Complement inhibition attenuates acute kidney injury after ischemia-reperfusion and limits progression to renal fibrosis in mice

The Lectin Pathway of the Complement System-Activation, Regulation, Disease Connections and Interplay with Other (Proteolytic) Systems

The complement system is the other major proteolytic cascade in the blood of vertebrates besides the coagulation-fibrinolytic system. Among the three main activation routes of complement, the lectin pathway (LP) has been discovered the latest, and it is still the subject of intense research. Mannose-binding lectin (MBL), other collectins, and ficolins are collectively termed as the pattern recognition molecules (PRMs) of the LP, and they are responsible for targeting LP activation to molecular patterns, e.g., on bacteria. MBL-associated serine proteases (MASPs) are the effectors, while MBL-associated proteins (MAps) have regulatory functions. Two serine protease components, MASP-1 and MASP-2, trigger the LP activation, while the third component, MASP-3, is involved in the function of the alternative pathway (AP) of complement. Besides their functions within the complement system, certain LP components have secondary ("moonlighting") functions, e.g., in embryonic development. They also contribute to blood coagulation, and some might have tumor suppressing roles. Uncontrolled complement activation can contribute to the progression of many diseases (e.g., stroke, kidney diseases, thrombotic complications, and COVID-19). In most cases, the lectin pathway has also been implicated. In this review, we summarize the history of the lectin pathway, introduce their components, describe its activation and regulation, its roles within the complement cascade, its connections to blood coagulation, and its direct cellular effects. Special emphasis is placed on disease connections and the non-canonical functions of LP components.

Innate immune modulation in transplantation: mechanisms, challenges, and opportunities

Organ transplantation is characterized by a sequence of steps that involve operative trauma, organ preservation, and ischemia-reperfusion injury in the transplant recipient. During this process, the release of damage-associated molecular patterns (DAMPs) promotes the activation of innate immune cells via engagement of the toll-like receptor (TLR) system, the complement system, and coagulation cascade. Different classes of effector responses are then carried out by specialized populations of macrophages, dendritic cells, and T and B lymphocytes; these play a central role in the orchestration and regulation of the inflammatory response and modulation of the ensuing adaptive immune response to transplant allografts. Organ function and rejection of human allografts have traditionally been studied through the lens of adaptive immunity; however, an increasing body of work has provided a more comprehensive picture of the pivotal role of innate regulation of adaptive immune responses in transplant and the potential therapeutic implications. Herein we review literature that examines the repercussions of inflammatory injury to transplantable organs. We highlight novel concepts in the pathophysiology and mechanisms involved in innate control of adaptive immunity and rejection. Furthermore, we discuss existing evidence on novel therapies aimed at innate immunomodulation and how this could be harnessed in the transplant setting.

Mannose binding lectin-associated serine protease-1 is a novel contributor to myocardial ischemia/reperfusion injury

BACKGROUND

The lectin pathway has been demonstrated to play a critical role in the pathological process of myocardial ischemia/reperfusion injury (IRI). Mannose-binding lectin (MBL)-associated serine protease-1 (MASP-1), especially different from other components of the lectin pathway, mediates proinflammatory and procoagulant reactions independent of complement cascades. However, the role of MASP-1 in myocardial IRI remains unknown so far.

METHODS

Myocardial IRI was established with 45 min ischemia and 24 h reperfusion in mice. C1 inhibitor, as the natural inhibitor of MASP-1, was administrated at 20 IU/Kg via tail vein 5 min before surgical operation. Cardiac function and myocardial infarct size were assessed. Myocardial histology and fibrosis were evaluated by H&E and Masson staining, respectively. Deposition of MASP-1, expression of PAR-1/4 and neutrophil extracellular traps (NET) were investigated on myocardium tissue by IHC staining. Cell apoptosis was detected by TUNEL assay. Levels of myocardial enzymes and proinflammatory cytokines were determined by ELISA.

RESULTS

Inhibition of MASP-1 with C1 INH improved cardiac function and alleviated myocardium tissue injury (infarct size, enzymes, histology and fibrosis) after myocardial IRI. Deposition of MASP-1 and expression PAR-1, as well as NET formation in myocardial tissue were suppressed by MASP-1 inhibitor, while PAR-4 was elevated. Levels of apoptosis, HMGB-1 and IL-6 were lower after blocking MASP-1. Yet, IL-8 and TNF-α remained unchanged.

CONCLUSIONS

MASP-1, as a new contributor, played a critical role in myocardial IRI. Inhibition of MASP-1 protected myocardial tissue from IRI probably via regulation of PARs/NET pathway. This may provide a novel target strategy against myocardial IRI.

