Glomerular charge alterations in human minimal change nephropathy

State of the art in childhood nephrotic syndrome: concrete discoveries and unmet needs

Nephrotic syndrome (NS) is a clinical entity characterized by proteinuria, hypoalbuminemia, and peripheral edema. NS affects about 2-7 per 100,000 children aged below 18 years old yearly and is classified, based on the response to drugs, into steroid sensitive (SSNS), steroid dependent, (SDNS), multidrug dependent (MDNS), and multidrug resistant (MRNS). Forms of NS that are more difficult to treat are associated with a worse outcome with respect to renal function. In particular, MRNS commonly progresses to end stage renal failure requiring renal transplantation, with recurrence of the original disease in half of the cases. Histological presentations of NS may vary from minimal glomerular lesions (MCD) to focal segmental glomerulosclerosis (FSGS) and, of relevance, the histological patterns do not correlate with the response to treatments. Moreover, around half of MRNS cases are secondary to causative pathogenic variants in genes involved in maintaining the glomerular structure. The pathogenesis of NS is still poorly understood and therapeutic approaches are mostly based on clinical experience. Understanding of pathogenetic mechanisms of NS is one of the 'unmet needs' in nephrology and represents a significant challenge for the scientific community. The scope of the present review includes exploring relevant findings, identifying unmet needs, and reviewing therapeutic developments that characterize NS in the last decades. The main aim is to provide a basis for new perspectives and mechanistic studies in NS.

Proteinuria in thrombotic microangiopathy is associated with partial podocytopathy

BACKGROUND

Thrombotic microangiopathy (TMA) results in acute kidney injury, but the cause of heavy proteinuria in this disorder is puzzling. The goal of this study was to determine if there were significant effacement of foot processes and CD133-positive hyperplastic podocytes in TMA to explain the proteinuria.

METHODS

The study included 12 negative controls (renal parenchyma removed from renal cell carcinoma) and 28 thrombotic microangiopathy due to different etiologies. The percent of foot process effacement was estimated, and proteinuria level was obtained for each TMA case. Both groups of cases were stained for CD133 by immunohistochemical method, and the number of positive CD133 in hyperplastic podocytes was counted and analyzed.

RESULTS

Nineteen (19) of 28 (68%) TMA cases had nephrotic range proteinuria (urine protein/creatinine >3). Twenty-one (21) of 28 (75%) TMA cases showed positive CD133 staining in scattered hyperplastic podocytes within Bowman's space but was absent in control cases. The percent of foot process effacement (56 ± 4%) correlated with proteinuria (protein/creatinine ratio 4.4 ± 0.6) (r = 0.46, p = .0237) in TMA group.

CONCLUSION

Our data indicate that the proteinuria in TMA can be associated with significant effacement of foot processes. CD133-positive hyperplastic podocytes can be seen in the majority of TMA cases of this cohort, indicating a partial podocytopathy.

PodoSighter: A Cloud-Based Tool for Label-Free Podocyte Detection in Kidney Whole-Slide Images

BACKGROUND

Podocyte depletion precedes progressive glomerular damage in several kidney diseases. However, the current standard of visual detection and quantification of podocyte nuclei from brightfield microscopy images is laborious and imprecise.

METHODS

We have developed PodoSighter, an online cloud-based tool, to automatically identify and quantify podocyte nuclei from giga-pixel brightfield whole-slide images (WSIs) using deep learning. Ground-truth to train the tool used immunohistochemically or immunofluorescence-labeled images from a multi-institutional cohort of 122 histologic sections from mouse, rat, and human kidneys. To demonstrate the generalizability of our tool in investigating podocyte loss in clinically relevant samples, we tested it in rodent models of glomerular diseases, including diabetic kidney disease, crescentic GN, and dose-dependent direct podocyte toxicity and depletion, and in human biopsies from steroid-resistant nephrotic syndrome and from human autopsy tissues.

RESULTS

The optimal model yielded high sensitivity/specificity of 0.80/0.80, 0.81/0.86, and 0.80/0.91, in mouse, rat, and human images, respectively, from periodic acid-Schiff-stained WSIs. Furthermore, the podocyte nuclear morphometrics extracted using PodoSighter were informative in identifying diseased glomeruli. We have made PodoSighter freely available to the general public as turnkey plugins in a cloud-based web application for end users.

CONCLUSIONS

Our study demonstrates an automated computational approach to detect and quantify podocyte nuclei in standard histologically stained WSIs, facilitating podocyte research, and enabling possible future clinical applications.

Mechanism Underlying Selective Albuminuria in Minimal Change Nephrotic Syndrome

As water and solutes are filtered through the slit membrane, it is an a priori concept that a slit membrane is an essential filtration barrier for proteins, including albumin. However, in cases of minimal change nephrotic syndrome, the number of slit membranes is reduced by the foot process effacement and tight junction-like cell adhesion. Furthermore, albumin endocytosis is enhanced in the podocytes under condition of minimal change disease, and albumin is selectively transported by the albumin receptor FcRn. Suppressing the endocytosis of albumin with anti-FcRn antibody decreases the urinary protein level. The expression of motor molecules, such as cytoplasmic dynein 1 and myosin IX, is increased in the podocytes under conditions of minimal change nephrotic syndrome, suggesting the enhanced transport of vesicles containing albumin. Podocyte vesicle transport may play an important role in the pathology of selective albuminuria in cases of nephrotic syndrome.

Low molecular weight heparin may benefit nephrotic remission in steroid‑sensitive nephrotic syndrome via inhibiting elastase

