Successful transplant of a kidney with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis: Risk for recurrence and interventions to optimize outcomes following recurrence

BACKGROUND

FSGS is a common indication for kidney transplant with a high-risk of posttransplant recurrence.

METHODS

In this review, we summarize current knowledge about FSGS recurrence after kidney transplantation, including epidemiology, pretransplant planning, posttransplant management, and investigational treatments.

RESULTS

FSGS recurs in 14%-60% of first transplants, likely associated with a circulating permeability factor. Pretransplant counseling regarding recurrence is critical, and patients with FSGS should undergo pretransplant genetic screening. Rapid progression to ESKD, initial steroid responsiveness, younger age at diagnosis, race/ethnicity, and mesangial hypercellularity or minimal change histology on native biopsy may be associated with recurrence. Living donation is not contraindicated but does not result in improved graft survival relative to deceased donation. Pretransplant nephrectomy may be performed for a variety of reasons, but does not decrease recurrence. Pretransplant therapy with rituximab and/or PE is understudied but not clearly effective at preventing recurrence. Patients with FSGS typically present early with rapid-onset severe proteinuria. Diagnosis can be confirmed by biopsy showing foot process effacement; typical FSGS lesions are not seen on light microscopy in the early stages. There is no established effective treatment for recurrent FSGS, but renin-angiotensin-aldosterone system inhibition and extracorporeal therapies, including PE and IA, are most commonly used. Adjunct or alternative therapies may include rituximab, lipopheresis, and cyclosporine.

Assessment of increased glomerular permeability associated with recurrent focal segmental glomerulosclerosis using an in vitro model of the glomerular filtration barrier

The presence of circulating permeability factors (cPFs) has been hypothesized to be associated with recurrence of focal segmental glomerulosclerosis (rFSGS) in renal allografts. The available methods to detect cPFs are complex, not easily repeatable and inappropriate to represent the anatomical characteristics of the three-layer glomerular filtration barrier (GFB). Here we describe a novel method which measures the permeability to bovine serum albumin (BSA) through a three-layer device (3LD). The 3 layers comprise: (1) conditionally immortalized human podocytes (HCiPodo), (2) collagen type IV coated porous membrane and (3) human glomerular endothelial cells (HCiGEnC). Using this method, we found that sera from all rFSGS patients increased albumin permeability, while sera from non recurrent (nrFSGS) and genetic (gFSGS) forms of FSGS did not. The mechanisms underlying the increase of albumin permeability are probably due to endothelial cell damage as an initial event, which was demonstrated by the decrease of Platelet endothelial cell adhesion molecule (PECAM-1 or CD31), while the podocytes' expressions of synaptopodin and podocin were normal. Furthermore, we also found that the plasmapheretic treatment (PPT) eliminated the effect of increasing BSA permeability in sera from rFSGS patients. These preliminary data suggest that our in vitro GFB model could not only be useful in predicting the recurrence of FSGS after renal transplantation (RTx), but also be a valuable in vitro model to study podocyte and endothelial cell biology.

Idiopathic Nephrotic Syndrome: Characteristics and Identification of Prognostic Factors

There are various histopathological forms of idiopathic nephrotic syndrome, including minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). Whereas some relapse predictor factors have been identified in renal transplantation, the clinical future of idiopathic nephrotic syndrome in the native kidney remains uncertain. We designed a multicentric retrospective descriptive cohort study including all patients aged 15 years and over whose renal biopsy confirmed MCD or FSGS between January 2007 and December 2014. We studied 165 patients with idiopathic nephrotic syndrome; 97 with MCD and 68 with FSGS. In the MCD cohort, 91.7% of patients were treated with corticosteroids for a median total duration of 13 months. During 45 months of follow-up, 92.8% of patients achieved remission and 45.5% experienced relapse. In this cohort, 5% of patients experienced terminal kidney disease. With respect to FSGS patients, 51.5% were treated with corticosteroids for a median total duration of 15 months. During 66 months of follow-up, 73.5% of patients achieved remission and 20% experienced relapse. In this cohort, 26.5% of patients experienced terminal kidney disease. No statistical association was observed between clinical and biological initial presentation and relapse occurrence. This study describes the characteristics of a cohort of patients with the nephrotic idiopathic syndromes of MCD and FSGS from the time of renal biopsy and throughout follow-up.

