The Role of Complement in Microangiopathic Lesions of IgA Nephropathy

Impact of intrarenal arterial lesions on prognosis of IgA nephropathy: insights from a retrospective cohort study

BACKGROUND

IgA nephropathy (IgAN) presents a challenging spectrum of outcomes, often complicated by intrarenal arterial/arteriolar lesions (IALs) in affected individuals. Despite their clinical relevance, existing criteria for classifying and assessing the severity of these lesions remain undefined. This study aimed to establish semi-quantitative assessment criteria for grading IALs and to evaluate their prognostic significance in patients with IgAN.

METHOD

We conducted a retrospective cohort study of 417 cases of primary IgAN in which IALs were meticulously scored in individual biopsies. Kaplan-Meier survival analysis was employed to compare the time to the renal composite endpoint between different IALs severity groups. The association between the severity of IALs and clinical outcomes was further evaluated using multivariate Cox regression models to control for potential confounders.

RESULTS

Among the 417 patients studied, 230 (55.2%) exhibited IALs. Kaplan-Meier curve analysis showed a higher cumulative incidence of the composite endpoint in patients with IALs (p < 0.001). In a compelling multivariate analysis, we identified IALs and its subclassifications, including moderate to severe intimal fibrosis and hyalinosis, as strong independent risk factors for poor prognosis (IALs: HR = 2.15, p = 0.009; moderate to severe hyalinosis: HR = 3.58, p = 0.001; moderate to severe intimal fibrosis: HR = 3.56, p = 0.001).

CONCLUSION

Our findings underscore the prognostic significance of IALs in IgAN, particularly moderate to severe intimal fibrosis and hyalinosis and highlight the urgent need for novel therapeutic strategies specifically designed to mitigate the impact of IALs in high-risk IgAN patients.

Tailored management strategies for IgA nephropathy based on clinical presentations

The treatment landscape for immunoglobulin A nephropathy is rapidly evolving with the introduction of novel therapies targeting diverse disease pathways. Some have already been approved in different countries, while others are under investigation in randomized controlled trials (RCTs) with encouraging results. However, almost all performed RCTs have included only patients with refractory non-nephrotic proteinuria and preserved renal function. Other clinical presentations (rapidly progressive forms, malignant hypertension, thrombotic microangiopathy, nephrotic syndrome) have received less attention and are systematically excluded from RCTs. In contrast, certain aspects, such as the impact of haematuria or management in special populations (e.g. pregnant patients or transplant recipients), remain underexplored. This review proposes therapeutic algorithms to guide treatment decisions in different clinical scenarios while highlighting gaps in current research.

Moderate to severe chronic arteriolar lesions is an independent risk factor for adverse renal outcomes in IgA nephropathy

BACKGROUND

The impact of chronic arteriolar lesions on the prognosis of IgA nephropathy remains controversial. This study aims to explore the value of chronic arteriolar lesions of varying degrees in predicting the prognosis of IgA nephropathy patients and analyze the associated risk factors that contribute to the formation.

METHODS

A retrospective analysis was conducted on 853 patients diagnosed with IgA nephropathy through renal biopsy at Guangdong Provincial Hospital of Traditional Chinese Medicine between September 1, 2005, and December 31, 2021. Eventually, a total of 574 cases were included in this study. According to the degree of chronic arteriolar lesions, the patients were divided into four groups: no lesion group (n=115), mild lesion group (n=287), moderate lesion group (n=131), and severe lesion group (n=41). Relevant clinical and pathological features and renal outcomes were recorded. Kaplan-Meier analysis, Cox proportional hazards regression, and receiver operating characteristic (ROC) curve analysis were utilized to examine the relationship between different degrees of chronic arteriolar lesions and the prognosis of IgA nephropathy. Additionally, risk factors associated with the development of moderate to severe chronic arteriolar lesions were identified.

