Interaction of Flavonoids from Woodwardia unigemmata with Bovine Serum Albumin (BSA): Application of Spectroscopic Techniques and Molecular Modeling Methods

Caseinate-coated zein nanoparticles as potential delivery vehicles for guavinoside B from guava: Molecular interactions and encapsulation properties

Guavinoside B (GUB) is a characteristic constituent from guava with strong antioxidant activity; however, its low water solubility limits its utilization. Herein, we investigated the interaction between GUB and zein, a prolamin with self-assembling property, using multiple spectroscopic methods and fabricated GUB-zein-NaCas nanoparticles (GUB-Z-N NPs) via the antisolvent coprecipitation approach. GUB caused fluorescence quenching to zein via the static quenching mechanism. Fourier-transform infrared spectroscopy and computational analysis revealed that GUB bound to zein via van der Waals interaction, hydrogen bond, and hydrophobic forces. The GUB-Z-N NPs were in the nanometric size range (< 200 nm) and exhibited promising encapsulation efficiency and redispersibility after freeze-drying. These particles remained stable for up to 31 days at 4 °C and great resistance to salt and pH variation, and displayed superior antioxidant activity to native GUB. The current study highlights the potential of zein-based nanoparticles as delivery vehicles for GUB in the food industry.

The traditional utilization, biological activity and chemical composition of edible fern species

ETHNOPHARMACOLOGICAL RELEVANCE

Ferns form an important part of the human diet. Young fern fiddleheads are mostly consumed as vegetables, while the rhizomes are often extracted for starch. These edible ferns are also often employed in traditional medicine, where all parts of the plant are used, mostly to prepare extracts. These extracts are applied either externally as lotions and baths or internally as potions, decoctions and teas. Ailments traditionally treated with ferns include coughs, colds, fevers, pain, burns and wounds, asthma, rheumatism, diarrhoea, or skin diseases (eczema, rashes, itching, leprosy).

AIM OF THE REVIEW

This review aims to compile the worldwide knowledge on the traditional medicinal uses of edible fern species correlating to reported biological activities and isolated bioactive compounds.

MATERIALS AND METHODS

The articles and books published on edible fern species were searched through the online databases Web of Science, Pubmed and Google Scholar, with critical evaluation of the hits. The time period up to the end of 2022 was included.

RESULTS

First, the edible fern species were identified based on the literature data. A total of 90 fern species were identified that are eaten around the world and are also used in traditional medicine. Ailments treated are often associated with inflammation or bacterial infection. However, only the most common and well-known fern species, were investigated for their biological activity. The most studied species are Blechnum orientale L., Cibotium barometz (L.) J. Sm., Diplazium esculentum (Retz.) Sw., Marsilea minuta L., Osmunda japonica Thunb., Polypodium vulgare L., and Stenochlaena palustris (Burm.) Bedd. Most of the fern extracts have been studied for their antioxidant, anti-inflammatory and antimicrobial activities. Not surprisingly, antioxidant capacity has been the most studied, with results reported for 28 edible fern species. Ferns have been found to be very rich sources of flavonoids, polyphenols, polyunsaturated fatty acids, carotenoids, terpenoids and steroids and most of these compounds are remarkable free radical scavengers responsible for the outstanding antioxidant capacity of fern extracts. As far as clinical trials are concerned, extracts from only three edible fern species have been evaluated.

CONCLUSIONS

The extracts of edible fern species exert antioxidant anti-inflammatory and related biological activities, which is consistent with their traditional medicinal use in the treatment of wounds, burns, colds, coughs, skin diseases and intestinal diseases. However, studies to prove pharmacological activities are scarce, and require chemical-biological standardization. Furthermore, correct botanical classification needs to be included in publications to simplify data acquisition. Finally, more in-depth phytochemical studies, allowing the linking of traditional use to pharmacological relevance are needed to be done in a standardized way.

