Application of tea polyphenols in animal models
Application of tea polyphenols in animal models
Tea polyphenols are found in medical practice and scientific research as a good antioxidant with good free radical scavenging effects in response to oxidative stress. Since oxidative stress is closely related to the occurrence and development of many chronic diseases in humans. Tea polyphenols was documented to prevent and treat various diseases . Cancer is a chronic disease that poses a huge threat to the health of the people. In China, these diseases often occur due to the aging of the population and unhealthy lifestyles . The production and accumulation of MDA increases the risk of cancer in humans. In the primary stage of cancer, lipid peroxide-induced DNA mutations are increased by the accumulation of MDA . The levels of adducts produced by MDA and DNA in breast cancer patients are significantly higher than those in healthy individuals. Studies have shown that matrix metalloproteinases (MMP) are involved in the pathogenesis of breast cancer. EGCG inhibits the development of disease by mediating the epigenetic induction of MMP-3 and inhibiting the activity of MMP-2 and MMP-9 in breast cancer cells . A rat colon cancer model was induced with azomethane (AOM) to investigate the therapeutic effects of tea polyphenols on human colon cancer. The number of aberrant crypt foci (ACF) and its extent by AOM were significantly decreased after feeding rats with 0.24% of composite polyphenols containing 65% EGCG for 8 wk. The expression levels of β-catenin and cyclin D1 were decreased and ACF cell apoptosis was increased . Tea polyphenols have also been shown to prevent respiratory cancers, digestive cancers, and urinary cancers caused by different pathogenic factors in animal models. In addition to antioxidant properties, tea polyphenols also prevent mutations in genetic material, regulate detoxification enzyme activity, and inhibit tumorigenesis in the process of preventing cancer .
Cardiovascular and cerebrovascular diseases are collectively referred to as ischemic or hemorrhagic diseases of the heart, brain and systemic tissues caused by hyperlipidemia, atherosclerosis, and hypertension. It is more common among the middle-aged and elderly people over the age of 50. The number of people who die of cardiovascular and cerebrovascular diseases every year in the world is as high as 15 million, ranking first in all causes of death. The rat model of cardiac hypertrophy was established by abdominal aortic constriction (AC). The MDA content in the rat heart was gradually increased and the antioxidant enzyme activity was decreased. EGCG has the ability to inhibit telomere shortening and loss of telomere repeat-binding factor 2 (TRF2) in cardiac cells to reduce apoptosis of cardiomyocytes . Oral EGCG can cause significant increase in antioxidant enzyme activity in rats with isoproterenol-induced myocardial infarction, and lipid peroxidation is inhibited to ensure the integrity of myocardial cell membrane and reduce the incidence of myocardial infarction With the deepening of lipoprotein research, it is found that the level of low-density lipoprotein cholesterol (LDL-C) is positively correlated with the occurrence of atherosclerosis. Tea polyphenols have multiple phenolic hydroxyl groups to inhibit the oxidation of cholesterol. Inhibition of deposition of lipids on the walls of blood vessels. On the other hand, the oxidation of unsaturated fatty acids is prevented, thereby reducing the content of cholesterol in the serum and maintaining the dynamic balance of the normal entry and exit of lipids in the arterial wall, and has an anti-atherosclerotic effect.
