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.     

Prevalence, genetics, and clinical features of patients carrying podocin mutations in steroid-resistant nonfamilial focal segmental glomerulosclerosis.

Podocin mutations (NPHS2 gene) are responsible for the autosomal recessive form of steroid-resistant nephrotic syndrome. As a result of a screening for these gene alterations in a cohort of Italian patients with nonfamilial nephrotic syndrome and histologic focal segmental glomerulosclerosis (FSGS), nine patients with NPHS2 gene homozygous or composite heterozygous mutations were found. In addition to the previously described defects, two novel mutations at exon 4 were identified (frameshift, L169P); four single nucleotide polymorphisms (SNPs) and one dinucleotide repeat were also identified. On the basis of haplotype analysis, a founder effect was suggested for the 419delG mutation, the most frequently observed in the patients studied. Patients carrying NPHS2 mutations and without a family history of nephrotic syndrome were indistinguishable from those with idiopathic FSGS on the basis of the clinical phenotype. Two of the nine patients had normal renal function at 3 and 10 yr of age, despite the presence of the nephrotic syndrome. The other seven had reached end-stage renal failure at a mean age of 9.6 yr (range, 4 to 17 yr) and had received renal allografts. In those presenting with end-stage renal failure, the clinical and laboratory features both before and after transplantation were similar, including the age at onset, the amount of proteinuria, and the absence of any response to steroids and other immunosuppressants. Finally, two children presented recurrence of mild proteinuria after transplantation, which promptly remitted after plasmapheresis combined with cyclophosphamide. These data demonstrate that podocin mutations in nonfamilial cases of steroid-resistant nephrotic syndrome are frequent and may be due in one case to a founder effect. The pretransplantation and posttransplantation outcomes in the group of patients with mutations of the podocin gene are similar to classical idiopathic FSGS, including the possibility of recurrence of proteinuria that is mild and responsive to plasmapheresis. These observations support a role of molecular screening of the podocin gene in patients with nephrotic syndrome before immunosuppressive treatment is started.     

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.     

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.     

Glomerular tip lesion: a distinct entity within the minimal change disease/focal segmental glomerulosclerosis spectrum

BACKGROUND: The glomerular tip lesion (GTL) is a distinctive but controversial histopathologic lesion occurring in patients with idiopathic nephrotic syndrome. The relationship of GTL to minimal change disease (MCD) and idiopathic focal segmental glomerulosclerosis (FSGS) has been disputed. METHODS: In order to define the clinical features and natural history of GTL, we retrospectively reviewed the presenting clinical features, biopsy findings and outcome of 47 cases. Presenting clinical features of GTL were compared to those of controls with MCD (N= 61) or idiopathic FSGS (N= 50). RESULTS: The cohort of GTL consisted of 45 adults and two children (mean age 47.5 years; range 12 to 79 years), including 76.6% Caucasians and 53% males. At presentation, 93.6% of patients had edema, 89.1% had nephrotic syndrome (mean urine protein 8.31 g, mean serum albumin 2.27 g/dL, and mean cholesterol 340.6 mg/dL), and 34.8% had renal insufficiency. Mean time from onset of renal disease to biopsy was 2.4 months. At biopsy, glomerular segmental lesions included GTL alone in 26%, GTL and peripheral lesions in 6%, GTL and indeterminate lesions in 36%, and GTL with peripheral and indeterminate lesions in 32%. No initial biopsy contained perihilar sclerosis and most (81%) segmental lesions were cellular. Follow-up data were available in 29 patients, of whom 21 received steroids alone and eight received sequential therapy with steroids and a cytotoxic agent. At a mean follow-up of 21.5 months, 58.6% of patients achieved complete remission of nephrotic syndrome, 13.8% had partial remission, and 27.6% had persistent nephrotic proteinuria. Only one patient progressed to end-stage renal disease (ESRD). Predictors of nonremission included severity of proteinuria at presentation and % peripheral lesions. When compared to controls with MCD and idiopathic FSGS, GTL more closely resembled MCD with respect to high incidence of nephrotic syndrome (P < 0.001), severity of proteinuria (P < 0.05), short duration from onset to biopsy (P < 0.001), and absence of chronic tubulointerstitial disease (P < 0.0054). CONCLUSION: Within the MCD/FSGS spectrum, GTL is a distinctive and prognostically favorable clinical-pathologic entity whose presenting features and outcome more closely approximate those of MCD.     

