Predictive prognostic value of glomerular C3 deposition in IgA nephropathy

Role of serum complement C3 and C4 on kidney outcomes in IgA nephropathy

IgA Nephropathy (IgAN) is the most prevalent glomerular disease worldwide. Complement system activation is crucial in its pathogenesis. Few studies correlated serum C3 and C4 with disease activity and prognosis. This retrospective study investigated the prognostic value of serum complement at the time of diagnosis in patients with IgAN. Specifically we evaluated whether adding serum C3 and C4 levels to established predictive models-one based on variables related to chronic kidney disease (CKD) progression and another incorporating variables from the International IgA Prediction Tool (IntIgAPT)-enhances the accuracy of outcome prediction. A composite renal outcome was defined as 50% decline in eGFR or onset of kidney failure. 101 patients were stratified according to baseline C3 levels in three groups (Low, Medium and High). During a median follow-up of 54 months, the Low group exhibited higher incidence of primary outcome (16.3 events vs 2.9 and 1.7 events × 100 pts/year, p = 0.0026). Model-1 (M1), consisting of CKD progression variables, and Model-3 (M3), comprising IntIgANPT variables, were implemented with baseline C3 and C4 to create Model-2 (M2) and Model-4 (M4), respectively. M2 demonstrated better predictive performance over M1, showing higher discrimination (lower AIC and BIC, higher C-index and NR2). Similarly, M4 outperformed M3, showing enhanced outcome prediction when C3 and C4 levels were added. Implementation of serum C3 and C4 can enhance prediction accuracy of already-validated prognostic models in IgAN. Lower C3 and higher C4 levels were associated with poorer prognosis, highlighting a more 'Complement-Pathic' subset of patients.

Could mesangial C3 deposition be an independent prognostic marker in immunoglobulin A nephropathy?

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is a common primary glomerulonephropathy. There is evidence that mesangial C3 deposition plays a role in the development of the disease. The aim of this study was to examine the effect of C3 deposition on the prognosis of IgAN patients.

METHOD

The study included 1135 patients with biopsy-confirmed IgAN from the database of the Turkish Nephrology Association Glomerular Diseases Working Group (TSN-GOLD). Patients were excluded from the study if they were aged < 18 or > 75 years or if C3 staining had not been performed in the immunofluorescent analysis. C3 deposition was defined as an immunofluorescence intensity of C3 ≥ 2 + within the mesangium. The primary endpoints were the development of end-stage renal disease, a 30% decrease in glomerular filtration rate compared to the basal value or an elevation in proteinuria to a nephrotic level (3.5 gr/day).

RESULTS

Mesangial C3 deposition was observed in 603 (53.1%) patients. No statistically significant difference was found at baseline between the groups with and without mesangial C3 deposition, as for age, sex, BMI, proteinuria level, or the presence of hypertension. In the follow-up period with a mean duration of 78 months, no significant difference was found between the two groups regarding the primary endpoints (p = 0.43). A significant correlation between C3 deposition and segmental glomerulosclerosis (S1) according to the Oxford MEST-C classification was found (p = 0.001).

CONCLUSION

Although a correlation was observed between mesangial C3 deposition and the S1 MEST-C classification, mesangial C3 deposition was not a prognostic factor in IgAN.

Non-enzymatic glycation and diabetic kidney disease

Chronic diabetes leads to various complications including diabetic kidney disease (DKD). DKD is a major microvascular complication and the leading cause of morbidity and mortality in diabetic patients. Varying degrees of proteinuria and reduced glomerular filtration rate are the cardinal clinical manifestations of DKD that eventually progress into end-stage renal disease. Histopathologically, DKD is characterized by renal hypertrophy, mesangial expansion, podocyte injury, glomerulosclerosis, and tubulointerstitial fibrosis, ultimately leading to renal replacement therapy. Amongst the many mechanisms, hyperglycemia contributes to the pathogenesis of DKD via a mechanism known as non-enzymatic glycation (NEG). NEG is the irreversible conjugation of reducing sugars onto a free amino group of proteins by a series of events, resulting in the formation of initial Schiff's base and an Amadori product and to a variety of advanced glycation end products (AGEs). AGEs interact with cognate receptors and evoke aberrant signaling cascades that execute adverse events such as oxidative stress, inflammation, phenotypic switch, complement activation, and cell death in different kidney cells. Elevated levels of AGEs and their receptors were associated with clinical and morphological manifestations of DKD. In this chapter, we discussed the mechanism of AGEs accumulation, AGEs-induced cellular and molecular events in the kidney and their impact on the pathogenesis of DKD. We have also reflected upon the possible options to curtail the AGEs accumulation and approaches to prevent AGEs mediated adverse renal outcomes.

