The results of this study showed that tea blend composed of Enshi-Selenium-enriched tea, Gynostemma pentaphyllum and Apenema could dose-dependently reduce the level of blood lipid. The effect of different concentrations of tea blend on lowering blood lipid was close to that of atorvastatin. Furthermore, drinking the tea blend early could effectively prevent the occurance of hyperlipidemia. The possible reasons for the reduction of blood lipid in tea blend are as follows. On the one hand, tea polyphenols in tea leaves could bind with lipids after forming oxidized tea polyphenols, reduce lipid deposition in liver and visceral white adipose tissue, thereby improving lipid metabolism to a large extent.10 Other studies have shown that tea polyphenols could regulate blood lipid levels by improving the gut microbiome associated with a high-fat diet.11 On the other hand, Gynostemma pentophyllum could increase lipid absorption and reduce lipid deposition in blood vessel walls by inhibiting TMAO pathway. In addition, Apenema leaves affect lipid metabolism by acting on AKT1 pathway and MAPK pathway.
The reason why the tea blend reversed the damage to liver and kidney function may reside in that epigallocatechin-3-gallate (EGCG) can reduce the reabsorption of bile acids and reduce the absorption of lipids. Meanwhile, EGCG also has a protective effect on kidney function due to its antioxidant and anti-inflammatory properties. 12–14 Low dose tea caused greater damage to liver and kidney function, possibly because its antioxidant and anti-inflammatory effects were not enough to offset the burden on liver and kidney metabolism.
This study also demonstrated that administration of the tea blend, at different doses tested or with different timing, could reduce the levels of TNF-α, IFN-γ, IL-6 and other inflammatory factors, especially when administered from an early time or at a high dose. In fact, whether given early or in high doses, the effect was similar to that of atorvastatin in inhibiting inflammatory cytokine release. This is consistent with previous reports showing that tea polyphenols could inhibit the signal transduction of Toll-like receptor 4 (TLR4) pathway, and thus reduced the levels of inflammatory factors such as TNF-α and IL-6.14, 15
When the average body weight and tissue weight of mice in each group were compared between different groups, it was found that the body weight and tissue weight of mice given the tea solution were not significantly different from those of the control group. Neither tea nor atorvastatin had significant effects on the body weight, liver and kidney tissue weight of mice. However, difference might emerge if more prolonged treatment were given to the animals.
With HE staining, it was observed under the light microscope that the tea blend could reduce the damage of hepatocytes in metabolism-related fatty liver disease and improve the disordered hepatic cord structure caused by lipids. Our data strongly suggested that early administration of the tea blend could efficiently prevent hepatocyte adipogenesis.
Previous studies have shown that HL mainly decomposes TG in CM, HDL and MDL, and participates in the formation of LDL and the cholesterol anti-transport process. HSL is the rate-limiting enzyme of lipolysis, which is involved in the decomposition of triglycerides and diglycerides (DG) to generate free fatty acids (FFA), regulating fatty acid β oxidation, which provide energy for the body. 16 Both HL and HSL play critical roles in lipid metabolism, overall energy balance, and cellular events that may involve fatty acid signaling.17–19 The results of this study showed that the mechanism of tea blend lowering blood lipid may be closely related to maintaining high levels of HL and HSL.
The results showed that the tea and atorvastatin also increased LXRs levels in hyperlipidemic mice. However, compared with high-fat control group, low dose tea could not effectively increase the level of LXRs. Studies have shown that the activation of LXRs can promote the reverse transport of cholesterol, increase the transcription of rate-limiting enzymes in the process of bile acid synthesis in the liver, 20 accelerate the degradation of low-density lipoprotein receptor(LDLR) and thereby reduce cholesterol uptake in liver cells.21 PPARα is expressed primarily in hepatocytes and is a transcriptional activator of fibroblast growth factors 21, FGF21, ACOX1 and ATF6. It is a key regulator of glucose and lipid metabolism by regulating ketogenesis, gluconeogenesis and lipolysis in liver. The results of this study showed that compared with the hyperlipidemia control group, both the tea blend and atorvastatin could significantly increase PPARα level, and the effect of early tea administration had the strongest effect on PPARα level. PPARα may reduce lipid synthesis by inhibiting HMG-CoA reductase, and this effect may be synergistic with LXRs. Thus, the tea blend can regulate lipid metabolism by regulating the expression of PPARα and LXRs. 22
In summary, this study confirmed that drinking the tea blend composed of Enshi Selenium-rich tea, Gynostemma pentaphyllum and Apocynma significantly reduced blood lipid in mice with hyperlipidemia, and was safe. For hyperlipidemia patients with good liver and kidney function, various dose of tea blend is appropriate to drink. While for hyperlipidemia patients with liver and kidney dysfunction, it is recommended to drink medium or high dose tea blend. For people who are used to high-fat diet, early start administration of a medium dose of tea blend, can effectively prevent the onset of dietary hyperlipidemia.
The limitations of this study are as follows: on the one hand, this study is a cross-sectional study, so there may be some limitations in the results, and the conclusions need to be verified by further longitudinal studies. On the other hand, this study has not gone deep into the molecular mechanism, and further experiments are needed to explore the mechanism of tea blend lowering blood lipid.