Comparison of Antioxidant Properties of a Conjugate of Taxifolin with Glyoxylic Acid and Selected Flavonoids

It is known that flavonoids can react with toxic carbonyl compounds in the process of the storage, aging, and digestion of flavonoid-rich foods and beverages. However, the effect of these reactions on the antioxidant properties of the polyphenolic fraction and the properties of the resulting products remain poorly studied. The aim of the present work was to study the antioxidant activity of quercetin, taxifolin, catechin, eriodictyol, hesperetin, naringenin and a product of the condensation of taxifolin with glyoxylic acid, as well as to reveal the structure–activity relationship of these polyphenols. It was found that flavonoids containing the catechol moiety exhibited higher antioxidant activity than hesperetin and naringenin. The product showed the highest hydrogen peroxide scavenging activity, a lower metal-reducing and a higher iron-binding ability than catechol-containing flavonoids, and a lipid peroxidation inhibitory activity comparable with that of taxifolin. Thus, the condensation of flavonoids with toxic carbonyl compounds might lead to the formation of products exhibiting high antioxidant activity. Meanwhile, the conditions under which parent flavonoids and their products exhibit the maximal antioxidant activity may differ. The data suggest that the antioxidant profile of the polyphenolic fraction and bioavailability of polyphenols, carbonyl compounds, and metal ions may change when these reactions occur.

Effect ofVetiveria zizanioidesEssential Oil on Melanogenesis in Melanoma Cells: Downregulation of Tyrosinase Expression and Suppression of Oxidative Stress

The major objective of this study was to estimate the hypopigmentation function of the essential oil fromVetiveria zizanioides(VZ-EO). Our results indicated that VZ-EO exhibits potent lipid peroxidation inhibitory activity to moderate the bleaching ofβ-carotene and to maintain the cellular glutathione (GSH) levels. VZ-EO can markedly decrease melanin production and tyrosinase activity inα-melanin-stimulating-hormone- (α-MSH-) stimulated B16 cells. The effect of VZ-EO on melanogenesis is achieved by the suppression of cellular tyrosinase expression. The results demonstrated that the activity of VZ-EO on melanogenesis might be the result of its potent antioxidative ability, which was reflected in the decreased cellular oxidant and malondialdehyde (MDA) levels and the recovered activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT) inα-MSH-stimulated B16 cells. The most abundant compound in VZ-EO is cedr-8-en-13-ol (12.4%), which has a strong capability to inhibit lipid peroxidation. Therefore, VZ-EO has the potential to become an ingredient in future hypopigmentation drugs, foods, and cosmetics.

IN VITRO LIPID PEROXIDATION INHIBITORY AND ANTI-ARTHRITIC ACTIVITIES OF SOME INDIAN MEDICINAL PLANTS

Anti-lipid peroxidation effect of aqueous extracts of Ocimum sanctum, Tinospora cordifolia and Withania somnifera was evaluated against Fe2+-ascorbic acid-induced lipid peroxidation using rat liver mitochondria as model system, whereas, anti-arthritic activity was evaluated by proteinase inhibitory assay. O. sanctum showed potent anti-lipid peroxidation and anti-arthritic activities. T. cordifolia exhibited moderate anti-lipid peroxidation activity, but considerable anti-arthritic activity, whereas, W. somnifera revealed least lipid peroxidation inhibitory activity and considerable anti-arthritic activity. Besides, Folin-Ciocalteu reagent in terms of gallic acid equivalent achieved the total phenolic content and the trend was found to be O. sanctum > T. cordifolia > W. somnifera.

Limonoids from Meliaceae with Lipid Peroxidation Inhibitory Activity

In this study the antioxidant activity of natural limonoids from Meliaceae swietenolide (1), 3,6-O,O-diacetylswietenolide (2), swietenine (3), swietemahonin G (4) and 2-hydroxyswietenine (5) were investigated along with the semisynthetic analogues (6-25) of compounds 1, 3-4. Lipid peroxidation (LPO) inhibitory assays revealed 85.6, 13.3, 77.3, 61.2 and 24.6 % inhibition for the natural compounds 1-5. Excellent antioxidant activity was seen for the semisynthetic analogues 10 (98.3 %), 16-17, 21-22 and 25 (100 %), which were more active than the positive controls BHA (91.3 %) and TBHQ (95.7 %).