Rapid identification and characterization of antioxidants from <Emphasis Type="Italic">Ligularia fischeri</Emphasis>

The objectives of this study were to investigate the radical-scavenging activity of Ligularia fischeri on oxidative damage by the radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and to rapidly identify the active components using the bioassay-linked fractionation method. The MeOH extract and fractions of CH₂Cl₂, BuOH, and H₂O from L. fischeri showed DPPH radical-scavenging effects in a dose-dependent manner (p < 0.01). In particular, the BuOH fraction had the most effective (p < 0.05) antioxidative capacity. The active constituents from the BuOH fraction of L. fischeri were rapidly isolated by bioassay-linked HPLC method and identified as hyperoside and 2″-acetylhyperoside with potent antioxidant effects against the DPPH radical, with IC₅₀ values of 1.31 and 7.09 μg/mL, respectively. They have not been reported from L. fischeri yet.     

Re-evaluation of the antioxidant prenylated flavonoids from the roots of Sophora flavescens

The objective of this research was to re-evaluate the antioxidant effects of the prenylated flavonoids from Sophora flavescens via in vitro 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), peroxynitrite (ONOO(-)), and total reactive oxygen species (ROS) assays. In addition, a further examination of kuraridinol, kurarinol, and kurarinone, also isolated from S. flavescens, was carried out by the inhibition of tert-butylhydroperoxide (t-BHP)-induced intracellular ROS generation and t-BHP-induced activation of nuclear factor-kappaB (NF-kappaB). Upon re-examination of the ethyl acetate (EtOAc) soluble fraction of S. flavescens, two major prenylated chalcones, including kuraridin and kuraridinol, along with a minor prenylated flavonol, kushenol C, were isolated as good DPPH scavengers. This was in contrast to the prenylated flavanones, sophoraflavanone G and kurarinone, which were isolated from the methylene chloride (CH(2)Cl(2)) fraction of the same source. Five flavanones consisting of kushenol E, leachianone G, kurarinol, sophoraflavanone G, and kurarinone exhibited significant antioxidant potentials in the ABTS, ONOO(-), and total ROS assays; however, the prenylated chalcones and prenylated flavonol showed more potent scavenging/inhibitory activities than the prenylated flavanones. Therefore, the prenylated chalcones and prenylated flavonol, rather than the prenylated flavanones, may make important contributions toward the marked antioxidant capacities of S. flavescens. Furthermore, kuraridinol, kurarinol, and kurarinone showed significant inhibitory activities against intracellular ROS levels as well as NF-kappaB activation by t-BHP. Overall, the results indicate that S. flavescens and its prenylated flavonoids may possess good anti-inflammatory activity, which is implicated in their significant antioxidant activity.     

Tyrosinase inhibitory prenylated flavonoids from Sophora flavescens

For the purpose of the development of a skin-whitening agent, Sophora flavescens was evaluated for tyrosinase inhibitory activity and its active principles were identified following activity-guided isolation. The ethanol extract and dichloromethane fraction from S. flavescens showed significant inhibition of mushroom tyrosinase. From the dichloromethane fraction, three known prenylated flavonoids, sophoraflavanone G, kuraridin, and kurarinone, were isolated. Compared with kojic acid (IC(50)=20.5 microM), these compounds possessed more potent tyrosinase inhibitory activity. The IC(50) values were 6.6, 0.6, and 6.2 microM for sophoraflavanone G, kuraridin, and kurarinone, respectively.     

Lavandulyl flavanones from Sophora flavescens protect mouse hippocampal cells against glutamate-induced neurotoxicity via the induction of heme oxygenase-1

Lavandulyl flavanones of Sophora flavescens roots are anti-malarial, anti-inflammatory, and cytotoxic. Here, we examined whether four lavandulyl flavanones, (2S)-2'-methoxykurarinone (1), sophoraflavanone G (2), leachianone A (3), and (-)-kurarinone (4), isolated from S. flavescens could protect HT22 immortalized hippocampal cells against glutamate-induced oxidative stress. Compounds 1 and 2 induced the expression of heme oxygenase (HO)-1 and increased HO activity dose- and time-dependently. These two compounds also suppressed glutamate-induced reactive oxygen species generation in HT22 cells, whereas compounds 3 and 4 were not protective. These two lavandulyl flavanones (compounds 1, 2) may protect against glutamate-induced neurotoxicity via HO-1 induction.     