A Novel Antimicrobial Mechanism of Azalomycin F Acting on Lipoteichoic Acid Synthase and Cell Envelope

Lipoteichoic acid (LTA) plays an essential role in bacterial growth and resistance to antibiotics, and LTA synthetase (LtaS) was considered as an attractive target for combating Gram-positive infections. Azalomycin F, a natural guanidyl-containing polyhydroxy macrolide, can target the LTA of Staphylococcus aureus. Using various technologies including enzyme-linked immunosorbent assay, transmission electron microscope, proteomics, and parallel reaction monitoring, here, the experimental results indicated that azalomycin F can accelerate the LTA release and disrupt the cell envelope, which would also lead to the feedback upregulation on the expressions of LtaS and other related enzymes. Simultaneously, the reconstituted enzyme activity evaluations showed that azalomycin F can significantly inhibit the extracellular catalytic domain of LtaS (eLtaS), while this was vague for LtaS embedded in the liposomes. Subsequently, the fluorescence analyses for five incubation systems containing azalomycin F and eLtaS or the LtaS-embedded liposome indicated that azalomcyin F can spontaneously bind to the active center of LtaS. Combining the mass spectroscopy analyses and the molecular dockings, the results further indicated that this interaction involves the binding sites of substrates and the LTA prolongation, especially the residues Lys299, Phe353, Trp354 and His416. All these suggested that azalomycin F has multiple antibacterial mechanisms against S. aureus. It can not only inhibit LTA biosynthesis through the interactions of its guanidyl side chain with the active center of LtaS but also disrupt the cell envelope through the synergistic effect of accelerating the LTA release, damaging the cell membrane, and electrostatically interacting with LTA. Simultaneously, these antibacterial mechanisms exhibit a synergistic inhibition effect on S. aureus cells, which would eventually cause the cellular autolysis.

Digital Database of Absorption Spectra of Diverse Flavonoids Enables Structural Comparisons and Quantitative Evaluations

Flavonoids play diverse roles in plants, comprise a non-negligible fraction of net primary photosynthetic production, and impart beneficial effects in human health from a plant-based diet. Absorption spectroscopy is an essential tool for quantitation of flavonoids isolated from complex plant extracts. The absorption spectra of flavonoids typically consist of two major bands, band I (300-380 nm) and band II (240-295 nm), where the former engenders a yellow color; in some flavonoids the absorption tails to 400-450 nm. The absorption spectra of 177 flavonoids and analogues of natural or synthetic origin have been assembled, including molar absorption coefficients (109 from the literature, 68 measured here). The spectral data are in digital form and can be viewed and accessed at http://www.photochemcad.com. The database enables comparison of the absorption spectral features of 12 distinct types of flavonoids including flavan-3-ols (e.g., catechin, epigallocatechin), flavanones (e.g., hesperidin, naringin), 3-hydroxyflavanones (e.g., taxifolin, silybin), isoflavones (e.g., daidzein, genistein), flavones (e.g., diosmin, luteolin), and flavonols (e.g., fisetin, myricetin). The structural features that give rise to shifts in wavelength and intensity are delineated. The availability of digital absorption spectra for diverse flavonoids facilitates analysis and quantitation of these valuable plant secondary metabolites. Four examples are provided of calculations─multicomponent analysis, solar ultraviolet photoprotection, sun protection factor (SPF), and Förster resonance energy transfer (FRET)─for which the spectra and accompanying molar absorption coefficients are sine qua non.

Studies on the interactions of theaflavin-3,3'-digallate with bovine serum albumin: Multi-spectroscopic analysis and molecular docking

Tea cream, produced by interactions among tea ingredients, is undesirable in tea beverage industry. The interaction between bovine serum albumin (BSA) and theaflavin-3,3'-digallate (TFDG, an important component in tea cream and functional substance of black tea) was investigated by fluorescence spectroscopy, ultraviolet-visible (UV-vis) absorption spectroscopy, synchronous fluorescence spectroscopy, fourier-transform infrared (FT-IR) spectroscopy, and molecular docking technique. Multi-spectroscopic experiments demonstrated that TFDG interacted with BSA via static quenching, and the microenvironment around BSA became more hydrophobicity. FT-IR showed that the α-helix of BSA was increased when binding with TFDG. Thermodynamic parameters and molecular docking demonstrated that hydrophobic interactions and hydrogen bonds dominated the interaction between TFDG and BSA. The mechanism proposed in this research could further develop some nanoparticles to excellent biochemical properties while reducing the formation of tea cream, and explore the potential of BSA as transport carrier for TFDG.

