Membranous nephropathy: integrating basic science into improved clinical management

Primary Membranous Glomerulonephritis: The Role of Serum and Urine Biomarkers in Patient Management

The detection of phospholipase A2 receptor (PLA2R) and thrombospondin domain containing 7A THSD7A among primary membranous glomerulonephritis (MGN) patients transformed the diagnosis, treatment monitoring, and prognosis. Anti-PLA2R can be detected in 70-90% of primary MGN patients while anti-THSD7A in 2-3% of anti-PLA2R negative primary MGN patients depending on the technique used. Serum and urine samples are less invasive and non-invasive, respectively, and thus can detect the presence of anti-PLA2R and anti-THSD7A with higher sensitivity and specificity, which is significant in patient monitoring and prognosis. It is better than exposing patients to a frequent biopsy, which is an invasive procedure. Different techniques of detection of PLA2R and THSD7A in patients' urine and sera were reviewed to provide newer and alternative techniques. We proposed the use of biomarkers (PLA2R and THSD7A) in the diagnosis, treatment decision, and follow-up of patients with primary MGN. In addition, other prognostic renal biomarkers like retinol binding protein (RBP) and beta-2 microglobulin were reviewed to detect the progression of renal damage for early intervention.

Histological grading in primary membranous nephropathy is essential for clinical management and predicts outcome of patients

Aims

Diagnosis of primary membranous nephropathy (PMN) is mainly based on immunofluorescence/immunohistochemistry findings. However, assessment of specific features on optical microscopy can help to estimate the severity of the disease, guide treatment and predict the response. The aim of this study was to identify, classify and grade the precise histological findings in PMN to predict renal function outcome and guide treatment.

Methods and results

Histological parameters, including focal segmental sclerosis (FSGS), tubular atrophy (TA), interstitial fibrosis (IF) and vascular hyalinosis (VH), were re‐evaluated in 752 patients with PMN. Their predictive value was estimated separately, and also in a combination score (FSTIV) graded from 0 to 4. Finally, the impact of histology was assessed in the response to immunosuppressive treatment. Mean age of patients was 53.3 (15–85) years and most presented with nephrotic syndrome. FSGS was present in 32% and VH in 51% of the patients, while TA and IF were graded as stage ≥1 in 52% and 51.4%, respectively. The follow‐up period was 122.3 (112–376) months. FSGS, TA and IF and VH were associated with impaired renal function at diagnosis (P = 0.02, P < 0.0001, P = 0.001 and P = 0.02, respectively) and at the end of follow‐up (P = 0.004, P < 0.0001, P < 0.0001 and P = 0.04, respectively). In multiple regression and binary logistic analysis, the presence of FSGS and degree of TA were the most significant parameters predicting renal function outcome, defined either by eGFR (end), FSGS (r = 0.6, P < 0.0001) and TA (r = 0.6, P < 0.0001), or by the endpoint of >50% eGFR reduction, FSGS (P = 0.001) and TA (P = 0.02). Also, patients presented with FSGS, IF, VH and/or with FSTIV > 1 could benefit from immunosuppression, regardless of clinical presentation.

Conclusions

The presence and degree of four histological indices, FSGS, VH, TA and IF, assessed separately or in combination, and FSTIV score not only predict renal function outcome after long‐term follow‐up, but can also help in the choice of appropriate treatment. Decisions concerning immunosuppressive treatment can be guided by pathology regardless of clinical findings.

Long-term outcomes of patients with end-stage kidney disease due to membranous nephropathy: A cohort study using the Australia and New Zealand Dialysis and Transplant Registry

Background

Clinical outcomes of patients with end-stage kidney disease (ESKD) secondary to membranous nephropathy (MN) have not been well described. This study aimed to evaluate patient and/or allograft outcomes of dialysis or kidney transplantation in patients with ESKD secondary to MN.

Material and methods

All adult patients with ESKD commencing renal replacement therapy in Australia and New Zealand from January 1998 to December 2010 were extracted retrospectively from ANZDATA registry on 31^st December 2013. Outcomes of MN were compared to other causes of ESKD. In a secondary analysis, outcomes of MN were compared to all patients with ESKD due to other forms of glomerulonephritis.

Results

Of 32,788 included patients, 417 (1.3%) had MN. Compared to other causes of ESKD, MN experienced lower mortality on dialysis (adjusted hazard ratio [aHR] 0.79, 95% CI 0.68–0.92, p = 0.002) and following kidney transplantation (aHR 0.57, 95% CI 0.33–0.97, p = 0.04), had a higher risk of death-censored kidney allograft failure (aHR 1.55, 95% CI: 1.00–2.41, p = 0.05) but comparable risk of overall kidney allograft failure (aHR 1.35, 95% CI 0.91–2.01, p = 0.13). Similar results were obtained using competing-risk regression analyses. MN patients were significantly more likely to receive a kidney transplant (aHR 1.38, 95% CI 1.16–1.63, p<0.001) and to experience primary kidney disease recurrence in the allograft (aHR 4.92, 95% CI 3.02–8.01, p<0.001). Compared to other forms of glomerulonephritis, MN experienced comparable dialysis and transplant patient survival, but higher rates of kidney transplantation, primary renal disease recurrence and death-censored allograft failure.

