Proteomics and Metabolomics for AKI Diagnosis

Potential therapeutic applications of circular RNA in acute kidney injury

Acute kidney injury (AKI) is a common clinical syndrome characterized by a rapid deterioration in renal function, manifested by a significant increase in creatinine and a sharp decrease in urine output. The incidence of morbidity and mortality associated with AKI is on the rise, with most patients progressing to chronic kidney disease or end-stage renal disease. Treatment options for patients with AKI remain limited. Circular RNA (circRNA) is a wide and diverse class of non-coding RNAs that are present in a variety of organisms and are involved in gene expression regulation. Studies have shown that circRNA acts as a competing RNA, is involved in disease occurrence and development, and has potential as a disease diagnostic and prognostic marker. CircRNA is involved in the regulation of important biological processes, including apoptosis, oxidative stress, and inflammation. This study reviews the current status and progress of circRNA research in the context of AKI.

<sc>A</sc> multi-hierarchical approach reveals <sc>d</sc>-serine as a hidden substrate of sodium-coupled monocarboxylate transporters

Transporter research primarily relies on the canonical substrates of well-established transporters. This approach has limitations when studying transporters for the low-abundant micromolecules, such as micronutrients, and may not reveal physiological functions of the transporters. While d-serine, a trace enantiomer of serine in the circulation, was discovered as an emerging biomarker of kidney function, its transport mechanisms in the periphery remain unknown. Here, using a multi-hierarchical approach from body fluids to molecules, combining multi-omics, cell-free synthetic biochemistry, and ex vivo transport analyses, we have identified two types of renal d-serine transport systems. We revealed that the small amino acid transporter ASCT2 serves as a d-serine transporter previously uncharacterized in the kidney and discovered d-serine as a non-canonical substrate of the sodium-coupled monocarboxylate transporters (SMCTs). These two systems are physiologically complementary, but ASCT2 dominates the role in the pathological condition. Our findings not only shed light on renal d-serine transport, but also clarify the importance of non-canonical substrate transport. This study provides a framework for investigating multiple transport systems of various trace micromolecules under physiological conditions and in multifactorial diseases.

COVID-19 and Comorbidities: What Has Been Unveiled by Metabolomics?

The COVID-19 pandemic has brought about diverse impacts on the global population. Individuals with comorbidities were more susceptible to the severe symptoms caused by the virus. Within the crisis scenario, metabolomics represents a potential area of science capable of providing relevant information for understanding the metabolic pathways associated with the intricate interaction between the viral disease and previous comorbidities. This work aims to provide a comprehensive description of the scientific production pertaining to metabolomics within the specific context of COVID-19 and comorbidities, while highlighting promising areas for exploration by those interested in the subject. In this review, we highlighted the studies of metabolomics that indicated a variety of metabolites associated with comorbidities and COVID-19. Furthermore, we observed that the understanding of the metabolic processes involved between comorbidities and COVID-19 is limited due to the urgent need to report disease outcomes in individuals with comorbidities. The overlap of two or more comorbidities associated with the severity of COVID-19 hinders the comprehension of the significance of each condition. Most identified studies are observational, with a restricted number of patients, due to challenges in sample collection amidst the emergent situation.

Urinary proteomics reveals biological processes related to acute kidney injury in Bothrops atrox envenomings

Acute kidney injury (AKI) is a critical systemic complication caused by Bothrops envenoming, a neglected health problem in the Brazilian Amazon. Understanding the underlying mechanisms leading to AKI is crucial for effectively mitigating the burden of this complication. This study aimed to characterize the urinary protein profile of Bothrops atrox snakebite victims who developed AKI. We analyzed three groups of samples collected on admission: healthy subjects (controls, n = 10), snakebite victims who developed AKI (AKI, n = 10), and those who did not evolve to AKI (No-AKI, n = 10). Using liquid-chromatography tandem mass spectrometry, we identified and quantified (label-free) 1190 proteins. A panel of 65 proteins was identified exclusively in the urine of snakebite victims, with 32 exclusives to the AKI condition. Proteins more abundant or exclusive in AKI's urine were associated with acute phase response, endopeptidase inhibition, complement cascade, and inflammation. Notable proteins include serotransferrin, SERPINA-1, alpha-1B-glycoprotein, and NHL repeat-containing protein 3. Furthermore, evaluating previously reported biomarkers candidates for AKI and renal injury, we found retinol-binding protein, beta-2-microglobulin, cystatin-C, and hepcidin to be significant in cases of AKI induced by Bothrops envenoming. This work sheds light on physiological disturbances caused by Bothrops envenoming, highlighting potential biological processes contributing to AKI. Such insights may aid in better understanding and managing this life-threatening complication.

Multiple blood gas variables predict AKI survival in an independent manner

BACKGROUND AND AIM

Acute kidney injury (AKI) is becoming increasingly prevalent among hospitalized patients and carries a poor prognosis. While new biomarkers show promise in identifying early stages of AKI, accurately predicting severe outcomes such as the need for kidney replacement therapy (KRT) or death remains a challenge. However, blood gas analyses (BGA) can be used to diagnose life-threatening complications associated with AKI. The objective of this study was to assess the role of BGA as a biomarker panel in both emerging and established cases of AKI.

METHODS

Retrospective observational study examining subjects with newly developed acute kidney injury (AKI). The study will document venous and arterial pH, pCO2, and actual bicarbonate levels upon hospital admission and at the onset of AKI. The primary endpoints include in-hospital mortality, the need for kidney replacement therapy (KRT), and the recovery of kidney function (ROKF).

RESULTS

A total of 202 individuals were included in the study. Three variables were found to be independent predictors of in-hospital survival: admission arterial pH, arterial pH at acute kidney injury (AKI) onset, and arterial pCO2 at AKI onset. Additionally, venous pCO2 at AKI onset was identified as an independent predictor for the need of kidney replacement therapy (KRT).

CONCLUSIONS

Our study suggests that blood gas analysis may have a potential role in predicting severe outcome variables in acute kidney injury (AKI). The associated costs are minimal.

A simple, rapid and sensitive HILIC LC-MS/MS method for simultaneous determination of 16 purine metabolites in plasma and urine

Purine intermediates play important roles in physiological function and participate in the kidney disorders, while a targeted quantification of the metabolic alterations in the purine metabolism in acute kidney injury (AKI) individuals has not been conducted. In the study, a novel, rapid and sensitive LC-MS method for simultaneous quantification of 16 purine metabolites was developed using hydrophilic interaction separation mode in human plasma and urine. The developed method was validated by using charcoal-stripped plasma and urine as blank matrix. The results showed that the method was good linear (R2 > 0.99) and the lower limit of quantification (LLOQ) ranged from 0.833 ng/mL to 800 ng/mL. The recovery and matrix effect were repeatable and stable. The intraday precision ranged from 0.7% to 12.7%, while the inter-day precision ranged from 1.6% to 18.5%. Most analytes were stable in the autosampler and could subject three freeze-thaw cycles. The method provided a wider coverage of purine metabolites and completed good separation of interfering compounds of nucleosides, deoxynucleosides and their corresponding nucleobases without derivatization, which was time-saving and labor-saving for the large-scale analysis. Furthermore, the method was successfully applied to plasma and urine samples of hospitalized patients without and with AKI. The results showed certain purine intermediates were up-regulated in plasma and down-regulated in urine of AKI inpatients, indicating that AKI stress may associate with inflammatory responses. The novel method can facilitate the quantitative analysis of purine metabolites in biological fluids, and exhibit great prospects in providing more information on the pathogenesis of AKI.

