Interaction of phenolic acids and their derivatives with human serum albumin: Structure-affinity relationships and effects on antioxidant activity

Comparison of Protective Effects of Phenolic Acids on Protein Glycation of BSA Supported by In Vitro and Docking Studies

Several diabetic complications are associated with forming advanced glycation end products (AGEs). Different chemical and natural compounds are able to prevent the development of these products. In this study, glycosylation was induced as a model by incubating bovine serum albumin (BSA) with glucose. Consequently, BSA was treated with glucose and different concentrations (1.25, 2.5, and 5 μM) of syringic acid, gallic acid, ellagic acid, ferulic acid, paracoumaric acid, and caffeic acid for 4 and 6 weeks. Biochemical experiments comprise measurements of fluorescent AGEs, protein carbonyl contents, total thiol, hemolysis tests, and also malondialdehyde (MDA) levels in RBC. These demonstrated the antiglycating mechanism of these phenolic acids. Most of the phenolic acids used in this study reduced MDA levels and protected thiol residues in protein structures. They also inhibited the formation of fluorescent AGEs and RBC lysis, except gallic acid. Moreover, ferulic acid, paracoumaric acid, and caffeic acid proteins significantly prevent carbonylation. Molecular docking and simulation studies showed that ellagic, caffeic, gallic, and syringic acids could interact with lysine and arginine residues in the active site of BSA and stabilize its structure to inhibit the formation of AGEs. Our results suggest that phenolic acid could be used as a potential phytochemical against protein glycation and related diabetic complications.

Detailing Protein-Bound Uremic Toxin Interaction Mechanisms with Human Serum Albumin in the Pursuit of Designing Competitive Binders

Chronic kidney disease is the gradual progression of kidney dysfunction and involves numerous co-morbidities, one of the leading causes of mortality. One of the primary complications of kidney dysfunction is the accumulation of toxins in the bloodstream, particularly protein-bound uremic toxins (PBUTs), which have a high affinity for plasma proteins. The buildup of PBUTs in the blood reduces the effectiveness of conventional treatments, such as hemodialysis. Moreover, PBUTs can bind to blood plasma proteins, such as human serum albumin, alter their conformational structure, block binding sites for other valuable endogenous or exogenous substances, and exacerbate the co-existing medical conditions associated with kidney disease. The inadequacy of hemodialysis in clearing PBUTs underscores the significance of researching the binding mechanisms of these toxins with blood proteins, with a critical analysis of the methods used to obtain this information. Here, we gathered the available data on the binding of indoxyl sulfate, p-cresyl sulfate, indole 3-acetic acid, hippuric acid, 3-carboxyl-4-methyl-5-propyl-2-furan propanoic acid, and phenylacetic acid to human serum albumin and reviewed the common techniques used to investigate the thermodynamics and structure of the PBUT-albumin interaction. These findings can be critical in investigating molecules that can displace toxins on HSA and improve their clearance by standard dialysis or designing adsorbents with greater affinity for PBUTs than HSA.

Food Antioxidants and Their Interaction with Human Proteins

Common to all biological systems and living organisms are molecular interactions, which may lead to specific physiological events. Most often, a cascade of events occurs, establishing an equilibrium between possibly competing and/or synergistic processes. Biochemical pathways that sustain life depend on multiple intrinsic and extrinsic factors contributing to aging and/or diseases. This article deals with food antioxidants and human proteins from the circulation, their interaction, their effect on the structure, properties, and function of antioxidant-bound proteins, and the possible impact of complex formation on antioxidants. An overview of studies examining interactions between individual antioxidant compounds and major blood proteins is presented with findings. Investigating antioxidant/protein interactions at the level of the human organism and determining antioxidant distribution between proteins and involvement in the particular physiological role is a very complex and challenging task. However, by knowing the role of a particular protein in certain pathology or aging, and the effect exerted by a particular antioxidant bound to it, it is possible to recommend specific food intake or resistance to it to improve the condition or slow down the process.

