Permeability factors in focal segmental glomerulosclerosis

Role of glomerular filtration rate-modifying drugs in the development of anticoagulant-related nephropathy

Introduction

Anticoagulant‐related nephropathy (ARN), that was described in humans first as warfarin‐related nephropathy, is characterized by acute kidney injury and red blood cell (RBC) tubular casts in the kidney. 5/6 nephrectomy (5/7NE) rats treated with warfarin or dabigatran show changes in kidney function and morphology that are similar to human disease. The role of glomerular filtration rate (GFR) in the pathogenesis of ARN is not clear. The aim of these studies was to elucidate the role of GFR in the pathogenesis of dabigatran‐induced ARN in 5/6NE rats.

Methods

5/6NE rats were treated per os with 150 mg/kg/day dabigatran alone or with drugs that lower (enalapril, 1.5 mg/kg/day) or increase (albuterol, 4.0 mg/kg/day) GFR for 7 days. Changes in coagulation and kidney function were recorded daily. Kidney morphology was evaluated on day 7 after the treatment.

Results

Dabigatran resulted in activated partial thromboplastin time increase that was not affected by GFR‐modifying drugs. Blood pressure was significantly lower in 5/6NE rats treated with enalapril and dabigatran as compared to dabigatran alone. The GFR was decreased by 35% in enalapril/dabigatran‐ and increased by 26% in albuterol/dabigatran‐treated animals. There were no changes in serum creatinine, hematuria or urinary kidney injury molecule (KIM‐1) levels when GFR‐modifying drugs were added to dabigatran. All dabigatran‐treated animals had RBC casts in the kidney regardless of the GFR modification.

Conclusions

GFR does not play a significant role in the dabigatran‐induced acute kidney injury in 5/6 nephrectomy model in rats. Based in these data, modification of GFR in patients with ARN is not warranted.

Circulating CASK is associated with recurrent focal segmental glomerulosclerosis after transplantation

Introduction

Focal and Segmental GlomeruloSclerosis (FSGS) can cause nephrotic syndrome with a risk of progression to end-stage renal disease. The idiopathic form has a high rate of recurrence after transplantation, suggesting the presence of a systemic circulating factor that causes glomerular permeability and can be removed by plasmapheresis or protein-A immunoadsorption.

Results

To identify this circulating factor, the eluate proteins bound on therapeutic immunoadsorption with protein-A columns were analyzed by comparative electrophoresis and mass spectrometry. A soluble form of calcium/calmodulin-dependent serine protein kinase (CASK) was identified. CASK was immunoprecipitated only in the sera of patients with recurrent FSGS after transplantation and not in control patients. Recombinant-CASK (rCASK) induced the reorganization of the actin cytoskeleton in immortalized podocytes, a redistribution of synaptopodin, ZO-1,vinculin and ENA. rCASK also induced alterations in the permeability of a monolayer of podocytes and increased the motility of pdodocytes in vitro. The extracellular domain of CD98, a transmembrane receptor expressed on renal epithelial cells, has been found to co-immunoprecipitated with rCASK. The invalidation of CD98 with siRNA avoided the structural changes of rCask treated cells suggesting its involvement in physiopathology of the disease. In mice, recombinant CASK induced proteinuria and foot process effacement in podocytes.

Conclusion

Our results suggest that CASK can induce the recurrence of FSGS after renal transplantation.

Cryptococcosis as a cause of nephrotic syndrome? A case report and review of the literature

We present a case of a 74 years old male with cutaneous cryptococcosis of the right forearm. Cryptococcus neoformans var. neoformans was cultivated from the skin and from the bloodstream. He was diagnosed with nephrotic syndrome (focal segmental glomerulosclerosis) 21 months prior to admission, which was steroid-dependent. He was treated with prednisone and cyclosporine A. Concurrently with his renal disease he was also diagnosed as having disseminated severe tinea mannum, tinea corporis and tinea cruris; onychomycosis, skin eczema and psoriasis. After a prolonged course of anti-fungal therapy, his skin lesions as well as his nephrotic syndrome recovered completely. Follow up after 7 months without any anti-fungal or immunosuppression showed no skin or renal recurrence. We assume that the renal disease was related to the pre-existing cutaneous cryptococcosis, aggravated by immunosuppression, and discuss the close association between cutaneous cryptococcosis and nephrotic syndrome, as well as similar case reports in the literature.

Soluble CD40 ligand directly alters glomerular permeability and may act as a circulating permeability factor in FSGS

CD40/CD40 ligand (CD40L) dyad, a co-stimulatory bi-molecular complex involved in the adaptive immune response, has also potent pro-inflammatory actions in haematopoietic and non-haematopoietic cells. We describe here a novel role for soluble CD40L (sCD40L) as modifier of glomerular permselectivity directly acting on glomerular epithelial cells (GECs). We found that stimulation of CD40, constitutively expressed on GEC cell membrane, by the sCD40L rapidly induced redistribution and loss of nephrin in GECs, and increased albumin permeability in isolated rat glomeruli. Pre-treatment with inhibitors of CD40-CD40L interaction completely prevented these effects. Furthermore, in vivo injection of sCD40L induced a significant reduction of nephrin and podocin expression in mouse glomeruli, although no significant increase of urine protein/creatinine ratio was observed after in vivo injection. The same effects were induced by plasma factors partially purified from post-transplant plasma exchange eluates of patients with focal segmental glomerulosclerosis (FSGS), and were blocked by CD40-CD40L inhibitors. Moreover, 17 and 34 kDa sCD40L isoforms were detected in the same plasmapheresis eluates by Western blotting. Finally, the levels of sCD40Lwere significantly increased in serum of children both with steroid-sensitive and steroid-resistant nephrotic syndrome (NS), and in adult patients with biopsy-proven FSGS, compared to healthy subjects, but neither in children with congenital NS nor in patients with membranous nephropathy.

