Predicting acute kidney injury: current status and future challenges

Integrating socio-economic vulnerability factors improves neighborhood-scale wastewater-based epidemiology for public health applications

Wastewater Based Epidemiology (WBE) of COVID-19 is a low-cost, non-invasive, and inclusive early warning tool for disease spread. Previously studied WBE focused on sampling at wastewater treatment plant scale, limiting the level at which demographic and geographic variations in disease dynamics can be incorporated into the analysis of certain neighborhoods. This study demonstrates the integration of demographic mapping to improve the WBE of COVID-19 and associated post-COVID disease prediction (here kidney disease) at the neighborhood level using machine learning. WBE was conducted at six neighborhoods in Seattle during October 2020 - February 2022. Wastewater processing and RT-qPCR were performed to obtain SARS-CoV-2 RNA concentration. Census data, clinical data of COVID-19, as well as patient data of acute kidney injury (AKI) cases reported during the study period were collected and the distribution across the city was studied using Geographic Information System (GIS) mapping. Further, we analyzed the data set to better understand socioeconomic impacts on disease prevalence of COVID-19 and AKI per neighborhood. The heterogeneity of eleven demographic factors (such as education and age among others) was observed within neighborhoods across the city of Seattle. Dynamics of COVID-19 clinical cases and wastewater SARS-CoV-2 varied across neighborhood with different levels of demographics. Machine learning models trained with data from the earlier stages of the pandemic were able to predict both COVID-19 and AKI incidence in the later stages of the pandemic (Spearman correlation coefficient of 0·546 - 0·904), with the most predictive model trained on the combination of wastewater data and demographics. The integration of demographics strengthened machine learning models' capabilities to predict prevalence of COVID-19, and of AKI as a marker for post-COVID sequelae. Demographic-based WBE presents an effective tool to monitor and manage public health beyond COVID-19 at the neighborhood level.

Review of the limitations of current biomarkers in acute kidney injury clinical practices

Acute kidney injury is a prevalent disease in hospitalized patients and is continuously increasing worldwide. Various efforts have been made to define and classify acute kidney injury to understand the progression of this disease. Furthermore, deviations from structure and kidney function and the current diagnostic guidelines are not adequately placed due to baseline serum creatinine values, which are rarely known and estimated based on glomerular function rate, resulting in misclassification of acute kidney injury staging. Hence, the current guidelines are still developing to improve and understand the clinical implications of risk factors and earlier predictive biomarkers of acute kidney injury. Yet, studies have indicated disadvantages and limitations with the current acute kidney injury biomarkers, including lack of sensitivity and specificity. Therefore, the present narrative review brings together the most current evidenced-based practice and literature associated with the limitations of the gold standard for acute kidney injury diagnoses, the need for novel acute kidney injury biomarkers, and the process for biomarkers to be qualified for diagnostic use under the following sections and themes. The introduction section situates the anatomy and normal and abnormal kidney functions related to acute kidney injury disorders. Guidelines in providing acute kidney injury definitions and classification are then considered, followed by a discussion of the disadvantages of standard markers used to diagnose acute kidney injury. Characteristics of an ideal acute kidney injury biomarker are discussed concerning sensitivity, specificity, and anatomic location of injury. A particular focus on the role and function of emerging biomarkers is discussed in relation to their applications and significance to the prognosis and severity of acute kidney injury. Findings show emerging markers are early indicators of acute kidney injury prediction in different clinical settings. Finally, the process required for a biomarker to be applied for diagnostic use is explained.

Continuous Risk Estimation of Acute Kidney Failure with Dense Temporal Data for ICU Patients

Acute kidney failure is a dangerous complication for ICU patients, and it is difficult to identify at early stage with conventional medical analysis. In recent years, machine learning approaches have been applied to tackle medical diagnosis tasks with great performance. In this work, we deploy machine learning models for early detection of acute kidney failure that can handle static, temporal, sparse and dense data of ICU patients. We investigate different pre-processing methods for patient data to achieve higher prediction performance and how they influence the contribution of different physiological signals in the prediction process.

Extracellular vesicles: Emerged as a promising strategy for regenerative medicine

Cell transplantation therapy has certain limitations including immune rejection and limited cell viability, which seriously hinder the transformation of stem cell-based tissue regeneration into clinical practice. Extracellular vesicles (EVs) not only possess the advantages of its derived cells, but also can avoid the risks of cell transplantation. EVs are intelligent and controllable biomaterials that can participate in a variety of physiological and pathological activities, tissue repair and regeneration by transmitting a variety of biological signals, showing great potential in cell-free tissue regeneration. In this review, we summarized the origins and characteristics of EVs, introduced the pivotal role of EVs in diverse tissues regeneration, discussed the underlying mechanisms, prospects, and challenges of EVs. We also pointed out the problems that need to be solved, application directions, and prospects of EVs in the future and shed new light on the novel cell-free strategy for using EVs in the field of regenerative medicine.

Gray level co-occurrence matrix and wavelet analyses reveal discrete changes in proximal tubule cell nuclei after mild acute kidney injury

Acute kidney injury (AKI) relates to an abrupt reduction in renal function resulting from numerous conditions. Morbidity, mortality, and treatment costs related to AKI are relatively high. This condition is strongly associated with damage to proximal tubule cells (PTCs), generating distinct patterns of transcriptional and epigenetic alterations that result in structural changes in the nuclei of this epithelium. To this date, AKI-related nuclear chromatin redistribution in PTCs is poorly understood, and it is unclear whether changes in PTC chromatin patterns can be detected using conventional microscopy during mild AKI, which can progress to more debilitating forms of injury. In recent years, gray level co-occurrence matrix (GLCM) analysis and discrete wavelet transform (DWT) have emerged as potentially valuable methods for identifying discrete structural changes in nuclear chromatin architecture that are not visible during the conventional histopathological exam. Here we present findings indicating that GLCM and DWT methods can be successfully used in nephrology to detect subtle nuclear morphological alterations associated with mild tissue injury demonstrated in rodents by inducing a mild form of AKI through ischemia-reperfusion injury. Our results show that mild ischemic AKI is associated with the reduction of local textural homogeneity of PTC nuclei quantified by GLCM and the increase of nuclear structural heterogeneity indirectly assessed with DWT energy coefficients. This rodent model allowed us to show that mild ischemic AKI is associated with the significant reduction of textural homogeneity of PTC nuclei, indirectly assessed by GLCM indicators and DWT energy coefficients.

Urine metabolites for preoperative prediction of acute kidney injury after coronary artery bypass graft surgery

OBJECTIVE

Acute kidney injury is a common complication after on-pump coronary artery bypass grafting. Prediction of acute kidney injury remains a challenge. Our study aims to identify a panel of urine metabolites for preoperative warning of acute kidney injury after on-pump coronary artery bypass grafting.

METHODS

A total of 159 patients undergoing isolated on-pump coronary artery bypass grafting were enrolled from July 7, 2017, to May 17, 2019. Preoperative urine samples were analyzed with the approach of liquid chromatography-mass spectrometry-based urine metabolomics. The study end point was the episode of acute kidney injury within 48 hours postoperatively. The predictive performance was determined by the area under the curve and calibration curve. The results were validated using bootstrap resampling.

RESULTS

The acute kidney injury (n = 55) and nonacute kidney injury (n = 104) groups showed significant different metabolic profiling. A total of 28 metabolites showed significant differences between the acute kidney injury and nonacute kidney injury groups. A metabolite panel of 5 metabolites (tyrosyl-gamma-glutamate, deoxycholic acid glycine conjugate, 5-acetylamino-6-amino-3-methyluracil, arginyl-arginine, and L-methionine) was discovered to have a good predicting performance (area under the curve, 0.89; 95% confidence interval, 0.82-0.93), which is higher than the clinical factor-based model (area under the curve, 0.63; 95% confidence interval, 0.53-0.72). Internal validation by bootstrap resampling showed an adjusted area under the curve of 0.88, and the calibration curve demonstrated good agreement between prediction and observation in the probability of postoperative acute kidney injury. Decision curve analysis revealed a superior net benefit of the metabolite model over the traditional clinical factor-based model.

CONCLUSIONS

We present 5 urine metabolites related to acute kidney injury after coronary artery bypass grafting. This metabolite model may serve as a preoperative warning of acute kidney injury after on-pump coronary artery bypass grafting.

Machine learning models for predicting acute kidney injury: a systematic review and critical appraisal

BACKGROUND

The number of studies applying machine learning (ML) to predict acute kidney injury (AKI) has grown steadily over the past decade. We assess and critically appraise the state of the art in ML models for AKI prediction, considering performance, methodological soundness, and applicability.

METHODS

We searched PubMed and ArXiv, extracted data, and critically appraised studies based on the Transparent Reporting of a Multivariable Prediction Model for Individual Prognosis or Diagnosis (TRIPOD), Checklist for Critical Appraisal and Data Extraction for Systematic Reviews of Prediction Modelling Studies (CHARMS), and Prediction Model Risk of Bias Assessment Tool (PROBAST) guidelines.

