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Al-Nahas, Castangia, Belgacem, Stubiger, and Al-Shaqha: Direct analysis of lipids from blood using matrix-assisted laser desorption ionization (MALDI) mass spectrometry

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 matrix-assisted 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 15–20 μl 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 337 nm nitrogen laser was used in the analysis. Measurements were performed in reflectron positive mode using an acceleration voltage of 20 kV. Red phosphorus was used as the calibrant.

Results: A method for direct lipid blood analysis was developed and described as follows. A volume of 10 µl of blood was mixed 1:1 v/v with a solution of CH3OH/CHCl3 (1:1 v/v). The solution was vortexed and left to separate for 10 minutes, resulting in 6 μl of recoverable solution. After we obtained the blood and made the solution, 10 µl of blood was centrifuged for 4 minutes (30k relative centrifugal force) and 4 µl of plasma recovered. The plasma was then diluted 1:2 v/v with the CH3OH-CHCl3 solution. Stirring and extraction were carried out as above and 4 µl from the organic phase was collected and subjected to MALDI analysis. THAP (2′,4′,6′-Trihydroxyacetophenone) (10 mg/ml) was dissolved in 7:3 v/v CH3OH/H2O (50 mM ammonium citrate) and used as the matrix. Samples were mixed 1:1 v/v with the matrix solution and 1 µl spotted on the MALDI target.

Conclusions: By using only 10 μl of blood, it was possible to obtain a fingerprint of plasma lipids for diagnostic assessment.

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