Low molecular weight heparin (LMWH) has a structure similar to heparan sulfate, which exerts anti-inflammatory effects via inhibiting elastase (Ela) activity. Release of Ela along the glomerular capillary wall may induce glomerular injury and proteinuria. The present study aimed to investigate the influence of LMWH on steroid-sensitive nephrotic syndrome (SSNS) and the potential underlying mechanism. A total of 40 SSNS patients and 20 healthy controls were recruited. SSNS patients were treated with LMWH and prednisone simultaneously (LMWH+pred group) or with prednisone alone (pred group). Proteinuria, urinary glycosaminoglycans (GAGs), serum Ela and urinary creatinine levels were measured. The nephrotic period of SSNS was 15.93±5.78 days. The nephrotic period of SSNS in LMWH+pred group was significantly reduced compared with the pred group (14.13±4.56 vs. 18.63±6.49 days; P<0.05). At the follow-up of the SSNS patients, there was no statistically significant difference in number of relapses between the LMWH+pred and pred groups. Proteinuria (2.51±0.97 g/24 h), urinary GAG levels (4.92±0.87 mg/mmol creatinine) and serum Ela levels (77.64±10.99 ng/l) were significantly greater in the nephrotic period of SSNS compared with the remission period (0.107±0.026 g/24 h, 1.53±0.27 mg/mmol Cr and 41.92±7.81 ng/l, respectively) and the healthy control group (0.098±0.027 g/24 h, 1.40±0.26 mg/mmol creatinine and 38.43±9.83 ng/l, respectively; P<0.05). During the remission period, urinary GAG and serum Ela levels in the LMWH+pred group were significantly reduced compared with the pred group (P<0.05), whereas proteinuria did not differ between these groups (P>0.05). Positive correlations were revealed between urinary GAG excretion and proteinuria (r=0.877; P<0.05), proteinuria and serum Ela levels (r=0.844; P<0.05) and serum Ela levels and urinary GAG excretion (r=0.881; P<0.05). The results of the present study indicated that elevated serum Ela levels may induce proteinuria by degrading GAGs in the glomerular basement membrane in children with SSNS. LMWH may benefit nephrotic remission of SSNS via inhibiting Ela.

Disruption of glomerular basement membrane charge through podocyte-specific mutation of agrin does not alter glomerular permselectivity

Glomerular charge selectivity has been attributed to anionic heparan sulfate proteoglycans (HSPGs) in the glomerular basement membrane (GBM). Agrin is the predominant GBM-HSPG, but evidence that it contributes to the charge barrier is lacking, because newborn agrin-deficient mice die from neuromuscular defects. To study agrin in adult kidney, a new conditional allele was used to generate podocyte-specific knockouts. Mutants were viable and displayed no renal histopathology up to 9 months of age. Perlecan, a HSPG normally confined to the mesangium in mature glomeruli, did not appear in the mutant GBM, which lacked heparan sulfate. Moreover, GBM agrin was found to be derived primarily from podocytes. Polyethyleneimine labeling of fetal kidneys revealed anionic sites along both laminae rarae of the GBM that became most prominent along the subepithelial aspect at maturity; labeling was greatly reduced along the subepithelial aspect in agrin-deficient and conditional knockout mice. Despite this severe charge disruption, the glomerular filtration barrier was not compromised, even when challenged with bovine serum albumin overload. We conclude that agrin is not required for establishment or maintenance of GBM architecture. Although agrin contributes significantly to the anionic charge to the GBM, both it and its charge are not needed for glomerular permselectivity. This calls into question whether charge selectivity is a feature of the GBM.

Glycosaminoglycan excretion in children with nephrotic syndrome

Although most childhood nephrotic syndromes respond to steroid treatment, steroid resistant nephrotic syndrome (SRNS) is also common and is particularly difficult to treat. This study investigated the role of glycosaminoglycans (GAG) in the pathogenesis and clinical course of nephrotic syndrome in children. Thirty-four children (21 males and 13 females, mean age 3.7+/-1.6 years) with steroid-sensitive nephrotic syndrome and 20 children with steroid-resistant nephrotic syndrome (12 males and 8 females, mean age 10.9+/-3.8 years; of the twenty, four had primary SRNS (FSGS) and the others had secondary SRNS) were included the study. Mean urine levels of GAG relative to creatinine (U(GAG)/U(Cr)) in patients with SRNS (n=20, 113.01+/-78.46 mg g(-1) Cr) and in patients experiencing the nephrotic period of steroid-sensitive nephrotic syndrome (n=34, 132.15+/-101.55 mg g(-1) Cr) were both significantly higher than mean U(GAG)/U(Cr) for control subjects (n=30, 51.83+/-47.66 mg g(-1) Cr) (P<0.01 for both). Patients excreted significantly more GAG during the nephrotic period of steroid-sensitive nephrotic syndrome than during remission (132.15+/-101.55 vs 39.11+/-42.73 mg g(-1) Cr, respectively; P<0.01). There was, however, no significant difference between U(GAG)/U(Cr) for patients with steroid-resistant nephrotic syndrome and U(GAG)/U(Cr) in the nephrotic period of steroid-sensitive nephrotic syndrome. Urine GAG excretion correlated significantly with the severity of proteinuria. The results suggest that GAG play a significant role in the pathogenesis of nephrotic syndrome but that GAG excretion is not a marker for response to steroid treatment in pediatric patients with this condition.

Impact of cyclosporin on podocyte ZO-1 expression in puromycin aminonucleoside nephrosis rats

Puromycin aminonucleoside (PAN)-induced nephrosis is a well-described model of human idiopathic nephrotic syndrome, but the mechanism of PAN's effect is not completely understood. To investigate whether proteinuria in the PAN model is associated with an alteration of zonula occludens-1 (ZO-1) expression within the glomeruli, and whether cyclosporin A (CsA) has an effect on proteinuria and ZO-1 expression in this model, eighteen Sprague Dawley (SD) rats were assigned into three groups. Twelve rats received a single intraperitoneal injection of PAN (15 mg/100 g). The other six rats received an equal volume of saline (normal control group; control). CsA solution was administered intraperitoneally once a day for 20 days after the PAN injection (n=6, PAN+CsA). The remaining six rats received PAN, but they didn't receive CsA (n=6, PAN). Compared to control rats (35.1+/-5.4 mg/day), the 24-hour urinary protein excretion on day 18 was significantly higher in the PAN rats (1021.9+/-128.9 mg/day, p<0.01), and the CsA treatment partly reversed the increase in proteinuria in the PAN rats (556.4+/-102.3 mg/day, p<0.05). Glomerular ZO-1 protein expressions were significantly increased in the PAN rats as compared to the control group on day 20 (176%, p<0.01). CsA treatment for 20 days in the PAN rats inhibited the increase in ZO-1 protein expression by 71.1% (p<0.05). CsA treatment significantly diminished the glomerular ZO-1 expression in the PAN rats as assessed by immunohistochemistry. CsA treatment significantly reduced proteinuria and the diminished glomerular ZO-1 expression in a PAN nephrosis rat model. These findings suggest the potential role of the slit diaphragm associated proteins in the development of the nephrotic syndrome, and CsA decreased the proteinuria probably by a direct action on the expression of these proteins in podocytes. Further investigations are needed to clarify the role of slit diaphragm associated proteins in the development of PAN nephrosis.

