Histopathological Findings Predict Renal Recovery in Severe ANCA-Associated Vasculitis Requiring Intensive Care Treatment

Relevance of histopathological findings for predictive scoring of short-term treatment response to plasma exchange in severe ANCA-associated renal vasculitides

Introduction

Rapidly progressive glomerulonephritis (RPGN) is characterized by a rapid loss of kidney function, affecting both renal and overall patient survival. Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a small vessel vasculitis affecting multiple organ systems including the kidney, and among most frequent causes of RPGN. We here aimed to validate a recently described scoring system for short-term treatment response to therapeutic plasma exchange (PLEX) in a well-characterized and independent cohort of severe renal AAV presenting with RPGN. Furthermore, we compared this scoring with established classification systems in renal AAV including histopathological findings.

Methods

We here directly compare the scoring system with retrospective data about PLEX treatment in our own clinical practice and according to current recommendations in a cohort of 53 patients with severe AAV presenting with RPGN confirmed by kidney biopsy.

Results

We here confirm that PLEX scoring is capable to identify patients at risk for short-term poor outcome in severe AAV presenting with RPGN (p<0.0001). Furthermore, multiple stepwise regression analysis revealed that the PLEX score with renal biopsy performed best to predict poor outcome in this patient population (p<0.0001).

Conclusion

Our observations underscore the relevance of performing a kidney biopsy in this patient population that is often challenged in the setting of intensive care treatment, requirement of KRT with need for anticoagulation and bleeding risk. Therefore, validation of our observations and this recent scoring system for treatment response to PLEX in independent cohorts would be of great clinical relevance in the treatment of patients with severe AAV presenting with RPGN.

Low hemoglobin levels are associated with Bowman's capsule rupture and peritubular capillaritis in ANCA-associated renal vasculitis: a link of vascular injury to anemia?

BACKGROUND

Anemia in anti-neutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis is a severe complication that predicts renal survival. We here conducted correlative analyses to evaluate correlations of low hemoglobin levels and histopathological characteristics in ANCA-associated renal vasculitis.

METHODS

Fifty-two patients with biopsy-proven ANCA-associated renal vasculitis observed between 2015 and 2020 were retrospectively evaluated. Spearman's correlation was performed to assess correlations, and statistical evaluation was performed by simple and stepwise multivariable regression.

RESULTS

Regarding laboratory anemia parameters, no significant association with serum hemoglobin levels was observed. Serum hemoglobin levels were associated with the estimated glomerular filtration rate in the total cohort (β = 0.539, p < 0.001), and in the MPO-ANCA subgroup (β = 0.679, p = 0.008). Among tubulointerstitial lesions, decreased serum hemoglobin levels correlated with peritubular capillaritis in the whole cohort (β = - 0.358, p = 0.013), and was suggested in the MPO-ANCA subgroup (p = 0.029, r = - 0.446). Regarding glomerular lesions, the prevalence of necrotic glomeruli significantly associated with low serum hemoglobin levels in PR3-ANCA (β = - 0.424, p = 0.028). In the total cohort, a significant correlation between decreased serum hemoglobin levels and the occurrence of diffuse Bowman's capsule rupture was identified (β = - 0.374, p = 0.014), which was implied in the MPO-ANCA subgroup (p = 0.013, r = - 0.546; p = 0.0288, slope = - 16.65).

CONCLUSION

Peritubular capillaritis and Bowman's capsule rupture correlate with low hemoglobin levels; this may indicate that histopathological lesions are linked with inflammatory vascular injury and  relative erythropoietin deficiency in ANCA-associated renal vasculitis.

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.

