Identification of the Catechin Uptake Transporter Responsible for Intestinal Absorption of Epigallocatechin Gallate in Mice

Effect of Green Tea Supplementation on Inflammatory Markers among Patients with Metabolic Syndrome and Related Disorders: A Systematic Review and Meta-Analysis

Several randomized controlled trials (RCTs) have investigated the potential benefits of green tea on the inflammatory process in metabolic syndrome (MetS). However, the results are inconclusive and inconsistent. In the present study, we performed a literature review and meta-analysis to evaluate the effect of green tea supplementation on inflammatory markers [e.g., tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), and interleukin-6 (IL-6)] among patients with MetS and related disorders. We systematically searched for relevant publications up to March 2022 in the PubMed, Scopus, Web of Science, and SciELO databases. The review was registered with PROSPERO (CRD42022320345). Mean differences with 95% confidence intervals were pooled on the basis of the random effects model to compare the effects of green tea with placebo. We used meta-regression and subgroup analyses to determine the cause of heterogeneity and performed study quality assessment using the Grading of Recommendations Assessment, Development, and Evaluation method. We assessed publication bias using funnel plots and Egger's tests. Out of the total 15 RCTs that were included in this systematic review, 12 were chosen for the meta-analysis. The results revealed that green tea significantly decreased TNF-α levels but did not affect CRP and IL-6 levels. Subgroup analysis showed that green tea supplementation in studies lasting ≤8 weeks significantly increased CRP levels. Furthermore, meta-regression analysis demonstrated a significant association between increasing IL-6 concentration and treatment duration. According to our meta-analysis, green tea was shown to considerably lower circulating TNF-α levels. To confirm these findings, carefully planned trials are required.

The intestinal-level metabolic benefits of green tea catechins: Mechanistic insights from pre-clinical and clinical studies

BACKGROUND

The intestinal-level host-microbiota interaction has been implicated in the pathogenesis of chronic diseases. The current review is intended to provide a comprehensive insight into deciphering whether intestinal-level bioactivities mediate the overall metabolic health benefits of green tea catechins.

PURPOSE

We have comprehensively discussed pre-clinical and clinical evidences of intestinal-level changes in metabolism, microbiota, and metabolome due to catechin-rich green tea treatments, ultimately limiting metabolic diseases. Exclusive emphasis has been given to purified catechins and green tea, and discussions on extraintestinal mechanisms of metabolic health benefits were avoided.

METHODS

A literature search for relevant pre-clinical and clinical studies was performed in various online databases (e.g., PubMed) using specific keywords (e.g., catechin, intestine, microbiota). Out of all the referred literature, ∼15% belonged to 2021-2023, ∼51% were from 2011-2020, and ∼32% from 2000-2010.

RESULT

The metabolic health benefits of green tea catechins are indeed influenced by the intestinal-level bioactivities, including reduction of mucosal inflammation and oxidative stress, attenuation of gut barrier dysfunction, decrease in intestinal lipid absorption and metabolism, favorable modulation of mucosal nuclear receptor signaling, alterations of the luminal global metabolome, and mitigation of the gut dysbiosis. The results from the recent clinical studies support the pre-clinical evidences. The challenges and pitfalls of the currently available knowledge on catechin bioactivities have been discussed, and constructive directions to harness the translational benefits of green tea through future interventions have been provided.

CONCLUSION

The metabolism, metabolome, and microbiota at the intestinal epithelia play critical roles in catechin metabolism, pharmacokinetics, bioavailability, and bioactivities. Especially the reciprocal interaction between the catechins and the gut microbiota dictates the metabolic benefits of catechins.

Preferential transport activity of DkDTX5/MATE5 affects the formation of different astringency in persimmon

