Structural Determination of Lysosphingomyelin-509 and Discovery of Novel Class Lipids from Patients with Niemann-Pick Disease Type C

Elevated Bile Acid 3β,5α,6β-Trihydroxycholanoyl Glycine in a Subset of Adult Ataxias Including Niemann-Pick Type C

Ataxia is a common neurological feature of Niemann-Pick disease type C (NPC). In this disease, unesterified cholesterol accumulates in lysosomes of the central nervous system and hepatic cells. Oxidation by reactive oxygen species produces oxysterols that can be metabolised to specific bile acids. These bile acids have been suggested as useful biomarkers to detect NPC. Concentrations of 3β,5α,6β-trihydroxycholanyl glycine (3β,5α,6β-triOH-Gly) and 3β,7β-dihydroxy-5-cholenyl glycine (3β,7β-diOH-Δ5-Gly) were measured in plasma of 184 adults with idiopathic ataxia. All patients were tested with whole genome sequencing containing hereditary ataxia panels, which include NPC1 and NPC2 mutations and other genetic causes of ataxia. Plasma 3β,5α,6β-triOH-Gly above normal (>90 nM) was found in 8 out of 184 patients. One patient was homozygous for the p.(Val1165Met) mutation in the NPC1 gene. The remaining seven included one patient with Friedreich's ataxia and three patients with autoimmune diseases. Oxidative stress is known to be increased in Friedreich's ataxia and in autoimmune diseases. Therefore, this subset of patients possibly shares a common mechanism that determines the increase of this bile acid. In a large cohort of adults with ataxia, plasma 3β,5α,6β-triOH-Gly was able to detect the one patient in the cohort with NPC1 disease, but also detected oxidation of cholesterol by ROS in other disorders. Plasma 3β,7β-diOH-Δ5-Gly is not a potential biomarker for NPC1.

Hepatomegaly and Splenomegaly: An Approach to the Diagnosis of Lysosomal Storage Diseases

Clinical findings of hepatomegaly and splenomegaly, the abnormal enlargement of the liver and spleen, respectively, should prompt a broad differential diagnosis that includes metabolic, congestive, neoplastic, infectious, toxic, and inflammatory conditions. Among the metabolic diseases, lysosomal storage diseases (LSDs) are a group of rare and ultrarare conditions with a collective incidence of 1 in 5000 live births. LSDs are caused by genetic variants affecting the lysosomal enzymes, transporters, or integral membrane proteins. As a result, abnormal metabolites accumulate in the organelle, leading to dysfunction. Therapeutic advances, including early diagnosis and disease-targeted management, have improved the life expectancy and quality of life of people affected by certain LSDs. To access these new interventions, LSDs must be considered in patients presenting with hepatomegaly and splenomegaly throughout the lifespan. This review article navigates the diagnostic approach for individuals with hepatosplenomegaly particularly focusing on LSDs. We provide hints in the history, physical exam, laboratories, and imaging that may identify LSDs. Additionally, we discuss molecular testing, arguably the preferred confirmatory test (over biopsy), accompanied by enzymatic testing when feasible.

Recent Analytical Methodologies in Lipid Analysis

Lipids represent a large group of biomolecules that are responsible for various functions in organisms. Diseases such as diabetes, chronic inflammation, neurological disorders, or neurodegenerative and cardiovascular diseases can be caused by lipid imbalance. Due to the different stereochemical properties and composition of fatty acyl groups of molecules in most lipid classes, quantification of lipids and development of lipidomic analytical techniques are problematic. Identification of different lipid species from complex matrices is difficult, and therefore individual analytical steps, which include extraction, separation, and detection of lipids, must be chosen properly. This review critically documents recent strategies for lipid analysis from sample pretreatment to instrumental analysis and data interpretation published in the last five years (2019 to 2023). The advantages and disadvantages of various extraction methods are covered. The instrumental analysis step comprises methods for lipid identification and quantification. Mass spectrometry (MS) is the most used technique in lipid analysis, which can be performed by direct infusion MS approach or in combination with suitable separation techniques such as liquid chromatography or gas chromatography. Special attention is also given to the correct evaluation and interpretation of the data obtained from the lipid analyses. Only accurate, precise, robust and reliable analytical strategies are able to bring complex and useful lipidomic information, which may contribute to clarification of some diseases at the molecular level, and may be used as putative biomarkers and/or therapeutic targets.