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.

Physiological aspects of pig-to-primate renal xenotransplantation

BACKGROUND

Few data exist on the physiological aspects of pig-to-primate renal xenotransplantation.

METHODS

Use of organs transgenic for human decay accelerating factor has allowed assessment of the metabolic and hormonal functions of these xenografts.

RESULTS

Porcine renal xenografts largely maintain plasma electrolyte homeostasis. An increase in proteinuria was detected that may result from graft injury. In contrast to allotransplantation a severe anaemia developed requiring recipient treatment with exogenous human erythropoietin.

CONCLUSIONS

Our experience provides qualified encouragement for the likely physiological compatibility of pig and primate species, but identifies areas where a xenograft may not match the performance of an allograft.

Effects of filtration rate on the glomerular barrier and clearance of four differently shaped molecules

The effect of shape on the transglomerular passage of solutes has not been hitherto systematically studied. We perfused isolated rat kidneys to determine the fractional clearances (theta) at various filtration rates for four molecules of different shapes but with similar Stokes-Einstein radii (aSE = 34-36 A). The theta for hyaluronan, bikunin, and Ficoll36 A were 66, 16, and 11%, respectively, at a glomerular filtration rate (GFR) of 0.07 ml x min(-1) x g wet wt(-1) and decreased to 46, 14, and 7%, respectively, on a fivefold increase in GFR. Under the same conditions, theta for albumin increased from 0.15 to 0.74%, and similar behavior was observed for larger Ficolls (aSE >45 A). Pore analysis showed that the "apparent neutral" solute radii of Ficoll, albumin, bikunin, and hyaluronan were 35, 64, 33, and 24 A, respectively, despite similar aSE. In addition, the properties of the glomerular filter changed with increasing GFR and hydrostatic pressure. We conclude that elongated shape, irrespective of size and charge, drastically increases the transglomerular passage of a solute, an effect that is related to its frictional ratio.

Glomerular basement membrane polyanion distribution and nitric oxide in spontaneous hypertensive rats: effects of salt loading and antihypertensive therapy with propranolol

Cationic colloidal gold (CCG), a polycationic histochemical probe, was used to analyze the distribution of glomerular basement membrane (GBM) polyanions, mainly heparan sulfate proteoglycan in spontaneous hypertensive rats (SHR) with or without salt loading and antihypertensive treatment with propranolol. The changes of mean GBM width and anionic sites distribution were assessed by electron microscopy. Plasma and urinary nitrates (NO(x)) were measured by nitrite (NO2) + nitrate (NO3), stable metabolites of NO. SHR had decreased NO production and increased GBM width (27%) compared with the control Wistar-Kyoto (WKY) rats. The chronic high dietary salt intake resulted in a significant increase in blood pressure, proteinuria, and renal function in the SHR rats. The chronic high salt dietary intake resulted in a decrease in NO in the WKY and a further reduction in NO production in the SHR. The GBM anionic sites count was similar in the SHR and WKY nonsalt-loaded groups, 13.5 +/- 0.5 and 12.8 +/- 0.4 CCG counts/microm GBM, respectively, but significantly lower in both salt-loaded SHR and WKY, 9.9 +/- 0.55 (P < .01) and 9.6 +/- 0.55 (P < .01) CCG counts/microm GBM, respectively. Antihypertensive treatment with propranolol in the salt-loaded SHR group resulted in lower blood pressure, a further decrease in NO production, but no significant changes in GBM width and anionic sites count. It is concluded that chronic high salt intake may be deleterious to the permselectivity of the GBM. A low NO production state that results from chronic salt loading in already hypertensive rats will result in more severe organ (renal) damage, most probably by the addition of the loss of GBM permselectivity to the existing pathomorphologic changes.

Edmund Randerath (1899-1961): experimental proof for the glomerular origin of proteinuria

A century ago, Edmund Randerath (1899-1961), who was one of the pioneers in nephrology that provided indirect experimental proof for the glomerular origin of proteinuria, was born. In the first decades of this century, the concept prevailed that "nephrosis" was a process of primary tubular cell degeneration. In contrast to prevailing opinion, he interpreted these changes to be the result of the uptake and storage of serum proteins after they had been filtered in the glomerulus. Edmund Randerath proved the glomerular origin of proteinuria by astute experiments in amphibia. In the salamander, an intraperitoneal injection of albumin provoked the supposedly "degenerative" changes of tubular epithelial cells in only those nephrons that drained the coelomic cavity and were devoid of glomeruli, but not in those nephrons that were closed and attached to glomeruli. This observation provided incontrovertible evidence that the presence of serum proteins in tubular fluid was a prerequisite for the development of the tubular epithelial cell changes typically seen in nephrotic patients.

Fractional clearance of high molecular weight proteins in conscious rats using a continuous infusion method

BACKGROUND

The purported existence of "large pores" in the glomerular capillary wall has been derived primarily from studies using dextrans and Ficolls. Systematic studies using high molecular weight proteins have not been performed. One of the difficulties is that recent studies have demonstrated that albumin and other proteins undergo degradation during renal passage. Our study took into account this renal degradation in measuring the fractional clearance of various high molecular weight proteins (the hydrodynamic radii range was between 48 to 70 A).

METHODS

Fractional clearances of tritium-labeled proteins were measured using ALZET osmotic pumps, which are designed to release a slow continuous infusion of tracer. Blood and urine collections were taken at 24-hour intervals over seven days and were counted for radioactivity, and glomerular filtration rate was measured by a creatinine assay.

RESULTS

Steady-state levels of [3H]protein in plasma were obtained by day 6. The [3H]proteins in the plasma showed no degradation. The fractional clearances (mean +/- sd, N = 5) of the various proteins were albumin (radius = 36 A; 0.0023 +/- 0.0009), transferrin (48 A; 0.0046 +/- 0.0007), lactoperoxidase (58 A; 0. 0045 +/- 0.0005), immunoglobulin G (62 A; 0.0043 +/- 0.0009), lactate dehydrogenase (64 A; 0.0041 +/- 0.0009), and glucose oxidase (70 A; 0.0036 +/- 0.0011).

