Complement-mediated inflammation and injury in brain dead organ donors

Ischemia-Reperfusion Injury in Kidney Transplantation: Mechanisms and Potential Therapeutic Targets

Kidney transplantation offers a longer life expectancy and a better quality of life than dialysis to patients with end-stage kidney disease. Ischemia-reperfusion injury (IRI) is thought to be a cornerstone in delayed or reduced graft function and increases the risk of rejection by triggering the immunogenicity of the organ. IRI is an unavoidable event that happens when the blood supply is temporarily reduced and then restored to an organ. IRI is the result of several biological pathways, such as transcriptional reprogramming, apoptosis and necrosis, innate and adaptive immune responses, and endothelial dysfunction. Tubular cells mostly depend on fatty acid (FA) β-oxidation for energy production since more ATP molecules are yielded per substrate molecule than glucose oxidation. Upon ischemia-reperfusion damage, the innate and adaptive immune system activates to achieve tissue clearance and repair. Several cells, cytokines, enzymes, receptors, and ligands are known to take part in these events. The complement cascade might start even before organ procurement in deceased donors. However, additional experimental and clinical data are required to better understand the pathogenic events that take place during this complex process.

Systemic and local complement activation in peritoneal dialysis patients via conceivably distinct pathways

BACKGROUND

Despite several advantages compared to haemodialysis (HD), peritoneal dialysis (PD) remains an underused dialysis technique due to its high technique failure rate related to membrane fibrosis and peritonitis events. Previous work has suggested a harmful role for the complement system in these processes, highlighting the need for a more comprehensive examination in PD.

METHODS

Plasma levels of C1q, mannose-binding lectin (MBL), Properdin, Factor D, C3d/C3-ratio and soluble membrane attack complex (sC5b-9) were determined in PD patients (n = 55), HD patients (n = 41), non-dialysis chronic kidney disease (CKD) patients (n = 15) and healthy controls (n = 14). Additionally, C1q, MBL, Properdin, Factor D and sC5b-9 levels were assessed in the peritoneal dialysis fluid (PDF). In a subgroup, interleukin-6, matrix metalloproteinase-2 (MMP-2), myeloperoxidase (MPO) and elastase were measured in the PDF.

RESULTS

PD patients had significantly higher systemic levels of sC5b-9 compared to healthy controls, CKD and HD patients (p < 0.001). Plasma levels of C1q and C3d/C3-ratios were significantly associated with systemic sC5b-9 levels (p < 0.001). Locally, sC5b-9 was detected in the PDF of all PD patients, and levels were approximately 33% of those in matched plasma, but they did not correlate. In the PDF, only Properdin levels remained significantly associated with PDF sC5b-9 levels in multivariate analysis (p < 0.001). Additionally, PDF levels of sC5b-9 positively correlated with elastase, MPO and MMP-2 levels in the PDF (p < 0.01).

CONCLUSIONS

Our data reveal both systemic and local complement activation in PD patients. Furthermore, these two processes seem independent considering the involvement of different pathways and the lack of correlation.

Complement activation and kidney transplantation; a complex relationship

Although kidney transplantation is the best treatment for end stage kidney disease, the benefits are limited by factors such as the short fall in donor numbers, the burden of immunosuppression and graft failure. Although there have been improvements in one-year outcomes, the annual rate of graft loss beyond the first year has not significantly improved, despite better therapies to control the alloimmune response. There is therefore a need to develop alternative strategies to limit kidney injury at all stages along the transplant pathway and so improve graft survival. Complement is primarily part of the innate immune system, but is also known to enhance the adaptive immune response. There is increasing evidence that complement activation occurs at many stages during transplantation and can have deleterious effects on graft outcome. Complement activation begins in the donor and occurs again on reperfusion following a period of ischemia. Complement can contribute to the development of the alloimmune response and may directly contribute to graft injury during acute and chronic allograft rejection. The complexity of the relationship between complement activation and allograft outcome is further increased by the capacity of the allograft to synthesise complement proteins, the contribution complement makes to interstitial fibrosis and complement's role in the development of recurrent disease. The better we understand the role played by complement in kidney transplant pathology the better placed we will be to intervene. This is particularly relevant with the rapid development of complement therapeutics which can now target different the different pathways of the complement system. Combining our basic understanding of complement biology with preclinical and observational data will allow the development and delivery of clinical trials which have best chance to identify any benefit of complement inhibition.

Comparison of acute kidney injury following brain death between male and female rats

BACKGROUND

Clinical reports associate kidneys from female donors with worse prognostic in male recipients. Brain Death (BD) produces immunological and hemodynamic disorders that affect organ viability. Following BD, female rats are associated with increased renal inflammation interrelated with female sex hormone reduction. Here, the aim was to investigate the effects of sex on BD-induced Acute Kidney Injury (AKI) using an Isolated Perfused rat Kidney (IPK) model.