RESULTS

Worse clinical and pathological features were observed in the moderate to severe lesions group (P<0.05). Moderate to severe chronic arteriolar lesions (aHR=3.357, 95%CI: 1.018-11.071, P=0.047), creatinine, S1, E1, T2, and C2 were identified as independent risk factors for adverse renal outcomes. Cox multivariate regression analysis on moderate to severe chronic arteriolar lesions demonstrated that creatinine, T2, and C2 were independent risk factors for adverse renal outcomes in patients with moderate to severe chronic arteriolar lesions.

CONCLUSION

Moderate to severe chronic arteriolar lesions independently increases the risk of adverse renal outcomes.

Heterozygous mutations in factor H aggravate pathological damage in a stable IgA deposition model induced by Lactobacillus casei cell wall extract

Introduction

Activation of complement through the alternative pathway (AP) has a key role in the pathogenesis of IgA nephropathy (IgAN). We previously showed, by intraperitoneal injection of Lactobacillus casei cell wall extract (LCWE), C57BL/6 mice develop mild kidney damage in association with glomerular IgA deposition. To further address complement activity in causing glomerular histological alterations as suggested in the pathogenesis of IgAN, here we used mice with factor H mutation (FHW/R) to render AP overactivation in conjunction with LCWE injection to stimulate intestinal production of IgA.

Methods

Dose response to LCWE were examined between two groups of FHW/R mice. Wild type (FHW/W) mice stimulated with LCWE were used as model control.

Results

The FHW/R mice primed with high dose LCWE showed elevated IgA and IgA-IgG complex levels in serum. In addition to 100% positive rate of IgA and C3, they display elevated biomarkers of kidney dysfunction, coincided with severe pathological lesions, resembling those of IgAN. As compared to wild type controls stimulated by the same high dose LCWE, these FHW/R mice exhibited stronger complement activation in the kidney and in circulation.

Discussion

The new mouse model shares many disease features with IgAN. The severity of glomerular lesions and the decline of kidney functions are further aggravated through complement overactivation. The model may be a useful tool for preclinical evaluation of treatment response to complement-inhibitors.

Systematic Review of the Link Between Oxford MEST-C Classification and Complement Activation in IgA Nephropathy

INTRODUCTION

IgA nephropathy's (IgAN's) MEST-C classification relationship with complement activation is still not fully understood because of limited and conflicting evidence. Our study aimed to delineate this relationship through a systematic review.

METHODS

We adhered to the Preferred Reporting Items for Systematic Review and Meta-analysis guidelines and conducted a systematic review, utilizing databases like MEDLINE (PubMed), Embase, Scopus, and Cochrane from January 2016 (year of updated MEST-C classification) to January 2023. We specifically selected studies that employed established methods to evaluate complement activation and the MEST-C classification.

RESULTS

A total of 34 studies with 10,082 patients were included. Among these, 7 studies focused on the pediatric population (500 patients), and 22 studies involved 8128 patients from Asian populations. C4d, C3, C5b9, MBL, C4, and factor H-related protein 5 (FHR5) were the most frequently studied complement proteins in relation to the MEST-C classification. Complement activation assessment was primarily conducted using immunofluorescence and immunohistochemistry on kidney biopsy specimens. All complement proteins investigated showed associations with the C1-2 class. Notably, FB, FH, MASP1/3, MASP2, C5a, and C5b9 from the alternative, lectin, and terminal pathways were uniquely present in the C1-2 class. Whereas C3, FHR5, C4, and C4d were associated with all the MEST-C classes.

CONCLUSION

We found evidence supporting the involvement of alternative and lectin complement pathways across all MEST-C classes. All examined complement factors were associated with the C1-2 class, emphasizing the critical role of complement activation, possibly at the endothelial surface. These findings may guide the development of personalized treatment strategies targeting complement pathways in relation to the MEST-C lesions.