CONCLUSIONS

These values suggest a weak dependence of fractional clearance on size-selective filtration, except for albumin, which undergoes a specific type of postglomerular processing. The fractional clearances were higher than expected from previous data on dextrans and Ficolls of equivalent hydrodynamic radius, and thus demonstrate that "large pores" may already exist in normal glomerular capillary walls.

Glomerular charge selectivity for proteins larger than serum albumin as revealed by lactate dehydrogenase isoforms

It is well known that macromolecules like albumin are markedly restricted in their passage across the glomerular capillary wall. However, the relative importance of solute size, charge and shape is currently debated since much of the previous work is based on dextran in neutral or charge-modified forms. These polymers have certain drawbacks that make them less suitable for analysis of capillary permeability and the notion of a glomerular charge barrier has therefore been questioned. Moreover, macromolecules larger than albumin (mol. wt. 69,000) have been suggested to pass through nonselective 'shunt' pathways. In order to study glomerular permeability, isolated rat kidneys were perfused with albumin solutions containing trace amounts of two differently radiolabelled isoenzymes of lactate dehydrogenase (LDH) at low temperature to inhibit tubular function. The isoenzymes have similar size (mol. wt. 140,000) and shape but differ in charge, one carrying a negative net surface charge (LDH1, -19) and the other being slightly cationic (LDH5, +2). The urine and perfusate samples were subjected to high pressure liquid chromatography (HPLC) gel-filtration to allow for measurements of intact LDH. The fractional clearance was 0.11% +/- 0.04% for the anionic LDH1 and 0.56% +/- 0.07% for LDH5, whereas that for albumin was 0.21% +/- 0.03% at a glomerular filtration rate of 0.11 +/- 0.01 mL min-1 g-1 kidney wet weight. The results were analysed using a homogenously charged membrane model and are compatible with a charge density of 35 mEq L-1, with 95% confidence interval of 26-41 mEq L-1. These findings suggest a significant glomerular charge selectivity for proteins substantially larger than albumin. The charge density is, however, far less than estimated from dextran studies.

Effect of an increased intraperitoneal pressure on fluid and solute transport during CAPD

The effect of an increased intraperitoneal pressure on fluid and solute transport was studied in eight stable CAPD patients. Two permeability tests of two hours each with continuous registration of the intraperitoneal pressure were performed while patients were in supine position. The intra-abdominal pressure was raised by means of a tightening girdle with inflatable cuffs in one of the experiments. Intraperitoneally administered dextran 70 was used as a volume marker in order to determine the peritoneal fluid kinetics. The increment in the intra-abdominal pressure of 10.0 +/- 1.0 mm Hg caused a decline in the net ultrafiltration. This was mainly determined by an increase in the lymphatic absorption: 1.07 +/- 0.18 ml/min (without compression) versus 1.86 +/- 0.25 ml/min (with compression; P < 0.01), whereas the transcapillary ultrafiltration rate tended to decrease: 2.02 +/- 0.23 versus 1.73 +/- 0.27 ml/min (P = 0.08). External compression also diminished solute transport from the circulation to the peritoneal cavity. The decline in the mass transfer area coefficient of urea, creatinine, urate and beta 2-microglobulin was 13%, indicating a smaller effective peritoneal surface area caused by external compression probably due to a decrease in the number of the perfused peritoneal capillaries. The fall in the peritoneal protein clearances was more pronounced the higher the molecular weight of the protein, consistent with a decline in the intrinsic permeability of the peritoneum. Kinetic modeling using computer simulations was used to analyse these effects in terms of the pore theory, using a convection model (large pore radius 184 +/- 14 A) and a diffusion model (large pore radius 1028 +/- 218 A) for the transport of macromolecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephrotic edema--pathogenesis and treatment

The cardinal features of the nephrotic syndrome are albuminuria, hypoalbuminemia, and edema. Traditionally, albuminuria was thought to be responsible primarily for the development of hypoalbuminemia. A decreased plasma-albumin concentration accompanied by a decreased plasma-oncotic pressure was thought responsible for the development of edema and secondary salt retention by the kidney. However, new findings have prompted a reevaluation of these relationships. For example, increased renal catabolism and blunted hepatic synthesis appear to play major roles in the development of hypoalbuminemia. Evidence suggests that primary, rather than secondary, salt retention by the kidney and activation of mechanisms that limit fluid movement across the capillary wall participate in the pathogenesis of the nephrotic syndrome and related edema. The treatment of patients with the nephrotic syndrome should limit proteinuria. This can be accomplished by administering angiotensin-converting enzyme inhibitors, lowering the protein content of the diet, and cautiously using non-steroidal antiinflammatory agents.

Glomerular extracellular matrices and anionic sites in aging ddY mice: a morphometric study

A morphometric study was undertaken to examine age-related changes in glomerular ultrastructure and anionic sites in ddY male mice at various ages. A progressive increase in glomerular extracellular matrices, including thickening of the glomerular basement membrane (GBM), formation of GBM nodules, and mesangial matrix increase, was found to be the primary age-related ultrastructural change in aging mice; there were also electron-dense deposits in mesangial and subepithelial regions. The extent of GBM thickening in mice was less than was reported in rats. Rather, the GBM nodules, which had the same electron density as the lamina densa (LD) and protruded on the subepithelial side of the GBM, were more striking. Quantitative evaluation showed that GBM thickness, number and size of GBM nodules, and the area of the mesangial matrix were significantly correlated with the age of the mice. The distribution of anionic sites in the glomeruli of aging animals was described for the first time. No statistically significant differences were noted between the number of glomerular anionic sites in the different age groups. These results indicate that the increase in glomerular extracellular matrices reported in aged rats was also present in aged mice, although the extent of various changes was different. The results also indicate that this increase in glomerular extracellular matrices with age was not accompanied by significant alteration in glomerular anionic sites.

