Stangl G I, Nöstelbacher K, Eder K, Kirchgessner M
Institut für Ernährungswissenschaften Technische Universität München-Weihenstephan, Freising Germany.
Eur J Nutr. 2000 Jun;39(3):112-20. doi: 10.1007/s003940070027.
Metallothionein (MT)# synthesis can be stimulated in many organs not only by various metals such as cadmium, zinc, and copper, but also by many nonmetallic compounds or experimental conditions such as oxidative stress. The latter lead to the hypothesis that MT is induced in response to free radicals formed in tissues and lipid peroxidation.
Whether the relationship between lipid peroxidation and MT synthesis is a common phenomenon also valid for lipid peroxidation induced by dietary factors such as chronic vitamin E inadequacy and autoxidation products of polyenoic fatty acids derived from thermally oxidized oil was investigated in the present study.
The relationship between the induction of metallothionein isoforms I and II (MT-I and MT-II) in response to diet-induced lipid peroxidation using a rat model system in which lipid peroxidation was examined in vivo by chronic vitamin E inadequacy or by administration of lipid peroxidation products from a thermally treated polyenoicrich oil with either basal (dietary zinc concentration: 48 mg/kg; experiment 1) or Zn-stimulated MT levels (dietary zinc concentration: 305 mg/kg; experiment 2) was studied. In both experiments, growing male rats were fed diets containing either a fresh or a thermally treated soybean oil with deficient or sufficient amounts of vitamin E (14 and 11 vs. 648 and 560 mg alpha-tocopherol equivalents per kg diet) over 40 days according to a bifactorial experimental design. Plasma and liver concentrations of tocopherols and hepatic levels of thiobarbituric acid-reactive substances (TBARS) were measured by high performance liquid chromatography. MT isoform concentrations in rat liver were isolated and quantified by ion-exchange high performance liquid chromatography and atomic absorption spectrometry.
Irrespective of the zinc supply, rats receiving inadequate amounts of vitamin E with the diet had markedly lower plasma and liver concentrations of alpha-tocopherol and total tocopherols than vitamin E-sufficient rats. ANOVA also revealed an interaction between the diet factors vitamin E and oil on tocopherols in plasma and liver of rats from both experiments. In experiment 1, where rats received normal amounts of dietary zinc, ingestion of the thermally treated oil impaired the tocopherol status compared to the treatment with the fresh oil, although this effect was only obvious in the vitamin E-deficient groups. In experiment 2, where rats received excessive amounts of zinc, the thermally treated oil did not contribute to a reduction of the tocopherol status in plasma and liver. In both experiments a significant increase in TBARS level, indicative of lipid peroxidation, was observed in the liver at chronic vitamin E inadequacy, but no effect of the oil was observed. Here, we show that the dietary treatments had some effects on the synthesis of liver metallothionein isoforms. In groups, receiving normal amounts of zinc, there was a significant interaction between the dietary treatments on the levels of MT-I and MT-II in liver. Chronic vitamin E inadequacy which was accompanied by diminished tocopherol levels in liver induced the synthesis of MT-I and MT-II. When vitamin E inadequacy was combined with the ingestion of a thermally treated polyenoic acid-rich oil hepatic levels of MT-I and MT-II remained low. In experiment 2, where rats were fed the high zinc diet, vitamin E inadequacy caused an increase of hepatic MT-I level just as in experiment 1, although this MT stimulating effect was irrespective of the oil. For MT-II there was a 43% increase in the vitamin E-deficient group fed the fresh oil compared to all the other groups, although this effect was not statistically significant. The liver MT isoform response to stress was similar in rats with basal MT levels and Zn-induced liver MT levels. The failing effect of the thermally treated oil on MT levels which were stimulated by vitamin E deficiency in experiment 2 wa
金属硫蛋白（MT）的合成不仅能在许多器官中被镉、锌和铜等各种金属刺激，还能被许多非金属化合物或实验条件如氧化应激所刺激。后者引发了这样一种假说，即MT是在组织中形成的自由基和脂质过氧化反应的刺激下被诱导产生的。
本研究调查了脂质过氧化与MT合成之间的关系是否也是一种普遍现象，这一现象对于由饮食因素如慢性维生素E缺乏和热氧化油衍生的多不饱和脂肪酸的自氧化产物所诱导的脂质过氧化同样有效。
利用大鼠模型系统研究了饮食诱导的脂质过氧化反应中金属硫蛋白同工型I和II（MT-I和MT-II）的诱导情况，在该模型系统中，通过慢性维生素E缺乏或给予热处理的富含多不饱和脂肪酸的油的脂质过氧化产物来在体内检测脂质过氧化，实验分为基础锌供应组（饮食锌浓度：48毫克/千克；实验1）或锌刺激的MT水平组（饮食锌浓度：305毫克/千克；实验2）。在两个实验中，根据双因素实验设计，让生长中的雄性大鼠在40天内喂食含有新鲜或热处理大豆油的饮食，维生素E含量分别为不足或充足（每千克饮食中α-生育酚当量分别为14和11毫克与648和560毫克）。通过高效液相色谱法测量血浆和肝脏中的生育酚浓度以及肝脏中硫代巴比妥酸反应性物质（TBARS）的水平。通过离子交换高效液相色谱法和原子吸收光谱法分离并定量大鼠肝脏中的MT同工型浓度。
无论锌供应情况如何，饮食中维生素E摄入不足的大鼠血浆和肝脏中的α-生育酚和总生育酚浓度均明显低于维生素E充足的大鼠。方差分析还显示，两个实验中大鼠血浆和肝脏中维生素E和油这两个饮食因素之间存在相互作用。在实验1中，大鼠摄入正常量的饮食锌，与喂食新鲜油相比，摄入热处理油会损害生育酚状态，尽管这种影响仅在维生素E缺乏组中明显。在实验2中大鼠摄入过量锌，热处理油对血浆和肝脏中生育酚状态的降低没有作用。在两个实验中，慢性维生素E缺乏时肝脏中TBARS水平显著升高，表明存在脂质过氧化，但未观察到油的影响。在此，我们表明饮食处理对肝脏MT同工型的合成有一些影响。在摄入正常量锌的组中，饮食处理对肝脏中MT-I和MT-II水平存在显著相互作用。慢性维生素E缺乏伴随着肝脏中生育酚水平降低，诱导了MT-I和MT-II的合成。当维生素E缺乏与摄入热处理的富含多不饱和脂肪酸的油同时存在时，肝脏中MT-I和MT-II水平仍然较低。在实验2中，大鼠喂食高锌饮食，维生素E缺乏与实验1一样导致肝脏MT-I水平升高，尽管这种MT刺激作用与油无关。对于MT-II，与所有其他组相比，喂食新鲜油的维生素E缺乏组增加了43%，尽管这种影响在统计学上不显著。基础MT水平的大鼠和锌诱导肝脏MT水平的大鼠肝脏MT同工型对应激的反应相似。实验2中热处理油对维生素E缺乏刺激的MT水平没有作用。
