Complement activation at a particular location is determined by the balance of activating and inhibitory proteins. Factor H is a key regulator of the alternative pathway of complement, and genetic... Show moreComplement activation at a particular location is determined by the balance of activating and inhibitory proteins. Factor H is a key regulator of the alternative pathway of complement, and genetic or acquired impairments in Factor H are associated with glomerular injury. The human Factor H-related proteins (FHRs) comprise a family of five proteins that are structurally related to Factor H. Variations in the genes or expression levels of the FHRs are also associated with glomerular disease, although the mechanisms of glomerular protection/injury are incompletely understood. To explore the role of the FHRs on complement regulation/ dysregulation in the kidney, we expressed and purified recombinant murine FHRs (FHRs A, B, C and E). These four distinct FHRs contain binding regions with high amino acid sequence homology to binding regions within Factor H, but we observed different interactions of the FHRs with Factor H binding ligands, including heparin and C3d. There was differential binding of the FHRs to the resident kidney cell types (mesangial, glomerular endothelial, podocytes, and tubular epithelial). All four FHRs caused complement dysregulation on kidney cell surfaces in vitro, although the magnitude of the effect differed among the FHRs and also varied among the different kidney cells. However, only FHR E caused glomerular complement dysregulation when injected in vivo but did not exacerbate injury when injected into mice with ischemic acute kidney injury, an alternative pathway-mediated model. Thus, our experiments demonstrate that the FHRs have unique, and likely context-dependent, effects on the different cell types within the kidney. Show less
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... Show morePrimary 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. Show less
Faria, B.; Costa, M.G. da; Lima, C.; Willems, L.; Brandwijk, R.; Berger, S.P.; ... ; Poppelaars, F. 2020
Introduction Various studies have reported the importance of complement regulators in preventing mesothelial damage during peritoneal dialysis (PD). Its assessment, however, is limited in clinical... Show moreIntroduction Various studies have reported the importance of complement regulators in preventing mesothelial damage during peritoneal dialysis (PD). Its assessment, however, is limited in clinical practice due to the lack of easy access to the peritoneal membrane. Recently, a soluble form of the complement regulatory protein CD59 (sCD59) has been described. We therefore aimed to investigate the role of sCD59 in PD.Methods Plasma sCD59 was measured in 48 PD patients, 41 hemodialysis patients, 15 non-dialysis patients with chronic kidney disease and 14 healthy controls by ELISA (Hycult; HK374-02). Additionally, sCD59 and sC5b-9 were assessed in the peritoneal dialysate.Results sCD59 and sC5b-9 were detectable in the peritoneal dialysate of all patients, and marginally correlated (r = 0.27, P = 0.06). Plasma sCD59 levels were significantly higher in PD patients than in patients with chronic kidney disease and healthy controls, but did not differ from hemodialysis patients. During follow-up, 19% of PD patients developed peritoneal membrane failure and 27% of PD patients developed loss of residual renal function. In adjusted models, increased sCD59 levels in the dialysate (HR 3.44, 95% CI 1.04-11.40, P = 0.04) and in plasma (HR 1.08, 95% CI 1.01-1.17, P = 0.04) were independently associated with the occurrence of peritoneal membrane failure. Higher plasma levels of sCD59 were also associated with loss of residual renal function (HR 1.10, 95% CI 1.04-1.17, P < 0.001).Conclusions Our study suggests that sCD59 has potential as a biomarker to predict peritoneal membrane function and loss of residual renal function in PD, thereby offering a tool to improve patient management. Show less
