稳定性同位素示踪技术的蛋白质代谢动力学研究

同位素示踪技术是公认的用于研究蛋白质代谢动力学的最佳方法。起初,由于放射性同位素具有方便、经济、检测技术成熟等优点而得到广泛应用,但因它的放射性限制了在人体代谢研究中的应用。随着稳定性同位素标记技术的成熟和质谱分析技术的发展和普及,稳定性同位素被广泛用于人体代谢动力学研究中。以下就稳定性同位素用于研究蛋白质代谢动力学中的基本原理、方法、检测手段和应用作一综述。     

双标稳定性同位素测定微量元素吸收率

迄今为止 ,测定微量元素吸收率较准确的方法依然是同位素法。由于放射线同位素的危害性 ,使得放射线同位素在某些人群中的应用受到限制。随着稳定性同位素技术的发展 ,应用稳定性同位素来研究微量元素的吸收和利用成为近年来在微量元素营养研究中的热点。特别是双标稳定性同位素技术更以其准确性高而受到微量元素学家的关注。然而目前普遍使用的计算方法多数以估计的机体血液体积及血红蛋白掺入率为基础 ,从而人为地引入了误差。为了更为有效地利用已有资料、准确地计算微量元素的生物利用 ,在前人工作的基础上 ,作者在本文对使用双标稳定性同位素技术测定微量元素的吸收率的方法进行了较为详细地讨论 ,对该方法的理论假设、实验方法、所需的基础数据、计算思路及其具体的计算过程都作了具体的说明。本文所介绍的方法可方便地用于具体的实验中     

稳定性同位素技术对锌代谢的评价

稳定性同位素技术作为目前研究微量元素代谢的重要分析技术之一 ,正日益广泛而深入的应用到营养科学领域。本文就该技术在必需微量元素锌代谢方面的应用做一编译。     

095 稳定性同位素技术对锌代谢的评价

稳定性同位素技术作为目前研究微量元素代谢的重要分析技术之一，正日益广泛而深入的应用到营养科学领域。本文就该技术在必需微量元素锌代谢方面的应用做一编译。     

生殖对钙、锌、硒生物利用率的影响

在妊娠期和哺乳期，为维持胎儿生长和乳汁合成，营养物的需要量增加。为满足这些需要所进行的生理调节是改变营养物质的生物利用率。以稳定性同位素作标记，测定妊娠期妇女钙、锌、硒的体内平衡。研究结果显示，在生殖期这三种无机物的生物利用率不同。     

可利用锌的摄入量与食物中植酸含量的关系

采用离子交换法测定分析了87种食物植酸含量,通过对841名成年人的膳食调查对锌的生物利用率进行评估。成年人锌的平均摄入量(男性为9.5 mg,女性为7.5 mg)低于韩国的每日推荐摄入量。谷类(68.6%)和豆类(19.3%)是膳食中植酸的主要来源。植酸与锌的平均比值男性为9.5,女性为10.5。9.6%的被调查者(植酸与锌的摩尔比低于5)锌的生物利用率较高,而13.2%的被调查者(植酸与锌的摩尔比高于15)锌的生物利用率较低。54.3%的被调查者(男性61.8%、女性49.5%)的锌摄入量符合标准。应进一步研究增加锌的摄入量和提高锌的生物利用率,来改善韩国人群体内锌的营养状况。     

稳定性同位素评价膳食锌吸收率的几种方法

锌吸收在其生物利用过程中是极其重要的环节 ,因此评价人体锌的生物利用情况就必须尽可能对吸收率进行准确、快捷的评定 ,而科学的评价方法尤显重要。放射性同位素锌的潜在危害已经限制了它们在人体试验中的继续应用 ,当前主要是将天然丰度较低的稳定性同位素 6 7Zn (4.1% )和 70 Zn(0 .6 2 % )浓集后作为示踪剂 ,以不明显增加人体锌负荷同时又能被高分辨率质谱仪 (如感耦等离子体质谱仪和热电离质谱仪 )检测出来的示踪剂量 (口服 <3mg,静脉注射 <1mg)给予受试者 ,从而评价锌吸收率。本综述旨在对锌吸收率的几种评价方法作一番介绍 ,并比较…     

大豆发酵断乳食品锌吸收率研究

本文介绍利用稳定性同位素~(70)Zn中子活化分析法观测发酵对提高断乳食品中锌吸收利用率的研究。结果表明,儿童食用大豆发酵断乳食品的~(70)Zn吸收率、机体总锌净吸收量、体内锌营养水平及儿童生长发育等方面观察指标均比大豆未发酵和传统的谷类断乳食品为佳。7～18月儿童每日加食以大豆发酵断乳食品为主的平衡膳食,其中锌供给量达每人每日7.3mg时即可满足机体对锌的生理需要量。     

口服用稳定性同位素钙制剂的合成

<正>稳定性同位素示踪技术用于研究体内矿物质的吸收和代谢始于1963年[1],其优越性在于灵敏度高;可在正常生理条件下进行;实验操作简单;试验期较短等,亦可用于高风险人群代谢组学的研究,如婴儿、儿童、孕妇以及哺乳期妇女,因此     

用锌稳定性同位素对人体快速交换性锌池的定量

用锌稳定性同位素对人体快速交换性锌池的定量［日］／横井克彦…∥日卫志·—１９９７，５２（１）·—１０７一般认为快速交换性锌池（ＥＺＰ）相当于代谢活性高的锌。但是，测定方法以及同机体的关系尚未确立。本文用锌的稳定性同位素６７Ｚｎ测定ＥＺＰ和血浆锌代谢周...     

