|
|
【原文标题】Food Safety Assessment of Genetically Modified Crops
【中文标题】关于转基因农作物食品安全性的评估
【来源网址】http://agron.scijournals.org/cgi/content/full/92/4/793#top
【原文库链接】http://bbs.m4.cn/thread-227620-1-1.html
【译者】Zhongdong_Wang
【翻译方式】人工翻译
【特别声明】本翻译供Anti-CNN使用，未经AC或译者许可，不得转载
【译文】
ABSTRACT
摘要
Following the production of the first transgenic plants, health issues concerning the safety of using genetically modified (GM) crops in foods and feeds have been discussed, debated, and evaluated. The main concerns regarding GM foods include toxin or allergen production, changes in nutrient levels, and development of antibiotic resistance. The U.S. Food and Drug Administration established extensive guidelines to address the concerns and ensure the safe commercial introduction of GM crops for use in food or feed. The guidelines were developed through evaluation of scientific data from several disciplines related to genetic engineering and food safety, and consultation with experts from around the world. Foods containing GM crops meeting the FDA guidelines are deemed to be as safe and nutritious as their non-GM counterparts already on the market.
紧随着首批转基因植物投入生产，涉及在食品和饲料中使用转基因农作物的安全性问题也展开了探讨、辩论和评估。涉及转基因食品的主要疑问包括毒素或者过敏原的产生、营养水平的改变和抗菌素耐药性的发展。美国食品药物管理局建立了广泛的指导方针来说明所关注的这些问题并确保用于食品和饲料的转基因农作物引入商业的安全性。这些指导方针通过对科学数据的评估从和基因工程和食品安全相关且与来世界各地的专家们商讨过的一些原则中发展而来。符合美国食品药物管理局指导方针包含有转基因作物的食品被认为和已经上市出售的非转基因对照物一样安全和有营养。
Abbreviations:GM, genetically modified • FDA, Food and Drug Administration • USEPA, U.S. Environmental Protection Agency • USDA, U.S. Department of Agriculture • APHIS, Animal and Plant Health Inspection Service • GRAS, generally recognized as safe • ECSCF, European Commission Scientific Committee for Food
缩写词：GM，转基因的●FDA，食品药物管理局●USEPA，美国环境保护署●USDA，美国农业部●APHIS，动植物检验局●GRAS，一般认为安全的●ECSCF，食品科学欧洲委员会
INTRODUCTION
介绍
IN the 5 yr since the first large-scale commercial harvest, the area planted to transgenic crops in the U.S. has grown to more than 28.4 million ha (more than 71 million acres) in 1999, where approximately 35% of all corn (Zea mays L.) and 55% of all soybean [Glycine max (L.) Merr.] planted were transgenic (James, 1999). Because soybean and corn are used as ingredients in a wide range of food products, many foods on grocery store shelves currently contain ingredients derived from genetically engineered crops. Barring a consumer backlash, the area planted to transgenic crops will continue to rise, resulting in ever more foods derived from transgenic crops (GM foods) in the marketplace.
Throughout the development and commercialization of transgenic crops, health and food safety concerns have been raised and regulatory procedures established to ensure the safety of GM foods. The main concerns voiced have been questions about the potential of GM crops to:
Inadvertently introduce toxins
Introduce allergens
Change the levels of essential nutrients, and/or
Compromise antibiotic therapies
Issues of food safety from GM crops came to the fore with a report that a greater number of laboratory rats (Rattus rattus) suffered from abnormalities in their small intestines after 10 d of feeding on GM potato diets (Solanum tuberosum L.), relative to those feeding on non-GM potato diets (Ewen and Pusztai, 1999). In an extraordinarily unusual step within the scientific field, the same journal that published the paper simultaneously published the rebuttal (Kuiper et al., 1999). The rebuttal made it clear that the potato diet was inappropriate for rats, that similar intestinal abnormalities are well known in rats fed similar diets, and that the sample size (six rats) was too small to draw any conclusions.
The report by Ewen and Pusztai (1999) was seized upon by anti-GM advocates to support their contention that proper regulatory oversight is either lacking or inadequate. This paper was written to address those concerns and to provide information on the assessment criteria and regulatory mechanisms that are in place in the U.S. to ensure the safety of GM foods.