Assessment of Polyphenols Bioaccessibility, Stability, and Antioxidant Activity of White Mugwort (Artemisia lactiflora Wall.) during Static In Vitro Gastrointestinal Digestion

White mugwort (Artemisia lactiflora Wall.), a traditional Chinese medicine, has been widely consumed in different forms for health care purposes. In this study, the in vitro digestion model of INFOGEST was used to investigate the bioaccessibility, stability, and antioxidant activity of polyphenols from two different forms of white mugwort, including dried powder (P 50, 100, and 150 mg/mL) and fresh extract (FE 5, 15, and 30 mg/mL). During digestion, the bioaccessibility of TPC and antioxidant activity were influenced by the form and ingested concentration of white mugwort. The highest bioaccessibility of the total phenolic content (TPC) and relative antioxidant activity were found at the lowest P and FE concentrations, as calculated relative to the TPC and antioxidant activity of P-MetOH and FE-MetOH based on the dry weight of the sample. Post-digestion, in comparison to P, FE had higher bioaccessibility (FE = 287.7% and P = 130.7%), relative DPPH radical scavenging activity (FE = 104.2% and P = 47.3%), and relative FRAP (FE = 673.5% and P = 66.5%). Nine compounds, 3-caffeoylquinic acid, 5-caffeoylquinic acid, 3,5-di-caffeoylquinic acid, sinapolymalate, isovitexin, kaempferol, morin, rutin, and quercetin, identified in both samples were modified during digestion, yet still provided strong antioxidant activity. These findings suggest that white mugwort extract possesses a higher polyphenol bioaccessibility, showing great potential as a functional ingredient.

New look at the metabolism of nonsteroidal anti-inflammatory drugs: influence on human serum albumin antioxidant activity

Body's homeostasis is dependent on many factors, such as maintaining balance between free radicals formation and degradation. Human serum albumin (HSA) also plays an important role in homeostasis. The aim of this study was thermodynamic analysis of the interaction between ketoprofen (KET), naproxen (NPX), diclofenac (DIC) and HSA, as well as the effect of drug-albumin binding on HSA antioxidant activity using calorimetric and spectrophotometric techniques. Based on the calorimetric analysis it has been shown that accompanied by hydrophobic interaction drugs-albumin binding is an exoenergetic reaction. All analyzed drugs and HSA showed the ability to react with free radicals such as a radical cation, formed as a result of the reaction between 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and potassium persulfate (K₂S₂O₈). Using ABTS assay a synergistic effect of ketoprofen (KET) and naproxen (NPX) on HSA antioxidant activity was observed while the effect of diclofenac (DIC) binding with albumin was probably additive. Because some medications including KET, NPX and DIC belong to over the counter (OTC) non-steroidal anti-inflammatory drugs (NSAIDs), it is necessary to understand their influence on HSA antioxidant activity.Communicated by Ramaswamy H. Sarma.

p-Hydroxybenzoic Acid Ameliorates Colitis by Improving the Mucosal Barrier in a Gut Microbiota-Dependent Manner

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory disease characterized by intestinal inflammatory cell infiltration and intestinal mucosal damage. The mechanism by which diet contributes to the pathogenesis of IBD remains largely unknown. In this study, we explored the therapeutic effect of p-hydroxybenzoic acid (HA), a phenolic acid mainly derived from dietary polyphenols in the gut, on DSS-induced colitis. HA intervention effectively relieved the dextran sulfate sodium salt (DSS)-induced colitis, reduced inflammation, and enhanced mucosal barrier function, as evidenced by an increment of goblet cell numbers and MUC2. These effects were largely dependent on the gut microbiota (GM), as antibiotics treatment substantially attenuated the improvement of colitis by HA. On the other hand, transplantation of GM from colitis mice treated with HA significantly reduced the colitis induced by DSS. Our study demonstrates that HA ameliorates DSS-induced colitis by improving the mucosal barrier in a GM-dependent manner. This study provides new dietary choices for the prevention and treatment of IBD.

