Smooth muscle calcium and endothelium-derived relaxing factor in the abnormal vascular responses of acute renal failure

Utilizing pathophysiological concepts of ischemia-reperfusion injury to design renoprotective strategies and therapeutic interventions for normothermic ex vivo kidney perfusion

Normothermic machine perfusion (NMP) has emerged as a promising tool for the preservation, viability assessment, and repair of deceased-donor kidneys prior to transplantation. These kidneys inevitably experience a period of ischemia during donation, which leads to ischemia-reperfusion injury when NMP is subsequently commenced. Ischemia-reperfusion injury has a major impact on the renal vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis. With an increased understanding of the underlying pathophysiological mechanisms, renoprotective strategies and therapeutic interventions can be devised to minimize additional injury during normothermic reperfusion, ensure the safe implementation of NMP, and improve kidney quality. This review discusses the pathophysiological alterations in the vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis of deceased-donor kidneys and delineates renoprotective strategies and therapeutic interventions to mitigate renal injury and improve kidney quality during NMP.

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.

Fluid overload and renal function in children after living-donor renal transplantation: a single-center retrospective analysis

BACKGROUND

We aimed to compare renal function after kidney transplantation in children who were treated with higher vs. lower fluid volumes.

METHODS

A retrospective analysis of 81 living-donor renal transplantation pediatric patients was performed between the years 2007 and 2018. We analyzed associations of the decrease in serum creatinine (delta creatinine) with fluid balance, central venous pressure (CVP), pulmonary congestion, mean arterial pressure (MAP), and MAP-CVP percentiles in the first 3 postoperative days. After correcting creatinine for fluid overload, we also assessed associations of these variables with the above parameters. Finally, we evaluated the association between delta creatinine and estimated glomerular filtration rate (eGFR) at 3 months follow-up.

RESULTS

Both delta creatinine and delta-corrected creatinine were found to be associated with pulmonary congestion on the second and third postoperative days (p < 0.02). In addition, trends for positive correlations were found of delta creatinine with fluid balance/kg (p = 0.07), and of delta-corrected creatinine with fluid balance/kg and CVP (p = 0.06-0.07) on the second postoperative day. An association was also demonstrated between the accumulated fluid balance of the first 2 days and eGFR at 3 months after transplantation (p = 0.03).

CONCLUSIONS

An association was demonstrated between indices of fluid overload, >80 ml/kg, and greater improvement in renal function.

IMPACT

There is no consensus regarding the optimal fluid treatment after pediatric renal transplantation. In our cohort, indices of fluid overload were associated with better renal function immediately after the transplantation and 3 months thereafter. Fluid overload after living-donor renal transplantation in children may have short- and long-term benefits on renal function.

Renin-angiotensin aldosterone inhibitor use at hospital discharge among patients with moderate to severe acute kidney injury and its association with recurrent acute kidney injury and mortality

Recurrent episodes of acute kidney injury (AKI) are common among AKI survivors. Renin-angiotensin aldosterone inhibitors (RAASi) are often indicated for these patients but may increase the risk for recurrent AKI. Here, we examined whether RAASi associates with a higher risk for recurrent AKI and mortality among survivors of moderate to severe AKI in a retrospective cohort of Veterans who survived Stage II or III AKI. The primary exposure was RAASi at hospital discharge and the primary endpoint was recurrent AKI within 12 months. Cox proportional hazards models were fit on a propensity score-weighted cohort to compare time to recurrent AKI and mortality by RAASi exposure. Among 96,983 patients, 40% were on RAASi at discharge. Compared to patients who continued RAASi use, those discontinuing use experienced no difference in risk for recurrent AKI but had a significantly higher risk of mortality [hazard ratio 1.33 (95% confidence interval1.26-1.41)]. No differences in recurrent AKI risk was observed for non-users started or not on RAASi compared to prevalent users who continued RAASi. Subgroup analyses among those with diabetes, chronic kidney disease, heart failure, and malignancy were similar with exception of a modest reduction in recurrent AKI risk among RAASi discontinuers with chronic kidney disease. Thus, RAASi use among survivors of moderate to severe AKI was associated with little to no difference in risk for recurrent AKI but was associated with improved survival. Reinitiating or starting RAASi among patients with strong indications is warranted but should be balanced with individual overall risk for recurrent AKI and with adequate monitoring.

Vasoreactivity to Acetylcholine During Porcine Kidney Perfusion for the Assessment of Ischemic Injury

BACKGROUND

The effects of renal allograft ischemic injury on vascular endothelial function have not been clearly established. The aim of this study was to examine vascular reactivity to acetylcholine (ACh) in kidneys subjected to ischemic injury and reperfusion.

METHODS

Porcine kidneys were exposed to different combinations of warm ischemic time (WIT) and cold ischemic time (CIT) as follows: 15 min (n = 7), 60 min (n = 6), 90 min (n = 6), or 120 min (n = 4) WIT + 2 h CIT or 15 min WIT + 16 h CIT (n = 8). Kidneys were reperfused at 38°C for 3 h. After reperfusion, ACh was infused into the circuit to assess endothelium-dependent vascular reactivity.

RESULTS

The dose-response relationships between renal blood flow and ACh demonstrated that ACh doses of 10^-10 to 10^-7 mmol/L caused vasodilatation, whereas doses in the range 10^-6 to 10^-4 mmol/L led to vasoconstriction. For kidneys exposed to 15-90 min WIT, there was a clear relationship between increasing ischemic injury and reduced vasodilatation to ACh. In contrast, kidneys subjected to 120 min WIT completely lost vasoreactivity. The vasodilatory response to ACh was diminished, but not lost, when CIT was increased from 2 h to 16 h. Peak renal blood flow after ACh infusion correlated with the functional parameters in kidneys with 2 h CIT (P < 0.05).

