A metabolomic study reveals novel plasma lyso-Gb3 analogs as Fabry disease biomarkers

Fabry disease is an X-linked, multisystemic lysosomal storage disorder due to alpha-galactosidase A deficiency. It is characterized by the accumulation of glycosphingolipids, mainly globotriaosylceramide (Gb(3)), in biological fluids, vascular endothelium, heart, and kidneys. Treatment by enzyme replacement therapy has been shown to be beneficial in both males and females affected with the disease. In addition to Gb(3), increased concentrations of globotriaosylsphingosine (lyso-Gb(3)) have recently been reported in urine and plasma of Fabry patients. The overall objective of this metabolomic study was to identify and characterize new potential plasma biomarkers in treated and untreated males and females affected with Fabry disease which might better reflect disease severity and progression. We employed a time-of-flight mass spectrometry metabolomic approach using plasma samples of Fabry patients compared to age-matched controls. We found three new lyso-Gb(3) analogs in Fabry patients presenting m/z ratios at 802, 804, and 820. As previously detected by our group, we also found a m/z ratio of 784 corresponding to the lyso-Gb(3) molecule minus two hydrogen atoms. Using exact mass measurements and tandem mass spectrometry, we confirmed that these analogs result from modifications of the lyso-Gb(3) sphingosine moiety. We evaluated the relative plasma concentration by measuring area counts for each lyso-Gb(3) analog. None of these analogs was detected in the majority of healthy controls. The relative concentration of each analog was higher in males compared to female Fabry patients. We demonstrated that mass spectrometry combined to a metabolomic approach is a powerful tool to detect and identify new potential biomarkers.

A metabolomic study to identify new globotriaosylceramide-related biomarkers in the plasma of Fabry disease patients

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency of the enzyme α-galactosidase A, which results in the progressive accumulation of glycosphingolipids. In addition to the two biomarkers, globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3), which are routinely used for detection and high-risk screening of Fabry disease patients, novel urinary Gb3-related isoforms/analogues as well as newly defined lyso-Gb3 analogues in plasma and urine from Fabry patients have recently been described by our group. The aim of this study was to extend our recent analyses to identify and evaluate new potential Gb3-related biomarkers in the plasma of untreated male Fabry disease patients using a mass spectrometry metabolomic approach. A multivariate statistical analysis revealed five Gb3-related novel biomarkers in the plasma of male Fabry patients. Three of these new biomarkers correspond to Gb3, which has an extra double bond on the sphingosine with C16:0, C18:0, and C22:1 fatty acid chains. The fourth biomarker corresponds to a mixture of two structural isomers, the first with a d16:1 sphingosine and a C16:0 fatty acid and the second with a d18:1 sphingosine and a C14:0 fatty acid. To our knowledge, it is the first time that a Gb3 analogue with a d16:1 sphingosine moiety has been reported. In addition, this Gb3 analogue was also present in its methylated form. These biomarkers are part of a metabolic profile that may provide insight into the pathophysiology of Fabry disease.

Novel gb(3) isoforms detected in urine of fabry disease patients: a metabolomic study

Fabry disease is characterized by the accumulation of globotriaosylsphingosine (lyso-Gb(3)) and globotriaosylceramide (Gb(3)) in biological fluids and tissues. Metabolomic studies recently undertaken by our group, showed the presence of novel plasma and urine lyso-Gb(3)-related analogs in male and female Fabry patients. These analogs are distinguished by differences in structure of the sphingosine moiety. The principal aim of this study was to evaluate the possibility of detecting other Fabry disease biomarkers structurally related to Gb(3). A time-of-flight mass spectrometry metabolomic approach, focusing on mass-to-charge (m/z) ratios from 1000 to 1200 Da, was devised. This m/z window corresponds to the isoforms and potential analogs of Gb(3). Five different categories of Gb(3)- related isoforms/analogs were detected: Gb(3)-related isoforms with saturated fatty acids, methylated Gb(3)-related isoforms, Gb(3)-related isoforms/analogs with one double bond, Gb(3) analogs with hydrated sphingosine, and Gb(3)-related isoforms/analogs with two double bonds. A secondary objective was to elucidate the relationship between Gb(3) and lyso-Gb(3). The methylation observed on Gb(3)-related analogs was not detected on lyso-Gb(3). We speculate that the methylated Gb(3) may be an intermediate compound in the deacylation of Gb(3) to generate the lyso-Gb(3) molecule. We are in the process of devising a quantification methodology for these methylated Gb(3)-related analogs in Fabry patients to try to understand the underlying biochemical mechanisms involved in this complex disease.

