Antioxidant mechanisms reactive oxygen species

LIN J K s, LEE F, HUANG Y T, LiN-SHiAU s Y (1995) Signal transduction and oncogene expression mediated by reactive oxygen species. In Proceedings of the International Symposium on Natural Antioxidants - Molecular Mechanisms and Health Effects. Eds Packer, L, Traber, M G, Xin, W Champaign, I L, USA AOCS Press, 303-19. 

In the literature, most dmg-induced apoptosis is well known to require intracellular hyper-production of reactive oxygen species and several antioxidants inhibit apoptotic cell death. While it is clear that peroxidation reactions induce apoptosis, the precise molecular mechanism of how reactive oxygen species convey death-signals is unknown. 

Figure 9.2. Mechanisms of aminoglycoside toxicity. This schematic representation summarizes the principles of aminoglycoside toxicity discussed in the text. Treatment with the drugs leads to the formation of reactive oxygen species through a redox-active complex with iron and unsaturated fatty acid or by triggering superoxide production by way of NADPH oxidase. An excess of reactive oxygen species, not balanced by intracellular antioxidant systems, will cause an oxidative imbalance potentially severe enough to initiate cell death pathways. Augmenting cellular defenses by antioxidant therapy can reverse the imbalance and restore homeostasis to protect the cell.

Oxidative stress involves an imbalance between cellular reactive oxygen species (ROS) and antioxidant mechanisms that keep these in check. ROS include hydrogen peroxide (H202), superoxide anion radical (02- ), and the hydroxyl radical ( OH). 02 and OH are free radicals, that is, they possess an unpaired electron. As such, free radicals are extremely reactive and will seek an electron from nearby electron-rich macromolecules, for example, proteins, lipids, and DNA, which can lead to disruption of cellular functions. 

Is TAC, representing mainly the second line of antioxidant defense (interception of reaction of uncontrolled oxidation), as important as specific antioxidant mechanisms of the first line of antioxidant defense (preventing the formation of reactive oxygen species) If so, one should perhaps expect high TAC values of biological fluids of crucial importance such as seminal plasma. Instead, TAC of blood plasma and seminal plasma is comparable with that of urine and much lower than that of feces (Tables 8 and 10). 

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