One-Step Detection of Major Lipid Components in Submicroliter Volumes of Unpurified Liposome and Cell Suspensions

Abstract

Liposomes and cells have high lipid contents, which are the main components of the external and internal membranes. Mass spectrometry (MS) is widely used in the analysis of the lipids present in the biological matrixes. However, MS analysis of liposome and cell suspensions is challenging due to the presence of other high-abundance matrix components (e.g., salts, buffers, and growth media) that cause ion suppression. These interfering species would normally be removed by dialysis or centrifugation. Here we propose a simple and fast method to detect major lipid components in cells and cell suspensions by MS while circumventing dialysis and centrifugation. Capillary hydrodynamic chromatography (HDC) has been coupled online with the aid of an electrospray ionization (ESI) interface to an ion-trap mass spectrometer. Complex samples containing biopartides and a large amount of potential interferences (buffer, inorganic salts, amino acids) were separated hydrodynamically, detected optically (by light absorption/scattering), and immediately transferred to the MS interface. Liposomes and animal cells are disintegrated during electrospray, and the constituent lipids are ionized. The signal-to-noise ratios are similar to 10x higher in HDC-ESI-MS than in direct infusion ESI-MS experiments (with or without dilution). This method has been tested on liposomes (containing phosphatidylcholine and phosphatidylglycerol) and four types of animal/human cells, i.e., mouse macrophages (RAW 264.7), human breast cancer cells (T47D and HsS78T), and mouse preadipoc-yte cells (3T3-L1). We suggest that HDC-ESI-MS can be used in quality control analyses of bioparticle suspensions in the fields of biotechnology, molecular biology, drug discovery, and cosmetics.