从首次大规模商业收获起的五年里，在美国种植的转基因作物面积已经增长到1999年的2800万公顷（710万多英亩），其中种植的约35%玉米（Zea mays即拉丁语玉米）和55%大豆【Glycine max即拉丁语大豆】为转基因品种（詹姆斯，1999年）。由于大豆和玉米被广泛用作食物产品成份，杂货店货架上许多食品现在含有来源于转基因工程处理后的作物成份。忽略消费者的强烈反应的话，种植转基因作物的面积将会继续上升，使得市场上始终有来源于转基因作物的食品（转基因食品）。
在转基因作物发展和商业化的整个过程中，提出了对卫生和食品安全的疑虑并因此建立了管理程序保证转基因食品的安全。表达的主要疑虑针对的是关于转基因作物潜在的如下问题：
有毒物质的引入
过敏原的引入
主要营养成分水平的变化，以及/或者
抗菌素抗性的衰退
来自转基因作物的食品安全问题开始凸现出来，一份报告表明有较大数量的实验鼠（Rattus rattus）在喂食了10天转基因马铃薯食物（Solanum turrosum即拉丁语马铃薯）后相对于那些喂食非转基因马铃薯食物（埃文和普斯陶伊，1999年）的对照组出现了小肠异常。以科学领域里异乎寻常罕见的速度，刊登了这份资料的同一本杂志上同期登出了对这个资料的反驳文章（柯伊伯等人，1999年）。反驳使这一点变得很明确，那就是，马铃薯食物不适合喂食老鼠，喂食相似食物的老鼠中出现相似的小肠异常是毫无疑问的，而且试验样本的数量太小（六只老鼠）不足以用来得出任何结论。
埃文和普斯塔伊的这份报告被反对转基因提倡者利用来支持他们的论点，那就是，要么缺乏正确的调控监管要么就是没有正确地调控监管。这份材料是写出来解释那些疑虑，并提供与评估准则和美国设置来确保转基因食品安全的调节机制相关的信息的。
Safety Assurance for Foods Derived from Genetically Modified Crops
Before marketing, GM crops must undergo extensive food, feed, and environmental safety assessments. The Food and Drug Administration (FDA), the U.S. Environmental Protection Agency (USEPA), and the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) all have jurisdiction for monitoring and regulating the development, testing, and release of GM plants and plant products.
The Federal Food, Drug, and Cosmetic Act grants the FDA authority to regulate commercialization and marketing of most domestic and imported foods in the U.S. market. Under the 1992 Policy interpretation (USFDA, 1992), GM foods and food ingredients must comply with the same standards that apply to other food products. This means that GM foods must be as safe and nutritious as their non-GM counterparts in grocery stores today. The Act places legal duty on developers to ensure that the foods they market to consumers are safe to eat. Transgenic crops containing novel proteins classified as food additives are subjected to additional testing and must receive premarket approval by the FDA before commercialization, while whole foods made from transgenic crops passing GRAS (generally recognized as safe) standards are subject to FDA regulation after commercialization. The FDA has the broad authority to take legal action against developers of any food or food additive that poses a hazard to the public.
The FDA published its 1992 policy to assist developers in addressing food safety and regulatory issues before products reach the market. The policy statement contains a comprehensive "guidance to industry" section that discusses scientific issues for assuring food safety and identifies scientific and regulatory questions that developers must consider to determine if they should consult with the FDA before commercial release of a genetically engineered food crop. Developers are encouraged to consult with the FDA through the Office of Premarket Approval of the Center for Food Safety and Applied Nutrition and the Office of Surveillance and Compliance of the Center for Veterinary Medicine before the commercialization of a new GM variety to ensure that the variety will meet all safety requirements. The FDA requires a full evaluation of a genetically engineered food crop when uncharacterized DNA sequences are used, or when food products may contain significantly altered nutrient levels, different compositions from substances currently found in foods, allergenic proteins, new antibiotic resistance markers, or levels of toxins significantly above those found naturally in edible varieties of the same species.
