Catechin Conjugates Research Articles

Chitooligosaccharide-catechin conjugate: Antimicrobial mechanisms toward Vibrio parahaemolyticus and its use in shucked Asian green mussel

Vibrio parahaemolyticus often contributes to a serious foodborne disease outbreak when marine mussels are consumed. The number of drug-resistant isolates of bacteria has also been increased, which makes clinical treatment more challenging. In general, a single food preservative cannot inhibit drug-resistant V. parahaemolyticus in seafood effectively. Inhibition effect of shrimp shell chitooligosaccharide (COS)-catechin (CAT) conjugate toward V. parahaemolyticus was studied. COS-CAT conjugate was able to inhibit V. parahaemolyticus with minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.256 and 1.024 mg/L, respectively. Based on time-killing profiles, V. parahaemolyticus cells in shucked Asian green mussels were inactivated by 84% after 2 MIC (0.512 mg/mL) treatment for 6 h. The COS-CAT conjugate mainly caused membrane disruptions and damages as witnessed by numerous pores and concaves on the cell surface. Membrane damages were further confirmed by the increases in conductivity, extracellular malondialdehyde content, and potassium and magnesium ion leakages. Furthermore, the virulence factors of V. parahaemolyticus, involving extracellular polysaccharide, biofilm production and motility, were significantly inhibited. COS-CAT conjugate might attach to genomic DNA after cell deformation. Hence, COS-CAT conjugate could be used as a promising food-grade antibacterial agent, particularly against V. parahaemolyticus in the seafood sector.

Autoxidation-Resistant, ROS-Scavenging, and Anti-Inflammatory Micellar Nanoparticles Self-Assembled from Poly(acrylic acid)-Green Tea Catechin Conjugates.

(-)-Epigallocatechin-3-O-gallate (EGCG), the most bioactive catechin in green tea, has drawn significant interest as a potent antioxidant and anti-inflammatory compound. However, the application of EGCG has been limited by its rapid autoxidation at physiological pH, which generates cytotoxic levels of reactive oxygen species (ROS). Herein, we report the synthesis of poly(acrylic acid)-EGCG conjugates with tunable degrees of substitution and their spontaneous self-assembly into micellar nanoparticles with enhanced resistance against autoxidation. These nanoparticles not only exhibited superior oxidative stability and cytocompatibility over native EGCG, but also showed excellent ROS-scavenging and anti-inflammatory effects. This work presents a potential strategy to overcome the stability and cytotoxicity issues of EGCG, making it one step closer toward its widespread application.

Structure, stability and antioxidant activity of dialdehyde starch grafted with epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate.

Catechins, a member of the flavonoids, exist widely in teas, and have health benefits. However, catechins have poor stability, which greatly limits their application. In order to improve the stability of catechins, different catechins including (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG) were conjugated onto dialdehyde starch by acid-mediated coupling method. The structure, stability and antioxidant activity of dialdehyde starch-catechin conjugates were determined. Thin-layer chromatography and ultraviolet-visible spectroscopy, fluorescence, nuclear magnetic resonance and infrared spectra revealed that catechins were successfully conjugated onto dialdehyde starch, coupling between 6-H/8-H of catechins' A ring and dialdehyde starch's aldehyde groups. The conjugates presented an amorphous structure and sheet-like and/or blocky morphologies. As compared to dialdehyde starch, the conjugates showed enhanced thermal stability. Furthermore, the stability of catechins in pH 7.4 phosphate-buffered saline was improved after conjugating onto dialdehyde starch. The conjugates exhibited significantly higher antioxidant activities than dialdehyde starch, decreasing in the following order: dialdehyde starch-ECG, dialdehyde starch-EGCG, dialdehyde starch-EC, dialdehyde starch-EGC and dialdehyde starch. Dialdehyde starch-catechin conjugates have great potential as stable antioxidant agents. © 2022 Society of Chemical Industry.

