New approaches to the treatment of dense deposit disease

Glomerular basement membrane heparan sulfate in health and disease: A regulator of local complement activation

The glomerular basement membrane (GBM) is an essential component of the glomerular filtration barrier. Heparan sulfate proteoglycans such as agrin are major components of the GBM, along with α345(IV) collagen, laminin-521 and nidogen. A loss of GBM heparan sulfate chains is associated with proteinuria in several glomerular diseases and may contribute to the underlying pathology. As the major determinants of the anionic charge of the GBM, heparan sulfate chains have been thought to impart charge selectivity to the glomerular filtration, a view challenged by the negligible albuminuria in mice that lack heparan sulfate in the GBM. Recent studies provide increasing evidence that heparan sulfate chains modulate local complement activation by recruiting complement regulatory protein factor H, the major inhibitor of the alternative pathway in plasma. Factor H selectively inactivates C3b bound to surfaces bearing host-specific polyanions such as heparan sulfate, thus limiting complement activation on self surfaces such as the GBM, which are not protected by cell-bound complement regulators. We discuss mechanisms whereby the acquired loss of GBM heparan sulfate can impair the local regulation of the alternative pathway, exacerbating complement activation and glomerular injury in immune-mediated kidney diseases such as membranous nephropathy and lupus nephritis.

Complement inhibition in C3 glomerulopathy

C3 glomerulopathy (C3G) describes a spectrum of glomerular diseases defined by shared renal biopsy pathology: a predominance of C3 deposition on immunofluorescence with electron microscopy permitting disease sub-classification. Complement dysregulation underlies the observed pathology, a causal relationship that is supported by well described studies of genetic and acquired drivers of disease. In this article, we provide an overview of the features of C3G, including a discussion of disease definition and a review of the causal role of complement. We discuss molecular markers of disease and how biomarkers are informing our evolving understanding of underlying pathology. Research advances are laying the foundation for complement inhibition as a targeted approach to treatment of C3G.

Effectiveness of sulodexide might be associated with inhibition of complement system in hepatitis B virus-associated membranous nephropathy: An inspiration from a pilot trial

BACKGROUND

The activation of complement system is associated with the development of hepatitis B virus-associated membranous nephropathy (HBV-MN) and heparin could inhibit the activation of complement system.

METHODS

This was a three-center trial. Seventy-nine patients with HBV-MN participated in the study. The follow-up of the study consisted of two periods: Stage 1 (S1) and Stage 2 (S2). All patients received 0.5mg entecavir plus 150-300mg/day of irbesartan but sulodexide was prescribed during S1. They were randomized into 4 groups according to sulodexide dose: blank (Group 1), 250 lipasemic unit (lsu)/day for 1year (Group 2), 500 lsu/day for 1year (Group 3) and 1000 lsu/day for 6months followed by 250 lsu/day for 6months (Group 4). Major clinical outcomes were valid remission (VR): (1) urine albumin/creatinine ratio (UACR) <150mg/mmol and >50% decline of baseline; (2) albumin >35g/L; (3) glomerular filtration rate (GFR) >90ml/(min*1.73m(2)).

RESULTS

(1) Groups 3 and 4 had significantly lower UACR and higher albumin than did Groups 1 and 2 at major visits; (2) Groups 3 and 4 achieved more VR compared with Group 1 (42.1% and 60.0% vs. 9.1%, p both<0.05); (3) in Groups 3 and 4, instead of Groups 1 and 2, more C3 deposition in the kidney was observed in those achieving VR; (4) plasma C3a, C5a and C5b-9 decreased significantly in Groups 3 and 4 during S1.

CONCLUSIONS

(1) The prescription of both sulodexide and entecavir could improve the prognosis of patients with HBV-MN but their mechanisms might be different; (2) the renoprotection of sulodexide in HBV-MN might probably relate to the inhibition of complement system.

Understanding the complement-mediated glomerular diseases: focus on membranoproliferative glomerulonephritis and C3 glomerulopathies

An enhanced understanding of the role of complement in the pathogenesis of membranoproliferative glomerulonephritis has led to reclassification of the latter into immunoglobulin-mediated and non-immunoglobulin-mediated disease. The new classification schema resulted in improved diagnostic clinical algorithms, while it brought into light again the diseases, which are characterized by the presence of glomerular deposits, composed predominantly by C3, in the absence of significant amounts of immunoglobulins in renal biopsy, namely, C3 glomerulopathies (dense deposit disease and C3 glomerulonephritis). Despite the lack of randomized controlled trials following the advances in the understanding of the pathogenetic pathways involved in membranoproliferative glomerulonephritis, it is important that the new mechanistic approach has opened new roads for the exploration and discovery of targeted therapies.

From orphan drugs to adopted therapies: Advancing C3-targeted intervention to the clinical stage

Complement dysregulation is increasingly recognized as an important pathogenic driver in a number of clinical disorders. Complement-triggered pathways intertwine with key inflammatory and tissue destructive processes that can either increase the risk of disease or exacerbate pathology in acute or chronic conditions. The launch of the first complement-targeted drugs in the clinic has undeniably stirred the field of complement therapeutic design, providing new insights into complement's contribution to disease pathogenesis and also helping to leverage a more personalized, comprehensive approach to patient management. In this regard, a rapidly expanding toolbox of complement therapeutics is being developed to address unmet clinical needs in several immune-mediated and inflammatory diseases. Elegant approaches employing both surface-directed and fluid-phase inhibitors have exploited diverse components of the complement cascade as putative points of therapeutic intervention. Targeting C3, the central hub of the system, has proven to be a promising strategy for developing biologics as well as small-molecule inhibitors with clinical potential. Complement modulation at the level of C3 has recently shown promise in preclinical primate models, opening up new avenues for therapeutic intervention in both acute and chronic indications fueled by uncontrolled C3 turnover. This review highlights recent developments in the field of complement therapeutics, focusing on C3-directed inhibitors and alternative pathway (AP) regulator-based approaches. Translational perspectives and considerations are discussed, particularly with regard to the structure-guided drug optimization and clinical advancement of a new generation of C3-targeted peptidic inhibitors.