METHODS

Wistar rats, females, and males (8 weeks old), were maintained for 4h after BD. A left nephrectomy was performed and the kidney was preserved in a cold saline solution (30 min). IPK was performed under normothermic temperature (37°C) for 90 min using WME as perfusion solution. AKI was assessed by morphological analyses, staining of complement system components and inflammatory cell markers, perfusion flow, and creatinine clearance.

RESULTS

BD-male kidneys had decreased perfusion flow on IPK, a phenomenon that was not observed in the kidneys of BD-females (p < 0.0001). BD-male kidneys presented greater proximal (p = 0.0311) and distal tubule (p = 0.0029) necrosis. However, BD-female kidneys presented higher expression of eNOS (p = 0.0060) and greater upregulation of inflammatory mediators, iNOS (p = 0.0051), and Caspase-3 (p = 0.0099). In addition, both sexes had increased complement system formation (C5b-9) (p=0.0005), glomerular edema (p = 0.0003), and nNOS (p = 0.0051).

CONCLUSION

The present data revealed an important sex difference in renal perfusion in the IPK model, evidenced by a pronounced reduction in perfusate flow and low eNOS expression in the BD-male group. Nonetheless, the upregulation of genes related to the proinflammatory cascade suggests a progressive inflammatory process in BD-female kidneys.

Complement inhibition alleviates donor brain death-induced liver injury and posttransplant cascade injury by regulating phosphoinositide 3-kinase signaling

Brain death (BD) donors are the primary source of donor organs for liver transplantation. However, the effects of BD on donor livers and outcomes after liver transplantation remain unclear. Here, we explored the role of complement and the therapeutic effect of complement inhibition in BD-induced liver injury and posttransplantation injury in a mouse BD and liver transplantation model. For complement inhibition, we used complement receptor 2 (CR2)-Crry, a murine inhibitor of C3 activation that specifically targets sites of complement activation. In the mouse model, BD resulted in complement activation and liver injury in donor livers and a cascade liver injury posttransplantation, mediated in part through the C3a-C3aR (C3a receptor) signaling pathway, which was ameliorated by treatment with CR2-Crry. Treatment of BD donors with CR2-Crry improved graft survival, which was further improved when recipients received an additional dose of CR2-Crry posttransplantation. Mechanistically, we determined that complement inhibition alleviated BD-induced donor liver injury and posttransplant cascade injury by regulating phosphoinositide 3-kinase (PI3K) signaling pathways. Together, BD induced donor liver injury and cascade injury post-transplantation, which was mediated by complement activation products acting on PI3K signaling pathways. Our study provides an experimental basis for developing strategies to improve the survival of BD donor grafts in liver transplantation.

The Complement System in Kidney Transplantation

Kidney transplantation is the therapy of choice for patients who suffer from end-stage renal diseases. Despite improvements in surgical techniques and immunosuppressive treatments, long-term graft survival remains a challenge. A large body of evidence documented that the complement cascade, a part of the innate immune system, plays a crucial role in the deleterious inflammatory reactions that occur during the transplantation process, such as brain or cardiac death of the donor and ischaemia/reperfusion injury. In addition, the complement system also modulates the responses of T cells and B cells to alloantigens, thus playing a crucial role in cellular as well as humoral responses to the allograft, which lead to damage to the transplanted kidney. Since several drugs that are capable of inhibiting complement activation at various stages of the complement cascade are emerging and being developed, we will discuss how these novel therapies could have potential applications in ameliorating outcomes in kidney transplantations by preventing the deleterious effects of ischaemia/reperfusion injury, modulating the adaptive immune response, and treating antibody-mediated rejection.

Immune response associated with ischemia and reperfusion injury during organ transplantation

Background

Ischemia and reperfusion injury (IRI) is an ineluctable immune-related pathophysiological process during organ transplantation, which not only causes a shortage of donor organs, but also has long-term and short-term negative consequences on patients. Severe IRI-induced cell death leads to the release of endogenous substances, which bind specifically to receptors on immune cells to initiate an immune response. Although innate and adaptive immunity have been discovered to play essential roles in IRI in the context of organ transplantation, the pathway and precise involvement of the immune response at various stages has not yet to be elucidated.

Methods

We combined “IRI” and “organ transplantation” with keywords, respectively such as immune cells, danger signal molecules, macrophages, neutrophils, natural killer cells, complement cascade, T cells or B cells in PubMed and the Web of Science to search for relevant literatures.

