To elucidate the inhibiting mechanisms of fat accumulation by catechins, caffeine, and epigallocatechin gallate (EGCG), ICR mice were fed diets containing either 0.3% catechins or 0.1% EGCG and/or 0.05% caffeine for 4 weeks. After the feeding, intraperitoneal adipose tissues weights were significantly lower in the caffeine, catechins + caffeine, and EGCG + caffeine groups compared to controls. Hepatic fatty acid synthase (FAS) activity in the catechins + caffeine group was significantly lower, and the activities of acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase-II (CPT-II) were significantly higher, compared to the control group. However, these activities were not observed in the other groups. FAS mRNA expression levels in the catechins + caffeine group were significantly lower than in the control group. ACO and CPT-II mRNA levels were not different among all of the treatment groups. These findings indicate that the inhibitory effects of fat accumulation via a combination of catechins, EGCG, or caffeine were stronger collectively than by either catechins, EGCG, or caffeine alone. Moreover, it was demonstrated that the combination of catechins and caffeine induced inhibition of fat accumulation by suppression of fatty acid synthesis and upregulation of the enzymatic activities involved in β-oxidation of fatty acid in the liver, but this result was not observed by combination of EGCG and caffeine.

To elucidate effects of catechins and caffeine on lipid metabolism in adipocytes and identify the mechanism of action, differentiated 3T3‐L1 adipocytes were incubated in culture media containing catechins at 1, 2.5, 5, and 10 µg/mL and caffeine at 50 and 100 µg/mL, singly or in combination, for 8 days. Intracellular lipid accumulation and glycerol‐3‐phosphate dehydrogenase activity were strongly suppressed by catechins and caffeine combination treatment. The mRNA expression of PPARɤ, GLUT4, HSL, UCP‐1, and TMEM26 were significantly increased in the combined groups. These findings suggest that the combined treatment inhibited lipid synthesis and improved lipid metabolism in adipocytes. Moreover, it was indicated that the differentiated 3T3‐L1 adipocytes could be transformed from white adipocytes to beige‐like adipocytes by catechins and caffeine, and accordingly that this transformation could promote calorigenic action.Practical ApplicationIn this study, we revealed that the combined treatment of catechins and caffeine inhibited lipid synthesis and improved lipid metabolism in adipocytes. Moreover, the treatment may contribute to the transforming from white adipocytes to beige‐like adipocytes, which could strongly promote calorigenic action.

No abstract