The histopathology of septic acute kidney injury: a systematic review

PGC-1α promotes recovery after acute kidney injury during systemic inflammation in mice

Sepsis-associated acute kidney injury (AKI) is a common and morbid condition that is distinguishable from typical ischemic renal injury by its paucity of tubular cell death. The mechanisms underlying renal dysfunction in individuals with sepsis-associated AKI are therefore less clear. Here we have shown that endotoxemia reduces oxygen delivery to the kidney, without changing tissue oxygen levels, suggesting reduced oxygen consumption by the kidney cells. Tubular mitochondria were swollen, and their function was impaired. Expression profiling showed that oxidative phosphorylation genes were selectively suppressed during sepsis-associated AKI and reactivated when global function was normalized. PPARγ coactivator-1α (PGC-1α), a major regulator of mitochondrial biogenesis and metabolism, not only followed this pattern but was proportionally suppressed with the degree of renal impairment. Furthermore, tubular cells had reduced PGC-1α expression and oxygen consumption in response to TNF-α; however, excess PGC-1α reversed the latter effect. Both global and tubule-specific PGC-1α-knockout mice had normal basal renal function but suffered persistent injury following endotoxemia. Our results demonstrate what we believe to be a novel mechanism for sepsis-associated AKI and suggest that PGC-1α induction may be necessary for recovery from this disorder, identifying a potential new target for future therapeutic studies.

Prevention of post-cardiopulmonary bypass acute kidney injury by endothelin A receptor blockade

OBJECTIVE

The aim of this study was to determine whether administration of a specific endothelin A receptor antagonist, sitaxsentan sodium, would prevent the development of post-cardiopulmonary bypass acute kidney injury in swine.

DESIGN

Experimental study.

SETTING

Cardiovascular Research Institute.

INTERVENTIONS

Adult pigs (n = 8 per group) were randomized to undergo a sham procedure, cardiopulmonary bypass, or cardiopulmonary bypass plus administration of endothelin A receptor antagonist (RA), with recovery and reassessment at 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Cardiopulmonary bypass resulted in a significant reduction in creatinine clearance relative to sham pigs (mean difference for cardiopulmonary bypass vs. sham, -50.3 mL/min [95% confidence interval -89.2 to -11.4 mL/min], p = .008). This was reversed by the administration of endothelin A RA during cardiopulmonary bypass (mean difference for cardiopulmonary bypass + endothelin A RA vs. cardiopulmonary bypass, +43.3 mL/min [95% confidence interval +3.3 to +83.4 mL/min], p = .030). Cardiopulmonary bypass also resulted in a significant rise in the specific urinary biomarker of acute kidney injury interleukin-18 compared to sham procedures (mean difference +209 pg/mL [95% confidence interval +119 to +299 pg/mL], p < .001) that was reversed by endothelin A receptor antagonist administration. Post-cardiopulmonary bypass kidney injury was associated with vascular endothelial injury and dysfunction, reduced nitric oxide bioavailability, inflammation, and a significant increase in the expression of the paracrine vasoconstrictors adenosine and endothelin-1. In post-cardiopulmonary bypass kidneys at 24 hrs there was persistent hypoxia at the level of the outer medulla, cortical adenosine triphosphate depletion, and evidence of proximal tubule epithelial cell stress manifest as phenotypic change. There was no evidence of acute tubular necrosis. Administration of endothelin A RA to cardiopulmonary bypass pigs reversed endothelial dysfunction, regional hypoxia, inflammation, and tubular changes.

CONCLUSION

In this model, post-cardiopulmonary bypass acute kidney injury is associated with endothelial dysfunction, regional tissue hypoxia, and proximal tubular epithelial cell stress but not acute tubular necrosis. Antagonism of the endothelin-1 A receptor reversed these changes and may represent a therapeutic target for the prevention of post-cardiac surgery acute kidney injury.

