Spatial Analysis of Phosphatidylinositol Molecular Species in Pork Chop Tissues Using Matrix-assisted Laser Desorption/ionization-Mass Spectrometry Imaging

Matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) is a powerful technique for visualizing lipids in biological tissues. Phosphatidylinositol (PI), a phospholipid in pork, is a major source of inositol in animal-derived foods believed to be protective against diseases related to pregnancy and cancer. However, the distribution of PI molecular species in pork is not well understood. Here, we performed MALDI-MSI analysis to investigate the distribution and composition of PI molecular species in pork chop comprising Longissimus thoracis et lumborum muscle (loin), intermuscular fat tissue, transparent tissue, and spinalis muscle. Twelve diacyl-PI molecular species were identified using liquid chromatography-electrospray ionization-tandem mass spectrometry (MS/MS) and MALDI-MS/MS analysis and visualized using MALDI-MSI. Spinalis muscle had the highest amount of identified PI molecular species, followed by loin, transparent tissue, and intermuscular fat tissue. The diacyl-PI molecular species containing hexadecadienoic, oleic, linoleic and eicosadienoic acids at the sn-2 position were mainly abundant in the loin and spinalis muscle, whereas those containing mead, arachidonic, docosatetraenoic, and docosapentaenoic acids at the sn-2 position were mainly abundant in both muscles as well as transparent tissues. Notably, the balance of PI molecular species differed among the tissues depending on fatty acid compositions at the sn-2 position. These results suggested that MALDI-MSI is a promising tool for assessing the association between individual pork tissues and the protective effects of PI molecular species against diseases related to pregnancy and cancer. To the best of our knowledge, this is the first report showing tissue-specific distributions of PI molecular species in pork chop using MALDI-MSI.