Complement activation is a crucial driver of acute kidney injury in rhabdomyolysis

Harnessing complement biomarkers for precision cancer care

The tumor microenvironment (TME) consists of various immune and non-immune cells, along with proteins from different origins, and plays a crucial role in tumor development, treatment response, and patient prognosis. Complement system is a key player in the TME. It is a proteolytic cascade that generates cleavage fragments capable to activate cells through specific receptors or deposit on cells and tissues. This review summarizes current data on the complement system as a potential biomarker in cancer. Transcriptomic analyses have classified tumors based on the impact of complement gene expression on prognosis. Immunostaining provides insights into the expression and deposition of complement proteins and fragments in tumors and TME cells. In body fluids such as blood, measuring complement activation fragments and detecting anti-complement autoantibodies have identified non-invasive biomarkers relevant to certain cancer types. With the rise of complement-targeting therapies and new tools for analyzing the complement system in tumors and body fluids, it is time to define its role in cancer management. This includes its potential for cancer detection, staging, and potentially for treatment monitoring.

Enhanced renal ischemia/reperfusion injury repair potential of exosomes derived from B7-H1high mesenchymal stem cells

Two subgroups with high expression of B7-H1 and low expression of B7-H1 were successfully isolated from primitive human umbilical cord mesenchymal stem cells. And exosomes with high B7-H1 expression and low B7-H1 expression were successfully isolated. In comparison to the sham-operated group, mice in the IRI group demonstrated elevated serum levels of blood urea nitrogen (BUN) and serum creatinine (Scr), accompanied by a more pronounced degree of renal tissue damage. The administration of exosomes via the tail vein markedly accelerated the recovery of renal function in IRI mice, with the therapeutic effect beingmore pronounced in those treated with B7-H1high-Exo. Moreover RNA sequencing of mouse kidney treated with B7-H1high-Exo and B7-H1low-Exo showed that eight genes (C3, IRF7, AREG, CXCL10, Aldh1l2, Fnip2, Vcam1, St6galnac3) were involved in the pathophysiological process of ischemia-reperfusion injury. The in vitro and in vivo experiments showed that the expression level of C3 protein was significantly decreased, which indicated that B7-H1high-Exo played a therapeutic role by down-regulating C3.

Molecular mechanisms and therapeutic interventions in acute kidney injury: a literature review

Acute kidney injury (AKI) is a clinical challenge characterized by elevated morbidity and a substantial impact on individual health and socioeconomic factors. A comprehensive examination of the molecular pathways behind AKI is essential for its prevention and management. In recent years, vigorous research in the domain of AKI has concentrated on pathophysiological characteristics, early identification, and therapeutic approaches across many aetiologies and highlighted the principal themes of oxidative stress, inflammatory response, apoptosis, necrosis, and immunological response. This review comprehensively reviewed the molecular mechanisms underlying AKI, including oxidative stress, inflammatory pathways, immune cell-mediated injury, activation of the renin-angiotensin-aldosterone (RAAS) system, mitochondrial damage and autophagy, apoptosis, necrosis, etc. Inflammatory pathways are involved in the injuries in all four structural components of the kidney. We also summarized therapeutic techniques and pharmacological agents associated with the aforementioned molecular pathways. This work aims to clarify the molecular mechanisms of AKI thoroughly, offer novel insights for further investigations of AKI, and facilitate the formulation of efficient therapeutic methods to avert the progression of AKI.

Idiopathic inflammatory myopathy and C3 glomerulopathy: a rare association

Idiopathic inflammatory myopathies represent a spectrum of autoimmune disorders primarily characterized by muscle inflammation. While renal involvement in idiopathic inflammatory myopathies has historically been considered rare, recent findings indicate a prevalence of approximately 21-23%. Renal manifestations in idiopathic inflammatory myopathies are generally secondary to acute renal injury from rhabdomyolysis or, more rarely, occur through autoimmune mechanisms leading to glomerulonephritis. Here, we present the case of a 21-year-old male diagnosed with idiopathic inflammatory myopathy positive for anti-Jo antibodies and concurrent C3 glomerulonephritis, which improved following Rituximab therapy. The description of this case provides insights for future research into the role of alternative complement pathway dysregulation in idiopathic inflammatory myopathy-associated C3 glomerulopathy.

The roles of collectins in renal diseases and transplantation

The collectins are soluble C-type lectins and a group of proteins characterized with common structural features: a collagen-like domain and a carbohydrate-binding domain. These proteins are essential components of the innate immune system, pivotal for recognizing and eliminating pathogens to protect against infections. Over recent decades, research has significantly advanced our understanding of collectins. Beyond their fundamental role in host defense, collectins have been emerged as multifunctional proteins involved in modulating inflammatory and immune responses, facilitating the clearance of cellular debris, and even stimulating cell proliferation. These diverse roles are critical for maintaining physiological balance and hold substantial implications in various disease processes, particularly in renal diseases and transplantation. Here, we review the roles of collectins in renal diseases and transplantation focusing on four prominent members of the collectin family: mannose-binding lectin (MBL), surfactant proteins (SP-A and SP-D), and collectin-11 (CL-11). These proteins have gained considerable attention in current research due to their roles in renal diseases and transplantation, shedding light on their impact beyond traditional immune defense mechanisms. Understanding their involvement in these contexts is crucial for exploring potential therapeutic avenues and interventions aimed at mitigating renal pathology and improving outcomes in transplantation settings.

Efficacy of haemoadsorption combined with continuous renal replacement therapy in patients with rhabdomyolysis and acute kidney injury: a retrospective study

Background

Clearance of circulating myoglobin is crucial to prevent further damage in patients with rhabdomyolysis (RM) and acute kidney injury (AKI). The objective of the present study was to evaluate the efficacy and safety of haemoadsorption (HA) combined with continuous renal replacement therapy (CRRT) in critically ill patients with RM and AKI.

Methods

Patients with RM and AKI who received CRRT + HA or CRRT with concomitant creatine kinase (CK) >10 000 IU/l in our intensive care unit (ICU) between May 2021 and December 2023 were retrospectively included. The primary outcome was 90-day mortality; secondary outcomes were kidney function recovery and CK decline rate. Adverse events were also evaluated, including hypotension, circuit clotting, albumin leakage and blood loss. Propensity score matching and Cox retrospective analysis were performed.

Results

A total of 111 RM patients with AKI were ultimately included. The ICU and in-hospital mortality were significantly lower in the CRRT + HA group compared with the CRRT group (ICU mortality: 18% versus 42%, P = .025; in-hospital mortality: 21% versus 42%, P = .048). However, the CRRT + HA group only showed a non-significant reduction in 90-day mortality compared with the CRRT group (47% versus 68%, P = .063). After treatment for 90 days, the number of patients with kidney function recovery was not significantly different between the CRRT + HA and CRRT groups (95% versus 84%, P = .639). Moreover, the incidence of hypotension and circuit clotting events did not increase during CRRT + HA treatment. In addition, the CRRT + HA group also appeared to have a higher rate of CK reduction and reduction of CK than the CRRT group at 24 and 48 hours after the initiation of CRRT. A multivariate Cox regression model demonstrated that CRRT + HA {hazard ratio [HR] 0.477 [95% confidence interval (CI) 0.234-0.972], P = .042}, mean arterial blood pressure [per 1 mmHg; HR 0.967 (95% CI 0.943-0.992), P = .009] and CRRT treatment duration [per 1 h; HR 0.995 (95% CI 0.992-0.998), P = .002] played a favourably important role in the survival prognosis of RM and AKI patients. In contrast, serum phosphate before RRT [per 1 mmol/l; HR 1.531 (95% CI 1.113-2.106), P = .009] and McMahon score [per 1 score; HR 1.15 (95% CI 1.006-1.313), P = .04] were independent risk factors for 90-day mortality.

Conclusions

CRRT combined with HA therapy reduced ICU and in-hospital mortality in patients with RM and AKI and also had a cleansing effect on creatine kinase without significant adverse events.

