Metformin requires functional mitochondrial electron transport to suppress de novo lipogenesis.

A–B. Abundance and distribution of U-[13C]-glucose-derived citrate in metformin-treated 143B osteosarcoma cells. 143Bwt and 143Bcytb cells were cultured with (+) or without (−) metformin (10 mM) for 12 h, and intracellular metabolites extracted and analyzed by GC-MS. U-[13C]-glucose was added for the final 6 h of culture. Shown is the isotopomer distribution (A) and relative abundance (B) of U-[13C]-glucose-derived citrate in 143Bwt and 143Bcytb cells treated as indicated. Data are normalized to cell number and are presented as mean ± SEM for each condition (n = 3), and are representative of two independent experiments. C–D. Abundance and distribution of U-[13C]-glutamine-derived citrate in metformin-treated 143B cells. 143B Cells were treated as in (A), with U-[13C]-glutamine added for the final 6 h of culture. Isotopomer distribution (C) and relative abundance (D) of U-[13C]-glutamine-derived citrate in 143Bwt and 143Bcytb cells is shown. Data are normalized to cell number. E. Relative palmitate abundance in 143Bwt and 143Bcytb cells cultured with (+) or without (−) metformin (10 mM) for 72 h. Data are normalized to cell number and presented as mean ± SEM for each condition (n = 3). F–G. Relative abundance of U-[13C]-glucose-derived (F) and U-[13C]-glutamine-derived (G) lipogenic acetyl-CoA and palmitate in 143Bwt and 143Bcytb cells cultured in the presence (+) or absence (−) of metformin (10 mM) for 72 h. Cells were cultured for 72 h, with U-[13C]-glucose or U-[13C]-glutamine added for the final 24 h of culture. Data are normalized to cell number, are presented as mean ± SEM for triplicate samples, and are representative of three independent experiments. *, p < 0.05; **, p < 0.01. Raw data for this figure can be found in S5 Data.