Acute kidney injury: controversies revisited

This paper addresses the epidemiology of AKI specifically in relation to recent changes in AKI classification and revisits the controversies regarding the timing of initiation of dialysis and the use of peritoneal dialysis as a renal replacement therapy for AKI. In summary, the new RIFLE/AKIN classifications of AKI have facilitated more uniform diagnosis of AKI and clinically significant risk stratification. Regardless, the issue of timing of dialysis initiation still remains unanswered and warrants further examination. Furthermore, peritoneal dialysis as a treatment modality for AKI remains underutilised in spite of potential beneficial effects. Future research should be directed at identifying early reliable biomarkers of AKI, which in conjunction with RIFLE/AKIN classifications of AKI could facilitate well-designed large randomised controlled trials of early versus late initiation of dialysis in AKI. In addition, further studies of peritoneal dialysis in AKI addressing dialysis dose and associated complications are required for this therapy to be accepted more widely by clinicians.

The implications and management of septic acute kidney injury

Sepsis is the most common and severe cause of morbidity and mortality among critically ill patients. Multiple organ dysfunction syndrome often complicates sepsis, leading to a worse prognosis that is proportional to the severity and number of damaged organs. Acute kidney injury (AKI) also complicates sepsis, with a linear relationship between the severity of kidney damage and sepsis prognosis. The management of sepsis and septic AKI involves intensive proactive preventive measures, medical and extracorporeal treatment of established sepsis, support of failing organs and rehabilitation of the residual effects left by this devastating syndrome. Unfortunately, although some innovations in the clinical management of sepsis are now available, their beneficial effects on renal function are still uncertain. The aim of this Review is to provide an update on the current state of interventions in sepsis-related AKI. Prevention, pharmacological support and extracorporeal blood purification for septic AKI will be reviewed and discussed.

Fresh and cryopreserved, uncultured adipose tissue-derived stem and regenerative cells ameliorate ischemia-reperfusion-induced acute kidney injury

Background. Acute kidney injury (AKI) represents a major clinical problem with high mortality and limited causal treatments. The use of cell therapy has been suggested as a potential modality to improve the course and outcome of AKI.

Methods. We investigated the possible renoprotection of freshly isolated, uncultured adipose tissue-derived stem and regenerative cells (ADRCs) before and after cryopreservation in a rat ischemia–reperfusion (I–R) model of AKI.

Results. We demonstrated that ADRC therapy drastically reduced mortality (survival 100% vs. 57%, ADRC vs. controls, respectively) and significantly reduced serum creatinine (sCr on Day 3: 3.03 ± 1.58 vs. 7.37 ± 2.32 mg/dL, ADRC vs. controls, respectively). Histological analysis further validated a significantly reduced intratubular cast formation, ameliorated acute tubular epithelial cell necrosis and mitigated macrophage infiltration. Furthermore, a reduced RNA expression of CXCL2 and IL-6 was found in the ADRC group which could explain the reduced macrophage recruitment. Use of cryopreserved ADRCs resulted in an equally high survival (90% vs. 33% in the control group) and similarly improved renal function (sCr on Day 3: 4.64 ± 2.43 vs. 7.24 ± 1.40 mg/dL in controls).

Conclusions. Collectively, these results suggest a potential clinical role for ADRC therapy in patients with AKI. Importantly, cryopreservation of ADRCs could offer an autologous treatment strategy for patients who are at high risk for AKI during planned interventions.

Histopathology of septic shock induced acute kidney injury: apoptosis and leukocytic infiltration

PURPOSE

Septic shock is one of the leading causes of acute kidney injury. The mechanisms of this injury remain mostly unknown notably because of the lack of data on renal histological lesions in humans.

METHODS

Kidney biopsy was performed immediately post-mortem in consecutive patients who died of septic shock. Comparisons were made with specimens from eight patients who died of trauma on scene and nine ICU patients that died of non-septic causes.