A Newly Identified Protective Role of C5a Receptor 1 in Kidney Tubules against Toxin-Induced Acute Kidney Injury

Acute kidney injury (AKI) remains a major reason for hospitalization with limited therapeutic options. Although complement activation is implicated in AKI, the role of C5a receptor 1 (C5aR1) in kidney tubular cells is unclear. Herein, aristolochic acid nephropathy (AAN) and folic acid nephropathy (FAN) models were used to establish the role of C5aR1 in kidney tubules during AKI in germline C5ar1-/-, myeloid cell-specific, and kidney tubule-specific C5ar1 knockout mice. After aristolochic acid and folic acid injection, C5ar1-/- mice had increased AKI severity and a higher degree of tubular injury. Macrophage depletion in C5ar1-/- mice or myeloid cell-specific C5ar1 deletion did not affect the outcomes of aristolochic acid-induced AKI. RNA-sequencing data from renal tubular epithelial cells (RTECs) showed that C5ar1 deletion was associated with the down-regulation of mitochondrial metabolism and ATP production transcriptional pathways. Metabolic studies confirmed reduced mitochondrial membrane potential at baseline and increased mitochondrial oxidative stress after injury in C5ar1-/- RTECs. Moreover, C5ar1-/- RTECs had enhanced glycolysis, glucose uptake, and lactate production on injury, corroborated by metabolomics analysis of kidneys from AAN mice. Kidney tubule-specific C5ar1 knockout mice recapitulated exacerbated AKI observed in C5ar1-/- mice in AAN and FAN. These data indicate that C5aR1 signaling in kidney tubules exerts renoprotective effects against toxin-induced AKI by limiting overt glycolysis and maintaining mitochondrial function, thereby revealing a novel link between the complement system and tubular cell metabolism.

Astragalus Polysaccharide Mitigates Rhabdomyolysis-Induced Acute Kidney Injury via Inhibition of M1 Macrophage Polarization and the cGAS-STING Pathway

Purpose

This study aimed to examine the impact of APS on acute kidney injury induced by rhabdomyolysis (RIAKI), exploring its association with macrophage M1 polarization and elucidating the underlying mechanisms.

Methods

C57BL/6J mice were randomly assigned to one of three groups: a normal control group, a RIAKI model group, and an APS treatment group. Techniques such as flow cytometry and immunofluorescence were employed to demonstrate that APS can inhibit the transition of renal macrophages to the M1 phenotype in RIAKI. Furthermore, the raw264.7 macrophage cell line was chosen and induced into the M1 phenotype to further examine the impact of APS on this model and elucidate the underlying mechanism.

Results

Administration of APS led to a significant decrease in UREA levels by 25.2% and CREA levels by 60.9% within the model group. Also, APS exhibited an inhibitory effect on the infiltration of M1 macrophages and the cGAS-STING pathway in kidneys within the RIAKI, subsequently leading to decreased serum concentrations of IL-1β, IL-6 and TNF-α by 44.5%, 12.9%, and 10.3%, respectively, consistent with the results of in vitro experiments. Furthermore, APS exhibited an anti-apoptotic effect on MPC5 cells when co-cultured with M1 macrophages.

Conclusion

Astragalus polysaccharide (APS) potentially mitigated rhabdomyolysis-induced renal damage by impeding the M1 polarization of macrophages. This inherent mechanism might involve the suppression of the cGAS-STING pathway activation within macrophages. Furthermore, APS could endow protective effects on podocytes through the inhibition of apoptosis.

Complement activation in wasp venom-induced acute kidney injury

Previous studies have highlighted the significant role of complement activation in kidney injuries induced by rhabdomyolysis, intravascular hemolysis, sepsis, and ischemia-reperfusion. Nevertheless, the specific role and mechanism of complement activation in acute kidney injury (AKI) caused by wasp venom remain unclear. The aim of this study was to elucidate the specific complement pathway activated and investigate complement activation in AKI induced by wasp venom. In this study, a complement-depleted mouse model was used to investigate the role of complement in wasp venom-induced AKI. Mice were randomly categorized into control, cobra venom factor (CVF), AKI, and CVF + AKI groups. Compared to the AKI group, the CVF + AKI group showed improved pathological changes in kidneys and reduced blood urea nitrogen (BUN) levels. The expression levels of renal complement 3 (C3), complement 5 (C5), complement 1q (C1q), factor B (FB), mannose-binding lectin (MBL), and C5b-9 in AKI group were upregulated compared with the control group. Conversely, the renal tissue expression levels of C3, C5, C1q, FB, MBL, and C5b-9 were decreased in the CVF + AKI group compared to those in the AKI group. Complement activation occurs through all three pathways in AKI induced by wasp venom. Furthermore, complement depletion by CVF attenuates wasp venom-induced nephrotoxicity, suggesting that complement activation plays a primary role in the pathogenesis of wasp venom-induced AKI.

Is Hemopexin a Nephrotoxin or a Marker of Kidney Injury in Renal Ischemia-Reperfusion?

Destabilization of heme proteins is recognized to play a role in acute kidney injury (AKI). Hemopexin (Hpx), known for its role in binding heme, mitigates free heme toxicity. Despite this, the potential adverse effects of Hpx deposition in kidney tissues and its impact on kidney function are not fully understood. Deferoxamine (DFO) chelates iron released from heme and mitigates associated kidney damage. Therefore, this study aimed to evaluate whether Hpx contributes to kidney injury in an ischemia-reperfusion injury (IRI) induced AKI model and to investigate if DFO could alleviate this damage. Mice were categorized into five groups: Sham-Vehicle, Sham-Hpx, IRI-Vehicle, IRI-Hpx, and IRI-Hpx-DFO. Decline in kidney function was observed exclusively in the IRI group, independent of Hpx injection. Serum Hpx levels remained comparable across all groups, and administration of Hpx did not alter serum Hpx levels or kidney function after 24 hours. Although increased Hpx deposition in kidneys was noted in both the IRI and Hpx groups, this accumulation did not correlate with impaired kidney function. Additionally, DFO did not exhibit a protective effect against kidney injury. In summary, Hpx does not directly induce kidney injury and cannot be considered a biomarker for kidney damage caused by IRI.

Harnessing the potential of red blood cells in immunotherapy

Red blood cell (RBC) transfusion represents one of the earliest and most widespread forms of cellular therapy. While the primary purpose of RBC transfusions is to enhance the oxygen-carrying capacity of the recipient, RBCs also possess unique properties that make them attractive vehicles for inducing antigen-specific immune tolerance. Preclinical studies have demonstrated that RBC transfusion alone, in the absence of inflammatory stimuli, often fails to elicit detectable alloantibody formation against model RBC antigens. Several studies also suggest that RBC transfusion without inflammation may not only fail to generate a detectable alloantibody response but can also induce a state of antigen-specific non-responsiveness, a phenomenon potentially influenced by the density of the corresponding RBC alloantigen. The unique properties of RBCs, including their inability to divide and their stable surface antigen expression, make them attractive platforms for displaying exogenous antigens with the goal of leveraging their ability to induce antigen-specific non-responsiveness. This could facilitate antigen presentation to the host's immune system without triggering innate immune activation, potentially enabling the induction of antigen-specific tolerance for therapeutic applications in autoimmune disorders, preventing immune responses against protein therapeutics, or reducing alloreactivity in the setting of transfusion and transplantation.

Multiple site inflammation and acute kidney injury in crush syndrome

Crush syndrome, which frequently occurs in earthquake disasters, often leads to rhabdomyolysis induced acute kidney injury (RIAKI). Recent findings indicate that systemic inflammatory response syndrome (SIRS) exacerbates muscle collapse, contributing to RIAKI. The purpose of this study is to investigate the involvement of multiple site inflammation, including intraperitoneal, in crush syndrome. In a mouse model of RIAKI, elevated levels of inflammatory mediators such as TNFα, IL-6, myoglobin, and dsDNA were observed in serum and the peritoneal cavity, peaking earlier in the intraperitoneal cavity than in serum or urine. Our previously developed novel peptide inhibiting leukocyte extracellular traps was administered intraperitoneally and blocked all of these mediators in the intraperitoneal cavity and serum, ameliorating muscle damage and consequent RIAKI. Although further studies are needed to determine whether intraperitoneal inflammation associated with muscle collapse can lead to systemic inflammation, resulting in more severe and prolonged muscle damage and renal injury, early suppression of multiple site inflammation, including intraperitoneal, might be an effective therapeutic target.