A review of protein-phenolic acid interaction: reaction mechanisms and applications

Phenolic acids (PA) are types of phytochemicals with health benefits. The interaction between proteins and PAs can cause minor or extensive changes in the structure of proteins and subsequently affect various protein properties. This study investigates the protein/PA (PPA) interaction and its effects on the structural, physicochemical, and functional properties of the system. This work particularly focused on the ability of PAs as a subgroup of phenolic compounds (PC) on the modification of proteins. Different aspects including the influence of structure affinity relationship and molecular weight of PA on the protein interaction have been discussed in this review. The physicochemical properties of PPA change mainly due to the change of hydrophilic/hydrophobic parts and/or the formation of some covalent and non-covalent interactions. Furthermore, PPA interactions affecting functional properties were discussed in separate sections. Due to insufficient studies on the interaction of PPAs, understanding the mechanism and also the type of binding between protein and PA can help to develop a new generation of PPA. These systems seem to have good capabilities in the formulation of low-fat foods like high internal Phase Emulsions, drug delivery systems, hydrogel structures, multifunctional fibers or packaging films, and 3 D printing in the meat processing industry.

Spectroscopic Analysis of an Antimalarial Drug’s (Quinine) Influence on Human Serum Albumin Reduction and Antioxidant Potential

Quinine (Qi) is a well-known drug used in malaria therapy; it is also a potential anti-arrhythmic drug used in the treatment of calf cramps, rheumatoid arthritis, colds, and photodermatitis. Moreover, it is used in the food industry for the production of tonics. This study aimed to analyze the interaction between quinine and a transporting protein—human serum albumin (HSA)—as well as the influence of Qi on both protein reduction and antioxidant potential. It was found that Qi (via spectrofluorometric measurements and circular dichroism spectroscopy) binds to HSA with a low affinity and slightly affects the secondary structure of albumin. As demonstrated by the use of ABTS and FRAP assays, HSA has a higher antioxidant and reduction potential than Qi, while their mutual interaction results in a synergistic effect in antioxidant activity and reduction potential.

The Q-junction and the inflammatory response are critical pathological and therapeutic factors in CoQ deficiency

Defects in Coenzyme Q (CoQ) metabolism have been associated with primary mitochondrial disorders, neurodegenerative diseases and metabolic conditions. The consequences of CoQ deficiency have not been fully addressed, and effective treatment remains challenging. Here, we use mice with primary CoQ deficiency (Coq9R239X), and we demonstrate that CoQ deficiency profoundly alters the Q-junction, leading to extensive changes in the mitochondrial proteome and metabolism in the kidneys and, to a lesser extent, in the brain. CoQ deficiency also induces reactive gliosis, which mediates a neuroinflammatory response, both of which lead to an encephalopathic phenotype. Importantly, treatment with either vanillic acid (VA) or β-resorcylic acid (β-RA), two analogs of the natural precursor for CoQ biosynthesis, partially restores CoQ metabolism, particularly in the kidneys, and induces profound normalization of the mitochondrial proteome and metabolism, ultimately leading to reductions in gliosis, neuroinflammation and spongiosis and, consequently, reversing the phenotype. Together, these results provide key mechanistic insights into defects in CoQ metabolism and identify potential disease biomarkers. Furthermore, our findings clearly indicate that the use of analogs of the CoQ biosynthetic precursor is a promising alternative therapy for primary CoQ deficiency and has potential for use in the treatment of more common neurodegenerative and metabolic diseases that are associated with secondary CoQ deficiency.

Investigation on detoxication effects of 2-hydroxypropyl-β-cyclodextrin over two halogenated aromatic DBPs 2,4,6-trichlorophenol and 2,4,6-tribromophenol binding with human serum albumin

The health effects of disinfection byproducts (DBPs) in drinking water drew great attention recently. Herein, by using in vitro (fluorescence quenching, UV absorbance, circular dichroism) and in silico (molecular docking) method, binding interactions of two halophenolic DBPs (2,4,6-trichlorophenol [TCP] and 2,4,6-tribromophenol [TBP]) with human serum albumin (HSA) and the influence of hydroxypropyl-beta-cyclodextrin (HPCD) on the interactions were investigated. TCP/TBP could form complexes with HSA mainly by hydrogen bonding, while changing its secondary structure, among which TBP showed more influential effect. Interestingly, the binding constants for halophenol-HSA complexes decreased obviously with the involvement of HPCD. Molecular docking results revealed that HPCD could include TCP/TBP into its cavity and change their original binding sites from subdomain IB to IIA, resulting in a more stable binding system. These findings are beneficial for understanding the toxicity of halophenols inside the human body and indicated that HPCD could be a promising detoxication agent for DBPs.

