the activity of vascular smooth muscle cells. P-selectin is a membrane component of the platelet alpha-granule and the endothelial cell-specific Wiebel–Palade body that plays a central role in mediating interactions between platelets and both leukocytes and the endothelium. The experiment was designed to evaluate the effect of novel microspheres with L-arg targeting P-selectin on the formation of deep vein thrombosis and repair of vascular wall in a rat model. Thrombosis of the inferior vena cava was induced by applying a piece of filter paper (5 mm × 10 mm) saturated with 10% FeCl₃ solution for 5 min. Targeted microspheres with L-arg, targeted microspheres with water, and saline were injected into the tail veins of the rats after 30 min of applying the filter paper saturated with 10% FeCl₃ solution. The dry weight and length of the thrombus isolated from the inferior vena cava were significantly decreased in the group with L-arg in microsphere after 24 h. No significant differences in prothrombin time, activated partial thromboplastin time, thrombin time, and fibrinogen among the groups were indicated. Images revealed that apoptosis in the vascular wall was less in the group injected with targeted microspheres with L-arg than in the other two groups at 1 and 8 d postsurgery. Meanwhile, cell proliferation was considerably excessive in the group injected with L-arg wrapped in targeted microspheres. Therefore, these novel microspheres could decrease the formation of thrombus in the early stages and in the subsequent periods of thrombosis. The microspheres can also enhance the vitality of impaired endothelial cells and reduce cell apoptosis.

Restored nitric oxide bioavailability reduces the severity of acute-to-chronic transition in a mouse model of aristolochic acid nephropathy

Aristolochic Acid (AA) nephropathy (AAN) is a progressive tubulointerstitial nephritis characterized by an early phase of acute kidney injury (AKI) leading to chronic kidney disease (CKD). The reduced nitric oxide (NO) bioavailability reported in AAN might contribute to renal function impairment and progression of the disease. We previously demonstrated that L-arginine (L-Arg) supplementation is protective in AA-induced AKI. Since the severity of AKI may be considered a strong predictor of progression to CKD, the present study aims to assess the potential benefit of L-Arg supplementation during the transition from the acute phase to the chronic phase of AAN. C57BL/6J male mice were randomly subjected to daily i.p. injections of vehicle or AA for 4 days. To determine whether renal AA-induced injuries were linked to reduced NO production, L-Arg was added to drinking water from 7 days before starting i.p. injections, until the end of the protocol. Mice were euthanized 5, 10 and 20 days after vehicle or AA administration. AA-treated mice displayed marked renal injury and reduced NO bioavailability, while histopathological features of AAN were reproduced, including interstitial cell infiltration and tubulointerstitial fibrosis. L-Arg treatment restored renal NO bioavailability and reduced the severity of AA-induced injury, inflammation and fibrosis. We concluded that reduced renal NO bioavailability contributes to the processes underlying AAN. Furthermore, L-Arg shows nephroprotective effects by decreasing the severity of acute-to-chronic transition in experimental AAN and might represent a potential therapeutic tool in the future.

Effects of Platelet-Rich Plasma (PRP) on a Model of Renal Ischemia-Reperfusion in Rats

Renal ischemia-reperfusion injury is a major cause of acute renal failure, causing renal cell death, a permanent decrease of renal blood flow, organ dysfunction and chronic kidney disease. Platelet-rich plasma (PRP) is an autologous product rich in growth factors, and therefore able to promote tissue regeneration and angiogenesis. This product has proven its efficacy in multiple studies, but has not yet been tested on kidney tissue. The aim of this work is to evaluate whether the application of PRP to rat kidneys undergoing ischemia-reperfusion reduces mid-term kidney damage. A total of 30 monorrenal Sprague-Dawley male rats underwent renal ischemia-reperfusion for 45 minutes. During ischemia, PRP (PRP Group, n = 15) or saline solution (SALINE Group, n = 15) was administered by subcapsular renal injection. Control kidneys were the contralateral organs removed immediately before the start of ischemia in the remaining kidneys. Survival, body weight, renal blood flow on Doppler ultrasound, kidney weight, kidney volume, blood biochemistry and histopathology were determined for all subjects and kidneys, as applicable. Correlations between these variables were searched for. The PRP Group showed significantly worse kidney blood flow (p = 0.045) and more histopathological damage (p<0.0001). Correlations were found between body weight, kidney volume, kidney weight, renal blood flow, histology, and serum levels of creatinine and urea. Our study provides the first evidence that treatment with PRP results in the deterioration of the kidney’s response to ischemia-reperfusion injury.

Agmatine improves renal function in gentamicin-induced nephrotoxicity in rats

The present study was designed to explore the possible protective effects of agmatine, a known nitric oxide (NO) synthase inhibitor, against gentamicin-induced nephrotoxicity in rats. For this purpose, we quantitatively evaluated gentamicin-induced renal structural and functional alterations using histopathological and biochemical approaches. Furthermore, the effect of agmatine on gentamicin-induced hypersensitivity of urinary bladder rings to acetylcholine (ACh) was evaluated. Twenty-four male Wistar albino rats were randomly divided into 3 groups, namely control, gentamicin (100 mg/kg, i.p.), and gentamicin plus agmatine (40 mg/kg, orally). At the end of the study, all rats were sacrificed and then blood and urine samples and kidneys were taken. Administration of agmatine significantly decreased kidney/body mass ratio, serum creatinine, lactate dehydrogenase (LDH), renal malondialdehyde (MDA), myeloperoxidase (MPO), NO, and tumor necrosis factor-alpha (TNF-α) while it significantly increased creatinine clearance and renal superoxide dismutase (SOD) activity when compared with the gentamicin-treated group. Additionally, agmatine ameliorated tissue morphology as evidenced by histological evaluation and reduced the responses of isolated bladder rings to ACh. Our study indicates that agmatine administration with gentamicin attenuates oxidative-stress associated renal injury by reducing oxygen free radicals and lipid peroxidation, restoring NO level and inhibiting inflammatory mediators such as TNF-α.