Optimum Care of AKI Survivors Not Requiring Dialysis after Discharge: An AKINow Recovery Workgroup Report

AKI survivors experience gaps in care that contribute to worse outcomes, experience, and cost.Challenges to optimal care include issues with information transfer, education, collaborative care, and use of digital health tools.Research is needed to study these challenges and inform optimal use of diagnostic and therapeutic interventions to promote recovery AKI affects one in five hospitalized patients and is associated with poor short-term and long-term clinical and patient-centered outcomes. Among those who survive to discharge, significant gaps in documentation, education, communication, and follow-up have been observed. The American Society of Nephrology established the AKINow taskforce to address these gaps and improve AKI care. The AKINow Recovery workgroup convened two focus groups, one each focused on dialysis-independent and dialysis-requiring AKI, to summarize the key considerations, challenges, and opportunities in the care of AKI survivors. This article highlights the discussion surrounding care of AKI survivors discharged without the need for dialysis. On May 3, 2022, 48 patients and multidisciplinary clinicians from diverse settings were gathered virtually. The agenda included a patient testimonial, plenary sessions, facilitated small group discussions, and debriefing. Core challenges and opportunities for AKI care identified were in the domains of transitions of care, education, collaborative care delivery, diagnostic and therapeutic interventions, and digital health applications. Integrated multispecialty care delivery was identified as one of the greatest challenges to AKI survivor care. Adequate templates for communication and documentation; education of patients, care partners, and clinicians about AKI; and a well-coordinated multidisciplinary posthospital follow-up plan form the basis for a successful care transition at hospital discharge. The AKINow Recovery workgroup concluded that advancements in evidence-based, patient-centered care of AKI survivors are needed to improve health outcomes, care quality, and patient and provider experience. Tools are being developed by the AKINow Recovery workgroup for use at the hospital discharge to facilitate care continuity.

Plasma oxidative lipidomics reveals signatures for sepsis-associated acute kidney injury

BACKGROUND

Oxidized lipids are essential bioactive lipid mediators generated during infection that regulate oxidative stress and the inflammatory response, but their signatures in patients with sepsis-associated acute kidney injury (SA-AKI) are poorly understood. This study analyzed the oxidative lipidomics of plasma from patients with SA-AKI to reveal the underlying biomarkers and pathophysiological mechanisms involved in sepsis.

MATERIALS

A total of 67 patients with SA-AKI and 20 age- and sex-matched healthy controls (HCs) participated in this prospective cohort study. Among the patients with SA-AKI, 14 cases had stage I-II AKI and 53 cases had stage III AKI. Oxidative lipidomic analysis of plasma samples was conducted using ultra performance liquid chromatography coupled with tandem mass spectrometric (UPLC-MS /MS) detection.

RESULTS

Among 21 kinds of differentially oxidized lipids, 5(S),12(S)-DiHETE, 5-isoPGF2VI, 5,6-DiHETrE, 11,12-EET and 9,10-DiHOME showed the best performance. The prediction model incorporating them has shown highly sensitive and specific in distinguishing different stages of SA-AKI from HCs. The annotation of Kyoto Encyclopedia of Genes and Genomes illustrated that the overall downregulation of vascular smooth muscle contraction was closely related to the pathophysiological mechanism of SA-AKI.

CONCLUSION

This study revealed alterations in the characteristic oxidized lipids in the plasma of SA-AKI patients, and these lipids had high diagnostic efficiency and potential targeted intervention value for SA-AKI.

Mitochondrial antiviral signaling protein: a potential therapeutic target in renal disease

Mitochondrial antiviral signaling protein (MAVS) is a key innate immune adaptor on the outer mitochondrial membrane that acts as a switch in the immune signal transduction response to viral infections. Some studies have reported that MAVS mediates NF-κB and type I interferon signaling during viral infection and is also required for optimal NLRP3 inflammasome activity. Recent studies have reported that MAVS is involved in various cancers, systemic lupus erythematosus, kidney diseases, and cardiovascular diseases. Herein, we summarize the structure, activation, pathophysiological roles, and MAVS-based therapies for renal diseases. This review provides novel insights into MAVS's role and therapeutic potential in the pathogenesis of renal diseases.

Recent Advances of Proteomics in Management of Acute Kidney Injury

Acute Kidney Injury (AKI) is currently recognized as a life-threatening disease, leading to an exponential increase in morbidity and mortality worldwide. At present, AKI is characterized by a significant increase in serum creatinine (SCr) levels, typically followed by a sudden drop in glomerulus filtration rate (GFR). Changes in urine output are usually associated with the renal inability to excrete urea and other nitrogenous waste products, causing extracellular volume and electrolyte imbalances. Several molecular mechanisms were proposed to be affiliated with AKI development and progression, ultimately involving renal epithelium tubular cell-cycle arrest, inflammation, mitochondrial dysfunction, the inability to recover and regenerate proximal tubules, and impaired endothelial function. Diagnosis and prognosis using state-of-the-art clinical markers are often late and provide poor outcomes at disease onset. Inappropriate clinical assessment is a strong disease contributor, actively driving progression towards end stage renal disease (ESRD). Proteins, as the main functional and structural unit of the cell, provide the opportunity to monitor the disease on a molecular level. Changes in the proteomic profiles are pivotal for the expression of molecular pathways and disease pathogenesis. Introduction of highly-sensitive and innovative technology enabled the discovery of novel biomarkers for improved risk stratification, better and more cost-effective medical care for the ill patients and advanced personalized medicine. In line with those strategies, this review provides and discusses the latest findings of proteomic-based biomarkers and their prospective clinical application for AKI management.

Characterization of a proteomic profile associated with organ dysfunction and mortality of sepsis and septic shock

INTRODUCTION

The search for new biomarkers that allow an early diagnosis in sepsis and predict its evolution has become a necessity in medicine. The objective of this study is to identify, through omics techniques, potential protein biomarkers that are expressed in patients with sepsis and their relationship with organ dysfunction and mortality.

METHODS

Prospective, observational and single-center study that included adult patients (≥ 18 years) who were admitted to a tertiary hospital and who met the criteria for sepsis. A mass spectrometry-based approach was used to analyze the plasma proteins in the enrolled subjects. Subsequently, using recursive feature elimination classification and cross-validation with a vector classifier, an association of these proteins with mortality and organ dysfunction was established. The protein-protein interaction network was analyzed with String software.

RESULTS

141 patients were enrolled in this study. Mass spectrometry identified 177 proteins. Of all of them, and by recursive feature elimination, nine proteins (GPX3, APOB, ORM1, SERPINF1, LYZ, C8A, CD14, APOC3 and C1QC) were associated with organ dysfunction (SOFA > 6) with an accuracy of 0.82 ± 0.06, precision of 0.85 ± 0.093, sensitivity 0.81 ± 0.10, specificity 0.84 ± 0.10 and AUC 0.82 ± 0.06. Twenty-two proteins (CLU, LUM, APOL1, SAA1, CLEBC3B, C8A, ITIH4, KNG1, AGT, C7, SAA2, APOH, HRG, AFM, APOE, APOC1, C1S, SERPINC1, IGFALS, KLKB1, CFB and BTD) were associated with mortality with an accuracy of 0.86 ± 0.05, a precision of 0.91 ± 0.05, a sensitivity of 0.91 ± 0.05, a specificity of 0.72 ± 0.17, and an area under the curve (AUC) of 0.81 ± 0.08 with a confidence interval of 95%.

CONCLUSION

In sepsis there are proteomic patterns associated with organ dysfunction and mortality.

A universal predictive and mechanistic urinary peptide signature in acute kidney injury

BACKGROUND

The delayed diagnosis of acute kidney injury (AKI) episodes and the lack of specificity of current single AKI biomarkers hamper its management. Urinary peptidome analysis may help to identify early molecular changes in AKI and grasp its complexity to identify potential targetable molecular pathways.

METHODS

In derivation and validation cohorts totalizing 1170 major cardiac bypass surgery patients and in an external cohort of 1569 intensive care unit (ICU) patients, a peptide-based score predictive of AKI (7-day KDIGO classification) was developed, validated, and compared to the reference biomarker urinary NGAL and NephroCheck and clinical scores.

RESULTS

A set of 204 urinary peptides derived from 48 proteins related to hemolysis, inflammation, immune cells trafficking, innate immunity, and cell growth and survival was identified and validated for the early discrimination (&lt; 4 h) of patients according to their risk to develop AKI (OR 6.13 [3.96-9.59], p &lt; 0.001) outperforming reference biomarkers (urinary NGAL and [IGFBP7].[TIMP2] product) and clinical scores. In an external cohort of 1569 ICU patients, performances of the signature were similar (OR 5.92 [4.73-7.45], p &lt; 0.001), and it was also associated with the in-hospital mortality (OR 2.62 [2.05-3.38], p &lt; 0.001).