转基因农作物食品的安全保证
在进入市场前，转基因作物必须接受广泛的食品、饲料和环境安全评估。食品药物管理局（FDA）、美国环境保护署（USEPA）和美国农业部（USDA）的动植物检验局（APHIS）都有监控和调节开发、测试和发布转基因植物和植物产品的管辖权。
联邦食品药物化妆品法案授予食品药物管理局权力来管理美国市场上国内和进口的大部分食品的商品化和营销工作。根据1992年政策解释（美国食品药物管理局，1992年），转基因食品和食品成分必须遵守适用于其他食物产品的相同标准。这就意味着转基因食品必须和现在杂货店里的非转基因同类食品一样安全和有营养。这个法案将职责定位在开发者身上以保证他们经销给消费者的食品可以安全食用。含有用作食品添加剂的新颖蛋白质的转基因作物要经受附加的检验且必须在商业化上市前获得食品药物管理局许可，同时转基因作物通过一般认为安全标准后制成的全部食品要经受食品药物管理局的商业化后监管。食品药物管理局拥有广泛的权力采取法律行动制裁造成公众危害的任何食品或者食品添加剂的制造者。
食品药物管理局1992年颁布了政策帮助开发商在产品进入市场前解释清楚食品安全和调控管理方面的问题。这项政策声明包含了综合的“产业化指导”章节，论述保证食品安全的科学问题，明确科学和管控方面开发商必须考虑以决定是否要在基因转化工程处理过的粮食作物商品化发布前与食品药物管理局商讨的问题。鼓励开发商在商业化一种新转基因品种前与食品药物管理局通过食品安全应用营养学中心上市前许可办公室和兽医中心监督承诺办公室商讨以保证该品种符合所有安全要求。当使用不明特征DNA时或者当食物产品营养水平可能显著改变的、有不同于目前食品中组成成分的、有过敏原蛋白的、有新抗菌素抗体标记的或者毒素水平显著超出同物种可食用各品种中天然存在的这些情况出现时，食品药物管理局将要求完整评估一种基因工程处理过的粮食作物。
Inadvertent Synthesis or Increase in Toxins
毒素的自然合成或增加
Many plants produce a number of toxins and antinutritional factors that are thought to provide resistance to natural herbivores (Kessler et al., 1992). In most domesticated crop species, the concentrations of such toxins are so low that they present no health concerns. In other species (e.g., potato), breeders routinely screen new varieties to make sure that toxins are within a safe limit. In some crop species (e.g., cassava, Manihot esculenta Crantz), the food product must be cooked or processed to inactivate toxic substances. In GM crop plants, toxins are of concern in any species in which unsafe levels have been found in its lines, varieties or relatives, or if transgenes are derived from such species. In those cases, developers of GM crops must determine that toxins are absent, or present within a safe range, before commercialization of the crop. In addition, a number of groups of proteins present in common foods are toxic or antinutritional. Development of GM crop plants with gene sequences encoding such proteins is not recommended, and if developed, such varieties would be subject to a full food safety review.
Another concern is the potential for silent toxin pathways to be reactivated in GM crops due to the genetic engineering process. Plants, like other organisms, have metabolic pathways that no longer function due to mutations that occurred during evolution. Products or intermediates from some of these pathways may be toxins. Questions have been raised as to the potential for genetic engineering to reactivate those pathways. However, a determination was made that the likelihood of such events occurring in food plants with a long history of safe use is remote, and that the potential would likely have been detected during breeding evaluations of the crop and its use for food (reviewed in Kessler et al., 1992). Currently, all transgenic food crops approved for commercialization in the USA (e.g., corn, soybean, potato, etc.) have long histories of breeding and use as foods, and this history can be used to evaluate potential for toxin production. Transgenic crops that have breeding and/or food use histories that indicate a potential for toxin production are subject to a full food safety evaluation prior to commercialization. Similar safety evaluations would be necessary for new crops lacking a long history of breeding and use in food, since the potential for toxin production would be difficult to predict in these crops.
Toxins present in the food supply do not necessarily come from the plant itself, but rather can come from pathogens growing on the plant. A recent report (Munkvold et al., 1999) indicates that corn engineered to resist the European corn borer (Ostrina nubilalis) has lower concentrations of the fungal mycotoxin, fumonisin. The corn borer wounds the plant and facilitates infection by Fusarium ear rot (Fusarium verticilliodes), hence reductions in insect damage lead to reductions in fungal infection, which ultimately lead to lower levels of fungal toxin accumulation.