Protective effect of nitric oxide in aristolochic acid-induced toxic acute kidney injury: an old friend with new assets

Aristolochic acid (AA) nephropathy (AAN), a progressive tubulointerstitial injury of toxic origin, is characterized by early and transient acute tubular necrosis. This process has been demonstrated to be associated with reduced nitric oxide (NO) production, which can disrupt the regulation of renal function. In this study, we tested the hypothesis that L-arginine (L-Arg) supplementation could restore renal function and reduce renal injury after AA intoxication. C57BL/6 J male mice were randomly subjected to daily i.p. injection of either sterile saline solution or AA (2.5 mg kg(-1)) for 4 days. To determine whether AA-induced renal injuries were linked to reduced NO production, L-Arg, a substrate for NO synthase, was supplemented (5%) in drinking water. Mice intoxicated with AA exhibited features of rapid-onset acute kidney injury, including polyuria, significantly increased plasma creatinine concentrations, proteinuria and fractional excretion of sodium (P < 0.05), along with severe proximal tubular cell injury and increased NADPH oxidase 2 (Nox2)-derived oxidative stress (P < 0.05). This was associated with a significant reduction in NO bioavailability. L-Arg supplementation in AA-treated mice significantly increased NO bioavailability, which in turn improved renal function (creatininaemia, polyuria, proteinuria, fractional excreted sodium and N-acetyl-β-D-glucosaminidase enzymuria) and renal structure (tubular necrosis and tubular cell apoptosis). These changes were associated with significant reductions in Nox2 expression and in production of reactive oxygen species and with an increase in antioxidant concentrations. Our results demonstrate that preservation of NO bioavailability leads to renal protection in AA-induced acute kidney injury by reducing oxidative stress and maintaining renal function.

Clinical Relevance of Biomarkers of Oxidative Stress

SIGNIFICANCE

Oxidative stress is considered to be an important component of various diseases. A vast number of methods have been developed and used in virtually all diseases to measure the extent and nature of oxidative stress, ranging from oxidation of DNA to proteins, lipids, and free amino acids.

RECENT ADVANCES

An increased understanding of the biology behind diseases and redox biology has led to more specific and sensitive tools to measure oxidative stress markers, which are very diverse and sometimes very low in abundance.

CRITICAL ISSUES

The literature is very heterogeneous. It is often difficult to draw general conclusions on the significance of oxidative stress biomarkers, as only in a limited proportion of diseases have a range of different biomarkers been used, and different biomarkers have been used to study different diseases. In addition, biomarkers are often measured using nonspecific methods, while specific methodologies are often too sophisticated or laborious for routine clinical use.

FUTURE DIRECTIONS

Several markers of oxidative stress still represent a viable biomarker opportunity for clinical use. However, positive findings with currently used biomarkers still need to be validated in larger sample sizes and compared with current clinical standards to establish them as clinical diagnostics. It is important to realize that oxidative stress is a nuanced phenomenon that is difficult to characterize, and one biomarker is not necessarily better than others. The vast diversity in oxidative stress between diseases and conditions has to be taken into account when selecting the most appropriate biomarker.

Combined L-citrulline and glutathione supplementation increases the concentration of markers indicative of nitric oxide synthesis

Background

Nitric oxide (NO) is endogenously synthesized from L-arginine and L-citrulline. Due to its effects on nitric oxide synthase (NOS), reduced glutathione (GSH) may protect against the oxidative reduction of NO. The present study determined the effectiveness of L-citrulline and/or GSH on markers indicative of NO synthesis in in vivo conditions with rodents and humans and also in an in vitro condition.

Methods

In phase one, human umbilical vein endothelial cells (HUVECs) were treated with either 0.3 mM L-citrulline, 1 mM GSH (Setria®) or a combination of each at 0.3 mM. In phase two, Sprague–Dawley rats (8 weeks old) were randomly assigned to 3 groups and received either purified water, L-citrulline (500 mg/kg/day), or a combination of L-citrulline (500 mg/kg/day) and GSH (50 mg/kg/day) by oral gavage for 3 days. Blood samples were collected and plasma NOx (nitrite + nitrate) assessed. In phase three, resistance-trained males were randomly assigned to orally ingest either cellulose placebo (2.52 g/day), L-citrulline (2 g/day), GSH (1 g/day), or L-citrulline (2 g/day) + GSH (200 mg/day) for 7 days, and then perform a resistance exercise session involving 3 sets of 10-RM involving the elbow flexors. Venous blood was obtained and used to assess plasma cGMP, nitrite, and NOx.

Results

In phase one, nitrite levels in cells treated with L-citrulline and GSH were significantly greater than control (p < 0.05). In phase two, plasma NOx with L-citrulline + GSH was significantly greater than control and L-citrulline (p < 0.05). In phase three, plasma cGMP was increased, but not significantly (p > 0.05). However, nitrite and NOx for L-citrulline + GSH were significantly greater at 30 min post-exercise when compared to placebo (p < 0.05).

Conclusions

Combining L-citrulline with GSH augments increases in nitrite and NOx levels during in vitro and in vivo conditions.

