What does Oxidant Stress Cause

A sudden and large increase in ROS load can overwhelm local antioxidant defenses and induce severe oxidant stress, with cell damage, cell death, and subsequent organ failure. However, less dramatic chronic oxidant stress may lead to depletion of defenses and accumulation of damage and ultimately cause physiological dysfunction and pathological change resulting in disability and disease. This is because oxidant stress causes oxidative changes to DNA, lipid, and protein. These changes lead in turn to DNA breaks, mutagenesis, changed pheno-typic expression, membrane disruption, mitochon-drial dysfunction, adenosine triphosphate depletion, intracellular accumulation of non-degradable oxidized proteins, increased atherogenicity of low-density lipoproteins, and crosslinking of proteins with subsequent loss of function of specialized protein structures, for example, enzymes, receptors, and the crystallins of the ocular lens. In addition, the aldehydic degradation products of oxidized polyunsaturated fatty acids (PUFAs) are carcinogenic and cytotoxic. Increased oxidant stress can also trigger apoptosis, or programed cell death, through a changed redox balance, damage to membrane ion-transport channels, and increased intra-cellular calcium levels (Figure 3).

Oxidant stress, through its effects on key biological sites and structures, is implicated in chronic noncommunicable diseases such as coronary heart disease, cancer, cataract, dementia, and stroke (Figure 4). Oxidant stress is also thought to be a key player in the aging process itself. A cause-and-effect relationship between oxidant stress and aging and disease has not been confirmed, however, and it is very unlikely that oxidant stress is the sole cause of aging and chronic degenerative disease. Nonetheless, there is evidence that oxidant stress contributes substantially to age-related physiological decline and pathological changes. Consequently, if it is accepted that oxidant stress is associated with aging and degenerative disease, then opposing oxidant stress by increasing antiox-idant defense offers a potentially effective means of delaying the deleterious effects of aging, decreasing the risk of chronic disease, and achieving functional longevity. For this reason, there has been great interest in recent years in the source, action, and potential health benefits of dietary antioxidants.

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