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

<p>A–B. Abundance and distribution of U-[<sup>13</sup>C]-glucose-derived citrate in metformin-treated 143B osteosarcoma cells. 143B<i>wt</i> and 143B<i>cytb</i> cells were cultured with (+) or without (−) metformin (10 mM) for 12 h, and intracellular metabolites extracted and analyzed by GC-MS. U-[<sup>13</sup>C]-glucose was added for the final 6 h of culture. Shown is the isotopomer distribution (<b>A</b>) and relative abundance (<b>B</b>) of U-[<sup>13</sup>C]-glucose-derived citrate in 143B<i>wt</i> and 143B<i>cytb</i> cells treated as indicated. Data are normalized to cell number and are presented as mean ± SEM for each condition (<i>n</i> = 3), and are representative of two independent experiments. <b>C–D.</b> Abundance and distribution of U-[<sup>13</sup>C]-glutamine-derived citrate in metformin-treated 143B cells. 143B Cells were treated as in (<b>A</b>), with U-[<sup>13</sup>C]-glutamine added for the final 6 h of culture. Isotopomer distribution (<b>C</b>) and relative abundance (<b>D</b>) of U-[<sup>13</sup>C]-glutamine-derived citrate in 143B<i>wt</i> and 143B<i>cytb</i> cells is shown. Data are normalized to cell number. <b>E</b>. Relative palmitate abundance in 143B<i>wt</i> and 143B<i>cytb</i> 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 (<i>n</i> = 3). <b>F–G</b>. Relative abundance of U-[<sup>13</sup>C]-glucose-derived (<b>F</b>) and U-[<sup>13</sup>C]-glutamine-derived (<b>G</b>) lipogenic acetyl-CoA and palmitate in 143B<i>wt</i> and 143B<i>cytb</i> cells cultured in the presence (+) or absence (−) of metformin (10 mM) for 72 h. Cells were cultured for 72 h, with U-[<sup>13</sup>C]-glucose or U-[<sup>13</sup>C]-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. *, <i>p</i> < 0.05; **, <i>p</i> < 0.01. Raw data for this figure can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002309#pbio.1002309.s005" target="_blank">S5 Data</a>.</p>