Quantitative Analysis of Phospholipids Using Nanostructured Laser Desorption Ionization Targets |
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Authors: | Simona Colantonio John T Simpson Robert J Fisher Amichai Yavlovich Julie M Belanger Anu Puri Robert Blumenthal |
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Affiliation: | (1) Protein Chemistry Laboratory, Advanced Technology Program, SAIC-Frederick/NCI-Frederick, PO Box B, Bldg 469/Rm 237, Frederick, MD 21702, USA;(2) Membrane Structure and Function Section, Center for Cancer Research, Nanobiology Program, NCI-Frederick, NIH, Frederick, MD 21702, USA |
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Abstract: | Since its introduction as an ionization technique in mass spectrometry, matrix-assisted laser desorption ionization (MALDI)
has been applied to a wide range of applications. Quantitative small molecule analysis by MALDI, however, is limited due to
the presence of intense signals from the matrix coupled with non-homogeneous surfaces. The surface used in nano-structured
laser desorption ionization (NALDI) eliminates the need for a matrix and the resulting interferences, and allows for quantitative
analysis of small molecules. This study was designed to analyze and quantitate phospholipid components of liposomes. Here
we have developed an assay to quantitate the DPPC and DC8,9PC in liposomes by NALDI following various treatments. To test our method we chose to analyze a liposome system composed of
DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DC8,9PC (1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine), as DC8,9PC is known to undergo cross-linking upon treatment with UV (254 nm) and this reaction converts the monomer into a polymer.
First, calibration curves for pure lipids (DPPC and DC8,9PC) were created using DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) as an internal standard. The calibration curve for both DPPC and DC8,9PC showed an R2 of 0.992, obtained using the intensity ratio of analyte and internal standard. Next, DPPC:DC8,9PC liposomes were treated with UV radiation (254 nm). Following this treatment, lipids were extracted from the liposomes and
analyzed. The analysis of the lipids before and after UV exposure confirmed a decrease in the signal of DC8,9PC of about 90%. In contrast, there was no reduction in DPPC signal. |
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