Analysis of Fluorescent Ceramide and Sphingomyelin Analogs: A Novel Approach for in Vivo Monitoring of Sphingomyelin Synthase Activity

A novel sensitive high‐performance liquid chromatography‐fluorescence detection (HPLC‐FLD) method was developed for real‐time monitoring of relative sphingomyelin synthase (SMS) activity based on the measurement of a fluorescent ceramide (Cer) analog and its metabolite, a fluorescent sphingomyelin (CerP Cho) analog, in plasma. Analyses were conducted using HPLC‐FLD following a protein precipitation procedure. The chromatographic separations were carried out on an Agilent C18 RP column (150 × 4.6 mm, 5 μm) based on a methanol—0.1 % trifluoroacetic acid aqueous solution (88:12, by vol) elution at a flow‐rate of 1 mL/min. The limit of quantification in plasma was 0.05 μM for both the fluorescent Cer analog and its metabolite. Significant differences in the fluorescent Cer analog and its metabolite concentration ratio at 5 min were found between vehicle control group and three D2 (a novel SMS inhibitor) dose groups (P < 0.05). Dose‐dependent effects (D2 doses: 0, 2.5, 5, 10 mg/kg) were observed. Our method could be used to detect relative SMS activity in biochemical assays and to screen potential SMS inhibitors in vivo. D2 was found to be a potent SMS inhibitor in vivo, and may have a potential antiatherosclerotic effect, which is under further study. D609 was also selected as another model SMS inhibitor to validate our newly developed method.