Neutral lipids (TAGs, DAGs and CEs) were analyzed using a modified version of reverse-phase HPLC/MRM as previously described [33, 34]. Briefly, the lipids were separated on a Phenomenex Kinetex 2.6 μm C18 column (i.d. 4.6 × 100 mm2) using an isocratic mobile phase of chloroform:methanol:0.1 M ammonium acetate (100:100:4) at a flow rate of 170 µl/min for 17 min. Levels of short, medium, and long-chain TAGs were calculated by referencing the spiked internal standards of TAG(14:0)3-d5, TAG(16:0)3-d5 and TAG(18:0)3-d5 obtained from CDN isotopes, respectively. DAGs were quantified using d5-DAG16:0/16:0 and d5-DAG18:1/18:1 (Avanti Polar Lipids) as internal standards. Free cholesterols and cholesteryl esters were analyzed as previously described with d6-cholesterol and d6-C18:0 cholesteryl ester (CE) (CDN isotopes) as internal standards.
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