Conclusion

Comprehension of the immune mechanisms involved in organ transplantation is promising for the treatment of IRI, this review summarizes the similarities and differences in both innate and adaptive immunity and advancements in the immune response associated with IRI during diverse organ transplantation.

Complement Is Activated During Normothermic Machine Perfusion of Porcine and Human Discarded Kidneys

Background

The gap between demand and supply of kidneys for transplantation necessitates the use of kidneys from extended criteria donors. Transplantation of these donor kidneys is associated with inferior results, reflected by an increased risk of delayed graft function. Inferior results might be explained by the higher immunogenicity of extended criteria donor kidneys. Normothermic machine perfusion (NMP) could be used as a platform to assess the quality and function of donor kidneys. In addition, it could be useful to evaluate and possibly alter the immunological response of donor kidneys. In this study, we first evaluated whether complement was activated during NMP of porcine and human discarded kidneys. Second, we examined the relationship between complement activation and pro-inflammatory cytokines during NMP. Third, we assessed the effect of complement activation on renal function and injury during NMP of porcine kidneys. Lastly, we examined local complement C3d deposition in human renal biopsies after NMP.

Methods

NMP with a blood-based perfusion was performed with both porcine and discarded human kidneys for 4 and 6 h, respectively. Perfusate samples were taken every hour to assess complement activation, pro-inflammatory cytokines and renal function. Biopsies were taken to assess histological injury and complement deposition.

Results

Complement activation products C3a, C3d, and soluble C5b-9 (sC5b-9) were found in perfusate samples taken during NMP of both porcine and human kidneys. In addition, complement perfusate levels positively correlated with the cytokine perfusate levels of IL-6, IL-8, and TNF during NMP of porcine kidneys. Porcine kidneys with high sC5b-9 perfusate levels had significantly lower creatinine clearance after 4 h of NMP. In line with these findings, high complement perfusate levels were seen during NMP of human discarded kidneys. In addition, kidneys retrieved from brain-dead donors had significantly higher complement perfusate levels during NMP than kidneys retrieved from donors after circulatory death.

Conclusion

Normothermic kidney machine perfusion induces complement activation in porcine and human kidneys, which is associated with the release of pro-inflammatory cytokines and in porcine kidneys with lower creatinine clearance. Complement inhibition during NMP might be a promising strategy to reduce renal graft injury and improve graft function prior to transplantation.

First clinical-grade porcine kidney xenotransplant using a human decedent model

A radical solution is needed for the organ supply crisis, and the domestic pig is a promising organ source. In preparation for a clinical trial of xenotransplantation, we developed an in vivo pre-clinical human model to test safety and feasibility tenets established in animal models. After performance of a novel, prospective compatible crossmatch, we performed bilateral native nephrectomies in a human brain-dead decedent and subsequently transplanted two kidneys from a pig genetically engineered for human xenotransplantation. The decedent was hemodynamically stable through reperfusion, and vascular integrity was maintained despite the exposure of the xenografts to human blood pressure. No hyperacute rejection was observed, and the kidneys remained viable until termination 74 h later. No chimerism or transmission of porcine retroviruses was detected. Longitudinal biopsies revealed thrombotic microangiopathy that did not progress in severity, without evidence of cellular rejection or deposition of antibody or complement proteins. Although the xenografts produced variable amounts of urine, creatinine clearance did not recover. Whether renal recovery was impacted by the milieu of brain death and/or microvascular injury remains unknown. In summary, our study suggests that major barriers to human xenotransplantation have been surmounted and identifies where new knowledge is needed to optimize xenotransplantation outcomes in humans.

The Contribution of Complement to the Pathogenesis of IgA Nephropathy: Are Complement-Targeted Therapies Moving from Rare Disorders to More Common Diseases?

Primary IgA nephropathy (IgAN) is a leading cause of chronic kidney disease and kidney failure for which there is no disease-specific treatment. However, this could change, since novel therapeutic approaches are currently being assessed in clinical trials, including complement-targeting therapies. An improved understanding of the role of the lectin and the alternative pathway of complement in the pathophysiology of IgAN has led to the development of these treatment strategies. Recently, in a phase 2 trial, treatment with a blocking antibody against mannose-binding protein-associated serine protease 2 (MASP-2, a crucial enzyme of the lectin pathway) was suggested to have a potential benefit for IgAN. Now in a phase 3 study, this MASP-2 inhibitor for the treatment of IgAN could mark the start of a new era of complement therapeutics where common diseases can be treated with these drugs. The clinical development of complement inhibitors requires a better understanding by physicians of the biology of complement, the pathogenic role of complement in IgAN, and complement-targeted therapies. The purpose of this review is to provide an overview of the role of complement in IgAN, including the recent discovery of new mechanisms of complement activation and opportunities for complement inhibitors as the treatment of IgAN.

