Recent Progress in Deciphering the Etiopathogenesis of Primary Membranous Nephropathy

Yi Shen An, a Chinese traditional prescription, ameliorates membranous glomerulonephritis induced by cationic bovine serum albumin in rats

CONTEXT

Yi Shen An (YSA) is an investigational composite of traditional Chinese medicine (Reference: 2010L000974) for the treatment of renal disease.

OBJECTIVE

To investigate the protective effects of YSA against membranous glomerulonephritis (MGN).

MATERIALS AND METHODS

Male Sprague-Dawley rats were injected with cationic bovine serum albumin (C-BSA) to create a model of MGN. Then, rats were orally treated with YSA at doses of 0.25, 0.5, 1 and 2 g/kg for 35 successive days; prednisone (5 mg/kg) was used as a positive control. At the end of the experimental period, we performed a series of tests, including 24 h urinary protein, and biochemical, immunological, antioxidative, coagulation indices, and histopathological examination.

RESULTS

YSA-1 g/kg significantly lowered urinary protein from 68.37 to 30.74 mg (p < 0.01). Meantime, total protein (TP) and albumin (ALB) recovered from 66.26 and 20.51 g/L to 76.08 and 35.64 g/L (p < 0.01), respectively. YSA removed the deposition of immunoglobulin G (IgG) and complement 3c (C3c), prevented inter-capillary cell hyperplasia on the glomerular basement membrane (GBM), and reduced electron-dense deposits and fusion of podocytes. In addition, serum IgG and superoxide dismutase were significantly elevated. In contrast, malondialdehyde, total cholesterol, triglyceride, circulating immune complex (CIC), and immunoglobulin M decreased in the YSA-treated group. Moreover, the blood coagulation dysfunction was adjusted.

DISCUSSION AND CONCLUSIONS

These findings indicate YSA may exert a therapeutic effect against MGN through the inhibition of CIC formation, and the removal of IgG and C3c deposition from the GBM, thus supporting the development of further clinical trials.

Revisiting immunological and clinical aspects of membranous nephropathy

Idiopathic or primary membranous nephropathy (IMN) is one of the most frequent causes of nephrotic syndrome in adults and the elderly. It is characterized by a thickening of the wall of the glomerular capillaries due to the presence of immune complex deposits. 85% of membranous nephropathy cases are classified as primary or idiopathic (IMN). The rest are of secondary origin (SMN), caused by autoimmune conditions or malignant tumors as lung cancer, colon and melanomas. It is an organ-specific autoimmune disease in which the complement system plays an important role with the formation of the membrane attack complex (MAC; C5b-9), which produces an alteration of the podocyte structure. The antigen responsible for 70-80% of IMN is a podocyte protein called M-type phospholipase A2 receptor (PLA2R). More recently, another podocyte antigen has been identified, the "Thrombospondin type-1 domain-containing 7A" (THSD7A), which is responsible for 10% of the cases of negative IMN for anti- PLA2R.

The influence of PM2.5 exposure on kidney diseases

The harm of air pollution to public health has become a research hotspot, especially atmospheric fine-particulate matter (PM_2.5). In recent years, epidemiological investigations have confirmed that PM_2.5 is closely related to chronic kidney disease and membranous nephropathy Basic research has demonstrated that PM_2.5 has an impact on the normal function of the kidneys through accumulation in the kidney, endothelial dysfunction, abnormal renin-angiotensin system, and immune complex deposition. Moreover, the mechanism of PM_2.5 damage to the kidney involves inflammation, oxidative stress, apoptosis, DNA damage, and autophagy. In this review, we summarized the latest developments in the effects of PM_2.5 on kidney disease in human and animal studies, so as to provide new ideas for the prevention and treatment of kidney disease.

Characteristics of disease distribution for the 1 370 renal biopsy cases in two hospitals from Guilin and Jining

OBJECTIVES

To analyze the constitution and distribution characteristics of renal pathological disease spectrum in the 2 hospitals from Guilin city and Jining city in recent 5 years.

METHODS

The pathological results of inpatients with renal biopsy in the 2 hospitals from Guilin city and Jining city from April 1, 2014 to August 15, 2018 were retrospectively analyzed. A total of 1 370 renal biopsy cases were collected, including 706 cases in Affiliated Hospital of Jining Medical College (Jiyi) and 664 cases in Affiliated Hospital of Guilin Medical College (Guiyi).

