Maize is a staple food crop and important raw material for feed and industry because it is nutritious and historically has been inexpensive to grow, however competing weeds currently threaten the production rate and quality of maize. To combat the growth of weeds, the agricultural industry has implemented genetically modified crops that contain herbicidal resistance. The most dominant herbicidal resistant trait is that for glyphosate (RoundupÔ) tolerance. In this study, the food safety of GM maize with the G2-aroAgene for glyphosate tolerance was assessed in a 90-day feeding study and compared with a non-GM isogenic line. Seventy male and seventy female Sprague-Dawley rats were fed a diet composed of maize with the G2-aroA gene. The researchers conducted multiple tests to assess if there were any significant effects in GM-fed rats. This included a compositional analysis, survival and clinical observations, body weight gain and food consumption, hematology examination, serum chemistry, organ weight, and pathology examination. This sub-chronic toxicological study indicated significant differences in a few of these tests, however the researchers did not attribute this variance to the presence of G2-aroA maize grain. Thus, they concluded that G2-aroA maize grain does not cause adverse effects in Sprague-Dawley rats.
Zhu, Yaxi., He, Xiaoyun., Luo, Yunbo., Zou, Shiying., Zhou, Xin., Huang, Kunlun., Xu, Wentao., 2013. A 90-day feeding study of glyphosate-tolerant maize with the G2-aroA gene in Sprague-Dawley rats. Food and Chemical Toxicology 51, 280–287.
Glyphosate is an active ingredient in RoundupÒagricultural herbicides inhibits the biosynthesis of aromatic amino acids by suppressing the activity of the SPSPS enzyme. This enzyme is encoded by the aroA gene and its mutant allele was found to express a mutant EPSPS enzyme that is insensitive to glyphosate. Thus, by transforming crops to express the mutant aroA gene, glyphosate can be used to exterminate unwanted weeds while still allowing crops to grow. The G2-aroA gene studied by Zhu et al. is a new mutant strain found to have glyphosate resistance.
In order to test if the consumption of G2-aroA crops is safe, researchers compared Sprague-Dawley rats subjected to a 90-day diet of G2-aroA crops to ones on a non-GM diet. Flours from GM and non-GM maize were formulated into rodent diets at concentrations of 12.5%, 25%, and 50%. The researchers used seventy weaned male and seventy weaned female rats supplied by Vital River Laboratories Co. Ltd (Beijing, China). The rats had an average body weight of 80–100 g, were kept in groups of 5, at a regulated temperature, light cycle, and humidity. The rats had ad libitum access to water and feed and were observed daily for mortality and signs of toxicity or other notable behaviors. Body weight and food intake were measured once a week. Furthermore, blood tests such as white blood cell counts (WBC), red blood cell counts (RBC), and hemogloblin concentrations (MCHC) were evaluated. In addition, serum chemistry was conducted to observe glucose, protein, and cholesterol levels. Lastly, after the 13-week exposure test, selected organs were weighed and underwent histopathology examination.
The male rats in the 25% GM group had significantly higher body weights than the other male groups. However, the significance was not considered related to the addition of G2-aroA maize in the experimental diet because there were no differences observed in males consuming the 50% GM maize diets. The researchers further dismiss significant differences with the same reasoning. The values of RBC and hematocrit (HCT) of the 12.5% GM male group and the value of mean corpuscular volume (MCV) of the 12.5% GM female group were significantly different from the 12.5% non-GM group. Moreover, the mean values of MCH and MCHC of males fed 50% G2-aroA transgenic maize diets were higher (P < 0.05) than the values observed in the 50% non-GM groups. The mean values of MCV and MCHC of females fed with 25% GM maize were different (P < 0.05) from the values observed in the reference control group and the 25% non-GM group.
The serum chemistry results yielded significant differences as well, but the researchers did not attribute the adverse effects to the experimental diet. Statistically significant differences in the mean value of total cholesterol (CHO) were observed between the 12.5% GM and non-GM group in both genders. However, this change was not found in the 25%, 50%, and reference group and therefore dismissed as non-significant. Furthermore, the values of blood urea nitrogen (BUN) and triglycerides (TG) in the males and the value of LDG in the females in the 25% GM maize were significantly different from those of non-GM groups and reference control group. Other significant differences were found in the creatinine (CREA) values of males, alkaline phosphatase (ALP) in females, and total protein (TP) and albumin (ALB), when comparing between males and females in the 50% GM-group. Lastly, the weights of ovaries and brains of the females consuming the 25% GM maize diet were lower than those observed in the 25% non-GM control diet and the weight of the kidneys were higher in the female 50% GM group than those of the 50% non-GM group. The researchers did not attribute these significant differences to the experimental GM diet because these relationships were not observed at higher concentrations of GM maize diets.
This sub-chronic toxicological study was intended to determine the safety of long-term dietary exposure to grain from GM G2-aroA herbicide-tolerant maize. The researchers concluded that a high concentration of GM maize does not have adverse effects because none were observed in the 50% GM maize experimental groups. None of the significant differences were attributed to the GM maize diet and therefore the consumption of a GM G2-aroA maize diet was concluded to be safe at all concentration levels.