Proanthocyanidins (PAs) are specialized metabolites that influence persimmon fruit quality. Normal astringent (A)-type and non-astringent (NA)-type mutants show significant variation in PA accumulation, but the influencing mechanism remains unclear. In this study, among the six identified DTXs/MATEs proteins associated with PA accumulation, we observed that allelic variation and preferential transport by DkDTX5/MATE5 induced variation in PA accumulation for A-type and NA-type fruit. The expression pattern of DkDTX5/MATE5 was correlated with PA accumulation in NA-type fruit. Upregulation and downregulation of DkDTX5/MATE5 promoted and inhibited PA accumulation, respectively, in the NA-type fruit. Interestingly, transporter assays of Xenopus laevis oocytes indicated that DkDTX5/MATE5 preferentially transported the PA precursors catechin, epicatechin, and epicatechin gallate, resulting in their increased ratios relative to the total PAs, which was the main source of variation in PA accumulation between the A-type and NA-type. The allele lacking Ser-84 in DkDTX5/MATE5 was identified as a dominantly expressed gene in the A-type and lost its transport function. Site-directed mutagenesis revealed that DkDTX5/MATE5 binds to PA precursors via Ser-84. These findings clarify the association between the transporter function of DkDTX5/MATE5 and PA variation, and can contribute to the breeding of new cultivars with improved fruit quality.

Effect of Postnatal Epigallocatechin-Gallate Treatment on Cardiac Function in Mice Prenatally Exposed to Alcohol

Prenatal alcohol exposure affects the cardiovascular health of the offspring. Epigallocatechin-3-gallate (EGCG) may be a protective agent against it, but no data are available regarding its impact on cardiac dysfunction. We investigated the presence of cardiac alterations in mice prenatally exposed to alcohol and the effect of postnatal EGCG treatment on cardiac function and related biochemical pathways. C57BL/6J pregnant mice received 1.5 g/kg/day (Mediterranean pattern), 4.5 g/kg/day (binge pattern) of ethanol, or maltodextrin until Day 19 of pregnancy. Post-delivery, treatment groups received EGCG-supplemented water. At post-natal Day 60, functional echocardiographies were performed. Heart biomarkers of apoptosis, oxidative stress, and cardiac damage were analyzed by Western blot. BNP and Hif1α increased and Nrf2 decreased in mice prenatally exposed to the Mediterranean alcohol pattern. Bcl-2 was downregulated in the binge PAE drinking pattern. Troponin I, glutathione peroxidase, and Bax increased in both ethanol exposure patterns. Prenatal alcohol exposure led to cardiac dysfunction in exposed mice, evidenced by a reduced ejection fraction, left ventricle posterior wall thickness at diastole, and Tei index. EGCG postnatal therapy restored the physiological levels of these biomarkers and improved cardiac dysfunction. These findings suggest that postnatal EGCG treatment attenuates the cardiac damage caused by prenatal alcohol exposure in the offspring.

Therapeutic potential of green tea catechin, (-)-epigallocatechin-3-O-gallate (EGCG) in SARS-CoV-2 infection: Major interactions with host/virus proteases

BACKGROUND

The current COVID-19 pandemic from the human pathogenic virus SARS-CoV-2 has resulted in a major health hazard globally. The morbidity and transmission modality of this disease are severe and uncontrollable. As no effective clinical drugs are available for treatment of COVID-19 infection till to date and only vaccination is used as prophylaxis and its efficacy is restricted due to emergent of new variants of SARS-CoV-2, there is an urgent need for effective drugs for its treatment.

PURPOSE

The aim of this review was to provide a detailed analysis of anti-SARS-CoV-2 efficacy of (-)-epigallocatechin-3-O-gallate (EGCG), a major catechin constituent of green tea (Camellia sinensis (L.) Kuntze) beverage to highlight the scope of EGCG in clinical medicine as both prophylaxis and treatment of present COVID-19 infection. In addition, the factors related to poor oral bioavailabilty of EGCG was also analysed for a suggestion for future research in this direction.

STUDY DESIGN

We collected the published articles related to anti-SARS-CoV-2 activity of EGCG against the original strain (Wuhan type) and its newly emerged variants of SARS-CoV-2 virus.

METHODS

A systematic search on the published literature was conducted in various databases including Google Scholar, PubMed, Science Direct and Scopus to collect the relevant literature.

