Cyclosporine protects glomeruli from FSGS factor via an increase in glomerular cAMP

Tacrolimus ameliorates podocyte injury by restoring FK506 binding protein 12 (FKBP12) at actin cytoskeleton

FKBP12 was identified as a binding protein of tacrolimus (Tac). Tac binds to FKBP12 and exhibits immunosuppressive effects in T cells. Although it is reported that Tac treatment directly ameliorates the dysfunction of the podocyte in nephrotic syndrome, the precise pharmacological mechanism of Tac is not well understood yet. It is also known that FKBP12 functions independently of Tac. However, the localization and the physiological function of FKBP12 are not well elucidated. In this study, we observed that FKBP12 is highly expressed in glomeruli, and the FKBP12 in glomeruli is restricted in podocytes. FKBP12 in cultured podocytes was expressed along the actin cytoskeleton and associated with filamentous actin (F-actin). FKBP12 interacted with the actin-associated proteins 14-3-3 and synaptopodin. RNA silencing for FKBP12 reduced 14-3-3 expression, F-actin staining, and process formation in cultured podocytes. FKBP12 expression was decreased in the nephrotic model caused by adriamycin (ADR) and the cultured podocyte treated with ADR. The process formation was deteriorated in the podocytes treated with ADR. Tac treatment ameliorated these decreases. Tac treatment to the normal cells increased the expression of FKBP12 at F-actin in processes and enhanced process formation. Tac enhanced the interaction of FKBP12 with synaptopodin. These observations suggested that FKBP12 at actin cytoskeleton participates in the maintenance of processes, and Tac treatment ameliorates podocyte injury by restoring FKBP12 at actin cytoskeleton.

Combination of High-Dose Intravenous Cyclosporine and Plasma Exchange Treatment Is Effective in Post-Transplant Recurrent Focal Segmental Glomerulosclerosis: Results of Case Series

BACKGROUND

Idiopathic focal segmental glomerulosclerosis (FSGS) commonly recurs in the early post-transplant period. The treatment protocols and results are conflictive in recurrent FSGS. We aimed to present the results of our treatment protocol and basic approach to the disease recurrences.

METHODS

This prospective, single-center study was conducted between the years 2015 and 2018. Twelve patients who fit completely the diagnosis of idiopathic FSGS by clinical, laboratory, and biopsy findings were included. A specific treatment protocol which consists of plasma exchange and high dose intravenous cyclosporine was delivered to the patients independently of induction protocols. Twenty-four months of outcomes of graft functions were evaluated.

RESULTS

Nine patients completed the treatment protocol and were documented for evaluation. All patients achieved a complete or partial remission in an average 24 months of follow-up period.

CONCLUSION

Idiopathic FSGS is more commonly recurrent than thought to be. The early detection of proteinuria is crucial because the administration of a plasma exchange-based treatment protocol can reverse proteinuria. We think our treatment protocol is a well-established, efficient, and safe choice for post-transplant recurrent FSGS in adults.

Antifibrotic effects of 2-carba cyclic phosphatidic acid (2ccPA) in systemic sclerosis: contribution to the novel treatment

Background

Cyclic phosphatidic acid (cPA) has an inhibitory effect on the autotaxin (ATX)/lysophosphatidic acid (LPA) axis, which has been implicated to play an important role in the progression of fibrosis in systemic sclerosis (SSc). The purpose of this study is to assess the antifibrotic activity of cPA for the treatment of SSc using SSc skin fibroblasts and an animal model of bleomycin-induced skin fibrosis.

Methods

We used a chemically stable derivative of cPA (2ccPA). First, we investigated the effect of 2ccPA on extracellular matrix (ECM) expression in skin fibroblasts. Next, the effect of 2ccPA on the intracellular cAMP levels was determined to investigate the mechanisms of the antifibrotic activity of 2ccPA. Finally, we administered 2ccPA to bleomycin-induced SSc model mice to evaluate whether 2ccPA prevented the progression of skin fibrosis.

Results

2ccPA decreased ECM expression in SSc skin fibroblasts and TGF-β1-treated healthy skin fibroblasts without LPA stimulation. 2ccPA increased the intracellular cAMP levels in skin fibroblasts, suggesting that the antifibrotic effect of 2ccPA was the consequence of the increase in the intracellular cAMP levels. Administration of 2ccPA also ameliorated the progression of bleomycin-induced skin fibrosis in mice.