Kidney transplant outcomes in familial C3 glomerulopathy

C3 glomerulopathy, a newly designated entity, is characterized by glomerular disease associated with dysregulation of the alternative complement pathway and is a rare cause of end-stage kidney disease. Overall disease characteristics that include clinical presentation, laboratory assessment, histopathology and genetic background have only been unravelled in recent years and have led to the development of anti-complement therapies targeting different levels of the alternative pathway. We describe the long-term outcomes following kidney transplantation in an Irish family with familial C3 glomerulopathy due to a hybrid CFHR3-1 gene.

Discontinuation of dialysis with eculizumab therapy in a pediatric patient with dense deposit disease

BACKGROUND

Dense deposit disease (DDD) is a rare glomerular disease caused by an uncontrolled activation of the alternative complement pathway leading to end-stage renal disease in 50 % of patients. As such, DDD has been classified within the spectrum of complement component 3 (C3) glomerulopathies due to its pathogenesis from alternative pathway dysregulation. Conventional immunosuppressive therapies have no proven effectiveness. Eculizumab, a terminal complement inhibitor, has been reported to mitigate disease in some cases.

CASE-DIAGNOSIS/TREATMENT

We report on the efficacy of eculizumab in a pediatric patient who failed to respond to cyclophosphamide, corticosteroids, and plasma exchange. Complement biomarker profiling was remarkable for low serum C3, low properdin, and elevated soluble C5b-9. Consistent with these findings, the alternative pathway functional assay was abnormally low, indicative of alternative pathway activity, although neither C3-nephritic factors nor Factor H autoantibodies were detected. Eculizumab therapy was associated with significant improvement in proteinuria and renal function allowing discontinuation of hemodialysis (HD). Repeat C3 and soluble C5b-9 levels normalized, showing that terminal complement pathway activity was successfully blocked while the patient was receiving eculizumab therapy. Repeat testing for alternative pathway activation allowed for a successful decrease in eculizumab dosing.

CONCLUSIONS

The case reported here demonstrates the successful recovery of renal function in a pediatric patient on HD following the use of eculizumab.

[Clinical approach to primary membranoproliferative glomerulonephritis]

Membranoproliferative glomerulonephritis represent a heterogeneous group of nephropathies. During the last five years, our understanding of membranoproliferative glomerulonephritis has greatly improved. Animal models and the study of complement genetics led to the dissection of the physiopathology of membranoproliferative glomerulonephritis, to the individualization of a new entity, C3 glomerulopathy, and to a new classification of these nephropathies. The study of large cohorts has also changed the clinical picture of membranoproliferative glomerulonephritis that has been long dominated by the severity of a single type of dense deposits disease. Finally, the rediscovery of complement through the study of the atypical haemolytic uremic syndrome and the availability in clinical practice of complement inhibitors have paved the way for new therapeutic approaches of membranoproliferative glomerulonephritis.

Eculizumab use in kidney transplantation

PURPOSE OF REVIEW

Eculizumab suppresses the effector functions of the complement system and represents a therapeutic breakthrough for patients with paroxysmal nocturnal hemoglobinuria or atypical hemolytic uremic syndrome (aHUS). Safety monitoring is ongoing; so far, most notable is the expected increase in infection risk with encapsulated organisms. Despite potential applicability in multiple complement-mediated disorders, the off-label use of eculizumab has been limited, mainly by its prohibitive cost. The purpose of this review is to summarize the current data relevant to the use of eculizumab in kidney transplantation.

RECENT FINDINGS

In aHUS, prone to high rates of recurrence and allograft loss, eculizumab has made the most notable therapeutic impact. Further clarification of complement defects may help predict therapeutic responses and hopefully guide treatment duration. In C3 glomerulopathies, the clinical response to eculizumab appears more heterogeneous and less effective in processes mediated by upstream to C5 complement deregulation. A large clinical trial of eculizumab for prevention of delayed graft function is ongoing. In antibody-mediated rejection, the role of eculizumab is unclear as its use has been limited to very complex, mostly presensitized, patients in mixed combinations of therapeutic modalities.

SUMMARY

Overall, eculizumab has raised awareness of complement-mediated disorders as an exciting, new therapeutic option with multiple potential applications in kidney transplantation. Further research is needed to develop a better understanding of eculizumab applicability, efficacy, and treatment monitoring and beyond, to future therapeutic tools targeting the complement.

Overview of C3 Glomerulopathy

C3 glomerulopathy is an umbrella term, which includes several rare forms of glomerulonephritis (GN) with underlying defects in the alternate complement cascade. A common histological feature noted in all these GN is dominant C3 deposition in the glomerulus. In this review, we will provide an overview of the complement system as well as mediators, with an introduction to pharmaceutical agents that can alter the pathway.

Successful therapy of C3Nef-positive C3 glomerulopathy with plasma therapy and immunosuppression

BACKGROUND

C3 glomerulopathies (C3G) are characterized by uncontrolled activation of the alternative pathway of complement. In most patients these diseases progress towards end-stage renal disease, and the risk of recurrence after renal transplantation is high. In the majority of patients, only antibodies against the C3 convertase, termed C3Nef, can be found as a potential pathogenic factor. Although a large variety of therapeutic approaches have been used, no generally accepted therapy exists.

METHODS

In four consecutive patients with C3G in whom all known complement factor mutations were excluded and only C3Nef could be identified as a potential cause of disease, a multimodal therapeutic regimen with plasma therapy, corticosteroids and mycophenolate mofetil was used.

RESULTS

The multimodal regimen achieved normalization of renal function in all four patients, with complete remission in two patients and a distinct reduction of proteinuria in the other two patients. The single patient with C3 glomerulonephritis (C3GN) and marked terminal complement complex elevation only showed partial remission; further improvement was achieved following the addition of eculizumab to the therapeutic regimen. Repeatedly measured C3Nef levels did not correlate with disease course or therapeutic response in any of the patients.

CONCLUSIONS

As this multimodal therapeutic approach was effective in all four treated patients with suspected autoimmune etiology of C3G, it offers a treatment option for severely affected patients with this rare disease until more specific regimens are available.