[Up to date of pathophysiology mechanism of idiopathic nephrotic syndromes: Minimal change disease and focal and segmental glomerulosclerosis]

Idiopathic nephrotic syndrome represents up to 30% of adult glomerulopathies. However, its prognosis according to remission, relapse and renal failure remains unchanged since the 80s and prediction remains difficult. Physiopathology of adult idiopathic nephrotic syndrome is complex and multifactorial, including immunologic and environmental factors and a putative permeability-circulating factor, still unknown. In this point of view, we propose to summarize actual knowledge about idiopathic minimal change disease and focal and segmental glomerulosclerosis physiopathology.

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.

[Current insights about recurrence of glomerular diseases after renal transplantation]

Recurrence of glomerular disease after renal transplantation is a frequent cause of graft loss. Incidence, risk factors and outcome of recurrence are widely due to the underlying glomerular disease. Graft biopsy analysis is required to confirm the definitive diagnosis of recurrence and to start an appropriate therapy that, in some cases, remains challenging to prevent graft failure. Increased use of protocol biopsy and recent advances in our understanding of the pathogenesis of some glomerular diseases with the identification of some relevant biomarkers provide a unique opportunity to initiate kidney-protective therapy at early stages of recurrence on the graft. This review summarizes our current knowledge on the management of many recurrent primary and secondary glomerulonephritis after kidney transplantation.

The Incidence of Primary vs Secondary Focal Segmental Glomerulosclerosis: A Clinicopathologic Study

OBJECTIVES

To describe the change in the incidence rates of primary and secondary focal segmental glomerulosclerosis (FSGS) from 1994 through 2013 in Olmsted County, Minnesota, and to identify the clinical and biopsy characteristics that distinguish primary from secondary FSGS.

PATIENTS AND METHODS

Olmsted County adult residents with native kidney biopsy from January 1, 1994, through December 31, 2013, and FSGS as the only glomerulopathy were identified. The clinical and pathologic characterstics of primary and secondary FSGS were described and compared, and incidence rates were calculated.

RESULTS

Of 370 adults biopsied, 281 had glomerular diseases, of which 46 (16%) had FSGS. From 1994-2003 to 2004-2013, there were significant increases in kidney biopsy rates (14.7 [95% CI, 12.1-17.3] vs 22.9 [95% CI, 20.0-25.7] per 100,000 person-years, 17% increase per 5 years; P<.001) and total FSGS rates (1.4 [95% CI, 0.6-2.2] vs 3.2 [95% CI, 2.1-4.3] per 100,000 person-years, 41% increase per 5 years; P=.02). Compared with patients with limited foot process effacement (<80%), patients with diffuse effacement (≥80%) without an identifiable cause had lower serum albumin levels (P<.001), had higher proteinuria (P<.001), and were more likely to have nephrotic syndrome (100% vs 4%; P<.001). Patients with diffuse effacement without an identifiable cause were classified as primary FSGS, which accounted for 3 of 12 patients (25%) during 1994-2003 and 9 of 34 (26%) during 2004-2013.

CONCLUSION

Although the incidence of FSGS has increased, the proportions of primary and secondary FSGS have remained stable.

Is an 87-Year-Old Grandfather Too Marginal for Being a Kidney Donor? The View of Anesthesiologists

Living kidney donation has been accepted increasingly as a result of growth in the number of end-stage renal disease patients awaiting organ. In this aspect using grafts from marginal donors such as with advanced age is increasing in worldwide practice and also in Turkey. Therefore, anesthetic management of donors is particularly important. We herein report the anesthetic management of an 87-year-old grandfather donating his kidney to her granddaughter and review the current anesthetic strategies in a geriatric patient.