Proteomics analysis of lung tissue reveals protein makers for the lung injury of adjuvant arthritis rats

Lung injury is one of the common extra‑articular lesions in rheumatoid arthritis (RA). Due to its insidious onset and no obvious clinical symptoms, it can be easily dismissed in the early stage of diagnosis, which is one of the reasons that leads to a decline of the quality of life and subsequent death of patients with RA. However, its pathogenesis is still unclear and there is a lack of effective therapeutic targets. In the present study, tandem mass tag‑labeled proteomics was used to research the lung tissue proteins in RA model (adjuvant arthritis, AA) rats that had secondary lung injury. The aim of the present study was to identify the differentially expressed proteins related to RA‑lung injury, determine their potential role in the pathogenesis of RA‑lung injury and provide potential targets for clinical treatment. Lung tissue samples were collected from AA‑lung injury and normal rats. The differentially expressed proteins (DEPs) were identified by tandem mass spectrometry. Bioinformatic analysis was used to assess the biological processes and signaling pathways associated with these DEPs. A total of 310 DEPs were found, of which 244 were upregulated and 66 were downregulated. KEGG anlysis showed that 'fatty acid degradation', 'fatty acid metabolism', 'fatty acid elongation', 'complement and coagulation cascades', 'peroxisome proliferator‑activated receptor signaling pathway' and 'hypoxia‑inducible factor signaling pathway' were significantly upregulated in the lung tissues of AA‑lung injury. Immunofluorescence staining confirmed the increased expression of clusterin, serine protease inhibitors and complement 1qc in lung tissue of rats with AA lung injury. In the present study, the results revealed the significance of certain DEPs (for example, C9, C1qc and Clu) in the occurrence and development of RA‑lung injury and provided support through experiments to identify potential biomarkers for the early diagnosis and prevention of RA‑lung injury.

How to Best Protect Kidneys for Transplantation-Mechanistic Target

The increasing number of patients on the kidney transplant waiting list underlines the need to expand the donor pool and improve kidney graft utilization. By protecting kidney grafts adequately from the initial ischemic and subsequent reperfusion injury occurring during transplantation, both the number and quality of kidney grafts could be improved. The last few years have seen the emergence of many new technologies to abrogate ischemia-reperfusion (I/R) injury, including dynamic organ preservation through machine perfusion and organ reconditioning therapies. Although machine perfusion is gradually making the transition to clinical practice, reconditioning therapies have not yet progressed from the experimental setting, pointing towards a translational gap. In this review, we discuss the current knowledge on the biological processes implicated in I/R injury and explore the strategies and interventions that are being proposed to either prevent I/R injury, treat its deleterious consequences, or support the reparative response of the kidney. Prospects to improve the clinical translation of these therapies are discussed with a particular focus on the need to address multiple aspects of I/R injury to achieve robust and long-lasting protective effects on the kidney graft.

Immunopathology of terminal complement activation and complement C5 blockade creating a pro-survival and organ-protective phenotype in trauma

BACKGROUND AND PURPOSE

Traumatic haemorrhage (TH) is the leading cause of potentially preventable deaths that occur during the prehospital phase of care. No effective pharmacological therapeutics are available for critical TH patients yet. Here, we identify terminal complement activation (TCA) as a therapeutic target in combat casualties and evaluate the efficacy of a TCA inhibitor (nomacopan) on organ damage and survival in vivo.

EXPERIMENTAL APPROACH

Complement activation products and cytokines were analysed in plasma from 54 combat casualties. The correlations between activated complement pathway(s) and the clinical outcomes in trauma patients were assessed. Nomacopan was administered to rats subjected to lethal TH (blast injury and haemorrhagic shock). Effects of nomacopan on TH were determined using survival rate, organ damage, physiological parameters, and laboratory profiles.

KEY RESULTS

Early TCA was associated with systemic inflammatory responses and clinical outcomes in this trauma cohort. Lethal TH in the untreated rats induced early TCA that correlated with the severity of tissue damage and mortality. The addition of nomacopan to a damage-control resuscitation (DCR) protocol significantly inhibited TCA, decreased local and systemic inflammatory responses, improved haemodynamics and metabolism, attenuated tissue and organ damage, and increased survival.

CONCLUSION AND IMPLICATIONS

Previous findings of our and other groups revealed that early TCA represents a rational therapeutic target for trauma patients. Nomacopan as a pro-survival and organ-protective drug, could emerge as a promising adjunct to DCR that may significantly reduce the morbidity and mortality in severe TH patients while awaiting transport to critical care facilities.

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.

Complement-targeting therapeutics for ischemia-reperfusion injury in transplantation and the potential for ex vivo delivery

Organ shortages and an expanding waitlist have led to increased utilization of marginal organs. All donor organs are subject to varying degrees of IRI during the transplant process. Extended criteria organs, including those from older donors and organs donated after circulatory death are especially vulnerable to ischemia-reperfusion injury (IRI). Involvement of the complement cascade in mediating IRI has been studied extensively. Complement plays a vital role in the propagation of IRI and subsequent recruitment of the adaptive immune elements. Complement inhibition at various points of the pathway has been shown to mitigate IRI and minimize future immune-mediated injury in preclinical models. The recent introduction of ex vivo machine perfusion platforms provides an ideal window for therapeutic interventions. Here we review the role of complement in IRI by organ system and highlight potential therapeutic targets for intervention during ex vivo machine preservation of donor organs.

Circular RNAs in Acute Kidney Injury: Roles in Pathophysiology and Implications for Clinical Management

Acute kidney injury (AKI) is a common clinical condition, results in patient morbidity and mortality, and incurs considerable health care costs. Sepsis, ischaemia-reperfusion injury (IRI) and drug nephrotoxicity are the leading causes. Mounting evidence suggests that perturbations in circular RNAs (circRNAs) are observed in AKI of various aetiologies, and have pathogenic significance. Aberrant circRNA expressions can cause altered intracellular signalling, exaggerated oxidative stress, increased cellular apoptosis, excess inflammation, and tissue injury in AKI due to sepsis or IRI. While circRNAs are dysregulated in drug-induced AKI, their roles in pathogenesis are less well-characterised. CircRNAs also show potential for clinical application in diagnosis, prognostication, monitoring, and treatment. Prospective observational studies are needed to investigate the role of circRNAs in the clinical management of AKI, with special focus on the safety of therapeutic interventions targeting circRNAs and the avoidance of untoward off-target effects.