Our results demonstrate that sCD40L directly modifies nephrin and podocin distribution in GECs. Moreover, they suggest that sCD40L contained in plasmapheresis eluates from FSGS patients with post-transplant recurrence may contribute, presumably cooperating with other mediators, to FSGS pathogenesis by modulating glomerular permeability.

Recurrent focal segmental glomerulosclerosis after kidney transplantation

Focal segmental glomerulosclerosis (FSGS) is an important cause of glomerular disease in children and adolescents and nearly 50 % of affected patients will progress to end-stage kidney disease over a 5 to 10-year period. Unfortunately, there is no established treatment for disease in the native kidney. Moreover, up to 55 % of patients develop recurrent disease after receiving a kidney transplant, with a substantially higher risk in patients who have already experienced recurrent disease in a prior transplant. A number of clinical and laboratory factors have been identified as risk factors for this complication. In addition, new investigations into podocyte biology and circulating permeability factors have shed light on the cause of recurrent the disease. While a number of novel therapeutic agents have been applied in the management of this problem, there still is no proven treatment. In this review, we summarize recent advances in the epidemiology, pathophysiology, and treatment of recurrent FSGS in pediatric patients who have received a kidney transplant.

Epithelial cell foot process effacement in podocytes in focal and segmental glomerulosclerosis: a quantitative analysis

BACKGROUND/AIM

Effacement of the epithelial cell foot processes of glomerular podocytes are thought to be diffuse in the primary form of focal and segmental glomerulosclerosis (FSGS). In contrast, effacements that occur in the secondary form of FSGS are thought to be focal. To evaluate this theory, the extent of epithelial cell foot process effacement was analyzed and compared in podocytes from cases of primary and secondary FSGS.

METHODS

Consecutive cases of adult primary and secondary FSGS that were diagnosed between January 1997 and December 2010 were retrospectively retrieved and analyzed. The electron microscopy materials of all specimens were reviewed. Glomerular podocytes from each sample were counted, recorded and analyzed for the percentage of diffuse versus focal epithelial foot process effacement.

RESULTS

Seventeen primary and 16 secondary FSGS specimens were reviewed. In the 17 primary FSGS cases, 35.1% of the podocytes were focally fused, and 64.9% were diffusely fused. In the 16 secondary FSGS cases, 72.1% of the podocytes were focally fused. There were significantly more focally fused podocytes in secondary FSGS than in primary FSGS. In contrast, significantly more diffusely fused podocytes were observed in primary FSGS than in secondary FSGS.

CONCLUSION

This is the first study to perform a quantitative analysis of the extent of epithelial cell foot process effacement in podocytes in primary and secondary FSGS. This study also confirms that the electron microscopic characteristics of the podocyte effacement process can be used to facilitate the diagnosis of primary versus secondary FSGS.

Beneficial effect of LDL-apheresis in refractory nephrotic syndrome

LDL-apheresis is a method to correct dyslipidemia rapidly. It is expected to alleviate the tissue toxicity of persistent dyslipidemia in not only primary, but also in secondary dyslipidemia associated with refractory nephrotic syndrome, and to have a protective effect against glomerular and tubular injury as expected in atherosclerosis. In addition, the effectiveness of LDL-apheresis to promote the remission of nephrotic syndrome has been recognized. In Japan, LDL-A to control hyperlipidemia in patients with refractory nephrotic syndrome associated with focal segmental glomerulosclerosis is covered by national health insurance. Here, the hypothetical mechanism behind its effect and the evidence for its effectiveness over a long period are reviewed.

Proteomic analysis of renal diseases: unraveling the pathophysiology and biomarker discovery

Current biomedical applications of proteomics have been conducted with four main objectives: to better understand the normal biology and physiology of cells, microorganisms, tissues and organs; to explore the pathogenic mechanisms and better understand the pathophysiology of medical diseases; to identify novel biomarkers for early disease detection, prediction and prognosis; and to define new therapeutic targets, drugs and vaccines. This review focuses predominantly on proteomic applications to unravel the pathophysiology and to define novel biomarkers for various renal diseases (i.e., glomerular diseases, tubulointerstitial diseases, renal vascular disorders and renal cancers). In addition, proteomic evaluations of renal transplantation and renal replacement therapy (for acute renal failure and end-stage renal disease) are summarized. Personal opinion, future perspectives and information resources for the field of renal and urinary proteomics are provided.

B-cell-targeted therapy in adult glomerulonephritis

INTRODUCTION

There are many mechanisms through which B lymphocytes have been implicated in the pathogenesis of glomerulonephritis. There are a number of trials and clinical studies in glomerulonephritis involving depletion of CD20(+) B lymphocytes using rituximab. Newer anti-CD20 agents are currently under evaluation, as are drugs targeting alternative B-cell targets such as B lymphocyte stimulator. Such selective, targeted B-cell therapies, if shown to be effective, may be of value in minimising toxicity from more conventional agents.

AREAS COVERED

This article reviews the role of B cells as a target for therapy in adult renal disease resulting from primary glomerulonephritis and that occurring secondary to systemic disease. It will not address intracellular signalling or co-stimulatory pathways as therapeutic targets.

EXPERT OPINION

There are indications for B-cell targeted therapies in a number of adult glomerulonephritides, with varying degrees of evidence. Further understanding of the mechanisms of B-cell depletion and repletion, and interplay with B-cell survival factors, is necessary in order to identify patients who will respond favourably.

Podocyte foot process effacement in postreperfusion allograft biopsies correlates with early recurrence of proteinuria in focal segmental glomerulosclerosis

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a relatively prevalent glomerular disorder that often progresses to end-stage renal disease. Thirty to 80% of kidney transplant (KT) recipients with FSGS will experience recurrence characterized by proteinuria and podocyte damage. We hypothesized that the degree of podocyte foot process (FP) effacement in postreperfusion transplant biopsies can be used to predict the development of clinical recurrence of FSGS.

METHOD

Nineteen pairs of pre- and postreperfusion biopsy specimens were studied. We evaluated the degree of FP effacement in postreperfusion KT biopsies by counting the number of widened FP per capillary loop. Early recurrence of FSGS was defined as development of nephrotic range proteinuria between days 3 and 30 posttransplant.

