Pathogenesis Of Proteinuria Research Articles

Different roles of two types of endothelin receptors in partial ablation-induced chronic renal failure in rats

Recent work has drawn attention to endothelin as a likely contributor to renal pathogenesis. To elucidate the mechanism of progressive renal disease, we investigated the mRNA expression of endothelin and endothelin receptors, and the effect of endothelin ET A, and/or ET B receptor antagonists on disease progression in the remnant kidney model. Proteinuria progressively increased in rats subjected to 5/6 nephrectomy (Nx) after 8 weeks (from 25±3 to 221±28 μg min −1 kg −1). Creatinine clearance (Ccr) after renal ablation gradually decreased by 8 weeks (from 5.04±0.42 to 2.68±0.26 ml min −1 kg −1). Together with maximal proteinuria and decreased renal function, there was an increase in cortical mRNA expression of prepro endothelin-1 and endothelin ET A receptor expression, but a decrease in endothelin ET B receptor expression and in urinary excretion of endothelin-1. Administration (1–3 mg/day) of S-0139, (+)-disodium 27-[( E)-3-[2-[( E)-3-carboxylatoacryloylamino]-5-hydroxyphenyl]acrylayloxy]-3-oxoolean-12-en-28-oate, an endothelin ET A receptor-specific antagonist, had a beneficial effect on the evolution of the disease, preventing the appearance of intense proteinuria (113±11) and decreased Ccr (3.97±0.33). High blood pressure was observed in rats with 5/6 Nx and was decreased by S-0139 administration. To examine whether treatment modalities that decrease endothelin ET B receptor signaling have a deleterious effect on the kidney remnant, the effect of 97-618, an endothelin ET B receptor-specific antagonist, 4- tert-butyl- N-[5-(2-methoxyphenoxy)-6-(4-oxobutoxy)pyromidine-4-yl]benzenesulfonamide, was also examined on the action of S-0139. Concomitant administration of S-0139 and 97-618 reversed the beneficial effect of S-0139 alone in the remnant kidney on proteinuria and renal functional impairment. These findings indicate that endothelin participates in the pathogenesis of proteinuria and glomerular injury and that an endothelin ET A receptor-specific antagonist could be useful in the treatment of some forms of human nephritis. The loss of endothelin ET B receptor seems to be important in the progression of renal disease.

Lipid-lowering therapy in membranous nephropathy

Membranous nephropathy (MN) is a very common cause of nephrotic syndrome in adults, and lipid abnormalities are, therefore, frequently found in these subjects. Although efficient lipid-lowering therapy is available, almost nothing is known about the contribution of hyperlipidemia in the pathogenesis of progressive renal failure in MN. Studies in an experimental animal model of human MN, Heymann nephritis, have shown that lipids play an essential role in the pathogenesis of proteinuria. Local production of reactive oxygen species after subepithelial immune complex deposition leads to the formation of lipid peroxidation (LPO) adducts, which ultimately alter the composition of the glomerular basement membrane. As the magnitude of urinary protein excretion is associated with the long-term prognosis, a normalization of glomerular permselective properties has been used as a surrogate parameter for the beneficial effects of treatment. Probucol, a drug with LPO inhibitor potential, is able to reduce urinary protein excretion in rats with passive Heymann nephritis. In humans with MN, preliminary data also support this observation. It remains to be determined, however, if this intervention, which does not interfere with immune complex formation, will reduce the number of the patients reaching end-stage renal failure because of MN. In conclusion, lipids may contribute to glomerular injury in MN, as LPO might be an especially important factor, opening the possibility for new therapeutic interventions, thereby avoiding the side-effects of the currently used treatment regimen.

Platelet-activating factor stimulates gene expression and synthesis of matrix proteins in cultured rat and human mesangial cells: role of TGF-beta.

