A comprehensive narrative review of diagnostic biomarkers in human primary membranous nephropathy

Lactobacillus species ameliorate membranous nephropathy through inhibiting the aryl hydrocarbon receptor pathway via tryptophan-produced indole metabolites

BACKGROUND AND PURPOSE

Membranous nephropathy (MN) is an immune-mediated glomerular disease in adults. Antibody- and antigen-bonding mechanisms have been largely clarified, but the subepithelium immune complex deposition-mediated downstream molecular mechanisms are currently unresolved. Increasing evidence has suggested that gut microbiota contribute to MN pathogenesis.

EXPERIMENTAL APPROACH

In this study, we identified alterations in faecal gut microbiota and serum metabolites that mediate an aryl hydrocarbon receptor (AhR) mechanism in cationic bovine serum albumin (CBSA)-induced MN rats and in patients with idiopathic MN (IMN).

KEY RESULTS

Impaired renal function correlated with the relative abundance of reduced faecal probiotics, Lactobacillus and Bifidobacterium, and altered serum levels of tryptophan-produced indole derivatives (TPIDs) in MN rats. Further results showed that reduced relative abundance of five probiotics, namely Lactobacillus johnsonii, Lactobacillus murinus, Lactobacillus vaginalis, Lactobacillus reuteri and Bifidobacterium animalis, positively correlated with decreased levels of indole-3-pyruvic acid, indole-3-aldehyde and tryptamine and negatively correlated with increased levels of indole-3-lactic acid and indole-3-acetic acid in serum of MN rats. Altered five probiotics and five TPIDs also were observed in patients with IMN. Further studies showed that MN rats exhibited a significant increase in intrarenal mRNA expression of AhR and its target genes CYP1A1, CYP1A2 and CYP1B1, which were accompanied by protein expression of down-regulated cytoplasmic AhR, but up-regulated nuclear AhR, in MN rats and IMN patients.

CONCLUSION AND IMPLICATIONS

Activation of the intrarenal AhR signalling pathway may involve five TPIDs. These data suggest that gut microbiota could influence MN through TPIDs that engage host receptors.

Immunosuppressive Treatments for Idiopathic Membranous Nephropathy: A Pilot Study According to Histopathological Stages

BACKGROUND

No scholar has explored whether immunosuppressive treatments at different histopathological stages are different for idiopathic membranous nephropathy (IMN).

METHODS

From January 1, 2012, to January 1, 2018, all biopsy confirmed IMN cases treated with glucocorticoid (GC) plus cyclophosphamide (CTX) or GC were retrieved from the patients' medical records.

RESULTS

The present study included 67 patients who received GC alone (31 with stage I, 30 with stage II and 6 with stage III) and 157 patients who received GC + CTX (77 with stage I, 66 with stage II and 14 with stage III). Primary efficacy assessments included achieving complete remission and remission. Secondary efficacy assessments included proteinuria, serum albumin and adverse events. GC + CTX group showed higher complete remission rates than the GC group after 6 and 12 months in patients with stage II IMN (22% vs 10%, P = 0.04 and 59% vs 17%, P < 0.001, respectively). However, the two groups showed no difference in stages I and III (29% vs 26%, P = 0.61, 71% vs 52%, P = 0.09 and 14% vs 17%, P = 0.81, 21% vs 17%, P = 0.88, respectively). The GC + CTX group suffered a higher rate of gastrointestinal symptoms than the GC group in stage I and a higher rate of abnormal liver function in stage II.

CONCLUSIONS

Treatment with GC + CTX was more effective than GC in treating patients with stage II IMN; however, the advantage of GC + CTX was not significant for patients with stage I and III IMN.

A study of altered calcium sensing system caused primary membranous nephropathy to end-stage renal failure

PMN (primary membranous nephropathy) is the most prevalent source of idiopathic nephrotic syndrome, which further progressed to ESRD (end-stage renal disease) in non-diabetic adults worldwide. Autoantibodies circulating against podocyte membrane proteins PLA2R1 and THSD7A are present in approximately 75-80% of incidents. Furthermore, a research presented an unusual case of IgG4-RD correlated with elevated serum levels of calcium concluded that renal irregularities have been preceded and triggered by hypercalcemia. In-addition, previous research also indicates an elevated amount of calcium in the blood of PMN patients. However, we also found conflicting evidence from previous studies showing that autoantibodies that suppress the calcium-sensing receptor (CaSR) induce a high level of calcium in some cases of IgG4RD. Notably, the calcium ion plays a critical function not only as intracellular signaling molecule but binds extracellular receptor activity to intracellular events. Moreover, the raise in intracellular calcium levels during PMN is known as a crucial event involved in the activation of numerous nucleases, proteases and implicitly facilitates the release of prostaglandins, cytokines and superoxide radicals capable of causing cell damage and death. Thus, the precise mechanism of the PMN disease to renal failure is not fully clear and the disease incidence differs among patients. Therefore, we are hypothesizing the role of disrupted calcium signaling in PMN that progress to ESRD.

Advanced-Glycation End-Products Induce Podocyte Injury and Contribute to Proteinuria

The prevalence of diabetes reaches epidemic proportions. Diabetes is the leading cause of end-stage kidney disease (ESKD) since 30–40% of diabetic patients develop diabetic nephropathy. Albuminuria and glomerular filtration rate used to assess kidney function are considered surrogate outcomes of chronic kidney disease. The search for a biomarker that predicts progression to diabetic kidney disease is intense. We analyzed the association of serum advanced glycation end-products (AGEs) index (AGI) with impaired kidney function in poorly controlled type II diabetic patients. We observed an association between AGI and impaired kidney function in microalbuminuria patients with hyperglycemia. A significant association between AGEs, particularly carboxymethyl lysine (CML), and impaired kidney function were observed. Administration of AGEs to mice showed heavy proteinuria and glomerular abnormalities. Reduced podocyte number in mice administered with AGEs could be attributed to the epithelial-mesenchymal transition of podocytes. Our study suggests CML could be independently related to the podocyte injury and the risk of DN progression to ESKD in patients with microalbuminuria. AGEs in general or CML could be considered a prognostic marker to assess diabetic kidney disease.

Chronic kidney disease: a review of proteomic and metabolomic approaches to membranous glomerulonephritis, focal segmental glomerulosclerosis, and IgA nephropathy biomarkers

Chronic Kidney Disease (CKD) is a global health problem annually affecting millions of people around the world. It is a comprehensive syndrome, and various factors may contribute to its occurrence. In this study, it was attempted to provide an accurate definition of chronic kidney disease; followed by focusing and discussing on molecular pathogenesis, novel diagnosis approaches based on biomarkers, recent effective antigens and new therapeutic procedures related to high-risk chronic kidney disease such as membranous glomerulonephritis, focal segmental glomerulosclerosis, and IgA nephropathy, which may lead to end-stage renal diseases. Additionally, a considerable number of metabolites and proteins that have previously been discovered and recommended as potential biomarkers of various CKD_s using ‘-omics-’ technologies, proteomics, and metabolomics were reviewed.

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.