Aureusidin

Anti-inflammatory effects of Aureusidin in LPS-stimulated RAW264.7 macrophages via suppressing NF-kappaB and activating ROS- and MAPKs-dependent Nrf2/HO-1 signaling pathways.[Pubmed:31790703]

Toxicol Appl Pharmacol. 2020 Jan 15;387:114846.

Aureusidin, a naturally-occurring flavonoid, is found in various plants of Cyperaceae such as Heleocharis dulcis (Burm. f.) Trin., but its pharmacological effect and active mechanism are rarely reported. This study aimed to investigate the anti-inflammatory effect and action mechanism of Aureusidin in LPS-induced mouse macrophage RAW264.7 cells. The results suggested that lipopolysaccharide (LPS)-induced nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2) production were obviously inhibited by Aureusidin. Moreover, Aureusidin also significantly decreased the mRNA expression of various inflammatory factors in LPS-stimulated RAW264.7 cells. Furthermore, mechanistic studies showed that Aureusidin significantly inhibited nuclear transfer of nuclear factor-kappaB (NF-kappaB), while increasing the nuclear translocation of nuclear factor E2-related factor 2 (Nrf2) as well as expression of Nrf2 target genes such as heme oxygenase (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1), but the addition of the HO-1 inhibitor Sn-protoporphyrin (Snpp) significantly abolished the anti-inflammatory effect of Aureusidin in LPS-stimulated RAW264.7 cells, confirming the view that HO-1 was involved in the anti-inflammatory effect. In addition, Aureusidin increased the levels of reactive oxygen species (ROS) and mitogen-activated protein kinase (MAPK) phosphorylation in RAW264.7 cells. Antioxidant N-acetylcysteine (NAC) or three MAPK inhibitors blocked the nuclear translocation of Nrf2 and HO-1 expression induced by Aureusidin, indicating that Aureusidin activated the Nrf2/HO-1 signaling pathway through ROS and MAPKs pathways. At the same time, co-treatment with the NAC blocked the phosphorylation of MAPKs. Results from molecular docking indicated that Aureusidin inhibited the NF-kappaB pathway by covalently binding to NF-kappaB. Thus, Aureusidin exerted the anti-inflammatory activity through blocking the NF-kappaB signaling pathways and activating the MAPKs and Nrf2/HO-1 signaling pathways. Based on the above results, Aureusidin may be an attractive therapeutic candidate for the inflammation-related diseases.

Generation of Yellow Flowers of the Japanese Morning Glory by Engineering Its Flavonoid Biosynthetic Pathway toward Aurones.[Pubmed:31135027]

Plant Cell Physiol. 2019 Aug 1;60(8):1871-1879.

Wild-type plants of the Japanese morning glory (Ipomoea nil) produce blue flowers that accumulate anthocyanin pigments, whereas its mutant cultivars show wide range flower color such as red, magenta and white. However, I. nil lacks yellow color varieties even though yellow flowers were curiously described in words and woodblocks printed in the 19th century. Such yellow flowers have been regarded as 'phantom morning glories', and their production has not been achieved despite efforts by breeders of I. nil. The chalcone isomerase (CHI) mutants (including line 54Y) bloom very pale yellow or cream-colored flowers conferred by the accumulation of 2', 4', 6', 4-tetrahydoroxychalcone (THC) 2'-O-glucoside. To produce yellow phantom morning glories, we introduced two snapdragon (Antirrhinum majus) genes to the 54Y line by encoding Aureusidin synthase (AmAS1) and chalcone 4'-O-glucosyltransferase (Am4'CGT), which are necessary for the accumulation of Aureusidin 6-O-glucoside and yellow coloration in A. majus. The transgenic plants expressing both genes exhibit yellow flowers, a character sought for many years. The flower petals of the transgenic plants contained Aureusidin 6-O-glucoside, as well as a reduced amount of THC 2'-O-glucoside. In addition, we identified a novel aurone compound, Aureusidin 6-O-(6''-O-malonyl)-glucoside, in the yellow petals. A combination of the coexpression of AmAS1 and Am4'CGT and suppression of CHI is an effective strategy for generating yellow varieties in horticultural plants.