Platelet-activating factor (PAF) is a potent inflammatory mediator that participates in the pathogenesis of proteinuria and glomerular damage. However, the role of this lipid in glomerular sclerosis remains unknown. This study examines the effect of PAF on the regulation of extracellular matrix proteins by rat and human mesangial cells. PAF increased in a dose-dependent manner the gene expression of fibronectin and type IV collagen, but not type I collagen. Moreover, an increase in cell-associated and soluble fibronectin synthesis was also seen. These effects were abolished by BN52021 and WEB2086, two different PAF receptor antagonists. Because transforming growth factor (TGF)-beta has been considered a profibrogenic cytokine, this study also evaluated whether PAF effects might be mediated by the production of endogenous TGF-beta. PAF caused an increase in TGF-beta1 mRNA expression (by a protein kinase C-dependent pathway) and TGF-beta activity. Moreover, PAF-induced fibronectin synthesis was totally abolished when an anti-TGF-beta-neutralizing antibody was added to the culture medium, suggesting that PAF stimulates fibronectin synthesis, at least in part, through the induction of TGF-beta. Addition of cycloheximide, a protein synthesis inhibitor, upregulated PAF-induced fibronectin mRNA expression but downregulated PAF-induced TGF-beta1 gene expression, suggesting the existence of different regulatory transcriptional factors of the two proteins. These results suggest that PAF may be implicated in matrix accumulation during renal injury and therefore contribute to the pathogenesis of glomerulosclerosis.

Impairment of endothelial and subendothelial sites by a circulating plasma factor associated with minimal change disease

The pathogenesis of albuminuria in minimal change disease (MCD) is unknown. A human plasma factor (denoted as 100KF) is able to induce minimal change-like glomerular alterations, i.e. loss of glomerular sialoglycoproteins and decreased expression of glomerular ecto—ATPase, following in vitro incubation with kidney tissue. In addition, increased (selective) permeability for plasma proteins occurs after perfusion of 100KF into the rat kidney ex vivo . As in kidney tissue from subjects with minimal change disease, subendothelial injury has also been observed, i.e. reduced anionic sites in the lamina rara interna, the question was raised whether injury induced by the plasma factor 100KF involves vascular endothelium or subendothelial matrix of the glomerular capillary wall. Permeability studies were carried out by using confluent endothelial monolayers (HUVEC) cultured on a standard two—compartment system. The permeability for a macromolecular marker (horse radish peroxidase) was tested following incubation of the monolayers with either the native plasma factor 100KF or the control factor (heat—inactivated 100KF), in combination with histochemical evaluation of the cells for ecto—ATPase expression. Also quantification of glomerular anionic sites at the ultrastructural level was carried out, after ex vivo perfusion of 100KF or control factor into rat kidneys. The plasma factor 100KF is able to increase the permeability of human endothelial monolayers for macromolecules in a dose—dependent manner (relative increase 122.4±24, 178.4±34 and 236.1 ±58% after preincubation with 0.05; 0.5 and 1.5 mg/ml 100KF respectively), concomitant with induction of minimal change-like histochemical alterations such as reduced expression of ecto—ATPase. The number of anionic sites in the lamina rara interna of the glomerular capillary wall is significantly diminished following perfusion with the plasma factor 100KF versus control factor (7.58±1.60 versus 12.57±2.05 per 1000nm; P <0.02); in contrast to the lamina rara externa (22.71±3.15 versus 22.27±2.92 per 1000 nm; statistically not significant). Endothelial cells and subendothelial matrix along the glomerular filtration barrier may be considered as target structures for the plasma factor 100KF, leading to initial minimal change-like alterations associated with glomerular albumin leakage.

Impairment of endothelial and subendothelial sites by a circulating plasma factor associated with minimal change disease.

The pathogenesis of albuminuria in minimal change disease (MCD) is unknown. A human plasma factor (denoted as 100KF) is able to induce minimal change-like glomerular alterations, i.e. loss of glomerular sialoglycoproteins and decreased expression of glomerular ecto-ATPase, following in vitro incubation with kidney tissue. In addition, increased (selective) permeability for plasma proteins occurs after perfusion of 100KF into the rat kidney ex vivo. As in kidney tissue from subjects with minimal change disease, subendothelial injury has also been observed, i.e. reduced anionic sites in the lamina rara interna, the question was raised whether injury induced by the plasma factor 100KF involves vascular endothelium or subendothelial matrix of the glomerular capillary wall. Permeability studies were carried out by using confluent endothelial monolayers (HUVEC) cultured on a standard two-compartment system. The permeability for a macromolecular marker (horse radish peroxidase) was tested following incubation of the monolayers with either the native plasma factor 100KF or the control factor (heat-inactivated 100KF), in combination with histochemical evaluation of the cells for ecto-ATPase expression. Also quantification of glomerular anionic sites at the ultrastructural level was carried out, after ex vivo perfusion of 100KF or control factor into rat kidneys. The plasma factor 100KF is able to increase the permeability of human endothelial monolayers for macromolecules in a dose-dependent manner (relative increase 122.4 +/- 24, 178.4 +/- 34 and 236.1 +/- 58% after preincubation with 0.05; 0.5 and 1.5 mg/ml 100KF respectively), concomitant with induction of minimal change-like histochemical alterations such as reduced expression of ecto-ATPase. The number of anionic sites in the lamina rara interna of the glomerular capillary wall is significantly diminished following perfusion with the plasma factor 100KF versus control factor (7.58 +/- 1.60 versus 12.57 +/- 2.05 per 1000 nm; P < or = 0.02); in contrast to the lamina rara externa (22.71 +/- 3.15 versus 22.27 +/- 2.92 per 1000 nm; statistically not significant). Endothelial cells and subendothelial matrix along the glomerular filtration barrier may be considered as target structures for the plasma factor 100KF, leading to initial minimal change-like alterations associated with glomerular albumin leakage.

