IgA Nephropathy: the Lectin Pathway and Implications for Targeted Therapy

Prognostic role of mesangial IgM deposition in IgA nephropathy: a long-term cohort study

BACKGROUND

The clinical significance of mesangial immunoglobulin (Ig) M deposition in IgA nephropathy (IgAN) has been less explored and remains a topic of debate. Therefore, our study aimed to investigate the prognostic value of mesangial IgM deposition in a long-term follow-up cohort of IgAN patients.

METHODS

A unicentric retrospective study was conducted on 93 consecutive IgAN patients (median age 41 years, 68% male, eGFR 48.7 mL/min, proteinuria 1.1 g/g) from 2010 to 2015. They were followed until end-stage kidney disease (ESKD), death, or until the end of the study in January 2021, with a median follow-up of 7 years. An independent pathologist evaluated the IgM immunofluorescence pattern, Oxford MEST-C score, and transmission electron microscopy (TEM) lesions following a comprehensive protocol.

RESULTS

In our cohort, 70% had mesangial IgM-positive deposits, while 30% were IgM-negative. Both groups were similar in age, sex, prevalence of arterial hypertension, Charlson comorbidity scores, kidney function (eGFR and proteinuria), pathology findings (Oxford MEST-C score, IgG and C3 immune deposition), and TEM analysis. Treatment with RASI and immunosuppression, and death rates were also comparable. However, 37% of IgM-positive patients progressed to ESKD, significantly higher than the 11% in the IgM-negative group. Univariate and multivariate Cox proportional hazards regression analyses identified lower eGFR, higher Oxford MEST-C score, and mesangial IgM deposits as independent factors associated with shorter kidney survival.

CONCLUSIONS

Our study highlights mesangial IgM deposition as a potential risk factor for ESKD in patients with advanced IgAN, laying a foundation for further research in this area.

The prognostic role of activation of the complement pathways in the progression of advanced IgA nephropathy to end-stage renal disease

INTRODUCTION

The role of complement system in late stage of IgA nephropathy (IgAN) remains unknown. We therefore investigated the effects of complement system on worsening kidney function in advanced (stage 4 CKD) IgAN.

METHODS

Renal specimens of 69 IgAN patients who underwent renal biopsy during stage 4 CKD between 2010 and 2021, were stained using immunofluorescence (IF) and immunohistochemistry (IHC) for glomerular complement components. The primary outcome was progression to end-stage renal disease (ESRD). Associations of complement components with baseline clinicopathological characteristics and outcomes were assessed using multivariable Cox regression and Spearman analyses.

RESULTS

During a median follow-up of 18.0 months, 26 (37.7%) patients progressed to ESRD and none died. C1q and C3 deposition were detected in 12 and 66 patients, respectively. Higher eGFR [hazards ratio (HR), 0.852, 95% confidence interval (CI), 0.756-0.959; P = 0.008], higher C3 intensity (HR, 2.955, 95%CI, 1.063-8.220; P = 0.038) and T1-2 score (HR, 2.576, 95%CI, 1.205-5.576, P = 0.015) were predictive of time to ESRD in CKD 4 stage IgAN. Significant expressions of C1q (P = 0.005), C4d (P < 0.001), factor B (P < 0.001), C3 (P = 0.042) and C5b-9 (P = 0.004) were identified in ESRD group than in non-ESRD group by IHC, while MBL expression was low. Although they were not associated with baseline 24 h-UP, higher factor B and C1q expressions were both correlated with a lower baseline eGFR (P < 0.001 and = 0.04, respectively) and the deterioration of kidney function during follow-up (P = 0.046 and 0.015, respectively).

CONCLUSION

Complement deposition in IgAN patients with stage 4 CKD portends a faster deterioration of kidney function. Activation of classical and alternative complement pathways plays a major role in this stage.

Shen-yan-yi-hao oral solution ameliorates IgA nephropathy via intestinal IL-17/NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis in the world, it is one of the most common causes of kidney disease and can lead to end-stage kidney disease, however, its pathogenesis is still complicated. The Shen-yan-yi-hao oral solution (SOLI) is an effective prescription for the clinical treatment of IgAN while its specific mechanism remains to be further elucidated.

AIM OF THE STUDY

This study investigates SOLI's effects on IgAN in rats, particularly on the intestinal mucosal barrier, and identifies potential therapeutic targets through network pharmacology and molecular docking, validated experimentally.

MATERIALS AND METHODS

Target genes for SOLI in IgAN were identified and analysed through molecular docking and KEGG pathway enrichment. An IgAN rat model examined SOLI's effect on renal biomarkers and cytokines involved in specific pathways, ileum mucosal lesions, and the intestinal immune system. The IL-17 pathway's role was studied in IEC-6 cells with SOLI in vitro.