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.

Challenges in the Definitive Diagnosis of Niemann-Pick Type C-Leaky Variants and Alternative Transcripts

Niemann-Pick type C (NPC, ORPHA: 646) is a neuro-visceral, psychiatric disease caused predominantly by pathogenic variants in the NPC1 gene or seldom in NPC2. The rarity of the disease, and its wide range of clinical phenotypes and ages of onset, turn the diagnosis into a significant challenge. Other than the detailed clinical history, the typical diagnostic work-up for NPC includes the quantification of pathognomonic metabolites. However, the molecular basis diagnosis is still of utmost importance to fully characterize the disorder. Here, the authors provide an overview of splicing variants in the NPC1 and NPC2 genes and propose a new workflow for NPC diagnosis. Splicing variants cover a significant part of the disease-causing variants in NPC. The authors used cDNA analysis to study the impact of such variants, including the collection of data to classify them as leaky or non-leaky pathogenic variants. However, the presence of naturally occurring spliced transcripts can misdiagnose or mask a pathogenic variant and make the analysis even more difficult. Analysis of the NPC1 cDNA in NPC patients in parallel with controls is vital to assess and detect alternatively spliced forms. Moreover, nonsense-mediated mRNA decay (NMD) analysis plays an essential role in evaluating the naturally occurring transcripts during cDNA analysis and distinguishing them from other pathogenic variants' associated transcripts.

MicroRNA Profile, Putative Diagnostic Biomarkers and RNA-Based Therapies in the Inherited Lipid Storage Disease Niemann-Pick Type C

Lipids are essential for cellular function and are tightly controlled at the transcriptional and post-transcriptional levels. Dysregulation of these pathways is associated with vascular diseases, diabetes, cancer, and several inherited metabolic disorders. MicroRNAs (miRNAs), in particular, are a family of post-transcriptional gene repressors associated with the regulation of many genes that encode proteins involved in multiple lipid metabolism pathways, thereby influencing their homeostasis. Thus, this class of non-coding RNAs (ncRNAs) has emerged as a promising therapeutic target for the treatment of lipid-related metabolic alterations. Most of these miRNAs act at an intracellular level, but in the past few years, a role for miRNAs as intercellular signaling molecules has also been uncovered since they can be transported in bodily fluids and used as potential biomarkers of lipid metabolic alterations. In this review, we point out the current knowledge on the miRNA signature in a lysosomal storage disorder associated with lipid dysfunction, Niemann-Pick type C, and discuss the potential use of miRNAs as biomarkers and therapeutic targets for RNA-based therapies.

Consensus clinical management guidelines for acid sphingomyelinase deficiency (Niemann-Pick disease types A, B and A/B)

BACKGROUND

Acid Sphingomyelinase Deficiency (ASMD) is a rare autosomal recessive disorder caused by mutations in the SMPD1 gene. This rarity contributes to misdiagnosis, delayed diagnosis and barriers to good care. There are no published national or international consensus guidelines for the diagnosis and management of patients with ASMD. For these reasons, we have developed clinical guidelines that defines standard of care for ASMD patients.

METHODS

The information contained in these guidelines was obtained through a systematic literature review and the experiences of the authors in their care of patients with ASMD. We adopted the Appraisal of Guidelines for Research and Evaluation (AGREE II) system as method of choice for the guideline development process.

RESULTS

The clinical spectrum of ASMD, although a continuum, varies substantially with subtypes ranging from a fatal infantile neurovisceral disorder to an adult-onset chronic visceral disease. We produced 39 conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. In addition, these guidelines have identified knowledge gaps that must be filled by future research.