Effect of dapagliflozin on collectins and complement activation in plasma from patients with type 2 diabetes and albuminuria: Data from the DapKid cohort

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT- 2) inhibitors exert cardiovascular and kidney-protective effects in people with diabetes. Attenuation of inflammation could be important for systemic protection. The lectin pathway of complement system activation is linked to diabetic nephropathy. We hypothesized that SGLT-2 inhibitors lower the circulating level of pattern-recognition molecules of the lectin cascade and attenuate systemic complement activation.

METHODS

Analysis of paired plasma samples from the DapKid crossover intervention study where patients with type 2 diabetes mellitus (T2DM) and albuminuria were treated with dapagliflozin and placebo for 12 weeks (10 mg/day, n=36). ELISA was used to determine concentrations of collectin kidney 1 (CL-K1), collectin liver 1 (CL-L1), mannose-binding lectin (MBL), MBL-associated serine protease 2 (MASP-2), the anaphylatoxin complement factor 3a (C3a), the stable C3 split product C3dg and the membrane attack complex (sC5b-9).

RESULTS

As published before, dapagliflozin treatment lowered Hba1C from 74 (14.9) mmol/mol to 66 (13.9) mmol/mol (p<0.0001), and the urine albumin/creatinine ratio from 167.8 mg/g to 122.5 mg/g (p<0.0001). Plasma concentrations of CL-K1, CL-L1, MBL, and MASP-2 did not change significantly after dapagliflozin treatment (P>0.05) compared to placebo treatment. The plasma levels of C3a (P<0.05) and C3dg (P<0.01) increased slightly but significantly, 0.6 [0.2] units/mL and 76 [52] units/mL respectively, after dapagliflozin treatment. The C9-associated neoepitope in C5b-9 did not change in plasma concentration by dapagliflozin (P>0.05).

CONCLUSION

In patients with type 2 diabetes and albuminuria, SGLT-2 inhibition resulted in modest C3 activation in plasma, likely not driven by primary changes in circulating collectins and not resulting in changes in membrane attack complex. Based on systemic analyses, organ-specific local protective effects of gliflozins against complement activation cannot be excluded.

Inhibition of colon C5a/C5a receptor signalling pathway confers protection against LPS-induced acute kidney injury via gut microbiota-kidney axis

Acute kidney injury (AKI) is a critical condition often associated with systemic inflammation and dysregulated gut microbiota. This study aimed to investigate the effects of the C5a receptor antagonist W54011 on lipopolysaccharide (LPS)-induced AKI, focusing on the colon's C5a/C5a receptor pathway, intestinal barrier integrity, and gut microbiota. Our findings demonstrate that W54011 effectively ameliorated kidney injury in the LPS-induced AKI model by selectively inhibiting the colon's C5a/C5a receptor signalling pathway. Additionally, C5a receptor blockade resulted in the inhibition of colonic inflammation and the reconstruction of the intestinal mucosal barrier. Furthermore, W54011 administration significantly impacted the composition and stability of the gut microbiota, restoring the abundance of dominant bacteria to levels observed in the normal state of the intestinal flora and reducing the abundance of potentially harmful bacterial groups. In conclusion, W54011 alleviates LPS-induced AKI by modulating the interplay between the colon, gut microbiota, and kidneys. It preserves the integrity of the intestinal barrier and reinstates gut microbiota, thereby mitigating AKI symptoms. These findings suggest that targeting the colon and gut microbiota could be a promising therapeutic strategy for AKI treatment.

A guide to complement biology, pathology and therapeutic opportunity

Complement has long been considered a key innate immune effector system that mediates host defence and tissue homeostasis. Yet, growing evidence has illuminated a broader involvement of complement in fundamental biological processes extending far beyond its traditional realm in innate immunity. Complement engages in intricate crosstalk with multiple pattern-recognition and signalling pathways both in the extracellular and intracellular space. Besides modulating host-pathogen interactions, this crosstalk guides early developmental processes and distinct cell trajectories, shaping tissue immunometabolic and regenerative programmes in different physiological systems. This Review provides a guide to the system-wide functions of complement. It highlights illustrative paradigm shifts that have reshaped our understanding of complement pathobiology, drawing examples from evolution, development of the central nervous system, tissue regeneration and cancer immunity. Despite its tight spatiotemporal regulation, complement activation can be derailed, fuelling inflammatory tissue pathology. The pervasive contribution of complement to disease pathophysiology has inspired a resurgence of complement therapeutics with major clinical developments, some of which have challenged long-held dogmas. We thus highlight major therapeutic concepts and milestones in clinical complement intervention.

Nrf2/HO-1 as a therapeutic target in renal fibrosis

Chronic kidney disease (CKD) is one of the most prevalent chronic diseases and affects between 10 and 14 % of the world's population. The World Health Organization estimates that by 2040, the disease will be fifth in prevalence. End-stage CKD is characterized by renal fibrosis, which can eventually lead to kidney failure and death. Renal fibrosis develops due to multiple injuries and involves oxidative stress and inflammation. In the human body, nuclear factor erythroid 2-related factor 2 (Nrf2) plays an important role in the expression of antioxidant, anti-inflammatory, and cytoprotective genes, which prevents oxidative stress and inflammation damage. Heme oxygenase (HO-1) is an inducible homolog influenced by heme products and after exposure to cellular stress inducers such as oxidants, inflammatory chemokines/cytokines, and tissue damage as an outcome or downstream of Nrf2 activation. HO-1 is known for its antioxidative properties, which play an important role in regulating oxidative stress. In renal diseases-induced tissue fibrosis and xenobiotics-induced renal fibrosis, Nrf2/HO-1 has been targeted with promising results. This review summarizes these studies and highlights the interesting bioactive compounds that may assist in attenuating renal fibrosis mediated by HO-1 activation. In conclusion, Nrf2/HO-1 signal activation could have a renoprotective effect strategy against CKD caused by oxidative stress, inflammation, and consequent renal fibrosis.

The role of complement in kidney disease

The complement cascade comprises soluble and cell surface proteins and is an important arm of the innate immune system. Once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammatory, vasoactive and metabolic responses. Although complement is crucial to host defence and homeostasis, its inappropriate or uncontrolled activation can also drive tissue injury. For example, the complement system has been known for more than 50 years to be activated by glomerular immune complexes and to contribute to autoimmune kidney disease. Notably, the latest research shows that complement is also activated in kidney diseases that are not traditionally thought of as immune-mediated, including haemolytic-uraemic syndrome, diabetic kidney disease and focal segmental glomerulosclerosis. Several complement-targeted drugs have been approved for the treatment of kidney disease, and additional anti-complement agents are being investigated in clinical trials. These drugs are categorically different from other immunosuppressive agents and target pathological processes that are not effectively inhibited by other classes of immunosuppressants. The development of these new drugs might therefore have considerable benefits in the treatment of kidney disease.

The Diagnostic Significance of C3d Antigen in Kidney and Skin Histopathology - The Current State-Of-The-Art and Practical Examples

The aim of this narrative review is to summarize recent knowledge about the diagnostic significance of immunobiological detection of C3d with a focus on renal and skin tissue biopsies. We completed the present narrative review with our own experiences with preparation and practical use of monoclonal C3d antibodies at a small national level.

Urinary exosomes: a promising biomarker of drug-induced nephrotoxicity

Drug-induced nephrotoxicity (DIN) is a big concern for clinical medication, but the clinical use of certain nephrotoxic drugs is still inevitable. Current testing methods make it hard to detect early renal injury accurately. In addition to understanding the pathogenesis and risk factors of drug-induced nephrotoxicity, it is crucial to identify specific renal injury biomarkers for early detection of DIN. Urine is an ideal sample source for biomarkers related to kidney disease, and urinary exosomes have great potential as biomarkers for predicting DIN, which has attracted the attention of many scholars. In the present paper, we will first introduce the mechanism of DIN and the biogenesis of urinary exosomes. Finally, we will discuss the changes in urinary exosomes in DIN and compare them with other predictive indicators to enrich and boost the development of biomarkers of DIN.