The use of stable isotopes in mineral nutrition research

Stable isotopes are valuable tools for research on mineral bioavailability and metabolism. They can be used as tracers with no exposure to radiation and they do not decay over time. Attempts to use stable isotopes of minerals as metabolic tracers were first described only 25 years ago. There were relatively few reports of their use over the next 15 years, but interest in stable isotopes has expanded markedly in the last 10 years. The advantages of stable isotope tracers are so great that scientists have been willing to accept the laborious and costly nature of mineral isotope analysis, and substantial progress has been made in the field. New applications for stable isotopes and new analytical methods have been introduced recently. However, limitations to the approach and methodological problems remain to be resolved. This review describes early work in the field and discusses the advantages and disadvantages of stable isotope tracers and of the various methods of analysis. Information discovered with stable isotopes is reviewed, and probable future applications are discussed.     

Dietary phytate reduction improves zinc absorption in Malawian children recovering from tuberculosis but not in well children

High dietary phytate content that compromises zinc nutriture is thought to be a major problem among children of the developing world. Zinc stable isotope techniques permit the quantitative assessment of the effect of phytate reduction on zinc homeostasis. We tested the hypothesis that zinc absorption would be increased in Malawian children fed a reduced-phytate corn-plus-soy diet compared with a standard high phytate diet. Twenty-three children hospitalized in Blantyre, Malawi, were enrolled. Children were selected from those recovering from tuberculosis and from well children (those with minor injuries, those awaiting elective surgery or healthy siblings). Children received a diet of corn-plus-soy porridge (either low phytate or high phytate) for a period of 3-7 d and then participated in a zinc stable isotope study. The study included the administration of oral and intravenous zinc stable isotopes and 7-d collections of urine and stool. The diet was maintained throughout the duration of specimen collection. Zinc isotopic enrichments in urine and stool were measured, and zinc fractional absorption, total zinc absorption, endogenous fecal zinc, net zinc retention and size of the exchangeable zinc pool were calculated. Among the 14 children recovering from tuberculosis, dietary phytate reduction resulted in higher fractional absorption (0.41 +/- 0.14 versus 0.24 +/- 0.09, mean +/- SD, P: < 0.05) and total zinc absorption (169 +/- 55 versus 100 +/- 46 microg/(kg. d), P: < 0.05). No effect of phytate reduction was seen in the well children (n = 9). Phytate reduction did not decrease the absolute endogenous fecal zinc, but it did decrease it relative to total absorbed zinc. These preliminary results indicate that phytate reduction may be beneficial in improving zinc nutriture in groups with increased zinc requirements who consume a cereal-based diet.     

The Potential for Zinc Stable Isotope Techniques and Modelling to Determine Optimal Zinc Supplementation

It is well recognised that zinc deficiency is a major global public health issue, particularly in young children in low-income countries with diarrhoea and environmental enteropathy. Zinc supplementation is regarded as a powerful tool to correct zinc deficiency as well as to treat a variety of physiologic and pathologic conditions. However, the dose and frequency of its use as well as the choice of zinc salt are not clearly defined regardless of whether it is used to treat a disease or correct a nutritional deficiency. We discuss the application of zinc stable isotope tracer techniques to assess zinc physiology, metabolism and homeostasis and how these can address knowledge gaps in zinc supplementation pharmacokinetics. This may help to resolve optimal dose, frequency, length of administration, timing of delivery to food intake and choice of zinc compound. It appears that long-term preventive supplementation can be administered much less frequently than daily but more research needs to be undertaken to better understand how best to intervene with zinc in children at risk of zinc deficiency. Stable isotope techniques, linked with saturation response and compartmental modelling, also have the potential to assist in the continued search for simple markers of zinc status in health, malnutrition and disease.     