许多植物产生一些被认为用来对抗天然食草动物的毒素和抗营养因子（凯斯勒等人，1992年）。在许多已适应人类种植的作物品种里，这类毒素的聚集非常少以至于并不呈现出对健康的危害问题。在其他一些品种里（比如马铃薯），养殖者经常筛选新变种以确保毒素控制在安全限制内。在有些作物品种里（比如木薯Manihot esculenta Crantz），食物产品必须经过烹煮或加工处理从而使有毒物质失去活跃性。转基因植物里，其同谱系、变种或亲属中发现的不合安全标准的毒素在任何品种中都值得引起注意。那样的话，转基因作物开发者必须在将作物商业化之前决定是否允许毒素在安全范围内出现。另外，许多普通食品中出现的蛋白质群体是有毒或有抗营养性的。不推荐用基因序列编码这类蛋白质开发转基因农作植物，如果开发了，这类品种须受到全面的食品安全审查。
另一个需要关注的问题是在基因工程处理过程中存在的导致转基因作物内“沉寂的”毒素被重新激活的潜在可能途径。像其他有机生物体一样，植物也有在进化过程中发生突变导致失去功能的代谢途径。部分这些途径制造的产品或中间物可能会是毒素。这些问题就成了提供给基因改造工程重新激活这些途径的潜在因素。然而，已经做出了一项决定使得在安全使用的漫长历程中食用植物内发生这类事件的可能性是遥不可及的事情，并且这种潜在可能性已经很可能在培育评估这种作物和用它制造食品过程中发现了（参看，凯斯勒等人，1992年）。目前所有允许在美国商业化生产的转基因食用作物（比如玉米、大都、马铃薯等等）已有了培育和用作食品的悠久历史，这个历史可以用来评估产生毒素的潜在可能性。具有培育和/或食用历史表明有潜在产生毒素可能性的转基因作物在商业化前会经受全面的食品安全评测。同样的安全评测对缺少长久培育和用作食品历史的新作物也是必不可少的，因为在这些作物中产生毒素的潜在可能性是难以预测的。
出现在食物供应中的毒素不一定来自植物本身，而相当可能来自植物上成长起来的致病菌。最近的一份报告（孟轲沃尔德等人，1999）显示转基因处理过用来抵抗欧洲玉米螟（Ostrina nubilalis）的玉米对真菌毒素、烟曲霉毒素的积聚作用很小。玉米螟伤害植株并容易造成镰刀菌素穗腐病感染。因此，减少昆虫损害致使真菌感染减少，从根本上致使降低真菌毒素累积水平。
Changes in Essential Nutrients
主要营养成分的变化
Certain crop plants are major suppliers of essential nutrients to the human diet. For example citrus crops are major sources of vitamin C, carrot (Daucus carota L.) is a source of vitamin A, and grain legumes are a source of protein and essential amino acids. Under FDA policy, developers of new food crop varieties, including GM crops, must determine that levels of essential nutrients in the new variety are not significantly different from levels traditionally associated with those crops. If, after reveiw of results from tests, levels of essential nutrients are found to be significantly different in the new crop, the FDA has the authority to disallow commercialization of the crop, or require that foods derived from the crop be labeled to inform the consumer of the altered nutrient content.
Genetically modified crops are being developed with enhanced nutritional qualities, such as increased iron or vitamin A content in edible plant parts (Goto et al., 1999; Ye et al., 2000). In such cases, the transgenic crop could be subject to a full food safety evaluation before approval for commercialization and to labeling requirements following commercialization (USFDA, 1992).
A recent paper by Lappé et al. (1998) reported that GM soybean had lower levels of isoflavones, considered important for human health, than non-GM soybean, which allegedly demonstrates the inadequacy of the current regulatory system. The American Soybean Association promptly reacted by providing documentation that the changes observed by Lappé et al. (1998) were well within the normal range of isoflavone concentrations for soybean (ASA, 1999).
