Role of p38 mitogen-activated protein kinase activation in podocyte injury and proteinuria in experimental nephrotic syndrome

Podocytes play an important role in maintaining normal glomerular function and structure, and podocyte injury leads to proteinuria and glomerulosclerosis. The family of mitogen-activated protein kinases (MAPK; extracellular signal-regulated kinase [ERK], c-Jun N-terminal kinase, and p38) may be implicated in the progression of various glomerulopathies, but the role of MAPK in podocyte injury remains elusive. This study examined phosphorylation of p38 MAPK in clinical glomerulopathies with podocyte injury, as well as in rat puromycin aminonucleoside (PAN) nephropathy and mouse adriamycin (ADR) nephropathy. The effect of treatment with FR167653, an inhibitor of p38 MAPK, was also investigated in rodent models. In human podocyte injury diseases, the increased phosphorylation of p38 MAPK was observed at podocytes. In PAN and ADR nephropathy, the phosphorylation of p38 MAPK and ERK was marked but transient, preceding overt proteinuria. Pretreatment with FR167653 (day -2 to day 14, subcutaneously) to PAN or ADR nephropathy completely inhibited p38 MAPK activation and attenuated ERK phosphorylation, with complete suppression of proteinuria. Electron microscopy and immunohistochemistry for nephrin and connexin43 revealed that podocyte injury was markedly ameliorated by FR167653. Furthermore, early treatment with FR167653 effectively prevented glomerulosclerosis and renal dysfunction in the chronic phase of ADR nephropathy. In cultured podocytes, PAN or oxidative stress induced the phosphorylation of p38 MAPK along with actin reorganization, and FR167653 inhibited such changes. These findings indicate that the activation of MAPK is necessary for podocyte injury, suggesting that p38 MAPK and, possibly, ERK should become a potential target for therapeutic intervention in proteinuric glomerulopathies.     

足细胞分子高表达致阿霉素肾病大鼠发生蛋白尿

目的 动态观察足细胞裂孔隔膜复合体分子nephrin、podocin、CD2AP及α-actinin-4在阿霉素肾病大鼠蛋白尿发生发展中的表达变化，探讨其在蛋白尿发生发展中的分子行为及其机制。方法 尾静脉注射阿霉素建立阿霉素肾病大鼠模型，3、7、14、28 d每组处死6只大鼠留取肾脏标本。应用间接免疫荧光染色、实时定量PCR、Western 印迹分别检测各个时间点nephrin、podocin、CD2AP、α-actinin-4的分布、mRNA和蛋白表达量的变化。结果 (1)14 d肾病组大鼠24 h尿蛋白显著高于对照组(P < 0.01)，增高持续到28 d。(2)透射电镜显示14 d肾病组足突不同程度变宽，28 d足突弥漫性融合。(3)与对照组相比，从第7天开始肾病组nephrin和podocin染色从沿肾小球毛细血管袢线样分布向不连续粗颗粒样的分布模式转变；CD2AP节段染色增强区逐渐扩大，有的区域呈斑片状和连续线状增强；α-actinin-4从沿肾小球毛细血管袢均匀的点线样分布向不均匀粗颗粒的分布转变，而且随时间进展这种转变逐渐加重。(4)与对照组相比，肾病组于7 d时nephrin mRNA表达显著增高(P < 0.01)；podocin mRNA表达14 d时显著增高(P < 0.05)，直至28 d(P < 0.05)；CD2AP mRNA表达28 d时显著增高(P < 0.05)。(5)与对照组相比，肾病组nephrin蛋白表达28 d时显著增高(P < 0.05)；podocin蛋白表达于7 d时显著增高(P < 0.05)，而28 d时又显著降低(P < 0.05)；CD2AP蛋白表达于14 d时显著增高(P < 0.05)，直至28 d (P < 0.05)。(6)α-actinin-4 mRNA与蛋白表达在实验过程中未出现明显变化。结论 nephrin、podocin和CD2AP的表达增加及分布异常是导致阿霉素肾病大鼠蛋白尿发生发展的分子机制，而分子表达的增加是足细胞抵抗损伤的一种代偿反应。     

