Fluoride And Oxidative Stress by Dariusz Chlubek

Biological reduction of molecular oxygen (O2) generates products collectively termed reactive oxygen species (ROS). By accepting a single electron, O2 is transformed into the superoxide radical anion ·O2 - , which plays a key role in biological systems. Superoxide radicals are generated under natural conditions during mitochondrial respiration, by UV-B radiation, and in phagocytosis of cells engaged in immune response. 1 The superoxide radical anion is the substrate for the most reactive form of ROS the hydroxyl radical (OH·) generated in the Haber-Weiss and Fenton reactions. ROS exhibit a wide spectrum of pathogenic properties. Their uncontrolled overproduction has been implicated in atherosclerosis, diabetes, and inflammatory disorders. They react with methylene groups of polyunsaturated fatty acids (PUFA), initiating the peroxidation of membrane lipids and producing malondialdehyde (MDA) as one of the end products. Determinations of MDA levels provide a good measure of peroxidation, which is among the chief mechanisms of cell damage leading to necrosis or apoptosis. Living organisms possess several antioxidative species and mechanisms protecting them against the harmful action of ROS. These include the enzymes superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GSH-Px, EC 1.11.1.9), and catalase (CAT, EC 1.11.1.6), together with nonenzymatic antioxidants, like selenium compounds, vitamins A, E, and C, and compounds containing thiol groups. Imbalance between ROS and anti- oxidants is referred to as oxidative stress. 

Link : http://www.fluorideresearch.org/364/files/FJ2003_v36_n4_p217-228.pdf