Wasp venom-induced acute kidney injury: current progress and prospects

Wasp venom can trigger local and systemic reactions, with the kidneys being commonly affected, potentially causing acute kidney injury (AKI). Despite of the recent advances, our knowledge on the underlying mechanisms of toxicity and targeted therapies remain poor. AKI can result from direct nephrotoxic effects of the wasp venom or secondary rhabdomyolysis and intravascular hemolysis, which will release myoglobin and free hemoglobin. Inflammatory responses play a central role in these pathological mechanisms. Noteworthily, the successful establishment of a suitable experimental model can assist in basic research and clinical advancements related to wasp venom-induced AKI. The combination of therapeutic plasma exchange and continuous renal replacement therapy appears to be the preferred treatment for wasp venom-induced AKI. In addition, studies on cilastatin and varespladib for wasp venom-induced AKI treatment have shown their potential as therapeutic agents. This review summarizes the available evidence on the mechanisms and treatment of wasp venom-induced AKI, with a particular focus on the role of inflammatory responses and potential targets for therapeutic drugs, and, therefore, aiming to support the development of clinical treatment against wasp venom-induced AKI.

Complement component C3 as a new target to lower albuminuria in hypertensive kidney disease

BACKGROUND AND PURPOSE

Complement activation may drive hypertension through its effects on immunity and tissue integrity.

EXPERIMENTAL APPROACH

We examined expression of C3, the central protein of the complement cascade, in hypertension.

KEY RESULTS

Increased C3 expression was found in kidney biopsies and micro-dissected glomeruli of patients with hypertensive nephropathy. Renal single cell RNA sequence data from normotensive and hypertensive patients confirmed expression of C3 in different cellular compartments of the kidney. In angiotensin II (Ang II) induced hypertension renal C3 expression was up-regulated. C3-/- mice revealed a significant lower albuminuria in the early phase of hypertension. However, no difference was found for blood pressure, renal injury (histology, glomerular filtration rate, inflammation) and cardiac injury (fibrosis, weight, gene expression) between C3-/- and wildtype mice after Ang II infusion. Also, in deoxycorticosterone acetate (DOCA) salt hypertension, a significantly lower albuminuria was found in the first weeks of hypertension in C3 deficient mice but no significant difference in renal and cardiac injury. Down-regulation of C3 by C3 targeting GalNAc (n-acetylgalactosamine) small interfering RNA (siRNA) conjugate decreased C3 in the liver by 96% and lowered albuminuria in the early phase but showed no effect on blood pressure and end-organ damage. Inhibition of complement C5 by siRNA showed no effect on albuminuria.

CONCLUSION AND IMPLICATIONS

Increased C3 expression is found in the kidneys of hypertensive mice and men. Genetic and therapeutic knockdown of C3 improved albuminuria in the early phase of hypertension but did not ameliorate arterial blood pressure nor renal and cardiac injury.

Renal injury, biomarkers, and myositis, an understudied aspect of disease: prospective study in the MyoCite cohort

INTRODUCTION

The mechanisms leading to chronic kidney disease (CKD) in patients with idiopathic inflammatory myopathies (IIMs) are poorly understood. We assessed the prevalence of subclinical renal injury in patients with IIMs, through elevation in biomarker levels of tubular injury and fibrosis (NGAL, KIM1, Activin A, CD163, and Cys-c), and assessed differences between subtypes of IIMs, and the effect of disease activity and duration.

MATERIALS AND METHODS

Clinical data, core set measures, sera and urine were prospectively collected from all patients enrolled in the MyoCite cohort from 2017 to 2021. Twenty healthy subjects (HC) and 16 patients with acute kidney injury (AKI) were included as controls. Baseline and follow up data for IIMs were included. Enzyme-linked immunosorbent assay (ELISA) was used to measure urine NGAL (Human Lipocalin-2/NGAL Duoset ELISA, Cat no: DY1757), KIM1 (Human TIM-1/KIM 1/HAVCR Duoset ELISA, Cat.no: DY1750B), Activin A (Human Activin A Duoset ELISA, Cat no: DY338), CD163 (Human CD163 Duoset ELISA,Cat no: DY1607-05), and Cys-c (Human Cystatin C Duoset ELISA, Cat. no.: DY1196) levels, while eGFR (unit mL/min/1.73 m2) was calculated by the Cockcroft-Gault formula and CKD-EPI formula.

RESULTS

Analysis of 201 visits of 110 adult patients with IIMs indicated higher normalized biomarker levels compared to HCs, and comparable to patients with AKI, with the exception of NGAL, which was higher in the AKI group. Notably 72 (49%) patients with IIMs had eGFR<90; the levels of the 5 biomarkers were comparable between active and inactive IIMs, and different subtypes of IIMs. Similarly, a poor correlation between urine biomarker levels and core set measures of activity and damage was found. Changes in biomarker levels on follow-up did not correlate with eGFR changes.

DISCUSSION

This exploratory analysis of urinary biomarkers identified low eGFR and elevated biomarkers of CKD in nearly half of the patients with IIMs, comparable to patients with AKI and higher than HCs, indicative of potential renal damage in IIMs that may have a lead to complications in other systems.

IgA Nephropathy: the Lectin Pathway and Implications for Targeted Therapy

Many patients with IgA nephropathy (IgAN) progress to end-stage kidney disease even with optimal supportive care. An improved understanding of the pathophysiology of IgAN in recent years has led to the investigation of targeted therapies with acceptable tolerability that may address the underlying causes of IgAN or the pathogenesis of kidney injury. The complement system - particularly the lectin and alternative pathways of complement - have emerged as key mediators of kidney injury in IgAN and possible targets for investigational therapy. This review will focus on the lectin pathway. Examination of kidney biopsies has consistently shown glomerular deposition of mannan-binding lectin (one of six pattern-recognition molecules that activate the lectin pathway) together with IgA1 in up to 50% of patients with IgAN. Glomerular deposition of pattern-recognition molecules for the lectin pathway is associated with more severe glomerular damage and more severe proteinuria and hematuria. Emerging research suggests that the lectin pathway may also contribute to tubulointerstitial fibrosis in IgAN, and that collectin-11 is a key mediator of this association. This review summarizes the growing scientific and clinical evidence supporting the role of the lectin pathway in IgAN and examines the possible therapeutic role of lectin pathway inhibition for these patients.

Study of the Relationship Between Liver Function Markers and Traumatic Rhabdomyolysis: A Retrospective Study of Hemorrhagic Patients Admitted to Intensive Care Unit in a Level I Trauma Center

BACKGROUND

Traumatic rhabdomyolysis (RM) is common and contributes to the development of medical complications, of which acute renal failure is the best described. Some authors have described an association between elevated aminotransferases and RM, suggesting the possibility of associated liver damage. Our study aims to evaluate the relationship between liver function and RM in hemorrhagic trauma patients.

METHODS

This is a retrospective observational study conducted in a level 1 trauma center analyzing 272 severely injured patients transfused within 24 hours and admitted to intensive care unit (ICU) from January 2015 to June 2021. Patients with significant direct liver injury (abdominal Abbreviated Injury Score [AIS] >3) were excluded. Clinical and laboratory data were reviewed, and groups were stratified according to the presence of intense RM (creatine kinase [CK] >5000 U/L). Liver failure was defined by a prothrombin time (PT)-ratio <50% and an alanine transferase (ALT) >500 U/L simultaneously. Correlation analysis was performed using Pearson's or Spearman's coefficient depending on the distribution after log transformation to evaluate the association between serum CK and biological markers of hepatic function. Risk factors for the development of liver failure were defined with a stepwise logistic regression analysis of all relevant explanatory factors significantly associated with the bivariate analysis.

RESULTS

RM (CK >1000 U/L) was highly prevalent in the global cohort (58.1%), and 55 (23.2%) patients presented with intense RM. We found a significant positive correlation between RM biomarkers (CK and myoglobin) and liver biomarkers (aspartate transferase [AST], ALT, and bilirubin). Log-CK was positively correlated with log-AST (r = 0.625, P < .001) and log-ALT (r = 0.507, P < .001) and minimally with log-bilirubin (r = 0.262, P < .001). Intensive care unit stays were longer for intense RM patients (7 [4-18] days vs 4 [2-11] days, P < .001). These patients required increased renal replacement therapy use (4.1% vs 20.0%, P < .001) and transfusion requirements. Liver failure was more common (4.6% vs 18.2%, P < .001) for intense RM patients. It was associated with bivariate and multivariable analysis with intense RM (odds ratio [OR], 4.51 [1.11-19.2]; P = .034), need for renal replacement therapy, and Sepsis-Related Organ Failure Assessment Score (SOFA) score on day 1.