Improved ways to screen for patients with Fabry disease, involving optometry in a multidisciplinary approach

Purpose: Fabry disease is considered a rare disease, based on its prevalence. It is recognized, however, that there are many individuals aff ected who are unscreened. This article aims to demonstrate how optometrists can help to defi ne improved ways to screen patients aff ected by this rare metabolic disorder, in a multidisciplinary perspective. Methods: A screening model, based on continuous education for optometrists was developed. Under this model, suspect patients identifi ed by optometrists are referred to Université de Montréal's vision clinic (EOUM) for further testing and assessment. Should ocular manifestations and/or case history prove relevant to these rare diseases, a urinary test is then performed to fi nd related biomarkers. When suspicions narrow to probable Fabry disease, the subjects are referred to metabolic disorder specialists for complete DNA testing and medical follow-up of their condition. Results: Continuous education lectures were given across Quebec, reaching nearly 60% of the province’s optometrists. Sixteen months following the model's implementation, ten suspected patients were referred. Of these, two new Fabry patients were confi rmed, leading to the diagnosis of fi ve other relatives with the disease. Two additional persons, diagnosed as Fabry patients, but lost to medical follow-up for many years, were once again placed under the care of Fabry experts. To this point, because of optometric involvement, seven new patients of Fabry were diagnosed and two were brought back under experts care.  Conclusion: Continuous education lectures were given across Quebec, reaching near 60% of the province’s optometrists. Sixteen months following the model's implementation, ten suspected patients were referred. Of these, two new Fabry patients were confi rmed, leading to the diagnosis of fi ve other relatives with the disease. Two additional persons, diagnosed as Fabry patients, but lost to medical follow-up for many years, were once again placed under the care of Fabry experts. To this point, because of optometric involvement, seven new patients of Fabry were diagnosed and two were brought back under experts care.

Mutations in the sarcosine dehydrogenase gene in patients with sarcosinemia

Sarcosinemia is an autosomal recessive metabolic trait manifested by relatively high concentrations of sarcosine in blood and urine. Sarcosine is a key intermediate in 1-carbon metabolism and under normal circumstances is converted to glycine by the enzyme sarcosine dehydrogenase. We encountered six families from two different descents (French and Arab), each with at least one individual with elevated levels of sarcosine in blood and urine. Using the "candidate gene approach" we sequenced the gene encoding sarcosine dehydrogenase (SARDH), which plays an important role in the conversion of sarcosine to glycine, and found four different mutations (P287L, V71F, R723X, R514X) in three patients. In an additional patient, we found a uniparental disomy in the region of SARDH gene. In two other patients, we did not find any mutations in this gene. We have shown for the first time that mutations in the SARDH gene are associated with sarcosinemia. In addition, our results indicate that other genes are most probably involved in the pathogenesis of this condition.

Urinary globotriaosylsphingosine-related biomarkers for Fabry disease targeted by metabolomics

Fabry disease is a lysosomal storage disorder caused by deficiency of α-galactosidase A, resulting in glycosphingolipid accumulation in organs and tissues, including plasma and urine. Two disease-specific Fabry biomarkers have been identified and quantified in plasma and urine: globotriaosylceramide (Gb(3)) and globotriaosylsphingosine (lyso-Gb(3)). The search continues for biomarkers that might be reliable indicators of disease severity and response to treatment. The main objective of this study was to target other urinary biomarkers using a time-of-flight mass spectrometry metabolomic approach. Urinary metabolites of 63 untreated Fabry patients and 59 controls were analyzed. A multivariate statistical analysis performed on a subset of male samples revealed seven novel Fabry biomarkers in urine, all lyso-Gb(3) analogues having modified sphingosine moieties. The empirical formulas of the sphingosine modifications were determined by exact mass measurements (- C(2)H(4), - C(2)H(4) + O, - H(2), - H(2) + O, + O, + H(2)O(2), + H(2)O(3)). We evaluated the relative concentration of lyso-Gb(3) and its seven analogues by measuring area counts for each analogue in all Fabry patients. All samples were normalized to creatinine. We found higher concentrations for males with Fabry disease compared to females. None of these biomarkers were detected in controls. To our knowledge, this is the first time that lyso-Gb(3)-related Fabry disease biomarkers are detected in urine.

