Theaflavin-3,3'-digallate effectively attenuates biofilm formation by Enterococcus faecalis via the targeting of specific quorum sensing pathways.

Enterococcus faecalis, an opportunistic pathogen responsible for nosocomial infections, exhibits increased pathogenicity via biofilm formation. Theaflavin-3,3'-digallate (TF3), a theaflavin extracted from black tea, exhibits potent antibacterial effects. In the present study, we investigated the inhibitory effect of TF3 on E. faecalis. Our results indicated that TF3 significantly inhibited E. faecalis ATCC 29212 biofilm formation. This observation was further confirmed via crystal violet staining, confocal laser scanning microscopy, and field emission-scanning electron microscopy. To disclose the underlying mechanisms, RNA-seq was applied. TF3 treatment significantly altered the transcriptomic profile of E. faecalis, as evidenced by identification of 248 differentially expressed genes (DEGs). Through functional annotation of these DEGs, several quorum-sensing pathways were found to be suppressed in TF3-treated cultures. Further, gene expression verification via real-time PCR confirmed the downregulation of gelE, sprE, and secY by TF3. These findings highlighted the ability of TF3 to impede E. faecalis biofilm formation, suggesting a novel preventive strategy against E. faecalis infections.

Targeted quantitative metabolomic and flavor objective quantification technique reveal the impact mechanism of shaking on black tea quality and non-volatile metabolites.

Shaking constitutes a pivotal technique for enhancing black tea quality; nevertheless, its impact on the transformation mechanism of non-volatile metabolites (NVMs) in black tea remains obscure. The present study aimed to investigate the impact of shaking-withering methods (SWM) and traditional-withering methods (TWM) on black tea quality and NVMs conversion. A total of 57 NVMs and 14 objective quantitative indicators were obtained. SWM enhanced sweetness and umami taste, as well as appearance and liquor color brightness of black tea. Eight key differential NVMs were identified by multivariate statistical and dose over threshold value analysis. Metabolic pathway and evolution law analysis revealed that SWM enhanced the oxidation of catechins and flavonol glycosides, promoted the decarboxylation of glutamic acid, then facilitated the formation of theaflavin-3,3'-digallate, finally enhanced the taste and color quality of black tea. This study offers theoretical guidance and technical support for the targeted processing of high-quality black tea.

Molecular insights into the interactions of theaflavin and epicatechin with different lipid bilayer membranes by molecular dynamics simulation.

At present, consumers increasingly favored the natural food preservatives with fewer side-effects on health. The green tea catechins and black tea theaflavins attracted considerable interest, and their antibacterial effects were extensively reported in the literature. Epicatechin (EC), a green tea catechin without a gallate moiety, showed no bactericidal activity, whereas the theaflavin (TF), also lacking a gallate moiety, exhibited potent bactericidal activity, and the antibacterial effects of green tea catechins and black tea theaflavins were closely correlated with their abilities to disrupt the bacterial cell membrane. In our present study, the mechanisms of membrane interaction modes and behaviors of TF and EC were explored by molecular dynamics simulations. It was demonstrated that TF exhibited markedly stronger affinity for the POPG bilayer compared to EC. Additionally, the hydrophobic interactions of tropolone/catechol rings with the acyl chain part could significantly contribute to the penetration of TF into the POPG bilayer. It was also found that the resorcinol/pyran rings were the key functional groups in TF for forming hydrogen bonds with the POPG bilayer. We believed that the findings from our current study could offer useful insights to better understand the stronger antibacterial effects of TF compared to EC.

The enzymatic synthesis of theaflavin-3-gallate oxidation product and its determination.

