A549 cells were cultured in serum-free DMEM under the following conditions: normoxia, 100 µM CoCl₂, 150 µM CoCl₂, or 200 µM CoCl₂ for 24 hrs.

<p>A: Western blot analysis of HIF-1α in A549 cells under different levels of hypoxia (n = 3). B: Western blot analysis of UCP2 in A549 cells under different levels of hypoxia (n = 3). C: The relationship between apoptosis and hypoxia in A549 cells. Data are mean ± SEM (n = 5). *P<0.05, compared with normoxic conditions.