ABSTRACT
Metformin is widely used for the treatment of type 2 diabetes mellitus. Although this biguanide derivative has been used for more than 50 years, its mechanism of action has not been fully elucidated. In this article we describe the latest achievements concerning the mechanisms of antihyperglycemic action of metformin. They include: decrease of glucose absorption in the small intestine, increase of glucose transport into cells, decrease in the plasma free fatty acid concentrations and inhibition of gluconeogenesis. Activation of AMP-activated protein kinase (AMPK) plays an important role in these processes. The latest discoveries have revealed mechanisms of anti-atherosclerotic, hypotensive and anticancer action of metformin and its impact on vein endothelial function. The pleiotropic actions of metformin include impact on plasma lipid profile, decrease of oxidative stress, and increase in plasma fibrinolytic activity. Although metformin is not metabolized, the latest research has shown that it is actively transported into hepatocytes and renal tubular epithelium, by OCT1 (organic cation transporter 1, encoded by the SLC22A1 gene) and OCT2 (organic cation transporter 2, encoded by the SLC22A2 gene), respectively. However, MATE1 transporter (multidrug and toxin extrusion 1 protein) is encoded by the SLC47A1 gene and facilitates metformin excretion from these cells into bile and urine. Metformin transporter gene polymorphisms may contribute to significant variation in drug response. Further studies of mechanisms of metformin action could contribute to its wider use for the prevention of type 2 diabetes mellitus, cancer, and Alzheimer's disease, and for the treatment of type 1 diabetes mellitus, and polycystic ovary syndrome (PCOS).