Erythrocyte sialic acid in human sickle-cell disease

Membrane-bound erythrocyte surface sialic acid concentrations in sickle-cell human patients (SS) and in control patients with sickle-cell trait (AS) and normal genes (AA) were assayed. The erythrocyte sialic acid concentration was significantly (P less than 0.001) higher in sickle-cell patients than in non-sicklers and although the concentration was higher in AS than AA individuals the difference was not significant (P greater than 0.05). The anaemic state of the SS patients was shown by a significantly (P less than 0.001) lower PCV than in non-sicklers. This finding is discussed in relation to membrane toughness and subsequent membrane loss leading to irreversible sickling of red cells in the deoxygenated state.     

Renal handling of free sialic acid in normal humans and patients with Salla disease or renal disease

The renal handling of free sialic acid, a negatively charged sugar, was investigated in normal humans and in patients with impaired sialic acid metabolism or impaired renal function. A sensitive assay for sialic acid, based upon the specific degradation of free sialic acid by N-acetylneuraminic acid aldolase, was developed to measure small amounts of sialic acid in human plasma. Using this assay on plasma from patients with disorders of sialic acid metabolism, we determined that the fractional excretion of sialic acid was maintained at approximately 98% over a wide range of filtered loads, i.e., from 40 to 2617 nmoles/minute. In other patients with different degrees of renal insufficiency, free sialic acid clearance varied directly with creatinine clearance, indicating filtration of this sugar by renal glomeruli. In patients with renal Fanconi syndrome, the urinary excretion of free sialic acid was independent of the severity of the generalized tubular defect, indicating that sialic acid was not reabsorbed by renal tubular cells. These findings indicate that sialic acid is filtered but not reabsorbed by the human kidney, in contrast with the handling of other sugars known to be reabsorbed by renal tubular cells. In addition, three of eight patients with Salla disease, a storage disorder due to impaired lysosomal transport of free sialic acid, were found to have reduced creatinine clearances, but all Salla disease patients had entirely normal renal tubular function.     

Serum sialic acid levels in health and disease

Sialic acid levels in normal and pathological sera estimated by the improved Svennerholm technique are reported. The increased levels demonstrable in rheumatoid arthritis, cirrhosis, γ myelomata, and macroglobulinaemia are demonstrated as being explicable on the basis of increased production of proteins of normal sialic content.     

Glomerular podocytic injury in protein overload proteinuria

Injection of rats with large doses of bovine serum albumin causes proteinuria which may persist long after the period of overload has ended. In order to assess in this model of proteinuria the relative importance of podocytic epithelial changes versus alterations in anionic groups in the glomerular capillary wall a morphological study has been made of animals in which the kidneys were fixed by vascular perfusion or by in situ drip fixation. By transmission electron microscopy, podocytes showed protein droplets, cytoplasmic vacuoles, spreading of epithelial cytoplasm with loss of foot processes, and focal separation of epithelium from the glomerular basement membrane, occasionally with cytoplasmic disruption. Staining with colloidal iron showed no reduction in the density of anionic groups per unit area on epithelial cell surfaces or elsewhere in glomeruli. However, the reduced surface area of epithelial cells caused by the changes to their structure accounts adequately for the less intense glomerular colloidal iron staining evident by light microscopy. Changes in podocyte structure, particularly those leading to focal cytoplasmic defects on the outer surface of the glomerular basement membrane, appear to be more important than loss of glomerular anionic groups for the development of proteinuria in protein overload nephropathy.     

Hypoxia in renal disease with proteinuria and/or glomerular hypertension

Despite the increasing need to identify and quantify tissue oxygenation at the cellular level, relatively few methods have been available. In this study, we developed a new hypoxia-responsive reporter vector using a hypoxia-responsive element of the 5' vascular endothelial growth factor untranslated region and generated a novel hypoxia-sensing transgenic rat. We then applied this animal model to the detection of tubulointerstitial hypoxia in the diseased kidney. With this model, we were able to identify diffuse cortical hypoxia in the puromycin aminonucleoside-induced nephrotic syndrome and focal and segmental hypoxia in the remnant kidney model. Expression of the hypoxia-responsive transgene increased throughout the observation period, reaching 2.2-fold at 2 weeks in the puromycin aminonucleoside model and 2.6-fold at 4 weeks in the remnant kidney model, whereas that of vascular endothelial growth factor showed a mild decrease, reflecting distinct behaviors of the two genes. The degree of hypoxia showed a positive correlation with microscopic tubulointerstitial injury in both models. Finally, we identified the localization of proliferating cell nuclear antigen-positive, ED-1-positive, and terminal dUTP nick-end labeled-positive cells in the hypoxic cortical area in the remnant kidney model. We propose here a possible pathological tie between chronic tubulointerstitial hypoxia and progressive glomerular diseases.     