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.

Role of Complement System in Kidney Transplantation: Stepping From Animal Models to Clinical Application

Kidney transplantation is a life-saving strategy for patients with end-stage renal diseases. Despite the advances in surgical techniques and immunosuppressive agents, the long-term graft survival remains a challenge. Growing evidence has shown that the complement system, part of the innate immune response, is involved in kidney transplantation. Novel insights highlighted the role of the locally produced and intracellular complement components in the development of inflammation and the alloreactive response in the kidney allograft. In the current review, we provide the updated understanding of the complement system in kidney transplantation. We will discuss the involvement of the different complement components in kidney ischemia-reperfusion injury, delayed graft function, allograft rejection, and chronic allograft injury. We will also introduce the existing and upcoming attempts to improve allograft outcomes in animal models and in the clinical setting by targeting the complement system.

Macrophages in the kidney in health, injury and repair

Macrophages are a key component of the renal mononuclear phagocyte system, playing a major role in defense against infection, renal injury and repair. Yolk sac macrophage precursors seed the early embryonic kidney and are important for renal development. Later, renal macrophages are derived from hematopoietic stem cells and in adult life, there is a significant contribution from circulating monocytes, which is enhanced in response to infection or injury. Macrophages are highly plastic and can alter their phenotype in response to cues from parenchymal renal cells. Danger-associated molecules released from injured kidney cells may activate macrophages toward a pro-inflammatory phenotype, mediating further recruitment of inflammatory cells, exacerbating renal injury and activating renal fibroblasts to promote scarring. In acute kidney injury, once the injury stimulus has abated, macrophages may adopt a more reparative phenotype, dampening the immune response and promoting repair of renal tissue. However, in chronic kidney disease ongoing activation of pro-inflammatory monocytes and persistence of reparative macrophages leads to glomerulosclerosis and tubulointerstitial fibrosis, the hallmarks of end-stage kidney disease. Several strategies to inhibit the recruitment, activation and secretory products of pro-inflammatory macrophages have proven beneficial in pre-clinical models and are now undergoing clinical trials in patients with kidney disease. In addition, macrophages may be utilized in cell therapy as a "Trojan Horse" to deliver targeted therapies to the kidney. Single-cell RNA sequencing has identified a previously unappreciated spectrum of macrophage phenotypes, which may be selectively present in injury or repair, and ongoing functional analyses of these subsets may identify more specific targets for therapeutic intervention.

Targeting Inflammation and Oxidative Stress as a Therapy for Ischemic Kidney Injury

Inflammation and oxidative stress are the main pathological processes that accompany ischemic injury of kidneys and other organs. Based on this, these factors are often chosen as a target for treatment of acute kidney injury (AKI) in a variety of experimental and clinical studies. Note, that since these two components are closely interrelated during AKI development, substances that treat one of the processes often affect the other. The review considers several groups of promising nephroprotectors that have both anti-inflammatory and antioxidant effects. For example, many antioxidants, such as vitamins, polyphenolic compounds, and mitochondria-targeted antioxidants, not only reduce production of the reactive oxygen species in the cell but also modulate activity of the immune cells. On the other hand, immunosuppressors and non-steroidal anti-inflammatory drugs that primarily affect inflammation also reduce oxidative stress under some conditions. Another group of therapeutics is represented by hormones, such as estrogens and melatonin, which significantly reduce severity of the kidney damage through modulation of both these processes. We conclude that drugs with combined anti-inflammatory and antioxidant capacities are the most promising agents for the treatment of acute ischemic kidney injury.

Postconditioning attenuates myocardial ischemia-reperfusion injury by inhibiting complement activation and upregulation of miR-499

The complement system plays a vital role in myocardial ischemia/reperfusion (I/R) injury. microRNA (miR)-499 is involved in the cardioprotection of ischemic postconditioning (IPostC). The present study aimed to study the role of the complement system and miR-499 in IPostC. Rat hearts were subjected to coronary ligation for 30 min, followed by reperfusion for 2 h. IPostC was introduced at the onset of reperfusion with three cycles of reperfusion for 30 sec and coronary artery occlusion for 30 sec. To study the role of miR-499 in IPostC, adeno-associated virus (AAV) vectors of miR-499-5p (AAV-miR-499-5p) and miR-499-5p-sponge (AAV-miR-499-5p-sponge) were transfected via tail vein injection, followed by IPostC protocols. Cardiac injury as well as the status of local and systemic complement activation and inflammation were assessed. IPostC significantly attenuated I/R-induced rat cardiomyocyte apoptosis and the myocardial infarct size. These beneficial effects were accompanied by decreased local and circulating complement component (C)3a and C5a levels, decreased inflammatory marker expression, decreased NF-κB signaling and increased cardiac miR-499 expression. AAV-miR-499-5p prevented local and systemic complement activation and inflammation as well as enhanced the cardioprotection of IPostC, whereas AAV-miR-499-5p-sponge produced the opposite effects. In summary, IPostC protected the rat myocardium against I/R injury, by inhibiting local and systemic complement activation; inflammation; NF-κB signaling; and upregulation of miR-499. As such, miR-499 may have a critical role in IPostC-mediated cardioprotection against I/R injury.

