Inhibitory effects of tannic acid in the early stage of 3T3-L1 preadipocytes differentiation by down-regulating PPARγ expression
Obesity is a medical condition of excess body fat negatively influencing morbidity and mortality via non-communicable disease risks. Adipogenesis, the process in which preadipocytes differentiate into adipocytes, plays a pivotal role in obesity. Our previous study proved that tannic acid (TA) showed anti-adipogenesis effect in 3T3-L1 preadipocytes. However, the precise mechanism involved in the inhibition in adipocytes differentiation by TA is unclear, and thus this is the subject of the present investigation. In this study, we determined the effect of TA on different stages of 3T3-L1 preadipocytes differentiation, and found that when treating in the early stage of differentiation, TA reduced lipid accumulation significantly. However, TA did not reduce lipid accumulation when treating in mid- and late-stages of adipocyte differentiation. To further study which gene TA had an impact on in the early stage of differentiation, we identified a number of genes associated with lipid metabolism. The results showed that compared to the control group, the mRNA levels of FAS, C/EBPα, and PPARγ were significantly decreased (p < 0.05), whereas the mRNA levels of adipsin, ap2 were increased (p < 0.05). However, TA had no effect on mRNA levels of ACC1 and ACC2. Western blot results showed that TA down-regulated the expression of PPARγ, which is a major factor in preadipocyte differentiation. In addition, TA did not affect the PI3 K/AKT pathway. These results indicate that the anti-adipogenesis effect of TA involves down-regulation of PPARγ in the early stage of 3T3-L1 preadipocyte differentiation. Some potential limitations of this study should be considered. All the results in this study were based on cell experiments. However, the human bioavailability of TA is not clear. In the present study, the concentration of TA was 5 μM; therefore, there were concerns about whether oral intake of TA could reach the effective concentrations. This important point needs to be clarified in vivo.