CONCLUSION

These guidelines can inform care providers, care funders, patients and their carers about best clinical practice and leads to a step change in the quality of care for patients with ASMD with or without enzyme replacement therapy (ERT).

Diagnostic value of plasma lysosphingolipids levels in a Niemann-Pick disease type C patient with transient neonatal cholestasis

OBJECTIVES

Niemann-Pick disease type C (NPC) is a lysosomal storage disease due to impaired intracellular lipid trafficking caused by biallelic pathogenic variants in NPC1 or NPC2 genes. NPC is classified according to the age of onset of neurological manifestations. Cholestatic liver disease can be transient or lead to liver failure. Accompanying neurological findings can be observed at any age. In this report, an infant with a homozygous pathogenic variant in NPC1 gene whose diagnosis was eventually confirmed by specific biomarkers is described.

CASE PRESENTATION

A sixteen-day-old male was admitted to hospital with prolonged jaundice. He had mild hepatosplenomegaly, conjugated hyperbilirubinemia, elevated liver transaminases, and mild hypoalbuminemia. Cholestasis resolved spontaneously and patient was readmitted due to progressive hepatosplenomegaly without any neurologic findings when he was 8 months old. Molecular investigations detected homozygous c.1123A > C (p.Thr375Pro) pathogenic variant in NPC1 gene. NPC-specific lysosomal biomarkers such as Lysosphingomyelin and Lysosphingomyelin-509 were elevated, confirming the diagnosis.

CONCLUSIONS

The clinical features of NPC are highly heterogeneous, from disease severity or age of onset to disease progression. Patients presenting with transient neonatal cholestasis and should be regularly followed for neurodevelopmental status and visceromegaly. In the case of variants of unknown significance in NPC1 gene, lysosomal biomarkers play an important role when genetic analyses are inconclusive.

Metabolic Alteration Analysis of Steroid Hormones in Niemann-Pick Disease Type C Model Cell Using Liquid Chromatography/Tandem Mass Spectrometry

Niemann–Pick disease type C (NPC) is an autosomal recessive disease caused by a functional deficiency of cholesterol-transporting proteins in lysosomes, and exhibits various clinical symptoms. Since mitochondrial dysfunction in NPC has recently been reported, cholesterol catabolism to steroid hormones may consequently be impaired. In this study, we developed a comprehensive steroid hormone analysis method using liquid chromatography/tandem mass spectrometry (LC–MS/MS) and applied it to analyze changes in steroid hormone concentrations in NPC model cells. We investigated the analytical conditions for simultaneous LC–MS/MS analysis, which could be readily separated from each other and showed good reproducibility. The NPC phenotype was verified as an NPC model with mitochondrial abnormalities using filipin staining and organelle morphology observations. Steroid hormones in the cell suspension and cell culture medium were also analyzed. Steroid hormone analysis indicated that the levels of six steroid hormones were significantly decreased in the NPC model cell and culture medium compared to those in the wild-type cell and culture medium. These results indicate that some steroid hormones change during NPC pathophysiology and this change is accompanied by mitochondrial abnormalities.

Impact of Intravenous Trehalose Administration in Patients with Niemann-Pick Disease Types A and B