Follow-up of steroid-resistant nephrotic syndrome: tubular proteinuria and enzymuria

The aim of this study was to examine the compromise of proximal tubule cells in steroid-resistant nephrotic syndrome patients with a histologic diagnosis of focal segmental glomerulosclerosis (FSGS) through assessment of the urinary levels of β₂-microglobulin (β₂M) and N-acetyl-β-d-glucosaminidase (NAG) during active disease and remission over a follow-up period of 3 years. We studied 34 children with nephrotic syndrome: 12 with steroid-resistant nephrotic syndrome (SRNS) and massive proteinuria, 7 with steroid-dependent nephrotic syndrome (SDNS) and 15 with steroid-sensitive nephrotic syndrome (SSNS). Of the SSNS patients, 8 children were in remission (RM) and 7 were in relapse (RL). Seven healthy children were included as controls. Urinary β₂M, measured by enzyme-linked immunosorbent assay, was significantly increased in the SRNS group as compared to the SDNS group (P<0.01), SSNS in remission (P<0.01), and controls (P<0.01). There were no differences between the SRNS group and SSNS in relapse. Analysis of urinary N-acetyl-β-d-glucosaminidase (U-NAG) by colorimetric assay showed significantly higher values in the SRNS group of patients than in SDNS, SSNS, and control groups. A positive correlation between U-NAG and proteinuria was demonstrated (r=0. 73, P<0.01). The SRNS group of patients (n=12, 11 with a histologic diagnosis of FSGS and one with diffuse mesangial proliferation) was treated with the same protocol of i.v. methylprednisone and oral cyclophosphamide. Long-term follow-up showed a progressive decrease in U-β₂M and U-NAG excretion to control values in the 3rd year, except in one patient who did not respond to the treatment. In the FSGS patients, evaluation of the contribution of structural interstitial histological abnormalities, including each of the histological parameters considered in interstitial scarring to the functional tubule abnormalities assessed by β₂M and NAG excretion, was performed by multiple regression analysis. The r ² values for β₂M and NAG were 53.99%, P=0.19, and 57.90%, P=0.14, respectively; neither was significant. We conclude that: (1) proximal tubule cell dysfunction, partially affected by massive albuminuria, may account for the higher values of β₂M and NAG excretion in the SRNS patients and (2) urine β₂M and NAG levels are not helpful in identifying histological evidence of structural tubulointerstitial damage in children with steroid-resistant nephrotic syndrome. Received: 28 December 1999 / Revised: 20 July 2000 / Accepted: 21 July 2000     

Effects of mineralocorticoid and angiotensin II receptor blockers on proteinuria and glomerular podocyte protein expression in a model of minimal change nephrotic syndrome

Aim: Several proteins constituting the slit diaphragm are considered important for maintaining capillary wall permselectivity. Early intervention with blockers of angiotensin II receptors (AR) and mineralocorticoid receptors (MR) is effective against proteinuria in models of chronic hypertensive and protein‐induced renal damage. However, the effects of AR and/or MR blockers in a model of acute nephrotic syndrome remain unknown. The effects of AR and MR blockers were examined in puromycin aminonucleoside (PAN)‐treated rats. Methods: Six week old male Sprague–Dawley (SD) rats were injected with PAN or vehicle and assigned to groups as follows: vehicle (group C); PAN (group P); PAN followed 3 days later by administration of the MR blocker, eplerenone (group MR), and by the AR blocker, losartan (group AR). Blood pressure and urinary protein excretion were measured and all rats were killed for immunohistochemical investigation on day 14 after PAN administration. Results: Blood pressure did not change throughout the study period. Proteinuria was decreased in groups MR and AR compared with group P (on day 14 after PAN administration, respectively; group P vs AR, P < 0.01; group P vs MR, P < 0.05). Nephrin, podocin and podocalyxin staining was preserved in the glomeruli of groups MR and AR compared with group P. Conclusion: The MR and AR blockers decreased proteinuria in the acute model of nephrotic syndrome with preserved expression of glomerular podocyte protein independently of blood pressure.     

