Comparison Of Hypoglycemic Activities Of Different Chinese Dark Teas And Exploration Of Hypoglycemic Mechanisms

Tea is one of the most popular beverages and its hypoglycemic effect has been widely reported.Dark tea,as one of the six major teas,has the most special manufacturing process and the most complex ingredients,while its hypoglycemic effect is the best relative to other types of teas.At present,there have been some reports on the efficacy of dark tea and its active ingredients in regulating blood sugar and ameliorating the symptoms of diabetes.However,there is a lack of comparative analysis of the effects of different types of dark teas,the mechanism of their intervention in diabetes is still unclear,and the research on its mechanism is less.Therefore,we measured the basic ingredients of four kinds of Chinese dark teas,including Fuzhuan brick tea?FBT?,Qingzhuan brick tea?QBT?,Puerh tea?PET?and Liubao brick tea?LBT?,analyzed the inhibitory activities on glycosidase and scavenging activities on free radicals of them,and conducted a comparative analysis of the in vivo hypoglycemic activity of different dark teas and their capacity to intervene insulin resistance.At the same time,we conducted a concentration gradient analysis of intervening in insulin resistance,hypoglycemic activity in vivo and regulation of intestinal flora of LBT.The basic components analysis showed that the content of basic components of different types of dark tea was different and there were significant differences among the groups.The contents of tea polysaccharides,tea polyphenols and thearubigins in FBT were the highest,the highest content of the soluble protein,theaflavins and theabrownins in PET,and the highest content of theanine in LBT.The element content analysis associated with hypoglycemia showed that FBT had the highest contribution to the constant elements,while LBT had the highest contribution to the trace elements.The results of in vitro hypoglycemic experiments showed that the inhibition rates of the four dark tea aqueous extracts on glycosidase generally exhibited a relationship with concentration-dependent,of which PET had the highest inhibition rates of ?-glucosidase and ?-amylase,and reached 96.82% and 85.79%,respectively,at the highest concentration.The results of in vitro antioxidant experiments showed that the free radical scavenging rates of the four dark tea aqueous extracts also had a concentration-dependent relationship,but the difference between the groups was not obvious,and all of them could reach around 90% at the highest concentration.The results of different dark tea aqueous extracts on hypoglycemic activity of T2 DM mice showed that FBT had the best regulation of T2 DM mice's body weight,while LBT had the best hypoglycemic activity in vivo.In terms of ameliorating inflammation in the body,all of them had shown certain effects on anti-inflammation and protecting the liver.The results of cellular insulin resistance showed that LBT had the optimum proliferation and ameliorating insulin resistance effect on HepG2 cells under insulin resistance,and was 0.73 and 3 times higher than that of the control group,respectively.The experimental results of regulating lipid metabolism factors showed that different dark tea aqueous extracts could enhance lipid metabolism disorders caused by insulin resistance,and LBT has an optimum regulating effect than others.The results of oxidative stress and inflammatory factor level analysis showed that different dark tea aqueous extracts all could ameliorate the liver cell oxidative stress and inflammation caused by insulin resistance,but the effects of various samples were not completely consistent,and no prominent dark tea was found.The results of insulin resistant cellular experiment showed that different concentrations of LBT could promote the proliferation of HepG2 cells without showing cytotoxicity,and its effect on ameliorating insulin resistance of HepG2 cells was optimum as the concentration was 500 ?g/mL.Furthermore,LBT could regulate the lipid metabolism of HepG2 cells under insulin resistance in a concentration-dependent manner.On the one hand,LBT could significantly increase the enzyme activity of SOD,CAT and GSH-Px and showed a concentration-dependent relationship,thereby ameliorating the oxidative stress of liver cells.On the other hand,it also could significantly inhibit the key enzymes activity in gluconeogenesis of PEPCK and G-6-Pase,and could significantly enhance the key enzyme activity of GCK in glycolysis,thus exerting its effect of ameliorating insulin resistance.Through the intervention of different concentrations of LBT on T2 DM mice,the results showed that LBT at different concentrations could increase the body weight of T2 DM mice and reduce their blood sugar levels.At the same time,different concentrations of LBT could also increase the organ index of T2 DM mice to achieve the effect of protecting related organs and tissues.Furthermore,different concentrations of LBT could also regulate lipid metabolism in T2 DM mice in a concentrationdependent manner and exhibit predominant regulatory effects.Finally,different concentrations of LBT also showed a protective effect on the kidneys and liver in a concentration-dependent manner.These all indicated that LBT could ameliorate T2DM-related syndromes while palliating T2 DM hyperglycemia symptoms so as to achieve the purpose of treating T2 DM.Through the analysis of intestinal flora in T2 DM mice,our outcomes revealed that both LBT with distinct concentrations and Actlns could have a prominent effect on the gut microbiota of T2 DM mice.The LBT-M group exhibited the highest community richness and diversity and could reverse the gut microbiota destroyed by hyperglycemia,causing its clustering to move closer to the normal group.Bacterial species composition analysis showed that the phylum composition of the intestinal microflora of all groups was mainly composed of Firmicutes and Bacteroidetes,but differed in proportions.Further genus composition analysis indicated that the Actlns group could significantly reduce the level of unclassified f_Muribaculaceae,the LBT-L and LBT-H group could significantly increase the level of Akkermansia and Ruminococcus₁,and reduce the level of Bacteroides;the LBT-M group could significantly increase the level of the corresponding genus flora belonged to Lachnospiraceae family;each dose group of LBT could significantly increase the relative levels of Lactobacillus and Bifidobacterium,whereas their changes were closely related to blood glucose.Moreover,COG functional analysis of metabolic pathways of intestinal flora indicated that the metabolic pathways involved in the impact of each intervention group on intestinal flora included energy production and conversion,amino acid transport and metabolism,carbohydrate transport and metabolism,translation,ribosomal structure and biogenesis,transcription,replication,recombination and repair,cell wall/membrane/envelope biogenesis,inorganic ion transport and metabolism,signal transduction mechanisms,defense mechanisms.The above results indicate that LBT has a good hypoglycemic effect and can be further developed into corresponding functional foods or additives.