RESULTS

Early recurrence occurred in 7 of 19 grafts (36.8%) at a mean of 4.29±1.89 days. The mean score of FP effacement in postreperfusion allograft biopsies was 0.72±0.31 and 1.35±0.63 in the nonrecurrent and recurrent group, respectively (P=0.039). There was an association between FP effacement and proteinuria (P = 0.04). The FP effacement score predicts early recurrence with a sensitivity of 71.4% and specificity of 91.7%.

CONCLUSION

FP effacement can be observed within minutes after reperfusion in renal transplantation of recipients with FSGS that will ultimately develop recurrent FSGS. This suggests a key role for the podocyte injury in the pathogenesis of recurrent FSGS and further supports the presence of circulating factors causing FP effacement. The FP effacement score in the postreperfusion KT biopsy may become a useful predictive test if validated in larger studies.

The plasma permeability factor in nephrotic syndrome: indirect evidence in pediatric peritoneal dialysis

BACKGROUND

Nephrotic syndrome (NS) in children has been associated with a systemic circulating permeability factor. Therefore, once peritoneal dialysis (PD) has been started, peritoneal protein losses should be higher in the nephrotic than in the non-nephrotic population.

OBJECTIVE

We compared peritoneal protein losses in children with and without NS on PD.

METHODS

Our retrospective 4-year study analyzed Hispanic patients with NS under PD. Data at dialysis entry and 6 months later were compared. Nutritional support was given according to recommended dietary allowances and recommendations from the Kidney Disease Outcomes Quality Initiative. Clinical and biochemical data were obtained, and 24-hour dialysate and urine samples were collected to measure protein losses. Dialysis dose (Kt/V), daily protein intake (DPI), normalized protein equivalent of nitrogen appearance (nPNA), peritoneal equilibration test (PET), and peritonitis rate were determined. All measurements took place at least 4 weeks after resolution of a peritonitis episode. All patients received automated PD using a HomeChoice PD System cycler (Baxter Healthcare Corporation, Deerfield, IL, USA), with an exchange volume of 1100 mL/m(2) and a dextrose concentration of 1.5% - 2.5%. A control group of non-NS children on PD matched by age and sex were also studied. Data are reported as mean ± standard deviation. Differences between groups were calculated using the Mann-Whitney U-test, and p < 0.05 was considered significant.

RESULTS

Each study group consisted of 10 patients [NS patients: 4 boys, mean age of 7.3 ± 4.1 years; control patients: 6 boys, mean age of 7.2 ± 4.7 years (p = nonsignificant)]. In the group with NS, 8 patients were diagnosed by biopsy as having focal segmental glomerulosclerosis, and 2 as having minimal-change disease. At study entry, patients with NS had hourly urinary protein losses of 398 ± 313 mg/m(2) and daily peritoneal protein losses of 3.4 ± 1.9 g/m(2), compared with 29.9 ± 31 mg/m(2) and 1.5 ± 1.1 g/m(2) respectively in the control group (p < 0.05). The same statistical difference was found 6 months later. We observed no statistical differences in PET results, daily exchange volume, and mean dextrose concentration of dialysate. Similarly, no significant between-group differences were observed for Kt/V, DPI, nPNA, and biochemical parameters.

CONCLUSIONS

Hispanic children with NS on PD show higher peritoneal protein losses than do their control counterparts. Such differences could be secondary to increased peritoneal permeability caused by a systemic permeability factor.

Focal segmental glomerulosclerosis and chronic kidney disease in pediatric patients

Focal segmental glomerulosclerosis (FSGS) is one of the most common forms of acquired glomerular disease leading to end-stage kidney disease. Its incidence is rising around the world. There is no proven therapy for those patients who do not respond to corticosteroids and it can recur in 20% to 25% of patients who receive a kidney transplant. The disease can be primary, or it can be secondary to various conditions including vesicoureteral reflux, obesity, medications, and infections. Recent advances have demonstrated the important role of genetic mutations in podocyte proteins as a cause of FSGS. There is an urgent need for randomized clinical trials to develop safe and effective therapy for FSGS that occurs in the native or transplanted kidney.

Deficiency of liver sinusoidal scavenger receptors stabilin-1 and -2 in mice causes glomerulofibrotic nephropathy via impaired hepatic clearance of noxious blood factors

Tissue homeostasis and remodeling are processes that involve high turnover of biological macromolecules. Many of the waste molecules that are by-products or degradation intermediates of biological macromolecule turnover enter the circulation and are subsequently cleared by liver sinusoidal endothelial cells (LSEC). Besides the mannose receptor, stabilin-1 and stabilin-2 are the major scavenger receptors expressed by LSEC. To more clearly elucidate the functions of stabilin-1 and -2, we have generated mice lacking stabilin-1, stabilin-2, or both stabilin-1 and -2 (Stab1–/– Stab2–/– mice). Mice lacking either stabilin-1 or stabilin-2 were phenotypically normal; however, Stab1–/– Stab2–/– mice exhibited premature mortality and developed severe glomerular fibrosis, while the liver showed only mild perisinusoidal fibrosis without dysfunction. Upon kidney transplantation into WT mice, progression of glomerular fibrosis was halted, indicating the presence of profibrotic factors in the circulation of Stab1–/– Stab2–/– mice. While plasma levels of known profibrotic cytokines were unaltered, clearance of the TGF-β family member growth differentiation factor 15 (GDF-15) was markedly impaired in Stab1–/– Stab2–/– mice but not in either Stab1–/– or Stab2–/– mice, indicating that it is a common ligand of both stabilin-1 and stabilin-2. These data lead us to conclude that stabilin-1 and -2 together guarantee proper hepatic clearance of potentially noxious agents in the blood and maintain tissue homeostasis not only in the liver but also distant organs.