Dipeptidyl peptidase-IV inhibitory activity of dimeric dihydrochalcone glycosides from flowers of Helichrysum arenarium.[Pubmed:25921859]

J Nat Med. 2015 Oct;69(4):494-506.

A methanol extract of everlasting flowers of Helichrysum arenarium L. Moench (Asteraceae) was found to inhibit the increase in blood glucose elevation in sucrose-loaded mice at 500 mg/kg p.o. The methanol extract also inhibited the enzymatic activity against dipeptidyl peptidase-IV (DPP-IV, IC50 = 41.2 mug/ml), but did not show intestinal alpha-glucosidase inhibitory activities. From the extract, three new dimeric dihydrochalcone glycosides, arenariumosides V-VII (2-4), were isolated, and the stereostructures were elucidated based on their spectroscopic properties and chemical evidence. Of the constituents, several flavonoid constituents, including 2-4, were isolated, and these isolated constituents were investigated for their DPP-IV inhibitory effects. Among them, chalconaringenin 2'-O-beta-D-glucopyranoside (16, IC50 = 23.1 muM) and Aureusidin 6-O-beta-D-glucopyranoside (35, 24.3 muM) showed relatively strong inhibitory activities.

Facile, protection-free, one-pot synthesis of aureusidin.[Pubmed:25532281]

Nat Prod Commun. 2014 Nov;9(11):1563-6.

A new, reliable, and convenient protection-free one-pot method for the synthesis of Aureusidin (1) is described. The present synthetic approach involves the condensation of 4,6-dihydroxybenzofuranone with 3,4-dihydroxybenzaldehyde in the presence of concentrated HCl to afford Aureusidin (1) in good yield with high purity. This procedure offers a short and simple route for the preparation of Aureusidin (1), a bioactive natural product from several vegetal species, as well as for synthesis of other aurones.

Type-3 copper proteins: recent advances on polyphenol oxidases.[Pubmed:25458353]

Adv Protein Chem Struct Biol. 2014;97:1-35.

Recent investigations in the study of plant, fungal, and bacterial type-3 copper proteins are reviewed. Focus is given to three enzymes: catechol oxidases (CO), tyrosinases, and Aureusidin synthase. CO were mostly found in plants, however, in 2010 the first fungal CO was published. The first plant-originated tyrosinase was published in 2014, before tyrosinases were only reported in fungi, bacteria, and human. Aureusidin synthase from yellow snapdragon (Antirrhinum majus) was first published in 2000, as part of yellow flower coloration pathway. In the last years, many important results on type-3 copper enzymes originated from X-ray crystallographic investigations. In addition, studies on site-directed mutagenesis of amino acids around the active site were performed to identify the regions determining monophenolase and/or diphenolase activity. Although X-ray crystallographic structures of CO and tyrosinases are available, many questions like the response for the activation via proteases, sequence-based or structural-based differences between CO, as well as the physiological roles of many polyphenol oxidases still remain to be addressed.

Potential neuroprotective flavonoid-based inhibitors of CDK5/p25 from Rhus parviflora.[Pubmed:23927974]

Bioorg Med Chem Lett. 2013 Sep 15;23(18):5150-4.

Rhus parviflora (Anacardiaceae) is an indigenous medicinal shrub found in South Asia with flavonoid rich edible fruit. This study examined flavonoid derivatives of R. parviflora fruit with CDK5/p25 inhibition activity. Evaluation by in vitro assay and docking simulations for CDK5/p25 revealed that the aurones, sulfuretin (1) and Aureusidin (2), the aurone glycoside, Aureusidin-6-O-beta-D-glucopyranoside (3) and hovetrichoside C (4), the flavonoid glycoside, quercetin-3-O-beta-D-galactopyranoside (5), and the biflavonoid, cupressuflavone (6), had the potential to inhibit CDK5/p25, which could be useful in the treatment of neurodegenerative disorders such as Alzheimer's disease. Compound2 showed the significant in vitro inhibition capacity (IC50 value of 4.81 muM) as well as binding affinity with docking energy of -8.73 (kcal/mol) for active sites CYS83 and GLN130 of CDK5/p25 enzyme in comparison to reference compound R-roscovitine.