Complement Evasion Mediated by Enhancement of Captured Factor H: Implications for Protection of Self-Surfaces from Complement

In an attempt to evade annihilation by the vertebrate complement system, many microbes capture factor H (FH), the key soluble complement-regulating protein in human plasma. However, FH is normally an active complement suppressor exclusively on self-surfaces and this selective action of FH is pivotal to self versus non-self discrimination by the complement system. We investigated whether the bacterially captured FH becomes functionally enhanced and, if so, how this is achieved at a structural level. We found, using site-directed and truncation mutagenesis, surface plasmon resonance, nuclear magnetic resonance spectroscopy, and cross-linking and mass spectrometry, that the N-terminal domain of Streptococcus pneumoniae protein PspC (PspCN) not only binds FH extraordinarily tightly but also holds it in a previously uncharacterized conformation. Functional enhancement arises from exposure of a C-terminal cryptic second binding site in FH for C3b, the activation-specific fragment of the pivotal complement component, C3. This conformational change of FH doubles its affinity for C3b and increases 5-fold its ability to accelerate decay of the binary enzyme (C3bBb) responsible for converting C3 to C3b in an amplification loop. Despite not sharing critical FH-binding residues, PspCNs from D39 and Tigr4 S. pneumoniae exhibit similar FH-anchoring and enhancing properties. We propose that these bacterial proteins mimic molecular markers of self-surfaces, providing a compelling hypothesis for how FH prevents complement-mediated injury to host tissue while lacking efficacy on virtually all other surfaces. In hemolysis assays with 2-aminoethylisothiouronium bromide–treated erythrocytes that recapitulate paroxysmal nocturnal hemoglobinuria, PspCN enhanced protection of cells by FH, suggesting a new paradigm for therapeutic complement suppression.

Eculizumab in Pediatric Dense Deposit Disease

BACKGROUND AND OBJECTIVES

Dense deposit disease (DDD), a subtype of C3 glomerulopathy, is a rare disease affecting mostly children. Treatment options are limited. Debate exists whether eculizumab, a monoclonal antibody against complement factor C5, is effective in DDD. Reported data are scarce, especially in children.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The authors analyzed clinical and histologic data of five pediatric patients with a native kidney biopsy diagnosis of DDD. Patients received eculizumab as therapy of last resort for severe nephritic or nephrotic syndrome with alternative pathway complement activation; this therapy was given only when the patients had not or only marginally responded to immunosuppressive therapy. Outcome measures were kidney function, proteinuria, and urine analysis.

RESULTS

In all, seven disease episodes were treated with eculizumab (six episodes of severe nephritic syndrome [two of which required dialysis] and one nephrotic syndrome episode). Median age at treatment start was 8.4 (range, 5.9-13) years. For three treatment episodes, eculizumab was the sole immunosuppressive treatment. In all patients, both proteinuria and renal function improved significantly within 12 weeks of treatment (median urinary protein-to-creatinine ratio of 8.5 [range, 2.2-17] versus 1.1 [range, 0.2-2.0] g/g, P<0.005, and eGFR of 58 [range, 17-114] versus 77 [range, 50-129] ml/min per 1.73 m(2), P<0.01). A striking finding was the disappearance of leukocyturia within 1 week after the first eculizumab dose in all five episodes with leukocyturia at treatment initiation.

CONCLUSIONS

In this case series of pediatric patients with DDD, eculizumab treatment was associated with reduction in proteinuria and increase in eGFR. Leukocyturia resolved within 1 week of initiation of eculizumab treatment. These results underscore the need for a randomized trial of eculizumab in DDD.

Eculizumab-induced reversal of dialysis-dependent kidney failure from C3 glomerulonephritis

C3 glomerulopathy (C3G) is characterized by C3 deposits with minimal immunoglobulin deposition caused by alternative complement pathway dysregulation. Unfortunately, no therapeutic intervention has consistently improved outcomes for patients with C3G. Eculizumab, a monoclonal antibody to C5, is currently the only approved complement-specific agent with some efficacy in the treatment of C3 glomerulonephritis (C3GN). Here, we describe a patient with acute crescentic C3GN with no identified complement mutation or family history of renal disease who required dialysis for 6 months. Five months after initiation of eculizumab, she became dialysis independent, showing improvement is possible after adequate time on eculizumab.

Complement genetics and susceptibility to inflammatory disease. Lessons from genotype-phenotype correlations

Different genome-wide linkage and association studies performed during the last 15 years have associated mutations and polymorphisms in complement genes with different diseases characterized by tissue damage and inflammation. These are complex disorders in which genetically susceptible individuals usually develop the pathology as a consequence of environmental triggers. Although complement dysregulation is a common feature of these pathologies, how the disease phenotype is determined is only partly understood. One way to advance understanding is to focus the research in the analysis of the peculiar genotype-phenotype correlations that characterize some of these diseases. I will review here how understanding the functional consequences of these disease-associated complement genetic variants is providing us with novel insights into the underpinning complement biology and a better knowledge of the pathogenic mechanisms underlying each of these pathologies. These advances have important therapeutic and diagnostic implications.

The role of complement in C3 glomerulopathy

C3 glomerulopathy describes a spectrum of disorders with glomerular pathology associated with C3 cleavage product deposition and with defective complement action and regulation (Fakhouri et al., 2010; Sethi et al., 2012b). Kidney biopsies from these patients show glomerular accumulation or deposition of C3 cleavage fragments, but no or minor deposition of immunoglobulins (Appel et al., 2005; D'Agati and Bomback, 2012; Servais et al., 2007; Sethi and Fervenza, 2011). At present the current situation asks for a better definition of the underlining disease mechanisms, for precise biomarkers, and for a treatment for this disease. The complement system is a self activating and propelling enzymatic cascade type system in which inactive, soluble plasma components are activated spontaneously and lead into an amplification loop (Zipfel and Skerka, 2009). Activation of the alternative pathway is spontaneous, occurs by default, and cascade progression leads to amplification by complement activators. The system however is self-controlled by multiple regulators and inhibitors, like Factor H that control cascade progression in fluid phase and on surfaces. The activated complement system generates a series of potent effector components and activation products, which damage foreign-, as well as modified self cells, recruit innate immune cells to the site of action, coordinate inflammation and the response of the adaptive immune system in form of B cells and T lymphocytes (Kohl, 2006; Medzhitov and Janeway, 2002; Ogden and Elkon, 2006; Carroll, 2004; Kemper and Atkinson, 2007; Morgan, 1999; Muller-Eberhard, 1986; Ricklin et al., 2010). Complement controls homeostasis and multiple reactions in the vertebrate organism including defense against microbial infections (Diaz-Guillen et al., 1999; Mastellos and Lambris, 2002; Nordahl et al., 2004; Ricklin et al., 2010). In consequence defective control of the spontaneous self amplifying cascade or regulation is associated with numerous human disorders (Ricklin and Lambris, 2007; Skerka and Zipfel, 2008; Zipfel et al., 2006). Understanding the exact action and regulation of this sophisticated homeotic cascade system is relevant to understand disease pathology of various complement associated human disorders. Furthermore this knowledge is relevant for a better diagnosis and appropriate therapy. At present diagnosis of C3 glomerulopathy is primarily based on the kidney biopsy, and histological, immmunohistological and electron microscopical evaluation (D'Agati and Bomback, 2012; Fakhouri et al., 2010; Medjeral-Thomas et al., 2014a,b; Sethi et al., 2012b). The challenge is to define the actual cause of the diverse glomerular changes or damages, to define how C3 deposition results in the reported glomerular changes, the location of the cell damage and the formation of deposits.