Relevance of Complement C4 Deposits Localized to Distinct Vascular Compartments in ANCA-Associated Renal Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a small-vessel vasculitis affecting multiple organ systems, including the kidney. Small vessels in the kidney include small-sized arteries, capillaries, and venules. Intrarenal C4 deposits are now increasingly recognized as a potential marker and pathogenic mechanism of autoantibody-mediated tissue damage in ANCA-associated renal vasculitis. We here describe the relevance of complement C4 deposits localized to distinct vascular compartments in a cohort of biopsy-proven ANCA-associated renal vasculitis. A cohort of 43 biopsy-proven cases of ANCA-associated renal vasculitis with myeloperoxidase (MPO) or proteinase 3 (PR3) seropositivity were retrospectively enrolled in a single-center observational study. Univariate and multivariate regression analysis was performed to identify parameters associated with intrarenal C4 deposits in ANCA-associated renal vasculitis. We here show that C4 deposits localize to distinct vascular compartments in ANCA-associated renal vasculitis, and provide evidence for an association with better short-term survival (p = 0.008), implicating that this subgroup had a superior response to remission induction therapy. Second, C4 deposits in interlobular arteries were associated with eosinophilic infiltrates in renal vasculitis with MPO-ANCA seropositivity (p = 0.021). In renal vasculitis positive for MPO-ANCA, the absence of C4 deposits in the glomerular tuft was associated with sclerotic class ANCA-associated renal vasculitis (p < 0.001), and tubular RBC casts (p = 0.024). Fourth, complement C4 in interlobular arteries is associated with tubular atrophy specifically in renal vasculitis with PR3-ANCA seropositivity (p = 0.006). Finally, complement C4 deposits in peritubular capillaries associated specifically with hyaline casts in cases positive for PR3-ANCA (p = 0.025), implicating a role in tubular injury. Interestingly, C4 deposits were localized to distinct vascular compartments independent of the systemic activation of the complement system, reflected by the consumption of respective serum complement molecules in ANCA-associated renal vasculitis. In summary, we here show that C4 deposits localize to distinct vascular compartments in ANCA-associated renal vasculitis, and provide evidence for an association with survival and distinct histopathological lesions. Considering recent advances in AAV therapy with the emergence of new therapeutics that inhibit complement activation, we here provide novel insights into complement C4 as a potential marker to identify patients who may benefit most from these drugs. Thus, our results may contribute to a more personalized treatment approach of AAV depending on the relevance of distinct intrarenal complement deposits.

Low levels of hemoglobin associate with critical illness and predict disease course in patients with ANCA-associated renal vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a small vessel vasculitis often leading to critical illness by multi-organ failure. Data for patients with specifically ANCA-associated renal vasculitis requiring intensive care unit (ICU) supportive care are limited and have mainly focused on long-term renal and overall outcome. Particularly, data on critical illness during the initial course of disease are scarce and remain poorly determined. Therefore, the purpose of this retrospective study was to identify predictors of critical illness in a cohort of patients with ANCA-associated renal vasculitis. We retrospectively included a total number of 53 cases with confirmed ANCA-associated renal vasculitis between 2015 till 2020 in a single-center cohort study. We here identified an association between low hemoglobin levels and requirement of ICU supportive care in patients with ANCA-associated renal vasculitis. Furthermore, levels of hemoglobin below 9.8 g/dL at admission independently predicted prolonged requirement of ICU supportive care in critically ill patients with ANCA-associated renal vasculitis. These findings confirm that low levels of hemoglobin negatively affect short-term outcome and could further improve our current understanding for the role of anemia in ANCA-associated renal vasculitis.

Comparative Histological Subtyping of Immune Cell Infiltrates in MPO-ANCA and PR3-ANCA Glomerulonephritis

Background

Acute kidney injury (AKI) is a common and severe complication of anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV), potentially leading to chronic kidney disease (CKD), end-stage renal disease (ESRD), or death. Pathogenic ANCAs, in particular proteinase 3 (PR3) and myeloperoxidase (MPO), trigger a deleterious immune response with intrarenal immune cell infiltration resulting in a pauci-immune necrotizing and crescentic glomerulonephritis (GN). However, a systematic analysis of intrarenal immune cell subtypes concerning neutrophils, eosinophils, plasma cells, and mononuclear cell infiltrates (macrophages, lymphocytes) in ANCA GN remains elusive. Therefore, we aimed to compare distinct immune cell infiltrates in association with clinicopathological findings in ANCA GN.

Methods

A total of 53 kidney biopsies with ANCA GN at the University Medical Center Göttingen were retrospectively analyzed. Histological infiltrates of neutrophils, eosinophils, plasma cells, and mononucleated cells (macrophages, lymphocytes) were quantified as a fraction of the total area of inflammation.

Results

Neutrophilic infiltrates were associated with glomerular necrosis and severe kidney injury in ANCA GN. Among tubulointerstitial lesions, intrarenal neutrophils correlated with interstitial inflammation, tubulitis, and inflammation in areas of interstitial fibrosis/tubular atrophy (IFTA), representing active inflammatory lesions. Concerning eosinophils, infiltrates were associated with severe kidney injury, interstitial inflammation, and cellular casts independent of glomerular lesions, implicating a distinct role in inflammation and damage in ANCA GN. Plasma cell infiltrates correlated with tubulitis and interstitial fibrosis and were associated with renal replacement therapy during the short-term disease course. Finally, mononuclear cell infiltrates correlated with severe kidney injury and active histopathological lesions (glomerular crescents, interstitial inflammation, tubulitis, inflammation, and tubulitis in areas of IFTA) besides chronic lesions (interstitial fibrosis and tubular atrophy) in ANCA GN. Interestingly, intrarenal subtypes of immune cell infiltrates differed in MPO-ANCA versus PR3-ANCA GN and were associated with distinct glomerular and tubulointerstitial lesions, implicating different pathogenic mechanisms of kidney injury in ANCA subtypes.

