Diabetic wounds are a serious complication of diabetes mellitus (DM) that can lead to persistent infection, amputation, and even death. Prolonged oxidative stress has been widely recognized as a major instigator in the development of diabetic wounds; therefore, oxidative stress is considered a promising therapeutic target. In the present study, Keap1/Nrf2 signaling was confirmed to be activated in streptozotocin (STZ)-induced diabetic mice and methylglyoxal (MGO)-treated human umbilical vein endothelial cells (HUVECs). Knockdown of Keap1 by siRNA reversed the increase in Keap1 levels, promoted the nuclear translocation of Nrf2, and increased the expression of HO-1, an antioxidant protein. To explore therapeutic delivery strategies, milk-derived exosomes (mEXOs) were developed as a novel, efficient, and non-toxic siRNA carrier. SiRNA-Keap1 (siKeap1) was loaded into mEXOs by sonication, and the obtained mEXOs-siKeap1 were found to promote HUVEC proliferation and migration while relieving oxidative stress in MGO-treated HUVECs. Meanwhile, in a mouse model of diabetic wounds, injection of mEXOs-siKeap1 significantly accelerated diabetic wound healing with enhanced collagen formation and neovascularization. Taken together, these data support the development of Keap1 knockdown as a potential therapeutic strategy for diabetic wounds and demonstrated the feasibility of mEXOs as a scalable, biocompatible, and cost-effective siRNA delivery system.

Graphical Abstract

The therapeutic effect of siKeap1-loaded mEXOs on diabetic wound healing was assessed. First, we found that the expression of Keap1 was upregulated in the wounds of diabetic mice and in human umbilical vein endothelial cells (HUVECs) pretreated with methylglyoxal (MGO). Next, we extracted exosomes from raw milk by differential centrifugation and loaded siKeap1 into milk-derived exosomes by sonication. The in vitro application of the synthetic complex (mEXOs-siKeap1) was found to increase the nuclear localization of Nrf2 and the expression of the antioxidant protein HO-1, thus reversing oxidative stress. Furthermore, in vivo mEXOs-siKeap1 administration significantly accelerated the healing rate of diabetic wounds (Scheme 1).

Scheme 1 Schematic diagram. A Synthesis of mEXOs-siKeap1 complex. B Mechanism of mEXOs-siKeap1 in vitro. C The treatment effect of mEXOs-siKeap1 on an in vivo mouse model of diabetic wounds