<Emphasis Type="Italic">NPHS2</Emphasis> mutation associated with recurrence of proteinuria after transplantation

Mutations in the NPHS2 gene encoding podocin are associated with steroid-resistant nephrotic syndrome (SRNS) in childhood. Patients usually present with focal segmental glomerulosclerosis (FSGS). It is unclear to what extent SRNS due to NPHS2 mutations predisposes to recurrence of proteinuria/FSGS after renal transplantation (RTx). A 4-year-old girl with infantile SRNS was started on peritoneal dialysis because of end-stage renal disease due to FSGS. Mutational screening of the patient and her parents revealed a novel single nucleotide deletion in exon 8 of the NHPS2 gene (948delT), for which the patient was homozygous and her parents confirmed heterozygous asymptomatic carriers. At the age of 4.5 years the patient received a renal graft from her mother. On day 7 after RTx, the patient developed progressive proteinuria (urine protein/creatinine ratio 2.4 g/g), which responded within 1 week to prednisone pulse therapy, an increased cyclosporin A dosage, and ramipril therapy. The patient has maintained stable graft function and no further recurrence of proteinuria has been observed. In conclusion, patients with SRNS due to NPHS2 mutations are not protected from recurrence of proteinuria after RTx. The quick response to increased immunosuppression in our patient suggests an immune-mediated pathomechanism for recurrence of proteinuria.     

家族性激素反应性肾病综合征一家系报告及文献复习

目的 报道家族性激素反应性肾病综合征，分析其临床病理特点及家族发病的特点，及其与NPHS2基因的关系。方法 分析患者临床及病理表现特点，并对其家族成员患病情况进行调查；与文献报告的家族性激素反应性肾病综合征对比。运用高效液相色谱(DHPLC)的方法检测该家系NPHS2基因突变。结果 该家族的患病情况符合文献报告的家族性激素反应性肾病综合征的定义，临床表现为肾病综合征，病理改变为肾小球微小病变，对足量的强的松治疗反应敏感，易复发，但发病年龄较国际上报道的中位年龄高。同国外同类报道一样，该家族中未发现NPHS2突变。结论 首次在国内报告家族激素反应性肾病综合征。该疾病在此家系中的发生与NPHS2无明显关系.     

Recurrence of proteinuria 10 years post-transplant in NPHS2-associated focal segmental glomerulosclerosis after conversion from cyclosporin A to sirolimus

Mutations in the NPHS2 gene, which encodes podocin, are associated with steroid-resistant nephrotic syndrome in childhood. Renal histology frequently presents focal segmental glomerulosclerosis (FSGS). Post-transplant recurrence of proteinuria in patients affected by homozygous or compound heterozygous NPHS2 mutation is encountered rarely (1–2%) compared to 30% recurrence in nonhereditary FSGS. We report on a pediatric kidney transplant recipient with NPHS2-associated nephrotic syndrome and FSGS, who developed biopsy-proven recurrence of FSGS 10 years post-transplant in temporal association with conversion from cyclosporin A (CsA)- to sirolimus (SRL)-based immunosuppression, due to histological evidence of severe CsA-induced nephrotoxicity. Reswitch of the immunosuppressive regimen from SRL to CsA led to a noticeable decrease of proteinuria and to stabilization of graft function. We conclude that patients with hereditary FSGS are not entirely protected from post-transplant recurrence of proteinuria, even in the long term. The close temporal relationship of FSGS recurrence with CsA withdrawal and conversion to SRL suggests that caution should be exercised in the use of CsA-free immunosuppression also in patients with NPHS2-associated FSGS.     

