Oxidant stress antioxidant defence mechanism

There is considerable body of (indirect) evidence which makes oxidative stress one of the best accepted hypothesis for explaining the cause of Parkinson s disease. For example, the Fe(II)/Fe(III) ratio in the substantia nigra is shifted from 2 1 in the normal brain to 1 2 in Parkinsonian brain.131,132 In the Parkinsonian brain several enzymes which constitute the antioxidative defence mechanisms (glutathione peroxidase, catalase) have a decreased activity, while the activity of superoxide dismutase is increased, relative to the normal brain.133 Furthermore, specific products of radical damage, such as lipid hydroperoxides, were detected at a 10-fold increased level in the Parkinsonian brain.134... 

Oxidative stress is a condition in which free radicals and their products are present in excess of antioxidant defence mechanisms, leading to oxidative damage and structural and functional modifications of proteins, DNA, and RNA. Radicals can be formed through different mechanisms. ROS are formed by the reduction of molecular oxygen to water superoxide (O "), peroxyl radical (OH ), and hydrogen peroxide (H O ). RNS (NO and peroxynitrite) can also cause oxidative stress. 

Whilst biological systems have developed a number of sophisticated mechanisms to repair the damage caused to cells by oxidative stress [31], a key element of the defence against such damage lies in prevention. A combination of antioxidant defence enzymes and simple low molecular mass antioxidant molecules are generally used to prevent oxidative damage [21]. 

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