Permeability factors in idiopathic nephrotic syndrome: historical perspectives and lessons for the future

The term idiopathic nephrotic syndrome (iNS) traditionally covers minimal change disease and primary focal segmental glomerulosclerosis (FSGS), now thought to be separate disease entities. Clinical and experimental evidence suggest that circulating permeability factors are involved in their pathogenesis. In the past four decades, many investigators have searched for the responsible factors, thus far with little success. The recent report of the soluble urokinase plasminogen activator receptor as a causative factor in FSGS has received much attention, but again the initially promising findings were not confirmed. We describe the history of the search for permeability factors, discuss the pitfalls that are likely responsible for the lack of success and propose criteria that should be used in future studies when evaluating candidate permeability factors.

Relationship between serum soluble urokinase plasminogen activator receptor level and steroid responsiveness in FSGS

BACKGROUND AND OBJECTIVES

Soluble urokinase plasminogen activator receptor (suPAR) was initially proposed as a pathogenic and predictive biomarker of primary FSGS, but the findings were controversial. This study aimed to clarify the clinical implications of suPAR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study enrolled 109 patients with biopsy-proven primary FSGS who were administered prednisone between January 2011 and May 2013 and followed up for 6-24 months (median duration of follow-up, 12 months). Ninety-six healthy volunteers, 20 patients with minimal-change disease (MCD), and 22 patients with membranous nephropathy (MN) served as controls. Serum suPAR levels were measured using ELISA.

RESULTS

suPAR levels in patients with FSGS (median, 3512 [interquartile range (IQR), 2232-4231] pg/ml) were significantly higher than in healthy controls (median, 1823 [IQR, 1563-2212] pg/ml; P<0.001), patients with MCD (median, 1678 [IQR, 1476-2182] pg/ml; P<0.001), and patients with MN (median, 1668 [IQR, 1327-2127] pg/ml; P<0.001). With 3000 pg/ml used as a threshold, suPAR levels were elevated in 48.6% of patients with FSGS, in contrast to 5% of patients with MCD and 4.5% of those with MN. suPAR levels were independently associated with steroid response in patients with FSGS (odds ratio, 85.02; P=0.001). Patients who were sensitive to steroids had significantly higher suPAR levels than nonsensitive patients (median, 3426 [IQR, 2670-5655] pg/ml versus 2523 [IQR, 1977-3460] pg/ml; P=0.001). A suPAR level of 3400 pg/ml was chosen as the optimal cutoff value for steroid response. At the 6-month follow-up in 84 patients with FSGS, suPAR levels were significantly decreased in those with suPAR level ≥ 3400 pg/ml (median, 4553 [IQR, 3771-6120] pg/ml versus 3149 [IQR, 2278-3953]; P=0.002) but were unchanged in patients with suPAR level <3400 pg/ml (median, 2359 [IQR, 2023-2842] pg/ml versus 2490 [IQR, 1916-3623] pg/ml; P=0.09).

CONCLUSIONS

suPAR is specifically elevated in some patients with FSGS, which differs from the finding in patients with MCD and MN. A suPAR assay may help predict steroid response in patients with primary FSGS.

Focal segmental glomerulosclerosis: towards a better understanding for the practicing nephrologist

Focal and segmental glomerulosclerosis (FSGS) is a common histopathological lesion that can represent a primary podocytopathy, or occur as an adaptive phenomenon consequent to nephron mass reduction, a scar from a healing vasculitic lesion, direct drug toxicity or viral infection among other secondary causes. Thus, the presence of an FSGS lesion in a renal biopsy does not confer a disease diagnosis, but rather represents the beginning of an exploratory process, hopefully leading ultimately to identification of a specific etiology and its appropriate treatment. We define primary FSGS as a 'primary' podocytopathy characterized clinically by the presence of nephrotic syndrome in a patient with an FSGS lesion on light microscopy and widespread foot process effacement on electron microscopy (EM). Secondary FSGS is commonly characterized by the absence of nephrotic syndrome and the presence of segmental foot process effacement on EM. Failure to accurately differentiate between the primary and secondary forms of FSGS has resulted in many patients undergoing unnecessary immunosuppressive treatment. Here, we review some key points that may assist the practicing nephrologist to distinguish between primary and secondary FSGS.