LncRNA TUG1 regulates the development of ischemia-reperfusion mediated acute kidney injury through miR-494-3p/E-cadherin axis

Background

Acute kidney injury (AKI) results from renal dysfunction caused by various causes, resulting in high mortality. The underlying mechanisms of ischemia-reperfusion (I/R) induced AKI is very complicated and needed for further research. Here, we sought to found out the functions of lncRNA TUG1 in I/R-induced AKI.

Methods

In vivo model was constructed by I/R-induced mice and in vitro model was constructed by hypoxia/reoxygenation (H/R)-induced HK-2 cell. Kidney tissue damage was evaluated through H&E staining in mice. Cell flow cytometry was used to detect the degree of apoptosis. TUG1, miR-494-3p and E-cadherin were determined both by RT-PCR and western blot. Dual luciferase assay was employed to validate the relationships between TUG1, miR-494-3p and E-cadherin. Inflammatory factors including IL-1β, TNFɑ and IL-6 were evaluated by ELISA.

Results

lncRNA TUG1 was decreased while miR-494-3p was elevated in vivo and in vitro. Overexpression of TUG1 or transfection with miR-494-3p inhibitor significantly alleviated cell apoptosis. MiR-494-3p directly targeted E-cadherin and TUG1 suppressed cell apoptosis via serving as a miR-494-3p sponge to disinhibit E-cadherin.

Conclusion

lncRNA TUG1 alleviated I/R-induced AKI through targeting miR-494-3p/E-cadherin.

Renoprotective effect of vildagliptin following hepatic ischemia/reperfusion injury

Remote renal injury is a drastic consequence of hepatic ischemia/reperfusion (IR) injury. Vildagliptin (V) is a dipeptidyl peptidase-4 inhibitor that has a hepatorenal protective effect against models of liver and renal IR. This research was done to explore the protective role of vildagliptin against renal injury following hepatic IR injury as well as the possible involvement of transforming growth factor-beta (TGF-β)/Smad/alpha-smooth muscle actin (α-SMA) expressions in the pathophysiological mechanism of the remote renal injury. Three groups of male Wistar rats were organized into: sham group, IR group, and V + IR group in which 10 mg/kg/day of vildagliptin was pretreated for 10 days intraperitoneally. Blood in addition to renal and hepatic tissue samples was used for biochemical and histopathological studies. Hepatic IR induced a marked increase in serum creatinine, blood urea nitrogen, liver enzymes, renal nitric oxide, malondialdehyde, tumor necrosis factor-alpha levels with a marked upregulation of renal mRNA expressions of TGF-β, Smad2, Smad3, and α-SMA in addition to a marked decline in renal catalase content comparing to the sham group. Abnormal histopathological findings of hepatic and renal injury were detected in the IR group. Vildagliptin significantly improved these biochemical markers as well as the histopathological changes. The upregulation of renal TGF-β/Smad/α-SMA mRNA expressions was involved for the first time in the pathogenesis of the renal injury following hepatic IR and vildagliptin ameliorated this renal injury through blocking these expressions.

Targeted donor complement blockade after brain death prevents delayed graft function in a nonhuman primate model of kidney transplantation

Delayed graft function (DGF) in renal transplant is associated with reduced graft survival and increased immunogenicity. The complement-driven inflammatory response after brain death (BD) and posttransplant reperfusion injury play significant roles in the pathogenesis of DGF. In a nonhuman primate model, we tested complement-blockade in BD donors to prevent DGF and improve graft survival. BD donors were maintained for 20 hours; kidneys were procured and stored at 4°C for 43-48 hours prior to implantation into ABO-compatible, nonsensitized, MHC-mismatched recipients. Animals were divided into 3 donor-treatment groups: G1 - vehicle, G2 - rhC1INH+heparin, and G3 - heparin. G2 donors showed significant reduction in classical complement pathway activation and decreased levels of tumor necrosis factor α and monocyte chemoattractant protein 1. DGF was diagnosed in 4/6 (67%) G1 recipients, 3/3 (100%) G3 recipients, and 0/6 (0%) G2 recipients (P = .008). In addition, G2 recipients showed superior renal function, reduced sC5b-9, and reduced urinary neutrophil gelatinase-associated lipocalin in the first week posttransplant. We observed no differences in incidence or severity of graft rejection between groups. Collectively, the data indicate that donor-management targeting complement activation prevents the development of DGF. Our results suggest a pivotal role for complement activation in BD-induced renal injury and postulate complement blockade as a promising strategy for the prevention of DGF after transplantation.

