Hypoxia, acidification and oxidative stress in cells cultured at large distances from an oxygen source

Hypoxia is a condition frequently encountered by cells in tissues, whether as a normal feature of their microenvironment or subsequent to deregulated growth. Hypoxia can lead to acidification and increased oxidative stress, with profound consequences for cell physiology and tumorigenesis. Therefore, the interplay between hypoxia and oxidative stress is an important aspect for understanding the effects of hypoxic microenvironments on cells. We have used a previously developed variant of the method of coverslip-induced hypoxia to study the process of acidification in a hypoxic microenvironment and to simultaneously visualize intracellular levels of hypoxia and oxidative stress. We observed high accumulation of CO₂ in hypoxic conditions, which we show is the main contributor to acidification in our model. Also, increased levels of oxidative stress were observed in moderately hypoxic cells close to the oxygen source, where the mitochondrial membrane potential was preserved. Conversely, cells at large distances from the oxygen source showed higher levels of hypoxia, milder oxidative stress and reduced mitochondrial membrane potential. Our results contribute to characterize the interplay between reduced oxygen levels, acidification and oxidative stress in a simple in vitro setting, which can be used to model cell responses to an altered environment, such as the early tumor microenvironment.