Conclusion

MN was associated with superior survival on dialysis and following kidney transplantation compared to patients with other causes of ESKD, and comparable patient survival compared to patients with other forms of glomerulonephritis. However, patients with MN exhibited a higher rate of death-censored allograft loss as a result of primary kidney disease recurrence.

Recurrent and de novo Glomerulonephritis After Kidney Transplantation

The prevalence, pathogenesis, predictors, and natural course of patients with recurrent glomerulonephritis (GN) occurring after kidney transplantation remains incompletely understood, including whether there are differences in the outcomes and advances in the treatment options of specific GN subtypes, including those with de novo GN. Consequently, the treatment options and approaches to recurrent disease are largely extrapolated from the general population, with responses to these treatments in those with recurrent or de novo GN post-transplantation poorly described. Given a greater understanding of the pathogenesis of GN and the development of novel treatment options, it is conceivable that these advances will result in an improved structure in the future management of patients with recurrent or de novo GN. This review focuses on the incidence, genetics, characteristics, clinical course, and risk of allograft failure of patients with recurrent or de novo GN after kidney transplantation, ascertaining potential disparities between “high risk” disease subtypes of IgA nephropathy, idiopathic membranous glomerulonephritis, focal segmental glomerulosclerosis, and membranoproliferative glomerulonephritis. We will examine in detail the management of patients with high risk GN, including the pre-transplant assessment, post-transplant monitoring, and the available treatment options for disease recurrence. Given the relative paucity of data of patients with recurrent and de novo GN after kidney transplantation, a global effort in collecting comprehensive in-depth data of patients with recurrent and de novo GN as well as novel trial design to test the efficacy of specific treatment strategy in large scale multicenter randomized controlled trials are essential to address the knowledge deficiency in this disease.

Immunosuppressive regimens based on Cyclophospamide or Calcineurin inhibitors: Comparison of their effect in the long term outcome of Primary Membranous Nephropathy

INTRODUCTION

Management of the Primary Membranous Nephropathy (PMN) usually involves administration of immunosuppressives. Cyclophosphamide (Cyclo) and Calcineurin Inhibitors (CNIs) are both widely used but only limited data exist to compare their efficacy in long term follow-up.

AIM

The aim of the present study was to estimate and compare long term effects of Cyclo and CNIs in patients with PMN.

PATIENTS-METHODS

Clinical data, histologic findings and long term outcome were retrospectively studied. The response to treatment and rate of relapse was compared between patients treated with CNIs or Cyclo based immunosuppressive regimens.

RESULTS

Twenty three centers participated in the study, with 752 PMN patients (Mean age 53.4(14-87) yrs, M/F 467/285), followed for 10.1±5.7 years. All patients were initially treated with Renin Angiotensin Aldosterone System inhibitors (RAASi) for at least 6 months. Based on their response and tolerance to initial treatment, patients were divided into 3 groups, group I with spontaneous remission, who had no further treatment, group II, continued on RAASi only, and group III on RAASi+immunosuppression. Immunosuppressive regimes were mainly based on CNIs or Cyclo. Frequent relapses and failure to treatment were more common between patients who had started on CNIs (n = 381) compared to those initially treated with Cyclo (n = 110), relapse rate: 25.2% vs. 6.4%, p<0.0001, and no response rate: 22.5% vs. 13.6%, p = 0.04, respectively.

CONCLUSIONS

Long term follow up showed that administration of Cyclo in PMN is followed by better preservation of renal function, increased response rate and less frequent relapses, compared to CNIs.

Prognostic value of phospholipase A2 receptor in primary membranous nephropathy: a systematic review and meta-analysis

PURPOSE

We aimed to evaluate the prognostic value of serum anti-PLA2R and glomerular PLA2R deposit (gPLA2R) in predicting remission of proteinuria in Primary Membranous Nephropathy (PMN) patients.

METHODS

PUBMED, EMBASE, WEB OF SCIENCE, COCHRANE LIBRARY and CNKI were searched from 2008 January to December 2018. Heterogeneity was assessed by Cochran Q test and I². Source of heterogeneity was explored by subgroup analysis and sensitivity analysis.