锌代谢池—判断人体锌营养状况的可靠指标

用稳定性同位素锌(~(68)Zn和~(70)Zn)对2例志愿者进行了历时15周不同锌营养水平的代谢实验。结果表明,锌代谢池能正确地反映人体的锌营养状况。空腹和餐后血浆锌浓度的差别比单独测定空腹血浆锌浓度更为可靠。每日尿锌和粪锌的排泄量则有一定的局限性。粪便中内源性锌排泄量的测定对确定人体每日锌的供给量标准,具有一定的参考价值。     

锌代谢池—判断人体锌营养状况的可靠指标

用稳定性同位素锌(~(68)Zn和~(70)Zn)对2例志愿者进行了历时15周不同锌营养水平的代谢实验。结果表明,锌代谢池能正确地反映人体的锌营养状况。空腹和餐后血浆锌浓度的差别比单独测定空腹血浆锌浓度更为可靠。每日尿锌和粪锌的排泄量则有一定的局限性。粪便中内源性锌排泄量的测定对确定人体每日锌的供给量标准,具有一定的参考价值。     

Zinc homeostasis in Malawian children consuming a high-phytate,maize-based diet

BACKGROUND: Zinc deficiency in children is an important public health concern in the developing world, and the consumption of predominantly cereal-based diets with a high phytate content may contribute to the risk. The gastrointestinal tract plays a central role in absorbing and conserving zinc, yet it has not been carefully studied in such children. OBJECTIVE: This study investigated zinc homeostasis in healthy, free-living Malawian children with habitually high-phytate diets to better understand the role of the gastrointestinal tract. DESIGN: We evaluated zinc homeostasis in 10 children aged 2-5 y who were consuming a maize-based diet (phytate:zinc molar ratio of 23:1). Zinc stable isotopes were administered orally and intravenously. The tracer and tracee were measured in urine and feces. RESULTS: Endogenous fecal zinc was high in comparison with results for this measure in previous studies. Typical correlations seen in subjects consuming a low-phytate diet between total absorbed zinc, the size of the exchangeable zinc pool, and endogenous fecal zinc were not observed. Fractional absorption of zinc was 0.24. CONCLUSIONS: Zinc homeostasis was perturbed, particularly by large, endogenous fecal zinc losses, in this vulnerable population. The effects of interventions to improve zinc status, including dietary phytate reduction, on zinc homeostasis merit further study.     

New approaches for designing and evaluating food fortification programs

Historically, food fortification programs were often undertaken with little attention to issues such as micronutrient bioavailability, optimal levels of addition, or efficacy or to monitoring impact on nutritional status, health, and human function. Several developments in recent years have enabled substantial progress to be made in the design and evaluation of fortification programs. The methodology for estimating the prevalence of inadequate nutrient intakes in a population and tolerable upper intake levels has been established and can be used as the basis for estimating desirable amounts of nutrient addition. More attention is being paid to assessing the bioavailability of nutrients (especially minerals) using stable and radioactive isotopes, and bioavailability of iron compounds can be estimated from changes in total body iron calculated from the ratio of transferrin receptors to serum ferritin. Procedures for quality control of the fortification process have been established. New approaches to monitoring the impact of fortification over time include assessment of liver retinol stores using retinol isotope dilution. In summary, the design and evaluation of food fortification programs now requires a series of formative research procedures on the part of nutritionists, which were not often expected or conducted in the past.     

Exchangeable Zinc Pool Size Reflects Form of Zinc Supplementation in Young Children and Is Not Associated with Markers of Inflammation

A sensitive and reliable biomarker of zinc status has yet to be identified, but observational research suggests that the exchangeable zinc pool (EZP) size may be a possible biomarker. This randomized, placebo-controlled trial aimed to compare the change in EZP size from baseline to endline in 174 children who were preventatively supplemented with 10 mg of zinc as part of a multiple micronutrient power (MNP) or as a standalone dispersible tablet for 24 weeks versus a placebo powder. The effects of systemic inflammation on EZP size were also evaluated. Zinc stable isotopes were administered intravenously to children at baseline and endline, and the EZP was measured by the urine extrapolation method. A total of 156 children completed the study with the zinc dispersible tablet group having the greatest increase in EZP (14.1 mg) over 24 weeks when compared with the MNP group (6.8 mg) (p < 0.01) or placebo group (2.0 mg) (p < 0.001). Median EZP size was not different between children with normal or elevated serum inflammatory markers. EZP size was responsive to longitudinal zinc supplementation and reflected the expected difference in bioavailability for two forms of supplementation. The apparent absence of an effect of inflammation on EZP size may offer an advantage for use as a biomarker for group comparisons between different interventions.     

Effect of dietary zinc sources and pregnancy on zinc utilization in adult women fed controlled diets

Five nonpregnant and 10 pregnant women participated in 21-day confined metabolic studies. Two diets each providing 16 mg of zinc per day were fed. In one diet 70% of the total zinc was provided by animal products and 30% was contributed by plant sources. In the second diet the proportions were reversed. Apparent absorption of zinc was determined using the balance technique. During the last 15 days of the study, zinc intake was only slightly greater than the amount of zinc excreted in feces. Mean apparent absorption values did not exceed 5% and did not vary due to diet or pregnancy. Zinc bioavailability was also assessed by measuring the apparent absorption of a stable isotope of zinc (70Zn) added to the diet. There was no significant effect of either diet or pregnancy on 70Zn absorption, which averaged about 25%. Serum zinc values were normal throughout the study and did not change significantly as a function of diet. The pregnant women, however, maintained values that were 19-27% lower than those of the nonpregnant women. In summary, the substitution of animal sources of zinc by plant products did not reduce zinc bioavailability or alter zinc utilization.