RESULTS

The findings of this search demonstrate that EGCG shows potent antiviral activity against SARS-CoV-2 virus by preventing viral entry and replication in host cells in vitro models. The studies on the molecular mechanisms of EGCG in inhibition of SARS-CoV-2 infection in host cells reveal that EGCG blocks the entry of the virus particles by interaction with the receptor binding domain (RBD) of viral spike (S) protein to host cell surface receptor protease angiotensin-converting enzyme 2 (ACE2) as well as suppression of the expressions of host proteases, ACE2, TMPRSS2 and GRP78, required for viral entry, by Nrf2 activation in host cells. Moreover, EGCG inhibits the activities of SARS-CoV-2 main protease (Mpro), papain-like protease (PLpro), endoribonuclease Nsp15 in vitro models and of RNA-dependent RNA polymerase (RdRp) in molecular docking model for suppression of viral replication. In addition, EGCG significantly inhibits viral inflammatory cytokine production by stimulating Nrf2- dependent host immune response in virus-infected cells. EGCG significantly reduces the elevated levels of HMGB1, a biomarker of sepsis, lung fibrosis and thrombotic complications in viral infections. EGCG potentially inhibits the infection of original (Wuhan type) strain of SARS-CoV-2 and other newly emerged variants as well as the infections of SARS-CoV-2 virus spike-protein of WT and its mutants-mediated pseudotyped viruses . EGCG shows maximum inhibitory effect against SARS-CoV-2 infection when the host cells are pre-incubated with the drug prior to viral infection. A sorbitol/lecithin-based throat spray containing concentrated green tea extract rich in EGCG content significantly reduces SARS-CoV-2 infectivity in oral mucosa. Several factors including degradation in gastrointestinal environment, low absorption in small intestine and extensive metabolism of EGCG are responsible for its poor bioavailability in humans. Pharmacokinetic and metabolism studies of EGCG in humans reveal poor bioavailability of EGCG in human plasma and EGCG-4"-sulfate is its major metabolite. The concentration of EGCG-4"-sulfate in human plasma is almost equivalent to that of free EGCG (Cmax 177.9 vs 233.5 nmol/L). These findings suggest that inhibition of sulfation of EGCG is a crucial factor for improvement of its bioavailability. In vitro study on the mechanism of EGCG sulfonation indicates that sulfotransferases, SULT1A1 and SULT1A3 are responsible for sulfonation in human liver and small intestine, respectively. Some attempts including structural modifications, and nanoformulations of EGCG and addition of nutrients with EGCG have been made to improve the bioavailability of EGCG.

CONCLUSIONS

The findings of this study suggest that EGCG has strong antiviral activity against SARS-CoV-2 infection independent of viral strains (Wuhan type (WT), other variants) by inhibition of viral entry and replication in host cells in vitro models. EGCG may be useful in reduction of this viral load in salivary glands of COVID-19 patients, if it is applied in mouth and throat wash formulations in optimal concentrations. EGCG could be a promising candidate in the development of effective vaccine for prevention of the infections of newly emergent strains of SARS-CoV-2 virus. EGCG might be useful also as a clinical medicine for treatment of COVID-19 patients if its bioavailability in human plasma is enhanced.

Green tea improves cognitive function through reducing AD-pathology and improving anti-oxidative stress capacity in Chinese middle-aged and elderly people

Background: Numerous benefits of green tea have been reported. However, the effects of green tea on cognitive function remain disputable and the mechanism is still unclear.

Objective: To investigate the relationship of green tea consumption with cognitive function and related blood biomarkers among Chinese middle-aged and elderly people.

Methods: A total of 264 participants aged 50–70 years old were enrolled from Zhongnan Hospital of Wuhan University. They were interviewed about green tea consumption patterns and underwent neuropsychological tests covering five main cognitive domains to assess cognition including Montreal Cognitive Assessment (MoCA) and the other 10 scales. Then we detected serum oxidative stress biomarkers including Superoxide Dismutase (SOD), Malondialdehyde (MDA), Glutathione Peroxidase (GPx), Glutathione Reductase (GR), and Alzheimer’s disease (AD) markers including β-amyloid (Aβ)₄₀, Aβ₄₂, and phosphorylated tau-181 (pTau₁₈₁).

Results: In the tea-consuming group, the MoCA scores (P = 0.000), Hopkins Verbal Learning Test (HVLT) immediate recall (P = 0.012) and delayed recall (P = 0.013) were significantly higher while Trail Making Test-B (P = 0.005) and Victoria Stroop test interference (P = 0.000) were lower. In terms of oxidative stress markers, the tea-consuming group had lower serum MDA levels (P = 0.002) and higher serum SOD (P = 0.005) and GPx (P = 0.007) levels. In terms of AD markers, serum pTau₁₈₁ (P < 0.000), Aβ₄₂ (P = 0.019) and total Aβ levels (P = 0.034) but not serum Aβ₄₀ levels, were lower in the tea-consuming group. In the logistic regression analysis, there was a significant negative correlation between green tea consumption and cognitive impairment (OR = 0.26, 95 % CI 0.13 0.52 for high group).