Renal endothelial dysfunction in acute kidney ischemia reperfusion injury

Acute kidney injury is associated with alterations in vascular tone that contribute to an overall reduction in GFR. Studies in animal models indicate that ischemia triggers alterations in endothelial function that contribute significantly to the overall degree and severity of a kidney injury. Putative mediators of vasoconstriction that may contribute to the initial loss of renal blood flow and GFR are highlighted. In addition, there is discussion of how intrinsic damage to the endothelium impairs homeostatic responses in vascular tone as well as promotes leukocyte adhesion and exacerbating the reduction in renal blood flow. The timing of potential therapies in animal models as they relate to the evolution of AKI, as well as the limitations of such approaches in the clinical setting are discussed. Finally, we discuss how acute kidney injury induces permanent alterations in renal vascular structure. We posit that the cause of the sustained impairment in kidney capillary density results from impaired endothelial growth responses and suggest that this limitation is a primary contributing feature underlying progression of chronic kidney disease.

Role of reactive oxygen species in neonatal pulmonary vascular disease

SIGNIFICANCE

Abnormal lung development in the perinatal period can result in severe neonatal complications, including persistent pulmonary hypertension (PH) of the newborn and bronchopulmonary dysplasia. Reactive oxygen species (ROS) play a substantive role in the development of PH associated with these diseases. ROS impair the normal pulmonary artery (PA) relaxation in response to vasodilators, and ROS are also implicated in pulmonary arterial remodeling, both of which can increase the severity of PH.

RECENT ADVANCES

PA ROS levels are elevated when endogenous ROS-generating enzymes are activated and/or when endogenous ROS scavengers are inactivated. Animal models have provided valuable insights into ROS generators and scavengers that are dysregulated in different forms of neonatal PH, thus identifying potential therapeutic targets.

CRITICAL ISSUES

General antioxidant therapy has proved ineffective in reversing PH, suggesting that it is necessary to target specific signaling pathways for successful therapy.

FUTURE DIRECTIONS

Development of novel selective pharmacologic inhibitors along with nonantioxidant therapies may improve the treatment outcomes of patients with PH, while further investigation of the underlying mechanisms may enable earlier detection of the disease.

L-Arginine and its metabolites in kidney and cardiovascular disease

L-Arginine is a semi essential amino acid synthesised from glutamine, glutamate and proline via the intestinal-renal axis in humans and most mammals. L-Arginine degradation occurs via multiple pathways initiated by arginase, nitric-oxide synthase, Arg: glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine and agmatine with each having enormous biological importance. Several disease are associated to an L-arginine impaired levels and/or to its metabolites: in particular various L-arginine metabolites may participate in pathogenesis of kidney and cardiovascular disease. L-Arginine and its metabolites may constitute both a marker of pathology progression both the rationale for manipulating L-arginine metabolism as a strategy to ameliorate these disease. A large number of studies have been performed in experimental models of kidney disease with sometimes conflicting results, which underlie the complexity of Arg metabolism and our incomplete knowledge of all the mechanisms involved. Moreover several lines of evidence demonstrate the role of L-arg metabolites in cardiovascular disease and that L-arg administration role in reversing endothelial dysfunction, which is the leading cause of cardiovascular diseases, such as hypertension and atherosclerosis. This review will discuss the implication of the mains L-arginine metabolites and L-arginine-derived guanidine compounds in kidney and cardiovascular disease considering the more recent literature in the field.

Glucocorticoid receptor agonist dexamethasone attenuates renal ischemia/reperfusion injury by up-regulating eNOS/iNOS

The aim of this study was to determine the effect of dexamethasone (DEX) on renal ischemia/reperfusion injury (IRI). C57BL/6 mice were randomly divided into Sham group, IRI group and DEX group. The mice in IRI and DEX groups subjected to renal ischemia for 60 min, were treated with saline or DEX (4 mg/kg, i.p.) 60 min prior to I/R. After 24 h of reperfusion, the renal function, renal pathological changes, activation of extracellular signal-regulated kinase (ERK) and glucocorticoid receptor (GR), and the levels of iNOS and eNOS were detected. The results showed DEX significantly decreased the damage to renal function and pathological changes after renal IRI. Pre-treatment with DEX reduced ERK activation and down-regulated the level of iNOS, whereas up-regulated the level of eNOS after renal IRI. DEX could further promote the activation of GR. These findings indicated GR activation confers preconditioning-like protection against acute IRI partially by up-regulating the ratio of eNOS/iNOS.

Differential effect of COX1 and COX2 inhibitors on renal outcomes following ischemic acute kidney injury

BACKGROUND/AIMS

We have previously shown that 1 mg/kg indomethacin improves expression and functionality of renal organic anion transporters Oat1 and Oat3 after renal ischemia and furthermore improves renal outcome after ischemia. As we detected differential effects of COX1 or COX2 inhibitors on organic anion transport after ischemia and reperfusion in culture, we investigated the effect of the SC560 (COX1 inhibitor) and SC58125 (COX2 inhibitor) on expression of Oat1/3 and renal outcome after ischemic acute kidney injury (iAKI).

METHODS

iAKI was induced in rats by bilateral clamping of renal arteries for 45 min. SC560 or SC58125 (1 mg/kg each) were given intraperitoneally as soon as reperfusion started. Sham-treated animals served as controls. Oat1/3 were determined by qPCR and Western blot. Glomerular filtration rate (GFR), p-aminohippurate (PAH) clearance and PAH extraction ratio was determined. All parameters were detected 24 h after ischemia. Renal plasma flow was calculated.

RESULTS

In clamped animals SC560 (COX1 inhibitor) restored expression of Oat1/3, as well as renal perfusion. Additionally, SC560 substantially improved kidney function as measured by GFR. Application of the COX2 inhibitor SC58125 did not exert these beneficial effects.