Characterization of flavonoids in the extract of Sophora flavescens Ait. by high-performance liquid chromatography coupled with diode-array detector and electrospray ionization mass spectrometry

A method coupling high-performance liquid chromatography (HPLC) with diode-array detector (DAD) and electrospray ionization mass spectrometry (ESI) was established for the separation and characterization of flavonoids in Sophora flavescens Ait. Based on the chromatographic separation of most flavonoids present in S. flavescens Ait., a total of 24 flavonoids were identified. Fourteen compounds were unambiguously identified comparing experimental data for retention time (t(R)), UV and MS spectra with those of the authentic compounds: 3',7-dihydroxy-4'-methoxy-isoflavone (13), trifolirhizin (14), kurarinol (18), formononetin (19), 7,4'-dihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (22), maackiain (21), isoxanthohumol (23), kuraridine (26), kuraridinol (27), sophoraflavanone G (30), xanthohumol (31), isokurarinone (33), kurarinone (35) and kushenol D (38), and additional 10 compounds were tentatively identified as kushenol O (10), trifolirhizin-6'-malonate (15), sophoraisoflavanone A (20), norkurarinol/kosamol Q (24), kushenol I/N (25), kushenol C (28), 2'-methoxykurarinone (29), kosamol R (32), kushecarpin A (34) and kushenol A (37) by comparing experimental data for UV and MS spectra with those of literature. Furthermore, fragmentation pathways in positive ions mode of 24 flavonoid compounds of types of flavanone, flavanonol, flavonol, chalcone, isoflavone, isoflavanone and ptercocarpane were summarized. Some common features, such as CH(3)., H(2)O, CO, CO(2), C(3)O(2) and C(2)H(2)O losses, together with Retro-Diels-Alder fragmentations were observed in the prenylated flavonoids in S. flavescens Ait. The loss of the lanandulyl chain was their characteristic fragmentation, which might help deducing the structure of unknown flavonoid compounds. The present study provided an approach to rapidly characterize bioactive constituents in S. flavescens Ait.     

Antioxidant activities of the flaxseed lignan secoisolariciresinol diglucoside, its aglycone secoisolariciresinol and the mammalian lignans enterodiol and enterolactone in vitro.

The flaxseed lignan secoisolariciresinol diglucoside (SDG) and mammalian lignans enterodiol (ED) and enterolactone (EL) were previously shown to be effective antioxidants against DNA damage and lipid peroxidation. Others reported inhibition of activated cell chemiluminescence by supra-physiological concentrations of secoisolariciresinol (SECO), ED and EL. Thus, we evaluated the antioxidant efficacy of potential physiological concentrations of SDG, SECO, ED and EL against 1,1-diphenyl-2-picrylhydrazyl (DPPH()), and 2,2'-azo-bis(2-amidinopropane) dihydrochloride (AAPH)-initiated peroxyl radical plasmid DNA damage and phosphatidylcholine liposome lipid peroxidation. SDG and SECO were effective (p<0.01) antioxidants against DPPH() at 25-200muM; whereas, ED and EL were inactive. Efficacy of lignans and controls against AAPH peroxyl radical-induced DNA damage was: SDG>SECO=17alpha-estradiol>ED=EL>genistein>daidzein. Lignan efficacy against AAPH-induced liposome lipid peroxidation was: SDG>SECO=ED=EL. Plant lignan antioxidant activity was attributed to the 3-methoxy-4-hydroxyl substituents of SDG and SECO, versus the meta mono-phenol structures of ED and EL. Benzylic hydrogen abstraction and potential resonance stabilization of phenoxyl radicals in an aqueous environment likely contributed to the antioxidant activity of the mammalian lignans. These represent likely extra- and intracellular antioxidant activities of flax-derived lignans at concentrations potentially achievable in vivo.     