Interactions of 3-deoxyanthocyanins with gum arabic and sodium alginate contributing to improved pigment aqueous stability

3-Deoxyanthocyanins (3DXA) are of interest as food colorants but readily precipitated in aqueous solutions, limiting their potential applications. This work investigated ability of gum arabic vs alginate to stabilize 3DXA in aqueous systems and mechanisms involved. Apigeninidin and luteolinidin, and sorghum extracts dominant in these compounds, API-EX and LUT-EX, respectively, were prepared in pH 3 and 5 polysaccharide solutions (0.5-1.0 g/L), and colloidal properties and 10-week stability measured. Alginate equally stabilized both pigments at pH 5 (75% retention), but only LUT-EX at pH 3 (65%); viscosity and H-bonding contributed to the effects. By contrast, gum arabic highly stabilized API-EX (100%, pH 5), but not LUT-EX. Gum arabic formed a stable complex with apigeninidin via hydrophobic encapsulation, but much weaker complex with luteolinidin due to its more hydroxylated B-ring. Structure of 3DXA is critical to its interaction with hydrocolloids, thus pigment profile must be considered when selecting stabilizing polysaccharides.

The interaction between bovine serum albumin and [6]-,[8]- and [10]-gingerol: An effective strategy to improve the solubility and stability of gingerol

In this study, the binding mechanism between bovine serum albumin (BSA) and three gingerols ([6]-, [8]- and [10]-gingerol) was evaluated to explore an effective strategy for improving solubility and stability of gingerols. The fluorescence analysis suggested gingerols could bind with BSA to form a stable BSA/gingerols complex and [10]-gingerol had the strongest binding affinity (K_a = 4.016 × 10⁴ L/mol) at 298 K. Thermodynamic parameters and molecular modeling validated that hydrophobic interaction and hydrogen bonds were the main driving force for the interaction of BSA/gingerols. Gingerols bound to BSA at site I (subdomain IIA) resulted in a conformational change of BSA with a structure shrinkage, which was responsible for the decrease of surface hydrophobicity. The formation of BSA/gingerols complexes promoted the solubility of [6]-, [8]- and [10]-gingerol increasing by 1.50, 6.04 and 23.50 times, respectively. In addition, the stability and antioxidant capacity of gingerols was significantly improved after binding with BSA.

Bioactive compounds: Application of albumin nanocarriers as delivery systems

Enriched products with bioactive compounds (BCs) show the capacity to produce a wide range of possible health effects. Most BCs are essentially hydrophobic and sensitive to environmental factors; so, encapsulation becomes a strategy to solve these problems. Many globular proteins have the intrinsic ability to bind, protect, encapsulate, and introduce BCs into nutraceutical or pharmaceutical matrices. Among them, albumins as human serum albumin (HSA), bovine serum albumin (BSA), ovalbumin (OVA) and α-lactalbumin (ALA) are widely abundant, available, and applied in many industrial sectors, becoming promissory materials to encapsulate BCs. Therefore, this review focuses on researches about the main groups of natural origin BCs (namely phenolic compounds, lipids, vitamins, and carotenoids), the different types of nanostructures based on albumins to encapsulate them and the main fields of application for BCs-loaded albumin systems. In this context, phenolic compounds (catechins, quercetin, and chrysin) are the most extensively BCs studied and encapsulated in albumin-based nanocarriers. Other extensively studied subgroups are stilbenes and curcuminoids. Regarding lipids and vitamins; terpenes, carotenoids (β-carotene), and xanthophylls (astaxanthin) are the most considered. The main application areas of BCs are related to their antitumor, anti-inflammatory, and antioxidant properties. Finally, BSA is the most used albumin to produced BCs-loaded nanocarriers.

