Fagopyrins and Protofagopyrins: Detection, Analysis, and Potential Phototoxicity in Buckwheat

Fagopyrins from Buckwheat Flowers: Structural and Stereochemical Characterization Through Combined NMR/CD Spectroscopy and Theoretical Calculations

Fagopyrins are phenantroperylenequinones present in the flowers of Fagopyrum esculentum (buckwheat) endowed with photodynamic activity. It has been reported that fagopyrin extracts actually contain a complex mixture of closely related compounds, differing only on the nature of the perylenequinone substituents. We report our systematic and detailed study on the chemical composition of fagopyrin extracts by a combination of preparative and analytical techniques. The combined use of 1H-NMR and CD spectroscopy was found to be particularly suited to fully characterize all stereochemical aspects of the extracted fagopyrins. For the first time nine isomers have been structurally characterized and their stereochemistry fully elucidated. The presence of two different heterocyclic ring substituents, two stereogenic centers and the inherent axial chirality of the aromatic system provides a complex stereochemical relationships among isomers, thus giving account of the high level of molecular multiplicity found in the extract.

Fagopyrin F fraction from Fagopyrum tataricum demonstrates photodynamic inactivation of skin infecting bacterium and squamous cell carcinoma (A431) cells

Photodynamic therapy (PDT) stands out as a noteworthy development as an alternative targeted treatment against skin ailments. While PDT has advanced significantly, research into photo-activatable "Green drugs" derived from plants which are less toxic than the synthetic drugs has not kept pace. This study investigates the potential of Fagopyrin F Containing Fraction (FCF) derived from Fagopyrum tataricum in mediating PDT against Staphylococcus aureus and skin cancer cells (A431). FCF was isolated from the plant extract using thin-layer chromatography, followed by identification of the compound through high-performance liquid chromatography and high-resolution liquid chromatography-mass spectrometry. FCF was tested to determine its antibacterial and anticancer efficacy. Results revealed that FCF-mediated PDT exhibited potent action against S. aureus, significantly reducing bacterial viability (MIC 19.5 μg/100 μL). Moreover, FCF-mediated PDT showed good efficacy against A431 cells, resulting in a notable reduction in cell viability (IC50 29.08 μg/mL). Given the known association between S. aureus and squamous cell carcinoma (SCC), FCF shows the potential to effectively target and eradicate both SCC and the related S. aureus present within the lesions. In silico study reveals that Fagopyrin F effectively binds with the epidermal growth factor (EGFR), one among the highly expressed proteins in the A431 cells, with a binding energy of - 9.6 kcal/mol. The affinity of Fagopyrin F for EGFR on A431 cancer cells along with its cytotoxicity against skin cancer cells while safeguarding the normal cells (L929) plays a major part in the way it targets cancer cells. However, its safety, efficacy, and long-term advantages in treating skin conditions require more investigation, including in vivo investigations and clinical trials.

Phytochemistry, Bioactivities of Metabolites, and Traditional Uses of Fagopyrum tataricum

In Tartary buckwheat (Fagopyrum tataricum), the edible parts are mainly grain and sprouts. Tartary buckwheat contains protecting substances, which make it possible for plants to survive on high altitudes and under strong natural ultraviolet radiation. The diversity and high content of phenolic substances are important for Tartary buckwheat to grow and reproduce under unfriendly environmental effects, diseases, and grazing. These substances are mainly flavonoids (rutin, quercetin, quercitrin, vitexin, catechin, epicatechin and epicatechin gallate), phenolic acids, fagopyrins, and emodin. Synthesis of protecting substances depends on genetic layout and on the environmental conditions, mainly UV radiation and temperature. Flavonoids and their glycosides are among Tartary buckwheat plants bioactive metabolites. Flavonoids are compounds of special interest due to their antioxidant properties and potential in preventing tiredness, diabetes mellitus, oxidative stress, and neurodegenerative disorders such as Parkinson's disease. During the processing and production of food items, Tartary buckwheat metabolites are subjected to molecular transformations. The main Tartary buckwheat traditional food products are bread, groats, and sprouts.