Proteomic analysis of machine perfusion solution from brain dead donor kidneys reveals that elevated complement, cytoskeleton and lipid metabolism proteins are associated with 1-year outcome

Assessment of donor kidney quality is based on clinical scores or requires biopsies for histological assessment. Noninvasive strategies to identify and predict graft outcome at an early stage are, therefore, needed. We evaluated the perfusate of donation after brain death (DBD) kidneys during nonoxygenated hypothermic machine perfusion (HMP). In particular, we compared perfusate protein profiles of good outcome (GO) and suboptimal outcome (SO) 1‐year post‐transplantation. Samples taken 15 min after the start HMP (T1) and before the termination of HMP (T2) were analysed using quantitative liquid chromatography–tandem mass spectrometry (LC‐MS/MS). Hierarchical clustering of the 100 most abundant proteins showed discrimination between grafts with a GO and SO at T1. Elevated levels of proteins involved in classical complement cascades at both T1 and T2 and a reduced abundance of lipid metabolism at T1 and of cytoskeletal proteins at T2 in GO versus SO was observed. ATP‐citrate synthase and fatty acid‐binding protein 5 (T1) and immunoglobulin heavy variable 2‐26 and desmoplakin (T2) showed 91% and 86% predictive values, respectively, for transplant outcome. Taken together, DBD kidney HMP perfusate profiles can distinguish between outcome 1‐year post‐transplantation. Furthermore, it provides insights into mechanisms that could play a role in post‐transplant outcomes.

Protective role of 17β-estradiol treatment in renal injury on female rats submitted to brain death

Background

Clinical and experimental data highlight the consequences of brain death on the quality of organs and demonstrate the importance of donor state to the results of transplantation. Female rats show higher cardio-pulmonary injury linked to decreased concentrations of female sex hormones after brain-dead (BD). This study evaluated the effect of 17β-estradiol on brain death induced renal injury in female rats.

Methods

Female Wistar rats were randomically allocated into 4 groups: false-operation (Sham), BD, treatment with 17β-estradiol (50 µg/mL, 2 mL/h) 3 h after brain death (E2-T3), or immediately after brain death confirmation (E2-T0). Creatinine, urea, cytokines, and complement system components were quantified. Renal injury markers, such as KIM-1, Caspase-3, BCL-2 and MMP2/9 were evaluated.

Results

Brain death leads to increased kidney KIM-1 expression and longer 17β-estradiol treatment resulted in downregulation (P<0.0001). There was increase of neutrophil numbers in kidney from BD rats and E2 treatment was able to reduce it (P=0.018). Regarding complement elements, E2-T3 group evidenced E2 therapeutic effects, reducing C5b-9 (P=0.0004), C3aR (P=0.054) and C5aR (P=0.019). In parallel, there were 17β-estradiol effects in reducing MMP2 (P=0.0043), MMP9 (P=0.011), and IL-6 (P=0.024). Moreover, E2-T3 group improved renal function in comparison to BD group (P=0.0938).

Conclusions

17β-estradiol treatment was able to reduce acute kidney damage in BD female rats owing to its ability to prevent tissue damage, formation of C5b-9, and local synthesis of inflammatory mediators.

Systemic Complement Activation in Donation After Brain Death Versus Donation After Circulatory Death Organ Donors

OBJECTIVES

Complement activation in organs from deceased donors is associated with allograft injury and acute rejection. Because use of organs from donors after circulatory death is increasing, we characterized relative levels of complement activation in organs from donors after brain death and after circulatory death and examined associations between donor complement factor levels and outcomes after kidney and liver transplant.

MATERIALS AND METHODS

Serum samples from 65 donors (55 donations after brain death, 10 donations after circulatory death) were analyzed for classical, lectin, alternative, and terminal pathway components by Luminex multiplex assays. Complement factor levels were compared between groups, and associations with posttransplant outcomes were explored.

RESULTS

Serum levels of the downstream complement activation product C5a were similar in organs from donors after circulatory death versus donors after brain death. In organs from donors after circulatory death, complement activation occurred primarily via the alternative pathway; the classical, lectin, and alternative pathways all contributed in organs from donors after brain death. Donor complement levels were not associated with outcomes after kidney transplant. Lower donor complement levels were associated with need for transfusion, reintervention, hospital readmission, and acute rejection after liver transplant.

CONCLUSIONS

Complement activation occurs at similar levels in organs donated from donors after circulatory death versus those after brain death. Lower donor complement levels may contribute to adverse outcomes after liver transplant. Further study is warranted to better understand how donor complement activation contributes to posttransplant outcomes.