Interference of anthocyanin extracted from black soybean coats on aflatoxin B1-human serum albumin in the binding process

The effect of the anthocyanin cyanidin-3-O-glucoside (C3G) and its main gastrointestinal metabolites (PCA and PGA) on the binding of AFB1 and HSA were studied via spectrometry. C3G is relatively stable in the gastric environment, and the intestinal environment promotes its metabolism into PCA and PGA. Binary fluorescence experiments showed that both AFB1 and C3G, including PCA and PGA, can react with HSA. AFB1, C3G and PCA can bind at site I and site II of HSA; PGA binds at site II. The presence of C3G/PCA/PGA inhibits the degree of quenching. C3G/PCA does not change the quenching mechanism; it is still static quenching; however, dynamic quenching occurs in the (AFB1-HSA)-PGA system. In addition, the apparent binding constant and number of binding sites of AFB1-HSA also diminish to different degrees. C3G and its metabolites (PCA and PGA) interfere with the interaction between AFB1 and HSA, and can reduce AFB1 transport at pH 7.4 in vitro.Abbreviations: C3G: cyanidin-3-O-glucoside; M: metabolite; PCA: protocatechuic acid; PGA: phloroglucinol aldehyde; AFB1: aflatoxin B1; HSA: human serum albumin.

Dragon Fruits as a Reservoir of Natural Polyphenolics with Chemopreventive Properties

Dragon fruits are a valued source of bioactive compounds with high potential to become a functional food. The aim of the study was to evaluate and compare the chemopreventive potential and chemical composition of fruits harvested in Thailand and Israel. The amount of different compounds in water and methanol extracts and antioxidant activity was investigated. Moreover, cytotoxic activity against cancer and normal cells of skin, prostate, and gastrointestinal origin was performed, accompanied by anti-inflammatory assay based on NO production in RAW 264.7 macrophage model. Additionally, the quenching properties of polyphenols from fruits were determined by the interaction of the main drug carrier in blood human serum (HSA). The chemometric analysis was used to reveal the relationships between the determined parameters. Dragon fruits harvested in Israel revealed higher antioxidant properties and total content of polyphenols and betacyanins when compared to those from Thailand. The examined fruits of both origins showed significant cytotoxic activity toward colon and prostate cancer cells, with no toxic effect on normal cells, but also no anti-inflammatory effect. Moreover, a high binding ability to HSA was observed for water extracts of dragon fruits. All these predestine dragon fruits are the candidates for the attractive and chemopreventive elements of daily diet.

Integrated multi-spectroscopic and molecular modeling techniques to study the formation mechanism of hidden zearalenone in maize

Hidden mycotoxins have been reported to be "protected" by macromolecular substances to escape routine determination, but release to free mycotoxins under gastrointestinal conditions. Nowadays, the hidden zearalenone (ZEN) that binding with macromolecular zein has been found in maize. However, the binding mechanism of ZEN with zein in maize has not been clarified. In this study, the formation of ZEN-zein complex was investigated applying ultrafiltration, multi-spectroscopic and molecular modeling techniques. The steady-state and transient fluorescence analysis suggested the ZEN could interact with zein to form the complex driven by hydrophobic force and hydrogen bonds, which is in accordance with the molecular modeling studies. The conformational changes of zein induced by binding with ZEN were revealed by Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD). Elucidating the binding mechanism between zein and ZEN could help the development of detecting hidden ZEN and guarantee the safety of maize products.