Background and Aims: Niemann–Pick disease (NPD) types A (NPA) and B (NPB) are caused by deficiency of the acid sphingomyelinase enzyme, which is encoded by the SMPD1 gene, resulting in progressive pathogenic accumulation of lipids in tissues. Trehalose has been suggested as an autophagy inducer with therapeutic neuroprotective effects. We performed a single-arm, open-label pilot study to assess the potential efficacy of trehalose treatment in patients with NPA and NPB patients. Methods: Five patients with NPD type A and B were enrolled in an open-label, single-arm clinical trial. Trehalose was administrated intravenously (IV) (15 g/week) for three months. The efficacy of trehalose in the management of clinical symptoms was evaluated in patients by assessing the quality of life, serum biomarkers, and high-resolution computed tomography (HRCT) of the lungs at the baseline and end of the interventional trial (day 0 and week 12). Results: The mean of TNO-AZL Preschool children Quality of Life (TAPQOL) scores increased in all patients after intervention at W12 compared to the baseline W0, although the difference was not statistically significant. The serum levels of lyso-SM-509 and lyso-SM were decreased in three and four patients out of five, respectively, compared with baseline. Elevated ALT and AST levels were decreased in all patients after 12 weeks of treatment; however, changes were not statistically significant. Pro-oxidant antioxidant balance (PAB) was also decreased and glutathione peroxidase (GPX) activity was increased in serum of patients at the end of the study. Imaging studies of spleen and lung HRCT showed improvement of symptoms in two patients. Conclusions: Positive trends in health-related quality of life (HRQoL), serum biomarkers, and organomegaly were observed after 3 months of treatment with trehalose in patients with NPA and NPB. Although not statistically significant, due to the small number of patients enrolled, these results are encouraging and should be further explored.

Searching, Structural Determination, and Diagnostic Performance Evaluation of Biomarker Molecules for Niemann-Pick Disease Type C Using Liquid Chromatography/Tandem Mass Spectrometry

Niemann-Pick disease type C (NPC) is an autosomal recessive disorder that is characterized by progressive neuronal degeneration. Patients with NPC have a wide age of onset and various clinical symptoms. Therefore, the discovery and diagnosis of NPC are very difficult. Conventional laboratory tests are complicated and time consuming. In this context, biomarker searches have recently been performed. Our research group has previously also investigated NPC biomarkers based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) and related techniques. To identify biomarker candidates, nontargeted analysis with high-resolution MS and MS/MS scanning is commonly used. Structural speculation has been performed using LC/MS/MS fragmentation and chemical derivatization, while identification is performed by matching authentic standards and sample specimens. Diagnostic performance evaluation was performed using the validated LC/MS/MS method and analysis of samples from patients and control subjects. NPC biomarkers, which have been identified and evaluated in terms of performance, are various classes of lipid molecules. Oxysterols, cholenoic acids, and conjugates are cholesterol-derived molecules detected in the blood or urine. Plasma lyso-sphingolipids are biomarkers for both NPC and other lysosomal diseases. N-palmitoyl-O-phosphocholine-serine is a novel class of lipid biomarkers for NPC. This article reviews biomarkers for NPC and the analysis methods employed to that end.

Advancing Diagnosis and Treatment of Niemann-Pick C disease through Biomarker Discovery

Niemann-Pick C is a rare neurodegenerative, lysosomal storage disease caused by accumulation of unesterified cholesterol. Diagnosis of the disease is often delayed due to its rarity, the heterogeneous presentation and the early non-specific symptoms. The discovery of disease-specific biomarkers - cholestane-3β,5α,6β-triol (C-triol), trihydroxycholanic acid glycinate (TCG) and N-palmitoyl-O-phosphocholineserine (PPCS, initially referred to as lysoSM-509) - has led to development of non-invasive, blood-based diagnostics. Dissemination of these rapid, sensitive, and specific clinical assays has accelerated diagnosis. Moreover, the superior receiver operating characteristic of the TCG bile acid biomarker and its detection in dried blood spots has also facilitated development of a newborn screen for NPC, which is currently being piloted in New York state. The C-triol, TCG and PPCS biomarkers have also proven useful for monitoring treatment response in peripheral tissues, but are uninformative with respect to treatment efficacy in the central nervous system (CNS). A major gap for the field is the lack of a validated, non-invasive biomarker to monitor the course of disease and CNS response to therapy.

