Direct analysis of lipids from blood using matrix-assisted laser desorption ionization (MALDI) mass spectrometry

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Introduction: Lipids are essential biological pathways involved in metabolism, signalling and energy storing. However, abnormal lipid levels, such as cholesterol, play a crucial role in heart diseases and type 2 diabetes mellitus. Knowing cholesterol levels is therefore essential in monitoring the metabolic functions of the individual and preventing chronic and lethal diseases. Objectives: To evaluate the potential of matrixassisted laser desorption ionization (MALDI) mass spectrometry as a fast and reliable method for the direct screening of patients. Materials and methods: An aliquot consisting of 15– 20μl of human blood was collected from the finger. Lipids were extracted from blood either by direct extraction or after a preliminary centrifugation and plasma separation. An Axima Performance MALDI-ToF-ToF (Shimadzu, Manchester, UK) equipped with a 337nm nitrogen laser was used in the analysis. Measurements were performed in reflectron positive mode using an acceleration voltage of 20kV. Red phosphorus was used as the calibrant. Results: A method for direct lipid blood analysis was developed and described as follows. A volume of 10μl of blood was mixed 1:1 v/v with a solution of CH3 OH/ CHCl3 (1:1 v/v). The solution was vortexed and left to separate for 10 minutes, resulting in 6μ l of recoverable solution. After we obtained the blood and made the solution, 10μl of blood was centrifuged for 4 minutes (30k relative centrifugal force) and 4μl of plasma recovered. The plasma was then diluted 1:2 v/v with the CH3 OH-CHCl3 solution. Stirring and extraction were carried out as above and 4μl from the organic phase was collected and subjected to MALDI analysis. THAP (2′ ,4′ ,6′ -Trihydroxyacetophenone) (10mg/ml) was dissolved in 7:3 v/v CH3 OH/H2 O (50mMammonium citrate) and used as the matrix. Samples were mixed 1:1 v/v with the matrix solution and 1μl spotted on the MALDI target. Conclusions: By using only 10μ l of blood, it was possible to obtain a fingerprint of plasma lipids for diagnostic assessment.