Abstract
In vivo studies show that α-tocotrienol and γ-tocotrienol accumulate in adipose tissue. Furthermore, a recent study reports that the oral administration of γ-tocotrienol from a tocotrienol-rich fraction from palm oil (TRF) decreases body fat levels in rats. The objective of this study was to evaluate the effect of TRF and its components on adipocyte differentiation in 3T3-L1 preadipocytes, which differentiated into adipocytes in the presence of 1.8 μmol/L insulin. TRF suppressed the insulin-induced mRNA expression of adipocyte-specific genes such as PPARγ, adipocyte fatty acid-binding protein (aP2), and CCAAT/enhancer-binding protein-α (C/EBPα) compared with the differentiation of 3T3-L1 preadipocytes into adipocytes only in the presence of insulin. To confirm the suppressive effect of TRF, the major components of TRF, such as α-tocotrienol, γ-tocotrienol, and α-tocopherol, were investigated. α-Tocotrienol and γ-tocotrienol decreased the insulin-induced PPARγ mRNA expression by 55 and 90%, respectively, compared with insulin, whereas α-tocopherol increased the mRNA expression. In addition, γ-tocotrienol suppressed the insulin-induced aP2 and C/EBPα mRNA expression, triglyceride accumulation, and PPARγ protein levels compared with insulin. The current results also revealed that γ-tocotrienol inhibited the insulin-stimulated phosphorylation of Akt but not extracellular signal-regulated kinase (ERK)1/2 in the insulin signaling pathway of 3T3-L1 preadipocytes. Thus, the antiadipogenic effect of TRF depends on α-tocotrienol and γ-tocotrienol, and γ-tocotrienol may be a more potent inhibitor of adipogenesis than α-tocotrienol. Therefore, the results of this study suggest that tocotrienol suppresses insulin-induced differentiation and Akt phosphorylation in 3T3-L1 preadipocytes. Furthermore, tocotrienol could act as an antiadipogenic vitamin in the nutrient-mediated regulation of body fat through its effects on differentiation.
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