Conclusions

Our data indicated that 2ccPA had inhibitory effects on the progression of skin fibrosis by abrogating ECM production from activated skin fibroblasts. These cells were repressed, at least in part, by increased intracellular cAMP levels. 2ccPA may be able to be used to treat fibrotic lesions in SSc.

Multiple Targets for Novel Therapy of FSGS Associated with Circulating Permeability Factor

A plasma component is responsible for altered glomerular permeability in patients with focal segmental glomerulosclerosis. Evidence includes recurrence after renal transplantation, remission after plasmapheresis, proteinuria in infants of affected mothers, transfer of proteinuria to experimental animals, and impaired glomerular permeability after exposure to patient plasma. Therapy may include decreasing synthesis of the injurious agent, removing or blocking its interaction with cells, or blocking signaling or enhancing cell defenses to restore the permeability barrier and prevent progression. Agents that may prevent the synthesis of the permeability factor include cytotoxic agents or aggressive chemotherapy. Extracorporeal therapies include plasmapheresis, immunoadsorption with protein A or anti-immunoglobulin, or lipopheresis. Oral or intravenous galactose also decreases P_alb activity. Studies of glomeruli have shown that several strategies prevent the action of FSGS sera. These include blocking receptor-ligand interactions, modulating cell reactions using indomethacin or eicosanoids 20-HETE or 8,9-EET, and enhancing cytoskeleton and protein interactions using calcineurin inhibitors, glucocorticoids, or rituximab. We have identified cardiotrophin-like cytokine factor 1 (CLCF-1) as a candidate for the permeability factor. Therapies specific to CLCF-1 include potential use of cytokine receptor-like factor (CRLF-1) and inhibition of Janus kinase 2. Combined therapy using multiple modalities offers therapy to reverse proteinuria and prevent scarring.

Role of calcineurin (CN) in kidney glomerular podocyte: CN inhibitor ameliorated proteinuria by inhibiting the redistribution of CN at the slit diaphragm

Although calcineurin (CN) is distributed in many cell types and functions in regulating cell functions, the precise roles of CN remained in each type of the cells are not well understood yet. A CN inhibitor (CNI) has been used for steroid‐resistant nephrotic syndrome. A CNI is assumed to ameliorate proteinuria by preventing the overproduction of T‐cell cytokines. However, recent reports suggest that CNI has a direct effect on podocyte. It is accepted that a slit diaphragm (SD), a unique cell–cell junction of podocytes, is a critical barrier preventing a leak of plasma protein into urine. Therefore, we hypothesized that CNI has an effect on the SD. In this study, we analyzed the expression of CN in physiological and in the nephrotic model caused by the antibody against nephrin, a critical component of the SD. We observed that CN is expressed at the SD in normal rat and human kidney sections and has an interaction with nephrin. The staining of CN at the SD was reduced in the nephrotic model, while CN activity in glomeruli was increased. We also observed that the treatment with tacrolimus, a CNI, in this nephrotic model suppressed the redistribution of CN, nephrin, and other SD components and ameliorated proteinuria. These observations suggested that the redistribution and the activation of CN may participate in the development of the SD injury.

Renal and Hematological Effects of CLCF-1, a B-Cell-Stimulating Cytokine of the IL-6 Family

CLCF-1 is a cytokine known for B-cell stimulation and for neurotrophic properties. We have identified CLCF-1 as a potential injurious factor in the human renal disease focal segmental glomerulosclerosis (FSGS). We investigated its effects on renal cells and renal function in in vitro and in vivo studies. Methods include measurement of the effect of CLCF-1 on phosphorylation of target molecules of the JAK/STAT pathway, on cytoskeleton and cell morphology in cultured podocytes, on albumin permeability of isolated rat glomeruli, and on tissue phosphorylation and urine albumin after acute or chronic CLCF-1 injection. In addition, cell sorting was performed to determine the presence of cells expressing CLCF-1 in spleen and bone marrow of normal mice and the effect of CLCF-1 infusion on splenic B-cell populations. CLCF-1 increased phosphorylation of STAT3 in multiple cell types, activated podocytes leading to formation of lamellipodia and decrease in basal stress fibers, increased glomerular albumin permeability, and increased STAT3 phosphorylation of peripheral blood cells and renal cortex. CLCF-1 increased urine albumin/creatinine ratio in mice and increased B-cell expression of IgG in mouse spleen. We conclude that CLCF-1 has potentially important systemic effects, alters podocyte function, and may contribute to renal dysfunction and albuminuria.

