Isotope-dilution UPLC-MS/MS determination of cell-secreted bioactive lipids

Secreted bioactive lipids play critical roles in cell-to-cell communication and have been implicated in inflammatory immune responses such as anaphylaxis, vasodilation, and bronchoconstriction. Analysis of secreted bioactive lipids can be challenging due to their relatively short lifetimes and structural diversity. Herein, a method has been developed using ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to quantify five cell-secreted, structurally and functionally diverse bioactive lipids (PGD ₂, LTC₄, LTD₄, LTE₄, PAF) that play roles in inflammation. Sample analysis time is 5 min, and isotopically labeled internal standards are used for quantification. This method was applied to an immortal secretory cell line (RBL-2H3), a heterogeneous primary cell culture containing peritoneal mast cells, and murine platelets. In RBL cell supernatant samples, intrasample precisions ranged from 7.32-21.6%, averaging 17.0%, and spike recoveries in cell supernatant matrices ranged from 88.0-107%, averaging 97.0%. Calibration curves were linear from 10 ng mL^-1 to 250 ng mL^-1, and limits of detection ranged from 0.0348 ng mL^-1 to 0.803 ng mL^-1. This method was applied to the determination of lipid secretion from mast cells and platelets, demonstrating broad applicability for lipid measurement in primary culture biological systems.