Urinary lipid profiling for the identification of fabry hemizygotes and heterozygotes

An expert consensus on practical clinical recommendations and guidance for patients with classic Fabry disease

Fabry disease is an X-linked inherited lysosomal disorder that causes accumulation of glycosphingolipids in body fluids and tissues, leading to progressive organ damage and reduced life expectancy. It can affect both males and females and can be classified into classic or later-onset phenotypes. In classic Fabry disease, α-galactosidase A (α-Gal A) activity is absent or severely reduced and disease manifestations have an early onset that can affect multiple organs. In contrast, in later-onset Fabry disease, patients have residual α-Gal A activity and clinical features are primarily confined to the heart. Individualized therapeutic goals in Fabry disease are required due to varying phenotypes and patient characteristics, and the wide spectrum of disease severity. An international group of expert physicians convened to discuss and develop practical clinical recommendations for disease- and organ-specific therapeutic goals in Fabry disease, based on expert consensus and evidence identified through a structured literature review. Biomarkers reflecting involvement of various organs in adult patients with classic Fabry disease are discussed and consensus recommendations for disease- and organ-specific therapeutic goals are provided. These consensus recommendations should support the establishment of individualized approaches to the management of patients with classic Fabry disease by considering identification, diagnosis, and initiation of disease-specific therapies before significant organ involvement, as well as routine monitoring, to reduce morbidity, optimize patient care, and improve patient health-related quality of life.

Metabolomic Studies of Lipid Storage Disorders, with Special Reference to Niemann-Pick Type C Disease: A Critical Review with Future Perspectives

Lysosomal storage disorders (LSDs) are predominantly very rare recessive autosomal neurodegenerative diseases.Sphingolipidoses, a sub-group of LSDs, result from defects in lysosomal enzymes involved in sphingolipid catabolism, and feature disrupted storage systems which trigger complex pathogenic cascades with other organelles collaterally affected. This process leads to cell dysfunction and death, particularly in the central nervous system. One valuable approach to gaining insights into the global impact of lysosomal dysfunction is through metabolomics, which represents a discovery tool for investigating disease-induced modifications in the patterns of large numbers of simultaneously-analysed metabolites, which also features the identification of biomarkers Here, the scope and applications of metabolomics strategies to the investigation of sphingolipidoses is explored in order to facilitate our understanding of the biomolecular basis of these conditions. This review therefore surveys the benefits of applying ’state-of-the-art’ metabolomics strategies, both univariate and multivariate, to sphingolipidoses, particularly Niemann-Pick type C disease. Relevant limitations of these techniques are also discussed, along with the latest advances and developments. We conclude that metabolomics strategies are highly valuable, distinctive bioanalytical techniques for probing LSDs, most especially for the detection and validation of potential biomarkers. They also show much promise for monitoring disease progression and the evaluation of therapeutic strategies and targets.

Laboratory Diagnosis of Lysosomal Diseases: Newborn Screening to Treatment

The goal of screening programs for inborn errors of metabolism (IEM) is early detection and timely intervention to significantly reduce morbidity, mortality and associated disabilities. Phenylketonuria exemplifies their success as neonates are identified at birth and then promptly treated allowing normal neurological development. Lysosomal diseases comprise about 50 IEM arising from a deficiency in a protein required for proper lysosomal function. Typically, these defects are in lysosomal enzymes with the concomitant accumulation of the enzyme's substrate as the cardinal feature. None of the lysosomal diseases are screened at birth in Australia and in the absence of a family history, traditional laboratory diagnosis of the majority, involves demonstrating a deficiency of the requisite enzyme. Diagnostic confusion can arise from interpretation of the degree of residual enzyme activity causative of disease and is impractical when the disorder is not due to an enzyme deficiency per se. Advances in mass spectrometry technologies has enabled simultaneous measurement of the enzymes' substrates and their metabolites which facilitates the efficiency of diagnosis. Employing urine chemistry as a reflection of multisystemic disease, individual lysosomal diseases can be identified by a characteristic substrate pattern complicit with the enzyme deficiency. Determination of lipids in plasma allows the diagnosis of a further class of lysosomal disorders, the sphingolipids. The ideal goal would be to measure biomarkers for each specific lysosomal disorder in the one mass spectrometry-based platform to achieve a diagnosis. Confirmation of the diagnosis is usually by identifying pathogenic variants in the underlying gene, and although molecular genetic technologies can provide the initial diagnosis, the biochemistry will remain important for interpreting molecular variants of uncertain significance.

Urine-derived cells: a promising diagnostic tool in Fabry disease patients

Fabry disease is a lysosomal storage disorder resulting from impaired alpha-galactosidase A (α-Gal A) enzyme activity due to mutations in the GLA gene. Currently, powerful diagnostic tools and in vivo research models to study Fabry disease are missing, which is a major obstacle for further improvements in diagnosis and therapy. Here, we explore the utility of urine-derived primary cells of Fabry disease patients. Viable cells were isolated and cultured from fresh urine void. The obtained cell culture, modeling the renal epithelium, is characterized by patient-specific information. We demonstrate that this non-invasive source of patient cells provides an adequate cellular in vivo model as cells exhibit decreased α-Gal A enzyme activity and concomitant globotriaosylceramide accumulation. Subsequent quantitative proteomic analyses revealed dysregulation of endosomal and lysosomal proteins indicating an involvement of the Coordinated Lysosomal Expression and Regulation (CLEAR) network in the disease pathology. This proteomic pattern resembled data from our previously described human podocyte model of Fabry disease. Taken together, the employment of urine-derived primary cells of Fabry disease patients might have diagnostic and prognostic implications in the future. Our findings pave the way towards a more detailed understanding of pathophysiological mechanisms and may allow the development of future tailored therapeutic strategies.