Selection and validation of reference genes for normalisation of gene expression in ischaemic and toxicological studies in kidney disease

Normalisation to standard reference gene(s) is essential for quantitative real-time polymerase chain reaction (RT-qPCR) to obtain reproducible and comparable results of a gene of interest (GOI) between subjects and under varying experimental conditions. There is limited evidence to support selection of the commonly used reference genes in rat ischaemic and toxicological kidney models. Employing these models, we determined the most stable reference genes by comparing 4 standard methods (NormFinder, qBase+, BestKeeper and comparative ΔCq) and developed a new 3-way linear mixed-effects model for evaluation of reference gene stability. This new technique utilises the intra-class correlation coefficient as the stability measure for multiple continuous and categorical covariates when determining the optimum normalisation factor. The model also determines confidence intervals for each candidate normalisation gene to facilitate selection and allow sample size calculation for designing experiments to identify reference genes. Of the 10 candidate reference genes tested, the geometric mean of polyadenylate-binding nuclear protein 1 (PABPN1) and beta-actin (ACTB) was the most stable reference combination. In contrast, commonly used ribosomal 18S and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were the most unstable. We compared the use of PABPN1×ACTB and 2 commonly used genes 18S and GAPDH on the expression of 4 genes of interest know to vary after renal injury and expressed by different kidney cell types (KIM-1, HIF1α, TGFβ1 and PECAM1). The less stable reference genes gave varying patterns of GOI expression in contrast to the use of the least unstable reference PABPN1×ACTB combination; this improved detection of differences in gene expression between experimental groups. Reduced within-group variation of the now more accurately normalised GOI may allow for reduced experimental group size particularly for comparison between various models. This objective selection of stable reference genes increased the reliability of comparisons within and between experimental groups.

A Randomized Trial of Recombinant Human C1-Esterase-Inhibitor in the Prevention of Contrast-Induced Kidney Injury

OBJECTIVES

This study sought to determine the efficacy profile and safety of recombinant human C1 esterase inhibitor (rhC1INH) in the prevention of contrast-associated acute kidney injury after elective coronary angiography.

BACKGROUND

Contrast-associated acute kidney injury is caused by tubular cytotoxicity and ischemia/reperfusion injury. rhC1INH is effective in reducing renal ischemia/reperfusion injury in experimental models.

METHODS

In this placebo-controlled, double-blind, single-center trial 77 patients with chronic kidney disease were randomized to receive 50 IU/kg rhC1INH before and 4 h after elective coronary angiography or placebo. The primary outcome was the peak change of urinary neutrophil gelatinase-associated lipocalin within 48 h, a surrogate marker of kidney injury.

RESULTS

Median peak change of urinary neutrophil gelatinase-associated lipocalin was lower in the rhC1INH group (4.7 ng/ml vs. 22.5 ng/ml; p = 0.038) in the per-protocol population but not in the modified intention-to-treat analysis, and in patients with percutaneous coronary interventions (median, 1.8 ng/ml vs. 26.2 ng/ml; p = 0.039 corresponding to a median proportion peak change of 11% vs. 205%; p = 0.002). The incidence of a cystatin C increase ≥10% within 24 h was lower in the rhC1INH group (16% vs. 33%; p = 0.045), whereas the frequency of contrast-associated acute kidney injury was comparable. Adverse events during a 3-month follow-up were similarly distributed.

CONCLUSIONS

Administration of rhC1INH before coronary angiography may attenuate renal injury as reflected by urinary neutrophil gelatinase-associated lipocalin and cystatin C. The safety profile of rhC1INH was favorable in a patient population with multiple comorbidities. (Recombinant Human C1 Esterase Inhibitor in the Prevention of Contrast-induced Nephropathy in High-risk Subjects [PROTECT]; NCT02869347).

GSPE alleviates renal fibrosis by inhibiting the activation of C3/ HMGB1/ TGF-β1 pathway

Grape seed proanthocyanidin extract (GSPE) has been reported to exhibit a variety of protective effects, such as antioxidant, anti-atherosclerosis and other pharmacological effects. As a member of the complement system, complement component 3 (C3) deposition in the glomerulus is recognized as an important causative mediator of various kidney diseases. In this study, we aimed to identify the effect of GSPE on C3 in the chronic kidney fibrosis and evaluate the possible mechanism. We observed that administration of GSPE relieves inflammation and chronic renal fibrosis in mouse models of UUO. GSPE inhibited C3 secreted by macrophages to relieve renal interstitial inflammation. In vitro, we found that C3 stimulated HMGB1 translocation form nucleus to cytoplasm and promote the expression of pro-inflammatory cytokines including TGF-β1 in primary renal tubular epithelial cells (PTEC), which could be inhibited by GSPE. Meanwhile, GSPE could also decreased HMGB1-induced EMT of PTEC through suppresses the HMGB1/TLR4/p65/TGF-β1 pathway. In addition, the myofibroblast activation was inhibited by GSPE via TGF-β1/Smad2/3 signaling pathways in normal rat kidney fibroblast (NRK-49F) cells. Overall, these observations provide that GSPE alleviates renal fibrosis by inhibiting the C3/HMGB1/TGF-β1 pathway and could thus lead to find the potential therapy for the suppression of renal fibrosis.

Three-Year Outcomes of a Randomized, Double-Blind, Placebo-Controlled Study Assessing Safety and Efficacy of C1 Esterase Inhibitor for Prevention of Delayed Graft Function in Deceased Donor Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

Delayed graft function is related to ischemia-reperfusion injury and may be complement dependent. We previously reported from a randomized, placebo-controlled trial that treatment with C1 esterase inhibitor was associated with a shorter duration of delayed graft function and higher eGFR at 1 year. Here, we report longer-term outcomes from this trial.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This is a post hoc analysis of a phase 1/2, randomized, controlled trial enrolling 70 recipients of deceased donor kidney transplants at risk for delayed graft function (NCT02134314). Subjects were randomized to receive C1 esterase inhibitor 50 U/kg (n=35) or placebo (n=35) intraoperatively and at 24 hours. The cumulative incidence functions method was used to compare graft failure and death over 3.5 years. eGFR slopes were compared using a linear mixed effects model.