Analysis of glycosaminoglycans in cerebrospinal fluid from patients with mucopolysaccharidoses by isotope-dilution ultra-performance liquid chromatography-tandem mass spectrometry

BACKGROUND

New therapies for the treatment of mucopolysaccharidoses that target the brain, including intrathecal enzyme replacement, are being explored. Quantitative analysis of the glycosaminoglycans (GAGs) that accumulate in these disorders is required to assess the disease burden and monitor the effect of therapy in affected patients. Because current methods lack the required limit of quantification and specificity to analyze GAGs in small volumes of cerebrospinal fluid (CSF), we developed a method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS).

METHODS

Samples of CSF (25 μL) were evaporated to dryness and subjected to methanolysis. The GAGs were degraded to uronic acid-N-acetylhexosamine dimers and mixed with internal standards derived from deuteriomethanolysis of GAG standards. Specific dimers derived from heparan, dermatan and chondroitin sulfates (HS, DS and CS) were separated by UPLC and analyzed by electrospray ionization MS/MS using selected reaction monitoring for each targeted GAG product and its corresponding internal standard.

RESULTS

CSF from control pediatric subjects (n = 22) contained <0.38 mg/L HS, 0.26 mg/L DS, and 2.8 mg/L CS, whereas CSF from patients with Hurler syndrome (n = 7) contained concentrations of DS and HS that were at least 6-fold greater than the upper control limits. These concentrations were reduced by 17.5% to 82.5% after allogeneic transplantation and treatment with intrathecal and intravenous enzyme replacement therapy.

CONCLUSIONS

The method described here has potential value in monitoring patients with mucopolysaccharidoses receiving treatment targeted to the brain.

Efficient analysis of urinary glycosaminoglycans by LC-MS/MS in mucopolysaccharidoses type I, II and VI

Mucopolysaccharidoses (MPSs) are complex storage disorders caused by specific lysosomal enzyme deficiencies, resulting in the accumulation of glycosaminoglycans (GAGs) in urine, plasma, as well as in various tissues. We devised and validated a straightforward, but accurate and precise tandem mass spectrometry methodology coupled to high performance liquid chromatography (LC-MS/MS) for the quantification of GAGs in urine. The method is applicable to the investigation of patients with MPS I, II, and VI, by quantifying dermatan sulfate (DS) and heparan sulfate (HS) in urine. We analyzed urine samples from 28 MPS patients, aged 1 to 42 years, and 55 control subjects (41 days to 18 years old). Levels of DS and HS in urine from healthy controls of all ages were below the limit of quantification. The levels of DS and HS in urine from 6 treated patients with MPS I were lower than in 6 untreated patients in DS (0.7-45 vs 9.3-177 mg/mmol creat) and HS (0-123 mg/mmol creatinine vs 38-418 mg/mmol creatinine); similar results were obtained for 9 patients with MPS II and 7 patients with MPS VI. Analyses were performed on as little as 250 μL of urine. Methanolysis took 75 min per sample; the total analysis run time for each LC-MS/MS injection was 8 min. Results indicate that the method is applicable to a wide variety of situations in which high accuracy and precision are required, including the evaluation of the effectiveness of existing and emerging treatments.