RESULT

Rats developed increased proteinuria and kidney damage marked by IgA deposition and inflammation. SOLI treatment significantly ameliorated these symptoms, reduced galactose-deficient Ig A1 (Gd-IgA1), and decreased cytokines like IL-17, TNF-α, IL-6 and IL-1β etc. SOLI also normalized intestinal tight junction protein expression, ameliorated intestinal damage, and regulated intestinal immune response (focused on IL-17/NF-κB signal pathway). SOLI moderated the abnormally activated IL-17 pathway, which damages intestinal epithelial cells, suggesting IgAN treatment potential.

CONCLUSION

SOLI reduces proteinuria and enhances intestinal mucosal function in IgAN rats, kidney protection in the IgAN rat model may initiate from modulating the intestinal IL-17/NF-κB pathway and subsequent Gd-IgA1 accumulation.

C4d Is an Independent Predictor of the Kidney Failure in Primary IgA Nephropathy

Background: C4d deposits are present in a substantial proportion of patients with IgA nephropathy (IgAN), indicating the activation of the lectin pathway (LP) of the complement system. It seems that patients with activated LP have worse renal prognosis. The aim of this study was to investigate the prevalence and prognostic significance of C4d in our cohort of patients with primary IgA nephropathy (pIgAN). Methods: Patients with pIgAN were recruited from a hospital register of kidney biopsies of the Department of Nephrology and Dialysis, Dubrava University Hospital, Zagreb. Additional immunohistochemistry staining for C4d was performed on paraffin-embedded kidney tissue, and patients were stratified into being C4d positive or C4d negative. The clinical and histologic features of patients were analyzed and compared regarding C4d positivity. The primary outcome was defined as kidney failure (KF), and predictor variables of KF and renal survival were analyzed. Results: Of a total of 95 patients with pIgAN included in the study, C4d was present in 43 (45.3%). C4d-positive patients had a higher value of systolic (p = 0.039) and diastolic (p = 0.006) blood pressure at diagnosis as well as higher 24 h proteinuria (p = 0.018), serum urate (p = 0.033), and lower eGFR (p < 0.001). C4d-positive patients had worse renal survival (p < 0.001), higher rates of disease progression to KF (p < 0.001), and higher proteinuria (p < 0.001) and lower eGFR (p < 0.001) at the last follow-up. Glomerular C4d was an independent predictor of disease progression to KF (HR = 5.87 [0.95 CI 1.06-32.44], p = 0.032). Conclusions: C4d is an independent predictor of disease progression in patients with pIgAN. C4d may be used as an additional marker of progressive disease course in IgAN. The therapeutic implications of C4d status in IgAN, particularly in terms of complement inhibitors application, are not yet known.

Unveiling biomarkers and therapeutic targets in IgA nephropathy through large-scale blood transcriptome analysis

INTRODUCTION

IgA nephropathy (IgAN) is the most prevalent form of glomerulonephritis. Unfortunately, molecular biomarkers for IgAN derived from omics studies are still lacking. This research aims to identify critical genes associated with IgAN through large-scale blood transcriptome analysis.

METHODS

We constructed novel blood transcriptome profiles from peripheral blood mononuclear cells (PBMCs) of 53 Chinese IgAN patients and 28 healthy individuals. Our analysis included GO, KEGG, and GSEA for biological pathways. We analyzed immune cell profiles with CIBERSORT and constructed PPI networks with STRING, visualized in Cytoscape. Key differentially expressed genes (DEGs) were identified using CytoHubba and MCODE. We assessed the correlation between gene expressions and clinical data to evaluate clinical significance and identified hub genes through machine learning, validated with an open-access dataset. Potential drugs were explored using the CMap database.

RESULTS

We identified 333 DEGs between IgAN patients and healthy controls, mainly related to immune response and inflammation. Key pathways included NK cell mediated cytotoxicity, complement and coagulation cascades, antigen processing, and B cell receptor signaling. Cytoscape revealed 16 clinically significant genes (including KIR2DL1, KIR2DL3, VISIG4, C1QB, and C1QC, associated with sub-phenotype and prognosis). Machine learning identified two hub genes (KLRC1 and C1QB) for a diagnostic model of IgAN with 0.92 accuracy, validated at 1.00 against the GSE125818 dataset. Sirolimus, calcifediol, and efaproxiral were suggested as potential therapeutic agents.

CONCLUSION

Key DEGs, particularly VISIG4, KLRC1, and C1QB, emerge as potential specific markers for IgAN, paving the way for future targeted personalized treatment options.

New therapies for immunoglobulin A nephropathy: what's the standard of care in 2023?