An orally active ETA/ETB receptor antagonist ameliorates proteinuria and glomerular lesions in rats with proliferative nephritis

The proliferation of mesangial cells and the extracellular matrix expansion constitute the most outstanding morphological aspects of the majority of progressive glomerular diseases. In vitro, endothelin-1 (ET-1) is mitogenic for mesangial cells and induces matrix protein synthesis. We studied the possible participation of ET-1 in the pathogenesis of renal damage in a normotensive model of proliferative nephritis. Coincidentally with maximal proteinuria and glomerular lesions, an increase was found in the glomerular mRNA expression of preproET-1 and the ETA receptor (10 and 6 times compared to controls, respectively), but not of the ETB receptor, and in ET-1 urinary excretion (217 +/- 33 vs. 84 +/- 4 pg ET-1/24 hr, N = 4 to 5, P < 0.05). By in situ hybridization, an increase in preproET-1 mRNA expression in glomerular endothelial, epithelial and mesangial cells, and in come tubular cells was observed. The administration of bosentan, an ETA/ETB receptor antagonist, had a beneficial effect on the evolution of nephritis preventing the appearance of intense proteinuria (76 +/- 35 vs. 380 +/- 77 mg/24 hr, N = 4 to 5, P < 0.05), the morphological lesions and the renal function impairment (creatinine clearance 367 +/- 46 vs. 268 +/- 33 microliters/min/100 g, N = 4 to 5). Simultaneously, there was a decrease in ET-1 urinary excretion (88 +/- 14 vs. 217 +/- 33 pgET-1/24 hr, N = 4,5, P < 0.05) and in the renal preproET-1 mRNA expression. The mean systolic blood pressures remained in the normal range in all animals. These data indicate that ET-1 participates in the pathogenesis of proteinuria and glomerular injury in a model of proliferative nephritis. The nonpeptidic orally active ETA/ETB receptor antagonists could be useful in the treatment of some human nephritis.

Alterations in Glomerular Anionic Sites in the Autologous Phase of Canine Anti-Glomerular Basement Membrane Nephritis

There have been a few studies on canine nephrotoxic glomerulonephritis produced by anti-glomerular basement membrane serum (AGBM), but these reports have not focused on an alteration in the charge properties of glomerular basement membrane (GBM). In this study, rabbit AGBM or normal rabbit serum (NRS) was given intravenously (2 ml/kg body weight) to 16 male beagle dogs. An alteration of anionic sites (ASs) of GBM was studied quantitatively using polyethyleneimine as a cationic probe by electron microscopy at weeks 1, 2, 4, and 8 postinjection. In AGBM-treated dogs, severe or mild proteinuria continued until week 2. At weeks 4 and 8, there was no significant difference in the intensity of proteinuria between AGBM- and NRS-treated groups. Until week 2 postinjection, there were significantly fewer ASs of GBM in AGBM-treated dogs than in NRS-treated dogs. At week 8, however, there was no difference in ASs of GBM between AGBM- and NRS-treated dogs. The fact that a reduction of glomerular AS occurred in AGBM-treated dogs with severe or mild proteinuria and the recovery of AS in the GBM coincided with an improvement of proteinuria suggested that alteration of the glomerular ASs might play an important role in the pathogenesis of proteinuria in canine anti-GBM nephritis.

Differential effects of diabetes and glomerulonephritis on glomerular basement membrane composition.