CONCLUSION

Our study indicates that COX1 inhibitor SC560 applied after ischemia prevents ischemia-induced downregulation of Oat1/3 during reperfusion and has a substantial protective effect on kidney function. Whether and to what particular extent this apparent improvement of function is mechanistically due to beneficial effects on tubular function, renal perfusion or glomerular filtration will be the scope of future studies.

l-Arginine supplementation improves antioxidant defenses through l-arginine/nitric oxide pathways in exercised rats

l-Arginine (l-Arg) supplementation has been shown to enhance physical exercise capacity and delay onset of fatigue. This work investigated the potential beneficial mechanism(s) of l-Arg supplementation by examining its effect on the cellular oxidative and nitrosative stress pathways in the exercised rats. Forty-eight rats were randomly divided into six groups: sedentary control; sedentary control with l-Arg treatment; endurance training (daily swimming training for 8 wk) control; endurance training with l-Arg treatment; an exhaustive exercise (one time swimming to fatigue) control; and an exhaustive exercise with l-Arg treatment. l-Arg (500 mg/kg body wt) or saline was given to rats by intragastric administration 1 h before the endurance training and the exhaustive swimming test. Expression levels and activities of the l-Arg/nitric oxide (NO) pathway components and parameters of the oxidative stress and antioxidant defense capacity were investigated in l-Arg-treated and control rats. The result show that the l-Arg supplementation completely reversed the exercise-induced activation of NO synthase and superoxide dismutase, increased l-Arg transport capacity, and increased NO and anti-superoxide anion levels. These data demonstrate that l-Arg supplementation effectively reduces the exercise-induced imbalance between oxidative stress and antioxidant defense capacity, and this modulation is likely mediated through the l-Arg/NO pathways. The findings of this study improved our understanding of how l-Arg supplementation prevents elevations of reactive oxygen species and favorably enhances the antioxidant defense capacity during physical exercise.

Increased symmetrical dimethylarginine in ischemic acute kidney injury as a causative factor of renal L-arginine deficiency

Availability of L-arginine, the exclusive substrate for nitric oxide synthases, plays an important role in kidney ischemia/reperfusion injury. The endogenous L-arginine derivatives asymmetrical dimethylarginine (ADMA) and symmetrical dimethylarginine (SDMA) block cellular L-arginine uptake competitively, thereby inhibiting the production of nitric oxide. ADMA also blocks nitric oxide synthase activity directly. Here, we investigate the pathomechanistic impact of ADMA and SDMA on ischemic acute kidney injury. Rats were subject to bilateral renal ischemia (60 minutes)/reperfusion (24 hours) injury. Impairment of renal function was determined with inulin clearance (glomerular filtration rate) and para-aminohippurate (PAH) clearance (renal plasma flow). L-arginine, ADMA, and SDMA levels were measured by liquid chromatography-tandem mass spectrometry. L-arginine was extracted from renal tissue and analyzed by enzyme-linked immunosorbent assay, and protein and messenger RNA expressions were determined by Western blot and real-time reverse transcription polymerase chain reaction. Renal function deteriorated severely after ischemia/reperfusion injury, as demonstrated by inulin and PAH clearance. Serum ADMA and SDMA increased, but tissue expression of specific ADMA or SDMA synthesizing and metabolizing enzymes (protein arginine methyltransferases and dimethyl arginine dimethylaminohydrolases) did not alter. Serum L-arginine increased as well, whereas intracellular L-arginine concentration diminished. Renal messenger RNA expression of cationic amino acid transporters, which mediate L-arginine uptake, remained unchanged. In serum, the ratio of L-arginine to ADMA did not alter after ischemia/reperfusion injury, whereas the ratios of L-arginine to SDMA and ADMA to SDMA decreased. A marked increase in serum SDMA, especially when accompanied by a diminished L-arginine-to-SDMA ratio, might reflect competitive inhibition of cellular L-arginine uptake by SDMA. As a consequence, a pathologic renal L-arginine deficiency in ischemic acute kidney injury results.

Development and characterization of glutamyl-protected N-hydroxyguanidines as reno-active nitric oxide donor drugs with therapeutic potential in acute renal failure

Acute renal failure (ARF) has high mortality and no effective treatment. Nitric oxide (NO) delivery represents a credible means of preventing the damaging effects of vasoconstriction, central to ARF, but design of drugs with the necessary renoselectivity is challenging. Here, we developed N-hydroxyguanidine NO donor drugs that were protected against spontaneous NO release by linkage to glutamyl adducts that could be cleaved by γ-glutamyl transpeptidase (γ-GT), found predominantly in renal tissue. Parent NO donor drug activity was optimized in advance of glutamyl adduct prodrug design. A lead compound that was a suitable substrate for γ-GT-mediated deprotection was identified. Metabolism of this prodrug to the active parent compound was confirmed in rat kidney homogenates, and the prodrug was shown to be an active vasodilator in rat isolated perfused kidneys (EC50 ~50 μM). The data confirm that glutamate protection of N-hydroxyguanidines is an approach that might hold promise in ARF.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Rosiglitazone affects nitric oxide synthases and improves renal outcome in a rat model of severe ischemia/reperfusion injury

Background. Nitric oxide (NO)-signal transduction plays an important role in renal ischemia/reperfusion (I/R) injury. NO produced by endothelial NO-synthase (eNOS) has protective functions whereas NO from inducible NO-synthase (iNOS) induces impairment. Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor (PPAR)-γ agonist exerted beneficial effects after renal I/R injury, so we investigated whether this might be causally linked with NOS imbalance. Methods. RGZ (5 mg/kg) was administered i.p. to SD-rats (f) subjected to bilateral renal ischemia (60 min). Following 24 h of reperfusion, inulin- and PAH-clearance as well as PAH-net secretion were determined. Morphological alterations were graded by histopathological scoring. Plasma NO_x-production was measured. eNOS and iNOS expression was analyzed by qPCR. Cleaved caspase 3 (CC3) was determined as an apoptosis indicator and ED1 as a marker of macrophage infiltration in renal tissue. Results. RGZ improves renal function after renal I/R injury (PAH-/inulin-clearance, PAH-net secretion) and reduces histomorphological injury. Additionally, RGZ reduces NO_x plasma levels, ED-1 positive cell infiltration and CC3 expression. iNOS-mRNA is reduced whereas eNOS-mRNA is increased by RGZ. Conclusion. RGZ has protective properties after severe renal I/R injury. Alterations of the NO pathway regarding eNOS and iNOS could be an explanation of the underlying mechanism of RGZ protection in renal I/R injury.

