Mass Spectrometry Imaging of Lipid and Metabolite Distributions in Cysts of <i>Besnoitia besnoiti</i>-Infected Bovine Skin

Bovine besnoitiosis is a disease caused by the obligate intracellular parasite <i>Besnoitia besnoiti</i>. During its chronic stage, the parasite forms large, thick-walled cysts of up to 600 μm in diameter in the skin and other tissues. To assess an overview of parasite-induced metabolic changes during chronic infection, <i>B. besnoiti</i>-infected skin samples were analyzed by high-resolution atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI). Overall, infection-driven, significant changes of 467 lipids and metabolites were found in comparison to noninfected control samples. Most of them belong to the group of phosphatidic acids (PAs), phosphatidylserines (PSs), phosphatidylcholines (PCs)/phosphatidylethanolamines (PEs), triacylglycerides (TGs), phosphatidylinositols (PIs) and phosphatidylglycerols (PGs). When these quantitative data were combined with analyses on the lateral distribution of respective infection markers, MS images of significantly changed ion signals with specific lateral distributions were generated, matching with typical biological structures as observed in Hematoxylin and eosin (H&E)-stained tissue sections. Ultrahigh-resolution MALDI MSI with a pixel size of 2 μm and 3-dimensional reconstruction gave further insights into cyst construction.