CONCLUSIONS

Our study established the presence of an association between trauma-related RM and classical hepatic biomarkers. Liver failure was associated with the presence of intense RM in bivariate and multivariable analysis. Traumatic RM could have a role in the development of other system failures, specifically at the hepatic level, in addition to the already known and well-described renal failure.

New insight of complement system in the process of vascular calcification

The complement system defences against pathogenic microbes and modulates immune homeostasis by interacting with the innate and adaptive immune systems. Dysregulation, impairment or inadvertent activation of complement system contributes to the pathogenesis of some autoimmune diseases and cardiovascular diseases (CVD). Vascular calcification is the pivotal pathological basis of CVD, and contributes to the high morbidity and mortality of CVD. Increasing evidences indicate that the complement system plays a key role in chronic kidney diseases, atherosclerosis, diabetes mellitus and aging-related diseases, which are closely related with vascular calcification. However, the effect of complement system on vascular calcification is still unclear. In this review, we summarize current evidences about the activation of complement system in vascular calcification. We also describe the complex network of complement system and vascular smooth muscle cells osteogenic transdifferentiation, systemic inflammation, endoplasmic reticulum stress, extracellular matrix remodelling, oxidative stress, apoptosis in vascular calcification. Hence, providing a better understanding of the potential relationship between complement system and vascular calcification, so as to provide a direction for slowing the progression of this burgeoning health concern.

Association between preoperative serum myoglobin and acute kidney injury after Stanford Type A aortic dissection surgery

BACKGROUND

Acute kidney injury (AKI) is a common complication after Type A aortic dissection (TAAD) surgery, and it is associated with poor outcomes. The nephrotoxic effect of myoglobin was established, but its correlation with AKI following TAAD repair still lacks sufficient evidence. We clarified the correlation between preoperative serum myoglobin (pre-sMyo) concentrations and AKI after TAAD surgery.

METHOD

A retrospective analysis was performed on the perioperative data of 382 patients treated with TAAD surgery at Beijing Anzhen Hospital. AKI was defined and classified according to the criteria established by the Kidney Disease: Improving Global Outcomes Acute Kidney Injury Work Group. We attempted to determine the correlation between pre-sMyo concentrations and postoperative AKI.

RESULTS

The incidences of Stage 1, 2, and 3 AKI were 37.3 % (57/153), 23.5 % (36/153), and 39.2 % (60/153), respectively. The pre-sMyo concentrations of the AKI group were significantly increased than the non-AKI group [43.1 (21.4, 107.5) vs 26.4 (18.0, 37.2), P < 0.001]. Pre-sMyo concentrations have a linear correlation with preoperative renal function-related indicators. The multivariable logistic regression analysis showed that Ln (pre-sMyo) was an independent risk factor for AKI. When the pre-sMyo concentration was at the fourth quartile [109.3 (64.8, 213.4) ng/ml], the risk of developing any-stage and severe AKI was significantly increased (OR = 4.333, 95 % CI: 2.364-7.943, P < 0.001; OR = 3.862, 95 %, CI: 2.011-7.419, P < 0.001). This difference persisted after adjustment (OR = 3.830, 95 % CI: 1.848-7.936, P < 0.001; OR = 2.330, 95 % CI: 1.045-5.199, P = 0.039). Furthermore, pre-sMyo concentrations were not affected by lower limb malperfusion, myocardial malperfusion, and cardiac tamponade.

CONCLUSIONS

Increased pre-sMyo concentrations correlated with postoperative AKI in TAAD, which may increase the risk of developing any-stage AKI and severe AKI after TAAD surgery.

Phospholipase A2 induces acute kidney injury by complement mediated mitochondrial apoptosis via TNF-α/NF-κB signaling pathway

OBJECTIVE

Acute kidney injury (AKI) is one of common complications of wasp/bee stings. Phospholipase A₂ (PLA₂) is a vital pathogenic composition of wasp/bee venom. We aimed to investigate the role of complement mediated mitochondrial apoptosis in PLA₂ induced AKI.

MATERIALS AND METHODS

PLA₂ induced AKI model was established by injecting PLA₂ into via tail vein on mice. The pathological changes and the microstructural changes of kidney, complement activation, inflammation and apoptosis were detected in vitro and in vivo respectively.

RESULTS

The results showed that PLA₂ induced AKI models were successfully established in vivo and vitro. Compared with control, serum creatinine and urea nitrogen levels were elevated. Complement system activation and mitochondrial damage were observed. Expressions of IL-6, TNF-α, cleaved caspase-3 and cleaved caspase-9, and Bax/Bcl-2 increased in PLA₂ induced AKI models. TNF-α/NF-κB signaling pathway activation in AKI models.

CONCLUSION

In the present study, PLA₂ induced AKI model was first successfully established to our knowledge. The role of complement mediated mitochondrial apoptosis pathway in renal tubular epithelial cells in PLA₂ induced AKI were verified in vitro and vivo.

C3-dependent effector functions of complement

C3 is the central effector molecule of the complement system, mediating its multiple functions through different binding sites and their corresponding receptors. We will introduce the C3 forms (native C3, C3 [H₂ O], and intracellular C3), the C3 fragments C3a, C3b, iC3b, and C3dg/C3d, and the C3 expression sites. To highlight the important role that C3 plays in human biological processes, we will give an overview of the diseases linked to C3 deficiency and to uncontrolled C3 activation. Next, we will present a structural description of C3 activation and of the C3 fragments generated by complement regulation. We will proceed by describing the C3a interaction with the anaphylatoxin receptor, followed by the interactions of opsonins (C3b, iC3b, and C3dg/C3d) with complement receptors, divided into two groups: receptors bearing complement regulatory functions and the effector receptors without complement regulatory activity. We outline the molecular architecture of the receptors, their binding sites on the C3 activation fragments, the cells expressing them, the diversity of their functions, and recent advances. With this review, we aim to give an up-to-date analysis of the processes triggered by C3 activation fragments on different cell types in health and disease contexts.

Local complement synthesis-A process with near and far consequences for ischemia reperfusion injury and transplantation

The model of the solid organ as a target for circulating complement deposited at the site of injury, for many years concealed the broader influence of complement in organ transplantation. The study of locally synthesized complement especially in transplantation cast new light on complement's wider participation in ischaemia-reperfusion injury, the presentation of donor antigen and finally rejection. The lack of clarity, however, has persisted as to which complement activation pathways are involved and how they are triggered, and above all whether the distinction is relevant. In transplantation, the need for clarity is heightened by the quest for precision therapies in patients who are already receiving potent immunosuppressives, and because of the opportunity for well-timed intervention. This review will present new evidence for the emerging role of the lectin pathway, weighed alongside the longer established role of the alternative pathway as an amplifier of the complement system, and against contributions from the classical pathway. It is hoped this understanding will contribute to the debate on precisely targeted versus broadly acting therapeutic innovation within the aim to achieve safe long term graft acceptance.

Exertional Rhabdomyolysis Combined with Acute Kidney Injury and Complicated by Posterior Reversible Encephalopathy Syndrome

Posterior reversible encephalopathy syndrome is an uncommon syndrome in exertional rhabdomyolysis. We herein report a case of rhabdomyolysis and acute kidney injury after intense exercise. The patient also had generalized hypertension, headache, and painless complete loss of vision in both eyes, which was consistent with the symptoms of posterior reversible encephalopathy syndrome detected by magnetic resonance imaging of the brain. The patient fully recovered through active fluid replacement, diuresis, blood pressure control, alkalization of urine and blood purification, and supportive measures. This case report describes an infrequent neurological complication of exertional rhabdomyolysis. Understanding the range of complications is critical for improving patient outcomes.

Earlier continuous renal replacement therapy is associated with reduced mortality in rhabdomyolysis patients

Background

Continuous renal replacement therapy (CRRT) is commonly employed for rhabdomyolysis (RM) patients. However, the optimal initiation timing of CRRT and prognostic factors were not well evaluated for patients with RM. We aimed to investigate the efficacy of CRRT timing on mortality and the risk factors for death in RM patients who received CRRT.

Methods

RM patients who received CRRT between 1 May 2010 and 31 May 2021 in our center were retrospectively included. Univariate and multivariate logistic analyses were performed to identify the risk factors for primary outcome (90-day mortality).

