The Effects And Mechanisms Of The Main Components Of Green Tea In Lipid Metabolism In Caenorhabditis Elegans

Obesity and its complications,such as cardiovascular disease,high blood pressure and certain types of cancer,have become global health problems.Obesity is due to the imbalance between energy intake and consumption.Current methods for the prevention and treatment of obesity are encountered with weak patient compliance,or insignificant long-term effects,or unacceptable side effects.Some studies have reported that habitual tea consumption could control body weight and reduce body fat,but other studies have not observed this effect.The inconsistent results may be related to the different components and concentrations of bioactive substances contained in separate tea leaves.Animal and epidemiological experiments have found that caffeine and catechins contained in tea could increase the energy consumption,regulate lipid metabolism,and have anti-obesity effects.The catechins in green tea mainly include epigallocatechin-3-gallate(EGCG),epigallocatechin(EGC),epicatechin-3-gallate(ECG),epicatechin(EC).The EGCG,which is considered as the component with the highest biological activity in green tea,has been declared to have anti-inflammation,anti-oxidation,and lipid-modulating effects.At present,fat reduction effects and relative mechanisms of the above four catechins and caffeine have not been fully elucidated.Caenorhabditis elegans(C.elegans)has small body size,short life cycle,and is easy to be maintained and operated in laboratory condition.In addition,many components and signaling pathways which are essential for the control of lipid metabolism in humans are conserved in C.elegans.Thus,the C.elegans is an important model animal for the research of liquid metabolism.Objectives:The objectives of this study are to evaluate the effects of major components of green tea(four catechins and caffeine)on the fat production in nematodes under normal physiological conditions and under stress(high glucose stimulation),and to analyze the changes of genes expression involved in fat metabolism.Finally,the potential components of tea which regulate lipid metabolism and relative genetic mechanism were identified to build a basis for prevention and control of obesity.Methods:Fat reducion effects and mechanisms of four catechins and caffeine were investigated using C.elegans under normal physiological or stress conditions.Firstly,the nematode growth media plate(NGM)with or without 10 m M glucose was inoculated with inactivated Escherichia coli(E.coli)OP50 which was mixed with EGCG,EGC,ECG,EC,caffeine,respectively.The final concentrations of four catechins and caffeine were set at 25 ?M,50 ?M,100 ?M,200 ?M,Then the synchronized L1 stage nematodes was transferred to the NGM plates and incubated at 20 °C for 48 hours.Next,the nematodes were dyed with Nile Red and the fat content was quantified under a fluorescence microscope.And the gene expression related to the lipid metabolism,including the sbp-1,nhr-49,fat-7,fat-6,fat-5,acs-2,ech-1,mdt-15,kat-1,atgl-1 was determined through the real-time fluorescent quantitative Polymerase Chain Reaction(PCR).The C.elegans treated with 145 ?g/ml orlistat was set as the positive control and the C.elegans treated with 1% dimethyl sulfoxide(DMSO)was set as the negative control.Results:1.The effects of EGCG,EGC,ECG,EC and caffeine on fat production in nematodes.Under normal physiological state,100 ?M and 200 ?M EGCG,EGC and caffeine could reduce the fat production in nematodes,while 50 ?M,100 ?M and 200 ?M ECG and EC could reduce fat production in nematodes.Under high glucose stimulated stress,100 ?M or 200 ?M caffeine could reduce the fat production in nematodes,while 50 ?M,100 ?M or 200 ?M EGCG,EGC,ECG and EC could reduce the fat production in nematodes.2.Effects of EGCG,EGC,ECG,EC and caffeine on the expression of genes involved in lipid metabolism.For nematodes under the normal physiological state,EGCG had no significant effect on the m RNA expression of the gene fat-7,nhr-49,ech-1,kat-1,but increased the m RNA expression of the gene fat-6,and decreased the m RNA expression of the gene mdt-15,sbp-1,fat-5,acs-2,atgl-1.EGC had no significant effect on the m RNA expression of the gene sbp-1,fat-7,ech-1,but increased the m RNA expression of the gene mdt-15,fat-5,nhr-49,kat-1,atgl-1,and decreased the m RNA expression of the gene fat-6,acs-2.ECG increased the m RNA expression of the gene mdt-15,nhr-49,sbp-1,fat-6,ech-1,kat-1,atgl-1,and decreased the m RNA expression of the gene fat-5,fat-7,acs-2.EC had no significant effect on the m RNA expression of the gene mdt-15,increased the m RNA expression of the gene nhr-49,and decreased the m RNA expression of the gene sbp-1,fat-5,fat-6,fat-7,acs-2,ech-1,kat-1,atgl-1.Caffeine had no significant effect on the m RNA expression of the gene sbp-1,but increased the m RNA expression of the gene fat-6,nhr-49,ech-1,kat-1,atgl-1,and decreased the m RNA expression of the gene mdt-15,fat-5,fat-7,acs-2.For nematodes under high glucose stimulation stress,EGCG reduced the m RNA expression of all tested genes(mdt-15,nhr-49,sbp-1,fat-5,fat-6,fat-7,acs-2,ech-1,kat-1,atgl-1).EGC had no significant effect on the m RNA expression of the gene mdt-15,sbp-1,acs-2,kat-1,atgl-1,but decreased the m RNA expression of the gene sbp-1,fat-5,fat-6,fat-7,ech-1.ECG had no significant effect on the m RNA expression of ech-1,kat-1,atgl-1,but decreased the m RNA expression of the gene mdt-15,nhr-49,sbp-1,fat-5,fat-6,fat-7,acs-2.EC increased the m RNA expression of the gene mdt-15,and decreased the m RNA expression of the gene sbp-1,fat-5,fat-6,fat-7,nhr-49,acs-2,ech-1,kat-1,atgl-1.Caffeine reduced the m RNA expression of all tested genes(mdt-15,nhr-49,sbp-1,fat-5,fat-6,fat-7,acs-2,ech-1,kat-1,atgl-1).Conclusions:1.EGCG,EGC,ECG,EC and caffeine could reduce the fat production of nematodes under normal physiological state or high glucose-stimulated stress.2.EGCG,EGC,ECG,EC and caffeine may reduce fat production in C.elegans under normal physiological condition by the following mechanisms: EGCG decreases fat synthesis through mdt-15-sbp-1 pathway;EGC,ECG and caffeine increase lipolysis by promoting mdt-15-nhr-49 pathway mediating fatty acid ?-oxidation and by activating atgl-1;EC decreases fat synthesis via activating sbp-1 and increases lipolysis via activating nhr-49.EGCG,EGC,ECG,EC and caffeine may reduce fat production in C.elegans under high glucose stress by the following mechanisms: EGCG,ECG and caffeine decrease fat synthesis through mdt-15-sbp-1 pathway.EGC and EC decrease fat synthesis by activating sbp-1.