In Vitro Test for the Effectiveness of Antioxidants as Inhibitors of Thiyl Radical-Induced Reactions with Unsaturated Fatty Acids

Abstract

Attacks of thiyl radicals on the double bonds of unsaturated fatty acids lead to stereomutation (cis-, trans-isomerization without double-bond migration) and addition reactions (thioether formation). On the basis of these findings, an in vitro test system has been developed which allows the study of the effectiveness of specific antioxidants in preventing thiyl radical-induced attacks on unsaturated fatty acids. The test involves thermal treatment of a mixture of oleic (cis-9-octadecenoic) acid and 1-tetradecanethiol with the antioxidant, followed by measurement of the extent of formation of the products of stereomutation and addition (i.e., elaidic (trans-9-octadecenoic) acid and isomeric 9(10)-S-tetradecylstearic acids, respectively) by gas chromatography of their methyl esters as a function of antioxidant concentration. Antioxidants such as octyl gallate, ascorbic acid 6-O-palmitate, ubiquinone 50 (coenzyme Q(10)), rac-alpha-tocopherol, and 2,6-di-tert-butyl-4-methylphenol (BHT) were tested for their ability to protect the >C=C< double bond of oleic acid against attacks of thiyl radicals generated from 1-tetradecanethiol by heating. The results show that octyl gallate, ascorbic acid 6-O-palmitate and, to some extent, ubiquinone 50 (coenzyme Q(10)) were highly effective in preventing reactions of free thiyl radicals with oleic acid, whereas rac-alpha-tocopherol and BHT were moderately effective.

Gallic Acid Induces the Apoptosis of Human Osteosarcoma Cells In Vitro and In Vivo via the Regulation of Mitogen-Activated Protein Kinase Pathways

“…various natural products, and exhibits a wide variety of biological effects, including antibacterial, 11 antioxidant, 12,13 antifungal and antimalarial, 14 and antiherpetic action. 15 In addition, the antiviral capacity of GA is related to its antioxidant activity.…”

Biomimetic chemistry on the protection of cis phospholipid from the thiyl radical isomerization by common antioxidants

“…21 Herein, the cis-trans isomerization of fatty acid residues in LUVs by thiyl radicals in the absence and presence of various antioxidants has been extensively studied and the data have been rationalized based on kinetic data available in the literature from pulse radiolysis. [20][21][22] Using the methanolic injection method, it is possible to affect the liposome size 31 and in our experiments the preparation of vesicles was performed to reproduce the same size of vesicles obtained by the extrusion technique, ascertained by Dynamic Light Scattering (DLS) measurements. 32 It was gratifying to find that similar dose profiles of the cis-trans isomerization by HOCH 2 CH 2 S• radicals (MS•) were observed for extruded DOPC vesicle suspensions added with 1.2 M MeOH and vesicle suspensions obtained by an appropriate methanolic DOPC injection in water (dashed line in Figure 2).…”

“…We observed that the ability to scavenge thiyl radicals generated by γ-radiolysis in aqueous vesicle suspensions increases along the series ArOH < retinol < UH 3 < AH 2 , a different order to that observed in organic solutions or using multilamellar vesicles (MLVs) described in previous studies. [20][21][22] The proposed anti-isomerizing activity is based not only on the relative chemical reactivity of the antioxidants, but also on their partition coefficient, i.e., the localization of the free radical scavengers in the aqueous or lipid compartment. …”

Gallic acid induces apoptosis in A375.S2 human melanoma cells through caspase-dependent and -independent pathways

“…Gallic acid (3,4,5-trihydroxybenzoic acid, GA), an intermediate component of plant metabolism from the hydrolysis of tannins (5), has been associated with a wide variety of biological actions including antioxidant (6), antibacterial (7), antifungal and antimalarial (8), and antiherpetic action (5). The main interest in GA is related to its antitumoral activity.…”