Localization of sialic acid in the human trabecular meshwork

The localization of sialic acid in the trabecular meshworks of the normal human primary open-angle (POAG), congenital and juvenile glaucomatous eyes was investigated using both an electron microscope and lectins specifically binding with sialic acid. Sialic acid was always localized in fine fibrils lying underneath the canal wall and around collagen fibrils of the whole trabecular tissue. In both congenital and juvenile glaucoma, sialic acid was detected not only in the fine fibrils but also in the basement membrane-like materials in compact tissue present 3 μm underneath the canal wall. Sialated glycoprotein appears to play an important role in the pathogenesis of both diseases.     

Infantile sialic acid storage disease: Biochemical studies

Infantile free sialic acid storage disease (ISSD), is an inherited metabolic disorder characterized by hyperexcretion of free sialic acid in the urine and by its storage in the lysosomes of different tissues. In order to obtain more reliable data on the amount of total and free sialic acid, we analyzed the urine, brain, cerebellum, liver, spleen, and kidneys from a 3-month-old baby who died with a diagnosis of ISSD. The lysosomal nature of the disease was confirmed by an electron microscopic study of cells in culture. No significant abnormalities were found involving cholesterol, total phospholipids, glycolipids, and gangliosides in the tissues examined. However, differences in the tissue distribution of individual glycolipids and gangliosides were observed. The amount of free and total sialic acid was markedly increased, due to the storage of free sialic acid accompanied by its hyperexcretion in the urine. These results demonstrate and confirm that only acid monosaccharide transport from the lysosome compartment is involved in the pathogenesis of ISSD. © 1995 Wiley-Liss, Inc.     

Clinical spectrum of infantile free sialic acid storage disease

Infantile free sialic acid storage disease (ISSD) is a rare autosomal recessive metabolic disorder caused by a lysosomal membrane transport defect, resulting in accumulation of free sialic acid within lysosomes. Only a few cases have been described. We report on three new cases of ISSD with different modes of presentation: an infant with nephrotic syndrome, a case of fetal and neonatal ascites with heart failure, and a case of fetal ascites with esophageal atresia type III. From these patients and a review of the literature (27 cases total) we draw the following conclusions. 1) "Coarse facies," fair complexion, hepatosplenomegaly, and severe psychomotor retardation are constant findings in this disorder. 2) Nephrotic syndrome occurred in most cases (four in seven) in which renal evaluation was performed. Therefore, ISSD is an important cause of nephrosis in infants with a storage disorder phenotype. 3) Fetal/neonatal ascites or hydrops was the mode of presentation in 13 (60%) of 21 cases. Thus, ISSD enters in the differential diagnosis of hydrops fetalis with a storage disease phenotype. 4) Cardiomegaly was evident in nine cases. 5) Corneae were always clear, and albinoid fundi were reported in five cases. 6) Dysostosis multiplex was not prominent. 7) Bone marrow aspiration could be negative. 8) Death ensued in early infancy with a mean age of 13.1 months. All reported deaths were caused by respiratory infections.     

Infantile type of sialic acid storage disease with sialuria

We describe a male infant of Austrian ancestry, the main clinical features including attacks of dyspnea due to laryngomalacia, severe mental and motor retardation, pronounced splenohepatomegaly and vacuolisation of peripheral lymphocytes. The clinical condition deteriorated progressively and the child died at the age of 21 months. Phase and electron microscopy of cultured skin fibroblasts showed multiple vacuoles and inclusions suggestive of a lysosomal storage disorder. Increased excretion of free sialic acid was demonstrated by resorcinol staining after routine thin-layer screening for urinary oligosaccharides. Quantitative analyses of urine, leucocytes and cultured fibroblasts revealed 10 to 30-fold increased concentration of free sialic acid. In addition, 3-fold elevated amounts of sialyloligosaccharides were found in the urine. The activities of a variety of lysosomal enzymes, including sialidase, were normal. Our case is compared with infantile sialic acid storage disease recently observed by other authors. The close convergence of clinical, morphological and biochemical signs support the concept of a distinct lysosomal disease entity. The basic defect is so far unknown.     

Serum and saliva sialic acid in periodontitis patients with and without cardiovascular disease

Serum total sialic acid (sTSA) has recently been shown to be a cardiovascular risk factor. However, there is little information about the role of sTSA and TSA in saliva in periodontitis, a chronic and inflammatory disease known to be a risk factor for cardiovascular disease (CVD). We aimed to investigate the changes in sTSA and TSA levels in saliva in patients having both periodontitis and CVD versus periodontitis patients without diagnosed CVD. The study group consisted of 26 patients with proven periodontitis and 26 controls with no diagnosed systemic disease but periodontitis. sTSA and saliva TSA levels were determined by the thiobarbituric acid method, and C-reactive protein (CRP) was evaluated by the nephelometric method. The severity of periodontitis has been determined by the community periodontal index of treatment needs (CPITN). TSA in blood and saliva and CRP levels in blood were significantly increased in CVD patients compared with the control group. CPITN ranged from 2 to 4 in both groups. Significant and positive correlations were found between sTSA and saliva SA levels in patients and controls and between tooth loss and TSA both in blood and saliva. Therefore, TSA in saliva may be a useful marker similar to sTSA in CVD patients.     

