Figure 1.

Available methodology to recapitulate in vitro oxygen levels found in the atmosphere, normal tissues, and tumors. (A) The schematic representations illustrate the oxygen concentration of atmospheric oxygen concentration (20.8%), as well as healthy tissues (1–11%) and tumors (0.3–4%). (B) Physoxic concentrations vary among the body tissues. The different oxygen concentrations are shown in parenthesis. (C–G) Many methods have been used to induce hypoxia. Cobalt chloride (C) is a method to achieve a chemically induced pseudo-hypoxia, whereby HIF-1α is upregulated to mimic hypoxia without truly adjusting the oxygen concentration. Gas-controlled incubator (D), glove boxes (E), acrylic incubator chambers (F), and here the use of deoxidizing absorbers (G) represent current methodologies that utilize nitrogen and carbon dioxide gas to achieve hypoxia. (H) Each methodology for achieving hypoxia, including the one we present in this manuscript, has benefits and limitations as shown in the table.