Clinical trials treating focal segmental glomerulosclerosis should measure patient quality of life

Optimal therapy of patients with steroid-resistant primary focal segmental glomerulosclerosis (FSGS) remains controversial. This report describes the initial study design, baseline characteristics, and quality of life of patients enrolled in the FSGS Clinical Trial, a large multicenter randomized study of this glomerulopathy comparing a 12-month regimen of cyclosporine to the combination of mycophenolate mofetil and oral dexamethasone. Patients with age ranging 2-40 years, with an estimated glomerular filtration rate > 40 ml/min per 1.73 m², a first morning urine protein-to-creatinine ratio over one, and resistant to corticosteroids were eligible. The primary outcome was complete or partial remission of proteinuria over 52 weeks after randomization. In all, 192 patients were screened, of whom 138 were randomized for treatment. Ethnic distributions were 53 black, 78 white, and 7 other. By self- or parent-proxy reporting, 26 of the 138 patients were identified as Hispanic. The baseline glomerular filtration rate was 112.4 (76.5, 180.0) ml/min per 1.73 m², and urine protein was 4.0 (2.1, 5.3) g/g. Overall, the quality of life of the patients with FSGS was lower than healthy controls and similar to that of patients with end-stage renal disease. Thus, the impact of FSGS on quality of life is significant and this measurement should be included in all trials.

Posttransplant recurrence of primary glomerulonephritis

All forms of primary GN may recur after kidney transplantation and potentially jeopardize the survival of the graft. IgA nephritis (IgAN) may recur in approximately one third of patients, more frequently in younger patients and in those with a rapid progression of the original disease. However, with the exception of few patients with rapid progression, there is no evidence that recurrence of IgAN has a deleterious effect on graft survival at least up to 10 years. Recurrence of focal segmental glomerulosclerosis (FSGS) is often associated with nephrotic proteinuria and is more frequent in children, in patients with rapid progression of the original disease, and in those who lost a previous transplant from recurrence. The natural course of recurrent FSGS is usually unfavorable. Early and intensive plasmapheresis may obtain complete or partial response in several patients. Good results have also been reported with rituximab. Idiopathic membranous nephropathy (IMN) may recur in 30% to 40% of patients. The graft survival in patients with IMN is not different than that of patients with other renal diseases. Good results with rituximab have been reported. Membranoproliferative GN (MPGN) may recur in 27% to 65% of patients. The recurrence is more frequent and the prognosis is more severe in type II MPGN. Although recurrent GN is relatively frequent and may worsen the outcome of renal allografts in some patients, its effect is diluted by several other risk-factors that may have a greater effect than recurrent GN on the long-term graft survival.

Circulating permeability factors in idiopathic nephrotic syndrome and focal segmental glomerulosclerosis

Circulating permeability factors may be important in idiopathic nephrotic syndrome (INS) including focal segmental glomerulosclerosis (FSGS) and in recurrence after renal transplantation. Evidence for plasma factors includes posttransplant recurrence of proteinuria and its response to plasmapheresis or immunoadsorption and induction of proteinuria in experimental animals by infusion of patient plasma or its fractions. The authors and other investigators have used proteomic techniques to seek pathogenic molecules. The authors have recently proposed cardiotrophin-like cytokine-1 (CLC-1) as an active factor in FSGS. Other potential permeability factors include hemopexin and vascular permeability factor in minimal change nephrotic syndrome (MCNS) and soluble urokinase receptor in FSGS. In the authors' studies, in vitro plasma permeability activity is blocked by diverse substances that may decrease levels of active molecules or block the effects of circulating permeability factors. It has been shown that the simple sugar galactose blocks the effect of FSGS serum on albumin permeability in vitro and decreases permeability activity when administered to patients. Because identities of permeability factors and their mechanisms of action are not well defined, therapy of INS/FSGS is empiric. Corticosteroids are the mainstay of initial therapy whereas calcineurin inhibitors such as cyclosporine A (CsA) and immunosuppressive medications provide adjunctive therapy. Nonspecific therapies such as blocking the renin-angiotensin system and controlling blood pressure and plasma lipids may also diminish proteinuria and slow progression. Identification of molecules that initiate proteinuria and application of findings from in vitro studies may lead to development of new treatments to arrest progression and prevent recurrence after transplantation.

Recurrence of focal segmental glomerulosclerosis in renal allograft: an in-depth review

Focal segmental glomerulosclerosis is a major cause of chronic kidney disease requiring transplantation in children. Recurrence rate in the renal allograft transplantation is as high as 50%. Recurrence of FSGS is associated with renal dysfunction and early graft loss. To date, there is no established therapy for recurrent FSGS after renal transplant. We have reviewed the current English literature in order to summarize current practices with emphasis on graft outcome. We conclude that despite multiple approaches to the post transplant management of recurrent FSGS, none have been shown to be consistently beneficial. Currently, pheresis combined with high dose anti-calcineurin with or without rituximab seems to be the most promising. Further controlled studies are needed to define the optimal therapeutic regimens to treat recurrent of FSGS.

Antibodies to protein tyrosine phosphatase receptor type O (PTPro) increase glomerular albumin permeability (P(alb))

Glomerular capillary filtration barrier characteristics are determined in part by the slit-pore junctions of glomerular podocytes. Protein tyrosine phosphatase receptor-O (PTPro) is a transmembrane protein expressed on the apical surface of podocyte foot processes. Tyrosine phosphorylation of podocyte proteins including nephrin may control the filtration barrier. To determine whether PTPro activity is required to maintain glomerular macromolecular permeability, albumin permeability (P(alb)) was studied after incubation of glomeruli from normal animals with a series of monoclonal (mAb) and polyclonal antibodies. Reagents included mAbs to rabbit and rat PTPro and polyclonal rabbit immune IgG to rat PTPro. mAb 4C3, specific to the amino acid core of PTPro, decreased its phosphatase activity and increased P(alb) of rabbit glomeruli in a time- and concentration-dependent manner. In contrast, mAb P8E7 did not diminish phosphatase activity and did not alter P(alb). Preincubation of 4C3 with PTPro extracellular domain fusion protein blocked glomerular binding and abolished permeability activity. In parallel experiments, P(alb) of rat glomeruli was increased by two mAbs (1B4 and 1D1) or by polyclonal anti-rat PTPro. We conclude that PTPro interaction with specific antibodies acutely increases P(alb). The identity of the normal ligand for PTPro and of its substrate, as well as the mechanism by which phosphatase activity of this receptor affects the filtration barrier, remain to be determined.