Overexpression of cGMP-dependent protein kinase I (PKG-I) attenuates ischemia-reperfusion-induced kidney injury

cGMP-dependent protein kinase (PKG) is a multifunctional protein. Whether PKG plays a role in ischemia-reperfusion-induced kidney injury (IRI) is unknown. In this study, using an in vivo mouse model of renal IRI, we determined the effect of renal IRI on kidney PKG-I levels and also evaluated whether overexpression of PKG-I attenuates renal IRI. Our studies demonstrated that PKG-I levels (mRNA and protein) were significantly decreased in the kidney from mice undergoing renal IRI. Moreover, PKG-I transgenic mice had less renal IRI, showing improved renal function and less tubular damage compared with their wild-type littermates. Transgenic mice in the renal IRI group had decreased tubular cell apoptosis accompanied by decreased caspase 3 levels/activity and increased Bcl-2 and Bag-1 levels. In addition, transgenic mice undergoing renal IRI demonstrated reduced macrophage infiltration into the kidney and reduced production of inflammatory cytokines. In vitro studies showed that peritoneal macrophages isolated from transgenic mice had decreased migration compared with control macrophages. Taken together, these results suggest that PKG-I protects against renal IRI, at least in part through inhibiting inflammatory cell infiltration into the kidney, reducing kidney inflammation, and inhibiting tubular cell apoptosis.

The association of receptor of advanced glycated end products and inflammatory mediators contributes to endothelial dysfunction in a prospective study of acute kidney injury patients with sepsis

The pathogenesis of acute kidney injury (AKI) occurring due to sepsis is incompletely understood. Endothelial activation, defined as up-regulation of adhesion molecules by proinflammatory cytokines, may be central to the development of sepsis-induced AKI. Our aim was to determine levels of circulating adhesion molecules endothelial (E)-selectin, intercellular adhesion molecule (ICAM), and vascular cell adhesion molecule (VCAM), inflammatory mediators; tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β), vasoactive mediators; endothelin-1 (ET-1) and nitric oxide (NO), soluble receptor for advanced glycated end products (sRAGE) and serum fetuin-A in septic AKI patients before and after antibiotic therapy. Nineteen AKI patients with sepsis and fifteen healthy controls were enrolled in this prospective study. Results revealed that 12 weeks of therapy caused amelioration of endothelial and inflammatory injuries as well as renal function markers. Moreover, the positive correlations between levels of RAGE and E-selectin (r=0.88), ET-1 (r=0.90), and TNF-α (r=0.94) and negative with NO (r=-0.75-0.95) suggest that possible interaction of RAGE and inflammation may contribute to endothelial dysfunction in septic AKI patients.

Safety and efficacy of the terminal complement inhibitor eculizumab in Japanese patients with paroxysmal nocturnal hemoglobinuria: the AEGIS clinical trial

Paroxysmal nocturnal hemoglobinuria (PNH) is a progressive and life-threatening disease characterized by complement-mediated chronic hemolysis, resulting in serious life-threatening complications and early mortality. Eculizumab, a humanized anti-C5 monoclonal antibody that inhibits terminal complement activation, has been shown to reduce hemolysis in PNH patients. The pivotal open-label, 12-week phase II registration study (AEGIS) was designed to evaluate the efficacy and safety of eculizumab in Japanese patients with PNH. This trial achieved its primary endpoint of reducing intravascular hemolysis with high statistical significance. Twenty-seven of the 29 patients responded to eculizumab treatment, resulting in an 87% reduction in hemolysis (P < 0.0001) and subsequent improvement in anemia (P = 0.0003) despite reduction in transfusion requirements (P = 0.006). Fatigue and dyspnea significantly improved within 1-2 weeks of eculizumab treatment and the improvement was independent of changes in hemoglobin. Chronic kidney disease (CKD) was common (66%) and eculizumab treatment improved CKD in 41% of patients at 12 weeks (P < 0.001). Elevated thrombotic risk was evident in Japanese PNH patients and eculizumab treatment normalized D: -dimer levels in 45% of patients with elevated D: -dimers at baseline (P < 0.001). The AEGIS results demonstrate that eculizumab is effective, safe and well tolerated in Japanese patients with PNH.