Effects of sophoraflavanone G,a prenylated flavonoid from Sophora flavescens,on cyclooxygenase-2 and in vivo inflammatory response

Previously, several prenylated flavonoids having a C-8 lavandulyl moiety were found to inhibit cyclooxygenase-1 (COX-1) as well as 5-lipoxygenase (5-LOX), and sophoraflavanone G was the most potent inhibitor against these eicosanoid generating enzymes among 19 prenylated flavonoids tested. In this investigation, effects of sophoraflavanone G on COX-2 induction from RAW 264.7 cells and in vivo inflammatory response were studied. Sophoraflavanone G inhibited prostaglandin E2 (PGE2) production from lipopolysaccharide (LPS)-treated RAW cells by COX-2 down-regulation at 1-50 uM. Other prenylated flavonoids including kuraridin and sanggenon D also down-regulated COX-2 induction at 10-25 uM, while kurarinone and echinoisoflavanone did not. In addition, sophoraflavanone G showed in vivo anti-inflammatory activity against mouse croton oil-induced ear edema and rat carrageenan paw edema via oral (2-250 mg/kg) or topical administration (10-250 microg/ear). Although the potencies of inhibition were far less than that of a reference drug, prednisolone, this compound showed higher anti-inflammatory activity when applied topically, suggesting a potential use for several eicosanoid-related skin inflammation such as atopic dermatitis.     

Evaluation of polyphenolic acid esters as potential antioxidants

Six polyphenolic acid esters were synthesized and their antioxidative properties were evaluated in three model systems [2,2'-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay, 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH)-induced lipid peroxidation system, and the dye-bleaching assay of peroxynitrite radical]. Among these compounds, we found that compounds 4 [3,4-dihydroxy-benzoic acid-(2-phenoxyethyl ester)], and 5 [3,4-dihydroxy-cinnamic acid-(2-phenoxyethyl ester)] provided comparable activity to caffeic acid phenethyl ester (CAPE) in the DPPH model. Compound 3 [2,5-dihydroxy-benzoic acid-(2-phenoxyethyl ester)], was found to be more active than CAPE in the AAPH system, it also displayed about 2-fold greater activity than CAPE in the peroxynitrite radical model. These results suggest that these phenolic acid ester derivatives, with their potent anti-oxidant activities, may have useful applications as antioxidants.     

Low density lipoprotein (LDL)-antioxidant flavonoids from roots of Sophora flavescens

Oxidation of low density lipoprotein (LDL) is strongly implicated as a key process in the onset of atherosclerosis. In this study, nine alkylated (C10-C5) flavonoids from Sophora flavescens were examined for their inhibitory effects on copper-induced LDL oxidation. Of the flavonoids tested, sophoraflavanone G (1), kurarinone (2), kurarinol (3), norkurarinol (4), and kuraridin (9) inhibited the generation of thiobarbituric acid reactive substances (TBARS) with IC50s of 7.9, 14.5, 22.0, 26.9, and 17.5 microM, respectively. The most potent inhibitor, compound 1, also demonstrated significant activities in complementary in vitro investigations, such as lag time (130 min at 5 microM), relative electrophoretic mobility (REM) of ox-LDL (80% inhibition at 20 microM), and fragmentation of apoB-100 (inhibition of 71% at 20 microM). Analysis of the structures of these compounds reveals that a resorcinol moiety in the B-ring is strongly correlated with protection of LDL-oxidation.     

Antimalarial activity of lavandulyl flavanones isolated from the roots of Sophora flavescens

Four lavandulyl flavanones, (2S)-2'-methoxykurarinone (1), sophoraflavanone G (2), leachianone A (3), and (-)-kurarinone (4), which are isolated from the roots of Sophora flavescens have been tested for in vitro antimalarial activity against Plasmodium falciparum. Compounds 1-3 showed moderate antimalarial activities with EC(50) values of 2.4 x 10(-6), 2.6 x 10(-6), and 2.1 x 10(-6) M, respectively. These compounds did not show selective toxicity against P. falciparum in the toxicity test on mouse mammalian tumor cells, however, it is suggested that the position of methoxyl groups in flavanone skeleton plays an important role on antimalarial activity.     