RESULTS

Totally 2345 patients from 29 cohort studies were eligible for inclusion. The results suggested that PMN patients with negative anti-PLA2R at the time of biopsy had a 1.31 times (95% CI 1.12-1.46, p < 0.05) higher possibility in achieving remission than those with positive anti-PLA2R. The clearance of anti-PLA2R at the end of immunosuppressive therapy showed an even greater chance of achieving remission (RR = 2.86, 95% CI 1.75-4.69, p < 0.05). The relative ratios for complete remission and spontaneous remission with negative anti-PLA2R were 1.65 (95% CI 1.46-1.87, p < 0.05) and 1.93, respectively (95% CI 1.53-2.45, p < 0.05), and heterogeneity percentages were I² = 18% and 46%, respectively. The possibility for remission was significantly greater among PMN patients with negative gPLA2R (RR = 1.30, 95% CI 1.13-1.50, p < 0.05). Subgroup analyses revealed that retrospective design of study might be the potential source of heterogeneity.

CONCLUSIONS

Negative anti-PLA2R or gPLA2R might predict higher possibility of remission, and the presence of anti-PLA2R or gPLA2R might serve as a useful biomarker for clinical outcome and predicting response to immunosuppressive therapy in PMN.

Emerging immunotherapies for autoimmune kidney disease

Autoimmunity is a leading cause of chronic kidney disease and loss of native and transplanted kidneys. Conventional immunosuppressive therapies can be effective but are non-specific, noncurative, and risk serious side effects such as life-threatening infection and cancer. Novel therapies and targeted interventions are urgently needed. In this brief review we explore diverse strategies currently in development and under consideration to interrupt underlying disease mechanisms in immune-mediated renal injury. Because autoantibodies are prominent in diagnosis and pathogenesis in multiple human glomerulopathies, we highlight several promising therapies that interfere with functions of early mediators (IgG and complement) of the effector arm and with an epicenter (the germinal center) for induction of humoral immunity.

Treatment-resistant PLA2R-negative membranous nephropathy responsive to low-density lipoprotein apheresis

Idiopathic membranous nephropathy is the most common cause of nephrotic syndrome in nondiabetic adults. The antibody most often implicated is the M-type phospholipase A2 receptor (PLA2R) antibody, found in >70% of primary membranous nephropathy cases. First-line therapy is immunosuppressive in nature, but for patients who are treatment-resistant there is a significant risk of end-stage renal disease and mortality. Hypercholesterolemia is not only a side effect of nephrotic syndrome, but also its presence may worsen renal function. A recent single-arm observational study in Japan found that low-density lipoprotein apheresis (LDL-A) was able to ameliorate nephrotic syndrome in half of patients who were resistant to medication. We present a case of treatment resistant PLA2R negative membranous nephropathy who had significant improvement following two courses of LDL-A. To our knowledge, this is the first such reported case in the United States.

Characterization of autoantibodies in primary membranous nephropathy and their clinical significance

Introduction: Membranous nephropathy (MN) is the most common cause of a nephrotic syndrome in Caucasian adults. The identification of target antigens in MN in the last decade has had a major impact on the clinical approach to these patients. Areas covered: Since the discoveries in animal models in the 1980s that circulating autoantibodies induce disease upon in situ binding to glomerular podocytes, many attempts have been undertaken to define the human antigens responsible for disease induction. Only in 2009 was Phospholipase A₂ Receptor 1 described as the major antigen responsible for MN onset in about 70% of patients. Subsequently, in 2014, Thrombospondin Type-1 Domain-Containing 7A was identified as a second antigen, accounting for 2-3% of patients with MN. The knowledge of the role of these antibodies in MN has improved the diagnosis and management of patients and helped to better define the need for immunosuppressive treatment. Expert commentary: These discoveries over the last 10 years in the discipline of nephrology have clearly shown the improvements a better understanding of disease pathogenesis can bring for patient care.

The role of osteopontin in kidney diseases

BACKGROUND

Osteopontin (OPN) is a pleiotropic glycoprotein expressed in various cell types in animals and in humans, including bone, immune, smooth muscle, epithelial and endothelial cells. Moreover, OPN is found in kidneys (in the thick ascending limbs of the loop of Henle and in distal nephrons) and urine. The protein plays an important role in mineralization and bone resorption. In addition, OPN is involved in the regulation of immunity and inflammation, angiogenesis and apoptosis. It was demonstrated that OPN and some OPN gene polymorphic variants are associated with the pathogenesis and progression of multiple disorders, such as cancer, autoimmune, neurodegenerative and cardiovascular diseases. Moreover, recent studies suggested that OPN is associated with the pathogenesis of renal failure.

METHODS

In this review, I briefly discussed the role of OPN and its gene polymorphisms in kidney physiology, as well as in various kidney diseases.

FINDINGS AND CONCLUSION

Most studies reported that OPN expression is elevated in urolithiasis, and also in acute and chronic kidney diseases, and in renal allograft dysfunction. Moreover, it was demonstrated that polymorphic variants of the OPN gene may be associated with renal failure. However, some reports suggested that OPN is essential for tubulogenesis, and that it inhibits calcium oxalate crystal formation and retention, nitric oxide synthesis, cell apoptosis and promotes cell regeneration. Thus, further studies are required to fully understand the role of OPN in kidney physiology and pathology. Eventually, these studies may result in the identification of OPN as a valuable marker for renal dysfunction prognosis and treatment.