RESULTS

Forty-six studies from 3166 titles were included. Thirty-eight studies developed a model, five developed and externally validated one, and three studies externally validated one. Flexible ML methods were used more often than deep learning, although the latter was common with temporal variables and text as predictors. Predictive performance showed an area under receiver operating curves ranging from 0.49 to 0.99. Our critical appraisal identified a high risk of bias in 39 studies. Some studies lacked internal validation, whereas external validation and interpretability of results were rarely considered. Fifteen studies focused on AKI prediction in the intensive care setting, and the US-derived Medical Information Mart for Intensive Care (MIMIC) data set was commonly used. Reproducibility was limited as data and code were usually unavailable.

CONCLUSIONS

Flexible ML methods are popular for the prediction of AKI, although more complex models based on deep learning are emerging. Our critical appraisal identified a high risk of bias in most models: Studies should use calibration measures and external validation more often, improve model interpretability, and share data and code to improve reproducibility.

Acute kidney injury defined by cystatin C may be superior for predicting the outcomes of liver cirrhosis with acute gastrointestinal bleeding

BACKGROUND & AIMS

Acute kidney injury (AKI) is conventionally evaluated by a dynamic change of serum creatinine (Scr). Cystatin C (CysC) seems to be a more accurate biomarker for assessing kidney function. This retrospective multicenter study aims to evaluate whether AKI re-defined by CysC can predict the in-hospital outcomes of patients with liver cirrhosis and acute gastrointestinal bleeding.

METHODS

Overall, 677 cirrhotic patients with acute gastrointestinal bleeding, in whom both Scr and CysC levels were detected at admissions, were screened. eGFR_Scr, eGFR_CysC, and eGFR_Scr-CysC were calculated. MELD-Na score and AKI were re-evaluated by CysC instead of Scr. Odds ratios (ORs) were calculated in the logistic regression analyses. The receiver operating characteristic (ROC) curve analyses were performed.

RESULTS

Univariate logistic regression analyses demonstrated that baseline Scr and CysC levels, eGFR_Scr, eGFR_CysC, eGFR_Scr-CysC, original MELD-Na score defined by Scr, MELD-Na score re-defined by CysC, and AKI re-defined by CysC, but not conventional AKI defined by Scr, were significantly associated with in-hospital death. ROC analyses showed that baseline CysC level, eGFR_Scr, eGFR_CysC, eGFR_Scr-CysC, original MELD-Na score defined by Scr, and MELD-Na score re-defined by CysC, but not baseline Scr level, could significantly predict the risk of in-hospital death.

CONCLUSIONS

AKI re-defined by CysC may be superior for predicting the in-hospital mortality of cirrhotic patients with acute gastrointestinal bleeding.

The rate of acute kidney injury (AKI) alert detection by the attending physicians was associated with the prognosis of patients with AKI

Introduction

Early identification of AKI was always considered to improve patients' prognosis. Some studies found that AKI early warning tools didn't affect patients' prognosis. Therefore, additional studies were necessary to explore the reasons.

Methods

This study was a secondary analysis of a multicenter randomized controlled trial that found electronic health record warnings for AKI did not influence patients' prognoses. Univariate, multivariate, subgroup, curve fitting, and threshold effect analysis were used to explore the association between AKI warnings detected by attending physicians and the patient's prognosis.

Results

A total of 6,030 AKI patients were included in the study. The patients were classified into two groups based on the rate of AKI alerts detected by attending physicians: the partial group (n = 5,377), and the complete group (n = 653). In comparison to the partial group, the complete group significantly decreased 14-day AKI progression, 14-day dialysis, and 14-day mortality, with adjusted ORs of 0.48 (0.33, 0.70), 0.26 (0.09, 0.77), and 0.53 (0.33, 0.84) respectively, and the complete group significantly improve the discharge to home, with an OR value of 1.50 (1.21, 1.87). When the rate of AKI alerts detected by the attending physicians as a continuity variable, we found that the rate of alerts seen by attending physicians was associated with 14-day mortality and the discharge to home, with adjusted ORs of 1.76 (1.11, 2.81) and 1.42 (1.13, 1.80). The sensitivity analysis, curve-fitting analysis, and threshold effect analysis also showed that the rate of alert seen by the attending physician was correlated with the patient's prognosis.

Conclusion

The rate of AKI alert detection by attending physician were related to the patient's prognosis. The higher the rate of AKI alert detection by attending physicians, the better the prognosis of patients with AKI.

Features of Kidney Function in Patients With Comorbidity of Arterial Hypertension and Chronic Obstructive Pulmonary Disease

Background and objective Chronic kidney disease (CKD) and hypertension are closely linked in terms of cause and effect. Decreased renal function is usually associated with increased blood pressure, and a steady increase in blood pressure accelerates the decline in renal function. In this study, we aimed to investigate laboratory parameters of renal function - blood creatinine level, urine creatinine level, urea blood level, urine albumin level, and in particular, serum cystatin C level - as early predictors of kidney damage and assess the filtration function of the kidneys based on the glomerular filtration rate (GFR) in patients with isolated arterial hypertension, those with a comorbid pathology of hypertension and chronic obstructive pulmonary disease (COPD). and those with isolated COPD. Materials and methods The study included a total of 101 patients (the final sample consisted of 88 patients) with hypertension and COPD, who were divided into three groups: Group I consisted of 38 patients with hypertension, Group II comprised 27 patients with hypertension and COPD, and Group III was made up of 23 patients with COPD. The average age of patients in groups - presented as mean [standard deviation (SD)] - was as follows - Group I: 55.7 (11.2) years, Group II: 59.3 (9.2) years, and Group III: 57.8 (9.1) years. For statistical data processing, the program Statistics 10 was used. Results The level of blood creatinine - presented as median (Me) and interquartile range (IQR) - was statistically significantly different between the groups, and the values in the three groups were as follows - Group I (patients with hypertension): 88.3 (84.2; 102.7) μmol/l, Group II (patients with comorbid pathology of arterial hypertension and COPD): 99.0 (80.0; 115.0) μmol/l, and Group III (patients with COPD): 84.6 (75.0; 94.2) μmol/l (p=0.008). The highest level was determined in patients with hypertension and comorbid COPD, while the lowest was in the comparison group, in patients with COPD. Urinary creatinine levels were as follows - Group I: 1081.0 (578.0; 1749.0) mg/l, Group II: 1318.5 (1124.0; 1817.0) mg/l, and Group III: 822.0 (625.0; 1320.5) mg/l (p=0.08). Blood urea values were as follows - Group I: 5.7 (5.2; 6.0) mmol/l, Group II: 5.7 (4.9; 6.6) mmol/l, Group III: 5.9 (4.4; 7.7) mmol/l. The calculation of GFR revealed a statistically significant difference between the three groups - Group I: 70.5 (56.0; 83.0) ml/min, Group II: 66.5 (57.0; 77.0) ml/min, and Group III: 81.5 (70.0; 88.0) ml/min (p=0.02). The cystatin C level was 1.16 (1.03; 1.27) mg/l in Group I, 1.3 (1.22; 1.38) mg/l in Group II, and 1.05 (0.96; 1.05) mg/l in Group III. Conclusions In patients of all three groups, there was a decrease in renal filtration function based on the results of creatinine and cystatin C levels. Even in the group of patients with COPD without kidney disease, a decrease in GFR was observed. We noted a negative aggravating effect of COPD on renal function in patients with hypertension, which can be attributed to increased endothelial dysfunction and increased general inflammation in this group of patients.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Therapeutic Use and in Bioengineering Applications

Extracellular vesicles (EVs) are small lipid bilayer-delimited particles that are naturally released from cells into body fluids, and therefore can travel and convey regulatory functions in the distal parts of the body. EVs can transmit paracrine signaling by carrying over cytokines, chemokines, growth factors, interleukins (ILs), transcription factors, and nucleic acids such as DNA, mRNAs, microRNAs, piRNAs, lncRNAs, sn/snoRNAs, mtRNAs and circRNAs; these EVs travel to predecided destinations to perform their functions. While mesenchymal stem cells (MSCs) have been shown to improve healing and facilitate treatments of various diseases, the allogenic use of these cells is often accompanied by serious adverse effects after transplantation. MSC-produced EVs are less immunogenic and can serve as an alternative to cellular therapies by transmitting signaling or delivering biomaterials to diseased areas of the body. This review article is focused on understanding the properties of EVs derived from different types of MSCs and MSC-EV-based therapeutic options. The potential of modern technologies such as 3D bioprinting to advance EV-based therapies is also discussed.

