CAT and cancer: As we expected, antioxidant systems including Catalase (CAT), peroxidase (Prx), glutathione peroxidase (Gpx), glutathione reductase (GR), glutaredoxins (Grxs), thioredoxins (Trxs), NF-E2-related factor 2 (Nrf2) were all upregulated in cancer cells in response to hypoxia, but they decreased or are unchanged in non-cancerous cells (Fig. 7a–d,f).