Theabrownins Produced via Chemical Oxidation of Tea Polyphenols Inhibit Human Lung Cancer Cells in vivo and in vitro by Suppressing the PI3K/AKT/mTOR Pathway Activation and Promoting Autophagy

State-of-the-art review of theabrownins: from preparation, structural characterization to health-promoting benefits

As far as health benefit is concerned, dark tea is one of the best beverages in the world. Theabrownins are the major ingredient contributing to the health benefits of dark tea and known as "the soft gold in dark tea." A growing body of evidence indicated that theabrownins are macromolecular pigments with reddish-brown color and mellow taste, and mainly derived from the oxidative polymerization of tea polyphenols. Theabrownins are the main active ingredients in dark tea which brings multiple health-promoting effects in modulating lipid metabolism, reducing body weight gain, attenuating diabetes, mitigating NAFLD, scavenging ROS, and preventing tumors. More importantly, it's their substantial generation in microbial fermentation that endows dark tea with much stronger hypolipidemic effect compared with other types of tea. This review firstly summarizes the most recent findings on the preparation, structural characteristics, and health-promoting effects of theabrownins, emphasizing the underlying molecular mechanism, especially the different mechanisms behind the effect of theabrownins-mediated gut microbiota on the host's multiple health-promoting benefits. Furthermore, this review points out the main limitations of current research and potential future research directions, hoping to provide updated scientific evidence for their better theoretical research and industrial utilization.

Theabrownins in dark tea form complexes with tea polysaccharide conjugates

BACKGROUND

Theabrownins (TBs) are one of most important quality components in dark tea, but have not been produced industrially. In this study, the aqueous extract was obtained from Pu-erh ripe tea, one kind of dark tea. Caffeine, theaflavin, catechin and saponin were removed by trichloromethane, ethyl acetate and n-butanol in turn to obtain a TB isolate. The TB isolate was subjected to column chromatography using a macroporous resin HPD-750 and eluted with a gradient of 0-700 g kg-1 ethanol aqueous solution. Four fractions were obtained, and named as TBs-FC1, TBs-FC2, TBs-FC3 and TBs-FC4.

RESULTS

These four fractions contained polysaccharides and no small molecules such as catechins, caffeine and theaflavins as well as average molecular weights of 123.000 kDa, 23.380 kDa, 89.870 kDa and 106.600 kDa. It was revealed that they were complexes of TBs and tea polysaccharide conjugates (TPCs). Ultraviolet-visible (UV-visible) and infrared (IR) spectra showed the properties of TBs and TPCs. Their zeta potentials ranged from -13.40 mV to -38.80 mV in aqueous solutions at pH 3.0-9.0.

CONCLUSION

This study reveals that TBs do not exist in free state but in combined state in dark tea, which provide the theoretical basis for the industrialization of TBs. © 2024 Society of Chemical Industry.

Theabrownin: a dietary nutraceutical with diverse anticancer mechanisms

Cancer, a highly deadly disease, necessitates safe, cost-effective, and readily accessible treatments to mitigate its impact. Theabrownin (THBR), a polyphenolic pigment found in Pu-erh tea, has garnered attention for its potential benefits in memory, liver health, and inflammation control. By observing different biological activities of THBR, recently researchers have unveiled THBR's promising anticancer properties across various human cancer types. By examining existing studies, it is evident that THBR demonstrates substantial potential in inhibiting cell proliferation and reducing tumour size with minimal harm to normal cells. These effects are achieved through the modulation of key molecular markers such as Bcl-2, Bax, various Caspases, Poly (ADP-ribose) polymerase cleavage (Cl-PARP), and zinc finger E box binding homeobox 1 (ZEB 1). This review aims to provide in-depth insights into THBR's role in cancer research. This review also elucidates the underlying anticancer mechanisms of THBR, offering promise as a novel anticancer drug to alleviate the global cancer burden.

Dietary Polyphenols against Oxidative Stress in Head and Neck Cancer: What's New, What's Next

Head and neck cancers (HNC) are a worldwide health problem, accounting for over 5% of all types of cancers. Their varied nature makes it sometimes difficult to find clear explanations for the molecular mechanisms that underline their onset and development. While chemio- and radiotherapy are clearly not to be dismissed, we cannot undervalue the effect that polyphenols - especially dietary polyphenols - can have in helping us to cope with this medical emergency. By influencing several different proteins involved in numerous different metabolic pathways, polyphenols can have a broad spectrum of biological action and can hopefully act synergistically to tackle down head and neck cancer. Moreover, being natural molecules, polyphenols does not present any side effects and can even enhance drugs efficacy, making our clinical therapy against head and neck cancer more and more effective. Certainly, oxidative stress plays an important role, altering several molecular pathways, lowering the body's defenses, and ultimately helping to create a microenvironment conducive to the appearance and development of the tumor. In this regard, the regular and constant intake of foods rich in polyphenols can help counteract the onset of oxidative stress, improving the health of the general population. In this review, we highlight the role of polyphenols in managing oxidative stress, with such positive effects that they can be considered new tools to use in our anti-head and neck cancer strategy.