Separation and Analysis of Lactosylceramide, Galabiosylceramide, and Globotriaosylceramide by LC-MS/MS in Urine of Fabry Disease Patients

Fabry disease is an X-linked lysosomal storage disorder caused by α-galactosidase A (α-GAL A) deficiency. This enzyme contributes to the cellular recycling of glycosphingolipids such as galabiosylceramide (Ga₂), globotriaosylceramide (Gb₃), and globotriaosylsphingosine (lyso-Gb₃) by hydrolyzing the terminal α-galactosyl moiety. Urine and plasma α-GAL A substrates are currently analyzed as biomarkers for the detection, monitoring, and follow-up of Fabry disease patients. The sensitivity of the analysis of Ga₂ is decreased by the co-analysis of its structural isomer, lactosylceramide (LacCer), which is not an α-GAL A substrate. A normal-phase ultraperformance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) methodology, allowing the baseline separation of 12 Ga₂ isoforms/analogues from their lactosylceramide counterparts, was developed and validated in urine. The method was multiplexed with the analysis of 12 Gb₃ isoforms/analogues having the same fatty acid moieties as those of Ga₂ for comparison, and with creatinine for sample normalization. Urine samples were studied from 34 untreated and 33 Fabry males treated by enzyme replacement therapy (ERT) and 54 untreated and 19 ERT-treated Fabry females, along with 34 male and 25 female healthy controls. The chromatographic separation of Ga₂ from LacCer increased the sensitivity of analysis, especially in women. One untreated Fabry female and two treated Fabry females presented abnormal levels of Ga₂ but normal levels of Gb₃, supporting the importance of analyzing Ga_2, in addition to Gb₃. Our results show that urine LacCer levels from females were significantly higher than those from males. Moreover, LacCer levels were not affected by Fabry disease for both males and females.

A simple method for quantification of plasma globotriaosylsphingosine: Utility for Fabry disease

Fabry disease (FD) results from impaired globotriaosylceramide (Gb3) catabolism, due to a deficiency of the lysosomal hydrolase, α-galactosidase A (α-GalA). As a direct consequence, the deacetylated derivative, globotriaosylsphingosine (lyso-Gb3), is produced and contemporary evidence exemplifies its use as a biomarker. Here we developed a simple method to enable quantification of lyso-Gb3 in just 0.01mL of plasma and explored its concentration in a cohort of 73 Australian FD patients, as well as in individuals with other sphingolipidoses. In 2000 patients without FD, but with related metabolic conditions, lyso-Gb3 returned concentrations of <5pmol/mL. In the FD cohort, 53/60 patients with classical mutations returned lyso-Gb3 concentrations≥5pmol/mL whereas only 4/13 patients with "late-onset" mutations had lyso-Gb3≥5pmol/mL. Five females with normal α-GalA activity and genetically confirmed FD returned lyso-Gb3≥5pmol/mL. The prevalence of clinically significant disease including cardiomyopathy, nephropathy and cerebrovascular disease was congruent with higher lyso-Gb3 concentrations. Repeat testing was available for 51 patients-26 undergoing enzyme replacement therapy-and concentrations of lyso-Gb3 remained unaltered throughout 6-18 months independent of sex, mutation or treatment status. Our data suggest that the optimum use of lyso-Gb3 resides in laboratory confirmation of classical FD and for monitoring at least the initial response to therapeutic intervention. There is no evidence that lyso-Gb3 can inform on clinical events.

Cross-Classification of Human Urinary Lipidome by Sex, Age, and Body Mass Index

Technological advancements in past decades have led to the development of integrative analytical approaches to lipidomics, such as liquid chromatography-mass spectrometry (LC/MS), and information about biogenic lipids is rapidly accumulating. Although several cohort-based studies have been conducted on the composition of urinary lipidome, the data on urinary lipids cross-classified by sex, age, and body mass index (BMI) are insufficient to screen for various abnormalities. To promote the development of urinary lipid metabolome-based diagnostic assay, we analyzed 60 urine samples from healthy white adults (young (c.a., 30 years) and old (c.a., 60 years) men/women) using LC/MS. Women had a higher urinary concentration of omega-3 12-lipoxygenase (LOX)-generated oxylipins with anti-inflammatory activity compared to men. In addition, young women showed increased abundance of poly-unsaturated fatty acids (PUFAs) and cytochrome P450 (P450)-produced oxylipins with anti-hypertensive activity compared with young men, whereas elderly women exhibited higher concentration of 5-LOX-generated anti-inflammatory oxylipins than elderly men. There were no significant differences in urinary oxylipin levels between young and old subjects or between subjects with low and high BMI. Our findings suggest that sex, but neither ages nor BMI could be a confounding factor for measuring the composition of urinary lipid metabolites in the healthy population. The information showed contribute to the development of reliable biomarker findings from urine.

Glycosphingolipid storage in Fabry mice extends beyond globotriaosylceramide and is affected by ABCB1 depletion

Aim:

Fabry disease is caused by α-galactosidase A deficiency leading to accumulation of globotriaosylceramide (Gb₃) in tissues. Clinical manifestations do not appear to correlate with total Gb₃ levels. Studies examining tissue distribution of specific acyl chain species of Gb₃ and upstream glycosphingolipids are lacking.

