Atlantic salmon fed Bt corn had altered enzyme activity in liver
and intestine as well as altered proportions and numbers of different
white blood cells.
Maize (Zea mays L.).
Inserted Transgene and Intended Effect:
The crylAb gene derived from the bacterium Bacillus
thuringiensis (Bt), which gives the plant the ability to
produce an insecticidal delta-endotoxin and confers resistance to the
European cornborer, Ostrinia nubilalis. The researchers used
Monsanto's commercial variety MON810, known as Bt corn or maize.
Atlantic Salmon (Salmo salar L.).
Goal of This Study:
Investigate whether the health of post-smolt Atlantic salmon is affected
when they are fed genetically modified Bt maize (event MON810) as
a starch source. The study evaluated particular substances as biomarkers
for toxic and immunological stress.
In a 3-month feeding study, post-smolt Atlantic salmon were fed
experimental diets differing in the type of maize used as the only starch
source: genetically modified Bt corn (in this study called GM maize),
an untransformed near-isogenic parental line of Bt corn (in this study
called nGM maize), and commercial suprex maize from Condrico AB, Den
Haag, The Netherlands. There were five experimental diets: control diet
with suprex maize; two nGM maize diets with half (low) or all (high) of
suprex maize replaced with nGM maize; two GM maize diets with half (low)
or all (high) of suprex maize replaced with Gm maize. Low GM maize diet
contained 15% (150g. per kg.) GM maize and the high GM maize diet 30%.
Results of This Study:
The salmon fed GM maize diets had significantly lower activity of the
enzyme catalase (CAT) in the liver and higher activity of the enzyme
superoxide dismutase (SOD) in the liver and distal intestine in comparison
to salmon fed the control or nGM diet.
The salmon fed GM maize diets had significantly higher activity of CAT
in the distal intestine and higher levels of the heat-shock protein 70
(HSP70, which is a protective protein reported to respond to a variety of
stressors) in the liver in comparison to salmon fed the control diet.
There were also changes in the proportions and numbers of the different
kinds of white blood cells. The salmon fed GM maize diets had a
significantly higher proportion of granulocytes and a lower proportion
of lymphocytes in comparison to salmon fed high nGM maize. The sum of
granulocytes and monocytes was also significantly higher. These findings
may indicate "some immune response resulting from the presence of GM maize
in the diet. It might be that the gene modification process has resulted
in the formation of new and unknown proteins that act as weak allergens"
The authors summarize: "Thus, this study has shown that feeding
Atlantic salmon GM maize resulted in small changes in CAT and SOD enzyme
activities in liver and distal intestine, and HSP70 protein level in
liver. These signs were indicative of a mild stress response, but were
not correlated with changes in normalized gene expression of these stress
proteins. Differential leukocyte counts showed altered proportions of
white blood cell populations, suggestive of an immune response taking
place in the blood as a response to the GM maize in the diet" (p. 211).
Sagstad, A., M. Sanden, O. Haugland, A.-C. Hansen et
al. (2007). "Evaluation of Stress- and Immune-Response Biomarkers in
Atlantic Salmon, Salmo salar L., Fed Different Levels of Genetically
Modified Maize (Bt Maize), Compared With its Near-Isogenic Parental
Line and a Commercial Suprex Maize," Journal of Fish Diseases vol. 30,
National Institute of Nutrition and Seafood Research, NIFES, Bergen,
Norway; Department of Basic Sciences and Aquatic Medicine, Norwegian
School of Veterinary Science, Oslo, Norway.
Over half the corn planted in the U.S. in 2006 was Bt corn, and
this corn is commonly fed to farm animals (cattle, pigs, and poultry).
Since farm-raised fish are also fed corn, it is likely that they, too,
are receiving Bt corn.
Copyright 2008 The Nature