CONCLUSIONS

The loss of renal vascular reactivity after 120 min WIT suggests endothelial dysfunction leading to loss of nitric oxide synthesis/release. Measurement of vasoreactivity to ACh in an isolated organ perfusion system has the potential to be developed as a marker of ischemic renal injury before transplantation.

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.

Neuroendocrine stress response: implications for cardiac surgery-associated acute kidney injury

Surgical stress causes biochemical and physiologic perturbations of every homeostatic axis. These alterations include volume/baroreceptor regulation, sympathetic activation, parasympathetic suppression, neuroendocrine activation, acute phase response protein synthesis and secretion, immune response modulation and long-term behavioral adaptation. The kidney is central to the stress response because of its main role in the maintenance of water, electrolyte balance and hence, intracellular and extracellular compartments, including the intravascular volume. Acute kidney injury after cardiac surgery occurs as a result of numerous factors including ischemia-reperfusion, inflammation, oxidative stress, neurohormonal activation, metabolic factors, and nephrotoxicity or pigment nephropathy. The neuroendocrine stress response has a central role in initiating renal injury during cardiac surgery through an increased release of arginine-vasopressin and activation of the sympathetic nervous system and the intrarenal and systemic renin-angiotensin-aldosterone system. The contribution of an exaggerated neuroendocrine stress response to cardiac surgery and cardiopulmonary bypass as key pathophysiologic mechanism for acute kidney injury after cardiac surgery represents an opportunity for scientific exploration.

Hydrodynamic Isotonic Fluid Delivery Ameliorates Moderate-to-Severe Ischemia-Reperfusion Injury in Rat Kidneys

Highly aerobic organs like the kidney are innately susceptible to ischemia-reperfusion (I/R) injury, which can originate from sources including myocardial infarction, renal trauma, and transplant. Therapy is mainly supportive and depends on the cause(s) of damage. In the absence of hypervolemia, intravenous fluid delivery is frequently the first course of treatment but does not reverse established AKI. Evidence suggests that disrupting leukocyte adhesion may prevent the impairment of renal microvascular perfusion and the heightened inflammatory response that exacerbate ischemic renal injury. We investigated the therapeutic potential of hydrodynamic isotonic fluid delivery (HIFD) to the left renal vein 24 hours after inducing moderate-to-severe unilateral IRI in rats. HIFD significantly increased hydrostatic pressure within the renal vein. When conducted after established AKI, 24 hours after I/R injury, HIFD produced substantial and statistically significant decreases in serum creatinine levels compared with levels in animals given an equivalent volume of saline via peripheral infusion (P<0.05). Intravital confocal microscopy performed immediately after HIFD showed improved microvascular perfusion. Notably, HIFD also resulted in immediate enhancement of parenchymal labeling with the fluorescent dye Hoechst 33342. HIFD also associated with a significant reduction in the accumulation of renal leukocytes, including proinflammatory T cells. Additionally, HIFD significantly reduced peritubular capillary erythrocyte congestion and improved histologic scores of tubular injury 4 days after IRI. Taken together, these results indicate that HIFD performed after establishment of AKI rapidly restores microvascular perfusion and small molecule accessibility, with improvement in overall renal function.

High prevalence of non-steroidal anti-inflammatory drug use among acute kidney injury survivors in the southern community cohort study

Background

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used and have been linked to acute kidney injury (AKI), chronic kidney disease (CKD) and cardiovascular disease (CVD). Patients who survive an AKI episode are at risk for future adverse kidney and cardiovascular outcomes. The objective of our study was to examine the prevalence and predictors of NSAID use among AKI survivors.

Methods

The Southern Community Cohort Study is a prospective study of low-income adults aged 40–79 in the southeastern US. Through linkage with Centers for Medicare and Medicaid Services, 826 participants with an AKI diagnosis (ICD-9 584.5-584.9) at any age prior to cohort enrollment were identified. At baseline, data were collected on regular use of prescription and over-the-counter NSAIDs, as well as demographic, medical and other characteristics. Additional comorbidities were ascertained via linkage with CMS or the US Renal Data System.

Results

One hundred fifty-four AKI survivors (19%) reported regular NSAID use at cohort enrollment (52 prescription, 81 OTC, 21 both) and the percentage of NSAID users did not vary by time since AKI event. Over 58% of users were taking NSAIDS regularly both before and after their AKI event. Hypertension (83%), arthritis (71%), heart failure (44%), CKD (36%) and diabetes (35%) were prevalent among NSAID users. In a multivariable model, history of arthritis (OR: 3.00; 95% CI: 1.92, 4.68) and acetaminophen use (OR: 2.43; 95% CI: 1.50, 3.93) were significantly associated with NSAID use, while prevalent CKD (OR: 0.63; 95% CI: 0.41, 0.98) and diabetes (OR: 0.44; 95% CI: 0.29, 0.69) were significantly inversely associated.

Conclusions

NSAID use among AKI survivors is common and highlights the need to understand physician and patient decision-making around NSAIDs and to develop effective strategies to reduce NSAID use in this vulnerable population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0411-7) contains supplementary material, which is available to authorized users.

