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Black tea is one of the six major tea categories and has a variety of bioactivities. However, little is known about its comprehensive evaluation of hypoglycemic effects and potential mechanisms. In this study, we investigated the in vivo hypoglycemic activity and potential mechanism for aqueous extracts of ordinary black tea (BT) and selenium-enriched black tea (Se-BT) by using an established high-fat diet together with streptozotocin (STZ)-induced hyperglycemic mouse model. Additionally, we also explored their α-glucosidase inhibition activity. The results show that both BT and Se-BT had a favorable glycosidase inhibitory activity. Moreover, the intervention of BT and Se-BT could regulate the mRNA expression and the level of serum parameters related to glucose and lipid metabolisms. Accordingly, they could activate the phosphoinositide-3-kinase/protein kinase B (PI3K/Akt) signaling pathway and alleviate insulin resistance (IR) and hyperglycemia. Moreover, supplementation of BT and Se-BT increased the richness and diversity of intestinal flora and altered the abundance of beneficial and harmful bacteria. Both BT and Se-BT could regulate glucose metabolism, alleviate tissue damage, and restore intestinal flora dysbiosis, suggesting that they could be used as a natural functional food for preventing hyperglycemia., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Various functional components in tea have been well developed, but less research has been explored on glycoproteins in tea. In this paper, three types of glycoprotein fractions, namely tea selenium-binding glycoprotein1-1 (TSBGP1-1), TSBGP2-1, and TSBGP3-1, respectively, were extracted and purified from selenium-enriched coarse green tea. Chemical analysis revealed that three fractions were glycoproteins, but their selenium content, molecular weight, and monosaccharide composition were significantly different. Fourier transforms infrared (FT-IR) analysis indicated that three fractions contained characteristic absorption peaks of glycoproteins but differed in secondary structural composition. Thermogravimetric (TG) analysis showed that the thermal stability of the three fractions was dramatically distinct. The in vitro hypoglycemic activity showed that TSBGPs significantly activated the insulin receptor substrate 2 (IRS2)/protein kinase B (Akt) pathway in LO2 cells, then enhanced glucose metabolism and inhibited gluconeogenesis, and finally ameliorated insulin resistance (IR) and glucose metabolism disorders. Furthermore, Pearson correlation analysis reveals that the hypoglycemic activity was significantly correlated with Se, protein, monosaccharide composition (especially glucose), molecular weight, and secondary structure. Our results show that Se-enriched tea glycoprotein is a desirable candidate for developing anti-diabetic food, and TSBGP-2 and TSBGP-3 had a better regulation effect. Our results can provide a research reference for the extraction, physicochemical property, and function of selenium-enriched plant glycoproteins., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

In recent years, selenium-enriched polysaccharides (Se-PS) have been paid more and more attention, and the activity of many Se-PSs has been studied but little on their structure. This study aimed to investigate the activity, structural characterization and present forms of selenium in two different artificial selenium-enriched tea polysaccharides (Se-TPS). The physicochemical analysis showed that both CSe-tps1 and ASe-tps1 were acidic heteropolysaccharides with different monosaccharide composition, molar ratio, and selenium content. Structural investigations including FT-IR, Raman spectra and 1D, 2D NMR analysis revealed that selenium in CSe-tps1 replaced the hydroxyl group at the C-6 position in the polysaccharide with the form of selenyl ester, while most of the selenium in ASe-tps1 replaced the hydroxyl group at the C-1 and C-6 position in the form of the SeH bond on the branch of the polysaccharide. Besides, a series of studies on the structural characteristics of the Congo red test, I 2 -KI reaction, FESEM, DSC, and XRD analysis showed that the two artificial Se-TPSs had a triple helix structure and more branches. However, there were significant differences in crystal morphology, apparent morphology, heat release ability, and the α-glucosidase inhibition activity. These results indicated that the difference in artificial selenization methods not only made the polysaccharide exhibit different structural characteristics and the hypoglycemic activity, but also had a significant effect on the form of selenium in polysaccharides., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Selenium (Se)-containing polysaccharide, a Se-conjugate macromolecule, generally exhibited higher antitumor activity than its regular polysaccharide. Previously, we extracted Se-containing tea polysaccharides (Se-TPS) from Se-enriched tea, and explored its structure and antioxidant activity. In this study, we investigated antitumor activity of Se-TPS on sarcoma 180 (S-180), and compared with its regular polysaccharides TPS and dietary supplement Se-yeast. In vitro antitumor activity of Se-TPS was evaluated by MTT and LDH assays, and the results indicated that Se-TPS can significantly inhibit the proliferation of S-180 in dose-dependent manner (R 2 =0.97, p<0.0001). In S-180 cancer xenograft model in Kunming mice, Se-TPS oral administration at three doses of 50, 100 and 200mg/kg body weight daily for 13days resulted in significant tumor regression. At the same dose, Se-TPS exhibited significantly higher antitumor activity than TPS and Se-yeast. Importantly, Se-TPS can significantly increase the spleen and thymus indices of tumor-bearing mice, suggesting the safety and immunomodulatory activity of Se-TPS. Therefore, Se-TPS may be a desirable antitumor agent for therapeutic and immunomodulatory applications., (Copyright © 2018. Published by Elsevier B.V.)