Gut microbiota balances nutrient acquisition and energy regulation by processing the indigestible components of our daily diet. There are more than 1,000 different types of bacteria and microorganisms in the human digestive system, and the composition of the microbial ecosystem in the body plays a vital role in human health. When the microbial composition is altered, it will induce or trigger the production of certain diseases . The metabolism and absorption of dietary polyphenols by the human body mainly depend on the biotransformation of microorganisms in the intestine. Some polyphenols enter the colon and are converted into small molecule compounds under the action of bacterial enzymes and microorganisms, and the other part enters the hepatic and intestinal circulation to exert physiological functions . The synergistic use of 4% green tea powder and Lactobacillus plantarum can significantly increase the microbial diversity in the intestinal tract of C57BL/6J mice and selectively reduce the number of harmful bacteria . The mechanism of tea polyphenols in improving intestinal microbial composition mainly focuses on tea polyphenols providing metabolic substrates for beneficial bacteria such as bifidobacteria and lactic acid bacteria, and its antibacterial activity can affect the cell membrane function and energy metabolism of harmful bacteria, inhibits the growth of Bacteroides and Pachybacteria . Short-chain fatty acids (SCFA) are the major metabolites produced by bacteria that ferment dietary fiber in the gastrointestinal tract, various studies have confirmed its regulatory effect on metabolic syndromes . Tea polyphenols can produce SCFA by intestinal fermentation. Increasing SCFA production can achieve the purpose of acidifying the intestinal environment, in order to promote the absorption of nutrients, especially minerals, and inhibit the growth of pathogenic bacteria . Tea polyphenols can show better effects in Improving intestinal function, indicating that the bioactive components in tea are digested and absorbed in the intestinal tract of animals. However, studies have shown that only 0.1% of EGCG will be bioavailable after entering the body , and it can be seen that the bioavailability of tea polyphenols is very low. The reason for the conjecture may be related to the rapid metabolism of polyphenols and poor intestinal transport capacity . Although the bioavailability of animals to tea polyphenols is low, higher levels of tea polyphenols still cause toxicity to the body. Feeding high doses (1%) of tea polyphenols in colitis mice can cause symptoms of nephrotoxicity and affect liver and kidney function, causing oxidative damage in the body. The same results were obtained in experiments in healthy mice. However, using low-dose (0.01% or 0.1%) tea polyphenols to feed colitis mice, it was found that tea polyphenols showed protective effects on liver and kidney and other organs . Therefore, the optimal use of tea polyphenols in the prevention and treatment of different diseases needs to be confirmed.
At present, in addition to being a health care drug, tea polyphenols are widely used as a safe feed additive in livestock and poultry farming. In the production of pigs, it can improve animal production performance and immunity, reduce the body's lipid oxidation level, protect cell structure and functional integrity, and prevent organ damage and animal diseases caused by lipid peroxidation . Currently, lipid oxidation has been recognized as the main deteriorating mode of frozen meat Proteins are degraded by oxidation, causing impaired protein function and loss of nutritional value. Tea polyphenols also has the effect of prolonging the storage time of meat products and improving the quality of meat. Piglets were injected with diquat to establish an oxidative stress model. After 7 d of dietary supplementation with tea polyphenols, it was found that immune damage and growth inhibition caused by oxidative stress were alleviated and improved, and T lymphocyte proliferation and activation were promoted Studies have shown that tea polyphenols help to increase the number of beneficial bacteria in the intestines of pigs, reduce the number of Clostridium, and reduce the amount of feces and ammonia. In this way, the control of nitrogen-containing substances with animal excrement is important for environmental protection and the promotion of healthy farming Green tea extract has anti-avian adenovirus type 4 (fadv4) and anti-avian influenza (H5N2) effect during poultry farming and is superior to catechins such as EGCG, EGC and ECG. As antibiotics are banned worldwide, finding good antibiotic substitutes is an important direction for the healthy development of animal husbandry. Studies have shown that broilers fed diets containing 0.5% to 2% tea polyphenols can improve growth performance, muscle antioxidant capacity and meat quality, and the effect is better than diet supplemented with 0.1% oxytetracycline calcium . It has been proved that tea polyphenols have the potential to replace antibiotics. Studying the effect of tea polyphenols on egg quality showed that under the premise of lowering the cholesterol content of egg yolk and improving the fatty acid composition, the antioxidant level of eggs was increased and the storage time of eggs was prolonged . However, there have also been reports that feeding tea to egg poultry will reduce egg weight and eggshell quality, mainly because the tea contains the anti-nutritional factor tannin . Therefore, in the further development and utilization of such resources, we should pay attention to solve this problem and explore the optimal use of tea.