Material & methods/Results:

Thorough characterization of the Fabry mouse sphingolipid profile by LC-MS revealed unique Gb₃ acyl chain storage profiles. Storage extended beyond Gb₃; all Fabry tissues also accumulated monohexosylceramides. Depletion of ABCB1 had a complex effect on glycosphingolipid storage.

Conclusion:

These data provide insights into how specific sphingolipid species correlate with one another and how these correlations change in the α-galactosidase A-deficient state, potentially leading to the identification of more specific biomarkers of Fabry disease.

Fabry disease is caused by a shortage of the enzyme α-galactosidase A leading to storage of a fat called globotriaosylceramide (Gb₃) in tissues. Disease severity does not appear to correlate directly with total Gb₃. Importantly, Gb₃ is comprised of many highly related but distinct species. We examined levels of Gb₃ species and precursor molecules in Fabry mice. Gb₃ species and storage are unique to each tissue. Furthermore, storage is not limited to Gb₃; precursor fats are also elevated. Detailed analyses of differences in storage between the normal and α-galactosidase A-deficient state may provide a better understanding of the causes of Fabry disease.

Tandem Mass Spectrometry of Sphingolipids: Applications for Diagnosis of Sphingolipidoses

In recent years, mass spectrometry (MS) has become the dominant technology in lipidomic analysis. It is widely used in diagnosis and research of lipid metabolism disorders including those characterized by impairment of lysosomal functions and storage of nondegraded-degraded substrates. These rare diseases, which include sphingolipidoses, have severe and often fatal clinical consequences. Modern MS methods have contributed significantly to achieve a definitive diagnosis, which is essential in clinical practice to begin properly targeted patient care. Here we summarize MS and tandem MS methods used for qualitative and quantitative analysis of sphingolipids (SL) relative to the diagnostic process for sphingolipidoses and studies focusing on alterations in cell functions due to these disorders. This review covers the following topics: Tandem MS is sensitive and robust in determining the composition of sphingolipid classes in various biological materials. Its ability to establish SL metabolomic profiles using MS bench-top analyzers, significantly benefits the first stages of a diagnosis as well as metabolic studies of these disorders. It can thus contribute to a better understanding of the biological significance of SL.

Differential human urinary lipid profiles using various lipid-extraction protocols: MALDI-TOF and LIFT-TOF/TOF analyses

Changes in lipid levels/profiles can reflect health status and diseases. Urinary lipidomics, thus, has a great potential in clinical diagnostics/prognostics. Previously, only chloroform and methanol were used for extracting lipids from the urine. The present study aimed to optimize lipid extraction and examine differential lipid classes obtained by various extraction protocols. Urine samples were collected from eight healthy individuals and then pooled. Lipids were extracted by six solvent protocols, including (i) chloroform/methanol (1:1, v/v), (ii) chloroform/methanol (2:1, v/v), (iii) hexane/isopropanol (3:2, v/v), (iv) chloroform, (v) diethyl ether, and (vi) hexane. Lipid profiles of the six extracts were acquired by MALDI-TOF mass spectrometry (MS) and some lipid classes were verified by LIFT-TOF/TOF MS/MS. The data revealed that phosphatidylglycerol (PG) and phosphatidylinositol (PI) could be detected by all six protocols. However, phosphatidylcholine (PC) and sphingomyelin (SM) were detectable only by protocols (i)–(iv), whereas phosphatidylserine (PS) was detectable only by protocols (iii)–(vi), and phosphatidylethanolamine (PE) was detectable only by protocols (v)–(vi). In summary, we have demonstrated differential lipidome profiles yielded by different extraction protocols. These data can serve as an important source for selection of an appropriate extraction method for further highly focused studies on particular lipid classes in the human urine.

A Novel Rapid MALDI-TOF-MS-Based Method for Measuring Urinary Globotriaosylceramide in Fabry Patients

Fabry disease is an X-linked lysosomal storage disorder caused by deficiency of α-galactosidase A, resulting in the accumulation of glycosphingolipids in various organs. Globotriaosylceramide (Gb3) and its isoforms and analogues have been identified and quantified as biomarkers of disease severity and treatment efficacy. The current study aimed to establish rapid methods for urinary Gb3 extraction and quantitation. Urine samples from 15 Fabry patients and 21 healthy control subjects were processed to extract Gb3 by mixing equal volumes of urine, methanol containing an internal standard, and chloroform followed by sonication and centrifugation. Thereafter, the lower phase was analyzed by MALDI-TOF MS and the relative peak areas of the internal standard and four major species of Gb3 determined. The results showed high reproducibility with intra- and inter-assay coefficients variation of 9.9% and 13.7%, respectively. The limit of detection was 0.15 ng/μL and the limit of quantitation was 0.30 ng/μL. Total urinary Gb3 levels in both genders of classic Fabry patients were significantly higher than in healthy controls (p < 0.0001). Gb3 levels in Fabry males were higher than in Fabry females (p = 0.08). We have established a novel assay for urinary total Gb3 that takes less than 15 min from start to finish. Graphical Abstract ᅟ.

Interfering parameters in the determination of urinary globotriaosylceramide (Gb3) in patients with chronic kidney disease

INTRODUCTION

Globotriaosylceramide (Gb3, CD77) represents a pivotal part of the cell membrane. Measuring the urinary Gb3 content can be used to screen patients with chronic kidney disease (CKD) for Fabry disease, a disorder caused by hampered Gb3 degradation. However, little is known about factors influencing urinary Gb3 excretion other than Fabry disease. The aim of the present study was to identify routine diagnostic parameters as predictors of urinary Gb3 excretion in patients with CKD.