Altered leaf colour is associated with increased superoxide-scavenging activity in aureusidin-producing transgenic plants.[Pubmed:22924954]

Plant Biotechnol J. 2012 Dec;10(9):1046-55.

The health-promoting property of diets rich in fruits and vegetables is based, in part, on the additive and synergistic effects of multiple antioxidants. In an attempt to further enhance food quality, we introduced into crops the capability to synthesize a yellow antioxidant, Aureusidin, that is normally produced only by some ornamental plants. For this purpose, the snapdragon (Antirrhinum majus) chalcone 4'-O-glucosyltransferase (Am4'CGT) and Aureusidin synthase (AmAs1) genes, which catalyse the synthesis of Aureusidin from chalcone, were expressed in tobacco (Nicotiana tabacum) and lettuce (Lactuca sativa) plants that displayed a functionally active chalcone/flavanone biosynthetic pathway. Leaves of the resulting transgenic plants developed a yellow hue and displayed higher superoxide dismutase (SOD) inhibiting and oxygen radical absorbance capacity (ORAC) activities than control leaves. Our results suggest that the nutritional qualities of leafy vegetables can be enhanced through the introduction of aurone biosynthetic pathways.

Evaluation of anti-oxidant activity and identification of major polyphenolics of the invasive weed Oxalis pes-caprae.[Pubmed:22552843]

Phytochem Anal. 2012 Nov-Dec;23(6):642-6.

INTRODUCTION: Phytochemical analyses of weeds, many of which have been used in traditional medicine worldwide, could lead to the identification of secondary metabolites with significant biological activity. OBJECTIVE: To perform an assessment of the chemical composition and exploitation potential of the invasive weed Oxalis pes-caprae. To evaluate the anti-oxidant activity of its extracts and isolate and characterise polyphenolic metabolites using LC-DAD-MS (ESI+) and NMR methods. METHODOLOGY: Aerial parts of the invasive weed O. pes-caprae were extracted with solvents of increasing polarity and their major polyphenolic metabolites were identified by LC-DAD-MS (ESI+). The total phenolic content of the extracts was determined using the Folin-Ciocalteu method, while their anti-oxidant activity was evaluated on the basis of their ability to scavenge the stable free radical 1,1-diphenyl-2-picrylhydrazyl and hydrogen peroxide. RESULTS: The major polyphenolic constituents of the extracts were tentatively characterised as chlorogenic acid, quinic ferulate, luteolin glucoside and cernuoside according to their MS and UV spectroscopic data. Cernuoside, an Aureusidin glucoside, was isolated from the methanolic extract of the weed's flowers and its structure was unambiguously identified by 1D- and 2D-NMR spectroscopy. The butanol extract of O. pes-caprae displayed the highest anti-oxidant activity. CONCLUSION: The metabolic profile of O. pes-caprae was studied and the structures of the major polyphenolic metabolites based on their MS and UV-vis spectra were tentatively assigned. The Aureusidin glucoside cernuoside was isolated and characterised for the first time from O. pes-caprae. The extracts exhibited high levels of anti-oxidant activity.

Homology modeling and dynamics study of aureusidin synthase--an important enzyme in aurone biosynthesis of snapdragon flower.[Pubmed:21470561]

Int J Biol Macromol. 2011 Aug 1;49(2):134-42.