Depletion of clusterin in renal diseases causing nephrotic syndrome

BACKGROUND: Clusterin is a lipoprotein that has anti-complement effects in membranous nephropathy (MN). In focal segmental glomerulosclerosis (FSGS), it inhibits permeability plasma factor activity and could influence proteinuria. Moreover, with aging, knockout mice for clusterin develop a progressive glomerulopathy with sclerosis. METHODS: Since little is known about clusterin metabolism in humans, we determined clusterin levels and composition in the sera and urine of 23 patients with MN, 25 with FSGS and 23 with steroid-responsive nephrotic syndrome (NS). Renal localization was evaluated by immunofluorescence and morphometry. RESULTS: Serum clusterin was markedly reduced in active MN, in FSGS and in children with NS compared to controls; after stable remission of proteinuria, nearly normal levels were restored. Among various biochemical variables, serum clusterin was inversely correlated with hypercholesterolemia. Urinary clusterin, representing a 0.01 fraction of serum, was higher in the urine from normal subjects and FSGS patients in remission with proteinuric MN, FSGS and idiopathic NS; clusterin was inversely correlated with proteinuria. In all cases, urinary and serum clusterin was composed of the same 80 kD isoforms. Finally, a decrease in focal segmental or global clusterin staining was found in FSGS glomeruli, especially in areas of sclerosis. Instead, in MN an overall increment of staining was observed that ranged from mild/focal to very intense/diffuse. CONCLUSIONS: The overall pool of clusterin is reduced in glomerular diseases causing nephrotic syndrome, with hypercholesterolemia appearing as the unifying feature. Depletion of clusterin should negatively affect the clinical outcome in nephrotic patients and efforts should be aimed at normalizing clusterin overall pool.     

NPHS2 mutations in sporadic steroid-resistant nephrotic syndrome in Japanese children

Podocin is an integral membrane protein encoded by NPHS2, which is mapped to 1q25-31 and is exclusively expressed in glomerular podocytes. NPHS2 mutations are responsible for autosomal recessive familial steroid-resistant nephrotic syndrome (SRNS) with minor glomerular abnormalities or focal segmental glomerulosclerosis (FSGS), which is characterized by early childhood onset (age less than 6 years) and rapid progression to chronic renal insufficiency. This gene mutation is also responsible for an adolescent/adult onset form of autosomal recessive familial FSGS with heavy proteinuria. It has been demonstrated that sporadic SRNS and heavy proteinuria are also due to NPHS2 gene mutations. We isolated genomic DNA from 36 Japanese children with chronic renal insufficiency caused by SRNS or heavy proteinuria, and analyzed all eight exons and exon-intron boundaries of NPHS2 using the polymerase chain reaction and direct sequencing. The age at onset of disease was 3.9+/-0.5 years. There were 29 patients with SRNS and 7 with heavy proteinuria without nephrotic syndrome at the onset, but all patients developed chronic renal insufficiency 4.6+/-0.8 years after the onset. A new homozygous missense variant of NPHS2, G34E (G101A) in exon 1, was detected in 1 of 36 patients. However, this homozygous variant was also found in 1 of 44 normal controls, suggesting that the mutation is a polymorphism. Two silent variants (T954C and A1038G) in exon 8 of this gene were also identified in some of the patients and normal controls, indicating that the silent variants are also polymorphisms. There was no significant difference in the genotypic and allelic frequencies of T954C and A1038G polymorphisms between the patients and normal controls. In conclusion, NPHS2 gene mutations are not a major cause of chronic renal insufficiency caused by sporadic SRNS or heavy proteinuria in Japanese children.     