In this work, the oxidation of theaflavin-3-gallate (TF-3-G) was investigated using (-)-epicatechin (EC) and (-)-epigallocatechin gallate (EGCG) as substrates in a one-pot reaction. The resulting TF-3-G oxidation product was acquired by employing acetonitrile/water and ethanol/water as eluents, respectively, which was identified as theanaphthoquinone-3'-gallate (TNQ-3'-G). Surprisingly, we discovered that TNQ-3'-G could react with certain protic solvents to form new and unstable complexes through intermolecular hydrogen bond. This reactivity was also confirmed by the presence of irregular peaks in reverse-phase high-performance liquid chromatography (RP-HPLC) besides spectroscopic data. Therefore, we inferred that the number of carboxyl groups may increase through the successive oxidative polymerization of the TFs oxidation products. The high-molecular polymer could also interact with biomacromolecules in a similar manner to their interaction with protic solvents. This interaction might be one of the main factors contributing to the broad hump of thearubigins (TRs) on the RP-HPLC baseline. Additionally, these findings lay a solid foundation for interpreting the structures of TRs and understanding their generation mechanism.

Theaflavin -3,3'-digallate/ethanol: a novel cross-linker for stabilizing dentin collagen.

Objectives: To study the ability of theaflavin-3,3'-digallate (TF3)/ethanol solution to crosslink demineralized dentin collagen, resist collagenase digestion, and explore the potential mechanism. Methods: Fully demineralized dentin blocks were prepared using human third molars that were caries-free. Then, these blocks were randomly allocated into 14 separate groups (n = 6), namely, control, ethanol, 5% glutaraldehyde (GA), 12.5, 25, 50, and 100 mg/ml TF3/ethanol solution groups. Each group was further divided into two subgroups based on crosslinking time: 30 and 60 s. The efficacy and mechanism of TF3's interaction with dentin type I collagen were predicted through molecular docking. The cross-linking, anti-enzymatic degradation, and biomechanical properties were studied by weight loss, hydroxyproline release, scanning/transmission electron microscopy (SEM/TEM), in situ zymography, surface hardness, thermogravimetric analysis, and swelling ratio. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were utilized to explore its mechanisms. Statistical analysis was performed using one and two-way analysis of variance and Tukey's test. Results: TF3/ethanol solution could effectively crosslink demineralized dentin collagen and improve its resistance to collagenase digestion and biomechanical properties (p < 0.05), showing concentration and time dependence. The effect of 25 and 50 mg/ml TF3/ethanol solution was similar to that of 5% GA, whereas the 100 mg/mL TF3/ethanol solution exhibited better performance (p < 0.05). TF3 and dentin type I collagen are mainly cross-linked by hydrogen bonds, and there may be covalent and hydrophobic interactions. Conclusion: TF3 has the capability to efficiently cross-link demineralized dentin collagen, enhancing its resistance to collagenase enzymatic hydrolysis and biomechanical properties within clinically acceptable timeframes (30 s/60 s). Additionally, it exhibits promise in enhancing the longevity of dentin adhesion.

Construction of recombinant fluorescent LSDV for high-throughput screening of antiviral drugs.

Lumpy skin disease virus (LSDV) infection is a major socio-economic issue that seriously threatens the global cattle-farming industry. Here, a recombinant virus LSDV-ΔTK/EGFP, expressing enhanced green fluorescent protein (EGFP), was constructed with a homologous recombination system and applied to the high-throughput screening of antiviral drugs. LSDV-ΔTK/EGFP replicates in various kidney cell lines, consistent with wild-type LSDV. The cytopathic effect, viral particle morphology, and growth performance of LSDV-ΔTK/EGFP are consistent with those of wild-type LSDV. High-throughput screening allowed to identify several molecules that inhibit LSDV-ΔTK/EGFP replication. The strong inhibitory effect of theaflavin on LSDV was identified when 100 antiviral drugs were screened in vitro. An infection time analysis showed that theaflavin plays a role in the entry of LSDV into cells and in subsequent viral replication stages. The development of this recombinant virus will contribute to the development of LSDV-directed antiviral drugs and the study of viral replication and mechanisms of action.

Efficient enzymatic synthesis of theaflavin and its production mechanism.