Molecular Shield for Protection of Buckwheat Plants from UV-B Radiation

Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) and common buckwheat (Fagopyrum esculentum Moench) are adapted to growing in harsh conditions of high altitudes. Ultraviolet radiation at high altitudes strongly impacts plant growth and development. Under the influence of ultraviolet radiation, protecting substances are synthesized in plants. The synthesis of UV-B defense metabolites is genetically conditioned, and their quantity depends on the intensity of the ultraviolet radiation to which the plants and plant parts are exposed. These substances include flavonoids, and especially rutin. Other substances with aromatic rings of six carbon atoms have a similar function, including fagopyrin, the metabolite specific for buckwheat. Defensive substances are formed in the leaves and flowers of common and Tartary buckwheat, up to about the same concentration in both species. In comparison, the concentration of rutin in the grain of Tartary buckwheat is much higher than in common buckwheat. Flavonoids also have other functions in plants so that they can protect them from pests and diseases. After crushing the grains, rutin is exposed to contact with the molecules of rutin-degrading enzymes. In an environment with the necessary humidity, rutin is turned into bitter quercetin under the action of rutin-degrading enzymes. This bitterness has a deterrent effect against pests. Moreover, flavonoids have important functions in human nutrition to prevent several chronic diseases, including obesity, cardiovascular diseases, gallstone formation, and hypertension.

Theoretical Studies on the Structure and Intramolecular Interactions of Fagopyrins-Natural Photosensitizers of Fagopyrum

Simple Summary

The study determines the spatial structure and intramolecular interactions of fagopyrins—natural photosensitizers of Fagopyrum species. In silico calculations show many fagopyrin conformers characterized by the formation of strong intramolecular interactions.

Abstract

Compounds characterized by a double-anthrone moiety are found in many plant species. One of them are fagopyrins—naturally occurring photosensitizers of Fagopyrum. The photosensitizing properties of fagopyrins are related to the selective absorption of light, which is a direct result of their spatial and electronic structure and many intramolecular interactions. The nature of the interactions varies in different parts of the molecule. The aim of this study is to determine the structure and intramolecular interactions of fagopyrin molecules. For this purpose, in silico calculations were used to perform geometry optimization in the gas phase. QTAIM and NCI analysis suggest the formation of the possible conformers in the fagopyrin molecules. The presence of a strong OHO hydrogen bond was shown in the anthrone moiety of fagopyrin. The minimum energy difference for selected conformers of fagopyrins was 1.1 kcal∙mol⁻¹, which suggested that the fagopyrin structure may exist in a different conformation in plant material. Similar interactions were observed in previously studied structures of hypericin and sennidin; however, only fagopyrin showed the possibility of brake the strong OHO hydrogen bond in favor of forming a new OHN hydrogen bond.

Antibacterial Photodynamic Inactivation of Fagopyrin F from Tartary Buckwheat (Fagopyrum tataricum) Flower against Streptococcus mutans and Its Biofilm

The objective of this study was to determine reactive oxygen species (ROS) produced by fagopyrin F-rich fraction (FFF) separated from Tartary buckwheat flower extract exposed to lights and to investigate its antibacterial photodynamic inactivation (PDI) against Streptococcus mutans and its biofilm. ROS producing mechanisms involving FFF with light exposure were determined using a spectrophotometer and a fluorometer. S. mutans and its biofilm inactivation after PDI treatment of FFF using blue light (BL; 450 nm) were determined by plate count method and crystal violet assay, respectively. The biofilm destruction by ROS produced from FFF after exposure to BL was visualized using confocal laser scanning microscopy (CLSM) and field emission scanning electron microscope (FE-SEM). BL among 3 light sources produced type 1 ROS the most when applying FFF as a photosensitizer. FFF exposed to BL (5 and 10 J/cm2) significantly more inhibited S. mutans viability and biofilm formation than FFF without the light exposure (p < 0.05). In the PDI of FFF exposed to BL (10 J/cm2), an apparent destruction of S. mutans and its biofilm were observed by the CLSM and FE-SEM. Antibacterial PDI effect of FFF was determined for the first time in this study.