Discovery and Targeted Isolation of Phenylpropanoid-Substituted Ester-Catechins Using UPLC-Q/TOF-HRMS/MS-Based Molecular Networks: Implication of the Reaction Mechanism among Polyphenols during Green Tea Processing

Tea is an important beverage source of dietary polyphenols and well known for containing phenolic structure diversity. A series of phenylpropanoid-substituted catechins, flavonols, flavan-3-hexoside, and proanthocyanidin are present in different herbs with various biological activities, inspiring our exploration of phenylpropanoid-substituted ester type of catechins (PSECs) due to the enrichment of galloylated catechins in tea. In this study, we used a guiding-screening-location-isolation integrated route including creating a hypothesized PSEC dataset, MS/MS data acquiring, construction of molecular networks, and traditional column chromatography and preliminarily identified 14 PSECs by MS/MS spectrum. Two of these PSECs were further purified and elucidated by NMR and CD spectra. Further MS detection in tea products and fresh leaves suggests that the production of the two new compounds was enhanced during tea processing. The synthesis mechanism was proposed to obtain these types of components for further investigation on their roles in human health protection. This study provides an example for the exploration of new functional ingredients from food sources guided by MS/MS data-based networking, and also new insights into the reaction mechanism to form new catechin conjugates among polyphenols in green tea.

Hyaluronic acid-green tea catechin conjugates as a potential therapeutic agent for rheumatoid arthritis.

Fibroblast-like synoviocytes are a key effector cell type involved in the pathogenesis of rheumatoid arthritis. The major green tea catechin, epigallocatechin-3-O-gallate (EGCG), has attracted significant interest for rheumatoid arthritis therapy because of its ability to suppress the proliferation and interleukin-6 secretion of synoviocytes. However, therapeutic efficacy of EGCG has been limited by a lack of target cell specificity. Herein we report hyaluronic acid–EGCG (HA–EGCG) conjugates as an anti-arthritic agent that is capable of targeting fibroblast-like synoviocytes via HA–CD44 interactions. These conjugates exhibited superior anti-proliferative and anti-inflammatory activities compared with EGCG under simulated physiological conditions. Near-infrared fluorescence imaging revealed preferential accumulation of the conjugates at inflamed joints in a collagen-induced arthritis rat model, and their anti-arthritic efficacy was investigated by measuring a change in the edema and histopathological scores. Our findings suggest the potential of HA–EGCG conjugates as an anti-arthritic agent for the treatment of rheumatoid arthritis.

A two-pronged anti-leukemic agent based on a hyaluronic acid-green tea catechin conjugate for inducing targeted cell death and terminal differentiation.

Acute myeloid leukemia (AML) is an aggressive malignancy that leads to a poor prognosis even with intensive chemotherapy. As the key feature of AML is the blockade of hematopoietic cell maturation, considerable attention has been paid to 'differentiation therapy' aimed at transforming AML cells into more mature, benign phenotypes using pharmacological agents. Here we report a hyaluronic acid-(-)-epigallocatechin-3-O-gallate (HA-EGCG) conjugate as a unique anti-leukemic agent, capable of selectively killing AML cells as well as promoting their terminal differentiation into monocytes and granulocytes. This 'two-pronged' effect of the HA-EGCG conjugate was demonstrated in two different AML cell lines (NB4 and HL60), but absent in a physical mixture (HA + EGCG), highlighting the importance of HA conjugation for targeting of EGCG moieties to AML cells. Moreover, administration of the HA-EGCG conjugate not only suppressed AML progression, but also prolonged survival in the HL60 xenograft mouse model. Our study suggests new opportunities for designing two-pronged anti-leukemic agents for more effective AML treatment.

Celamonols A–D, four triterpenoid and catechin conjugates with immunosuppressive activities from the stems of Celastrus monospermus

Celamonols A–D (1–4), four dimers between a friedelane-type triterpenoid and a catechin, were isolated from the stems of Celastrus monospermus.

Dark chocolate modulates platelet function with a mechanism mediated by flavan-3-ol metabolites.

