Sterling: Anthocyanins (2001)

1. Elliot. Inhibition of glutathione reductase by flavonoids. A structure-activity study. Biochem Pharmacol 1992;44(8): 1603-8.

A structure-activity study of fourteen chemically related flavonoids was conducted to evaluate their abilities to inhibit glutathione reductase (GR). By comparing the I50 values of flavonoids from different classes possessing an identical hydroxyl configuration, we determined the following order of potency for inhibition of GR: anthocyanidin > dihydroflavonol = chalcone > flavonol > catechin. Enzyme inhibition by delphinidin chloride and myricetin was partially prevented in a N2 atmosphere which implicates a role for oxygen in the mechanism of inhibition. To determine the role of oxygen species in enzyme inhibition, GR was preincubated with either mannitol, diethylenetriaminepenta-acetic acid (DETAPAC), superoxide dismutase (SOD), catalase (CAT), or SOD and CAT prior to assays for enzyme inhibition by flavonoids. Enzyme inhibition by delphinidin chloride and myricetin was suppressed by the addition of SOD, suggesting that superoxide (O2-.) is involved. However, inhibition by quercetin and morin was not sensitive to antioxidants. To further investigate the role of O2-. in GR inhibition, a superoxide generating system was utilized in the presence and absence of flavonoid. The O2-. generating system failed to inhibit GR in the absence of flavonoid but enhanced the inhibition by myricetin, indicating that the O2-. did not directly inhibit GR but reacted directly with certain flavonoids to form a reactive intermediate which, in turn, inhibited GR. These findings suggest that the mechanism of inhibition of GR by flavonoids is complex and may have oxygen-dependent and oxygen-independent components.

2. Wang SY, Jiao H. Scavenging capacity of berry crops on superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. J Agric Food Chem 2000 Nov;48(11):5677-84.

The antioxidant activities against superoxide radicals (O2), hydrogen peroxide (H2O2), hydroxyl radicals (OH•), and singlet oxygen ('O2) was evaluated in fruit juice from different cultivars of thornless blackberries (Rubus sp.), blueberries (Vaccinium spp.), cranberries (Vaccinium macrocarpon Aiton), raspberries (Rubus idaeus L. and Rubus occidentalis L.), and strawberries (Fragaria x ananassa Duch.). Among the different cultivars, juice of 'Hull Thornless' blackberry, 'Earliglow' strawberry, 'Early Black' cranberry, 'Jewel' raspberry, and 'Elliot' blueberry had the highest antioxidant capacity against superoxide radicals (O2), hydrogen peroxide (H2O2), hydroxyl radicals (OH•), and singlet oxygen ('O2). In general, blackberries had the highest antioxidant capacity inhibition of O2, H2O2, and OH•. Strawberry was second best in the antioxidant capacity assay for these same free radicals. With regard to 'O2 scavenging activity, strawberry had the highest value, while blackberry was second. Cranberries had the lowest inhibition of H2O2 activity. Meanwhile, blueberries had the lowest antioxidant capacity against OH• and 'O2. There were interesting and marked differences among the different antioxidants in their abilities to scavenge different reactive oxygen species. beta-Carotene had by far the highest scavenging activity against 'O2 but had absolutely no effect on H2O2. Ascorbic acid was the best at inhibiting H2O2 free radical activity. For OH•, there was a wide range of scavenging capacities from a high of 15.3% with alpha-tocopherol to a low of 0.88% with ascorbic acid. Glutathione had higher O2 scavenging capacity compared to the other antioxidants.

3. Igarashi K, et al. Preventive effects of dietary cabbage acylated anthocyanins on paraquat-induced oxidative stress in rats. Biosci Biotechnol Biochem 2000 Aug;64(8):1600-7.

The preventive effects of acylated anthocyanins from red cabbage on paraquat-induced oxidative stress were determined in rats. Decreased food intake and body weight gain, and increased lung weight and atherogenic index by feeding the rats on a diet containing paraquat were clearly suppressed by supplementing acylated anthocynins to the paraquat diet. Paraquat feeding increased the concentration of thiobarbituric acid-reactive substances (TBARS) in liver lipids, and decreased the liver triacylglycerol level. These effects tended to be suppressed by supplementing acylated anthocynins to the paraquat diet. In addition, the catalase activity in the liver mitochondrial fraction was markedly decreased by feeding on the paraquat diet, this decrease being partially suppressed by supplementing the paraquat diet with acylated anthocyanins. An increase in the NADPH-cytochrome-P450-reductase activity in the liver microsome fraction by paraquat was suppressed by supplementing the paraquat diet with acylated anthocyanins. These results suggest that acylated anthocyanins from red cabbage acted preventively against the oxidative stress in vivo that may have been due to active oxygen species formed through the action of paraquat.