Results

A total of 134 patients were included in our study. The 90-day mortality rate was 38.06%. The median time from CRRT initiation to peak CK occurrence was 4.8 h (IQR −16, 14), 67 patients received CRRT before 4.8 h after peak CK occurrence (early CRRT), and 67 patients received CRRT beyond 4.8 h after peak CK occurrence (late CRRT). Multivariate logistic regression analysis showed that the time from CRRT initiation to the peak CK (per 1 h, OR 1.026, 95% CI 1.004–1.049, p = 0.023), late CRRT (OR 3.082, 95% CI 1.072–8.859, p = 0.037), elevated serum cardiac troponin I (cTnI) (per 1 ng/mL, OR 1.218, 95% CI 1.011–1.468, p = 0.038), older age (per 1 year, OR 1.042, 95% CI 1.003–1.081, p = 0.032), and need of mechanical ventilation support (OR 4.632, 95% CI 1.292–16.61, p = 0.019) were independent risk factors for 90-day mortality.

Conclusions

Earlier CRRT initiation before 4.8 h after peak CK occurrence was associated with lower 90-day patient mortality.

Heme Proteins and Kidney Injury: Beyond Rhabdomyolysis

Heme proteins, the stuff of life, represent an ingenious biologic strategy that capitalizes on the biochemical versatility of heme, and yet is one that avoids the inherent risks to cellular vitality posed by unfettered and promiscuously reactive heme. Heme proteins, however, may be a double-edged sword because they can damage the kidney in certain settings. Although such injury is often viewed mainly within the context of rhabdomyolysis and the nephrotoxicity of myoglobin, an increasing literature now attests to the fact that involvement of heme proteins in renal injury ranges well beyond the confines of this single disease (and its analog, hemolysis); indeed, through the release of the defining heme motif, destabilization of intracellular heme proteins may be a common pathway for acute kidney injury, in general, and irrespective of the underlying insult. This brief review outlines current understanding regarding processes underlying such heme protein-induced acute kidney injury (AKI) and chronic kidney disease (CKD). Topics covered include, among others, the basis for renal injury after the exposure of the kidney to and its incorporation of myoglobin and hemoglobin; auto-oxidation of myoglobin and hemoglobin; destabilization of heme proteins and the release of heme; heme/iron/oxidant pathways of renal injury; generation of reactive oxygen species and reactive nitrogen species by NOX, iNOS, and myeloperoxidase; and the role of circulating cell-free hemoglobin in AKI and CKD. Also covered are the characteristics of the kidney that render this organ uniquely vulnerable to injury after myolysis and hemolysis, and pathobiologic effects emanating from free, labile heme. Mechanisms that defend against the toxicity of heme proteins are discussed, and the review concludes by outlining the therapeutic strategies that have arisen from current understanding of mechanisms of renal injury caused by heme proteins and how such mechanisms may be interrupted.

The complement system in pediatric acute kidney injury

The complement cascade is an important part of the innate immune system. In addition to helping the body to eliminate pathogens, however, complement activation also contributes to the pathogenesis of a wide range of kidney diseases. Recent work has revealed that uncontrolled complement activation is the key driver of several rare kidney diseases in children, including atypical hemolytic uremic syndrome and C3 glomerulopathy. In addition, a growing body of literature has implicated complement in the pathogenesis of more common kidney diseases, including acute kidney injury (AKI). Complement-targeted therapeutics are in use for a variety of diseases, and an increasing number of therapeutic agents are under development. With the implication of complement in the pathogenesis of AKI, complement-targeted therapeutics could be trialed to prevent or treat this condition. In this review, we discuss the evidence that the complement system is activated in pediatric patients with AKI, and we review the role of complement proteins as biomarkers and therapeutic targets in patients with AKI.

Phospholipase A2 inhibitor varespladib prevents wasp sting-induced nephrotoxicity in rats

This study aimed to clarify whether varespladib, a phospholipase A₂ (PLA₂) inhibitor, can be used as a therapeutic agent for wasp sting-induced acute kidney injury (AKI). Rats were divided into control, AKI, and AKI + varespladib groups. The AKI model was established by subcutaneously injecting wasp venom at five different sites in rats. Varespladib treatment showed a significant inhibitory effect on wasp venom PLA₂in vitro and in vivo. Moreover, we observed that varespladib decreased the levels of rhabdomyolysis and hemolysis markers compared with that in the AKI group. Histopathological changes in the kidney decreased significantly, and rat serum creatinine levels were reduced after varespladib administration. The significantly regulated genes in the kidney of the AKI group were mostly involved in inflammatory response pathway, and the administration of varespladib remarkably attenuated the expression of these genes. Therefore, varespladib inhibited wasp sting-induced functional and pathological damage to the kidneys. We propose that the PLA₂ inhibitor varespladib protects the kidney tissue in a wasp sting-induced AKI model by inhibiting PLA₂ activity.

Ulinastatin Alleviates Rhabdomyolysis-Induced Acute Kidney Injury by Suppressing Inflammation and Apoptosis via Inhibiting TLR4/NF-κB Signaling Pathway

Acute kidney injury (AKI) is an important complication of rhabdomyolysis (RM), but there is lack of effective treatments. Ulinastatin (UTI) is a broad-spectrum serine protease inhibitor isolated and purified from human urine with strong anti-inflammatory and cytoprotective actions. The aim of this research was to investigate the effect and potential mechanism of UTI on RM-induced AKI (RM-AKI). We established RM-induced AKI model and myoglobin (Mb)-stimulated NRK-52E cell model. In vivo, twenty-four rats were randomly divided into three groups (n = 8): control, RM-AKI, and RM-AKI + UTI. In vitro, the NRK-52E cells were divided into six groups according to the different treatment method. Mb-stimulated NRK-52E cells were treated with UTI or si-TLR4 transfection to characterize the mechanisms of UTI in RM-AKI. Indicators of the kidney injury, cell viability, cell cycle, oxidative stress, inflammation, apoptosis, and TLR4/NF-κB signaling pathway were assessed. In vivo and in vitro, UTI significantly decreased the expression of TLR4 and p65. In vivo, UTI significantly improved renal function and reduced inflammatory reaction and kidney injury. In vitro, UTI protected NRK-52E cells from Mb stimulation by suppressing cell cytotoxicity, cell cycle inhibition, overproduction of ROS, inflammation, and apoptosis. Additionally, UTI played a protective role by downregulating the TLR4 expression. The results indicate that UTI alleviates RM-AKI by suppressing the inflammatory response and apoptosis via inhibiting TLR4/NF-κB signaling pathway. Our study provides a new mechanism for the protective effect of UTI on RM-AKI.

The Rational Use of Complement Inhibitors in Kidney Diseases

The development of complement inhibitors represented one of the major breakthroughs in clinical nephrology in the last decade. Complement inhibition has dramatically transformed the outcome of one of the most severe kidney diseases, the atypical hemolytic uremic syndrome (aHUS), a prototypic complement-mediated disorder. The availability of complement inhibitors has also opened new promising perspectives for the management of several other kidney diseases in which complement activation is involved to a variable extent. With the rapidly growing number of complement inhibitors tested in a rapidly increasing number of indications, a rational use of this innovative and expensive new therapeutic class has become crucial. The present review aims to summarize what we know, and what we still ignore, regarding complement activation and therapeutic inhibition in kidney diseases. It also provides some clues and elements of thoughts for a rational approach of complement modulation in kidney diseases.