RESULTS

Nineteen septic patients were included, 11 were male, and age was 72 +/- 12 years. Anuria occurred in all patients 2.2 +/- 1.4 days before death. Seven patients had disseminated intravascular coagulation. In all patients we observed (1) acute tubular lesions whose intensity correlated with blood lactate concentration; (2) intense infiltration by leukocytes, mainly monocytic, in glomeruli and interstitial capillaries as compared to controls; (3) presence of tubular cell apoptosis proved by the presence of apoptotic bodies (2.9% of tubular cells) significantly more frequently than in controls and confirmed by TUNEL and activated caspase-3 staining. Arteriolar/arterial thromboses were observed in only 4 of 19 patients, without any association with presence of disseminated intravascular coagulation.

CONCLUSIONS

Kidney lesions in septic shock go beyond those associated with simple acute tubular injury, notably capillary leukocytic infiltration and apoptosis. Vascular thrombosis, however, did not appear to play a major role in the majority of patients. The extent to which these lesions are specific to sepsis or are common to all multi-organ failure independent of its cause is yet to be elucidated. Electronic supplementary material The online version of this article (doi:10.1007/s00134-009-1723-x) contains supplementary material, which is available to authorized users.

[Acute renal failure in critically ill patients]

BACKGROUND

Acute renal failure is common in critically ill patients and is associated with a high mortality rate. This paper reviews current management of patients with acute renal failure admitted to an intensive care unit.

MATERIAL AND METHODS

Literature search in databases (Medline, Cochrane database of systematic reviews, UpToDate).

RESULTS

The prevalence of acute renal failure is 5-20 % in patients admitted to intensive care units; the associated hospital mortality is 30-60 %. The aetiology is usually multifactorial; inflammation (sepsis, surgery), hypovolaemia and drug toxicity commonly precipitate acute renal failure. There is no effective drug treatment, but early onset of renal replacement therapies with haemodialysis or haemofiltration is likely to prolong survival.

INTERPRETATION

Despite modern intensive care, mortality is high in acute renal failure and preventive measures should therefore be vigorously pursued. Haemodialysis and haemofiltration should be introduced early in acute renal failure, and should be available in all intensive care units.

Protective effect of resin adsorption on septic plasma-induced tubular injury

Introduction

A pro-apoptotic effect of circulating mediators on renal tubular epithelial cells has been involved in the pathogenesis of sepsis-associated acute kidney injury (AKI). Adsorption techniques have been showed to efficiently remove inflammatory cytokines from plasma. The aim of this study was to evaluate the efficiency of the hydrophobic resin Amberchrom CG161 M to adsorb from septic plasma soluble mediators involved in tubular injury.

Methods

We enrolled in the study 10 critically ill patients with sepsis-associated AKI and we evaluated the effects of their plasma on granulocyte adhesion, apoptosis and functional alterations of cultured human kidney tubular epithelial cells. We established an in vitro model of plasma adsorption and we studied the protective effect of unselective removal of soluble mediators by the Amberchrom CG161 M resin on septic plasma-induced tubular cell injury.

Results

Plasma from septic patients induced granulocyte adhesion, apoptosis and altered polarity in tubular cells. Plasma adsorption significantly decreased these effects and abated the concentrations of several soluble mediators. The inhibition of granulocyte adhesion to tubular cells was associated with the down-regulation of ICAM-1 and CD40. Resin adsorption inhibited tubular cell apoptosis induced by septic plasma by down-regulating the activation of caspase-3, 8, 9 and of Fas/death receptor-mediated signalling pathways. The alteration of cell polarity, morphogenesis, protein reabsorption and the down-regulation of the tight junction molecule ZO-1, of the sodium transporter NHE3, of the glucose transporter GLUT-2 and of the endocytic receptor megalin all induced by septic plasma were significantly reduced by resin adsorption.

Conclusions

Septic plasma induced a direct injury of tubular cells by favouring granulocyte adhesion, by inducing cell apoptosis and by altering cell polarity and function. All these biological effects are related to the presence of circulating inflammatory mediators that can be efficiently removed by resin adsorption with a consequent limitation of tubular cell injury.

Transient azotaemia is associated with a high risk of death in hospitalized patients

BACKGROUND

There are no suitably powered epidemiological studies of 'transient azotaemia' (TA). The objective of this study was to describe the epidemiology of TA and its independent association with hospital mortality. We hypothesized that TA would be associated with an independent increase in the risk of death.