C3 nephritic factor can be associated with membranous glomerulonephritis

BACKGROUND

C3 nephritic factor (C3NeF) has been described in association with membranoproliferative glomerulonephritis and is involved in 80 % of cases of dense deposit disease. C3NeF is an immunoglobulin G (IgG) autoantibody which binds to the complement component 3 (C3) convertase C3bBb, thereby inhibiting its decay and leading to massive C3 cleavage. Commonly associated with C3NeF are low C3 levels, decreased total haemolytic complement (CH50) and normal C4 levels. C3NeF patients often present with proteinuria, haematuria and high blood pressure. Evolution to end-stage renal disease is common. Treatment consists of steroids and/or immunosuppressants, with variable efficiency. Renal transplantation is marked by histological recurrence, leading to higher rates of allograft loss.

CASES

We report C3NeF in association with membranous glomerulonephritis type 3-4 in two unrelated children. We also demonstrate that, under adequate immunosuppressive therapy, proteinuria is significantly lowered, blood pressure is kept within normal range and long-term renal function remains normal.

CONCLUSIONS

C3NeF can be associated with membranous glomerulonephritis in children. Clinical presentation is mild, and mid-term outcome is favourable under adequate therapy. However, complement anomalies persist for several years.

Histopathology of MPGN and C3 glomerulopathies

'Membranoproliferative' describes glomerular injury characterized by capillary wall thickening and mesangial expansion owing to increased matrix deposition and hypercellularity. The presence of immune deposits is indicative of membranoproliferative glomerulonephritis (MPGN). Historically, MPGN was further classified into three types according to the appearance and site of the electron-dense deposits seen by electron microscopy, but it is now recognized that many cases show only deposition of the complement component C3, owing to abnormal control of the alternative pathway of complement activation-these cases are now classified as C3 glomerulopathies. Not all cases of C3 glomerulopathy, however, show an MPGN pattern. C3 glomerulopathies include dense deposit disease, which shows dense osmiophilic deposits, and C3 glomerulonephritis, which shows isolated deposits. In many cases, the genetic mutations or autoantibodies responsible for C3 deposition have been identified. Some patients in whom complement control is abnormal will accumulate small amounts of immunoglobulin in their glomeruli and so, in everyday practice, the morphological diagnosis of 'glomerulonephritis with dominant C3' is useful for identifying patients who require investigation of the complement pathway. The recognition that many cases of MPGN are C3 glomerulopathies and that the underlying cause can often be identified in immunoglobulin-associated cases means that the diagnosis of idiopathic MPGN is now very uncommon.

Current concepts in C3 glomerulopathy

Complement component 3 glomerulopathy (C3G) is a recently defined entity comprising of dense deposit disease and C3 glomerulonephritis. The key histological feature is the presence of isolated C3 deposits without immunoglobulins. Often masqueradng as some of the common glomerulonephritides this is a prototype disorder occurring from dysregulated alternate complement pathway with recently identified genetic defects and autoantibodies. We review the pathophysiology, clinical features, and diagnostic and treatment strategies.

Expression of human complement factor H prevents age-related macular degeneration-like retina damage and kidney abnormalities in aged Cfh knockout mice

Complement factor H (CFH) is an important regulatory protein in the alternative pathway of the complement system, and CFH polymorphisms increase the genetic risk of age-related macular degeneration dramatically. These same human CFH variants have also been associated with dense deposit disease. To mechanistically study the function of CFH in the pathogenesis of these diseases, we created transgenic mouse lines using human CFH bacterial artificial chromosomes expressing full-length human CFH variants and crossed these to Cfh knockout (Cfh(-/-)) mice. Human CFH protein inhibited cleavage of mouse complement component 3 and factor B in plasma and in retinal pigment epithelium/choroid/sclera, establishing that human CFH regulates activation of the mouse alternative pathway. One of the mouse lines, which express relatively higher levels of CFH, demonstrated functional and structural protection of the retina owing to the Cfh deletion. Impaired visual function, detected as a deficit in the scotopic electroretinographic response, was improved in this transgenic mouse line compared with Cfh(-/-) mice, and transgenics had a thicker outer nuclear layer and less sub-retinal pigment epithelium deposit accumulation. In addition, expression of human CFH also completely protected the mice from developing kidney abnormalities associated with loss of CFH. These humanized CFH mice present a valuable model for study of the molecular mechanisms of age-related macular degeneration and dense deposit disease and for testing therapeutic targets.

Eculizumab in dense-deposit disease after renal transplantation

BACKGROUND

Dense-deposit disease (DDD) is a rare glomerulopathy characterized by electron-dense deposits in the glomerular basement membrane. About 50 % of patients with DDD progress to end-stage kidney disease and require dialysis within 10 years of diagnosis, and the disease often recurs after renal transplantation.