RESULTS

There was no significant difference in gender, age, seasonal distribution and the total proportion of primary and secondary glomerular diseases between the 2 hospitals (all P>0.05). The ratio of male to female in the 2 hospitals was 1.18 (Jiyi) and 0.98 (Guiyi). IgA nephropathy (IgAN) was the major disease in 14-30 years old patients, and membranous nephropathy (MN) was the most common in 40-50 years old patients. There are 15 kinds of same diseases and 10 kinds of different diseases in the 2 hospitals. Among them, three pathological diseases (3 cases) including obesity-related nephropathy, primary Sjogren's syndrome renal damage, and pregnancy-induced hypertensive renal damage only appeared in Jiyi, while 7 diseases (55 cases) including focal segmental glomerulosclerosis (FSGS), focal proliferative glomerulonephritis (FGN), proliferative sclerosing glomerulonephritis (PSGN), endocapillary proliferative glomerulonephritis (EPGN), multiple myeloma renal damage, eosinophilic tumor renal damage and angiomyolipoma renal damage only appeared in Guiyi. Primary glomerular diseases (82% in Jiyi/79% in Guiyi) were higher than secondary nephropathy. The top two diseases in biopsy rate were MN and IgAN. The incidence rate of some diseases in Jiyi was higher than that in Guiyi, and these diseases included MN (48.87%, 31.78%), minimal change disease (MCD) (11.47%, 2.71%), allergic purpura nephritis (Henoch-Schlein purpura nephritis, HSPN) (3.97%, 1.51%), hypertensive renal damage (3.12%, 0.15%), diabetic nephropathy (DN) (2.97%, 1.36%). The incidence rate of other diseases in Guiyi were higher than that in Jiyi, and these diseases included IgAN (22.59%, 19.14%), mesangial proliferative glomerulonephritis (MsPGN) (11.45%, 0.99%), lupus nephritis (LN) (8.58%, 4.67%), hepatitis B virus associated nephritis (HBVGN) (7.53%, 1.84%), there were significant difference between the 2 hospitals in the above diseases (all P<0.05).

CONCLUSIONS

The disease distribution of renal biopsy cases in the 2 hospitals displays both similarities and characteristics. Primary glomerular disease is still the main disease. MN has surpassed IgAN and jumped to the first place. The high incidence age of MN is 40-50 years old, and IgAN is 14-30 years old. The incidence rates of MN, MCD, HSPN, hypertensive renal damage, DN and other related diseases of air quality and lifestyle in Jiyi are higher than those in Guiyi. IgAN, MsPGN, LN, HBVGN and other diseases related to infection and tumor factors were higher in Guiyi than those in Jiyi. The prevention and control strategies in the 2 regions need to be adapted to local conditions. More attention should be paid to the impact of environment and lifestyle on kidney health in East China. We should pay attention to the damage to kidney caused by infectious diseases in Southern China, especially in female patients.

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.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Efficacy and safety of rituximab in the treatment of membranous nephropathy: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

Rituximab (RTX) is considered to be a promising drug for curing membranous nephropathy. However, the efficacy and safety of RTX in treating membranous nephropathy remain uncertain. This meta-analysis aimed to investigate the efficacy and safety of RTX in patients with membranous nephropathy.

METHODS

A literature search was performed using Pubmed, Embase, OVID, and Cochrane Library and randomized controlled trials (RCTs) case-controls and cohort studies published till 30 July 2019 were assessed. The studies assessing the efficacy and safety of RTX in patients with membranous nephropathy were included.