In Vitro Free Radical and ONOO- Scavengers from Sophora flavescens

Activity-guided fractionation of the CH2Cl2-soluble fraction of the roots of Sophora flavescens furnished five 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavengers: trans-hexadecyl ferulic acid (1), cis-octadecyl ferulic acid (2), trans-hexadecyl sinapic acid (3), (-)-4-hydroxy-3-methoxy-(6aR,11aR)-8,9-methylenedioxypterocarpan (4) and desmethylanhydroicaritin (8), along with nine known inactive compounds: (-)-maackiain (5), xanthohumol (6), formononetin (7), (2S)-2'-methoxykurarinone (9), (2S)-3beta,7,4'-trihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (10), (2S)-7,4'-dihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (11), umbelliferone (12), kuraridin (13), and trifolirhizin (14). Compounds 1-4 and 8 exhibited DPPH free radical scavenging effects at IC50 values of 33.01 +/- 0.20, 57.06 +/- 0.16, 39.84 +/- 0.36, 35.83 +/- 0.47, and 18.11 +/- 0.04 microM, respectively. L-Ascorbic acid, when used as a positive control, exhibited an IC50 value of 7.39 +/- 0.01 microM. Compounds 1-4 and 8 also appeared to exert significant scavenging effects on authentic ONOO-, with IC50 values of 5.76 +/- 1.19, 15.06 +/- 1.64, 8.17 +/- 4.97, 1.95 +/- 0.29, and 4.06 +/- 2.41 microM, respectively. Penicillamine (IC50 = 2.36 +/- 0.79 microM) was used as a positive control. In addition, compounds 2, 4, 6, 8, and 10 were isolated from this plant for the first time.     

A potent antioxidant, lycopene, affords neuroprotection against microglia activation and focal cerebral ischemia in rats

We investigated the effects of a potent antioxidant, lycopene, on the free radical-scavenging activity as evaluated by the DPPH test and lipid peroxidation in rat brain homogenates as well as nitric oxide (NO) formation in cultured microglia stimulated by lipopolysaccharide. In addition, we also investigated the therapeutic effect of lycopene in attenuating ischemia/reperfusion brain injury induced by middle cerebral artery (MCA) occlusion in rats. Lycopene (1, 2 and 5 microM) exerted increased DPPH decolorization in the DPPH test, and increased inhibition of iron-catalyzed lipid peroxidation (TBARS formation) in rat brain homogenates in concentration-dependent manners. Furthermore, lycopene (5 and 10 microM) significantly inhibited nitrite production by about 31% and 61% in microglia stimulated by LPS, respectively. Rats which received lycopene at a dosage of 4 mg/kg, but not at 2 mg/kg, showed significant infarct size reductions compared with those which received the solvent control (20% Tween 80). In conclusion, we demonstrate a protective effect of lycopene on ischemic brain injury in vivo. Lycopene, through its antioxidative property, mediates at least a portion of free radical-scavenging activity and inhibits microglia activation, resulting in a reduction in infarct volume in ischemia/reperfusion brain injury.     

Protective effect of icariin on DNA against radical-induced oxidative damage

Icariin (2-(4'-methoxylphenyl)-3-rhamnosido-5-hydroxyl-7-glucosido-8-(3'-methyl-2-butylenyl)-4-chromanone) is a flavonoid with a rhamnose as ligand. It is the major component in Herba epimedii, widely used for the treatment of atherosclerosis and neuropathy in Chinese traditional medicine, and its antioxidative property has attracted much scientific interest. The major objective of this work is to determine the antioxidative effect of icariin against oxidative DNA damage induced by 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). The oxidative damage of DNA was followed by measuring the formation of carbonyl compounds that can react with thiobarbituric acid (TBA) to form thiobarbituric acid reactive substance (TBARS). We found that icariin protects DNA against AAPH-induced oxidative damage in a concentration-dependent manner, although it does not affect the rate of AAPH-induced DNA damage. This result indicates that icariin is a concentration-dependent chemopreventor in protecting DNA against radical-induced damage.     

Antimutagenic and antioxidant characteristics of Chukrasia tabularis A Juss extracts

The current study aims to evaluate the antioxidative and antimutagenic activities of methanol extract and different fractions of Chukrasia tabularis leaves. The antioxidative potential was evaluated using 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation and superoxide anion radical-scavenging assay. The antimutagenic potential was evaluated against direct-acting mutagens, 4-nitro-o-phenylenediamine and sodium azide; and S9-dependent mutagen, 2-aminofluorene in TA98 and TA100 strains of Salmonella typhimurium using Ames assay. It has been found that methanol extract and its fractions were more efficient against S9-dependent mutagen in pre-incubation mode of treatment as compared to direct-acting mutagens in both the strains. Methanol extract and its fractions also exhibited strong radical-scavenging potential. High-performance liquid chromatography (HPLC) analysis of methanol extract showed the presence of gallic acid, epicatechin, 7-hydroxycoumarin, and rutin. From the study, it could be concluded that antioxidative and antimutagenic activity of methanol extract and its fractions was related to the synergistic interactions among different chemical compounds.     