CASE-DIAGNOSIS/TREATMENT

We describe a 14-year-old girl with recurrent DDD in her transplanted kidney. Clinical onset was at 8 years of age, when steroid-resistant nephrotic syndrome was diagnosed with microhematuria, severe hypocomplementemia and normal kidney function. Although remission was initially observed after several plasma exchanges, nephrotic proteinuria returned and kidney function further declined 1 year later. The patient received a living-related kidney transplant. Initial allograft function was good, but proteinuria reappeared 3 months after transplantation, accompanied by a slight deterioration in kidney function. After histological confirmation of DDD recurrence and subsequent management with plasmapheresis, the patient was treated for 30 months with eculizumab, a humanized monoclonal antibody that binds to C5 complement protein. This intervention proved effective and resulted in complement inhibition, sustained remission of proteinuria and preservation of renal function. A graft biopsy 6 months later showed no progression of the renal lesions.

CONCLUSIONS

Early clinical and histological recurrence of DDD in the transplanted kidney in this 14-year-old patient was treated for 30 months with eculizumab. The patient remains asymptomatic, has no proteinuria and her kidney function is intact.

Heterogeneous histologic and clinical evolution in 3 cases of dense deposit disease with long-term follow-up

Dense deposit disease is characterized by dense deposits in the glomerular and tubular basement membranes. We report 3 cases with long-term follow-up differing in histologic pattern and clinical evolution. Clinical and histologic data were collected between 1976 and 2012. Age at the first manifestations was 6, 11, and 23 years, respectively. They included proteinuria (patient 1) and nephrotic syndrome (patients 2 and 3); renal function was normal in all cases. Two patients (1 and 3) had low complement component 3 (C3) levels. All patients had C3 nephritic factor. Genetic analysis revealed a rare variant of the factor I gene (patient 1) and a heterozygous mutation in complement factor H-related 5 gene (patient 2). Patient 1 underwent 3 biopsies during her 38 years of follow-up. Thickening of the capillary walls of the glomerular and tubular basement membranes was observed, with mild mesangial proliferation and progressive C3 and complement membrane attack complex mesangial deposits. However, renal function remained normal. Patient 2 also underwent 3 biopsies (22 years of follow-up), revealing a gradual decrease in C3 deposition and mesangial cell proliferation. He presented mild renal insufficiency. Patient 3 underwent 2 biopsies, which displayed unusual bulky membranous deposits, confirmed by electron microscopy, with no mesangial cell proliferation and little C3 and complement membrane attack complex deposits. Kidney function remained normal. These 3 cases of dense deposit disease differed in histologic pattern evolution: accumulation of C3 deposits, decrease in C3 deposits and proliferation, and isolated dense deposits. The histologic factors involved in clinical progression remain to be identified.

Treatment of choroidal neovascularisation secondary to membranoproliferative glomerulonephritis type II with intravitreal ranibizumab

Membranoproliferative glomerulonephritis type II (MPGN II) is characterised by electron-dense deposits of complement components in the glomerular basement membrane and retinal pigment epithelium. Approximately, 10% of affected individuals develop serious ocular complications similar to age-related macular degeneration such as choroidal neovascularisation (CNV), which has been managed with photocoagulation or photodynamic therapy; however, these treatments can impact visual acuity. We report the case of a 42-year-old woman with MPGN II presenting with decreased visual acuity and paracentral scotoma in her left eye due to an extrafoveal choroidal neovascular membrane (growth of new vessels under the retina). The patient was successfully treated with intravitreal ranibizumab (Lucentis) with restoration of visual function. This case highlights the successful management of CNV secondary to MPGN II with the antivascular endothelial growth factor agent ranibizumab and emphasises the importance of early referral of patients with MPGN II who are reporting of visual 'distortion'.

Chronic kidney disease: a new look at pathogenetic mechanisms and treatment options

The concept of renoprotection has evolved significantly, driven by improved understanding of the pathophysiology of chronic kidney disease (CKD) and the advent of novel treatment options. Glomerular hyperfiltration, hypertension and proteinuria represent key mediators of CKD progression. It is increasingly recognized that proteinuria may actually be pathological and etiological in CKD progression and not just symptomatic. It initiates a sequence of events involving activation of proinflammatory and profibrotic signaling pathways in proximal tubular epithelial cells with transmission of the disease to the tubulointerstitium and progression to end-stage kidney disease (ESKD). Although the etiology and epidemiology of pediatric CKD differs to that in adults, studies in the various animal models of kidney disease, from obstructive uropathy to glomerulonephritis, have revealed that many common proinflammatory and profibrotic pathways are induced in progressive proteinuric CKD, irrespective of the primary disease. This pathomechanistic overlap therefore translates into the potential for common treatment targets for a wide spectrum of kidney diseases. In this review we therefore discuss the experimental and clinical evidence for an array of prospective future drug treatments of CKD progression. While conceptually promising, clear definitive evidence beyond preclinical data does not exist for many of these treatments, and others are limited by serious adverse effects. More studies are needed before general recommendations can be given.

Blockade of alternative complement pathway in dense deposit disease

A patient aged 17 with dense deposit disease associated with complement activation, circulating C3 Nef, and Factor H mutation presented with nephrotic syndrome and hypertension. Steroid therapy, plasma exchange, and rituximab failed to improve proteinuria and hypertension despite a normalization of the circulating sC5b9 complex. Eculizumab, a monoclonal antibody directed against C5, was used to block the terminal product of the complement cascade. The dose was adapted to achieve a CH50 below 10%, but proteinuria and blood pressure were not improved after 3 months of treatment.

C3 nephritic factor associated with C3 glomerulopathy in children

BACKGROUND

C3 glomerulopathy (C3G) is characterized by predominant C3 deposits in glomeruli and dysregulation of the alternative pathway of complement. Half of C3G patients have a C3 nephritic factor (C3NeF). C3G incorporated entities with a range of features on microscopy including dense deposit diseases (DDD) and C3 glomerulonephritis (C3GN). The aim of this work was to study children cases of C3G associated with C3NeF.

METHODS

We reviewed 18 cases of C3G with a childhood onset associated with C3NeF without identified mutations in CFH, CFI, and MCP genes.

RESULTS

Clinical histories started with recurrent hematuria for seven patients, nephrotic syndrome for four, acute post-infectious glomerulonephritis for three and acute renal failure for four. Twelve patients had a low C3 at first investigation. Kidney biopsy showed ten C3GN and eight DDD. Twenty-three percent of the patients tested presented elevated sC5b9. Seven patients relapsed 3 to 6 years after the onset. At the end of follow-up, two patients were under dialysis, 11 had a persistent proteinuria, five had none; four patients did not follow any treatment. Steroids were first used in 80 % of cases.

