Effects Of Tea Polyphenols On Lipid Metabolism And The Underlying Molecular Mechanism In Broiler Chickens

In poultry husbandry, due to the continuous advancement of genetic and food nutrient improvement, the growth rate of broilers keep fasting in recent years. However, the meat quality deceases because of excessive lipid deposition. With the rapid development of economy and increasing labor costs, there has been substantial surplus green tea production during summer-autumn. In addition, the large amount of tea dust was generated during green tea processing. Since 2005, the previous work in our lab have shown that green tea powder, tea polyphenols and EGCG could reduce excessive fat deposition and improve the quality of poultry products in laying hens. And the dose-effect relationship of green tea in poultry animals has been defined. In this dissertation, the effects of green tea polyphenols on lipid metabolism and the underlying molecular mechanism was examined in middle-late aged broiler chickens. The results of this research could provide theoretical basis for application of green tea’s (especially summer-autumn green tea) in poultry food industry, and could further understand anti-obesity mechanism of green tea polyphenols. The main findings of this dissertation are as follows:1 Green tea polyphenols significantly decreased the serum and lipid level in broilersThe current study investigated the effects of green tea polyphenols (GTPs) on lipid metabolism using broiler chickens (Gallus gallus domesticus). Seventy-two male chickens (28-days old) had been subjected to an oral administration of GTPs at a dosage of 0,80 (Low) and 160 (High) mg/kg body weight for 28 days. Our results showed that GTPs significantly decreased the serum triglyceride, low-density lipoprotein-cholesterol levels of broilers, and notably increased the serum high-density lipoprotein-cholesterol, free fatty acid concentration of chickens compared with that of the control after 4-week administration. Meanwhile, the abdominal, subcutaneous and intramuscular fat mass, the tissue fat content in liver, thigh muscle and breast muscle of chickens from GTPs groups were also remarkably decreased compared with that of the control. However, there was no significant difference in the serum and body lipid indicators of birds among different experimental groups after 2-week administration.Furthermore, GTPs significantly decreased monounsaturated fatty acids, and increased the polyunsaturated fatty acids percentage in the liver and thigh muscle of broilers compared with that of control. Interestingly,2 weeks oral administration of GTPs remarkably altered the hepatic fatty acid composition; while the thigh muscle fatty acid composition was not changed until sampling at the end of this experiment.In conclusion, GTPs significantly decreased the serum and body lipid level in mid-growth stage broiler chickens. In addition, GTPs also notably increased polyunsaturated fatty acids percentages of the skeletal muscle of broilers, and increased the chicken meat quality.2 Green tea polyphenols notably altered the lipid metabolism related gene expression and key enzyme activityIn present dissertation, the mRNA expression of key lipid metabolism related genes and transcriptional factors in liver, abdominal fat and skeletal muscles of broilers was measured by using Real-time quantitative PCR (RT-qPCR) to elucidate the molecular mechanism of the anti-obesity actions of green tea in vivo. And the activity of hepatic lipid metabolism key enzymes was also investigated at the same time. Our results showed that the expression level for hepatic lipid anabolism genes (FAS, ACC, SCD1, SREBP-1c) were significantly down-regulated compared with that of control, while the expression level of fat catabolism and utilization related genes (CPT-1, ACOX1, PPARa, ATGL, LPL) in liver, abdominal fat and skeletal muscles were notably up-regulated. Consistently, GTPs significantly reduced the activity of hepatic fatty acid de novo synthesis key enzymes (FAS, ACC), and remarkably raised the fatty acid beta-oxidation key enzyme (CPT1) activity in liver of birds. Nevertheless, unlike the serum and body lipid indicators, the mRNA level of lipid metabolism related genes was significantly altered after 2-week GTPs oral administration. Our data suggested that the expression level of functional genes was interfered before its related phenotype, which compliance with the laws of animal nutrient regulation.Our data also revealed that green tea polyphenols alleviate obesity and serum lipid levels in broiler chickens by suppressing fatty acid synthesis and stimulating lipolysis and utilization. Simultaneously, among three tissues listed above, liver is more susceptible to GTPs intervention, indicating that the liver is the main target organ for lipid metabolism regulation by green tea in broiler chickens.3 Green tea polyphenols activated the hepatic AMPK/ACC signal pathwayLiver play a central role in the lipid metabolism in poultry animals, and is also a main target organ for green tea intervention. The molecular mechanism of the anti-obesity action of green tea polyphenols in chickens remains to be elucidated. In this dissertation, we investigated the effects of GTPs on the hepatic AMPK/ACC signal pathway of broilers in vivo. Our results showed that 2-week oral administration of GTPs significantly increased the serum leptin concentration and the hepatic phosphorylated FAS and ACC protein level, notably enhanced the AMPK enzyme activity and decreased the malonyl CoA (specific substrate of ACC) concentration in the liver of birds. Therefore, our data indicated that GTPs raised serum leptin content, activated hepatic AMPK/ACC pathway, increased fatty acid oxidation and decreased lipid anabolism of broiler chickens.Moreover, our results also demonstrated that the expression level of SCD1 was significantly down-regulated by GTPs in the liver of broilers. And several papers have already reported that SCD1 has close regulating relationship with letptin and AMPK pathway. Conclusively, we speculate that GTPs might regulate lipid metabolism through or partially through Leptin-SCD1-AMPK-ACC-CPT1 pathway, which playing important roles in alleviating the excessive lipid deposition in broiler chickens.