Effect of galactose on glomerular permeability and proteinuria in steroid-resistant nephrotic syndrome

Background

Idiopathic steroid-resistant nephrotic syndrome (SRNS) has been associated with the presence of a circulating focal sclerosis permeability factor (FSPF) thought to damage the glomerular barrier and increase permeability to albumin. Galactose binds and inactivates FSPF in vitro, but its effect in vivo is uncertain.

Methods

A prospective clinical trial was conducted to investigate the effect of oral galactose on FSPF and proteinuria in children with SRNS. Seven pediatric subjects with idiopathic SRNS and positive FSPF activity (>0.5) were treated with oral galactose (0.2 gm/kg/dose twice daily) for 16 weeks. Post-treatment FSPF and proteinuria were measured.

Results

Focal sclerosis permeability factor activity of the seven subjects decreased from 0.69?±?0.11 to 0.35?±?0.21 (p?=?0.009) in response to galactose. The two subjects with post-transplant recurrence of focal segmental glomerulosclerosis (FSGS) demonstrated the most significant improvement in FSPF (p?=?0.006). Despite this decrease in FSPF, the pre- and post-treatment urine protein:creatinine ratio remained unchanged and no subject achieved remission.

Conclusions

Galactose decreases FSPF in children with SRNS, with the most significant improvement in those with post-transplant FSGS recurrence, but it fails to improve proteinuria. At the present time there is no evidence to support the use of galactose in children with FSGS, either pre- or post-transplant. Future studies to investigate the role of galactose as preemptive therapy to decrease the risk of post-transplant FSGS recurrence may be useful.     

Genetic forms of nephrotic syndrome

Mutations of NPHS1, NPHS2 , or WT1 may be responsible for severe forms of nephrotic syndrome in children, progressing to end-stage renal failure. Recent studies have shown that congenital nephrotic syndrome may be secondary to mutations of one of these three genes and that some patients have a digenic inheritance of NPHS1 and NPHS2 mutations. The clinical spectrum of NPHS2 mutations has broadened, with the demonstration that mutations in the respective gene podocin may be responsible for nephrotic syndrome occurring at birth, in childhood, or in adulthood. It is now well recognized that podocin mutations are found in 10%–30% of sporadic cases of steroid-resistant nephrotic syndrome with focal segmental glomerulosclerosis. Data from large cohorts indicate that the risk of recurrence of nephrotic syndrome after renal transplantation in patients with podocin mutations is very low.     

Role of the podocyte in proteinuria

In recent years, the podocyte, with its elaborate cytoarchitecture and slit diaphragm, has been the focus of extensive research, yet its precise role in the glomerular filtration barrier is still debated. There are puzzling observations indicating that a comprehensive mechanistic model for glomerular filtration is still necessary. There is no doubt that podocytes are essential for glomerular filtration barrier integrity. However, most albumin never reaches the podocyte because it is prevented from entering the glomerular filter at the endothelium level. Another puzzling observation is that the glomerular filter never clogs despite its high load of several kilograms of plasma proteins per day. Recently, we proposed a novel model in which an electrical potential difference is generated across the glomerular filtration barrier by filtration. The model offers novel potential solutions to some of the riddles regarding the glomerular filter.     