CONCLUSIONS

C3NeF associated C3G has a heterogeneous presentation and outcome. Anti-proteinuric agents may control the disease during follow-up, even after nephrotic syndrome at the onset. The efficiency of immunosuppressive therapy remains questionable.

Clinical findings, pathology, and outcomes of C3GN after kidney transplantation

C3 glomerulonephritis (C3GN) results from abnormalities in the alternative pathway of complement, and it is characterized by deposition of C3 with absent or scant Ig deposition. In many patients, C3GN progresses to ESRD. The clinical features, pathology, and outcomes of patients with C3GN receiving kidney transplantation are unknown. Between 1996 and 2010, we identified 21 patients at our institution who received a kidney transplant because of ESRD from C3GN. The median age at the time of initial diagnosis of C3GN at kidney biopsy was 20.8 years. The median time from native kidney biopsy to dialysis or transplantation was 42.3 months. Of 21 patients, 14 (66.7%) patients developed recurrent C3GN in the allograft. The median time to recurrence of disease was 28 months. Graft failure occurred in 50% of patients with recurrent C3GN, with a median time of 77 months to graft failure post-transplantation. The remaining 50% of patients had functioning grafts, with a median follow-up of 73.9 months. The majority of patients had hematuria and proteinuria at time of recurrence. Three (21%) patients were positive for monoclonal gammopathy and had a faster rate of recurrence and graft loss. Kidney biopsy at the time of recurrence showed mesangial proliferative GN in eight patients and membranoproliferative GN in six patients. All allograft kidney biopsies showed bright C3 staining (2-3+), with six biopsies also showing trace/1+ staining for IgM and/or IgG. To summarize, C3GN recurs in 66.7% of patients, and one half of the patients experience graft failure caused by recurrence.

Childhood-onset dense deposit disease: a rare cause of proteinuria

Introduction

Dense deposit disease (DDD) is a rare renal disease related to the dysregulation of the alternative pathway of the complement cascade, caused by several factors including the presence of an autoantibody to C3 nephritic factor, mutations in factor H and autoantibodies to this protein. DDD is characterized by C3 accumulation with absent or scanty immunoglobulin deposition.

Case Presentation

Herein we report the case of a child with benign course of DDD, who presented with moderate proteinuria and lack of clinical symptoms without immunosuppressive treatment. Laboratory testing revealed moderate proteinuria, normal serum creatinine, total protein, and albumin levels, but significantly decreased serum C3 level. The results of renal biopsy were consistent with DDD. Genetic analysis revealed that the patient carried one copy of the H402 risk allele of factor H. The level of proteinuria did not change during the follow-up period and no nephrotic syndrome signs occurred. Renal function was stable.

Conclusion

In conclusion, a program of urine screening for asymptomatic proteinuria and hematuria to detect children with kidney disease before they experience loss of kidney functions should be considered. Children diagnosed with DDD should have the opportunity to get treatment early on and to be followed very closely.

Dense deposit disease and C3 glomerulopathy

C3 glomerulopathy refers to those renal lesions characterized histologically by predominant C3 accumulation within the glomerulus, and pathogenetically by aberrant regulation of the alternative pathway of complement. Dense deposit disease is distinguished from other forms of C3 glomerulopathy by its characteristic appearance on electron microscopy. The extent to which dense deposit disease also differs from other forms of C3 glomerulopathy in terms of clinical features, natural history, and outcomes of treatment including renal transplantation is less clear. We discuss the pathophysiology of C3 glomerulopathy, with evidence for alternative pathway dysregulation obtained from affected individuals and complement factor H (Cfh)-deficient animal models. Recent linkage studies in familial C3 glomerulopathy have shown genomic rearrangements in the Cfh-related genes, for which the novel pathophysiologic concept of Cfh deregulation has been proposed.

C3 glomerulonephritis: clinicopathological findings, complement abnormalities, glomerular proteomic profile, treatment, and follow-up

C3 Glomerulonephritis (C3GN) is a recently described disorder that typically results from abnormalities in the alternative pathway of complement. Here, we describe the clinical features, kidney biopsy findings, alternative pathway abnormalities, glomerular proteomic profile, and follow-up in 12 cases of C3GN. This disorder equally affected all ages, both genders, and typically presented with hematuria and proteinuria. In both the short and long term, renal function remained stable in the majority of patients with native kidney disease. In two patients, C3GN recurred within one year of transplantation and resulted in a decline in allograft function. Kidney biopsy mainly showed a membranoproliferative pattern; although both mesangial proliferative and diffuse endocapillary proliferative glomerulonephritis were noted. Alternative pathway abnormalities were heterogeneous; both acquired and genetic. The most common acquired abnormality was the presence of C3 nephritic factors, while the most common genetic finding was the presence of H402 and V62 alleles of Factor H. In addition to these risk factors, other abnormalities included Factor H auto-antibodies and mutations in CFH, CFI and CFHR genes. Laser dissection and mass spectrometry of glomeruli from patients with C3GN showed accumulation of alternative pathway and terminal complement complex proteins. Thus, C3GN results from diverse abnormalities of the alternative complement pathway leading to subsequent glomerular injury.

The endothelial glycocalyx as a potential modifier of the hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (HUS) is a renal disease due to complement dysregulation. Many of the known causes of atypical HUS originate from genetic mutations of complement regulatory proteins, such as complement factor H (CFH) and thrombomodulin. However, atypical HUS has only a genetic penetrance of 40-50% of the cases and usually appears in adulthood. We introduce a novel factor that may be involved in the onset and development of atypical HUS, i.e. the endothelial surface glycocalyx. The glycocalyx is a highly interactive matrix covering the luminal side of vascular endothelial cells and consists of glycosaminoglycans, proteoglycans and glycoproteins, which has an important role in maintaining homeostasis of the vasculature. The surface-bound glycocalyx glycosaminoglycan constituent heparan sulfate is crucial for CFH binding and function, both in recognition of host tissue and prevention of spontaneous complement activation via the alternative pathway. Most of the clinically relevant genetic mutations in CFH result in incorrect binding to heparan sulfate. In addition, a role between proper function of thrombomodulin and the endothelial glycocalyx has also been observed. We suggest that not only changes in binding properties of the complement regulatory proteins play a role but also changes in the endothelial glycocalyx are involved in increased risk of clinical manifestation of atypical HUS. Finally, vascular glycocalyx heterogeneity in turn could dictate the specific vulnerability of the glomerular vascular bed in atypical HUS and may provide new therapeutic targets to intervene with endothelial cell activation and local complement pathway regulation.