Long-term effect of the complement inhibitor eculizumab on kidney function in patients with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a debilitating and life-threatening disease in which lysis of PNH red blood cells frequently manifests with chronic hemolysis, anemia, and thrombosis. Renal damage in PNH is associated with chronic hemosiderosis and/or microvascular thrombosis. We determined the incidence of renal dysfunction or damage, defined by stages of chronic kidney disease (CKD), in a large cohort of PNH patients and evaluated the safety and efficacy of the complement inhibitor eculizumab in altering its progression. Renal dysfunction or damage was observed in 65% of the study population at baseline with 21% of patients with later stage CKD or kidney failure (glomerular filtration rate [GFR] <or=60 ml/min/1.73 m(2); Stage 3, 4, or 5). Eculizumab treatment was safe and well-tolerated in patients with renal dysfunction or damage and resulted in the likelihood of improvement as defined as categorical reduction in CKD stage (P < 0.001) compared with baseline and to placebo (P = 0.04). Improvement in renal function was more commonly seen in patients with baseline CKD Stages 1-2 (67.1% improvement, P < 0.001) although improvement was also observed in patients with CKD Stages 3-4 (P = 0.05). Improvements occurred quickly and were sustained for at least 18 months of treatment. Patients categorized at CKD Stages 3-5 did not worsen during treatment with eculizumab. Overall, 40 (21%) of 195 patients who demonstrated renal dysfunction or damage at baseline were no longer classified as such after 18 months of treatment. Administration of eculizumab to patients with renal dysfunction or damage was well tolerated and was usually associated with clinical improvement.

L-arginine restores endothelial nitric oxide synthase-coupled activity and attenuates monocrotaline-induced pulmonary artery hypertension in rats

L-arginine can attenuate pulmonary hypertension (PH) by a mechanism that are not fully understood. This study investigated the molecule mechanism of L-arginine attenuating PH. Sprague Dawley rats were treated with monocrotaline (MCT) with or without L-arginine for 3 or 5 wk. Right ventricular systolic pressure (RVSP), right heart hypertrophy, survival rate, pulmonary artery wall thickness, nitric oxide (NO) concentration, and superoxide anion (O(2)(*-)) generation in the lung were measured. Expressions of endothelial nitric oxide synthase (eNOS) and heat shock protein 90 (HSP90), phosphorylation of eNOS at Ser(1177), and the association of eNOS and HSP90 in the lung were determined by Western blot and immunoprecipitation experiments. MCT increased RVSP, right heart hypertrophy, mortality, pulmonary artery wall thickness, and O(2)(*-) generation and decreased eNOS and HSP90 expression and association, phosphorylation of eNOS at Ser(1177), and NO production. L-arginine decreased RVSP, right heart hypertrophy, mortality, O(2)(*-) generation, and pulmonary artery wall thickness and increased NO production. L-arginine increased eNOS expression, phosphorylation of eNOS at Ser(1177), and association of eNOS and HSP90 without significantly altering HSP90 expression. L-arginine may act through three pathways, providing a substrate for NO generation, preserving eNOS expression/phosphorylation, and maintaining the association of eNOS and HSP90, which allows restoration of eNOS activity and coupling activity, to maintain the balance between NO and O(2)(*-) and delay the development of PH.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.

Low-dose indomethacin after ischemic acute kidney injury prevents downregulation of Oat1/3 and improves renal outcome

We have previously shown that expression of renal organic anion transporters Oat1 and Oat3 is diminished by prostaglandin E2 (PGE2) and that both transporters are downregulated after renal ischemia. Because PGE2 is increased after renal ischemia and is generated by cyclooxygenases (COX), we investigated the effect of the COX inhibitor indomethacin on expression of Oat1/3 after ischemic acute kidney injury (iAKI). iAKI was induced in rats by bilateral clamping of renal arteries for 45 min. Indomethacin (1 mg/kg) was given intraperitoneally as soon as reperfusion started. Sham-treated animals served as controls. Oat1/3 were determined by qPCR and Western blot. PGE2 in blood and urine was measured by enzyme-linked immunosorbent assay. Invasion of monocytes/macrophages was determined. Glomerular filtration rate and renal plasma flow were determined. All parameters were detected 24 h after ischemia. PAH net secretion, as well as clearance and secretion of PGE2 were calculated. In clamped animals, indomethacin restored expression of Oat1/3, as well as PAH net secretion, PGE2 clearance, or PGE2 secretion. Additionally, indomethacin substantially improved kidney function as measured by glomerular filtration and PAH clearance. Indomethacin did not affect ischemia-induced invasion of monocytes/macrophages. In conclusion, our study indicates that low-dose indomethacin applied after ischemia prevents ischemia-induced downregulation of Oat1/3 during reperfusion and has a substantial protective effect on kidney function after iAKI. The beneficial effect of low-dose indomethacin on renal outcome is likely due to an effect different from inhibition of inflammation. In accordance to the decreased PAH net secretion, renal excretion of an endogenous organic anion (PGE2) is also impaired after ischemia and reperfusion.

Nebivolol reduces experimentally induced warm renal ischemia reperfusion injury in rats

Ischemia/reperfusion injury, which is commonly seen in the field of renal surgery or transplantation, is a major cause of acute renal failure. The objective of the present study was to examine the role of nebivolol in modulating peroxynitrite species-induced inflammation and apoptosis after renal warm ischemia/reperfusion injury in rats. The present study was designed to investigate the effects of nebivolol on the renal warm ischemia/reperfusion injury in rats treated with the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester. After right nephrectomy, nebivolol was administered for 15 days. On the 16(th) day, ischemia was induced in contra lateral kidney for 45 min, followed by reperfusion for 24 hr. Renal function, inflammation, and apoptosis were estimated at the end of 24 hr reperfusion. Nebivolol improved the renal dysfunction and reduced inflammation and apoptosis after renal ischemia/reperfusion injury. In conclusion, nebivolol shows potent anti-apoptotic and anti-inflammatory properties due to its NO-releasing property. These findings may have major implications in the treatment of human ischemic acute renal failure.

