The treatment of idiopathic focal segmental glomerulosclerosis in adults

Mechanism of protective actions of sparsentan in the kidney: lessons from studies in models of chronic kidney disease

Simultaneous inhibition of angiotensin II AT1 and endothelin ETA receptors has emerged as a promising approach for treatment of chronic progressive kidney disease. This therapeutic approach has been advanced by the introduction of sparsentan, the first dual AT1 and ETA receptor antagonist. Sparsentan is a single molecule with high affinity for both receptors. It is US Food and Drug Administration approved for immunoglobulin A nephropathy (IgAN) and is currently being developed as a treatment for rare kidney diseases, such as focal segmental glomerulosclerosis. Clinical studies have demonstrated the efficacy and safety of sparsentan in these conditions. In parallel with clinical development, studies have been conducted to elucidate the mechanisms of action of sparsentan and its position in the context of published evidence characterizing the nephroprotective effects of dual ETA and AT1 receptor inhibition. This review summarizes this evidence, documenting beneficial anti-inflammatory, antifibrotic, and hemodynamic actions of sparsentan in the kidney and protective actions in glomerular endothelial cells, mesangial cells, the tubulointerstitium, and podocytes, thus providing the rationale for the use of sparsentan as therapy for focal segmental glomerulosclerosis and IgAN and suggesting potential benefits in other renal diseases, such as Alport syndrome.

Current understanding of the molecular mechanisms of circulating permeability factor in focal segmental glomerulosclerosis

The pathogenetic mechanisms underlying the onset and the post-transplant recurrence of primary focal segmental glomerulosclerosis (FSGS) are complex and remain yet to be fully elucidated. However, a growing body of evidence emphasizes the pivotal role of the immune system in both initiating and perpetuating the disease. Extensive investigations, encompassing both experimental models and patient studies, have implicated T cells, B cells, and complement as crucial actors in the pathogenesis of primary FSGS, with various molecules being proposed as potential "circulating factors" contributing to the disease and its recurrence post kidney-transplantation. In this review, we critically assessed the existing literature to identify essential pathways for a comprehensive characterization of the pathogenesis of FSGS. Recent discoveries have shed further light on the intricate interplay between these mechanisms. We present an overview of the current understanding of the engagement of distinct molecules and immune cells in FSGS pathogenesis while highlighting critical knowledge gaps that require attention. A thorough characterization of these intricate immune mechanisms holds the potential to identify noninvasive biomarkers that can accurately identify patients at high risk of post-transplant recurrence. Such knowledge can pave the way for the development of targeted and personalized therapeutic approaches in the management of FSGS.

Construction and evaluation of novel αvβ3 integrin ligand-conjugated ultrasmall star polymer micelles targeted glomerular podocytes through GFB permeation

As glomerular cells, podocytes are the last line of defense for glomerular filtration barriers (GFB) and play a critical role in chronic kidney disease (CKD). Podocyte-targeted drug delivery is a promising direction in the treatment of CKD. In this study, we constructed four-arm star polymers conjugated with a novel linear RWrNM peptide. And poly ε-caprolactone (PCL) hydrophobic core and brush poly (2-hydroxyethyl methacrylate) (PHEMA) hydrophilic shell were synthesized by ROP and SET LRP polymerization. The PHEMA modified by succinic anhydride was coupled with the novel linear RWrNM peptide, and then the PCL hydrophobic core was loaded with dexamethasone acetate (Dexac) to form micelles with stable dimensions. Our findings showed that the novel micelles had an ultrasmall particle size of 16-30 nm. We, for the first time, showed that the specific affinity of the novel linear RWrNM peptide to primary podocytes (24.9 ± 1.7 times of the free RhB uptake) through the αvβ3 integrin receptor mediation was comparable to that of B16F10 cells (24.4 ± 1.2 times of the free RhB uptake). In vivo studies showed that the novel ultrasmall micelles possessed a significant kidney-targeted effect, excellent podocyte colocalization effect, and GFB permeability at 49%-60 % in normal SD rats. Besides, the novel ultrasmall micelles decreased the plasma elimination half-life of Dexac to 1.62-2.09 h and showed good safety in vitro and in vivo. Both in vitro and in vivo results demonstrated the novel ultrasmall micelles could be used as a promising drug delivery strategy for actively targeted therapy of CKD.