METHODS

Our study included 609 subjects with CKD stage I-V. We analyzed the influence of age, gender, renal function, urinary cell content and chemical characteristics on urinary Gb3 concentrations (total Gb3, Gb3-24 isoform, and Gb3-24:18 isoform ratio), determined by direct electrospray ionization mass spectrometry.

RESULTS

In 609 subjects the median total urinary Gb3 was 233 ng/mg and the Gb3-24:18 isoform ratio was 1.2. Twenty-one patients, none of whom had Fabry disease, had a Gb3-24:18 isoform ratio ≥2.3. Females excreted a higher total amount of Gb3, but the Gb3-24:18 isoform ratio was comparable to males. Renal function and age had no influence on total Gb3, Gb3 isoforms or the ratio. Only a distinct load of bacteria and leukocytes was associated with an increased Gb3 excretion. Urinary leukocytes, erythrocytes, bacteria, or protein content did not affect the Gb3-24:18 isoform ratio.

CONCLUSION

The Gb3-24:18 isoform ratio is unaffected by several potential influencing variables and may thus be applied for screening for Fabry disease in unselected cohorts of patients presenting with CKD.

Lipidomics in the study of lipid metabolism: Current perspectives in the omic sciences

The advances in systems biology and in the development of new technological tools in analysis, as well as in the omic sciences, among which, metabolomics, and more specifically, lipidomics, have made it possible to investigate the structural and functional complexity of lipids in biological systems. Liquid chromatography and mass spectrometry are the analytical approaches most used in lipid research. Biomedical research, with the development of specific markers for lipids, together with new software development, have both enabled the early diagnosis of several illnesses, besides the evaluation of drug activity and treatment efficacy.

Risk of death in heart disease is associated with elevated urinary globotriaosylceramide

Background

Elevated urinary globotriaosylceramide (Gb₃) has been considered a hallmark of Fabry disease, an X‐linked lysosomal disorder that is a risk factor for most types of heart disease.

Methods and Results

We screened 1421 consecutive patients with common forms of heart disease for Fabry disease by measuring urinary Gb₃ in whole urine using tandem mass spectrometry, α‐galactosidase A activity in dried blood spots, and we looked for GLA mutations by parallel sequencing of the whole gene (exons and introns) in pooled genomic DNA samples followed by Sanger sequencing verification. GLA variants were found in 13 patients. In the 1408 patients without GLA mutations, urinary Gb₃ levels were significantly higher in heart disease patients compared to 116 apparently healthy controls (median difference=10.0 ng/mL and P<0.001). Urinary lipid profiling showed that levels of 5 other lipids significantly distinguished between urine of patients with Fabry disease (n=7) and heart disease patients with elevated urinary Gb₃ (n=6). Sphingomyelin and Gb₃ levels were abnormal in the left ventricular wall of patients with ischemic heart failure. Elevated levels of urinary Gb₃ were independently associated with increased risk of death in the average follow‐up of 17 months (hazard ratio=1.59 for increase in Gb₃ of 200, 95% CI=1.36 and 1.87, and P<0.0001).

Conclusions

In heart disease patients who do not have Fabry disease or GLA gene mutations, a higher level of urinary Gb₃ is positively associated with near‐term mortality. The elevation of urinary Gb₃ and that of other lipids suggests that heart disease is associated with multiorgan lipid abnormalities.

Clinical Trial Registration

URL: clinicaltrials.gov. Unique Identifier: NCT01019629.

Reduced glucosylceramide in the mouse model of Fabry disease: correction by successful enzyme replacement therapy

Fabry disease is an X-linked lysosomal storage disease (LSD) caused by deficient activity of α-Galactosidase A (α-Gal A). As a result, glycosphingolipids, mainly globotriaosylceramide (Gb3), progressively accumulate in body fluids and tissues. Studies aiming at the identification of secondary lipid alterations in Fabry disease may be potentially useful for the monitorization of the response to enzyme replacement therapy (ERT) and development of future therapies. The focus of this study was to evaluate if α-Gal A deficiency has an effect on two key groups of molecules of sphingolipids metabolism: glucosylceramides (GlucCers) and ceramides (Cers). Studies performed in a mouse model of Fabry disease showed reduced level of GlucCer and normal level of Cer in plasma, liver, spleen, kidney and heart. Moreover, analysis of GlucCer isoforms in Fabry knockout mice showed that GlucCer isoforms are unequally reduced in different tissues of these animals. ERT had a specific effect on the liver's GlucCer levels of Fabry knockout mice, increasing hepatic GlucCer to the levels observed in wild type mice. In contrast to Fabry knockout mice, plasma of Fabry patients had normal GlucCer and Cer but an increased GlucCer/Cer ratio. This alteration showed a positive correlation with plasma globotriaosylsphingosine (lyso-Gb3) concentration. In conclusion, this work reveals novel secondary lipid imbalances caused by α-Gal A deficiency.

A Phase 2 study of migalastat hydrochloride in females with Fabry disease: selection of population, safety and pharmacodynamic effects

BACKGROUND

Fabry disease (FD) is a genetic disorder resulting from deficiency of the lysosomal enzyme α-galactosidase A (α-Gal A) which leads to globotriaosylceramide (GL-3) accumulation in multiple tissues. We report on the safety and pharmacodynamics of migalastat hydrochloride, an investigational pharmacological chaperone given orally every other day (QOD) to females with FD.

