Inhibition by antioxidants

In addition to the well-known iron effects on peroxidative processes, there are also other mechanisms of iron-initiated free radical damage, one of them, the effect of iron ions on calcium metabolism. It has been shown that an increase in free cytosolic calcium may affect cellular redox balance. Stoyanovsky and Cederbaum [174] showed that in the presence of NADPH or ascorbic acid iron ions induced calcium release from liver microsomes. Calcium release occurred only under aerobic conditions and was inhibited by antioxidants Trolox C, glutathione, and ascorbate. It was suggested that the activation of calcium releasing channels by the redox cycling of iron ions may be an important factor in the stimulation of various hepatic disorders in humans with iron overload. 

B. Yerushalmi, R. Dahl, M. W. Devereaux, E. Gumpricht and R. J. Sokol, Bile-acid-induced rat hepatocyte apoptosis is inhibited by antioxidants and blockers of the mitochondrial permeability transition. Hepatology, 2001, 33(3), 616. 

Benzoyl peroxide forms radicals that are involved in its covalent binding to macromolecules. Its biological effects are inhibited by antioxidants. 

Peroxy radicals are known to be responsible for the bleaching of carotenoid pigments, such as crocin. Such bleaching can be inhibited by antioxidants.468 492 493 In determining the residual radical scavenging activity of tomato juice, crocin bleaching and the DPPH method gave parallel results 446... 

The degradation of polymers is mostly promoted by autoxidation. The propagation of autoxidation can be inhibited by antioxidants (e.g. hindered phenols and amines). 

Konopacka, M., Rzeszowska-Wolny, J. (2006). The bystander effect-induced formation of micronucleated cells is inhibited by antioxidants, hut the parallel induction of apoptosis and loss of viability are not affected. Mutat. Res. 593 32-8. 

This chain reaction can be effectively inhibited by antioxidants of many classes, of which the polyphenolic are of primary importance. Further, a simple hydrogen abstraction reaction is the most important mechanism for breaking the reaction chain and inhibiting peroxidation (Uri, 1961). 

One of the lipid abnormalities that has been associated with T2DM is an increased plasma TG levels [60,61], Most fasting plasma TG is carried in the form of very low-density lipoprotein (VLDL) [62,63], Increased secretion of VLDL by the liver, and decreased clearance of VLDL and intestinally derived chylomicrons result in prolonged plasma retention of TG-rich particles in the plasma that lead to the accumulation of TG-rich lipoproteins. Studies by Chisolm and cowoikers [64] as well by Henriksen et al. [65] over 4 decades showed that diabetic serum was toxic to cells and such toxicity could be inhibited by antioxidants. They also showed most of the toxicity resided in the TG-rich lipoproteins. 

Arroyo PL, Hatch-Pigott V, Mower HF et al (1992) Mutagenicity of nitric oxide and its inhibition by antioxidants. Mutat Res 281 193-202... 

Peroxy radicals interact rapidly with antioxidants which may be present to give monohydroperoxides (cf. 3.7.3.1). Thus, it is not only the chain reaction which is inhibited by antioxidants, but also P-fragmentation and peroxy radical cyclization. Fragmentation occurs when a hydroperoxidee-pidioxide is heated, resulting in formation of aldehydes and aldehydic acids. For example. 

The formation of heterocychc amines of the IQ type is effectively inhibited by antioxidants. The presence of phenohc compounds such as flavanones and flavan-3-ols significantly inhibits their formation. The mechanism of the inhibitory effect is partly based on the ehmination of Strecker aldehydes, precursors of IQ mutagens, by condensation with phenols. For example, phenylacetaldehyde, a decarboxylation product of phenylalanine and a precursor of PhIP, produces two adducts, ( )-8-(phenylethenyl)naringenin and ( )-6-(phenylethenyl)naringenin withnaringenin (Figure 12.2). 

This oxidative degradation process of lipids in food can be inhibited by antioxidant compounds. Beyond the preservation of food, antioxidants absorb free radicals and help prevent cardiovascular, neurological, and carcinogenic diseases in biological systems (Andre et al., 2010). 

Nocardia [23] and P. aeruginosa were shown to break the cis-PI chain by an oxidative mechanism since aldehyde groups were found to accumulate during microbial degradation. This is always the first product formed during the abiotic peroxidation of cis-Fl and the evidence suggests that the bacteria initiate a radical-chain peroxidation, which is inhibited by antioxidants. This will be discussed further in the context of poyolefin biodegradation. 

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