The Clinical and Pathological Effects of Serum C3 Level and Mesangial C3 Intensity in Patients with IgA Nephropathy

Objective

To investigate the clinical and pathological effects of serum C3 level, mesangial C3 deposition intensity and blood lipid on IgA nephropathy.

Methods

According to the deposition intensity of immunofluorescence (IF) complement C3 in mesangial region, a total of 151 patients were divided into: (1) negative group (65 cases), (2) weak positive group (51 cases), and (3) strong positive group (35 cases). According to the level of serum C3, the patients were divided into two groups: (1) 33 patients with decreased serum C3 (<85 mg/dL); (2) 118 patients with normal serum C3. The clinicopathological data of the patients were analyzed retrospectively according to the groups.

Results

(1) With the increase of C3 deposition in mesangial region, the mean value of serum C3 level decreased, and the difference was statistically significant (P=0.001). (2) Compared with the normal serum C3 group, the blood urea nitrogen (BUN), serum creatinine (Scr), and albumin (Alb) in the serum C3 decreased group were higher, and the differences were statistically significant (P < 0.05), while the fasting blood glucose (FBG), low-density lipoprotein (LDL), triglyceride and 24-hr urinary protein (24hUTP) were lower, which difference was statistically significant (P < 0.05). (3) Compared with negative group and weak positive group, BUN, uric acid (UA), and Scr were higher in the strong positive group with C3 deposition, while eGFR was lower, with statistical significance (P < 0.05). However, C3 deposition in the mesangial region was related to T and enhanced mesangial C3 deposition was associated with more severe tubular atrophy and/or interstitial fibrosis, with statistically significant differences (P=0.001).

Conclusion

Patients with strong mesangial C3 deposition and elevated lipid levels had more severe tubule atrophy and/or interstitial fibrosis, as well as more severe pathological lesions, suggesting that activation of the complement system is involved in the pathogenesis of IgA nephropathy and increases the metabolic burden of the kidney.

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.

Clinical significance of IgM and C3 deposition in children with primary immunoglobulin A nephropathy

BACKGROUND

Mesangial IgM and C3 deposition is commonly observed in patients with primary immunoglobulin A nephropathy (IgAN), but its characteristics and prognosis have rarely been reported. The aim of this study was to investigate the relationship between combined mesangial IgM and C3 deposition and disease progression in children with IgAN.

METHODS

One hundred sixteen children diagnosed with IgAN between 2016 and 2020 were selected. Renal biopsies were scored by Oxford classification including the presence of mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis and crescents. The primary renal outcome was an event of either ≥ 50% reduction of eGFR from the baseline value or the onset of end-stage renal disease within the follow-up period. Cox regression analysis was performed to examine the effect of the combined mesangial IgM and C3 deposition on renal outcomes.

RESULTS

Forty-seven (40.52%) patients presented combined mesangial IgM and C3 deposition. Compared with children without combined IgM and C3 deposition, children with combined IgM and C3 deposition presented higher mesangial hypercellularity, endocapillary hypercellularity and cresentic lesions in kidney biopsies, and higher prevalence of renal dysfunction (19.15% versus 2.90%; P = 0.007). Renal outcome was also significantly worse as revealed by Kaplan-Meier curves (P = 0.0034). Multivariable Cox analysis identified tubular atrophy/interstitial fibrosis lesions [hazard ratio (HR) 14.843, 95% CI, 3.497-62.997, P < 0.001] and intensity of IgM deposition (HR 2.838, 95% CI, 1.321-6.094, P = 0.007) as independent risk factors for poor renal function.

CONCLUSIONS

Combined mesangial IgM and C3 deposition was associated with unfavorable histopathological features. Mesangial IgM deposition was an independent risk factor for poor renal outcomes in children with primary IgAN.

Eculizumab as a therapeutic approach for severe crescentic recurrence of immunoglobulin A nephropathy after kidney transplantation

Crescentic forms of immunoglobulin A nephropathy (IgAN) are rare but can be associated with rapid kidney failure and a high rate of end-stage renal disease despite immunosuppression therapy. Complement activation has emerged as a key driver of glomerular injury in IgAN. Therefore, complement inhibitors may be a rational treatment option in patients unresponsive to first-line immunosuppressive therapy. Here, we describe the case of a 24-year-old woman presenting with crescentic IgAN recurrence a few months after living kidney transplantation. Considering the dramatic graft failure accompanied by malignant hypertension and thrombotic microangiopathy features worsening after a first-line of high-dose steroids and 3 sessions of plasma exchanges, eculizumab was started as a rescue therapy. For the first time, the clinical response to eculizumab was highly successful, with a complete graft recovery without any relapse after 1 year of treatment. Further clinical studies are strongly needed to specify which patients might benefit from terminal complement blockade.

