ReviewAssessment of the health impact of GM plant diets in long-term and multigenerational animal feeding trials: A literature review
Highlights
► Effects of GM diets in all long-term and multigenerational studies were analyzed. ► No sign of toxicity in analyzed parameters has been found in long-term studies. ► No sign of toxicity in parameters has been found in multigenerational studies. ► The 90-day OECD Guideline seems adequate for evaluating health effects of GM diets. ► Benefits of harmonizing experimental protocols in fundamental research are discussed.
Introduction
In Europe, GM food and feed safety is assessed by the European Food Safety Authority (EFSA), which recommended that “the safety assessment of GM plants and derived food and feed follows a comparative approach, i.e. the food and feed are compared with their non-GM counterparts in order to identify intended and unintended (unexpected) differences which subsequently are assessed with respect to their potential impact on the environment, safety for humans and animals, and nutritional quality” (EFSA, 2008). With different methods, key elements of the assessment procedure such as molecular, compositional, phenotypic, and agronomic traits are analyzed in both the GM line and its near isogenic counterpart (EFSA, 2008). When “molecular, compositional, phenotypic, agronomic and other analyses have demonstrated equivalence of the GM food/feed, animal feeding trials do not add to the safety assessment” (EFSA, 2009; updated in EFSA, 2011). However, animal feeding studies may provide additional and useful information to complement safety and nutritional value assessments of whole GM food and feed, especially when unintended effects are suspected. The EFSA experts panel recommend that “the use of 90-days studies in rodents should be considered for the detection of possible unintended effects in food and feed derived from GM plants which have been more extensively modified in order to cope with environmental stress conditions like drought or high salt conditions, or GM plants with quality or output traits with the purpose to improve human or animal nutrition and/or health” (EFSA, 2008).
The protocols for in vivo toxicological studies are adapted from the 90-day rodent study as described in OECD Test Guideline No. 408 (Organisation for Economic Co-operation and Development, 1998), which defines the experimental material to test and the practical conditions used to test it (target animal species, housing, number of doses administered, gender and number of animals, etc.). The appropriate methods used to measure phenotypic responses (body weight, food consumption, clinical biochemistry, etc.) in test animals throughout the test are also provided. Over the last few decades, these parameters have been refined for an improved toxicological assessment of low molecular weight xenobiotics such as drugs, pesticides or additives, and serve as a foundation for the evaluation of GM-based food or feed. While feeds are identical between animal groups (treated or control) in the normal 90-day rodent study, adaptation of this test to food safety studies raises many specific questions on the strengths and weaknesses of such tests. For example, to assess the potential health effects of GM-based food or feed, 33% GM animal feed is usually incorporated (see recommendations of Agence nationale de sécurité sanitaire de l’alimentation, de l’environnement et du travail, ANSES, 2011). Feeding experiments using rodent models allow whole GM material to be tested, this assessment being motivated by either a modification in the GM plant composition, or by indications of potential unintended effects (EFSA, 2006, EFSA, 2008). More precisely, 90-day animal feeding studies do not search for one particular effect of a given molecule, but are supposedly designed to detect most of the changes that may occur, including those potentially generated by the genetic modification as well as those resulting from a compositional change which is directly or not linked to the transgene. Thus, these studies might appear too wide and insufficient to detect weak effects, as EFSA (2008) has already stated “It is unlikely that substances present in small amounts and/or with a low toxic potential will result in any observable unintended effects”. The key point is that in the case of a chemically defined molecule for which human exposure is very low, one can increase its dose in the classical 90-day feeding studies, whereas one cannot do so with a food or with a quantitatively important constituent in the diet.
Moreover EFSA (2008) states that “the subchronic, 90-day rodent feeding study is not designed to detect effects on reproduction or development, other than effects on adult reproductive organ weights and histopathology. Thus, in some cases, testing of the whole food and feed beyond a 90-day rodent feeding study may be needed. In cases where structural alerts, indications from the subchronic study or other information on the whole GM plant derived food and feed are available that suggest the potential for reproductive, developmental or chronic toxicity, the performance of such testing should be considered”.
Possibly, some 90-day rodent feeding studies may be insufficient to reveal the presence of late effects in animals. Therefore, long-term studies, namely those performed for longer than 90 days, as well as multigenerational studies, will evaluate whether unintended effects are only detected by such studies and whether long-term studies have different findings than 90-day studies. In this paper we address the following question: Do recently published studies on long-term effects of GM plants, i.e. studies significantly longer than the 90-day sub-chronic tests, as well as multigenerational studies, present new evidence indicative of some adverse effects? The goal of this review is to compile and discuss the results of recently published studies on long-term effects as well as multigenerational studies for GM plants on which 90-day studies are also available. Twelve long-term and twelve multigenerational studies are examined. This review highlights the knowledge generated by these recently published studies to evaluate the possible existence of long-term health effects. The necessity to renew the current regulatory designs will also be discussed.
Section snippets
Material and methods
For this systematic review, 55 peer-reviewed references were identified from our database (‘BergeRicrochGMLibrary’; Ricroch et al., 2010), which includes 32,000 references on transgenic plants, collected since 1996, using the keywords “GM plant”, “health”, “long term” and “multigenerational”. Studies that were neither multigenerational nor longer than 96 days (OECD protocols + 10%), nor concerning animal feeding trials were discarded.
The duration and number of generations in every study concerned
90-day feeding studies
Based on the EFSA (2008) review, we referenced the 90-day studies using GM feed for which long-term or multigenerational studies were conducted (Table 1). Eight 90-day feeding trials conducted using transgenic maize, rice and soybean were performed on rats. The five studies using maize (Hammond et al., 2004, Hammond et al., 2006a, Hammond et al., 2006b, Mackenzie et al., 2007, Malley et al., 2007) found no differences between the diets containing GM material and the ones which did not. These
Discussion
General principles outlined in the OECD Test Guideline (1998) or discussed by EFSA (2008) have been built or adjusted to get a robust evaluation for the safety of GM-based diet in a case-by-case basis. These are based on i) the substantial equivalence principle, the use of which is intended to compare chemical composition in macro and micro nutrients and known anti-nutrients and natural toxicants of GM lines and near unmodified isogenic lines, and ii) the toxico-nutritional response of animals
Conclusion
Long-term and multigenerational studies have been used as part of exploratory fundamental research projects. Up to now, none of them have provided supplementary information indicating that 90-day rodent feeding studies defined by the Guideline No. 408 (OECD, 1998) would not be sufficient to serve as a sound experimental basis for regulatory assessment of new GM traits. Indeed, only the 90-day rodent feeding studies are recommended in some specific cases to detect any hazard as discussed
Conflict of Interest
The authors declare that there are no conflicts of interests.
Funding source
The French National Center for Scientific Research (CNRS), AgroParisTech (Ministry of Agriculture, Food and Rural Affairs) and the University Paris-Sud, France, provided financial support for the preparation of the article.
Acknowledgments
This paper is dedicated to the memory of our colleague and co-author, Dr. Jean-Baptiste Bergé, who recently passed away. We are grateful to Erika Roach for the English revision of this manuscript.
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