The hallmark of renal diseases involving the glomerulus is the presence of proteinuria. While the routes of pathogenesis of proteinuria have not been established, alterations in the barrier function of the glomerular basement membrane (GBM) have been implicated. We evaluated the effect of streptozotocin diabetes and passive Heymann nephritis (PHN) over time on the macromolecular composition of rat GBM to determine if changes in composition correlate with proteinuria. Six to twelve rats from each group (control, diabetic, and PHN) were sacrificed 1, 5, 28, 56, or 84 days after induction of disease. Identical amounts of GBM were subjected to a sequential extraction procedure, and type IV collagen, entactin, laminin, fibronectin, and anionic charge content were quantitated in the extracts. Type IV collagen and entactin content did not change with time or disease. Both laminin and fibronectin contents increased with time in GBM in all groups, but this increase was significantly greater in diabetic GBM. A significant decrease in anionic charge content of GBM coincided with the onset of albuminuria at Day 28 in diabetes, but no change was seen in PHN. In diabetic rats, the increase in laminin content over control preceded the onset of albuminuria, while the increase in fibronectin was not apparent until after albuminuria was present. In PHN, no differences in type IV collagen, entactin, laminin, fibronectin, or anionic charge content of GBM were found compared with control, even though profound albuminuria was evident from Day 5 through 84. Thus, while alterations in laminin and fibronectin content may contribute to the loss of glomerular permselectivity in streptozotocin diabetes, such changes apparently are not involved in PHN.

Proteinuria and impaired glomerular permselectivity in uninephrectomized fawn-hooded rats

Previous studies of glomerular permselectivity have indicated that both size selectivity and charge selectivity changes play a role in the pathogenesis of proteinuria. In this study, we measured Ficoll sieving coefficients, hemodynamic parameters, and urinary protein excretion rates in the FHH strain of fawn-hooded rats. These animals spontaneously develop systemic and glomerular hypertension, proteinuria, and focal and segmental glomerulosclerosis at a relatively young age. Three groups of FHH rats were studied: two-kidney controls (2K), untreated uninephrectomized rats (CON-NX), and uninephrectomized rats treated with the angiotensin I converting enzyme inhibitor enalapril (ENA-NX). CON-NX rats had higher glomerular transcapillary pressures (delta P) and higher urinary excretion rates of both total protein (UpV) and albumin (UaV) than did 2K rats, whereas treatment with enalapril prevented both glomerular hypertension and the increased proteinuria. Ficoll sieving coefficients were significantly higher in both groups of NX rats compared with 2K rats only for Stokes-Einstein radii (rs) > or = 46 A. Fits of sieving data to pore models showed a small increase in the number of large, nonselective pores in NX, which was not prevented by enalapril treatment. Total clearances of Ficoll with rs = 36 A (the size of albumin) in CON-NX and ENA-NX groups were unchanged compared with 2K animals. In contrast, UaV in CON-NX rats was more than six times that of 2K and ENA-NX rats. Across groups, UpV, UaV, and the ratio (UaV)/(UpV) all correlated strongly with delta P.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in glomerular anionic sites in canine anti-glomerular basement membrane nephritis with onset of severe proteinuria.

Rabbit anti-glomerular basement membrane serum (AGBM) or normal rabbit serum (NRS) were given intravenously (2 ml/kg body weight) to 8 male beagle dogs. Light and transmission electron microscopy and immunofluorescence were performed on the kidneys on day 7 postinjection. Alterations of anionic sites (ASs) of glomerular basement membrane (GBM) in peripheral, proximal, and paramesangial portions were studied quantitatively by electron microscopy using polyethyleneimine (PEI; molecular weight = 1,800) as a cationic probe. Severe or mild proteinuria developed on day 1 and continued until day 6 postinjection. On day 7 after AGBM injection, the number of PEI granules per 1,000 nm length of the lamina rara externa of GBM in all portions was significantly less than that in NRS-treated dogs (10.48 +/- 1.78 versus 14.19 +/- 2.35 granules per 1,000 nm of GBM in peripheral portion, 10.81 +/- 1.91 versus 14.97 +/- 1.35 granules per 1,000 nm of GBM in proximal portion, 8.44 +/- 1.76 vs 13.43 +/- 2.10 granules per 1,000 nm of GBM in paramesangial portion; p < 0.001). These results indicate that a reduction glomerular AS occurs in AGBM-treated dogs in association with severe or mild proteinuria and alterations in glomerular ASs might play an important role in the pathogenesis of proteinuria in the canine anti-GBM nephritis in addition to morphological changes.

