Variation in charge on red cells of patients with different glomerulopathies

Erythrocytic membrane anionic charge, sialic acid content, and their correlations with urinary glycosaminoglycans in preeclampsia and eclampsia

Compared to healthy pregnant women, changes in erythrocytic membrane anionic charge (EAC) and urinary glycosaminoglycans (U_GAGS) have been reported in African women with preeclampsia. A single previous study showed a decrease in erythrocytic membrane sialic acid (EMSA) in preeclampsia compared to healthy pregnancy; however, EMSA was not significantly different between women with preeclampsia and non-pregnant women. No study has focused on the relationships between EAC, EMSA, and U_GAGS in preeclampsia and eclampsia compared to healthy pregnant and non-pregnant women of reproductive age. Moreover, the erythrocyte membrane contains sialoglycoproteins and proteoglycans involved in creating the negatively charged cell surface, disruption of which leads to erythrocyte aggregation seen in preeclampsia/eclampsia. However, the etiopathogenesis of preeclampsia and eclampsia remains unclear. Therefore, we evaluated the relationship between EAC, U_GAGS, and EMSA in preeclampsia and eclampsia. Three groups of 30 women each were enrolled: Group A (non-pregnant women), Group B (healthy pregnant women without complications), and Group C (women with preeclampsia/eclampsia). EMSA was diminished under oxidative stress prevalent in eclampsia and preeclampsia which might have caused a decreased EAC. EAC was negatively correlated with U_GAGS and positively correlated with EMSA (p < .001). EMSA was negatively correlated with U_GAGS (p < .001). In conclusion, a loss of sialic acid from the erythrocyte membrane causes a significant decrease in the EAC which mirrors the decrease in the negative charge of the renal glomerular basement membrane and might lead to proteinuria and increased U_GAGS excretion in preeclampsia and eclampsia.

Sialic acid supplementation ameliorates puromycin aminonucleoside nephrosis in rats

Defects in sialylation are known to have serious consequences on podocyte function leading to collapse of the glomerular filtration barrier and the development of proteinuria. However, the cellular processes underlying aberrant sialylation in renal disease are inadequately defined. We have shown in cultured human podocytes that puromycin aminonucleoside (PAN) downregulates enzymes involved in sialic acid metabolism and redox homeostasis and these can be rescued by co-treatment with free sialic acid. The aim of the current study was to ascertain whether sialic acid supplementation could improve renal function and attenuate desialylation in an in vivo model of proteinuria (PAN nephrosis) and to delineate the possible mechanisms involved. PAN nephrotic rats were supplemented with free sialic acid, its precursor N-acetyl mannosamine or the NADPH oxidase inhibitor apocynin. Glomeruli, urine, and sera were examined for evidence of kidney injury and therapeutic efficacy. Of the three treatment regimens, sialic acid had the broadest efficacy in attenuating PAN-induced injury. Proteinuria and urinary nephrin loss were reduced. Transmission electron microscopy revealed that podocyte ultrastructure, exhibited less severe foot process effacement. PAN-induced oxidative stress was ameliorated as evidenced by a reduction in glomerular NOX4 expression and a downregulation of urine xanthine oxidase levels. Sialylation dysfunction was improved as indicated by reduced urinary concentrations of free sialic acid, restored electrophoretic mobility of podocalyxin, and improved expression of a sialyltransferase. These data indicate that PAN induces alterations in the expression of enzymes involved in redox control and sialoglycoprotein metabolism, which can be ameliorated by sialic acid supplementation possibly via its properties as both an antioxidant and a substrate for sialylation.

