Metformin is the first-line medication for Type 2 diabetes (T2D) treatment, and it is the only US FDA approved oral antidiabetic medication for pediatric patients with T2D 10 years and older. Metformin is also used to treat polycystic ovary syndrome (PCOS), another condition with underlying insulin resistance. The clinical applications of metformin are continuing to expand into other fields including cancer, aging, cardiovascular diseases, and neurodegenerative diseases. Metformin modulates multiple biological pathways. Its novel properties and effects continue to evolve; however, its molecular mechanism of action remains incompletely understood. In this chapter, we focus on the recent translational research and clinical data on the molecular action of metformin and the evidence linking the effects of metformin on insulin resistance, prediabetes, diabetes, aging, cancer, PCOS, cardiovascular diseases, and neurodegenerative diseases. Metformin 2
Mechanisms of actionThe potential mechanisms of metformin action involve several pathways. The AMPK-pathway plays an important role in metformin actions [2, 3]. Metformin inhibits the mitochondrial respiratory chain (complex I), which increases the AMP to ATP ratio, leading to the phosphorylation of AMP-activated protein kinase (AMPK) at Thr-172. We have demonstrated that metformin treatment increases protein level of phosphorylated AMPK in high-glucose-treated endothelial cells [4]. The phosphorylated AMPK subsequently phosphorylates multiple downstream effectors to regulate cellular metabolism and energy homeostasis [5]. These downstream effectors include thioredoxin interacting protein (TXNIP) and TBC1D1, a RAB-GTPase activating protein and a member of the tre-2/BUB2/cdc1 domain family. Phosphorylated TXNIP and TBC1D1 increase the plasma membrane localization of glucose transporter 1 (GLUT1) and GLUT4, respectively [6, 7], and regulate glycogen synthases (GYS1 and GYS2) to prevent the storage of glycogen [8]. Some actions of metformin have been found to be AMPK-independent [9].In diabetic mice, metformin has an effect on gut microbiota by inducing a profound shift in the gut microbial community profile, resulting in an increase in the Akkermansia spp. population [10] and cAMP-induced agmatine production [11], which may decrease absorption of glucose from the gastrointestinal tract and increase lipid metabolism respectively. In addition, metformin decreases insulin-induced suppression of fatty acid oxidation and lowers lipid content of hepatic cells [12].New Insight into Metformin Mechanism of Action and Clinical Application DOI: http://dx.doi.org/10.5772/intechopen.91148 association with insulin resistance. Metformin decreases the level of circulating branched-chain amino acids and reduces insulin resistance in a high-fat diet mouse model [22]. Metformin treatment lowers plasma ADMA which is associated with improved glycemic control in patients with T2D [23].Recent studies indicate that phosphatidylinositol-3-kinase/protein kinase B protein (PI3K/PKB, also known as ...