Current topics in childhood lupus nephritis.

Lupus nephritis is a major predictor of the prognosis of systemic lupus erythematosus (SLE). The present paper discusses lupus nephritis from clinical and immunopathological points of view. Although recent advances in diagnosis and treatment improve the prognosis of children with SLE, there remain many unsolved clinical problems. One of the current topics in the treatment for SLE is intermittent intravenous cyclophosphamide therapy which is effective even for the steroid-resistant patients with severe lupus nephritis, at least for short-term observation. Immunopathologically, the following issues are discussed: (i) The C5b-9 terminal complement complex plays an important role in the pathogenesis of lupus nephritis. The possible interaction of vitronectin and SP-40,40 is also mentioned; (ii) A semi-quantitative analysis of the charge barrier of the glomerular basement membrane reveals that the charge barrier dysfunction plays an important role in the pathogenesis of proteinuria in lupus nephritis. This study also demonstrates that the charge of immune deposits is important for the initiation of glomerular injury in lupus nephritis; (iii) It is demonstrated that the histopathological diversity of lupus nephritis is based on biological properties of nephritogenic auto-antibodies in murine lupus models.

Castration inhibits glomerular hypertrophy and proteinuria in uninephrectomized male rats

Renal mass reduction may lead to glomerular hypertrophy, proteinuria and focal glomerulosclerosis (FGS) in humans and rats. In humans and rats, females are less susceptible than males to these phenomena. This study was undertaken to evaluate the effect of male rat castration on the pathogenesis of proteinuria and FGS. Urinary protein was measured in 60-day-old male and female rats. Uninephrectomy was performed in all rats, and castration in half of the males. After 180 days, proteinuria, glomerular filtration rate (GFR) and blood biochemistry were determined. Kidneys were resected, weighed and subjected to morphologic studies. Following uninephrectomy, male rats developed severe proteinuria: 132.3 +/- 40.9 mg 24 h-1, most of which was accounted for by an albuminuria of 70.9 +/- 19.3 mg 24 h-1. In contrast, protein excretion in female and castrated male rats remained within normal limits: 8.0 +/- 1.8 and 4.2 +/- 0.5 mg 24 h-1, respectively. Mean glomerular volume in male rats was 1.18 +/- 0.08 x 10(6) microns3; much higher than in female rats, 0.84 +/- 0.04 x 10(6) micron3, and castrated male rats, 0.87 +/- 0.03 x 10(6) micron3 (P less than 0.005). On light and electron microscopy, glomeruli of female and castrated male rats were completely normal. In contrast, in four of seven male rats, mild glomerular changes were observed. They consisted mainly of mesangial expansion, electron-dense deposits and collapse of capillary loops. These data suggest that castration confers protection against the development of glomerular hypertrophy and proteinuria in uninephrectomized male rats. Endogenous testosterone may be associated with this development.

Longitudinal evaluation of the renal clearance of glycated albumin in the diabetic rat

This study has examined glycation of serum albumin and its role in evolving diabetic proteinuria. Renal clearances of endogenous glycated and nonglycated albumin were studied in groups of normal and streptozotocin-induced diabetic Wistar-Kyoto rats over a 32 week period. Concentrations of glycated and nonglycated albumin in serum and urine were measured by rat albumin radioimmunoassay following separation on m-aminophenylboronate affinity columns. Levels of glycated serum albumin in diabetic rats were significantly higher than in normal rats (5.9 ± 0.7% vs 4.4 ± 0.3%, P < 0.05). Median total urinary albumin excretion increased from 120 μg/24 h at baseline to 879 μg/24 h ( P < 0.05) 28–32 weeks after induction of diabetes. The renal clearance of glycated albumin was approximately twice as great as that of nonglycated albumin in both normal ( P < 0.01) and diabetic ( P < 0.01) rats. However, the glycated albumin/nonglycated albumin clearance ratio in diabetic rats did not correlate with duration of diabetes or with the level of albuminuria. These results indicate that glycation of albumin does not contribute disproportionately to the development of proteinuria in the diabetic rat, during which median renal albumin clearance increased 7-fold. Other factors, such as glycation of the glomerular filtration surface, may have a more important role in the pathogenesis of proteinuria in experimental diabetes.