Changes of physico-chemical characteristics of red blood cells in children with nephrotic syndrome

Changes of milieu interieur in nephrotic syndrome (NS) have many consequences in various organs. We have measured the electrical charge of erythrocytes (Ery) with binding of alcian blue (AB) in 18 children with relapse of NS (12 minimal changes, 3 membranous and 3 mesangioproliferative glomerulonephritis) and 15 healthy children. The most important finding was that the binding of AB to Ery in patients with minimal change nephrotic syndrome (MCNS) and other aetiologies of NS was significantly less than that in the control group (p < 0.05). In addition, we have studied the thermal denaturation of the Ery membranes by differential scanning microcalorimetry. In some children with NS we have seen the splitting of B transition. We suppose that these phenomena occur as the result of structural change, which may involve lipoprotein components of the cytoskeletal network.

Disturbance of sialic acid metabolism by chronic cadmium exposure and its relation to proteinuria

In workers exposed to Cd (8 years on the average), we have found a significant decrease of sialic acid in erythrocyte membranes (22.61 +/- 1.84 vs 25.80 +/- 3.01 micrograms/mg of protein in controls, p less than 0.05) and an increase of sialic acid concentration in both urine (276.7 +/- 132.3 vs 174.5 +/- 70.9 micrograms/g of creatinine, p less than 0.05) and plasma (761.8 +/- 83.5 vs 640.4 +/- 70.7 micrograms/ml, p less than 0.01). In rats exposed to Cd (100 ppm in drinking water for 5.5 months), we have observed a reduction of the sialic acid level in erythrocyte membranes (31.4 +/- 1.2 vs 33.4 +/- 1.1 micrograms/mg of protein, p less than 0.01) and glomeruli (12.5 +/- 1.3 vs 13.9 +/- 1.6 micrograms/mg of protein, p less than 0.05). These effects in Cd treated rats were accompanied by a loss of the glomerular barrier selectively as reflected by an increased urinary output of albumin and transferrin. After 10 months of Cd exposure, the albuminuria and transferrinuria were negatively correlated with the sialic acid content of glomerular membranes (r = -0.47 and -0.51, p less than 0.05), which suggests that the depletion of sialic acid is involved in the loss of glomerular barrier function induced by long term Cd exposure. In Cd-treated rats, sialidase activity was enhanced in kidney cortex and in serum but not in glomeruli.

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)

Urinary proteins and red blood cell membrane negative charges in diabetes mellitus

The nature and origin of proteinuria in diabetes mellitus have been investigated by measuring the urinary excretion of seven specific proteins of low (beta 2-microglobin, retinol-binding protein) or high molecular weight (albumin, transferrin, hemopexin and IgG). Using the Alcian Blue binding test, we also measured negative charges on red blood cell (RBC) membrane which according to recent studies might mirror the glomerular polyanion charge. A group of 190 diabetics was examined, including 90 patients with type I diabetes, 23 type II diabetics treated with diet and/or hypoglycaemic agents and 77 longstanding type II diabetics requiring insulin therapy. With the exception of beta 2-microglobulin all proteins measured were excreted in the urine of diabetics in significantly higher amounts than in controls. The assay of transferrin proved the most sensitive (58% positive) followed by albumin (49%), IgG (34%), hemopexin (28%) and retinol-binding protein (26%). Practically the same ranking was obtained when only type I diabetics were considered. RBC membrane negative charges were diminished in diabetics and negatively correlated with the urinary excretion of albumin (r = -0.61, n = 190). RBC charges were also negatively correlated with other urinary proteins of high molecular mass (r between - 0.5 and - 0.2) but presented no relation with urinary beta 2-microglobulin or retinol-binding protein. The loss of RBC charges in diabetics most likely reflects the concomitant depletion of the glomerular polyanion responsible for the increased glomerular leakage of high molecular mass plasma proteins. The preferential increase in transferrin excretion together with the progressive rise in the urinary excretion of IgG lead us to postulate that the loss of glomerular polyanion in diabetes is accompanied, from the early stage, by a progressive decrease in the size-selectivity of the glomerular filter. The urinary excretion of retinol-binding protein was weakly correlated with albuminuria (r = 0.26, n = 186). Eight % of diabetics showed an elevation of urinary retinol-binding protein without evidence of microalbuminuria, which clearly demonstrates that a proximal tubular impairment can occur independently of the glomerular alterations in the course of diabetic nephropathy.

