Liver factor B silencing to cure C3 glomerulopathy: Evidence from a mouse model of complement dysregulation

Uncontrolled activation of the alternative pathway (AP) of complement, due to genetic and/or acquired defects, plays a primary pathogenetic role in C3 glomerulopathy (C3G), a rare and heterogeneous disease characterised by predominant C3 fragment deposition within the glomerulus, as well as glomerular damage. There are currently no approved disease-specific treatments for C3G, but new drugs that directly counteract AP dysregulation, targeting components of the pathway, have opened promising new perspectives for managing the disease. Complement factor B (FB), which is primarily synthesised by hepatocytes, is a key component of the AP, as it drives the central amplification loop of the complement system. In this study we used a GalNAc (N-Acetylgalactosamine)-conjugated siRNA to selectively target and suppress liver FB expression in two mouse models characterised by the complete (Cfh-/- mice) or partial (Cfh+/-) loss of function of complement factor H (FH). Homozygous deletion of FH induced a severe C3G phenotype, with strong dysregulation of the AP of complement, glomerular C3 deposition and almost complete C3 consumption. Mice with a heterozygous deletion of FH had intermediate C3 levels and exhibited slower disease progression, resembling human C3G more closely. Here we showed that FB siRNA treatment did not improve serum C3 levels, nor limit glomerular C3 deposition in Cfh-/- mice, while it did normalise circulating C3 levels, reduce glomerular C3 deposits, and limit mesangial electron-dense deposits in Cfh+/- mice. The present data provide important insights into the potential benefits and limitations of FB-targeted inhibition strategies and suggest RNA interference-mediated FB silencing in the liver as a possible therapeutic approach for treating C3G patients with FH haploinsufficiency.

Disease profiles in the Indigenous Australian population are suggestive of a common complement control haplotype

Aboriginal and Torres Strait Islander People (respectfully referred to as Indigenous Australians herein) are disparately burdened by many infectious and chronic diseases relative to Australians with European genetic ancestry. Some of these diseases are described in other populations to be influenced by the inherited profile of complement genes. These include complement factor B, H, I and complement factor H-related (CFHR) genes that can contribute to a polygenic complotype. Here the focus is on the combined deletion of CFHR1 and 3 to form a common haplotype (CFHR3-1Δ). The prevalence of CFHR3-1Δ is high in people with Nigerian and African American genetic ancestry and correlates to a higher frequency and severity of systemic lupus erythematosus (SLE) but a lower prevalence of age-related macular degeneration (AMD) and IgA-nephropathy (IgAN). This pattern of disease is similarly observed among Indigenous Australian communities. Additionally, the CFHR3-1Δ complotype is also associated with increased susceptibility to infection with pathogens, such as Neisseria meningitidis and Streptococcus pyogenes, which also have high incidences in Indigenous Australian communities. The prevalence of these diseases, while likely influenced by social, political, environmental and biological factors, including variants in other components of the complement system, may also be suggestive of the CFHR3-1Δ haplotype in Indigenous Australians. These data highlight a need to define the Indigenous Australian complotypes, which may lead to the discovery of new risk factors for common diseases and progress towards precision medicines for treating complement-associated diseases in Indigenous and non-Indigenous populations. Herein, the disease profiles suggestive of a common complement CFHR3-1Δ control haplotype are examined.

Clinical Outcomes of Patients with C3G or IC-MPGN Treated with the Factor D Inhibitor Danicopan: Final Results from Two Phase 2 Studies

INTRODUCTION

C3 glomerulopathy (C3G) is an ultrarare, chronic and progressive nephropathy mediated by dysregulation of the alternative pathway of complement (AP), with poor prognosis and limited treatment options. Targeted inhibition of proximal AP through factor D (FD) blockade represents a rational treatment approach. We present two phase 2 proof-of-concept clinical studies of the orally active FD inhibitor danicopan in patients with C3G and immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) (NCT03369236 and NCT03459443).

METHODS

A double-blind, placebo-controlled study in patients with C3G and a single-arm, open-label study in patients with C3G or IC-MPGN treated with danicopan are reported. The studies evaluated pharmacokinetic/pharmacodynamic (PK/PD), efficacy, and safety outcomes. The co-primary endpoints were change from baseline in composite biopsy score and the proportion of patients with a 30% reduction in proteinuria relative to baseline at 6 or 12 months.

RESULTS

Optimal systemic concentrations of danicopan were not achieved for complete and sustained inhibition of AP, although there was evidence that blockade of FD reduced AP activity shortly after drug administration. Consequently, limited clinical response was observed in key efficacy endpoints. While stable disease or improvement from baseline was seen in some patients, response was not consistent. The data confirmed the favorable safety profile of danicopan.