Postischemic microvasculopathy and endothelial progenitor cell-based therapy in ischemic AKI: update and perspectives

Acute kidney injury (AKI) dramatically increases mortality of hospitalized patients. Incidences have been increased in recent years. The most frequent cause is transient renal hypoperfusion or ischemia which induces significant tubular cell dysfunction/damage. In addition, two further events take place: interstitial inflammation and microvasculopathy (MV). The latter evolves within minutes to hours postischemia and may result in permanent deterioration of the peritubular capillary network, ultimately increasing the risk for chronic kidney disease (CKD) in the long term. In recent years, our understanding of the molecular/cellular processes responsible for acute and sustained microvasculopathy has increasingly been expanded. The methodical approaches for visualizing impaired peritubular blood flow and increased vascular permeability have been optimized, even allowing the depiction of tissue abnormalities in a three-dimensional manner. In addition, endothelial dysfunction, a hallmark of MV, has increasingly been recognized as an inductor of both vascular malfunction and interstitial inflammation. In this regard, so-called regulated necrosis of the endothelium could potentially play a role in postischemic inflammation. Endothelial progenitor cells (EPCs), represented by at least two major subpopulations, have been shown to promote vascular repair in experimental AKI, not only in the short but also in the long term. The discussion about the true biology of the cells continues. It has been proposed that early EPCs are most likely myelomonocytic in nature, and thus they may simply be termed proangiogenic cells (PACs). Nevertheless, they reliably protect certain types of tissues/organs from ischemia-induced damage, mostly by modulating the perivascular microenvironment in an indirect manner. The aim of the present review is to summarize the current knowledge on postischemic MV and EPC-mediated renal repair.

Clinical SYNTAX Score Can Predict Acute Kidney Injury following On-Pump but Not Off-Pump Coronary Artery Bypass Surgery

BACKGROUND

The complexity of coronary artery disease is usually a neglected factor in risk stratification systems. We aimed to analyze the discriminative ability of the clinical SYNTAX score (CSS) for acute kidney injury (AKI) following on- and off-pump coronary artery surgery.

METHODS

A total of 193 patients were reviewed in this study. Patients were divided into two groups according to the surgical procedure (group I: off-pump coronary artery bypass grafting, n = 89; group II: on-pump coronary artery bypass grafting, n = 104). Preoperative demographic data, the CSS and postoperative renal functions were evaluated. The postoperative AKI classification was made using the RIFLE (Risk, Injury, Failure, Loss of function, and End-stage renal disease) criteria.

RESULTS

Postoperative AKI occurred in 14 of 89 patients (15.7%) in group I and in 29 of 104 patients in group II (27.8%; p = 0.046). The CSS did not vary much between the groups (31.52 ± 13.08 vs. 29.89 ± 15.70; p = 0.638). In group I, the CSS was not different between patients with AKI and those without AKI (30.167 ± 3.93 vs. 31.91± 14.75; p = 0.78). In group II, the CSS was 36.85 ± 18.33 in patients with AKI and 28.02 ± 12.32 in those without, and the difference was significant (p = 0.02). The discriminative ability of the CSS for postoperative AKI using the AUC analysis was 0.500 in group I and 0.840 in group II.

CONCLUSION

The CSS may be a simple and successful means of risk prediction of postoperative AKI in on-pump coronary artery surgery.

Predictors of Recurrent AKI

Recurrent AKI is common among patients after hospitalized AKI and is associated with progressive CKD. In this study, we identified clinical risk factors for recurrent AKI present during index AKI hospitalizations that occurred between 2003 and 2010 using a regional Veterans Administration database in the United States. AKI was defined as a 0.3 mg/dl or 50% increase from a baseline creatinine measure. The primary outcome was hospitalization with recurrent AKI within 12 months of discharge from the index hospitalization. Time to recurrent AKI was examined using Cox regression analysis, and sensitivity analyses were performed using a competing risk approach. Among 11,683 qualifying AKI hospitalizations, 2954 patients (25%) were hospitalized with recurrent AKI within 12 months of discharge. Median time to recurrent AKI within 12 months was 64 (interquartile range 19-167) days. In addition to known demographic and comorbid risk factors for AKI, patients with longer AKI duration and those whose discharge diagnosis at index AKI hospitalization included congestive heart failure (primary diagnosis), decompensated advanced liver disease, cancer with or without chemotherapy, acute coronary syndrome, or volume depletion, were at highest risk for being hospitalized with recurrent AKI. Risk factors identified were similar when a competing risk model for death was applied. In conclusion, several inpatient conditions associated with AKI may increase the risk for recurrent AKI. These findings should facilitate risk stratification, guide appropriate patient referral after AKI, and help generate potential risk reduction strategies. Efforts to identify modifiable factors to prevent recurrent AKI in these patients are warranted.

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.

Is it time to rethink cord management when resuscitation is needed?

A newborn who receives a placental transfusion at birth, either from cord milking or delayed cord clamping, obtains about 30% more blood volume than the newborn whose cord is cut immediately. Receiving an adequate blood volume from placental transfusion at birth may be protective for the distressed neonate as it prevents hypovolemia and can support optimal perfusion to all organs. New research shows that ventilating before clamping the umbilical cord can reduce large swings in cardiovascular function and help to stabilize the newborn. Hypovolemia, often associated with nuchal cord or shoulder dystocia, may lead to an inflammatory cascade and subsequent ischemic injury. A sudden unexpected neonatal asystole at birth may occur from severe hypovolemia. The restoration of blood volume is an important action to protect the hearts and brains of these neonates. Current protocols for resuscitation imply immediate cord clamping and the care of the newborn away from the mother's bedside. We suggest that an intrapartum care provider can achieve placental transfusion for the distressed neonate by milking the cord several times or resuscitating the neonate at the perineum with an intact cord. Milking the cord can be done quickly within the current Neonatal Resuscitation Program guidelines. Cord blood gases can be collected with delayed cord clamping. Bringing the resuscitation to the mother's bedside is a novel concept and supports an intact cord. Adopting a policy for resuscitation with an intact cord in a hospital setting will take concentrated effort and team work by obstetrics, pediatrics, midwifery, and nursing.