Concentrations of Phenolic Acids Are Differently Genetically Determined in Leaves, Flowers, and Grain of Common Buckwheat (Fagopyrum esculentum Moench)

Common buckwheat (Fagopyrum esculentum Moench) is a valuable source of proteins, B vitamins, manganese, tryptophan, phytochemicals with an antioxidant effect, and the natural flavonoid rutin. Due to its composition, buckwheat supports the human immune system, regulates blood cholesterol, and is suitable for patients with diabetes or celiac disease. The study aimed to compare the allocation of selected phenolic acids (neochlorogenic acid, chlorogenic acid, trans-caffeic acid, trans-p-coumaric acid, trans-sinapic acid, trans-ferulic acid) and flavonoids (rutin, vitexin, quercetin, kaempferol) in the leaves, flowers, and grain of buckwheat cultivars of different origin. The content of individual phenolics was determined by the HPLC-DAD method. The results confirmed the determining role of cultivar on the relative content of chlorogenic acid, trans-caffeic acid, trans-sinapic acid, vitexin, and kaempferol in buckwheat plants. A significantly negative correlation among concentrations of phenolic acids in different common buckwheat plant parts shows that there are different mechanisms of genetic influences on the concentration of phenolic substances in common buckwheat flowers, leaves, and grain. These differences should be taken into account when breeding buckwheat for a high concentration of selected phenolic substances.

Changes in Agricultural Performance of Common Buckwheat Induced by Seed Treatment with Cold Plasma and Electromagnetic Field

The aim of this study was to determine the effects of pre-sowing seed treatment with cold plasma (CP) and an electromagnetic field (EMF) on the agricultural performance of two cultivars of common buckwheat (Fagopyrum esculentum Moench)—‘VB Vokiai’ and ‘VB Nojai’. For this, the effects of CP and EMF on seed germination, plant growth in the field, photosynthetic efficiency, biomass production, seed yield, and the amount of secondary metabolites and minerals in the harvested seeds were estimated. Although the percentage of seedlings that emerged under field conditions decreased by 11–20%, seed treatments strongly improved buckwheat growth and yield. Irrespective of differences in the dynamics of changes in the growth and photosynthetic activity between the two cultivars, the weight of seeds collected per plant for both cultivars was significantly higher (up to 70–97%) compared to the control. The biochemical composition of the harvested seeds (Fe, Zn, quercetin content) was also altered by seed treatments. Thus, pre-sowing treatment of buckwheat seeds with CP and EMF substantially stimulated plant growth in the field, increased biomass production, seed yield and nutritional quality. The results obtained strongly support the idea that plant seed treatment with physical stressors has great potential for use in agriculture.

Implications of Fagopyrin Formation In Vitro by UV Spectroscopic Analysis

The present work aims at studying the possible biosynthesis of fagopyrin in buckwheat plants with an attempt to address the existing gaps. The developed method of differential spectrophotometry can be used for identification of naphthodianthrones fagopyrins. It was found that in the vegetative mass of buckwheat plants, fagopyrin precursor-2-(piperidine-2-yl)-emodindianthron could be present. As fagopyrin can be produced by light effect, the temperature factor may influence the formation of protofagopyrin in vitro. An optimum temperature range was estimated for protofagopyrin formation. A possible fagopyrin biosynthesis under in vitro conditions was suggested.

Antioxidant and Rutin Content Analysis of Leaves of the Common Buckwheat (Fagopyrum esculentum Moench) Grown in the United Kingdom: A Case Study

The common buckwheat, Fagopyrum esculentum Moench (Polygonaceae) is a gluten-free pseudocereal that has been gaining in popularity in recent years as a low-calorie and nutrient-rich healthy food option. Buckwheat farming is common in Eastern European countries and the Far East, while in the UK and other Western European countries, the plant has limited medicinal or food applications. The vegetative parts, particularly the leaves and flowers, are among the best-known sources of the bioactive compound, rutin. Hence, functional foods originated from buckwheat leaves are common, although the scope of such applications is limited by phototoxicity associated with the fagopyrin composition. Here, the antioxidant and rutin composition of the leaves of the plant grown in the UK are assessed. The methanol extract of the leaves displayed a potent DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging effect along with reducing power. Quantitative High Performance Liquid Chromatography (HPLC)-based analysis showed the rutin content of the leaves as 3417 mg/100g (on dry weight (DW) basis). The identity of rutin was also confirmed by isolation and structural elucidation based on spectroscopic studies. From the chemical content analysis, including fagopyrin levels and the antioxidant assays, UK-grown buckwheat has potential as a commercial source of rutin or as a functional food.

