A Mechanistic Study of the Effects of Antioxidants on the Formation of Malondialdehyde‐Like Products in the Reaction of Hydroxyl Radicals with Deoxyribose

Abstract

The reactions of (*)OH radicals with deoxyribose, DR, form five different DR(*) radicals, only one of which is transformed into malondialdehyde (MDA)-like products. The radiolytic yield of the MDA-like products increases with the increase in the DR concentration indicating that some of the initially formed "unproductive" radicals react with DR to form the "productive" radicals. The yield of the MDA-like products also increases with the dose rate delivered to the solution suggesting that the formation of the MDA-like products involves the reaction of the "productive" radicals with a radical. The addition of ascorbate, AH(-), to the solution decreases the yield of the MDA-like products as expected from the relative rates of the reaction of DR and AH(-) with (*)OH radicals. On the other hand the addition of the exogenous thiol, N-acetylcysteine (NAC), to the solutions decreases the yield of the MDA-like products considerably more than expected from the rate constants of the reaction with (*)OH radicals. The addition of the endogenous thiol, glutathione (GSH), to the solutions affects the yield of the MDA-like products at low concentration less than expected and at "high" concentrations more than expected from the rate constant of the reaction. Addition of low concentration of AH(-) to solutions containing GSH increases considerably its antioxidant activity whereas addition of small concentrations of AH(-) to solutions containing NAC has no effect on its antioxidant activity. The results point out that the DR(*) radicals react differently with NAC and GSH and that the GS(*) and NAC(*) radicals react differently with DR, the GS(*) radical being considerably more active than the NAC(*) radical. Thus it has to be concluded that the relative activity of antioxidants depends also on the rate constants of many secondary reactions and on the concentrations of all the solutes present in the system.

Kinetics of malonaldehyde content in enriched chicken meat during isothermal cooking

“…MA is formed by lipid oxidation mechanisms from a long chain polyunsaturated fatty acid (PUFA) containing at least three double bonds . MA is known to be formed in vivo, thus contributing to metabolic oxidative stress and ex vivo, notably during meat processing . MA can be measured directly by GC or by liquid chromatography .…”

Importance of Iron Complexation for Fenton-Mediated Hydroxyl Radical Production at Circumneutral pH

“…The extent of deoxyribose degradation by Fe(II)cit was similar to that observed with Fe(II)EDTA, whereas inorganic Fe(II) produced ∼3 to 4-fold more TBARS, suggesting that inorganic Fe(II) may produce HO • . Results from this work should be considered with some caution in light of more recent evidence regarding the inherent complexity of interpreting results from the TBARS method (Rachmilovich-Calis et al, 2009b).…”

Is Measuring OH. Radical Scavenging a Reasonable Measurement of Antioxidant Properties?

“…">The formation of malonaldehyde like products, MDA, in lipid peroxidation and in deoxyribose oxidation is attributed to processes initiated by the hydroxyl radical 21–23. However when a detailed study of the mechanism of formation of the “desired” product was carried out, it was found that at least a part of the MDA is formed in processes initiated by secondary radicals 24. Thus measuring the effect of antioxidants on the yield of MDA is not related only to their ability to scavenge hydroxyl radicals 24.…”

“…However when a detailed study of the mechanism of formation of the “desired” product was carried out, it was found that at least a part of the MDA is formed in processes initiated by secondary radicals 24. Thus measuring the effect of antioxidants on the yield of MDA is not related only to their ability to scavenge hydroxyl radicals 24. Furthermore the results indicate that the combined effect of ascorbate and glutathione, GSH, differs from that of ascorbate and N ‐acetyl‐cysteine, NAC, thus pointing out that the RS .…”

“…Furthermore the results indicate that the combined effect of ascorbate and glutathione, GSH, differs from that of ascorbate and N ‐acetyl‐cysteine, NAC, thus pointing out that the RS . radicals formed by the oxidation of GSH and NAC, two known antioxidants, have a different reactivity towards deoxyribose 24 …”