Comparison of urinary excretion of four lysosomal hydrolases in healthy elderly and young adults.

The activities of four lysosomal enzymes and creatinine levels were measured in the plasma and urine of 17 healthy elderly and 7 young adults. Fractional enzyme excretion (FE ENZ) values for beta-hexosaminidase (N-acetylglucosaminidase), alpha-galactosidase, beta-galactosidase and beta-glucuronidase were calculated and compared between the two groups of subjects. FE ENZ was calculated as the ratio of enzyme clearance to creatinine clearance. The FE ENZ values for alpha-galactosidase, beta-galactosidase and beta-glucuronidase between the elderly and young populations were not statistically different; however, relative to the young control group, the FE ENZ value for beta-hexosaminidase was elevated approximately 2-fold in the elderly population (P = 0.06). The mean urinary alpha-galactosidase activity for the elderly population, when expressed on the basis of creatinine, was 50% lower than that of the control group (P = 0.03), whereas the mean urinary beta-hexosaminidase activity for the elderly was significantly higher compared to the control group (P = 0.008). When data for all subjects was analyzed, no correlation was observed between the urinary excretion of beta-hexosaminidase or alpha-galactosidase and glomerular filtration rate. These data indicate that with advancing age there are changes in the tubular secretion or reabsorption of selective lysosomal enzymes, particularly beta-hexosaminidase and alpha-galactosidase. These biochemical changes may provide a means of assessing subtle progressive deterioration of renal function.