Aurones, a class of plant flavonoids, provide bright yellow color on some important ornamental flowers, such as cosmos, coreopsis, and snapdragon (Antirrhinum majus). Recently, it has been elucidated that Aureusidin synthase (AUS), a homolog of plant polyphenol oxidase (PPO), plays a key role in the yellow coloration of snapdragon flowers. In addition, it has been shown that AUS is a chalcone-specific PPO specialized for aurone biosynthesis. AUS gene has been successfully demonstrated as an attractive tool to engineer yellow flowers in blue flowers. Despite these biological studies, the structural basis for the specificity of substrate interactions of AUS remains elusive. In this study, we performed homology modeling of AUS using Grenache PPO and Sweet potato catechol oxidase (CO). An AUS-inhibitor was then developed from the initial homology model based on the CO and subsequently validated. We performed a thorough study between AUS and PTU inhibitor by means of interaction energy, which indicated the most important residues in the active site that are highly conserved. Analysis of the molecular dynamics simulations of the apo enzyme and ligand-bound complex showed that complex is relatively stable than apo and the active sites of both systems are flexible. The results from this study provide very helpful information to understand the structure-function relationships of AUS.

A continuous spectrophotometric assay for determination of the aureusidin synthase activity of tyrosinase.[Pubmed:20029997]

Phytochem Anal. 2010 May-Jun;21(3):273-8.

INTRODUCTION: Aurones (Aureusidin glycosides) are plant flavonoids that provide yellow colour to the flowers of some ornamental plants. In this study we analyse the capacity of tyrosinase to catalyse the synthesis of Aureusidin by tyrosinase from the chalcone THC (2',4',6',4-tetrahydroxychalcone). OBJECTIVE: To develop a simple continuous spectrophotometric assay for the analysis of the spectrophotometric and kinetic characteristics of THC oxidation by tyrosinase. METHODOLOGY: THC oxidation was routinely assayed by measuring the increase in absorbance at 415 nm vs. reaction time. RESULTS: According to the mechanism proposed for tyrosinase, the enzymatic reaction involves the o-hydroxylation of the monophenol THC to the o-diphenol (PHC, 2',4',6',3,4 - pentahydroxychalcone), which is then oxidised to the corresponding o-quinone in a second enzymatic step. This product is highly unstable and thus undergoes a series of fast chemical reactions to produce Aureusidin. In these experimental conditions, the optimum pH for THC oxidation is 4.5. The progress curves obtained for THC oxidation showed the appearance of a lag period. The following kinetic parameters were also determined: K(m )= 0.12 mM, V(m )= 13 microM/min, V(m)/K(m )= 0.11/min. CONCLUSION: This method has made it possible to analyse the spectrophotometric and kinetic characteristics of THC by tyrosinase. This procedure has the advantages of a short analysis time, straightforward measurement techniques and reproducibility. In addition, it also allows the study of tyrosinase inhibitors, such as tropolone.

Natural and synthetic 2'-hydroxy-chalcones and aurones: synthesis, characterization and evaluation of the antioxidant and soybean lipoxygenase inhibitory activity.[Pubmed:19853459]

Bioorg Med Chem. 2009 Dec 1;17(23):8073-85.

A series of 2'-hydroxy-chalcones and their oxidative cyclization products, aurones, have been synthesized and tested for their antioxidant and lipoxygenase inhibitory activity. The natural product Aureusidin (31) was synthesized in high yield by a new approach. An extensive structure-relationship study was performed and revealed that several chalcones and aurones possess an appealing pharmacological profile combining high antioxidant and lipid peroxidation activity with potent soybean LOX inhibition.

Yellow flowers generated by expression of the aurone biosynthetic pathway.[Pubmed:16832053]

Proc Natl Acad Sci U S A. 2006 Jul 18;103(29):11075-80.

