Pathogenesis of Acute Renal Failure

Advances and Challenges on New Therapies and Clinical Targets of Acute Kidney Injury

Acute kidney injury (AKI) is encountered in high-risk hospital settings where patients often suffer systemic illnesses, undergo surgery, or receive medications toxic to the kidneys. It is associated with high morbidity and mortality. Despite advances in understanding the pathophysiologic mechanisms involved in AKI, our ability to detect AKI early is limited, and outcomes remain unchanged. Once AKI is identified by the traditional markers of urine output and serum creatinine, the main therapeutic intervention is usually supportive care and/or renal replacement therapy until renal injury resolves. Urine biomarkers provide an optimistic future, offering the ability to identify patients at high risk for AKI such that preventative measures can be introduced. In this article, the etiologies of AKI are discussed, new biomarkers are assessed, and areas for further investigation are suggested.

Acute and Subchronic Toxicity Study of the Median Septum of Juglans regia in Wistar Rats

Purpose: Median septum of Juglans regia L. (Juglandaceae) with anti-diabetic effects has been used in Iranian traditional medicine. The present study estimates both oral acute and subchronic toxicities. Methods: In the oral acute toxicity study, female Wistar rats were treated with doses of 10, 100, 1000, 1600, 2900 and 5000 mg/ kg of the Juglans regia septum of methanol extract (JRSME), and were monitored for 14 days. In subchronic study, JRSME was administered by gavage at dose of 1000 mg/kg daily in Wistar rats for 28 days. Antioxidant status and biochemical examinations were fulfilled, and the vital organs were subjected to pathological analyses. Results: The extract did not produce any toxic signs or deaths; the medium lethal dose must be higher than 5000 mg/kg. In subchronic study, No significant morphological and histopathological changes were observed in the studied tissues. There was a significant increase in serum malondialdehyde (MDA) level in treated group compared to control after 4 weeks of JRSME intake. The treatment of rats resulted in a significant reduction of serum urea level (p<0.05), kidney's xanthine dehydrogenase (XDH) activity (p<0.001) and elevation of aldehyde oxidase (AO) activity (p<0.05) in kidney. In the treated group, the mean diameter of glomerulus and proximal urine tube epithelium stature was slightly greater than control group. A significant increase in serum MDA level is subject for further studies. Conclusion: This study showed that the extract has no acute or subacute adverse effects with dose of 1000 mg/kg. The administration of JRSME may improve kidney structure and function and help in treatment of some chronic diseases.

Acute kidney injury following cardiac surgery: current understanding and future directions

Acute kidney injury (AKI) complicates recovery from cardiac surgery in up to 30 % of patients, injures and impairs the function of the brain, lungs, and gut, and places patients at a 5-fold increased risk of death during hospitalization. Renal ischemia, reperfusion, inflammation, hemolysis, oxidative stress, cholesterol emboli, and toxins contribute to the development and progression of AKI. Preventive strategies are limited, but current evidence supports maintenance of renal perfusion and intravascular volume while avoiding venous congestion, administration of balanced salt as opposed to high-chloride intravenous fluids, and the avoidance or limitation of cardiopulmonary bypass exposure. AKI that requires renal replacement therapy occurs in 2–5 % of patients following cardiac surgery and is associated with 50 % mortality. For those who recover from renal replacement therapy or even mild AKI, progression to chronic kidney disease in the ensuing months and years is more likely than for those who do not develop AKI. Cardiac surgery continues to be a popular clinical model to evaluate novel therapeutics, off-label use of existing medications, and nonpharmacologic treatments for AKI, since cardiac surgery is fairly common, typically elective, provides a relatively standardized insult, and patients remain hospitalized and monitored following surgery. More efficient and time-sensitive methods to diagnose AKI are imperative to reduce this negative outcome. The discovery and validation of renal damage biomarkers should in time supplant creatinine-based criteria for the clinical diagnosis of AKI.

Deficiency in the Formation of 20-Hydroxyeicosatetraenoic Acid Enhances Renal Ischemia-Reperfusion Injury

Ischemia-reperfusion (IR) injury is the most common cause of AKI. The susceptibility to develop AKI varies widely among patients. However, little is known about the genes involved. 20-Hydroxyeicosatetraenoic acid (20-HETE) has an important role in the regulation of renal tubular and vascular function and has been implicated in IR injury. In this study, we examined whether a deficiency in the renal formation of 20-HETE enhances the susceptibility of Dahl salt-sensitive (SS) rats to ischemic AKI. Transfer of chromosome 5 containing the CYP4A genes responsible for the formation of 20-HETE from the Brown Norway (BN) rat onto the SS genetic background increased renal 20-HETE levels after ischemia and reduced plasma creatinine levels (±SEM) 24 hours after IR from 3.7±0.1 to 2.0±0.2 mg/dl in an SS.5(BN)-consomic strain. Transfer of this chromosome also prevented the secondary decline in medullary blood flow and ischemia that develops 2 hours after IR in the susceptible SS strain. Blockade of the synthesis of 20-HETE with HET0016 reversed the renoprotective effects in SS.5(BN) rats. Similar results were observed in an SS.5(Lew)-congenic strain, in which a smaller region of chromosome 5 containing the CYP4A genes from a Lewis rat was introgressed onto the SS genetic background. These results indicate that 20-HETE has a protective role in renal IR injury by maintaining medullary blood flow and that a genetic deficiency in the formation of 20-HETE increases the susceptibility of SS rats to ischemic AKI.

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.