Scientist's rebut of critique of Bt toxin in human blood supply study
Aris A, Leblanc S. Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada. Reproductive Toxicology. 2011; 31(4).
Kuntz's critique of Aris and Leblanc's study was re-published by David Tribe on the Biofortified website:
In the exchange below, Marcel Kuntz's comments are indicated by the initials MK and the scientist's comments are indicated by the initials SC.
Scientist's rebut of Kuntz critique of Aris and Leblanc's study on Bt toxin in human blood
MK: A publication lacking credibility
Only claims of Aris and Leblanc on Cry1Ab are discussed here for the time being.
The Cry1Ab protein is produced by some Bt cotton and corn (e.g. MON810). Aris and Leblanc claim they detected this protein in 93% of pregnant women and 69% of non-pregnant women tested and believe that this is linked to the consumption of foods derived from Bt varieties, which in Canada must mean corn rather than cottonseed oil.
Surprisingly, the authors do not consider that the origin of Cry1Ab could be food from organic farming (which sprays Cry1Ab, or bacteria producing it, on fruit or vegetable crops) or from its use in gardening (CryA1b is part of available "natural insecticide" formulations).
SC: True, there is no guarantee, that the Bt toxin comes from GM food. However, if it is detected in the serum, it must come from somewhere. ALL GM CROPS CONTAINING BT TOXIN(S) were realised on the basis that Bt toxin degrades quickly in the alimentary canal – never mind the origin. The most important outcome of the study that Bt toxin does not degrade in the alimentary canal. It is taken up into circulation and is distributed to all organs. If the Bt toxin comes from natural insecticidal formulation, then not only is the safety of Bt toxin GM crops in question, but that of formulations containing Bt.
MK: If we examine the possibility of a Bt corn food origin for Cry1Ab, since these proteins do not bioaccumulate, it is necessary to consider recent consumption.
SC: Bt toxins are lectins. Lectins are proteins which bind to specific sugar structures. The surface of cells contain sugar structures which are able to bind lectins. Therefore, lectins are nature's natural tools for cell to cell communication. Most plants contain lectins. The major characteristics of plant lectins are their ability to bind and exert a biological function, and their resistance to degradation in the alimentary canal, although they are readily degradable in in vitro digestibility tests, as with phytohaemagglutinin. The Bt toxin family belongs to the family of AB-type toxins. This group of proteins contain molecules, which are formed by the connection of two protein subunits: one subunit is responsible for binding (this is the lectin); the other subunit is the toxin.
Therefore, it is very feasible that these molecules are able to bind to the gut wall, and then to serum proteins, and [that they] bioaccumulate there, since they are pretty resistant to degradation in vivo.
Therefore the answer for the two very naive questions below is a definite YES!
MK: First question: do 93% of pregnant women in Canada actually consume corn almost daily?
Second question: are the values in blood reported by Aris and Leblanc consistent with the levels present in Bt corn kernels? The answer is no. Here is why:
The authors reported average values of 0.19 nanograms per milliliter (ng / ml) of blood from pregnant women. Knowing that, in corn MON810 for example, levels of Cry1Ab in the grain are between 190 and 390 ng / g fresh weight, assuming that 1% will pass into the blood (which is on the high side taking into account losses during corn storage, cooking, gastric digestion and the intestinal barrier), this would require a woman of 60 kg to consume 120 g of corn (for the mean blood value of 0,19 ng / ml, assuming a plasma volume of 2.5 liters) and about 1.5 kg (for the maximum reported blood values of 2.28 ng / ml), which seems unrealistic ... And even more if one takes into account all extracellular fluids (10 liters, which would imply an average consumption of 490 g of corn and 5.8 kg in order to reach the maximum value in blood).
Third question (which follows logically the above-mentioned findings): is the Cry1Ab detection method used by Aris and Leblanc reliable?
Note first that the test used, marketed by Agdia, is claimed to detect the protein Cry1Ab from 1 ng / ml (read the introduction to this article). While Aris and Leblanc claim to have detected average concentrations lower than the detection limit, e.g. 0.04 ng / ml in umbilical cords!
SC: In their paper the authors give a calibration curve from 0.1-10 ng/ml. Let's give them the benefit of the doubt that they actually did it. Therefore, the values between NOT DETECTABLE to 1.5 ng/ml (MEAN : 0.19±0.30 ng/ml, a calculated value) and from NOT DETECTABLE to 0.14 ng/ml (MEAN: 0.04±0.04ng/ml, a calculated value) shoud be easily readable from the calibration curve with reasonable safety.
MK: One can cite the publication by Lutz et al. (J. Agric. Food Chem. 2005, 53 (5) :1453-6) showing that the ELISA test used by Aris and Leblanc is not sufficient to guarantee the identity of positive signals (« to avoid misinterpretation, samples tested positive for Cry1Ab protein by ELISA should be reassessed by another technique »).
Note that Aris and Leblanc did not discuss this issue, nor the results of Chowdhury et al. (J. Animal Sci., 2003, 81:2546-2551) which indicate that these ELISAs do not work for blood (from pigs).
SC: THEY [these authors] SAY IT DID NOT WORK IN THEIR CASE! ANYWAY, THIS WAS NOT BLOOD, BUT SERUM.
MK: Moreover, they do not cite the publication by Paul et al. (Analytica Chimica Acta 2008, 607: 106-113) that discusses the validity of the tests available on the market...
(Provisional) answers to the questions that arise: in the absence of the validation of the detection of Cry1Ab, it is likely that the authors, incorrectly, conclude that any signal was indicative of the presence of the Cry1Ab protein, whereas they most likely correspond to false positives.
SC: FALSE POSITIVES DO NOT COME BY IN 69-93% FREQUENCY!
MK: A possible validation, which surprisingly is lacking in the work of Aris and Leblanc, is the electrophoretic separation of plasma proteins and immunodetection of the protein Cry1Ab ('Western blot', a common laboratory technique).
It therefore appears that this publication, in its present state, is of unsufficient quality to be convincing. It has not undergone a proper review process according to the standards of a scientific journal, which would have required the validation of the results and their discussion in relation to available literature.
SC: The criticism of asking for proper review process according to the standards of a scientific journal is quite surprising, since this paper had gone through peer review and was published in a scientific journal, after answering editorial questions, as it is indicated by the dates: "received 29 June 2010, received in revised form26 January 2011, Accepted 13 February 2011."
There are several ways to do things, even experiments. As the saying goes, there is more than one way to skin a cat!