Recurrence of glomerulonephritis after renal transplantation

Recurrence of glomerulonephritis following renal transplantation is considered an important cause of allograft failure. The incidence of recurrence of glomerulonephritis varies widely depending on the definition of recurrence (pathologic recurrence or clinicopathologic recurrence) and the original glomerular disease. Moreover the impact of recurrence of glomerular disease on allograft outcome varies widely between different forms of glomerulonephritis. Whereas IgA nephritis recurs in up to one third of transplanted patients, this is not associated with adverse effects on graft survival. In contrast, recurrent focal segmental glomerulosclerosis and membranoproliferative glomerulopathy have an unfavorable prognosis. Overall, long-term graft survival in patients transplanted for glomerulonephritis is comparable to survival in patients with other causes of ESRD. In recent years, several mechanisms for recurrent disease after transplantation (e.g. PLA2R antibodies in membranous nephropathy and suPAR in FSGS) have been identified, and these findings have helped to elucidate the pathogenesis of glomerular diseases. Although renal transplantation is the treatment of choice for end-stage renal disease as a consequence of glomerulonephritis, further studies are required to develop optimal strategies to prevent, diagnose and treat recurrent glomerular diseases.

Soluble CR1 therapy improves complement regulation in C3 glomerulopathy

Dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are widely recognized subtypes of C3 glomerulopathy. These ultra-rare renal diseases are characterized by fluid-phase dysregulation of the alternative complement pathway that leads to deposition of complement proteins in the renal glomerulus. Disease triggers are unknown and because targeted treatments are lacking, progress to end stage renal failure is a common final outcome. We studied soluble CR1, a potent regulator of complement activity, to test whether it restores complement regulation in C3 glomerulopathy. In vitro studies using sera from patients with DDD showed that soluble CR1 prevents dysregulation of the alternative pathway C3 convertase, even in the presence of C3 nephritic factors. In mice deficient in complement factor H and transgenic for human CR1, soluble CR1 therapy stopped alternative pathway activation, resulting in normalization of serum C3 levels and clearance of iC3b from glomerular basement membranes. Short-term use of soluble CR1 in a pediatric patient with end stage renal failure demonstrated its safety and ability to normalize activity of the terminal complement pathway. Overall, these data indicate that soluble CR1 re-establishes regulation of the alternative complement pathway and provide support for a limited trial to evaluate soluble CR1 as a treatment for DDD and C3GN.

Treatment options for C3 glomerulopathy

PURPOSE OF REVIEW

The purpose of this review is to discuss emerging nomenclature, review the salient clinicopathological features and describe the therapeutic options available for the treatment of C3 glomerulopathy (C3G).

RECENT FINDINGS

C3G is minimally responsive to traditional immune suppression and randomized controlled trials to support therapy are absent. The burgeoning understanding of the role of the alternative complement pathway in C3G combined with animal data supporting the use of terminal complement blockade and a few reports suggesting that the anticomplement drug eculizumab may offer a therapeutic advantage have triggered great interest in the field of complement-mediated renal disease.

SUMMARY

Anticellular immune suppression and plasma therapy have limited efficacy in C3G. Data suggest that eculizumab may ameliorate disease in some C3G patients. The limited, recently published cohort data highlight crucial aspects of this group of diseases and support the need for extensive genetic and biomarker research to validate the pathologic mechanisms, delineate the spectrum of disease and guide the design of the rigorous trials to identify effective therapies for the treatment of C3G.

KDOQI US commentary on the 2012 KDIGO clinical practice guideline for glomerulonephritis

Glomerulonephritis (GN) is an important cause of morbidity and mortality in patients of all ages throughout the world. Because these disorders are relatively rare, it is difficult to perform randomized clinical trials to define optimal treatment for many of the specific glomerulopathies. In the absence of high-grade evidence to guide the care of glomerular diseases, in June 2012, KDIGO (Kidney Disease: Improving Global Outcomes) published an international clinical guideline for GN. The Work Group report represents an important review of the literature in this area and offers valid and useful guidelines for the most common situations that arise in the management of patients with glomerular disease. This commentary, developed by a panel of clinical experts convened by the National Kidney Foundation, attempts to put the GN guideline into the context of the US health care system. Overall, we support the vast majority of the recommendations and highlight select areas in which epidemiological factors and medical practice patterns in this country justify modifications and adjustments in order to achieve favorable outcomes. There remain large gaps in our knowledge of the best approaches to treat glomerular disease and we strongly endorse an expanded clinical research effort to improve the health and long-term outcomes of children and adults with GN.

Functional anatomy of complement factor H

Factor H (FH) is a soluble regulator of the proteolytic cascade at the core of the evolutionarily ancient vertebrate complement system. Although FH consists of a single chain of similar protein modules, it has a demanding job description. Its chief role is to prevent complement-mediated injury to healthy host cells and tissues. This entails recognition of molecular patterns on host surfaces combined with control of one of nature's most dangerous examples of a positive-feedback loop. In this way, FH modulates, where and when needed, an amplification process that otherwise exponentially escalates the production of the pro-inflammatory, pro-phagocytic, and pro-cytolytic cleavage products of complement proteins C3 and C5. Mutations and single-nucleotide polymorphisms in the FH gene and autoantibodies against FH predispose individuals to diseases, including age-related macular degeneration, dense-deposit disease, and atypical hemolytic uremic syndrome. Moreover, deletions or variations of genes for FH-related proteins also influence the risk of disease. Numerous pathogens hijack FH and use it for self-defense. As reviewed herein, a molecular understanding of FH function is emerging. While its functional oligomeric status remains uncertain, progress has been achieved in characterizing its three-dimensional architecture and, to a lesser extent, its intermodular flexibility. Models are proposed, based on the reconciliation of older data with a wealth of recent evidence, in which a latent circulating form of FH is activated by its principal target, C3b tethered to a self-surface. Such models suggest hypotheses linking sequence variations to pathophysiology, but improved, more quantitative, functional assays and rigorous data analysis are required to test these ideas.

