Mapping Out Lipids

French researchers have used mass spectrometry imaging to map the distributions of lipids in biopsies of patients with nonalcoholic fatty liver disease (Anal. Chem., DOI: 10.1021/ac900045m). In this disease, triacylglycerols (TAGs) and diacylglycerols (DAGs) accumulate in the liver. Alain Brunelle of the Institute of Natural Substances Chemistry, in Gif-sur-Yvette, and coworkers used time-of-flight secondary-ion mass spectrometry (TOF-SIMS) to map the lipids in liver tissue samples at the micrometer scale. One hallmark of nonalcoholic fatty liver disease is a condition known as steatosis, which is characterized by the formation of vesicles enriched in lipids, especially TAGs and DAGs. In steatotic regions of the liver samples, the researchers observed the accumulation of TAGs, DAGs, monoacylglycerols, and fatty acids. They detected more DAGs than TAGs, even though TAGs are usually a major component of steatotic vesicles. Some of the observed DAGs could be the result of TAG fragmentation in the mass spectrometer source, the researchers note. They also compared the lipid profiles of nonsteatotic regions of fatty liver with those of normal liver and found significant differences in lipid composition. Such measurements could help understand the earliest stages of nonalcoholic fatty liver disease.