Comparative study on the protective role of vitamin C and L-arginine in experimental renal ischemia reperfusion in adult rats

Ischemia reperfusion (I/R) injury is a main cause of transplanted kidney dysfunction and rejection. Reactive oxygen species (ROS) play a causal role in cellular damage induced by I/R. Antioxidant vitamins and Nitric oxide (NO) were postulated to play renoprotective effects against I/R. This study compares the protective effects of vitamin C with that of the nitric oxide donor, L-arginine, on renal I/R injury in adult rats. The study was performed on 50 adult Wistar rats of both sexes, divided into 5 groups: I: Control group, receive daily intraperitoneal (i.p.) saline for 3 days. II: Renal I/R group, received i.p saline for 3 days and subjected to renal I/R. III: L-arginine Pretreated, 400 mg/kg/day i.p. for 3 days prior to I/R. IV: Vitamin C Pretreated, 500 mg/kg/day i.p. 24 hours prior to I/R. V: combined L-arginine and Vitamin C Pretreated, exposed to Renal I/R group. At the end of the experiment, plasma urea and creatinine were determined. Kidney tissue malondialdehyde (MDA), NO, catalase and superoxide dismutase (SOD) activity were measured and kidneys were examined histologically.

RESULTS

I/R group showed significant increase in plasma urea, creatinine, and renal MDA, and a significant decrease in renal catalase with marked necrotic epithelial cells and infiltration by inflammatory cells in kidney section compared to the control group. All the treated groups showed significant decrease in urea, creatinine, and MDA, and a significant increase in catalase with less histopathological changes in kidney sections compared to I/R group. However, significant improvements in urea, MDA, and catalase were found in vitamin C pretreated and combined treated groups than L-arginine pretreated group.

CONCLUSION

Oxidative stress is the primary element involved in renal I/R injury. So, antioxidants play an important renoprotective effects than NO donors.

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.

Nephroscreen™: a diagnostic test for predicting acute renal failure?

Acute renal failure is a frequent and often fatal complication of hospitalized patients. While the risk of acute renal failure among select patient groups is well recognized, physicians currently rely on diagnostic tests such as changes of serum creatinine and indirect assessment of the glomerular filtration rate to diagnose acute renal failure. Although these parameters capture the degree of kidney function lost, they are not warning signs of evolving kidney injury. While the clinical emergence of acute renal failure is sudden, the pathologic changes preceding loss of kidney function are not so sudden. Nephroscreen is a fast and easy-to-use urine enzyme-linked immunosorbent assay test designed to quantify specific pathologic events preceding death of renal proximal tubule cells. It detects acute kidney damage days before serum creatinine rises and may open new avenues to defining acute renal failure as well as treating acute renal failure patients earlier and more effectively.

Nuclear Factor-kappaB-Mediated Endothelin Receptor Up-Regulation Increases Renal Artery Contractility in Rats

Increased renal artery contractility leads to renal vasospasm and ischaemia as well as kidney damage. This study was designed to examine the hypothesis that organ culture of renal arteries induces transcriptional up-regulation of endothelin type A (ETA ) and type B2 (ETB2 ) receptors in the smooth muscle cells via activation of nuclear factor-kappaB (NF-κB) and subsequently increases renal artery contractility. Rat renal artery segments were organ-cultured for 6 or 24 hr to increase endothelin receptor-mediated contraction. To dissect molecular mechanisms involved in this process, inhibitors for NF-κB signalling pathway (MG-132 and BMS345541), transcription (actinomycin D) and translation (cycloheximide) were used during organ culture. Endothelin receptors were studied using a sensitive myograph (functional contractility), real-time PCR (mRNA analysis) and immunohistochemistry (protein localization). Compared with fresh segments, contractile responses to endothelin-1 (non-selective endothelin receptor agonist) and sarafotoxin 6c (selective ETB receptor agonist) were significantly increased in the segments after 24 hr of organ culture; ETB2 receptor-mediated maximal contraction increased from 2.7 ± 0.5 to 135.3 ± 5.1 (p < 0.001), and potency (pEC50 ) of ETA receptor agonist increased from 8.20 ± 0.04 to 8.72 ± 0.07 (p < 0.001). This was in parallel with increased corresponding mRNA and protein expression for ETA and ETB2 receptors. BMS345541, MG-132, actinomycin D or cyclohexamide, respectively, suppressed the up-regulation of ETA and ETB2 receptors. Immunostaining performed with specific antibody showed that IκB was phosphorylated during organ culture. In conclusion, activation of NF-κB mediates up-regulation of ETA and ETB2 receptors and subsequently increases renal artery contractility, which may contribute to renal vasospasm and ischaemia as well as kidney damage.

Earlier-start versus usual-start dialysis in patients with community-acquired acute kidney injury: a randomized controlled trial

BACKGROUND

Optimum timing of the initiation of dialysis therapy in acute kidney injury is not clear.

STUDY DESIGN

Prospective, open label, 2-arm, randomized, controlled trial.

SETTING & PARTICIPANTS

208 adults with acute kidney injury with progressively worsening azotemia at the artificial kidney dialysis unit of a tertiary-care referral center in western India.

INTERVENTION

Earlier-start dialysis was initiated when serum urea nitrogen and/or creatinine levels increased to 70 and 7 mg/dL, respectively, whereas the usual-start dialysis patients (control group) received dialysis when clinically indicated as judged by treating nephrologists.

OUTCOMES

Primary outcome was in-hospital mortality and dialysis dependence at 3 months. Secondary outcome in patients receiving dialysis was time to recovery of kidney function, computed from time of enrollment to the last dialysis session.

RESULTS

Of 585 screened patients, 102 were assigned to earlier-start dialysis, and 106 to usual-start dialysis. Baseline characteristics were similar between randomized groups. 93 (91.1%) and 88 (83.1%) participants received dialysis in the intervention and control groups, respectively. Mean serum urea nitrogen and serum creatinine levels at dialysis therapy initiation were 71.7 ± 21.7 (SD) and 7.4 ± 5.3 mg/dL, respectively, in the intervention group versus 100.9 ± 32.6 and 10.41 ± 3.3 mg/dL in the control group. Data on primary outcome were available for all patients. In-hospital mortality was 20.5% and 12.2% in the intervention and control groups, respectively (relative risk, 1.67; 95% CI, 0.88-3.17; P = 0.2). 4.9% and 4.7% of patients in the intervention and control groups, respectively, were dialysis dependent at 3 months (relative risk, 1.04; 95% CI, 0.29-3.7; P = 0.9).