Immunopathogenesis of idiopathic nephrotic syndrome with relapse

Idiopathic change nephrotic syndrome (INS), the most frequent glomerular disease in children and young adults, is characterized by heavy proteinuria and a relapsing remitting course. Although the mechanisms underlying the pathophysiology of proteinuria remain unclear, clinical and experimental observations suggest that lymphocyte and podocyte disturbances are two sides of the disease. The current hypothesis suggests that immune cells release a putative factor, which alters podocyte function resulting in nephrotic proteinuria. Besides T-cell abnormalities, recent evidence of B-cell depletion efficacy in sustained remissions added a new challenge in understanding the immunological mechanisms of INS. In this review, we discuss recent insights related to podocyte disorders occurring in INS and their relevance in human diseases.

[Pathogenesis and treatment of idiopathic nephrotic syndrome in adults]

Idiopathic nephrotic syndrome is the most frequent glomerular disease in children and in young adults. While genetic analyses have provided new insights into disease pathogenesis through the discovery of several podocyte genes mutated in distinct forms of inherited nephrotic syndrome, the molecular bases of minimal change nephrotic syndrome and focal and segmental glomerulosclerosis with relapses remain unclear. Although immune cell disorders, which may involve both innate and adaptive immunity, appear to play a role in the pathogenesis of steroid sensitive minimal change nephrotic syndrome, the mechanisms by which they induce podocyte dysfunction remain unresolved. It was postulated that podocyte injury results from a circulating factor secreted by abnormal T cells, but the possibility that bipolarity of the disease results from a functional disorder shared by both immune cells and the podocytes is not excluded. Minimal change nephrotic syndrome relapses are associated with an expansion of T and B cell compartments and production of growth factors as well as many cytokines. Dysfunction of T cells is supported by several findings including, inhibition of a type IV hypersensitivity reaction and unclassical T helper polarization, resulting from transcriptional interference between Th1 and Th2 transcriptional factors. A low serum level of some IgG fractions is frequently observed suggesting a defect in T-B cell cooperation, which remains to be explored. In this review, we discuss recent advances in the pathogenesis and the therapy of idiopathic nephrotic syndrome.

Basic and translational concepts of immune-mediated glomerular diseases

Genetically modified immune responses to infections and self-antigens initiate most forms of GN by generating pathogen- and danger-associated molecular patterns that stimulate Toll-like receptors and complement. These innate immune responses activate circulating monocytes and resident glomerular cells to release inflammatory mediators and initiate adaptive, antigen-specific immune responses that collectively damage glomerular structures. CD4 T cells are needed for B cell-driven antibody production that leads to immune complex formation in glomeruli, complement activation, and injury induced by both circulating inflammatory and resident glomerular effector cells. Th17 cells can also induce glomerular injury directly. In this review, information derived from studies in vitro, well characterized experimental models, and humans summarize and update likely pathogenic mechanisms involved in human diseases presenting as nephritis (postinfectious GN, IgA nephropathy, antiglomerular basement membrane and antineutrophil cytoplasmic antibody-mediated crescentic GN, lupus nephritis, type I membranoproliferative GN), and nephrotic syndrome (minimal change/FSGS, membranous nephropathy, and C3 glomerulopathies). Advances in understanding the immunopathogenesis of each of these entities offer many opportunities for future therapeutic interventions.

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.

New insights into the pathophysiology of idiopathic nephrotic syndrome

Corticoresistant idiopathic nephrotic syndrome (INS) is a glomerulopathy of unknown etiology whose original aspect is its recurrence after kidney transplantation in 30 to 50% of patients with end-stage renal disease. This suggests the involvement of circulating factors that would alter the glomerular filtration barrier, but whose nature remains elusive. Although a T cell immune origin has been suggested, the actual role of these cells in INS recurrence is still unclear. Here we present an 8-year-old patient with corticoresistant INS who developed a recurrence of her initial disease after kidney transplantation. Rituximab therapy was proposed 11 months after transplantation; although no immediate effect was induced, a slow but persistent decrease in proteinuria began a few months after Rituximab infusions despite cessation of plasma exchanges and steroid therapy. The pathophysiology of INS and the putative mechanisms of action of Rituximab are discussed.

