title: High levels of vitamin E affect retinol binding protein but not CYP26A1 in liver and hepatocytes from laying hens.
abstract: This study was conducted to determine the influence of vitamin E on the retinol binding protein (RBP) and cytochrome p450 family 26 subfamily A polypeptide 1 (CYP26A1), which are specific transporters and catabolic enzymes of vitamin A, respectively. In the in vivo experiments, a total of 450 laying hens was fed 5 levels of vitamin E (0, 20, 80, 320, and 1,280 IU/kg of feed) supplementation. For the in vitro assays, hepatocytes from laying hens were cultured in 4 levels of α-tocopherol (0, 10, 50, and 100 μM). High dietary vitamin E increased the concentration of vitamin A in liver (P < 0.05). The RBP and its mRNA expression in liver and hepatocytes were markedly inhibited by dietary vitamin E (320 and 1,280 IU/kg) and α-tocopherol (100 μM) in culture medium (P < 0.05). However, CYP26A1 and its mRNA expression were not affected by vitamin E in both liver and hepatocytes (P > 0.05). The results indicate that excessive vitamin E could increase the concentration of vitamin A in liver by inhibiting RBP synthesis in hepatocytes.
authors.affiliation: Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: X D
authors.initials: XD
authors.lastname: Zhou
authors.forename: X F
authors.initials: XF
authors.lastname: Dong
authors.forename: J M
authors.initials: JM
authors.lastname: Tong
authors.forename: P
authors.initials: P
authors.lastname: Xu
authors.forename: Z M
authors.initials: ZM
authors.lastname: Wang
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002645:Chickens / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D019587:Dietary Supplements; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D007328:Insulin / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D010058:Oviposition / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000072516:Retinoic Acid 4-Hydroxylase; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D014815:Vitamins / Q000008:administration & dosage / Q000494:pharmacology; D024502:alpha-Tocopherol / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D007328:Insulin; D012333:RNA, Messenger; D012177:Retinol-Binding Proteins; D014815:Vitamins; D003577:Cytochrome P-450 Enzyme System; D000072516:Retinoic Acid 4-Hydroxylase; D024502:alpha-Tocopherol