The immune system in minimal change nephrotic syndrome.

Numerous examples of abnormal immune responsiveness have been described in minimal change nephrotic syndrome (MCNS). The of MCNS with allergy and with certain genetic markers of immune responsiveness, as well as the excellent response of proteinuria to immunomodulatory agents, has suggested a causal relationship between the immunological and renal abnormalities. However, the nature of this relationship is uncertain. Before it can be clarified, the basic mechanism(s) involved in disturbed immunity in patients with MCNS must be better characterized. Studies of humoral and cellular immune function support the hypothesis that immune regulation is abnormal. However, conclusive evidence of participation by a defined immunoregulatory system in the events leading to immune dysfunction has not been obtained. Thus, considerable work remains to be done in determining the nature and cause of abnormal immunity in MCNS prior to investigating its potential role in the pathogenesis of proteinuria.

Immune complex effects on glomerular eicosanoid production and renal hemodynamics

We examined the effect of glomerular immune complex (IC) deposition on glomerular eicosanoid synthesis and the role of the eicosanoids in glomerular pathophysiology. Rats received daily 10 mg i.v. injections of native bovine gamma-globulin (NBGG) or cationic bovine gamma-globulin (CBGG) for 21 days; age-matched controls were maintained. Immunofluorescence and electron microscopy showed mesangial deposits of IC in the NBGG group and capillary wall deposits in the CBGG group, without light or electron microscopic evidence of leukocyte infiltration. One week after the last antigen dose, GFR was similar in all three groups, but RPF increased in the rats given CBGG; (8.37 +/- 0.90 vs. control 5.54 +/- 0.56 ml/min, P less than 0.05). Glomerular synthesis of prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) was normal in animals that received NBGG. Rats given CBGG had increased glomerular production of PGE2, (2.23 +/- 0.37 vs. control 1.03 +/- 0.16 ng/mg glomerular dry wt, P less than 0.05) and TxB2 (3.12 +/- 0.50 vs. control 0.48 +/- 0.07 ng/mg glomerular dry wt, P less than 0.001). Proteinuria only developed in the rats given CBGG, 86.6 +/- 18 mg/24 hr, which correlated with glomerular TxA2 synthesis, r = 0.82, P = 0.01. Acute administration of the TxA2 synthesis inhibitor, UK-38,485, and a TxA2 receptor antagonist, EP-092, to rats given CBGG did not affect GFR or RPF. The cyclo-oxygenase inhibitor, indomethacin, reduced both GFR and RPF by up to 40% in CBGG-immunized rats. Oral administration of UK-38,485 for six days to nephrotic rats did not result in a statistically significant reduction of proteinuria despite 85% inhibition of glomerular TxB2. We conclude that cationic antigen induces a glomerular disease pathologically similar to membranous nephropathy. The increment of RPF is most probably due to increased glomerular PGE2. The increased TxA2 has no effect on glomerular hemodynamics and probably is not a component in the pathogenesis of proteinuria.

Complement-induced glomerular epithelial cell injury. Role of the membrane attack complex in rat membranous nephropathy.

In passive Heymann nephritis (PHN) in rats, antibody (anti-Fx1A) reacts in situ with a glomerular epithelial antigen and induces complement (C)-mediated cell-independent proteinuria. To assess the role of the membrane attack complex (MAC), we determined the need for C8 in the pathogenesis of proteinuria in an autologous-phase model of PHN. Isolated rat kidneys, containing nonnephritogenic, non-C-fixing gamma 2 sheep anti-Fx1A (planted antigen), when perfused in vitro with C-fixing guinea pig anti-sheep IgG and a source of C (fresh human plasma 50% vol/vol in buffer containing bovine serum albumin), developed marked proteinuria after 20 min (0.58 +/- 0.08 mg/min X g, n = 8) that increased further to 3.20 +/- 0.93 mg/min X g after 80 min. In contrast, identical kidneys perfused with antibody and heat-inactivated or C8-deficient human plasma and normal kidneys perfused with antibody and fresh plasma excreted only 0.27 +/- 0.03 (n = 6), 0.27 +/- 0.04 (n = 5), and 0.40 +/- 0.05 mg/min X g (n = 6) after 20 min, and 0.13 +/- 0.02, 0.22 +/- 0.03, and 0.32 +/- 0.05 mg/min X g after 80 min, respectively. When C8-deficient plasma was reconstituted with sources of C8 (n = 3), proteinuria was restored to the level observed with fresh normal plasma. Differences in protein excretion could not be explained by quantitative differences in glomerular antigen or antibody content. Extensive ultrastructural damage to glomerular visceral epithelial cells was exclusively seen in antigen-containing kidneys perfused with antibody and C8-replete plasma. Thus, glomerular injury in this model results from an antigen-specific, antibody-directed, C8-dependent reaction involving assembly of the MAC. The ultrastructural findings argue in favor of MAC-induced cytotoxicity of the glomerular visceral epithelial cells.