METHODS

We retrospectively studied all patients admitted to a university-affiliated hospital in Australia between January 2000 and December 2002. Patients were excluded if they were <15 years old, were on chronic dialysis, had kidney transplant or if their length of hospital stay was <24 hours. We defined TA as rapidly recovering acute kidney injury (AKI) (return to no-AKI risk, injury, failure, loss, end stage (RIFLE) class within 72 hours of onset). We performed descriptive and comparative statistical analysis of data. The primary outcome of the study was the association between TA and hospital mortality in multivariate logistic regression analysis.

RESULTS

Among 20 126 study patients, 3641 (18.1%) had AKI according to the RIFLE criteria and 1600 had AKI, which recovered during their hospital stay. Recovery of AKI occurred most commonly within 1 day after diagnosis (37.7%, n = 603). Furthermore, 1172 patients (73.3%) who recovered from AKI did so within 3 days (TA). After correcting for confounding factors, compared with patients without AKI, patients with TA had a significantly higher odds ratio for hospital mortality (2.26; 95% confidence interval: 1.85-2.76).

CONCLUSIONS

Transient azotaemia is common in hospital patients, represents close to a third of all cases of AKI and is independently associated with a significantly higher risk of death.

Fluid balance and acute kidney injury

Intravenous fluids are widely administered to patients who have, or are at risk of, acute kidney injury (AKI). However, deleterious consequences of overzealous fluid therapy are increasingly being recognized. Salt and water overload can predispose to organ dysfunction, impaired wound healing and nosocomial infection, particularly in patients with AKI, in whom fluid challenges are frequent and excretion is impaired. In this Review article, we discuss how interstitial edema can further delay renal recovery and why conservative fluid strategies are now being advocated. Applying these strategies in critical illness is challenging. Although volume resuscitation is needed to restore cardiac output, it often leads to tissue edema, thereby contributing to ongoing organ dysfunction. Conservative strategies of fluid management mandate a switch towards neutral balance and then negative balance once hemodynamic stabilization is achieved. In patients with AKI, this strategy might require renal replacement therapy to be given earlier than when more-liberal fluid management is used. However, hypovolemia and renal hypoperfusion can occur in patients with AKI if excessive fluid removal is pursued with diuretics or extracorporeal therapy. Thus, accurate assessment of fluid status and careful definition of targets are needed at all stages to improve clinical outcomes. A conservative strategy of fluid management was recently tested and found to be effective in a large, randomized, controlled trial in patients with acute lung injury. Similar randomized, controlled studies in patients with AKI now seem justified.

Plasma and urine neutrophil gelatinase-associated lipocalin in septic versus non-septic acute kidney injury in critical illness

OBJECTIVE

Sepsis is the most common trigger for acute kidney injury (AKI) in critically ill patients. We sought to determine whether there are unique patterns to plasma and urine neutrophil gelatinase-associated lipocalin (NGAL) in septic compared with non-septic AKI.

DESIGN

Prospective observational study.

SETTING

Two adult ICUs in Melbourne, Australia.

PATIENTS

Critically ill patients with septic and non-septic AKI.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood and urine specimens collected at enrollment, 12, 24 and 48 h to measure plasma and urine NGAL. Eighty-three patients were enrolled (septic n = 43). Septic AKI patients had more co-morbid disease (p = 0.005), emergency surgical admissions (p < 0.001), higher illness severity (p = 0.008), more organ dysfunction (p = 0.008) and higher white blood cell counts (p = 0.01). There were no differences at enrollment between groups in AKI severity. Septic AKI was associated with significantly higher plasma (293 vs. 166 ng/ml) and urine (204 vs. 39 ng/mg creatinine) NGAL at enrollment compared with non-septic AKI (p < 0.001). Urine NGAL remained higher in septic compared with non-septic AKI at 12 h (p < 0.001) and 24 h (p < 0.001). Plasma NGAL showed fair discrimination for AKI progression (area under receiver-operator characteristic curve 0.71) and renal replacement therapy (AuROC 0.78). Although urine NGAL performed less well (AuROC 0.70, 0.70), peak urine NGAL predicted AKI progression better in non-septic AKI (AuROC 0.82).