Insights into the protective capacity of human dental pulp stem cells and its secretome in cisplatin-induced nephrotoxicity: effects on oxidative stress and histological changes

OBJECTIVES

Acute renal injury (AKI) is a major limiting factor for cisplatin administration. Recent evidence suggests the potential contribution of mesenchymal stem cells (MSCs) to rehabilitation from several disorders via both direct and indirect routes. Thus, the present study aimed, for the first time, to explore and compare the reno-protective potential of human dental pulp-derived stem cells (hDPSCs) vs. hDPSC-conditioned medium (hDPSC-CM) in recovery of impaired kidney tissues in a rat animal model of cisplatin-induced AKI.

METHODS

AKI was induced via cisplatin injection (n=36). One day after, 24 rats were treated with either hDPSCs or hDPSC-CM (n=12). An extra set of rats (n=12) served as sham group. On days 2 or 7 (n=6), rats were humanly sacrificed for further analysis. Renal injury was explored via measuring serum creatinine and BUN. Renal level of oxidative stress was assessed by determining malondialdehyde, and enzymatic activities of superoxide dismutase and catalase. Renal histopathological changes were scored for comparison among different experimental groups.

RESULTS

A single dose of cisplatin resulted in considerable renal dysfunction and oxidative stress. Treatment with hDPSCs or hDPSC-CM resulted in significantly restored renal function, reduced level of oxidative stress, and improved histopathological manifestations. Furthermore, as compared to hDPSC-CM, administration of hDPSCs led to superior results in AKI-induced animals.

CONCLUSIONS

The current study described the first comparative evidence of reno-protective potential of hDPSCs and their CM against cisplatin-induced nephrotoxicity in an AKI rat model, proposing them as useful adjunctive therapy in AKI. Yet, future explorations are still needed.

Extracellular DNA concentrations in various aetiologies of acute kidney injury

Extracellular DNA (ecDNA) in plasma is a non-specific biomarker of tissue damage. Urinary ecDNA, especially of mitochondrial origin, is a potential non-invasive biomarker of kidney damage. Despite prominent tissue damage, ecDNA has not yet been comprehensively analysed in acute kidney injury (AKI). We analysed different fractions of ecDNA, i.e. total, nuclear and mitochondrial, in plasma and urine of children, and different animal models of AKI. We also analysed the activity of the deoxyribonuclease (DNase), which is contributes to the degradation of ecDNA. Patients with AKI had higher total and nuclear ecDNA in both, plasma and urine (sixfold and 12-fold in plasma, and 800-fold in urine, respectively), with no difference in mitochondrial ecDNA. This was mainly found for patients with AKI due to tubulointerstitial nephritis and atypical haemolytic uremic syndrome. Increased plasma ecDNA was also found in animal models of AKI, including adenine nephropathy (fivefold), haemolytic uremic syndrome (fourfold), and ischemia–reperfusion injury (1.5-fold). Total urinary ecDNA was higher in adenine nephropathy and ischemia–reperfusion injury (1300-fold and twofold, respectively). DNase activity in urine was significantly lower in all animal models of AKI in comparison to controls. In conclusion, plasma total and nuclear ecDNA and urinary total ecDNA is increased in patients and animals with particular entities of AKI, suggesting a mechanism-dependent release of ecDNA during AKI. Further studies should focus on the dynamics of ecDNA and its potential role in the pathogenesis of AKI.

Advances in the study of subclinical AKI biomarkers

Acute kidney injury (AKI) is a prevalent and serious illness in all clinical departments, with a high morbidity and death rate, particularly in intensive care units, where prevention and treatment are crucial. As a result, active prevention, early detection, and timely intervention for acute kidney injury are critical. The current diagnostic criteria for acute kidney injury are an increase in serum creatinine concentration and/or a decrease in urine output, although creatinine and urine output merely reflect changes in kidney function, and AKI suggests injury or damage, but not necessarily dysfunction. The human kidney plays a crucial functional reserve role, and dysfunction is only visible when more than half of the renal mass is impaired. Tubular damage markers can be used to detect AKI before filtration function is lost, and new biomarkers have shown a new subset of AKI patients known as “subclinical AKI.” Furthermore, creatinine and urine volume are only marginally effective for detecting subclinical AKI. As a result, the search for new biomarkers not only identifies deterioration of renal function but also allows for the early detection of structural kidney damage. Several biomarkers have been identified and validated. This study discusses some of the most promising novel biomarkers of AKI, including CysC, NGAL, KIM-1, lL-18, L-FABP, IGFBP7, TIMP-2, Clusterin, and Penkid. We examine their performance in the diagnosis of subclinical AKI, limitations, and future clinical practice directions.

Development and validation of AKI prediction model in postoperative critically ill patients: a multicenter cohort study

BACKGROUND

Acute kidney injury (AKI) is a common complication, especially among postoperative critically ill patients. Early identification of AKI is essential for reducing mortality.

METHODS

Multicenter data were used to develop an AKI prediction model for critically ill postoperative patients. A total of 1731 patients admitted to intensive care units (ICUs) were divided into a development set (n=1196) and a validation set (n=535) according to the principle of 7:3 randomization. Multivariate logistic regression analysis was performed on the predictors identified by univariate analysis, and a nomogram was created based on the predictors. The area under the receiver operating characteristic curve (AUROC) was used to assess the discrimination of the model. Calibration curves were generated, and the Hosmer-Lemeshow (HL) goodness of fit test was carried out. Decision curve analysis (DCA) was performed to assess the net clinical benefit.

RESULTS

The final model included 7 predictors: age, emergency surgery, abnormal basal creatinine level (BCr), chronic kidney disease (CKD), use of nephrotoxic drugs, diuretic use, and the Sequential Organ Failure Assessment (SOFA) score. A nomogram was drawn based on the predictors. The AUROC of the model in the development set was 0.725 (95% confidence interval (CI): 0.696-0.754). In the validation set, the AUROC was 0.706 (95% CI: 0.656-0.744). The model showed good discrimination (>70%) in both sets, and the HL test indicated that the model fit was good (P>0.05). DCA showed that our model is clinically useful.

CONCLUSION

The novel prediction model can be used to identify high-risk postoperative patients and provide a scientific and effective basis for clinicians to identify AKI early with a nomogram.

Biomarkers of acute kidney injury after pediatric cardiac surgery: a meta-analysis of diagnostic test accuracy

Acute kidney injury (AKI) occurs frequently after cardiac surgery in children. Although current diagnostic criteria rely on serum creatinine and urine output, changes occur only after considerable loss of kidney function. This meta-analysis aimed to synthesize the knowledge on novel biomarkers and compare their ability to predict AKI. PubMed/MEDLINE, Embase, Scopus, and reference lists were searched for relevant studies published by March 2021. Diagnostic accuracy parameters were extracted and analyzed using hierarchical summary receiver operating characteristic (HSROC) method. Pooled estimates of the area under the curve (AUC) were calculated using conventional random-effects meta-analysis. Fifty-six articles investigating 49 biomarkers in 8617 participants fulfilled our eligibility criteria. Data from 37 studies were available for meta-analysis. Of the 10 biomarkers suitable for HSROC analysis, urinary neutrophil gelatinase-associated lipocalin (uNGAL) to creatinine (Cr) ratio yielded the highest diagnostic odds ratio (91.0, 95% CI 90.1-91.9), with a sensitivity of 91.3% (95% CI 91.2-91.3%) and a specificity of 89.7% (95% CI 89.6-89.7%). These results were confirmed in pooled AUC analysis, as uNGAL-to-Cr ratio and uNGAL were the only elaborately studied biomarkers (> 5 observations) with pooled AUCs ≥ 0.800. Liver fatty acid-binding protein (L-FABP), serum cystatin C (sCysC), serum NGAL (sNGAL), and interleukin-18 (IL-18) all had AUCs ≥ 0.700.

CONCLUSION

A variety of biomarkers have been proposed as predictors of cardiac surgery-associated AKI in children, of which uNGAL was the most prominent with excellent diagnostic qualities. However, more consolidatory evidence will be required before these novel biomarkers may eventually help realize precision medicine in AKI management.

WHAT IS KNOWN

• Acute kidney injury (AKI) occurs in about 30-60% of children undergoing cardiac surgery and is associated with increased in-hospital mortality and adverse short-term outcomes. However, in current clinical practice, AKI definitions and detection often rely on changes in serum creatinine and urine output, which are late and insensitive markers of kidney injury. • Although various novel biomarkers have been studied for the diagnosis of AKI in children after cardiac surgery, it remains unclear how these compare to one another in terms of diagnostic accuracy.

WHAT IS NEW

• Pooled analyses suggest that for the diagnosis of AKI in children who underwent cardiac surgery, NGAL is the most accurate among the most frequently studied biomarkers. • A number of other promising biomarkers have been reported, although they will require further research into their diagnostic accuracy and clinical applicability.

