Eder K, Kirchgessner M
Institut für Ernährungsphysiologie, Technischen Universität München-Weihenstephan, Freising, Germany.
Lipids. 1998 Mar;33(3):277-83. doi: 10.1007/s11745-998-0206-x.
Diets rich in polyunsaturated fatty acids (PUFA) are well known to suppress hepatic lipogenic enzymes compared to fat-free diets or diets rich in saturated fatty acids. However, the mechanism underlying suppression of lipogenic enzymes is not quite clear. The present study was undertaken to investigate whether lipid peroxidation products are involved in suppression of lipogenic enzymes. Therefore, an experiment with growing male rats assigned to six groups over a period of 40 d was carried out. Rats received semisynthetic diets containing 9.5% coconut oil and 0.5% fresh soybean oil (coconut oil diet, peroxide value 5.1 meq O2/kg oil), 10% fresh soybean oil (fresh soybean oil diet, peroxide value 9.5 meq O2/kg oil), or 10% thermally treated soybean oil (oxidized soybean oil diet, peroxide value 74 meq O2/kg oil). To modify the antioxidant state of the rats, we varied the vitamin E supply (11 and 511 mg alpha-tocopherol equivalents per kg of diet) according to a bi-factorial design. Food intake and body weight gain were not influenced by dietary fat and vitamin E supply. Activities of hepatic lipogenic enzymes were markedly influenced by the dietary fat. Feeding either fresh or oxidized soybean oil diets markedly reduced activities of fatty acid synthase, (FAS), acetyl CoA-carboxylase, (AcCX), glucose-6-phosphate dehydrogenase, (G6PDH), 6-phosphogluconate dehydrogenase, and ATP citrate lyase (ACL) relative to feeding the coconut oil diet. Moreover, feeding oxidized soybean oil slightly, but significantly, lowered activities of FAS, AcCX, and ACL compared to feeding fresh soybean oil. Activities of hepatic lipogenic enzymes were reflected by concentrations of triglycerides in liver and plasma. Rats fed the coconut oil diet had markedly higher triglyceride concentrations in liver and plasma than rats consuming fresh or oxidized soybean oil diets, and rats fed oxidized soybean oil had lower concentrations than rats fed fresh soybean oil. The vitamin E supply of the rats markedly influenced concentrations of thiobarbituric acid-reactive substances in liver, but it did not influence activities of hepatic lipogenic enzymes. Because the vitamin E supply had no effect, and ingestion of an oxidized oil had only a minor effect, on activities of hepatic lipogenic enzymes, it is strongly suggested that neither exogenous nor endogenous lipid peroxidation products play a significant role in the suppression of hepatic lipogenic enzymes by diets rich in PUFA. Therefore, we assumed that dietary PUFA themselves are involved in regulation of hepatic lipogenic enzymes. Nevertheless, the study shows that ingestion of oxidized oils, regardless of the vitamin E supply, also affects hepatic lipogenesis, and hence influences triglyceride levels in liver and plasma.
与无脂饮食或富含饱和脂肪酸的饮食相比，富含多不饱和脂肪酸（PUFA）的饮食能显著抑制肝脏脂肪生成酶，这一点已广为人知。然而，脂肪生成酶受抑制的潜在机制尚不完全清楚。本研究旨在探究脂质过氧化产物是否参与脂肪生成酶的抑制过程。为此，我们对生长中的雄性大鼠进行了一项为期40天的实验，将其分为六组。大鼠分别接受含有9.5%椰子油和0.5%新鲜大豆油的半合成饮食（椰子油饮食，过氧化值5.1 meq O2/kg油）、10%新鲜大豆油的饮食（新鲜大豆油饮食，过氧化值9.5 meq O2/kg油）或10%经热处理的大豆油的饮食（氧化大豆油饮食，过氧化值74 meq O2/kg油）。为改变大鼠的抗氧化状态，我们根据双因素设计改变了维生素E的供应量（每千克饮食中含11和511毫克α-生育酚当量）。食物摄入量和体重增加不受饮食脂肪和维生素E供应的影响。肝脏脂肪生成酶的活性受饮食脂肪的显著影响。与喂食椰子油饮食相比，喂食新鲜或氧化大豆油饮食均显著降低了脂肪酸合酶（FAS）、乙酰辅酶A羧化酶（AcCX）、葡萄糖-6-磷酸脱氢酶（G6PDH）、6-磷酸葡萄糖酸脱氢酶和ATP柠檬酸裂解酶（ACL）的活性。此外，与喂食新鲜大豆油相比，喂食氧化大豆油使FAS、AcCX和ACL的活性略有但显著降低。肝脏脂肪生成酶的活性通过肝脏和血浆中甘油三酯的浓度反映出来。喂食椰子油饮食的大鼠肝脏和血浆中的甘油三酯浓度明显高于食用新鲜或氧化大豆油饮食的大鼠，而喂食氧化大豆油的大鼠的甘油三酯浓度低于喂食新鲜大豆油的大鼠。大鼠的维生素E供应显著影响肝脏中硫代巴比妥酸反应性物质的浓度，但不影响肝脏脂肪生成酶的活性。由于维生素E供应对肝脏脂肪生成酶的活性没有影响，摄入氧化油对其活性也只有轻微影响，因此强烈表明，无论是外源性还是内源性脂质过氧化产物在富含PUFA的饮食对肝脏脂肪生成酶的抑制中均不起重要作用。因此，我们推测饮食中的PUFA本身参与了肝脏脂肪生成酶的调节。尽管如此，该研究表明，无论维生素E供应情况如何，摄入氧化油也会影响肝脏脂肪生成，进而影响肝脏和血浆中的甘油三酯水平。