Advances in the biology and genetics of the podocytopathies: implications for diagnosis and therapy

CONTEXT

Etiologic factors and pathways leading to altered podocyte phenotype are clearly numerous and involve the activity of different cellular function.

OBJECTIVE

To focus on recent discoveries in podocyte biology and genetics and their relevance to these human glomerular diseases, named podocytopathies.

DATA SOURCES

Genetic mutations in genes encoding for proteins in the nucleus, slit diaphragm, podocyte cytoplasm, and cell membrane are responsible for podocyte phenotype and functional abnormalities. Podocyte injury may also derive from secondary stimuli, such as mechanical stress, infections, or use of certain medications. Podocytes can respond to injury in a limited number of ways, which include (1) effacement, (2) apoptosis, (3) arrest of development, and (4) dedifferentiation. Each of these pathways results in a specific glomerular morphology: minimal change nephropathy, focal segmental glomerulosclerosis, diffuse mesangial sclerosis, and collapsing glomerulopathy.

CONCLUSIONS

Based on current knowledge of podocyte biology, we organized etiologic factors and morphologic features in a taxonomy of podocytopathies, which provides a novel approach to the classification of these diseases. Current and experimental therapeutic approaches are also discussed.

Advances in the biology and genetics of the podocytopathies: implications for diagnosis and therapy

CONTEXT

Etiologic factors and pathways leading to altered podocyte phenotype are clearly numerous and involve the activity of different cellular function.

OBJECTIVE

To focus on recent discoveries in podocyte biology and genetics and their relevance to these human glomerular diseases, named podocytopathies.

DATA SOURCES

Genetic mutations in genes encoding for proteins in the nucleus, slit diaphragm, podocyte cytoplasm, and cell membrane are responsible for podocyte phenotype and functional abnormalities. Podocyte injury may also derive from secondary stimuli, such as mechanical stress, infections, or use of certain medications. Podocytes can respond to injury in a limited number of ways, which include (1) effacement, (2) apoptosis, (3) arrest of development, and (4) dedifferentiation. Each of these pathways results in a specific glomerular morphology: minimal change nephropathy, focal segmental glomerulosclerosis, diffuse mesangial sclerosis, and collapsing glomerulopathy.

CONCLUSIONS

Based on current knowledge of podocyte biology, we organized etiologic factors and morphologic features in a taxonomy of podocytopathies, which provides a novel approach to the classification of these diseases. Current and experimental therapeutic approaches are also discussed.

The Urine Proteome as a Biomarker of Radiation Injury: Submitted to Proteomics- Clinical Applications Special Issue: "Renal and Urinary Proteomics (Thongboonkerd)"

Terrorist attacks or nuclear accidents could expose large numbers of people to ionizing radiation, and early biomarkers of radiation injury would be critical for triage, treatment and follow-up of such individuals. However, no such biomarkers have yet been proven to exist. We tested the potential of high throughput proteomics to identify protein biomarkers of radiation injury after total body X-ray irradiation in a rat model. Subtle functional changes in the kidney are suggested by an increased glomerular permeability for macromolecules measured within 24 hours after TBI. Ultrastructural changes in glomerular podocytes include partial loss of the interdigitating organization of foot processes. Analysis of urine by LC-MS/MS and 2D-GE showed significant changes in the urine proteome within 24 hours after TBI. Tissue kallikrein 1-related peptidase, cysteine proteinase inhibitor cystatin C and oxidized histidine were found to be increased while a number of proteinase inhibitors including kallikrein-binding protein and albumin were found to be decreased post-irradiation. Thus, TBI causes immediately detectable changes in renal structure and function and in the urinary protein profile. This suggests that both systemic and renal changes are induced by radiation and it may be possible to identify a set of biomarkers unique to radiation injury.

Remission of steroid-resistant nephrotic syndrome due to focal and segmental glomerulosclerosis using rituximab

BACKGROUND

Therapeutic options are limited in cases of focal and segmental glomerulosclerosis (FSGS) that fail to respond to steroids and calcineurin inhibitors. We describe a case in which steroid-resistant nephrotic syndrome (SRNS) secondary to FSGS did not respond to conventional treatment, but was successfully treated with rituximab. Unlike previous reports in which rituximab was used in conjunction with a calcineurin inhibitor, we present the first case where rituximab was used as the sole therapeutic agent.

CASE REPORT

An 11-month-old boy presented with severe manifestations of primary nephrotic syndrome with a subsequent non-responsive steroid course. A renal biopsy confirmed FSGS, with normal staining for podocin and nephrin. Genetic studies for podocin were normal. The child developed ciclosporin-induced hemolytic uremic syndrome (HUS), and the response to plasma exchange, following ciclosporin withdrawal, was only temporary. A trial of a combination of mycophenolate and dexamethasone did not have any effect on proteinuria or fluid status. Four weekly rituximab infusions at 375 mg/m2/dose induced a complete remission without any adverse effects.

CONCLUSIONS

This case suggests that rituximab may be used as the sole therapeutic agent in the treatment of SRNS secondary to FSGS, especially in cases where calcineurin inhibitors are contraindicated.

