Dietary α-Tocopherol Attenuates the Impact of γ-Tocotrienol on Hepatic 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity in Chickens

The concentration-dependent impact of γ-tocotrienol on serum cholesterol can be traced to the posttranscriptional down-regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. γ-Tocotrienol also suppresses tumor growth. Palmvitee, the tocopherol and tocotrienol-rich fraction of palm oil, is the sole commercial source of γ-tocotrienol. Contrary to the universal findings of the efficacy of γ-tocotrienol there are conflicting reports of the impact of Palmvitee on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, serum cholesterol concentrations and tumor development. These conflicting reports led us to examine the impact of α-tocopherol on the cholesterol-suppressive action of γ-tocotrienol. Control and experimental diets were fed to groups of White Leghorn chickens (n = 10) for 26 d. The control diet was supplemented with 21 nmol α-tocopherol/g. All experimental diets provided 141 nmol of blended tocols/g diet. The α-tocopherol and γ-tocotrienol concentrations of the experimental diets ranged from 21 to 141 and 0 to 120 nmol/g, respectively. We now report that including α-tocopherol in tocol blends containing adequate γ-tocotrienol to suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase activity results in an attenuation of the tocotrienol action (P < 0.001). A summary of results from studies utilizing different Palmvitee preparations shows that effective preparations consist of 15-20% α-tocopherol and ∼60% γ-(and δ-) tocotrienol, whereas less effective preparations consist of ≥30% α-tocopherol and 45% γ- (and δ-) tocotrienol.