Duodenal Schwannoma as a Rare Association With Membranous Nephropathy: A Case Report

Membranous nephropathy (MN) associated with malignancies is a well-known entity. However, its association with benign neoplasm is not broadly recognized. A 69-year-old man with recurrent nephrotic syndrome presented with pedal edema and proteinuria of 5 months' duration. Laboratory results showed hypoalbuminemia and hyperlipidemia. Proteinuria was estimated to be protein excretion of 3.5g/d. Studies were negative for viral hepatitis, syphilis, human immunodeficiency virus, autoimmune diseases, and paraproteinemia. Kidney biopsy disclosed MN with negative phospholipase A₂ receptor (PLA₂R) staining, favoring a secondary form of MN. Computed tomography detected a 7.6-cm duodenal schwannoma. Elective surgical resection was performed. Pathologic study showed that THSD7A (thrombospondin type 1 domain-containing 7A) was positive in both glomeruli and schwannoma. Commonly, secondary MN is related to underlying conditions, including lupus, hepatitis, and neoplasm, and can be medication induced. The risk for developing a concomitant neoplasm among patients with PLA₂R-negative MN is up to 12 times higher than in the general population. Most of these neoplasms are malignancies, and the presence of autoantibodies directed at similar tissue targets is hypothesized as the potential mechanism. In our case, THSD7A may be the autoantibody that has linked the schwannoma and the development of MN. Although benign tumors rarely produce renal manifestations, effective treatment may lead to resolution of nephrotic syndrome.

Recurrent venous thromboembolism in primary membranous nephropathy despite direct Xa inhibitor therapy

Clinically apparent venous thromboembolism (VTE) occurs in approximately 7% of patients with membranous nephropathy. Hypoalbuminemia at diagnosis is an independent risk factor for VTE, and risk increases significantly as albumin falls. Optimal prophylactic and treatment anticoagulation regimens in the nephrotic syndrome remain unproven but novel oral anti-coagulants have become attractive therapeutic options. We describe a patient diagnosed with anti-phospholipase A2 receptor antibody positive membranous nephropathy and recurrent VTE while on therapeutic dosing of apixaban. A direct factor Xa inhibitor, apixaban has been shown to be non-inferior to warfarin for the treatment of VTE in the general population. However, because it is highly protein-bound, apixaban may have altered pharmacokinetics and pharmacodynamics in patients with nephrotic syndrome and hypoalbuminemia. This case report highlights the need for further studies of direct oral anticoagulants to fully assess their effectiveness in this high-risk population.

CureGN Study Rationale, Design, and Methods: Establishing a Large Prospective Observational Study of Glomerular Disease

RATIONALE & OBJECTIVES

Glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and immunoglobulin A (IgA) nephropathy, share clinical presentations, yet result from multiple biological mechanisms. Challenges to identifying underlying mechanisms, biomarkers, and new therapies include the rarity of each diagnosis and slow progression, often requiring decades to measure the effectiveness of interventions to prevent end-stage kidney disease (ESKD) or death.

STUDY DESIGN

Multicenter prospective cohort study.

SETTING & PARTICIPANTS

Cure Glomerulonephropathy (CureGN) will enroll 2,400 children and adults with minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, or IgA nephropathy (including IgA vasculitis) and a first diagnostic kidney biopsy within 5 years. Patients with ESKD and those with secondary causes of glomerular disease are excluded.

EXPOSURES

Clinical data, including medical history, medications, family history, and patient-reported outcomes, are obtained, along with a digital archive of kidney biopsy images and blood and urine specimens at study visits aligned with clinical care 1 to 4 times per year.

OUTCOMES

Patients are followed up for changes in estimated glomerular filtration rate, disease activity, ESKD, and death and for nonrenal complications of disease and treatment, including infection, malignancy, cardiovascular, and thromboembolic events.

ANALYTICAL APPROACH

The study design supports multiple longitudinal analyses leveraging the diverse data domains of CureGN and its ancillary program. At 2,400 patients and an average of 2 years' initial follow-up, CureGN has 80% power to detect an HR of 1.4 to 1.9 for proteinuria remission and a mean difference of 2.1 to 3.0mL/min/1.73m² in estimated glomerular filtration rate per year.

LIMITATIONS

Current follow-up can only detect large differences in ESKD and death outcomes.

CONCLUSIONS

Study infrastructure will support a broad range of scientific approaches to identify mechanistically distinct subgroups, identify accurate biomarkers of disease activity and progression, delineate disease-specific treatment targets, and inform future therapeutic trials. CureGN is expected to be among the largest prospective studies of children and adults with glomerular disease, with a broad goal to lessen disease burden and improve outcomes.