Brain Death Enhances Activation of the Innate Immune System and Leads to Reduced Renal Metabolic Gene Expression

BACKGROUND

Brain death (BD)-associated inflammation has been implicated in decreased kidney allograft function and survival, but the underlying mechanisms have not been well distinguished from the conditions of critical care itself. We have developed a clinically translatable model to separate and investigate strategies to improve donor management and critical care.

METHODS

Brain-dead (n = 12) and sham (n = 5) rhesus macaques were maintained for 20 hours under intensive care unit-level conditions. Samples were collected for immunophenotyping, analysis of plasma proteins, coagulation studies, and gene analysis for changes in immune and metabolic profile with comparison to naive samples (n = 10).

RESULTS

We observed an increase in circulating leukocytes and cytokines, activation of complement and coagulation pathways, and upregulation of genes associated with inflammation in both brain-dead and sham subjects relative to naïve controls. Sham demonstrated an intermediate phenotype of inflammation compared to BD. Analysis of gene expression in kidneys from BD kidneys revealed a similar upregulation of inflammatory profile in both BD and sham subjects, but BD presented a distinct reduction in metabolic and respiratory processes compared to sham and naïve kidneys.

CONCLUSION

BD is associated with activation of specific pathways of the innate immune system and changes to metabolic gene expression in renal tissue itself; however, sham donors presented an intermediate inflammatory response attributable to the critical care environment. The early onset and penetrating impact of this inflammatory response underscores the need for early intervention to prevent perioperative tissue injury to transplantable organs.

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.

Indicadores clínicos para o diagnóstico de enfermagem Síndrome do equilíbrio fisiológico prejudicado para doadores de órgãos

RESUMO Objetivo Selecionar indicadores clínicos para o diagnóstico de enfermagem em desenvolvimento Síndrome do equilíbrio fisiológico prejudicado para potenciais doadores de órgãos em morte encefálica. Método Estudo de consenso de especialistas, realizado através da técnica Delphi, dos indicadores clínicos de um diagnóstico de enfermagem em desenvolvimento. A amostra do estudo foi intencional mediante convite e constituída por 37 enfermeiros que atenderam a critérios de inclusão. Os indicadores que obtiveram um consenso igual ou maior que 70% foram considerados validados. Resultados Especialistas recomendaram 25 dos 44 indicadores avaliados, dos quais oito pertenciam ao grupo Alterações endócrino-metabólicas, sete ao grupo Alterações hemodinâmicas e/ou cardiovasculares, cinco ao grupo Alterações ventilatórias, dois ao grupo Alterações nutricionais e três ao grupo Alterações de coagulação, inflamatórias e/ou imunológicas. Conclusão e implicações para a prática Esse novo diagnóstico de enfermagem pode colaborar com o desenvolvimento de conhecimento da enfermagem na área de doação de órgãos, contribuindo para o ensino e pesquisa, além de acarretar implicações para a prática, proporcionando acurácia diagnóstica e embasando a implementação e a avaliação de intervenções que impactam na melhora da manutenção do potencial doador.

Blocking Complement Factor B Activation Reduces Renal Injury and Inflammation in a Rat Brain Death Model

Introduction: The majority of kidneys used for transplantation are retrieved from brain-dead organ donors. In brain death, the irreversible loss of brain functions results in hemodynamic instability, hormonal changes and immunological activation. Recently, brain death has been shown to cause activation of the complement system, which is adversely associated with renal allograft outcome in recipients. Modulation of the complement system in the brain-dead donor might be a promising strategy to improve organ quality before transplantation. This study investigated the effect of an inhibitory antibody against complement factor B on brain death-induced renal inflammation and injury. Method: Brain death was induced in male Fischer rats by inflating a balloon catheter in the epidural space. Anti-factor B (anti-FB) or saline was administered intravenously 20 min before the induction of brain death (n = 8/group). Sham-operated rats served as controls (n = 4). After 4 h of brain death, renal function, renal injury, and inflammation were assessed. Results: Pretreatment with anti-FB resulted in significantly less systemic and local complement activation than in saline-treated rats after brain death. Moreover, anti-FB treatment preserved renal function, reflected by significantly reduced serum creatinine levels compared to saline-treated rats after 4 h of brain death. Furthermore, anti-FB significantly attenuated histological injury, as seen by reduced tubular injury scores, lower renal gene expression levels (>75%) and renal deposition of kidney injury marker-1. In addition, anti-FB treatment significantly prevented renal macrophage influx and reduced systemic IL-6 levels compared to saline-treated rats after brain death. Lastly, renal gene expression of IL-6, MCP-1, and VCAM-1 were significantly reduced in rats treated with anti-FB. Conclusion: This study shows that donor pretreatment with anti-FB preserved renal function, reduced renal damage and inflammation prior to transplantation. Therefore, inhibition of factor B in organ donors might be a promising strategy to reduce brain death-induced renal injury and inflammation.