In this study, a novel preparation method of theaflavin (TF) has been established. Our findings indicated that the formation of TF was significantly enhanced by using an ice bath (2-3°C). Additionally, increasing the ratio of (-)-epigallocatechin (EGC) under the ice bath could further improve its yield. This approach prevented the appearance of a dark solution within 3 h, effectively protecting TF from oxidation. Our study on the generation mechanism of TF suggested that EGC-quinone I (EGC-Q-I) with two carbanions could potentially serve as one of synthons based on the retrosynthetic analysis of the bicyclo[3.2.1]octane-type intermediate. Subsequently, quantum mechanical calculations further supported this hypothesis. Practical Application: In this study, we have developed a novel method for the synthesis of theaflavin (TF), demonstrating that the use of ice bath significantly enhanced its yield. Increasing the ratio of (-)-epigallocatechin (EGC) under the ice bath further improved TF yields and prevented darkening of the solution for at least 3 h, thereby protecting TF from oxidation. Our study suggested that EGC-quinone I is a potential synthon based on the retrosynthetic analysis of the bicyclo[3.2.1]octane-type intermediate (BOI). This hypothesis is supported by QM calculations.

Theaflavin pretreatment ameliorates renal ischemia/reperfusion injury by attenuating apoptosis and oxidative stress in vivo and in vitro.

Oxidative stress-induced apoptosis is an important pathological process in renal ischemia/reperfusion injury (RIRI). Theaflavin (TF) is the main active pigment and polyphenol in black tea. It has been widely reported because of its biological activity that can reduce oxidative stress and protect against many diseases. Here, we explored the role of theaflavin in the pathological process of RIRI. In the present study, the RIRI model of 45 min ischemia and 24 h reperfusion was established in C57BL/6 J male mice, and theaflavin was used as an intervention. Compared with the RIRI group, the renal filtration function, renal tissue damage and antioxidant capacity of the theaflavin intervention group were significantly improved, while the level of apoptosis was reduced. TCMK-1 cells were incubated under hypoxia for 48 h and then reoxygenated for 6 h to simulate RIRI in vitro. The application of theaflavin significantly promoted the translocation of p53 from cytoplasm to nucleus, upregulated the expression of glutathione peroxidase 1 (GPx-1) in cells, and inhibited oxidative stress damage and apoptosis. Transfection with p53 siRNA can partially inhibit the effect of theaflavin. Thus, theaflavin exerted a protective effect against RIRI by inhibiting apoptosis and oxidative stress via regulating the p53/GPx-1 pathway. We conclude that theaflavin has the potential to become a candidate drug for the prevention and treatment of RIRI.

Antiviral activity of theaflavins against Zika virus in vivo and in vitro.

INTRODUCTION: The prevalence and infection of the Zika virus (ZIKV) have recently posed a major threat to global public health security. However, there is currently a lack of specific vaccines and effective antiviral drugs for ZIKV infection. METHODS: Theaflavins TF1 and TF2 were selected by evaluating the anti-Zika virus activity of four kinds of theaflavins in vitro. Subsequently, in vivo, we investigated the effects of TF1 and TF2 on weight, survival, tissue viral load, and cytokines in ZIKV-infected mice. RESULTS: We compared the anti-ZIKV activity of four theaflavins (TFs) in cells and found that TF1 and TF2b significantly inhibited the replication of ZIKV/Z16006 toxic strain in BHK and Vero cells by inhibiting the replication and release of ZIKV, while no similar effects were observed for TF2a and TF3. In vivo assay, we only found that TF2b improved the survival rate of infected mice. In tissues of ZIKV-infected mice, the viral load was higher in spleen and blood, followed by liver, epididymis, and testis, the lowest in muscle. Additionally, TF2b treatment significantly reduced the expression of cytokines (IL-6, IL-1ß, TNF-α) and chemokines (CCL2, CCL5, CXCL10) induced by ZIKV infection. CONCLUSIONS: These findings suggest that TF2b has a potent antiviral effect and can be used as a potential candidate for the treatment of ZIKV infection.

Inhibitory effect of theaflavin-3,3'-digallate can involve its binding to the "stem" domain of α-hemolysin of Staphylococcus aureus.