某些农作植物是人类食物主要营养成分的重要提供者。比如柑桔类作物是维他命C的主要来源，胡萝卜（Daucus carota拉丁语胡萝卜属胡萝卜）是维他命A的来源，而豆类是蛋白质和必须氨基酸的来源。根据食品药物管理局政策，包括转基因作物在内的新食用作物品种开发者必须确定新品种的主要营养成分水平并无显著区别于传统同类作物水准之处。如果，审查检测结果后发现该新作物主要营养成分水平显著不同，食品药物管理局有权力不允许这种作物的商业化生产，或者要求源自该作物的食品打上标记告知消费者其营养成分发生了变化。
转基因作物正在开发成有增强的营养品质，诸如在植物可食用部分增加的铁或维他命A成分之类。在这些情况中，转基因作物应该在获准商业化生产前接受全面的安全评测并要求在商业化生产后进行标记（美国食品药物管理局，1992年）。
最近拉贝等人（1998年）的一份材料报告，被认为对人类健康很重要的大豆黄酮素含量水平低于非转基因大豆，据称这证明了目前的调控系统的不完善性。美国大豆协会迅捷地作出反应，提供了文件材料说明拉贝等人（1998年）观察到的变化完全在大豆黄酮素正常含量范围以内（美国大豆协会，1999年）。
Introduction of Allergens
过敏原介绍
Food allergies occur in <1 to 2% of the population, and most sufferers have been shown to be allergic to only a few specific proteins in one or two specific foods (reviewed in Hefle et al., 1996; Metcalfe et al., 1996). Eight foods (peanut [Arachis hypogaea L.], soybean, tree nuts, milk, eggs, fish, crustaceans, and wheat [Triticum aestivum L.]) account for >90% of food allergies worldwide (reviewed in Metcalfe et al., 1996; Taylor and Lehrer, 1996). Food allergies are of major concern, as people with allergies to those foods can exhibit reactions that are sudden, severe, and life-threatening (reviewed in Taylor and Lehrer, 1996).
Guidelines for assessing the allergenic potential of GM crops were established by the FDA following extensive review of research on food allergies and consultation with leading researchers in the areas of food safety, food allergies, immunology, biotechnology, and diagnostics (USFDA, 1994). Under FDA guidelines, developers of crops engineered with transgenes from any of the foods listed above are instructed to demonstrate scientifically that the allergenic substance is not present in the new food.
All known food allergens are proteins, many of which share several features: amino acid sequence similarity to each other, molecular weight between 10 and 70 kDa, glycosylation, acidic isoelectric points, and resistance to heat, acid treatment, proteolysis, and digestion (reviewed in Lehrer et al., 1996; Taylor and Lehrer, 1996). Nevertheless, exceptions exist. Therefore, to ensure that new GM crops do not contain a new allergen, its allergenic potential must be assessed based on:
The gene source (did it come from a species known to cause food allergy?)
The crop to be engineered (do foods derived from that crop cause food allergies?)
The gene and protein sequence (does it share traits with known allergens?)
To aid in evaluation of those criteria, a decision tree strategy was formulated (Metcalfe et al., 1996). If the answer is yes to any of the questions posed in the diagram, specific tests and assays are recommended. If allergenic potential is indicated, the FDA will require labeling to inform consumers of the allergenic potential, or to take legal action against commercialization.
To illustrate how the regulatory system works, Pioneer Hi-Bred International scientists introduced a gene from the Brazil nut (Bertholletia excelsa Humb. & Bonpl.) into soybean to improve the methionine content of the protein. Because allergic reactions to Brazil nut had been previously documented, skin prick tests, inhibition immunoassays, and immunoblotting were recommended for testing the allergenic potential of the Brazil nut protein engineered into soybean. During the required evaluation process, the protein made by the introduced gene was found to be allergenic (Nordlee et al., 1996), and Pioneer announced it was discontinuing the work with the Brazil nut gene.
