Investigation of the Lipid Changes That Occur in Hypertrophic Muscle due to Fish Protein-feeding Using Mass Spectrometry Imaging

: Alaska pollack protein (APP) was previously shown to reduce serum triacylglycerol and the atherogenic index and significantly increase gastrocnemius muscle mass in rats. To determine which myofibers are involved in this observed hypertrophy, we stained the gastrocnemius muscle with fast and slow fiber-specific antibodies and measured the muscle fiber diameter. We observed muscle hypertrophy in both the fast and slow fibers of APP-fed rats. Although muscle hypertrophy leads to drastic lipid changes, the amount of lipids did not differ significantly between casein-fed and APP-fed rats. To determine the lipid changes at the molecular species level and their localization, we performed matrix-assisted laser desorption/ionization mass spectrometry imaging to visualize lipids in the gastrocnemius muscles. We determined that lipid molecules were significantly changed due to APP feeding. Thus, APP feeding changes muscle lipid metabolism, and these metabolic changes might be related to hypertrophy.