Mimic hypoxia improves angiogenesis in ischaemic random flaps

Abstract

Hypoxia is the original signal to promote angiogenesis in ischaemic tissues. However, hypoxia-induced angiogenesis usually cannot compensate for the ischaemic injury in surgery, resulting in tissue necrosis. Mimic hypoxia may be an option to improve angiogenesis for the purpose of preventing or reducing necrosis. In this study, the authors explored the feasibility of applying hypoxic mimic--deferoxamine (DFO) to the treatment of ischaemic random skin flaps. Ischaemic random skin flap models were developed in 18 nude mice using a cutaneous marking technique. The mice were divided into a DFO-treated group and a control group. Vascular endothelial growth factor (VEGF) protein level, vessel density and flap survival rate were evaluated on the seventh postoperative day. In vitro, both VEGF mRNA expression and protein level were investigated in endothelial cells and fibroblasts under DFO, hypoxia and normoxia conditions. The (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to study the impact of DFO-induced VEGF up-regulation on endothelial cell viability after severe hypoxia injury. The flap survival rate, vessel density and VEGF level in the DFO group are significantly higher than in the control group. In vitro, DFO-induced increase in VEGF mRNA expression translated into 2.3- and 5.8-fold increases in VEGF protein secretion in DFO-conditioned media of endothelial cells and fibroblasts, respectively. The MTT assay showed that the cell viability both in the DFO group and in the VEGF group was significantly higher than in the control group. VEGF praracrine and autocrine secretion in fibroblasts and in endothelial cells play an important role in DFO-induced angiogenesis, which improves ischaemic flap survival. DFO-induced VEGF autocrine secretion also protects endothelial cells from severe hypoxia injury.