Prednisone-induced fluctuations of proteinuria in patients with a nephrotic syndrome

We studied the effect of prednisone on urinary protein excretion in 19 patients with a nephrotic syndrome, who were treated with prednisone (125-150 mg) on alternate days. We found a typical, fluctuating pattern of proteinuria resulting from an increased protein excretion rate on prednisone days and a decreased protein excretion rate on nonprednisone days. The urinary protein excretion on prednisone days was 9.9 +/- 3.3 g/24 h, as compared to 5.7 +/- 3.8 g/24 h on nonprednisone days (mean +/- SD). In the whole group of patients the percentual change in proteinuria was significantly correlated with the endogenous creatinine clearance. However, systematic differences between creatinine excretion rates on prednisone and nonprednisone days were not found in individual patients. In 6 patients, renal hemodynamics were studied more precisely, using a single injection technique. Only a slight and nonsignificant decrease in glomerular filtration rate was found on nonprednisone days (delta = -9.6 +/- 16.3%; mean +/- SD). Filtration fraction remained unchanged. It is therefore suggested that the effects of prednisone on proteinuria are not simply mediated by overall changes in renal hemodynamics.     

Decreases of proteinuria during alternate-day prednisone therapy in nephrotic syndrome

Treatment of patients with membranous glomerulonephritis with prednisone on alternate days results in a decreased proteinuria on non-prednisone days. We have studied this phenomenon in more detail in 14 patients (11 M, 3 F) with membranous glomerulonephritis. Mean age +/- SD of the patients was 47 +/- 14 years, mean endogenous creatinine clearance 94 +/- 35 ml/min, and median proteinuria 8.8 g/24 h (range 5.0-30.0 g/24 h). Glomerular filtration rate (GFR, inulin clearance), effective renal plasma flow ERPF, PAH clearance), and proteinuria were measured on a control day (C), and six days after the start of alternate-day prednisone treatment, on the third non-prednisone day (NP3, 24-28 h after the last dose of prednisone). Proteinuria decreased from 6.1 mg/min (3.2-9.8 mg/min) (C) to 2.5 mg/min (1.0-7.7 mg/min) at NP3 (median, interquartile range; P less than 0.01), the percentage decrease averaged 45 +/- 8%. The decrease of proteinuria was correlated with baseline GFR (r = 0.75; P less than 0.01). GFR and ERPF did not change significantly, but filtration fraction decreased significantly from 14.5 +/- 0.8% (C) to 13.5 +/- 0.9% (NP3; P less than 0.05). Fractional excretion of albumin, IgG, and transferrin decreased significantly, by -40 +/- 8%, -52 +/- 6%, and -52 +/- 7% respectively. Fractional excretion of beta 2-microglobulin decreased significantly less by -12 +/- 10%. We conclude that proteinuria is decreased on non-prednisone days in patients with membranous glomerulonephritis treated with alternate-day steroids. The observed decrease of filtration fraction suggests that a reduction of glomerular pressure is involved. In addition, the magnitude of the decrease of proteinuria might indicate a change in glomerular permselectivity characteristics.     

Circulating mediators of proteinuria in idiopathic minimal lesion nephrotic syndrome

The pathogenesis of proteinuria in idiopathic minimal lesion nephrotic syndrome (IMLNS) remains to be elucidated. The most-accepted hypothesis is that the increased glomerular permeability to plasma proteins results from the effect of circulating factors on glomerular capillaries. This report critically reviews the current studies that have attempted to isolate and characterize this putative factor(s). Products released from hepatocyte or peripheral blood mononuclear cells or isolated by chromatography from serum or plasma have been tested in rats for their role in inducing proteinuria. These factors have been infused into the isolated kidney preparation or into the intact animal as a single venous injection, or continuously by pump for a period of 4 h to 7 days. Several of these isolated factors have been shown to induce proteinuria in rats. However, their exclusive pathogenetic role is questionable since none is always present in all IMLNS patients during relapse. Therefore, the increase in proteinuria in these patients may result from a single or a variety of factors as yet to be identified. Received: 1 September 1999 / Revised: 4 November 1999 / Accepted: 4 November 1999     

足细胞骨架蛋白相关分子网络在足细胞损伤和蛋白尿发生中的作用

足细胞,即肾小球脏层上皮细胞,具有复杂的细胞形态和结构,包括胞体以及从胞体依次伸出的主足突和次级足突(foot process)[1]".毗邻足细胞的足突之间形成的裂孔隔膜(slit diaphragm,SD)构成肾小球滤过的最后一道屏障.近来SD组成分子如nepbrin、podocin和CD2AP以及离子通道蛋白TRPC6的发现进一步证实足细胞足突及其SD结构和功能异常是蛋白尿发生的重要原因[2].     