Diminished NO generation by injured endothelium and loss of macula densa nNOS may contribute to sustained acute kidney injury after ischemia-reperfusion

In postischemic acute kidney injury (AKI) or acute renal failure, a dissipation of glomerular filtration pressure is associated with an altered renal vascular tone and reactivity, as well as a loss of vascular autoregulation. To test the hypothesis that renal nitric oxide (NO) generation reflects endothelial damage in the kidney after ischemia-reperfusion, we quantified the urinary NO levels and identified the site of its generation in postischemic AKI. Subjects were 50 recipients of cadaveric renal allografts: 15 with sustained AKI and 35 with recovering renal function. Urine and blood samples were obtained after transplant, and intraoperative allograft biopsies were performed to examine NO synthases (NOSs) in the kidney. In the sustained AKI group, urinary nitrite and nitrate excretion (in mumol/g urine creatinine) was lower (12.3 +/- 1.8 and 10.0 +/- 1.4 on postoperative days 0 and 3) than in the recovery group [20.0 +/- 3.6 and 35.1 +/- 5.3 (P < 0.005 vs. sustained AKI on days 0 and 3) on postoperative days 0 and 3]. Endothelial NOS expression diminished from the peritubular capillaries of 6 of 7 subjects in the sustained AKI group but from only 6 of 16 subjects in the recovery group. No differences were observed in the inducible NOS staining pattern between the two groups. Neuronal NOS staining was rarely observed in the macula densae of subjects but was prominent in control tissues. These findings suggest that a diminished NO generation by injured endothelium and loss of macula densa neuronal NOS could impair the vasodilatory ability of the renal vasculature and contribute to the reduction in the glomerular filtration rate in postischemic AKI.

Kidney damage after renal ablation is worsened in endothelial nitric oxide synthase -/- mice and improved by combined administration of L-arginine and antioxidants

AIM

Reduction in nitric oxide (NO) levels during kidney failure has been related to the reaction of NO with superoxide anions to yield peroxynitrite which possesses the biological activity responsible for renal damage. However, stimulation of the NO pathway ameliorates the progression of kidney failure. Thus, it is unclear whether NO prevents or acts as the compound responsible for the cytotoxicity observed during kidney failure.

METHODS

We evaluated the development of kidney failure in animals that were wild type and deficient in endothelial NO synthase (eNOS -/-) and tested the effects of an antioxidant treatment and NO precursors on the generation of superoxide anion and kidney failure parameters.

RESULTS

In wild-type mice, five-sixths nephrectomy increased proteinuria from 3.0 +/- 0.35 to 14.5 +/- 0.76 mg protein/24 h (P < 0.05), blood pressure from 83.1 +/- 1.8 to 126.6 +/- 1.7 mmHg (P < 0.05), and superoxide production from 1.4 +/- 0.6% to 74.3 +/- 0.8% (P < 0.05). The effects of five-sixths nephrectomy on the eNOS -/- mice were greater compared with wild-type mice. Proteinuria increased from 6.7 +/- 0.5 to 22.7 +/- 2.0 mg protein/24 h (P < 0.05), blood pressure increased from 93.3 +/- 0.9 to 151.2 +/- 3.4 mmHg (P < 0.05), and superoxide production increased from 12.9 +/- 0.5% to 99.8 +/- 1.3% (P < 0.05). The nitrotyrosine levels were lower in eNOS -/- mice as compared to wild-type mice. A combination of L-arginine and antioxidant treatment ameliorated renal damage. The effect was improved in wild-type animals.

CONCLUSION

Our data support the relevance of NO as an antagonist to superoxide in renal tissues and suggest that the loss of this mechanism promotes the progression of kidney failure.

The endothelial cell in ischemic acute kidney injury: implications for acute and chronic function

Recent evidence suggests that injury to the renal vasculature may play an important role in the pathogenesis of both early and chronic ischemic acute kidney injury (AKI). Established and new data support the suggestion that vascular injury, in particular, endothelial cell injury, participates in the extent and maintenance of AKI by pathways that are related to vascular tone. Early alterations in peritubular capillary blood flow during reperfusion has been documented and associated with loss of normal endothelial cell function, which can be replaced pharmacologically or with cell replacement interventions. Distorted peritubular capillary morphology is associated with loss of barrier function that may contribute to early alterations in vascular stasis. In addition, ischemia induces alterations in endothelial cells that may promote inflammation and procoagulant activity, thus contributing to vascular congestion. Reductions in microvasculature density may play a critical part in the progression of chronic kidney disease following initial recovery from ischemia/reperfusion-induced AKI. The exact nature of how capillary loss alters renal function and predisposes renal disease is thought to be due at least in part to hypoxia. Finally, the loss of endothelial cell function may represent an important therapeutic target in which nitric oxide, vascular trophic support, and/or endothelial progenitor cells may show potential importance in ameliorating the acute and/or chronic effects of ischemic AKI.

Downregulation of organic anion transporters OAT1 and OAT3 correlates with impaired secretion ofpara-aminohippurate after ischemic acute renal failure in rats

Ischemic acute renal failure (iARF) was described to reduce renal extraction of the organic anion para-aminohippurate (PAH) in humans. The rate-limiting step of renal organic anion secretion is its basolateral uptake into proximal tubular cells. This process is mediated by the organic anion transporters OAT1 and OAT3, which both have a broad spectrum of substrates including a variety of pharmaceutics and toxins. Using a rat model of iARF, we investigated whether impairing the secretion of the organic anion PAH might be associated with downregulation of OAT1 or OAT3. Inulin and PAH clearance was determined starting from 6 up to 336 h after ischemia-reperfusion (I/R) injury. Net secretion of PAH was calculated and OAT1 as well as OAT3 expression was analyzed by RT-PCR and Western blotting. Inulin and PAH clearance along with PAH net secretion were initially diminished after I/R injury with a gradual recovery during follow-up. This initial impairment after iARF was accompanied by decreased mRNA and protein levels of OAT1 and OAT3 in clamped animals compared with sham-operated controls. In correlation to the improvement of kidney function, both mRNA and protein levels of OAT1 and OAT3 were upregulated during the follow-up. Thus decreased expression of OAT1 and OAT3 is sufficient to explain the decline of PAH secretion after iARF. As a result, this may have substantial impact on excretion kinetics and half-life of organic anions. As a consequence, the biological effects of a variety of organic anions may be affected after iARF.

