Aim of study:In the past,overeating was regarded as the main cause of increasing adiposity,but now a new viewpoint from JAMA suggested that energy metabolic defects may precede overeating in obesity.Mitochondrial deacetylase SIRT3 activator was reported to increase the energy metabolic in mitochonion,and it was suggested as a new anti-obesity therapeutic target.We obtained a purine alkaloid,theacrine,from Chinese herbal medicine Camellia sinensis Kucha,which is structurally similar to caffeine but without properties of central nervous system stimulation and addiction.In this study,a high fat fed mice model was employed to study the anti-obesity effect of theacrine and the probable mechanism was explored.Methods and Results:The C57BL/6J mice were fed with high fat diet for seventeen weeks to induce obesity.At the eleventh week,theacrine (10,20 mg/kg) were orally given to obese mice for six weeks.Dramatic reductions in body weight,body fat mass,plasma total cholesterol,average size of white adipocytes,fat droplets in brown adipose tissue (BAT) but no change in daily food intake were noticed after obese mice treated with theacrine.The results demonstrated that theacrine possessed anti-obesity effect in high fat dietary mice.It was also noticed that theacrine could reverse the decreased expression of SIRT3 in liver or BAT.In addition,we found that a 24-hour treatment of 2 mM theacrine increased protein expression of SIRT3 in HepG2 cells and theacrine above 1.5 mM could enhance SIRT3 deacetylation when added into purified SIRT3.Combined with the data that the lowest binding free energy of the SIRT3 and theacrine complex among several ligands of purine alkaloids,we suggested that theacrine could directly activate SIRT3.After investigating the anti-obesity mechanism of theacrine,we found that 20 mg/kg theacrine could increase hepatic ATP production and reverse the declining trend of dorsum temperature in obese mice under cool condition,and this themogenesis was probably induced by the activation of BAT.In addition,UCPI gene expression was increased but gene expression of long-chain fatty acyl coenzyme dehydrogenase (LCAD) and ATP5c did not change after theacrine treatment,however,the ratio of acetylated LCAD to LCAD decreased.It implied that the energy metabolism promotion of theacrine might involve in SIRT3-mediated deacetylation on acetylated LCAD.Moreover,the results demonstrated that theacrine could decrease the ratio of long-chain fatty acids to short-chain fatty acids and drive fatty acid oxidation dependent on SIRT3.It suggested that theacrine stimulated fatty acid utilization.For exploring the signaling pathway of theacrine on SIRT3 activation,the results demonstrated that theacrine treatment increased hepatic cAMP and CREB phosphorylation,activated cAMP/PKAJCREB signaling pathway.However,the inhibition of PKA did not affect the activation of SIRT3 and the promotion of fatty acid oxidation by theacrine treatment.This result demonstrated that theacrine might directly target SIRT3 but not depend on cAMP/PKA/CREB signaling pathway.Conclusions:In summary,theacrine may be a novel SIRT3 activation and possesses an anti-obesity effect through promoting fatty acid oxidation.