| 摘要: | 維生素 E 為動物體內最重要的抗氧化劑，體內維生素 E 含量受到組織保留能力、氧化需求及代謝速率各層面所影響。前人研究指出炸油餵食會降低大鼠體內維生素 E 的營養狀況，但是至今其影響機制未明，本研究目的即欲探討炸油飲食影響維生素 E 營養狀況的可能機制。實驗一以二倍維生素E補充飼料，觀察炸油對維生素 E代謝機制之影響，採用 21 隻離乳 Wistar 雄鼠，依飼料不同分成三組：控制組 (CO組，新鮮油組) 和兩組炸油組 (FO組和FOE組)，其中的炸油來源為新鮮大豆油以 205±5℃ 油炸巧果 24 小時所製得；已知維生素 E 吸收率會因為炸油飲食而下降，因此特別設計 FOE 組，在炸油飼料中額外添加 50 ppm 維生素 E。大鼠飼養六週後於犧牲前收集 24 小時尿液以供 a-生育醇 (a-TOH) 代謝產物 (2,5,7,8- tetramethyl- 2-(2’-carboxyethyl)-6-
hydroxychroman ; a-CEHC) 之分析。FO 組和FOE組血漿 a-TOH濃度顯著低於CO組 (P＜0.05)，但肝臟 a-TOH濃度則以 FO 組顯著最低，FOE 組次之 (P＜0.05)。而肝臟 TBARS (Thiobarbituric acid- reactive substances) 含量與Catalase (CAT) 蛋白質含量皆以兩炸油組顯著高於CO組；且炸油組的 CAT 蛋白質含量約增為控制組的三倍之多。肝臟CYP3A2蛋白質表現以FO組顯著最高 (P＜0.05) ， FOE組次之。尿液中 a-CEHC 的排出量以 FO 組顯著低於其餘兩組 (P＜0.05)。MDR和a-TTP蛋白質含量於三組間並無顯著差異。實驗二以注射方式給予維生素E，觀察炸油對維生素E代謝機制之影響，並且額外分析CYP3A與PXR mRNA表現。炸油組肝臟 a-TOH含量顯著較低、TBARS 含量與 CAT蛋白質含量則顯著較高，此結果皆與實驗一相似 (P＜0.05)，炸油組 PXR mRNA 表現量顯著高於新鮮油組 (P＜0.05)，其下游基因CYP3A不論是蛋白質或是mRNA之表現皆不受炸油所影響，但兩個實驗皆指出炸油會顯著誘導CYP4A1蛋白質的表現。綜合本實驗結果，炸油餵食顯著誘導肝臟中PXR mRNA的表現量，但並未促進尿液中 a-CEHC 排出量以及肝中 a-TTP與 MDR 之蛋白質表現
Vitamin E is the most important lipid-soluble antioxidant in the body . The previous study showed that the retention of dietary vitamin E in rat tissues was affected by dietary frying oil , but the mechanism is still unclear . The purpose of this study is to investigate the effects of oxidized frying oil on the expression of protein and genes relative to vitamin E metabolism in rat liver. In experiment 1 , three groups of male Wistar weanling rats were fed the control diet (CO , containing 15% fresh soyben oil ) or test diets (FO and FOE , containing 15% frying oil ) . Frying oil was obtained by frying dough sheet in fresh soybean oil at 205±5℃ for four 6-periods . The FOE diet contained 100ppm vitamin E which is about 2 fold of normal vitamin E levels in control diet . After 6 weeks feeding , rats were then moved into metabolic cage to collect urine for 24 hours . Urine samples were analyzed for a-CEHC ( 2,5,7,8 - tetramethyl -2- (2’-carboxyethyl) - 6 -hydroxychroman) content . At the end of the feeding period , the rats were sacrificed and blood collected and liver were excised for various biochemical analysis. The plasma a-tocopherol concentration were significantly lower in FO and FOE groups than that of CO group . Liver a-tocopherol levels were significantly lowest in FO group among the three groups . FO and FOE groups showed significantly higher liver TBARS concentration when compared with the CO group ; The CAT protein levels in livers of rats fed FO and FOE diet showed significantly 3 fold higher than that of CO group . The amount of urine a-CEHC in FO groups were significantly lower than that of CO and FOE groups . All the protein levels of -TTP , CYP3A1 and MDR protein in liver had no significant difference among the three groups . The frying oil diet could promote the lipid proxidation and induce the protein levels of CAT in liver ; but did not alter the protein levels of other proteins relative to vitamin E metabolism . In experiment 2 , rats were divided into 2 groups (oxidized frying oil , O ; vitamin E-stripped fresh oil , C) and a-tocopherol were also collected . The results of liver a-tocopherol , TBARS and protein levels of CAT were similar to that of experiment 1 . The O group showed a significantly increase in liver PXR mRNA expression . The mRNA expression of CYP3A , the downstream gene of PXR , showed no significant difference between the two groups . In conclusion , the mRNA expression levels of PXR were induced by oxidized frying oil in rat liver . The excretion amount of urinea-CEHC , and the protein levels of a-TTP and MDR in rat liver were not influeuced by oxidized frying oil feeding |