RESULTS

Three deaths occurred among C1 esterase inhibitor-treated patients compared with none receiving placebo. Seven graft failures developed in the placebo group compared with one among C1 esterase inhibitor-treated recipients; the cumulative incidence of graft failure was lower over 3.5 years among C1 esterase inhibitor-treated recipients compared with placebo (P=0.03). Although no difference in eGFR slopes was observed between groups (P for group-time interaction =0.12), eGFR declined in placebo-treated recipients (-4 ml/min per 1.73 m² per year; 95% confidence interval, -8 to -0.1) but was stable in C1 esterase inhibitor-treated patients (eGFR slope: 0.5 ml/min per 1.73 m² per year; 95% confidence interval, -4 to 5). At 3.5 years, eGFR was 56 ml/min per 1.73 m² (95% confidence interval, 42 to 70) in the C1 esterase inhibitor group versus 35 ml/min per 1.73 m² (95% confidence interval, 21 to 48) in the placebo group, with an estimated mean eGFR difference of 21 ml/min per 1.73 m² (95% confidence interval, 2 to 41 ml/min per 1.73 m²).

CONCLUSIONS

Treatment of patients at risk for ischemia-reperfusion injury and delayed graft function with C1 esterase inhibitor was associated with a lower incidence of graft failure.

Complement Inhibitors in Clinical Trials for Glomerular Diseases

Defective complement action is a cause of several human glomerular diseases including atypical hemolytic uremic syndrome (aHUS), anti-neutrophil cytoplasmic antibody mediated vasculitis (ANCA), C3 glomerulopathy, IgA nephropathy, immune complex membranoproliferative glomerulonephritis, ischemic reperfusion injury, lupus nephritis, membranous nephropathy, and chronic transplant mediated glomerulopathy. Here we summarize ongoing clinical trials of complement inhibitors in nine glomerular diseases and show which inhibitors are used in trials for these renal disorders (http://clinicaltrials.gov).

Complement Membrane Attack Complexes Assemble NLRP3 Inflammasomes Triggering IL-1 Activation of IFN-γ-Primed Human Endothelium

RATIONALE

Complement activation contributes to multiple immune-mediated pathologies. In late allograft failure, donor-specific antibody deposits complement membrane attack complexes (MAC) on graft endothelial cells (ECs), substantially increasing their immunogenicity without causing lysis. Internalized MAC stabilize NIK (NF-κB [nuclear factor kappa-light-chain-enhancer of activated B cells]-inducing kinase) protein on Rab5+MAC+ endosomes, activating noncanonical NF-κB signaling. However, the link to increased immunogenicity is unclear.

OBJECTIVE

To identify mechanisms by which alloantibody and internalized MAC activate ECs to enhance their ability to increase T-cell responses.

METHODS AND RESULTS

In human EC cultures, internalized MAC also causes NLRP3 (NOD-like receptor family pyrin domain containing 3) translocation from endoplasmic reticulum to Rab5+MAC+NIK+ endosomes followed by endosomal NIK-dependent inflammasome assembly. Cytosolic NIK, stabilized by LIGHT (lymphotoxin-like inducible protein that competes with glycoprotein D for herpesvirus entry on T cells), does not trigger inflammasome assembly, and ATP-triggered inflammasome assembly does not require NIK. IFN-γ (interferon-γ) primes EC responsiveness to MAC by increasing NLRP3, pro-caspase 1, and gasdermin D expression. NIK-activated noncanonical NF-κB signaling induces pro-IL (interleukin)-1β expression. Inflammasome processed pro-IL-1β, and gasdermin D results in IL-1β secretion that increases EC immunogenicity through IL-1 receptor signaling. Activation of human ECs lining human coronary artery grafts in immunodeficient mouse hosts by alloantibody and complement similarly depends on assembly of an NLRP3 inflammasome. Finally, in renal allograft biopsies showing chronic rejection, caspase-1 is activated in C4d⁺ ECs of interstitial microvessels, supporting the relevance of the cell culture findings.

CONCLUSIONS

In response to antibody-mediated complement activation, IFN-γ-primed human ECs internalize MAC, triggering both endosomal-associated NIK-dependent NLRP3 inflammasome assembly and IL-1 synthesis, resulting in autocrine/paracrine IL-1β-mediated increases in EC immunogenicity. Similar responses may underlie other complement-mediated pathologies.