Cell-cycle regulatory proteins in podocyte cell in idiopathic nephrotic syndrome of childhood

BACKGROUND: The podocyte cell is believed to play an important role in idiopathic nephrotic syndrome (INS) of childhood. In adults with cellular and collapsing focal segmental glomerulosclerosis (FSGS), the expression of cell-cycle regulatory proteins such as p27, p57, and cyclin D is decreased and expression of cyclin A, Ki-67, and p21 is observed in podocyte cells suggestive of a dysregulated podocyte phenotype. We investigated for alterations in the expression of cyclin kinase inhibitors, p27, p57, p21, and cyclins D and A in the podocyte cell of children with INS. METHODS: Forty-two kidney biopsies were investigated; 14 with minimal-change disease (MCD), seven with diffuse mesangial hypercellularity (DMH), 12 with FSGS, four with Alport syndrome (AS), and five normal biopsies. The sections were examined by immunohistochemistry using dual staining method. Podocyte cells were first identified by Wilm's tumor-1 staining after which expressions of cell-cycle regulatory proteins were analyzed. A quantitative analysis was performed for the proportion of podocyte cells that expressed each cell cycle regulatory protein. RESULTS: On light microscopy, all podocyte cells expressed p27, while p57 and p21 expression was seen in a portion of podocyte cells in normal kidney biopsies. Cyclin D was expressed in a small percent of podocyte cells though the expression was more marked in mesangial and endothelial cells. Cyclin A expression was not seen in normal biopsies. The mean expression of p27 decreased significantly in order from normal (100%), MCD (45.9%), DMH (22.4%), and FSGS (16.7%), and the difference between MCD and FSGS was significant. p21 was significantly and equally reduced in MCD (2.3%), DMH (0%), and FSGS (0.7%) compared to normal (66.6%). There was no significant difference in expression of p57, cyclin D and cyclin A in the podocyte cells between normal and children with INS. Children with AS showed a significant decrease in p27 and p21 expression, while the expression of p57, cyclin D and cyclin A were unchanged from normal, thus demonstrating a pattern similar to INS. CONCLUSION: The podocyte cell in children with INS down-regulates expression of cyclin kinase inhibitors such as p21 and p27, but not p57, but does not up-regulate cyclin D and cyclin A that are needed to overcome the G1/S transition and move the cell forward in the cell cycle process. Thus, the podocyte cell remains trapped in the G1 arrest phase. In children with INS or AS, the dysregulated podocyte phenotype is different than the one described in adults with cellular or collapsing FSGS.     

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     

Inducible podocyte injury and proteinuria in transgenic zebrafish

Damage or loss of podocytes causes glomerulosclerosis in murine models, and mutations in podocyte-specific genes cause nephrotic syndrome in humans. Zebrafish provide a valuable model for kidney research, but disruption of pronephroi leads to death within a few days, thereby preventing the study of CKD. In this study, we generated an inducible model of podocyte injury in zebrafish (pod::NTR-mCherry) by expressing a bacterial nitroreductase, which converts metronidazole to a cytotoxin, specifically in podocytes under the control of the zebrafish nphs2/podocin promoter. Application of the prodrug metronidazole to the transgenic fish induces acute damage to the podocytes in pronephroi of larval zebrafish and the mesonephroi of adult zebrafish, resulting in foot-process effacement and podocyte loss. We also developed a functional assay of the glomerular filtration barrier by creating transgenic zebrafish expressing green fluorescent protein (GFP)-tagged vitamin D-binding protein (VDBP) as a tracer for proteinuria. In the VDBP-GFP and pod::NTR-mCherry double-transgenic fish, induction of podocyte damage led to whole-body edema, and the proximal tubules reabsorbed and accumulated VDBP-GFP that leaked through the glomeruli, mimicking the phenotype of human nephrotic syndrome. Moreover, expression of wt1b::GFP, a marker for the developing nephron, extended into the Bowman capsule in response to podocyte injury, suggesting that zebrafish have a podocyte-specific repair process known to occur in mammalian metanephros. These data support the use of these transgenic zebrafish as a model system for studies of glomerular pathogenesis and podocyte regeneration.     