PURPOSE OF REVIEW

As the most common primary glomerulonephritis, immunoglobulin A (IgA) nephropathy (IgAN) is an important cause of kidney failure and mortality. Until recently, therapeutic options were limited. Fortunately, there have been numerous recent clinical trials demonstrating efficacy of new therapies in slowing chronic kidney disease (CKD) progression at varying stages of disease.

RECENT FINDINGS

The TESTING trial has provided high-quality evidence for slowing estimated glomerular filtration rate (eGFR) decline with a reduced-dose glucocorticoid regimen, while demonstrating an improved safety profile. Targeted-release budesonide represents a well tolerated therapy for reducing eGFR decline. Mycophenolate mofetil may reduce CKD progression in some populations, while hydroxychloroquine is efficacious in reducing proteinuria. Sodium-glucose cotransporter (SGLT2) inhibitors and sparsentan are effective therapies for CKD due to IgAN, but should not be used in lieu of disease-modifying immunosuppressive therapy. Many new therapies are approaching readiness for clinical use.

SUMMARY

Numerous therapeutic options now exist and include disease-modifying and nephroprotective drugs. Identifying the right treatment for the right patient is now the clinical challenge and, with new drugs on the horizon, represents the primary unmet research need in this rapidly-developing field.

Identification of GMFG as a novel biomarker in IgA nephropathy based on comprehensive bioinformatics analysis

Background

IgA nephropathy (IgAN) stands as the most prevalent form of glomerulonephritis and ranks among the leading causes of end-stage renal disease worldwide. Regrettably, we continue to grapple with the absence of dependable diagnostic markers and specific therapeutic agents for IgAN. Therefore, this study endeavors to explore novel biomarkers and potential therapeutic targets in IgAN, while also considering their relevance in the context of tumors.

Methods

We gathered IgAN datasets from the Gene Expression Omnibus (GEO) database. Subsequently, leveraging these datasets, we conducted an array of analyses, encompassing differential gene expression, weighted gene co-expression network analysis (WGCNA), machine learning, receiver operator characteristic (ROC) curve analysis, gene expression validation, clinical correlations, and immune infiltration. Finally, we carried out pan-cancer analysis based on hub gene.

Results

We obtained 1391 differentially expressed genes (DEGs) in GSE93798 and 783 DGEs in GSE14795, respectively. identifying 69 common genes for further investigation. Subsequently, GMFG was identified the hub gene based on machine learning. In the verification set and the training set, the GMFG was higher in the IgAN group than in the healthy group and all of the GMFG area under the curve (AUC) was more 0.8. In addition, GMFG has a close relationship with the prognosis of malignancies and a range of immune cells.

Conclusions

Our study suggests that GMFG could serve as a promising novel biomarker and potential therapeutic target for both IgAN and certain types of tumors.

Improving Kidney Disease Care: One Giant Leap for Nephrology

Nephrology is an ever-evolving field of medicine. The importance of such a discipline is related to the high clinical impact of kidney disease. In fact, abnormalities of kidney function and/or structure are common in the general population, reaching an overall prevalence of about 10%. More importantly, the onset of kidney damage is related to a strikingly high risk of cardiovascular events, mortality, and progression to kidney failure which, in turn, compromises quality and duration of life. Attempts to comprehend the pathogenesis and molecular mechanisms involved in kidney disease occurrence have prompted the development and implementation of novel drugs in clinical practice with the aim of treating the 'specific cause' of kidney disease (including chronic kidney disease, glomerular disease, and genetic kidney disorders) and the main immunological complications following kidney transplantation. Herein, we provide an overview of the principal emerging drug classes with proved efficacy in the context of the aforementioned clinical conditions. This can represent a simplified guide for clinical nephrologists to remind them of the vast and heterogeneous armamentarium of drugs that should be used in the present and the future to improve the management of patients suffering from kidney disease.

The role of BAFF and APRIL in IgA nephropathy: pathogenic mechanisms and targeted therapies

Immunoglobulin A nephropathy (IgAN), characterized by mesangial deposition of galactose-deficient-IgA1 (Gd-IgA1), is the most common biopsy-proven primary glomerulonephritis worldwide. Recently, an improved understanding of its underlying pathogenesis and the substantial risk of progression to kidney failure has emerged. The "four-hit hypothesis" of IgAN pathogenesis outlines a process that begins with elevated circulating levels of Gd-IgA1 that trigger autoantibody production. This results in the formation and deposition of immune complexes in the mesangium, leading to inflammation and kidney injury. Key mediators of the production of Gd-IgA1 and its corresponding autoantibodies are B-cell activating factor (BAFF), and A proliferation-inducing ligand (APRIL), each playing essential roles in the survival and maintenance of B cells and humoral immunity. Elevated serum levels of both BAFF and APRIL are observed in patients with IgAN and correlate with disease severity. This review explores the complex pathogenesis of IgAN, highlighting the pivotal roles of BAFF and APRIL in the interplay between mucosal hyper-responsiveness, B-cell activation, and the consequent overproduction of Gd-IgA1 and its autoantibodies that are key features in this disease. Finally, the potential therapeutic benefits of inhibiting BAFF and APRIL in IgAN, and a summary of recent clinical trial data, will be discussed.