The lectin pathway in renal disease: old concept and new insights

The complement system is composed of a network of at least 40 proteins, which significantly contributes to health and disease. The lectin pathway (LP) is one of three pathways that can activate the complement system. Next to protection of the host against pathogens, the LP has been shown to play a crucial role in multiple renal diseases as well as during renal replacement therapy. Therefore, several complement-targeted drugs are currently being explored in clinical trials. Among these complement inhibitors, specific LP inhibitors are also being tested in renal abnormalities such as in immunoglobulin A nephropathy and lupus nephritis. Using various in vitro models, Yaseen et al. (Lectin pathway effector enzyme mannan-binding lectin-associated serine protease-2 can activate native complement component 3 (C3) in absence of C4 and/or C2. FASEB J 2017; 31: 2210-2219) showed that Mannan-associated serine protease2 can directly activate C3 thereby bypassing C2 and C4 in the activation of the LP. These new findings broaden our understanding of the mechanisms of complement activation and could potentially impact our strategies to inhibit the LP in renal diseases. In support of these findings, we present data of human renal biopsies, demonstrating the occurrence of the LP bypass mechanism in vivo. In conclusion, this review provides a detailed overview of the LP and clarifies the recently described bypass mechanism and its relevance. Finally, we speculate on the role of the C4 bypass mechanism in other renal diseases.

C3 glomerulonephritis secondary to mutations in factors H and I: rapid recurrence in deceased donor kidney transplant effectively treated with eculizumab

Background

C3 glomerulonephritis (C3GN) is caused by alternate complement pathway over-activation. It frequently progresses to end-stage renal disease, recurs in two-thirds of transplants and in half of these cases progresses to allograft loss. There is currently no proven treatment for C3GN.

Case Presentation

We describe a family segregating pathogenic alleles of complement factor H and I (CFH and CFI). The only member carrying both mutations developed C3GN. Prolonged delayed graft function after deceased donor transplantation, heavy proteinuria and isolated C3 hypocomplementemia prompted an allograft biopsy confirming diagnosis of recurrent C3GN.

Discussion

This is the first report of early recurrence of C3GN in an allograft in a patient with known mutations in complement regulatory genes and no preexisting para-proteinemia. Complement activation resulting from ischemia-reperfusion injury from prolonged cold ischemia time unabated in the setting of deficiency of two major complement regulators likely led to the early and severe recurrence. In atypical hemolytic uremic syndrome, the terminal complement cascade activation in the sentinel event initiating endothelial injury; blockade at the level of C5 convertase with eculizumab is uniformly highly effective in management. C3 glomerulopathies (C3GN and dense deposit disease) are a more complex and heterogeneous group. The relative degree of dysregulation at the levels of C3 and C5 convertases and therefore response to eculizumab varies among patients. In our patient, the clinical response to eculizumab was dramatic with recovery of allograft function and complete resolution of proteinuria. We review all cases of recurrent C3 glomerulopathy treated with eculizumab and discuss how complement biomarkers may aid in predicting response to therapy.

The systematic identification and mRNA expression profiles post viral or bacterial challenge of complement system in grass carp Ctenopharyngodon idella

Complement system is an immemorial and pivotal element in innate immunity, protecting individuals from invading pathogens. Due to the emergence of whole genomes and functional researches, systematic identifications of complement system are feasible in many non-model species. In the present study, BLAST analysis was employed to systematically identify and characterize complement system in grass carp (Ctenopharyngodon idella). The results showed that C. idella complement system consists of 64 members, including the complement system pattern recognition, proteases, complement components, receptors and regulators. In which, most genes were well conserved with those in higher vertebrates over the course of evolution. Phylogenetic and syntenic analyses revealed their homologous relationships with other species. mRNA expression analyses of complement system related genes indicated that many members are sustainably expressed in multiple tissues before and after grass carp reovirus (GCRV) or Aeromonas hydrophila infection, which provide in vivo evidence for the response patterns of complement system after viral or bacterial infection. Meanwhile, this study also explored the evolution of complement system from ancestral protists to mammals and then investigated the changes in gene diversification during the evolution. These results will serve the comparative studies on the complement system in evolution and further functional investigations in C. idella.

Complement Therapeutics in the Multi-Organ Donor: Do or Don't?