食品过敏发生在人群小于1%到2%的范围内，且多数过敏者表现为只对一两种特定食品的很少几种特定蛋白质过敏（参看：海福乐等人，1996年；梅特卡夫等人，1996年）。八种食品（花生【Arachis hypogaea即拉丁语落花生】、大豆、树坚果、奶类、蛋类、鱼类、甲壳类和小麦【Triticum aestivum即拉丁语小麦】）占全世界食品过敏原90%以上（参看：麦特卡夫等人，1996年；泰勒和莱勒，1996年）。食品过敏原是主要关注的问题，因为对那些食品过敏的人会出现突然、剧烈和威胁生命的反应（参看：泰勒和莱勒，1996年）。
评测转基因作物这种导致过敏的潜在因素的指导方针已经由食品药物管理局在广泛参照了食品过敏研究和同食品安全、食品过敏、免疫学、生物技术及诊断学这些领域的主要研究者们进行了商讨之后制定出来了（美国食品药物管理局，1994年）。按照食品药物管理局指导方针，用上述所列任何食品的转基因进行工程处理的作物的开发者们要按照规定科学地证明新食品中没有出现致敏物质。
所有已知食品过敏原都是蛋白质，它们中的许多有共同的几项特征：氨基酸序列彼此相似、分子重量在10到70分子量之间、糖基化、酸性等电位点和耐热性、酸处理、蛋白质水解和消化吸收（参看：莱勒等人，1996年；泰勒和莱勒，1996年）。即便如此，仍有存在例外的可能。因此，为了保证新转基因作物不包含新过敏原，新转基因作物的潜在致敏性因按照以下基准必须接受评估：
基因来源（基因是否来自一个已知会导致食品过敏的种类？）
用来工程处理的作物（来源于那种作物的食品是否会导致食品过敏？）
基因和蛋白质序列（是否和已知过敏原有共同特征？）
为了帮助评测那些标准，形成了一种决策树（梅特卡夫，1996年）。如果对图表中提出的任何问题的答案是肯定的，那么建议进行特定测试和化验。如果显示有导致过敏潜在因素，食品药物管理局会要求打上标记告知消费者存在导致过敏的潜在因素，或者采取法律措施禁止其商业化生产。
为了说明调控机制是如何发挥作用的，“国际先锋种子公司”的科学家们向大豆中引入了巴西胡桃（Bertholletia excelsa巴西坚果）的基因以改变大豆蛋白质的蛋氨酸成分。因为对巴西胡桃的过敏反应事先已经有证明文件备案，所以推荐使用皮刺测试、免疫抑制和免疫印迹法以测试处理到大豆中的巴西胡桃蛋白质的致敏潜在因素。在要求评测的过程中，发现引入基因产生的蛋白质具有导致过敏作用（诺德里等人，1996年），并且“先锋”宣布已处于停止使用巴西胡桃基因的工作中。
Reduced Efficacy of Antibiotics
降低抗生素作用
Genetic engineering of plant cells is an inefficient process, and only a very small percentage of the cells targeted for DNA delivery actually integrate and express the new transgenes. To isolate the transgenic cells from the millions of nontransgenic cells in a tissue, scientists usually link what is known as a selectable marker gene, usually a gene encoding for antibiotic resistance to the transgene(s) of interest. Cells are then grown in a laboratory culture medium containing the antibiotic. Only those cells that have integrated the antibiotic resistance transgene live and grow into plants.
Early in the development of transgenic crops, a concern was raised that the transfer of the antibiotic resistance transgene from plants to pathogens in the environment or in the gut of humans or animals would compromise antibiotic therapy by rendering pathogens immune to the effects of the antibiotic. Accordingly, the 1992 FDA policy statement (USFDA, 1992) and the recently published Guidance for Industry: Use of Antibiotic Resistance Marker Genes in Transgenic Plants (USFDA, 1998) specifically discuss the safety evaluation of GM crops and food products containing antibiotic resistance transgenes, by addressing:
The potential toxicity of the protein encoded by the antibiotic resistance gene
The potential for the protein to elicit allergenic reactions
The importance of the antibiotic as a medication
The frequency of use of the antibiotic
Whether the antibiotic is orally administered
The uniqueness of the antibiotic
The potential for transfer of the antibiotic resistance transgene from plants to microorganisms, and whether such a transfer would enhance the survival of the microorganisms that incorporated the antibiotic resistance gene
The frequency of antibiotic resistance naturally found in bacterial populations
These guidelines were established following consultation with experts in the fields of microbiology, medicine, bacterial and mycotic diseases, and food safety. Additional confirmation of the guidelines' ability to ensure that GM crops containing antibiotic resistance transgenes are safe was provided by national and international food safety regulatory agencies including the USEPA, the European Commission Scientific Committees for Food and Animal Nutrition, the Nordic Working Group on Food Toxicology and Risk Assessment, and the World Health Organization/Food and Agriculture Organization (ECSCF, 1996; Karenlampi, 1996; USEPA, 1994; WHO, 1993, 1996).