Cocoa is a rich source bioactive compounds, i.e., flavan-3-ols, and its consumption has been associated with several beneficial effects, such as the positive modulation of the hemostasis targeted by the platelet function. However, these phenolic compounds have a very low bioavailability and extensively undergo phase I and II metabolism, with the appearing into the bloodstream of (epi)catechin conjugates and phenyl-γ-valerolactones and their conjugates, at different times.The aims of this study were to explore the effect of dark chocolate on platelet function and to investigate the relationship between this interplay and flavan-3-ol derived metabolites.Eighteen healthy male volunteers ingested 50 g of 90% cocoa chocolate within 5 minutes. Blood samples were collected immediately before chocolate ingestion (T0) and 4 hours afterwards (T1). Platelet function analyzer (PFA)-100 closure time was assessed using collagen/adenosine-5′-diphosphate (COL/ADP) and collagen/epinephrine (COL/EPI) cartridges. Plasma flavan-3-ol metabolites were identified and quantified by means of liquid chromatography coupled to a triple quadrupole mass spectrometer (UHPLC-ESI-MS/MS).Results evidenced a significant increase of COL/ADP-induced PFA-100 closure time, but not COL/EPI, 4 hours after ingestion of dark chocolate. Total plasma structurally-related (epi)catechin metabolite (SREM) concentration significantly increased at T1, together with 4 out of the 6 detected metabolites. Total phenyl-γ-valerolactone concentrations remained unchanged. Spearman correlations evidenced a strong correlation between COL/ADP closure time and SREMs, mainly led by (epi)catechin-sulfate isomers.These data confirm that the potential beneficial effect of dark chocolate on primary hemostasis may be mediated by flavan-3-ol circulating metabolites.

Phytochemical profile of seeds from 21 Bambara groundnut landraces via UPLC-qTOF-MS

Bambara groundnut is one of the under-utilized African legume crops, valued for its nutritional and health benefits, and for which ongoing studies will help to distinguish its many landraces and select the promising one for breeding programs. To describe the polar metabolome of the seed from 21 Bambara groundnut landraces, untargeted metabolomics approach using UPLC-qTOF-MS (Ultra performance liquid chromatography-Quadrupole time of flight mass spectrometry) was performed. Metabolites belonging to varied compound classes were detected and identified. The total phenolic, flavonoid and anthocyanin contents varied from 0.75 to 17.71 mg GAE.g−1, 0.01 to 2.51 mg QUE.g−1 and 0.03 to 1.31 mg CYE.g−1, respectively. Unsupervised statistics highlighted differences in the metabolome of different landraces. Principal component analysis revealed that caffeic and catechin conjugates are the most decisive marker compounds discriminating the landraces. This study provides the most complete map of metabolites in Bambara groundnut seeds and demonstrates that UPLC-qTOF-MS coupled with chemometric is an excellent tool for differentiation between landraces. These findings highlight the potential of Bambara groundnuts as an economic source of natural antioxidants for human consumption and food industries, and therefore open horizons to the industrial use of Bambara groundnut flours in the development of functional food and feed products.

Highly Augmented Drug Loading and Stability of Micellar Nanocomplexes Composed of Doxorubicin and Poly(ethylene glycol)-Green Tea Catechin Conjugate for Cancer Therapy.

Low drug loading and instability in blood circulation are two key challenges that impede the successful clinical translation of nanomedicine, as they result in only marginal therapeutic efficacy and toxic side effects associated with premature drug leakage, respectively. Herein, highly stable and ultrahigh drug loading micellar nanocomplexes (MNCs) based on the self-assembly of the anticancer drug doxorubicin (DOX) and a poly(ethylene glycol)-epigallocatechin-3-O-gallate (EGCG) conjugate are developed. The formation of these MNCs is facilitated by strong favorable intermolecular interactions between the structurally similar aromatic EGCG and DOX molecules, which impart exceptionally high drug-loading capability of up to 88% and excellent thermodynamic and kinetic stability. Unlike two clinical formulations of DOX-free DOX and liposomal DOX, which are not effective below their lethal dosages, these DOX-loaded MNCs demonstrate significant tumor growth inhibition in vivo on a human liver cancer xenograft mouse model with minimal unwanted toxicity. Overall, these MNCs can represent a safe and effective strategy to deliver DOX for cancer therapy.