Focal segmental glomerulosclerosis and renal transplantation

Primary focal segmental glomerulosclerosis (FSGS) is a major cause of nephrotic syndrome and eventual end-stage renal disease. It is known to be due to an abnormality of the visceral epithelial cells (podocytes) of the glomerulus. The morphological hallmark of primary FSGS is diffuse effacement of podocyte foot processes. The etiology of the podocyte damage is not been clearly established. FSGS can also be a secondary process due to underlying conditions including obesity and heroin use. In the secondary processes, the mechanism appears to be a decreased ratio of podocytes to the glomerular filtration surface area. Familial forms of FSGS also exist due to alterations of several different podocyte proteins. Primary FSGS is an increasing cause of end-stage renal disease. Recurrence of severe FSGS in renal allograft recipients presents a major challenge to transplant physicians. The incidence of recurrence is generally accepted to be between 20% and 30%. Risk factors for and characteristics of recurrence include a rapid progression of the primary disease to end-stage renal failure, early onset of nephrotic range proteinuria after allografting, frequent loss of the allograft, a high frequency of recurrence in subsequent allografts, and children less than 15 years of age. Some investigators have identified a circulating factor called the FSGS factor that appears to be associated with recurrence after transplantation. This factor has been shown to be a protein between 30 and 50 kd molecular weight. Logically, the possibility of a circulating factor associated with recurrence of FSGS led investigators to treat patients with plasmapheresis. Several studies have been reported with varying success. The response of patients to plasmapheresis seems to be completely individual. Other studies have added cyclophosphamide and/or mycophenolate mofetil to the plasmapheresis protocol. Again success in these studies has been variable. However, because some patients show complete recovery with plasmapheresis, individuals who develop recurrent FSGS after transplantation usually are given a trial of plasmapheresis therapy.     

NPHS2 variation in Chinese southern infants with late steroid-resistant nephrotic syndrome

NPHS2 mutations are responsible for autosomal recessive familial steroid-resistant nephrotic syndrome (SRNS) with minor glomerular abnormalities or focal segmental glomerulosclerosis (FSGS), which is characterized by early childhood onset and rapid progression to chronic renal insufficiency. This gene mutation is also responsible for an adolescent onset form of autosomal recessive familial FSGS with heavy proteinuria. Many infants with late steroid-resistant nephrotic syndrome (late SRNS) are prone to an implicated clinical and therapeutic course. The etiopathogenesis and the long-term prognosis of late SRNS remain obscure. Considering the similar steroid resistance between late and initial SRNS, analysis of NPHS2 variation was performed in 70 sporadic Chinese infants with late SRNS and 70 controls in the present study to investigate the possible role of NPHS2 gene in late SRNS. The variation analysis revealed three polymorphisms (288C?>?T heterozygous in exon 2, 954T?>?C heterozygous and homozygous, and 1038A?>?G heterozygous in exon 8) in 22 out of 70 patients studied. In conclusion, NPHS2 gene mutations are not a major cause of chronic renal insufficiency caused by late SRNS in Chinese southern infants.     

Podocyte foot process effacement as a diagnostic tool in focal segmental glomerulosclerosis

Podocyte foot process effacement is characteristic of proteinuric renal diseases. In minimal change nephrotic syndrome (MCNS) foot processes are diffusely effaced whereas the extent of effacement varies in focal segmental glomerulosclerosis (FSGS). Here we measured foot process effacement in FSGS and compared it to that in MCNS and in normal kidneys. A clinical diagnosis was used to differentiate idiopathic FSGS from secondary FSGS. Median foot process width, determined morphometrically by electron microscopy, was 3236 nm in 17 patients with idiopathic FSGS, 1098 nm in 7 patients with secondary FSGS, and 1725 nm in 15 patients with MCNS, as compared to 562 nm in 12 control patients. Multivariate analysis showed that foot process width did not correlate with proteinuria or serum albumin levels but was significantly associated as an independent factor with the type of disease. Foot process width over 1500 nm differentiated idiopathic from secondary FSGS with high sensitivity and specificity. Our results show that quantitative analysis of foot processes may offer a potential tool to distinguish idiopathic from secondary FSGS.     

Low prevalence of NPHS2 mutations in African American children with steroid-resistant nephrotic syndrome

In African American (AA) children, focal segmental glomerulosclerosis (FSGS) is the leading cause of nephrotic syndrome (NS). It has been shown that AA children suffer from FSGS and steroid-resistant nephrotic syndrome (SRNS) at a higher frequency and with a more severe renal outcome in comparison with Caucasian children. Previous mutation analysis of large cohorts revealed that a high percentage of childhood SRNS is monogenic and that mutations in podocin (NPHS2) and Wilms' tumor gene 1 (WT1) account for approximately 30% of SRNS in children. To test whether AA children with SRNS have a similar or a higher mutation rate, we performed mutation analysis of NPHS2 and WT1 in a cohort of AA children with SRNS. Direct sequencing was carried out for all exons of NPHS2 and for exons 8 and 9 of WT1. We ascertained 18 children of AA descent in whom renal biopsy findings showed FSGS in 13 patients (72%) and minimal-change disease in five patients (28%). In both NPHS2 and WT1, no disease-causing mutations were detected. Our data strongly suggest that in AA children with SRNS, the frequency of NPHS2 mutations is much lower than in large cohorts of pediatric SRNS patients in the general population. Knowledge of mutation rate of NPHS2 in different populations of SRNS patients facilitates the physician in planning a suitable genetic screening strategy for patients.     

