Niemann-Pick disease type B is a hereditary rare condition caused by deficiency of the acid sphingomyelinase (ASM) that is needed for lysosomal hydrolysis of sphingomyelin to ceramide and phosphocholine. This deficiency leads to a massive accumulation of sphingomyelin in cells throughout the body， predominantly in the liver， spleen and lungs. Currently， there is no effective treatment available. Olipudase alfa (recombinant human acid sphingomyelinase; rhASM) is an investigational drug that has shown promising results. However， dose-dependent toxicity was observed in mice upon the intravenous administration of rhASM， potentially due to the systemic release of ceramide upon the extracellular degradation... More
Niemann-Pick disease type B is a hereditary rare condition caused by deficiency of the acid sphingomyelinase (ASM) that is needed for lysosomal hydrolysis of sphingomyelin to ceramide and phosphocholine. This deficiency leads to a massive accumulation of sphingomyelin in cells throughout the body， predominantly in the liver， spleen and lungs. Currently， there is no effective treatment available. Olipudase alfa (recombinant human acid sphingomyelinase; rhASM) is an investigational drug that has shown promising results. However， dose-dependent toxicity was observed in mice upon the intravenous administration of rhASM， potentially due to the systemic release of ceramide upon the extracellular degradation of sphingomyelin by rhASM. Using a nanocarrier to deliver the rhASM to cells could improve the therapeutic window by shielding the rhASM to prevent the off-target degradation of sphingomyelin. For this aim， we recombinantly expressed hASM in human cells and loaded it into different liposomal formulations at a drug-to-lipid ratio of 4% (w/w). Among four formulations， the liposomal rhASM formulation with the composition DPPC:DOPS:BMP:CHOL:DiD (59:20:10:10:1 mol%) was selected because of its superiority concerning the encapsulation efficiency of rhASM (21%) and cellular uptake by fibroblasts and macrophages. The selected liposomal rhASM formulation significantly reduced the accumulated lyso-sphingomyelin in NPD-B fibroblasts by 71%， part of this effect was stimulated by the used lipids， compared to 55% when using the free rhASM enzyme. More importantly， the undesired extracellular degradation of sphingomyelin was reduced when using the selected liposomal rhASM by 61% relative to the free rhASM. The presented in vitro data indicate that the liposomal rhASM is effective and may provide a safer intervention than free rhASM.
