Global Proteomics for Identifying the Alteration Pathway of Niemann-Pick Disease Type C Using Hepatic Cell Models.

Niemann-Pick disease type C (NPC) is an autosomal recessive disorder with progressive neurodegeneration. Although the causative genes were previously identified, NPC has unclear pathophysiological aspects, and patients with NPC present various symptoms and onset ages. However, various novel biomarkers and metabolic alterations have been investigated; at present, few comprehensive proteomic alterations have been reported in relation to NPC. In this study, we aimed to elucidate proteomic alterations in NPC and perform a global proteomics analysis for NPC model cells. First, we developed two NPC cell models by knocking out NPC1 using CRISPR/Cas9 (KO1 and KO2). Second, we performed a label-free (LF) global proteomics analysis. Using the LF approach, more than 300 proteins, defined as differentially expressed proteins (DEPs), changed in the KO1 and/or KO2 cells, while the two models shared 35 DEPs. As a bioinformatics analysis, the construction of a protein-protein interaction (PPI) network and an enrichment analysis showed that common characteristic pathways such as ferroptosis and mitophagy were identified in the two model cells. There are few reports of the involvement of NPC in ferroptosis, and this study presents ferroptosis as an altered pathway in NPC. On the other hand, many other pathways and DEPs were previously suggested to be associated with NPC, supporting the link between the proteome analyzed here and NPC. Therapeutic research based on these results is expected in the future.

Development of a Highly Sensitive and Rapid Liquid Chromatography-Tandem Mass Spectrometric Method Using a Basic Mobile Phase Additive to Determine the Characteristics of the Urinary Metabolites for Niemann-Pick Disease Type C.

As Niemann-Pick disease type C (NPC) is difficult to diagnose owing to its various clinical symptoms; biomarker tests have been developed. Previously, we revealed urinary sulfated cholesterol metabolites as noninvasive biomarkers for NPC. However, LC/tandem mass spectrometry (LC/MS/MS) requires long separation time and large urine volumes. Recently, a basic mobile phase was reported to increase the MS intensity. Thus, we developed a highly sensitive and rapid LC/MS/MS method for analyzing urinary cholesterol metabolites using a basic mobile phase additive. 3ß-Sulfooxy-7ß-N-acetylglucosaminyl-5-cholenic acid, its glycine and taurine conjugates, 3ß-sulfooxy-7ß-hydroxy-5-cholenic acid, and 7-oxo form were measured, with selected reaction monitoring in negative ion mode. Oasis HLB and L-column 3 were used for column-switching LC/MS/MS and urine diluted 10-fold was employed as the sample. After trapping, gradient separation was performed using solutions containing 1% (v/v) ammonium solution. On average, a 16-fold increase in peak areas was observed compared to that obtained at pH 5.5 with the mobile phases. Although the previous method needed 60 min for separation from interference peaks, we succeeded to separate them in 7 min with optimized LC condition. Further, all compounds showed good linearity from 0.3-1000 ng/mL, with satisfactory intra- and inter-day reproducibility. The developed method was applied to the urinalysis of healthy participants and NPC patients. Overall, the concentrations of metabolites correlated with those obtained using the previous method. Therefore, we succeeded to increasing MS intensity and shorten LC running time; and the method is useful for the noninvasive diagnostic screening of patients with NPC.