Metformin is a widely used drug for treatment of type 2 diabetes with no defined cellular mechanism of action. Its glucose-lowering effect results from decreased hepatic glucose production and increased glucose utilization. Metformin's beneficial effects on circulating lipids have been linked to reduced fatty liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of lipid and glucose metabolism. Here we report that metformin activates AMPK in hepatocytes; as a result, acetyl-CoA carboxylase (ACC) activity is reduced, fatty acid oxidation is induced, and expression of lipogenic enzymes is suppressed. Activation of AMPK by metformin or an adenosine analogue suppresses expression of SREBP-1, a key lipogenic transcription factor. In metformin-treated rats, hepatic expression of SREBP-1 (and other lipogenic) mRNAs and protein is reduced; activity of the AMPK target, ACC, is also reduced. Using a novel AMPK inhibitor, we find that AMPK activation is required for metformin's inhibitory effect on glucose production by hepatocytes. In isolated rat skeletal muscles, metformin stimulates glucose uptake coincident with AMPK activation. Activation of AMPK provides a unified explanation for the pleiotropic beneficial effects of this drug; these results also suggest that alternative means of modulating AMPK should be useful for the treatment of metabolic disorders.

/pdf/role-of-amp-activated-protein-kinase-in-mechanism-of-3m7xecnts5.pdf

Role of AMP-activated protein kinase in mechanism of metformin action

A large number of tiny noncoding RNAs have been cloned and named microRNAs (miRs). Recently, we have reported that miR-15a and miR-16a, located at 13q14, are frequently deleted and/or down-regulated in patients with B cell chronic lymphocytic leukemia, a disorder characterized by increased survival. To further investigate the possible involvement of miRs in human cancers on a genome-wide basis, we have mapped 186 miRs and compared their location to the location of previous reported nonrandom genetic alterations. Here, we show that miR genes are frequently located at fragile sites, as well as in minimal regions of loss of heterozygosity, minimal regions of amplification (minimal amplicons), or common breakpoint regions. Overall, 98 of 186 (52.5%) of miR genes are in cancer-associated genomic regions or in fragile sites. Moreover, by Northern blotting, we have shown that several miRs located in deleted regions have low levels of expression in cancer samples. These data provide a catalog of miR genes that may have roles in cancer and argue that the full complement of miRs in a genome may be extensively involved in cancers.

https://www.pnas.org/content/pnas/101/9/2999.full.pdf

Human microRNA genes are frequently located at fragile sites and genomic regions involved in cancers

https://www.cell.com/cell/pdf/S0092-8674(05)00109-1.pdf

Mitochondria, Oxidants, and Aging

AMP-activated protein kinase: Ancient energy gauge provides clues to modern understanding of metabolism

Metabolic Reprogramming: A Cancer Hallmark Even Warburg Did Not Anticipate

Dimethylbiguanide inhibits cell respiration via an indirect effect targeted on the respiratory chain complex I.

Carbonylated proteins were visualized in single cells of the budding yeast Saccharomyces cerevisiae, revealing that they accumulate with replicative age. Furthermore, carbonylated proteins were not inherited by daughter cells during cytokinesis. Mother cells of a yeast strain lacking the sir2 gene, a life-span determinant, failed to retain oxidatively damaged proteins during cytokinesis. These findings suggest that a genetically determined, Sir2p-dependent asymmetric inheritance of oxidatively damaged proteins may contribute to free-radical defense and the fitness of newborn cells.

http://science.sciencemag.org/content/sci/299/5613/1751.full.pdf

Asymmetric inheritance of oxidatively damaged proteins during cytokinesis.

The Warburg and Crabtree effects: On the origin of cancer cell energy metabolism and of yeast glucose repression.

Mitochondria are the main source of reactive oxygen species in the cell These reactive oxygen species have long been known as being involved in oxidative stress This is a review of the mechanisms involved in reactive oxygen species generation by the respiratory chain and some of the dehydrogenases and the control by thermodynamic and kinetic constraints Mitochondrial ROS produced at the level of the bc1 complex as well at the level of complex I are discussed It was recognized more than a decade ago that they can also function as signaling molecules This signaling role will be developed both in terms of mechanism and in terms of mitochondrial ROS signaling The notion that hydrogen peroxide acts not only as a damaging oxidant but also as a signaling molecule was proposed more than a decade ago Hydrogen peroxide signaling can be either direct (oxidation of its target) or indirect (involving peroxiredoxins, for example) The consequences of ROS signaling on crucial biologic processes such as c

Mitochondrial ROS Generation and Its Regulation: Mechanisms Involved in H2O2 Signaling

Mitochondrial reactive oxygen species (ROS) production was investigated in mitochondria extracted from liver of rats treated with or without metformin, a mild inhibitor of respiratory chain complex 1 used in type 2 diabetes. A high rate of ROS production, fully suppressed by rotenone, was evidenced in non-phosphorylating mitochondria in the presence of succinate as a single complex 2 substrate. This ROS production was substantially lowered by metformin pretreatment and by any decrease in membrane potential (Delta Phi(m)), redox potential (NADH/NAD), or phosphate potential, as induced by malonate, 2,4-dinitrophenol, or ATP synthesis, respectively. ROS production in the presence of glutamate-malate plus succinate was lower than in the presence of succinate alone, but higher than in the presence of glutamate-malate. Moreover, while rotenone both increased and decreased ROS production at complex 1 depending on forward (glutamate-malate) or reverse (succinate) electron flux, no ROS overproduction was evidenced in the forward direction with metformin. Therefore, we propose that reverse electron flux through complex 1 is an alternative pathway, which leads to a specific metformin-sensitive ROS production.

Michel Rigoulet

Papers

Dimethylbiguanide inhibits cell respiration via an indirect effect targeted on the respiratory chain complex I.

Asymmetric inheritance of oxidatively damaged proteins during cytokinesis.

The Warburg and Crabtree effects: On the origin of cancer cell energy metabolism and of yeast glucose repression.

Mitochondrial ROS Generation and Its Regulation: Mechanisms Involved in H2O2 Signaling

The ROS Production Induced by a Reverse-Electron Flux at Respiratory-Chain Complex 1 is Hampered by Metformin