Role of the renal sympathetic nervous system in mediating renal ischaemic injury-induced reductions in renal haemodynamic and excretory functions

The Role of the Superior Cervical Sympathetic Ganglion in Ischemia Reperfusion-Induced Acute Kidney Injury in Rats

Acute kidney injury (AKI) has been found to be a serious clinical problem with high morbidity and mortality, and is associated with acute inflammatory response and sympathetic activation that subsequently play an important role in the development of AKI. It is well known that the sympathetic nervous system (SNS) and immune system intensely interact and mutually control each other in order to maintain homeostasis in response to stress or injury. Evidence has shown that the superior cervical sympathetic ganglion (SCG) participates in the bidirectional network between the immune and the SNS, and that the superior cervical ganglionectomy has protective effect on myocardial infarction, however, the role of the SCG in the setting of renal ischemic reperfusion injury has not been studied. Here, we sought to determine whether or not the SCG modulates renal ischemic reperfusion (IR) injury in rats. Our results showed that bilateral superior cervical ganglionectomy (SCGx) 14 days before IR injury markedly reduced the norepinephrine (NE) in plasma, and down-regulated the increased expression of tyrosine hydroxylase (TH) in the kidney and hypothalamus. Sympathetic denervation by SCGx in the AKI group increased the level of blood urea nitrogen (BUN) and kidney injury molecule-1 (KIM-1), and exacerbated renal pathological damage. Sympathetic denervation by SCGx in the AKI group enhanced the expression of pro-inflammatory cytokines in plasma, kidney and hypothalamus, and increased levels of Bax in denervated rats with IR injury. In addition, the levels of purinergic receptors, P2X3R and P2X7R, in the spinal cord were up-regulated in the denervated rats of the IR group. In conclusion, these results demonstrate that the sympathetic denervation by SCGx aggravated IR-induced AKI in rats via enhancing the inflammatory response, thus, the activated purinergic signaling in the spinal cord might be the potential mechanism in the aggravated renal injury.

Renal denervation alleviates renal ischemic reperfusion injury-induced acute and chronic kidney injury in rats partly by modulating miRNAs

BACKGROUND

Renal denervation (RDN) has been used to promote kidney injury repair, whereas miRNAs have been found to be involved in the pathophysiology of renal injury. However, the miRNA alterations that occur after RDN and the related protective mechanisms remain to be determined.

METHODS

Renal ischemic reperfusion injury (IRI) rat model was established and RDN was performed. Animals were killed at 24 h and 2 weeks following the operation. Tyrosine hydroxylase (TH) levels, renal function, tubular cell apoptosis and histological sections were examined at 24 h, whereas renal fibrosis and capillary vessels were assessed at 2 weeks. Furthermore, the expression of miRNAs in the injured kidney was determined using micro-array and the target genes were analyzed.

RESULTS

We found that TH was eliminated and that renal function was improved in the denervation group at 24 h. RDN reduced tubular cell apoptosis and mitigated the histological lesion. Furthermore, an increase of capillary vessel density and reduction of renal fibrosis were observed after 2 weeks. Moreover, the numbers of miRNAs were up-regulated after RDN treatment, and the miRNAs targeted pro-angiogenic, anti-fibrotic and inflammatory pathways.

CONCLUSIONS

RDN is a reliable method for alleviating IRI-induced acute and chronic kidney injury, and modulating the miRNA-related pro-angiogenic, anti-fibrotic or inflammatory pathways involved in this process.

