Glutathione peroxidase 3 (GPX3) in plasma reduces hydrogen peroxide (H2O2) with glutathione to yield oxidized glutathione and water (Maddipati and Marnett 1987, Takahashi et al. 1987, Chung et al. 2009, Ottaviano et al. 2009). Glutathione is synthesized in the liver and exported into the plasma.