Uncovering the antioxidant characteristics of black tea by coupling in vitro free radical scavenging assay with UHPLC-HRMS analysis

Pancreatic lipase immobilization on cellulose filter paper for inhibitors screening and network pharmacology study of anti-obesity mechanism

The discovery of pancreatic lipase (PL) inhibitors is an essential route to develop new anti-obesity drugs. In this experiment, chitosan was used to add amino groups to cellulose filter paper (CFP) and then glutaraldehyde was used to covalently combine PL with amino-modified CFP through the Schiff base reaction. Under optimal immobilization conditions, CFP immobilized PL has a wide range of pH and temperature tolerance, as well as excellent reproducibility, reusability and storage stability. Subsequently, 26 natural products (NPs) were screened by immobilized PL with black tea extract having the highest inhibition rate. Three compounds with binding effects on PL (epigallocatechin gallate, theaflavin-3-gallate and theaflavin-3,3'-digallate) were captured. Molecular docking proved that these three compounds have a strong binding affinity for PL. Fluorescence spectra further revealed that theaflavin-3,3'-digallate could statically quench the intrinsic fluorescence of pancreatic lipase. The molecular docking and thermodynamic parameters indicated that electrostatic interaction was considered as the main interaction force between PL and theaflavin-3,3'-digallate. Finally, the potential anti-obesity targets and pathways of the three compounds were discussed through network pharmacology. This study not only proposes a simple and efficient method for screening PL inhibitors, but also sheds light on the anti-obesity mechanism of active compounds in black tea.

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.

The Effects of Structure and Oxidative Polymerization on Antioxidant Activity of Catechins and Polymers

Polyphenols are key free radical scavengers in tea. This study screened the antioxidant active groups of catechins and dimers and analyzed the effects of the degree of oxidative polymerization and oxidative dimerization reaction on their antioxidant activities. ABTS+· free radical scavenging activity, DPPH free radical scavenging activity, and total antioxidant capacity of catechins and polymers were systematically analyzed and compared in this study. Results manifested antioxidant activities of catechins were dominated by B-ring pyrogallol and 3-galloyl, but were not decided by geometrical isomerism. 3-galloyl had a stronger antioxidant activity than B-ring pyrogallol in catechins. The number, not the position, of the galloyl group was positively correlated with the antioxidant activities of theaflavins. Theasinensin A has more active groups than (-)-epigallocatechin gallate and theaflavin-3,3'-digallate, so it had a stronger antioxidant activity. Additionally, the higher the degree of oxidation polymerization, the weaker the antioxidant activities of the samples. The oxidative dimerization reaction hindered the antioxidant activities of the substrate-catechin mixture by reducing the number of active groups of the substrate and increasing the molecular structure size of the product. Overall, pyrogallol and galloyl groups were antioxidant active groups. The degree of oxidative polymerization and the oxidative dimerization reaction weakened the antioxidant activity.

Effects of Key Components on the Antioxidant Activity of Black Tea

Many components (such as tea polyphenols, catechins, theaflavins, theasinensins, thearubigins, flavonoids, gallic acid, etc.) in black tea have antioxidant activities. However, it is not clear which components have a greater influence on the antioxidant activity of black tea. In this study, the antioxidant activity and contents of tea polyphenols, catechins, theaflavins, thearubigins, theabrownins, TSA, total flavonoids, amino acids, caffeine, and total soluble sugar were analyzed in 51 black teas. Principal component analysis (PCA), orthogonal partial least-squares discrimination analysis (OPLS-DA), and the correlation analysis method were used for data analysis. The results showed that catechins in tea polyphenols were the most important components that determine the antioxidant activity of black tea. Among them, epicatechin gallate (ECG), epi-gallocatechin gallate (EGCG), epicatechin (EC), and epi-gallocatechin (EGC) were significantly positively correlated with the antioxidant activity of black tea, and theabrownin was negatively correlated with the antioxidant activity of black tea. Furthermore, this study analyzed the correlation between the changes in catechin and its oxidized polymers with antioxidant activity during black tea fermentation; it verified that catechins were significantly positively correlated with the antioxidant activity of black tea, and theabrownin showed a negative correlation. And the antioxidant activity of catechins and their oxidation products in vitro and their correlation in black tea processing were used as validation. This study provides a comparison method for comparing the antioxidant activity of black tea.