Targeting complement in IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Recent years have witnessed significant improvements in the understanding of the pathogenesis of IgAN and particularly, the pathogenic role of complement activation. The alternative complement pathway is the major complement cascade activator in IgAN, and glomerular C3 deposition has been shown to correlate with disease progression. In addition, several studies have provided insight into the pathogenic role of factor H-related proteins -1 and -5 in IgAN, as independent players in complement dysregulation. The lectin pathway has also been shown to be associated with the severity of IgAN. Glomerular deposition of C4d has been associated with increased histologic disease activity, faster decline in estimated glomerular filtration rate and higher risk of kidney failure. On the other hand, although overlooked in the Oxford classification, numerous studies have shown that the coexistence of thrombotic microangiopathy in IgAN is a significant indicator of a poorer prognosis. All the breakthroughs in the understanding of the contributing role of complement in IgAN have paved the way for the development of new complement-targeted therapies in this disease. Several ongoing trials are evaluating the efficacy of new agents against factor B (iptacopan, Ionis-FB-LRX), C3 (pegcetacoplan), factor D (vemircopan, pelecopan), C5 (ravulizumab, cemdisiran) and C5a receptor 1 (avacopan). In this study, we provide a comprehensive review of the role of complement in IgAN, including the emerging mechanisms of complement activation and the promising potential of complement inhibitors as a viable treatment option for IgAN.

Evaluating Progression Risk in Patients With Immunoglobulin A Nephropathy

The highly variable rate of decline in kidney function in patients with immunoglobulin A nephropathy (IgAN) provides a major clinical challenge. Predicting which patients will progress to kidney failure, and how quickly, is difficult. Multiple novel therapies are likely to be approved in the short-term, but clinicians lack the tools to identify patients most likely to benefit from specific treatments at the right time. Noninvasive and validated markers for selecting at-risk patients and longitudinal monitoring are urgently needed. This review summarizes what is known about demographic, clinical, and histopathologic prognostic markers in the clinician's toolkit, including the International IgAN Prediction Tool. We also briefly review what is known on these topics in children and adolescents with IgAN. Although helpful, currently used markers leave clinicians heavily reliant on histologic features from the diagnostic kidney biopsy and standard clinical data to guide treatment choice, and very few noninvasive markers reflect treatment efficacy over time. Novel prognostic and predictive markers are under clinical investigation, with considerable progress being made in markers of complement activation. Other areas of research are the interplay between gut microbiota and galactose-deficient IgA1 expression; microRNAs; imaging; artificial intelligence; and markers of fibrosis. Given the rate of therapeutic advancement, the remaining gaps in biomarker research need to be addressed. We finish by describing our route to clinical utility of predictive and prognostic markers in IgAN. This route will provide us with the chance to improve IgAN prognosis by using robust, clinically practical markers to inform patient care.

The complement system in IgAN: mechanistic context for therapeutic opportunities

The complement system plays a crucial role in innate immunity, providing essential defense against pathogens. However, uncontrolled or prolonged activation of the complement cascade can significantly contribute to kidney damage, especially in cases of glomerulonephritis. Immunoglobulin A nephropathy (IgAN), the most prevalent form of primary glomerulonephritis, has growing evidence supporting the involvement of complement alternative and lectin pathways. In fact, patients with IgAN experience complement activation within their kidney tissue, which may be involved in the development of glomerular damage and the progression of IgAN. Complement activation has emerged as a significant area of interest in IgAN, with numerous complement-targeting agents currently being explored within this field. Nevertheless, the exact mechanisms of complement activation and their role in IgAN progression require comprehensive elucidation. This review seeks to contextualize the proposed mechanisms of complement activation within the various stages ("hits") of IgAN pathogenesis, while also addressing the clinical implications and anticipated outcomes of complement inhibition in IgAN.

Clinicopathological characteristics, risk factors and prognostic value of intrarenal vascular lesions in IgA nephropathy

BACKGROUND

The aim was to study clinicopathological characteristics, risk factors and renal outcome in IgA nephropathy (IgAN) patients with vascular lesions.