Infections caused by Staphylococcus aureus are currently a worldwide threat affecting millions of individuals. The pathogenicity of S. aureus is associated with numerous virulence factors, including cell surface proteins, polysaccharides, and secreted toxins. The pore-forming α-hemolysin, known as α-toxin, is produced by nearly all virulent strains of S. aureus and is implicated in several diseases including skin and soft tissue infections, atopic dermatitis, and pneumonia. There are currently no vaccines available for the prevention of S. aureus infections and the efficacy of available antibiotics has been fading. In this study we examined the mode of antihemolytic activity of theaflavin-3,3'-digallate against α-hemolysin of methicillin-resistant S. aureus by molecular docking using AutoDock Vina as the molecular docking tool. The theaflavin-3,3'-digallate docked the molecular sequence of the Hla (PDB ID:7ahl). The scores of the top 10 binding modes obtained were between -9.0 and -8.5 kcal mol-1, and the best binding mode was -9.0 kcal mol-1. Direct binding sites of theaflavin-3,3'-digallate to the "stem" domain of Hla were revealed which primarily targeted of the residues Met113, Thr117, Asn139. The disclosure of this potential binding mode warrants further clinical evaluation of theaflavin-3,3'-digallate as an anti-hemolytic compound in order to practically validate our results.

Milk Casein Inhibits Effect of Black Tea Galloylated Theaflavins to Inactivate SARS-CoV-2 In Vitro.

Continuing caution is required against the potential emergence of SARS-CoV-2 novel mutants that could pose the next global health and socioeconomical threats. If virus in saliva can be inactivated by a beverage, such a beverage may be useful because the saliva of infected persons is the major origin of droplets and aerosols that mediate human-to-human viral transmission. We previously reported that SARS-CoV-2 was significantly inactivated by treatment in vitro with tea including green tea and black tea. Catechins and its derived compounds galloylated theaflavins (gTFs) bound to the receptor-binding domain (RBD) of the S-protein and blocked interaction between RBD and ACE2. Black tea is often consumed with sugar, milk, lemon juice, etc., and it remains unclarified whether these ingredients may influence the anti-SARS-CoV-2 effect of black tea. Here, we examined the effect of black tea on Omicron subvariants in the presence of these ingredients. The infectivity of Omicron subvariants was decreased to 1/100 or lower after treatment with black tea for 10 s. One or two teaspoons of milk (4~8 mL) completely blocked the anti-viral effect of a cup of tea (125 mL), whereas an addition of sugar or lemon juice failed to do so. The suppressive effect was dose-dependently exerted by milk casein but not whey proteins. gTFs were coprecipitated with casein after acidification of milk-supplemented black tea, strongly suggesting the binding of gTFs to casein. The present study demonstrates for the first time that an addition of milk cancelled the anti-SARS-CoV-2 effect of black tea due to binding of casein to gTFs.

Molecular dynamics simulation and in vitro digestion to examine the impact of theaflavin on the digestibility and structural properties of myosin.

In this study, the interaction mechanism between theaflavin and myosin was explored to confirm the potential application of theaflavin in the meat protein system. A series of theaflavin and myosin solutions were prepared for spectroscopic studies. Spectroscopy results showed that theaflavins formed complexes with myosin and affected the microenvironment of myosin. And that addition of theaflavin cause static quenching of the myosin solution. Theaflavin and bovine myosin combined through hydrophobic interaction to form a complex, and gradually increasing the temperature was conducive to the binding of theaflavin and bovine myosin. This interaction results in a decrease in the α -helix content of myosin. Molecular dynamics simulation results confirmed that hydrophobic interactions and hydrogen bonds made the protein structure more compact and stable. And the in vitro digestion process was simulated. The results showed that the addition of theaflavin could significantly reduce the digestibility of myosin.

Theaflavin inhibits African swine fever virus replication by disrupting lipid metabolism through activation of the AMPK signaling pathway in virto.

