title: Metformin increases mitochondrial energy formation in L6 muscle cell cultures.
abstract: A popular hypothesis for the action of metformin, the widely used anti-diabetes drug, is the inhibition of mitochondrial respiration, specifically at complex I. This is consistent with metformin stimulation of glucose uptake by muscle and inhibition of gluconeogenesis by liver. Yet, mitochondrial inhibition is inconsistent with metformin stimulation of fatty acid oxidation in both tissues. In this study, we measured mitochondrial energy production in intact cells adapting an in vivo technique of phosphocreatine (PCr) formation following energy interruption ("PCr recovery") to cell cultures. Metformin increased PCr recovery from either dinitrophenol (DNP) or azide in L6 cells. We found that metformin alone had no effect on cell viability as measured by total ATP concentration, trypan blue exclusion, or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction. However, treatments with low concentrations of DNP or azide reversibly decreased ATP concentration. Metformin increased 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction during recovery from either agent. Viability measured by trypan blue exclusion indicated that cells were intact under these conditions. We also found that metformin increased free AMP and, to a smaller extent, free ADP concentrations in cells, an action that was duplicated by a structurally unrelated AMP deaminase inhibitor. We conclude that, in intact cells, metformin can lead to a stimulation of energy formation, rather than an inhibition.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy and Health Sciences, St. John's University, Queens, New York 11439, USA.
authors.forename: Veeravenkata S
authors.initials: VS
authors.lastname: Vytla
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Ochs
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001386:Azides / Q000494:pharmacology; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004140:Dinitrophenols / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007004:Hypoglycemic Agents / Q000494:pharmacology; D008687:Metformin / Q000494:pharmacology*; D008931:Mitochondria, Muscle / Q000187:drug effects* / Q000378:metabolism; D032342:Muscle Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D013997:Time Factors; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D001386:Azides; D004140:Dinitrophenols; D007004:Hypoglycemic Agents; D014475:Uncoupling Agents; D010725:Phosphocreatine; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D008687:Metformin
keywords: AMP; AMP Kinase; AMP-activated kinase (AMPK); ATP; Cell Metabolism; Metabolic Regulation; Mitochondrial Metabolism