LIMITATIONS

Study was not double blind, event rate (ie, mortality) was less than predicted, wide CIs preclude definitive findings.

CONCLUSIONS

Our data do not support the earlier initiation of dialysis therapy in community-acquired acute kidney injury.

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.

Fenoldopam use in a burn intensive care unit: a retrospective study

BACKGROUND

Fenoldopam mesylate is a highly selective dopamine-1 receptor agonist approved for the treatment of hypertensive emergencies that may have a role at low doses in preserving renal function in those at high risk for or with acute kidney injury (AKI). There is no data on low-dose fenoldopam in the burn population. The purpose of our study was to describe our use of low-dose fenoldopam (0.03-0.09 mug/kg/min) infusion in critically ill burn patients with AKI.

METHODS

We performed a retrospective analysis of consecutive patients admitted to our burn intensive care unit (BICU) with severe burns from November 2005 through September 2008 who received low-dose fenoldopam. Data obtained included systolic blood pressure, serum creatinine, vasoactive medication use, urine output, and intravenous fluid. Patients on concomitant continuous renal replacement therapy were excluded. Modified inotrope score and vasopressor dependency index were calculated. One-way analysis of variance with repeated measures, Wilcoxson signed rank, and chi-square tests were used. Differences were deemed significant at p < 0.05.

RESULTS

Seventy-seven patients were treated with low-dose fenoldopam out of 758 BICU admissions (10%). Twenty (26%) were AKI network (AKIN) stage 1, 14 (18%) were AKIN stage 2, 42 (55%) were AKIN stage 3, and 1 (1%) was AKIN stage 0. Serum creatinine improved over the first 24 hours and continued to improve through 48 hours (p < 0.05). There was an increase in systolic blood pressure in the first 24 hours that was sustained through 48 hours after initiation of fenoldopam (p < 0.05). Urine output increased after initiation of fenoldopam without an increase in intravenous fluid requirement (p < 0.05; p = NS). Modified inotrope score and vasopressor dependency index both decreased over 48 hours (p < 0.0001; p = 0.0012).

CONCLUSIONS

These findings suggest that renal function was preserved and that urine output improved without a decrease in systolic blood pressure, increase in vasoactive medication use, or an increase in resuscitation requirement in patients treated with low-dose fenoldopam. A randomized controlled trial is required to establish the efficacy of low-dose fenoldopam in critically ill burn patients with AKI.

Recovery from renal ischemia-reperfusion injury is associated with altered renal hemodynamics, blunted pressure natriuresis, and sodium-sensitive hypertension

The present studies evaluated intrarenal hemodynamics, pressure natriuresis, and arterial blood pressure in rats following recovery from renal ischemia-reperfusion (I/R) injury. Acute I/R injury, induced by 40 min of bilateral renal arterial occlusion, resulted in an increase in plasma creatinine that resolved within a week. Following 5 wk of recovery on a 0.4% NaCl diet, the pressure-natriuresis response was assessed in anesthetized rats in which the kidney was denervated and extrarenal hormones were administered intravenously. Increasing renal perfusion pressure (RPP) from 107 to 141 mmHg resulted in a fourfold increase in urine flow and sodium excretion in sham control rats. In comparison, pressure diuresis and natriuresis were significantly attenuated in post-I/R rats. In sham rats, glomerular filtration rate (GFR) averaged 1.6 +/- 0.2 mlxmin(-1)xg kidney weight(-1) and renal blood flow (RBF) averaged 7.8 +/- 0.7 mlxmin(-1)xg kidney weight(-1) at RPP of 129 mmHg. Renal cortical blood flow, measured by laser-Doppler flowmetry, was well autoregulated whereas medullary blood flow and renal interstitial hydrostatic pressure increased directly with elevated RPP in sham rats. In contrast, GFR and RBF were significantly reduced whereas medullary perfusion and interstitial pressure demonstrated an attenuated response to RPP in post-I/R rats. Further experiments demonstrated that conscious I/R rats develop hypertension when sodium intake is increased. The present data indicate that the pressure-natriuretic-diuretic response in I/R rats is blunted because of a decrease in GFR and RBF and the depressed pressure-dependent increase in medullary blood flow and interstitial pressure.

Blood oxygen level-dependent MR imaging of the kidneys

Oxygenation status plays a major role in renal physiology and pathophysiology, and thus has attracted considerable attention in recent years. While much of the early work and a significant amount of present work is based on invasive methods or ex vivo analysis, and is therefore restricted to animal models, blood oxygen level-dependent (BOLD) MR imaging has been shown to extend these findings to human beings. BOLD MR imaging is most useful in monitoring effects of physiologic or pharmacologic maneuvers. Several teams around the world have demonstrated reproducible data and have illustrated several useful applications. Studies supporting the use of renal BOLD MR imaging in characterizing disease with prognostic value have also been reported. This article provides an overview of current state-of-the art of renal BOLD MR imaging.