Cyclic nucleotide signalling in kidney fibrosis

Kidney fibrosis is an important factor for the progression of kidney diseases, e.g., diabetes mellitus induced kidney failure, glomerulosclerosis and nephritis resulting in chronic kidney disease or end-stage renal disease. Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were implicated to suppress several of the above mentioned renal diseases. In this review article, identified effects and mechanisms of cGMP and cAMP regarding renal fibrosis are summarized. These mechanisms include several signalling pathways of nitric oxide/ANP/guanylyl cyclases/cGMP-dependent protein kinase and cAMP/Epac/adenylyl cyclases/cAMP-dependent protein kinase. Furthermore, diverse possible drugs activating these pathways are discussed. From these diverse mechanisms it is expected that new pharmacological treatments will evolve for the therapy or even prevention of kidney failure.

Permeability factors in nephrotic syndrome and focal segmental glomerulosclerosis

Circulating permeability factors have been identified in the plasma of patients with focal segmental glomerulosclerosis (FSGS). Post-transplant recurrence of proteinuria, improvement of proteinuria after treatment with plasmapheresis, and induction of proteinuria in experimental animals by plasma fractions each provide evidence for such plasma factors. Advanced proteomic methods have identified candidate molecules in recurrent FSGS. We have proposed cardiotrophin-like cytokine-1 as an active factor in FSGS. Another potential permeability factor in FSGS is soluble urokinase receptor. In our studies, in vitro plasma permeability activity is blocked by substances that may decrease active molecules or block their effects. We have shown that the simple sugar galactose blocks the effect of FSGS serum in vitro and decreases permeability activity when administered to patients. Since the identities of permeability factors and their mechanisms of action are not well defined, treatment of FSGS is empiric. Corticosteroids are the most common agents for initial treatment. Calcineurin inhibitors, such as cyclosporine A, and tacrolimus and immunosuppressive medications, including mycophenylate, induce remission is some patients with steroid-resistant or -dependent nephrotic syndrome. Therapies that diminish proteinuria and slow progression in FSGS as well as other conditions include renin-angiotensin blockade, blood pressure lowering and plasma lipid control. Use of findings from in vitro studies, coupled with definitive identification of pathogenic molecules, may lead to new treatments to arrest FSGS progression and prevent recurrence after transplantation.

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.

Suppression of nephrin expression by TNF-alpha via interfering with the cAMP-retinoic acid receptor pathway

Nephrin, a crucial component of the slit diaphragm, is downregulated in proteinuric glomerular diseases including glomerulonephritis. We previously reported that 1) expression of nephrin in cultured podocytes is reinforced by retinoic acid (RA) and 1,25-dihydroxyvitamin D(3), 2) these effects are mediated by retinoic acid receptor (RAR) and vitamin D receptor (VDR), and 3) basal and inducible expression of nephrin is downregulated by TNF-alpha. In the present investigation, we identified that TNF-alpha selectively represses activity of RAR but not VDR. To elucidate mechanisms underlying this observation, we tested involvement of downstream targets for TNF-alpha: nuclear factor-kappaB (NF-kappaB), mitogen-activated protein (MAP) kinases, phosphatidylinositol 3-kinase (PI3K)-Akt, and cAMP-protein kinase A (PKA). TNF-alpha caused activation of NF-kappaB, MAP kinases, and PI3K-Akt in podocytes, whereas blockade of these molecules did not affect inhibition of RAR by TNF-alpha. In contrast, TNF-alpha depressed activity of cAMP-PKA, and blockade of PKA inhibited basal and RA-induced activation of RAR. Furthermore, activity of RAR was significantly upregulated by cAMP, and the suppressive effect of TNF-alpha on RAR was reversed by cAMP-elevating agents. These results suggest that 1) expression of nephrin in podocytes is regulated by the cAMP-RAR pathway and 2) suppression of nephrin by TNF-alpha is caused, at least in part, through selective inhibition of this pathway.