Rationale & Objective: Glomerular C4d (C4dG) as an indicator of the lectin pathway of complement activation in immunoglobulin A nephropathy (IgAN) has been associated with more severe kidney... Show moreRationale & Objective: Glomerular C4d (C4dG) as an indicator of the lectin pathway of complement activation in immunoglobulin A nephropathy (IgAN) has been associated with more severe kidney damage. Recent studies have suggested that vascular lesions in IgAN biopsy specimens with complement deposition are also associated with disease progression. We aimed to study the clinical significance of arteriolar C4d (C4dA) in IgAN kidney biopsy tissue.Study Design: Retrospective cohort study.Setting & Participants: Kidney biopsy specimens from 126 adults with IgAN diagnosed by Oxford classification criteria were stained using immunohistochemistry and classified according to C4dG and C4dA deposition. Additionally, vascular lesions including acute and chronic microangiopathy, arteriolar hyalinosis, and arterial intima fibrosis were characterized.Predictor: C4dA.Outcome: Progressive kidney disease, defined as a decline in estimated glomerular filtration rate by >= 50% or occurrence of kidney failure.Analytical Approach: The association of C4dA and C4dG with baseline clinical and histologic characteristics, as well as progressive kidney disease, were assessed with survival analysis using multivariable Cox regression analysis.Results: C4dA was identified in 21 (17%) patients and was associated with mean arterial pressure, arterial intima fibrosis, and chronic microangiopathy. C4dA was also significantly associated with C4dG and both were associated with progressive kidney disease. In regression analysis, C4dA remained significantly associated with progressive kidney disease after adjusting for other significant predictors, including baseline estimated glomerular filtration rate, mean arterial pressure, and the presence of crescents.Limitations: Findings based on the retrospective evaluation of a single center's experience, limited number of events, a small number of patients with a broad range of kidney disease stages, and use of immunohistochemistry rather than immunofluorescence to detect C4d.Conclusions: C4dA is a potential biomarker for disease progression in IgAN. It should be further investigated in larger cohorts to determine the value of C4dA in improving prediction of IgAN disease progression. Show less
Jager, N.M.; Zanden, J.E. van; Subias, M.; Leuvenink, H.G.D.; Daha, M.R.; Cordoba, S.R. de; ... ; Seelen, M.A. 2019
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... Show moreIntroduction: 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. Show less
Faria, B.; Costa, M.G. da; Poppelaars, F.; Franssen, C.F.M.; Pestana, M.; Berger, S.P.; ... ; Seelen, M.A. 2019
Background: Intravenous (IV) iron is widely used to treat anemia in chronic kidney disease patients. Previously, iron formulations were shown to induce immune activation in-vitro. The current study... Show moreBackground: Intravenous (IV) iron is widely used to treat anemia in chronic kidney disease patients. Previously, iron formulations were shown to induce immune activation in-vitro. The current study aimed to investigate the effect of IV iron on complement activation in-vivo, and whether this subsequently induces inflammation and/or oxidative stress.Methods: Two distinct patient groups were included: 51 non-dialysis and 32 dialysis patients. The non-dialysis group received iron sucrose or ferric carboxymaltose, based on physicians' choice. Plasma samples were collected prior to and 1 h after completion of IV iron infusion. The dialysis group received iron sucrose exclusively. Plasma samples were collected at the start and end of two consecutive hemodialysis sessions, one with and one without IV iron. Finally, plasma levels of MBL, C1q, properdin, factor D, sC5b-9, MPO, PTX3 were assessed by ELISA.Results: In the non-dialysis group, sC5b-9 levels significantly increased after IV iron by 32%, while levels of factor D and MBL significantly dropped. Subgroup analysis demonstrated that iron sucrose induced complement activation whereas ferric carboxymaltose did not. In the dialysis group, levels of sC5b-9 significantly increased by 46% during the dialysis session with IV iron, while factor D levels significantly fell. Furthermore, the relative decrease in factor D by IV iron correlated significantly with the relative increase in sC5b-9 by IV iron. MPO levels rose significantly during the dialysis session with IV iron, but not in the session without iron. Moreover, the relative increase in MPO and sC5b-9 by IV iron correlated significantly. PTX3 levels were not affected by IV iron.Conclusions: Iron sucrose but not ferric carboxymaltose, results in complement activation possibly via the lectin and alternative pathway partially mediating oxidative stress but not inflammation. Show less
Costa, M.G. da; Poppelaars, F.; Berger, S.P.; Daha, M.R.; Seelen, M.A. 2018
