Elevation of urinary trehalase in mercuric chloride-induced nephrotoxic rabbits: urinary trehalase as a specific indicator of renal brush border damage

Urinary enzymes in nephrotic syndrome

Tubular damage is a complication associated with nephrotic syndrome and increased levels of urinary enzymes are of significant value in detection of the same. The aim of our study was to evaluate the use of urinary lysozyme and trehalase as markers of tubular dysfunction in nephrotic syndrome. This study assessed 35 nephrotic syndrome patients and 30 healthy controls matched for age and sex. Urine samples were examined at pretreatment and post treatment (8 weeks) stages for proteinuria, lysozyme and trehalase. At pretreatmant stage there was significant increase in urinary lysozyme and trehalase as compared to controls (p<0.001). A good correlation was observed between degree of proteinuria and urinary lysozyme (p<0.001;r=0.80) and trehalase (p<0.001; r=0.74). At the end of 8 weeks of treatment, the patients showed significant decrease in their urinary lysozyme and trehalase activity (p<0.001) but no correlation with degree of proteinuria was observed. Our results indicate that enzymes like lysozyme and trehalase can be used as markers of tubular dysfunction.

ELISA for urinary trehalase with monoclonal antibodies: a technique for assessment of renal tubular damage

BACKGROUND

alpha,alpha-Trehalase, located on renal proximal tubules, is a glycoprotein that hydrolyses alpha,alpha-trehalose to two glucose molecules. Urinary trehalase reflects damage to renal proximal tubules, but its activity has not been measured routinely because measurement of catalytic activity is rather complicated and because conventional assays for enzyme activity might not reflect all of the trehalase protein because of enzyme inactivation in urinary samples.

METHODS

We established novel monoclonal antibodies for human trehalase and a sandwich ELISA for quantification of urinary trehalase. We determined the urinary trehalase protein concentration with this ELISA and trehalase catalytic activity, and the results of these two methods were compared.

RESULTS

The ELISA system was more sensitive than the detection of enzyme activity and could detect a subtle difference in the amount of trehalase present in renal diseases. The within- and between-assay CVs in the ELISA were 6.7-7.6% and 6.2-8.2%, respectively. Highly significant increases in both the quantity and activity were seen in patients with nephrotic syndrome (acute phase), Lowe syndrome, and Dent disease. The quantities were 70- to 200-fold greater, whereas enzyme activities were, at most, 10-fold higher than those of control subjects. In the detection of small amounts of trehalase in patients with chronic glomerulonephritis and renal anomalies, quantities were better than enzyme activities.

CONCLUSIONS

We have established an ELISA system for quantification of urinary trehalase that uses novel monoclonal antibodies. Our ELISA system is simpler and more sensitive than a conventional activity assay and reflects trehalase protein. This ELISA can be a useful as a common tool for clinical assessment of renal proximal tubular damage.

Molecular cloning, sequencing and expression of cDNA encoding human trehalase

A complete cDNA clone encoding human trehalase, a glycoprotein of brush-border membranes, has been isolated from a human kidney library. The cDNA encodes a protein of 583 amino acids with a calculated molecular weight of 66,595. Human enzyme contains a typical cleavable signal peptide at amino terminus, five potential glycosylation sites, and a hydrophobic region at carboxyl terminus where the protein is anchored to plasma membranes via glycosylphosphatidylinositol. The deduced amino acid sequence of the human enzyme showed similarity to sequences of the enzyme from rabbit, silk worm, Tenebrio molitor, Escherichia coli and yeast. Northern blots revealed that human trehalase mRNA of approx. 2.0 kb was found mainly in the kidney, liver and small intestine. Expression of the recombinant trehalase in E. coli provided a high level of the enzyme activity. The isolation and expression of cDNA for human trehalase should facilitate studies of the structure of the gene, as well as a basis for a better understanding of the catalytic mechanism.

Age-related changes in brush border enzymes under different dietary conditions

We examined the age-related changes of renal brush border enzymes of male Donryu rats under different dietary conditions. High protein diet (51% casein) markedly decreased the activity of renal leucine aminopeptidase as compared with low protein diet (8% casein). No significant difference, however, was observed in the activity of renal maltase between high and low protein diets. Alkaline phosphatase activity from young adult (3-month-old) rats in the high protein diet group was significantly lower than that in the low protein diet groups. From these results, it is inferred that dietary conditions affect the age-related alteration of renal brush border enzymes. Together with the previous results, it is suggested that proteins of renal brush borders are altered differently during the aging process.

Elevation of urinary trehalase activity in patients of itai-itai disease

The elevation of urinary trehalase activity in patients of itai-itai disease was examined. Urinary trehalase was correlated with tubular reabsorption of phosphorus (%TRP): the lower the trehalase activity, the worse was %TRP. Furthermore, this activity was inversely correlated with urinary glucose and urinary total protein. In itai-itai disease, the excretion of beta 2-microglobulin seems to be maximal, and urinary trehalase activity was low in the latter stages of the disease. It is inferred that itai-itai disease produces extremely severe tubular damage as well as glomerular dysfunction.

Urinary trehalase as an early indicator of cadmium-induced renal tubular damage in rabbit

The significance of urinary trehalase as a possible early indicator of renal disorder was examined using Cd-treated rabbits, which received 1 mg/kg Cd thrice weekly for 3 months subcutaneously. The results showed that urinary trehalase increased significantly from 1 week after treatment, earlier than LAP, ALP, proteinuria and glucosuria, with no changes in plasma trehalase level. A marked decrease in trehalase activity in renal brush border membranes prepared from Cd-treated rabbits was observed. It was also confirmed by immunohistological techniques that Cd treatment resulted in a marked decrease in specific fluorescence compared with controls. Ouchterlony double diffusion analysis demonstrated that urine and renal brush border extracts formed precipitation lines against anti-renal trehalase IgG, indicating that urinary trehalase and renal trehalase had the same antigenicity. Therefore, the facts presented here would suggest that urinary trehalase originated from the renal brush border, indicating its superiority as a diagnostic tool over other indicative indicating its superiority as a diagnostic tool over other indicative enzymes like LAP and ALP in detecting injury to renal proximal tubular cells in the early stage.

Urinary trehalase activity and renal brush-border damage in inhabitants of a cadmium-polluted area (Jinzu River basin)

Elevated urinary trehalase activity was observed in the inhabitants of the Jinzu River basin. Urinary trehalase activity was correlated with other urinalysis components, such as beta 2-microglobulin, glucose, amino nitrogen, and cadmium, of which a high level was observed in cadmium-polluted areas as compared with the reference area. Renal trehalase is specifically localized in tubular brush borders [M. Nakano, J. Histochem. Cytochem., 30 (1982) 1243-1248]. From these results it is inferred that tubular brush-border damage occurs in inhabitants of the Jinzu River basin.

Age-related change in brush borders of rat kidney cortex

Age-related change of rat renal brush borders was examined with electron microscopy and biochemical procedures. Total activity of renal brush border enzymes, such as alkaline phosphatase and leucine aminopeptidase in the homogenate, was significantly decreased with age. Acid phosphatase activity and protein content were not significantly changed with age. Specific activity of leucine aminopeptidase in brush border fraction was significantly decreased at a later stage of age. Protein content of brush border fraction was decreased significantly with age. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, some of the proteins disappeared during aging. Electron microscopic observations of kidney cortex showed that microvilli of renal brush borders from old rats were observed to be fewer than those from the young; epithelial cells in young rats have more densely packed brush border projections than those in old rats. From these results, it is suggested that during aging renal brush borders are degraded, and that protein components of the brush borders were different between old and young.