Molecular allergen profiling in horses by microarray reveals Fag e 2 from buckwheat as a frequent sensitizer

Background

Companion animals are also affected by IgE‐mediated allergies, but the eliciting molecules are largely unknown. We aimed at refining an allergen microarray to explore sensitization in horses and compare it to the human IgE reactivity profiles.

Methods

Custom‐designed allergen microarray was produced on the basis of the ImmunoCAP ISAC technology containing 131 allergens. Sera from 51 horses derived from Europe or Japan were tested for specific IgE reactivity. The included horse patients were diagnosed for eczema due to insect bite hypersensitivity, chronic coughing, recurrent airway obstruction and urticaria or were clinically asymptomatic.

Results

Horses showed individual IgE‐binding patterns irrespective of their health status, indicating sensitization. In contrast to European and Japanese human sensitization patterns, frequently recognized allergens were Aln g 1 from alder and Cyn d 1 from Bermuda grass, likely due to specific respiratory exposure around paddocks and near the ground. The most prevalent allergen for 72.5% of the tested horses (37/51) was the 2S‐albumin Fag e 2 from buckwheat, which recently gained importance not only in human but also in horse diet.

Conclusion

In line with the One Health concept, covering human health, animal health and environmental health, allergen microarrays provide novel information on the allergen sensitization patterns of the companion animals around us, which may form a basis for allergen‐specific preventive and therapeutic concepts.

Enhancement of Phenolic Production and Antioxidant Activity from Buckwheat Leaves by Subcritical Water Extraction

To enhance the production of phenolic compounds with high antioxidant activity and reduce the level of phototoxic fagopyrin, buckwheat leaves were extracted with subcritical water (SW) at 100~220°C for 10~50 min. The major phenolic compounds were quercetin, gallic acid, and protocatechuic acid. The cumulative amount of individual phenolic compounds increased with increasing extraction temperature from 100°C to 180°C and did not change significantly at 200°C and 220°C. The highest yield of individual phenolic compounds was 1,632.2 μg/g dry sample at 180°C, which was 4.7-fold higher than that (348.4 μg/g dry sample) at 100°C. Total phenolic content and total flavonoid content increased with increasing extraction temperature and decreased with increasing extraction time, and peaked at 41.1 mg gallic acid equivalents/g and 26.9 mg quercetin equivalents/g at 180°C/10 min, respectively. 2,2-Diphenyl-1-picrylhydrazyl free radical scavenging activity and ferric reducing ability of plasma reached 46.4 mg ascorbic acid equivalents/g and 72.3 mmol Fe²⁺/100 g at 180°C/10 min, respectively. The fagopyrin contents were reduced by 92.5~95.7%. Color values L* and b* decreased, and a* increased with increasing extraction temperature. SW extraction enhanced the yield of phenolic compounds with high antioxidant activity and reduced the fagopyrin content from buckwheat leaves.

Buckwheat phenolic metabolites in health and disease

Buckwheat (Fagopyrum esculentum Moench, F. tataricum Gaertner) groats and flour have been established globally as nutritional foods because of their high levels of proteins, polyphenols and minerals. In some regions, buckwheat herb is used as a functional food. In the present study, reports of in vitro studies, preclinical and clinical trials dealing with the effect of buckwheat and its metabolites were reviewed. There are numerous reports of potential health benefits of consuming buckwheat, which may be in the form of food, dietary supplements, home remedies or possibly pharmaceutical drugs; however, adverse effects, including those resulting from contamination, must be considered. There are reports of antioxidative activity of buckwheat, which contains high levels of rutin and quercetin. On the other hand, both cytotoxic and antigenotoxic effects have been shown. Reduction of hyperlipidaemia, reduction of blood pressure and improved weight regulation have been suggested. Consuming buckwheat may have a beneficial effect on diabetes, since lower postprandial blood glucose and insulin response have been reported. In addition, buckwheat metabolites, such as rutin, may have intrinsic protective effects in preserving insulin signalling. Rutin has also been suggested to have potential therapeutic applications for the treatment of Alzheimer’s disease. The literature indicates that buckwheat is safe to consume and may have various beneficial effects on human health.