Regulation of HeLa cell proliferation and apoptosis by bovine lactoferrin

Cervical cancer is one of the foremost common cancers in women. Lactoferrin (LF) has many biological functions, such as antitumor. This study aimed to explore the regulatory effect of bovine lactoferrin (bLF) on the proliferation and apoptosis of cervical cancer HeLa cells and to clarify the potential mechanism of action of bLF against HeLa cells. This study used CCK-8, Trypan blue staining, and colony formation assays to verify the effect of bLF on HeLa cell proliferation. Hoechst 33258 fluorescence staining, AO/EB staining, and western blotting were used to determine the effects of bLF on apoptosis and autophagy in HeLa cells. We discovered that bLF significantly reduced the proliferation of HeLa cells in a dose- and time-dependent manner compared to the control group. Furthermore, bLF primarily induced apoptosis in HeLa cells by increasing the expression of the proapoptotic proteins p53, Bax, and Cleaved-caspase-3 and downregulating the expression of the antiapoptotic protein Bcl-2. In addition, the present study also showed that bLF treatment significantly activated autophagy-related proteins LC3B-II and Beclin I and down regulated the autophagosome transporter protein p62, indicating that bLF treatment can induce autophagy in HeLa cells. After pretreatment with the autophagy inhibitor, 3-MA, which markedly found that autophagy inhibition by 3-MA reversed bLF-induced apoptosis, indicating that bLF can induce apoptosis by activating intracellular autophagy in HeLa cells. In the present study, our results support the theory of bLF significantly inhibited the proliferation of Hela cells by promoting apoptosis and reinforcing autophagy. The study will play an important role in therapying cervical cancer.

Preventive and therapeutic effects of green tea on lung cancer: a narrative review of evidence from clinical and basic research

Background and Objective

Green tea is a popular beverage worldwide and has numerous health-promoting properties. Accumulating evidence indicates that green tea has preventive and therapeutic effects on lung cancer. This study aimed to investigate the association between green tea consumption and lung cancer.

Methods

We performed a narrative review to summarized the association between green tea consumption and lung cancer.

Key Content and Findings

Green tea consumption is known to decrease lung cancer risk in the general population, as indicated by meta-analyses of observational studies. Two active components of green tea, theabrownin and (-)-epigallocatechin gallate (EGCG), mediate the antitumor activity of green tea. Theabrownin promotes apoptosis, induces cell cycle arrest, and inhibits the migration, clone formation, and proliferation of lung cancer cell lines in vitro and in vivo. EGCG inhibits lung cancer cell proliferation and promotes apoptosis, agenesis, and epithelial-mesenchymal transition (EMT). In addition, EGCG sensitizes lung cancer cells to cisplatin and tyrosine kinase inhibitors (TKIs). The possible molecular mechanisms underlying the antitumor activity of EGCG and theabrownin were reviewed.

Conclusions

Observational studies have indicated that green tea has preventive effects on lung cancer. In vitro and animal studies have indicated that green tea has therapeutic effects on lung cancer. Further clinical trials are needed to illustrate the therapeutic effects of green tea or its active components (i.e., theabrownin, EGCG) on lung cancer.

Physicochemical and Colon Cancer Cell Inhibitory Properties of Theabrownins Prepared by Weak Alkali Oxidation of Tea Polyphenols

Existing studies on the biological activity of theabrownins are not based on their free state but on the complexes of theabrownins, polysaccharides, proteins, and flavonoids. In this study, theabrownins (TBs-C) were prepared by weak alkali oxidation of tea polyphenols. The ultraviolet-visible scanning spectrum of TBs-C showed two characteristic absorption peaks at 203 and 270 nm. The zeta potential of the TBs-C aqueous solution was negative, and the values varied from - 6.26 to -19.55 mV with a solution pH of 3-9. Storage conditions of pH 5.0-7.0 and around 25 °C were beneficial for the physical and chemical stability of the TBS-C solution. Cells were treated with series concentrations and examined by MTT, HE staining, PI immunofluorescence staining, flow cytometry, and real-time PCR to investigate the antiproliferative effect of TBs-C on human colon cancer HT-29 cells. The results showed that TBs-C, particularly at 500 µg/mL, inhibited cell growth. TBs-C induced HT-29 cell apoptosis, as confirmed by morphological changes, nucleus propidium iodide staining, and distributions of the cell cycle. The apoptotic mechanism may be due to the intracellular redox imbalance induced by TBs-C.

Theabrownin Alleviates Colorectal Tumorigenesis in Murine AOM/DSS Model via PI3K/Akt/mTOR Pathway Suppression and Gut Microbiota Modulation

Colorectal cancer (CRC) is one of the most common and fatal cancers worldwide, yet therapeutic options for CRC often exhibit strong side effects which cause patients’ well-being to deteriorate. Theabrownin (TB), an antioxidant from Pu-erh tea, has previously been reported to have antitumor effects on non-small-cell lung cancer, osteosarcoma, hepatocellular carcinoma, gliomas, and melanoma. However, the potential antitumor effect of TB on CRC has not previously been investigated in vivo. The present study therefore aimed to investigate the antitumor effect of TB on CRC and the underlying mechanisms. Azoxymethane (AOM)/dextran sodium sulphate (DSS) was used to establish CRC tumorigenesis in a wild type mice model. TB was found to significantly reduce the total tumor count and improve crypt length and fibrosis of the colon when compared to the AOM/DSS group. Immunohistochemistry staining shows that the expression of the proliferation marker, Ki67 was reduced, while cleaved caspase 3 was increased in the TB group. Furthermore, TB significantly reduced phosphorylation of phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt), and the downstream mechanistic target of rapamycin (mTOR)and cyclin D1 protein expression, which might contribute to cell proliferation suppression and apoptosis enhancement. The 16s rRNA sequencing revealed that TB significantly modulated the gut microbiota composition in AOM/DSS mice. TB increased the abundance of short chain fatty acid as well as SCFA-producing Prevotellaceae and Alloprevotella, and it decreased CRC-related Bacteroidceae and Bacteroides. Taken together, our results suggest that TB could inhibit tumor formation and potentially be a promising candidate for CRC treatment.