Treatment of focal segmental glomerulosclerosis with immunophilin modulation: when did we stop thinking about pathogenesis?

Nephrotic focal segmental glomerulosclerosis (FSGS) represents a difficult therapeutic challenge. FSGS has long been considered a subset of idiopathic nephrotic syndrome, lumping together FSGS and minimal change disease (MCD). The time-honored 'Shalhoub hypothesis' has led to treating FSGS as a T-cell-driven condition in which a lymphokine, considered without proof as being the 'glomerular permeability factor,' induces proteinuria and podocyte functional and structural derangement. This has led to trying, in addition to steroids, every new drug marketed in the field of organ transplantation, first cyclosporine (CsA) and then other immunophilin modulators. The fact that alkylating agents and mycophenolate mofetil have obtained a poor and inconstant favorable effect, and that rituximab may obtain remissions, although inconstantly, has not led to reconsidering the T-cell hypothesis. This wrong thinking has fostered innumerable, mostly uncontrolled, treatment trials with various immunosuppressive agents. In fact, clinicians have not considered the fact that some but not all immunophilin modulators may be effective as nonspecific antiproteinuric agents, rather than as immunosuppressive drugs, and that treatment success does not exclude a non-immunologic pathophysiology. Recent findings on the mode of action of CsA and FK-506 have lent support to this concept. This review should be considered as a plea to reconsider the pathogenesis of nephrotic FSGS, applying all efforts to the identification of the factor, or factors, responsible for nephrotic FSGS, and to fund treatment to counteract the 'factor,' rather than pursuing costly and non-evidence-based immunosuppressive therapeutic trials.

Recurrent glomerulonephritis after renal transplantation: an unsolved problem

BACKGROUND AND OBJECTIVES

Despite advances in prevention of acute rejection and improved short- and long-term kidney graft survival, recurrent glomerulonephritis remains problematic and poorly characterized. This study analyzed prevalence and outcome of recurrent glomerulonephritis from various registries.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Definition, classification, and limitations in evaluating epidemiology of native and recurrent glomerulonephritis are discussed. Epidemiology of native glomerulonephritis as the cause of end-stage renal failure and subsequent recurrence of individual glomerulonephritis was evaluated using data from various registries, and pathogenesis of individual glomerulonephritis is discussed.

RESULTS

Analysis of data from transplant registries revealed that glomerulonephritis is an important cause of end-stage renal disease in white and pediatric recipients; however, glomerulonephritis as the cause of end-stage renal disease is not characterized well in black recipients, and many of them are perhaps labeled to have hypertensive nephrosclerosis as the cause of renal disease without renal biopsy. A systematic approach toward urinalysis after transplantation and utility of immunofluorescence and electron microscopic examination of renal biopsy tissues will identify the true prevalence of recurrent glomerulonephritis. Data on recurrent glomerulonephritis should be compiled by either using registry analysis or pooling data from multiple centers. This will provide true data on prevalence and outcome and could potentially initiate translational research studies.

CONCLUSIONS

The understanding of the pathogenesis of recurrent glomerulonephritis is critical to optimize prevention as well as to treat individual recurrent glomerulonephritis, which can enhance long-term graft survival.

Recurrence of proteinuria following renal transplantation in congenital nephrotic syndrome of the Finnish type