Characterization of catechin-α-lactalbumin conjugates and the improvement in β-carotene retention in an oil-in-water nanoemulsion

The goal of this study was to prepare and characterize α-lactalbumin (ALA)-catechin conjugates as a novel emulsifier in improving the retention of β-carotene (BC) in nanoemulsions via a free radical method. Covalent modification was observed and at least one catechin molecule was binding with ALA according to ESI–MS results. Far-UV CD indicated that the secondary structure of ALA was changed after conjugation. The Z-average particle diameters of nanoemulsions stabilized with ALA and ALA-catechin conjugates were 158.8 and 162.7nm, respectively. The increase of mean particle size and the degradation of BC at 50°C were both larger than at 25°C during 30days storage. BC retention stabilized with ALA-catechin conjugates was appreciably greater than ALA (control), which was attributed to the increase of ALA’s radicals-scavenging and free metal ion binding ability after grafting with catechin. The chemical antioxidant activities of ALA-catechin conjugates were increased with increasing concentrations from 0.1 to 1.0mg/ml. In general, labile phytochemicals, like BC, can be protected against oxidation during storage by proteins-polyphenols conjugates without any side effects.

Self-assembled ternary complexes stabilized with hyaluronic acid-green tea catechin conjugates for targeted gene delivery

Nanosized polyelectrolyte complexes are attractive delivery vehicles for the transfer of therapeutic genes to diseased cells. Here we report the application of self-assembled ternary complexes constructed with plasmid DNA, branched polyethylenimine and hyaluronic acid-green tea catechin conjugates for targeted gene delivery. These conjugates not only stabilize plasmid DNA/polyethylenimine complexes via the strong DNA-binding affinity of green tea catechin, but also facilitate their transport into CD44-overexpressing cells via receptor-mediated endocytosis. The hydrodynamic size, surface charge and physical stability of the complexes are characterized. We demonstrate that the stabilized ternary complexes display enhanced resistance to nuclease attack and polyanion-induced dissociation. Moreover, the ternary complexes can efficiently transfect the difficult-to-transfect HCT-116 colon cancer cell line even in serum-supplemented media due to their enhanced stability and CD44-targeting ability. Confocal microscopic analysis demonstrates that the stabilized ternary complexes are able to promote the nuclear transport of plasmid DNA more effectively than binary complexes and hyaluronic acid-coated ternary complexes. The present study suggests that the ternary complexes stabilized with hyaluronic acid-green tea catechin conjugates can be widely utilized for CD44-targeted delivery of nucleic acid-based therapeutics.

Beta-carotene chemical stability in Nanoemulsions was improved by stabilized with beta-lactoglobulin-catechin conjugates through free radical method.

Beta-lactoglobulin (BLG)–catechin conjugates were prepared by a free radical method and investigated with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), electrospray ionization–mass spectrometry (ESI-MS), and far-UV circular dichroism (CD). Covalent binding between BLG and catechin were confirmed with SDS-PAGE and ESI-MS. About 93% of beta-lactoglobulin was conjugated with catechin or catecin fragments according to the gel intensity analysis software. Far-UV CD results showed that the content of β-sheet decreased with a corresponding increase in unordered structures after grafting. Both nanoemulsions with mean particle size between 160 and 170 nm were prepared. Both the rate of particle growth and the total beta-carotene (BC) loss at 50 °C were significantly greater than at 4 and 25 °C. The retention rates of BC in nanoemulsions were 27.8% and 48.6% for BLG and BLG–catechin conjugates, respectively, after 30 days of storage at 50 °C. The BC retention encapsulated in nanoemulsion was significantly improved using BLG–catechin conjugates, compared with BLG alone. The increase of BC retention in nanoemulsions encapsulated with BLG–catechin conjugates was due to the significant improvement of antioxidative properties (reducing power, free radical scavenging activity, and hydroxyl radical scavenging activity) of BLG after covalent binding with catechin. The results indicated that the proteins modified with polyphenols can be widely used in a labile bioactive compounds encapsulation delivery system.

