Interaction and reactivity of urocanic acid towards peroxyl radicals

Abstract

The capacity of urocanic acid to interact with peroxyl radicals has been evaluated in several systems: oxidation in the presence of a free radical source (2,2'-azobis(2-amidinopropane; AAPH), protection of phycocyanin bleaching elicited by peroxyl radicals, and Cu(II)- and AAPH-promoted LDL oxidation. The results indicate that both isomers (cis and trans) are mild peroxyl radical scavengers. For example, trans-urocanic acid is nearly 400 times less efficient than Trolox in the protection of the peroxyl radical promoted bleaching of phycocyanin. Regarding the removal of urocanic acid by peroxyl radicals, nearly 100 muM trans-urocanic acid is required to trap half of the produced radicals under the employed conditions (10 mM AAPH, 37 degrees C). Competitive experiments show that the cis-isomer traps peroxyl radicals 30% less efficiently than the trans-isomer. Given the high concentrations that trans-urocanic acid reaches in skin, its capacity to trap peroxyl radicals could contribute to the protection of the tissue towards ROS-mediated processes. Furthermore, both isomers, and particularly the cis-isomer, protect LDL from Cu(II)-induced oxidation.

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology

“…26 In addition to its ability to photosensitise production of excited oxygen species, trans-UCA is an effective hydroxyl scavenger, although an inefficient peroxyl radical scavenger. 27, 28 In vitro studies using hydroxyl radical generating systems suggest that several UCA oxidation products may be produced from both trans-UCA and cis-UCA after UVB exposure, particularly imidazole-4-carboxaldehyde (ImCHO), its oxidation product imidazole-4-carboxylic acid (ImCOOH), imidazole-4-acetic acid (ImAc) and glyoxylic acid (GLX). Under more physiological conditions, ImCHO, ImAc and ImCOOH were shown to be formed in corneal scrapings of human skin after UVB, but not UVA irradiation.…”

Assessment of Radical Scavenging Capacity and Lipid Peroxidation Inhibiting Capacity of Antioxidant

“…The lag phase was obtained graphically by extrapolating the slope of maximal probe decay to intersect with the slope of minimal probe decay at the initial stage. The area under the curve (AUC) was measured as reported in the literature , . Briefly, the ratio of absorbance at time t to that at the start, (Abs) t /(Abs) 0 , was plotted as a function of time.…”

“…The objective of the present study was to compare the capacity of several antioxidants for scavenging free radicals as assessed by the effect on the probe decay and that for inhibition of lipid peroxidation as assessed by the formation of lipid peroxidation products in the oxidation of human plasma. Pyranine (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt) was used as a probe − . Although pyranine has been used less frequently than other probes such as fluorescein, phycoerythrin, and crocin, it is a suitable probe because it reacts with free radicals at an appreciable rate and yet more slowly than many biological antioxidants.…”

“…This is advantageous for obtaining a clear lag phase. Furthermore, its decay can be measured easily by following its maximum absorption at 454 nm or fluorescence intensity (excitation at 460 nm and emission at 510 nm) − .…”

Assessment of antioxidative activity of extract from fermented grain food mixture using chemical and cellular systems

“…2A (1.38) and that of Trolox (115) obtained previously under the same reaction conditions [17], it was estimated that 1 g of AOB was capable of scavenging (1.38 × 2)/(115 × 250) = 96 µmol radicals, assuming that each Trolox can scavenge 2 molecules of free radicals and that the molecular weight of Trolox is 250. In addition to the lag phase, the area under curve (AUC) was measured as described in the literature [18,11] from the difference between the integrated areas under the absorption decay curves in the presence and absence of the antioxidants, i.e., net AUC = AUC (with antioxidant) -AUC (without antioxidant). The AUC obtained by using the AOB extract and Trolox was directly proportional to the amount of AOB extract and Trolox added respectively (Fig.…”