Clinical features and mutational survey of NPHS2 (podocin) in Japanese children with focal segmental glomerulosclerosis who underwent renal transplantation

Recurrent FSGS is a major challenge in the field of nephrology. To clarify the role of NPHS2 defects in the pathogenesis of FSGS recurrence, we sequenced all eight exons of NPHS2 in 11 Japanese pediatric FSGS patients with or without post-transplant recurrence. All patients had biopsy-proven primary FSGS, had no family history of renal diseases or consanguinity, were steroid-resistant, and received living-related renal transplantation. The mean age at onset was 5.0 +/- 3.1 yr and mean age at renal transplantation was 10.4 +/- 4.1 yr. Mutational analysis of NPHS2 was performed using polymerase chain reaction and direct sequencing. We found a synonymous T/C polymorphism at alanine 318 (GCC to GCT) in seven of 11 patients but no other causative NPHS2 mutations. FSGS recurred immediately after transplant in seven patients, while the remaining four patients had no recurrence for 3.2-5.8 yr. There were no differences between recurrent and non-recurrent patients in the onset age and the interval from onset to ESRD. In conclusion, we detected no causative NPHS2 mutations in Japanese pediatric FSGS patients with or without post-transplant recurrence. Further studies on the involvement of other genes are required to better understand recurrent FSGS.

Immunoadsorbtion and rituximab therapy in a second living-related kidney transplant patient with recurrent focal segmental glomerulosclerosis

A 29-year-old patient with focal segmental glomerulosclerosis (FSGS) and recurrence of the disease in a living donor kidney transplant received a second living-related kidney graft. She received pre- and postoperative immunoadsorptions and immunosuppression with tacrolimus, mycophenolate mofetil, basiliximab and steroids. Serum creatinine returned to normal values and only minor proteinuria was detected post-transplant (400 mg/24 h). However, recurrence of proteinuria with up to 3.3 g/24 h occurred 2 months after transplantation and the patient underwent intermediate immunoadsorption sessions with immediate reduction of proteinuria for the following year. She then received three doses of rituximab (600 mg, 375 mg/m(2)) that caused immediate reduction of proteinuria with only minimal increase in the following 12 months. Graft function is excellent 2 years after transplantation. These findings suggest that intermittent immunoadsorption combined with B-cell depletion by rituximab treatment induced prolonged reduction of proteinuria in a high-risk patient for recurrence of FSGS in the graft.

Pathophysiology of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a major cause of idiopathic steroid-resistant nephrotic syndrome (SRNS) and end-stage kidney disease (ESKD). In recent years, animal models and studies of familial forms of nephrotic syndrome helped elucidate some mechanisms of podocyte injury and disease progression in FSGS. This article reviews some of the experimental and clinical data on the pathophysiology of FSGS.

Collapsing and non-collapsing focal segmental glomerulosclerosis in kidney transplants

BACKGROUND

The aetiological and clinical associations of collapsing focal segmental glomerulosclerosis (cFSGS) following kidney transplantation (KTx) are poorly described. In this study, post-transplant cFSGS and non-collapsing FSGS (ncFSGS) were compared in recent KTx recipients. Evidence for intragraft viral infection was sought.

METHODS

Twenty-nine cases of post-KTx FSGS were identified and classified as cFSGS (n = 10) or ncFSGS (n = 19). Biopsies were scored using Banff '97 criteria and subjected to in situ hybridization (ISH) for parvovirus B19 (pvB19), simian virus 40 (SV40) and BK virus (BKV).

RESULTS

cFSGS and ncFSGS patients were comparable for age, gender, weight, delayed function, human leucocyte antigen (HLA) matching, acute rejection and median time to diagnosis. Deceased donor source was more common among cFSGS cases (70 vs 32%, P = 0.05). FSGS was recurrent in 2/10 cFSGS cases compared with 8/19 ncFSGS (P = NS). cFSGS was associated with more proteinuria (11.9 vs 7.2 g/day, P = 0.05) and higher serum creatinine (4.2 vs 1.9 mg/dl, P = 0.0001) at diagnosis. Plasmapheresis was used in two out of 10 cFSGS and seven out of 19 ncFSGS cases with treatment response in 0 of two and three of seven, respectively. Graft loss was more rapid with cFSGS compared with ncFSGS (P = 0.02). Histologically, cFSGS was associated with more severe chronic vascular abnormalities. All biopsies were negative for pvB19, SV40 and BKV by ISH.

CONCLUSIONS

cFSGS following KTx presents with higher proteinuria, diminished renal function, more severe vascular disease and higher rate of graft loss compared with the non-collapsing form. There was no evidence for infection by pvB19 or polyomaviruses.

Focal and Segmental Glomerulosclerosis: Varying Biologic Mechanisms Underlie a Final Histopathologic End Point

Focal and segmental glomerulosclerosis (FSGS) is a pathologic entity that is a common and increasing cause of end-stage renal disease. Typical manifestations include proteinuria, hypertension, worsening renal insufficiency, and, frequently, renal failure. The etiology, however, remains unknown in a majority of patients. There is an estimated recurrence rate of 30% to 40% in renal transplant patients, suggesting that the pathogenesis is not solely a result of intrinsic kidney disease. Although some of its characteristics have been reported, the precise identification of a circulating factor associated with FSGS has not been made. Remarkable progress has been made in recent years regarding biologic mechanisms surrounding FSGS and proteinuria. Insight into the pathogenesis of FSGS has been gained through the study of hereditary forms of FSGS and nephrotic syndromes. Mutations in cytoskeletal proteins that affect podocyte structure have been the target until recently. Here we review the current understanding of this glomerular disease and areas for future concentration.

Single-centre experience with cyclosporin in 106 children with idiopathic focal segmental glomerulosclerosis

BACKGROUND

Although remission is achieved in most children with nephrotic syndrome by treatment with corticosteroids, a significant proportion of patients experience relapses. Continuous or repeated use of corticosteroids inevitably induces features of steroid side-effects. Cyclosporin (CsA) has been used in the treatment of idiopathic steroid-dependent and -resistant nephrotic syndrome. However, relapse often occurs shortly after the CsA treatment is terminated. Furthermore, long-term clinical outcome of patients treated with CsA is unclear.

METHODS

We retrospectively reviewed the data of 106 nephrotic children having primary focal segmental glomerulosclerosis (FSGS) who received CsA between 1993 and 2002. Indications of CsA therapy were steroid resistance (n = 45) and steroid dependence with steroid toxicity (n = 61). Fifty-four patients received cyclophosphamide prior to CsA therapy. CsA starting dose was 6 mg/kg/day to be readjusted to maintain a whole blood trough level of 80-150 ng/ml. The drug was received for 6-48 months (mean: 22.1+/-11 months). The observation period was 5.8+/-3 and 6.1+/-1.9 years before and after CsA treatment, respectively.

