Green tea polyphenols: antioxidative and prooxidative effects.
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Animals↗
Biomedical subjects
Shengmin Sang
Publications and source records attributed to Shengmin Sang.
Chemical studies of the antioxidant mechanism of tea catechins: radical reaction products of epicatechin with peroxyl radicals.
Tea catechins, an important class of polyphenols, have been shown to have antioxidant activity and are thought to act as antioxidants in biological systems. However, the mechanisms of their antioxidant reactions remain unclear. The objective of this study was to characterize the reaction products of epicatechin with peroxyl radicals generated by thermolysis of the azo initiator azo-bisisobutyrylnitrile (AIBN). Structural elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. Eight reaction products were isolated and identified using high-field 1D and 2D NMR spectral analysis. The observation of these compounds confirmed that the B-ring is the initial site for formation of reaction products in the peroxyl radical oxidant system.
Antioxidants↗
New unusual iridoids from the leaves of noni (Morinda citrifolia L.) show inhibitory effect on ultraviolet B-induced transcriptional activator protein-1 (AP-1) activity.
A novel iridoid dimer in whose structure the two iridoid units are connected by a rare ether group, together with two new unusual iridoids showing significant inhibition of UVB-induced Activator Protein-1 (AP-1) activity in cell cultures, have been isolated from the leaves of noni (Morinda citrifolia L.). Their structures were determined on the basis of detailed high-field 1D and 2D spectral analysis. Their inhibitory effect on UVB-induced transcriptional Activator Protein-1 (AP-1) activity are also discussed.
Animals↗
Glucuronides of tea catechins: enzymology of biosynthesis and biological activities.
(-)-Epigallocatechin gallate (EGCG) and (-)-epigallocatechin (EGC) are major green tea catechins with antioxidant and anticancer activities. In this study, we characterized the glucuronidation of EGCG and EGC in human, mouse, and rat microsomes and by nine different human UGT 1A and 2B isozymes expressed in insect cells. Six EGCG and EGC glucuronides were biosynthesized, and their structures were identified for the first time. (-)-EGCG-4"-O-glucuronide was the major EGCG glucuronide formed in all incubations. The catalytic efficiency (V(max)/K(m)) for (-)-EGCG-4"-O-glucuronide formation followed the order: mouse intestine > mouse liver > human liver > rat liver >> rat small intestine. The UGT-catalyzed glucuronidation of EGC was much lower than that of EGCG. The V(max)/K(m) for (-)-EGC-3'-O-glucuronide followed the following order: mouse liver > human liver > rat liver > rat and mouse small intestine. Human UGT1A1, 1A8, and 1A9 had high activities with EGCG. UGT1A8, an intestine-specific UGT, had the highest V(max)/K(m) for EGCG but low activity with EGC. Mice appeared to be more similar to humans than rats to humans in the glucuronidation of EGCG and EGC. Some of these catechin glucuronides retained the activities of their parent compounds in radical scavenging and in inhibiting the release of arachidonic acid from HT-29 human colon cancer cells. These results provide foundations for understanding the biotransformation and biological activities of tea catechins.
Animals↗
Antifungal constituents from the seeds of Allium fistulosum L.
A new unsaturated fatty acid monoglyceride (1), glycerol mono-(E)-8,11,12-trihydroxy-9-octadecenoate, was isolated from the seeds of Allium fistulosum L. along with five known compounds: tianshic acid (2), 4-(2-formyl-5-hydroxymethylpyrrol-1-yl) butyric acid (3), p-hydroxybenzoic acid (4), vanillic acid (5), and daucosterol (6). The structures of 1-3 were established by interpretation and full assignments of NMR spectroscopic data. Both 1 and 2 were found to inhibit the growth of Phytophtohora capsici on V8 media.
Allium↗
Sphingolipid and other constituents from almond nuts (Prunus amygdalus Batsch).
One sphingolipid, 1-O-beta-D-glucopyranosyl-(2S,3R,4E,8Z)-2-[(2R)-2-hydroxyhexadecanoylamino]-4,8-octadecadiene-1,3-diol, and four other constituents, beta-sitosterol, daucosterol, uridine, and adenosine, have been isolated from the nuts of almond (Prunus amygdalus). Complete assignments of the proton and carbon chemical shifts for the sphingolipid were accomplished on the basis of high-resolution 1D and 2D NMR data. All of these compounds are being reported from almond nuts (P. amygdalus)for the first time.
Adenosine↗
Mechanism of the superoxide scavenging activity of neoandrographolide - a natural product from Andrographis paniculata Nees.