CONCLUSION

Septic AKI patients have higher detectable plasma and urine NGAL compared with non-septic AKI patients. These differences in NGAL values in septic AKI may have diagnostic and clinical relevance as well as pathogenetic implications.

Animal models of sepsis and sepsis-induced kidney injury

Sepsis is characterized by a severe inflammatory response to infection, and its complications, including acute kidney injury, can be fatal. Animal models that correctly mimic human disease are extremely valuable because they hasten the development of clinically useful therapeutics. Too often, however, animal models do not properly mimic human disease. In this Review, we outline a bedside-to-bench-to-bedside approach that has resulted in improved animal models for the study of sepsis - a complex disease for which preventive and therapeutic strategies are unfortunately lacking. We also highlight a few of the promising avenues for therapeutic advances and biomarkers for sepsis and sepsis-induced acute kidney injury. Finally, we review how the study of drug targets and biomarkers are affected by and in turn have influenced these evolving animal models.

Renal haemodynamic, microcirculatory, metabolic and histopathological responses to peritonitis-induced septic shock in pigs

Introduction

Our understanding of septic acute kidney injury (AKI) remains incomplete. A fundamental step is the use of animal models designed to meet the criteria of human sepsis. Therefore, we dynamically assessed renal haemodynamic, microvascular and metabolic responses to, and ultrastructural sequelae of, sepsis in a porcine model of faecal peritonitis-induced progressive hyperdynamic sepsis.

Methods

In eight anaesthetised and mechanically ventilated pigs, faecal peritonitis was induced by inoculating autologous faeces. Six sham-operated animals served as time-matched controls. Noradrenaline was administered to maintain mean arterial pressure (MAP) greater than or equal to 65 mmHg. Before and at 12, 18 and 22 hours of peritonitis systemic haemodynamics, total renal (ultrasound Doppler) and cortex microvascular (laser Doppler) blood flow, oxygen transport and renal venous pressure, acid base balance and lactate/pyruvate ratios were measured. Postmortem histological analysis of kidney tissue was performed.

Results

All septic pigs developed hyperdynamic shock with AKI as evidenced by a 30% increase in plasma creatinine levels. Kidney blood flow remained well-preserved and renal vascular resistance did not change either. Renal perfusion pressure significantly decreased in the AKI group as a result of gradually increased renal venous pressure. In parallel with a significant decrease in renal cortex microvascular perfusion, progressive renal venous acidosis and an increase in lactate/pyruvate ratio developed, while renal oxygen consumption remained unchanged. Renal histology revealed only subtle changes without signs of acute tubular necrosis.

Conclusion

The results of this experimental study argue against the concept of renal vasoconstriction and tubular necrosis as physiological and morphological substrates of early septic AKI. Renal venous congestion might be a hidden and clinically unrecognised contributor to the development of kidney dysfunction.

The Effect of Different Diagnostic Criteria on the Prevalence and Incidence of Post-Stroke Dementia

There is little agreement about the prevalence and incidence of vascular dementia (VaD) mainly because investigators have used different diagnostic criteria. The aim of this study was to examine the influence of different diagnostic criteria on the prevalence and cumulative incidence of VaD in first-ever stroke patients (n = 194) clinically evaluated at 1, 6, 12, and 24 months after stroke. Post-stroke VaD was diagnosed using the DSM-III, DSM-III-R, DSM-IV, ICD-10-NA, NINDS-AIREN, and ADDTC criteria. The prevalence of dementia was highest at 1 month; ranging from 11.3% with the NINDS-AIREN to 20.1% with the ICD-10-NA. The incidence was highest at 6 months, ranging from 2.6% with the ADDTC to 5.2% with the ICD-10-NA. Agreement among diagnostic criteria was high, with the exception of the ADDTC. In conclusion, both the prevalence and incidence of dementia are highest directly after stroke, but exact rates are influenced by the diagnostic criteria used.