RESULTS

Complete remission [proteinuria <4 mg/h/m2 body surface area (BSA)], partial remission (proteinuria 4.1-40 mg/h/m2 BSA) and resistance to CsA (proteinuria > or =45 mg/h/m2 BSA) were observed in 71.7, 7.5 and 20.8% of patients, respectively. CsA-sensitive and -resistant patients differed only in the percentage of steroid responsiveness, being 66.7% in the former group and 22.7% in the later (P<0.0001). Logistic regression analysis identified steroid resistance as the only predictor of resistance to CsA (odds ratio: 12.9; P = 0.03). Hypertension, renal impairment (>30% rise of serum creatinine), gingival hyperplasia and hypertrichosis occurred in 12.3, 6.6, 22.6 and 51.9% of patients, respectively. With the exception of hypertrichosis, side effects were significantly more frequent among CsA-resistant children. We were able to stop steroids in 91 patients, of whom 31 patients relapsed. Out of 20 patients for whom CsA was intentionally discontinued while in remission, 16 patients relapsed. Of these, four (25%) were resistant to a second course of CsA. At the last follow-up, one child had developed end-stage renal failure and three had chronic renal insufficiency.

CONCLUSIONS

CsA is effective in the treatment of children with idiopathic FSGS, but with a high relapse rate on drug withdrawal. Renal dysfunction and hypertension, which may be drug-induced or natural progression, are the most serious complications; therefore, close monitoring is essential.

Preemptive plasmapheresis and recurrence of FSGS in high-risk renal transplant recipients

Recurrent focal segmental glomerulosclerosis (FSGS) following transplantation is ascribed to the presence of a circulating FSGS permeability factor (FSPF). Plasmapheresis (PP) can induce remission of proteinuria in recurrent FSGS. This study addressed the efficacy of pre-transplant PP in decreasing the incidence of recurrence in high-risk patients. Ten patients at high-risk for FSGS recurrence because of rapid progression to renal failure (n = 4) or prior transplant recurrence of FSGS (n = 6) underwent a course of 8 PP treatments in the peri-operative period. Recurrences were identified by proteinuria >3 g/day and confirmed by biopsy. Seven patients, including all 4 with first grafts and 3 of 6 with prior recurrence, were free of recurrence at follow-up (238-1258 days). Final serum creatinine in 8 patients with functioning kidneys averaged 1.53 mg/dL. FSGS recurred within 3 months in 3 patients, each of whom had lost prior transplants to recurrent FSGS. Two of these progressed to end-stage renal disease (ESRD) and the third has significant renal dysfunction. Based on inclusion criteria, recurrence rates of 60% were expected if no treatment was given. Therefore, PP may decrease the incidence of recurrent FSGS in high-risk patients. Definitive conclusions regarding optimal management can only be drawn from larger, randomized, controlled studies.

Detection and Localization of Proteinuria by Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using MS325

After renal transplantation, persistent glomerular disease affecting the native kidneys typically causes albuminuria, at least for a period of time, making it difficult to determine in a noninvasive fashion whether proteinuria originates in the native kidneys or the renal allograft. To address this problem, dynamic contrast-enhanced magnetic resonance imaging (MRI) using gadolinium (Gd)-based albumin-bound blood pool contrast agent (MS325) to localize proteinuria was investigated. Glomerular proteinuria was induced in Sprague-Dawley rats by intravenous injection of puromycin aminonucleoside (PAN), whereas control rats received physiologic saline vehicle. Both groups of animals underwent a 40-min dynamic contrast-enhanced MRI using radio frequency spoiled gradient echo imaging sequence after injection of Gd-labeled MS325. Contrast uptake and clearance curves for cortex and medulla were determined from acquired MR images. Compared with controls, proteinuric rats exhibited significantly lower elimination rate constants. The use of gadopentetate dimeglumine (Gd-DTPA) as a contrast agent showed smaller and less specific differences between proteinuric and control groups. In rats with one proteinuric kidney (PAN-treated) and one normal kidney (transplanted from a normal rat), MRI using MS325 was able to differentiate between the two kidneys. The results suggest that MRI with an albumin-bound blood pool contrast agent may be a useful noninvasive way to localize proteinuria. If this technique can be successfully applied in human patients, it may allow for the localization of proteinuria after kidney transplant and thereby provide a noninvasive way to detect disease affecting the renal allograft.

Primary focal segmental glomerulosclerosis--long-term outcome after pediatric renal transplantation

Recurrence of the primary disease is a significant issue in pediatric renal transplantation (RTx). According to data reported by the North American Pediatric Renal Transplantation Cooperative Study, patients with focal segmental glomerulosclerosis (FSGS) as primary renal disease have a recurrence rate of 30% after the first RTx. The relative risk of an early graft loss because of recurrent disease is increased to 1.6-3.1 in pediatric patients with FSGS. In a German open multicenter study, which was initiated to investigate mycophenolate mofetil (MMF) after pediatric RTx [Transplantation 2001:71:638, Transplantation 2003:75:454], patients with FSGS were evaluated for recurrence rate, risk factors for recurrence, long-term graft function, glomerular filtration rate and transplant survival. All patients received immunosuppression with MMF, cyclosporine A and prednisone without induction therapy. Renal function and survival data for FSGS patients were compared with the results of patients with other primary renal diseases within the same study population. Among 86 patients transplanted between 1996 and 1999 eight patients suffered from FSGS as primary disease. Recurrence was diagnosed in two of the eight patients. One out of these two patients lost his graft as a result of recurrence. Risk factors such as time between diagnosis and end stage renal disease (ESRD) and age at onset did not predict recurrence. A three-year patient survival in the FSGS group was 100%, graft survival 87% vs. 97% in the non-FSGS group. Acute rejections occurred in three out of eight FSGS patients and in 37 out of 78 among the non-FSGS group. Long-term renal function, calculated using mathematical modeling based on glomerular filtration rate (GFR) data during 3 yr after RTx, was similar in FSGS patients - including a patient who had recurrence with a functioning graft - and those without FSGS. In patients with FSGS, recurring disease after RTx remains an important cause of graft loss (one of two patients in this population) even under modern immunosuppressants. Nevertheless, the immunosuppressive regimen used was associated with a similar graft survival rate and long-term renal function of FSGS patients compared with patients with other primary diseases.

