March 14 - 15, 2006 Charge / Question to the Panel
March 14-15, 2006 FIFRA Scientific Advisory Panel Regarding Scientific Issues Associated with MIR604 Modified Cry3A Protein Bt Corn Human Health and Environmental Assessments - Questions to the Panel
MIR604 Environmental Assessment
1. The weight of evidence from the reviewed data indicates that there will not be a hazard to wildlife from the commercialization of Event MIR604 corn. Although the mCry3A protein expressed by Event MIR604 corn is known to affect only coleopteran insect species, EPA assessed the potential risks, to a wide variety of non-target organisms ( i .e. mammals, birds, fish, invertebrates and plants), that could potentially result from exposure to this Bt protein. The emphasis of this non-target risk assessment, however, was on invertebrate species that dominate corn agroecosystems. The Agency also evaluated a soil fate study that was intended to provide information on the persistence and rate of degradation of mCry3A protein in the soil environment. After reviewing data submitted in support of the Event MIR604 Bt corn registration, EPA concluded that aquatic and terrestrial wildlife, including soil organisms, were not likely to be adversely affected and that this Bt corn product is not likely to threaten the long-term survival of any non-target wildlife populations.
The Panel is requested to comment on the Agency's analysis of the currently available data on the potential impacts of Event MIR604 corn on non-target species.
MIR604 Human Health and Characterization
(1) Previously submitted studies for Event MIR604 demonstrated the equivalence of the plant- and bacterial- produced test substances by showing similar molecular weights, purity of 90.3%, a lack of post-translational glycosylation of mCry3A from either source, and comparable toxicities toward western corn rootworm (WCRW). However, two forms of mCry3A (designated as mCry3A-sf and mCry3A-lf) were found in the bacterial-produced test material (MCRY3A-0102). The molecular weights of the short and long form of mCry3A were 67.5 kDa and 69.1 kDa, respectively, determined via SDS-PAGE and MALDI-TOF Mass spectrometry. The lesser of the two components, with the lower molecular weight, corresponded to the intended mCry3A protein with 598 amino acids. The other component contained the same 598 amino acids as the first component but also contained an additional 16 amino acids at the N-terminal end of the protein. Both mCry3A forms were insecticidally active against WCRW. On this basis, and taking into account the high degree of structural homology (97.4% amino acid identity), the two forms of mCry3A in test material MCRY3A-0102 were considered to be equivalent.
Please comment on the Agency's conclusion that the mCry3A proteins from corn event MIR604 and from recombinant E. coli are substantially the same for the purpose of the Agency's risk assessment; and that the equivalence is confirmed for the two forms of the bacterial-produced mCry3A test material (MCRY3A-0102).
(2) Previously submitted studies demonstrated the lack of toxicity of the mCry3A protein following acute oral high-dose exposure to mice, rapid degradation of mCry3A upon exposure to simulated mammalian gastric fluid, and the lack of significant amino acid sequence homology of the mCry3A protein to proteins known to be mammalian toxins or human allergens. Moreover, little to no human dietary exposure to mCry3A protein is expected to occur via transformed corn. Therefore, dietary exposure to mCry3A is not anticipated to pose any dietary risk to the U.S. population.
Please comment on the Agency's conclusions regarding the lack of mammalian toxicity and allergenicity of mCry3A.