Attenuation of ERK/RSK2-driven NFκB gene expression and cancer cell proliferation by kurarinone, a lavandulyl flavanone isolated from Sophora flavescens ait. roots

We have analyzed in molecular detail how kurarinone, a lavandulyl flavanone isolated from Sophora flavescens, suppresses nuclear factor-κB (NFκB)-driven interleukin-6 (IL6) expression and cancer cell growth. Interleukin-6 (IL6), involved in cancer-related inflammation, acts as an autocrine and paracrine growth factor, which promotes angiogenesis, metastasis, and subversion of immunity, and changes responsivity to hormones and to chemotherapeutics. Our results in estrogen-unresponsive fibroblasts, ribosomal S6 kinase 2 kinase (RSK2) knockout cells, and estrogen receptor (ER)-deficient breast tumor cells show that kurarinone can inhibit tumor cell proliferation and selectively block nuclear NFκB transactivation of specific target genes such as IL6, cyclin D1, SOD2 but not TNFAIP2. This occurs via attenuation of extracellular signal-regulated protein (ERK) and RSK2 kinase pathways and inhibition of S6 kinase ribosomal protein (S6RP) and histone H3 S10 phosphorylation. As constitutive NFκB and RSK2 activity are important hallmarks of human cancers, including hematopoietic malignancies and solid tumors, prenylated flavanones represent an attractive class of natural inhibitors of the ERK/RSK2 signaling pathway for cancer therapy.     

Inhibitory effects of kurarinol, kuraridinol, and trifolirhizin from Sophora flavescens on tyrosinase and melanin synthesis

Previously, it was reported that some prenylated flavonoids contained in the dichloromethane fraction of the ethanolic extract of Sophora flavescens, such as kuraridin, sophoraflavanone G, kurarinone, and kushenol F, are tyrosinase inhibitors; however, based on the level of these inhibitors in the extract, its inhibitory effect on tyrosinase activity was higher than expected. This has led us to further investigate other possible constituents that may contribute to the extract's strong inhibitory activity. The results of this study indicate that kurarinol (1), kuraridinol (2), and trifolirhizin (3), from the ethyl acetate fraction of Sophora extract, can inhibit tyrosinase activity. Compared with kojic acid (16.22+/-1.71 microM), compounds 1-3 possessed potent tyrosinase inhibitory activity with IC(50) values of 8.60+/-0.51, 0.88+/-0.06, and 506.77+/-4.94 microM, respectively. These three compounds were further tested for their inhibitory effects on melanogenesis. In cultured B16 melanoma cells, 1-3 markedly inhibited (>50%) melanin synthesis at 50 microM. This is the first study indicating that 1-3 exert varying degrees of inhibition on tyrosinase-dependent melanin biosynthesis, and therefore, are candidates as skin-whitening agents.     

Phenolic constituents of Malus doumeri var. formosana in the field of skin care

Plant phenolic compounds isolated from a 70% aqueous acetone extract of the leaves of Malus doumeri A. CHEV. var. formosana (KAWAK. & KOIDZ.) S. S. YING, a type of Taiwanese indigenous plant, were evaluated for potential application in the field of skin care. A phytochemical investigation of the active fractions resulted in the isolation of seven compounds of which the structures were identified by spectroscopic characterization. In the present study, the isolated phenolic compounds were evaluated for their free radical-scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and the superoxide radicals, anti-elastase, and for their anti-matrix metalloproteinase-1 (MMP-1) activity in human skin fibroblast cells. Of these compounds, 3-hydroxyphloridzin (2), 3-hydroxyphloretin (6), and quercetin (7) exhibited the strongest DPPH and superoxide radical-scavenging activities. The IC50 values of these compounds were 9.2, 7.7, and 15.4 microM, respectively, for the DPPH radical, and 25.0, 19.6, and 42.6 microM, respectively, for the superoxide radical. 3-Hydroxyphloridzin (2) and 3-hydroxyphloretin (6) also showed xanthine oxidase inhibitory activity, with IC(50) values of 52.1 and 22.4 muM, respectively. In the test for elastase inhibitory activity, phloretin (5) and 3-hydroxyphloretin (6) were the most potent compounds. Phloretin (5), 3-hydroxyphloretin (6), and quercetin (7) showed better inhibition of MMP-1 production in fibroblast cells. To the best of our knowledge, this is the first time that the active phenolic compounds from M. doumeri var. formosana have been isolated, reported, and described. The above results suggest that the extract of M. doumeri var. formosana containing phenolic compounds could be suitable naturally occurring active constituents for use in anti-aging or cosmetic products.     