Early recurrent nephrotic syndrome after renal transplantation in children with focal segmental glomerulosclerosis.

BACKGROUND: We analysed risk factors to predict the recurrence of nephrotic syndrome and the therapeutic efficacy of plasmapheresis combined with oral cyclophosphamide (PE+CPM) in early recurrent nephrotic syndrome after transplantation in children with focal segmental glomerulosclerosis (FSGS). METHODS: Medical records after 1990 of 16 children with biopsy-proven idiopathic FSGS and renal transplantation before the age of 18 years were reviewed. RESULTS: Early recurrence of nephrotic syndrome developed in six cases (37. 5%). While early kidney graft biopsies, performed within the first week after the onset of recurrence, revealed diffuse effacement of foot process only, late biopsies contained segmentally sclerosed glomeruli as well. Among several possible risk factors, the mean duration from onset of original nephrotic syndrome to development of end-stage renal disease was shorter in the recurrent group (P=0.045) and the percentage of globally sclerosed glomeruli was higher in the non-recurrent group (P=0.001). PE+CPM therapy resulted in complete remission of nephrotic syndrome if it was started early and if there was no evidence of accompanying acute rejection. CONCLUSION: These results support more liberal use of living-related donors for renal transplantation of children with FSGS and ESRD, considering the shortage of cadaveric donors in our society and relatively good efficacy of the early and intensive PE+CPM therapy for early recurrent nephrotic syndrome.     

Charge and size selectivity of proteinuria in children with idiopathic nephrotic syndrome

 Experimental studies have pointed to charge selectivity as an important determinant of glomerular permeability to macromolecules. Loss of glomerular basement membrane (GBM) polyanion has been proposed as a cause of the selective proteinuria in minimal change nephrotic syndrome (MCNS). However, the presence of less-anionic albumin in urine than plasma from MCNS and focal and segmental glomerulosclerosis (FSGS) patients has been interpreted both as evidence for partial maintenance of charge selectivity and for involvement of other pathogenic mechanisms. The exact role of charge selectivity in the pathogenesis of nephrotic proteinuria remains controversial. We have examined the clearance of endogenous proteins of differing size and charge in children with idiopathic nephrotic syndrome (NS). Chromatofocusing was used to determine the isoelectric points (pIs) of albumins in paired plasma and urine samples from patients with FSGS (n = 6) and MCNS (n = 6). Charge selectivity was assessed by comparing the pIs of the fractions with the highest albumin concentration (modal pI) in plasma and urine. The difference between the modal pIs was defined as the delta modal pI. Charge selectivity was also assessed from the albumin/transferrin and IgG4/IgG1 clearance ratios; size selectivity from the IgG1/albumin and IgG1/transferrin as well as the IgG4/albumin and IgG4/transferrin clearances. In children with FSGS, the mean (± SD) delta modal pI was  – 0.05 ± 0.16, and in MCNS  – 0.05 ± 0.11. Neither value differed significantly from zero. The albumin/transferrin clearance ratio showed no significant difference between FSGS and MCNS, but the IgG4/IgG1 clearance ratio was significantly higher in MCNS (P<0.05). Size selectivity was significantly reduced in FSGS compared with MCNS (for IgG1/transferrin P<0.01 and for IgG1/albumin P<0.05). For IgG4/transferrin and IgG4/albumin, P was <0.05. In conclusion, there was no evidence for residual charge selectivity in idiopathic NS associated with either MCNS or FSGS during nephrotic-range proteinuria. There was a significant loss of GBM size selectivity in children with FSGS with heavy proteinuria compared with children with MCNS with heavy proteinuria. Received August 7, 1996; received in revised form and accepted December 16, 1996     

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.