Se-containing polysaccharide is known to Se-conjugated macromolecule, with potent bioactivities due to the synergistic effects of Se and native polysaccharide. It is not only explored as a novel Se source in dietary supplement, but also as the superb bioactive component owning various functions, including antioxidant, antitumor, immune-enhancement, hepatoprotective, antidiabetic, anti-inflammatory and neuroprotective activities. Se-containing polysaccharide can exert the efficacy of Se and polysaccharide, and its activities are much higher than those of Se or polysaccharide. In the last decades, numerous reports on Se-containing polysaccharide (including natural Se-containing polysaccharide and selenylated polysaccharide) appeared in literature. For the first time, this article systematically introduces recent advances on preparation, structural characterization and bioactivities of Se-containing polysaccharide in details, and discusses its future prospects and the weaknesses in the current study., (Copyright © 2018. Published by Elsevier B.V.)

Se-polysaccharides from Se-enriched tea leaves were purified by DEAE-sepharose fast flow gel column (2.5×60cm) and three polysaccharide fractions (Se-TPS1, Se-TPS2, and Se-TPS3) were isolated and purified with yields of 6.5, 37.14, and 8.57%, respectively. The average sizes of Se-TPS1 and Se-TPS2 were determined by HPGPC system, with molecular weights of 1.1×10(5) and 2.4×10(5)Da, respectively. Se-TPS3 was a polysaccharide polymer with two peaks with molecular weights of 9.2×10(5) and 2.5×10(5)Da. Monosaccharide components analysis by ion chromatography revealed Se-polysaccharides were acidic polysaccharoses and different from each other in monosaccharide kinds and molar ratio. Elements of Se, C, H, N, S, and 14 kinds of mineral elements were analyzed by AFS, EA, and ICP-AES, respectively. Spectral analysis (IR and UV) indicated Se-polysaccharides were typical glycoproteins. Morphological analyses of the samples were determined by SEM and AFM. In addition, the DPPH and superoxide radicals scavenging activities were also discussed to assess antioxidant activities of the samples, and Se-polysaccharides showed higher antioxidant activities compared to the ordinary polysaccharides., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The research on the activity of selenium (Se)-enriched agricultural products is receiving increasing attention since Se was recognized for its antioxidant activities and for its enhancement of immunity in trace elements. In this study, antioxidant Se-containing peptides, namely, Se-TAPepI-1 and Se-TAPepI-2, were optimally separated and prepared from Se-enriched tea protein hydrolysates by ultrafiltration and Sephadex G-25 purification, and subsequently, their physicochemical properties, oligopeptide sequence, and potential antioxidant mechanism were analyzed. Through the optimization of enzymatic hydrolysis conditions, the Se-enriched tea protein hydrolyzed by papain exhibited a better free radical scavenging activity. After separation and purification of hydrolysates, the two peptide fractions obtained showed significant differences in selenium content, amino acid composition, apparent morphology, peptide sequence, and free radical scavenging activity. Therein, two peptides from Se-TAPepI-1 included LPMFG (563.27 Da) and YPQSFIR (909.47 Da), and three peptides from Se-TAPepI-2 included GVNVPYK (775.42 Da), KGGPGG (552.24 Da), and GDEPPIVK (853.45 Da). Se-TAPepI-1 and Se-TAPepI-2 could ameliorate the cell peroxidation damage and inflammation by regulating NRF2/ARE pathway expression. Comparably, Se-TAPepI-1 showed a better regulatory effect than Se-TAPepI-2 due to their higher Se content, typical amino acid composition and sequence, higher surface roughness, and a looser arrangement in their apparent morphology. These results expanded the functional activities of tea peptide and provided the theoretical basis for the development of Se-containing peptides from Se-enriched tea as a potential natural source of antioxidant dietary supplements. [ABSTRACT FROM AUTHOR]