N-Acetyl-DL-Leucine is an acetylated derivative of the essential amino acid leucine and a racemate (1:1) of N-Acetyl-L-Leucine and N-Acetyl-D-Leucine enantiomers. Previous observational clinical studies have demonstrated that N-Acetyl-DL-Leucine is effective in improving ataxia in patients with Niemann-Pick disease type C (NPC), a lysosomal storage disorder characterized at the cellular level by increased relative volume of the endosomal/lysosomal system. In this study, we sought to further

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... acterize the potential therapeutic benefit of N-acetyl-DL-leucine and its enantiomers for the treatment of NPC. We investigated the effectiveness of N-Acetyl-DL-Leucine, N-Acetyl-D-Leucine, and N-Acetyl-L-Leucine in reducing lysosomal volume in non-neuronal NPC1 cells using LysoTracker, a fluorescent dye that accumulates in acidic organelles. We report that both N-Acetyl-DL-Leucine and N-Acetyl-L-Leucine reduced relative lysosomal volume in NPC1-/- Chinese Hamster Ovary cells in a dose-dependent manner. Subsequently, we confirmed that N-Acetyl-L-Leucine was most effective at reducing relative lysosomal volumes in fibroblasts derived from NPC patients with severe disease (***p <0.001), followed by N-Acetyl-DL-Leucine (**p <0.01). Treatment with N-Acetyl-D-Leucine did not achieve statistical significance. Taken together, these results suggest that N-Acetyl-L-Leucine is the most effective enantiomer in correcting relative lysosomal volume in non-neuronal NPC cells, and support further research and development of the L-enantiomer.