METHODS

This was an open-label, uncontrolled, Phase 2 study of 12 weeks with extension to 48 weeks in nine females with FD. Doses of 50mg, 150 mg and 250 mg were given QOD. At multiple time points, α-Gal A activity and GL-3 levels were quantified in blood cells, kidney and skin. GL-3 levels were also evaluated through skin and renal histology. Each individual GLA mutation was retrospectively categorized as being amenable or not to migalastat HCl based on an in vitro α-Gal A transfection assay developed in human embryonic kidney (HEK)-293 cells.

RESULTS

Migalastat HCl was generally well tolerated. Patients with amenable mutations seem to demonstrate greater pharmacodynamic response to migalastat HCl compared to patients with non-amenable mutations. The greatest declines in urine GL-3 were observed in the three patients with amenable GLA mutations that were treated with 150 or 250 mg migalastat HCl QOD. Additionally, these three patients all demonstrated decreases in GL-3 inclusions in kidney peri-tubular capillaries.

CONCLUSIONS

Migalastat HCl is a candidate oral pharmacological chaperone that provides a potential novel genotype-specific treatment for FD. Treatment resulted in GL-3 substrate decrease in female patients with amenable GLA mutations. Phase 3 studies are ongoing.

Safety and pharmacodynamic effects of a pharmacological chaperone on α-galactosidase A activity and globotriaosylceramide clearance in Fabry disease: report from two phase 2 clinical studies

Background

Fabry disease (FD) is a genetic disorder resulting from deficiency of the lysosomal enzyme α-galactosidase A (α-Gal A), which leads to globotriaosylceramide (GL-3) accumulation in multiple tissues. We report on the safety and pharmacodynamics of migalastat hydrochloride, an investigational pharmacological chaperone given orally at 150 mg every-other-day.

Methods

Two open-label uncontrolled phase 2 studies of 12 and 24 weeks (NCT00283959 and NCT00283933) in 9 males with FD were combined. At multiple time points, α-Gal A activity and GL-3 levels were quantified in blood cells, kidney and skin. GL-3 levels were also evaluated through skin and renal histology.

Results

Compared to baseline, increased α-Gal A activity of at least 50% was demonstrated in blood, skin and kidney in 6 of 9 patients. Patients’ increased α-Gal A activities paralleled the α-Gal A increases observed in vitro in HEK-293 cells transfected with the corresponding mutant form of the enzyme. The same 6 patients who demonstrated increases of α-Gal A activity also had GL-3 reduction in skin, urine and/or kidney, and had α-Gal A mutations that responded in transfected cells incubated with the drug. The 3 patients who did not show a consistent response in vivo had α-Gal A mutations that did not respond to migalastat HCl in transfected cells. Migalastat HCl was well tolerated.

Conclusions

Migalastat HCl is a candidate pharmacological chaperone that provides a novel genotype-specific treatment for FD. It enhanced α-Gal A activity and resulted in GL-3 substrate decrease in patients with responsive GLA mutations. Phase 3 studies are ongoing.

Trial registration

Clinicaltrial.gov: NCT00283959 and NCT00283933

Ceramide sphingolipid signaling mediates Tumor Necrosis Factor (TNF)-dependent toxicity via caspase signaling in dopaminergic neurons

BACKGROUND

Dopaminergic (DA) neurons in the ventral midbrain selectively degenerate in Parkinson's disease (PD) in part because their oxidative environment in the substantia nigra (SN) may render them vulnerable to neuroinflammatory stimuli. Chronic inhibition of soluble Tumor Necrosis Factor (TNF) with dominant-negative TNF inhibitors protects DA neurons in rat models of parkinsonism, yet the molecular mechanisms and pathway(s) that mediate TNF toxicity remain(s) to be clearly identified. Here we investigated the contribution of ceramide sphingolipid signaling in TNF-dependent toxicity.

RESULTS

Ceramide dose-dependently reduced the viability of DA neuroblastoma cells and primary DA neurons and pharmacological inhibition of sphingomyelinases (SMases) with three different inhibitors during TNF treatment afforded significant neuroprotection by attenuating increased endoplasmic reticulum (ER) stress, loss of mitochondrial membrane potential, caspase-3 activation and decreases in Akt phosphorylation. Using lipidomics mass spectrometry we confirmed that TNF treatment not only promotes generation of ceramide, but also leads to accumulation of several atypical deoxy-sphingoid bases (DSBs). Exposure of DA neuroblastoma cells to atypical DSBs in the micromolar range reduced cell viability and inhibited neurite outgrowth and branching in primary DA neurons, suggesting that TNF-induced de novo synthesis of atypical DSBs may be a secondary mechanism involved in mediating its neurotoxicity in DA neurons.

CONCLUSIONS

We conclude that TNF/TNFR1-dependent activation of SMases generates ceramide and sphingolipid species that promote degeneration and caspase-dependent cell death of DA neurons. Ceramide and atypical DSBs may represent novel drug targets for development of neuroprotective strategies that can delay or attenuate the progressive loss of nigral DA neurons in patients with PD.

