Lab Rat

Changes seen are reminiscent of those caused by chemical irritants

Rats fed a triple-stacked trait GM maize engineered for insect resistance and herbicide tolerance developed leaky stomachs, according to a new peer-reviewed paper by Australian researchers.

In the experiment conducted by Irena M. Zdziarski of the University of Adelaide, Judy A. Carman of the Institute of Health and Environmental Research (IHER), and John W. Edwards of Flinders University, the rats were split into two groups of 10 males each.

One group was fed on the GM stacked-trait maize, containing Monsanto Bt insecticidal toxin traits MON863 and MON810, and glyphosate-tolerant trait NK603, for six months. That's twice as long as the typical rat feeding study performed by industry for regulatory authorisations. The GM maize was grown in the US.

The other group of rats was fed for the same amount of time on the control diet, which contained a commercially-grown non-GM maize grown in Australia. The control maize was not sourced from the US due to the difficulty of finding a non-GM corn variety from that country that would be uncontaminated with GM genes.

Thus the researchers did not compare a GM crop with a non-GM crop grown in the same conditions. In addition, they did not use the non-GM isogenic variety for the control maize because these do not exist for stacked-trait plants, which are produced by conventionally crossing several GM varieties. However, they point out in their paper that regulators across the world have declared the stacked-trait GM maize substantially equivalent to non-GM maize varieties, and therefore there should have been no differences between the two rat groups.

But this was not what they found. At the end of the experiment, the rats were killed and samples of their stomachs were examined under the microscope. The rats fed the GM maize diet had worrying changes in the lining of their stomachs.

Any two cells that line the stomach are normally held tightly against each other to form a “tight junction”. This stops bacteria, viruses or food particles from leaking out from the stomach into the tissues of the body. The researchers found that the rats fed the GM corn had gaps in their tight junctions. This is called “poor apposition”. On average, this was five times greater in rats fed the GM corn diet.

Poor apposition should not occur in normal, healthy stomachs. Yet every stomach section in rats fed the GM diet had these gaps between a number of cells. Seventy percent of the GM-fed rats had at least 30% of their tight junctions poorly apposed, compared to no rats on the non-GM diet. The risk of a rat having 30% or more of its tight junctions poorly apposed was more than 7 times higher if the rat was fed the GM diet.

Drs Zdziarski and Carman stated in a communication about their experiment, "Future experiments should be done to determine if the changes result in any actual leakage of substances from the stomach and hence any increased risk of developing allergies, or infections from microbes in food or water."

Changes were also seen in the lining of the stomach. The normal stomach lining has microscopic pits in it. Cells in the pits produce mucus to protect the stomach from stomach acid. The bottom of each pit divides into two long, straight glands. These glands produce stomach acid to help digest food. Drs Zdziarski and Carman said, "While we saw some dilated (i.e. swollen) glands in rats fed the GM diet and those fed the non-GM diet, the rats fed the non-GM diet had smaller swellings and the cells lining the glands looked normal. In contrast, the glands in the GM-fed group were much more swollen, they often contained debris or mucus, and the cells lining the glands were often abnormal. For example, some cells were stretched or longer than they should have been. More than six times as many rats had glands that were both swollen and lined with elongated cells in the GM-fed group. While every rat on the GM diet showed at least one gland that looked like that, none of the rats fed the non-GM diet showed this pathology."

In addition, some cells in the glands of GM-fed rats showed signs of dysplasia. This is a condition in which cells are abnormal. It may progress to cancer. Many tests that screen for cancer actually screen for dysplasia (e.g. a Pap smear for cervical cancer). In these GM-fed rats, dysplasia took the form of finding cells in a location where they would not normally occur. This kind of change often happens after injury or a drastic change in the stomach environment. Often, once such a trigger is removed, these abnormal cells can disappear. However, sometimes the damage is too severe for the tissue to recover and it can further develop into something more serious, such as cancer. Commenting on these changes, Drs Zdziarski and Carman said, "Future studies should investigate the risk of these kinds of serious conditions developing" in animals fed GM diets.

Meanwhile other cells, lying mostly at the base of the pits in the stomach, showed a statistically significant 21% reduction in the number of dividing cells in rats fed the GM diet compared to those fed the non-GM diet.

Drs Zdziarski and Carman said, "Joining together all the adverse findings into a single severity score, we found that the rats on the GM diet had a score that was 33% higher than rats on the non-GM diet. The changes we saw are closest to those seen with chemical gastropathy (also called reactive gastritis), caused by chemical irritants, such as aspirin, damaging the lining of the stomach."

One possible implication of the study is that the Bt proteins produced by GM crops may not be as safe as previously assumed. However, the changes found in the GM-fed animals could come from any one of several sources or a combination of sources, including the mixture of pesticides that the crop was grown with, or some other aspects of the GM crop resulting from the disruptive effect on gene function caused by the GM transformation process. The authors conducted an analysis for mycotoxins in the diets and plan to publish this in a followup study.

The new study:

Irena M. Zdziarski, Judy A. Carman, John W. Edwards (2018). Histopathological Investigation of the Stomach of Rats Fed a 60% Genetically Modified Corn Diet. Food and Nutrition Sciences 9(6). DOI: 10.4236/fns.2018.96058.