Glomerular lesions and urinary albumin excretion in type I diabetes without overt proteinuria

Since several studies have suggested that a slight increase in urinary albumin excretion (microalbuminuria) is predictive of nephropathy in patients with diabetes mellitus, we studied the relation of albumin excretion to renal structure in patients with insulin-dependent (Type I) diabetes. Renal biopsy specimens were evaluated with light- and electron-microscopical morphometric techniques in 48 patients who had had diabetes for 5 to 40 years and who excreted less than 200 mg of urinary albumin per 24 hours. Patients in Group I (n = 26) had normal urinary albumin excretion, creatinine clearance, and blood pressure; those in Group II (n = 10) had increased urinary albumin excretion but normal creatinine clearance and blood pressure; those in Group III (n = 12) had increased urinary albumin excretion and hypertension, decreased creatinine clearance, or both. Glomerular structure varied similarly, ranging from normal to abnormal in Groups I and II, but was consistently abnormal in Group III. The thickness of the glomerular basement membrane, the fractional volume of the mesangium, and the mesangial volume per glomerulus in Group III exceeded the corresponding values in the other groups significantly. Thus, microalbuminuria, when present with hypertension, decreased creatinine clearance, or both, indicates established abnormalities of glomerular structure. Normal albumin excretion, or microalbuminuria without these other functional abnormalities, does not accurately predict the severity of the underlying glomerular lesions in patients with Type I diabetes.     

Glomerular epithelial cell structure and function in chronic proteinuria induced by homologous protein-load

The pathogenesis of glomerular scarring in proteinuric diseases is unknown, but glomerular epithelial cell (GEC) injury has been implied by the glomerular pathology seen in patients with focal segmental glomerular sclerosis and the nephrotic syndrome. We studied the effect of proteinuria on glomerular histology and GEC structure and function in rats made proteinuric for up to 8 weeks by the daily parenteral injection of homologous serum albumin. Proteinuria in the albumin-injected rats peaked at a mean level of 131 +/- 12 mg/24 hours (mean +/- SD) during the 1st week. It subsequently plateaued at 41 +/- 6 mg/24 hours but remained significantly greater than the saline-injected controls throughout the study. The albumin-injected rats developed slight but significant increases in blood pressure, serum albumin, plasma volume, and urine urea nitrogen compared to the saline injected controls. The serum creatinine was not different from controls. In the albumin-injected rats no glomerular scarring was observed after 8 weeks of proteinuria. The GEC developed albumin reabsorption droplets and signs of activity including increased numbers of organelles, vacuoles, and cytoplasmic hypertrophy, but there were no signs of irreversible GEC damage. The GEC foot processes were quantitated morphometrically, and there was no evidence of effacement after eight 4 or 8 weeks of proteinuria. GEC endocytic function, evaluated by the technique of protamine heparin aggregate disappearance, was not different from the saline injected controls. Proteinuria caused by the chronic administration of homologous serum albumin for 8 weeks is regularly associated with increased blood pressure, plasma volume, and serum albumin and ultrastructural changes in the GEC. These morphologic changes in the GEC apparently represent a normal response to proteinuria and are not evidence for irreversible cell damage. Despite their avid endocytosis of filtered plasma proteins, GEC endocytic function remains normal. These experimental results imply that glomerular sclerosis is not a consequence of proteinuria per se.     

Glomerular perfusion in renal allograft biopsies

In the commonest causes of impaired renal transplant function there is reduced renal and glomerular perfusion. We investigated the possibility of identifying this phenomenon in renal transplant biopsies, by the crude but simple method of counting the mean numbers of glomerular capillary loops which contained erythrocytes. In cyclosporin toxicity, acute tubular necrosis and in acute cellular rejection there was a considerable reduction in the numbers of erythrocyte-containing glomerular capillaries. The separation of the acute tubular necrosis group from normal was almost complete. This feature is therefore not specific but appears to correlate well with states of impaired glomerular perfusion. We suggest that a simple assessment of glomerular erythrocyte 'load' forms a useful part of the histological examination of renal transplant biopsies.     

Diversity in cell surface sialic acid presentations: implications for biology and disease

Sialic acids (Sias) are typically found as terminal monosaccharides attached to cell surface glycoconjugates. They play many important roles in many physiological and pathological processes, including microbe binding that leads to infections, regulation of the immune response, the progression and spread of human malignancies and in certain aspects of human evolution. This review will provide some examples of these diverse roles of Sias and briefly address immunohistochemical approaches to their detection.     

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.