Cytotoxicity on human cells of Cry1Ab and Cry1Ac Bt insecticidal toxins alone or with a glyphosate-based herbicide

University of Caen, Risk Pole MRSH-CNRS, Laboratory of Biochemistry EA2608, Esplanade de la Paix, 14032, Caen cedex, France
Journal of Applied Toxicology (Impact Factor: 2.98). 07/2013; 33(7). DOI: 10.1002/jat.2712


The study of combined effects of pesticides represents a challenge for toxicology. In the case of the new growing generation of genetically modified (GM) plants with stacked traits, glyphosate-based herbicides (like Roundup) residues are present in the Roundup-tolerant edible plants (especially corns) and mixed with modified Bt insecticidal toxins that are produced by the GM plants themselves. The potential side effects of these combined pesticides on human cells are investigated in this work. Here we have tested for the very first time Cry1Ab and Cry1Ac Bt toxins (10 ppb to 100 ppm) on the human embryonic kidney cell line 293, as well as their combined actions with Roundup, within 24 h, on three biomarkers of cell death: measurements of mitochondrial succinate dehydrogenase, adenylate kinase release by membrane alterations and caspase 3/7 inductions. Cry1Ab caused cell death from 100 ppm. For Cry1Ac, under such conditions, no effects were detected. The Roundup tested alone from 1 to 20 000 ppm is necrotic and apoptotic from 50 ppm, far below agricultural dilutions (50% lethal concentration 57.5 ppm). The only measured significant combined effect was that Cry1Ab and Cry1Ac reduced caspases 3/7 activations induced by Roundup; this could delay the activation of apoptosis. There was the same tendency for the other markers. In these results, we argue that modified Bt toxins are not inert on nontarget human cells, and that they can present combined side-effects with other residues of pesticides specific to GM plants. Copyright

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    • "Moreover, almost all i.p. treatments promoted a significant increase in MN-PCE, as well as reducing the cell proliferation index in the bone marrow, confirming the above suggestion of cytotoxicity and also suggesting a possible genotoxicity for the i.p. route, not previously detected in the oral route (Mezzomo et al., 2013). This genotoxic result could be at least partially explained by the findings of Mesnage et al. (2013), which observed that Cry1Ab and Cry1Ac reduced caspases 3/7 activations on human embryonic kidney cell line 293, suggesting that this could delay the activation of apoptosis (Mesnage et al., 2013). Also, we cannot rule out that an i.p. injection may produce hepatic and renal toxicity, while the oral administration did not. "
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    ABSTRACT: Bacillus thuringiensis (Bt) has been widely used in foliar sprays as part of integrated pest management strategies against insect pests of agricultural crops. Since the advent of genetically modified plants expressing Bt δ-endotoxins, the bioavailability of Cry proteins has increased, and therefore for biosafety reasons their adverse effects should be studied, mainly for nontarget organisms. We evaluated, in Swiss mice, the hematotoxicity and genotoxicity of the genetically modified strains of Bt spore crystals Cry1Aa, 1Ab, 1Ac, or 2Aa at 27 mg/kg, and Cry1Aa, 1Ab and 2Aa also at 136 and 270 mg/kg, administered with a single intraperitoneal injection 24 h before euthanasia. Controls received filtered water or cyclophosphamide. Blood samples collected by cardiac puncture were used to perform hemogram, and bone marrow was extracted for the micronucleus test. Bt spore crystals presented toxicity for lymphocytes when in higher doses, which varied according to the type of spore crystal studied, besides promoting cytotoxic and genotoxic effects for the erythroid lineage of bone marrow, mainly at highest doses. Although the profile of such adverse side effects can be related to their high level of exposure, which is not commonly found in the environment, results indicated that these Bt spore crystals were not harmless to mice. This suggests that a more specific approach should be taken to increase knowledge about their toxicological properties and to establish the toxicological risks to nontarget organisms. © 2015 Wiley Periodicals, Inc. Environ Toxicol, 2015. © 2015 Wiley Periodicals, Inc.
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    • "It has been widely reported by scientific literature that Bt Cry toxins do not cause adverse effects to mammalian cells, since they do not possess specific receptors for Cry proteins binding [10] [11] [12]. On the other hand, studies have contested the innocuous nature of these proteins and some equivalent receptors have also been described to mammalian cells [13] [14]. Furthermore, it is widely known the antimicrobial property of Bt Cry toxins, which raises a concern about the effects of these proteins upon the microbiota of mammals gastrointestinal tract, whether monogastric or ruminants [15] [16] [17]. "
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    ABSTRACT: Studies have contested the innocuousness of Bacillus thuringiensis (Bt) Cry proteins to mammalian cells as well as to mammals microbiota. Thus, this study aimed to evaluate the cytotoxic and antimicrobial effects of two Cry proteins, Cry8Ka5 (a novel mutant protein) and Cry1Ac (a widely distributed protein in GM crops). Evaluation of cyto- and genotoxicity in human lymphocytes was performed as well as hemolytic activity coupled with cellular membrane topography analysis in mammal erythrocytes. Effects of Cry8Ka5 and Cry1Ac upon Artemia sp. nauplii and upon bacteria and yeast growth were assessed. The toxins caused no significant effects on the viability (IC50 > 1,000 µg/mL) or to the cellular DNA integrity of lymphocytes (no effects at 1,000 µg/mL). The Cry8Ka5 and Cry1Ac proteins did not cause severe damage to erythrocytes, neither with hemolysis (IC50 > 1,000 µg/mL) nor with alterations in the membrane. Likewise, the Cry8Ka5 and Cry1Ac proteins presented high LC50 (755.11 and >1,000 µg/mL, resp.) on the brine shrimp lethality assay and showed no growth inhibition of the microorganisms tested (MIC > 1,000 µg/mL). This study contributed with valuable information on the effects of Cry8Ka5 and Cry1Ac proteins on nontarget organisms, which reinforce their potential for safe biotechnological applications.
    BioMed Research International 07/2014; 2014:810490. DOI:10.1155/2014/810490 · 1.58 Impact Factor
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    • "While many genetic modifications represent the grafting of one naturally occurring and routinely encountered gene into a commonly eaten food, others signify what can be thought of as “self-spraying” elements; some GM plants internally produce pesticides or pesticide inhibitors in a manner that holds little functional difference from externally spraying the compound – examples include Bacillus thuringiensis (Bt) producing and glyphosate-resistance plants. Since pesticide-resistance genes tend to encourage increased use of pesticides [204], it is a concerning finding that pesticides like glyphosate induces cellular death in human umbilical, placental, embryonic, and peripheral blood mononuclear cells at physiologic levels [209-211]; further studies will be needed to either confirm or alleviate these concerns. In animal models, the combination of pesticide-producing GM maize and pesticide-resistant GM soy led to increased rates of severe stomach inflammation [212], although GM maize alone did not have significant effects on either inflammation or the make up of the gut microbiome of pigs [213] and direct consumption of high doses of Bt insecticide did not induce acute toxicity in humans or toxicity in mice [214]. "
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