Effect Of The Pigments From Pu-erh Tea On The Lipid Metabolism And Its Mechanisms In SD Rats

The modern way of life has led to a sharp rise in the number of obese people. Studies have shown that Pu’er tea has the effects of losing weight and lowering lipid. However, the clear mechanism remains unknown. Therefore, in this thesis, the effects of the puer tea pigments on lipid metabolism of SD(Sprague Dawley) rats and HepG2 cells were studied for clarifying their mechanism. The issue has been investigated from the following three parts: 1. Effect of pigments from Pu-erh tea on lipid metabolism(1) The normal SD rats were treated with different pigments concentrations for 12-week, then the triglyceride(TG) and total cholesterol(TC) were measured in rat liver. The results showed that: the pigments from Pu-erh tea had significantly lowering effects on TG and TC, and the effect indicated concentration dependent. Especially in the high concentration treated group, the levels changed from 0.345 mmol/g to 0.345 mmol/g for TG and from 0.186 mmol/g to 0.186 mmol/g for TC, which similar to those in the normal control group.(2) Porper pigments concentration range for HepG2 was determined by the MTT assays, and built the obesity model of HepG2 cells by culturing them at rich oleic acid medium. The contents of TG and TC in HepG2 cell line cultured with normal or oleic acid enriched cultures were determined by treating with the pigments from Pu-erh tea The results showed that the content of TG was significantly decreased with increasing pigments’ concentration, and in the experimental concentration range the maximum drop of TC content could be reduced 50.30%. In addition, pigments from Pu-erh tea could reduce the contents of TG and TC in normal cultured HepG2 in a dose dependent but the results was not significant. At the same time, staining results with oil red O showed that pigments from Pu-erh tea could decrease the fat accumulation in oleic acid enriched cultured HepG2 cells. Therefore, the pigments could effectively reduce the deposition of lipid in liver cells, and maintain normal morphology of liver cells. 2. Effects the pigments from Pu-erh tea on oxidative stress of HepG2 cellsThe activity of catalase(CAT), the contents of malondialdehyde(MDA) and glutathione(GSH) were investigated for studying the anti-oxidative capacity of the pigments from Pu-erh tea, using the models of HepG2 cell line cultured with normal or oleic acid enriched cultures. The results showed that the anti-oxidative capacity of pigments from Pu-erh tea was not significantly increased on the normal culture HepG2 model but did on the oleic acid induced HepG2 model. The anti-oxidative capacity of the pigments from Pu-erh tea depended on their concentrations. The extracellular GSH content and CAT activity increased 763.23% and 134.09% respectively, and MDA content in the cells reduced 49.59% after treatment 400 μg/mL pigments in the model of oleic acid enriched cultures for 24 h. So the pigments from Pu-erh tea shown the good antioxidant effect on HepG2 cells3. Study of lipid metabolism mechanism influenced bythe pigmentsfrom Pu-erh tea(1) The mRNA levels of FAS, SREBP-1c, CYP7A1, ABCA1 and HMGCR were determined by the method of reverse transcriptin-PCR(RT-PCR) for studying the mechanism of pigments influence lipid metabolism. The results indicated that the mRNA level of FAS, AREBP-1c and HMGCR were significantly down-regulated after the pigments from Pu-erh tea treatment for 12 weeks on SD rats. The mRNA level of FAS and AREBP-1c were significantly down-regulated, and the mRNA level of ABCA1 was significantly up-regulated, the mRNA level of CYP7A1 showed an increased tendency after the pigments from Pu-erh tea treatment 24 hours on oleic acid models of HepG2 cells.(2) With the method of Western blot, the expression level of p-AMPK protein in rat liver and HepG2 cells were detected. The results showed that the protein level of p-AMPK was significantly up-regulated. Therefore, the pigments from Pu-erh tea had the function of activating phosphorylation of AMPK.In summary, the pigments of puer tea have the functions of regulation of lipid metabolism, improvement the state of oxidant stress and up- or down-regulated the mRNA levels of enzymes and transcription factors about lipid metabolismto achieve intervention on lipid metabolism, prevention and/or treatment of obesity.