METHODS

We enrolled a Chinese cohort with 458 biopsy-confirmed primary IgAN patients for a retrospective analysis. They were divided into three groups according to vascular lesions: no vascular lesions (n = 239), arterio-/arteriolosclerosis (n = 181) and microangiopathic lesions (n = 38). The clinicopathological features and renal outcome were recorded. In univariate and multivariate models, association between vascular lesions and renal outcome and vascular lesions associated clinical factors were analyzed.

RESULTS

Patients with vascular lesions presented worse clinical characteristics with regard to blood pressure and kidney function, and segmental glomerulosclerosis (S1), tubular atrophy/interstitial fibrosis (T1/2) and lymphocytes and monocytes infiltration were more common. Furthermore, older age, hyperuricemia, proteinuria, global glomerulosclerosis and endocapillary hypercellularity (E1) were more severe in patients with simple arterio-/arteriolosclerosis. By multivariate logistic regression, age, MAP and eGFR were significantly associated with vascular lesions. Vascular lesions, especially arterio-/arteriolosclerosis, were significantly associated with poorer renal survival in IgAN patients, and renal survival was similar whether patients with arterio-/arteriolosclerosis received immunosuppressive therapy. In addition to eGFR, arterio-/arteriolosclerosis, along with arterial intimal fibrosis, was an independent predictor for renal survival in multivariate Cox analyses.

CONCLUSION

IgAN patients with vascular lesions, especially with arterio-/arteriolosclerosis, presented more severe clinicopathological features. Renal function, blood pressure and age contributed to distinguishing patients with vascular lesions. Arterio-/arteriolosclerosis lesions were associated with poorer renal survival.

Plasma D-dimer as a potential predictor of progression in IgA nephropathy: a cohort study

INTRODUCTION

Coagulation disorders play a key role in chronic kidney disease, and the formation or elevation of plasma D-dimer levels reflects activation of the coagulation system. However, its relationship with the severity and progression of kidney disease in IgA nephropathy (IgAN) remains unclear.

METHODS

We assessed 1818 patients with IgAN diagnosed between 2002 and 2019 at the First Affiliated Hospital, Zhejiang University School of Medicine. Plasma D-dimer levels were measured at the time of the renal biopsy. The association between plasma D-dimer levels and kidney disease progression events, defined as a 50% decline in eGFR and end-stage kidney disease (ESKD), was tested using restricted cubic splines and Cox proportional hazard models.

RESULTS

The median plasma D-dimer level was 220 (170-388.5) µg/L FEU, which was significantly higher than healthy controls 170 (170-202) µg/L FEU. Plasma D-dimer levels were positively correlated with proteinuria (r = 0.211, p < 0.001) and serum galactose-deficient IgA1 (r = 0.226, p = 0.004) and negatively correlated with eGFR (r=-0.127, p < 0.001) and Oxford T (p < 0.001) and C (p = 0.004) scores. After a median follow-up of 25.67 (13.03-47.44) months, 126 (6.93%) patients experienced composite kidney disease progression events. Higher plasma D-dimer levels were associated with an increased risk of kidney disease progression events (hazard ratio, 1.73; 95% confidence interval [95% CI], 1.40-2.23) per ln-transformed plasma D-dimer (p < 0.001), after adjustment for sex, age, proteinuria, Mean arterial pressure (MAP) and Oxford classification scores. In reference to the first tertile of plasma D-dimer, hazard ratios were 1.48 (95% CI, 0.76-2.88) for the second tertile, 3.03 (95% CI, 1.58-5.82) for the third tertile.

CONCLUSIONS

High plasma D-dimer levels were associated with the progression of kidney disease severity in IgA nephropathy.