[Minimal change nephrotic syndrome : new insights into disease pathogenesis]

Idiopathic nephrotic syndrome is the most frequent glomerular disease in children. While genetic analyses have provided new insights into disease pathogenesis through the discovery of several podocyte genes mutated in distinct forms of inherited nephrotic syndrome, the molecular bases of minimal change nephrotic syndrome (MCNS) and focal and segmental glomerulosclerosis (FSGS) with relapse remain unclear. Although immune cell disorders, which may involve both innate and adaptive immunity, appear to play a role in the pathogenesis of steroid sensitive MCNS, the mechanisms by which they induce podocyte dysfunction remain unresolved. It was postulated that podocyte injury results from a circulating factor secreted by abnormal T cells, but the possibility that bipolarity of the disease results from a functional disorder shared by both cell systems is not excluded. MCNS relapses are associated with an activation of the immune system, including an expansion of T and B cell compartments and production of growth factors as well as many cytokines. Dysfunction of T cells is supported by three main findings: (1) inhibition of a type III hypersensitivity reaction ; (2) defects in immunoglobulin switch ; (3) unclassical T helper polarization resulting from transcriptional interference between Th1 and Th2 transcriptional factors.

Immune mediators in idiopathic nephrotic syndrome: evidence for a relation between interleukin 8 and proteinuria

The pathogenesis of idiopathic nephrotic syndrome (INS) remains unknown. Several findings suggest a role for the immune system. This study aimed to evaluate immune mediators in INS by measuring plasma and urinary levels of transforming growth factor beta1 (TGF-beta1), monocyte chemoattractant protein-1 (MCP-1/CCL2), regulated on activation normal T-cell expressed and secreted (RANTES/CCL5) and IL-8 (IL-8/CXCL8) in pediatric patients with INS and in age-matched healthy controls. Patients were divided according to their response to corticosteroids: steroid-sensitive (SS, n = 8), or steroid-resistant (SR, n = 24). Immune mediators were also compared in regard with disease activity (relapse and remission). Immune mediators were measured by ELISA. Plasma TGF-beta1 levels in SR patients were approximately 2.8-fold higher than control values (p < 0.05). Urinary IL-8/CXCL8 was 2.9-fold higher in INS patients in relapse (proteinuria >100 mg/m2/24 h) when compared with patients in remission (p < 0.05), and levels had a positive correlation with individual proteinuria values (p < 0.05). Urinary IL-8/CXCL8 was significantly higher in relapsed SR than in SS patients in remission. No changes in MCP-1/CCL2 and RANTES/CCL5 levels were detected. Our findings suggest that IL-8/CXCL8 and TGF-beta1 are involved in the pathogenesis of INS: IL-8/CXCL8 associated with local changes in glomerular permeability and TGF-beta1 could be related to worse response to corticosteroids.

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.

Role of the immune system in the pathogenesis of idiopathic nephrotic syndrome

Idiopathic NS (nephrotic syndrome) is characterized by massive proteinuria, due to a leak in the glomerular barrier to proteins. Genetic defects that affect the function and the composition of the glomerular capillary wall, in particular of the visceral epithelial cells, have recently been recognized as the cause of familial forms of NS. MCNS (minimal change NS) and FSGS (focal and segmental glomerulosclerosis) are common non-familial forms of NS in which the causative defect has not yet been identified. Several studies have shown that non-familial NS is associated with the presence of circulating permeability factors and with complex disturbances in the immune system. Thus far, there is no direct evidence that these factors directly alter glomerular permeability to proteins, and some of these factors may be a consequence, rather than a cause, of NS. In this review, we will briefly highlight the mechanisms that underlie proteinuria in general and focus on the immunological disturbances associated with idiopathic NS, with attention to potential mechanisms whereby the immune system may directly act on the glomerular capillary filter.

Extended criteria for organ acceptance. Strategies for achieving organ safety and for increasing organ pool

The terms extended donor or expanded donor mean changes in donor acceptability criteria. In almost all cases, the negative connotations of these terms cannot be justified. Factors considered to affect donor or organ acceptability have changed with time, after showing that they did not negatively affect graft or patient survival per se or when the adequate measures had been adopted. There is no age limit to be an organ donor. Kidney and liver transplantation from donors older than 65 years can have excellent graft and patient actuarial survival and graft function. Using these donors can be from an epidemiological point of view the most important factor to esablish the final number of cadaveric liver and kidney transplantations. Organs with broad structural parenchyma lesion with preserved functional reserve and organs with reversible functional impairment can be safely transplanted. Bacterial and fungal donor infection with the adequate antibiotic treatment of donor and/or recipient prevents infection in the latter. The organs, including the liver, from donors with infection by the hepatitis B and C viruses can be safely transplanted to recipients with infection by the same viruses, respectively. Poisoned donors and non-heart-beating donors, grafts from transplant recipients, reuse of grafts, domino transplant and splitting of one liver for two recipients can be an important and safe source of organs for transplantation.