The antibiotic resistance transgene used to develop the GM crop plants currently in the market is the NPTII or APH(3')II gene, which provides resistance to the antibiotics kanamycin and neomycin by detoxifying them (reviewed in Flavell et al., 1992). A detailed description of the safety assessment of the NPTII gene and its protein product is provided by Calgene (1990), by USFDA (1994) and in the USFDA Guidance to Industry: Use of Antibiotic Resistance Marker Genes in Transgenic Plants (1998). In accordance with the criteria listed earlier, the NPTII gene was deemed safe for use (Calgene, 1990; reviewed in Flavell et al., 1992) based on the following:
No evidence of allergenicity or toxicity could be identified.
Kanamycin-resistant bacteria are so common in nature that the average human eats 1.2 million bacteria containing the NPTII gene each day, primarily on fresh vegetables.
Eating food containing NPTII would not compromise the oral use of kanamycin in humans because the protein is rapidly inactivated and degraded in the gut. Also, NPTII requires ATP to function, and ATP is present in only extremely low concentrations in the digestive system.
The transfer of the NPTII gene from plants to pathogenic bacteria was highly unlikely to occur, and even if it did, would not increase the amount of kanamycin-resistant bacteria. Each human gut naturally contains 1012 kanamycin-resistant bacteria. The worst-case scenario is that eating a tomato (Lycopersicon esculentum Mill.) with the NPTII gene would increase the frequency of kanamycin-resistant bacteria in the gut by 0.000001%.
Similar data were presented to demonstrate the safety of the NPTII gene in animal feed and in exposure of soil microorganisms to GM crops in large-scale production scenarios (USFDA, 1998).
Because the DNA used for genetic engineering is produced inside bacteria, a second antibiotic resistance gene, one expressed only in bacteria, is used to permit the preferential growth of bacterial cells containing the engineered DNA. One gene used frequently for the purpose is the bla or ampR gene, which gives resistance to ampicillin. Whenever a gene gun is used to engineer a plant, the bla gene can also get incorporated into the plant. Such is the case with Bt maize (Zea mays L.) developed by Novartis. However, the ampicillin gene is designed to express only in bacteria, and never in a plant tissue. Because no protein product is produced in plants by the ampicillin gene, its use has been deemed safe (USFDA, 1998).
The conclusion that the NPTII and the ampicillin resistance genes are safe to use in GM crops has also been reached by other scientific panels and regulatory agencies (USEPA, 1994; Karenlampi, 1996; ECSCF, 1996; WHO, 1993). Agreement among independent international organizations regarding the approval and safety of antibiotic resistance markers should reassure consumers of the safety of GM foods containing antibiotic resistance genes.
Nevertheless, the opposite has happened. The presence of the bla gene, and fears that it will be transferred from GM crops into pathogens in the environment, was cited as the specific reason why the European Union denied approval of the Novartis Bt maize (Salyers, 1996). Ironically, the ampicillin resistance gene was found and isolated in London, in 1963 (Sutcliffe, 1978), indicating the ampicillin resistance gene is already present in the European environment, and has been since long before GM crops were ever envisioned.
Finally, although evaluation of the safety of antibiotic resistance markers will continue as needed, it may become unnecessary in the future as new, nonresistance based selectable markers are being developed and used in place of antibiotic resistance markers (Ebinuma et al., 1997; Haldrup et al., 1998; Kaeppler et al., 2000).