Ultrasound combined with microbubbles enhances the renoprotective effects of methylprednisolone in rats with adriamycin-induced nephropathy

The purpose of this study was to investigate the effect of ultrasound combined with microbbules (SonoVue^TM) on the potency of methylprednisolone in attenuating the renal injury induced by adriamycin in rats. Animal model was established by two intravenous injections of 4 mg/kg adriamycin with a 2-week interval in rats. One week later, the adriamycin injected rats were randomly divided into 7 groups, receiving various treatments daily for 2 weeks. Two doses of methylprednisolone (20 or 40 mg/kg) were administrated alone or 20 mg/kg methylprednisolone and 100 µL SonoVue^TM microbbules (1-5 × 10⁸ bubbles/mL; mean diameter of bubbles: 2.5 µm) was co-administrated by intravenous injections from the tail vein. The ultrasound was applied at a frequency of 0.8 MHz and a spatial average temporal average intensity of 2.79 W/cm² for 5 min at a 50% duty cycle (1 s on 1 s off) on the back skin of the anatomic position of the kidney in rats of two groups combined with ultrasound. Renal injury were analyzed using immunohistochemical staining, real-time PCR, light and transmission electron microcopies. The kidney function related biochemical indexes were measured by automatic biochemistry analyzer. The results showed that adriamycin induced a typical renal injury and 40 mg/kg methylprednisolone injection significantly ameliorated the abnormality of key parameters such as proteinuria, renal mRNA and protein expression levels of nephrin, collagens III and IV as well as podocyte impairment, glomerulosclerosis and tubulointerstitial injury indexes. However, a sub-dose of methylprednisolone at 20 mg/kg was ineffective when administered intravenously, but its potency at this dosage was enhanced by co-administration with 100 µL SonoVue^TM microbubbles plus ultrasound irradiation. In conclusion, ultrasound combined with microbubbles can significantly increase local renal drug delivery leading to enhanced therapeutic effect of low dose methylprednisolone in ameliorating adriamycin-induced nephropathy in rats.

Emerging drugs for treatment of focal segmental glomerulosclerosis

BACKGROUND

Glomerulosclerosis represents the final stage of glomerular injury during the course of kidney disease and can result from a primary disturbance in disorders like focal segmental glomerulosclerosis or a secondary response to tubulointerstitial disease. Overall, primary focal glomerulosclerosis (FSGS), the focus of this review, accounts for 10-20% of patients of all ages who progress to end stage kidney disease. There are no FDA approved therapeutic options that effectively prevent or delay the onset of kidney failure.

AREAS COVERED

Current immunosuppressive therapy and conservative management including inhibitors of the renin-angiotensin-aldosterone axis and sodium-glucose cotransporter are reviewed. FSGS is now recognized to represent a heterogeneous entity with multiple underlying disease mechanisms. Therefore, novel approaches targeting the podocyte cytoskeleton, immunological, inflammatory, hemodynamic and metabolic pathways are highlighted.

EXPERT OPINION

A number of factors are driving the development of drugs to treat focal segmental glomerulosclerosis in particular and glomerulosclerosis in general including growing awareness of the burden of chronic kidney disease, improved scientific understanding of the mechanism of injury, and the development of noninvasive profiles to identify subgroups of patients with discrete mechanisms of glomerular injury.

Repository corticotropin injection versus corticosteroids for protection against renal damage in a focal segmental glomerulosclerosis rodent model

Background

Focal segmental glomerulosclerosis (FSGS) causes renal fibrosis and may lead to kidney failure. FSGS and its common complication, proteinuria, are challenging to treat. Corticosteroids are ineffective in many patients with FSGS, and alternative treatments often yield suboptimal responses. Repository corticotropin injection (RCI; Acthar® Gel), a naturally sourced complex mixture of purified adrenocorticotropic hormone analogs and other pituitary peptides, may have beneficial effects on idiopathic FSGS via melanocortin receptor activation.