Pathobiochemistry of nephrotic syndrome

Nephrotic syndrome is a clinical and laboratory syndrome caused by the increased permeability of the glomerular capillary wall for macromolecules. Nephrotic syndrome is a potentially life-threatening state and persistent nephrotic syndrome has a poor prognosis with a high risk of progression to end-stage renal failure and a high risk of cardiovascular complications due to severe hyperlipidemia. Pathogenesis of increased glomerular permeability in different glomerular diseases has not been fully elucidated. Recently, identification of the mutated genes for some podocyte proteins (nephrin, podocin, alpha-actinin-4) in rare familial forms of nephrotic syndrome shed has new light on the molecular mechanisms of glomerular permselectivity. Gradually it becomes apparent that sporadic mutations of podocyte proteins (e.g., podocin) may be present even in some patients with acquired nephrotic syndrome. Expression of other podocyte proteins may change during the course of experimental nephrotic syndrome, possibly as a response to podocyte damage resulting either in apoptosis or stimulation of proliferation and some form of repair, including glomerular sclerosis. Better understanding of these mechanisms could clearly also have therapeutic implications. Glomerular permeability factors are believed to play a role in some noninflammatory glomerular diseases, mainly minimal change disease and focal segmental glomerulosclerosis, but their molecular identification remains elusive, possibly due to the nonhomogeneous nature of the underlying diseases. As an example, focal segmental glomerulosclerosis possibly can be caused by the sporadic mutation of some genes for podocyte proteins, increased production of glomerular permeability factor (possibly by T lymphocytes), or the loss of inhibitors of glomerular permeability factors in nephrotic urine. Clearly the factors causing increased glomerular permeability and factors perpetuating glomerular sclerosis are not necessarily the same. Proteinuria does not seem to be only the consequence of glomerular damage, but it may possibly cause tubular damage and initiate interstitial fibrosis and thus contribute to the progression of chronic renal failure in proteinuric renal diseases. Recent insights into the mechanisms of tubular protein reabsorption may give new tools for preventing the progression of chronic renal disease. Cubilin inhibitors could potentially ameliorate tubular and interstitial damage in patients with heavy proteinuria refractory to treatment. Nephrotic hyperlipidemia is accompanied with increased risk of cardiovascular complications and should be treated in all patients with persistent nephrotic syndrome. The putative positive effect of hypolipidemic drugs (namely statins) on the cardiovascular risk and potentially also on the rate of progression of chronic renal failure remains to be demonstrated in prospective controlled studies. Recent progress in understanding podocyte biology in rare inherited glomerular diseases gives the chance to understand in the near future the molecular pathogenesis of increased glomerular permeability in the much more common acquired forms of nephrotic syndrome.

Nephrotic urine prevents increased rat glomerular albumin permeability induced by serum from the same patient with idiopathic nephrotic syndrome

BACKGROUND

The putative humoral mediator thought to be involved in the pathogenesis of idiopathic nephrotic syndrome has not yet been identified. However, components exist in normal serum that block the permeability activity of FSGS serum in vitro. The potential of FSGS serum to increase glomerular albumin permeability may result from an imbalance between permeability factors and naturally occurring inhibitors. We hypothesized that this imbalance may be favoured by loss of inhibitory factors in nephrotic urine.