Ex Vivo Test for Measuring Complement Attack on Endothelial Cells: From Research to Bedside

As part of the innate immune system, the complement system plays a key role in defense against pathogens and in host cell homeostasis. This enzymatic cascade is rapidly triggered in the presence of activating surfaces. Physiologically, it is tightly regulated on host cells to avoid uncontrolled activation and self-damage. In cases of abnormal complement dysregulation/overactivation, the endothelium is one of the primary targets. Complement has gained momentum as a research interest in the last decade because its dysregulation has been implicated in the pathophysiology of many human diseases. Thus, it appears to be a promising candidate for therapeutic intervention. However, detecting abnormal complement activation is challenging. In many pathological conditions, complement activation occurs locally in tissues. Standard routine exploration of the plasma concentration of the complement components shows values in the normal range. The available tests to demonstrate such dysregulation with diagnostic, prognostic, and therapeutic implications are limited. There is a real need to develop tools to demonstrate the implications of complement in diseases and to explore the complex interplay between complement activation and regulation on human cells. The analysis of complement deposits on cultured endothelial cells incubated with pathologic human serum holds promise as a reference assay. This ex vivo assay most closely resembles the physiological context. It has been used to explore complement activation from sera of patients with atypical hemolytic uremic syndrome, malignant hypertension, elevated liver enzymes low platelet syndrome, sickle cell disease, pre-eclampsia, and others. In some cases, it is used to adjust the therapeutic regimen with a complement-blocking drug. Nevertheless, an international standard is lacking, and the mechanism by which complement is activated in this assay is not fully understood. Moreover, primary cell culture remains difficult to perform, which probably explains why no standardized or commercialized assay has been proposed. Here, we review the diseases for which endothelial assays have been applied. We also compare this test with others currently available to explore complement overactivation. Finally, we discuss the unanswered questions and challenges to overcome for validating the assays as a tool in routine clinical practice.

Stem Cell-Derived Extracellular Vesicles as Potential Therapeutic Approach for Acute Kidney Injury

Acute kidney injury is a frequent complication of hospitalized patients and significantly increases morbidity and mortality, worsening costs and length of hospital stay. Despite this impact on healthcare system, treatment still remains only supportive (dialysis). Stem cell-derived extracellular vesicles are a promising option as they recapitulate stem cells properties, overcoming safety issues related to risks or rejection or aberrant differentiation. A growing body of evidence based on pre-clinical studies suggests that extracellular vesicles may be effective to treat acute kidney injury and to limit fibrosis through direct interference with pathogenic mechanisms of vascular and tubular epithelial cell damage. We herein analyze the state-of-the-art knowledge of therapeutic approaches with stem cell-derived extracellular vesicles for different forms of acute kidney injury (toxic, ischemic or septic) dissecting their cytoprotective, regenerative and immunomodulatory properties. We also analyze the potential impact of extracellular vesicles on the mechanisms of transition from acute kidney injury to chronic kidney disease, with a focus on the pivotal role of the inhibition of complement cascade in this setting. Despite some technical limits, nowadays the development of therapies based on stem cell-derived extracellular vesicles holds promise as a new frontier to limit acute kidney injury onset and progression.

Nephroprotective Plants: A Review on the Use in Pre-Renal and Post-Renal Diseases

Kidney diseases are expected to become the fifth leading cause of death by 2040. Several physiological failures classified as pre-, intra-, and post-renal factors induce kidney damage. Diabetes, liver pathologies, rhabdomyolysis, and intestinal microbiota have been identified as pre-renal factors, and lithiasis or blood clots in the ureters, prostate cancer, urethral obstructions, prostate elongation, and urinary tract infections are post-renal factors. Additionally, the nephrotoxicity of drugs has been highlighted as a crucial factor inducing kidney injuries. Due to the adverse effects of drugs, it is necessary to point to other alternatives to complement the treatment of these diseases, such as nephroprotective agents. Plants are a wide source of nephroprotective substances and can have beneficial effects in different levels of the physiological pathways which lead to kidney damage. In traditional medicines, plants are used as antioxidants, anti-inflammatories, diuretics, and anticancer agents, among other benefits. However, the mechanism of action of some plants empirically used remains unknown and scientific data are required to support their nephroprotective effects. The present work reviewed the plants with a beneficial effect on kidney diseases. The classification of nephroprotective plants according to the clinical definition of pre-renal, intrinsic, and post-renal factors is proposed to orient their use as complementary treatments.

Complement C3 activation in the ICU: Disease and therapy as Bonnie and Clyde

Patients in the intensive care unit (ICU) often straddle the divide between life and death. Understanding the complex underlying pathomechanisms relevant to such situations may help intensivists select broadly acting treatment options that can improve the outcome for these patients. As one of the most important defense mechanisms of the innate immune system, the complement system plays a crucial role in a diverse spectrum of diseases that can necessitate ICU admission. Among others, myocardial infarction, acute lung injury/acute respiratory distress syndrome (ARDS), organ failure, and sepsis are characterized by an inadequate complement response, which can potentially be addressed via promising intervention options. Often, ICU monitoring and existing treatment options rely on massive intervention strategies to maintain the function of vital organs, and these approaches can further contribute to an unbalanced complement response. Artificial surfaces of extracorporeal organ support devices, transfusion of blood products, and the application of anticoagulants can all trigger or amplify undesired complement activation. It is, therefore, worth pursuing the evaluation of complement inhibition strategies in the setting of ICU treatment. Recently, clinical studies in COVID-19-related ARDS have shown promising effects of central inhibition at the level of C3 and paved the way for prospective investigation of this approach. In this review, we highlight the fundamental and often neglected role of complement in the ICU, with a special focus on targeted complement inhibition. We will also consider complement substitution therapies to temporarily counteract a disease/treatment-related complement consumption.

Platelets Derived Transthyretin Participate In The Development of Sepsis Associated Acute Kidney Injury by Inducing Oxidative Stress and Apoptosis of Renal Tubular Epithelial Cells

ABSTRACT

The pathophysiology of sepsis-associated acute kidney injury (S-AKI) is not well elucidated. Platelets have been reported to play a critical role in the pathogenesis of AKI, but the true mechanism remains unknown. Herein, we established a mouse model of S-AKI by cecal ligation and puncture (CLP). Ticagrelor was given 24 hours before and after CLP by gastric gavage. Platelets were isolated and analyzed by the label-free proteome approach to identify platelet-derived damage-associated molecular patterns (DAMPs). Our results demonstrated that, among all differentially expressed proteins (DEPs), platelet-derived transthyretin (TTR) exerted effects in S-AKI. To examine the direct effects of platelet TTR on human renal proximal tubule epithelial (HK2) cells damage, platelets were co-cultured with HK2 cells. The results indicated that platelet TTR can cause reactive oxygen species production and apoptosis in HK2 cells. Further research found that platelet TTR can also result in increased levels of mRNA and protein for protein kinase B (AKT), phosphatidylinositol 3-kinase (PI3K), and extracellular regulated protein kinase (ERK), as analyzed by real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting. In conclusion, platelet-derived TTR may be one kind of DAMPs that plays an important role in the development of S-AKI.

Proteinuria is accompanied by intratubular complement activation and apical membrane deposition of C3dg and C5b-9 in kidney transplant recipients

Proteinuria predicts accelerated decline in kidney function in kidney transplant recipients (KTRs). We hypothesized that aberrant filtration of complement factors causes intraluminal activation, apical membrane attack on tubular cells, and progressive injury. Biobanked samples from two previous studies in albuminuric KTRs were used. The complement-activation split products C3c, C3dg, and soluble C5b-9-associated C9 neoantigen were analyzed by ELISA in urine and plasma using neoepitope-specific antibodies. Urinary extracellular vesicles (uEVs) were enriched by lectin and immunoaffinity isolation and analyzed by immunoblot analysis. Urine complement excretion increased significantly in KTRs with an albumin-to-creatinine ratio of ≥300 mg/g compared with <30 mg/g. Urine C3dg and C9 neoantigen excretion correlated significantly to changes in albumin excretion from 3 to 12 mo after transplantation. Fractional excretion of C9 neoantigen was significantly higher than for albumin, indicating postfiltration generation. C9 neoantigen was detected in uEVs in six of the nine albuminuric KTRs but was absent in non-albuminuric controls (n = 8). In C9 neoantigen-positive KTRs, lectin affinity enrichment of uEVs from the proximal tubules yielded signal for iC3b, C3dg, C9 neoantigen, and Na⁺-glucose transporter 2 but only weakly for aquaporin 2. Coisolation of podocyte markers and Tamm–Horsfall protein was minimal. Our findings show that albuminuria is associated with aberrant filtration and intratubular activation of complement with deposition of C3 activation split products and C5b-9-associated C9 neoantigen on uEVs from the proximal tubular apical membrane. Intratubular complement activation may contribute to progressive kidney injury in proteinuric kidney grafts.

