Quantification of diacylglycerols by capillary gas chromatography-negative ion chemical ionization-mass spectrometry

We describe a method for quantifying diacylglycerols as their 1-pentafluorobenzoyl-2-acyl-3-acetyl-glycerol derivatives by capillary gas chromatography-negative ion chemical ionization-mass spectrometry. The basis of the method resides in the sequential treatment of diacylglycerols with acetic anhydride, pancreatic lipase, and pentafluorobenzoyl chloride. Cultured rat mesenteric artery vascular smooth muscle cells (VSMC) were incubated for 20 min in the presence of vehicle or vasopressin (10(-7) M). The incubations were stopped by aspirating the medium and adding 2 ml of methanol containing 790 pmol of internal standard 1-stearoyl-2-(10,13)-nonadecadienoyl- glycerol. After extraction, diacylglycerols were isolated by thin-layer chromatography, acetylated, and treated with pancreatic lipase. The resulting 2-acyl-3-acetylglycerols were then purified by thin-layer chromatography, transformed into their 1-pentafluorobenzoyl-derivatives, and monitored by capillary gas chromatography-negative ion chemical ionization-mass spectrometry on the selected ion-monitoring mode (m/z 614 and 604 for 2-arachidonoyl and 2-nonadecadienoyl species, respectively). The levels of diacylglycerols bearing an arachidonoyl moiety were 128 +/- 26 pmol/100 nmol lipid phosphorus in resting cells and 333 +/- 28 in stimulated cells (mean +/- SD, n = 3, P < 0.01). The presence of diacylglycerol species bearing an oleoyl or a linoleoyl group at the second position could also be detected in VSMC preparations by this approach. This new method can be applied to quantitate various diacylglycerol species bearing distinct acyl moieties at the second position of the glycerol molecule.