SPECIFIC DEVELOPMENTAL PROFILES OF LYSOSOMAL AND BRUSH-BORDER ENZYMURIA IN THE HUMAN

Various enzymatic urinary activities have been proposed to assess rena l proximal tubule damage in children, including neonates. Nevertheless comprehensive knowledge on the developmental aspects of physiological enzymuria is limited, particularly with regard to lysosomal and brush border enzymuria. Urinary activities of two lysosomal enzymes, N-acet yl-beta-D-glucosaminidase (NAG) and beta-galactosidase (GAL), and of t wo brush border enzymes, alanine aminopeptidase (AAG) and gamma-glutam yltransferase (GGT) were comparatively investigated in normal prematur es (n = 28), term neonates (n = 52), infants aged less than 2 years (n = 19) and children (n = 33), and compared to urinary excretion of bet a(2)-microglobulin (B2M). Enzymatic activities were assayed using eith er spectrophotometrical (NAG, AAP, GGT) fluorimetrical (GAL) or radioi mmunological (B2M) methods, and were related to urinary creatinine exc retion. Developmental profiles of both the studied lysosomal enzymes a nd of B2M were similarly characterized with significantly decreasing v alues from prematures (NAG 9.29 +/- 1.44, GAL 2.26 +/- 0.26 IU/mmol cr eatinine, indicated as mean +/- SEM) to term neonates (6,94 +/- 0.58 a nd 1.76 +/- 0.15 IU/mmol creatinine, respectively) and order infants a nd children. Lysosomal enzymatic urinary activities correlated linearl y with a coefficient of r = 0.75, (p < 0.05), while correlations betwe en each lysosomal enzymatic activity and B2M urinary excretion were we aker. Profiles of both the studied brush border enzymes were character ized with lower activities in prematures (AAP 4.45 +/- 0.44, GGT 5.52 +/- 0.49 IU/mmol creatinine) than in term neonates (5.62 +/- 0.92 and 9.1 +/- 1.73 IU/mmol creatinine, respectively) or even in infants with respect to GGT (AAP 4.06 +/- 0.72 and GGT 11.54 +/- 1.71 IU/mmol crea tinine), with a consecutive decrease of activities in older infants or children. It is concluded that lysosomal and brush border enzymuria f ollow different developmental profiles in the normal human. Studies in volving enzymuria as a marker of tubular lesion should include the mea surements of at least one lysosomal and one brush border enzymatic act ivity, and should be interpreted with reference to the respective, spe cific developmental profiles.