Clinical value of a serum anti-PLA2R antibody in the diagnosis and monitoring of primary membranous nephropathy in adults

OBJECTIVE

To compare the positive rate of anti-PLA2R antibodies in patients with primary membranous nephropathy (PMN), secondary membranous nephropathy (SMN), and non-membrane nephropathy (non-MN); evaluate serum anti-PLA2R antibodies in the diagnosis of PMN; quantify the serum anti-PLA2R antibody levels during the treatment of PMN patients; and evaluate the clinical value of monitoring changes in serum anti-PLA2R antibody quantification levels.

METHODS

The kidney tissue was collected by kidney biopsy. The expression of PLA2R in glomeruli was detected by immunofluorescence, and ELISA was used to quantify the serum anti-PLA2R antibody. The positive rate of PLA2R expression in renal tissue and positive rate of the anti-PLA2R antibody in the three groups were compared and calculated using a statistical method. The specificity and coincidence rate of anti-PLA2R used in the differential diagnosis of PMN and SMN were evaluated. The clinical value of monitoring changes in serum anti-PLA2R antibody quantification levels was evaluated.

RESULT

The serum levels of the anti-PLA2R antibody were significantly higher in patients with PMN than in patients with SMN and non-MN group. The difference was statistically significant (P<0.05). The serum anti-PLA2R antibody became negative in the complete remission group. The serum anti-PLA2R antibody levels were significantly lower than before treatment in the partial remission group, and the difference was statistically significant (P<0.05). However, in the non-remission group, the serum anti-PLA2R antibody levels remained high.

CONCLUSION

Detection of the serum anti-PLA2R antibody has a high specificity for diagnosing PMN. The change of the serum anti-PLA2R antibody level is closely related to the status of the PMN: if the anti-PLA2R antibody level has decreased, it indicates that the condition has improved; and if the serum anti-PLA2R antibody continues to show high levels of positive or quantitative increase, the condition is not in remission or has relapsed.

Clinical and pathological features of idiopathic membranous nephropathy in young people

AIM

To investigate the clinico-pathological features of idiopathic membranous nephropathy (IMN) in youth.

METHODS

Patients with biopsy-proven IMN in Peking University Third Hospital from May 2015 to October 2017 (n = 147) were enrolled in this study. Patients were divided into youth (≤35 years old), middle-age (35-65 years old) and elderly group (>65 years old) accordingly. Medical records of patients were retrospectively analyzed.

RESULTS

Youth group exhibited shorter duration from onset to biopsy (3.49 ± 4.25 months in youth vs 8.71 ± 12.24 months in elderly) and milder clinical presentations in terms of less proteinuria and higher serum albumin (P < 0.05). Furthermore, lower anti-phospholipase A2 receptor (PLA2R) antibody titre (65.36 ± 101.14 RU/mL in youth vs 137.45 ± 215.12 RU/mL in middle-age), less C3 deposits (35.14% in youth vs 65.00% in elderly) and higher 6-month remission rate (63.64% in youth vs 36.00% in middle-age) were observed in youth (P < 0.05). Multiple linear regression confirmed C3 deposits (P = 0.005) and anti-PLA2R (P = 0.040) were independent factors influencing proteinuria, and age is an independent influencing factor for time from onset to biopsy (P = 0.043). Older age (OR = 2.044, 95% CI: 1.073-3.896, P = 0.030) and higher anti-PLA2R (OR = 1.413, 95% CI: 1.020-1.959, P = 0.038) were significantly associated with non-remission by 6 months.

CONCLUSION

Younger patients with IMN tend to have rapider onset and quicker remission than older patients. Milder clinical presentations in youth are associated with lower anti-PLA2R antibody titre and less C3 deposits.

Alternative Pathway Is Essential for Glomerular Complement Activation and Proteinuria in a Mouse Model of Membranous Nephropathy

Membranous nephropathy is an immune kidney disease caused by IgG antibodies that form glomerular subepithelial immune complexes. Proteinuria is mediated by complement activation, as a result of podocyte injury by C5b-9, but the role of specific complement pathways is not known. Autoantibodies-mediating primary membranous nephropathy are predominantly of IgG4 subclass, which cannot activate the classical pathway. Histologic evidence from kidney biopsies suggests that the lectin and the alternative pathways may be activated in membranous nephropathy, but the pathogenic relevance of these pathways remains unclear. In this study, we evaluated the role of the alternative pathway in a mouse model of membranous nephropathy. After inducing the formation of subepithelial immune complexes, we found similar glomerular IgG deposition in wild-type mice and in factor B-null mice, which lack a functional alternative pathway. Unlike wild-type mice, mice lacking factor B did not develop albuminuria nor exhibit glomerular deposition of C3c and C5b-9. Albuminuria was also reduced but not completely abolished in C5-deficient mice. Our results provide the first direct evidence that the alternative pathway is necessary for pathogenic complement activation by glomerular subepithelial immune complexes and is, therefore, a key mediator of proteinuria in experimental membranous nephropathy. This knowledge is important for the rational design of new therapies for membranous nephropathy.