Flower color is most often conferred by colored flavonoid pigments. Aurone flavonoids confer a bright yellow color on flowers such as snapdragon (Antirrhinum majus) and dahlia (Dahlia variabilis). A. majus Aureusidin synthase (AmAS1) was identified as the key enzyme that catalyzes aurone biosynthesis from chalcones, but transgenic flowers overexpressing AmAS1 gene failed to produce aurones. Here, we report that chalcone 4'-O-glucosyltransferase (4'CGT) is essential for aurone biosynthesis and yellow coloration in vivo. Coexpression of the Am4'CGT and AmAS1 genes was sufficient for the accumulation of Aureusidin 6-O-glucoside in transgenic flowers (Torenia hybrida). Furthermore, their coexpression combined with down-regulation of anthocyanin biosynthesis by RNA interference (RNAi) resulted in yellow flowers. An Am4'CGT-GFP chimeric protein localized in the cytoplasm, whereas the AmAS1(N1-60)-RFP chimeric protein was localized to the vacuole. We therefore conclude that chalcones are 4'-O-glucosylated in the cytoplasm, their 4'-O-glucosides transported to the vacuole, and therein enzymatically converted to aurone 6-O-glucosides. This metabolic pathway is unique among the known examples of flavonoid, including anthocyanin biosynthesis because, for all other compounds, the carbon backbone is completed before transport to the vacuole. Our findings herein not only demonstrate the biochemical basis of aurone biosynthesis but also open the way to engineering yellow flowers for major ornamental species lacking this color variant.

Localization of a flavonoid biosynthetic polyphenol oxidase in vacuoles.[Pubmed:16367960]

Plant J. 2006 Jan;45(2):133-43.

Aureusidin synthase, a polyphenol oxidase (PPO), specifically catalyzes the oxidative formation of aurones from chalcones, which are plant flavonoids, and is responsible for the yellow coloration of snapdragon (Antirrhinum majus) flowers. All known PPOs have been found to be localized in plastids, whereas flavonoid biosynthesis is thought to take place in the cytoplasm [or on the cytoplasmic surface of the endoplasmic reticulum (ER)]. However, the primary structural characteristics of Aureusidin synthase and some of its molecular properties argue against localization of the enzyme in plastids and the cytoplasm. In this study, the subcellular localization of the enzyme in petal cells of the yellow snapdragon was investigated. Sucrose-density gradient and differential centrifugation analyses suggested that the enzyme (the 39-kDa mature form) is not located in plastids or on the ER. Transient assays using a green fluorescent protein (GFP) chimera fused with the putative propeptide of the PPO precursor suggested that the enzyme was localized within the vacuole lumen. We also found that the necessary information for vacuolar targeting of the PPO was encoded within the 53-residue N-terminal sequence (NTPP), but not in the C-terminal sequence of the precursor. NTPP-mediated ER-to-Golgi trafficking to vacuoles was confirmed by means of the co-expression of an NTPP-GFP chimera with a dominant negative mutant of the Arabidopsis GTPase Sar1 or with a monomeric red fluorescent protein (mRFP)-fused Golgi marker (an H+-translocating inorganic pyrophosphatase of Arabidopsis). We identified a sequence-specific vacuolar sorting determinant in the NTPP of the precursor. We have demonstrated the biosynthesis of a flavonoid skeleton in vacuoles. The findings of this metabolic compartmentation may provide a strategy for overcoming the biochemical instability of the precursor chalcones in the cytoplasm, thus leading to the efficient accumulation of aurones in the flower.

Enzymology of aurone biosynthesis.[Pubmed:16233339]

J Biosci Bioeng. 2002;94(6):487-91.

Aurones belong to a class of plant flavonoids that provides the bright yellow color of some important ornamental flowers, such as snapdragon (Antirrhinum majus). Despite the potential significance of the enzyme(s) and gene(s) responsible for aurone biosynthesis in biotechnology, the enzymological details of aurone biosynthesis were not established until recently. During the past two years, however, the biosynthetic pathway of aurones in yellow snapdragon has been elucidated, and a key enzyme of the pathway, Aureusidin synthase, and its cDNA have been isolated. This enzyme was identified as a chalcone-specific homolog of plant polyphenol oxidase and this provides unambiguous evidence for a new biological function of plant polyphenol oxidases, i.e., flower coloration.