CONCLUSIONS

An overarching AKI physiopathology-driven urinary peptide signature shows significant promise for identifying, at an early stage, patients who will progress to AKI and thus to develop tailored treatments for this frequent and life-threatening condition. Performance of the urine peptide signature is as high as or higher than that of single biomarkers but adds mechanistic information that may help to discriminate sub-phenotypes of AKI offering new therapeutic avenues.

Exosomes from adipose-derived stem cells inhibit inflammation and oxidative stress in LPS-acute kidney injury

Acute renal damage presents a significant danger to kidney health. Previous research has found that acute kidney injury shows high levels of oxidative stress and inflammation caused by sepsis. Although mesenchymal stem cells (MSCs) can repair acute kidney injury. However, involvement of MSCs exosomes generated from adipose tissue and bone marrow in lipopolysaccharide-induced acute kidney damage is not clear. LPS (7.5 mg/kg) intraperitoneal injection was used to produce AKI, and 30 min before the LPS administration, adipose-derived MSCs (ADSCs) exosomes (1 × 10⁵ and 5 × 10⁵) and bone marrow-derived MSCs(BMSCs) exosomes (1 × 10⁵ and 5 × 10⁵) were delivered individually. The function of the rat kidney was explored. Inflammation, oxidative stress, and autophagy levels were further investigated. Both adipose-derived and bone marrow-derived MSCs can enhance renal function and structural damage, such as BUN, Creatinine, and cystatin C levels, as well as tubular damage scores. These findings indicate that both adipose-derived MSCs exosomes and bone marrow-derived MSCs exosomes decrease oxidative stress and inflammation, as well as make a substantial influence on kidney tissue in autophagy levels. Furthermore, compared to bone marrow-derived MSCs exosomes, adipose-derived MSCs exosomes improved kidney function and structure more significantly. We discovered that adipose-derived MSCs exosomes protect against LPS-induced AKI by inhibiting oxidative stress and inflammation.

Role of curcumin in the treatment of acute kidney injury: research challenges and opportunities

BACKGROUND

Acute kidney injury (AKI) is a common complication in clinical inpatients, and it continues a high morbidity and mortality rate despite many clinical treatment measures. AKI is triggered by infections, surgery, heavy metal exposure and drug side effects, but current chemical drugs often fall short of expectations for AKI treatment and have toxic side effects. Therefore, finding new interventions and treatments, especially of natural origin, is of remarkable clinical significance and application. The herbal monomer curcumin is a natural phenolic compound extracted from the plant Curcuma longa and showed various biological activities, including AKI. Furthermore, recent studies have shown that curcumin restores renal function by modulating the immune system and the release of inflammatory mediators, scavenging oxygen free radicals, reducing apoptosis and improving mitochondrial dynamics. However, curcumin has a low bioavailability, which limits its clinical application. For this reason, it is essential to investigate the therapeutic effects and molecular mechanisms of curcumin in AKI, as well as to improve its bioavailability for curcumin formulation development and clinical application.

PURPOSE

This review summarizes the sources, pharmacokinetics, and limitations in the clinical application of curcumin and explores methods to optimize its bioavailability using nanotechnology. In particular, the therapeutic effects and molecular mechanisms of curcumin on AKI are highlighted to provide a theoretical basis for AKI treatment in clinical practices.

METHODS

This review was specifically searched by means of a search of three databases (Web of Science, PubMed and Science Direct), till December 2021. Search terms were "Curcumin", "Acute kidney injury", "AKI", " Pharmacokinetics", "Mitochondria" and "Nano formulations". The retrieved data followed PRISMA criteria (preferred reporting items for systematic review) RESULTS: Studies have shown that curcumin responded to AKI-induced renal injury and restored renal tubular epithelial cell function by affecting multiple signaling pathways in AKI models induced by factors such as cisplatin, lipopolysaccharide, ischemia/reperfusion, gentamicin and potassium dichromate. Curcumin was able to affect NF-κB signaling pathway and reduce the expression of IL-1β, IL-6, IL-8 and TNF-α, thus preventing renal inflammatory injury. In the prevention of renal tubular oxidative damage, curcumin reduced ROS production by activating the activity of Nrf2, HO-1 and PGC-1α. In addition, curcumin restored mitochondrial homeostasis by upregulating OPA1 and downregulating DRP1 expression, while reducing apoptosis by inhibiting the caspase-3 apoptotic pathway. In addition, due to the low bioavailability and poor absorption of curcumin in vivo, curcumin nanoformulations including nanoparticles, liposomes, and polymeric micelles are formulated to improve the bioavailability.

CONCLUSION

This review provides new ideas for the use of curcumin in the prevention and treatment of AKI by modulating the molecular targets of several different cellular signaling pathways.

Urinary metabolomics to develop predictors for pediatric acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is characterized by an abrupt decline in glomerular filtration rate (GFR). We sought to identify separate early urinary metabolomic signatures at AKI onset (with-AKI) and prior to onset of functional impairment (pre-AKI).

METHODS

Pre-AKI (n=15), AKI (n=22), and respective controls (n=30) from two prospective PICU cohort studies provided urine samples which were analyzed by GC-MS and DI-MS mass spectrometry (193 metabolites). The cohort (n=58) was 8.7±6.4 years old and 66% male. AKI patients had longer PICU stays, higher PRISM scores, vasopressors requirement, and respiratory diagnosis and less commonly had trauma or post-operative diagnosis. Urine was collected within 2-3 days after admission and daily until day 5 or 14.

RESULTS

The metabolite classifiers for pre-AKI samples (1.5±1.1 days prior to AKI onset) had a cross-validated area under receiver operator curve (AUC)=0.93 (95%CI 0.85-1.0); with-AKI samples had an AUC=0.94 (95%CI 0.87-1.0). A parsimonious pre-AKI classifier with 13 metabolites was similarly robust (AUC=0.96, 95%CI 0.89-1.0). Both classifiers were similar and showed modest correlation of high-ranking metabolites (tau=0.47, p<0.001).

CONCLUSIONS

This exploratory study demonstrates the potential of a urine metabolite classifier to detect AKI-risk in pediatric populations earlier than the current standard of diagnosis with the need for external validation. A higher resolution version of the Graphical abstract is available as Supplementary information with inner reference to ESM for GA.

Choline supplementation attenuates experimental sepsis-associated acute kidney injury

Acute kidney injury (AKI) is common in critically ill patients, and sepsis is its leading cause. Sepsis-associated AKI (SA-AKI) causes greater morbidity and mortality than other AKI etiologies, yet the underlying mechanisms are incompletely understood. Metabolomic technologies can characterize cellular energy derangements, but few discovery analyses have evaluated the metabolomic profile of SA-AKI. To identify metabolic derangements amenable to therapeutic intervention, we assessed plasma and urine metabolites in septic mice and critically ill children and compared them by AKI status. Metabolites related to choline and central carbon metabolism were differentially abundant in SA-AKI in both mice and humans. Gene expression of enzymes related to choline metabolism was altered in the kidneys and liver of mice with SA-AKI. Treatment with intraperitoneal choline improved renal function in septic mice. Because pediatric patients with sepsis displayed similar metabolomic profiles to septic mice, choline supplementation may attenuate pediatric septic AKI.NEW & NOTEWORTHY Altered choline metabolism plays a role in both human and murine sepsis-associated acute kidney injury (SA-AKI), and choline administration in experimental SA-AKI improved renal function. These findings indicate that 1) mouse models can help interrogate clinically relevant mechanisms and 2) choline supplementation may ameliorate human SA-AKI. Future research will investigate clinically the impact of choline supplementation on human renal function in sepsis and, using model systems, how choline mediates its effects.