Elevated macrophage migration inhibitory factor (MIF) levels in the urine of patients with focal glomerular sclerosis

The pathogenesis of focal glomerular sclerosis (FGS) is poorly understood. Macrophage migration inhibitory factor (MIF) is a potent pro-inflammatory cytokine released from T cells and macrophages, and is a key molecule in inflammation. To examine further the possible role of MIF in FGS, we measured MIF levels in the urine. The purpose of the present study was to evaluate the involvement of MIF in FGS. Urine samples were obtained from 20 FGS patients. The disease controls included 40 patients with minimal-change nephrotic syndrome (MCNS) and membranous nephropathy (MN). A group of healthy subjects also served as controls. Biopsies were performed in all patients prior to entry to the study. The samples were assayed for MIF protein by a sandwich enzyme-linked immunosorbent assay (ELISA). The levels of MIF in the urine of FGS patients were significantly higher than those of the normal controls and patients with MCNS and MN. In contrast, the levels of urinary MIF (uMIF) in patients with MCNS and MN did not differ significantly from normal values. In the present study, attention also focused on the relationship between uMIF levels and pathological features. Among the patients with FGS, uMIF levels were significantly correlated with the grade of mesangial matrix increase and that of interstitial fibrosis. There was also a significant correlation between uMIF levels and the number of both intraglomerular and interstitial macrophages. Although the underlying mechanisms remain to be determined, our study presents evidence that urinary excretion of MIF is increased in FGS patients with active renal lesions.

High-dose oral cyclosporin therapy for recurrent focal segmental glomerulosclerosis in children

BACKGROUND

Focal segmental glomerular sclerosis (FSGS) has a high propensity for recurrence after renal transplantation, with a 50% risk for graft failure from recurrent disease.

METHODS

We report on the efficacy of high-dose oral cyclosporin A (CsA) in the treatment of recurrent FSGS in children. Between August 1991 and January 2003, a total of 24 patients with FSGS underwent transplantation at 1 institution. Sixteen patients (67%) had recurrent disease. In these 16 patients, CsA dose was increased gradually until remission was achieved or there was evidence of renal toxicity. Seven patients also underwent plasma exchange.

RESULTS

Thirteen patients (81%) achieved remission. Remission was complete in 11 patients and partial in 2 patients. The CsA dose necessary for inducing remission ranged from 6 to 25 mg/kg/d. Four of these patients also underwent plasma exchange. After remission, CsA dose was reduced gradually toward the standard posttransplantation regimen. Eleven of 13 responders have a functioning graft after a follow-up ranging from 10 months to 12 years. One graft was lost because of recurrent FSGS, and another graft because of recurrence and cellular rejection; noncompliance was a factor in both losses. The 3 patients with disease that did not respond to high-dose CsA therapy lost their grafts because of recurrent FSGS. A common factor in these 3 patients was the inability to increase the CsA dose because of early evidence of nephrotoxicity, evidenced by an increase in serum creatinine level.

CONCLUSION

High-dose oral CsA therapy is effective in producing long-lasting remission of recurrent nephrotic syndrome in children with FSGS.

Proteomics in nephrology: current status and future directions

Proteomics is one among various 'OMICS' fields that have been growing rapidly in the postgenomic era. During the past few years, proteomics has been extensively applied to several fields of medicine to better understand normal physiology, to define the pathophysiology of diseases, and to identify novel biomarkers and new therapeutic targets. This review focuses on current status and future directions of proteomics in the nephrology field. Recent studies of renal proteome, proteomes of individual intrarenal structures (i.e., glomerular, vascular, tubular, brush border membrane, mesangial, and podocyte proteomes), urinary proteome, and protein profiles in dialysate or ultrafiltrate removed by renal replacement therapy are summarized.

The focal segmental glomerulosclerosis permeability factor: biochemical characteristics and biological effects

Focal segmental glomerulosclerosis (FSGS) is characterized by steroid resistant nephrotic syndrome and progression to end-stage renal disease. Proteinuria in certain patients with FSGS may be caused by a circulating factor (FSGS permeability factor [FSPF]). The current report documents the biochemical characteristics and the biological and molecular effects of 70% ammonium sulfate supernatant of plasma from patients with recurrence of FSGS after transplantation (FSGS 70% supernatant). FS permeability activity, defined as the capacity of plasma from patients with FSGS to increase albumin permeability (P(alb)) of isolated glomeruli, was assessed in vitro. Permeability activity was not affected by lyophilization. FSPF bound strongly to matrices containing Mono-Q anion exchanger or protein A. It eluted from matrix-bound Cibacron blue F3GA over a wide range of salt concentrations, indicating a potential binding with other proteins, such as albumin. FSPF caused a maximal increase in P(alb) within 2 mins of incubation in vitro. Cellular proteins isolated from glomeruli with increased P(alb) showed decreased tyrosine phosphorylation of focal adhesion kinase, paxillin, and other proteins. Tyrosine phosphatase ]inhibition prevented the increase in P(alb). Intravenous administration of as little as 3 mg protein in FSGS 70% supernatant increased P(alb), while 9 mg or more were required to produce proteinuria. We conclude that FSPF is a low-molecular-weight protein, carries an anionic charge, and binds to protein A. Effects of FSPF on the glomerular permeability barrier are rapid and dose dependent and involve signaling through altered phosphorylation of cellular proteins. Identification of these biochemical and biological characteristics may be used to design strategies for removing FSPF from circulation and for purification and identification of this factor.