It was hypothesized that neoandrographolide might scavenge free radicals by donating the allylic hydrogen of the unsaturated lactone ring. It was found that the stoichiometry of the reaction between neoandrographolide and superoxide radical generated from KO(2) in DMSO was 2 to 1. One major reaction product was isolated and determined to be a diacid formed by the opening of the lactone ring. It was concluded that the antiradical activity of neoandrographolide proceeded by hydrogen abstraction from carbon C-15. A reaction mechanism was proposed.
Chromatography, High Pressure Liquid↗
Characterization of 2-methyl-4-amino-5-(2-methyl-3-furylthiomethyl)pyrimidine from thermal degradation of thiamin.
Thiamin hydrochloride was thermally degraded in phosphate buffer (pH 6.5) at 110 degrees C for 2 h. A major decomposition product was isolated by column chromatography and structurally identified by spectrometric techniques ((1)H NMR, (13)C NMR, 2D NMR, and MS) as 2-methyl-4-amino-5-(2-methyl-3-furylthiomethyl)pyrimidine (MAMP). The possible formation pathway of MAMP was studied using two model systems. It is proposed that MAMP is formed by nucleophilic attack of 2-methyl-3-furanthiol on the thiamin.
Buffers↗
Antioxidative phenolic compounds isolated from almond skins (Prunus amygdalus Batsch).
Nine phenolic compounds were isolated from the ethyl acetate and n-butanol fractions of almond (Prunus amygdalus) skins. On the basis of NMR data, MS data, and comparison with the literature, these compounds were identified as 3'-O-methylquercetin 3-O-beta-D-glucopyranoside (1); 3'-O-methylquercetin 3-O-beta-D-galactopyranoside (2); 3'-O-methylquercetin 3-O-alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside (3); kaempferol 3-O-alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranoside (4); naringenin 7-O-beta-D-glucopyranoside (5); catechin (6); protocatechuic acid (7); vanillic acid (8); and p-hydroxybenzoic acid (9). All of these compounds have been isolated from almond skins for the first time. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activities for compounds 1-9 were determined. Compounds 6 and 7 show very strong DPPH radical scavenging activity. Compounds 1-3, 5, 8, and 9 show strong activity, whereas compound 4 has very weak activity.
1-Butanol↗
Triterpene saponins from debittered quinoa (Chenopodium quinoa) seeds.
Twelve triterpene saponins have been isolated from the debittered seeds of quinoa (Chenopodium quinoa), and their structures were characterized on the basis of hydrolysis and spectral data, especially NMR evidence. Among them, three compounds, including 3-O-beta-D-glucuropyranosyl oleanolic acid (1), 3-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranosyl hederagenin (2), and the new compound 3-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranosyl-30-O-methyl spergulagenate 28-O-beta-D-glucopyranosyl ester (3), are identified for the first time from quinoa seeds. The other isolated saponins have been previously reported in quinoa.
Chenopodium quinoa↗
New prenylated benzoic acid and other constituents from almond hulls (Prunus amygdalus Batsch).
One new prenylated benzoic acid derivative, 3-prenyl-4-O-beta-D-glucopyranosyloxy-4-hydroxylbenzoic acid, and three known constituents, catechin, protocatechuic acid, and ursolic acid, have been isolated from the hulls of almond (Prunus amygdalus). Complete assignments of the proton and carbon chemical shifts for the new prenylated benzoic acid derivative were accomplished on the basis of high-resolution 1D and 2D nuclear magnetic resonance data. All of these compounds except ursolic acid are being reported from almond hulls (P. amygdalus) for the first time.
Anti-Infective Agents↗
Chemical studies on antioxidant mechanism of tea catechins: analysis of radical reaction products of catechin and epicatechin with 2,2-diphenyl-1-picrylhydrazyl.
Tea catechins, an important class of polyphenols, have been shown to have wide spectrum of antitumor activity believed to be due mainly to their antioxidative effect. In this study, the radical scavenging behavior of catechins on 2,2-diphenyl-1-picrylhydrazyl (DPPH) was studied. Two reaction products of (+)-catechin, and two reaction products of (-)-epicatechin were purified and identified. Their structures were determined on the basis of detailed high-field 1-D and 2-D NMR spectral analysis. Structure elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. A possible mechanism of the formation of reaction products is suggested.
Antioxidants↗
Identification and characterization of methylated and ring-fission metabolites of tea catechins formed in humans, mice, and rats.