Genetic determinants of complement activation in the general population

Complement is a fundamental innate immune response component. Its alterations are associated with severe systemic diseases. To illuminate the complement's genetic underpinnings, we conduct genome-wide association studies of the functional activity of the classical (CP), lectin (LP), and alternative (AP) complement pathways in the Cooperative Health Research in South Tyrol study (n = 4,990). We identify seven loci, encompassing 13 independent, pathway-specific variants located in or near complement genes (CFHR4, C7, C2, MBL2) and non-complement genes (PDE3A, TNXB, ABO), explaining up to 74% of complement pathways' genetic heritability and implicating long-range haplotypes associated with LP at MBL2. Two-sample Mendelian randomization analyses, supported by transcriptome- and proteome-wide colocalization, confirm known causal pathways, establish within-complement feedback loops, and implicate causality of ABO on LP and of CFHR2 and C7 on AP. LP causally influences collectin-11 and KAAG1 levels and the risk of mouth ulcers. These results build a comprehensive resource to investigate the role of complement in human health.

A new alternative: inhibiting complement activation in patients with IgA nephropathy

Mesangial complement C3 deposits, reflecting alternative and possibly lectin pathway activation, are characteristic in biopsies of patients with IgA nephropathy (IgAN). A recent randomized controlled trial tested the efficacy and safety of iptacopan, a factor B inhibitor, in patients with IgAN. Iptacopan dose-dependently reduced proteinuria, and there was a pronounced decrease of urinary C5b-9. This offers the perspective of "personalizing" therapy, which would be a unique feature of this novel approach to IgAN. A phase III clinical trial (APPLAUSE-IgAN) is ongoing.

Treatment of IgA Nephropathy: A Rapidly Evolving Field

The pivotal event in the pathophysiology of IgA nephropathy is the binding of circulating IgA-containing immune complexes to mesangial cells, with secondary glomerular and tubulointerstitial inflammation and fibrosis. The paramount difficulty in the management of IgA nephropathy is the heterogeneity in its clinical presentation and prognosis, requiring an individualized treatment approach. Goal-directed supportive care remains the bedrock of therapy for all patients, regardless of risk of progression. Sodium-glucose transporter 2 inhibitors and sparsentan should be integral to contemporary supportive care, particularly in patients with chronic kidney damage. Pending the development of reliable biomarkers, it remains a challenge to identify patients prone to progression due to active disease and most likely to derive a net benefit from immunosuppression. The use of clinical parameters, including the degree of proteinuria, the presence of persistent microscopic hematuria, and the rate of eGFR loss, combined with the mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis, crescents score, is currently the best approach. Systemic glucocorticoids are indicated in high-risk patients, but the beneficial effects wane after withdrawal and come at the price of substantial treatment-associated toxicity. Therapies with direct effect on disease pathogenesis are increasingly becoming available. While targeted-release budesonide has garnered the most attention, anti-B-cell strategies and selective complement inhibition will most likely prove their added value. We propose a comprehensive approach that tackles the different targets in the pathophysiology of IgA nephropathy according to their relevance in the individual patient.

IgA nephropathy

IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.

Novel agents for treating IgA nephropathy

PURPOSE OF REVIEW

In the past, the treatment of IgA nephropathy (IgAN), which is the most common glomerulonephritis worldwide, mostly relied on blockade of the renin-angiotensin system as a central component of so-called supportive therapy as well as on high-dose systemic corticosteroid therapy.

RECENT FINDINGS

The supportive treatment arm has been expanded by the addition of sodium-glucose cotransporter-2 inhibitors, hydroxychloroquine, and, most recently, endothelin A receptor blockers. Treatment with high-dose systemic corticosteroids has become more controversial, with some studies observing no benefit and others documenting the protection of kidney function. However, all recent studies on systemic corticosteroids consistently found significant toxicity. An important novel approach to IgAN, therefore, is therapy with a targeted release formulation of budesonide with preferential release in the distal small intestine, given the mounting evidence for a gut-kidney axis in the pathophysiology of IgAN. In addition, emerging new therapeutic options include a variety of complement inhibitors as well as agents targeting B-cell proliferation and differentiation.

SUMMARY

In recent years, IgAN has become the focus of a considerable number of clinical studies that will significantly advance the development of new therapy strategies.