Time for Precision Medicine in the Diagnosis of Acute Kidney Injury

How to cite this article: Ali U. Time for Precision Medicine in the Diagnosis of Acute Kidney Injury. Indian J Crit Care Med 2022;26(5):547–548.

Circulating Lipocalin-2 level is positively associated with cognitive impairment in patients with metabolic syndrome

The association between Lipocalin-2 (LCN2) and cognition in patients with metabolic syndrome (MetS) has not been thoroughly investigated. We aimed to evaluate whether serum LCN2 levels are associated with the alteration of cognitive function in patients with MetS. The total of 191 non-demented participants with MetS were enrolled onto the study in 2015, and a cohort study was conducted in a subpopulation in 2020. After adjustment for sex, age, waist circumference, creatinine levels, and HbA1C, an association between the higher serum LCN2 levels and the lower Montreal cognitive assessment (MoCA) scores was observed (B = − 0.045; 95%CI − 0.087, − 0.004; p 0.030). A total of 30 participants were followed-up in 2020. Serum LCN2 levels were decreased in correlation with age (23.31 ± 12.32 ng/ml in 2015 and 15.98 ± 11.28 ng/ml in 2020, p 0.024), while other metabolic parameters were unchanged. Magnetic resonance imaging studies were conducted on a subsample of patients in 2020 (n = 15). Associations between high serum LCN2 levels from 2015 and 2020 and changes in brain volume of hippocampus and prefrontal cortex from 2020 have been observed. These findings suggest a relationship between changes of the level of circulating LCN2, cognitive impairment, and changes in brain volume in patients with MetS. However, further investigation is still needed to explore the direct effect of circulating LCN2 on the cognition of MetS patients.

Renal Outcomes of Pregnancy-Related Acute Kidney Injury: a Single Centre Experience in India

Objective:This study aimed to investigate the incidence, clinical characteristics, and outcomes of acute kidney injury (AKI) during pregnancy in Indian population. Materials and methods:A prospective observational study was conducted in pregnant patients admitted to Pt. B.D. Sharma PGIMS, Rohtak, Haryana, India. Acute kidney injury was assessed using Risk, Injury, Failure, Loss of function, and End-stage renal disease (RIFLE) criteria. Patients were analyzed on the basis of demographic data, detailed history, clinical examination, and laboratory investigations. The primary outcome was maternal renal outcome, including return to normal renal function and progression to chronic kidney disease (CKD). The secondary outcomes included the mode of delivery, complications of pregnancy, intensive care unit (ICU) admission, and maternal death. Results:A total of 51 patients with an average age of 29.5 years were included in the present study. About 49.9% of subjects had severe anemia and 41.2% were primigravida. The main cause of AKI was pre-eclampsia and postpartum hemorrhage. There was a marked improvement in renal outcome with 33 patients having complete renal recovery and six patients developed CKD was observed during three months follow-up period. The peaked median value of blood urea was 62.0 mg% in patients with normal renal function, 178.5 mg% in those with CKD and 120.0 mg% in expired patients (P=0.001). A statistically significant change in serum potassium (P=0.010) and creatinine levels (P<0.001) was observed during the follow-up period. Liver enzymes, including serum glutamic oxaloacetic transaminase and serum glutamic pyruvic transaminase, were high in all patients at the time of admission, but decreased to normal on follow-up. Conclusion:Our study indicates that pregnancy-related AKI patients present with multiorgan complications and many of them require mechanical ventilation and renal replacement therapy. Most of these patients have poor outcome. Hence, the management of pregnancy-related AKI presents a challenge that requires proper evaluation of causative factors to facilitate appropriate treatment.

Prediction of Acute Kidney Injury by Cystatin C and [TIMP-2]*[IGFBP7] after Thoracic Aortic Surgery with Moderate Hypothermic Circulatory Arrest

(1) Background: Acute kidney injury (AKI) is a common complication following thoracic aortic surgery (TAS), with moderate hypothermic circulatory arrest (MHCA). However, prediction of AKI with classical tools remains uncertain. Therefore, it was the aim of the present study to evaluate the role of new biomarkers in patients after MHCA. (2) Methods: 101 consecutive patients were prospectively enrolled. Measurements of urinary [TIMP-2]*[IGFBP7] and Cystatin C in the blood were performed perioperatively. Primary endpoint was the occurrence of AKI stage 2 or 3 (KDIGO-classification) within 48 h after surgery (AKI group). (3) Results: Mean age of patients was 69.1 ± 10.9 years, 35 patients were female (34%), and 13 patients (13%) met the primary endpoint. Patients in the AKI group had a prolonged ICU-stay (6.9 ± 7.4 days vs. 2.5 ± 3.1 days, p < 0.001) as well as a higher 30-day-mortality (9/28 vs. 1/74, p < 0.001). Preoperative serum creatinine (169.73 ± 148.97 μmol/L vs. 89.74 ± 30.04 μmol/L, p = 0.027) as well as Cystatin C (2.41 ± 1.54 mg/L vs. 1.13 ± 0.35 mg/L, p = 0.029) were higher in these patients. [TIMP-2]*[IGFBP7] increased significantly four hours after surgery (0.6 ± 0.69 mg/L vs. 0.37 ± 0.56 mg/L, p = 0.03) in the AKI group. Preoperative Cystatin C (AUC 0.828, p < 0.001) and serum creatinine (AUC 0.686, p = 0.002) as well as [TIMP-2]*[IGFBP7] 4 h after surgery (AUC 0.724, p = 0.020) were able to predict postoperative AKI. The predictive capacity of Cystatin C was superior to serum creatinine (p = 0.0211) (4) Conclusion: Cystatin C represents a very sensitive and specific biomarker to predict AKI in patients undergoing thoracic surgery with MHCA even before surgery, whereas the predictive capacity of [TIMP-2]*[IGFBP7] is only moderate and inferior to that of serum creatinine.

Machine learning model for predicting acute kidney injury progression in critically ill patients

Background

Acute kidney injury (AKI) is a serve and harmful syndrome in the intensive care unit. Comparing to the patients with AKI stage 1/2, the patients with AKI stage 3 have higher in-hospital mortality and risk of progression to chronic kidney disease. The purpose of this study is to develop a prediction model that predict whether patients with AKI stage 1/2 will progress to AKI stage 3.

Methods

Patients with AKI stage 1/2, when they were first diagnosed with AKI in the Medical Information Mart for Intensive Care, were included. We used the Logistic regression and machine learning extreme gradient boosting (XGBoost) to build two models which can predict patients who will progress to AKI stage 3. Established models were evaluated by cross-validation, receiver operating characteristic curve, and precision–recall curves.

Results

We included 25,711 patients, of whom 2130 (8.3%) progressed to AKI stage 3. Creatinine, multiple organ failure syndromes were the most important in AKI progression prediction. The XGBoost model has a better performance than the Logistic regression model on predicting AKI stage 3 progression. Thus, we build a software based on our data which can predict AKI progression in real time.

Conclusions

The XGboost model can better identify patients with AKI progression than Logistic regression model. Machine learning techniques may improve predictive modeling in medical research.

The value of cystatin C in predicting perioperative and long-term prognosis of renal transplantation

This study aimed to evaluate the value of cystatin C (Cys C) in predicting the perioperative and long-term prognosis of renal transplantation (RT). The clinical data of 198 RT recipients were collected. Blood samples were obtained daily until 7 d after transplantation and then discharge day to determine the serum levels of Cys C. The receiver-operating characteristic (ROC) analysis and the area under the curve (AUC) were used to determine the diagnostic accuracy of Cys C for delayed graft function (DGF). The presence of shrunken pore syndrome (SPS) with a cystatin C-based estimate of glomerular filtration rate less than 70% of a creatinine-based estimate, was also evaluated as a prognostic factor for the development of DGF. The serum Cys C levels of patients with DGF were higher than those of the non-DGF group. Cys C showed a higher AUC (0.928) in the ROC analysis than did sCr (0.862). Compared to the non-SPS group, there were more patients diagnosed with SPS in the DGF group (p < .05). The follow-up data showed that patients diagnosed with SPS had higher levels of sCr and Cys C compared to other patients, suggesting a poor long-term prognosis. Our findings suggest that Cys C is a sensitive indicator of renal function during the perioperative period. Cys C at a concentration of 4.9 mg/L had the highest sum of sensitivity and specificity for prediction of DGF, with a sensitivity of 0.889 and a specificity of 0.8. SPS is associated with the development of DGF and the poor long-term prognosis of RT.