Over the last decade, striking progress has been made in the field of organ transplantation, such as better surgical expertise and preservation techniques. Therefore, organ transplantation is nowadays considered a successful treatment in end-stage diseases of various organs, e.g. the kidney, liver, intestine, heart, and lungs. However, there are still barriers which prevent a lifelong survival of the donor graft in the recipient. Activation of the immune system is an important limiting factor in the transplantation process. As part of this pro-inflammatory environment, the complement system is triggered. Complement activation plays a key role in the transplantation process, as highlighted by the amount of studies in ischemia-reperfusion injury (IRI) and rejection. However, new insight have shown that complement is not only activated in the later stages of transplantation, but already commences in the donor. In deceased donors, complement activation is associated with deteriorated quality of deceased donor organs. Of importance, since most donor organs are derived from either brain-dead donors or deceased after circulatory death donors. The exact mechanisms and the role of the complement system in the pathophysiology of the deceased donor have been underexposed. This review provides an overview of the current knowledge on complement activation in the (multi-)organ donor. Targeting the complement system might be a promising therapeutic strategy to improve the quality of various donor organs. Therefore, we will discuss the complement therapeutics that already have been tested in the donor. Finally, we question whether complement therapeutics should be translated to the clinics and if all organs share the same potential complement targets, considering the physiological differences of each organ.

Age and Sex-Associated Changes of Complement Activity and Complement Levels in a Healthy Caucasian Population

Introduction: The complement system is essential for an adequate immune response. Much attention has been given to the role of complement in disease. However, to better understand complement in pathology, it is crucial to first analyze this system under different physiological conditions. The aim of the present study was therefore to investigate the inter-individual variation in complement activity and the influences of age and sex.

Methods: Complement levels and functional activity were determined in 120 healthy volunteers, 60 women, 60 men, age range 20–69 year. Serum functional activity of the classical pathway (CP), lectin pathway activated by mannan (MBL-LP) and alternative pathway (AP) was measured in sera, using deposition of C5b-9 as readout. In addition, levels of C1q, MBL, MASP-1, MASP-2, ficolin-2, ficolin-3, C2, C4, C3, C5, C6, C7, C8, C9, factor B, factor D, properdin, C1-inhibitor and C4b-binding protein, were determined. Age- and sex-related differences were evaluated.

Results: Significantly lower AP activity was found in females compared to males. Further analysis of the AP revealed lower C3 and properdin levels in females, while factor D concentrations were higher. MBL-LP activity was not influenced by sex, but MBL and ficolin-3 levels were significantly lower in females compared to males. There were no significant differences in CP activity or CP components between females and males, nevertheless females had significantly lower levels of the terminal components. The CP and AP activity was significantly higher in the elderly, in contrast to MBL-LP activity. Moreover, C1-inhibitor, C5, C8, and C9 increased with age in contrast to a decrease of factor D and C3 levels. In-depth analysis of the functional activity assays revealed that MBL-LP activity was predominantly dependent on MBL and MASP-2 concentration, whereas CP activity relied on C2, C1-inhibitor and C5 levels. AP activity was strongly and directly associated with levels of C3, factor B and C5.

Conclusion: This study demonstrated significant sex and age-related differences in complement levels and functionality in the healthy population. Therefore, age and sex analysis should be taken into consideration when discussing complement-related pathologies and subsequent complement-targeted therapies.

C1-Inhibitor Treatment Decreases Renal Injury in an Established Brain-Dead Rat Model

BACKGROUND

Kidneys derived from brain-dead (BD) donors have lower graft survival rates compared with kidneys from living donors. Complement activation plays an important role in brain death. The aim of our study was therefore to investigate the effect of C1-inhibitor (C1-INH) on BD-induced renal injury.

METHODS

Brain death was induced in rats by inflating a subdurally placed balloon catheter. Thirty minutes after BD, rats were treated with saline, low-dose or high-dose C1-INH. Sham-operated rats served as controls. After 4 hours of brain death, renal function, injury, inflammation, and complement activation were assessed.

RESULTS

High-dose C1-INH treatment of BD donors resulted in significantly lower renal gene expression and serum levels of IL-6. Treatment with C1-INH also improved renal function and reduced renal injury, reflected by the significantly lower kidney injury marker 1 gene expression and lower serum levels of lactate dehydrogenase and creatinine. Furthermore, C1-INH effectively reduced complement activation by brain death and significantly increased functional levels. However, C1-INH treatment did not prevent renal cellular influx.

CONCLUSIONS

Targeting complement activation after the induction of brain death reduced renal inflammation and improved renal function before transplantation. Therefore, strategies targeting complement activation in human BD donors might clinically improve donor organ viability and renal allograft survival.

