Modulating and Measuring Intracellular H 2 O 2 Using Genetically Encoded Tools to Study Its Toxicity to Human Cells

Reactive oxygen species (ROS) such as H O play paradoxical roles in mammalian physiology. It is hypothesized that low, baseline levels of H O are necessary for growth and differentiation, while increased intracellular H O concentrations are associated with pathological phenotypes and genetic instability, eventually reaching a toxic threshold that causes cell death. However, the quantities of intracellular H O that lead to these different responses remain an unanswered question in the field. To address this question, we used genetically encoded constructs that both generate and quantify H O in a dose-response study of H O -mediated toxicity. We found that, rather than a simple concentration-response relationship, a combination of intracellular concentration and the cumulative metric of H O concentration multiplied by time (i.e., the area under the curve) determined the occurrence and level of cell death. Establishing the quantitative relationship between H O and cell toxicity promotes a deeper understanding of the intracellular effects of H O specifically as an individual reactive oxygen species, and it contributes to an understanding of its role in various redox-related diseases.