植物细胞基因工程处理是一项效率很低的进程，实际上只有很小百分比的选定为DNA传送对象的细胞集成并呈现转化后的新基因。为了把组织中转基因细胞从成百万非转基因细胞中隔离出来，科学家们经常连接一种称作可选标志基因的东西，通常是一种为了抗生素抗性编码到有用的转基因上的基因。然后细胞在一个含有这种抗菌素的实验室培养基中成长。只有集成了这种抗菌素抗性转基因的细胞存活并长成了植物。
在开发转基因作物早期，就提出了一个问题那就是，来自植物的抗菌素抗性转基因向外界环境、人类或动物肠道中的病原体的转移会赋予病原体对抗菌素效果的免疫能力而影响抗菌治疗。因此，1992年食品药物管理局政策声明（美国食品药物管理局，1992年）和近期颁布的“生产指南”表示：转基因植物中抗生素抗药性标志基因的使用（美国食品药物管理局，1998年）须专门讨论转基因作物和含有抗菌素抗药性转基因的食物产品的安全评测，并要说明：
由抗生素抗药基因编码的蛋白质的潜在毒性
蛋白质引起过敏反应的潜在可能性
抗生素用作药物治疗的重要性
抗生素使用频度
抗生素是否口服
抗生素的唯一性
植物抗生素抗药转基因向微生物转移的潜在可能性，以及此种转移有否可能加强吞并了这种抗菌素抗药基因的微生物存活
菌群中自然发现抗生素抗药性的频度
这些指导方针建立在和微生物学、医药学、细菌真菌性疾病和食品安全领域专家们商讨的基础上。证明这些指导方针有能力确保转基因作物所包含抗生素抗性基因是安全的附加文件由国家和国际食品安全管理机构提供，这些机构包括美国环境保护署、食品动物营养欧洲科学委员会、食品毒理学风险评估北欧工作组和世界卫生组织/粮农组织。
目前市场上用于开发转基因植物的抗生素抗性转基因是NPTII或者APH(3')II基因，这种基因提供对卡那霉素和新链丝菌素的去毒性抗药作用（参看：福拉威尔等人，1992年）。关于NPTII基因和它的蛋白质产品安全评测的详细描述由卡尔金（Calgene）、美国食品药物管理局和美国食品药物管理局“生产指南”的“转基因植物中抗生素抗药性标志基因的使用”提供。根据前述所列标准，NPTII基因被视为在使用上是安全的（卡尔金，1990年；参看：福拉威尔等人，1992），基于下述理由：
没有致敏性或毒性的明显迹象。
抗卡那霉素细菌在自然界很普通，人类平均每天会吃进1200万包含NPTII基因主要存在于新鲜蔬菜的细菌。
食用含有NPTII的食品不会降低人类口服卡那霉素的效果因为这种蛋白质会在肠道中快速钝化和降解。而且，NPTII要求三磷酸腺苷（ATP）才能发挥作用，而三磷酸腺苷在消化系统中的存积量极其少。
NPTII从植物向病原细菌的转移非常没有可能会发生，甚至即使发生了，也不会使卡那霉素抗药细菌大量增长。每个人类肠道中天然包含有10的12次方个卡那霉素抗药细菌。最糟糕的情形是吃进一个带NPTII基因的西红柿可能会使卡那霉素抗药细菌出现频度增加0.000001%。
也有相似数据表明动物饲料和大规模转基因作物生产场景中土壤微生物暴露于NPTII基因的安全性（美国食品药物管理局，1998年）。
由于基因工程处理使用的DNA是细菌体内产生的，所以一种仅出现在细菌中的次要抗生素抗药基因习惯上允许包含基因处理过的DNA的细菌细胞优先成长。为这一目的而频繁使用的一种基因是bla或ampR基因，这种基因提供对氨苄青霉素的抗性。任何时候当基因枪用于工程处理植物时，bla基因也会一同加入到植物中去。诺华公司开发的Bt玉米的案例就属于这种情况。然而，氨苄青霉素基因是设计成仅出现在细菌中的，而决不是出现在植物组织中的。
因为没有蛋白质产品是在植物中由氨苄青霉素基因生产的，它的使用被认为是安全的（美国食品药物管理局，1998年）。
NPTII和氨苄青霉素抗药基因在转基因作物中的使用是安全的这个结论也已经由其他科学委员会和管理机构得出。
在独立的国际组织中达成的共识，认为抗生素抗药性标记的认可和安全性，会使消费者恢复对包含抗生素抗药基因的转基因食品安全性的信心。
即便如此，也出现了对立的事物。bla基因的存在，以及对bla基因会从转基因作物转移到环境中的病原体中去的担心，被当做特定理由引用来说明欧盟拒绝给诺华玉米颁发许可的原因。具有讽刺意味的是，氨苄青霉素抗药基因1963年就在伦敦被发现和分离，这表明氨苄青霉素抗药基因在欧洲环境中已经出现，而且在转基因作物还只是设想之前已经存在很久了。
最后，尽管抗生素抗药标记的安全性评测会因为需要而继续，但在未来它将不再是必须的，因为新的、非抗药性为基础的可选标记正在开发和用于代替抗生素抗药标记中。 |
评分
-
1
查看全部评分
-
|
狗仔卡
发表于 2010-3-7 19:47
提升卡
变色卡
抢沙发
千斤顶
显身卡
楼主
