of new methods for safety evaluation of transgenic food crops
The ability to manipulate the genetic material of crop plants through
recombinant DNA technology may lead to food products with novel traits.
The majority of gene transfer work has been performed on Bacillus thuringiensis
(Bt) cry genes which convey resistance against pests such as Lepidoptera
insects. Genetically modified organisms should be handled carefully and
the putative hazards and risks should be carefully studied before their
The objectives of this project were to study safety issues related to
(i) the nutritional and toxicological consequences of inserted gene products,
(ii) the potential of pleiotropic (unintended) effects in the host organism
due to insertion, (iii) the allergenicity of expressed proteins and novel
foodstuffs and (iv) the potential of gene transfer to human and animal
Approach and methodology
We designed a strategy combining analytical in vitro and in
vivo toxicological methods. The work consisted of (i) isolation of
Bt-proteins from transgenic crops, (ii) development of methods to assess
posttranslational modification differences, (iii) development of chemical
fingerprint analysis to identify unintended effects, (iv) in vitro
toxicological profiling of Bt-proteins and (v) application of the Brown
Norway rat model for allergenicity testing. We studied the Bacillus
thuringiensis (Bt) cry genes (e.g. Cry1Ab5.PGS1 and
Cry9C.PGS2) in cauliflower, corn and tomato varieties together
with marker gene proteins (e.g. NPTII, PAT).
Main findings and outcome
Immunocytochemical screening revealed no interactions of the Cry proteins
with receptors in the gut of rodents and primates, including humans. Repeated
dose feeding studies (28-days) in rodents showed that the proteins Cry1Ab5,
NPTII and PAT are digested very rapidly and are unlikely to present a
health risk for humans. The Cry9C protein resisted proteolysis in the
stomach but showed a low bioavailability in rats and did not cause acute
or systemic toxic effects. In the Brown Norway rat model, the Cry9C protein
and related modified crops (e.g. corn) are capable of eliciting an IgE
reaginic (antibodies associated with allergy) response under 'worse-case'
conditions, but its potential as a human allergen is not proven as yet.
No major changes were observed in the agronomic and resistance characteristics
of greenhouse and field-tested crops, nor in the food processing characteristics
of the Bt-tomato expressing the Cry1Ab5 and NPTII proteins. The Cry1Ab5
protein isolated from Bt-tomato fruit appeared to be glycosylated unlike
the E. coli equivalent. We analysed the unintended effects of gene
insertion by chemical fingerprinting techniques in conjunction with conventional
chemical analysis of critical nutrients and key natural plant toxins.
No significant changes were observed in key nutrients, a-tomatine, metabolite
and N-glycan composition between Bt-crops and their non-modified counterparts.
Thus initial results suggest that the Bt-tomato variety expressing the
Cry1Ab5 protein is as safe as its traditionally bred counterpart when
consumed on a regular basis.
Progress has been made with the development of the principle of substantial
equivalence by establishing a hierarchy of comparisons, including
the choice of comparators and appropriate statistical analysis. Application
of these technologies improves current analytical testing of single compounds
and complements and will eventually reduce animal feeding studies. The
present approach provides a sound scientific basis for the evaluation
of the food safety of genetically modified Bt-crop plants and derived
foodstuffs. The technologies developed and the results obtained may serve
as general framework for testing the safety and nutritional value of genetically
modified crop plants.
Lommen A., Weseman J.M., Smith G.O., Noteborn H.P.J.M., "On
the detection of environmental effects on complex matrices combining
off-line liquid chromatography and 1H-NMR".
Biodegradation, 9, 1998, pp. 513-525.
H.P.J.M., Lommen A., van der Jagt R.C., Weseman J.M., "Chemical
fingerprinting for the evaluation of unintended secondary metabolic
changes in transgenic food crops".
Biotechnology, 77, 2000, pp. 103-114.
H.P.J.M., Bienenmann-Ploum M.E., van den Berg J.H.J., Alink G.M.,
Zolla L., Reynaerts A., Pensa M. and Kuiper H.A., "Safety assessment
of the Bacillus thuringiensis insecticidal crystal protein
Cry1A(b) expressed in transgenic tomatoes", in Genetically
Modified Foods. Safety Issues, Engel K.-H., Takeoka G.R., Teranishi
R. (eds.), ACS Symposium Series 605, Washington DC, 1995, pp. 134-147.
R, Altmann F, Praznik W., "Structural characterization of the
N-linked oligosaccharides from tomato fruit".
Phytochemistry, 51, 1999, pp. 199-210.
Atkinson H.A.C., Meredith C., "Assessment of allergenic potential
of novel proteins in food crops using the brown Norway rat model",
in Proceedings 3rd Karlsruhe Nutrition Symposium: European research
towards Safer and Better Food Part 1, Gaukel V, Spiess W.E.L.
(eds.), Bundesforschungsanstalt für Ernährung, Karlsruhe,
Germany, 1998, pp. 70-75.
January 1995 - May 1998
State Institute for Quality Control of Agricultural Products (RIKILT)
Aventis CropScience N.V.
Vrije Universiteit Brussel
Institute for Agrobiotechnology (IFA)
BIBRA Toxicology International