title: Dietary alpha-tocopherol attenuates the impact of gamma-tocotrienol on hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in chickens.
abstract: The concentration-dependent impact of gamma-tocotrienol on serum cholesterol can be traced to the posttranscriptional down-regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. gamma-Tocotrienol also suppresses tumor growth. Palmvitee, the tocopherol and tocotrienol-rich fraction of palm oil, is the sole commercial source of gamma-tocotrienol. Contrary to the universal findings of the efficacy of gamma-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 alpha-tocopherol on the cholesterol-suppressive action of gamma-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 alpha-tocopherol/g. All experimental diets provided 141 nmol of blended tocols/g diet. The alpha-tocopherol and gamma-tocotrienol concentrations of the experimental diets ranged from 21 to 141 and 0 to 120 nmol/g, respectively. We now report that including alpha-tocopherol in tocol blends containing adequate gamma-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% alpha-tocopherol and approximately 60% gamma- (and delta-) tocotrienol, whereas less effective preparations consist of > or = 30% alpha-tocopherol and 45% gamma- (and delta-) tocotrienol.
authors.affiliation: Advanced Medical Research, Madison, WI 53719, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Qureshi
authors.forename: B C
authors.initials: BC
authors.lastname: Pearce
authors.forename: R M
authors.initials: RM
authors.lastname: Nor
authors.forename: A
authors.initials: A
authors.lastname: Gapor
authors.forename: D M
authors.initials: DM
authors.lastname: Peterson
authors.forename: C E
authors.initials: CE
authors.lastname: Elson
mesh_terms: D000818:Animals; D002645:Chickens; D002784:Cholesterol / Q000097:blood / Q000378:metabolism; D002839:Chromans / Q000032:analysis / Q000494:pharmacology*; D004032:Diet; D015536:Down-Regulation; D005260:Female; D006903:Hydroxymethylglutaryl CoA Reductases / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D025782:Hydroxymethylglutaryl-CoA-Reductases, NADP-dependent; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D000073878:Palm Oil; D010938:Plant Oils / Q000737:chemistry / Q000494:pharmacology; D014810:Vitamin E / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000032:analysis / Q000494:pharmacology*
chemical_list: D002839:Chromans; D010938:Plant Oils; D014810:Vitamin E; C013649:plastochromanol 8; D000073878:Palm Oil; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D025782:Hydroxymethylglutaryl-CoA-Reductases, NADP-dependent