The Unpredictability of Idiopathic Membranous Nephropathy: An Illustrative Case Report

The case of a female patient with primary membranous nephropathy is presented. She was treated with corticosteroids and chlorambucil after conservative therapy had failed and went into remission for 5 years. Her nephrotic syndrome recurred but did not respond to the same regimen. She had another complete remission after treatment with corticosteroids and cyclosporine, but the nephrosis recurred after 7 years. Again, she failed to respond with retreatment of steroids plus cyclosporine. She was treated with alternate-day steroid plus mycophenolate and, once again, had a complete remission. She was maintained on low-dose mycophenolate for 7 more years. The mycophenolate had to be discontinued because of cytomegalovirus colitis. Treatment with ganciclovir abolished the colitis. She is still in remission 10 years later. The case is discussed with regard to current knowledge of the immune pathogenesis of membranous nephropathy as well as the unknowns of the immunogenesis of the disease.

Diagnostic Test Accuracy of Serum Anti-PLA2R Autoantibodies and Glomerular PLA2R Antigen for Diagnosing Idiopathic Membranous Nephropathy: An Updated Meta-Analysis

Background

M-type phospholipase A2 receptor (PLA2R) is known as a major antigen on podocytes, which is involved with the pathogenesis of idiopathic membranous nephropathy (iMN). Many studies have shown that serum anti-PLA2R autoantibodies (sPLA2R) are prevalent in patients with iMN but are rarely detected in secondary membranous nephropathy (SMN) or other glomerulonephritis. The anti-PLA2R is considered as a promising serum biomarker in iMN but reports about its diagnostic value are variable and inconsistent.

Objective

To evaluate the diagnostic test accuracy (DTA) of anti-PLA2R and glomerular PLA2R antigen (gPLA2R) for diagnosing iMN.

Method

MEDLINE, EMBASE, WEB OF SCIENCE, and COCHRANE LIBRARY were searched from 2009 January to February 2018. Heterogeneity was evaluated by Q test and I². Source of heterogeneity was explored by subgroup analysis and meta-regression. Meta-analysis was executed and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses statement.

Results

Totally, 35 studies were retrieved under the pre-set study eligibility criteria. Twenty-eight studies were included to evaluate the DTA of anti-PLA2R for differentiating iMN from non-iMN. They indicated a pooled sensitivity of 65% (63–67%), specificity of 97% (97–98%), positive likelihood ratio of 15.65 (9.95–24.62), and negative likelihood ratio of 0.37 (0.32–0.42) with a diagnostic OR (sDOR) of 50.41 (31.56 to 80.52) and AUC of 0.9393. No threshold effect was detected. The heterogeneity analysis for sDOR showed that I² = 50.3% and Cochran-Q = 54.29, df = 27 (p = 0.0014). Heterogeneity was significant. Meta-regression revealed that sample size might be the potential source of heterogeneity. Subgroup analysis demonstrated that method type and ratio of patients with nephrotic-range proteinuria at baseline might be the source of heterogeneity. Sixteen studies reported the diagnostic value of glomerular PLA2R antigen for differentiating iMN from non-iMN. The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, sDOR, and AUC were 79% (76–81%), 90% (88–92%), 8.17 (5.60–11.93), 0.25 (0.19–0.33), 39.37 (22.18–60.13), and 0.9278. Heterogeneity analysis showed that Cochran-Q = 35.36; df = 15 (p = 0.002), and I² for sDOR was 57.6%.

Conclusion

sPLA2R and gPLA2R demonstrated a good diagnostic accuracy in differentiating iMN and non-iMN.

Tissue staining for THSD7A in glomeruli correlates with serum antibodies in primary membranous nephropathy: a clinicopathological study

Thrombospondin type-1 domain-containing 7A (THSD7A) is the most recently recognized target antigen in patients with membranous nephropathy. We stained membranous nephropathy biopsies processed in our laboratory for phospholipase A₂ receptor and THSD7A over an 18-month period and selected all THSD7A-positive cases for study. Serum samples from most patients were tested by an indirect immunofluorescence assay for the presence of THSD7A antibodies (Euroimmun). A total of 31 patients were diagnosed with THSD7A-associated membranous nephropathy for a prevalence of 2.4% among patients with membranous nephropathy. The patients were most often male (male-to-female ratio of 1.6) with a mean age of 62 years and a mean proteinuria of 9.6 g per day (range 1.1-15.9). Two of the 31 patients had a history of cancer and none were diagnosed with malignancy on follow-up. Serum samples were available at the time of biopsy from 24 patients and all tested positive for antibodies against THSD7A. Conversely, all 20 serum samples from patients with membranous nephropathy who had negative staining for THSD7A were negative for serum reactivity to THSD7A. We conclude that THSD7A tissue staining of kidney biopsies with membranous nephropathy is a sensitive and specific method for the diagnosis of THSD7A-associated membranous nephropathy and it correlates strongly with the serum antibody testing. We also present the clinicopathologic details of the largest cohort to date of THSD7A-associated membranous nephropathy from a single institution.