Comprehensive-targeted lipidomic analysis in Niemann-Pick C disease

Niemann-Pick C disease (NPC) is a lysosomal disease caused by mutations in NPC1 or NPC2 genes responsible for intracellular accumulation of free cholesterol and glycosphingolipids in a variety of tissues. We collected plasma samples from 15 NPC1 patients and 15 age-matched controls to analyze the impairment of lipid metabolism. Comprehensive-targeted quantitative lipidomic analysis was per-formed by Ion Mobility Mass Spectrometry, while oxysterols and lyso-sphingolipids, the classical NPC biomarkers, were analyzed by LC-MS/MS. Lipidomic analysis allowed the quantitation of ~1100 lipid species, belonging to 13 different classes. Statistical analysis of collected data showed a significant differentiation between NPC patients and controls. Lipid profiling showed an elevation of arachidonic acid and total diacylglycerols. Conversely, sphingomyelins, phosphatidylethano-lamines, phosphatidylcholines, cholesterylesters, and lactosylceramides were decreased. Indeed, the lipid imbalance was consistent with the increased concentrations of oxysterols and lyso-sphingolipids. Our study revealed a novel disease biosignature suggesting new potential diagnostic biomarkers. The alteration in key lipids molecules involved in inflammatory pathways and in oxidative stress regulation, provides new insights in the complex pathophysiology of the disease, still largely un-known.

Efficacy and safety of arimoclomol in Niemann-Pick disease type C: Results from a double-blind, randomised, placebo-controlled, multinational phase 2/3 trial of a novel treatment

Niemann-Pick disease type C (NPC) is a rare, genetic, progressive neurodegenerative disorder with high unmet medical need. We investigated the safety and efficacy of arimoclomol, which amplifies the heat shock response to target NPC protein misfolding and improve lysosomal function, in patients with NPC. In a 12-month, prospective, randomised, double-blind, placebo-controlled, phase 2/3 trial (ClinicalTrials.gov identifier: NCT02612129), patients (2-18 years) were randomised 2:1 to arimoclomol:placebo, stratified by miglustat use. Routine clinical care was maintained. Arimoclomol was administered orally three times daily. The primary endpoint was change in 5-domain NPC Clinical Severity Scale (NPCCSS) score from baseline to 12 months. Fifty patients enrolled; 42 completed. At month 12, the mean progression from baseline in the 5-domain NPCCSS was 0.76 with arimoclomol vs 2.15 with placebo. A statistically significant treatment difference in favour of arimoclomol of -1.40 (95% confidence interval: -2.76, -0.03; P = .046) was observed, corresponding to a 65% reduction in annual disease progression. In the prespecified subgroup of patients receiving miglustat as routine care, arimoclomol resulted in stabilisation of disease severity over 12 months with a treatment difference of -2.06 in favour of arimoclomol (P = .006). Adverse events occurred in 30/34 patients (88.2%) receiving arimoclomol and 12/16 (75.0%) receiving placebo. Fewer patients had serious adverse events with arimoclomol (5/34, 14.7%) vs placebo (5/16, 31.3%). Treatment-related serious adverse events (n = 2) included urticaria and angioedema. Arimoclomol provided a significant and clinically meaningful treatment effect in NPC and was well tolerated.

Biomarker analysis of Niemann-Pick disease type C using chromatography and mass spectrometry

Niemann-Pick disease type C (NPC) is an autosomal recessive disorder with progressive degradation of central nervous system. The age of the onset varies from perinatal to adulthood. Patients with NPC are affected in the central nervous system, peripheral nerves, and systemic organs. From these background, it is extremely difficult to discover NPC clinically and diagnose it correctly. The procedure of the conventional laboratory methods are complicated and it takes long time to obtain the result. Because of the importance of early treatments and the shortcomings of conventional diagnostic methods for NPC, remarkable attention has been paid to biomarkers and chemical diagnoses. In the last decade, many NPC biomarkers have been reported. They are classified as cholesterol-related metabolites, sphingolipid metabolites, and novel phospholipid metabolites, respectively. Therefore, these are all lipid metabolites. Various chemical analysis methods have been used for their identification. In addition, chromatography and mass spectrometry are mainly used for their quantification. This review article outlines NPC biomarkers reported in the last decade and their analytical methods.