Exploring the Muscle Metabolomics in the Mouse Model of Sepsis-Induced Acquired Weakness

Background/Aim

We aimed to identify the differentially expressing metabolites (DEMs) in the muscles of the mouse model of sepsis-induced acquired weakness (sepsis-AW) using liquid chromatography-mass spectrometry (LC-MS).

Materials and Methods

Sepsis by cecal ligation puncture (CLP) with lower limb immobilization was used to produce a sepsis-AW model. After this, the grip strength of the C57BL/6 male mice was investigated. The transmission electron microscopy was utilized to determine the pathological model. LC-MS was used to detect the metabolic profiles within the mouse muscles. Additionally, a statistically diversified analysis was carried out.

Results

Compared to the sepsis group, 30 DEMs, including 17 upregulated and 13 down-regulated metabolites, were found in the sepsis-AW group. The enriched metabolic pathways including purine metabolism, valine/leucine/isoleucine biosynthesis, cGMP-PKG pathway, mTOR pathway, FoxO pathway, and PI3K-Akt pathway were found to differ between the two groups. The targeted metabolomics analysis explored significant differences between four amino acid metabolites (leucine, cysteine, tyrosine, and serine) and two energy metabolites (AMP and cAMP) in the muscles of the sepsis-AW experimental model group, which was comparable to the sepsis group.

Conclusion

The present work identified DEMs and metabolism-related pathways within the muscles of the sepsis-AW mice, which offered valuable experimental data for diagnosis and identification of the pathogenic mechanism underlying sepsis-AW.

Multi-Omics Techniques Make it Possible to Analyze Sepsis-Associated Acute Kidney Injury Comprehensively

Sepsis-associated acute kidney injury (SA-AKI) is a common complication in critically ill patients with high morbidity and mortality. SA-AKI varies considerably in disease presentation, progression, and response to treatment, highlighting the heterogeneity of the underlying biological mechanisms. In this review, we briefly describe the pathophysiology of SA-AKI, biomarkers, reference databases, and available omics techniques. Advances in omics technology allow for comprehensive analysis of SA-AKI, and the integration of multiple omics provides an opportunity to understand the information flow behind the disease. These approaches will drive a shift in current paradigms for the prevention, diagnosis, and staging and provide the renal community with significant advances in precision medicine in SA-AKI analysis.

Metabolomic profiling demonstrates evidence for kidney and urine metabolic dysregulation in a piglet model of cardiac surgery-induced acute kidney injury

Acute kidney injury (AKI) is a common cause of morbidity after congenital heart disease surgery. Progress on diagnosis and therapy remains limited, however, in part due to poor mechanistic understanding and a lack of relevant translational models. Metabolomic approaches could help identify novel mechanisms of injury and potential therapeutic targets. In the present study, we used a piglet model of cardiopulmonary bypass with deep hypothermic circulatory arrest (CPB/DHCA) and targeted metabolic profiling of kidney tissue, urine, and serum to evaluate metabolic changes specific to animals with histological acute kidney injury. CPB/DHCA animals with acute kidney injury were compared with those without acute kidney injury and mechanically ventilated controls. Acute kidney injury occurred in 10 of 20 CPB/DHCA animals 4 h after CPB/DHCA and 0 of 7 control animals. Injured kidneys showed a distinct tissue metabolic profile compared with uninjured kidneys (R² = 0.93, Q² = 0.53), with evidence of dysregulated tryptophan and purine metabolism. Nine urine metabolites differed significantly in animals with acute kidney injury with a pattern suggestive of increased aerobic glycolysis. Dysregulated metabolites in kidney tissue and urine did not overlap. CPB/DHCA strongly affected the serum metabolic profile, with only one metabolite that differed significantly with acute kidney injury (pyroglutamic acid, a marker of oxidative stress). In conclusion, based on these findings, kidney tryptophan and purine metabolism are candidates for further mechanistic and therapeutic investigation. Urine biomarkers of aerobic glycolysis could help diagnose early acute kidney injury after CPB/DHCA and warrant further evaluation. The serum metabolites measured at this early time point did not strongly differentiate based on acute kidney injury.

NEW & NOTEWORTHY This project explored the metabolic underpinnings of postoperative acute kidney injury (AKI) following pediatric cardiac surgery in a translationally relevant large animal model of cardiopulmonary bypass with deep hypothermic circulatory arrest. Here, we present novel evidence for dysregulated tryptophan catabolism and purine catabolism in kidney tissue and increased urinary glycolysis intermediates in animals who developed histological AKI. These pathways represent potential diagnostic and therapeutic targets for postoperative AKI in this high-risk population.

From cardiorenal syndromes to cardionephrology: a reflection by nephrologists on renocardiac syndromes

Cardiorenal syndromes (CRS) are broadly defined as disorders of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other. CRS are currently classified into five categories, mostly based on disease-initiating events and their acuity or chronicity. CRS types 3 and 4 (also called renocardiac syndromes) refer to acute and chronic kidney dysfunction resulting in acute and chronic heart dysfunction, respectively. The notion of renocardiac syndromes has broadened interest in kidney-heart interactions but uncertainty remains in the nephrological community's understanding of the clinical diversity, pathophysiological mechanisms and optimal management approaches of these syndromes. This triple challenge that renocardiac syndromes (and likely other cardiorenal syndromes) pose to the nephrologist can only be faced through a specific and demanding training plan to enhance his/her cardiological scientific knowledge and through an appropriate clinical environment to develop his/her cardiological clinical skills. The first must be the objective of the subspecialty of cardionephrology (or nephrocardiology) and the second must be the result of collaboration with cardiologists (and other specialists) in cardiorenal care units. This review will first consider various aspects of the challenges that renocardiac syndromes pose to nephrologists and, then, will discuss those aspects of cardionephrology and cardiorenal units that can facilitate an effective response to the challenges.

Identification of inflammatory response and alternative splicing in acute kidney injury and experimental verification of the involvement of RNA‑binding protein RBFOX1 in this disease

An increasing number of inflammatory responses and alternative splicing (AS) have been recently reported to be associated with various kidney diseases. The effect of inflammatory response on acute kidney injury (AKI) has not been fully clarified. In the present study, a mouse model of AKI induced by cisplatin and ischemia-reperfusion (IR) was established and genome-wide profiling analysis and identification of differentially expressed genes (DEGs) in kidney tissue was conducted by Gene Ontology (GO) functional analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, protein-protein interaction (PPI) network analysis and RT-qPCR. The results revealed that common DEGs in AKI induced by cisplatin and IR were enriched in the inflammatory response pathway, including hub genes CSF-1, CXCL1, CXCL10, IL-1β, IL-34, IL-6 and TLR2. AS in AKI was initially reported. Cisplatin-induced AS was enriched in the phosphorylation pathway, involving regulated AS genes CSNK1A1, PAK2, CRK, ADK and IKBKB. IR-induced AS was enriched in apoptosis and proliferation pathways, including DEGs ZDHHC16, BCL2L1 and FGF1 regulated by AS. The ability of RNA-binding proteins (RBPs) to regulate AS was coordinated with the function of context-dependent genetic mechanisms. A total of 49 common differentially expressed RBP genes were screened. RNA binding fox-1 homolog 1 (RBFOX1) was revealed to be the top downregulated gene. The relative levels of RBFOX1 in the nuclei of mouse renal tubular epithelial cells in mRNA and proteins were downregulated by cisplatin and IR. Moreover, the biological functions of RBFOX1 were investigated in human renal proximal tubular epithelial cells (HK-2 cells). Results of in vitro experiments revealed that exogenous RBFOX1 inhibited inflammation and oxidative stress to reduce hypoxia/reoxygenation-induced apoptosis of HK-2 cells. This phenomenon may be related to the inhibition of NF-κB and the activation of the NRF2/HO-1 signaling pathway. In conclusion, the inflammatory cytokines, AS and RBPs in AKI were analyzed in the present study via whole transcriptome sequencing. It was revealed that the RBP gene RBFOX1 was involved in the pathogenesis of AKI. Thus, the present study provided novel insights into the mechanism of AKI pathogenesis.