(-)-Epigallocatechin gallate (EGCG), the most abundant tea catechin, has been proposed to be beneficial to human health based on its strong antioxidative and other biological activities in vitro. Inadequate knowledge regarding the bioavailability and biotransformation of EGCG in humans, however, has limited our understanding of its possible beneficial health effects. In this study, 4',4' '-di-O-methyl-EGCG (4',4' '-DiMeEGCG) was detected in human plasma and urine by LC/MS/MS following green tea ingestion. Both 4',4' '-DiMeEGCG and EGCG reached peak plasma values (20.5 +/- 7.7 and 145.4 +/- 31.6 nM, respectively, in 4 subjects) at 2 h after the dose. The half-lives of 4',4' '-DiMeEGCG and EGCG were 4.1 +/- 0.8 and 2.7 +/- 0.9 h, respectively. The cumulative urinary excretion of 4',4' '-DiMeEGCG during a 24 h period was 140.3 +/- 48.6 microg, about 5-fold higher than that of EGCG, but the excreted 4',4' '-DiMeEGCG and EGCG in urine only accounted for about 0.1% of ingested EGCG. (-)-5-(3',4',5'-Trihydroxyphenyl)-gamma-valerolactone (M4) and (-)-5-(3',4'-dihydroxyphenyl)-gamma-valerolactone (M6), along with another possible ring-fission metabolite, (-)-5-(3',5'-dihydroxyphenyl)-gamma-valerolactone (M6'), were detected in human urine after green tea ingestion. The cumulative excretion of M4, M6', and M6 during a 24 h period ranged from 75 microg to 1.2 mg, 0.6 to 6 mg, and 0.6 to 10 mg, respectively. The combined excretion of all three ring-fission metabolites accounted for 1.5-16% of ingested catechins. M4, M6', and M6 were all observed after the ingestion of pure EGCG or EGC by human subjects, whereas only M6 was produced after EC ingestion. These metabolites as well as monomethylated EGCG were detected in mice and rats after tea or EGCG administration, and the tissue levels reflected the rather low bioavailability of EGCG in rats. The presently characterized methylated EGCG metabolites and ring-fission products exist in substantial quantities and may contribute to the biological activities of tea.
Adult↗
Determination of diarylheptanoids from Alpinia officinarum (Lesser Galangal) by HPLC with photodiode array and electrochemical detection.
Normal-phase column chromatography followed by semi-preparative reversed-phase HPLC has been used to isolate, from the rhizomes of Alpinia officinarum, five diarylheptanoids identified as 5-hydroxy-7-(4"-hydroxy-3"-methoxyphenyl)-1-phenyl-3-heptanone, 5-methoxy-7-(4"-hydroxy-3"-methoxyphenyl)-1-phenyl-3-heptanone, 7-(4"-hydroxyphenyl)-1-phenylhept-4-en-3-one, 7-(4"-hydroxy-3"-methoxyphenyl)-1-phenyl-hept-4-en-3-one, 1,7-diphenylhept-4-en-3-one. The levels of these five diarylheptanoids in root material were determined quantitatively by HPLC with UV detection and the assay methods so developed were simple, rapid and accurate. Four of the diarylheptanoids could also be detected by HPLC with electrochemical detection (ECD) in the oxidative mode, and ECD was found to have a higher sensitivity than photodiode array detection.
Alpinia↗
Redox properties of tea polyphenols and related biological activities.
Plant polyphenolic compounds are known to be strong antioxidants. Because oxidative stress is believed to contribute to many acute and chronic diseases, these polyphenols have been postulated to have many beneficial health effects, such as the prevention of cancer and cardiovascular diseases. Indeed, some of these beneficial effects have been demonstrated in animal models and in some, but not all, epidemiological studies. Nevertheless, only some of these activities have been demonstrated to be associated with the antioxidative activities of polyphenols. In studies with cell lines in culture, some of the observed activities may be due to superoxide and hydrogen peroxide produced during the autooxidation of polyphenols. Such pro-oxidation-dependent reactions may not happen in tissues where the oxygen partial pressure is much lower than that in cell culture medium. This review will use the well-studied tea polyphenol, (-)-epigallocatechin-3-gallate, as an example to illustrate the redox properties of polyphenols and their influence on signaling pathways related to anti-cancer activities. Existing data suggest, however, that most of the relevant mechanisms of cancer prevention by tea polyphenols are not related to their redox properties, but are due to the direct binding of the polyphenol to target molecules, including the inhibition of selected protein kinases, matrix metalloproteinases, and DNA methyltransferases.
Animals↗