A bibliometric analysis of complement in IgA nephropathy from 1991 to 2022

Introduction: IgA nephropathy is a common glomerular disease on a global scale, which has resulted in significant economic burdens. The complement system plays a vital role in enhancing the efficacy of antibodies and phagocytic cells in eliminating microbes and damaged cells, and promoting inflammation. Complement activation has been found to contribute to the progression of various renal diseases, including IgA nephropathy. Methods: In this study, a thorough analysis was conducted on publications related to complement in IgAN from 1991 to 2022, retrieved from the Web of Science Core Collection and Scopus database. The analysis focused on various aspects such as annual publications, country, institution, author, journal, keywords, and co-cited references, utilizing Citespace and Vosviewer. Results: A total of 819 publications were obtained, and while there were slight fluctuations in annual publications, an overall upward trend was observed. China, Japan and the United States were the leading countries in terms of publications, with China having the highest number of publications (201). Collaborative network analysis revealed that England, University of Alabama Birmingham, and Robert J Wyatt were the most influential country, institution, and author, respectively, in this field of research. Furthermore, the analysis of references and keywords indicated that complement activation contributes to IgAN, and immunosuppression in IgAN are a hot topic of research. Discussion: This study identifies current research hotspots and advanced tendencies in the study of complement in IgAN, providing scholars with crucial directions in this research area.

IgA Nephropathy: the Lectin Pathway and Implications for Targeted Therapy

Many patients with IgA nephropathy (IgAN) progress to end-stage kidney disease even with optimal supportive care. An improved understanding of the pathophysiology of IgAN in recent years has led to the investigation of targeted therapies with acceptable tolerability that may address the underlying causes of IgAN or the pathogenesis of kidney injury. The complement system - particularly the lectin and alternative pathways of complement - have emerged as key mediators of kidney injury in IgAN and possible targets for investigational therapy. This review will focus on the lectin pathway. Examination of kidney biopsies has consistently shown glomerular deposition of mannan-binding lectin (one of six pattern-recognition molecules that activate the lectin pathway) together with IgA1 in up to 50% of patients with IgAN. Glomerular deposition of pattern-recognition molecules for the lectin pathway is associated with more severe glomerular damage and more severe proteinuria and hematuria. Emerging research suggests that the lectin pathway may also contribute to tubulointerstitial fibrosis in IgAN, and that collectin-11 is a key mediator of this association. This review summarizes the growing scientific and clinical evidence supporting the role of the lectin pathway in IgAN and examines the possible therapeutic role of lectin pathway inhibition for these patients.

Complement factor H variants are associated with microangiopathy lesions in IgA nephropathy

BACKGROUND

Thrombotic microangiopathy (TMA) occurs in immunoglobulin A nephropathy (IgAN), and the pathogenesis is not known behind the endothelium injury. The genetic studies have indicated that complement factor H (CFH) and complement factor H-related protein genes (CFHRs)play a key role in IgAN. We perform a study to investigate the CFH /CFHRs gene variants and their roles in IgAN with microangiopathy based on a previous genome-wide association study (GWAS).

METHODS

We re-review microangiopathic lesions in 2055 IgAN patients by light microscopy. And 204 IgAN patients with MA and 1851 IgAN without MA are confirmed in this study. Nineteen single nucleotide polymorphisms (SNPs) across CFH and CFHRs genes information are extracted from GWAS data.

RESULTS

The results show that 204 out of 2055(9.93 %) MA patients are screened from our IgAN cohort. Patients with MA lesions are strongly associated with more severe clinical conditions and higher serum complement factor H (FH) levels than IgAN without MA(MA vs IgAN-non MA:428.16 ± 141.05 vs 364.62 ± 139.06ug/mL, p = 0.004). The genetic association study indicates the frequency of rs800292-G in CFH was significantly higher in the MA group (0.441 vs 0.374, odds ratio1.37[1.07-1.62], p = 0.010) compared with IgAN without MA. In addition, patients with the rs412852-G allele in CFH become an independent risk factor for end-stage renal disease (ESRD)in MA patients (Hazard Ratio 2.77[1.17-6.65], p = 0.021). However, the gene variants did not correlate with serum FH, serum C3, and C3 deposits in the renal specimens.

CONCLUSION

Our results indicated that variants in CFH are associated with the development and progression of IgAN with microangiopathy.