Near-drowning: new perspectives for human hypoxic acute kidney injury

Concepts regarding hypoxic acute kidney injury (AKI) are derived from widely used warm ischemia-reflow (WIR) models, characterized by extensive proximal tubular injury and associated with profound inflammation. However, there is ample clinical and experimental data indicating that hypoxic AKI may develop without total cessation of renal blood flow, with a different injury pattern that principally affects medullary thick limbs in the outer medulla. This injury pattern likely reflects an imbalance between blood and oxygen supply and oxygen expenditure, principally for tubular transport. Experimental models of hypoxic AKI other than WIR are based on mismatched oxygen delivery and consumption, particularly within the physiologically hypoxic outer medulla. However, evidence for such circumstances in human AKI is lacking. Recent analysis of the clinical course and laboratory findings of patients following near-drowning (ND) provides a rare glimpse into such a scenario. This observation supports the role of renal hypoxia in the evolution of AKI, as renal impairment could be predicted by the degree of whole-body hypoxia (reflected by lactic acidosis). Furthermore, there was a close association of renal functional impairment with indices of reduced oxygen delivery (respiratory failure and features of intense sympathetic activity) and of enhanced oxygen consumption for active tubular transport (extrapolated from the calculated volume of consumed hypertonic seawater). This unique study in humans supports the concept of renal oxygenation imbalance in hypoxic AKI. The drowning scenario, particularly in seawater, may serve as an archetype of this disorder, resulting from reduced oxygen delivery, combined with intensified oxygen consumption for tubular transport.

The sympathetic nervous system in acute kidney injury

Acute kidney injury (AKI) is frequently accompanied by activation of the sympathetic nervous system (SNS). This may result from pre-exisiting chronic diseases associated with sympathetic activation prior to AKI or it may be induced by stressors that ultimately lead to AKI such as endotoxins and arterial hypotension in circulatory shock. Conversely, sympathetic activation may also result from acute renal injury. Focusing on studies in experimental renal ischaemia and reperfusion (IR), this review summarizes the current knowledge on how the SNS is activated in IR-induced AKI and on the consequences of sympathetic activation for the development of acute renal damage. Experimental studies show beneficial effects of sympathoinhibitory interventions on renal structure and function in response to IR. However, few clinical trials obtained in scenarios that correspond to experimental IR, namely major elective surgery, showed that peri-operative treatment with centrally acting sympatholytics reduced the incidence of AKI. Apparently, discrepant findings on how sympathetic activation influences renal responses to acute IR-induced injury are discussed and future areas of research in this field are identified.

A Clinically Relevant Functional Model of Type-2 Cardio-Renal Syndrome with Paraventricular Changes consequent to Chronic Ischaemic Heart Failure

Cardiorenal syndrome, de novo renal pathology arising secondary to cardiac insufficiency, is clinically recognised but poorly characterised. This study establishes and characterises a valid model representative of Type 2 cardiorenal syndrome. Extensive permanent left ventricular infarction, induced by ligation of the left anterior descending coronary artery in Lewis rats, was confirmed by plasma cardiac troponin I, histology and cardiac haemodynamics. Renal function and morphology was assessed 90-days post-ligation when heart failure had developed. The involvement of the paraventricular nucleus was investigated using markers of inflammation, apoptosis, reactive oxygen species and of angiotensin II involvement. An extensive left ventricular infarct was confirmed following coronary artery ligation, resulting in increased left ventricular weight and compromised left ventricular diastolic function and developed pressure. Glomerular filtration was significantly decreased, fractional excretion of sodium and caspase activities were increased and basement membrane thickening, indicating glomerulosclerosis, was evident. Interestingly, angiotensin II receptor I expression and reactive oxygen species levels in the hypothalamic paraventricular nucleus remained significantly increased at 90-days post-coronary artery ligation, suggesting that these hypothalamic changes may represent a novel, valuable pharmacological target. This model provides conclusive morphological, biochemical and functional evidence of renal injury consequent to heart failure, truly representative of Type-2 cardiorenal syndrome.

Association of Acute Kidney Injury with Cardiovascular Events and Death in Systolic Blood Pressure Intervention Trial

RATIONALE AND OBJECTIVE

In the Systolic Blood Pressure Intervention Trial, the possible relationships between acute kidney injury (AKI) and risk of major cardiovascular events and death are not known.

STUDY DESIGN

Post hoc analysis of a multicenter, randomized, controlled, open-label clinical trial.