Update on prognosis driven classification of pediatric AKI

Acute kidney injury (AKI) affects a large proportion of hospitalized children and increases morbidity and mortality in this population. Initially thought to be a self-limiting condition with uniformly good prognosis, we now know that AKI can persist and progress to acute kidney disease (AKD) and chronic kidney disease (CKD). AKI is presently categorized by stage of injury defined by increase in creatinine, decrease in eGFR, or decrease in urine output. These commonly used biomarkers of acute kidney injury do not change until the injury is well established and are unable to detect early stage of the disease when intervention is likely to reverse injury. The kidneys have the ability to compensate and return serum creatinine to a normal or baseline level despite nephron loss in the setting of AKI possibly masking persistent dysfunction. Though these definitions are important, classifying children by their propensity for progression to AKD and CKD and defining these risk strata by other factors besides creatinine may allow for better prognosis driven discussion, expectation setting, and care for our patients. In order to develop a classification strategy, we must first be able to recognize children who are at risk for AKD and CKD based on modifiable and non-modifiable factors as well as early biomarkers that identify their risk of persistent injury. Prevention of initial injury, prompt evaluation and treatment if injury occurs, and mitigating further injury during the recovery period may be important factors in decreasing risk of AKD and CKD after AKI. This review will cover presently used definitions of AKI, AKD, and CKD, recent findings in epidemiology and risk factors for AKI to AKD to CKD progression, novel biomarkers for early identification of AKI and AKI that may progress to CKD and future directions for improving outcome in children with AKI.

Nouvelles approches diagnostiques de l’insuffisance rénale aiguë

L’insuffisance rénale, véritable problème de santé publique, concernerait plus de 82 000 personnes en France. On estime que 5 à 10 % de la population française souffriraient d’une maladie rénale pouvant conduire à une insuffisance rénale avec un taux de mortalité de plus de 10 % par an. À l’inverse de la maladie rénale chronique irréversible, l’insuffisance rénale aiguë est considérée comme un dysfonctionnement transitoire et réversible. Au-delà de l’intérêt de la prévention, le diagnostic précoce de l’insuffisance rénale aiguë permettrait de mettre en place des thérapeutiques adaptées et ciblées afin d’éviter l’évolution vers des lésions rénales irréversibles. Cependant, il demeure un véritable challenge pour le praticien puisque l’on présume que près de 10 % de la population française présenteraient des lésions rénales asymptomatiques. Bien que la définition de l’insuffisance rénale aiguë ait été simplifiée durant ces dernières années, il existe de nombreuses limites. En parallèle, des progrès majeurs ont été réalisés notamment en termes de diagnostic. L’objectif de cette mise au point est de faire un rappel sur l’évolution de l’insuffisance rénale aiguë, les définitions actuelles et de présenter les nouvelles approches diagnostiques en cours de développement.

Biomarkers of persistent renal vulnerability after acute kidney injury recovery

Acute kidney injury (AKI) is a risk factor for new AKI episodes, chronic kidney disease, cardiovascular events and death, as renal repair may be deficient and maladaptive, and activate proinflammatory and profibrotic signals. AKI and AKI recovery definitions are based on changes in plasma creatinine, a parameter mostly associated to glomerular filtration, but largely uncoupled from renal tissue damage. The evolution of structural and functional repair has been incompletely described. We thus aimed at identifying subclinical sequelae persisting after recovery from cisplatin-induced AKI in rats. Compared to controls, after plasma creatinine recovery, post-AKI kidneys showed histological alterations and attendant susceptibility to new AKI episodes. Tubular function (assessed by the furosemide stress test, FST) also remained affected. Lingering parenchymal and functional subclinical alterations were paralleled by tapering, but abnormally high levels of urinary albumin, transferrin, insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinases-2 (TIMP-2) and, especially, the [TIMP-2]*[IGFBP7] product. As subclinical surrogates of incomplete renal recovery, the FST and the urinary [TIMP-2]*[IGFBP7] product provide two potential diagnostic tools to monitor the sequelae and kidney vulnerability after the apparent recovery from AKI.

Analytical validation and reference intervals for a commercial multiplex assay to measure five novel biomarkers for acute kidney injury in canine urine

Novel urinary biomarkers are increasingly utilized for the diagnosis of acute kidney injury (AKI) in dogs. Magnetic-bead based immunoassays for the simultaneous measurement of multiple biomarkers represent a potentially efficient and cost effective tool for investigators; however there is limited data to support their reliable use in dogs. Analytical validation of a commercial multiplex assay for the measurement of five AKI biomarkers: clusterin, cystatin C, kidney-injury molecule 1 (KIM-1), monocyte chemoattractant protein 1 and neutrophil gelatinase-associated lipocalin (NGAL) in canine urine was performed. The effect of pre-analytical factors including potential interfering substances and sample storage methods were investigated. Urine from 110 healthy dogs was used to determine reference intervals for each biomarker measured, according to American Society of Veterinary Clinical Pathology guidelines. Additionally, urine from 21 dogs with pyuria was used to evaluate the impact of pyuria on biomarker concentration. The assay performed with acceptable accuracy and precision for the measurement of NGAL only. Clinically relevant urine concentrations of bilirubin, haemoglobin, and synthetic colloid solutions led to interference (mean percentage difference > +/- 15% compared to control) with measurement of all or some of the biomarkers. All biomarkers were stable in urine stored at 20-22 °C for 2 h, 4 °C for 12 h, or -20 °C for 6 months. Reference intervals could not be established for KIM-1 due to unacceptable measurement imprecision (intra- and inter assay coefficient of variation 45% and 20% respectively). Urine NGAL concentration was significantly elevated in pyuria (P < 0.001).

Acute Kidney Injury in the Intensive Care Unit: The Most Reliable Way to Predict the Future is to Create It

How to cite this article: Tripathy S. Acute Kidney Injury in the Intensive Care Unit: The Most Reliable Way to Predict the Future is to Create It. Indian J Crit Care Med 2021;25(7):747-749.

Preoperative Serum GDF-15, Endothelin-1 Levels, and Intraoperative Factors as Short-Term Operative Risks for Patients Undergoing Cardiovascular Surgery

Objectives: The Society of Thoracic Surgeons (STS) risk score is widely used for the risk assessment of cardiac surgery. Serum biomarkers such as growth differentiation factor-15 (GDF-15) and endothelin-1 (ET-1) are also used to evaluate risk. We investigated the relationships between preoperative serum GDF-15, ET-1 levels, and intraoperative factors and short-term operative risks including acute kidney injury (AKI) for patients undergoing cardiovascular surgery. Methods: In total, 145 patients were included in this study (92 males and 53 females, age 68.4 ± 13.2 years). The preoperative STS score was determined, and the serum GDF-15 and ET-1 levels were measured by ELISA. These were related to postoperative risks, including AKI, defined according to the Acute Kidney Injury Network (AKIN) classification criteria. Results: AKI developed in 23% of patients. The GDF-15 and ET-1 levels correlated with the STS score. The STS score and GDF-15 and ET-1 levels all correlated with preoperative eGFR, Alb, Hb, and BNP levels; perioperative data (urine output); ICU stay period; and postoperative admission days. Patients with AKI had longer circulatory pulmonary bypass (CPB) time, and male patients with AKI had higher ET-1 levels than those without AKI. In multivariable logistic regression analysis, the preoperative ET-1 level and CPB time were the independent determinants of AKI, even adjusted by age, sex, and BMI. The preoperative GDF-15 level, CPB time, and RCC transfusion were independent determinants of 30-day mortality plus morbidity. Conclusion: Preoperative GDF-15 and ET-1 levels as well as intraoperative factors such as CPB time may be helpful to identify short-term operative risks for patients undergoing cardiovascular surgery.

Renal effect of severe hypoxia evaluated By NGAL measurements: An in vivo and in vitro study

PURPOSE

To investigate possible renal damage in healthy men exposed to extreme hypobaric hypoxia, using urinary Neutrophil Gelatinase-Associated Lipocalin (NGAL) concentration as biomarker. The value of NGAL as a biomarker of proximal tubular cell damage under hypoxic conditions was also tested in vitro experiments.

METHODS

NGAL was assayed in a cohort of air cadets (n = 16) exposed to hypobaric hypoxia in a hypobaric chamber during their training program. In all subjects, urine creatinine (Cr) and urinary NGAL levels were measured immediately before, 3, and 24 h after hypobaric environment exposure. Three in vitro experiments using proximal tubular cell cultures were also performed to measure NGAL gene expression, NGAL secretion in the culture medium and to evaluate apoptosis under two cycles of hypoxia and reoxygenation.

RESULTS

In the in vivo study, geometric means of urinary NGAL/Cr ratio measured 24 h after hypobaric hypoxia in the hypobaric chamber were significantly lower than baseline values (13.4 vs 25.9 ng/mg, p = 0.01). In cell cultures, hypoxia down-regulated NGAL gene expression without significantly changing NGAL secretion in the culture medium. Hypoxia significantly increased the percentage of apoptotic/necrotic cells, especially after the second hypoxia-reoxygenation cycle.

CONCLUSIONS

Exposure to hypobaric-hypoxic environments does not cause significant and irreversible renal tubular injury in vivo and in vitro, except than in a late stage. The hypoxic insult does not seem to be mirrored by an increase of urinary NGAL in healthy men nor of NGAL gene expression in HK-2 cell culture or secretion in the culture medium in the in vitro conditions reported in the present study.