Understanding and Treating Niemann-Pick Type C Disease: Models Matter

Biomedical research aims to understand the molecular mechanisms causing human diseases and to develop curative therapies. So far, these goals have been achieved for a small fraction of diseases, limiting factors being the availability, validity, and use of experimental models. Niemann–Pick type C (NPC) is a prime example for a disease that lacks a curative therapy despite substantial breakthroughs. This rare, fatal, and autosomal-recessive disorder is caused by defects in NPC1 or NPC2. These ubiquitously expressed proteins help cholesterol exit from the endosomal–lysosomal system. The dysfunction of either causes an aberrant accumulation of lipids with patients presenting a large range of disease onset, neurovisceral symptoms, and life span. Here, we note general aspects of experimental models, we describe the line-up used for NPC-related research and therapy development, and we provide an outlook on future topics.

Clinical disease progression and biomarkers in Niemann-Pick disease type C: a prospective cohort study

Background

Niemann–Pick disease type C (NPC) is a rare, progressive, neurodegenerative disease associated with neurovisceral manifestations resulting from lysosomal dysfunction and aberrant lipid accumulation. A multicentre, prospective observational study (Clinical Trials.gov ID: NCT02435030) of individuals with genetically confirmed NPC1 or NPC2 receiving routine clinical care was conducted, to prospectively characterize and measure NPC disease progression and to investigate potential NPC-related biomarkers versus healthy individuals. Progression was measured using the abbreviated 5-domain NPC Clinical Severity Scale (NPCCSS), 17-domain NPCCSS and NPC clinical database (NPC-cdb) score. Cholesterol esterification and heat shock protein 70 (HSP70) levels were assessed from peripheral blood mononuclear cells (PBMCs), cholestane-3β,5α-,6β-triol (cholestane-triol) from serum, and unesterified cholesterol from both PBMCs and skin biopsy samples. The inter- and intra-rater reliability of the 5-domain NPCCSS was assessed by 13 expert clinicians’ rating of four participants via video recordings, repeated after ≥ 3 weeks. Intraclass correlation coefficients (ICCs) were calculated.

Results

Of the 36 individuals with NPC (2–18 years) enrolled, 31 (86.1%) completed the 6–14-month observation period; 30/36 (83.3%) were receiving miglustat as part of routine clinical care. A mean (± SD) increase in 5-domain NPCCSS scores of 1.4 (± 2.9) was observed, corresponding to an annualized progression rate of 1.5. On the 17-domain NPCCSS, a mean (± SD) progression of 2.7 (± 4.0) was reported. Compared with healthy individuals, the NPC population had significantly lower levels of cholesterol esterification (p < 0.0001), HSP70 (p < 0.0001) and skin unesterified cholesterol (p = 0.0006). Cholestane-triol levels were significantly higher in individuals with NPC versus healthy individuals (p = 0.008) and correlated with the 5-domain NPCCSS (Spearman’s correlation coefficient = 0.265, p = 0.0411). The 5-domain NPCCSS showed high ICC agreement in inter-rater reliability (ICC = 0.995) and intra-rater reliability (ICC = 0.937).

Conclusions

Progression rates observed were consistent with other reports on disease progression in NPC. The 5-domain NPCCSS reliability study supports its use as an abbreviated alternative to the 17-domain NPCCSS that focuses on the most relevant domains of the disease. The data support the use of cholestane-triol as a disease monitoring biomarker and the novel methods of measuring unesterified cholesterol could be applicable to support NPC diagnosis. Levels of HSP70 in individuals with NPC were significantly decreased compared with healthy individuals.

Trial registration

CT-ORZY-NPC-001: ClincalTrials.gov NCT02435030, Registered 6 May 2015, https://clinicaltrials.gov/ct2/show/NCT02435030; EudraCT 2014–005,194-37, Registered 28 April 2015, https://www.clinicaltrialsregister.eu/ctr-search/trial/2014-005194-37/DE. OR-REL-NPC-01: Unregistered.

