Hypocomplementemia at Diagnosis of Pauci-immune Glomerulonephritis Is Associated With Advanced Histopathological Activity Index and High Probability of Treatment Resistance

Current Understanding of the Pathogenesis of ANCA-Associated Vasculitis and Novel Treatment Options Targeting Complement Activation

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (ANCA-vasculitis) is an autoimmune disease characterized by inflammation and necrosis of small or medium vessels. In the past, the role of the complement in the pathogenesis of ANCA-vasculitis has been underestimated, due to the paucity of the complement at sites of injured glomeruli. Following evidence from animal models of the major role of the complement in pathogenesis of ANCA-vasculitis, the complement has again attracted interest. Immunohistology analysis of pauci-immune glomerulonephritis-ANCA glomerulonephritis (ANCA-GN)-reveals the presence of complement products and membrane attack complex, suggesting their involvement in the disease process. Researchers emphasize the complement classical or lectin pathway as a contributor to the development of ANCA-vasculitis. The era of targeted therapies to suspend the complement activation as a therapy for ANCA-vasculitis has arrived, and thus, the comprehension of its role is very important. This review summarizes recent insights on the important role of complement activation in the development of ANCA-vasculitis as well as the emerging therapeutic possibilities that target complement components for the treatment of this condition.

Evaluating Avacopan in the Treatment of ANCA-Associated Vasculitis: Design, Development and Positioning of Therapy

Recently, avacopan has been approved for the treatment of ANCA-associated vasculitis (AAV). Avacopan is an inhibitor of the C5a-receptor, which plays an important role in chemotaxis and the amplification loop of inflammation in AAV. In the most recent, international guidelines avacopan is recommended as steroid-sparing agents for the management of AAV. Here, we review the clinical trials that have led to demonstrate that avacopan is an effective treatment option in the management of AAV, where it can significantly reduce the cumulative dosage of glucocorticoids (GC). Despite the new guideline recommendations, clear guidance on how to employ avacopan in real-world clinical practice is lacking. We therefore also address in this review the data and clinical experience with avacopan obtained from real-world evidence. Combining preclinical studies, clinical trials, and real-world evidence helps to provide a better position of avacopan for the management of AAV in routine clinical practice, taking advantage of the GC-sparing effects of avacopan as a possible solution for the current challenge of reducing GC-toxicity in AAV patients. Furthermore, we delineate current knowledge gaps and future research areas that need to be addressed.

Serum Uric Acid Associates with Systemic Complement C3 Activation in Severe ANCA-Associated Renal Vasculitides

Involvement of the complement system is key to the pathogenesis of antineutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis, but immunometabolic implications, especially on serum uric acid (UA) levels, still need to be elucidated. A total of 34 patients with biopsy-proven ANCA-associated renal vasculitis between 2015 and 2020 were retrospectively enrolled. Serum UA levels were correlated with clinical and histopathological characteristics, separated for critically ill (CI, n = 19), myeloperoxidase (MPO)-ANCA (n = 21) and proteinase 3 (PR3)-ANCA (n = 13) subgroups. We here identified inverse correlations of serum UA levels and complement C3 levels in the total cohort (p = 0.005) and the CI subgroup (p < 0.001). Intrarenal complement C4d deposition in venules correlated with serum UA levels in the total cohort (p = 0.007) and in the CI subgroup (p = 0.016). Significant associations of serum UA levels and tubulitis in areas of scarred cortex (t-IFTA) were identified in the total cohort (p = 0.008), and both subgroups of CI (p = 0.034) and MPO-ANCA (p = 0.029). In PR3-ANCA, interstitial fibrosis (ci) was observed as the strongest association with serum UA levels (p = 0.022). Our observations broaden our current understanding of contributory metabolic factors that influence the initial disease course in ANCA-associated renal vasculitis.

Evaluation of hypertension in systemic sclerosis and systemic lupus erythematosus overlap

Patients with systemic sclerosis and systemic lupus erythematosus serologies present a unique challenge to the clinician when hypertension is detected in the outpatient setting. Treatment choices for non-renal crisis hypertension are different for systemic sclerosis versus systemic lupus erythematosus. Urgent laboratory studies and, in the presence of certain symptoms, imaging assessment are indicated in systemic sclerosis and systemic lupus erythematosus overlap patients with systemic hypertension. Long-term assessment of systemic hypertension may be enhanced by advances in non-contrast imaging that serve as valuable biomarkers for progressive vasculopathy. In this review, the diagnostic approach to systemic sclerosis and systemic lupus erythematosus overlap patients presenting with hypertension is discussed.