Conclusion

Our observations imply distinct pathomechanisms contributing to inflammation and renal injury in MPO vs. PR3-associated ANCA GN and potentially contribute to new therapeutic targets in specific ANCA subtypes.

Comprehensive Analysis of Sex Differences at Disease Manifestation in ANCA-Associated Glomerulonephritis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a small vessel vasculitis affecting multiple organ systems, including the kidney. Besides investigations focusing on renal outcomes, sex differences associated with distinct clinical and histopathological findings in ANCA glomerulonephritis (GN) have not been systematically investigated. Therefore, we here aimed to systematically analyze sex differences in patients with AAV and biopsy-proven ANCA GN. We provide a comprehensive analysis of 53 kidney biopsies with ANCA GN retrospectively included between 2015 and 2020 and identified specific sex differences in ANCA GN concerning laboratory parameters and systematic scoring of renal histopathology glomerular and tubulointerstitial lesions, and extrarenal manifestations of AAV. We did not observe any correlation between sex and short-term clinical AAV course or disease severity by comparing general AAV parameters. AAV manifestations in females occurred at an older age with more joint involvement. Regarding histopathological findings, we, again, observed no sex difference among ANCA GN classification, but a significant correlation between females and distinct histopathological findings with less tubulointerstitial inflammation and vasculitis of peritubular capillaries. Finally, we here identified fewer associations between clusters of clinical, laboratory parameters, and histopathological findings in females as compared to males. These findings are of great relevance and further improve our understanding of sex differences in the pathogenesis of ANCA GN. While future studies about specific sex differences and conclusions in these clusters are crucial, our observations further support that sex differences are relevant, affect distinct parameters, and influence clinical, laboratory parameters, and histopathological findings in AAV, particularly ANCA GN.

Different Patterns of Kidney Fibrosis Are Indicative of Injury to Distinct Renal Compartments

Kidney fibrosis is a common manifestation and hallmark of a wide variety of chronic kidney disease (CKD) that appears in different morphological patterns, suggesting distinct pathogenic causes. Broad macroscopically visible scars are the sequelae of severe focal injury and complete parenchymal destruction, reflecting a wound healing response as a consequence of infarction. In the kidney, chronic glomerular injury leads to atrophy of the corresponding tubule, degeneration of this specific nephron, and finally interstitial fibrosis/tubular atrophy (IF/TA). Compared to this glomerulus-induced focal replacement scar, diffuse fibrosis independent of tubular atrophy appears to be a different pathogenic process. Kidney fibrosis appears to develop in a compartment-specific manner, but whether focal and diffuse fibrosis has distinct characteristics associated with other glomerular or tubulointerstitial lesions remains elusive. In the present study, we aimed to analyze renal fibrotic patterns related to renal lesions, which directly contribute to renal fibrogenesis, to unravel fibrotic patterns and manifestations upon damage to distinct renal compartments. Patterns of kidney fibrosis were analyzed in experimental models of CKD and various renal pathologies in correlation with histopathological and ultrastructural findings. After the induction of isolated crescentic glomerulonephritis (GN) in nephrotoxic serum-nephritis (NTN), chronic glomerular damage resulted in predominantly focal fibrosis adjacent to atrophic tubules. By contrast, using unilateral ureteral obstruction (UUO) as a model of primary injury to the tubulointerstitial compartment revealed diffuse fibrosis as the predominant pattern of chronic lesions. Finally, folic acid-induced nephropathy (FAN) as a model of primary tubular injury with consecutive tubular atrophy independent of chronic glomerular damage equally induced predominant focal IF/TA. By analyzing several renal pathologies, our data also suggest that focal and diffuse fibrosis appear to contribute as chronic lesions in the majority of human renal disease, mainly being present in antineutrophil cytoplasmic antibody (ANCA)-associated GN, lupus nephritis, and IgA nephropathy (IgAN). Focal IF/TA correlated with glomerular damage and irreversible injury to nephrons, whereas diffuse fibrosis in ANCA GN was associated explicitly with interstitial inflammation independent of glomerular damage and nephron loss. Ultrastructural analysis of focal IF/TA versus diffuse fibrosis revealed distinct matrix compositions, further supported by different collagen signatures in transcriptome datasets. With regard to long-term renal outcome, only the extent of focal IF/TA correlated with the development of end-stage kidney disease (ESKD) in ANCA GN. In contrast, diffuse kidney fibrosis did not associate with the long-term renal outcome. In conclusion, we here provide evidence that a focal pattern of kidney fibrosis seems to be associated with nephron loss and replacement scarring. In contrast, a diffuse pattern of kidney fibrosis appears to result from primary interstitial inflammation and injury.