Quantification of the Fabry marker lysoGb3 in human plasma by tandem mass spectrometry

Morbus Fabry is a hereditary metabolic disorder with low prevalence and late clinical manifestation. A defect in the α-galactosidase gene leads to lysosomal accumulation of the glycolipid globotriaosylceramide (Gb3). Gb3 may be used for monitoring of enzyme replacement therapy (ERT), but diagnostic sensitivity is limited. Recently, globotriaosylsphingosine (lysoGb3) was introduced as a promising new marker with significantly better sensitivity. For Fabry diagnosis, clinical studies and possible therapy monitoring, we established a fast and reliable LC-MS/MS assay for quantification of lysoGb3 in human plasma. Protein precipitation and glycolipid extraction from EDTA plasma was performed using acetone/methanol. Samples were analyzed by UPLC-MS/MS in MRM mode. In contrast to HPLC with fluorescence detection, the LC-MS/MS method requires no derivatization, less sample preparation and less instrument analysis time (<3 min). As internal standard (ISTD), a glycine derivative of lysoGb3 was synthesized, and the product was purified by HPLC. ISTD properties such as polarity (affecting extraction and elution), ionization and fragmentation pathway were almost identical compared to the analyte. The new LC-MS/MS assay for the Fabry marker lysoGb3 shows good performance and allowed for better discrimination between Fabry patients and controls than Gb3.

Biomarkers in the diagnosis of lysosomal storage disorders: proteins, lipids, and inhibodies

A biomarker is an analyte indicating the presence of a biological process linked to the clinical manifestations and outcome of a particular disease. In the case of lysosomal storage disorders (LSDs), primary and secondary accumulating metabolites or proteins specifically secreted by storage cells are good candidates for biomarkers. Clinical applications of biomarkers are found in improved diagnosis, monitoring disease progression, and assessing therapeutic correction. These are illustrated by reviewing the discovery and use of biomarkers for Gaucher disease and Fabry disease. In addition, recently developed chemical tools allowing specific visualization of enzymatically active lysosomal glucocerebrosidase are described. Such probes, coined inhibodies, offer entirely new possibilities for more sophisticated molecular diagnosis, enzyme replacement therapy monitoring, and fundamental research.

Semisynthesis of C17:0 isoforms of sulphatide and glucosylceramide using immobilised sphingolipid ceramide N-deacylase for application in analytical mass spectrometry

Sphingolipid ceramide N-deacylase (SCDase, EC 3.5.1.69) is a hydrolytic enzyme isolated from Pseudomonas sp. TK 4. In addition to its primary deacylation function, this enzyme is able to reacylate lyso-sphingolipids under specific conditions. We immobilised this enzyme on magnetic macroporous cellulose and used it to semisynthesise C17:0 glucosylceramide and C17:0 sulphatide, which are required internal standards for quantification of the corresponding glycosphingolipids (GSL) by tandem mass spectrometry. A high rate of conversion was achieved for both lipids (80% for C17:0 sulphatide and 90% for C17:0 glucosylceramide). In contrast to synthesis with a soluble form of the enzyme, use of immobilised SCDase significantly reduced the contamination of the sphingolipid products with other isoforms, so further purification was not necessary. Our method can be effectively used for the simple preparation of specifically labelled sphingolipids of high isoform purity for application in mass spectrometry.

Biochemical profiling to predict disease severity in metachromatic leukodystrophy

Metachromatic leukodystrophy is a neurodegenerative disease that is characterized by a deficiency of arylsulfatase A, resulting in the accumulation of sulfatide and other lipids in the lysosomal network of affected cells. Accumulation of sulfatide in the nervous system leads to severe impairment of neurological function with a fatal outcome. Prognosis is often poor unless treatment is carried out before the onset of clinical symptoms. Pre-symptomatic detection of affected individuals may be possible with the introduction of newborn screening programs. The ability to accurately predict clinical phenotype and rate of disease progression in asymptomatic individuals will be essential to assist selection of the most appropriate treatment strategy. Biochemical profiling, incorporating the determination of residual enzyme protein/activity using immune-based assays, and metabolite profiling using electrospray ionization-tandem mass spectrometry, was performed on urine and cultured skin fibroblasts from a cohort of patients representing the clinical spectrum of metachromatic leukodystrophy and on unaffected controls. Residual enzyme protein/activity in fibroblasts was able to differentiate unaffected controls, arylsulfatase A pseudo-deficient individuals, pseudo-deficient compound heterozygotes and affected patients. Metachromatic leukodystrophy phenotypes were distinguished by quantification of sulfatide and other secondarily altered lipids in urine and skin fibroblasts; this enabled further differentiation of the late-infantile form of the disorder from the juvenile and adult forms. Prediction of the rate of disease progression for metachromatic leukodystrophy requires a combination of information on genotype, residual arylsulfatase A protein and activity and the measurement of sulfatide and other lipids in urine and cultured skin fibroblasts.

Prosaposin deficiency and saposin B deficiency (activator-deficient metachromatic leukodystrophy): report on two patients detected by analysis of urinary sphingolipids and carrying novel PSAP gene mutations

Prosaposin deficiency (pSap-d) and saposin B deficiency (SapB-d) are both lipid storage disorders caused by mutations in the PSAP gene that codes for the 65-70 kDa prosaposin protein, which is the precursor for four sphingolipid activator proteins, saposins A-D. We report on two new patients with PSAP gene defects; one, with pSap-d, who had a severe neurovisceral dystrophy and died as a neonate, and the other with SapB-d, who presented with a metachromatic leukodystrophy-like disorder but had normal arylsulfatase activity. Screening for urinary sphingolipids was crucial to the diagnosis of both patients, with electrospray ionization tandem mass spectrometry also providing quantification. The pSap-d patient is the first case with this condition where urinary sphingolipids have been investigated. Multiple sphingolipids were elevated, with globotriaosylceramide showing the greatest increase. Both patients had novel mutations in the PSAP gene. The pSap-d patient was homozygous for a splice-acceptor site mutation two bases upstream of exon 10. This mutation led to a premature stop codon and yielded low levels of transcript. The SapB-d patient was a compound heterozygote with a splice-acceptor site variant exclusively affecting the SapB domain on one allele, and a 2 bp deletion leading to a null, that is, pSap-d mutation, on the other allele. Phenotypically, pSap-d is a relatively uniform disease of the neonate, whereas SapB-d is heterogeneous with a spectrum similar to that in metachromatic leukodystrophy. The possible existence of genotypes and phenotypes intermediate between those of pSap-d and the single saposin deficiencies is speculated.