Variations of glomerular properties and their effect on glomerular disease

The possibility that inherited glomerular properties predispose individuals to certain glomerulopathies is an exciting new hypothesis. It opens new avenues to the investigation and treatment of patients which may be most easily applied in newly diagnosed diabetics and patients with multiple relapses of minimal change nephropathy. These treatments are unlikely to involve dangerous cytotoxic drugs which have been the fruit of years of investigation concentrated on the immune and inflammatory consequences of glomerular diseases. The differences between the two strains also cast doubt on the wisdom of extrapolating results obtained in the Munich Wistar rat to the rest of the animal kingdom.

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.

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.

Electrical anionic charges on red blood cells are reduced in insulin-dependent diabetic patients

The glomerular polyanion represents a charge-selective filter, restricting the passage of negatively charged plasma proteins, such as albumin. A specific loss of charges on the glomerular capillary wall (GCW) associated with an increased clearance of albumin has been reported in diabetes mellitus as well as many other nephropathies. The authors performed a chemical test based on the binding of the cationic dye Alcian Blue 8GX (AB) in 19 insulin-dependent diabetics, aged 34 +/- 4 years; all were Albustix negative, with normal renal function, normotensive, and in good metabolic control. The authors also studied 19 well-matched healthy controls. Each subject repeated the test on two separate occasions. The mean AB binding value was significantly lower (t-test: p less than 0.01) in diabetics than in controls: 87.5 +/- 2.3 vs. 100.5 +/- 1.6 ng/10(6) red cells. AB binding was not significantly correlated with age, duration of diabetes or metabolic control. A negative correlation was found between the negative charge on red cells and albumin excretion rate in microalbuminuric patients (n = 9). These results suggest a possible role for electrical charges in early stages of diabetic nephropathy.

Hydrophobic interaction of alcian blue with soluble and erythrocyte membrane proteins

Alcian Blue (AB), a cationic dye widely employed for monitoring negative surface charge variations on red blood cell (RBC), platelet and glomerular membranes of patients with nephrotic syndromes, was found in fact to aggregate with itself and precipitate in the pH range 7.0-7.8, i.e., at the physiological pH values used for performing the binding assay between the dye and cell surfaces. This aggregation appears to be essentially hydrophobic as it is insensitive to urea but fully prevented in presence of 2% zwitterionic detergent. In addition, AB binds to most RBC membrane proteins solubilized by urea-detergent extraction, again suggesting hydrophobic interaction. AB also interacts with freely soluble proteins such as haemoglobin and myoglobin; such binding is disrupted by ethylurea and/or 2% zwitterionic detergent, typical inhibitors of hydrophobic liaisons. AB also strongly binds to myoglobin with all the negative charges blocked by esterification of the carboxyl groups, again ruling out direct interaction via surface negative charges. It is concluded that AB binding to the RBC surface can hardly monitor variations in surface charge due to sialic acid residues but, at best, variations in surface hydrophobicity.

Surface charge of red blood cells in insulin-dependent diabetic patients with incipient and overt nephropathy

The negative surface charge of red blood cells was studied in adults with insulin-dependent diabetes mellitus, using a chemical assay based on the binding of the cationic dye Alcian-blue 8GX to anionic sites on the cell surface. Twenty-one healthy non-diabetic adults, 21 normo-albuminuric diabetic patients, 25 diabetic patients with incipient nephropathy, and 19 diabetic patients with overt nephropathy were studied. The diabetic patients were matched for age, duration of diabetes, and glycaemic control. The red cell surface charge was nearly identical in the four groups studied. Our study does not suggest that loss of membrane negative charge is a generalized phenomenon in insulin-dependent diabetic patients with albuminuria.