Comparative analysis of complement C3 and C4 serum levels for outcome prediction in ANCA-associated renal vasculitis

BACKGROUND

The activation of the complement system contributes essentially to the pathogenesis of anti-neutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis. We here aimed to directly compare levels of C3 and C4 for outcome prediction in ANCA-associated renal vasculitis.

METHODS

Serum levels of complement components C3 and C4 were directly compared in association with clinical and outcome data in a retrospective cohort of ANCA-associated renal vasculitis.

RESULTS

As compared to poor outcome prediction by low levels of complement C3 (p = 0.0093), low levels of complement C4 did not associate with early requirement of kidney replacement therapy (KRT) or death (p = 0.2396). In the subgroup that experienced KRT or death, low C3 levels identified 11/14 (78.6%, p = 0.0071) and C4 levels 9/14 (64.3%, p = 0.1786) cases. Interestingly, 2/14 (14.3%) patients that experienced KRT or death had isolated C4 lowering, and combining low C3 and/or C4 levels identified 13/14 (92.3%, p < 0.0001) cases in this subgroup. Non-superiority to predict poor outcome by low C3 and/or C4 as compared to C3 alone in the total cohort was attributed to 4/24 (16.7%) patients with isolated C4 lowering in the subgroup that did not experience KRT or death.

CONCLUSION

While low levels of complement C3 were superior in predicting poor outcome in ANCA-associated renal vasculitis, a minor fraction with poor outcome had isolated C4 lowering not captured by serum C3 measurements. Therefore, detailed knowledge of distinct complement components contributing to kidney injury could be of relevance to improve current strategies targeting the complement system in ANCA-associated renal vasculitis.

Old known and possible new biomarkers of ANCA-associated vasculitis

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) comprises a group of multisystem disorders involving severe, systemic, small-vessel vasculitis with short- and long term serious and life-threating complications. Despite the simplification of treatment, fundamental aspects concerning assessment of its efficacy and its adaptation to encountered complications or to the relapsing/remitting/subclinical disease course remain still unknown. The pathogenesis of AAV is complex and unique, and despite the progress achieved in the last years, much has not to be learnt. Foremost, there is still no accurate marker enabling us to monitoring disease and guide therapy. Therefore, the disease management relays often on clinical judgment and follows a" trial and error approach". In the recent years, an increasing number of new molecules s have been explored and used for this purpose including genomics, B- and T-cell subpopulations, complement system factors, cytokines, metabolomics, biospectroscopy and components of our microbiome. The aim of this review is to discuss both the role of known historical and clinically established biomarkers of AAV, as well as to highlight potential new ones, which could be used for timely diagnosis and monitoring of this devastating disease, with the goal to improve the effectiveness and ameliorate the complications of its demanding therapy.

Implication of platelets and complement C3 as link between innate immunity and tubulointerstitial injury in renal vasculitis with MPO-ANCA seropositivity

Introduction

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a potentially life-threatening systemic small-vessel vasculitis that is characterized by pauci-immune glomerulonephritis, depicting in turn a major denominator of AAV mortality. It is well established that AAV patients feature an increased risk of developing thrombotic events, and platelets are activated in AAV patients being triggered by the alternative complement pathway. Platelets guard vessels integrity and initiate thrombus formation in response to endothelial damage, further constituting a triangular interconnection with the activation of neutrophils and the complement system. We here aimed to systematically assess the relevance of platelet counts and systemic complement system activation regarding distinct histopathological lesions in ANCA-associated renal vasculitis.

Methods

A cohort of 53 biopsy-proven cases of ANCA-associated renal vasculitis were retrospectively enrolled in a single-center observational study. Univariate and multivariate regression analysis was performed to identify parameters associated with platelet counts in ANCA-associated renal vasculitis compared to disease controls. Finally, the relevance of platelets for disease course and recovery was assessed by survival analysis.

Results

Lower platelet counts correlated with markers of kidney injury including eGFR loss (p=0.0004) and lower complement C3 levels (p=0.0037). Multivariate and subgroup analysis revealed that this association was only present in the subgroup with MPO-ANCA seropositivity (eGFR loss: p=0.0009, lower C3: p=0.0032). While lower platelet counts correlated with kidney injury in the PR3-ANCA subgroup (eGFR loss: p=0.0272), we did not observe an independent association with complement C3 levels (p=0.4497). Independent of any glomerular lesion, lower platelet counts correlated with interstitial fibrosis (p=0.0313), tubular atrophy (p=0.0073), and tubulitis in areas of interstitial fibrosis and tubular atrophy (p=0.0033). Finally, we observed significant differences with increased requirement of kidney replacement therapy (KRT) or death in the subgroup below median platelet counts (HR: 4.1, 95% CI: 1.6-10, p=0.0047), associated with a lower probability of discharge and prolonged hospitalization in this subgroup (HR: 0.5, 95% CI: 0.3-0.9, p=0.0113).