Atrial natriuretic peptide, sodium retention, and proteinuria in nephrotic syndrome

BACKGROUND.: Oedema formation in the nephrotic syndrome is primarily dueto tubular sodium retention. The pathogenetic role of alphaatrial natriuretic peptide (ANP), a hormonal promoter of natriuresisis unknown. METHODS.: In 31 patients (aged 35±11 years) with nephrotic syndromeand histopathological evidence of primary glomerulonephritis,we investigated plasma ANP concentration and its influence onrenal haemodynamics, natriuresis, and proteinuria (total protein,albumin, IgG excretion). Patients with a compensated treatedform of nephrotic syndrome due to primary glomerulonephritiswere included in the study. Serum creatinine levels were 1.4mg/dl. Diuretic medication was discontinued at least 24 h beforethe investigation was started. Patients were randomly assignedto ANP infusion (0.005 µg/kg*min; group II, n=15) or receivedplacebo (group III, n=16). Ten healthy subjects (group I) servedas normal controls. RESULTS.: In normal subjects (group I), ANP caused an increase in natriuresisfrom 14.5±4.2mmol/h to 26.4±11.1 mmol/h (P<0.01).In patients with nephrotic syndrome (group II), baseline sodiumexcretion of 10.5±6.0 mmol/h was increased to 19.6±14.8mmol/h with ANP infusion (P<0.01). No changes were seen inthe placebo group III. The absolute increase in ANP inducednatriuresis was not significantly different between group Iand II. However, plasma ANP levels were significantly higherin patients with nephrotic syndrome (166±87 pg/ml vs.74±21 pg/ml, P<0.05) and also reached higher levelsafter ANP infusion (P<0.01). Therefore, natriuresis was significantlyreduced when circulating ANP levels were taken into account(P<0.05). ANP administration resulted in an increase of totalprotein excretion in patients with the nephrotic syndrome (groupII, from 219±277 mg/h to 264±268 mg/h). Albuminelimination rose from 128±151 mg/h to 167±170mg/h (P<0.05) and IgG excretion from 4.91±6.67mg/hto 9.27±10.78mg/h (P<0.05). Healthy subjects alsoshowed a small but significant increase in albuminuria (48±38%,P<0.05). Low-dose ANP infusion did not, however, induce anysignificant alteration in GFR, ERPF and blood pressure. CONCLUSION.: ANP plasma concentrations in the steady state are elevated inpatients with the nephrotic syndrome. The natriuretic effectof ANP is reduced when referring to circulating ANP plasma levels.Elevated ANP levels enhance urinary protein excretion in thenephrotic syndrome. This is not due to modulation of GFR orFF, but is most probably attributable to increased glomerularpermeability.     

Familial glomerular disease with asymptomatic proteinuria and nephrotic syndrome: a new clinical entity.

Seventy-three members of a 100-member kindred with asymptomatic proteinuria, nephrotic syndrome, and progressive renal failure were studied. Of those studied, 11 members had progressed to end-stage renal disease and seven had significant proteinuria (greater than 1 g/24 hours) with normal renal function. The genetic mode of inheritance was autosomal dominant with variable penetrance and expressivity. Histopathologic changes were variable but included focal segmental glomerulosclerosis and diffuse glomerulosclerosis. Renal failure usually occurred in the fifth decade of life. The most consistent clinical finding was proteinuria without microscopic hematuria or other significant urinary sediment elements. This disease differed from Alport's hereditary nephritis and congenital nephrotic syndrome in age of onset, urinary findings, and associated conditions, that is, nerve deafness. The hereditary proteinuria and nephrotic syndrome described in this kindred represents another facet in the spectrum of hereditary renal disease.     

