Metabolomics profiling of metformin-mediated metabolic reprogramming bypassing AMPKα.

BACKGROUND: Metformin is a first-line drug for treating type 2 diabetes and has gained considerable interest as a potential anticancer agent. Increasing evidence suggests that metformin antagonizes diabetes and tumors through disrupting metabolic homeostasis and altering energy state. However, whether AMP activated protein kinase (AMPK) contributes to such effects of metformin remains controversial.

METHODS: We performed integrative metabolomics analyses to systematically examine the effects of metformin on metabolic pathways in Prkaa1 wild type (WT) and knock-out (KO) mouse embryonic fibroblast (MEF) cells as well as human cells based on gas chromatography-mass spectrometry and capillary electrophoresis-mass spectrometry (CE-MS).

RESULTS: Metformin treatment induced metabolic reprogramming and reduced the energy state of both Prkaa1 WT and KO MEF cells, as evidenced by suppressed tricarboxylic acid (TCA) cycle, elevated lactate production as well as decreased NAD+ /NADH ratio. Additionally, metabolic flux analysis also showed that metformin Ampkα-independently increased metabolic flux from glucose to lactate and decreased metabolic flux from acetyl-CoA to TCA cycle as well as from pyruvate to malate. Moreover, metformin Ampkα-dependently upregulated P-Acc but Ampkα-independently inhibited the levels of P-mTor, PS6, Lc3, Atgl and P-Erk in MEF cells. Similarly, we demonstrated that a commonly used AMPK agonist 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) and fetal bovine serum (FBS) starvation, as a common model for energy stress, both led to Ampkα-independent metabolism alterations in MEF cells. Furthermore, these effects of metformin were also confirmed in human hepatocellular carcinoma (HCC) cells as well as in MCF10A shControl and shPRKAA1 cells. Importantly, we found that metformin could obviously inhibit colony conformation of HCC cells in an Ampkα-independent manner.

CONCLUSIONS: Our data highlight a comprehensive view of metabolic reprogramming mediated by metformin as well as AICAR. These observations suggest that metformin could affect cellular metabolism largely bypassing Ampkα, and may provide a new insight for its clinical usage.