The complement system in pediatric acute kidney injury

Kidney Injury Following Cardiac Surgery: A Review of Our Current Understanding

Around one-quarter of all patients undergoing cardiac procedures, particularly those on cardiopulmonary bypass, develop cardiac surgery-associated acute kidney injury (CSA-AKI). This complication increases the risk of several serious morbidities and of mortality, representing a significant burden for both patients and the healthcare system. Patients with diminished kidney function before surgery, such as those with chronic kidney disease, are at heightened risk of developing CSA-AKI and have poorer outcomes than patients without preexisting kidney injury who develop CSA-AKI. Several mechanisms are involved in the development of CSA-AKI; injury is primarily thought to result from an amplification loop of inflammation and cell death, with complement and immune system activation, cardiopulmonary bypass, and ischemia-reperfusion injury all contributing to pathogenesis. At present there are no effective, targeted pharmacological therapies for the prevention or treatment of CSA-AKI, although several preclinical trials have shown promise, and clinical trials are under way. Progress in the understanding of the complex pathophysiology of CSA-AKI is needed to improve the development of successful strategies for its prevention, management, and treatment. In this review, we outline our current understanding of CSA-AKI development and management strategies and discuss potential future therapeutic targets under investigation.

Urine Complement Factor Ba Identifies Persistent Acute Kidney Injury and Organ Failures in Critically Ill Adults

Introduction

Critically ill adults with acute kidney injury (AKI) have high morbidity and mortality and lack treatment options. We assessed the association between complement activation (urine Ba fragment levels), and AKI and organ failures.

Methods

A biorepository of critically ill adults was leveraged. AKI staging was based on the Kidney Disease Improving Global Outcomes serum creatinine (sCr) criteria. AKI recovery was defined as sCr reduction to <0.3 mg/dl above baseline within 48 hours after AKI diagnosis. Persistent AKI was defined as need for renal replacement or no sCr recovery. Urine was obtained at intensive care unit (ICU) admission, and at 12 and 24 hours after admission; and urine Ba levels were quantitated via enzyme-linked immunosorbent assay and natural log transformed. Regression analyses were performed to test the association between urine Ba and organ failure outcomes. We adjusted for age and the acute physiology and chronic health evaluation II (APACHE-II) score, which is used to classify ICU severity of illness.

Results

A total of 439 patients were included: 252 without AKI, 124 with stage 1 AKI, 43 with stage 2 AKI, and 20 with stage 3 AKI. After adjusting for covariates, urine Ba increased as AKI stage increased. Urine Ba was higher in patients with persistent AKI compared with patients with AKI recovery and without AKI. Increased urine Ba was associated with worse organ failure outcomes (fewer ventilator, ICU, and inotrope-free days, and fewer days alive).

Conclusion

Urine Ba is increased in patients with severe AKI and discriminates between patients who have AKI recovery and patients who develop persistent AKI. A doubling of urine Ba was associated with a 6.6-fold increased odds of persistent AKI. Future studies to validate these findings and to trial complement factor B inhibition are warranted.

The immune regulatory role of lymphangiogenesis in kidney disease

The renal lymphatic system is critical for maintaining kidney homeostasis and regulating the immune response inside the kidney. In various kidney pathological situations, the renal lymphatic network experiences lymphangiogenesis, which is defined as the creation of new lymphatic vessels. Kidney lymphangiogenesis controls immunological response inside the kidney by controlling lymphatic flow, immune cell trafficking, and immune cell regulation. Ongoing study reveals lymphangiogenesis's different architecture and functions in numerous tissues and organs. New research suggests that lymphangiogenesis in kidney disorders may regulate the renal immune response in various ways. The flexibility of lymphatic endothelial cells (LECs) improves the kidney's immunological regulatory function of lymphangiogenesis. Furthermore, current research has shown disparate findings regarding its impact on distinct renal diseases, resulting in contradictory outcomes even within the same kidney condition. The fundamental causes of the various effects of lymphangiogenesis on renal disorders remain unknown. In this thorough review, we explore the dual impacts of renal lymphangiogenesis on several kidney pathologies, with a particular emphasis on existing empirical data and new developments in understanding its immunological regulatory function in kidney disease. An improved understanding of the immunological regulatory function of lymphangiogenesis in kidney diseases might help design novel medicines targeting lymphatics to treat kidney pathologies.