A modern approach to selectivity of proteinuria and tubulointerstitial damage in nephrotic syndrome

BACKGROUND: The selectivity of proteinuria, introduced in clinical nephrology in 1960 and useful in predicting steroid responsiveness in nephrotic syndrome, found little place in clinical practice in subsequent decades, since its assessment did not appear to help predict histologic diagnosis or determine prognosis. The amount of proteinuria and the degree of tubulointerstitial damage appeared to be better predictors of functional outcome. A correlation between them has been found, referred to some toxicity of proteinuria on tubular cells, but so far no single feature or component of proteinuria has been identified as being responsible for this toxicity. METHODS: We evaluated 89 patients with nephrotic syndrome [9 with minimal change disease (MCD), 29 with primary focal segmental glomerulosclerosis (FSGS), and 51 with idiopathic membranous glomerulonephritis (MGN)] to determine if the selectivity of proteinuria was associated with tubulointerstitial damage. A semiquantitative grading of histologic lesions and qualitative evaluation of the "tubular" component of proteinuria expressed as a pattern of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and as fractional excretion of the low molecular weight (LMW) protein alpha1-microglobulin (FE alpha1m) were used. A second aim of the study was to assess the predictive value on functional outcome [remission or progression to chronic renal failure (CRF)] and response to therapy of the selectivity of proteinuria, considered alone and in combination with FE alpha1m. RESULTS: Proteinuria was classified as highly selective [selectivity index (SI) < or = 0.10, N = 15], moderately selective (SI > or = 0.11 < or = 0.20, N = 34), or nonselective (SI > or = 0.21, N = 40). A significant relationship was found between the SI and the histologic degree of tubulointerstitial damage (score 0 to 1 vs. score > or =2, P = 0.000), severity of the tubular component of proteinuria (mixed SDS-PAGE pattern with LMW proteins not lower than 23 kD vs. mixed pattern with LMW proteins up to 20 to 10 kD, P = 0.000), and FE alpha1m (values below vs. above a defined cut-off, P = 0.000). The functional outcome was evaluated in 60 patients with baseline normal renal function (serum creatinine 0.97 +/- 0.19 mg/dL). The patients with high, moderate, or nonselective proteinuria had 100, 50, and 29% of complete or partial remission (P = 0.0001) and 0, 25, and 35% of progression to CRF, respectively (P = 0.050). In 45 patients with moderately selective (N = 28) and nonselective (N = 17) proteinuria, according to some arbitrary cutoffs for FE alpha1m (MGN, < or = vs. > 0. 240% of creatinine clearance; FSGS and MCD, < or = vs. > 0.350%), the remission rate was 62 versus 6% in patients with FE alpha1m below or above the cutoffs (P = 0.0001), and progression to CRF was 7 and 69%, respectively (P = 0.0001). The response to therapy (complete or partial remission at the last observation), evaluated retrospectively in 40 patients, was 100, 67, and 33% in high, moderate, and nonselective proteinuria (P = 0.0002); in 30 patients with moderate and nonselective proteinuria, according to an FE alpha1m value that was < or = or > the cutoffs, the response rate was 75 versus 10% (P = 0.001). CONCLUSIONS: There is a significant relationship between selectivity of proteinuria and tubulointerstitial damage. Moreover, the selectivity of proteinuria has a predictive value on functional outcome. When proteinuria is highly selective, the tubulointerstitial damage is rather infrequent, and 100% of patients develop clinical remission. When proteinuria is moderately selective or nonselective, increasing numbers of patients develop tubulointerstitial damage; in these patients, the functional outcome and response to therapy is partly dependent on tubulointerstitial involvement, and the best predictor of functional outcome is the combination of SI and FE alpha1m.