Phytochemical profiling, antioxidant and antibacterial efficacy of a native Himalayan Fern: Woodwardia unigemmata (Makino) Nakai

Present work elucidates the antioxidant and antibacterial activity of Woodwardia unigemmata (Makino) Nakai along with chemical characterization using its aqueous (AEW), methanol (MEW), and hexane (HEW) extracts. Chemical profile of different extracts was illustrated by using Gas chromatography and mass spectrometry (GC-MS) analysis. Antioxidant activities were tested using DPPH and FRAP assays, total phenolic and flavonoid content by Folin-Ciocalteu and aluminum chloride method, respectively. Further, antibacterial activity against six plant and four animal pathogenic bacteria was analyzed by employing the disc diffusion assay. GC-MS analysis revealed the presence of catechol (21.96%), glycerol (20.22%), n-pentadecanoic acid (6.95%), glyceryl monoacetate (6.35 %), ethyl acetimidate (5.39 %) and 3-hydroxy-2,3-dihydromaltol (5.36%) in AEW; β-sitosterol (17.39%), pentadecanoic acid (9.81%), vitamin E (7.82%) and glycerol (7.05%) in MEW; γ-sitosterol (33.45%), vitamin E (10.04%) and campesterol (7.32%) in HEW as major constituents. Maximum phenolics (873 ± 6.01 mgGAE/g dry extract) as well as flavonoids (151 ± 11.44 mgQE/g dry extract) content was found in MEW, which also showed remarkable antioxidant potential (IC₅₀ 6.07 ± 1.4 µg/ml for DPPH and 768 ± 10.4 mg AAE/g dry extract for FRAP assay. In antibacterial activity, maximum inhibition (15 ± 0.9 mm) was observed for HEW against R. solanacearum, followed by AEW against A. tumefaciens and X. phaseoli (11 ± 0.3 mm each). MEW was found positive only against A. tumefaciens. Significant minimum inhibitory concentration (MIC) value observed for AEW against L. monocytogenes (10 mg/ml). Polar extracts had remarkable antioxidant potential, while non-polar extract did show significant antibacterial activity. Further, GC- MS reports indicated that this traditionally useful fern species can be an excellent source of biologically active compounds.

Spectroscopic methodologies and molecular docking studies on the interaction of antimalarial drug piperaquine and its metabolites with human serum albumin

Artemisinin-based combination therapy is widely used for the treatment of uncomplicated Plasmodium falciparum malaria, and piperaquine (PQ) is one of the important partner drugs. During the biotransformation of PQ, M1 (N-oxidation product), M2 (N-oxidation product), M3 (carboxylic acid product), M4 (N-dealkylation product), and M5 (N-oxidated product of M4) are formed by cytochrome P450 pathways. Despite decades of clinical use, the interactions between PQ and its main metabolites (PQs) with human serum albumin (HSA) have not been reported. In the present study, the binding of PQs with HSA under physiological conditions was investigated systematically through fluorescence, circular dichroism (CD) spectroscopy, and molecular docking methods. The experimental results show that the intrinsic fluorescence quenching of HSA was induced by those compounds resulting from the formation of stable HSA-compound complexes. The main forces involved in the interactions between PQ, M1, and M2 which bind to HSA were hydrogen s and van der Waals forces, while the interactions of M3, M4, and M5 were driven by hydrophobic forces. The main binding sites of the compounds to HSA were also examined by classical fluorescent marker experiments and molecular docking studies. Binding constants (K_b) revealed that the affinities of the PQ, M1, M2, M3, and M4 to HSA were stronger than that of M5. Additionally, the binding rates of PQs with HSA were determined by ultrafiltration methods. Consistent with the binding constant results, the binding rate of M5 was lower than the binding rates of PQ, M1, M2, M3, and M4. Furthermore, PQs binding to HSA led to conformational and structural alterations of HSA, as revealed by multi-spectroscopic studies. In order to investigate one possible mechanism by which PQs inhibit the growth of malaria-causing Plasmodium parasites, ¹H NMR spectroscopy was performed to investigate the interaction of the PQs with heme. This study is beneficial to enhance our understanding of the ecotoxicology and environmental behaviors of PQ and its metabolites.