We report a Caucasian boy of Italian descent with congenital nephrotic syndrome of the Finnish type (NPHS1, CNF, MIM 256300) who developed recurrence of proteinuria and hypoalbuminemia on the seventh post-operative day following living related renal transplantation from his paternal aunt. The allograft biopsy was normal except for effacement of podocyte foot processes on electron microscopy. He was treated by the substitution of mycophenolate mofetil with cyclophosphamide for 12 weeks, in addition to cyclosporine, prednisone and daclizumab. His proteinuria resolved quickly following the initiation of cyclophosphamide treatment, and he remains in remission 4 years after receiving his transplant. His native and allograft kidneys were evaluated for nephrin expression by immunohistochemistry, DNA analysis for the NPHS1 mutation, serum for the presence of auto-antibodies to nephrin by both enzyme-linked immunosorbent assay (ELISA) and fetal glomeruli immunofluorescence assay, and serum for glomerular permeability to albumin (Palb) activity using a functional in vitro assay for Palb. Nephrin expression was completely absent in the native kidney, while it was decreased in the allograft compared with normal. DNA analysis of the NPHS1 gene revealed mutations 3248G>T and 3250delG in exon 24, causing G1083V and 1084Vfs, respectively, inherited from his father, and 3478C>T in exon 27, that leads to R1160X, inherited from his mother. Serum was negative for auto-antibodies to nephrin. Interestingly, the Palb activity was increased at the time of recurrence of proteinuria following transplantation (Palb 0.73+/-0.10) and remained elevated when retested more than 3 years later (Palb 0.54+/-0.09). This is the first report of increased Palb activity in recurrence of proteinuria following transplantation in NPHS1. We speculate the role of increased Palb activity in the recurrence of proteinuria following transplantation in NPHS1.

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.

Glomerular albumin permeability as an in vitro model for characterizing the mechanism of focal glomerulosclerosis and predicting post-transplant recurrence

The putative mechanisms of proteinuria in idiopathic focal glomerulosclerosis and of its post-transplant recurrence are discussed. It is proposed that a balance between circulating factors with permeability activity on glomeruli and putative inhibitors play a key role. The characterization of inductors is currently in progress; most inhibitors appear to be apolipoproteins (mainly apoJ and apo E) but we cannot exclude other substances. The goal is now to evaluate the concentration of both inducers and inhibitors of glomerular permeability in vivo. Permeability activity in plasma of patients with FSGS with and without recurrence of the disease may be evaluated by an in vitro functional essay with isolated glomeruli. Published data on permeability activity evaluated with this method in different proteinuric states gave, however, controversial results and this test cannot be readily considered of clear clinical utility. Only the definitive characterization and quantification in vivo of the different molecules that play a role in FSGS may furnish adequate answer.

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.

Permeability factors in focal segmental glomerulosclerosis

The pathologic diagnosis of focal segmental glomerulosclerosis (FSGS) is associated with a syndrome of steroid-resistant nephrotic syndrome and progressive renal insufficiency. The incidence of FSGS has increased in recent years. Known causes of FSGS include genetic abnormalities, viral infections, decreased nephron number, and hyperperfusion/hyperfiltration. The etiology is unknown in the majority of cases. FSGS recurs after initial renal transplantation in as many as 30% to 50% of patients. Recent studies have verified the hypothesis that plasma of patients with FSGS contains a factor or factors that increase permeability of glomerular capillaries and cause proteinuria after injection into rats. Patients who experience posttransplant recurrence of FSGS and those with rapidly progressive disease exhibit this activity. Permeability activity has been verified in functional assays and defined by measurement of albumin permeability (P(alb)) or glomerular volume variation (GVV). Permeability activity is decreased by plasmapheresis or immunoadsorption and can be recovered from discarded plasma or eluate from adsorption materials. Studies from our laboratory indicate that permeability activity is carried by small, highly glycosylated, hydrophobic protein(s)/peptide(s). Normal plasma contains substances capable of blocking or inactivating the FSGS permeability factor. Pharmacologic agents including cyclosporine, indomethacin, and derivatives of Trypterigium wilfordii also block permeability activity in vitro. The observation that permeability activity can be blocked by diverse agents raises hope that specific therapy may be designed for FSGS. Future investigations will permit identification of the active FSGS permeability factor, of mechanisms that initiate and perpetuate proteinuria, and of interventions to prevent renal failure in native kidneys and recurrence of disease in renal allografts.

Cyclosporine in the treatment of idiopathic focal segmental glomerulosclerosis

Cyclosporine a known powerful immunosuppressive medication and has been used in the treatment of focal segmental glomerulosclerosis (FSGS) for over a decade. Its precise mechanism of action in this disorder is still debated and is likely at more than one level related to the pathophysiology of the disease. Multiple studies have been performed but the numbers of randomized trials of this drug in this disease are very limited. However, both the best studies in children and adults indicate in the steroid-resistant patients that 50% to 70% will have a response in terms of a significant reduction in proteinuria. Provided the total dose is kept to 5 mg/kg or less and duration to less than 12 months, the drug is safe but careful monitoring is required to maintain the blood pressure at ideal levels and to avoid nephrotoxicity. Relapses are common, but rather than considering this a failure of therapy the drug should be reintroduced because in most cases it will reestablish control of the proteinuria. Although in the past cyclosporine has been considered a second-line agent in FSGS, emerging data would suggest in the high-risk patients related to corticosteroid toxicity it should be considered primary therapy.

