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EC-sponsored Research on Safety of Genetically Modified Organisms - A Review of Results
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image Opportunities of transgenic food crops for the consumer and the food industry in the Community

Background and objectives

The main objective of the project was the analysis of the food quality of transgenic crops and their derivatives. The two different aspects to be analysed in detail were agronomic and processing quality and food safety. Transgenic tomato was chosen as a model crop.

We were primarily interested in analysing the insect resistance trait encoded by the Cry1Ab gene. However, as most, if not all, transgenic plants will, in addition to the trait of interest, also contain and express selectable marker genes which are necessary for the identification of transgenic cells in vitro, we have also included in the study one of the most frequently used examples of such genes, namely, neo (NPTII).

  image image On the right: tomatoes containing the
Bt gene.

On the left: control tomatoes.


Approach and methodology

Production and analyses of transgenic tomatoes

Based on greenhouse evaluations, two transgenic lines were chosen for the agronomic evaluation of the crop in the field. A field trial was done during the 1993 season in Piana di Monte Verna (Caserta, Italy). The harvested fruit was used for two purposes. Part was used for the preparation of different types of processed products: peeled tomatoes, chopped tomatoes and tomato concentrate. The remaining part of the harvest was concentrated by freeze-drying and used in a feeding trial. The composition of the freshly harvested tomatoes, including parameters important for processing such as percentage dry matter, pH and sugar content, was determined. Expression levels of Cry1Ab and neo were measured. Relevant chemical and physicochemical data, as well as Cry1Ab and NPTII content, were also determined on the processed products.
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Safety assessment

The safety assessment focused on the analysis of proteins purified from recombinant over-expressing micro-organisms. As Cry1Ab has known toxic effects in insects, emphasis was placed on studying this protein. Less exhaustive treatment of the marker protein was performed. A series of in vitro characteristics of the proteins were measured and the potential in vivo effects were estimated. This strategy was designed to answer the following questions:

Do the newly introduced proteins cause general toxic effects in mammals?

To answer this question both in vitro and in vivo approaches were designed. Degradation of the proteins was followed in the presence of digestive enzymes (pepsin, trypsin and chymotrypsin) in simulated conditions of the gastrointestinal tract. Digestibility of Cry1Ab has also been studied in vivo through feeding of unique high doses of Cry1Ab protein. General toxic effects were, in addition, analysed by short-term oral feeding in rats and rabbits. Effects on blood cells and human cell lines were also studied.

Does the introduced Cry1Ab protein show specific toxic effects in mammals similar to the effect observed in insects?

This analysis was based on the observation that the first step in the interaction between Bacillus thuringiensis insecticidal crystal proteins and the target insects consists in the interaction of the protein with specific receptors. Different tissues of the gastrointestinal tract of rodents and primates, including humans, were screened for the presence of receptors to these toxins.

Does the genetic modification of the tomato result in changes in nutrient content and the presence of naturally occurring toxins?

Lyophilised powders of tomatoes harvested were submitted to a detailed analysis. Beside the content of the newly introduced protein, total protein content, fat, carbohydrate, fibre, vitamin C and mineral content were compared. The lyophilised tomato powders were also mixed with rat feed at a concentration of 10 % and were used in a 90-day feeding trial.

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Main findings and outcome

No differences have been found between the characteristics of both transformants and their non-transgenic counterparts in fresh or processed products. Both Cry1Ab and NPTII proteins are unstable in simulated gastrointestinal conditions. They degrade into fragments with molecular weights below 10 kDaltons. The toxic effect of Cry1Ab on insects is highly specific and no specific receptors were found along the gastrointestinal tract of mammals. In addition, no histopathological effects were found upon ingestion of Cry1Ab by mammals. Orally administrated Cry1Ab does not exert adverse systemic effects in rats or mice. No indications of immunotoxic effects were found upon histological examination of lymph nodes, spleen and Peyer's patches of treated animals. In addition, no specific antibodies against Cry1Ab could be detected, nor was there a general increase in total IgG. No haemolytic potency of Cry1Ab was observed in in vitro experiments.

No major changes were observed in the chemical composition of transgenic tomatoes as a result of the insertion of the novel genes. Transgenic tomato powders mixed into the rat diet had no adverse effect on the development of the animals. The average daily intake of tomato powders corresponded to a daily human consumption of 13 kg fresh tomatoes. Food intake, body and organ weights were normal and examination of the tissues showed no indications of toxic effects.


Conclusions

It is strongly suggested that neither NPTII nor Cry1Ab presents major risks to the consumer in food, even at elevated concentrations.

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imageResearch project
 

Contract number
AGRF-CT90-0039

Period
April 1991 - March 1994

Coordinator
A. Reynaerts
Aventis CropScience N.V.
Gent (BE)

Project website address
http://exp.hispeed.com/
index.html


Follow-up of the project
This project was continued in EC project: AIR3-CT94-2311.

 
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Partners

G. Malgarini
SME Ricerche S.c.p.A.
Piana di Monte Verna (IT)

H.A. Kuiper
State Institute for Quality Control of Agricultural Products (RIKILT)
Wageningen (NL)

G. Venturi
Università degli Studi di Genova (IT)

 
 
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