In vitro inhibition and intracellular enhancement of lysosomal α- galactosidase a activity in fabry lymphoblasts by 1-deoxygalactonojirimycin and its derivatives

Fabry disease is a lysosomal storage disorder caused by deficient lysosomal α-galactosidase A (α-Gal A) activity. Deficiency of the enzyme activity results in progressive deposition of neutral glycosphingolipids with terminal α-galactosyl residue in vascular endothelial cells. We recently proposed a chemical chaperone therapy for this disease by administration of 1-deoxygalactonojirimycin, a potent inhibitor of the enzyme, at subinhibitory intracellular concentrations [Fan, J.-Q., Ishii, S., Asano, N. and Suzuki, Y. (1999) Nat. Med. 5, 112-115]. 1-Deoxygalactonojirimycin served as a specific chaperone for those mutant enzymes that failed to maintain their proper conformation to avoid excessive degradation. In order to establish a correlation between in vitro inhibitory activity and intracellular enhancement activity of the specific chemical chaperone, a series of 1- deoxygalactonojirimycin derivatives were tested for activity with both α-Gal A and Fabry lymphoblasts. 1-Deoxygalactonojirimycin was the most potent inhibitor of α-Gal A with an IC₅₀ value of 0.04 μM. α-Galacto- homonojirimycin, α-allo-homonojirimycin and β-1-C-butyl- deoxygalactonojirimycin were effective inhibitors with IC₅₀ values of 0.21, 4.3 and 16 μM, respectively. N-Alkylation, deoxygenation at C-2 and epimerization at C-3 of 1-deoxygalactonojirimycin markedly lowered or abolished its inhibition toward α-Gal A. Inclusion of 1- deoxygalactonojirimycin, α-galacto-homonojirimycin, α-allo-homonojirimycin and β-1-C-butyl-deoxygalactonojirimycin at 100 μM in culture medium of Fabry lymphoblasts increased the intracellular α-Gal A activity by 14-fold, 5.2-fold, 2.4-fold and 2.3-fold, respectively. Weaker inhibitors showed only a minimum enhancement effect. These results suggest that more potent inhibitors act as more effective specific chemical chaperones for the mutant enzyme, and the potent competitive inhibitors of α-Gal A are effective specific chemical chaperones for Fabry disease.