Conclusion: Regular green tea consumption is associated with better cognitive function among Chinese middle-aged and elderly people, mainly reflected in memory and executive function. It may achieve protective effects by reducing AD-related pathology and improving anti-oxidative stress capacity and higher levels of tea consumption have a stronger protective effect.

Chemico-biological aspects of (-)-epigallocatechin-3-gallate (EGCG) to improve its stability, bioavailability and membrane permeability: Current status and future prospects

Natural products have been a bedrock for drug discovery for decades. (-)-Epigallocatechin-3-gallate (EGCG) is one of the widely studied natural polyphenolic compounds derived from green tea. It is the key component believed to be responsible for the medicinal value of green tea. Significant studies implemented in in vitro, in cellulo, and in vivo models have suggested its anti-oxidant, anti-cancer, anti-diabetic, anti-inflammatory, anti-microbial, neuroprotective activities etc. Despite having such a wide array of therapeutic potential and promising results in preclinical studies, its applicability to humans has encountered with rather limited success largely due to the poor bioavailability, poor membrane permeability, rapid metabolic clearance and lack of stability of EGCG. Therefore, novel techniques are warranted to address those limitations so that EGCG or its modified analogs can be used in the clinical setup. This review comprehensively covers different strategies such as structural modifications, nano-carriers as efficient drug delivery systems, synergistic studies with other bioactivities to improve the chemico-biological aspects (e.g., stability, bioavailability, permeability, etc.) of EGCG for its enhanced pharmacokinetics and pharmacological properties, eventually enhancing its therapeutic potentials. We think this review article will serve as a strong platform with comprehensive literature on the development of novel techniques to improve the bioavailability of EGCG so that it can be translated to the clinical applications.

Fructooligosaccharides Increase in Plasma Concentration of (-)-Epigallocatechin-3-Gallate in Rats

(-)-Epigallocatechin-3-gallate (EGCG) undergoes auto-oxidation at physiological pH and therefore may be poorly absorbed in the intestine. Fructooligosaccharides (FOS), comprising a group of 1-kestose, nystose, and 1^F-β fructofuranosyl-nystose, are fermentable by gut bacteria and converted mainly into lactate. This study was conducted to determine whether dietary FOS may help to increase the plasma concentration of EGCG in rats by preventing it from auto-oxidation. Rats consumed an assigned diet, either a 0.3% (w/w) EGCG diet or an EGCG diet with additional 1, 3, or 5% (w/w) FOS, for 2 weeks. The results showed that the plasma concentration of EGCG was 0.21 ± 0.05 μM for the EGCG alone group, and it was significantly higher at 0.65 ± 0.12 μM for the EGCG plus 5% FOS group. Treatments with FOS resulted in a dose-dependent increase in the cecal level of lactate and brought the cecal pH down, with an accompanying alteration in the abundance of Lactobacillus and Collinsella. Because EGCG concentrations in the cecal digesta of rats fed the FOS-containing diet maintained comparatively high levels, FOS likely contributed to the protection of EGCG from auto-oxidation. In conclusion, FOS reduced the pH of the lumen of the intestine, kept EGCG intact to a certain degree, and consequently allowed EGCG to be taken into the blood circulation from the intestine.

Lactic acid as a major contributor to hand surface infection barrier and its association with morbidity to infectious disease

Although the surface of the human hands contains high antimicrobial activity, studies investigating the precise components involved and the relationship between natural antimicrobial activity and morbidity in infectious diseases are limited. In this study, we developed a method to quantitatively measure the antimicrobial activity of hand surface components. Using a clinical survey, we validated the feasibility of our method and identified antimicrobial factors on the surface of the human hand. In a retrospective observational study, we compared the medical histories of the participants to assess infectious diseases. We found that the antimicrobial activity on the surface of the hands was significantly lower in the high morbidity group (N = 55) than in the low morbidity group (N = 54), indicating a positive association with the history of infection in individuals. A comprehensive analysis of the hand surface components indicated that organic acids, especially lactic acid and antimicrobial peptides, are highly correlated with antimicrobial activity. Moreover, the application of lactic acid using the amount present on the surface of the hand significantly improved the antimicrobial activity. These findings suggest that hand hygiene must be improved to enhance natural antimicrobial activity on the surface of the hands.

