Drug metabolite heterogeneity in cultured single cells profiled by pico-trapping direct mass spectrometry.

We investigated the heterogeneity of tafluprost metabolism in primary human hepatocytes at a single-cell level by live single-cell mass spectrometry (MS). Picoliter volumes of cytoplasm were analyzed by nano-electrospray ionization MS in order to obtain single-cell metabolite profiles. The subcellular components of a single tafluprost-treated human hepatocyte were isolated and the single-cell metabolite profile was compared with those of traditional bulk hepatocyte analysis. In the bulk hepatocyte analysis, liquid chromatography-MS showed the averaged metabolism of tafluprost to tafluprost acid (TA) and β-oxidized metabolites. However, live single-cell MS showed that tafluprost metabolism varied among individual cells. In addition, there was significant variation in the quantities of TA and a major metabolite, dinor-TA, among cells, whereas there was no significant variation in 7-ethoxycoumarin metabolism. Thus, live single-cell MS successfully detected the heterogeneity of drug metabolism in individual living hepatocytes.