Proposed high-risk screening protocol for Fabry disease in patients with renal and vascular disease

Fabry disease is a complex, multisystemic and clinically heterogeneous disease with prominent urinary excretion of globotriaosylceramide (Gb(3)), the principal substrate of the deficient enzyme, alpha-galactosidase A. Some measure of specific treatment is possible with enzyme replacement therapy, which can be applied safely and effectively to Fabry patients. Incidence estimations of Fabry disease vary widely from 1:55 000 to 1:3000 male births. The true incidence is likely to be higher than originally thought, owing to the existence of milder variants of the disease. The main complications of Fabry disease are a 100-fold increased risk of ischaemic stroke, cardiac disease, a wide variety of arrhythmias, valvular dysfunction and cardiac vascular disease, as well as progressive renal failure usually associated with significant proteinuria. These clinical manifestations are non-specific and are often mistaken for symptoms of other disorders, thus complicating the confirmation of diagnosis. Other clinical features of the disease are often absent (angiokeratoma), subtle (corneal opacities and hypohidrosis), or unaccompanied by specific physical findings (acroparaesthesias) indicating the true nature of the underlying disease. We propose the hypothesis that alpha-galactosidase A deficiency is a modifiable cardiovascular risk factor in the general population. This hypothesis may be tested by a non-invasive high-risk screening protocol for Fabry patients with ischaemic strokes and a variety of cardiac, and renal complications. These patients would benefit from diagnosis, appropriate treatment, follow-up and surveillance. Early detection of Fabry patients would also benefit affected relatives, many of whom do not have a clear diagnosis of their clinical condition.

Fabry disease

Fabry disease, an X-linked disorder of glycosphingolipids that is caused by the deficiency of alpha-galactosidase A, is associated with dysfunction of many cell types and includes a systemic vasculopathy. As a result, patients have a markedly increased risk of developing small-fiber peripheral neuropathy, stroke, myriad cardiac manifestations and chronic renal disease. Virtually all complications of Fabry disease are non-specific in nature and clinically indistinguishable from similar abnormalities that occur in the context of more common disorders in the general population. Although Fabry disease was originally thought to be very rare, recent studies have found a much higher incidence of mutations of the GLA gene, suggesting that this disorder is under-diagnosed. Although the etiology of Fabry disease has been known for many years, the mechanism by which the accumulating alpha-D-galactosyl moieties cause this multi-organ disorder has only recently been studied and is yet to be completely elucidated. Specific therapy for Fabry disease has been developed in the last few years but its role in the management of the disorder is still being investigated. Fortunately, standard 'non-specific' medical and surgical therapy is effective in slowing deterioration or compensating for organ failure in patients with Fabry disease. All these aspects are discussed in detail in the present review.

Analytical strategies in lipidomics and applications in disease biomarker discovery

Lipidomics is a lipid-targeted metabolomics approach aiming at comprehensive analysis of lipids in biological systems. Recently, lipid profiling, or so-called lipidomics research, has captured increased attention due to the well-recognized roles of lipids in numerous human diseases to which lipid-associated disorders contribute, such as diabetes, obesity, atherosclerosis and Alzheimer's disease. Investigating lipid biochemistry using a lipidomics approach will not only provide insights into the specific roles of lipid molecular species in health and disease, but will also assist in identifying potential biomarkers for establishing preventive or therapeutic approaches for human health. Recent technological advancements in mass spectrometry and rapid improvements in chromatographic techniques have led to the rapid expansion of the lipidomics research field. In this review, emphasis is given to the recent advances in lipidomics technologies and their applications in disease biomarker discovery.

Profiling of human urinary phospholipids by nanoflow liquid chromatography/tandem mass spectrometry

Nanoflow liquid chromatography-electrospray ionization-tandem mass spectrometry (nanoLC-ESI-MS-MS) was used for the first time in a comprehensive analysis of human urinary phospholipids (PL). PL mixtures from human urine were separated with a reversed phase LC capillary column coupled to ESI-MS-MS. This study used the dual scan method in which two consecutive LC-ESI-MS-MS runs were done in both positive ion mode to detect phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and in negative ion mode to detect phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidic acid (PA), and phosphatidylglycerol (PG). We focused on identifying the maximum number of PLs from a healthy human urine sample by varying the extracted volume of urine along with the evaluation of extraction efficiency for urinary PLs. We found that 22 PCs, 14 PEs, 15 PIs, 13 PSs, 7 PAs, and 4 PGs were identified during nLC-ESI-MS-MS when phospholipids in urine were extracted by ultracentrifugation. The efficiency of lipid extraction by ultracentrifugation versus lyophilization was evaluated by reducing the initial urine volume. We found that lyophilization was more efficient than ultracentrifugation for extracting lipids from small volumes (1 mL) of urine.

