Quantitative Aspects of Pinocytosis and the Intracellular Fate of N-acetyl-α-D-glucosaminidase in Sanfilippo B Fibroblasts

The cellular uptake of N-acetyl-alpha-D-glucosaminidase, the deficient enzyme in Sanfilippo B disease, and the intracellular fate and metabolic effect of this enzyme have been investigated in Sanfilippo B and normal fibroblasts. For both genotypes the uptake is highly efficient (up to 0.025 mU/h/mg cell protein), specific and constant over a period of at least 6 days. It is probable that the enzyme protein is taken up by adsorptive pinocytosis. The enzymatic activity as well as the biological activity towards (35)SO(4)-labeled mucopolysaccharides persist in Sanfilippo B cells with a half-life of 34 h, indicating the intralysosomal localization of the pinocytosed enzyme. The data obtained are discussed with regard to a possible enzyme replacement therapy. For Sanfilippo B disease the doses used in the past are considered to be insufficient to cause measurable effects.