4. Tsuda T. The role of anthocyanins as an antioxidant under oxidative stress in rats. Biofactors 2000;13(1-4):133-9.

Cyanidin 3-O-β-D-glucoside (C3G) is included in anthocyanins, and expected to have a potency to scavenge active oxygen species in vivo. Rats were fed a diet containing C3G (2 g/kg diet) for 14 days, and then subjected to hepatic ischemia-reperfusion (I/R) as an oxidative stress model. I/R treatment elevated the liver thiobarbituric acid-reactive substance concentration and the serum activities of marker enzymes for liver injury, and lowered the liver reduced glutathione concentration. Feeding C3G significantly suppressed these changes caused by hepatic I/R. These results indicate that C3G functions as a potent antioxidant in vivo under oxidative stress. To clarify the mechanism of action of C3G, we investigated the absorption and metabolism of C3G in rats. C3G appeared in the plasma immediately after the oral administration of C3G. Protocatechuic acid, which seems to be produced by the degradation of cyanidin, was also present in the plasma. In the liver and kidneys, C3G was metabolized to methylated form.

5. Tsuda T. Dietary cyanidin 3-O-β-D-glucoside increases ex vivo oxidative resistance of serum in rats. Lipids 1998 Jun;33(6):583-8.

The effect of dietary cyanidin 3-O-β-d-glucoside (C3G), a typical anthocyanin pigment, on the generation of thiobarbituric acid reactive substances (TBARS) during serum formation ex vivoand susceptibility of serum to further lipid peroxidation was studied in rats. Rats were fed a diet containing C3G (2 g/kg) for 14 d. Feeding C3G resulted in a significant decrease in generation of TBARS during serum formation. The serum from the C3G-fed group showed a significantly lower susceptibility to further lipid peroxidation provoked by 2,2'-azobis (2-amidinopropane)hydrochloride or Cu2+ than that of the control group. No significant differences were observed in serum phospholipid, triglyceride, esterified cholesterol, and free fatty acid concentrations between the control and the C3G-fed groups. Concentrations of endogenous antioxidants remaining in the serum after blood coagulation were not affected by the C3G feeding. These results demonstrate that feeding C3G increases the ex vivo oxidation resistance of the serum without affecting serum endogeneous antioxidant levels, and reduces the TBARS generated during serum formation without changing the concentrations of serum lipids.

6. Rice-Evans CA. The relative antioxidant activities of plant-derived polyphenolic flavonoids. Free Radical Res 1995 Apr;22(4):3785-93.

The relative antioxidant activities, against radicals generated in the aqueous phase, of a range of plant-derived polyphenolic flavonoids, constituents of fruit, vegetables, tea and wine, have been assessed. The results show that compounds such as quercetin and cyanidin, with 3',4' dihydroxy substituents in the B ring and conjugation between the A and B rings, have antioxidant potentials four times that of Trolox, the vitamin E analogue. Removing the ortho-dihydroxy substitution, as in kaempferol, or the potential for electron delocalisation by reducing the 2,3 double bond in the C ring, as in catechin and epicatechin, decreases the antioxidant activity by more than 50%, but these structures are still more effective than alpha-tocopherol or ascorbate. The relative significance of the positions and extents of hydroxylation of the A and B rings to the total antioxidant activity of these plant polyphenolics is demonstrated.

7. Tsuda T. Mechanism for the peroxynitrite scavenging activity by anthocyanins. FEBS Lett 2000 Nov 10;484(3):207-10.

We show that anthocyanins can function as potent inhibitors of the formation of nitrated tyrosine in vitro, and clarified how pelargonidin (Pel), which has a mono-hydroxyl group on the B-ring, can scavenge peroxynitrite (ONOO) by detection of the reaction products. Pel was reacted with ONOO, then the reaction mixture was analyzed using high-performance liquid chromatography (HPLC). The HPLC analyses showed two novel peaks assumed to be the reaction products. Based on the instrumental analyses, the reaction products were identified as p-hydroxybenzoic acid and 4-hydroxy-3-nitrobenzoic acid. Pel can protect tyrosine from undergoing nitration through the formation of p-hydroxybenzoic acid and 4-hydroxy-3-nitrobenzoic acid.