African swine fever virus (ASFV) is the etiological agent of African swine fever (ASF), which is one of the most harmful swine diseases in the pig industry because of its nearly 100% mortality rate in domestic pigs and results in incalculable economic loss. Ever since ASF was initially reported, scientists have worked to develop anti-ASF vaccines; however, currently no clinically effective vaccine for ASF is available. Therefore, the development of novel measures to prevent ASFV infection and transmission is essential. In this study, we aimed to investigate the anti-ASF activity of theaflavin (TF), a natural compound mainly isolated from black tea. We found that TF potently inhibited ASFV replication at non-cytotoxic concentrations ex vivo in primary porcine alveolar macrophages (PAMs). Mechanistically, we found that TF inhibited ASFV replication by acting on cells rather than interacting directly with ASFV to inhibit viral replication. Further, we found that TF upregulated the AMPK (5'-AMP-activated protein kinase) signaling pathway in ASFV-infected and uninfected cells, and treatment with the AMPK agonist MK8722 upregulated the AMPK signaling pathway and inhibited ASFV proliferation in a dose-dependent manner. Notably, the effects of TF on AMPK activation and ASFV inhibition were partially reversed by the AMPK inhibitor dorsomorphin. In addition, we found that TF down-regulated the expression of genes related to lipid synthesis and decreased the intracellular accumulation of total cholesterol and total triglycerides in ASFV-infected cells, suggesting that TF may inhibit ASFV replication by disrupting lipid metabolism. In summary, our results demonstrated that TF is an ASFV infection inhibitor and revealed the mechanism by which ASFV replication is inhibited, providing a novel mechanism and potential lead compound for the development of anti-ASFV drugs.

Isolation and antioxidant characterization of theaflavin for neuroprotective effect in mice model.

The mandate of the current investigation was to elucidate the therapeutic and antioxidant perspective of black tea. Purposely, black tea compositional analysis followed by polyphenol extraction and antioxidant characterization was done. Moreover, the theaflavin from black tea extract was also isolated through the solvent partition method. Lastly, the neuroprotective effect of isolated theaflavin was assessed through a bio-efficacy trial. The outcomes delineated that black tea showed promising nutritional composition with special reference to protein and fiber. Among the extraction solvent, ethanol performed better as compared to methanol and water likewise, higher extraction was noticed at 60 min followed by 90 and 30 min. All the extracts indicated antioxidant activity reflected through significant DPPH, TPC, FRAP, and beta carotene as-69.13 ± 3.00, 1148.92 ± 14.01, 752.44 ± 10.30, and 65.74 ± 3.28, respectively. However, isolated theaflavin exhibited higher antioxidant capacity as-737.74 ± 12.55, 82.60 ± 2.33, and 853.77 ± 9.55, for TPC, DPPH, and FRAP, respectively, as compared to extracts. In 15 days' efficacy was physically induced with sciatic nerve injury h sciatic nerve injury physically and treated with isolated theaflavin. A total of 12 healthy albino mice were randomly assigned to either the control (n = 6) or theaflavin (5.0 mg/kg (n = 6)) groups. In these groups, behavioral tests were used to assess and compare enhanced functional recovery as well as skeletal muscle mass measurement. Serum samples included oxidative stress markers. In theaflavin leaves, behavioral tests revealed a statistically significant (p < .001) improvement in sensorimotor function restoration, muscle mass restoration, a substantial decrease in TOS, a significant increase in TAC, and enhanced antioxidative enzyme activity. Considering the above-mentioned therapeutic perspectives of theaflavin, the current research was planned to optimize the isolation of theaflavin from black tea and probed for their neuroprotective effect in mice models.

Anticariogenic Activity of Black Tea: An In Vivo Study.