Methods

Two studies in a preclinical (female Sprague-Dawley rats) puromycin aminonucleoside FSGS model assessed the effect of RCI on renal function and morphology: an 8-week comparison of a single RCI dose with methylprednisolone (N = 27), and a 12-week chronic RCI dose range study (N = 34). Primary outcomes were proteinuria and renal pathology improvements for measures of renal fibrosis, tubular damage, glomerular injury, and total kidney injury score. Impact of RCI treatment was also determined by assessing urinary biomarkers for renal injury, podocyte expression of podoplanin (a biomarker for injury), podocyte effacement by electron microscopy, and histological staining for fibrosis biomarkers.

Results

Compared with saline treatment, RCI 30 IU/kg significantly reduced proteinuria, with a 38% reduction in peak mean urine protein levels on day 28 in the 8-week model, and RCI 10 IU/kg, 30 IU/kg, and 60 IU/kg reduced peak mean urine protein in the 12-week model by 18, 47, and 44%, respectively. RCI also showed significant dose-dependent improvements in fibrosis, interstitial inflammation, tubular injury, and glomerular changes. Total kidney injury score (calculated from histopathological evaluations) demonstrated statistically significant improvements with RCI 30 IU/kg in the 8-week study and RCI 60 IU/kg in the 12-week study. RCI treatment improved levels of urinary biomarkers of kidney injury (KIM-1 and OPN), expression of podoplanin, and podocyte morphology. RCI also reduced levels of desmin and fibrosis-associated collagen deposition staining. Methylprednisolone did not improve renal function or pathology in this model.

Conclusions

These results provide evidence supporting the improvement of FSGS with RCI, which was superior to corticosteroid treatment in this experimental model. To the authors’ knowledge, this is the first evidence that a drug for the treatment of FSGS supports podocyte recovery after repeated injury.

The longitudinal relationship between patient-reported outcomes and clinical characteristics among patients with focal segmental glomerulosclerosis in the Nephrotic Syndrome Study Network

Background

Understanding the relationship between clinical and patient-reported outcomes (PROs) will help support clinical care and future clinical trial design of novel therapies for focal segmental glomerulosclerosis (FSGS).

Methods

FSGS patients ≥8 years of age enrolled in the Nephrotic Syndrome Study Network completed Patient-Reported Outcomes Measurement Information System PRO measures of health-related quality of life (HRQoL) (children: global health, mobility, fatigue, pain interference, depression, anxiety, stress and peer relationships; adults: physical functioning, fatigue, pain interference, sleep impairment, mental health, depression, anxiety and social satisfaction) at baseline and during longitudinal follow-up for a maximum of 5 years. Linear mixed-effects models were used to determine which demographic, clinical and laboratory features were associated with PROs for each of the eight children and eight adults studied.

Results

There were 45 children and 114 adult FSGS patients enrolled that had at least one PRO assessment and 519 patient visits. Multivariable analyses among children found that edema was associated with global health (-7.6 points, P = 0.02) and mobility (-4.2, P = 0.02), the number of reported symptoms was associated with worse depression (-2.7 per symptom, P = 0.009) and anxiety (-2.3, P = 0.02) and the number of emergency room (ER) visits in the prior 6 months was associated with worse mobility (-2.8 per visit, P < 0.001) and fatigue (-2.4, P = 0.03). Multivariable analyses among adults found the number of reported symptoms was associated with worse function in all eight PROMIS measures and the number of ER visits was associated with worse fatigue, pain interference, sleep impairment, depression, anxiety and social satisfaction. Laboratory markers of disease severity (i.e. proteinuria, estimated glomerular filtration rate and serum albumin) did not predict PRO in multivariable analyses, with the single exception of complete remission and better pain interference scores among children (+9.3, P = 0.03).

