Quantitation of ceramide phosphorylethanolamines containing saturated and unsaturated sphingoid base cores

Sphingomyelin (SM) and ceramide-phosphoethanolamines (cer-PEs) are related lipids present in mammals and insects, respectively. Owing to the critical roles that cer-PEs play in eukaryotic cellular function, there is a need to develop methods that provide accurate quantitation of these compounds. Results obtained in this study demonstrate that Drosophila contains cer-PEs with unsaturated sphingoid base cores as well as low levels of cer-PEs that possess saturated sphingoid base cores. Specifically, the method developed in this study enabled the quantitation of picogram amounts of cer-PE containing both unsaturated d14:1Δ4 and d16:1Δ4 and saturated d14:0 sphingoid base cores. Using this method, cer-PE compounds with both saturated and unsaturated sphingoid base cores were initially identified by neutral loss scanning, followed by quantitation using selected reaction monitoring (SRM) scans. The SRM scans measured a product ion originating from the sphingoid base backbone, rather than from the head group, increasing the specificity and sensitivity of the quantitation measurement.