Pharmacology of Catechins in Ischemia-Reperfusion Injury of the Heart

Catechins represent a group of polyphenols that possesses various beneficial effects in the cardiovascular system, including protective effects in cardiac ischemia-reperfusion (I/R) injury, a major pathophysiology associated with ischemic heart disease, myocardial infarction, as well as with cardioplegic arrest during heart surgery. In particular, catechin, (−)-epicatechin, and epigallocatechin gallate (EGCG) have been reported to prevent cardiac myocytes from I/R-induced cell damage and I/R-associated molecular changes, finally, resulting in improved cell viability, reduced infarct size, and improved recovery of cardiac function after ischemic insult, which has been widely documented in experimental animal studies and cardiac-derived cell lines. Cardioprotective effects of catechins in I/R injury were mediated via multiple molecular mechanisms, including inhibition of apoptosis; activation of cardioprotective pathways, such as PI3K/Akt (RISK) pathway; and inhibition of stress-associated pathways, including JNK/p38-MAPK; preserving mitochondrial function; and/or modulating autophagy. Moreover, regulatory roles of several microRNAs, including miR-145, miR-384-5p, miR-30a, miR-92a, as well as lncRNA MIAT, were documented in effects of catechins in cardiac I/R. On the other hand, the majority of results come from cell-based experiments and healthy small animals, while studies in large animals and studies including comorbidities or co-medications are rare. Human studies are lacking completely. The dosages of compounds also vary in a broad scale, thus, pharmacological aspects of catechins usage in cardiac I/R are inconclusive so far. Therefore, the aim of this focused review is to summarize the most recent knowledge on the effects of catechins in cardiac I/R injury and bring deep insight into the molecular mechanisms involved and dosage-dependency of these effects, as well as to outline potential gaps for translation of catechin-based treatments into clinical practice.

Matcha Green Tea Powder does not Prevent Diet-Induced Arteriosclerosis in New Zealand White Rabbits Due to Impaired Reverse Cholesterol Transport

INTRODUCTION

Green tea is associated with decreased risk for cardiovascular disease and stroke. Matcha is a special kind of powdered green tea known for its use in the Japanese tea ceremony. Due to its influence on lipoprotein parameters, it has been postulated to exert antiatherogenic effects. This study investigates whether it modulates the high-density lipoprotein (HDL) function and thereby influences the atherogenic process in an animal model with a strong influence on humans' situation.

METHODS AND RESULTS

After a pretreatment phase based on a standard diet, 10 female New Zealand White (NZW) rabbits are fed a high-fat diet for 20 weeks. The treatment group is additionally administered 1% matcha during the whole experiment. Long-term matcha treatment leads to lowered HDL cholesterol, impaired cholesterol transport manifested by reduced in vitro cholesterol efflux capacity, reduced cholesteryl ester transfer protein (CETP)-mediated cholesterol ester (CE) transfer between HDL and triglyceride-rich particles, and reduced macrophage-specific in vivo transfer, where ian increased absorption of cholesterol in the liver but a decreased secretion into bile is observed. Pulse wave velocity, assessed by nuclear magnetic resonance, is increased in matcha-treated animals, and a similar trend is observed for atherosclerotic lesion formation.

CONCLUSION

Long-term matcha green tea treatment of hypercholesterolemic rabbits cause impaired reverse cholesterol transport and increased vascular stiffness, and susceptibility for atherosclerotic lesion development.

Impact of dietary polyphenols on neuroinflammation-associated disorders

Neurodegenerative disorders like Alzheimer's, Parkinson's, and associated dementia typically originate with altered protein folding and aggregation of their β structures in the neurons. This self-aggregation leads to glial activation in the brain, causing neuroinflammation and leads to neuronal death. According to statistics provided by WHO, there are around 50 million people with dementia worldwide and every year, 10 million more cases are projected to increase. Also, around 5-8 percentage of people who are aged above 60 globally has dementia or associated disorders. Over 82 million in 2030 and 152 in 2050 are expected to have dementia. Most of these patients fall into low-middle-income countries which makes it even more essential to find an affordable and effective treatment method. Polyphenols of different origin are studied for their potential role as anti-neuro-inflammatory molecules. This review would summarize recent advances in three widely researched dietary polyphenols projected as potential therapeutic agents for disorders like Alzheimer's, Parkinson's, etc. They are Resveratrol, Catechins, and Tannins. The review would discuss the recent advances and challenges in using these polyphenols using specific examples as potential therapeutic agents against neuroinflammation associated disorders. An abstract of neuroinflammation-associated events and the effects by selected polyphenols.