CONCLUSION

While demonstrating a favorable safety profile, danicopan resulted in incomplete and inadequately sustained inhibition of AP, probably due to limitations in its PK/PD profile in C3G, leading to lack of efficacy. Complete and sustained AP inhibition is required for a clinical response in patients with C3G.

Amnion epithelial cells are an effective source of factor H and prevent kidney complement deposition in factor H-deficient mice

Complement factor H (FH) is the main plasma regulator of the alternative pathway of complement. Genetic and acquired abnormalities in FH cause uncontrolled complement activation amplifying, with the consequent accumulation of complement components on the renal glomeruli. This leads to conditions such as C3 glomerulopathy (C3G) and atypical hemolytic uremic syndrome (aHUS). There is no effective therapy for these diseases. Half of the patients progress to end-stage renal disease and the condition recurs frequently in transplanted kidneys. Combined liver/kidney transplantation is a valid option for these patients, but the risks of the procedure and donor organ shortages hamper its clinical application. Therefore, there is an urgent need for alternative strategies for providing a normal FH supply. Human amnion epithelial cells (hAEC) have stem cell characteristics, including the capability to differentiate into hepatocyte-like cells in vivo.Here, we administered hAEC into the livers of newborn Cfh^-/- mice, which spontaneously developed glomerular complement deposition and renal lesions resembling human C3G. hAEC engrafted at low levels in the livers of Cfh^-/- mice and produced sufficient human FH to prevent complement activation and glomerular C3 and C9 deposition. However, long-term engraftment was not achieved, and eventually hAEC elicited a humoral immune response in immunocompetent Cfh^-/- mice.hAEC cell therapy could be a valuable therapeutic option for patients undergoing kidney transplantation in whom post-transplant immunosuppression may protect allogeneic hAEC from rejection, while allogeneic cells provide normal FH to prevent disease recurrence.

Genetic and Protein Structural Evaluation of Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy

Atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) are associated with loss of regulation of the alternative pathway of complement and its resulting overactivation. As rare diseases, genetic variants leading to aHUS and C3G were previously analysed in relatively low patient numbers. To improve this analysis, data were pooled from six centres. Totals of 610 rare variants for aHUS and 82 for C3G were presented in an interactive database for 13 genes. Using allele frequency comparisons with the Exome Aggregation Consortium as a reference genome, the patients with aHUS showed significantly more protein-altering ultrarare variants (allele frequency <0.01%) in five genes CFH, CFI, CD46, C3, and DGKE. In patients with C3G, the corresponding association was only found for C3 and CFH. Protein structure analyses of these five proteins showed distinct differences in the positioning of these variants in C3 and FH. For aHUS, variants were clustered at the C-terminus of FH and implicated changes in the binding of FH to host cell surfaces. For C3G, variants were clustered at the N-terminal C3b binding site of FH and implicated changes in the fluid-phase regulation of C3b. We discuss the utility of the Web database as a patient resource for clinicians.

Characteristics of membranoproliferative glomerulonephritis based on a new classification at a single center

BACKGROUND

Recently, a new classification has been established for membranoproliferative glomerulonephritis (MPGN). However, the effect of the new classification on MPGN treatment is not fully understood.

METHODS

We conducted a retrospective study of 87 patients with biopsies diagnosed as MPGN. We reclassified 87 MPGN patients diagnosed between 1977 and 2014 at our hospital, according to the new classification, and analyzed both primary immune complex (IC)- and Alternative pathway (AP)-mediated MPGN [corrected] in terms of clinicopathological features, treatment, and renal prognosis.

RESULTS

Proteinuria was abundant in the IC-mediated MPGN group (p = 0.0063), and the serum albumin level was significantly lower in the IC-mediated MPGN group (p = 0.0186). The serum C3 value was significantly lower in the CP-mediated MPGN group (p = 0.0317). Serum CH50 values were also lower in the CP-mediated MPGN group (p = 0.0404). However, glomerular deposition of C3 showed no significant differences in immunofluorescence findings. The 148.6-month renal survival rate was similar in both groups (p = 0.445).

CONCLUSION

These results suggested no significant differences in complement activation of the solid phase in local glomeruli and therefore equivalent in renal prognosis [corrected].

