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

ArticleinJournal of Applied Toxicology 33(7) · July 2013with213 Reads
DOI: 10.1002/jat.2712
Abstract
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
    • "Indeed, it has been documented that activated Cry toxin interacts with the midgut epithelium of susceptible insects to form pores in the mem-brane that lead to the killing of specific insect targets via osmotic shock (Bravo et al., 2011; Zavala et al., 2011). In contrast, the direct biological effects of Cry proteins in mammalian cells have been rarely explored, but it has been argued that Cry1Ab and Cry1Ac do not appear to be inert in human fibroblasts and exert certain combinatory actions (Mesnage et al., 2013). In view of the described immunogenic properties of Cry1Ac and knowing that it is expressed in the form of a toxin in transgenic plants for human consumption (Rubio-Infante and Moreno-Fierros, 2016), we considered it important to determine if Cry1Ac exerts direct effects in immune system cells and to perform studies aimed at understanding the cellular bases of such effects. "
    [Show abstract] [Hide abstract] ABSTRACT: The Cry1Ac toxin from Bacillus thuringiensis is used commercially as a bio-insecticide and is expressed in transgenic plants that are used for human and animal consumption. Although it was originally considered innocuous for mammals, the Cry1Ac toxin is not inert and has the ability to induce mucosal and systemic immunogenicity. Herein, we examined whether the Cry1Ac toxin promotes macrophage activation and explored the signalling pathways that may mediate this effect. Treatment of primary and RAW264.7 macrophages with the Cry1Ac toxin resulted in upregulation of the costimulatory molecules CD80, CD86 and ICOS-L and enhanced production of nitric oxide, the chemokine MCP-1 and the proinflammatory cytokines TNF-α and IL-6. Remarkably, the Cry1Ac toxin induced phosphorylation of the mitogen-activated protein kinases (MAPKs) ERK1/2, JNK and p38 and promoted nuclear translocation of nuclear factor-kappa B (NF-κB) p50 and p65. p38 and ERK1/2 MAPKs were involved in this effect, as indicated by the Cry1Ac-induced upregulation of CD80 and IL-6 and TNF-α abrogation by the p38 MAPK inhibitor SB203580. Furthermore, treatment the MEK1/2 kinase inhibitor PD98059 blocked increases in MCP-1 secretion and augmented Cry1Ac-induced ICOS-L upregulation. These data demonstrate the capacity of the Cry1Ac toxin to induce macrophage activation via the MAPK and NF-κB pathways.
    Article · Jul 2016
    • "Given the frequency of spray applications using glyphosate, nasal inhalation exposure to the spray is extremely likely to occur. While there are no current reports regarding potential glyphosate toxicities following nasal inhalation, studies in cell culture (Slaninova et al., 2009; Koller et al., 2012; Mesnage et al., 2013; Prevot-D'Alvise et al., 2013) have suggested potential toxicities to several human cell types, including those obtained from the buccal, nasal, and lower gastrointestinal tract, and other investigations have demonstrated toxicity to the olfactory systems of several species of fish (Slaninova et al., 2009; Solomon et al., 2013). Although glyphosate itself has been shown to be extremely safe in humans following dermal exposure, toxicities from commercial products have been reported to be induced by the excipients contained in the products, especially the surfactants used to improve the permeability of glyphosate across plant cell walls (Gasnier et al., 2009; Allen and Levy, 2013). "
    [Show abstract] [Hide abstract] ABSTRACT: Glyphosate is one of the most commonly used herbicides worldwide due to its broad spectrum of activity and reported low toxicity to humans. Glyphosate has an amino acid-like structure that is highly polar and shows low bioavailability following oral ingestion and low systemic toxicity following intravenous exposures. Spray applications of glyphosate in agricultural or residential settings can result in topical or inhalation exposures to the herbicide. Limited systemic exposure to glyphosate occurs following skin contact, and pulmonary exposure has also been reported to be low. The results of nasal inhalation exposures, however, have not been evaluated. To investigate the mechanisms of glyphosate absorption across epithelial tissues, the permeation of glyphosate across Caco-2 cells, a gastrointestinal epithelium model, was compared with permeation across nasal respiratory and olfactory tissues excised from cows. Saturable glyphosate uptake was seen in all three tissues, indicating the activity of epithelial transporters. The uptake was shown to be ATP and Na(+) independent, and glyphosate permeability could be significantly reduced by the inclusion of competitive amino acids or specific LAT1/LAT2 transporter inhibitors. The pattern of inhibition of glyphosate permeability across Caco-2 and nasal mucosal tissues suggests that LAT1/2 play major roles in the transport of this amino-acid-like herbicide. Enhanced uptake into the epithelial cells at barrier mucosae, including the respiratory and gastrointestinal tracts, may result in more significant local and systemic effects than predicted from glyphosate's passive permeability, and enhanced uptake by the olfactory mucosa may result in further CNS disposition, potentially increasing the risk for brain-related toxicities.
    Full-text · Article · Feb 2016
    • "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. "
    [Show abstract] [Hide abstract] 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.
    Full-text · Article · Apr 2015
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