THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
Dear Friends and Colleagues
Serious Lack of Scientific Data on the Effects of Bt toxins
Two new studies shed further light on the Cry toxins from Bacillus thuringiensis (Bt), which are used in genetically modified (GM) insect-resistant crops.
The first study looks at the combinatorial effects of Cry toxins in stacked GM crops. Currently, there are no operational guidelines for testing procedures on how possible interactions of the toxins can be assessed in a risk assessment. The researchers found that the current knowledge on modes of action for Bt toxins is “clearly incomplete”, largely based on one laboratory study with a target pest species using a minimal combination of microbial Cry toxins. They also found that current measurements of efficacy were bound to result in sub-lethal and chronic effects being overlooked.
The second study summarizes the relevant information currently available regarding the biosafety and biological effects that Bt and its insecticidal Cry proteins elicit in mammals. The researchers discuss experimental studies performed on humans, mice, rats and sheep as well as in diverse mammalian cell lines. They find that some of the studies reviewed have demonstrated the capacity of these toxins to activate the immune system, which could produce allergic responses.
The researchers recommend expanding the parameters for evaluating the toxicity of Cry proteins beyond just the general aspects to more comprehensive examination of the systems, organs, tissues and cells, especially the gastrointestinal tract, the immune system, the genitourinary tract and the respiratory and nervous systems. They call for further studies on the sub-chronic, chronic and immunotoxicological effects of Cry toxins, particularly on humans.
The abstracts of both papers are reproduced below.
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Item 1
SPECIFICITY AND COMBINATORIAL EFFECTS OF BACILLUS THURINGIENSIS CRY TOXINS IN THE CONTEXT OF GMO ENVIRONMENTAL RISK ASSESSMENT
Angelika Hilbeck and Mathias Otto
Front. Environ. Sci., 2015 | http://dx.doi.org/10.3389/fenvs.2015.00071
journal.frontiersin.org/article/10.3389/fenvs.2015.00071/pdf
Stacked GM crops expressing up to six Cry toxins from Bacillus thuringiensis (Bt) are today replacing the formerly grown single-transgene GM crop varieties. Stacking of multiple Cry toxins not only increase the environmental load of toxins but also raise the question on how possible interactions of the toxins can be assessed for risk assessment, which is mandatory for GM crops. However, no operational guidelines for a testing strategy or testing procedures exist. From the developers point of view, little data testing for combinatorial effects of Cry toxins is necessary as the range of possibly affected organisms focuses on pest species and no evidence is claimed to exist pointing to combinatorial effects on non-target organisms. We have examined this rationale critically using information reported in the scientific literature. To do so, we address the hypothesis of narrow specificity of Cry toxins subdivided into three underlying different conceptual conditions (i) “efficacy” in target pests as indicator for “narrow specificity,” (ii) lack of reported adverse effects of Cry toxins on non-target organisms, and (iii) proposed modes of action of Cry toxins (or the lack thereof) as mechanisms underlying the reported activity/efficacy/specificity of Cry toxins. Complementary to this information, we evaluate reports about outcomes of combinatorial effect testing of Cry toxins in the scientific literature and relate those findings to the practice of environmental risk assessment of Bt-crops in general and of stacked Bt-events in particular.
Item 2
AN OVERVIEW OF THE SAFETY AND BIOLOGICAL EFFECTS OF BACILLUS THURINGIENSIS CRY TOXINS IN MAMMALS
Néstor Rubio-Infante and Leticia Moreno-Fierros
J Appl Toxicol. 2015 doi: 10.1002/jat.3252
http://www.ncbi.nlm.nih.gov/pubmed/26537666
Abstract
Crystal proteins (Cry) produced during the growth and sporulation phases of Bacillus thuringiensis (Bt) bacterium are known as delta endotoxins. These toxins are being used worldwide as bioinsecticides to control pests in agriculture, and some Cry toxins are used against mosquitoes to control vector transmission. This review summarizes the relevant information currently available regarding the biosafety and biological effects that Bt and its insecticidal Cry proteins elicit in mammals. This work was performed because of concerns regarding the possible health impact of Cry toxins on vertebrates, particularly because Bt toxins might be associated with immune-activating or allergic responses. The controversial data published to date are discussed in this review considering earlier toxicological studies of B. thuringiensis, spores, toxins and Bt crops. We discussed the experimental studies performed in humans, mice, rats and sheep as well as in diverse mammalian cell lines. Although the term ’toxic‘ is not appropriate for defining the effects these toxins have on mammals, they cannot be considered innocuous, as they have some physiological effects that may become pathological; thus, trials that are more comprehensive are necessary to determine their effects on mammals because knowledge in this field remains limited.