SOD1 and major depressive disorder: Peripheral biomarkers of oxidative stress according to severity of MDD patients compared to healthy controls. MDD: Major depressive disorder—GR: Glutathion Reductase—SOD: Superoxide dismutase (information about isoform was not provided)—MDA: Malondialdehyde—oxLDL: Oxide LDL—8-OhdG: 8-hydroxy-2′-deoxyguanosine—↗: Values significantly higher in depressed patients compared to controls—↘: Values significantly lower in depressed patients compared to controls—↔: No significant difference between depressed patients and controls.