Urine proteomics of primary membranous nephropathy using nanoscale liquid chromatography tandem mass spectrometry analysis

Background

Primary membranous nephropathy (PMN) is an important cause of nephrotic syndrome in adults. Urine proteome may provide important clues of pathophysiological mechanisms in PMN. In the current study, we analyzed and compared the proteome of urine from patients with PMN and normal controls.

Methods

We performed two technical replicates (TMT1 and TMT2) to analyze and compare the urine proteome from patients with PMN and normal controls by tandem mass tag (TMT) technology coupled with nanoscale liquid chromatography tandem mass spectrometry analysis (LC–MS/MS). Gene ontology (GO) enrichment analysis was performed to analyse general characterization of the proteins. The proteins were also matched against the database of Kyoto Encyclopedia of Genes and Genomes (KEGG). For validation, Western blot was used to analyze the selected proteins.

Results

A total of 509 proteins and 411 proteins were identified in TMT1 and TMT2, respectively. 249 proteins were both identified in two technical replicates. GO analysis and KEGG analysis revealed immunization and coagulation were predominantly involved. Among the differential protein, the overexcretion of alpha-1-antitrypsin (A1AT) and afamin (AFM) were validated by Western blot analysis.

Conclusions

Our data showed the important role of immunologic mechanism in the development of PMN, and the value of urinary A1AT and AFM in biomarker discovery of patients with PMN. The discovery of the overexcretion of A1AT and AFM in the urine can help to further elucidate pathogenetic mechanisms involved in PMN.

Electronic supplementary material

The online version of this article (10.1186/s12014-018-9183-3) contains supplementary material, which is available to authorized users.

Membranous Nephropathy and Anti-Podocytes Antibodies: Implications for the Diagnostic Workup and Disease Management

The discovery of circulating antibodies specific for native podocyte antigens has transformed the diagnostic workup and greatly improved management of idiopathic membranous nephropathy (iMN). In addition, their identification has clearly characterized iMN as a largely autoimmune disorder. Anti-PLA2R1 antibodies are detected in approximately 70% to 80% and anti-THSD7A antibodies in only 2% of adult patients with iMN. The presence of anti-THSD7A antibodies is associated with increased risk of malignancy. The assessment of PLA2R1 and THSD7A antigen expression in glomerular immune deposits has a better sensitivity than measurement of the corresponding autoantibodies. Therefore, in the presence of circulating anti-podocytes autoantibodies and/or enhanced expression of PLA2R1 and THSD7A antigens MN should be considered as primary MN (pMN). Anti-PLA2R1 or anti-THSD7A autoantibodies have been proposed as biomarkers of autoimmune disease activity and their blood levels should be regularly monitored in pMN to evaluate disease activity and predict outcomes. We propose a revised clinical workup flow for patients with MN that recommends assessment of kidney biopsy for PLA2R1 and THSD7A antigen expression, screening for circulating anti-podocytes antibodies, and assessment for secondary causes, especially cancer, in patients with THSD7A antibodies. Persistence of anti-podocyte antibodies for 6 months or their increase in association with nephrotic proteinuria should lead to the introduction of immunosuppressive therapies. Recent data have reported the efficacy and safety of new specific therapies targeting B cells (anti-CD20 antibodies, inhibitors of proteasome) in pMN which should lead to an update of currently outdated treatment guidelines.

THSD7A-associated membranous nephropathy in a patient with neurofibromatosis type 1