Improvement in dysmyelination by the inhibition of microglial activation in a mouse model of Sandhoff disease

Sandhoff disease (SD) is a genetic disorder caused by a mutation of the β-subunit gene β-hexosaminidase B (HexB) in humans, which results in the massive accumulation of the ganglioside GM2 and related glycosphingolipids in the nervous system. SD causes progressive neurodegeneration and changes in white matter in human infants. An animal model of SD has been established, Hexb-deficient (Hexb) mice, which shows abnormalities resembling the severe phenotype found in human infants. Previously, we reported that the activation state of microglia caused astrogliosis in the early stage of Hexb mouse development. To study how the symptoms of SD develop, we explored the difference in gene expression between 4-week-old Hexb and Hexb mouse cerebral cortices by microarray analysis. The data indicated not only the upregulation of immune system-related genes but also the downregulation of myelin-related genes in the 4-week-old Hexb mouse cerebral cortices. To test the correlation between inflammation and dysmyelination, we generated double-knockout mice of Hexb and the Fc receptor γ gene (Fcrγ), which is a regulator of autoimmune responses. Dysmyelination recovered in these double-knockout mice. The number of oligodendrocyte progenitors, which expressed platelet-derived growth factor receptor-α, did not change in the 2-week-old mouse brain. These results indicate that microglial activation plays an important role in the myelination process, without influencing the number of oligodendrocyte progenitors, in the development of Hexb mice.

Identification of Candidate Genes Involved in Renal Ischemia/Reperfusion Injury

Renal ischemia/reperfusion injury (IRI) is a main risk factor for the occurrence of delayed graft function or primary graft nonfunction of kidney transplantation. However, it lacks ideal molecular markers for indicating IRI in kidney transplantation. The present study is to explore novel candidate genes involved in renal IRI. Experimental renal IRI mouse models were constructed, and the differentially expressed genes were screened using a microarray assay. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were performed. The expression of genes was detected using real-time qPCR assay. Western blotting and immunohistochemistry staining assays were performed for protein determination. We identified that renal IRI induced the upregulation of SPRR2F, SPRR1A, MMP-10, and long noncoding RNA (lncRNA) Malat1 in kidney tissues for 479.3-, 4.98-, 238.1-, and 3.79-fold, respectively. The expression of miR-139-5p in kidney tissues of IRI-treated mice was decreased to 40.4% compared with the sham-operated mice. These genes are associated with keratinocyte differentiation, regeneration and repair of kidney tissues, extracellular matrix degradation and remodeling, inflammation, and cell proliferation in renal IRI. Identification of novel biomarkers involved in renal IRI may provide evidences for the diagnosis and treatment of renal IRI.

Barriers and Advances in Kidney Preservation

Despite the fact that a significant fraction of kidney graft dysfunctions observed after transplantation is due to ischemia-reperfusion injuries, there is still no clear consensus regarding optimal kidney preservation strategy. This stems directly from the fact that as of yet, the mechanisms underlying ischemia-reperfusion injury are poorly defined, and the role of each preservation parameter is not clearly outlined. In the meantime, as donor demography changes, organ quality is decreasing which directly increases the rate of poor outcome. This situation has an impact on clinical guidelines and impedes their possible harmonization in the transplant community, which has to move towards changing organ preservation paradigms: new concepts must emerge and the definition of a new range of adapted preservation method is of paramount importance. This review presents existing barriers in transplantation (e.g., temperature adjustment and adequate protocol, interest for oxygen addition during preservation, and clear procedure for organ perfusion during machine preservation), discusses the development of novel strategies to overcome them, and exposes the importance of identifying reliable biomarkers to monitor graft quality and predict short and long-term outcomes. Finally, perspectives in therapeutic strategies will also be presented, such as those based on stem cells and their derivatives and innovative models on which they would need to be properly tested.

A phase I/II, double-blind, placebo-controlled study assessing safety and efficacy of C1 esterase inhibitor for prevention of delayed graft function in deceased donor kidney transplant recipients

Delayed graft function (DGF) is defined as need for dialysis early posttransplant. DGF is related to ischemia-reperfusion injury (IRI) that diminishes allograft function and may be complement dependent. Here, we investigate the ability of C1 esterase inhibitor (C1INH) to prevent IRI/DGF in kidney transplant recipients. Seventy patients receiving deceased donor kidney transplants at risk for DGF were randomized to receive C1INH 50 U/kg (#35) or placebo (#35) intraoperatively and at 24 hours. The primary end point was need for hemodialysis during the first week posttransplant. Assessments of glomerular filtration rate and dialysis dependence were accomplished. Complications and safety of therapy were recorded. Similar characteristics with no significant differences in cold-ischemia time or risk factors for DGF were seen. C1INH did not result in reduction of dialysis sessions at 1 week posttransplant, but significantly fewer dialysis sessions (P = .0232) were required 2 to 4 weeks posttransplant. Patients at highest risk for DGF (Kidney Donor Profile Index ≥85) benefited most from C1INH therapy. Significantly better renal function was seen at 1 year in C1INH patients (P = .006). No significant adverse events were noted with C1INH. Although the primary end point was not met, significant reductions in need for dialysis and improvements in long-term allograft function were seen with C1INH treatment.

Perspectives on the Optimal Genetically Engineered Pig in 2018 for Initial Clinical Trials of Kidney or Heart Xenotransplantation

For a clinical trial today, what might realistically be the optimal pig among those currently available? Deletion of expression of the 3 pig carbohydrate antigens, against which humans have natural (preformed) antibodies (triple-knockout pigs), should form the basis of any clinical trial. However, because both complement and coagulation can be activated in the absence of antibody, the expression of human complement- and coagulation-regulatory proteins is likely to be important in protecting the graft further. Any genetic manipulation that might reduce inflammation of the graft, for example, expression of hemeoxygenase-1 or A20, may also be beneficial to the long-term survival of the graft. The transgene for human CD47 is likely to have a suppressive effect on monocyte/macrophage and T-cell activity. Furthermore, deletion of xenoantigen expression and expression of a human complement-regulatory protein are both associated with a reduced T-cell response. Although there are several other genetic manipulations that may reduce the T-cell response further, it seems likely that exogenous immunosuppressive therapy, particularly if it includes costimulation blockade, will be sufficient. We would therefore suggest that, with our present knowledge and capabilities, the optimal pig might be a triple-knockout pig that expressed 1 or more human complement-regulatory proteins, 1 or more human coagulation-regulatory proteins, a human anti-inflammatory transgene, and CD47. Absent or minimal antibody binding is important, but we suggest that the additional insertion of protective human transgenes will be beneficial, and may be essential.