Reversible renal failure in the nephrotic syndrome

Acute, usually reversible, renal failure has been observed in patients with normal or minimally altered glomeruli on renal biopsy. This review aims to examine the clinical features of acute renal failure in these patients and to evaluate factors that may contribute to the reduction in glomerular filtration rate (GFR). In an analysis of 79 cases affecting 75 patients reported in the English literature since 1966, with acute renal failure associated with minimal change disease or mild histopathological changes in glomeruli, the average age was 58 +/- 2 years (mean +/- 5 SEM), urine protein excretion 11.6 +/- 0.6 g/d, and serum albumin level 19 +/- 1 g/L (1.9 +/- 0.1 g/dL). Acute renal failure was documented an average of 29 +/- 5 days after onset of nephrotic syndrome, and persisted for 7 weeks in 62 episodes in the 58 patients in whom recovery of renal function occurred. Fourteen patients died of uremia or required chronic dialysis, and 3 were lost to follow-up. Although plasma volume depletion was sometimes cited as the cause of renal failure, objective signs of hypovolemia were not documented and most patients did not improve after treatment designed to correct volume deficits. In contrast, histopathological changes consistent with acute tubular necrosis (ATN) were observed in at least 60% of cases. Since the pathogenesis of acute renal failure in minimal change nephrotic syndrome is unknown, we evaluated hemodynamic determinants of GFR in patients with minimal change disease with normal or near-normal renal function, and in relevant animal models, to obtain insights into the effect of nephrotic syndrome on GFR. Although acute renal failure is uncommon, GFR is reduced concurrently with nephrotic syndrome in approximately 30% of children and adults. Absolute and effective blood volume and renal plasma flow are relatively well preserved. However, clinical and experimental observations suggest that the glomerular ultrafiltration coefficient may be reduced by as much as 50%. These findings, together with renal biopsy changes in cases with acute renal failure, suggest that severe reductions in GFR in some patients with minimal change nephrotic syndrome may result from an interaction between acute ischemic tissue injury and preexisting intrinsic renal abnormalities.

Interaction between cationic dyes and erythrocyte membranes in minimal change nephropathy: an electrophoretic approach

A study was undertaken to clarify the usefulness of two cationic dyes, alcian blue (AB) and ruthenium red (RR) in demonstrating the defect in cellular membranes noted in minimal change nephropathy (MCN). The binding of both dyes to RBC membranes purified from normal and nephrotic children was evaluated by electrophoretic titration curves. When examined separately, AB was found to precipitate spontaneously, producing macro-aggregates with no electrophoretic mobility at pH 5. This was presumed to be the result of hydrophobic interaction of the dye with itself. The same phenomenon was observed when this dye was incubated at 37 degrees C with RBC ghost's from normal children, when AB presented a sigmoidal curve with a net positive charge for pHs higher than 5.5 and lower than 5 and no electrophoretic mobility at pH 5. However, incubation of AB with RBC ghosts from children with MCN resulted in an improvement of the solubility of the dye which then migrated with a net positive charge along the whole gradient of pH from 3.5 to 9. The presence of zwitterionic neutral detergents such as CHAPS, but not of a charged substance such as protamine sulphate, inhibited precipitation at pH 5 when incubated with membranes from normal children, supporting the hydrophobic nature of the phenomenon. When RR was used instead of AB, it was fully protonated (i.e. did not precipitate) when analysed alone, but when incubated with normal RBC ghosts, it also revealed no electrophoretic mobility at pH 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of anionic sites from the glomerular basement membrane in human glomerulonephritides

Changes in glomerular anionic sites were analyzed in 31 patients with various types of glomerulonephritis using the high-iron diamine-thiocarbohydrazide-silver proteinate method. On the basis of the degree of proteinuria at the time of biopsy, the patients were divided into 3 groups as follows: Group 1, less than 10 mg/kg/24 h; Group 2, 10-50 mg/kg/24 h; Group 3, more than 50 mg/kg/24 h. The number of glomerular anionic sites per 300 nm length of the lamina rare externa was 16.20 +/- 3.37 in Group 1, 12.19 +/- 3.42 in Group 2 and 9.97 +/- 2.51 in Group 3. Moreover, smaller and irregularly distributed anionic sites, and a greater loss of anionic sites in the paramesangial region were observed in Groups 2 and 3. On the other hand, there was no significant correlation between the mesangial sclerosis index and the number of anionic sites (r = -0.40) in patients with IgA nephropathy (9 cases) and nephritis of Henoch-Schönlein purpura (6 cases). These results suggest that the proteinuria seen in various types of glomerulonephritis is related to the loss of glomerular anionic sites, i.e., dysfunction of the charge-selective barrier.

Do circulating factors play a role in the pathogenesis of minimal change nephrotic syndrome?

This review examines the studies which have been undertaken to test the hypothesis that minimal change nephrotic syndrome of childhood (MCNS) is a primary immune disorder and that there is altered T-cell function which results in release of a circulating factor. This factor alters glomerular permeability, perhaps by modifying charge sites in the glomerular capillary bed, and results in selective proteinuria. The abnormalities in immune function observed in MCNS are summarized, as are the studies of circulating factors which have been identified. Although some agents have been shown to alter capillary permeability, the unequivocal demonstration of such a factor causing selective proteinuria in vivo, either directly or indirectly, is lacking. The question is raised whether intrarenal release or activation of mediators of altered permeability, rather than the systemic release of such factors, may be important in the pathogenesis of MCNS.

The peritoneal transport of serum proteins and neutral dextran in CAPD patients

The peritoneal transport of five serum proteins and intravenously-administered neutral dextran was studied in 13 CAPD patients. In all patients a study was done three hours after the administration of dextran. In nine the study was repeated after 14 hours, and in six also after 38 hours. Using gel permeation chromatography of serum and dialysate it was possible to calculate fractional (relative to inulin) clearances for dextran fractions with Einstein-Stokes radii ranging from 30 to 90 A. In contrast to glomerular transport, we found that peritoneal clearances of serum proteins and corresponding dextran fractions were of a similar magnitude up to a radius of 90 A, especially in the follow-up studies. No evidence was found for a charge-selective barrier function of the peritoneum. It appeared likely that the peritoneal interstitium is probably a third compartment between blood and dialysate in which equilibrium with blood and dialysate is present for serum proteins, but initially not for dextran. For dextran this equilibrium is probably approached 14 to 38 hours after administration. The linear relationship between the reciprocal of fractional clearances and Einstein-Stokes radii indicates that restricted diffusion is the main transport mechanism of macromolecules across the peritoneal membrane. The slopes of the linear regression between the reciprocal of fractional clearances and radii ranged from 0.32 to 6.95 (slope for free diffusion 0.07) and provided an index of the permeability characteristics of the peritoneal membrane.