Conclusions

PROs provide important information about HRQoL for persons with FSGS that is not captured solely by the examination of laboratory-based markers of disease. However, it is critical that instruments capture the patient experience and FSGS clinical trials may benefit from a disease-specific instrument more sensitive to within-patient changes.

TRPC channels: Regulation, dysregulation and contributions to chronic kidney disease

Mutations in the gene encoding canonical transient receptor potential-6 (TRPC6) channels result in severe nephrotic syndromes that typically lead to end-stage renal disease. Many but not all of these mutations result in a gain in the function of the resulting channel protein. Since those observations were first made, substantial work has supported the hypothesis that TRPC6 channels can also contribute to progression of acquired (non-genetic) glomerular diseases, including primary and secondary FSGS, glomerulosclerosis during autoimmune glomerulonephritis, and possibly in type-1 diabetes. Their regulation has been extensively studied, especially in podocytes, but also in mesangial cells and other cell types present in the kidney. More recent evidence has implicated TRPC6 in renal fibrosis and tubulointerstitial disease caused by urinary obstruction. Consequently TRPC6 is being extensively investigated as a target for drug discovery. Other TRPC family members are present in kidney. TRPC6 can form a functional heteromultimer with TRPC3, and it has been suggested that TRPC5 may also play a role in glomerular disease progression, although the evidence on this is contradictory. Here we review literature on the expression and regulation of TRPC6, TRPC3 and TRPC5 in various cell types of the vertebrate kidney, the evidence that these channels are dysregulated in disease models, and research showing that knock-out or pharmacological inhibition of these channels can reduce the severity of kidney disease. We also summarize several areas that remain controversial, and some of the large gaps of knowledge concerning the fundamental role of these proteins in regulation of renal function.

FAM40A alters the cytoskeleton of podocytes in familial focal and segmental glomerulosclerosis by regulating F-actin and nephrin

INTRODUCTION

Familial focal and segmental glomerulosclerosis (FFSGS) was found in a large cohort of patients in our previous study. Under the sponsorship of the National Natural Science Foundation of China, we conducted linkage analysis and full exon sequencing on the genomes of 54 patients diagnosed with FFSGS. The results revealed a FAM40A gene signature in those patients. To determine whether FAM40A was associated with podocyte lesions and whether changes in the podocyte cytoskeleton could affect podocyte function, mouse podocytes (MPs) were used in this study.

MATERIAL AND METHODS

FAM40A silencing, over-expression and mutant-type over-expression models of renal MPs were established, whereby roles of wild-type FAM40A and mutant FAM40A (c.1562T>C, p521M>T) in regulating the function of the MP cytoskeleton were explored by using cellular immunofluorescence, RT-qPCR and Western blot.

RESULTS

FAM40A was expressed and localized in MPs and significantly enriched in the nucleus and perinuclear zone. Changes of FAM40A expression altered the morphology of the MPs and their cytoskeletal organization, which was characterized by disordered distribution of F-actin, loss of the foot process architecture and the functional protein of the slit diaphragm nephrin (p < 0.05 or p < 0.01). FAM40A mutation (p521M>T) led to the formation of round and blunt morphology of the MPs and loss of the foot-process structure. In addition, expression of the cytoskeletal protein F-actin was increased and concentrated in FAM40A mutated cells, whereas the expression of nephrin decreased in those cells (p < 0.01).

CONCLUSIONS

FAM40A played an important role in maintaining the normal morphology and function of MPs by stabilizing the cytoskeleton of MPs. Moreover, mutant FAM40A (p521M>T) was able to alter the morphology and cytoskeleton of the MPs, and to decrease the expression of nephrin, which may be the main factor contributing to FSGS.

