. "2. Potential Environmental and Human Health Implications of Pest-Protected Plants." Genetically Modified Pest-Protected Plants: Science and Regulation. Washington, DC: The National Academies Press, 2000.
The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
GENETICALLY MODIFIED PEST-PROTECTED PLANTS: SCIENCE AND REGULATION
sprayed microbial Bt toxins are protoxins, while some Bt plants produce activated toxins.
Information in peer reviewed studies indicates that plant-expressed Bt proteins are probably without human health risk. Nevertheless, a minimal number of properly defined tests are needed to determine if based on plant modification of the proteins, or if based on use of more novel Bt toxins or Bt toxins not found in currently registered microbial products (for example Cry9C), there is a potential impact on human health. Post-transcriptional modification is known to occur in plants and such characteristics as the degree of glycosylation might also affect stability and other physiochemical properties of proteins. Tests should preferably be conducted with the protein as produced in the plant (see also section 3.1.3). However, the committee recognizes that it is often difficult to obtain enough plant-expressed protein; in these cases, the committee recommends that
The EPA should provide clear, scientifically justifiable criteriafor establishing biochemical and functional equivalency when registrantsrequest permission to test non plant-expressed proteins in lieu ofplant-expressed proteins.
The strong likelihood that gene products currently found in commercial transgenic pest-protected plants are not allergens does not remove the need for a minimum of properly planned and executed tests. For example, allergenicity is assumed to be unimportant for many Bt endotoxins, more because of the common characteristics of food allergens than because of rigorous testing. The Cry 1Ab pesticide fact sheet (EPA 1998a) states that
current scientific knowledge suggests that common food allergens tend to be resistant to degradation by heat, acid and proteases, are glycosylated and present at high concentrations in the food. The delta endotoxins are not present at high concentrations, are not resistant to degradation by heat, acid and proteases, and are apparently not glycosylated when produced in plants.
In the case of Cry3A in potatoes (EPA 1995a), the company demonstrated that the endotoxin is not a major component of the food, is apparently not glycosylated in plants, and is digested by gastric enzymes. However, Cry9C toxin, unlike the Cry1A and 3A toxins, does not degrade rapidly in gastric fluids and is relatively more heat-stable (EPA 1998c); these characteristics of Cry9C raise concerns of allergenicity. It is important to note that levels of gastric enzymes may vary among individuals and that those variations may need to be considered.
Although the standard tests indicate nonallergenicity for Cry3A, they