Arteriolar hyalinization predicts delayed graft function in deceased donor renal transplantation

Delayed renal graft function (DGF) remains a largely unpredictable and burdensome consequence of deceased donor renal transplantation. There is growing evidence that histologic and molecular analyses of baseline donor kidney biopsies can predict both short- and long-term graft outcome. We performed histologic analyses of 172 preimplantation kidney biopsies to determine reliable histologic risk factors for DGF. Fifty-six recipients presented a DGF (incidence 32%). Univariate analysis revealed that arteriolar hyalinization (P=0.019), arterial intima fibrosis (0.004), donor age (P=0.001), duration of cold ischemia time (P=0.001), and recipient age (P=0.001) were significantly associated with DGF. Multivariate analysis revealed that the only independent histologic factor was arteriolar hyalinization (P=0.036). This histologic predictive factor, together with previously identified clinical risk factors, could guide clinical decisions regarding use, allocation, or immunosuppression protocols for minimization of DGF.

Renal hypoxia and dysoxia after reperfusion of the ischemic kidney

Ischemia is the most common cause of acute renal failure. Ischemic-induced renal tissue hypoxia is thought to be a major component in the development of acute renal failure in promoting the initial tubular damage. Renal oxygenation originates from a balance between oxygen supply and consumption. Recent investigations have provided new insights into alterations in oxygenation pathways in the ischemic kidney. These findings have identified a central role of microvascular dysfunction related to an imbalance between vasoconstrictors and vasodilators, endothelial damage and endothelium-leukocyte interactions, leading to decreased renal oxygen supply. Reduced microcirculatory oxygen supply may be associated with altered cellular oxygen consumption (dysoxia), because of mitochondrial dysfunction and activity of alternative oxygen-consuming pathways. Alterations in oxygen utilization and/or supply might therefore contribute to the occurrence of organ dysfunction. This view places oxygen pathways' alterations as a potential central player in the pathogenesis of acute kidney injury. Both in regulation of oxygen supply and consumption, nitric oxide seems to play a pivotal role. Furthermore, recent studies suggest that, following acute ischemic renal injury, persistent tissue hypoxia contributes to the development of chronic renal dysfunction. Adaptative mechanisms to renal hypoxia may be ineffective in more severe cases and lead to the development of chronic renal failure following ischemia-reperfusion. This paper is aimed at reviewing the current insights into oxygen transport pathways, from oxygen supply to oxygen consumption in the kidney and from the adaptation mechanisms to renal hypoxia. Their role in the development of ischemia-induced renal damage and ischemic acute renal failure are discussed.

Renal hypoxia and dysoxia after reperfusion of the ischemic kidney

Ischemia is the most common cause of acute renal failure. Ischemic-induced renal tissue hypoxia is thought to be a major component in the development of acute renal failure in promoting the initial tubular damage. Renal oxygenation originates from a balance between oxygen supply and consumption. Recent investigations have provided new insights into alterations in oxygenation pathways in the ischemic kidney. These findings have identified a central role of microvascular dysfunction related to an imbalance between vasoconstrictors and vasodilators, endothelial damage and endothelium-leukocyte interactions, leading to decreased renal oxygen supply. Reduced microcirculatory oxygen supply may be associated with altered cellular oxygen consumption (dysoxia), because of mitochondrial dysfunction and activity of alternative oxygen-consuming pathways. Alterations in oxygen utilization and/or supply might therefore contribute to the occurrence of organ dysfunction. This view places oxygen pathways' alterations as a potential central player in the pathogenesis of acute kidney injury. Both in regulation of oxygen supply and consumption, nitric oxide seems to play a pivotal role. Furthermore, recent studies suggest that, following acute ischemic renal injury, persistent tissue hypoxia contributes to the development of chronic renal dysfunction. Adaptative mechanisms to renal hypoxia may be ineffective in more severe cases and lead to the development of chronic renal failure following ischemia-reperfusion. This paper is aimed at reviewing the current insights into oxygen transport pathways, from oxygen supply to oxygen consumption in the kidney and from the adaptation mechanisms to renal hypoxia. Their role in the development of ischemia-induced renal damage and ischemic acute renal failure are discussed.

Tubular and glomerular L-arginine transport (uptake and transporters) and the nitric oxide synthases in ischemic acute renal failure (iARF) in streptozotocin-induced diabetic rats (STZ-DM)

BACKGROUND

L-arginine or its metabolites may be important pathogenetic factors in ischemic acute renal failure (iARF) in rats. It was found that the L-arginine-nitric oxide synthase-nitric oxide system plays an important role in the renal hemodynamic alterations in the early stages of diabetes. The iARF in diabetic rats is much more severe than the normal rats exposed to a same ischemia time. The purpose of the present study was to evaluated L-arginine uptake and its transporters and nitric oxide synthase isoform expression in tubuli and glomeruli of STZ-induced diabetic rats with iARF.

METHODS

iARF was induced by right nephrectomy and left renal artery clamping for 60 min followed by a 60 min reflow period. iARF was induced in STZ diabetes rats two weeks after intraperitoneal streptozotocin (60 mg/kg body weight) and in normal control rats. L-arginine uptake, L-arginine transporters (CAT1 and CAT2) and nitric oxide synthases (iNOS, eNOS, and bNOS) were determined by RT-PCR) in both glomeruli and tubuli preparations.

RESULTS

The STZ diabetic rats compared with the non diabetic normal rats have a higher glomerular L-arginine uptake, higher iNOS mRNA, lower eNOS mRNA, and lower tubular CAT1 mRNA, eNOS mRNA, and bNOS mRNA. The diabetic iARF after one hour of reperfusion had lower glomerular L-arginine uptake, lower CAT1 mRNA, lower eNOS mRNA, lower bNOS, and higher tubular iNOS mRNA compared with iARF in normal rats.

CONCLUSIONS

Our findings suggest a prolonged and more severe post-glomerular vasoconstriction very early after the reflow in the iARF of STZ diabetic rats compared with the iARF in the normal control rats. That may be a plausible explanation to the very significant decline in GFR and tubular necrosis that characterize the iARF in diabetic rats.

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.