Dynamic R2' Imaging can Be a Biomarker for Diagnosing and Staging Early Acute Kidney Injury in Animals

Background: Early diagnosis of acute kidney injury (AKI) is essential in clinical settings. None of the current biomarkers are widely applied. The combination of pulse-shifting multi-echo asymmetric spin-echo sequence (psMASE) and a modified hemodynamic response imaging (HRI) technique is promising. The purpose of this study was to evaluate the feasibility of psMASE combined with HRI in detecting early ischemic AKI in animal models of different severities.

Methods: Twenty rabbits were divided into four groups (mild, moderate, and severe AKI and control groups). Transarterial embolization with different doses of microspheres was performed to establish AKI animal models of different severities. The 3T psMASE and HRI scans of kidneys were conducted. The R2^*, R2, and R2' during room air and gas stimulation were acquired and the difference of R2' (dR2') was evaluated in different AKI groups.

Results: The values were not different in R2^* and R2 during room air and in R2^* and R2, and R2' during gas stimulation. The value of R2' was significantly different during room air (P = 0.014), but the difference was only found between control and moderate/severe AKI groups (P = 0.032 and 0.022). The values of dR2' were different among groups (P < 0.0001) and differences between every two groups except comparison of moderate and severe AKI groups were significant (P < 0.01).

Conclusion: The dR2' imaging acquired by a combination of renal psMASE and HRI technique can serve as a potential quantitative biomarker for early detection and staging of 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.

Multi-omic approaches to acute kidney injury and repair

The kidney has a remarkable regenerative capacity. In response to ischemic or toxic injury, proximal tubule cells can proliferate to rebuild damaged tubules and restore kidney function. However, severe acute kidney injury (AKI) or recurrent AKI events can lead to maladaptive repair and disease progression from AKI to chronic kidney disease (CKD). The application of single cell technologies has identified injured proximal tubule cell states weeks after AKI, distinguished by a pro-inflammatory senescent molecular signature. Epigenetic studies highlighted dynamic changes in the chromatin landscape of the kidney following AKI and described key transcription factors linked to the AKI response. The integration of multi-omic technologies opens new possibilities to improve our understanding of AKI and the driving forces behind the AKI-to-CKD transition, with the ultimate goal of designing tailored diagnostic and therapeutic strategies to improve AKI outcomes and prevent kidney disease progression.

Does Artificial Intelligence Make Clinical Decision Better? A Review of Artificial Intelligence and Machine Learning in Acute Kidney Injury Prediction

Acute kidney injury (AKI) is a common complication of hospitalization that greatly and negatively affects the short-term and long-term outcomes of patients. Current guidelines use serum creatinine level and urine output rate for defining AKI and as the staging criteria of AKI. However, because they are not sensitive or specific markers of AKI, clinicians find it difficult to predict the occurrence of AKI and prescribe timely treatment. Advances in computing technology have led to the recent use of machine learning and artificial intelligence in AKI prediction, recent research reported that by using electronic health records (EHR) the AKI prediction via machine-learning models can reach AUROC over 0.80, in some studies even reach 0.93. Our review begins with the background and history of the definition of AKI, and the evolution of AKI risk factors and prediction models is also appraised. Then, we summarize the current evidence regarding the application of e-alert systems and machine-learning models in AKI prediction.

An integrative proteomics metabolomics based strategy reveals the mechanisms involved in wasp sting induced acute kidney injury

The pathophysiological mechanisms involved in wasp-sting-induced acute kidney injury (AKI) remain largely unknown. Here, we combined proteomics and metabolomics to investigate the mechanisms behind multiple wasp sting-induced AKI. Interestingly, we found many differentially abundant proteins in the serum of AKI group compared with that of the non-AKI and control groups, involved in several metabolic pathways and the regulation of cellular processes. In addition, we also detected differentially abundant metabolites in the AKI group; among them many were involved in the glycerophospholipid metabolic pathway (the key pathway in the context of AKI): 50 metabolites, all downregulated in the AKI group. Importantly, the convergent analysis of metabolomics and proteomics data revealed that biomarkers of rhabdomyolysis (CA 3, MYL3, and LDH) and hemolysis (ALT and LDH) were integrated into a regulatory network with phospholipid metabolism products in the AKI group, indicating that wasp sting-induced AKI is secondary to rhabdomyolysis and intravascular hemolysis. Of note, such a phenotype suggests the disruption of the membrane of skeletal muscle cells and red blood cells mediated by the phospholipase A1 (PLA1), PLA2, and mastoparan in the wasp venom, via the disruption of membrane glycerophospholipids. Overall, our results highlight a potential new mechanism behind wasp sting-induced AKI and suggest that PLA inhibitors may be potential agents for the treatment of this condition.

Serum metabolic profile of postoperative acute kidney injury following infant cardiac surgery with cardiopulmonary bypass

BACKGROUND

We sought to determine differences in the circulating metabolic profile of infants with or without acute kidney injury (AKI) following cardiothoracic surgery with cardiopulmonary bypass (CPB).

METHODS

We performed a secondary analysis of preoperative and 24-h postoperative serum samples from infants ≤ 120 days old undergoing CPB. Metabolic profiling of the serum samples was performed by targeted analysis of 165 serum metabolites via tandem mass spectrometry. We then compared infants who did or did not develop AKI in the first 72 h postoperatively to determine global differences in the preoperative and 24-h metabolic profiles in addition to specific differences in individual metabolites.

RESULTS

A total of 57 infants were included in the study. Six infants (11%) developed KDIGO stage 2/3 AKI and 13 (23%) developed stage 1 AKI. The preoperative metabolic profile did not differentiate between infants with or without AKI. Infants with severe AKI could be moderately distinguished from infants without AKI by their 24-h metabolic profile, while infants with stage 1 AKI segregated into two groups, overlapping with either the no AKI or severe AKI groups. Differences in these 24-h metabolic profiles were driven by 21 metabolites significant at an adjusted false discovery rate of < 0.05. Prominently altered pathways include purine, methionine, and kynurenine/nicotinamide metabolism.

CONCLUSION

Moderate-to-severe AKI after infant cardiac surgery is associated with changes in the serum metabolome, including prominent changes to purine, methionine, and kynurenine/nicotinamide metabolism. A portion of infants with mild AKI demonstrated similar metabolic changes, suggesting a potential role for metabolic analysis in the evaluation of lower stage injury.

Proteomic Biomarkers in the Cardiorenal Syndrome: Toward Deciphering Molecular Pathophysiology

Cardiorenal syndrome (CRS) is defined by coexisting heart and renal dysfunctions. Malfunction of 1 organ may cause dysfunction of the other with variable causative disease that defines the type of CRS (1-5). Numerous studies showed that the prevalence of cardiovascular disease is increased in patients with chronic kidney disease (CKD). Similarly, CKD affects a large proportion of patients with heart failure. This overlap between primary heart or primary kidney disease blurs cause-effect inferences of the initiator/target organ. The classical subdivision of CRS in 5 categories does not provide pathophysiological suggestions for targeted intervention. It seems timely to revisit the value of CRS biomarkers in a pathophysiology-centered approach. We systematically reviewed the literature in CRS, which revealed 53 clinical studies describing the use of 44 biomarkers and 4 proteomic panels. All biomarkers are involved in at least one of the CRS comorbidities. Among the pathways affected, inflammation, aberrant glucose metabolism, neurohormonal activation, and oxidative stress are well described. There is growing evidence that fibrosis may be the "cornerstone" that unifies most of the pathways leading to CRS. Formation of excess fibrous connective tissue antedates CRS in many cases. This review highlights that biomarkers reflecting fibrosis may be of substantial clinical value in the early detection, prognostication, and guiding treatment of CRS. Biomarkers detecting changes in collagen turnover in the extracellular matrix of heart and kidney appear able to depict subclinical changes in the fibrotic remodeling of tissues and constitute a promising approach toward personalized intervention in CRS.

