Short-term hypoxia promotes vascularization in co-culture system consisting of primary human osteoblasts and outgrowth endothelial cells

Prevascularization of tissue constructs before implantation has been developed as a novel and promising concept for successful implantation. Since hypoxia might induce angiogenesis, we have investigated the effects of hypoxic treatment on vascularization by using co-cultures of primary human osteoblasts (POBs) and outgrowth endothelial cells. Our results show that: (a) repeated short-term hypoxia (2% O₂ for 8 hr), not long-term hypoxia (2% O₂ for 24 hr), over 1 or 2 weeks, significantly enhances microvessel formation in co-cultures; (b) sustained hypoxia, not short-term or long-term hypoxia, causes cytotoxicity in mono- and co-cultures; (c) the expression of some angiogenic and inflammatory factors such as vascular endothelial growth factor, platelet-derived growth factor subunit B, insulin-like growth factor 1, interleukin-8, and early growth response protein 1 increases significantly in hypoxia-treated POB monoculture and co-cultures after single or multiple 8- or 24-hr hypoxic treatments; (d) long-term (24 hr) hypoxic treatment induces more angiogenic inhibitors compared with short-term hypoxic treatment. Our findings suggest that hypoxia-induced vascularization/angiogenesis is regulated by a complex balance of angiogenic/antiangiogenic factors, and that repeated short-term hypoxia, but not repeated long-term hypoxia, promotes the vascularization and tissue regeneration of bone tissue constructs.