BACKGROUND: The prevention of dental caries has always remained a challenge. Caries prevention through dietary intervention holds promise. Studies have revealed that several constituents present in tea have anticariogenic properties. Tea is a widely consumed beverage and hence could be utilized as a suitable caries preventive agent. The purpose of this study was to determine the effect of black tea on caries progression in experimental animals. MATERIALS AND METHODS: This study was carried out in 17-day-old albino rat pups. The animals were divided into three groups, with eight animals in each group. They were fed on a cariogenic diet (MIT 200) and inoculated with Streptococcus mutans. Group I was given MIT 200 with water, Group II was placed on MIT 200 with black tea, and Group III was placed on MIT 200 with fluoridated water for a period of 45 days. After 45 days, the animals were killed under ether anesthesia, and their teeth were examined for caries. RESULTS: The carious lesions were scored for the first two molars in each quadrant. In each group, a total of 64 teeth were examined. The caries score between the upper and lower jaws was compared using ANOVA. CONCLUSION: From this study, it may be inferred that drinking black tea reduced the development of dental caries in young rats fed on a cariogenic diet. The tea used for this study was prepared using fluoride-free water, so we can assume that besides fluoride, certain components are present in tea leaves that possess anticariogenic properties.

Mitochondrial targets exploration of epigallocatechin gallate and theaflavin in regards to differences in stress protection under different temperatures.

The study investigated the impacts of epigallocatechin gallate (EGCG) and theaflavin (TF1) on temperature tolerance of nematodes and explored targets on mitochondria. Survival rates, mitochondrial membrane potential (MMP) and ATP content of nematodes at different temperatures incubated with EGCG or TF1 were quantified. Thermogenesis and function of ex-vivo mitochondria were characterized. Targeted proteins of substances were identified via drug affinity responsive target stability (DARTS) and RT-qPCR. It turned out that EGCG and TF1 increased survival rates of nematodes under heat and cold stress, respectively. TF1 exhibited lower MMP of nematodes and more mitochondrial thermogenesis than EGCG for the cold-protection. Meanwhile, TF1 up-regulated gpi-1, pgk-1, acox-1.2, acox-1.3, and acaa-2 to compensate the energy loss due to the uncoupling and downregulation of sdha-1 and atp-1. EGCG up-regulated ctl-1, hsp-60 and enol-1 expression for the thermo-protection, as well as pgk-1, acox-1.3, and acaa-2 to compensate energy loss due to the downregulation of sdha-1.

Theaflavin mitigates acute gouty peritonitis and septic organ injury in mice by suppressing NLRP3 inflammasome assembly.

Activation of NLR family pyrin domain-containing 3 (NLRP3) inflammasome plays important role in defending against infections, but its aberrant activation is causally linked to many inflammatory diseases, thus being a therapeutic target for these diseases. Theaflavin, one major ingredient of black tea, exhibits potent anti-inflammatory and anti-oxidative activities. In this study, we investigated the therapeutic effects of theaflavin against NLRP3 inflammasome activation in macrophages in vitro and in animal models of related diseases. We showed that theaflavin (50, 100, 200 µM) dose-dependently inhibited NLRP3 inflammasome activation in LPS-primed macrophages stimulated with ATP, nigericin or monosodium urate crystals (MSU), evidenced by reduced release of caspase-1p10 and mature interleukin-1ß (IL-1ß). Theaflavin treatment also inhibited pyroptosis as shown by decreased generation of N-terminal fragment of gasdermin D (GSDMD-NT) and propidium iodide incorporation. Consistent with these, theaflavin treatment suppressed ASC speck formation and oligomerization in macrophages stimulated with ATP or nigericin, suggesting reduced inflammasome assembly. We revealed that theaflavin-induced inhibition on NLRP3 inflammasome assembly and pyroptosis resulted from ameliorated mitochondrial dysfunction and reduced mitochondrial ROS production, thereby suppressing interaction between NLRP3 and NEK7 downstream of ROS. Moreover, we showed that oral administration of theaflavin significantly attenuated MSU-induced mouse peritonitis and improved the survival of mice with bacterial sepsis. Consistently, theaflavin administration significantly reduced serum levels of inflammatory cytokines including IL-1ß and attenuated liver inflammation and renal injury of mice with sepsis, concomitant with reduced generation of caspase-1p10 and GSDMD-NT in the liver and kidney. Together, we demonstrate that theaflavin suppresses NLRP3 inflammasome activation and pyroptosis by protecting mitochondrial function, thus mitigating acute gouty peritonitis and bacterial sepsis in mice, highlighting a potential application in treating NLRP3 inflammasome-related diseases.