Loss-of-function mutations in the glutamate transporter SLC1A1 cause human dicarboxylic aminoaciduria

Solute carrier family 1, member 1 (SLC1A1; also known as EAAT3 and EAAC1) is the major epithelial transporter of glutamate and aspartate in the kidneys and intestines of rodents. Within the brain, SLC1A1 serves as the predominant neuronal glutamate transporter and buffers the synaptic release of the excitatory neurotransmitter glutamate within the interneuronal synaptic cleft. Recent studies have also revealed that polymorphisms in SLC1A1 are associated with obsessive-compulsive disorder (OCD) in early-onset patient cohorts. Here we report that SLC1A1 mutations leading to substitution of arginine to tryptophan at position 445 (R445W) and deletion of isoleucine at position 395 (I395del) cause human dicarboxylic aminoaciduria, an autosomal recessive disorder of urinary glutamate and aspartate transport that can be associated with mental retardation. These mutations of conserved residues impeded or abrogated glutamate and cysteine transport by SLC1A1 and led to near-absent surface expression in a canine kidney cell line. These findings provide evidence that SLC1A1 is the major renal transporter of glutamate and aspartate in humans and implicate SLC1A1 in the pathogenesis of some neurological disorders.

How well does urinary lyso-Gb3 function as a biomarker in Fabry disease?

BACKGROUND

Fabry disease is characterized by accumulation of glycosphingolipids, such as globotriaosylceramide (Gb(3)), in many tissues and body fluids. A novel plasma biomarker, globotriaosylsphingosine (lyso-Gb(3)), is increased in patients with the disease. Until now, lyso-Gb(3) was not detectable in urine, possibly because of the presence of interfering compounds.

METHODS

We undertook to: 1) characterize lyso-Gb(3) in urine; 2) develop a method to quantitate urinary lyso-Gb(3) by mass spectrometry; 3) evaluate urinary lyso-Gb(3) as a potential biomarker for Fabry disease; and 4) determine whether lyso-Gb(3) is an inhibitor of α-galactosidase A activity. We analyzed urinary lyso-Gb(3) from 83 Fabry patients and 77 healthy age-matched controls.

RESULTS

The intraday and interday bias and precision of the method were <15%. Increases in lyso-Gb(3)/creatinine correlated with the concentrations of Gb(3) (r(2)=0.43), type of mutations (p=0.0006), gender (p<0.0001) and enzyme replacement therapy status (p=0.0012). Urine from healthy controls contained no detectable lyso-Gb(3). Lyso-Gb(3) did not inhibit GLA activity in dried blood spots. Increased urinary excretion of lyso-Gb(3) of Fabry patients correlated well with a number of indicators of disease severity.

CONCLUSION

Lyso-Gb(3) is a reliable independent biomarker for clinically important characteristics of Fabry disease.

Fabry disease urinary globotriaosylceramide/creatinine biomarker evaluation by liquid chromatography-tandem mass spectrometry in healthy infants from birth to 6 months

Fabry disease is an X-linked lysosomal storage disorder caused by deficiency of alpha-galactosidase A, resulting in accumulation of the principal substrate, globotriaosylceramide (Gb(3)), in various physiological fluids and tissues in affected patients. The recognition that accumulation of Gb(3) begins in utero, combined with the fact that the diagnosis of the disease is often delayed until after the development of irreversible tissue damage, has generated pressure to develop techniques for the early, pre-symptomatic diagnosis of the disease. Measurements of urinary Gb(3) have been shown to be useful for the diagnosis of Fabry disease in adults. The objective of this work was to measure the Gb(3)/creatinine biomarker in urine of healthy infants from birth to 6 months, including the establishment of reference ranges for urinary Gb(3) excretion at various postnatal ages, in male and female infants. We employed liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine Gb(3)/creatinine ratios in urine specimens dried on filter paper and mailed to the laboratory by participating parents. A total of 728 urine specimens were obtained at intervals from birth to 6 months of age from 68 healthy infants (35 male and 33 female). Parental participation was good, with 90% of the expected specimens received by the laboratory. The results of the analyses were grouped by the age of the infants into four periods. We have determined that both postnatal age and sex have an effect on urinary Gb(3) excretion levels which vary considerably in newborns. We conclude that screening for Fabry disease by measurement of urinary Gb(3) excretion is unlikely to be reliable before 30 days of age.