Modulating and Measuring Intracellular H2O2 Using Genetically Encoded Tools to Study Its Toxicity to Human Cells

Reactive oxygen species (ROS) such as H2O2 play paradoxical roles in mammalian physiology. It is hypothesized that low, baseline levels of H2O2 are necessary for growth and differentiation, while increased intracellular H2O2 concentrations are associated with pathological phenotypes and genetic instability, eventually reaching a toxic threshold that causes cell death. However, the quantities of intracellular H2O2 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 H2O2 in a dose–response study of H2O2-mediated toxicity. We found that, rather than a simple concentration–response relationship, a combination of intracellular concentration and the cumulative metric of H2O2 concentration multiplied by time (i.e., the area under the curve) determined the occurrence and level of cell death. Establishing the quantitative relationship between H2O2 and cell toxicity promotes a deeper under...