Metabolomic Discovery of Novel Urinary Galabiosylceramide Analogs as Fabry Disease Biomarkers

Fabry disease is an X-linked, complex, multisystemic lysosomal storage disorder presenting marked phenotypic and genotypic variability among affected male and female patients. Glycosphingolipids, mainly globotriaosylceramide (Gb(3)) isoforms/analogs, globotriaosylsphingosine (lyso-Gb(3)) and analogs, as well as galabiosylceramide (Ga-2) isoforms/analogs accumulate in the vascular endothelium, nerves, cardiomyocytes, renal glomerular and tubular epithelial cells, and biological fluids. The search for biomarkers reflecting disease severity and progression is still on-going. A metabolomic study using quadrupole time-of-flight mass spectrometry has revealed 22 galabiosylceramide isoforms/analogs in urine of untreated Fabry patients classified in seven groups according to their chemical structure: (1) Saturated fatty acid; (2) one extra double bond; (3) two extra double bonds; (4) hydroxylated saturated fatty acid; (5) hydroxylated fatty acid and one extra double bond; (6) hydrated sphingosine and hydroxylated fatty acid; (7) methylated amide linkage. Relative quantification of both Ga-2 and Gb(3) isoforms/analogs was performed. All these biomarkers are significantly more abundant in urine samples from untreated Fabry males compared with healthy male controls. A significant amount of Ga-2 isoforms/analogs, accounting for 18% of all glycosphingolipids analyzed (Ga-2 + Gb(3) and respective isoforms/analogs), were present in urine of Fabry patients. Gb(3) isoforms containing saturated fatty acids are the most abundant (60.9%) compared with 26.3% for Ga-2. A comparison between Ga-2 isoforms/analogs and their Gb(3) counterparts also showed that the proportion of analogs with hydroxylated fatty acids is significantly greater for Ga-2 (35.8%) compared with Gb(3) (1.9%). These results suggest different biological pathways involved in the synthesis and/or degradation of Gb(3) and Ga-2 metabolites.