Complement Components C3 and C4 Indicate Vasculitis Manifestations to Distinct Renal Compartments in ANCA-Associated Glomerulonephritis

Acute kidney injury (AKI) is a common and severe complication of antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) causing progressive chronic kidney disease (CKD), end-stage renal disease (ESRD) or death. Pathogenic ANCAs, in particular proteinase 3 (PR3) and myeloperoxidase (MPO), trigger a deleterious immune response resulting in pauci-immune necrotizing and crescentic glomerulonephritis (GN), a common manifestation of glomerular injury in AAV. However, there is growing evidence that activation of the complement pathway contributes to the pathogenesis and progression of AAV. We here aimed to compare glomerular and tubulointerstitial lesions in ANCA GN and extrarenal manifestation of AAV in association with levels of circulating complement components C3c and C4.

METHODS

Plasma levels of C3c and C4 in a total number of 53 kidney biopsies with ANCA GN were retrospectively included between 2015 and 2020. Glomerular and tubulointerstitial lesions were evaluated according to established scoring systems for ANCA GN and analogous to the Banff classification.

RESULTS

We here show that circulating levels of C3c and C4 in ANCA GN were comparable to the majority of other renal pathologies. Furthermore, hypocomplementemia was only detectable in a minor subset of ANCA GN and not correlated with renal or extrarenal AAV manifestations. However, low levels of circulating C3c correlated with AKI severity in ANCA GN independent of systemic disease activity or extrarenal AAV manifestation. By systematic scoring of glomerular and tubulointerstitial lesions, we provide evidence that low levels of circulating C3c and C4 correlated with vasculitis manifestations to distinct renal compartments in ANCA GN.

CONCLUSIONS

We here expand our current knowledge about distinct complement components in association with vasculitis manifestations to different renal compartments in ANCA GN. While low levels of C4 correlated with glomerulitis, our observation that low levels of circulating complement component C3c is associated with interstitial vasculitis manifestation reflected by intimal arteritis implicates that C3c contributes to tubulointerstitial injury in ANCA GN.

Systematic Scoring of Tubular Injury Patterns Reveals Interplay between Distinct Tubular and Glomerular Lesions in ANCA-Associated Glomerulonephritis

Background: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a small vessel vasculitis, most frequently presenting as microscopic polyangiitis (MPA) or granulomatosis with polyangiitis (GPA). Acute tubular injury with the presence of tubulitis was previously reported to be of prognostic value in ANCA glomerulonephritis (GN). In particular, distinct tubular injury lesions were associated with the deterioration of kidney function at AAV disease onset, as well as renal resistance to treatment, and higher risk of progression to composite outcome in patients with AAV. To expand our knowledge regarding distinct tubular lesions in AAV, we aimed to describe acute tubular injury patterns in association with glomerular lesions in ANCA GN by systematic histological scoring. Methods: A total number of 48 renal biopsies with confirmed renal involvement of AAV admitted to the University Medical Center Göttingen from 2015 to 2020 were retrospectively examined. By systematic scoring of tubular injury lesions, the association between clinical parameters, laboratory markers, and histopathological findings was explored. Results: We have shown that cellular casts in renal biopsies were frequently observed in the majority of cases with ANCA GN. Furthermore, we showed that tubular epithelial simplification with dilatation correlated with MPA and MPO subtypes, C3c hypocomplementemia, severe renal involvement, and uACR. Red blood cell (RBC) casts were associated with increased levels of C-reactive protein (CRP), leukocyturia, and hematuria. Finally, we found that hyaline casts were associated with an increased fraction of glomeruli with global glomerular sclerosis. Conclusions: Acute tubular injury patterns were correlated with active ANCA GN, whereas tubular injury lesions reflecting the later stages of kidney disease correlated with chronic glomerular lesions. These results suggest an interplay between different renal compartments.

