A Novel Molecular Neutralization Strategy for Cytotoxic Sphingolipid in a Neurogenetic Disorder

ABSTRACT The cyclodextrins (CDs) are cyclic oligosaccharides assembled in a ring configuration containing lipophilic central cavities and hydrophilic outer surfaces. These molecules are traditionally used as excipients and absorption enhancers of hydrophobic molecules. During in vivo experiments to characterize therapeutic small molecules as therapy for globoid-cell leukodystrophy (GLD), or Krabbe disease, we serendipitously observed that the Twitcher galctwi/twi (Twi, the C57BL6/J murine GLD model), receiving hydroxypropyl-b-cyclodextrin (HPbCD)-only (vehicle-control) showed significantly longer lifespan. To solubilize highly hydrophobic candidates for murine experiments, HPbCD was used as a dissolvent, as previously described. Ultrastructural and morphometric studies showed significant preservation of myelinated axons in the Twi galctwi/twi mice receiving HPbCD-only. In GLD, the deficiency of the lysosomal galactocerebrosidase results in progressive elevations of sphingolipids, including psychosine, which, at non-physiological high levels, becomes remarkably cytotoxic to myelin-forming cells in the nervous systems. The CDs have been shown to cross the blood-brain barrier at a slow rate by a non-saturable mechanism consistent with transcellular diffusion. Based on initial studies, we hypothesize that CD ‘sequesters’ the psychosine into its conical-shaped oligosaccharide cavity, displacing water and rending a coated ‘shield’ that prevents harmful interactions with other molecules. Our preliminary studies indicate that one of the CD analogs, the aCD, prevented the cytotoxicity of the psychosine in cultured GLD patient fibroblasts, and matured oligodendrocytes showed significant interactions with psychosine. The project goals are as follows: (1) synthesize novel aCD analogs to improve the aCD psychosine-sequestering and ‘shielding’ properties, neutralizing the cytotoxicity effects of psychosine; (2) further characterize and optimize the PK/PD properties of the aCD and their analogs as CNS therapeutic agents; (3) evaluate the efficacy of aCDs and its lead analogs to prevent or treat the neurological phenotype of GLD murine model. The molecular encapsulation of harmful chemical compounds by several types of CDs has drawn much attention in recent years. Thus, PK and PD profile improvements will potentiate their biological effects. In human studies, αCD is safe and well tolerated and reduces small LDL-particle numbers and fasting glucose. Herein, we propose to explore an innovative therapeutic approach to molecularly neutralize the effects of the accumulated cytotoxic psychosine and, eventually, alter the pathogenic course of GLD. The project's success will be a proof-of-principle of the novel approach, targeting a specific sphingolipid found at cytotoxic high levels secondary to a lysosomal enzymatic deficiency. Of utmost importance, over ten states' newborn screening (NBS) programs currently include GLD, as children with the infantile form benefit from early hematopoietic stem cell transplant. Therefore, the characterization and validation of aCD and its analogs become highly important as adjunctive therapy for improving outcomes in this devastating disorder.