Understanding What is oxidative stress?

Oxidative stress is caused due to an imbalance between production of reactive oxygen species (free radicals) and effectiveness of antioxidant defense. Reactive oxygen species (ROS) play a crucial role in cell signaling, however when the balance between ROS production and consumption is disrupted, it can lead to cell damage. Oxidative stress can cause damage to DNA, proteins and lipids. Reactive oxygen species are produced by electron leak from aerobic respiration by mitochondria. Enzymes like NADPH oxidases, xanthine oxidases, cytochrome P450 and other oxidases also produce ROS. There are enzymes and molecules in the body that serve as antioxidants such as superoxide dismutase (SOD), catalase, glutathione peroxidase and glutathione which removes ROS molecules from the living system.

Reduced glutathione (L-g-glutamyl-L-cysteinylglycine), a key antioxidant present in animals, plants, fungi and bacteria provides reducing equivalents in form of free thiol groups. Glutathione exist in reduced (GSH) and oxidized (GSSG; glutathione disulphide) forms in cells and tissues, and the concentration of glutathione range from 0.5 to 10mM in animal cells. The majority (90-95 %) of glutathione exist in reduced form (GSH) in healthy cells. GSH provides reducing equivalents to antioxidant enzymes, hydroxyl radicals, ROS and is itself oxidized to GSSG; therefore GSH/GSSG ratio is critical indicator of the health of cell. During oxidative stress there is decrease in levels of GSH and increase in levels of GSSG and thus GSH/GSSG ratio decreases.