Imaging of lipids in human adipose tissue by cluster ion TOF-SIMS.

Biopsies of human subcutaneous adipose tissue were taken from healthy donors. Samples were high-pressure frozen, freeze-fractured, and freeze dried. Imaging mass spectrometry of samples was performed in a TOF-SIMS mass spectrometer equipped with a bismuth cluster ion source. Blood vessels, the connective tissue, and adipocytes can be seen in TOF-SIMS images. Blood vessels were found labeled by a high content of sodium ions and potassium ions in their lumen and phosphocholine signal in smooth muscle cells of the vessel wall. The connective tissue showed high signal levels of CN(-) fragments, derived from proteins and nucleic acids. Adipocytes showed high signal levels of phosphocholine and cholesterol ubiquitously in their membranes and diacylglycerols in some membrane sites. The central part of adipocytes showed high levels of triacylglycerols and fatty acids. These results are in accordance to those of biochemical studies; however, a precise spatial localization of lipids in adipocytes is demonstrated with MS imaging.