In situ glucosylceramide synthesis and its pharmacological inhibition analysed in cells by 13 C5 -sphingosine precursor feeding and mass spectrometry

Glycosphingolipids fulfil diverse functions in cells. Abnormalities in their metabolism are associated with specific pathologies and, consequently, the pharmacological modulation of glycosphingolipids is considered a therapeutic avenue. The accurate measurement of in situ metabolism of glycosphingolipids and the modulatory impact of drugs is warranted. Employing synthesized sphingosine and sphinganine containing ¹³ C atoms, we developed a method to monitor the de novo synthesis of glucosylceramide, the precursor of complex glycosphingolipids, by the enzyme glucosylceramide synthase (GCS). We show that feeding cells with isotope-labelled precursor combined with LC-MS/MS analysis allows accurate determination of the IC₅₀ values of therapeutically considered inhibitors (iminosugars and ceramide mimics) of GCS in cultured cells. Acquired data were comparable to those obtained with an earlier method using artificial fluorescently labelled ceramide to feed cells.