METHODS

The study population consisted of seven patients with biopsy-proven FSGS, one with IgM nephropathy, and three with idiopathic nephrotic syndrome without biopsy, from whom frozen serum and dialysed and lyophilized urine samples were available. Glomerular albumin permeability (P(alb)) was determined from the change in glomerular volume induced by applying oncotic gradients across the basement membrane of normal isolated rat glomeruli pre-incubated with patient serum, normal control serum, patient serum mixed with an equal volume of urine from the same patient, or patient serum mixed with normal urine. Serum and urine apolipoproteins J and E were measured by dot-blot, utilizing peroxidase-labelled antibodies. The urinary capacity to scavenge oxygen radicals was determined after exposure of isolated glomeruli to superoxide generated by xanthine and xanthine oxidase.

RESULTS

The mean P(alb) of the patients was markedly elevated at 0.74+/-0.08. The addition of urine from the same patient significantly reduced P(alb) (mean 0.15+/-0.23) in all but one of the patients with FSGS. Normal urine had no inhibitory effect in the 10 patients in which it was tested (mean 0.71+/-0.09). Serum apo J was slightly decreased and serum apo E was slightly increased compared with controls. Urine levels of both lipoproteins were significantly decreased compared with controls. Urine from FSGS patients effectively neutralized superoxide, whereas normal urine did not.

CONCLUSIONS

Nephrotic urine but not normal urine contains components that block increased albumin permeability in isolated rat glomeruli induced by serum from patients with the idiopathic nephrotic syndrome. The inhibitory function of these components, which appear not to include apolipoproteins J and E, may involve scavenging of superoxide as a final common pathway. Loss in the urine from the serum of naturally occurring inhibitors in the initial stages of the disease may propagate proteinuria and glomerular injury.

Extrarenal effects on the pathogenesis and relapse of idiopathic nephrotic syndrome in Buffalo/Mna rats

Buffalo/Mna rats spontaneously develop a focal segmental glomerulosclerosis with a histological pattern similar to the human disease. In this study, we investigated the potential of recurrence of the disease by transplantation of normal kidneys into Buffalo/Mna recipients. Kidneys from healthy LEW.1W rats were grafted into proteinuric 6-month-old Buffalo/Mna rats without or with specific tolerance induction following donor-specific transfusion (DST) aimed at controlling host anti-donor immune responses. The inverse combination was carried out to determine whether a proteinuric Buffalo/Mna kidney can recover its permselectivity in a normal environment. As a control, LEW.1W kidneys were grafted into Wistar Furth recipients. After transplantation without DST, recurrence of proteinuria in LEW.1W kidneys appeared at approximately 10 days, possibly associated with rejection of the graft. In the same combination with DST, proteinuria occurred after 20 days, and the attendant glomerular damage suggested that the initial kidney disease had recurred. Transplanted control animals remained free of proteinuria. In the opposite combination, the proteinuria and the lesions of Buffalo/Mna kidneys regressed after transplantation into healthy LEW.1W rats. The recurrence of proteinuria after transplantation in Buffalo/Mna and the remission of lesions in Buffalo/Mna kidneys transplanted into normal hosts suggests that Buffalo/Mna rats express circulating albuminuric factors, which may be relevant to the relapse of idiopathic nephrotic syndrome in humans.

Characterization of plasma factors that alter the permeability to albumin within isolated glomeruli

Focal segmental glomerulosclerosis (FSGS) is responsible for intractable proteinuria and has become the leading cause of renal insufficiency in children. Protenuria in FSGS is probably due to the effect of one or more permeability plasma factors which increase the glomerular permeability to proteins. We fractioned serum from children with FSGS using two mixed chromatographic-electrophoretic approaches and have purified ten proteins among several hundreds which maintained the original permeability activity after renaturation, utilizing an isolated rat glomeruli assay. Six proteins were successfully characterized by mass spectometry as fibulin, apolipoprotein J, vitronectin, albumin isoforms, gamma chain fibrinogen and mannan-binding lectin-associated serine protease. Both procedures utilized for purification were based on affinity chromatography with Protein A-Sepharose and ended with two-dimensional electrophoresis, whereas the intermediate steps were different. Cross inhibition with zinc and aprotinin of purified factors and whole FSGS serum indicate strong homology. These are the first data demonstrating permeability activity for serum proteins, an observation with important implications in pathogenesis of proteinuria. Determination of the serum levels of each protein and a careful differentiation of FSGS from normal serum could provide the basis for clarifying the mechanism of proteinuria.