GM1 gangliosidosis is a glycosphingolipid (GSL) lysosomal storage disease caused by a genetic deficiency of acid b-galactosidase (b-gal), the enzyme that catabolyzes GM1 within lysosomes. Accumulation of GM1 and its asialo form (GA1) occurs primarily in the brain, leading to progressive neurodegeneration and brain dysfunction. Substrate reduction therapy aims to decrease the rate of GSL biosynthesis to counterbalance the impaired rate of catabolism. The imino sugar N-butyldeoxygalactonojirimycin (N B-DGJ) is a competitive inhibitor of the ceramide-specific glucosyltransferase that catalyzes the first step in GSL biosynthesis. Neonatal C57BL/6J (B6) and b-gal knockout (-/-) mice were injected daily from post-natal day 2 (p-2) to p-5 with either vehicle or N B-DGJ at 600 mg or 1200 mg/kg body weight. These drug concentrations significantly reduced total brain ganglioside and GM1 content in the B6 and the b-gal (-/-) mice. Drug treatment had no significant effect on viability, body weight, brain weight, or brain water content in the B6 and b-gal (-/-) mice. Significant elevations in neutral lipids (GA1, ceramide, and sphingomyelin) were observed in the N B-DGJ-treated b-gal (-/-) mice, but were not associated with adverse effects. Also, N B-DGJ treatment of B6 and b-gal (-/-) mice from p-2 to p-5 had no subsequent effect on brain ganglioside content at p-21. Our results show that N B-DGJ is effective in reducing total brain ganglioside and GM1 content at early neonatal ages. These findings suggest that substrate reduction therapy using N B-DGJ may be an effective early intervention for GM1 gangliosidosis and possibly other GSL lysosomal storage diseases.

GM1 gangliosidosis is a progressive neurodegenerative disease caused by deficiencies in lysosomal acid beta-galactosidase (beta-gal) and involves accumulation and storage of ganglioside GM1 and its asialo form (GA1) in brain and visceral tissues. Similar to the infantile/juvenile human disease forms, B6/129Sv beta-gal knockout (ko) mice express residual tissue beta-gal activity and significant elevations of brain GM1, GA1, and total gangliosides. Previous studies suggested that inbred DBA/2J (D2) mice may model a mild form of the human disease since total brain ganglioside and GM1 concentration is higher while beta-gal specific activity is lower (by 70-80%) in D2 mice than in inbred C57BL/6J (B6) mice and other mouse strains. A developmental genetic analysis was conducted to determine if the genes encoding beta-gal (Bgl) in the D2 and the ko mice were functionally allelic and if the reduced brain beta-gal activity in D2 mice could account for elevations in total brain gangliosides and GM1. Crosses were made between D2 mice homozygous for the Bgld allele (d/d), and either B6/129Sv mice heterozygous for the Bgl+ allele (+/-) or homozygous for the ko Bgl- allele (-/-) to generate d/+ and d/- mice. Specific beta-gal activity (nmol/mg protein/h) showed additive inheritance in brain, liver, and kidney at juvenile (21 days) and adult (255 days) ages with the d/- mice having only about 16% of the beta-gal activity as that in the +/+ mice. These results indicate that the Bgl genes in the D2 and the ko mice are noncomplementing functional alleles. However, the d/- mice did not express GA1 and had total brain ganglioside and GM1 concentrations similar to those in the d/+ and +/+ mice. These results suggest that the reduced brain beta-gal activity alone cannot account for the elevation of total brain gangliosides and GM1 in the D2 mice.

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