OUP accepted manuscript

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.

Mesangial C3 Deposition, Complement-Associated Variant, and Disease Progression in IgA Nephropathy

BACKGROUND

IgA nephropathy is the most common primary GN worldwide, with dominant deposition of IgA and co-deposits of complement component 3 (C3). Phenotypes and progression of IgA nephropathy varies among different ethnic populations, while patients with IgA nephropathy from Asia showed more severe clinical phenotypes, active kidney lesions, and rapid progression. Our previous genome-wide association study identified complement factor H ( CFH ) variant rs6677604, tightly linked with the deletion of CFH -related protein 3 and CFH -related protein 1 genes ( ΔCFHR3-1 ), as IgA nephropathy susceptible variant, and additionally revealed its effect on complement regulation in IgA nephropathy.

METHODS

To further explore the effect of rs6677604 on IgA nephropathy progression, here we enrolled a Chinese IgA nephropathy cohort of 1781 patients with regular follow-up for analysis. The rs6677604 genotype was measured, and the genotype-phenotype correlation was analyzed using the t test, the chi-squared test, or the nonparametric test, and the association between rs6677604 genotype or mesangial C3 deposition and IgA nephropathy prognosis was analyzed using Kaplan-Meier analysis and Cox regression.

RESULTS

We found that patients with rs6677604-GG genotype had a stronger intensity of mesangial C3 deposition than those with the rs6677604-AA/AG genotype. Patients with IgA nephropathy who had stronger intensity of C3 deposition manifested with more severe clinical and pathological manifestations, including lower eGFR and higher Oxford-M/S/T/C (mesangial hypercellularity, endocapillary cellularity, segmental sclerosis, interstitial fibrosis/tubular atrophy, and crescent) scores. In the survival analysis, stronger intensity of mesangial C3 deposition, but not rs6677604-GG genotypes, was associated with poor long-term kidney outcome in IgA nephropathy.

CONCLUSIONS

We found that in Chinese patients with IgA nephropathy, variant rs6677604 was associated with mesangial C3 deposition, and mesangial C3 deposition, but not rs6677604, was associated with IgA nephropathy severity and progression.

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.

Application of urinary N-acetyl-β-D-glucosaminidase combined with serum retinol-binding protein in early detection of diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a microangiopathy of type 2 diabetes mellitus (T2DM), which can damage the kidney through various ways and mechanisms due to the nature of the disease, involving the renal interstitium and glomeruli. However, in the early stage of the disease, patients only showed kidney volume increase and glomerular hyperthyroidism, and typical symptoms that are difficult to arouse individual attention were noticed.

AIM

To observe the expression of serum retinol-binding protein (RBP) and urinary N-acetyl-β-D-glucosaminidase (NAG) in patients with DN, and to analyze their value in disease prediction, so as to provide new targets for early diagnosis and treatment of DN.

METHODS

The baseline data of 50 T2DM patients treated in our hospital between January 2021 and December 2022 were retrospectively reviewed and included in group A. The baseline data of 50 patients with type 2 DN admitted to our hospital during the same period were collected and included in group B. The baseline data and serum RBP and urine NAG expression were compared between the two groups to analyze their value in the early prediction of DN.

RESULTS

There was no significant difference in age, gender, duration of diabetes, combined hyperlipidemia and combined hypertension between the two groups (P > 0.05); the expression of urinary NAG and serum RBP in group B was higher than that in group A, and the difference was statistically significant (P < 0.05); a multiple logistic regression model was established, and the results showed that urinary NAG and serum RBP were related to the presence or absence of injury in diabetic patients, and overexpression of urinary NAG and serum RBP may be risk factors for renal injury in T2DM patients (OR > 1, P < 0.05); receiver operating curve curve was plotted, and the results showed that the area under the curve of urinary NAG and serum RBP expression alone and in combination for predicting DN was > 0.80, and the predictive value was satisfactory; bivariate Spearman linear correlation analysis showed that there was a positive correlation between urinary NAG and serum RBP expression in patients with DN (r = 0.566, P = 0.000).

CONCLUSION

The increased expression of urinary NAG and serum RBP may be the risk factors leading to the progression of T2DM to DN. The possibility of DN can be considered in patients with urinary NAG and serum RBP overexpression by examining the expression of urinary NAG and serum RBP in patients with T2DM in clinical practice.

Association between glomerular C4d deposition, proteinuria, and disease severity in children with IgA nephropathy

BACKGROUND

C4d may be used as a marker to evaluate the condition and prognosis of adults with IgA nephropathy, but there have been few studies of children with IgA nephropathy.

METHODS

C4d immunohistochemical staining was performed on samples from children with IgA nephropathy with C1q-negative immunofluorescence. The clinical and pathological treatment and prognostic characteristics of children in the C4d-positive and -negative groups were compared.

RESULTS

A total of sixty-five children with IgA nephropathy were included in the study and were followed up for an average of 37 months. C4d was mainly deposited along the capillary loops. The urinary protein-to-creatinine ratio (UPCR) in the C4d-positive group was significantly higher than that in the C4d-negative group (3.97 vs. 0.81, P < 0.001), and the average integrated optical density value of each child was positively correlated with the UPCR (r = 0.441, P < 0.001). There was a significant difference in the proportions of children with mesangial hypercellularity (M1) (68.97% vs. 44.44%, P = 0.048) and segmental glomerulosclerosis (S1) (65.52% vs. 33.33%, P = 0.010) between the C4d-positive group and the C4d-negative group. The proportion of children who received immunosuppressants in the C4d-positive group was higher than that in the C4d-negative group (86.21% vs. 36.11%, P < 0.001). There was no significant difference in the proportion of children developing kidney failure between the two groups.

CONCLUSION

C4d was found to be associated with proteinuria, segmental lesions, and immunosuppressant treatment. Activation of the lectin pathway may reflect the severity of clinical and pathological manifestations of IgA nephropathy in children. A higher resolution version of the Graphical abstract is available as Supplementary information.