The PrPC protein, which is especially present in the cellular membrane of nervous system cells, has been extensively studied for its controversial antioxidant activity. In this study, we elucidated the free radical scavenger activity of purified murine PrPc in solution and its participation as a cell protector in astrocytes that were subjected to treatment with an oxidant. In vitro and using an EPR spin-trapping technique, we observed that PrPC decreased the oxidation of the DMPO trap in a Fenton reaction system (Cu2+/ascorbate/H2O2), which was demonstrated by approximately 70% less DMPO/OH. In cultured PrPC-knockout astrocytes from mice, the absence of PrPC caused an increase in intracellular ROS (reactive oxygen species) generation during the first 3 h of H2O2 treatment. This rapid increase in ROS disrupted the cell cycle in the PrPC-knockout astrocytes, which increased the population of cells in the sub-G1 phase when compared with cultured wild-type astrocytes. We conclude that PrPC in solution acts as a radical scavenger, and in astrocytes, it is essential for protection from oxidative stress caused by an external chemical agent, which is a likely condition in human neurodegenerative CNS disorders and pathological conditions such as ischemia. (C) 2011 Elsevier inc. All rights reserved.