Epigallocatechin-3-Gallate, the Main Polyphenol in Green Tea, Inhibits Porcine Epidemic Diarrhea Virus In Vitro

There are currently no licensed drugs against porcine epidemic diarrhea virus (PEDV), but vaccines are available. We identified a natural molecule, epigallocatechin-3-gallate (EGCG), the main polyphenol in green tea, which is effective against infection with PEDV. We used a variety of methods to test its effects on PEDV in Vero cells. Our experiments show that EGCG can effectively inhibit PEDV infections (with HLJBY and CV777 strains) at different time points in the infection using western blot analysis. We found that EGCG inhibited PEDV infection in a dose-dependent manner 24 h after the infection commenced using western blotting, plaque formation assays, immunofluorescence assays (IFAs), and quantitative reverse-transcriptase PCR (qRT-PCR). We discovered that EGCG treatment of Vero cells decreased PEDV attachment and entry into them by the same method analysis. Western blotting also showed that PEDV replication was inhibited by EGCG treatment. Whereas EGCG treatment was found to inhibit PEDV assembly, it had no effect on PEDV release. In summary, EGCG acts against PEDV infection by inhibiting PEDV attachment, entry, replication, and assembly.

Epigallocatechin 3-gallate inhibits the plasma membrane Ca2+-ATPase: effects on calcium homeostasis

Flavonoids are natural compounds responsible for the health benefits of green tea. Some of the flavonoids present in green tea are catechins, among which are: epigallocatechin, epicatechin-3-gallate, epicatechin, catechin and epigallocatechin-3-gallate (EGCG). The latter was found to induce apoptosis, reduce reactive oxygen species, in some conditions though in others it acts as an oxidizing agent, induce cell cycle arrest, and inhibit carcinogenesis. EGCG also was found to be involved in calcium (Ca2+) homeostasis in excitable and in non-excitable cells. In this study, we investigate the effect of catechins on plasma membrane Ca2+-ATPase (PMCA), which is one of the main mechanisms that extrude Ca2+ out of the cell. Our studies comprised experiments on the isolated PMCA and on cells overexpressing the pump. Among catechins that inhibited PMCA activity, the most potent inhibitor was EGCG. EGCG inhibited PMCA activity in a reversible way favoring E1P conformation. EGCG inhibition also occurred in the presence of calmodulin, the main pump activator. Finally, the effect of EGCG on PMCA activity was studied in human embryonic kidney cells (HEK293T) that transiently overexpress hPMCA4. Results show that EGCG inhibited PMCA activity in HEK293T cells, suggesting that the effects observed on isolated PMCA occur in living cells.

Catechins as Model Bioactive Compounds for Biomedical Applications

Research regarding polyphenols has gained prominence over the years because of their potential as pharmacological nutrients. Most polyphenols are flavanols, commonly known as catechins, which are present in high amounts in green tea. Catechins are promising candidates in the field of biomedicine. The health benefits of catechins, notably their antioxidant effects, are related to their chemical structure and the total number of hydroxyl groups. In addition, catechins possess strong activities against several pathogens, including bacteria, viruses, parasites, and fungi. One major limitation of these compounds is low bioavailability. Catechins are poorly absorbed by intestinal barriers. Some protective mechanisms may be required to maintain or even increase the stability and bioavailability of these molecules within living organisms. Moreover, novel delivery systems, such as scaffolds, fibers, sponges, and capsules, have been proposed. This review focuses on the unique structures and bioactive properties of catechins and their role in inflammatory responses as well as provides a perspective on their use in future human health applications.

Systematic Review of Phenolic Compounds in Apple Fruits: Compositions, Distribution, Absorption, Metabolism, and Processing Stability

As the most widely consumed fruit in the world, apple (Malus domestica Borkh.) fruits provide a high level of phenolics and have many beneficial effects on human health. The composition and content of phenolic compounds in natural apples differs according to the tissue types and cultivar varieties. The bioavailability of apple-derived phenolics, depending on the absorption and metabolism of phenolics during digestion, is the key determinant of their positive biological effects. Meanwhile, various processing technologies affect the composition and content of phenolic compounds in apple products, further affecting the bioavailability of apple phenolics. This review summarizes current understanding on the compositions, distribution, absorption, and metabolism of phenolic compounds in apple and their stability when subjected to common technologies during processing. We intend to provide an updated overview on apple phenolics and also suggest some perspectives for future research of apple phenolics.