SETTING AND PARTICIPANTS

Hypertensive adults without diabetes who were ≥50 years of age with prior cardiovascular disease, chronic kidney disease (CKD), 10-year Framingham risk score > 15%, or age > 75 years were assigned to a systolic blood pressure target of < 120 mm Hg (intensive) or < 140 mm Hg (standard).

PREDICTOR

AKI episodes.

OUTCOMES

The primary outcome was a composite of myocardial infarction, acute coronary syndrome, stroke, decompensated heart failure, or cardiovascular death. The secondary outcome was death from any cause. Analytical Approach: AKI was defined using the Kidney Disease: Improving Global Outcomes modified criteria based solely upon serum creatinine. AKI episodes were identified by serious adverse events or emergency room visits. Cox proportional hazards models assessed the risk for the primary and secondary outcomes by AKI status.

RESULTS

Participants were 68 ± 9 years of age, 36% women (3,332/9,361), and 30% Black race (2,802/9,361), and 17% (1,562/9,361) with cardiovascular disease. Systolic blood pressure was 140 ± 16 mm Hg at study entry. AKI occurred in 4.4% (204/4,678) and 2.6% (120/4,683) in the intensive and standard treatment groups respectively (p < 0.001). Those who experienced AKI had higher risk of cardiovascular events (hazard ratio [HR] 1.52, 95% CI 1.05-2.20, p = 0.026) and death from any cause (HR 2.33, 95% CI 1.56-3.48, p < 0.001) controlling for age, sex, race, baseline systolic blood pressure, body mass index, number of antihypertensive medications, cardiovascular disease and CKD status, hypotensive episodes, and treatment assignment.

LIMITATIONS

The study was not prospectively designed to determine relationships between AKI, cardiovascular events, and death.

CONCLUSIONS

Among older adults with hypertension at high cardiovascular risk, intensive treatment of blood pressure independently increased risk of AKI, which substantially raised risks of major cardiovascular events and death.

Post-treatment with JP-1302 protects against renal ischemia/reperfusion-induced acute kidney injury in rats

Ischemia/reperfusion injury is the most common cause of acute kidney injury. We previously revealed that pre-treatment with yohimbine or JP-1302 attenuated renal ischemia/reperfusion injury by inhibition of α2C-adrenoceptor antagonist. The aim of the present study is to investigate the effects of post-treatment with JP-1302 on renal ischemia/reperfusion injury in rats. Male Sprague Dawley rats were randomly divided into four groups: sham operation, ischemia/reperfusion, pre-treatment with JP-1302 (3.0 mg/kg) and post-treatment with JP-1302 groups. In ischemia/reperfusion injury, renal functional parameters, such as blood urea nitrogen, plasma creatinine and creatinine clearance, deteriorated after reperfusion. Renal venous norepinephrine concentrations, as well as inflammatory molecules in the kidney increased after reperfusion. Both pre- and post-treatment with JP-1302 improved renal dysfunction, tissue damage, renal venous norepinephrine concentrations and inflammatory molecules expression in the kidney. In conclusion, these results suggest that post-treatment with JP-1302 protects on ischemia/reperfusion-induced acute kidney injury by suppressing cytokine upregulation via α2C-adrenoceptors.

Acute Renal Failure Following Near-Drowning

Introduction

Acute kidney injury associated with near-drowning (ND-AKI) has rarely been reported and its incidence among survivors is unknown. A patient with AKI and urine biomarkers indicating tubular injury led us to assess the occurrence and clinical characteristics of ND-AKI and to evaluate possible causative mechanisms.

Methods

We evaluated medical records of patients rescued from near-drowning in the Mediterranean Sea and treated in a tertiary-level medical center during 2000 to 2017.

Results

Ninety-five patients with the diagnosis of near-drowning in seawater were treated. Forty-two of these patients (43%) developed ND-AKI and 17 (18%) were classified as AKI Kidney Disease: Improving Global Outcomes stages 2 to 3. ND-AKI was associated with the need for resuscitation and mechanical ventilation, with the calculated seawater volume ingestion (extrapolated from rising plasma sodium) and with the degree of acidemia, lactemia, and ventilatory failure. This series and 28 additional published cases of ND-AKI in the literature showed an overall male predisposition.

