Transcriptome analysis provides insight into the anti-diabetic mechanism of theaflavins in high-fat diet and streptozotocin-induced mice.

Black tea exhibits potential to improve hyperglycemia and insulin resistance, where theaflavins (TFs) are its characteristic components. The aim of this study was to explore the anti-diabetic mechanism of TFs. High-fat diet and streptozotocin-induced type 2 diabetes (T2D) mice were administered with TFs by gavage daily for 5 weeks. The biochemical analysis suggested that TFs possess potential anti-diabetic activity, which is comparable to that of metformin. RNA-sequencing analysis showed that TFs had a significant influence on the hepatic transcriptional profile of the T2D mice. The nine significantly enriched KEGG pathways were mainly associated with pancreatic secretion, digestion and metabolism of fat, protein and glycerolipid, and tight junctions. Quantitative real-time PCR and immunohistochemistry analysis verified that TFs improved pancreas function and intestine tight junction, with an increase in the expression of carboxyl ester lipase (Cel), chymotrypsinogen B (Ctrb1), pancreatic triglyceride lipase (Pnlip) and chymotrypsin-like elastase 3B (Cela3b) in the pancreas and cingulin and claudin-1 in the intestine. TFs improved mitochondrial biogenesis with the downregulation of peroxisome proliferator-activated receptor coactivator (PGC) 1α and 1ß in the liver, but had less effect on the muscle. This work revealed the comprehensive mechanism of TFs against T2D, suggesting that TFs are a potential natural agent for improving type 2 diabetes.

Simultaneous Determination and Quantification of Triterpene Saponins from Camellia sinensis Seeds Using UPLC-PDA-QTOF-MS/MS.

Saponins in the Camellia sinensis seeds have a broad spectrum of biological properties and application potentials. However, up to now, no chromatographic methods have been developed to provide full fingerprinting and quality assurance for these saponins. This research aimed to develop a novel method to tentatively identify and quantify saponins in C. sinensis seeds by ultra-high-performance liquid chromatography coupled with photo-diode array detector and quadrupole time-of-flight mass spectrometry (UPLC-PDA-QTOF-MS/MS), and compare it with the classic vanillin-sulfuric acid assay. Fifty-one triterpene saponins, including six potentially new compounds, were simultaneously detected by UPLC-PDA-MS/MS, and their chemical structures were speculated according to the retention behavior and fragmentation pattern. The total saponin content in the crude extract and the purified saponin fraction of C. sinensis seeds were quantified to be 19.57 ± 0.05% (wt %) and 41.68 ± 0.09% (wt %) respectively by UPLC-PDA at 210 nm, while the corresponding values were determined to be 43.11 ± 3.17% (wt %) and 56.60 ± 5.79% (wt %) respectively by the vanillin-sulfuric acid assay. The developed UPLC-PDA -MS/MS method could determine specified saponins, and is more reliable for quantifying the C. sinensis seed saponins than the classic spectrophotometric method. It is of great significance for the future investigations and applications of these saponins.

Theaflavins Improve Insulin Sensitivity through Regulating Mitochondrial Biosynthesis in Palmitic Acid-Induced HepG2 Cells.

Theaflavins, the characteristic and bioactive polyphenols in black tea, possess the potential improving effects on insulin resistance-associated metabolic abnormalities, including obesity and type 2 diabetes mellitus. However, the related molecular mechanisms are still unclear. In this research, we investigated the protective effects of theaflavins against insulin resistance in HepG2 cells induced by palmitic acid. Theaflavins significantly increased glucose uptake of insulin-resistant cells at noncytotoxic doses. This activity was mediated by upregulating the total and membrane bound glucose transporter 4 protein expressions, increasing the phosphor-Akt (Ser473) level, and decreasing the phosphorylation of IRS-1 at Ser307. Moreover, theaflavins were found to enhance the mitochondrial DNA copy number, down-regulate the PGC-1ß mRNA level and increase the PRC mRNA expression. Mdivi-1, a selective mitochondrial division inhibitor, could attenuate TFs-induced promotion of glucose uptake in insulin-resistant HepG2 cells. Taken together, these results suggested that theaflavins could improve hepatocellular insulin resistance induced by free fatty acids, at least partly through promoting mitochondrial biogenesis. Theaflavins are promising functional food ingredients and medicines for improving insulin resistance-related disorders.