Potential of Plant Bioactive Compounds as SARS-CoV-2 Main Protease (Mpro) and Spike (S) Glycoprotein Inhibitors: A Molecular Docking Study

Since the outbreak of the COVID-19 (coronavirus disease 19) pandemic, researchers have been trying to investigate several active compounds found in plants that have the potential to inhibit the proliferation of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). The present study aimed to evaluate bioactive compounds found in plants using a molecular docking approach to inhibit the main protease (Mpro) and spike (S) glycoprotein of SARS-CoV-2. The evaluation was performed on the docking scores calculated using AutoDock Vina (AV) as a docking engine. A rule of five (Ro5) was calculated to determine whether a compound meets the criteria as an active drug orally in humans. The determination of the docking score was performed by selecting the best conformation of the protein-ligand complex that had the highest affinity (most negative Gibbs' free energy of binding/ΔG). As a comparison, nelfinavir (an antiretroviral drug), chloroquine, and hydroxychloroquine sulfate (antimalarial drugs recommended by the FDA as emergency drugs) were used. The results showed that hesperidin, nabiximols, pectolinarin, epigallocatechin gallate, and rhoifolin had better poses than nelfinavir, chloroquine, and hydroxychloroquine sulfate as spike glycoprotein inhibitors. Hesperidin, rhoifolin, pectolinarin, and nabiximols had about the same pose as nelfinavir but were better than chloroquine and hydroxychloroquine sulfate as Mpro inhibitors. This finding implied that several natural compounds of plants evaluated in this study showed better binding free energy compared to nelfinavir, chloroquine, and hydroxychloroquine sulfate, which so far are recommended in the treatment of COVID-19. From quantum chemical DFT calculations, the ascending order of chemical reactivity of selected compounds was pectolinarin > hesperidin > rhoifolin > morin > epigallocatechin gallate. All isolated compounds' C=O regions are preferable for an electrophilic attack, and O-H regions are suitable for a nucleophilic attack. Furthermore, Homo-Lumo and global descriptor values indicated a satisfactory remarkable profile for the selected compounds. As judged by the RO5 and previous study by others, the compounds kaempferol, herbacetin, eugenol, and 6-shogaol have good oral bioavailability, so they are also seen as promising candidates for the development of drugs to treat infections caused by SARS-CoV-2. The present study identified plant-based compounds that can be further investigated in vitro and in vivo as lead compounds against SARS-CoV-2.

Regulation of Nrf2/ARE Pathway by Dietary Flavonoids: A Friend or Foe for Cancer Management?

The nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway is an important cell signaling mechanism in maintaining redox homeostasis in humans. The role of dietary flavonoids in activating Nrf2/ARE in relation to cancer chemoprevention or cancer promotion is not well established. Here we summarize the dual effects of flavonoids in cancer chemoprevention and cancer promotion with respect to the regulation of the Nrf2/ARE pathway, while underlying the possible cellular mechanisms. Luteolin, apigenin, quercetin, myricetin, rutin, naringenin, epicatechin, and genistein activate the Nrf2/ARE pathway in both normal and cancer cells. The hormetic effect of flavonoids has been observed due to their antioxidant or prooxidant activity, depending on the concentrations. Reported in vitro and in vivo investigations suggest that the activation of the Nrf2/ARE pathway by either endogenous or exogenous stimuli under normal physiological conditions contributes to redox homeostasis, which may provide a mechanism for cancer chemoprevention. However, some flavonoids, such as luteolin, apigenin, myricetin, quercetin, naringenin, epicatechin, genistein, and daidzein, at low concentrations (1.5 to 20 µM) facilitate cancer cell growth and proliferation in vitro. Paradoxically, some flavonoids, including luteolin, apigenin, and chrysin, inhibit the Nrf2/ARE pathway in vitro. Therefore, even though flavonoids play a major role in cancer chemoprevention, due to their possible inducement of cancer cell growth, the effects of dietary flavonoids on cancer pathophysiology in patients or appropriate experimental animal models should be investigated systematically.