Protein binding of 4-hydroxybenzoic acid and 4-hydroxy-3-methoxybenzoic acid to human serum albumin and their anti-proliferation on doxorubicin-sensitive and doxorubicin-resistant leukemia cells

4-Hydroxybenzoic acids (4-HBA) and 4-hydroxy-3-methoxybenzoic acid (Vanillic acid, VA) have exhibited several pharmacological activities. Generally, the biological activities of compounds are highly involved in the interaction between protein and compounds in blood plasma. The objective was to investigate the interaction of 4-HBA or VA with human serum albumin (HSA) and their anti-proliferation properties on doxorubicin-sensitive K562 and doxorubicin-resistant K562/Dox leukemia cells. The protein binding of 4-HBA or VA to HSA was investigated using fluorescence quenching at temperatures of 298 and 310 Kelvin (K) under the pH of 6.0, 7.4, and 8.0 conditions. The effect of 4-HBA and VA on anti-proliferation was also studied on doxorubicin-sensitive K562 and doxorubicin-resistant K562/Dox leukemia cells using resazurin assay. The results showed that 4-HBA and VA could interact with HSA. The fluorescence quenching process in HSA-4-HBA system might be attributed to static quenching mechanism. In contrast, a dynamic quenching mechanism might be mainly involved in the fluorescence quenching process in the HSA-VA system. Thermodynamic data suggested that the spontaneous interaction between HSA and 4-HBA or VA had occurred in the system and it also indicated that hydrogen bonds and Van der Waals forces contributed to the binding of HSA to 4-HBA or VA. In addition, 4-HBA and VA decreased K562 and K562/Dox cells viability in a dose- and time-dependence manner. In conclusions, the 4-HBA and VA could interact with HSA. In addition, the 4-HBA and VA decreased in cell viability for both doxorubicin-sensitive K562 and doxorubicin-resistant K562/Dox leukemia cells in a dose- and time-dependence manner. Therefore, these current studies could provide useful information about the nature of 4-HBA or VA binding to protein HSA and their anticancer activities in both of these types of leukemia cells. The cell death mechanisms should be investigated through future study.

Assessment of binding interaction dihydromyricetin and myricetin with bovine lactoferrin and effects on antioxidant activity

The binding interactions of bovine lactoferrin (BLF) with two flavonoids dihydromyricetin (DMY) and myricetin (MY) were investigated by the multi-spectroscopic, microscale thermophoresis (MST) techniques, molecular docking, and then their antioxidant activities were studied by detection of free radical scavenging activity against DPPH. Results of UV-vis and fluorescence spectroscopies showed that DMY/MY and BLF formed the ground state complex through the static quenching mechanism. Moreover, MY with more planar stereochemical structure had higher affinity for BLF than DMY with twisted stereochemical structure, according to the binding constant (K_b), free energy change (ΔG°), dissociation constant (K_d) and donor-acceptor distance (r). Thermodynamic parameters revealed that hydrogen bond and van der Waals force were major forces in the formation of BLF-DMY complex, while hydrophobic interactions played major roles in the formation of BLF-DMY complex. The circular dichroism (CD) study indicated that MY induced more conformational change in BLF than DMY. Furthermore, molecular modeling provided insights into the difference of binding interactions between BLF and two flavonoids. Finally, the radical scavenging activity assays indicated the presence of BLF delayed the decrease in antioxidant capacities of two flavonoids. These results were helpful to understand the binding mechanism and biological effects of non-covalent BLF-flavonoid interaction.

Insights into the Binding of Dietary Phenolic Compounds to Human Serum Albumin and Food-Drug Interactions

The distribution of drugs and dietary phenolic compounds in the systemic circulation de-pends on, among other factors, unspecific/specific reversible binding to plasma proteins such as human serum albumin (HSA). Phenolic substances, present in plant-derived feeds, foods, beverages, herbal medicines, and dietary supplements, are of great interest due to their biological activity. Recently, considerable research has been directed at the formation of phenol-HSA complexes, focusing above all on structure-affinity relationships. The nucleophilicity and planarity of molecules can be altered by the number and position of hydroxyl groups on the aromatic ring and by hydrogenation. Binding affinities towards HSA may also differ between phenolic compounds in their native form and conjugates derived from phase II reactions. On the other hand, food-drug interactions may increase the concentration of free drugs in the blood, affecting their transport and/or disposition and in some cases provoking adverse or toxic effects. This is caused mainly by a decrease in drug binding affinities for HSA in the presence of flavonoids. Accordingly, to avoid the side effects arising from changes in plasma protein binding, the intake of flavonoid-rich food and beverages should be taken into consideration when treating certain pathologies.