Serum metabolomics in chickens infected with Cryptosporidium baileyi

Background

Cryptosporidium baileyi is an economically important zoonotic pathogen that causes serious respiratory symptoms in chickens for which no effective control measures are currently available. An accumulating body of evidence indicates the potential and usefulness of metabolomics to further our understanding of the interaction between pathogens and hosts, and to search for new diagnostic or pharmacological biomarkers of complex microorganisms. The aim of this study was to identify the impact of C. baileyi infection on the serum metabolism of chickens and to assess several metabolites as potential diagnostic biomarkers for C. baileyi infection.

Methods

Ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) and subsequent multivariate statistical analysis were applied to investigate metabolomics profiles in the serum samples of chickens infected with C. baileyi, and to identify potential metabolites that can be used to distinguish chickens infected with C. baileyi from non-infected birds.

Results

Multivariate statistical analysis identified 138 differential serum metabolites between mock- and C. baileyi-infected chickens at 5 days post-infection (dpi), including 115 upregulated and 23 downregulated compounds. These metabolites were significantly enriched into six pathways, of which two pathways associated with energy and lipid metabolism, namely glycerophospholipid metabolism and sphingolipid metabolism, respectively, were the most enriched. Interestingly, some important immune-related pathways were also significantly enriched, including the intestinal immune network for IgA production, autophagy and cellular senescence. Nine potential C. baileyi-responsive metabolites were identified, including choline, sirolimus, all-trans retinoic acid, PC(14:0/22:1(13Z)), PC(15:0/22:6(4Z,7Z,10Z,13Z,16Z,19Z)), PE(16:1(9Z)/24:1(15Z)), phosphocholine, SM(d18:0/16:1(9Z)(OH)) and sphinganine.

Conclusions

This is the first report on serum metabolic profiling of chickens with early-stage C. baileyi infection. The results provide novel insights into the pathophysiological mechanisms of C. baileyi in chickens.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04834-y.

Non-invasive continuous renal tissue oxygenation monitoring to identify preterm neonates at risk for acute kidney injury

BACKGROUND

Near-infrared spectroscopy (NIRS) is an emerging tool to identify signs of inadequate tissue oxygenation in preterm neonates with acute kidney injury (AKI). Previous studies have shown a correlation between low renal tissue oxygenation (RrSO₂) in the first 24 hours of age and the later development of AKI. In this prospective clinical trial, NIRS monitoring was used to identify changes in RrSO₂ in comparison to traditional AKI markers, serum creatinine (SCr), and urine output (UOP).

METHODS

We enrolled 35 preterm neonates born less than 32 weeks' gestation and applied neonatal NIRS sensors at less than 48 hours of age. Neonates underwent 7 days of continuous monitoring. Renal and demographic information were collected for the first 7 days of age. AKI was determined by the modified neonatal Kidney Disease: Improving Global Outcomes (KDIGO) definition including UOP.

RESULTS

Three patients experienced AKI, all based on both SCr and UOP criteria. Each neonate with AKI had decreases in RrSO₂ over 48 hours prior to changes in SCr and UOP. Patients with AKI had lower median RrSO₂ values compared to patients without AKI over the first week of age, (32.4% vs. 60%, p < 0.001).

CONCLUSION

RrSO₂ monitoring identified preterm neonates at risk for AKI. NIRS detected a decline in RrSO₂ prior to changes in SCr and UOP and was significantly lower in patients with AKI compared to those without AKI. Further studies are needed to evaluate the ability of RrSO₂ monitoring to detect signs of kidney stress prior to the diagnosis of AKI. Graphical abstract.

Present Situation and Research Progress of Kidney Function Recoverability Evaluation of Acute Kidney Injury Patient

Acute kidney injury (AKI) is a critical illness in clinic. The guideline recommendation of kidney disease for improving global outcomes regards urine volume and creatinine as standards to evaluate kidney functions. However, urine volume and creatinine have a certain delay for kidney function evaluation, and these would be interfered by many factors. Whether the renal function of AKI patients can recover is very important, which affects the quality of life of patients. Therefore, the present study reviews the application situation and research progress of the recoverability evaluation of AKI patient kidney function from three aspects: conventional indexes, biomarkers, and imaging methods of kidney function.

The application of omic technologies to research in sepsis-associated acute kidney injury

Acute kidney injury (AKI) is common in critically ill children and adults, and sepsis-associated AKI (SA-AKI) is the most frequent cause of AKI in the ICU. To date, no mechanistically targeted therapeutic interventions have been identified. High-throughput "omic" technologies (e.g., genomics, proteomics, metabolomics, etc.) offer a new angle of approach to achieve this end. In this review, we provide an update on the current understanding of SA-AKI pathophysiology. Omic technologies themselves are briefly discussed to facilitate interpretation of studies using them. We next summarize the body of SA-AKI research to date that has employed omic technologies. Importantly, omic studies are helping to elucidate a pathophysiology of SA-AKI centered around cellular stress responses, metabolic changes, and dysregulation of energy production that underlie its clinical features. Finally, we propose opportunities for future research using clinically relevant animal models, integrating multiple omic technologies and ultimately progressing to translational human studies focusing therapeutic strategies on targeted disease mechanisms.

Acute kidney injury leading to CKD is associated with a persistence of metabolic dysfunction and hypertriglyceridemia

Fibrosis is the pathophysiological hallmark of progressive chronic kidney disease (CKD). The kidney is a highly metabolically active organ, and it has been suggested that disruption in its metabolism leads to renal fibrosis. We developed a longitudinal mouse model of acute kidney injury leading to CKD and an in vitro model of epithelial to mesenchymal transition to study changes in metabolism, inflammation, and fibrosis. Using transcriptomics, metabolic modeling, and serum metabolomics, we observed sustained fatty acid metabolic dysfunction in the mouse model from early to late stages of CKD. Increased fatty acid biosynthesis and downregulation of catabolic pathways for triglycerides and diacylglycerides were associated with a marked increase in these lipids in the serum. We therefore suggest that the kidney may be the source of the abnormal lipid profile seen in patients with CKD, which may provide insights into the association between CKD and cardiovascular disease.

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Following AKI, markers of fibrosis and inflammation go up simultaneously

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AKI is associated with reduced fatty acid oxidation and oxidative phosphorylation

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Changes in metabolism persist as chronic kidney disease develops

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Changes in metabolism are associated with increased serum levels of triglycerides

[Acute kidney injury following acute pancreatitis (AP-AKI): Definition, Pathophysiology, Diagnosis and Therapy]

Acute pancreatitis (AP) is the most frequent gastrointestinal cause for hospitalization and one of the leading causes of in-hospital deaths. Severe acute pancreatitis is often associated with multiorgan failure and especially with acute kidney injury (AKI). AKI can develop early or late in the course of the disease and is a strong determinator of outcome. The mortality in the case of dialysis-dependent AKI and acute pancreatitis raises exponentially in the affected patients. AP-induced AKI (AP-AKI) shows many similarities but also distinct differences to other causes of AKI occurring in the intensive care unit setting. The knowledge of the exact pathophysiology can help to adjust, control and improve therapeutic approaches to the disease. Unfortunately, there are only a few studies dealing with AP and AKI.In this review, we discuss recent data about pathogenesis, causes and management of AP-AKI in patients with severe acute pancreatitis and exploit in this regard the diagnostic and prognostic potential of respective newer serum and urine markers.

Clinical adoption of Nephrocheck® in the early detection of acute kidney injury

Acute kidney injury is a common complication of acute illnesses and is associated with increased morbidity and mortality. Over the past years several acute kidney injury biomarkers for diagnostication, decision-making processes, and prognosis of acute kidney injury and its outcomes have been developed and validated. Among these biomarkers, tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7), the so-called cell cycle arrest biomarkers, showed a superior profile of accuracy and stability even in patients with substantial comorbidities. Therefore, in 2014, the US Food and Drug Administration approved the use of the product of TIMP-2 and IGFBP7 ([TIMP-2] × [IGFBP7]), known as cell cycle arrest biomarkers, to aid critical care physicians and nephrologists in the early prediction of acute kidney injury in the critical care setting. To date, Nephrocheck® is the only commercially available test for [TIMP-2] × [IGFBP7]. In this narrative review, we describe the growing clinical and investigational momentum of biomarkers, focusing on [TIMP-2] × [IGFBP7], as one of the most promising candidate biomarkers. Additionally, we review the current state of clinical implementation of Nephrocheck®.