Synergistic effects of ischemic preconditioning and immediate post-conditioning in the protection against ischemia/reperfusion injury in rabbit submandibular glands

Submandibular gland autotransplantation is an effective approach for treating severe keratoconjunctivitis sicca. However, ischemia/reperfusion (I/R) injury, which inevitably occurs during transplantation, is involved in the hypofunction and structural damage that occur early after transplantation. Therefore, it is critical to identify effective strategies to ameliorate I/R injury in submandibular glands. In this study, we investigated the ability of immediate post-conditioning combined with ischemic preconditioning to attenuate I/R injury. We observed that after I/R injury, the level of reactive oxygen species was increased, inflammatory response was strengthened, and severe apoptosis had occurred. In addition, the salivary flow rate was greatly decreased. However, the pathogenesis of I/R injury was significantly ameliorated by ischemia post-conditioning or ischemia preconditioning treatments. In addition, the combination of ischemia preconditioning and post-conditioning achieved synergistic protective effects against I/R injury compared with ischemia preconditioning or ischemia post-conditioning alone. The secretion function was restored in the combination group. Furthermore, the combination treatment involved the same mechanisms of ischemia preconditioning or ischemia post-conditioning, including suppression of the inflammatory reaction and neutrophil accumulation, attenuation of oxidation stress, and inhibition of apoptosis. In conclusion, the combination of ischemia preconditioning and ischemia post-conditioning treatment is a simple and effective approach for treating I/R injury in submandibular glands.

Complement Activation in Liver Transplantation: Role of Donor Macrosteatosis and Implications in Delayed Graft Function

The complement system anchors the innate inflammatory response by triggering both cell-mediated and antibody-mediated immune responses against pathogens. The complement system also plays a critical role in sterile tissue injury by responding to damage-associated molecular patterns. The degree and duration of complement activation may be a critical variable controlling the balance between regenerative and destructive inflammation following sterile injury. Recent studies in kidney transplantation suggest that aberrant complement activation may play a significant role in delayed graft function following transplantation, confirming results obtained from rodent models of renal ischemia/reperfusion (I/R) injury. Deactivating the complement cascade through targeting anaphylatoxins (C3a/C5a) might be an effective clinical strategy to dampen reperfusion injury and reduce delayed graft function in liver transplantation. Targeting the complement cascade may be critical in donor livers with mild to moderate steatosis, where elevated lipid burden amplifies stress responses and increases hepatocyte turnover. Steatosis-driven complement activation in the donor liver may also have implications in rejection and thrombolytic complications following transplantation. This review focuses on the roles of complement activation in liver I/R injury, strategies to target complement activation in liver I/R, and potential opportunities to translate these strategies to transplanting donor livers with mild to moderate steatosis.

Calcineurin inhibitor-induced complement system activation via ERK1/2 signalling is inhibited by SOCS-3 in human renal tubule cells

One factor that significantly contributes to renal allograft loss is chronic calcineurin inhibitor (CNI) nephrotoxicity (CIN). Among other factors, the complement (C-) system has been proposed to be involved CIN development. Hence, we investigated the impact of CNIs on intracellular signalling and the effects on the C-system in human renal tubule cells. In a qPCR array, CNI treatment upregulated C-factors and downregulated SOCS-3 and the complement inhibitors CD46 and CD55. Additionally, ERK1/-2 was required for these regulations. Following knock-down and overexpression of SOCS-3, we found that SOCS-3 inhibits ERK1/-2 signalling. Finally, we assessed terminal complement complex formation, cell viability and apoptosis. Terminal complement complex formation was induced by CNIs. Cell viability was significantly decreased, whereas apoptosis was increased. Both effects were reversed under complement component-depleted conditions. In vivo, increased ERK1/-2 phosphorylation and SOCS-3 downregulation were observed at the time of transplantation in renal allograft patients who developed a progressive decline of renal function in the follow-up compared to stable patients. The progressive cohort also had lower total C3 levels, suggesting higher complement activity at baseline. In conclusion, our data suggest that SOCS-3 inhibits CNI-induced ERK1/-2 signalling, thereby blunting the negative control of C-system activation.

Complement in renal transplantation: The road to translation

Renal transplantation is the treatment of choice for patients with end-stage renal disease. The vital role of the complement system in renal transplantation is widely recognized. This review discusses the role of complement in the different phases of renal transplantation: in the donor, during preservation, in reperfusion and at the time of rejection. Here we examine the current literature to determine the importance of both local and systemic complement production and how complement activation contributes to the pathogenesis of renal transplant injury. In addition, we dissect the complement pathways involved in the different phases of renal transplantation. We also review the therapeutic strategies that have been tested to inhibit complement during the kidney transplantation. Several clinical trials are currently underway to evaluate the therapeutic potential of complement inhibition for the treatment of brain death-induced renal injury, renal ischemia-reperfusion injury and acute rejection. We conclude that it is expected that in the near future, complement-targeted therapeutics will be used clinically in renal transplantation. This will hopefully result in improved renal graft function and increased graft survival.