Abstract: ObjectiveTo study the relationship between hypoxia and the hypoxia inducible factor-1α (HIF-1α) from lung cancer cells,to reveal the possible mechanism of brain metastases of lung cancer. MethodsThe hypoxia model of A549 lung cancer cells was established. After hypoxia culture of A549 cells for 0.5,2,4,8,12 and 24 h (normal oxygen culture at the same time point was set as the control group),the mass concentration of HIF-1α in A549 lung cancer cell culture medium were determined by ELISA. Transwell chamber was used to construct an in vitro blood brain barrier model,was treated with A549 lung cancer cell culture medium after different time points of hypoxia,Tran endothelial resistance (TER) change of blood-brain barrier model in instrument,to reflect the changes of blood-brain barrier permeability in vitro; A549 lung cancer cells in the culture medium were counted under Transwell room. A549 lung cancer cells with hypoxia at different time points injected into Wistar rats via tail vein,Western blot method was used to menstruate expression of tight junction associated protein Claudin-5 in the brain tissues,Evans blue to detect the change of blood brain barrier permeability in rats. ResultsCompared with the control group,the HIF-1α mass concentration in the cell culture solution of A549 increased,the in vitro blood-brain barrier model TER decreased,and the cell number of A549 that passed through transwell into the lower chamber increased (all P<0.05) after hypoxia 2 h,the above effect was most obvious when hypoxia 8 h (all P<0.01). After hypoxia 24 h,it was restored to the control group level. In the in vivo experiment of rats,compared with the control group,the mass percent of Evans blue in rat brain tissues increased after A549 cell culture solution with hypoxia 2 h was injected via caudal vein,meaning increased the permeability of rat blood brain barrier,while the expression of Claudin-5 protein in rat brain tissues decreased (all P<0.05). The effect was most obvious when A549 cell culture solution with hypoxia 8 h was injected into rat tail vein (P<0.01 ). Ejectionof hypoxia 24 h A549 cell culture solution yielded the same effects as those in the control group. ConclusionHypoxia can induce the increase of HIF-1α in lung cancer cells. The increase of HIF-1α results in the decrease of Claudin-5 expression and increase of blood-brain barrier permeability,leading to lung cancer cells metastasis into the brain.