The efficacy of biomarkers in the diagnosis of acute kidney injury secondary to liver cirrhosis

ABSTRACT

This study is to investigate the role of neutrophil gelatinase-associated lipocalin (NGAL), cystatin C (CysC) and creatinine in the diagnosis of acute kidney injury (AKI) secondary to liver cirrhosis.A total of 825 patients (including 540 liver cirrhosis patients and 285 healthy controls) were enrolled. Liver cirrhosis patients were further subdivided into AKI secondary to liver cirrhosis group (AKI group, 210 patients) and simple liver cirrhosis group (LC group, 330 patients). Serum NGAL/urine NGAL (sNGAL/uNGAL), and serum creatinine (sCr) levels as well as estimated glomerular filtration rates were measured. The diagnostic performances of these indicators in AKI secondary to liver cirrhosis were evaluated.The levels of sNGAL, uNGAL, CysC and sCr in the AKI group were significantly higher than those of LC and healthy control groups. However, the eGFR and c-aGFR of AKI group were significantly lower. With the progression of AKI (AKI-S1→AKI-S2→AKI-S3), the levels of sNGAL, uNGAL, CysC and sCr increased gradually, while the levels of c-aGFR and eGFR decreased gradually. The sNGAL, uNGAL and CysC were positively correlated with sCr (r = 0.638, 0.635, and 0.650), but negatively correlated with c-aGFR (r = -0.617, -0.606 and -0.655). However, eGFR had a negative correlation with sCr (r = -0.711), but a positive correlation with c-aGFR (r = 0.736). ROC curve analysis showed that the area under the curve for uNGAL was the largest (0.976), followed by sNGAL (0.967). The diagnostic efficacy of uNGAL and sNGAL in AKI group were 0.907 and 0.870, and the risk degrees were OR = 54.524 and 5.115, respectively.NGAL might perform better than sCr and CysC in the diagnosis of AKI secondary to liver cirrhosis, while uNGAL might be a better indicator than sNGAL in AKI diagnosis.

Application of mesenchymal stem cell-derived exosomes in kidney diseases

Kidney injury (KI) has high morbidity and mortality; there has been no ideal practical treatment available in clinical practice until now. Exosomes are formed from fusing multisubunit body membranes and are secreted into the extracellular matrix, intercellular communication membracusses. As a cell-free treatment, it offers a new approach to the treatment of KI. Exosomes are spherical vesicles with or no separator cup that shapes proteins, and RNA acts on the target cells through various means to promote tissue damage and mitigate apoptosis, both inflammation and oxidative stress. Exosomes derived from mesenchymal stem cells (MSC) have a paracrine function in promoting tissue repair and immune regulation. The MSC-Exos provide specific benefits over the MSCs. The urinary exosomes closely follow the functions and diseases of the kidneys. Though much of the research in this field is only at the preliminary stages, previous research has demonstrated that MSC-Exos damaged tissues to offer proteins, mRNAs, and microRNAs as remedies for kidney injury. Although exosomes' role in tissue repair is currently is greatly debated, several key issues remain unaddressed. This is a summarization of the work done concerning MSC in the treatment of KI.

Acute kidney injury after lung transplantation: a narrative review

Acute kidney injury (AKI) is a commonly recognized complication after lung transplantation (LT) and is related to increased mortality and morbidity. With the improvement of survival after LT and the increasing number of lung transplant recipients, the detrimental impact of current management on renal function has become increasingly apparent. Multifarious risk factors in the perioperative setting contribute to the development of AKI, including the preoperative status and complications of the recipient, complex perioperative problems especially hemodynamic fluctuation, and exposure to nephrotoxic agents, mainly calcineurin inhibitors (CNIs) and antimicrobial drugs. Identification and minimization of the effects of these risk factors can relieve AKI severity and incidence in high-risk patients. Close monitoring of urine output and serum creatinine (sCr) levels and of specific biomarkers may promote early recognition of AKI and rapid nephrology intervention to improve outcomes. This review summarizes advances in the epidemiology, diagnostic criteria, biological markers of AKI, and further recommends appropriate treatment strategies for the long-term management of AKI related manifestations in lung transplant recipients. Future work will need to focus on developing more accurate measures of renal function and identifying patients before the occurrence of early renal damage. Combining renal protection strategies with the use of new biomarkers to develop early kidney risk identification and protection protocols is a promising idea that requires further investigation.

Beta-Trace Protein as a Potential Marker of Acute Kidney Injury: A Pilot Study

INTRODUCTION

Acute kidney injury (AKI) is a frequent complication among patients in the intensive care unit (ICU). The limitations of serum Cr (sCr) in timely detecting AKI are well known. Beta-trace protein (BTP) is emerging as a novel endogenous glomerular filtration rate marker. The aim of this study was to explore the role of BTP as a marker of AKI.

METHODS

Patients admitted to the ICU undergoing surgery were included. BTP, sCr, Cystatin C (CysC), and neutrophil gelatinase-associated lipocalin (NGAL) were measured preoperatively, postoperatively (post-op), and at the first (D1) and second (D2) post-op day. AKI was defined as an increase of sCr to ≥1.5-fold from baseline within 2 days after surgery.

RESULTS

Of the 52 patients studied, 10 patients (19%) developed AKI. Patients with AKI were older (69.6 ± 10.7 vs. 58.1 ± 16.7 years, p = 0.043) and had a longer length of ICU stay (13 [IQR 6-49] vs. 6 [IQR 5-8] days, p = 0.032). Between the 2 groups, the evolution of BTP, sCr, CysC, and NGAL over time differed significantly, with overall higher values in the AKI group. ROC analysis for the detection of AKI within 2 days after surgery showed a great accuracy for BTP. The area under the curve (AUC) for BTP post-op; D1; and D2 was, respectively, 0.869 ± 0.049; 0.938 ± 0.035; and 0.943 ± 0.032. The discriminative power of a BTP measurement on D1 was superior in detecting AKI compared to NGAL (adjusted p value = 0.027). We could not detect a significant difference between the AUCs of other biomarkers (NGAL, sCr, and CysC).

CONCLUSION

Serum BTP is a promising marker for diagnosing AKI in ICU patients undergoing surgery.

Platelet-rich plasma promotes MSCs exosomes paracrine to repair acute kidney injury via AKT/Rab27 pathway

Acute kidney injury (AKI) is defined by rapid deterioration of renal function, and is a common complication in hospitalized patients. Among the recent therapeutic options, mesenchymal stem cells (MSCs) are considered a promising therapeutic strategy for damaged tissue repair. Platelet rich plasma (PRP) regulates mesenchymal cells to repair tissue damage through the release of growth factors. In this study, we proposed a possible therapeutic use of MSCs stimulated by platelet-rich plasma (PRP-MSCs) in a glycerin-induced AKI murine model. In vivo and in vitro studies, showed that PRP-MSCs could significantly attenuate serum blood urea nitrogen and creatinine levels, and reverse the histopathological kidney damage. PRP-MSCs treatment reduced renal tubular cell apoptosis stimulated by glycerin. We confirmed that PRP promoted the proliferation and reinforced the stemness of MSCs by inducing YAP nucleus expression, and that PRP promoted MSCs exosomes in a paracrine manner to repair AKI through an activated AKT/Rab27 pathway. Our results revealed that the PRP stimulated MSCs paracrine pathway could effectively alleviate glycerin-induced AKI. Therefore, PRP pretreatment may be a new method to improve the therapeutic effect of MSCs.

Identification of risk factors for renal failure after cardiac surgery by RFILE classification

OBJECTIVE

Acute kidney injury (AKI) is a major complication after cardiovascular surgery. The unclear etiology of this highly complex event challenges definition, diagnosis and prediction of AKI, and hence hampers adequate patient management. Identification of associated risk factors have the potential to overcome this limitation.

METHODS

This retrospective study comprised 3574 patients who underwent cardiac surgery in a hospital in Germany. The patient cohort was interrogated for risk factors for AKI.

RESULTS

The analysis identified risk factors for AKI development, such as type of surgery (particularly bypass surgery) (P = 0.02), previous coronary surgeries (P < 0.01), the application of intra-aortic balloon pump in surgery (P < 0.01), and blood loss during surgery (P < 0.01). In addition, old age, duration of surgery as well as ischemia, perfusion and reperfusion times contributed to AKI development (P < 0.01). Further, perioperative hypothermia also appeared as putative risk factor in the analysis (P < 0.01).

CONCLUSIONS

This study identified several risk factors for the development of AKI after cardiac surgery. Further validation of these risk factors could allow the implementation of adequate patient management, and the appropriate implementation of risk-adverse interventions in cardiovascular surgery.