Continuous renal replacement therapy in the treatment of acute renal failure: critical assessment is required

A continuous approach to renal replacement therapy (CRRT) for critically ill patients was introduced in 1977 and was hailed almost immediately as an improved alternative to intermittent hemodialysis (IHD). Now that CRRT has been in clinical practice for three decades, it is fair to ask whether research-based evidence (rather than expert opinion) supports the use of this complex technology in comparison to IHD. Several randomized clinical trials have compared the outcomes of CRRT and IHD. In one trial, patients assigned to CRRT had a significantly higher intensive-care mortality rate. In other recent trials, there has been no significant difference in outcome. A meta-analysis of observational studies similarly shows no benefit of CRRT versus IHD, with recent trends actually favoring IHD. While considerable attention has been focused on perceived benefits of CRRT compared to IHD, comparatively less attention has been focused on the potential for increased risks. When examining the totality of evidence from recent observational studies and clinical trials, there is no convincing evidence to support superiority of CRRT over IHD in the treatment of critically ill patients with ARF.

Perioperative fluid management in renal transplantation: a narrative review of the literature

Adequate volume maintenance is essential to prevent acute renal failure during major surgery or to ensure graft function after renal transplantation. The various recommendations on the optimum fluid therapy are based, at best, on sparse evidence only from observational studies. This article reviews the literature on perioperative fluid management in renal transplantation. Crystalloid solutions not exerting any specific side-effects are the first choice for volume replacement in kidney transplantation. The use of colloids should be restricted to patients with severe intravascular volume deficits necessitating high volume restoration. The routine application of albumin, dopamine, and high dose diuretics is no longer warranted. Mannitol given immediately before removal of the vessel clamps reduces the requirement of post-transplant dialysis, but has no effects on graft function in the long term. There is insufficient evidence on the best use of dialysis, but it seems peritoneal dialysis pretransplant is associated with less delayed graft function, whereas the preference of dialysis post-transplant is not yet well-founded. This review article should provide better guidance for fluid management in kidney transplantation until best-evidence guidelines can be established based upon more research.

Renal endothelial dysfunction and impaired autoregulation after ischemia-reperfusion injury result from excess nitric oxide

Endothelial dysfunction in ischemic acute renal failure (IARF) has been attributed to both direct endothelial injury and to altered endothelial nitric oxide synthase (eNOS) activity, with either maximal upregulation of eNOS or inhibition of eNOS by excess nitric oxide (NO) derived from iNOS. We investigated renal endothelial dysfunction in kidneys from Sprague-Dawley rats by assessing autoregulation and endothelium-dependent vasorelaxation 24 h after unilateral (U) or bilateral (B) renal artery occlusion for 30 (U30, B30) or 60 min (U60, B60) and in sham-operated controls. Although renal failure was induced in all degrees of ischemia, neither endothelial dysfunction nor altered facilitation of autoregulation by 75 pM angiotensin II was detected in U30, U60, or B30 kidneys. Baseline and angiotensin II-facilitated autoregulation were impaired, methacholine EC(50) was increased, and endothelium-derived hyperpolarizing factor (EDHF) activity was preserved in B60 kidneys. Increasing angiotensin II concentration restored autoregulation and increased renal vascular resistance (RVR) in B60 kidneys; this facilitated autoregulation, and the increase in RVR was abolished by 100 microM furosemide. Autoregulation was enhanced by N(omega)-nitro-l-arginine methyl ester. Peri-ischemic inhibition of inducible NOS ameliorated renal failure but did not prevent endothelial dysfunction or impaired autoregulation. There was no significant structural injury to the afferent arterioles with ischemia. These results suggest that tubuloglomerular feedback is preserved in IARF but that excess NO and probably EDHF produce endothelial dysfunction and antagonize autoregulation. The threshold for injury-producing, detectable endothelial dysfunction was higher than for the loss of glomerular filtration rate. Arteriolar endothelial dysfunction after prolonged IARF is predominantly functional rather than structural.

Opposite effects of pre- and postischemic treatments with nitric oxide donor on ischemia/reperfusion-induced renal injury

We have demonstrated previously that preischemic treatment with FK409 [(+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide], a spontaneous nitric oxide (NO) donor, markedly improves ischemia/reperfusion-induced renal injury. However, there is conflicting information (renoprotective or cytotoxic) as to the contribution of NO to ischemic acute renal failure (ARF). In the present study, we investigated the effect of postischemic treatment with FK409 (1, 3, and 10 mg/kg i.v.) at 6 h after reperfusion on ischemic ARF, in comparison with the preischemic treatment effect. Ischemic ARF was induced by clamping of the left renal artery and vein for 45 min, followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function in ARF rats markedly decreased at 24 h after reperfusion. Histopathological examination of the kidney of ARF rats revealed severe renal damage. In contrast to the renoprotective effect by preischemic treatment, postischemic treatment with FK409 aggravated the ischemia/reperfusion-induced renal dysfunction and histological damage. Immunohistochemical analysis of renal sections obtained from ARF rats revealed positive staining for nitrotyrosine, a biomarker of peroxynitrite formation, in injured tubular cells, and more intense staining was observed in renal tissues from the animals that received postischemic treatment with FK409. On the other hand, the formation of nitrotyrosine, neutrophil infiltration into renal tissues, and renal superoxide production, all of which were enhanced in ARF rats, were efficiently attenuated by the preischemic treatment with FK409. These results demonstrate that, although preischemic treatment with an NO donor is renoprotective, postischemic treatment with the same agent aggravates the ischemia/reperfusion-induced renal injury, probably through peroxynitrite overproduction.

