Figure 5. Fatty acid composition of the SM and ceramide in liver, VLDL and LDL.

Acidified organic solvents were used to prepare total lipid extracts from liver homogenates, VLDL and LDL from asm^+/+/ldlr^−/− mice (three to five animals per group) fed either standard or modified diet. Ceramide and SM internal standards containing a C_17:0 fatty acid were added at the start to account for any losses during the extraction. Sphingolipid species containing different fatty acids were detected by monitoring species-specific precursor product ion pairs using HPLC–ESI–tandem MS and 4000 Q-Trap hybrid linear ion trap triple-quadrupole mass spectrometer. Levels of the respective dihydro species were sometimes too low for proper quantification and therefore were not included.