Peroxidative damage of the erythrocyte membrane in children with nephrotic syndrome

The structural composition of erythrocyte ghosts was analysed in children affected by steroid-responsive (SRNS) and unresponsive nephrotic syndrome (SUNS). No variation of either intrinsic or extrinsic ghost proteins was found by discontinuous SDS-electrophoresis associated with a very sensitive double staining technique. By contrast, the composition of inner-layer phospholipids--phosphatidyl ethanolamine (PE) and phosphatidyl serine (PS)--was altered in SRNS with minor changes also involving phosphatidic acid, phosphatidyl inositol and lysophosphatidyl choline. Signs of peroxidative damage were present in both SRNS and SUNS ghosts and inside the cells; these included high levels of fluorescent amino-iminopropene derivates of PE and PS, increased intraerythrocytic amounts of malonyldialdehyde and decreased levels of reduced glutathione. Taken together these results support the concept that in SRNS and SUNS erythrocytes are target cells for peroxidative damage. In SRNS peroxidation of membrane lipids results in a marked alteration of the phospholipid composition of erythrocyte ghosts.

Heparan sulfate proteoglycan from human and equine glomeruli and tubules

1. Proteoglycans were isolated from human and equine glomeruli or tubules by guanidine extraction and anion exchange chromatography. 2. These proteoglycan preparations contained about equal amounts of heparan sulfate and chondroitin sulfates. 3. During the preparation of glomerular or tubular basement membranes the main part of proteoglycans (greater than 50%) was extracted in the salt extract. Chondroitin sulfate proteoglycan was mainly found in the water and salt extracts of glomeruli and tubules, heparan sulfate proteoglycan in the deoxycholate extracts and the basement membranes. 4. The glomerular basement membrane (GBM) contains about 12% (human) or 20% (equine) of the proteoglycans of the total glomerulus. They consist of greater than 70% (equine) or 80% (human) of heparan sulfate. 5. Heparan sulfate proteoglycan was isolated from the proteoglycan preparations of human or equine glomeruli and tubules by additional treatment with nucleases and chondroitinase ABC followed by CsCl gradient centrifugation. 6. Protein accounts for about 40% (dry weight) of the heparan sulfate proteoglycans. Their amino acid composition is characterized by a high content of glycine, but 3-hydroxyproline, 4-hydroxyproline and hydroxylysine are lacking. 7. The biochemical characteristics of the heparan sulfate proteoglycan of human or equine glomeruli or tubules differ from that isolated from rat glomeruli by their higher protein content and their amino acid composition. The significance of these differences is discussed.

Characterization of cationic albumin in minimal change nephropathy

The presence of isoalbumins with a less anionic charge than the normal protein (pI = 4.7) is the hallmark of proteinuria in minimal change nephropathy (MCN). Steroid-induced restoration of near normal levels of proteinuria is characterized by the appearance in urines of isoalbumins with a pI still more anionic than the normal. In our search for an explanation for the pI changes, we used preparative isoelectric focusing in granulated gels to split the microheterogeneous bands obtained from nine MCN-affected children into four fractions (A1, A2, A3, A4) with decreasing pI from 5.8 to 4.0 and we have determined their fatty acid content. The least anionic fraction, A1, was the most defatted, followed by A2, A3 and A4 in which fatty acid content progressively increased, A4 being the most fatted fraction. Accordingly, the mean content of fatty acids in urinary albumin in proteinuric children was lower than in both the remission phase and in normal children (2.17 +/- 0.03 vs. 20.91 +/- 0.38 and 20.94 +/- 0.39, respectively) and was lower by a factor of 4 compared to serum albumin in the same phase of the disease (2.17 +/- 0.03 vs. 8.59 +/- 1.64). Among medium and long-chain fatty acids, the ratio between serum and urinary albumin was the highest for linoleic acid (approximately 7), followed by that of oleic acid, palmitic acid and lauric acid. At variance in five other patients affected by non-MCN nephrotic syndrome this ratio was for practically all FAs about 1.(ABSTRACT TRUNCATED AT 250 WORDS)

PVP-sieving curves as an estimate of glomerular hemodynamics in HgCl2 acute renal failure in the dog

In the present study, the pathophysiologic role of glomerular hemodynamic factors in the early phase of HgCl2-induced acute renal failure is evaluated in the dog. This model of moderate ARF is characterized by a parallel fall in glomerular filtration rate (delta GFR, -43%) and renal blood flow (delta RBF, -38%) within the first three hours after HgCl2 administration. Glomerular hemodynamics were studied by analysis of PVP-sieving curves. There was a significant shift of these curves upward and to the right during the 3 hours that followed the injection of HgCl2. From this analysis, no arguments for tubular back-leak could be found. Mathematical analysis of the curves revealed a fall in effective filtration pressure (EFP) in presence of an unchanged glomerular ultrafiltration coefficient (Kf) (delta EFP, -40 +/- 4%; p less than 0.01; delta Kf, +5 +/- 1%; p greater than 0.05 vs. control). No major changes occurred in glomerular colloid osmotic pressure. Subsequently, the early fall of GFR in this toxic model of acute renal failure was essentially attributed to a decrease of effective filtration pressure due to either tubular obstruction and/or mainly to renal hemodynamic changes.

Renal selectivity properties towards endogenous albumin in minimal change nephropathy

It is well accepted that the molecular charge and conformation of serum proteins are major determinants of their glomerular filtration, but few studies characterizing the molecular features of circulating proteins in renal diseases are currently available. In 11 children affected by minimal change nephropathy (MCN) we determined the electrical charge and the fluorescence quantum yield of Tyrosine (Tyr) and Tryptophan (Trp) (taken as index of conformation) of serum and urinary albumin before and after steroid-induced remission of proteinuria. In all proteinuric children at the onset of the disease, urinary albumin was formed by one band with an isoelectric point (pI) of 4.7 (pI of the native protein), and by numerous other, less anionic bands with pIs between 4.8 and 5.5 accounting for about 50% of the total amount of this protein. The normalization of proteinuria which followed steroid therapy was characterized by the disappearance in urines of the less anionic fraction and by the appearance of numerous isoforms with a pI still more anionic (pI less than 4.7) than normal. At the same time, in the proteinuric phase, the fluorescence quantum yield of Trp of urinary albumin was markedly quenched, returning to near normal levels after steroid-induced remission of proteinuria. These data indicate that in MCN the charge-dependent renal selectivity properties are partially maintained and that the less anionic isoforms of albumin are a main component of urinary albumin. Together with the electrical charge, the conformation of albumin as a major determinant of its urinary excretion in MCN must also be considered.