Improving Theaflavin-3,3'-digallate Production Efficiency Optimization by Transition State Conformation of Polyphenol Oxidase.

Theaflavins (TFs) are good for health because of their bioactivities. Enzymatic synthesis of TFs has garnered much attention; however, the source and activity of the enzymes needed limit their wide application. In this study, a microbial polyphenol oxidase from Bacillus megaterium was screened for the synthesis of theaflavin-3,3'-digallate (TFDG). Based on structural and mechanistic analyses of the enzyme, the O-O bond dissociation was identified as the rate-determining step. To address this issue, a transition state (TS) conformation optimization strategy was adopted to stabilize the spatial conformation of the O-O bond dissociation, which improved the catalytic efficiency of tyrosinase. Under the optimum transformation conditions of pH 4.0, temperature 25 °C, (-)-epigallocatechin gallate/epicatechin gallate molar ratio of 2:1, and time of 30 min, Mu4 (BmTyrV218A/R209S) produced 960.36 mg/L TFDG with a 44.22% conversion rate, which was 6.35-fold higher than that of the wild type. Thus, the method established has great potential in the synthesis of TFDG and other TFs.

Theaflavin Ameliorates Streptococcus suis-Induced Infection In Vitro and In Vivo.

Streptococcus suis (S. suis) is one of the most important zoonotic pathogens that threaten the lives of pigs and humans. Even worse, the increasingly severe antimicrobial resistance in S. suis is becoming a global issue. Therefore, there is an urgent need to discover novel antibacterial alternatives for the treatment of S. suis infection. In this study, we investigated theaflavin (TF1), a benzoaphenone compound extracted from black tea, as a potential phytochemical compound against S. suis. TF1 at MIC showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. TF1 had no cytotoxicity and decreased adherent activity of S. suis to the epithelial cell Nptr. Furthermore, TF1 not only improved the survival rate of S. suis-infected mice but also reduced the bacterial load and the production of IL-6 and TNF-α. A hemolysis test revealed the direct interaction between TF1 and Sly, while molecular docking showed TF1 had a good binding activity with the Glu198, Lys190, Asp111, and Ser374 of Sly. Moreover, virulence-related genes were downregulated in the TF1-treated group. Collectively, our findings suggested that TF1 can be used as a potential inhibitor for treating S. suis infection in view of its antibacterial and antihemolytic activity.

Study on the Interaction Mechanism of Theaflavin with Whey Protein: Multi-Spectroscopy Analysis and Molecular Docking.

The interaction mechanism of whey proteins with theaflavin (TF1) in black tea was analyzed using multi-spectroscopy analysis and molecular docking simulations. The influence of TF1 on the structure of bovine serum albumin (BSA), ß-lactoglobulin (ß-Lg), and α-lactoalbumin (α-La) was examined in this work using the interaction of TF1 with these proteins. Fluorescence and ultraviolet-visible (UV-vis) absorption spectroscopy revealed that TF1 could interact with BSA, ß-Lg and α-La through a static quenching mechanism. Furthermore, circular dichroism (CD) experiments revealed that TF1 altered the secondary structure of BSA, ß-Lg and α-La. Molecular docking demonstrated that the interaction of TF1 with BSA/ß-Lg/α-La was dominated by hydrogen bonding and hydrophobic interaction. The binding energies were -10.1 kcal mol-1, -8.4 kcal mol-1 and -10.4 kcal mol-1, respectively. The results provide a theoretical basis for investigating the mechanism of interaction between tea pigments and protein. Moreover, the findings offered technical support for the future development of functional foods that combine tea active ingredients with milk protein. Future research will focus on the effects of food processing methods and different food systems on the interaction between TF1 and whey protein, as well as the physicochemical stability, functional characteristics, and bioavailability of the complexes in vitro or in vivo.