Exposing cells to H2O2: a quantitative comparison between continuous low-dose and one-time high-dose treatments.

Most studies investigating the influence of H2O2 on cells in culture apply nonphysiological concentrations over nonphysiological time periods (i.e., a one-time bolus that is metabolized in minutes). As an alternative, the glucose oxidase/catalase (GOX/CAT) system allows application of physiologically relevant H2O2 concentrations (300nM-10µM) over physiologically relevant time periods (up to 24h). Recent findings suggest that bolus and GOX/CAT treatments can lead to opposing cellular responses, thus warranting a quantitative comparison between the two approaches. First, we established a reaction-diffusion model that can predict the behavior of the GOX/CAT system with spatiotemporal resolution, thus aiding selection of optimal experimental conditions for its application. Measurements of H2O2 concentration in the cellular supernatant with the luminol/hypochlorite system were consistent with the predictions of the model. Second, we compared the impact of bolus and GOX/CAT treatments on cytosolic H2O2 levels over time. Intracellular H2O2 was monitored by the response of the thiol peroxidase Prx2 and the H2O2 sensor roGFP2-Orp1. We found that Prx2 rapidly and reversibly responds to submicromolar H2O2 levels and accurately reflects kinetic competition with cellular catalase. Our measurements reveal fundamental differences in the dynamic response of cellular H2O2 concentrations following either bolus or GOX/CAT treatments. Thus, different, or even opposing, biological outcomes from differing means of H2O2 delivery may be expected. Cellular responses induced by bolus treatment may not occur under GOX/CAT conditions, and vice versa.