Antioxidant activities and molecular docking of 2-thioxobenzo[g]quinazoline derivatives

BackgroundOxidative stress and related diseases resulting from the overproduction of free radicals can be counteracted by designing and developing novel antioxidative agents that can protect the human body against the damage caused by free radicals.MethodsThe present study evaluated the antioxidant activities of 15 derivatives of 2-thioxobenzo[g]quinazoline using three different assays: 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging, reducing power capability, and ferric reduction antioxidant power.ResultsSome benzoquinazolines had good activity and had the capacity to deplete DPPH and free radicals compared to a positive control butylated hydroxyl toluene (BHT). A docking study identified the possible interactions between binding models and the antioxidant activities of the target compounds.ConclusionsThe active compounds can be used as templates for further development of more potent antioxidative agents.     

TMPDP, a tetramethylpyrazine derivative, protects vascular endothelial cells from oxidation damage by hydrogen peroxide

A novel ligustrazine derivative, tetramethylpyrazine diphenylmethyl piperazidine (TMPDP), prepared by hybridization and bioisosteric replacement of the molecular structure of TMP, was studied for its protective effects on oxidative damage of human umbilical vein endothelial cells (HUVECs) in response to hydrogen peroxide (H2O2). The antioxidative effect of TMPDP was assessed by the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) test. Cell viability was measured using a 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The activity of lactate dehydrogenase (LDH), superoxide dismutase (SOD) and glutathione peroxidase (GSH) and the content of malondialdehyde (MDA) in cells were determined by commercial kits. The intracellular formation of reactive oxygen species (ROS) and the concentration of free intracellular calcium ([Ca2+]i) were determined using DCFH-DA assay and with fura-2/AM fluorimetry, respectively. Results showed that TMPDP had a moderate antioxidative effect against DPPH. Cell viability was decreased markedly by exposure to H2O2. Introduction of TMPDP, however, significantly increased cell viability, markedly reduced LDH release from cells and decreased lipid peroxidation in response to H2O2 treatment. These effects of TMPDP were accompanied by increased activity of the endogenous antioxidant enzymes, SOD and GSH, reduced production of ROS and reduced intracellular concentration of Ca2+. These results suggest that TMPDP protects HUVECs against oxidative damage by scavenging ROS and regulates intracellular calcium concentration. This might have important implications for the development of new agents for the effective treatment of vascular disease.     

Characterization of the radical-scavenging reaction of 2-O-substituted ascorbic acid derivatives, AA-2G, AA-2P, and AA-2S: a kinetic and stoichiometric study

The aim of this study was to characterize the antioxidant activity of three ascorbic acid (AA) derivatives O-substituted at the C-2 position of AA: ascorbic acid 2-glucoside (AA-2G), ascorbic acid 2-phosphate (AA-2P), and ascorbic acid 2-sulfate (AA-2S). The radical-scavenging activities of these AA derivatives and some common low molecular-weight antioxidants such as uric acid or glutathione against 1,1-diphenyl-picrylhydrazyl (DPPH) radical, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS+), or galvinoxyl radical were kinetically and stoichiometrically evaluated under pH-controlled conditions. Those AA derivatives slowly and continuously reacted with DPPH radical and ABTS+, but not with galvinoxyl radical. They effectively reacted with DPPH radical under acidic conditions and with ABTS+ under neutral conditions. In contrast, AA immediately quenched all species of radicals tested at all pH values investigated. The reactivity of Trolox, a water-soluble vitamin E analogue, was comparable to that of AA in terms of kinetics and stoichiometrics. Uric acid and glutathione exhibited long-lasting radical-scavenging activity against these radicals under certain pH conditions. The radical-scavenging profiles of AA derivatives were closer to those of uric acid and glutathione rather than to that of AA. The number of radicals scavenged by one molecule of AA derivatives, uric acid, or glutathione was equal to or greater than that by AA or Trolox under the appropriate conditions. These data suggest the potential usage of AA derivatives as radical scavengers.