Role of Combined L-Arginine and Prostaglandin E1 in Renal Ischemia-Reperfusion Injury

BACKGROUND

L-Arginine (L-arg) and Prostaglandin E(1) (PGE(1)) have been used effectively as single agents to ameliorate renal ischemia-reperfusion injury. We hypothesized that combined treatment with L-arg and PGE(1 )would be more effective.

MATERIALS AND METHODS

The left renal artery of male Sprague-Dawley rats was clamped for 45 min and the right kidney was removed. Fifty six rats were randomly allocated into 5 groups each consisted of 12 rats except sham group (n = 8). (1) sham, underwent right nephrectomy only; (2) control, untreated ischemic rats; (3) L-arg group, L-arg-treated ischemic rats; (4) PGE(1) group, PGE(1)-treated ischemic rats; (5) L-arg+PGE(1) group, ischemic rats treated with both L-arg and PGE(1). Renal function and histology were assessed on days 2 and 7 postoperatively.

RESULTS

All rats, except control ones, showed a significant improvement of renal function towards normal on postoperative day 7. Serum creatinine and creatinine clearance were significantly better in L-arg+PGE(1) group compared to all other groups on day 7. With the exception of sham-operated and L-arg+PGE(1)-treated animals, all other groups showed significant increases in fractional excretion of sodium (FE(Na)) in response to renal ischemia-reperfusion. The severest tubular damage was determined in the kidneys of control rats. Rats treated with L-arg+PGE(1) had the least severe tubular damage.

CONCLUSION

The administration of either L-arg or PGE(1) attenuates both functional and structural consequences of renal warm ischemia. A near total protection might be achieved when both agents are administered concomitantly.

Gender differences in the renin-angiotensin and nitric oxide systems: relevance in the normal and diseased kidney

Female gender is associated with better renal function and resistance to renal injury, suggesting that an oestrogen-based effect or increased androgenic effects are responsible. Studies in rodents have confirmed a biological basis for this, based on the differential effects of androgens and oestrogens on the normal and diseased kidney. Many researchers in the field believe that the pre-menopausal levels of oestrogen are key to the protection observed in females. The key pressor effects of the renin-angiotensin (RA) system are due to both direct vasoconstrictory properties and alterations in renal control of extracellular fluid volume. Additionally, the RA has been shown to promote diverse aspects of renal injury. RA activity is positively modulated by androgens and antagonized by oestrogens. Nitric oxide (NO) is a potent vasorelaxant with a key role in renal control of extracellular fluid homeostasis. NO can variously have both protective and deleterious effects on renal injury. Endogenous oestrogen has an anti-hypertensive effect as well as protective effects against cell and organ damage, many of which are mediated via increases in NO generation. We examine how the RA- and NO-generating systems may underpin key aspects of gender differences in normal renal function and renal disease.

The role of L-arginine following trauma and blood loss

PURPOSE OF REVIEW

Vascular endothelial cells control vascular smooth muscle tone via the release of nitric oxide. Following adverse circulatory conditions, namely trauma and hemorrhage, endothelial cell dysfunction occurs, leading to a decrease in the release of endothelium-derived nitric oxide, which contributes to further alterations in tissue perfusion and organ function.

RECENT FINDINGS

Early administration of L-arginine (the precursor of nitric oxide) and the substrate for nitric oxide synthase in vascular endothelial cells has been found to restore the depressed organ blood flow and to reduce tissue injury following shock. This improvement in cardiovascular function was associated with restoration of the depressed cell-mediated immune responses and attenuation of the massive inflammatory response encountered under such conditions. Furthermore, the excessive infiltration of the liver with neutrophils following trauma-hemorrhage was decreased by L-arginine administration, thereby reducing hepatic injury. In addition, L-arginine treatment decreased the inflammatory response at the site of trauma and the improved wound-healing process following blood loss.

SUMMARY

Despite those promising results in animal models at present, none of the published clinical trials has demonstrated efficacy of L-arginine at doses above standard dietary practices on the outcome in critically ill surgical patients, besides the reduction in infectious complications.

Sex differences and the role of sex steroids in renal injury

PURPOSE

There is growing evidence that significant sex differences exist in the response of the kidney to injury. In this review we explored the cumulative clinical knowledge and experimental evidence of this phenomenon.

MATERIALS AND METHODS

The current clinical evidence of increased male susceptibility to acute and chronic renal injury, and experimental data elucidating potential mechanisms of this phenomenon were reviewed.

RESULTS

Renal damage induced by nephron reduction, patient age and renal ischemia is tolerated differently by the sexes. Sex differences in disease susceptibility have historically been attributed to the protective effects of estrogen but recent evidence suggests that male hormones also have an important role in these differences. Vascular mediators, such as endothelin, nitric oxide and angiotensin II, appear to be influenced by sex and sex steroids. Additionally, inflammatory mediators, such as transforming growth factor-beta1, tumor necrosis factor-alpha and p38 mitogen activating protein kinase, similarly show differential expression and activity based on sex and the presence of sex steroids. These mediators have a significant impact on the kidney response to inflammation and injury.

CONCLUSIONS

Greater understanding of the specific role of sex steroids in renal injury may provide new therapeutic strategies to protect against inflammatory injury and renal damage in the future.

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.