ARCHIVED - Insect-Resistant and Glufosinate-Tolerant Maize (Corn), DBT418

FD/OFB-97-05
June, 1997

Novel Food Information - Food Biotechnology

Health Canada has notified DEKALB Genetics Corporation that it has no objection to the food use of the transgenic maize line DBT418, which is resistant to lepidopteran insects, particularly European Corn Borer,and tolerant to glufosinate herbicides. The Department conducted a comprehensive assessment of DBT418 according to its Guidelines for the Safety Assessment of Novel Foods (September, 1994). These guidelines are based upon internationally-accepted principles for establishing the safety of foods derived from geneticallymodified organisms.

Background:

The following provides a summary regarding the DEKALB Genetics Corporation notification to Health Canada and contains no confidential business information.

1. Introduction

Maize line DBT418 was developed through genetic modification to be resistant to European corn borers and tolerant to glufosinate (also known as phosphinothricin, the active ingredient in the herbicides Basta®, Rely®, Ignite® and Liberty®). The modification will permits farmers to control European corn borer, an important pest in maize, without the use of conventional insecticides and to use glufosinate herbicides for weed control in the cultivation of corn.

2. Development of the Modified Plant

The BBT418 maize line was created by microprojectile bombardment of cultured maize cells (also known as corn or Zea mays L.) with gold particles coated with a plasmid DNA preparation containing the cryIA(c), bar, and pinII genes.

The cryIA(c) gene is a synthetic gene that encodes a protein that is identical to a portion of the naturally occurring Bacillus thuringiensis subsp. Kurstaki CryIA(c) insect control protein. The bar gene which was originally isolated from a common soil bacterium, Streptomyces hygroscopicus, encodes the protein phosphinothricin acetyltransferase (PAT). The pinII gene encodes the protease inhibitor II from potato. Also included on the introduced DNA is the -lactamase gene which encodes resistance to the antibiotic ampicillin. This gene was included as a selectable marker for the development of the introduced DNA in bacteria, but is not functional in plants.

3. Product Information

Expression of the cryIA(c) and bar genes in DBT418 plants result in the expression of the CryIA(c) and PAT proteins, respectively. This occurs in most, but not all, tissues of the corn plant. CryIA(c) and PAT levels are highest in leaves, with lower levels in roots, prop roots, stalk, tassel, cob, husk, and kernels. No CryIA(c) or PAT proteins have been detected in silk or pollen. Stability of expression of CryIA(c) and PAT was demonstrated to be consistent across several generations in several different genetic backgrounds.

The only newly expressed materials in DBT418 are the CryIA(c) and PAT proteins. The pinII gene in DBT418 is truncated and non-functional, while the -lactamase gene is under the control of a bacterial promoter and therefore not functional in DBT418 plants. The CryIA(c) insect control protein provides DBT418 plants with protection from lepidopteran insects and is highly specific for controlling these insects. The PAT protein is an enzyme which is highly specific for glufosinate and is not expected to have any effect on metabolic pathways in the plant other than detoxification of glufosinate herbicides. Agronomic performance and nutritional composition data (see section 5) demonstrated that DBT418 hybrids are comparable to their non-transgenic counterparts.

4. Dietary Exposure

Grain from DBT418 is primarily intended for animal feeding. However, such field corn may be dry- or wetmilled into various processed corn products for human food use. The human food uses of grain from DBT418 plants is not expected to be different from the uses of non-transgenic field corn varieties. As such, the dietary exposure of Canadians to grain fromDBT418 will not be different from that for other commercially available field corn varieties.

5. Nutrition

Forage and grain from DBT418 maize hybrids were analyzed for nutritional composition and compared to the nutritional composition of non-transgenic versions of the same maize hybrids. Proximate and amino acid analyses were performed. Small differences between DBT418 plants and their non-transgenic counterparts were occasionally observed. However, the nutrient composition of DBT418 maize falls within the range of variability for the relevant nutrients reported for maize. The use of corn products derived from DBT418 would therefore have no significant impact on the nutritional quality of the Canadian food supply.

6. Safety

a) Potential Toxicity:

The CryIA(c) and PAT proteins were compared to databases of known protein toxins and show no homology to known mammalian protein toxins. Both CryIA(c) and PAT proteins are rapidly degraded under conditions that simulate mammalian digestion. Acute mouse toxicity study was performed using microbially-produced, purified CryIA(c) or PAT protein. Administered doses 3325 mg of CryIA(c) protein or 2500 mg of PAT protein /kg body weight by oral gavage. No toxicity was observed for either protein. Based on the results of the studies, the acute oral LD50 was estimated to be greater than 3325 mg of CryIA(c) or 2500 mg of PAT/kg body weight.

b) Potential Allergenicity:

The CryIA(c) and PAT proteins are extremely unlikely to be allergens. The introduced proteins were compared to known allergens and demonstrated to not share homology to known allergens. In addition, the potential for allergicity was assessed based upon the characteristics of known food allergens (stability to digestion, stability to processing). The CryIA(c) and PAT proteins do not possess characteristics typical of known protein allergens.

Conclusion:

Health Canada's review of the information presented in support of the food use of insect resistant and glufosinate tolerant maize DBT418 concluded that this maize does not raise concerns related to human food safety. Health Canada is of the opinion that DBT418 is as safe and nutritious as current commercial maize varieties.

Health Canada's opinion deals only with the food use of this insect-resistant and glufosinate-tolerant maize. Issues related to growing insect resistant and glufosinate tolerant maize in Canada and its use as animal feed have been addressed separately through existing regulatory processes in Agriculture & Agri-Food Canada.

This Novel Food Information document has been prepared to summarize the opinion regarding the subject product provided by the Food Directorate, Health Protection Branch, Health Canada. This opinion is based upon the comprehensive review of information submitted by the petitioner according to the Guidelines for the Safety Assessment of Novel Foods.

For further information, please contact:

Office of Food Biotechnology
Food Directorate
Health Protection Branch
Health Canada
Tunney's Pasture
Ottawa, Ontario K1A 0L2
Telephone: (613) 952-5137
Facsimile: (613) 952-6400