Diagnostic Challenges and Emerging Pathogeneses of Selected Glomerulopathies

Recent progress in glomerular immune complex and complement-mediated diseases have refined diagnostic categories and informed mechanistic understanding of disease development in pediatric patients. Herein, we discuss selected advances in 3 categories. First, membranous nephropathy antigens are increasingly utilized to characterize disease in pediatric patients and include phospholipase A2 receptor (PLA2R), Semaphorin 3B (Sema3B), neural epidermal growth factor-like 1 (NELL1), and protocadherin FAT1, as well as the lupus membranous-associated antigens exostosin 1/2 (EXT1/2), neural cell adhesion molecule 1 (NCAM1), and transforming growth factor beta receptor 3 (TGFBR3). Second, we examine advances in techniques for paraffin and light chain immunofluorescence (IF), including the former's function as a salvage technique and their necessity for diagnosis in adolescent cases of membranous-like glomerulopathy with masked IgG kappa deposits (MGMID) and proliferative glomerulonephritis with monotypic Ig deposits (PGNMID), respectively. Finally, progress in understanding the roles of complement in pediatric glomerular disease is reviewed, with specific attention to overlapping clinical, histologic, and genetic or functional alternative complement pathway (AP) abnormalities among C3 glomerulopathy (C3G), infection-related and post-infectious GN, "atypical" post-infectious GN, immune complex mediated membranoproliferative glomerulonephritis (IC-MPGN), and atypical hemolytic uremic syndrome (aHUS).

Usefulness and analytical performances of complement multiplex assay for measuring complement biomarkers in plasma

INTRODUCTION

The complement system is involved in numerous diseases, through diverse mechanisms and degree of activation. With the emergence of complement targeting therapeutic, simple and accessible tools to evaluate the extent of complement activation are strongly needed.

METHODS

We evaluated two multiplex panels, measuring complement activation fragments (C4a, C3a, C5a, Bb, Ba, sC5b9) and intact components or regulators (C1q, C2, C3, C4, C5, FD, FP, FH, FI). The specificity of each measurement was assessed by using complement proteins depleted sera and plasma collected from patients with complement deficiencies. Normal values distribution was estimated using 124 plasma samples from healthy donors and complement activation profile was assessed in plasma collected from 31 patients with various complement-mediated disorders.

RESULTS

We observed good inter-assay variation. All tested protein deficiencies were accurately detected. We established assay-specific reference values for each analyte. Except for C3, C4 and C4a, the majority of the measurements were in good agreement with references methods or published data.

CONCLUSION

Our study substantiates the utility of the Complement Multiplex assay as a tool for measuring complement activation and deficiencies. Quantifying complement cleavage fragments in patients exhibiting classical or alternative pathway activation allowed evaluating the activation state of the whole cascade.

Molecular characterization of complement regulatory factor CD46 in Trachinotus ovatus and its role in the antimicrobial immune responses and complement regulation

CD46, as a cofactor of complement I factor, not only regulates the complement system but also functions as a pathogen receptor and is involved in controlling early pathogen infection through autophagy. In this study, a new CD46 gene (ToCD46) was identified from golden pompano (Trachinotus ovatus), which showed higher sequence homology with other teleosts CD46. Homology comparison showed that ToCD46 had higher sequence homology (46.95-52.85%) with other teleosts CD46 and lower homology with mammal. Tissue expression profile analysis showed that ToCD46 was generally expressed in all tissues with the highest expression level in liver, followed by head kidney, and showed different patterns of up-regulation in immune-related tissues after stimulation by Streptococcus agalactiae and Vibrio alginolyticus. The hemolytic activity analysis and apoptosis assay showed that rToCD46 decreased the hemolytic activity of serum of golden pompano and effectively inhibited the damage of A549 cells, suggesting that ToCD46 might be involved in the regulation of complement activation of golden pompano. In vitro antibacterial experiments showed that rToCD46 had antibacterial activity against gram negative bacteria V. alginolyticus but no effect on positive bacteria S. agalactiae. These results suggest that ToCD46 may be involved in the immune response of golden pompano to pathogens, which will provide important basic information for elucidating the evolutionary history of the complement system of golden pompano.

Involvement of Innate Immune System in the Pathogenesis of Sepsis-Associated Acute Kidney Injury

Although experimental models have shown that the innate immune system is a main contributor to acute kidney injury (AKI), its involvement in human sepsis-associated AKI (SA-AKI) remains unclear. We retrospectively evaluated 19 patients with SA-AKI who were treated with continuous renal replacement therapy (CRRT). Serum cytokine, complement components, and the proportion and functions of innate immune cells, such as CD56+ T cells, CD56+ natural killer (NK) cells, and monocytes, were analyzed. There were no differences in the proportions of CD56+ T and NK cells between patients with SA-AKI and healthy controls. In patients with SA-AKI, fas ligand (FasL) expression in CD56+ T cells was significantly upregulated, and the proportion of perforin-positive CD56+ T cells tended to be higher than that in healthy controls. The positive rate of both FasL and perforin of CD56+ T cells was significantly higher than that of CD56- T cells, which include cytotoxic T cells. Antigen-presenting capacity and phagocytic activity of monocytes in patients with SA-AKI were significantly decreased compared to those of healthy controls and did not recover soon after the initiation of CRRT. CD56+ T cells are involved in the disease processes of human SA-AKI through effector molecules such as FasL or perforin.