Curcumin and LOXblock-1 ameliorate ischemia-reperfusion induced inflammation and acute kidney injury by suppressing the semaphorin-plexin pathway

AIMS

Ischemia/reperfusion (I/R) is one of the most important causes of acute kidney injury (AKI), a clinical syndrome with kidney dysfunction and high mortality rates. New diagnostic biomarkers need to be defined to better illuminate the pathophysiology of AKI. For the first time, we aim to investigate the protective effects of Curcumin which is known for its antioxidant and anti-inflammatory properties and 12/15 lipoxygenase inhibitor LOXblock-1 on I/R induced AKI by modulating inflammatory processes, oxidative stress, apoptosis and semaphorin-plexin pathway.

MAIN METHODS

The rats were divided into five groups, with eight animals per group: Sham, I/R, I/R + DMSO (1%, i.p.), I/R + Curcumin (100 mg/kg, i.p.), I/R + LOXblock-1 (2 μg/kg, i.p.).

KEY FINDINGS

The renal function biomarkers (BUN, CREA and UA) in serum were significantly increased in the I/R group. The inflammatory (TNF-α, IL-6 and MCP-1), apoptotic (CYCS and CASP3) and oxidative stress parameters (MDA, MPO, TAS and TOS) measured by ELISA were significantly increased in the I/R group. In histopathological analysis, it was observed that I/R caused serious damage to kidney tissue. SEMA3A was found to increase both serum level and mRNA expression in I/R group. It was observed that curcumin and LOXblock-1 reduce inflammatory processes, oxidative stress and apoptosis via the semaphorin-plexin pathway by both measurements and histopathological analysis. Curcumin was proved more effective than LOXblock-1 with its antioxidant feature in I/R injury.

SIGNIFICANCE

The current study reveals the protective effects of Curcumin and LOXblock-1 on acute kidney injury by suppressing SEMA3A as a new biomarker.

Analytical techniques for metabolomic studies: a review

Metabolomics is the comprehensive study of small-molecule metabolites. Obtaining a wide coverage of the metabolome is challenging because of the broad range of physicochemical properties of the small molecules. To study the compounds of interest spectroscopic (NMR), spectrometric (MS) and separation techniques (LC, GC, supercritical fluid chromatography, CE) are used. The choice for a given technique is influenced by the sample matrix, the concentration and properties of the metabolites, and the amount of sample. This review discusses the most commonly used analytical techniques for metabolomic studies, including their advantages, drawbacks and some applications.

Recent advances in acute kidney injury and its consequences and impact on chronic kidney disease

PURPOSE OF REVIEW

Acute kidney injury (AKI) remains a major unmet medical need and associates with high morbidity, mortality, and healthcare costs. Among survivors, long-term outcomes of AKI can include development of chronic kidney disease (CKD) or progression of preexisting CKD. In this review, we focus on ongoing efforts by the AKI community to understand the human AKI to CKD continuum, with an emphasis on the cellular stress responses that underlie AKI and the maladaptive responses that persist in the acute-to-chronic phase. The emphasis is on work that has been published in the past year in this rapidly expanding field.

RECENT FINDINGS

Recent studies in preclinical models highlight the importance of mitochondrial dysfunction, cell death, and inflammation on the underlying pathogenesis of AKI. These pathogenic mechanisms can resolve with adaptive kidney repair but persist in maladaptive repair that leads to progressive chronic disease. The complexity and interconnections of these pathways involve cross-talk between the tubular epithelium, endothelium, and interstitial compartments.

SUMMARY

Approaches which lessen or counteract these cellular responses represent novel strategies to prevent AKI and stop or slow down the progression to CKD.

Biomarker Panels in Critical Care

Biomarker panels have the potential to advance the field of critical care medicine by stratifying patients according to prognosis and/or underlying pathophysiology. This article discusses the discovery and validation of biomarker panels, along with their translation to the clinical setting. The current literature on the use of biomarker panels in sepsis, acute respiratory distress syndrome, and acute kidney injury is reviewed.

Artificial Intelligence in Acute Kidney Injury Risk Prediction

Acute kidney injury (AKI) is a frequent complication in hospitalized patients, which is associated with worse short and long-term outcomes. It is crucial to develop methods to identify patients at risk for AKI and to diagnose subclinical AKI in order to improve patient outcomes. The advances in clinical informatics and the increasing availability of electronic medical records have allowed for the development of artificial intelligence predictive models of risk estimation in AKI. In this review, we discussed the progress of AKI risk prediction from risk scores to electronic alerts to machine learning methods.

Urinary Peptidomic Biomarkers in Kidney Diseases

In order to effectively develop personalized medicine for kidney diseases we urgently need to develop highly accurate biomarkers for use in the clinic, since current biomarkers of kidney damage (changes in serum creatinine and/or urine albumin excretion) apply to a later stage of disease, lack accuracy, and are not connected with molecular pathophysiology. Analysis of urine peptide content (urinary peptidomics) has emerged as one of the most attractive areas in disease biomarker discovery. Urinary peptidome analysis allows the detection of short and long-term physiological or pathological changes occurring within the kidney. Urinary peptidomics has been applied extensively for several years now in renal patients, and may greatly improve kidney disease management by supporting earlier and more accurate detection, prognostic assessment, and prediction of response to treatment. It also promises better understanding of kidney disease pathophysiology, and has been proposed as a “liquid biopsy” to discriminate various types of renal disorders. Furthermore, proteins being the major drug targets, peptidome analysis may allow one to evaluate the effects of therapies at the protein signaling pathway level. We here review the most recent findings on urinary peptidomics in the setting of the most common kidney diseases.

Sirt6 attenuates hypoxia-induced tubular epithelial cell injury via targeting G2/M phase arrest

Acute kidney injury (AKI) is a condition that has a high incidence and death rate. Unfortunately, the kidney may not recover completely after AKI, which then develops to chronic kidney disease (CKD). Therefore, it is necessary to identify potential curative targets to avoid its development to CKD. As an NAD⁺ -dependent deacetylase, sirtuin 6 (Sirt6) has been linked to different types of biological processes. In the present work, our group investigated the role of Sirt6 in tubular epithelial cells (TECs) under hypoxic stress. Sirt6 expression was examined in mouse kidney following ischemia/reperfusion (IR) injury and hypoxia-challenged TECs. Using Sirt6 plasmid and small interfering RNA, we also investigated how, in regard to inflammation and epithelial-to-mesenchymal transition, Sirt6 affects hypoxia-triggered injury. In addition, cell cycle was detected in hypoxia-challenged TECs. Sirt6 was downregulated in the kidney of mice with IR injury and hypoxia-challenged TECs. Consequently, Sirt6 depletion aggravated hypoxia-induced injury and G2/M phase arrest. Sirt6 overexpression attenuated hypoxia-triggered damage and G2/M phase arrest in TECs. Sirt6 prevented hypoxia-triggered TEC damage via suppressing G2/M phase arrest. Thus, Sirt6 is a possible candidate for alleviating the effects of kidney injury.

[Acute kidney injury: from creatinine to KIM‑1?]

In addition to the early detection of an acute kidney injury (AKI), several problems or questions have to be addressed. These include the identification of the etiology, the severity (functional or structural), the prognosis (recovery or transition to chronic renal failure), the course of the disease (dialysis or not), and the identification of specific treatment options for AKI. The following article provides an overview of established and new AKI biomarkers as well as an outlook on the potential of future biomarker-associated models of AKI.