Development and validation of a risk stratification model for predicting the mortality of acute kidney injury in critical care patients

Background

This study aimed to develop and validate a model for mortality risk stratification of intensive care unit (ICU) patients with acute kidney injury (AKI) using the machine learning technique.

Methods

Eligible data were extracted from the Medical Information Mart for Intensive Care (MIMIC-III) database. Calibration, discrimination, and risk classification for mortality prediction were evaluated using conventional scoring systems and the new algorithm. A 10-fold cross-validation was performed. The predictive models were externally validated using the eICU database and also patients treated at the Second People’s Hospital of Shenzhen between January 2015 to October 2018.

Results

For the new model, the areas under the receiver operating characteristic curves (AUROCs) for mortality during hospitalization and at 28 and 90 days after discharge were 0.91, 0.87, and 0.87, respectively, which were higher than for the Simplified Acute Physiology Score (SAPS II) and Sequential Organ Failure Assessment (SOFA). For external validation, the AUROC was 0.82 for in-hospital mortality, higher than SOFA, SAPS II, and Acute Physiology and Chronic Health Evaluation (APACHE) IV in the eICU database, but for the 28- and 90-day mortality, the new model had AUROCs (0.79 and 0.80, respectively) similar to that of SAPS II in the SZ2 database. The reclassification indexes were superior for the new model compared with the conventional scoring systems.

Conclusions

The new risk stratification model shows high performance in predicting mortality in ICU patients with AKI.

Extracellular vesicles from three dimensional culture of human placental mesenchymal stem cells ameliorated renal ischemia/reperfusion injury

BACKGROUND

Three-dimensional (3D) culture has been reported to increase the therapeutic potential of mesenchymal stem cells (MSCs). The present study assessed the therapeutic efficacy of extracellular vesicles (EVs) from 3D cultures of human placental MSCs (hPMSCs) for acute kidney injury (AKI).

METHODS

The supernatants from monolayer culture (2D) and 3D culture of hPMSCs were ultra-centrifuged for EVs isolation. C57BL/6 male mice were submitted to 45 min bilateral ischemia of kidney, followed by renal intra-capsular administration of EVs within a 72 h reperfusion period. Histological, immunohistochemical, and ELISA analyses of kidney samples were performed to evaluate cell death and inflammation. Kidney function was evaluated by measuring serum creatinine and urea nitrogen. The miRNA expression profiles of EVs from 2D and 3D culture of hPMSCs were evaluated using miRNA microarray analysis.

RESULTS

The 3D culture of hPMSCs formed spheroids with different diameters depending on the cell density seeded. The hPMSCs produced significantly more EVs in 3D culture than in 2D culture. More importantly, injection of EVs from 3D culture of hPMSCs into mouse kidney with ischemia-reperfusion (I/R)-AKI was more beneficial in protecting from progression of I/R than those from 2D culture. The EVs from 3D culture of hPMSCs were more efficient against apoptosis and inflammation than those from 2D culture, which resulted in a reduction in tissue damage and amelioration of renal function. MicroRNA profiling analysis revealed that a set of microRNAs were significantly changed in EVs from 3D culture of hPMSCs, especially miR-93-5p.

CONCLUSION

The EVs from 3D culture of hPMSCs have therapeutic potential for I/R-AKI.

Clinical Applications of Mesenchymal Stem/Stromal Cell Derived Extracellular Vesicles: Therapeutic Potential of an Acellular Product

In the last decade, the secreting activity of mesenchymal stem/stromal cells (MSCs) has been widely investigated, due to its possible therapeutic role. In fact, MSCs release extracellular vesicles (EVs) containing relevant biomolecules such as mRNAs, microRNAs, bioactive lipids, and signaling receptors, able to restore physiological conditions where regenerative or anti-inflammatory actions are needed. An actual advantage would come from the therapeutic use of EVs with respect to MSCs, avoiding the possible immune rejection, the lung entrapment, improving the safety, and allowing the crossing of biological barriers. A number of concerns still have to be solved regarding the mechanisms determining the beneficial effect of MSC-EVs, the possible alteration of their properties as a consequence of the isolation/purification methods, and/or the best approach for a large-scale production for clinical use. Most of the preclinical studies have been successful, reporting for MSC-EVs a protecting role in acute kidney injury following ischemia reperfusion, a potent anti-inflammatory and anti-fibrotic effects by reducing disease associated inflammation and fibrosis in lung and liver, and the modulation of both innate and adaptive immune responses in graft versus host disease (GVHD) as well as autoimmune diseases. However, the translation of MSC-EVs to the clinical stage is still at the initial phase. Herein, we discuss the therapeutic potential of an acellular product such as MSC derived EVs (MSC-EVs) in acute and chronic pathologies.

Ability of different assay platforms to measure renal biomarker concentrations during ischaemia-reperfusion acute kidney injury in dogs

Several protein biomarkers have been shown to be useful for the early diagnosis of acute kidney injury (AKI) in animals and people. Multiplex assays for measurement of a panel of renal biomarkers in canine samples have recently become available. This study compared the use of two such assays, versus previously validated ELISAs, to measure five biomarkers in canine samples during ischaemia-reperfusion (IR) AKI. Blood and urine was collected from six male anaesthetised greyhounds that underwent 1-h of renal ischaemia (severe hypotension induced by acute haemorrhage) and 2-h of reperfusion (intravenous fluid resuscitation). Histology confirmed presence of acute tubular injury at 2 h of reperfusion. Concentrations of clusterin, cystatin C, kidney-injury molecule 1 (KIM-1), monocyte chemoattractant protein 1, and neutrophil gelatinase-associated lipocalin (NGAL) at baseline and following IR, measured by two different multiplex assays and previously-validated single analyte immunoassays, were compared. Only NGAL was significantly elevated following IR with all assays investigated. Whether concentrations of the other four biomarkers were significantly increased following IR depended on the assay used. Concentrations of cystatin C and KIM-1 measured with the multiplex assays were of a vast magnitude lower than those measured with the corresponding single analyte ELISAs. We conclude that further validation is required before these assays can reliably be used to measure AKI biomarkers in canine samples.

Predicting Acute Kidney Injury: A Machine Learning Approach Using Electronic Health Records

Acute kidney injury (AKI) is a common complication in hospitalized patients and can result in increased hospital stay, health-related costs, mortality and morbidity. A number of recent studies have shown that AKI is predictable and avoidable if early risk factors can be identified by analyzing Electronic Health Records (EHRs). In this study, we employ machine learning techniques to identify older patients who have a risk of readmission with AKI to the hospital or emergency department within 90 days after discharge. One million patients’ records are included in this study who visited the hospital or emergency department in Ontario between 2014 and 2016. The predictor variables include patient demographics, comorbid conditions, medications and diagnosis codes. We developed 31 prediction models based on different combinations of two sampling techniques, three ensemble methods, and eight classifiers. These models were evaluated through 10-fold cross-validation and compared based on the AUROC metric. The performances of these models were consistent, and the AUROC ranged between 0.61 and 0.88 for predicting AKI among 31 prediction models. In general, the performances of ensemble-based methods were higher than the cost-sensitive logistic regression. We also validated features that are most relevant in predicting AKI with a healthcare expert to improve the performance and reliability of the models. This study predicts the risk of AKI for a patient after being discharged, which provides healthcare providers enough time to intervene before the onset of AKI.

Validation of a commercial magnetic bead-based multiplex assay for 5 novel biomarkers of acute kidney injury in canine serum

Interest is growing in measurement of novel biomarkers for the diagnosis of acute kidney injury. Multiplex assays may provide a rapid and cost-effective way of measurement; however, sparse information is published regarding their use in dogs. We aimed to validate a commercial magnetic bead-based assay for 5 biomarkers: clusterin (Clus), cystatin C (CysC), kidney injury molecule 1 (KIM-1), monocyte chemoattractant protein 1 (MCP-1), and neutrophil gelatinase-associated lipocalin (NGAL). Intra- and inter-assay imprecision, linearity under dilution (LUD), spike recovery (S-R), and hemoglobin interference were evaluated using serum from healthy and diseased dogs. Additionally, the effect of sample type (serum vs. plasma) was investigated. All values for Clus and MCP-1 were outside the assay's measurable range. Intra- and inter-assay precision were acceptable for NGAL (CVs 8.8% and 13.2%, respectively). Regression analysis of LUD and S-R indicated good linearity for CysC and NGAL. Hemolysis did not affect measurement of any biomarker. Measured concentrations of CysC (p = 0.018) and NGAL (p = 0.015) were significantly lower in sodium citrate plasma compared to serum. We conclude that this magnetic bead-based assay is precise and accurate for NGAL measurement in canine serum. Inappropriate standards for MCP-1 and Clus, and poor accuracy for KIM-1 measurement, suggest that this assay cannot reliably quantify those biomarkers in canine blood. Measurements of CysC in canine blood using this assay must be interpreted with caution given inter-assay imprecision.

