What is the ability of inflamed endothelium to uptake exogenous saturated fatty acids? A proof-of-concept study using spontaneous Raman, SRS and CARS microscopy

Endothelial cells (EC) in vivo buffer and regulate the transfer of plasma fatty acid (FA) to the underlying tissues. We hypothesize that inflammation could alter the functionality of the EC, i.e., their capacity and uptake of different FA. The aim of this work is to verify the functionality of inflamed cells by analyzing their ability to uptake and accumulate exogenous saturated FA. Control and inflammatory human microvascular endothelial cells stimulated in vitro with two deuterium-labeled saturated FA (D-FA), i.e., palmitic (D(31)-PA) and myristic (D(27)-MA) acids. Cells were measured both by spontaneous and stimulated Raman imaging to extract detailed information about uptaken FA, whereas coherent anti-Stokes Raman scattering and fluorescence imaging showed the global content of FA in cells. Additionally, we employed atomic force microscopy to obtain a morphological image of the cells. The results indicate that the uptake of D-FA in inflamed cells is dependent on their concentration and type. Cells accumulated D-FA when treated with a low concentration, and the effect was more pronounced for D(27)-MA, in normal cells, but even more so, in inflamed cells. In the case of D(31)-PA, a slightly increased uptake was observed for inflamed cells when administered at higher concentration. The results provide a better understanding of the EC inflammation and indicate the impact of the pathological state of the EC on their capacity to buffer fat. All the microscopic methods used showed complementarity in the analysis of FA uptake by EC, but each method recognized this process from a different perspective.