Significance of serum and urine neuraminidase activity and serum and urine level of sialic acid in diabetic nephropathy.

BACKGROUND: Prospective studies have reported associations among various markers of inflammation and the incidence of diabetes, and it has been proposed that inflammation has a causal role in the development of diabetes. The objective of this study was to investigate the significance of serum and urine neuraminidase activity (NA) and serum and urine sialic acid (SA) level in patients with Diabetic nephropathy. METHODS: In a prospective study, 190 diabetic patients with established diabetic nephropathy, 30 type 2 diabetes patients without any diabetic related nephropathy, and 36 non-diabetic patients with diagnosed nephropathy were enrolled. Two hundred and forty healthy individuals without diabetes or kidney disease were also enrolled as control group. Fasting venous blood samples and urine samples were collected and checked for serum and urine NA and SA level. RESULTS: In the diabetic nephropathy group, the mean value of serum and urine NA was 64.6 ± 2.6 and 11.7 ± 1.2 mU/ml, respectively, and mean values of serum and urine SA were 93.2 ± 3.6 and 17.7 ± 1.4 mg/dl, respectively. Serum and urine NA and SA levels were significantly higher in patient with diabetic nephropathy when compared to the other groups (P < 0.001). CONCLUSIONS: Our study suggests that there is a strong association between elevated serum and urine NA and serum and urine SA levels with the presence of diabetic nephropathy in type 2 diabetic patients. Further investigations are needed on the diagnostic and prognostic significance of these two inflammatory markers.

The effect of calcium and magnesium ions on urinary urokinase and sialidase activity.

The effect of a promoter (calcium) and an inhibitor (magnesium) of urolithiasis was spectrophotometrically studied on urokinase (0.45 IU) and sialidase (5 mM). Although these mineral did not affect the sialidase activity, total inhibition of urokinase activity was observed with either 0.05 M calcium chloride or 0.1 M magnesium chloride. This observation might explain why calcium and magnesium respectively function as a promoter and an inhibitor of stone formation.

Effects of bacteria involved with the pathogenesis of infection-induced urolithiasis on the urokinase and sialidase (neuraminidase) activity.

It has been hypothesized that urinary urokinase and sialidase may play a role in urolithiasis. If these theories have substance it is to be expected that microorganisms may also affect these enzymes, since the association between urinary tract infection and renal stone formation is well known. It is generally assumed that Proteus mirabilis and Staphylococcus albus, which produce the urea-splitting enzyme urease, are responsible for stone formation. However, the importance of non-urease-producing microorganisms (Escherichia coli and Enterococcus) in urolithiasis is unclear. Spectrophotometric studies were therefore devised to clarify this problem. Microorganisms associated with infection-induced stones (Proteus mirabilis and Escherichia coli) respectively inhibited the urokinase and stimulated the sialidase activity. In contrast, microorganisms which were not associated with infection stones (Bacillus subtilis) had significantly less effect on urokinase and sialidase activity. This study may explain infection-induced stone formation and could open a completely new line of research.

Sialic acid concentrations in the urine of men with and without renal stones.

It has been suggested that urinary sialidase may play a role in the formation of renal stones. The present study was therefore undertaken to compare spectrophotometrically the different types of sialic acid concentrations and sialidase activities in fresh first morning urine specimens of men (21-65 years) with (13) and without (9) calcium oxalate renal stones. Although the free urinary sialic acid concentrations of the two groups of men were statistically about the same (P = 0.0614), the total (P = 0.003) and bound (P = 0.0012) urinary sialic acid concentrations differed significantly. Both the total and bound sialic acid concentrations were lower in the urine specimens of the stone patients than in their healthy counterparts. This decrease in urinary sialic acid concentrations was firstly thought to be the result of elevated breakdown enzymes of sialic acid, which would favour the production of pyruvate. However, spectrophotometric determinations of the endogenous pyruvate concentrations of the two types of urine specimens did not differ significantly (P = 0.0708). Secondly, the decrease in total urinary total sialic acid concentration of stone patients, could be attributed to less sialic acid synthesis or less renal excretion. Therefore, the same experiments were repeated using serum of 13 patients and 9 healthy men. Conversely, the total (P = 0.4425) and bound (P = 0.2850) serum sialic acid concentrations were found to be similar in the two types of subjects. However, the free serum sialic acid concentration of stone patients was significantly lower than in the healthy subjects (P = 0.0062).(ABSTRACT TRUNCATED AT 250 WORDS)

Neuraminidase and hematopoietic factors from human urine.

Human urinary neuraminidase, an enzyme that releases sialic acid from hematopoietic factors found in urinary preparations, was partially characterized, and a method was developed to derive these hematopoietic factors free of enzyme activity. Neuraminidase in urinary preparations from healthy humans and aplastic anemic (AA) patients had optimal activity at pH 5.3 and hydrolyzed both alpha 2----3 and alpha 2----6 type ketosidic linkages of N-acetyl-neuramin lactose and alpha 1-acid glycoprotein. When subjected to Sephacryl S-300 gel filtration, urinary neuraminidase showed a single peak of activity with an apparent molecular weight of 380,000 daltons, even under denaturing conditions (6 M guanidine hydrochloride). Furthermore, among a variety of compounds tested, no potent inhibitor of the enzyme was found. Heat treatment of AA urinary preparations eliminated about 80% of neuraminidase activity, while successive two-step ethanol precipitation eliminated residual enzyme. Erythropoietin, megakaryocyte colony-stimulating factor (CSF) and granulocyte/macrophage phage CSF activities were retained after these treatments.

Isoelectric focusing patterns of urinary kallikrein in Dahl salt-hypertension susceptible and resistant rats.

Dahl salt-sensitive (S) rats which are susceptible to hypertension have lower urinary kallikrein excretion than salt-resistant (R) rats which are not susceptible. Some physicochemical characteristics of partially purified urinary kallikrein were compared between the S and R strains. The isoelectric focusing pattern of S kallikrein was shifted so that a higher proportion of enzyme was present in isoelectric forms that had higher pI values compared to the pattern for R kallikrein. This strain difference was unique to urinary kallikrein; it was not seen in kallikrein extracted from salivary glands. The isoelectric focusing pattern for R urinary kallikrein could be converted to an S-type pattern by treatment with neuraminidase, which suggests that the differing isoelectric focusing patterns arose from differences in the sialic acid content of the kallikrein. The S kallikrein was slightly more heat-labile than R kallikrein, which was also compatible with the lower sialic acid content of the S enzyme. Tests involving the active site of the enzyme (Km values, pH curves, and heat of activation) were identical for the S and R strains. It was concluded that the structural differences observed in urinary kallikrein between S and R strains were compatible with strain-specific posttranslational processing of the enzyme.