Immunopathogenesis of Acute Kidney Injury

Pathophysiologically, the classification of acute kidney injury (AKI) can be divided into three categories: (1) prerenal, (2) intrinsic, and (3) postrenal. Emerging evidence supports the involvement of renal tubular epithelial cells and the innate and adaptive arms of the immune system in the pathogenesis of intrinsic AKI. Pro-inflammatory damage-associated molecular patterns, pathogen-associated molecular patterns, hypoxia inducible factors, toll-like receptors, complement system, oxidative stress, adhesion molecules, cell death, resident renal dendritic cells, neutrophils, T and B lymphocytes, macrophages, natural killer T cells, cytokines, and secreted chemokines contribute to the immunopathogenesis of AKI. However, other immune cells and pathways such as M2 macrophages, regulatory T cells, progranulin, and autophagy exhibit anti-inflammatory properties and facilitate kidney tissue repair after AKI. Thus, therapies for AKI include agents such as anti-inflammatory (e.g., recombinant alkaline phosphatase), antioxidants (iron chelators), and apoptosis inhibitors. In preclinical toxicity studies, drug-induced kidney injury can be seen after exposure to a nephrotoxicant test article due to immune mechanisms and dysregulation of innate, and/or adaptive cellular immunity. The focus of this review will be on intrinsic AKI, as it relates to the immune and renal systems cross talks focusing on the cellular and pathophysiologic mechanisms of AKI.

Leukocyte-Associated Ig-like Receptor 1 Inhibits Th1 Responses but Is Required for Natural and Induced Monocyte-Dependent Th17 Responses

Leukocyte-associated Ig-like receptor 1 (LAIR1) is an ITIM-bearing collagen receptor expressed by leukocytes and is implicated in immune suppression. However, using a divalent soluble LAIR1/Fc recombinant protein to block interaction of cell surface LAIR1 with matrix collagen, we found that whereas T_h1 responses were enhanced as predicted, T_h17 responses were strongly inhibited. Indeed, LAIR1 on both T cells and monocytes was required for optimal T_h17 responses to collagen type (Col)V. For pre-existing "natural" T_h17 response to ColV, the LAIR1 requirement was absolute, whereas adaptive T_h17 and T_h1/17 immune responses in both mice and humans were profoundly reduced in the absence of LAIR1. Furthermore, the addition of C1q, a natural LAIR1 ligand, decreased T_h1 responses in a dose-dependent manner, but it had no effect on T_h17 responses. In IL-17-dependent murine organ transplant models of chronic rejection, LAIR1^+/+ but not LAIR1^-/- littermates mounted strong fibroproliferative responses. Surface LAIR1 expression was higher on human T_h17 cells as compared with T_h1 cells, ruling out a receptor deficiency that could account for the differences. We conclude that LAIR1 ligation by its natural ligands favors T_h17 cell development, allowing for preferential activity of these cells in collagen-rich environments. The emergence of cryptic self-antigens such as the LAIR1 ligand ColV during ischemia/reperfusion injury and early acute rejection, as well as the tendency of macrophages/monocytes to accumulate in the allograft during chronic rejection, favors T_h17 over T_h1 development, posing a risk to long-term graft survival.

TRPM7 in CHBP-induced renoprotection upon ischemia reperfusion-related injury

Transient receptor potential melastatin 7 (TRPM7) is a membrane ion channel and kinase. TRPM7 was abundantly expressed in the kidney, and up-regulated by ischemia reperfusion (IR) injury. Our previous studies showed that cyclic helix B peptide (CHBP) improved renal IR-related injury, but its underlying mechanism is not well defined. IR-related injury was established in renal tubular epithelial cells (TCMK-1 and HK-2) via 12 to 24-h hypoxia (H) followed by 2-24 h reoxygenation (R), and in mouse kidneys subjected to 30-min ischemia and 12-h to 7-day reperfusion. TRPM7-like current in TCMK-1 cells, TRPM7 mRNA and protein in the in vitro and in vivo models were increased, but reversed by CHBP. TRPM7 was also positively associated with LDH, HMGB1, caspase-3, Bax/Bcl-2, inflammation, apoptosis, tubulointerstitial damage and renal function respectively. Furthermore, silencing TRPM7 improved injury parameters, renal histology and function in the both models. Specific TRPM7 agonist, bradykinin, exaggerated HR induced injury in TCMK-1 cells, and partially blocked the renoprotection of CHBP as well. In conclusion, TRPM7 is involved not only in IR-related injury, but also CHBP-induced renoprotection, which are through its ion channel and subsequent affects inflammation and apoptosis. Therefore, TRPM7 could be a potential biomarker for IR-induced acute kidney injury.