Renal failure secondary to acute tubular necrosis: epidemiology, diagnosis, and management

Acute tubular necrosis (ATN) is a form of acute renal failure (ARF) that is common in hospitalized patients. In critical care units, it accounts for about 76% of cases of ARF. Despite the introduction of hemodialysis > 30 years ago, the mortality rates from ATN in hospitalized and ICU patients are about 37.1% and 78.6%, respectively. The purpose of this review is to discuss briefly the cause, diagnosis, and epidemiology of ARF, and to review in depth the clinical trials performed to date that have examined the influence of growth factors, hormones, antioxidants, diuretics, and dialysis. In particular, the role of the dialysis modality, dialyzer characteristics, and dosing strategies are discussed.

Urinary tract emergencies

A review of common emergencies of the urinary system is presented, with a focus on initial stabilization and treatment. Urethral obstruction, uroperitoneum, and acute renal failure are discussed.

Role of L-arginine in the pathogenesis and treatment of renal disease

L-arginine is a semi essential amino acid and also a substrate for the synthesis of nitric oxide (NO), polyamines, and agmatine. These L-arginine metabolites may participate in the pathogenesis of renal disease and constitute the rationale for manipulating L-arginine metabolism as a strategy to ameliorate kidney disease. Modification of dietary L-arginine intake in experimental models of kidney diseases has been shown to have both beneficial as well as deleterious effects depending on the specific model studied. L-arginine supplementation in animal models of glomerulonephritis has been shown to be detrimental, probably by increasing the production of NO from increased local expression of inducible NO synthase (iNOS). L-arginine supplementation does not modify the course of renal disease in humans with chronic glomerular diseases. However, beneficial effects of L-arginine supplementation have been reported in several models of chronic kidney disease including renal ablation, ureteral obstruction, nephropathy secondary to diabetes, and salt-sensitive hypertension. L-arginine is reduced in preeclampsia and recent experimental studies indicate that L-arginine supplementation may be beneficial in attenuating the symptoms of preeclampsia. Administration of exogenous L-arginine has been shown to be protective in ischemic acute renal failure. In summary, the role of L-arginine in the pathogenesis and treatment of renal disease is not completely understood and remains to be established.

Intrarenal administration of molsidomine, a molecule releasing nitric oxide, reduces renal ischemia-reperfusion injury in rats

Ischemia reperfusion (I-R)-induced renal damage is reduced by systemic administration of the NO-dependent vasodilator molsidomine. The aim of this study was to estimate the effect of direct intrarenal molsidomine administration on renal dysfunction and inflammatory reaction after experimental I-R in rats, in order to assess only renal NO effects and to obviate its systemic hemodynamic action. Ischemia was induced by renal pedicle ligation (60 min) followed by reperfusion and contralateral nephrectomy. Molsidomine (4 mg/kg) was infused into the renal artery 15 min before reperfusion and its effects were compared with those of the NO-independent vasodilator hydralazine (2 mg/kg). Survival rates after 7 days were 100% in the sham-operated group and 75% in the I-R rats. Molsidomine treatment almost completely prevented the I-R-induced renal dysfunction, and survival reached 100%. Molsidomine prevented an I-R-induced increase in superoxide anion and reduced plasma levels of pro-inflammatory cytokines (TNF-alpha, IL-1beta and IFN-gamma), whereas it enhanced anti-inflammatory cytokines (IL-6 and IL-10). Inflammatory cell infiltration and cell-adhesion molecules (ICAM-1, PECAM-1, VCAM-1 and P-selectin) were lower in the molsidomine-treated kidneys than in the untreated animals. All these protective effects were not observed after hydralazine administration. In conclusion, intrarenal administration of molsidomine before reperfusion improved renal function and decreased inflammatory responses after I-R.

Acute renal failure: definitions, diagnosis, pathogenesis, and therapy

Acute renal failure (ARF), characterized by sudden loss of the ability of the kidneys to excrete wastes, concentrate urine, conserve electrolytes, and maintain fluid balance, is a frequent clinical problem, particularly in the intensive care unit, where it is associated with a mortality of between 50% and 80%. In this review, the epidemiology and pathophysiology of ARF are discussed, including the vascular, tubular, and inflammatory perturbations. The clinical evaluation of ARF and implications for potential future therapies to decrease the high mortality are described.

Effect of U-74500A, a 21-aminosteroid on renal ischemia-reperfusion injury in rats

Renal ischemia-reperfusion injury constitutes the most common pathogenic factor for acute renal failure and is the main contributor to renal dysfunction in allograft recipients and revascularization surgeries. Many studies have demonstrated that reactive oxygen species play an important role in ischemic acute renal failure. The aim of the present study was to investigate the effects of the synthetic antioxidant U-74500A, a 21-aminosteroid in a rat model of renal ischemia-reperfusion injury. Renal ischemia-reperfusion was induced by clamping unilateral renal artery for 45 min followed by 24 h of reperfusion. Two doses of U-74500A (4.0 mg/kg, i.v.) were administered 45 min prior to renal artery occlusion and then 15 min prior to reperfusion. Tissue lipid peroxidation was measured as thiobarbituric acid reacting substances (TBARS) in kidney homogenates. Renal function was assessed by estimating serum creatinine, blood urea nitrogen (BUN), creatinine and urea clearance. Renal morphological alterations were assessed by histopathological examination of hematoxylin-eosin stained sections of the kidneys. Ischemia-reperfusion produced elevated levels of TBARS and deteriorated the renal function as assessed by increased serum creatinine, BUN and decreased creatinine and urea clearance as compared to sham operated rats. The ischemic kidneys of rats showed severe hyaline casts, epithelial swelling, proteinaceous debris, tubular necrosis, medullary congestion and hemorrhage. U-74500A markedly attenuated elevated levels of TBARS as well as morphological changes, but did not improve renal dysfunction in rats subjected to renal ischemia-reperfusion. These results clearly demonstrate the in vivo antioxidant effect of U-74500A, a 21-aminosteroid in attenuating renal ischemia-reperfusion injury.

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.