C3 glomerulonephritis associated with monoclonal gammopathy: a case series

BACKGROUND

C3 glomerulonephritis (GN) is a proliferative GN resulting from glomerular deposition of complement factors due to dysregulation of the alternative pathway of complement. Dysregulation of the alternative pathway of complement may occur as a result of mutations or functional inhibition of complement-regulating proteins. Functional inhibition of the complement-regulating proteins may result from a monoclonal gammopathy.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

32 Mayo Clinic patients with C3 GN, 10 (31%) of whom had evidence of a monoclonal immunoglobulin in serum.

OUTCOMES

Clinical features, hematologic and bone marrow biopsy findings, kidney biopsy findings, kidney measures, complement pathway abnormalities, treatment, and follow-up of patients with C3 GN that was associated with a monoclonal gammopathy.

RESULTS

Mean age of patients with C3 GN associated with monoclonal gammopathy was 54.5 years. Bone marrow biopsy done in 9 patients revealed monoclonal gammopathy of undetermined significance in 5 patients, small lymphocytic lymphoma/chronic lymphocytic leukemia in one patient, and no abnormal clones in the other 3 patients. Kidney biopsy showed membranoproliferative GN with bright capillary wall C3 staining in all 10 patients. Evaluation of the alternative pathway of complement showed abnormalities in 7 of 9 patients tested. No mutation in complement-regulating proteins was detected in any patient. As an index case, one patient with C3 GN and chronic lymphocytic leukemia was treated with rituximab, cyclophosphamide, vincristine, and prednisone, and one patient with C3 GN and monoclonal gammopathy of undetermined significance was treated with dexamethasone and bortezomib. Both patients showed significant decreases in hematuria and proteinuria and stabilization of kidney function.

LIMITATIONS

Studies to show evidence of direct activation of the alternative pathway by monoclonal immunoglobulin were not done.

CONCLUSIONS

The study highlights the association of C3 GN and monoclonal gammopathy, in particular in the older population, and the importance of targeting the underlying hematologic malignancy as an approach to treating C3 GN.

Properdin and factor h: opposing players on the alternative complement pathway "see-saw"

Properdin and factor H are two key regulatory proteins having opposite functions in the alternative complement pathway. Properdin up-regulates the alternative pathway by stabilizing the C3bBb complex, whereas factor H downregulates the pathway by promoting proteolytic degradation of C3b. While factor H is mainly produced in the liver, there are several extrahepatic sources. In addition to the liver, factor H is also synthesized in fetal tubuli, keratinocytes, skin fibroblasts, ocular tissue, adipose tissue, brain, lungs, heart, spleen, pancreas, kidney, muscle, and placenta. Neutrophils are the major source of properdin, and it is also produced by monocytes, T cells and bone marrow progenitor cell line. Properdin is released by neutrophils from intracellular stores following stimulation by N-formyl-methionine-leucine-phenylalanine (fMLP) and tumor necrosis factor alpha (TNF-α). The HEP G2 cells derived from human liver has been found to produce functional properdin. Endothelial cells also produce properdin when induced by shear stress, thus is a physiological source for plasma properdin. The diverse range of extrahepatic sites for synthesis of these two complement regulators suggests the importance and need for local availability of the proteins. Here, we discuss the significance of the local synthesis of properdin and factor H. This assumes greater importance in view of recently identified unexpected and novel roles of properdin and factor H that are potentially independent of their involvement in complement regulation.

Complement dysregulation and disease: from genes and proteins to diagnostics and drugs

During the last decade, numerous studies have associated genetic variations in complement components and regulators with a number of chronic and infectious diseases. The functional characterization of these complement protein variants, in addition to recent structural advances in understanding of the assembly, activation and regulation of the AP C3 convertase, have provided important insights into the pathogenic mechanisms involved in some of these complement related disorders. This knowledge has identified potential targets for complement inhibitory therapies which are demonstrating efficacy and generating considerable expectation in changing the natural history of these diseases. Comprehensive understanding of the genetic and non-genetic risk factors contributing to these disorders will also result in targeting of the right patient groups in a stratified medicine approach through better diagnostics and individually tailored treatments, thereby improving management of patients.

The complement cascade in kidney disease: from sideline to center stage

Activation of the complement pathway is implicated in the pathogenesis of many kidney diseases. The pathologic and clinical features of these diseases are determined in part by the mechanism and location of complement activation within the kidney parenchyma. This review describes the physiology, action, and control of the complement cascade and explains the role of complement overactivation and dysregulation in kidney disease. There have been recent advances in the understanding of the effects of upregulation of the complement cascade after kidney transplantation. Complement plays an important role in initiating and propagating damage to transplanted kidneys in ischemia-reperfusion injury, antibody-mediated rejection, and cell-mediated rejection. Complement-targeting therapies presently are in development, and the first direct complement medication for kidney disease was licensed in 2011. The potential therapeutic targets for anticomplement drugs in kidney disease are described. Clinical and experimental studies are ongoing to identify further roles for complement-targeting therapy.

Recent insights into C3 glomerulopathy

‘C3 glomerulopathy’ is a recent disease classification comprising several rare types of glomerulonephritis (GN), including dense deposit disease (DDD), C3 glomerulonephritis (C3GN) and CFHR5 nephropathy. These disorders share the key histological feature of isolated complement C3 deposits in the glomerulus. A common aetiology involving dysregulation of the alternative pathway (AP) of complement has been elucidated in the past decade, with genetic defects and/or autoantibodies able to be identified in a proportion of patients. We review the clinical and histological features of C3 glomerulopathy, relating these to underlying molecular mechanisms. The role of uncontrolled C3 activation in pathogenesis is emphasized, with important lessons from animal models. Methods, advantages and limitations of gene testing in the assessment of individuals or families with C3 glomerulopathy are discussed. While no therapy has yet been shown consistently effective, clinical evaluation of agents targeting specific components of the complement system is ongoing. However, limits to current knowledge regarding the natural history and the appropriate timing and duration of proposed therapies need to be addressed.