The polyol pathway, sorbinil, and renal dysfunction

Nephropathy is a serious complication of Type I or insulin-dependent diabetes mellitus (IDDM) with a poor prognosis after the onset of proteinuria. Since aldose reductase may be implicated in the pathogenesis of proteinuria, onset and reversal studies were performed with sorbinil at a dose of 20 mg/kg to determine whether inhibition of this enzyme promoted either diminution or reversal of the appearance of urinary proteins. In the onset study, age-matched control, streptozotocin-diabetic, and sorbinil-treated diabetic rats were maintained for ten weeks; their 24-hour urine samples were analyzed weekly for volume, glucose, ketones, total protein, and individual protein components with molecular weights between 15,000 and 120,000 daltons. These last were examined by polyacrylamide gel electrophoresis and quantitated by laser densitometric analysis. Results indicated that sorbinil administered daily for ten weeks effectively diminished total protein excretion throughout this period primarily by protecting against appearance of abnormal urinary proteins that characterized the untreated diabetic state; the latter exhibited albuminuria, numerous newly detected proteins between 30,000 and 65,000 daltons, and an additional 4 to 5 proteins between 70,000 and 120,000 daltons. These findings closely resembled protein patterns exhibited by 54-week spontaneously diabetic BB rats, another model for IDDM. In the reversal study, age-matched control and streptozotocin-induced diabetic rats were maintained for four weeks, and weekly 24-hour urine analyses were performed as previously described. Results indicated that four-week diabetic rats excreted urine containing elevated glucose, ketones, and 3 to 5 newly detected proteins both higher than albumin in molecular weight (70,000 to 100,000 daltons) and lower than albumin in molecular weight (30,000 to 65,000 daltons) in marked contrast to the controls, which exhibited only albumin and low-molecular-weight proteins (≤20,000 daltons). To alter the course of proteinuria, sorbinil 20 mg/kg was administered at four weeks of diabetes. Sorbinil halted the progression of proteinuria and restored protein patterns toward the normal state over a subsequent nine-week period. After 13 weeks of diabetes, only 1 to 2 proteins remained both greater than albumin in molecular weight (70,000 to 94,000 daltons) and lesser than albumin in molecular weight (50,000 to 65,000 daltons). These results suggest that the polyol pathway is implicated in proteinuria and inhibition of this enzyme may represent a therapeutic approach to diabetic nephropathy.

GLOMERULAR SIALIC ACID IN PROTEIN OVERLOAD PROTEINURIA

Sialic acid on the foot processes of the glomerular epithelial cell may be essential to maintain the gel filtration properties of the glomerular capillary filter. A decrease in glomerular sialic acid has been found in rats with experimental nephrotic syndrome and in children with nephrotic syndrome. Protein overload with heterologous albumin induces a degree of proteinuria similar to that found in aminonucleoside nephrosis but without the generalized epithelial cell foot process fusion found in aminonucleoside nephrosis. If the proteinuria induced by heterologous albumin overload was not associated with a significant decrease in glomerular sialic acid, it could be more safely assumed that the decreased concentration of glomerular sialic acid found in experimental and human nephrosis was a primary cause of proteinuria. Proteinuria greater than the range of control rats (25) was induced in 45 of 54, 100g, male rats by 4, daily intraperitoneal injections of 750 mg of bovine serum albumin. Glomerular sialic acid was determined histochemically by the colloidal iron reaction. The intensity of the glomerular colloidal iron stain in coded slides did not differ between control rats and the experimental, suggesting that proteinuria alone does not cause a decrease in glomerular sialic acid and that the decreases in glomerular sialic acid previously reported are significant in the pathogenesis of proteinuria.

The pathogenesis of proteinuria in the acutely congested kidney.

The pathogenesis of proteinuria in the acutely congested kidney.