Persistence of plant DNA sequences in the blood of dairy cows fed with genetically modified (Bt176) and conventional corn silage.
J. Agric. Food Chem.. 2009-01-05; 57(2): 509-516
DOI: 10.1021/jf802262c
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To determine whether plant sequences, including transgenic sequences, are present
in animal blood, we tested blood samples from Holstein cows fed with either Bt176
genetically modified corn or conventional corn. We used previously described
sensitive real-time PCR assays targeting transgenic sequences (35S promoter and
Bt176 specific junction sequence), a monocopy maize-specific sequence (ADH
promoter), and two multicopy sequences from plant nucleus (26S rRNA gene) and
chloroplast (psaB gene). The presence of Cry1A(b) protein in bovine blood samples
was also tested using a sandwich ELISA kit. Our study shows the ability of plant
nuclear and/or chloroplast DNA fragments to enter bovine blood circulation.
However, maize nuclear DNA, both mono- and multicopy sequences, was less detected
than chloroplast DNA, probably because the higher number of chloroplast copies
and also possibly because nuclear DNA might be less protected by the nuclear
membrane. Despite our data confirm the ability of small (ca.150 bp) plant DNA
fragments to cross the intestinal barrier, we were unable to demonstrate clearly
the presence of transgenic DNA or proteins in bovine blood. No sample tested
positive with the two real-time PCR assays targeting transgenic sequences (35S
promoter and Bt176 specific junction sequence). Only faint punctual positive
results occurred randomly and were probably due to postsample collection or
laboratory contamination or can be considered as artifact as they have never been
confirmed. Our data highlight the difficulties to detect transgenic sequences in
blood of dairy cows fed genetically modified corn (Bt176) silage. Those results
show that in order to meet the consumers’ demand of animals fed with GM products
there is currently no cost-effective analytical procedure to replace documentary
traceability.