Target antigens in idiopathic membranous nephropathy (MN) include the phospholipase A2 receptor (PLA₂R), and in some cases, the thrombospondin type 1 domain-containing 7A (THSD7A). A notable phenomenon is the high rate of cancer (reported to be as high as 20%) in patients with THSD7A-associated MN. Neurofibromatosis type 1 (NF1) is an autosomal dominant disease caused by NF1 gene mutation, and clinically characterized by multiple cutaneous neurofibromas and café-au-lait spots. In this article, we report a patient with NF1 who developed THSD7A-associated MN when the NF1 skin lesions deteriorated. The patient, a 62-year-old male, was referred to us for nephrotic syndrome for 6 months. Physical examination revealed multiple cutaneous nodules throughout the entire body, and the patient noted recent increase in the numbers of these skin lesions. Cutaneous nodules excisional biopsy suggested NF1 and Sanger sequencing using genomic DNA extracted from peripheral blood revealed a previously reported heterozygous frameshift NF1 mutation (c.1541_1542delAG, p. Gln514fs). Renal biopsy revealed MN and immunohistochemistry (IHC) showed enhanced staining of THSD7A as well as PLA₂R along the glomerular basement membrane whereas the serum level of THSD7A and PLA₂R were both within normal range. The neurofibroma tissues were positive for THSD7A but not for PLA₂R on IHC. The patient did not respond to 6-month treatment with glucocorticosteroid and cyclophosphamide. In this exceptional case, strong positive staining of THSD7A in both skin and renal biopsy samples, together with the temporal association between nephrotic syndrome and skin lesions and lack of treatment response, suggested the possibility that MN could be the result of immune response to THSD7A in NF1. This report may improve understanding of the mechanistic link between MN and cancer.

PLA2R and THSD7A: Disparate Paths to the Same Disease?

The phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) are the two major autoantigens in primary membranous nephropathy (MN), and define two molecular subclasses of this disease. Both proteins are large transmembrane glycoproteins expressed by the podocyte, and both induce IgG4-predominant humoral immune responses that produce circulating autoantibodies that can be used clinically for diagnostic and monitoring purposes. The biologic roles of these proteins remain speculative, although several features of THSD7A suggest a role in adhesion. PLA2R-associated MN was initially found to associate with risk alleles within HLA-DQA1, but subsequent studies have shifted the focus to the HLA-DRB locus. Three distinct humoral epitope-containing regions have been defined within the extracellular portion of PLA2R, and it appears that the number of targeted epitopes may determine disease severity. Although similar information is not yet available for THSD7A-associated MN, this form of MN may have a unique association with malignancy. Finally, it appears likely that other autoantigens in primary MN exist. Although protocols similar to those that identified PLA2R and THSD7A may be successful in the identification of novel antigenic targets in MN, newer techniques such as laser-capture mass spectrometry or protein arrays may be helpful as well.

Primary Membranous Nephropathy

Membranous nephropathy (MN) is a unique glomerular lesion that is the most common cause of idiopathic nephrotic syndrome in nondiabetic white adults. About 80% of cases are renal limited (primary MN, PMN) and 20% are associated with other systemic diseases or exposures (secondary MN). This review focuses only on PMN. Most cases of PMN have circulating IgG4 autoantibody to the podocyte membrane antigen PLA2R (70%), biopsy evidence PLA2R staining indicating recent immunologic disease activity despite negative serum antibody levels (15%), or serum anti-THSD7A (3%-5%). The remaining 10% without demonstrable anti-PLA2R/THSd7A antibody or antigen likely have PMN probably secondary to a different, still unidentified, anti-podocyte antibody. Considerable clinical and experimental data now suggests these antibodies are pathogenic. Clinically, 80% of patients with PMN present with nephrotic syndrome and 20% with non-nephrotic proteinuria. Untreated, about one third undergo spontaneous remission, especially those with absent or low anti-PLA2R levels, one-third progress to ESRD over 10 years, and the remainder develop nonprogressive CKD. Proteinuria can persist for months after circulating anti-PLA2R/THSD7A antibody is no longer detectable (immunologic remission). All patients with PMN should be treated with supportive care from the time of diagnosis to minimize protein excretion. Patients with elevated anti-PLA2R/THSD7A levels and proteinuria >3.5 g/d at diagnosis, and those who fail to reduce proteinuria to <3.5 g after 6 months of supportive care or have complications of nephrotic syndrome, should be considered for immunosuppressive therapy. Accepted regimens include steroids/cyclophosphamide, calcineurin inhibitors, and B cell depletion. With proper management, only 10% or less will develop ESRD over the subsequent 10 years.

Recent Treatment Advances and New Trials in Adult Nephrotic Syndrome

The etiology of nephrotic syndrome is complex and ranges from primary glomerulonephritis to secondary forms. Patients with nephrotic syndrome often need immunosuppressive treatment with its side effects and may progress to end stage renal disease. This review focuses on recent advances in the treatment of primary causes of nephrotic syndrome (idiopathic membranous nephropathy (iMN), minimal change disease (MCD), and focal segmental glomerulosclerosis (FSGS)) since the publication of the KDIGO guidelines in 2012. Current treatment recommendations are mostly based on randomized controlled trials (RCTs) in children, small RCTs, or case series in adults. Recently, only a few new RCTs have been published, such as the Gemritux trial evaluating rituximab treatment versus supportive antiproteinuric and antihypertensive therapy in iMN. Many RCTs are ongoing for iMN, MCD, and FSGS that will provide further information on the effectiveness of different treatment options for the causative disease. In addition to reviewing recent clinical studies, we provide insight into potential new targets for the treatment of nephrotic syndrome from recent basic science publications.