Challenges in IgA Nephropathy Management: An Era of Complement Inhibition

IgA nephropathy (IgAN) is the most common glomerular disease worldwide, with an estimated annual incidence of 25 per million adults. Despite optimized supportive care, some patients fail to achieve disease control and suffer progressive deterioration of kidney function. In this subpopulation of patients, the Kidney Disease: Improving Global Outcomes 2021 guidelines recommend consideration of corticosteroids; however, their use is associated with significant side effects. Ongoing clinical trials are expected to identify corticosteroid-sparing therapies to help improve treatment and prognosis for patients with IgAN. It has been well-documented that the complement system plays a significant role in IgAN pathogenesis, and several complement inhibitors are now entering late-stage clinical development. This review evaluates what we know about the role of complement in the pathophysiology of IgAN and considers how the availability of targeted complement inhibitors may impact future clinical practice. Key knowledge gaps are evaluated, and research opportunities are recommended to help guide clinical decision-making and optimize patient outcomes. Such gaps include evaluating the relative contribution of the alternative and lectin pathways to disease pathogenesis, and the importance of determining the dominant pathway driving IgAN progression. Continued research into the staining of complement proteins in kidney biopsies and identifying targeted biomarkers to assess disease progression and treatment responses will also be needed to support the implementation of newer therapies in clinical practice. Considering the future horizons for enhancing the care of patients with IgAN, tackling the outstanding challenges now will help prepare for the best possible future outcomes.

IgA Nephropathy: Current Treatment and New Insights

IgA Nephropathy (IgAN) is the most common cause of primary glomerulonephritis worldwide. Despite the histopathologic hallmark of mesangial IgA deposition, IgAN is a heterogenous autoimmune disease not only in terms of clinical presentation but also in long-term disease progression. The pathogenesis of the disease is complex and includes the generation of circulating IgA immune complexes with chemical and biological characteristics that favor mesangial deposition and reaction to mesangial under-glycosylated IgA1 accumulation, which leads to tissue injury with glomerulosclerosis and interstitial fibrosis. Patients with proteinuria over 1 g, hypertension, and impaired renal function at diagnosis are considered to be at high risk for disease progression and end-stage kidney disease (ESKD). Glucocorticoids have been the mainstay of treatment for these patients for years, but without long-term benefit for renal function and accompanied by several adverse events. A better understanding of the pathophysiology of IgAN in recent years has led to the development of several new therapeutic agents. In this review, we summarize the current therapeutic approach for patients with IgAN as well as all novel investigational agents.

Roles of mesangial C3 and C1q deposition in the clinical manifestations and prognosis of IgAN

BACKGROUND AND AIM

Immunoglobulin A nephropathy (IgAN) is regarded as the most common type of glomerulonephritis around the world and has the potential to result in renal failure. Complement activation has been addressed by a great body of evidence in the pathogenesis of IgAN. We aimed to evaluate the predictive value of C3 and C1q deposition for disease progression in IgAN patients in this retrospective study.

METHODS

We recruited 1191 biopsy-diagnosed IgAN patients, and they were divided into different groups according to their glomerular immunofluorescence examination of renal biopsy tissues: 1) C3 deposits ≥ 2 + group (N = 518) and C3 deposits < 2 + group (N = 673). 2) C1q deposit-positive group (N = 109) and C1q deposit-negative group (N = 1082). The renal outcomes were end-stage renal disease (ESRD) and/or an estimated glomerular filtration rate (eGFR) decrease greater than 50% from the baseline value. Kaplan-Meier analyses were performed to evaluate renal survival. Univariate and multivariate Cox proportional hazard regression models were used to evaluate the effect of C3 and C1q deposition on renal outcome in IgAN patients. In addition, we compared the predictive value of mesangial C3 and C1q deposition in IgAN patients.

RESULTS

The median follow-up period was 53 months (interquartile range 36-75 months). During follow-up, 7% (84) of patients progressed to ESRD, and 9% (111) of patients had an eGFR decline ≥ 50%. IgAN patients complicated with C3 deposits ≥ 2 + were associated with more severe renal dysfunction and pathologic lesions at the time of renal biopsy. The crude incidence rates for the endpoint were 12.5% (84 out of 673) and 17.2% (89 out of 518) in the C3 < 2 + and C3 ≥ 2 + groups, respectively (P = 0.022). Of C1q deposit-positive and C1q deposit-negative patients, 22.9% (25 out of 109) and 13.7% (148 out of 1082) reached the composite endpoint, respectively (P = 0.009). Adding C3 deposition to clinical and pathologic models had better predictability of renal disease progression than C1q.

CONCLUSION

Glomerular C3 and C1q deposits affected the clinicopathologic features of IgAN patients and emerged as independent predictors and risk factors for renal outcomes. In particular, the predictive ability of C3 was slightly better than that of C1q.