Conclusion

AKI is a common complication of near-drowning and is associated with increased in-hospital mortality. Data analysis suggests a predominant role of hypoxic tubular injury due to systemic hypoxemia in ND-AKI, combined with intense sympathetic activity (reflected by tachyarrhythmias, hyperglycemia, and relative hypokalemia) and increased oxygen expenditure for intensified distal tubular sodium transport. Androgen-related reduced renal vasodilatory capacity may explain male gender predominance.

Differential gene and lncRNA expression in the lower thoracic spinal cord following ischemia/reperfusion-induced acute kidney injury in rats

We used high-throughput RNA sequencing to analyze differential gene and lncRNA expression patterns in the lower thoracic spinal cord during ischemia/reperfusion (I/R)-induced acute kidney injury (AKI) in rats. We observed that of 32662 mRNAs, 4296 out were differentially expressed in the T8-12 segments of the spinal cord upon I/R-induced AKI. Among these, 62 were upregulated and 34 were downregulated in response to I/R (FDR < 0.05, |log₂FC| > 1). Further, 52 differentially expressed lncRNAs (35 upregulated and 17 downregulated) were identified among 3849 lncRNA transcripts. The differentially expressed mRNAs were annotated as “biological process,” “cellular components” and “molecular functions” through gene ontology enrichment analysis. KEGG pathway enrichment analysis showed that cell cycle and renin-angiotensin pathways were upregulated in response to I/R, while protein digestion and absorption, hedgehog, neurotrophin, MAPK, and PI3K-Akt signaling were downregulated. The RNA-seq data was validated by qRT-PCR and western blot analyses of select mRNAs and lncRNAs. We observed that Bax, Caspase-3 and phospho-AKT were upregulated and Bcl-2 was downregulated in the spinal cord in response to renal injury. We also found negative correlations between three lncRNAs (TCONS_00042175, TCONS_00058568 and TCONS_00047728) and the degree of renal injury. These findings provide evidence for differential expression of lncRNAs and mRNAs in the lower thoracic spinal cord following I/R-induced AKI in rats and suggest potential clinical applicability.

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.

High Thoracic Epidural in Cardiac Anesthesia

High thoracic epidural analgesia (HTEA) offers a distinctive opportunity to enhance postoperative recovery for the thoracic surgery patient. In the modern hospital setting with day of admission surgery, the logistics of insertion of the epidural catheter has become increasingly difficult. The greatest limitation to its use might be the believed increased risk of epidural hematoma associated with anticoagulation during cardiopulmonary bypass. The aim of this review is to give an overview of complications and effect on outcomes with focus on cardiac performance and postoperative glycemic control and kidney function. Patients with epidurals may have improved postoperative pulmonary function and shorter ventilation time, while impact on length of stay in the intensive care unit and hospital is not as evident. HTEA is effective in pain management, attenuates perioperative stress and seems to improve postoperative blood glucose control. Whether HTEA improves recovery and facilitates fast-track is still to be confirmed. With regard to serious postoperative complications, there is evidence of reduction in supraventricular arrhythmias and lower frequency of postoperative acute kidney injury and dialysis. There are some indications of lower short term mortality and frequency of postoperative myocardial infarctions, but only as a combined outcome. The present short-term mortality of 1% to 2% should be compared with the most pessimistic frequency of epidural hematoma being 1 in 4600 patients.

Acute kidney injury risk in patients with ST-segment elevation myocardial infarction at presentation to the ED

INTRODUCTION

Acute kidney injury (AKI) is common in acute myocardial infarction (AMI) patients and has serious prognostic implications. The early identification of patients at risk of developing AKI at the emergency department (ED) can reduce its incidence.

