Evaluation of N-nonyl-deoxygalactonojirimycin as a pharmacological chaperone for human GM1 gangliosidosis leads to identification of a feline model suitable for testing enzyme enhancement therapy.

Deficiencies of lysosomal ß-D-galactosidase can result in GM1 gangliosidosis, a severe neurodegenerative disease characterized by massive neuronal storage of GM1 ganglioside in the brain. Currently there are no available therapies that can even slow the progression of this disease. Enzyme enhancement therapy utilizes small molecules that can often cross the blood brain barrier, but are also often competitive inhibitors of their target enzyme. It is a promising new approach for treating diseases, often caused by missense mutations, associated with dramatically reduced levels of functionally folded enzyme. Despite a number of positive reports based on assays performed with patient cells, skepticism persists that an inhibitor-based treatment can increase mutant enzyme activity in vivo. To date no appropriate animal model, i.e., one that recapitulates a responsive human genotype and clinical phenotype, has been reported that could be used to validate enzyme enhancement therapy. In this report, we identify a novel enzyme enhancement-agent, N-nonyl-deoxygalactonojirimycin, that enhances the mutant ß-galactosidase activity in the lysosomes of a number of patient cell lines containing a variety of missense mutations. We then demonstrate that treatment of cells from a previously described, naturally occurring feline model (that biochemically, clinically and molecularly closely mimics GM1 gangliosidosis in humans) with this molecule, results in a robust enhancement of their mutant lysosomal ß-galactosidase activity. These data indicate that the feline model could be used to validate this therapeutic approach and determine the relationship between the disease stage at which this therapy is initiated and the maximum clinical benefits obtainable.

Beneficial effects of substrate reduction therapy in a mouse model of GM1 gangliosidosis.

GM1 gangliosidosis is an inherited neurodegenerative disorder caused by lysosomal beta-galactosidase deficiency, resulting in the storage of GM1 and GA1, primarily in the central nervous system. This disease typically afflicts infants and young children and there is currently no effective therapy. Substrate reduction therapy (SRT) could be of potential benefit. The imino sugars N-butyldeoxynojirimycin (NB-DNJ, miglustat, Zavesca) and N-butyldeoxygalactonojirimycin (NB-DGJ) used for SRT inhibit glucosylceramide synthase (GlcCerS) that catalyses the first committed step in glycosphingolipid biosynthesis. We have compared the efficacy and tolerability of NB-DNJ and NB-DGJ in the beta-galactosidase knockout mouse. NB-DGJ was better tolerated than NB-DNJ, due to intrinsic gastrointestinal tract dysfunction that was exacerbated by NB-DNJ. However, functional improvement was greatest with NB-DNJ treatment which may potentially be caused by novel anti-inflammatory properties of NB-DNJ.