Development of a Diagnostic Screening Strategy for Niemann-Pick Diseases Based on Simultaneous Liquid Chromatography-Tandem Mass Spectrometry Analyses of N-Palmitoyl-O-phosphocholine-serine and Sphingosylphosphorylcholine

Early diagnosis of Niemann-Pick diseases (NPDs) is important for better prognosis of such diseases. N-Palmitoyl-O-phosphocholine-serine (PPCS) is a new NPD biomarker possessing high sensitivity, and with its combination with sphingosylphosphocholine (SPC) it may be possible to distinguish NPD-C from NPD-A/B. In this study, a rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method (method 1) and a validated LC-MS/MS analysis (method 2) of PPCS and SPC were developed, and we have proposed a diagnostic screening strategy for NPDs using a combination of serum PPCS and SPC concentrations. Nexera and API 5000 were used as LC-MS/MS systems. C18 columns with lengths of 10 and 50 mm were used for method 1 and 2, respectively. ²H₃-Labeled PPCS and nor-SPC were used as internal standards. Selective reaction monitoring in positive-ion mode was used for MS/MS. Run times of 1.2 and 8 min were set for methods 1 and 2, respectively. In both methods 1 and 2, two analytes showed high linearity in the range of 1-4000 ng/mL. Method 2 provided high accuracy and precision in method validation. Serum concentrations of both analytes were significantly higher in NPD-C patients than those of healthy subjects in both methods. Serum PPCS correlated between methods 1 and 2; however, it was different in the case of SPC. The serum PPCS/SPC ratio was different in healthy subjects, NPD-C, and NPD-A/B. These results suggest that using a combination of the two LC-MS/MS analytical methods for PPCS and SPC is useful for diagnostic screening of NPDs.

Novel biomarkers for lysosomal storage disorders: Metabolomic and proteomic approaches

Lysosomal storage disorders (LSDs) are characterized by the accumulation of specific disease substrates inside the lysosomes of various cells, eventually leading to the deterioration of cellular function and multisystem organ damage. With the continuous discovery and validation of novel and advanced therapies for most LSDs, there is an urgent need to discover more versatile and clinically relevant biomarkers. The utility of these biomarkers should ideally extend beyond the screening and diagnosis of LSDs to the evaluation of disease severity and monitoring of therapy. Metabolomic and proteomic approaches provide the means to the discovery and validation of such novel biomarkers. This is achieved mainly through the application of various mass spectrometric techniques to common and easily accessible biological samples, such as plasma, urine and dried blood spots. In this review, we tried to summarize the complexity of the lysosomal disorders phenotypes, their current diagnostic and therapeutic approaches, the various techniques supporting metabolomic and proteomic studies and finally we tried to explore the newly discovered biomarkers for most LSDs and their reported clinical values.

Biomarkers for Lysosomal Storage Disorders with an Emphasis on Mass Spectrometry

Lysosomal storage disorders (LSDs) are characterized by an accumulation of various substances, such as sphingolipids, mucopolysaccharides, and oligosaccharides. The LSD enzymes responsible for the catabolism are active at acidic pH in the lysosomal compartment. In addition to the classically established lysosomal degradation biochemistry, recent data have suggested that lysosome plays a key role in the autophagy where the fusion of autophagosome and lysosome facilitates the degradation of amino acids. A failure in the lysosomal function leads to a variety of manifestations, including neurovisceral disorders. While affected individuals appear to be normal at birth, they gradually become symptomatic in childhood. Biomarkers for each condition have been well-documented and their proper selection helps to perform accurate clinical diagnoses. Based on the natural history of disorders, it is now evident that the existing treatment becomes most effective when initiated during presymptomatic period. Neonatal screening provides such a platform for inborn error of metabolism in general and is now expanding to LSDs as well. These are implemented in some areas and countries, including Taiwan and the U.S. In this short review, we will discuss several issues on some selected biomarkers for LSDs involving Fabry, Niemann–Pick disease type C, mucopolysaccharidosis, and oligosaccharidosis, with a focus on mass spectrometry application to biomarker discovery and detection.