Point-of-care creatinine measurements to predict acute kidney injury

BACKGROUND

Plasma creatinine (Cr) is a marker of kidney function and typically measured once daily. We hypothesized that Cr measured by point-of-care technology early after ICU admission would be a good predictor of acute kidney injury (AKI) the next day in critically ill patients.

METHODS

We conducted a retrospective database audit in a single tertiary ICU database. We included patients with normal first admission Cr (Cr_F ) and identified a Cr value (Cr_P ) obtained within 6-12 hours from ICU admission. We used their difference converted into percentage (delta-Cr-%) to predict subsequent AKI (based on Cr and/or need for renal replacement therapy) the next day. We assessed predictive value by calculating area under the receiver characteristic curve (AUC), logistic regression models for AKI with and without delta-Cr-%, and the category-free net reclassifying index (cfNRI).

RESULTS

We studied 780 patients. Overall, 70 (9.0%) fulfilled the Cr AKI definition by Cr_P measurement. On day 2, 148 patients (19.0%) were diagnosed with AKI. AUC (95% CI) for delta-Cr-% to predict AKI on day 2 was 0.82 (95% CI 0.78-0.86), and 0.74 (95% CI 0.69-0.80) when patients with AKI based on the Cr_P were excluded. Using a cut-off of 17% increment, the positive likelihood ratio (95% CI) for delta-Cr-% to predict AKI was 3.5 (2.9-4.2). The cfNRI was 90.0 (74.9-106.1).

CONCLUSIONS

Among patients admitted with normal Cr, early changes in Cr help predict AKI the following day.

Soluble Urokinase Receptor and Acute Kidney Injury

BACKGROUND

Acute kidney injury is common, with a major effect on morbidity and health care utilization. Soluble urokinase plasminogen activator receptor (suPAR) is a signaling glycoprotein thought to be involved in the pathogenesis of kidney disease. We investigated whether a high level of suPAR predisposed patients to acute kidney injury in multiple clinical contexts, and we used experimental models to identify mechanisms by which suPAR acts and to assess it as a therapeutic target.

METHODS

We measured plasma levels of suPAR preprocedurally in patients who underwent coronary angiography and patients who underwent cardiac surgery and at the time of admission to the intensive care unit in critically ill patients. We assessed the risk of acute kidney injury at 7 days as the primary outcome and acute kidney injury or death at 90 days as a secondary outcome, according to quartile of suPAR level. In experimental studies, we used a monoclonal antibody to urokinase plasminogen activator receptor (uPAR) as a therapeutic strategy to attenuate acute kidney injury in transgenic mice receiving contrast material. We also assessed cellular bioenergetics and generation of reactive oxygen species in human kidney proximal tubular (HK-2) cells that were exposed to recombinant suPAR.

RESULTS

The suPAR level was assessed in 3827 patients who were undergoing coronary angiography, 250 who were undergoing cardiac surgery, and 692 who were critically ill. Acute kidney injury developed in 318 patients (8%) who had undergone coronary angiography. The highest suPAR quartile (vs. the lowest) had an adjusted odds ratio of 2.66 (95% confidence interval [CI], 1.77 to 3.99) for acute kidney injury and 2.29 (95% CI, 1.71 to 3.06) for acute kidney injury or death at 90 days. Findings were similar in the surgical and critically ill cohorts. The suPAR-overexpressing mice that were given contrast material had greater functional and histologic evidence of acute kidney injury than wild-type mice. The suPAR-treated HK-2 cells showed heightened energetic demand and mitochondrial superoxide generation. Pretreatment with a uPAR monoclonal antibody attenuated kidney injury in suPAR-overexpressing mice and normalized bioenergetic changes in HK-2 cells.

CONCLUSIONS

High suPAR levels were associated with acute kidney injury in various clinical and experimental contexts. (Funded by the National Institutes of Health and others.).

Current understanding and future directions in the application of TIMP-2 and IGFBP7 in AKI clinical practice

NephroCheck® is the commercial name of a combined product of two urinary biomarkers, tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7), expressed as [TIMP-2]·[IGFBP7], used to identify patients at high risk of acute kidney injury (AKI). AKI is a common and harmful complication especially in critically-ill patients, which can induce devastating short- and long-term outcomes. Over the past decade, numerous clinical studies have evaluated the utility of several biomarkers (e.g. neutrophil gelatinase-associated lipocalin, interleukin-18, liver-type fatty acid binding protein and kidney injury molecule-1, cystatin C) in the early diagnosis and risk stratification of AKI. Among all these biomarkers, [TIMP-2]·[IGFBP7] was confirmed to be superior in early detection of AKI, before the decrease of renal function is evident. In 2014, the US Food and Drug Administration permitted marketing of NephroCheck® (Astute Medical) (measuring urinary [TIMP-2]·[IGFBP7]) to determine if certain critically-ill patients are at risk of developing moderate to severe AKI. It has since been applied to clinical work in many hospitals of the United States and Europe to improve the diagnostic accuracy and outcomes of AKI patients. Now, more and more research is devoted to the evaluation of its application value, meaning and method in different clinical settings. In this review, we summarize the current research status of [TIMP-2]·[IGFBP7] and point out its future directions.

Urinary Extracellular Vesicles Carrying Klotho Improve the Recovery of Renal Function in an Acute Tubular Injury Model

Acute kidney injury, defined by a rapid deterioration of renal function, is a common complication in hospitalized patients. Among the recent therapeutic options, the use of extracellular vesicles (EVs) is considered a promising strategy. Here we propose a possible therapeutic use of renal-derived EVs isolated from normal urine (urine-derived EVs [uEVs]) in a murine model of acute injury generated by glycerol injection. uEVs accelerated renal recovery, stimulating tubular cell proliferation, reducing the expression of inflammatory and injury markers, and restoring endogenous Klotho loss. When intravenously injected, labeled uEVs localized within injured kidneys and transferred their microRNA cargo. Moreover, uEVs contained the reno-protective Klotho molecule. Murine uEVs derived from Klotho null mice lost the reno-protective effect observed using murine EVs from wild-type mice. This was regained when Klotho-negative murine uEVs were reconstituted with recombinant Klotho. Similarly, ineffective fibroblast EVs acquired reno-protection when engineered with human recombinant Klotho. Our results reveal a novel potential use of uEVs as a new therapeutic strategy for acute kidney injury, highlighting the presence and role of the reno-protective factor Klotho.

Preventing acute kidney injury and improving outcome in critically ill patients utilizing risk prediction score (PRAIOC-RISKS) study. A prospective controlled trial of AKI prevention

BACKGROUND

Acute kidney injury (AKI) has significant impact on mortality and morbidity in critically ill patients.

METHODS

A prospective controlled interventional pilot study composed of observation and intervention arms was run at two different Intensive care unit (ICU) sites. A recently validated risk prediction score was used to predict the AKI in critically ill patients at high risk of developing AKI. All patients with established AKI at the time of recruitment were excluded from the study. A package of early preventive measures, including an early nephrology review was applied to high risk patients in the intervention arm to prevent AKI development.

RESULTS

We have recruited 108 patients at the intervention site and 98 patients at the observation site. The primary outcome measure was the AKI incidence. AKI incidence was significantly lower in the intervention arm than its incidence in the observation arm (11% vs 26%, p = 0.002). The median Time till recovery of AKI episodes was significantly lower in the intervention arm (3(1) vs. 5(2) days, p = 0.014) 0.30 day mortality was lower in the intervention arm, however, not statistically significant.

CONCLUSION

Our pilot study showed that it was feasible to apply a simple risk score to implement early preventive measures to high risk patients, consequently, mitigating the risk of AKI development and reducing the time till recovery of AKI episodes. Multicentre studies are needed to confirm this favourable effect.

Stem Cell-Derived Extracellular Vesicles and Kidney Regeneration

Extracellular vesicles (EVs) are membranous vesicles containing active proteins, lipids, and different types of genetic material such as miRNAs, mRNAs, and DNAs related to the characteristics of the originating cell. They possess a distinctive capacity to communicate over long distances. EVs have been involved in the modulation of several pathophysiological conditions and, more importantly, stem cell-derived EVs appear as a new promising therapeutic option. In fact, several reports provide convincing evidence of the regenerative potential of EVs released by stem cells and, in particular, mesenchymal stromal cells (MSCs) in different kidney injury models. Described mechanisms involve the reprogramming of injured cells, cell proliferation and angiogenesis, and inhibition of cell apoptosis and inflammation. Besides, the therapeutic use of MSC-EVs in clinical trials is under investigation. This review will focus on MSC-EV applications in preclinical models of acute and chronic renal damage including recent data on their use in kidney transplant conditioning. Moreover, ongoing clinical trials are described. Finally, new strategies to broaden and enhance EV therapeutic efficacy by engineering are discussed.