The profiling and identification of the metabolites of (+)‐catechin and study on their distribution in rats by HPLC‐DAD‐ESI‐IT‐TOF‐MSn technique

(+)-Catechin, a potential beneficial compound to human health, is widely distributed in plants and foods. A high-performance liquid chromatography with diode array detector and combined with electrospray ionization ion trap time-of-flight multistage mass spectrometry method was applied to profile and identify the metabolites of (+)-catechin in rats and to study the distribution of these metabolites in rat organs for the first time. In total, 51 phase II metabolites (44 new) and three phase I metabolites were tentatively identified, comprising 16 (+)-catechin conjugates, 14 diarylpropan-2-ol metabolites, 6 phenyl valerolactone metabolites and 18 aromatic acid metabolites. Further, 19 phase II metabolites were new compounds. The in vivo metabolic reactions of (+)-catechin in rats were found to be ring-cleavage, sulfation, glucuronidation, methylation, dehydroxylation and dehydrogenation. The numbers of detected metabolites in urine, plasma, small intestine, kidney, liver, lung, heart, brain and spleen were 53, 23, 27, 9, 7, 5, 3, 2 and 1, respectively. This indicated that small intestine, kidney and liver were the major organs for the distribution of (+)-catechin metabolites. In addition, eight metabolites were found to possess bioactivities according to literature. These results are very helpful for better comprehension of the in vivo metabolism of (+)-catechin and its pharmacological actions, and also can give strong indications on the effective forms of (+)-catechin in vivo.

Incorporation of carbon nanotubes into a gelatin–catechin conjugate: Innovative approach for the preparation of anticancer materials

A new hybrid material made of gelatin, catechin and carbon nanotubes was prepared by the non-covalent incorporation of carbon nanotubes (CNTs) into a gelatin-catechin covalent conjugate. The composite materials was tested by means of determination of the dispersion stability in water and the functionalization degree was assessed by the Folin-Ciocalteu method, finding a 0.9 mg of CT/g of protein conjugate. Subsequently, the complete retention of the antioxidant properties of the flavonoid after incorporation into the composite was proved by DPPH and ABTS assays and IC50 values of 5.74 mg mL(-1) and 0.39 mg mL(-1) were recorded. The presence of CNT into the materials did not interfere with the scavenging activities of the catechin. Finally, the anticancer activity on HeLa cancer cells was evaluated and a considerable increase in the therapeutic activity of the flavonoid was recorded moving from the free to the conjugated form in the presence of CNT, while in absence of CNT a reduction of the efficiency was observed.

Pharmacokinetic and chemoprevention studies on tea in humans

Green tea and its major polyphenols constituents, tea catechins, have been shown to have many health benefits including cancer prevention. Tea catechins and tea catechin metabolites/catabolites are bioavailable in the systemic circulation after oral intake of green tea or green tea catechins. The metabolites/catabolites identified in humans include glucuronide/sulfate conjugates, methylated tea catechin conjugates, and microflora-mediated ring fission products and phenolic acid catabolites. Plasma levels of unchanged tea catechins in humans are mostly in the sub-μM or nM concentration range, which is much lower than the effective concentrations determined in most in vitro studies. However, some of the catechin metabolites/catabolites are present in the systemic circulation at levels much higher than those of the parent catechins. The contribution of catechin derived metabolites/catabolites to the biological effects associated with green tea is yet to be defined. A limited number of chemoprevention trials of green tea or green tea catechins have been conducted to date and have observed potential preventive activity for oral, prostate, and colorectal cancer. Emerging data from multiple ongoing intervention trials will further contribute to defining the cancer preventive activity of green tea or green tea catechins.