Spectroscopic methodologies and molecular docking studies on the interaction of the soluble guanylate cyclase stimulator riociguat with human serum albumin

Interaction of riociguat with human serum albumin (HSA) is extremely important in understanding the drug's disposition and efficiency. In the current study, the binding of riociguat to HSA was explored using spectroscopic methods and molecular docking. The quenching constant, the binding constant, the number of binding sites, thermodynamic parameters, and the secondary structure of protein were determined. A fluorescence study revealed that riociguat quenched HSA fluorescence via static quenching with a binding constant of 1.55 × 10⁴ L mol^-1 at 298 K. The calculated thermodynamic parameters indicated that the binding process was spontaneous and that the main interaction force was hydrophobic interaction. Site marker competitive binding experiments and molecular docking studies suggested that riociguat was inserted into the subdomain IIA (site I) of HSA. Alterations in the protein secondary structure after drug complexation were predicted. Results indicated that the protein a-helix structure increased with an increasing concentration of riociguat. This indicated that a riociguat-HSA complex was formed and that the protein secondary structure was altered by the addition of riociguat.

Synthesis of novel genistein amino acid derivatives and investigation on their interactions with bovine serum albumin by spectroscopy and molecular docking

Genistein amino acid derivatives 4a-4d were synthesized and evaluated for their cytotoxic activities against MCF-7, Hela, MGC-803 and HCT-116 cell lines by MTT assays in vitro. The results revealed that compounds 4a-4d showed better activity than the parent compound genistein. Particularly, compound 4b displayed the most significant anticancer activity against MGC-803 with an IC50 value of 12.08 μM. In addition, the mechanisms of interaction between genistein, compounds 4a-4d and BSA were investigated via multi-spectroscopic techniques such as ultraviolet (UV) spectroscopy, fluorescence, circular dichroism (CD), and molecular docking under physiological conditions. The results suggested that endogenous fluorescence of BSA could be quenched by genistein and compounds 4a-4dvia forming BSA-compound complex, which meant a static quenching mechanism was involved. The negative values of enthalpy (ΔH) and entropy (ΔS) indicated that interactions between BSA and the ligands were spontaneous, and hydrogen bonding and van der Waals interactions were involved in the BSA-compound complexion formation. The UV, synchronous and 3D fluorescence results revealed that the micro-environment of tryptophan and conformation of BSA were changed after binding to ligands. CD analysis demonstrated the variation in the secondary structure and that the α-helix content of BSA decreased. Eventually, molecular docking was executed to forecast the binding forces and binding sites between BSA and compounds 4a-4d.

Interaction between Saikosaponin D, Paeoniflorin, and Human Serum Albumin

Saikosaponin D (SSD) and paeoniflorin (PF) are the major active constituents of Bupleuri Radix and Paeonia lactiflora Pall, respectively, and have been widely used in China to treat liver and other diseases for many centuries. We explored the binding of SSD/PF to human serum albumin (HSA) by using fluorospectrophotometry, circular dichroism (CD) and molecular docking. Both SSD and PF produced a conformational change in HSA. Fluorescence quenching was accompanied by a blue shift in the fluorescence spectra. Co-binding of PF and SSD also induced quenching and a conformational change in HSA. The Stern-Volmer equation showed that quenching was dominated by static quenching. The binding constant for ternary interaction was below that for binary interaction. Site-competitive experiments demonstrated that SSD/PF bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for the binary association. Also, there was energy transfer upon binary interaction. Molecular docking supported the experimental findings in conformation, binding sites and binding forces.