Functional Characterization of Putative Novel MicroRNA-1133 in the Antioxidant Effects of Metformin in Hyperglycemia-Induced Endothelial Cells

Diabetes mellitus induces endothelial dysfunction and oxidative stress, contributing to the development of vascular complications. Although metformin exerts well-established vasculoprotective and antioxidant effects, the molecular mechanisms underlying these actions remain incompletely understood. Novel miR-1133 was previously identified as a metformin-responsive putative microRNA (miRNA), and bioinformatic analysis identified PIK3CA as a biologically plausible candidate target for further investigation. This study investigated the functional significance of novel miR-1133 in the antioxidant effects of metformin in hyperglycemia-induced human umbilical vein endothelial cells (HUVECs). HUVECs were exposed to normal glucose (5.5 mmol/L), hyperglycemia (33.3 mmol/L), or hyperglycemia supplemented with metformin (10 μM) for 24 h. Metformin-treated hyperglycemic HUVECs were subsequently transfected with a novel miR-1133 mimic during continued hyperglycemic and metformin exposure. PIK3CA expression and oxidative stress markers, including reactive oxygen species (ROS), superoxide dismutase (SOD), and 8-hydroxy-2′-deoxyguanosine (8-OHdG), were evaluated. Hyperglycemia increased novel miR-1133 expression, whereas metformin reduced its expression. Metformin treatment was associated with increased PIK3CA mRNA and protein expression, reduced ROS and 8-OHdG levels, and increased SOD expression and activity. Novel miR-1133 mimic transfection was associated with reduced PIK3CA expression, increased ROS and 8-OHdG levels, and decreased SOD expression and activity compared with the corresponding transfection control. Collectively, these findings demonstrate that metformin attenuates oxidative stress in hyperglycemia-induced endothelial cells and overall provide the first functional characterization of novel miR-1133. The reciprocal changes in PIK3CA expression and oxidative stress observed following novel miR-1133 mimic transfection suggest that novel miR-1133 may represent a candidate mediator of the endothelial antioxidant responses associated with metformin. Further studies are required to validate the direct interaction between novel miR-1133 and PIK3CA and to elucidate the underlying molecular mechanisms.