Urinary Enzymes and Proteins

Stonard MD, Gore CW, Oliver JA, et al. 1987. Urinary enzymes and protein patterns as indicators of injury to different regions of the kidney. Fund AppI Toxicol 9 339-351. 

Jung K. Urinary enzymes and low-molecular-weight proteins as markers of tubular dysfunction. Kidney Int Suppl 1994 47 S29-S33. 

Uto, I., Ishimatsu, T., Hirayama, H., Ueda, S., Tsuruta, J., and Kambara, T. (1991) Determination of urinary Tamm-Horsfall protein by ELISA using a maleimide method for enzyme-antibody conjugation. J. Immunol. Meth. 138, 87-94. 

Relative kidney weight was increased on exposure to the individual compounds at their LONEL and, to about the same extent, on combined exposure at the NONEL or the LONEL/3. The other endpoints studied (histopathology, concentrating abihty, urinary excretion of glucose, protein and marker enzymes, and plasma creatinine and urea) were not or only scarcely affected upon combined exposure at the NONEL or LONEL/3. As assessed by the effect on kidney weight, the renal toxicity of the mixtures corresponded to the effect expected on the basis of the additivity assumption (Feron et al. 1995a, Jonker et al. 1996). 

Urinary enzyme activity provides a means to determine the presence and location of renal tubular injury as opposed to an index to the functional status of the nephron. Urine enzymes provide several advantages over urine protein for the assessment of tubular injury (Stonard et al. 1987 Vanderlinde et al. 1981 Price 1982 Plummer et al. 1986 Clemo 1998 Dubach et al. 1988 Westhuyzen et al. 2003) ... 

Examples of possible uses of biological materials (pooled collections of scrum, urine, etc.) as standards are in methods for estimating total protein concentration in serum, for measuring enzyme activities in serum and other body fluids, and for determining urinary steroids and their metabolites. The special requirements of multichannel analysis will be considered separately (Section 3.1.1.3), and the reasons why these three different investigations can perhaps best be standardized in relation to biological materials will now be discussed. 

Phosphate is abundant in the body and is an importiint intracellular and extracellular anion. Much of the phosphate inside cells is covalently attached to lipids and proteins. Phosphorylation and dephosphorylation of enzymes are important mechanisms in the regulation of metabolic activity. Most of the body s phosphate is in bone (Fig. 1). Phosphate changes accompany calcium deposition or resorption of bone. Control of ECF phosphate concentration is achieved by the kidney, where tubular rcabsorption is reduced by PTH. The phosphate which is not reabsorbed in the renal tubule acts as an important urinary buffer. 

Although the aminotransferases AST and ALT are present in urine, they have not proved to be useful in monitoring nephrotoxic effects. The measurement of lysozyme (muramidase), which could be useful in monitoring lysosomal protein turnover, is limited by changes during urinary tract and other infections because this enzyme is secreted from phagocytic cells, macrophages, and monocytes. Therefore, it is an equivocal marker. 

Sulfamethoxazole inhibits bacterial synthesis of dihydrofohc acid, and trimethoprim blocks the production of tetrahydrofolic acid by inhibiting the enzyme dihydrofolate reductase. Thus two consecutive steps ate blocked in the biosynthesis of nucleic acids and proteins essential to many bacteria. In vitro serial dilution tests have shown that the combination of sulfamethoxazole and trimethoprim [738-70-5] inhibits the growth of common urinary tract pathogens with the exception of Pseudomonas aeruginosa. Table 3 illustrates the enhanced effect of the combination over that of either agent alone. 

The receptor-binding of high-uptake forms of lysosomal enzymes to human diploid skin fibroblasts has been demonstrated directly by using a sensitive assay for the bound enzyme. a-L-Iduronidase-deficient cells were incubated with human urinary a-L-iduronidase and the cell-associated enzyme was assayed with 4-methylumbelliferyl a-L-idopyranosiduronic acid. D-Mannose 6-phosphate greatly accelerated the dissociation of the bound enzyme, and during uptake of a-L-iduronidase the receptors were regenerated every few minutes, even in the absence of protein synthesis. 

The first enzyme to be crystallized (and hence the first evidence that enzymes are proteins) was urease, which catalyses the hydrolysis of urea to ammonium and carbon dioxide. The original preparation of urease was from plant material, but the enzyme is also known to occur in a number of bacteria. In this study, a group of volunteers were given an intravenous infusion of 20 mmol urea labelled with both and and their urinary excretion of label was measured over 24 hours. Complete recovery of the label in urine would amount to 40 mmol and 20 mmol C. The results are shown in column 2 of Table 9.19. The experiment was repeated a week later, after they had received the antibiotic neomycin for 4 days to sterilize the gut these results are shown in column 3. 

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