Characterization, spectroscopic and crystallographic analyses of β-lactoglobulin and docosahexaenoic acid nanocomplexes

In this work, we investigated the interaction of docosahexaenoic acid (DHA) with β-lactoglobulin (β-Lg) using spectroscopic and crystallographic methods. The fluorescence results showed that DHA formed complexes with β-Lg with a binding constant of 4.13 × 10⁴ M^-1. The secondary structure of β-Lg was not significantly (p > 0.05) changed after binding with DHA. Dynamic light scattering showed the particle size of β-Lg-DHA complexes was about 5 nm, the same as that of β-Lg alone. The turbidity of DHA in aqueous solution decreased after binding with β-Lg. The crystallographic results showed that DHA was bound at one site in the calyx of β-Lg and that the aliphatic chain was hidden inside the hydrophobic β-barrel while the carboxyl group was located at the calyx entrance. These findings indicate that β-Lg can act as an effective nanocarrier for DHA.

Testing the Pharmacokinetic Interactions of 24 Colonic Flavonoid Metabolites with Human Serum Albumin and Cytochrome P450 Enzymes

Flavonoids are abundant polyphenols in nature. They are extensively biotransformed in enterocytes and hepatocytes, where conjugated (methyl, sulfate, and glucuronide) metabolites are formed. However, bacterial microflora in the human intestines also metabolize flavonoids, resulting in the production of smaller phenolic fragments (e.g., hydroxybenzoic, hydroxyacetic and hydroxycinnamic acids, and hydroxybenzenes). Despite the fact that several colonic metabolites appear in the circulation at high concentrations, we have only limited information regarding their pharmacodynamic effects and pharmacokinetic interactions. Therefore, in this in vitro study, we investigated the interactions of 24 microbial flavonoid metabolites with human serum albumin and cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes. Our results demonstrated that some metabolites (e.g., 2,4-dihydroxyacetophenone, pyrogallol, O-desmethylangolensin, and 2-hydroxy-4-methoxybenzoic acid) form stable complexes with albumin. However, the compounds tested did not considerably displace Site I and II marker drugs from albumin. All CYP isoforms examined were significantly inhibited by O-desmethylangolensin; nevertheless, only its effect on CYP2C9 seems to be relevant. Furthermore, resorcinol and phloroglucinol showed strong inhibitory effects on CYP3A4. Our results demonstrate that, besides flavonoid aglycones and their conjugated derivatives, some colonic metabolites are also able to interact with proteins involved in the pharmacokinetics of drugs.

Spectroscopic demonstration of sinapic acid methyl ester complexes with serum albumins

The methyl ester of sinapic acid (MESA) is a molecule with confirmed antioxidant properties. It is important to establish whether it can be transported across humans and animals. Therefore, we investigated MESA interactions with serum albumins, namely, human serum albumin (HSA), bovine serum albumin (BSA), rabbit serum albumin (RSA), and sheep serum albumin (SSA). Experiments were performed in a pH range from 5.9 to 10.7 using absorption and fluorescence techniques. It was found that MESA formed complexes with every albumin in the entire pH range under examination, which was confirmed by the appearances of new absorption and fluorescence complex bands. Fluorescence intensities were much higher (up to 20 times) and lifetimes were up to 340 times as compared to those for unbound MESA. The quenching experiments at pH 7.4 showed that the stoichiometry for every albumin was 1 : 1; the binding constant was the highest for HSA, which reached 52 000 M⁻¹. The obtained results suggested that MESA preferred the hydrophobic binding sites in albumins. The analysis of the fluorescence spectra and fluorescence lifetimes showed two possibly different binding sites in BSA, RSA, and SSA as well as three binding sites in HSA.

Known antioxidant, methyl ester of sinapic acid (MESA) can interact with serum albumins.