Shiga toxin triggers endothelial and podocyte injury: the role of complement activation

Shiga toxin (Stx)-producing Escherichia coli (STEC) is the offending agent in post-diarrhea-associated hemolytic uremic syndrome (HUS), a disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney failure, with thrombi occluding the renal microvasculature. Endothelial dysfunction has been recognized as the trigger event in the development of microangiopathic processes. Glomerular endothelial cells are susceptible to the toxic effects of Stxs that, via nuclear factor kappa B (NF-κB) activation, induce the expression of genes encoding for adhesion molecules and chemokines, culminating in leukocyte adhesion and platelet thrombus formation on the activated endothelium. Complement activation via the alternative pathway has been seen in patients during the acute phase of STEC-associated HUS. Experimental evidence has highlighted the role of complement proteins in driving glomerular endothelium toward a thrombogenic phenotype. At the glomerular level, podocytes are also an important target of Stx-induced complement activation. Glomerular injury as a consequence of podocyte dysfunction and loss is thus a mechanism that might affect long-term renal outcomes in the disease. New approaches to targeting the complement system may be useful therapeutic options for patients with STEC-HUS.

C3 Glomerulopathy and post-infectious glomerulonephritis define a disease spectrum

BACKGROUND

Post-infectious glomerulonephritis (PIGN) usually follows a benign course, but few children have an atypical, severe presentation, and these exceptional cases have been linked to the dysregulation of the complement alternative pathway (CAP). There is a considerable overlap in the histopathological features of PIGN and C3 glomerulopathy (C3G), which is also associated with CAP dysregulation but has a poorer outcome. We hypothesized that PIGN and C3G define a disease spectrum, and that in the past there may be some children with C3G who were misclassified with PIGN before C3G was described as a separate disease entity.

METHODS

Children with PIGN (n = 33) diagnosed between 1985 and 2010 who underwent a renal biopsy due to their unusual course were reviewed and of them, 8 were reclassified into C3G based on the current classification criteria. Outcome was based on the degree of proteinuria, C3 level, and renal function at follow-up.

RESULTS

Sixteen (72.7%) children with typical PIGN recovered completely as compared to only 2 (25%) with C3G. Of note, children with "typical" PIGN had a more severe disease course at onset; however, the outcome at last follow up was favorable.

CONCLUSIONS

Our results support the hypothesis that PIGN and C3G form a disease spectrum and have different long-term clinical implications and management strategies.

Anti-complement activity of the Ixodes scapularis salivary protein Salp20

Complement, a major component of innate immunity, presents a rapid and robust defense of the intravascular space. While regulatory proteins protect host cells from complement attack, when these measures fail, unrestrained complement activation may trigger self-tissue injury, leading to pathologic conditions. Of the three complement activation pathways, the alternative pathway (AP) in particular has been implicated in numerous disease and injury states. Consequently, the AP components represent attractive targets for therapeutic intervention. The common hard-bodied ticks from the family Ixodidae derive nourishment from the blood of their mammalian hosts. During its blood meal the tick is exposed to host immune effectors, including the complement system. In defense, the tick produces salivary proteins that can inhibit host immune functions. The Salp20 salivary protein of Ixodes scapularis inhibits the host AP pathway by binding properdin and dissociating C3bBbP, the active C3 convertase. In these studies we examined Salp20 activity in various complement-mediated pathologies. Our results indicate that Salp20 can inhibit AP-dependent pathogenesis in the mouse. Its efficacy may be part in due to synergic effects it provides with the endogenous AP regulator, factor H. While Salp20 itself would be expected to be highly immunogenic and therefore inappropriate for therapeutic use, its emergence speaks for the potential development of a non-immunogenic Salp20 mimic that replicates its anti-properdin activity.

[C3 glomerulopathy]

C3 glomerulopathy is an heterogeneous group of glomerular diseases associated with acquired or genetic abnormalities of complement alternative pathway (AP) components. It is characterized by predominant C3 deposits in the mesangium and along the glomerular basement membrane (GBM). Presenting features comprise proteinuria (sometimes with nephritic syndrome), haematuria, hypertension and renal failure. C3 glomerulopathy have a poor renal prognosis with progression to end stage renal disease (ESRD) in 50% of cases during the first decade after initial presentation. Moreover, C3 deposits recur in most of cases after renal transplantation. Patients frequently have low serum C3 level attributed to the activation of the alternative pathway of complement. Animal models have confirmed the role of excessive C3 activation in the pathogenesis of C3 glomerulopathy. To date, the optimal treatment remains unknown. It is currently based on the use of angiotensin-converting-enzyme inhibitors (ACEI) and angiotensin II-receptor blockers (ARB), sometimes associated with immunosuppressive therapy. Blockade of C5a release with eculizumab, a monoclonal anti-C5 antibody, may be of particular interest in the treatment of C3G.