Exploring the Promotive Effects and Mechanisms of Different Polyphenolic Extracts from Prinsepia utilis Royle Seed Shell on Tyrosinase

Prinsepia utilis Royle (P. utilis) is commonly used as a food ingredient and herbal medicine according to folk records, yet little research has been done on the seed shell, a processing waste. The aim of this study was to investigate the distribution of polyphenolic components and the tyrosinase activation activity of different extracts from the seed shell by UHPLC-ESI-HRMS/MS, in vitro tyrosinase activity assay, molecular docking and molecular dynamics. A total of 16 phytochemicals were identified, of which (+)-catechin and (-)-epicatechin were the major polyphenolic compounds. Both the esterified and insoluble bound polyphenols exhibited tyrosinase activation activity, and the esterified polyphenols showed better tyrosinase activation activity. (+)-Catechin and (-)-epicatechin might be the main activators of tyrosinase, both of which may act as substrate to affect tyrosinase activity. By molecular docking and molecular dynamics simulation studies, (+)-catechin and (-)-epicatechin can be efficiently and stably bound to the tyrosinase active site through hydrogen bonds, van der Waals forces and π-bonds. The results of this study may not only provide a scientific basis for exploring P. utilis seed shell as a potential activator of tyrosinase, but also contribute to the high value utilization of P. utilis processing by-products.

A New Approach for Quantifying Purpurogallin in Brewed Beverages Using LC-MS in Combination with Solid Phase Extraction

Purpurogallin (PPG) is a phenolic compound known for its high antioxidant properties in plant-based food materials. However, there is no easy and reliable method for direct determination of PPG in brewed beverages owing to its hydrophobicity, which makes it hard to separate from the background hydrophobic components. Therefore, a method employing solid-phase extraction (SPE) and liquid chromatography-mass spectrometry (LC-MS) was developed for detection and quantification of PPG in brewed beverages, and PPG content was quantified in commercial coffee, cocoa, and tea samples. The limits of detection and quantification were 71.8 and 155.6 ng/g dry weight (dw), respectively. The recovery with SPE was 26.6%. When combined with acetonitrile extraction (ANE), the recovery was 6.8%, higher than 2.6% with water extraction (WTE). Test tube extractions were better than moka pot brewing (MPB) for PPG quantification. Total PPG content of ground coffees prepared by ANE, WTE, and MPB ranged between 635 and 770, 455 and 630, and 85 and 135 ng/g dw, respectively. PPG was detected in two English breakfast tea samples (335−360 ng/g dw) using WTE, but not in cocoa samples. ANE showed higher (p < 0.05) PPG levels, but WTE (r = 0.55, p < 0.01) correlated better with MPB than ANE (r = 0.43, p < 0.01). The result indicated that WTE is the best method to determine PPG in brewed beverages. This work demonstrated that PPG was significant in brewed coffee, and our pioneer study in developing the method for beverage sample preparation and LC-MS analysis has made possible industrial applications and provided new perspectives for future research.

Processing, chemical signature and food industry applications of Camellia sinensis teas: An overview

The plant Camellia sinensis is the source of different teas (white, green, yellow, oolong, black, and pu-ehr) consumed worldwide, which are classified by the oxidation degree of their bioactive compounds. The sensory (taste, aroma, and body of the drink) and functional properties of teas are affected by the amount of methylxanthines (caffeine and theobromine), amino acids (l-theanine) and reducing sugars in their composition. Additionally, flavan-3-ols, mainly characterized by epicatechins, catechins, and their derivatives, represent on average, 60% of the bioactive compounds in teas. These secondary metabolites from teas are widely recognized for their antioxidant, anti-cancer, and anti-inflammatory properties. Thus, Camellia sinensis extracts and their isolated compounds have been increasingly used by the food industry. However, bioactive compounds are very susceptible to the oxidation caused by processing and degradation under physiological conditions of gastrointestinal digestion. In this context, new approaches/technologies have been developed for the preservation of these compounds. This review presents the main stages involved in production of Camellia sinensis teas following a description of their main bioactive compounds, biological properties, stability and bioaccessibility. Besides, and updated view of Camellia sinensis teas in the field of food science and technology was provided by focusing on novel findings and innovations published in scientific literature over the last five years.

The Gut Microbiota Metabolite Urolithin B Improves Cognitive Deficits by Inhibiting Cyt C-Mediated Apoptosis and Promoting the Survival of Neurons Through the PI3K Pathway in Aging Mice

Background: Despite considerable advances in pharmacotherapy, more effective therapeutic interventions for aging-related neurodegenerative disorders (NDs), such as Alzheimer’s disease (AD), remain limited. Urolithin B (UB), one of the major subcategories of urolithins (microbiota metabolites) found in various tissues after ellagitannin consumption, has been shown to possess antioxidant, anti-inflammatory, and antiapoptotic effects. However, the neuroprotective effect of UB on brain aging in mice and its potential mechanisms were still unknown.

Methods: In the current research, we first assessed the ameliorative effects of UB on oxidative injury and apoptosis induced by H₂O₂ in neuro-2a cells. Then a subcutaneous injection of D-galactose in mice for 8 weeks was used to establish the aging model to evaluate the protective effects of UB. The capacity of memory and learning, alterations of hippocampus histology and corresponding molecular mechanisms were all evaluated.