Consideration of Therapeutic Plasma Exchange in Association With Inflammatory Lesions in ANCA-Associated Glomerulonephritis: A Real-World Retrospective Study From a Single Center

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic vasculitis, most frequently presenting as microscopic polyangiitis (MPA) or granulomatosis with polyangiitis (GPA). Pathogenic ANCAs trigger a deleterious immune response resulting in pauci-immune necrotizing and crescentic glomerulonephritis (GN). Standard therapeutical regimens include aggressive immunosuppressive therapy. Since some patients require renal replacement therapy (RRT) despite intensive immunosuppressive therapy, additional therapeutic plasma exchange (PEX) to deplete pathogenic ANCAs has been recommended but its value has recently been questioned. Because therapeutic decision making is crucial in these critically ill patients, we here aimed to identify inflammatory lesions in association with PEX consideration in a retrospective study from a single center tertiary hospital in a real-world population of 46 patients with severe AAV requiring intensive care treatment. The decision to consider PEX was more likely in patients with need for intensive care treatment and severe renal dysfunction. In contrast, short-term outcomes did not depend on clinical, or laboratory characteristics assessed at admission. Histopathological analysis confirmed active disease reflected by increased glomerular necrosis and crescents, but these histopathological findings did not associate with short-term outcome either. Interestingly, only increased global glomerular sclerosis in renal biopsies associated with a detrimental short-term outcome. In conclusion, our study investigated determinants for the consideration of therapeutic PEX in patients with severe AAV requiring intensive care treatment. This aspect underscores the need for renal biopsy and requires further investigation in a prospective controlled setting for therapeutic decision making especially in patients with severe AAV requiring intensive care treatment, especially important for treating intensivists.

Proteinuria Indicates Decreased Normal Glomeruli in ANCA-Associated Glomerulonephritis Independent of Systemic Disease Activity

Background: Renal involvement is a common and severe complication of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), potentially resulting in a pauci-immune necrotizing and crescentic ANCA glomerulonephritis (GN) with acute kidney injury (AKI), end-stage renal disease (ESRD) or death. There is recent evidence that the degree of proteinuria at diagnosis is associated with long-term renal outcome in ANCA GN. Therefore, we here aimed to systematically describe the association between proteinuria and clinicopathological characteristics in 53 renal biopsies with ANCA GN and corresponding urinary samples at admission. Methods: A total number of 53 urinary samples at admission and corresponding renal biopsies with confirmed renal involvement of AAV were retrospectively included from 2015 to 2021 in a single-center study. Results: Proteinuria correlated with myeloperoxidase (MPO) subtype, diagnosis of microscopic polyangiitis (MPA) and severe deterioration of kidney function. Proteinuria was most prominent in sclerotic class ANCA GN and ANCA renal risk score (ARRS) high risk attributed to nonselective proteinuria, including both glomerular and tubular proteinuria. Finally, there was no association between proteinuria and systemic disease activity, suggesting that proteinuria reflected specific renal involvement in AAV rather that systemic disease activity. Conclusions: In conclusion, proteinuria correlated with distinct clinicopathological characteristics in ANCA GN, mostly attributed to a reduced fraction of normal glomeruli. Furthermore, proteinuria in ANCA GN reflected specific renal involvement in AAV rather than systemic disease activity. Therefore, urinary findings could further improve our understanding of mechanisms promoting kidney injury and progression of ANCA GN.

Systematic Histological Scoring Reveals More Prominent Interstitial Inflammation in Myeloperoxidase-ANCA Compared to Proteinase 3-ANCA Glomerulonephritis

Background: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic vasculitis, most frequently presenting as microscopic polyangiitis (MPA) or granulomatosis with polyangiitis (GPA). Kidney involvement is a common and severe complication of ANCA AAV which is observed in a considerable subset of patients, mainly affecting glomeruli. However, tubulointerstitial lesions have also been described in ANCA glomerulonephritis (GN). Therefore, we aim to describe active and chronic tubulointerstitial lesions in ANCA GN subtypes by systematic scoring analogous to the Banff scoring system while also utilizing clinical and laboratory findings. Methods: A total of 49 kidney biopsies with ANCA GN were retrospectively included in a single-center cohort study between 2015–2020. Results: We report that MPO-ANCA GN is associated with more severe deterioration of kidney function independent of systemic markers of AAV disease activity, and is also associated with increased proteinuria in MPO-ANCA GN and a decreased fraction of normal glomeruli. Finally, MPO-ANCA GN showed distinct, active, and chronic tubulointerstitial lesions. Conclusion: New insights into the pathophysiology of both entities, as well as differences in the clinical presentation of MPO- versus PR3-ANCA GN, could potentially pave the way for more precise treatment regimens. Therefore, it is important to understand the differences in histopathological presentation, especially in yet underestimated active tubulointerstitial lesions of ANCA GN subtypes. This research could further improve our understanding of distinct pathophysiological mechanisms.