RESULTS

Eight relevant trials involving 542 patients were included in the meta-analysis. It was found that RTX did not significantly improve serum albumin levels and e-GFR when compared with the control group (including cyclosporine and cyclophosphamide, chlorambucil, prednisone, non-immunosuppressive anti-proteinuria treatment), serum albumin levels (OR = 0.31, 95%CI-0.12-0.74, P = .15), e-GFR (OR = -1.49, 95%CI-17.14-14.17, P = .85). However, RTX did reduce the serum creatinine (OR = -0.01, 95%CI-0.36-0.34, P = .95) and urinary protein (OR = -2.39, 95%CI -7.30 -2.53, P = .34) levels. Also, in comparison to the control group, RTX did improve the total remission rate (OR = 1.63, 95%CI 0.48-5.54, P = .43), achieve a higher rate of complete remission (OR = 2.54, 95%CI 1.65-3.90, P < .01) and also reduced the amount of M-type phospholipase A2 receptor-Antibody depletion in patients (OR = 5.59, 95%CI 1.81-17.2, P = .003). RTX-related adverse events were mostly mild (most infusion-related reactions) in nature and serious adverse events were rare.

CONCLUSION

RTX proved to be efficient, well-tolerated and a safe drug in the treatment of membranous nephropathy. Most patients reach complete remission during the follow-up period, and relapse is rare. RTX may turn out to be promising in membranous nephropathy patients.

Immunoadsorption in nephrotic syndrome: Where are we now and where are we going from here?

Idiopathic nephrotic syndrome (INS) is characterized by three different entities, namely minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS) and membranous nephropathy (MN). While there is an increasing understanding of primary MN with the discovery of antibodies directed against phospholipase A2 receptor (PLA2R Ab) and thrombospondin type 1 domain-containing 7A, circulatory factors causative of inducing MCD and FSGS remain in part elusive. Extracorporeal treatment forms (mostly plasma exchange) have been reserved for patients with either a disease course refractory to commonly prescribed immunosuppressive drugs or to patients with recurrence after kidney transplantation. There is a paucity of data supporting the use of immunoadsorption (IAS) in the management of MCD and MN and evidence to perform LDL-apheresis in the former is limited to reports from Japan. Treatment with IAS in primary FSGS has shown mixed responses, possibly biased by including treatment-resistant cases in the absence of genetic testing. In those with recurrence of the disease following kidney transplantation, IAS has shown high remission rates with an acceptable safety profile. There is a need to compare IAS to plasma exchange (PLEX) in this indication and due to a higher amount of plasma processed during one session, IAS may have advantages over PLEX. Removal of PLA2R Ab by IAS is currently being tested in a phase II clinical trial. More clinical trials in a prospective and randomized fashion need to be designed to prove the concept that IAS may be a treatment option for INS. While PLEX is still the leading extracorporeal treatment form in these indications, this review aims to highlight the efficacy and safety of IAS in the management of INS.

A New Classification System for IgG4 Autoantibodies

IgG4 autoimmune diseases are characterized by the presence of antigen-specific autoantibodies of the IgG4 subclass and contain well-characterized diseases such as muscle-specific kinase myasthenia gravis, pemphigus, and thrombotic thrombocytopenic purpura. In recent years, several new diseases were identified, and by now 14 antigens targeted by IgG4 autoantibodies have been described. The IgG4 subclass is considered immunologically inert and functionally monovalent due to structural differences compared to other IgG subclasses. IgG4 usually arises after chronic exposure to antigen and competes with other antibody species, thus "blocking" their pathogenic effector mechanisms. Accordingly, in the context of IgG4 autoimmunity, the pathogenicity of IgG4 is associated with blocking of enzymatic activity or protein-protein interactions of the target antigen. Pathogenicity of IgG4 autoantibodies has not yet been systematically analyzed in IgG4 autoimmune diseases. Here, we establish a modified classification system based on Witebsky's postulates to determine IgG4 pathogenicity in IgG4 autoimmune diseases, review characteristics and pathogenic mechanisms of IgG4 in these disorders, and also investigate the contribution of other antibody entities to pathophysiology by additional mechanisms. As a result, three classes of IgG4 autoimmune diseases emerge: class I where IgG4 pathogenicity is validated by the use of subclass-specific autoantibodies in animal models and/or in vitro models of pathogenicity; class II where IgG4 pathogenicity is highly suspected but lack validation by the use of subclass specific antibodies in in vitro models of pathogenicity or animal models; and class III with insufficient data or a pathogenic mechanism associated with multivalent antigen binding. Five out of the 14 IgG4 antigens were validated as class I, five as class II, and four as class III. Antibodies of other IgG subclasses or immunoglobulin classes were present in several diseases and could contribute additional pathogenic mechanisms.