Metformin promotes the survival of random skin flaps via the activation of Nrf2/HO-1 signaling

The random flap is one of the commonly used techniques for tissue defect repair in surgery and orthopaedics, however the risk of ischaemic necrosis at the distal end of the flap limits its size and clinical application. Metformin (Met) is a first-line medication in the treatment of type 2 diabetes, with additional effects such as anti-tumor, anti-aging, and neuroprotective properties. In this study, we aimed to investigate the biological effects and potential mechanisms of Met in improving the survival of random skin flaps. Twenty-four male Sprague-Dawley rats and 12 male C57BL/6J mice underwent McFarlane flap surgery and divided into control (Ctrl) and Met groups (100 mg/kg). The survival rate of the flap were evaluated on day 7. Angiography, Laser doppler blood flow imaging, and H&E staining were used to assess blood flow supply and the levels of microvascular density. Then, reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were measured by test kits. Immunohistochemistry analysis was conducted to evaluate the expression of Vascular Endothelial Growth Factor A (VEGFA), Vascular endothelial cadherin (VE-cadherin) and CD31. Rats and mice in the Met group exhibited higher flap survival rate, microcirculatory flow, and higher expression levels of VEGFA and VE-cadherin compared with the Ctrl group. In addition, the level of oxidative stress was significantly lower in the met group. And then we demonstrated that the human umbilical vein endothelial cells (HUVECs) treated with Met can alleviate tert-butyl hydroperoxide (TBHP)-stimulated cellular dysfunction and oxidative stress injury. Mechanistically, Met markedly stimulated the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1), and promoted Nrf2 nuclear translocation. Silencing of Nrf2 partially abolished the antioxidant and therapeutic effects of Met. In summary, our data have confirmed that Met has a positive effect on flap survival and reduces necrosis. The mechanism of action involves the regulation of the Nrf2/HO-1 signaling pathway to combat oxidative stress and reduce damage.