Comparative Kinetics of Acetyl- and Butyryl-Cholinesterase Inhibition by Green Tea Catechins|Relevance to the Symptomatic Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is characterised by the apoptosis of cholinergic neurons and the consequent attenuation of acetylcholine mediated neurotransmission, resulting in neurodegeneration. Acetyl-cholinesterase (AChE) and butyryl-cholinesterase (BuChE) are attractive therapeutic targets in the treatment of AD since inhibition of these enzymes can be used to restore synaptic concentrations of acetylcholine. Whilst inhibitors for these enzymes such as galantamine and rivastigmine have been approved for use, none are able to halt the progression of AD and are responsible for the production of troublesome side-effects. Efficacious cholinesterase inhibitors have been isolated from natural plant-based compounds with many demonstrating additional benefits beyond cholinesterase inhibition, such as antioxidation and anti-inflammation, which are key parts of AD pathology. In this study, five natural flavan-3-ol (catechin) compounds: ((-)-epicatechin (EC), catechin, (-)-epicatechin-3-gallate (ECG),) (-)-epigallocatechin (EGC), (-)-epigallocatechin-3-gallate (EGCG), isolated from green tea, were screened for their cholinesterase inhibitory activity using the Ellman assay. The kinetics of inhibition was determined using reciprocal Lineweaver-Burk plots. EGCG was the only compound found to produce statistically significant, competitive inhibition, of both AChE (p < 0.01) and BuChE (p < 0.01) with IC50 values of 0.0148 µmol/mL and 0.0251 µmol/mL respectively. These results, combined with previously identified antioxidative and anti-inflammatory properties, highlight the potential use of EGCG in the treatment of AD, provided it can be delivered to cholinergic neurons in therapeutic concentrations. Further testing of EGCG in vivo is recommended to fully characterise the pharmacokinetic properties, optimal method of administration and efficacy of this novel plant-based compound.

Potential of Plant Bioactive Compounds as SARS-CoV-2 Main Protease (Mpro) and Spike (S) Glycoprotein Inhibitors: A Molecular Docking Study

Since the outbreak of the COVID-19 (coronavirus disease 19) pandemic, researchers have been trying to investigate several active compounds found in plants that have the potential to inhibit the proliferation of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). The present study aimed to evaluate bioactive compounds found in plants using a molecular docking approach to inhibit the main protease (M^pro) and spike (S) glycoprotein of SARS-CoV-2. The evaluation was performed on the docking scores calculated using AutoDock Vina (AV) as a docking engine. A rule of five (Ro5) was calculated to determine whether a compound meets the criteria as an active drug orally in humans. The determination of the docking score was performed by selecting the best conformation of the protein-ligand complex that had the highest affinity (most negative Gibbs' free energy of binding/ΔG). As a comparison, nelfinavir (an antiretroviral drug), chloroquine, and hydroxychloroquine sulfate (antimalarial drugs recommended by the FDA as emergency drugs) were used. The results showed that hesperidin, nabiximols, pectolinarin, epigallocatechin gallate, and rhoifolin had better poses than nelfinavir, chloroquine, and hydroxychloroquine sulfate as spike glycoprotein inhibitors. Hesperidin, rhoifolin, pectolinarin, and nabiximols had about the same pose as nelfinavir but were better than chloroquine and hydroxychloroquine sulfate as M^pro inhibitors. This finding implied that several natural compounds of plants evaluated in this study showed better binding free energy compared to nelfinavir, chloroquine, and hydroxychloroquine sulfate, which so far are recommended in the treatment of COVID-19. From quantum chemical DFT calculations, the ascending order of chemical reactivity of selected compounds was pectolinarin > hesperidin > rhoifolin > morin > epigallocatechin gallate. All isolated compounds' C=O regions are preferable for an electrophilic attack, and O-H regions are suitable for a nucleophilic attack. Furthermore, Homo-Lumo and global descriptor values indicated a satisfactory remarkable profile for the selected compounds. As judged by the RO5 and previous study by others, the compounds kaempferol, herbacetin, eugenol, and 6-shogaol have good oral bioavailability, so they are also seen as promising candidates for the development of drugs to treat infections caused by SARS-CoV-2. The present study identified plant-based compounds that can be further investigated in vitro and in vivo as lead compounds against SARS-CoV-2.