Lactate uptake and metabolism in human breast cells and metabolite excretion.

<p>¹³C NMR spectra of human breast lines indicated evidence of ¹³C-lactate (arrow, 19 ppm) uptake after 24 h exposure to 10 mM ¹³C-3-lactate (<b>A</b>). Lactate measurements of cell media after 5 day incubation with 20 mM unlabeled sodium lactate in glucose-free media showed a significant difference in lactate consumption between MCF7 and MDA-MB-231 cells (mean overall decrease in lactate concentrations were 0.4 mM for the no-cell media control plate, 5.5 mM for MDA-MB-231 media and 18.3 mM for MCF7 media, n = 5, *p < 0.001 compared to MDA-MB-231 and media control, Student’s T-test, <b>B</b>). The increase in cell number of MCF7 and MDA-MB-231 cells at the beginning (day 0) and end (day 5) of lactate treatment show no significant difference (<b>C</b>). Heteronuclear multiple quantum coherence (HMQC) NMR plots of cell lysates treated for 24 h (n = 2) with 10 mM 3-¹³C-lactate (no glucose) showed ¹³C-lactate (dark green “<b>L</b>”) uptake and ¹³C-glutamate (blue “<b>G</b>”), ¹³C-alanine (orange “<b>A</b>”), and ¹³C-pyruvate (red “<b>P</b>”) generation in HMEC (<b>D</b>), MCF7 (<b>E</b>), and MDA-MB-231 cells (<b>F</b>). ¹³C NMR spectra of R3230Ac, MCF7 and MDA-MB-231 cell lysates (bottom) and media (top) show evidence of ¹³C-metabolites in the media of each cell line and in the lysate of MCF7 and MDA-MB-231 cells after 24 h incubation with 40 mM lactate (<b>G</b>). Numeric labels: 1 = ¹³C-Glu γ, 2 = ¹³C-Glu β, 3 = methyl ¹³C- lactate, 4 = methyl ¹³C-Ala