Non-invasive differentiation of non-rejection kidney injury from acute rejection in pediatric renal transplant recipients

Acute kidney injury (AKI) is a major concern in pediatric kidney transplant recipients, where non-alloimmune causes must be distinguished from rejection. We sought to identify a urinary metabolite signature associated with non-rejection kidney injury (NRKI) in pediatric kidney transplant recipients. Urine samples (n = 396) from 60 pediatric transplant participants were obtained at time of kidney biopsy and quantitatively assayed for 133 metabolites by mass spectrometry. Metabolite profiles were analyzed via projection on latent structures discriminant analysis. Mixed-effects regression identified laboratory and clinical predictors of NRKI and distinguished NRKI from T cell-mediated rejection (CMR), antibody-mediated rejection (AMR), and mixed CMR/AMR. Urine samples (n = 199) without rejection were split into NRKI (n = 26; ΔSCr ≥25%), pre-NRKI (n = 35; ΔSCr ≥10% and <25%), and no NRKI (n = 138; ΔSCr <10%) groups. The NRKI discriminant score (dscore) distinguished between NRKI and no NRKI (AUC = 0.86; 95% CI = 0.79-0.94), confirmed by leave-one-out cross-validation (AUC = 0.79; 95% CI = 0.68-0.89). The NRKI dscore also distinguished between NRKI and pre-NRKI (AUC = 0.82; 95% CI = 0.71-0.93). In a linear mixed-effects regression model to account for repeated measures, the NRKI dscore was independent of concurrent rejection, but there was a non-statistical trend for higher dscores with rejection severity. A second exploratory classifier developed to distinguish NRKI from clinical rejection had similar test characteristics (AUC = 0.81, 95% CI = 0.70-0.92, confirmed by LOOCV). This study demonstrates the potential of a urine metabolite classifier to detect NRKI in pediatric kidney transplant patients and non-invasively discriminate NRKI from rejection.

Acute kidney injury overview: From basic findings to new prevention and therapy strategies

Acute kidney injury (AKI) is defined as a decrease in kidney function within hours, which encompasses both injury and impairment of renal function. AKI is not considered a pathological condition of single organ failure, but a syndrome in which the kidney plays an active role in the progression of multi-organ dysfunction. The incidence rate of AKI is increasing and becoming a common (8-16% of hospital admissions) and serious disease (four-fold increased hospital mortality) affecting public health costs worldwide. AKI also affects the young and previously healthy individuals affected by infectious diseases in Latin America. Because of the multifactorial pathophysiological mechanisms, there is no effective pharmacological therapy that prevents the evolution or reverses the injury once established; therefore, renal replacement therapy is the only current alternative available for renal patients. The awareness of an accurate and prompt recognition of AKI underlying the various clinical phenotypes is an urgent need for more effective therapeutic interventions to diminish mortality and socio-economic impacts of AKI. The use of biomarkers as an indicator of the initial stage of the disease is critical and the cornerstone to fulfill the gaps in the field. This review discusses emerging strategies from basic science toward the anticipation of features, treatment of AKI, and new treatments using pharmacological and stem cell therapies. We will also highlight bioartificial kidney studies, addressing the limitations of the development of this innovative technology.

Proteomic profiling of urine: implications for lupus nephritis

INTRODUCTION

Lupus nephritis (LN) is a common and significant manifestation, affecting 60% of adults and 80% of children with systemic lupus erythematosus, with up to 30% of patients progressing to end stage renal disease. There remains an unmet need for non-invasive markers of disease activity, damage, and response to therapy. In addition, non-invasive biomarkers that predict therapeutic efficacy are needed to enable cost-effective clinical trials of novel agents. Areas covered: This review examines the methodological aspects of urinary proteomics, the role of proteome profiling in identifying promising urinary biomarkers in LN, and the translation of research findings into clinically useful tools in the management of LN. Expert opinion: Targeted and unbiased proteomics have identified several promising urinary biomarkers that predict LN activity, damage (chronicity), and response to therapy. In particular, a combination of biologically plausible urinary biomarkers termed as RAIL (Renal Activity Index for Lupus) has emerged as an excellent predictor of LN activity as well as response to therapy, being able to predict efficacy within 3 months of therapy. If validated in additional large prospective studies, the RAIL biomarkers will transform the care of patients with LN, allowing for a personalized and predictive approach and improved outcomes.

Effects of Changes in the Levels of Damage-Associated Molecular Patterns Following Continuous Veno-Venous Hemofiltration Therapy on Outcomes in Acute Kidney Injury Patients With Sepsis

Background: We investigated the association of damage-associated molecular pattern (DAMP) removal with mortality in sepsis patients undergoing continuous veno–venous hemofiltration (CVVH).

Methods: Circulating levels of DAMPs [mitochondrial DNA (mtDNA); nuclear DNA (nDNA); heat shock protein 70 (HSP70); and high mobility group box 1 (HMGB1)] and cytokines were measured at baseline, 6 and 12 h after initiation of CVVH. Urinary DNA levels were analyzed at baseline and end of CVVH. The expression of human leukocyte antigen (HLA)-DR was assayed at 0, 3, and 7 days after initiation of CVVH. Moreover, the effects of HSP70 and HMGB1 clearance on survival were analyzed.

Results: We evaluated 43 patients with acute kidney injury (AKI) (33 sepsis patients). Twenty-two sepsis patients (67%) and three non-sepsis patients (30%) expired (P = 0.046). Significant reductions in the levels of circulating interleukin-6 (P = 0.046) and tumor necrosis factor-α (P = 0.008) were found in the sepsis group. The levels of mtDNA were increased (ND2, P = 0.035; D-loop, P = 0.003), whereas that of HSP70 was reduced (P = 0.000) in all patients during the first 12 h. The levels of DAMPs in the plasma were markedly increased after blood passage from the inlet through the dialyzer in survivor sepsis patients. The clearance rates of HSP70 and HMGB1 were good predictors of mortality [area under the curve (AUC) = 0.937, P = 0.000; AUC = 0.90, P = 0.001, respectively]. The level of HLA-DR was increased in response to higher HSP70 clearance (P = 0.006). Survival was significantly worse in groups with higher clearance rates of HSP70 and HMGB1 than the cut-off value (log-rank test: P = 0.000 for both). Higher HSP70 clearance was a significant independent predictor of mortality (odds ratio = 1.025, 95% confidence interval [CI]: 1.012–1.039, P = 0.000). The urinary nDNA (β-globin) level before CVVH was an independent risk factor for the duration of CVVH in patients with sepsis (sRE = 0.460, 95% CI: 1.720–8.857, P = 0.005).

Conclusion: CVVH removes inflammatory factors, reduces urinary DAMPs, and removes plasma DAMPs. However, survival decreases in response to higher HSP70 clearance.

Kidney histopathology in lethal human sepsis

Purpose

The histopathology of sepsis-associated acute kidney injury (AKI) in critically ill patients remains an understudied area. Previous studies have identified that acute tubular necrosis (ATN) is not the only driver of sepsis-AKI. The focus of this study was to identify additional candidate processes that may drive sepsis-AKI. To do this we immunohistochemically characterized the histopathological and cellular features in various compartments of human septic kidneys.

Methods

We studied the following histopathological features: leukocyte subsets, fibroblast activation, cellular proliferation, apoptosis, and fibrin deposition in the glomerulus and the tubulointerstitium in human post-mortem kidney biopsy tissue. Biopsy tissue samples from 27 patients with sepsis-AKI were collected 33 min (range 24–150) after death in the ICU. The unaffected part of the kidneys from 12 patients undergoing total nephrectomy as a result of renal carcinoma served as controls.

Results

Immunohistochemical analysis revealed the presence of more neutrophils and macrophages in the glomeruli and more neutrophils in the tubulointerstitium of renal tissue from patients with sepsis compared to control renal tissue. Type II macrophages were predominant, with some macrophages expressing both type I and type II markers. In contrast, there were almost no macrophages found in control kidneys. The number of activated (myo)fibroblasts was low in the glomeruli of sepsis-AKI kidneys, yet this was not observed in the tubulointerstitium. Cell proliferation and fibrin deposition were more pronounced in the glomeruli and tubulointerstitium of sepsis-AKI than in control kidneys.

Conclusions

The extensive heterogeneity of observations among and within patients emphasizes the need to thoroughly characterize patients with sepsis-AKI in a large sample of renal biopsy tissue from patients with sepsis.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2287-3) contains supplementary material, which is available to authorized users.