Apolipoprotein A-Ib as a biomarker of focal segmental glomerulosclerosis recurrence after kidney transplantation: diagnostic performance and assessment of its prognostic value - a multi-centre cohort study

Recurrence of idiopathic focal segmental glomerulosclerosis (FSGS) is a serious complication after kidney transplantation. FSGS relapse is suspected by a sudden increase in proteinuria but there is not an accurate noninvasive diagnostic tool to confirm this entity or to detect patients at risk. We aimed to validate the diagnostic performance of ApoA-Ib to detect FSGS relapses by measuring urinary ApoA-Ib in a retrospective cohort of 61 kidney transplanted patients (37 FSGS and 24 non-FSGS). In addition, to assess the ApoA-Ib predictive ability, ApoA-Ib was measured periodically in a prospective cohort of 13 idiopathic FSGS patients who were followed during 1 year after transplantation. ApoA-Ib had a sensitivity of 93.3% and a specificity of 90.9% to diagnose FSGS relapses, with a high negative predictive value (95.2%), confirming our previous results. In the prospective cohort, ApoA-Ib predated the recurrence in four of five episodes observed. In the nonrelapsing group (n = 9), ApoA-Ib was negative in 37 of 38 samples. ApoA-Ib has the potential to be a good diagnostic biomarker of FSGS relapses, providing a confident criterion to exclude false positives even in the presence of high proteinuria. It has also the potential to detect patients at risk of relapse, even before transplantation.

Pharmacological and genetic inhibition of downstream targets of p38 MAPK in experimental nephrotic syndrome

Nie X, Chanley MA, Pengal R, Thomas DB, Agrawal S, Smoyer WE. Pharmacological and genetic inhibition of downstream targets of p38 MAPK in experimental nephrotic syndrome. Am J Physiol Renal Physiol 314: F602-F613, 2018. First published November 29, 2017; doi: 10.1152/ajprenal.00207.2017 .-The p38 MAPK pathway plays a crucial role in various glomerulopathies, with activation being associated with disease and inhibition being associated with disease amelioration. We hypothesized that the downstream targets of p38 MAPK, MAPK-activated protein kinase 2 and/or 3 (MK2 and/or MK3), play an important role in mediating injury in experimental nephrotic syndrome via their actions on their downstream substrates heat shock protein B1 (HSPB1) and cyclooxygenase-2 (COX-2). To test this hypothesis, the effects of both pharmacological and genetic inhibition of MK2 and MK3 were examined in mouse adriamycin (ADR) and rat puromycin aminonucleoside (PAN) nephropathy models. MK2^-/-, MK3^-/-, and MK2^-/-MK3^-/- mice were generated in the Sv129 background and subjected to ADR-induced nephropathy. MK2 and MK3 protein expression was completely abrogated in the respective knockout genotypes, and massive proteinuria and renal histopathological changes developed after ADR treatment. Furthermore, renal cortical HSPB1 was induced in all four genotypes by day 21, but HSPB1 was activated only in the wild-type and MK3^-/- mice. Expression of the stress proteins HSPB8 and glucose-regulated protein 78 (GRP78) remained unaltered across all genotypes. Finally, while MK2 and/or MK3-knockout downregulated the proinflammatory enzyme COX-2, ADR significantly induced renal cortical COX-2 only in MK2^-/- mice. Additionally, pharmacological MK2 inhibition with PF-318 during PAN-induced nephropathy did not result in significant proteinuria reduction in rats. Together, these data suggest that while the inhibition of MK2 and/or MK3 regulates the renal stress response, our currently available approaches are not yet able to safely and effectively reduce proteinuria in experimental nephrotic syndrome and that other p38MAPK downstream targets should also be considered to improve the future treatment of glomerular disease.