Ultrastructural alterations in the sialic acid distribution in minimal change disease and membranous glomerulonephritis

Kidney biopsy specimens from patients with minimal change disease and membranous glomerulonephritis were embedded in glycolmethacrylate and stained with phosphotungstic acid (PTA) at low pH. Biopsy specimens from patients without proteinuria served as a control. The PTA staining at low pH on glycolmethacrylate sections was used to study the changes in the sialic acid content of the lamina rara externa of the glomerular basement membrane. This method also gives a clear picture of the changes occurring at the epithelial cell coat and these alterations have implications on the distribution of the negative charges. In minimal change disease no alterations could be observed in the sialic acid content of the lamina rara externa. But the luminal epithelial cell coat showed obvious changes in conjunction with extensive foot process widening. In membranous glomerulonephritis with heavy deposits the staining of the lamina rara externa became almost completely negative and the foot process architecture was strongly affected. Obvious defects at the luminal epithelial cell coat, as observed in minimal change disease, were also found regularly. The alterations at the epithelial cell coat are tentatively related to the selective proteinuria reported in minimal change disease. In addition the non-selective proteinuria observed in non-minimal glomerulopathies, may find its origin in the absence of sialic acid molecules from the lamina rara externa.

Urinary excretion of neutral proteinases in nephrotic rats with a glomerular disease

A proliferative glomerulonephritis was induced in rats pre-immunized with rabbit IgG by injecting intravenously a sub-nephrotoxic dose of rabbit anti-glomerular basement membrane (GBM) IgG (A rats). Most rats (80%) developed a severe proteinuria (greater than 100 mg/24 hr) within two to five days after the injection of anti-GBM IgG. At the same time, microscopic examination of the kidneys revealed a glomerular infiltration by mononuclear phagocytes and a prominent decrease in the intensity of the colloidal iron reaction in glomeruli. A non-proliferative glomerular disease was induced in another group of rats (B rats) by intraperitoneal administration of aminonucleoside of puromycin. A marked proteinuria (greater than 100 mg/24 hr) occurred after six days in 90% of animals. Histochemical studies then revealed a decrease in staining intensity of glomeruli for polyanion. No glomerular hypercellularity was noted. In normal rats and in non-proteinuric A or B rats, the 24 hour urinary excretion of neutral proteinases ranged from 1.4 to 7.8 units (mean value +/- SEM, 4.69 +/- 0.60, N = 11), that of laminin ranged from 100 to 3,900 ng (mean value +/- SEM, 1,154 +/- 325, N = 10), and that of type IV collagen ranged from 160 to 420 ng (mean value +/- SEM, 306 +/- 26.5 ng, N = 8). In proteinuric rats from groups A (N = 11) and B (N = 9), the 24 hour urinary excretion of neutral proteinases significantly increased (mean values +/- SEM, 38.55 +/- 8.66 U for A rats and 42.17 +/- 7.92 U for B rats) and ran parallely with that of proteins, laminin and type IV collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of anionic sites in glomerular capillary basement membranes of Samoyed dogs with hereditary glomerulopathy

Samoyed hereditary glomerulopathy (SHG) is an X-linked dominant disease characterized by proteinuria and renal failure in affected male dogs. Electron microscopic examination of glomerular capillary basement membranes (GCBM) shows widespread multilaminar splitting of the lamina densa, identical to that in Alport's syndrome. Anionic sites in GCBM of three affected males and five unaffected dogs were labeled using polyethyleneimine to determine whether proteinuria was associated with an alteration in their number. No significant differences were noted in the number of anionic sites in the lamina rara externa, whereas small but statistically significant increases were seen in the number of sites in the lamina rara interna of affected males. In the lamina densa, affected males showed a striking increase in anionic sites, particularly in regions of GCBM which were split. Thus, although proteinuria in some glomerular diseases has been attributed to a reduction in anionic sites in GCBM, this was not so in SHG.

Puromycin aminonucleoside nephropathy: ultrastructure, glomerular polyanion, and cell surface markers

Puromycin aminonucleoside nephropathy with heavy proteinuria and oedema was induced in rats by 10 consecutive daily subcutaneous injections of aminonucleoside (1.67 mg/100 g of body weight). The main ultrastructural lesions were vacuolation of podocytes and total fusion of foot processes with loss of colloidal iron-reactive polyanion layer on the epithelial surface adjacent to the basement membrane. On the other hand the outer surface of podocytes and intravacuolar granular substance stained with colloidal iron. In scanning electron microscopy of freeze-fractured tissue the swollen podocytes and the urinary spaces displayed granular and filamentous precipitates. Seven cell surface antigens were examined by indirect enzyme immunohistochemistry with a series of MRC OX monoclonal antibodies. Glomeruli of control rats exhibited rare isolated Ia- positive endocapillary cells, possibly monocytes; these elements were significantly reduced in puromycin aminonucleoside nephropathy but there was an increase in Ia- positive cells in the cortical interstitium. Control kidneys harboured scanty interstitial T lymphocytes. These latter, especially the T8- positive cytotoxic/suppressor subpopulation, were markedly augmented in puromycin aminonucleoside nephropathy. The expression of class I histocompatibility antigens and of differentiation antigens (Thy 1) was not altered by aminonucleoside.

The effects of polycations on vascular permeability in the rat. A proposed role for charge sites

This study investigated whether charge sites in the walls of the microvasculature may play a role in maintaining the impermeability of the nonrenal capillaries to albumin. All experiments were performed in nephrectomized rats, studied in the awake state. The intravenous injection of protamine sulfate (4 mg/100 g body wt dissolved in 0.9% saline) was followed by a mean increase of 29.1% in hematocrit and a decrease of 28.4% in plasma albumin concentration over a 10-min period, indicating a significant 50-60% loss of albumin from the vascular space; a finding confirmed by studies using exogenous 125I-labeled albumin. Changes persisted for the remaining 80 min of observation, and could be reproduced by the injection of two other polycations, hexadimethrine and poly-l-lysine. These effects were not prevented by the antihistamine diphenhydramine hydrochloride. In contrast to 125I-labeled albumin, 14C-labeled neutral dextran of comparable size was not confined to the vascular space; its apparent volume of distribution progressively increased during the 90 min of observation. Intravenous injection of protamine sulfate was followed by a significantly smaller loss of 14C-dextran (36.5%) than albumin (59.1%) from the vascular space (P less than 0.01). Protamine sulfate could not be demonstrated to result in any changes in the physicochemical characteristics of albumin. These observations suggest that the negative charge sites present in nonglomerular capillary walls have functions similar to equivalent sites present in the glomerular capillaries. Thus, charge sites could contribute to the low permeability of the microvasculature to negatively charged macromolecules such as albumin. This may be an important mechanism for retaining albumin in the vascular space and preventing edema formation in health.

