The liver was homogenized in four volumes (v:wt) of cold methanol/chloroform (1:2, by volume)
containing 0.01% BHT. Dinonadecanoyl phosphatidylcholine (PC 19:0/19:0) and diheptadecanoyl
phosphatidylethanolamine (PE 17:0/17:0) were added to the homogenate as internal standards with
final concentrations of 1 and 0.75 µmol/g of tissue respectively. The total lipids were extracted as
described previously [20] and stored at −80 °C until analysis. The liver extracts were analyzed on a
QTRAP 5500 mass spectrometer (AB Sciex, Concord, Vaughan, Canada) combined with a Nanomate
Triversa robotic nanospray source (Advion Biosciences, Ithaca, NY, USA). All samples were infused
with a spray gas pressure of 0.4 psi and voltage of 1.2 kV. Lipid extracts were diluted 100-fold into
MeOH/CHCl3 (2:1, by volume) containing 7.5 mM ammonium acetate. PC was identified by precursor
ion scanning for the m/z 184.1 product ion in the positive mode. PE was identified by neutral loss
scanning for a loss of 141 Da in the positive mode. Collision energy was set at 55 and 30 eV respectively
for precursor ion and neutral loss experiments and 400 scans were summed for each experiment. Data
were analyzed with LipidView [21] including de-isotoping, smoothing and isotope correction. Lipid
concentrations were calculated using LipidView by comparison with internal standards. Lipid
concentrations were then exported to Excel [22]. The ratio of PC to PE was calculated as PC
concentration per PE concentration (mol/mol).