Investigational drugs in development for focal segmental glomerulosclerosis

INTRODUCTION

Focal segmental glomerulosclerosis is an important cause of end stage kidney disease and is a paradigm for the study of glomerular scarring. There are no FDA approved treatments for this condition. Current therapies, assessed based on reduction in proteinuria, are generally effective in a subset of patients which suggests that FSGS is a heterogeneous group of glomerular disorders or podocytopathies that converge on a common histopathological phenotype. Areas covered: We searched for investigational drugs agents that target different pathophysiological pathways using the key words 'FSGS' and 'podocyte' in American and European clinical trial registers (clinicaltrials.gov; clinicaltrialsregister.eu). Published articles were searched in PubMed, Medline, the Web of Science and the Cochrane Central Register of Controlled Trials Library. Expert opinion: Progress is being made in defining the mechanism of action of subtypes of FSGS. Current and investigational therapies for FSGS target these different pathways of injury. It is anticipated that advances in systems biology will further refine the classification of FSGS by subdividing the disease based on the primary mechanism of glomerular injury, identify biomarkers to discriminate between different subtypes, and enable appropriate selection of appropriate therapy for each individual in accordance with the goals of precision medicine.

Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a leading cause of kidney disease worldwide. The presumed etiology of primary FSGS is a plasma factor with responsiveness to immunosuppressive therapy and a risk of recurrence after kidney transplant-important disease characteristics. In contrast, adaptive FSGS is associated with excessive nephron workload due to increased body size, reduced nephron capacity, or single glomerular hyperfiltration associated with certain diseases. Additional etiologies are now recognized as drivers of FSGS: high-penetrance genetic FSGS due to mutations in one of nearly 40 genes, virus-associated FSGS, and medication-associated FSGS. Emerging data support the identification of a sixth category: APOL1 risk allele-associated FSGS in individuals with sub-Saharan ancestry. The classification of a particular patient with FSGS relies on integration of findings from clinical history, laboratory testing, kidney biopsy, and in some patients, genetic testing. The kidney biopsy can be helpful, with clues provided by features on light microscopy (e.g, glomerular size, histologic variant of FSGS, microcystic tubular changes, and tubular hypertrophy), immunofluorescence (e.g, to rule out other primary glomerulopathies), and electron microscopy (e.g., extent of podocyte foot process effacement, podocyte microvillous transformation, and tubuloreticular inclusions). A complete assessment of renal histology is important for establishing the parenchymal setting of segmental glomerulosclerosis, distinguishing FSGS associated with one of many other glomerular diseases from the clinical-pathologic syndrome of FSGS. Genetic testing is beneficial in particular clinical settings. Identifying the etiology of FSGS guides selection of therapy and provides prognostic insight. Much progress has been made in our understanding of FSGS, but important outstanding issues remain, including the identity of the plasma factor believed to be responsible for primary FSGS, the value of routine implementation of genetic testing, and the identification of more effective and less toxic therapeutic interventions for FSGS.

Albumin-based nanoparticles as methylprednisolone carriers for targeted delivery towards the neonatal Fc receptor in glomerular podocytes

Glucocorticoids (GCs) are commonly used in the treatment of nephrotic syndrome. However, high doses and long periods of GC therapy can result in severe side effects. The present study aimed to selectively deliver albumin-methylprednisolone (MP) nanoparticles towards glomerular podocytes, which highly express the specific neonatal Fc receptor (FcRn) of albumin. Bovine serum albumin (BSA) was labeled with a fluorescent dye and linked with modified MP via an amide bond. The outcome nanoparticle named BSA633-MP showed a uniform size with a diameter of approximately 10 nm and contained 12 drug molecules on average. The nanoconjugates were found to be stable at pH 7.4 and acid-sensitive at pH 4.0, with approximately 72% release of the MP drug after 48 h of incubation. The nanoparticle demonstrated a 36-fold uptake in receptor-specific cellular delivery in the FcRn-expressing human podocytes compared to the uptake in the non-FcRn-expressing control cells. Co-localization further confirmed that uptake of the nanoconjugates involved receptor-mediated endocytosis followed by lysosome associated transportation. In vitro cellular experiments indicated that the BSA633-MP ameliorated puromycin aminonucleoside-induced podocyte apoptosis. Moreover, in vivo fluorescence molecular imaging showed that BSA633-MP was mainly accumulated in the liver and kidney after intravenous dosing for 24 h. Collectively, this study may provide an approach for the effective and safe therapy of nephrotic syndrome.