Conclusion

Based on our observation that an association between platelets and complement system activation is only observed in the MPO-ANCA subgroup, this could implicate that platelets and complement C3 link innate immunity to tubulointerstitial injury in the presence of MPO-ANCA autoantibodies.

Relationship Between Serum Complement C3 Levels and Outcomes Among Patients With Anti-GBM Disease

Background

IgG and complement 3 (C3) are generally found to be deposited along the glomerular basement membrane (GBM) in human anti-GBM disease. The pathogenic role of complement activation in kidney damage of anti-GBM disease has been explored in recent years. Therefore, we investigated the relationship between serum C3 and outcomes among patients with anti-GBM disease in this study.

Methods

Ninety-four anti-GBM disease patients between January 2004 and December 2020 at the National Clinical Research Center of Kidney Diseases Jinling Hospital were retrospectively analyzed, and were divided into the low C3 group and the normal C3 group according to serum C3 levels at diagnosis. Fifty-six patients had undergone renal biopsy. We analyzed the clinical manifestations, laboratory tests, kidney pathology, treatment, and outcomes between the two groups. The primary endpoint was kidney failure. Cox regression and smooth curve fitting of generalized additive mixed model analysis were used to explore the correlation between serum C3 and kidney failure. The outcomes of the two groups were compared by the Kaplan–Meier curve.

Results

A total of 94 patients (aged 43.6 ± 16.2; male patients, 46%) with anti-GBM disease were enrolled. There were 26 patients with low C3 levels and 68 patients with normal C3 levels. Compared with the normal C3 group, patients in the low C3 group have a higher proportion of glomerular sclerosis progressing to kidney failure. Multivariate Cox regression analysis suggested that C3 is associated with kidney outcomes in patients with anti-GBM disease (HR = 0.782, 95% CI = 0.673–0.907, p = 0.001). Smooth curve fitting of generalized additive mixed model analysis indicated that the level of C3 had a linear relationship with the changing trend of kidney failure. The Kaplan–Meier curve showed that there was a statistical difference between the two groups in terms of kidney failure (p = 0.033).

Conclusion

The kidney outcomes of anti-GBM disease in the low C3 group were poorer than those in the normal C3 group. The influence of C3 on the kidney outcomes of patients with anti-GBM disease may be of clinical relevance.

A meta-analysis of the safety and efficacy of maintenance therapies for anti-neutrophil cytoplasmic antibody small-vessel vasculitis

Introduction

To compare the efficacy and safety of different regimens used for maintenance of remission in patients with antineutrophil cytoplasmic antibody (ANCA) vasculitis.

Methods

This network meta-analysis studied adult patients with ANCA vasculitis in complete remission, who were maintained with various regimens, excluding patients with eosinophilic granulomatosis with polyangiitis (GPA) and those who have ended up in end-stage kidney disease. Outcomes of interest included relapse (any/major), relapse-free survival, and adverse effects. PubMed, Scopus, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, and Google Scholar were systematically searched from inception.

Results

Overall, the meta-analysis was based on 10 reports, describing the outcomes of 7 randomized controlled trials (RCTs) including 752 patients with ANCA vasculitis. Relapse-free survival was significantly worse with the use of azathioprine (hazard ratio [HR]: 2.11, 95% CI: 1.19–3.74), methotrexate (HR: 2.51, 95% CI: 1.24–5.08), and mycophenolate mofetil (HR: 3.57, 95% CI: 1.70–7.46) compared with the use of rituximab. Outcomes estimated for azathioprine (HR: 0.59, 95% CI: 0.37–0.94), cyclophosphamide (HR: 0.39, 95% CI: 0.20–0.75), and leflunomide (HR: 0.30, 95% CI: 0.11–0.84) were better than those for mycophenolate mofetil. When examining relapse-free survival, relapses were more likely with use of azathioprine (odds ratio [OR]: 2.15, 95% CI: 1.00–4.59) and mycophenolate mofetil (OR: 4.42, 95% CI: 1.63–11.94) compared with the use of rituximab. The risk of major relapse calculated for azathioprine (OR: 2.39, 95% CI: 1.10–5.19), methotrexate (OR: 3.18, 95% CI: 1.14–8.89), and mycophenolate mofetil (OR: 5.20, 95% CI: 1.65–16.37) was higher than that for rituximab. The rates of serious adverse effects did not differ significantly among interventions.

Conclusion

Rituximab appears predominant in maintaining remission in patients with ANCA vasculitis with no cost in adverse events.