Results: The D-gal-induced accelerated aging model in vivo demonstrated that UB could significantly ameliorate deficits in learning and memory by inhibiting the accumulation of advanced glycation end products (AGEs) and elevating the expression and activity of Cu, Zn-SOD and CAT. Furthermore, UB downregulated the c-Jun N-terminal kinase (JNK) signaling pathway and prevented cytochrome c release from isolated mitochondria, thereby inhibiting neuronal apoptosis during the aging process. More importantly, UB stimulation of aging mice activated ERK and phosphoinositide 3-kinase (PI3K), leading to neuronal survival along with Akt and p44/42 mitogen-activated protein kinase (MAPK) phosphorylation and activation.

Conclusion: In summary, UB effectively alleviated cognitive deficits and ameliorated brain aging-related conditions and could be considered a healthcare product to prevent aging-associated NDs such as AD.

UPLC-Triple-TOF/MS characterization of phenolic constituents and the influence of natural deep eutectic solvents on extraction of Carya cathayensis Sarg. peels: Composition, extraction mechanism and in vitro biological activities

Natural deep eutectic solvent (NADES) has received increasing interest as a green alternative to traditional organic solvents for efficient extraction of bioactive compounds from natural sources. In this study, phytochemicals in Carya cathayensis Sarg. peels extracted with Choline chloride-Malic acid (ChCl-MA) were identified using UPLC-Triple-TOF/MS. Effect of NADES on phenolic composition, antioxidant properties and inhibition of α-glucosidase and α-amylase were evaluated. Furthermore, extraction mechanism caused by different solvents were investigated by quantum chemical calculation combined with molecular dynamic simulation. A total of 29 phytochemicals were identified, and catechin, procyanidin B1, 2,3-dihydroxybenzoic acid, pinocembrin, procyanidin B3, myricetrin were the most abundant compounds. The extract using ChCl-MA exhibited the highest phenolic compounds content, antioxidant capacity, and α-glucosidase and α-amylase inhibition activities. Larger solvent accessible surface area, more hydrogen bonds between ChCl-MA and extract, longer lifetime of the hydrogen bonds, and lower intermolecular interaction energy account for higher extraction efficiency of ChCl-MA.

Theaflavin protects against oxalate calcium-induced kidney oxidative stress injury via upregulation of SIRT1

Renal tubular cell injury induced by calcium oxalate (CaOx) is a critical initial stage of kidney stone formation. Theaflavin (TF) has been known for its strong antioxidative capacity; however, the effect and molecular mechanism of TF against oxidative stress and injury caused by CaOx crystal exposure in kidneys remains unknown. To explore the potential function of TF on renal crystal deposition and its underlying mechanisms, experiments were conducted using a CaOx nephrocalcinosis mouse model established by glyoxylate intraperitoneal injection, and HK-2 cells were subjected to calcium oxalate monohydrate (COM) crystals, with or without the treatment of TF. We discovered that TF treatment remarkably protected against CaOx-induced kidney oxidative stress injury and reduced crystal deposition. Additionally, miR-128-3p expression was decreased and negatively correlated with SIRT1 level in mouse CaOx nephrocalcinosis model following TF treatment. Moreover, TF suppressed miR-128-3p expression and further abolished its inhibition on SIRT1 to attenuate oxidative stress in vitro. Mechanistically, TF interacted with miR-128-3p and suppressed its expression. In addition, miR-128-3p inhibited SIRT1 expression by directly binding its 3'-untranslated region (UTR). Furthermore, miR-128-3p activation partially reversed the acceerative effect of TF on SIRT1 expression. Taken together, TF exhibits a strong nephroprotective ability to suppress CaOx-induced kidney damage through the recovery of the antioxidant defense system regulated by miR-128-3p/SIRT1 axis. These findings provide novel insights for the prevention and treatment of renal calculus.

Comparing the inhibitory abilities of epigallocatechin-3-gallate and gallocatechin gallate against tyrosinase and their combined effects with kojic acid

Inhibition of tyrosinase activity contributes to the control of food browning and skin pigmentation diseases. Herein, the inhibitory mechanism of epigallocatechin-3-gallate (EGCG) and gallocatechin gallate (GCG) on tyrosinase were investigated. Both EGCG and GCG inhibited tyrosinase in a mixed manner with the IC₅₀ values of 39.4 ± 0.54 μM and 36.8 ± 0.21 μM, and showed a synergism with their combination, while EGCG and GCG combined with kojic acid (IC₅₀ = 19.2 ± 0.26 μM) exhibited antagonism and additive effect, respectively. EGCG and GCG interacted with tyrosinase mainly by hydrogen bonding and hydrophobic interactions and induced a looser conformation of tyrosinase. Molecular docking indicated that EGCG and GCG bound to the active center of tyrosinase and interacted with copper ions and key amino acid residues. Molecular dynamics simulation further characterized the structure and property of EGCG/GCG-tyrosinase complex. This study provides novel insights into the mechanism of catechins as tyrosinase inhibitors.