METHODS

Patients with ST-segment elevation myocardial infarction (STEMI) at the ED were included. Associated factors playing a role at ED presentation and during hospitalization were collected, and independent risk factors of developing AKI were assessed.

RESULTS

Mean age among patients (n = 406, 69.7% male) was 62.5 ± 12.5 years. At ED admission, the mean glomerular filtration rate (GFR) was 70.5 ± 28.1 mL/min per 1.73 m(2), and 140 (34.5%) patients had a GFR <60 mL/min per 1.73 m(2). Eighty-three patients (20.4%) developed AKI: 47 (11.6%) with stage 1, 26 (6.4%) with stage 2 and 10 (2.5%) with stage 3. Mortality was 11.8% and was higher in patients with AKI (34.9% vs 5.9%, P < .0001). Univariate analysis disclosed age, reduced GFR at presentation, severe Killip class, heart rate and longer door-to-needle time as risk factors to develop AKI. Moreover, these patients received less β-blocker and angiotensin-converting enzyme inhibitor/angiotensin receptor blocker in the ED. Multivariate analysis revealed that age, Killip class, heart rate, door-to-needle time, and β-blocker non-use were independent factors associated with AKI. These factors provided the ED physician with good accuracy in identifying patients at high risk of developing AKI.

CONCLUSION

Factors associated with AKI in STEMI patients allowed physicians to identify patients at high risk in the ED. Moreover, reduced door-to-needle time and β-blocker use were associated with renal protection in AMI patients.

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.

Toward the optimal clinical use of the fraction excretion of solutes in oliguric azotemia

While the fractional excretion of solutes have long been considered excellent research tools to investigate tubular physiology, their clinical use has become common over the last 40 years in the diagnoses of many disorders; however, none have reached the clinical utility of the fractional excretion of sodium in the ability to distinguish pre-renal azotemia from acute tubular necrosis. Nevertheless, there are many drugs and medical conditions that interfere with that utility and recently other solutes, including urea, uric acid and lithium, have been recently investigated to improve the diagnostic ability in clinical situations where the fractional excretion of sodium is known to be unreliable. We review the tubular physiology of these solutes and show how the differences in tubular physiology might be exploited to develop a strategy for their optimal clinical use.

Renal sympathetic nervous system hyperactivity in early streptozotocin-induced diabetic kidney disease

AIM

We assessed the role of renal sympathetic nervous system in the deterioration of renal hemodynamic and excretory functions in rats with streptozotocin (STZ)-induced diabetic kidney disease (DKD).

METHODS

Male Sprague-Dawley (SD) rats were induced with diabetes mellitus (DM) using STZ (55 mg/kg, i.p.). The acute studies were conducted on denervated anesthetized rats 7 days after STZ administration. Two sets of experiments were performed: clearance experiments in which six 20-min urine and plasma collections were carried out to measure kidney function parameters, and hemodynamic experiments in which the renal nerves were electrically stimulated and responses in renal vascular resistance (RVR) and renal blood flow (RBF) were recorded.

RESULTS

Renal denervation in STZ-induced diabetic rats produced higher fractional excretion of sodium (FE(Na) ) but lower plasma sodium (P(Na) ), glomerular filtration rate (GFR), and plasma creatinine (P(Cr) ) (all P<0.05 vs. innervated diabetic rats). In innervated diabetic rats, renal nerve stimulation (RNS) caused significant attenuation in the renal vasoconstrictor responses (all P<0.05 vs. innervated control). Renal denervation in diabetic rats significantly blunted these responses (all P<0.05 vs. innervated diabetic rats); however, they were significantly higher (all P<0.05) while compared to denervated control counterparts.

CONCLUSIONS

The data demonstrate an early role for the renal sympathetic innervation in the pathogenesis of DKD. If the kidney is prevented from renal sympathetic nerve action renal functional parameters are markedly improved. The data further suggest an early enhancement in renal sensitivity to intrarenal norepinephrine (NE) upon the removal of renal sympathetic tone in STZ-induced diabetic rats.