Acute glomerulonephritis. A clinical overview

Acute glomerulonephritis is a syndrome characterized by the abrupt onset of hematuria often accompanied by proteinuria, hypertension, edema, and renal dysfunction. Acute glomerulonephritis can be subdivided into primary glomerular disease, postinfectious glomerulonephritis, and glomerulonephritis associated with systemic disease. With few exceptions, the underlying mechanism of acute glomerulonephritis is an immunologic one. To differentiate clinically the specific etiology of the glomerulonephritis, attention must be focused on the presence of signs or symptoms of systemic disease, changes in the environment of the patient, family history of renal disease, and recent history of infectious disease.

Nature of the renal injury following total renal ischemia in man

The effects of total renal ischemia (TRI) of 15-87 min duration due to suprarenal clamping of the aorta were studied in 15 mannitol-treated patients undergoing abdominal aortic surgery. 15 patients undergoing similar surgery but requiring only infrarenal clamping served as controls. 1-2 h following TRI, GFR was reduced to only 39% of that in controls, 23 +/- 5 vs. 59 +/- 7 ml/min (P less than 0.001). This could not be ascribed to impaired renal plasma flow (RPF), which was mildly reduced to 331 +/- 71 and was not different from the value in controls, 407 +/- 66 ml/min. However, impaired PAH extraction (43 +/- 7%) and isosthenuria, not present in controls, suggest a primary role for tubular injury in lowering GFR at this time. 24 h following TRI, the GFR remained depressed below controls, 45 +/- 8 vs. 84 +/- 8 ml/min (P less than 0.005), while the transglomerular sieving of neutral dextrans was significantly enhanced (radius interval, 24-40 A). A theoretical analysis of transcapillary solute exchange revealed that these findings could be largely explained by a selective reduction of either RPF (-61%) or of transmembrane hydraulic pressure difference (-18%) below control values. Alternately, a combination of these two factors with changes of smaller magnitude could explain the findings. In contrast, a selective increase in oncotic pressure or decrease of the glomerular ultrafiltration coefficient could be excluded as a cause of hypofiltration 24 h after TRI. These observations lead us to suggest that the transient azotemia observed following TRI is due to a self-limited injury to the nephron that is identical to that seen in overt and sustained forms of acute renal failure.

An ultrastructural study of the effect of the steroid in puromycin aminonucleoside nephrosis rats

In order to investigate the significance of the histological change in glomerular epithelial cells in minimal change nephrotic syndrome in man (MCNS) and to help in clarifing the mechanism of action of a steroid in this disease, methylprednisolone was administered to rats with puromycin aminonucleoside nephrosis (PAN). This is an experimental nephrosis having a close resemblance morphologically and physiologically, to human MCNS. Morphological changes in the glomerulus were observed ultrastructurally. The administration of the steroid to PAN rats showed remarkable changes including, rapid disappearance of proteinuria in PAN rats in a manner similer to that seen in human MCNS, and significantly faster recovery of changes in glomerular epithelial cells when compared with spontaneous recovery. From the present study, it is clear that the steroid is effective in rapidly restoring the normal shape of glomerular epithelial cells in PAN rats. The filtration barrier in the glomerular capillary wall (GCW) is also thought to have recovered and proteinuria is cured. Based on these considerations, it may be suggested that proteinuria in human MCNS is caused by changes in glomerular epithelial cells, and that the clinical treatment of proteinuria in MCNS is effective when glomerular epithelial cells have functionally recovered.

Ultrafiltration in single isolated human glomeruli

To determine the ultrafiltration properties of human glomeruli, we induced filtration in vitro and estimated the glomerular ultrafiltration coefficient, Kf or LpA, and the glomerular capillary hydraulic conductivity, Lp, in single glomeruli from 17 human kidneys retrieved for allotransplantation. Cadaver donors ranged in age from 2 to 46 years. Filtration was induced in individual isolated glomeruli by abruptly lowering the protein concentration of the medium surrounding a glomerulus to produce a transcapillary oncotic gradient. The events which occurred were recorded on videotape for analysis. Kf was calculated from the maximum rate of glomerular swelling during filtration. Initial glomerular diameter for the individuals studied ranged from 146 +/- 2 microns (age, 2 years) to 292 +/- 6 microns (age, 42 years). Kf ranged from 5.1 +/- 0.8 to 30.7 +/- 3.0 nl/min . mm Hg and varied directly with donor age and glomerular size. The glomerular filtering area was estimated from the formula A = 3 pi D2 and from morphometrically measured basement membrane surface density. Lp was calculated from Lp = Kf/A. Lp using A = 3 pi D2 (LpD) averaged 3.7 +/- 0.2 microliter/min . mm Hg . cm2. To compare the hydraulic conductivity of glomeruli from children and adults, Lp was also calculated using the total basement membrane area derived from measured surface density (LpS).(ABSTRACT TRUNCATED AT 250 WORDS)

Heparan sulfate--rich anionic sites in the human glomerular basement membrane. Decreased concentration in congenital nephrotic syndrome

Recent work suggests that the normal barrier to penetration of the renal glomerular basement membrane by anionic plasma proteins may depend in part on the existence of negatively charged sites within the membrane. We describe an in vitro cytochemical method for the quantitative demonstration of anionic sites in the normal human glomerular basement membrane. In five normal subjects, ranging in age from 10 days to 57 years, the sites were distributed at regular intervals in the lamina rara externa, with a frequency of 23.8 +/- 6.8 sites per 1000-nm length of membrane. A similar distribution was observed in the basement membranes from three normal human fetuses. Ex vivo perfusion of one cadaver kidney revealed a similar distribution of anionic sites. The number of anionic sites in the glomerular basement membranes of five patients with the congenital nephrotic syndrome was reduced to 8.9 +/- 3.7 (P less than 0.001). Prior incubation of sections of normal kidney in purified heparinase resulted in a marked reduction in the number of anionic sites. We conclude that congenital nephrosis results from failure of heparan sulfate--rich anionic sites to develop in the lamina rara externa of the glomerular basement membrane.