8. Noda Y. Antioxidant activity of nasunin, an anthocyanin in eggplant peels. Toxicology 2000 Aug 7;148(2-3):119-23.

The free radical scavenging activities and inhibitory effect of lipid peroxidation of a delphinidin derivative in eggplant were investigated. Delphinidin-3-(p-coumaroylrutinoside)-5-glucoside (nasunin), an anthocyanin, was isolated as purple colored crystals from eggplant peels. Using electron spin resonance spectrometry and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), hydroxyl radicals (•OH) or superoxide anion radicals (O2) generated by the Fenton reaction or the hypoxanthine-xanthine oxidase system were measured as DMPO–OH or DMPO–OOH spin adducts. l-Ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6yl-hydrogen phosphate] potassium salt (EPC-K1) and bovine erythrocyte superoxide dismutase (SOD) were used as standards for •OH and O2scavengers, respectively. Nasunin showed potent O2 scavenging (143±8 SOD-equivalent U/mg) and •OH scavenging (0.65±0.07 EPC-K1-equivalent µmol/mg) activities. Then, by changing the concentration of DMPO to vary the trapping rate of •OH, the presence of a competitive reaction between nasunin and •OH was studied. The 50% inhibition dose (ID50) obtained from the inhibition curve did not change, indicating •OH scavenging of nasunin is not due to direct scavenging but inhibition of •OH generating system by chelating ferrous ion. Nasunin protection against H2O2-induced lipid peroxidation in rat brain homogenate was measured at 586 nm using the indicator of malonaldehyde and 4-hydroxyalkenals. Nasunin (<50 µM) protected against lipid peroxidation of brain homogenates. The findings suggest that nasunin is a potent O2 scavenger and has protective activity against lipid peroxidation.

9. Bertuglia S, et al. Effect of Vaccinium myrtillus anthocyanosides on ischemia reperfusion injury in hamster cheek pouch microcirculation. Pharmacol Res 1995;31(3/4):183-7.

The effects of Vaccinium Myrtillus anthocyanosides (Myrtocyan, VMA; CAS 84082-34-8) on arteriolar vasomotion were assessed in cheek pouch microcirculation of anesthetized hamsters and in skeletal muscle microvasculature of unanesthetized hamster skin fold window preparation. Intravenously injected VMA induced vasomotion in cheek pouch arterioles and terminal arterioles with higher frequency in smaller vessels. In the skeletal muscle arteriolar networks VMA increased vasomotion frequency and amplitude in all vessel orders. The results indicate that VMA are effective in promoting and enhancing arteriolar rhythmic diameter changes, that play a role in the redistribution of microvascular blood flow and interstitial fluid formation.

10. Quecan B. X. V. et al. Effect of Quercetin Rich Onion Extracts on Bacterial Quorum Sensing. Front. Microbiol., (24 April 2019)

Quorum sensing (QS) regulates bacterial gene expression and studies suggest quercetin, a flavonol found in onion, as a QS inhibitor. There are no studies showing the anti-QS activity of plants containing quercetin in its native glycosylated forms. This study aimed to evaluate the antimicrobial and anti-QS potential of organic extracts of onion varieties and its representative phenolic compounds quercetin aglycone and quercetin 3-β-D-glucoside in the QS model bacteria Chromobacterium violaceum ATCC 12472, Pseudomonas aeruginosa PAO1, and Serratia marcescens MG1. Three phenolic extracts were obtained: red onion extract in methanol acidified with 2.5% acetic acid (RO-1), white onion extract in methanol (WO-1) and white onion extract in methanol ammonium (WO-2). Quercetin 4-O-glucoside and quercetin 3,4-O-diglucoside were identified as the predominant compounds in both onion varieties using HPLC-DAD and LC-ESI-MS/MS. However, quercetin aglycone, cyanidin 3-O-glucoside and quercetin glycoside were identified only in RO-1. The three extracts showed minimum inhibitory concentration (MIC) values equal to or above 125 µg/ml of dried extract. Violacein production was significantly reduced by RO-1 and quercetin aglycone, but not by quercetin 3-β-D-glucoside. Motility in P. aeruginosa PAO1 was inhibited by RO-1, while WO-2 inhibited S. marcescens MG1 motility only in high concentration. Quercetin aglycone and quercetin 3-β-D-glucoside were effective at inhibiting motility in P. aeruginosa PAO1 and S. marcescens MG1. Surprisingly, biofilm formation was not affected by any extracts or the quercetins tested at sub-MIC concentrations. In silico studies suggested a better interaction and placement of quercetin aglycone in the structures of the CviR protein of C. violaceum ATCC 12472 than the glycosylated compound which corroborates the better inhibitory effect of the former over violacein production. On the other hand, the two quercetins were well placed in the AHLs binding pockets of the LasR protein of P. aeruginosa PAO1. Overall onion extracts and quercetin presented antimicrobial activity, and interference on QS regulated production of violacein and swarming motility.