Kinetics and mechanism on laccase catalyzed synthesis of poly(allylamine)–catechin conjugate

The conjugation reaction of catechin with poly(allylamine) has been studied in aqueous methanol using free, immobilized and cross-linked enzyme crystals (CLEC) of laccase from Trametes versicolor with particular emphasis on the effect of pertinent variables and kinetic aspects of the reaction. The stability of the CLEC was better than that of the free and immobilized enzymes for practical application. The kinetics of the conjugation reaction conformed to the so-called Substituted-enzyme mechanism with catechin inhibition. In case of immobilized laccase system marginal diffusional limitation could be inferred from the experimental data. The kinetic parameters K m(paa) and K m(cat) estimated by non-linear regression analysis were found to be 0.75, 1.8967, 2.135 and 11.769, 15.1816, 29.489 for free, immobilized and CLEC laccase, respectively.

Laccase catalysed conjugation of catechin with poly(allylamine): Solvent effect

The Trametes versicolor laccase catalysed the synthesis of poly(allylamine) catechin conjugate by conjugation of catechin with poly(allylamine) was studied in 11 different solvents in order to deduce the solvent effect through an attempt to correlate the initial reaction rate with solvent properties such as hydrophobicity (log P), water solubility (log S w), electron pair acceptance ( E T N ) and donation abilities ( D N N ), polarisibility and dielectric constant. The initial rate was found to exhibit reasonable correlation with log P, log S w, E T N + D N N , polarisibility and dielectric constant. The probable explanation for the deviation has been put forward based on established hypothesis. The study revealed, in general that polar solvents favour the initial reaction rate. The organic solvent interferes neither with the laccase–substrate binding process nor with the catalytic mechanism. The contribution of the substrate–solvent interactions to enzyme kinetics was accounted by replacing the substrate concentration by thermodynamic activities.

Novel separation of bioactive catechin derivatives from complex plant mixtures by anion-exchange chromatography

The paper presents the use of anion-exchange chromatography to separate bioactive cysteine containing catechin conjugates from underivatised polyphenols and oligomeric material. The conjugates were excluded from the anion-exchange resin using a low percentage of organic solvent, enough to eliminate the weak hydrophobic interactions with the matrix. The rest of the uncharged polyphenols were unexpectedly retained by the matrix and eluted by the addition of salt. Cation–π interactions between the quaternary amino group on the resin and the electron-rich faces of the flavanol's aromatic rings might be responsible for this unexpected behaviour. Because immobilized anions retain uncharged polyphenolic material, anion-exchange chromatography may be a convenient approach to separate polyphenols from other bioactive compounds in complex mixtures of plant origin.

Electron‐transfer capacity of catechin derivatives and influence on the cell cycle and apoptosis in HT29 cells

Galloylated and nongalloylated catechin conjugates with cysteine derivatives have been synthesized and evaluated for their capacity to scavenge free radicals and to influence crucial functions (cell cycle, apoptosis) in HT29 colon carcinoma cells. We show that the nonphenolic part of the molecule modified the capacity of catechins to donate hydrogen atoms and to transfer electrons to free radicals. Nongalloylated derivatives did not significantly influence either the cell cycle or apoptosis. Among the galloylated species, 4beta-[S-(O-ethyl-cysteinyl)]epicatechin 3-O-gallate, which showed a high electron-transfer capacity (5 e- per molecule), arrested the cell cycle and induced apoptosis as expected for galloylated catechins such as tea (-)-epigallocatechin 3-O-gallate. 4beta-[S-(N-Acetyl-O-methyl-cysteinyl)]epicatechin 3-O-gallate, which showed the highest hydrogen-donating capacity (10 H per molecule) while keeping the electron-transfer capacity low (2.9 e- per molecule), did not trigger any significant apoptosis. The gallate moiety did not appear to be sufficient for the pro-apoptotic effect of the catechin derivatives in HT29 cells. Instead, a high electron-transfer capacity is more likely to be behind this effect. The use of stable radicals sensitive exclusively to electron transfer may help to design molecules with either preventive scavenging action (high hydrogen donation, low electron transfer) or therapeutic pro-apoptotic activity (high electron transfer).