Urinary globotriaosylceramide excretion correlates with the genotype in children and adults with Fabry disease

Fabry disease is a complex, multisystemic and clinically heterogeneous disease, in which the urinary excretion of globotriaosylceramide (Gb3), the principal substrate of the deficient enzyme, alpha-galactosidase A, is more prominent than the increased concentrations of the lipid in the plasma of affected hemizygotes and heterozygotes. We have developed and validated a simultaneous analysis of Gb3 and creatinine in a 2.6-min run using filter paper discs saturated with urine and analyzed by LC-MS/MS. Using this method, we studied the relationship between urinary levels of total Gb3/creatinine excretion and four types of mutations in the GLA gene (missense, nonsense, frameshift, and splice-site defects) in 32 children and 78 adult patients with Fabry disease. Forty-one patients were treated by enzyme replacement therapy and 69 were untreated. Our results show that the mean recoveries of Gb3 and creatinine from the urine filter paper standards were 91% and 97%, respectively, with precision, reproducibility, and linearity within acceptable ranges. Statistical analysis using the independent variables of sex, age, types of mutations and treatment showed that the mutation factor has a statistically significant impact on urinary Gb3 excretion (p = 0.0007). This means that the levels of urinary excretion of Gb3/creatinine in children and adults with Fabry disease are directly related to the types of mutations. The same correlation was found for the sex (p < 0.0001) and treatment (p = 0.0011). In conclusion, we studied 35 mutations in 110 children and adults with Fabry disease and found a significant correlation between the types of mutations and total Gb3 excretion in Fabry patients.

Maladie de Fabry: propositions d'ungroupe d'experts français concernant le diagnostic, le traitement et le suivi des patients

Fabry disease is a rare and under-recognized disease associated with an altered X-linked gene controlling hydrolase alpha-galactosidase A activity. This mutation impairs the glycosphingolipid metabolism. A multisystemic disease with a highly variable clinical presentation, its principal symptom is acroparesthesia. Manifestations of Fabry disease occur mostly in hemizygous males but also in heterozygous females. Before enzyme replacement therapy was available, life expectancy was about 50 years in men and 70 years in women. Early diagnosis is essential to prevent irreversible organ damage. Diagnosis is based on an assay of alpha-galactosidase A activity in male patients and on genetic analysis in female patients. Prognosis is related principally to three complications: involvement of the central nervous system, kidneys, and heart. Management of Fabry patients should in all cases combine symptomatic therapy and regular clinical, laboratory and morphological follow-up by specialists in genetic metabolic diseases. Enzyme replacement therapy should be considered in all adult male patients and should probably begin early. In adult heterozygous female patients and in children, this treatment should be considered only for patients with severe pain, organ damage, or central nervous system, kidney, or heart involvement. After a proband is identified, a genealogical tree should be used to identify other affected members of the family.

[Neurological aspects of Fabry's disease]

Fabry disease is a rare X-linked disorder caused by deficient activity of the lysosomal enzyme alpha-galactosidase A. Progressive accumulation in lysosomes of the undegraded glycosphingolipids leads to a multi-system disease with dermatological, ocular, renal, cardiac, and neurological manifestations. Peripheral nerve involvement, neuropathic pain and chronic acroparesthesiae, are frequent and early-onset signs revealing the disease. They are due to the involvement of small nerve fiber, thus explaining the normality of electroneuromyography. Cochleo-vestibular and autonomic nervous system involvement is frequent. Besides rare aseptic meningitis, central nervous system involvement is essentially represented by cerebrovascular events (stroke, transient ischemic attack). Affecting essentially the posterior circulation, their etiologies have to be clarified: progressive stenosis of small vessels with globotriasocylceramide deposits, arterial remodeling, endothelial dysfunction, pro-thrombotic state, cerebral hypoperfusion consecutive to dysautonaumy, cardiac embolism. MRI shows numerous silent lesions, increasing with age, mainly in small perforant arteries (periventricular white matter, brainstem, cerebellum, basal ganglia). Pulvinar calcifications, due to an increase in cerebral hyperperfusion, could be specific of Fabry disease. Positon tomography analysis shows a reduced cerebral flow velocity and impaired cerebral autoregulation, secondary to the glycosphingolipid storage in vascular endothelial cells. Enzyme replacement therapy has to be carefully monitored.

Diagnosis and management of kidney involvement in Fabry disease

Interest in the diagnosis and treatment of Fabry disease has been greatly stimulated by the availability of Food and Drug Administration-approved, effective enzyme replacement therapy. This review will update the progress in this area since enzyme replacement therapy has become available. Fabry disease is often associated with proteinuric chronic kidney disease (CKD), and it appears that the treatment paradigms that have proven to be so effective in diabetes mellitus and other forms of proteinuric kidney disease are also effective in conjunction with enzyme replacement therapy for treating the kidney manifestations of Fabry disease. As such, Fabry disease represents an interesting example of progressive proteinuric kidney disease in which the usual blood pressure is lower than in other forms of CKD. This makes the use of effective antiproteinuric therapy challenging, especially considering the autonomic dysfunction that appears to be part of the disease. Comprehensive therapy for Fabry disease includes enzyme replacement therapy and all of the adjunctive therapies that are currently used to treat all forms of proteinuric CKD. It is anticipated that this approach will preserve kidney function and also benefit the cardiac and cerebrovascular systems in patients with Fabry disease.