NEW & NOTEWORTHY The present study proposes a mechanistic coupling between proteinuria and aberrant filtration of complement precursors, intratubular complement activation, and apical membrane attack in kidney transplant recipients. C3dg and C5b-9-associated C9 neoantigen associate with proximal tubular apical membranes as demonstrated in urine extracellular vesicles. The discovery suggests intratubular complement as a mediator between proteinuria and progressive kidney damage. Inhibitors of soluble and/or luminal complement activation with access to the tubular lumen may be beneficial.

Association of D-dimer and acute kidney injury associated with rhabdomyolysis in patients with exertional heatstroke: an over 10-year intensive care survey

Patients with rhabdomyolysis (RM) following exertional heatstroke (EHS) are often accompanied by dysfunction of coagulation and acute kidney injury (AKI). The purpose of this study was to investigate the relationship between D-dimer and AKI in patients with RM following EHS. A retrospective study was performed on patients with EHS admitted to the intensive care unit over 10-year. Data including baseline clinical information at admission, vital organ dysfunction, and 90-day mortality were collected. A total of 84 patients were finally included, of whom 41 (48.8%) had AKI. AKI patients had more severe organ injury and higher 90-day mortality (34.1 vs.0.0%, p < 0.001) than non-AKI patients. Multivariate logistic analysis showed that D-dimer (OR 1.3, 95% CI 1.1–1.7, p = 0.018) was an independent risk factor for AKI with RM following EHS. Curve fitting showed a curve relationship between D-dimer and AKI. Two-piecewise linear regression showed that D-dimer was associated with AKI in all populations (OR 1.3, 95% CI 1.2–1.5, p < 0.001) when D-dimer <10.0 mg/L, in RM group (OR 1.3, 95% CI 1.1–1.5, p < 0.001) when D-dimer >0.4 mg/L, in the non-RM group (OR 6.4, 95% CI 1.7–23.9, p = 0.005) when D-dimer <1.3 mg/L and D-dimer did not increase the incidence of AKI in the non-RM group when D-dimer >1.3 mg/L. AKI is a life-threatening complication of RM following EHS. D-dimer is associated with AKI in critically ill patients with EHS. The relationship between D-dimer and AKI depends on whether RM is present or not.

Gluteal muscle damage and rhabdomyolysis after olanzapine poisoning: a case report

Olanzapine is a widely adopted atypical antipsychotic medication used to manage schizophrenia. Reports show that the incidence rate of adverse reactions to olanzapine is significantly lower than those of other classic antipsychotic medications. However, olanzapine overdose may be associated with severe consequences. Herein, we report a 21-year-old female patient who had taken nearly 700 mg (70 tablets) of olanzapine; she was found after 30 hours. As her condition progressed, she presented with rhabdomyolysis, swelling in the thighs and hips, paralytic ileus, digestive tract hemorrhage, and elevated serum amylase and lipase levels; notably, she recovered after treatment. This intractable case is of great clinical significance and suggests that early-phase hemoperfusion plays a critical role in olanzapine poisoning-related rhabdomyolysis.

Heme Burden and Ensuing Mechanisms That Protect the Kidney: Insights from Bench and Bedside

With iron at its core, the tetrapyrrole heme ring is a cardinal prosthetic group made up of many proteins that participate in a wide array of cellular functions and metabolism. Once released, due to its pro-oxidant properties, free heme in sufficient amounts can result in injurious effects to the kidney and other organs. Heme oxygenase-1 (HO-1) has evolved to promptly attend to such injurious potential by facilitating degradation of heme into equimolar amounts of carbon monoxide, iron, and biliverdin. HO-1 induction is a beneficial response to tissue injury in diverse animal models of diseases, including those that affect the kidney. These protective attributes are mainly due to: (i) prompt degradation of heme leading to restraining potential hazardous effects of free heme, and (ii) generation of byproducts that along with induction of ferritin have proven beneficial in a number of pathological conditions. This review will focus on describing clinical aspects of some of the conditions with the unifying end-result of increased heme burden and will discuss the molecular mechanisms that ensue to protect the kidneys.

Case Report: Adult Post-COVID-19 Multisystem Inflammatory Syndrome and Thrombotic Microangiopathy

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic has affected millions of people worldwide. A clinical series of Kawasaki-like multisystem inflammatory syndrome (MIS), occurring after SARS-CoV-2 infection, have been described in children (MIS-C) and adults (MIS-A), but the pathophysiology remains unknown.

CASE PRESENTATION

We describe a case of post-COVID-19 MIS-A in a 46-year-old man with biopsy-proven renal thrombotic microangiopathy (TMA). Specific complement inhibition with eculizumab was initiated promptly and led to a dramatic improvement of renal function.

CONCLUSION

Our case suggests that that TMA could play a central role in the pathophysiology of post-COVID-19 MIS-A, making complement blockers an interesting therapeutic option.

NAicotinamide retains Klotho expression and ameliorates rhabdomyolysis-induced acute kidney injury

OBJECTIVES

Acute kidney injury (AKI) is a severe complication of rhabdomyolysis that significantly increases mortality. Unfortunately, the therapeutic approach is limited. Inflammation plays a critical role in the pathogenesis of rhabdomyolysis-induced AKI, which is a potential therapeutic target. Nicotinamide, a form of vitamin B3 and a precursor of nicotinamide adenine dinucleotide, has been shown to have potent antiinflammation effects. Klotho is a tubular highly expressed renoprotective protein. Therefore, we explored the effect of nicotinamide on rhabdomyolysis-induced AKI and the underlying mechanisms.

METHODS

We intramuscularly injected glycerol to induce rhabdomyolysis, and intraperitoneally administrated nicotinamide to observe the effect on kidney injury. Interleukin-1 beta, tumor necrosis factor alpha, nuclear factor kappa B (NF-κB), and Klotho were determined by Western blot. Chromatin immunoprecipitation was used to assess the interaction of NF-κB, nuclear receptor corepressor, and histone deacetylase 1 with Klotho promoters. Small interfering RNA was used to evaluate the role of Klotho in nicotinamide-related renoprotection.

RESULTS

The results showed that nicotinamide attenuated renal pathologic morphology, kidney functional abnormalities, and kidney inflammatory response in rhabdomyolysis. Moreover, nicotinamide effectively blocked the recruitment of NF-κB, nuclear receptor corepressor, and histone deacetylase 1 to the promoter of Klotho, and preserved Klotho expression. More importantly, the renoprotection effect of nicotinamide was abrogated when Klotho was knocked down by small interfering RNA in rhabdomyolysis mice.

CONCLUSIONS

Our study demonstrated that Klotho preservation is essential for the renoprotection effect of nicotinamide, and provides a new preventive strategy for rhabdomyolysis-induced AKI.

Exogenous Biological Renal Support Improves Kidney Function in Mice With Rhabdomyolysis-Induced Acute Kidney Injury

Background: Rhabdomyolysis (RM) is a clinical syndrome characterized by breakdown of skeletal muscle fibers and release of their contents into the circulation. Myoglobin-induced acute kidney injury (AKI) is one of the most severe complications of RM. Based on our previous research, exogenous biological renal support alleviates renal ischemia–reperfusion injury in elderly mice. This study aimed to determine whether exogenous biological renal support promotes renal recovery from RM-induced AKI and to preliminarily explore the mechanisms involved.

Methods: A parabiosis animal model was established to investigate the effects of exogenous biological renal support on RM-induced AKI. Mice were divided into three groups: the control group (in which mice were injected with sterile saline), the RM group (in which mice were injected with 8 mL/kg glycerol), and the parabiosis + RM group (in which recipient mice were injected with glycerol 3 weeks after parabiosis model establishment). Blood samples and kidney tissue were collected for further processing 48 h after RM induction. Bioinformatics analysis was conducted via Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis, functional enrichment analysis, and clustering analysis.

Results: No mice died within 48 h after the procedure. Exogenous biological renal support attenuated the histological and functional deterioration in mice with RM-induced AKI. Bioinformatics analysis identified key pathways and proteins involved in this process. We further demonstrated that exogenous biological renal support ameliorated AKI through multiple mechanisms, including by suppressing the complement system; attenuating oxidative stress, inflammation, and cell death; and increasing proliferation.

Conclusions: Exogenous biological renal support provided by parabiosis can improve renal function in RM-induced AKI by suppressing the complement system; decreasing oxidative stress, inflammation, and cell death; and promoting tubular cell proliferation. Our study provides basic research evidence for the use of bioartificial kidneys to treat RM-induced AKI.