Binding Constants of Substituted Benzoic Acids with Bovine Serum Albumin

Experimental data on the affinity of various substances to albumin are essential for the development of empirical models to predict plasma binding of drug candidates. Binding of 24 substituted benzoic acid anions to bovine serum albumin was studied using spectrofluorimetric titration. The equilibrium constants of binding at 298 K were determined according to 1:1 complex formation model. The relationships between the ligand structure and albumin affinity are analyzed. The binding constant values for m- and p-monosubstituted acids show a good correlation with the Hammett constants of substituents. Two- and three-parameter quantitative structure–activity relationship (QSAR) models with theoretical molecular descriptors are able to satisfactorily describe the obtained values for the whole set of acids. It is shown that the electron-density distribution in the aromatic ring exerts crucial influence on the albumin affinity.

Combination mode of antimalarial drug mefloquine and human serum albumin: Insights from spectroscopic and docking approaches

The interaction between mefloquine (MEF), the antimalarial drug, and human serum albumin (HSA), the main carrier protein in blood circulation, was explored using fluorescence, absorption, and circular dichroism spectroscopic techniques. Quenching of HSA fluorescence with MEF was characterized as static quenching and thus confirmed the complex formation between MEF and HSA. Association constant values for MEF-HSA interaction were found to fall within the range of 3.79-5.73 × 10⁴  M^-1 at various temperatures (288, 298, and 308 K), which revealed moderate binding affinity. Hydrogen bonds and hydrophobic interactions were predicted to connect MEF and HSA together in the MEF-HSA complex, as deduced from the thermodynamic data (ΔS = +133.52 J mol^-1 K^-1 and ΔH = +13.09 kJ mol^-1 ) of the binding reaction and molecular docking analysis. Three-dimensional fluorescence spectral analysis pointed out alterations in the microenvironment around aromatic amino acid (tryptophan and tyrosine) residues of HSA consequent to the addition of MEF. Circular dichroic spectra of HSA in the wavelength ranges of 200-250 and 250-300 nm hinted smaller changes in the protein's secondary and tertiary structures, respectively, induced by MEF binding. Noncovalent conjugation of MEF to HSA bettered protein thermostability. Site marker competitive drug displacement results suggested HSA Sudlow's site I as the MEF binding site, which was also supported by molecular docking analysis.

Structure-affinity relationship of the binding of phenolic acids and their derivatives to bovine serum albumin

Phenolic acids perform biological effects which are largely influenced by their binding to serum albumin. Therefore, investigating structure-affinity relationship of binding between phenolic acids and serum albumin is important. In this study, 114 phenolic acids and their derivatives, sharing the benzoic acid core with different substituents groups, were selected to investigate structure-affinity relationships with bovine serum albumin. The binding constants were obtained through fluorescence quenching, and a comprehensive mathematical model with inner-filter effect correction was applied. The results showed that the hydroxy group at the 2-position led to stronger binding affinity, while it had a negative influence at the 4-position. Substituting hydroxy groups with methoxy groups at 4-position and with methyl groups at 3-position both strengthened the binding affinity, respectively. Hydrogen bonding was one of the key binding forces for this binding interaction. Our findings provide a fundamental insight on the binding mechanism of phenolic acids to bovine serum albumin.

Comparing the binding interaction between β-lactoglobulin and flavonoids with different structure by multi-spectroscopy analysis and molecular docking

Four kinds of flavonoids (apigenin, naringenin, kaempferol, genistein) were skillfully selected to investigate the interaction between flavonoids and β-lactoglobulin (β-LG) by multi-spectroscopy analysis and molecular docking. Hydrogenation on C2C3 double bond weakened the affinity of apigenin for β-LG and it's most obvious, followed by hydroxylation of C3 and position isomerism of phenyl ring B. The main interaction force for apigenin and naringenin binding to β-LG (van der Waals forces and hydrogen bonds) was different from that of genistein and kaempferol (hydrophobic interactions). Circular dichroism and fluorescence experiments indicated that conformation of β-LG became loose and surface hydrophobicity of β-LG was reduced in the presence of flavonoids. Molecular docking indicated that flavonoids interacted with specific amino acid residues located on the outer surface of β-LG. These findings can provide a deep understanding about the interaction mechanism between flavonoids and protein, and it may be valuable in dairy incorporation with flavonoids.