Serial estimates of serum permeability activity and clinical correlates in patients with native kidney focal segmental glomerulosclerosis

A serum or plasma factor in certain patients with focal segmental glomerulosclerosis (FSGS) has been found to increase glomerular albumin permeability (P(alb)) and causes proteinuria in experimental animals. High P(alb) is associated with recurrence of FSGS after transplantation, but serial studies of P(alb) activity in patients with native kidney FSGS have not been performed, and the relationship between P(alb) and remission of proteinuria is not known. This study was designed to determine P(alb) activity before, during, and after 24 wk of treatment with cyclosporine or placebo given as part of a randomized controlled trial in steroid-resistant FSGS patients with nephrotic range proteinuria. Pretreatment P(alb) averaged 0.36 +/- 0.22 and was not significantly different between treatment groups and was not altered during or after the test medication. There was no association between P(alb) activity and remission or relapse in proteinuria. The average P(alb) activity in native kidney FSGS was lower than in previously reported patients with posttransplant recurrence of the disease, and its level did not vary during the course of the study. The antiproteinuric effect of cyclosporine appeared independent of changes in P(alb). This finding is consistent with a direct effect of cyclosporine on glomerular barrier function and/or that within this group of patients the variations in proteinuria are not reflected in changes in Palb because of its limits in terms of reproducibility and responsiveness.

cAMP pathway in podocytes

Podocytes possess receptors for a variety of hormones. The following receptors whose stimulation results in increased cAMP levels have been detected in podocytes: adrenergic beta(2) receptor, dopamine D(1) receptor, prostaglandin IP and EP(4) receptors, and parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor. Besides activating protein kinase A, increased levels of cAMP depolarize podocytes via opening of chloride channels. Relatively little is known about the impact of the cAMP pathway on podocyte function. Results obtained in a limited number of studies indicate that cAMP in podocytes may regulate cell morphology, actin assembly, and matrix production. In addition, cAMP seems to attenuate the action of hormones, which activate the Ca(2+)/protein kinase C pathway. Effects of the cAMP pathway on further aspects of podocyte biology, such as contractility, phosphorylation state of slit membrane-associated proteins, glomerular permeability, cell cycle control, and synthesis of reactive oxygen species can be anticipated from studies on other cell types and from studies on isolated glomeruli. In summary, the data available indicate that the cAMP pathway affects several aspects of podocyte biology in an overall glomerulo-protective manner.

Consideration of vaccination against the FSGS factor

Focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic disease in adults, and it is thought to be increasing in incidence. FSGS is often difficult to treat and even has a high propensity to relapse after transplant. Indeed, this suggests that there might be some circulating factor responsible for proteinuria ('FSGS factor'). Here I suggest that if and when the FSGS factor is found, vaccination against this factor might be a useful treatment modality for FSGS.

Single-center analysis of early recurrence of nephrotic syndrome following renal transplantation in children

Recurrence of nephrotic syndrome (NS) after transplantation (Tx) occurs in 20-50% of renal transplant recipients, with a median time to recurrence of 14 days and a 50% rate of graft loss. We performed a retrospective analysis of 22 pediatric patients with NS who received renal transplants at the Children's Hospital, Boston, between 1982 and 1999. During the first 14 days following Tx, 13 (59%) patients developed clinical recurrent nephrotic syndrome (RNS). RNS developed in 50% of living donor recipients and in 70% of cadaveric donor recipients (p= non-significant). Seven of the 13 patients with RNS were treated with plasmapheresis, while six received standard immunosuppressive induction therapy only. Two of the seven treated patients and one of the six untreated patients lost their grafts to RNS, yielding a total RNS graft loss rate of 23%. However, patients with RNS who achieved remission had significantly higher cumulative graft survival at 5 yr than did RNS patients who did not achieve remission (p< 0.001). Overall cumulative graft survival at 5 yr was not significantly different between the two groups: 67% in those with non-recurrent nephrotic syndrome (NRNS) vs. 64% in those with RNS, p= non-significant. We conclude that successful reversal of early RNS improves long-term graft survival in pediatric RNS. Multi-center studies are sorely needed to develop novel, less toxic therapies for native and recurrent NS.