Identification and validation of the diagnostic signature associated with immune microenvironment of acute kidney injury based on ferroptosis-related genes through integrated bioinformatics analysis and machine learning

Background: Acute kidney injury (AKI) is a common and severe disease, which poses a global health burden with high morbidity and mortality. In recent years, ferroptosis has been recognized as being deeply related to Acute kidney injury. Our aim is to develop a diagnostic signature for Acute kidney injury based on ferroptosis-related genes (FRGs) through integrated bioinformatics analysis and machine learning. Methods: Our previously uploaded mouse Acute kidney injury dataset GSE192883 and another dataset, GSE153625, were downloaded to identify commonly expressed differentially expressed genes (coDEGs) through bioinformatic analysis. The FRGs were then overlapped with the coDEGs to identify differentially expressed FRGs (deFRGs). Immune cell infiltration was used to investigate immune cell dysregulation in Acute kidney injury. Functional enrichment analysis and protein-protein interaction network analysis were applied to identify candidate hub genes for Acute kidney injury. Then, receiver operator characteristic curve analysis and machine learning analysis (Lasso) were used to screen for diagnostic markers in two human datasets. Finally, these potential biomarkers were validated by quantitative real-time PCR in an Acute kidney injury model and across multiple datasets. Results: A total of 885 coDEGs and 33 deFRGs were commonly identified as differentially expressed in both GSE192883 and GSE153625 datasets. In cluster 1 of the coDEGs PPI network, we found a group of 20 genes clustered together with deFRGs, resulting in a total of 48 upregulated hub genes being identified. After ROC analysis, we discovered that 25 hub genes had an area under the curve (AUC) greater than 0.7; Lcn2, Plin2, and Atf3 all had AUCs over than this threshold in both human datasets GSE217427 and GSE139061. Through Lasso analysis, four hub genes (Lcn2, Atf3, Pir, and Mcm3) were screened for building a nomogram and evaluating diagnostic value. Finally, the expression of these four genes was validated in Acute kidney injury datasets and laboratory investigations, revealing that they may serve as ideal ferroptosis markers for Acute kidney injury. Conclusion: Four hub genes (Lcn2, Atf3, Pir, and Mcm3) were identified. After verification, the signature's versatility was confirmed and a nomogram model based on these four genes effectively distinguished Acute kidney injury samples. Our findings provide critical insight into the progression of Acute kidney injury and can guide individualized diagnosis and treatment.

Urine Complement Factor Ba Is Associated with AKI in Critically Ill Children

Key Points

Complement activation, specifically factor B, is implicated in AKI pathogenesis in animal models. Urine Ba (an activation fragment of factor B) was significantly higher in critically ill children with stage 3 AKI and sepsis-AKI. If larger studies show similar association between urine Ba and AKI severity, clinical trials of factor B inhibition are warranted.

Background:

Critically ill children with AKI have high morbidity and mortality rates and lack treatment options. Complement activation is implicated in AKI pathogenesis, which could be treated with complement-targeted therapeutics. We assessed for an association between urine Ba, an activation fragment of the alternative complement pathway, and AKI in a large cohort of critically ill children.

Methods:

A biorepository of children requiring mechanical ventilation was leveraged. AKI was based on pediatric version of the RIFLE criteria—stage 1: 25% decreased eGFR or urine output (UOP) <0.5ml/kg per hour for 8 hours; stage 2: 50% decreased eGFR or UOP <0.5 ml/kg per hour for 16 hours; stage 3: 75% decreased eGFR or UOP <0.3ml/kg per hour for 24 hours or anuric for 12 hours. ELISAs were performed to quantitate urine Ba values. Log Ba was used in ANOVA with pairwise comparison by the Tukey method. Logistic regression was performed to test the association between urine Ba and AKI diagnosis.

Results:

Seventy-three patients were included, of which 56 had AKI: 26 (46%) stage 1, 16 (29%) stage 2, and 14 (25%) stage 3. Ba was significantly higher in patients with stage 3 AKI compared with all other stages. Ba was higher in sepsis-associated AKI compared with non–sepsis-associated AKI. Multivariate analysis included urine Ba, urine IL-18, urine NGAL, sepsis, and Pediatric Risk of Mortality Scores-II (an estimate of illness severity) and showed a significant association between urine Ba and AKI (odds ratio 1.57, 95% confidence interval, 1.13 to 2.20; P 0.007).

Conclusion:

Urine Ba is significantly increased in patients with AKI compared with patients without AKI. In patients with similar illness severity, a doubling of urine Ba level was associated with a 57% increase in AKI diagnosis of any stage. Further studies are needed to study complement inhibition in treatment or prevention of AKI in critically ill children.