Long-term treatment of focal segmental glomerulosclerosis in children with cyclosporine given as a single daily dose

Cyclosporine (CsA) has been successfully used for treatment of children with focal segmental glomerulosclerosis (FSGS) and nephrotic syndrome (NS) for the last decade. Response rates of 50% to 100% have been reported using twice-daily dosing of 5 to 32 mg/kg/d, achieving trough blood levels of 70 to 500 ng/mL. Treatment has been associated with a high incidence of side effects, including nephrotoxicity, hypertension, gingival hyperplasia, and hirsutism. To determine whether once-daily low-dose CsA could minimize side effects and still induce remission, 21 children with biopsy-proven FSGS and NS, each treated with CsA, 4.6 +/- 0.8 mg/kg/d, with no predetermined target trough blood levels, were studied. Eleven of 21 children (52%) attained complete remission and 5 of 21 children (24%) attained partial remission, for a total response rate of 76%. Mean time to response was 2.8 +/- 0.8 months, and mean duration of therapy was 20.6 +/- 13.7 months. CsA dosage was tapered or stopped in 9 responders; 3 of these patients maintained remission at last follow-up 6 to 13 months later, and 6 patients relapsed at 1.5 to 18.7 months (mean, 8.7 months). Five of these 6 patients responded again when CsA therapy was restarted or the dosage was increased. Twelve of 16 responders were still being administered CsA at last follow-up 11 to 60 months (mean, 24.6 months) later. Five of 21 patients (24%) had no response to CsA during 2 to 27 months of therapy; 4 of these 5 patients developed end-stage renal disease after CsA therapy was stopped. Side effects of CsA therapy were minimal: 1 patient each developed new-onset hypertension or gingival hyperplasia, and no patient had hirsutism or nephrotoxicity. Single daily low-dose CsA appears to be effective for long-term treatment of children with FSGS and NS, with fewer side effects than twice-daily dosing.

Components of normal serum block the focal segmental glomerulosclerosis factor activity in vitro

BACKGROUND

Sera from some patients with focal segmental glomerulosclerosis (FSGS) increase glomerular albumin permeability (P(alb)) in vitro. The hypothesis that a component of normal serum can protect the glomerular permeability barrier was tested using sera from FSGS patients, normal individuals, and several mammalian and avian species.

METHODS

In most experiments, isolated rat glomeruli were incubated in medium containing FSGS serum known to increase P(alb) in vitro, normal serum, or both active FSGS and normal serum. In other experiments, fractions of normal serum and serum from other vertebrate species were incubated with active FSGS serum. P(alb) was calculated from glomerular capillary expansion in response to an oncotic gradient. To enrich the blocking activity, normal pooled human plasma was subjected to various biochemical manipulations.

RESULTS

Normal human serum prevented the increase in P(alb) (active FSGS sera, 0.77 +/- 0.12; active FSGS sera:normal serum, 1:1 mix, 0.06 +/- 0.30, P < 0.001). Protection diminished as the concentration of normal serum was decreased. Specific fractions of human serum, including human albumin and immunoglobulin fractions, were not protective. Blocking activity was present in 80% ammonium sulfate precipitate and certain fractions from size-exclusion chromatography of normal pooled human plasma. Normal serum from each of the vertebrate species tested also prevented the increase in P(alb). Preincubation with normal serum was protective during subsequent incubation with FSGS serum, but normal serum was not protective after preincubation with FSGS serum.

CONCLUSIONS

We conclude that a factor or factors in normal serum block the permeability effect of active FSGS sera. This phenomenon may account for variability in proteinuria among patients with FSGS and may explain inconsistent proteinuria following injection of FSGS sera into experimental animals. Characterization of the protective substance(s) and the mechanism by which the increase in permeability is blocked may provide insight into the pathogenesis of FSGS.