Science in Society Archive

GM food safe?

Recent incidents and scientific findings cast grave doubts over the safety of GM food and feed. We shall be circulating a selection of the following reports.

  1. Cows Ate GM Maize & Died
  2. Transgenic DNA and Bt Toxin Survive Digestion
  3. Bt Toxin Binds to Mouse Intestine
  4. Syngenta’s Spanish GM Trojan Horse
  5. Liver of Mice Fed GM Soya Works Overtime
  6. Animals Avoid GM, for Good Reasons

Transgenic DNA & Bt Toxin Survive Digestion

Neither DNA nor toxin protein breaks down completely in the gut. Dr. Mae-Wan Ho reports.

Scientists in the Safety Research Division of the Institute of Animal Health, in Tsukuba, Ibaraki, Japan, have been conducting a series of experiments on the fate of transgenic Bt toxin protein and DNA in food. They have amply confirmed that the Bt toxin, as well as transgenic DNA from Bt maize, survives digestion in the gut of livestock.

This research is partly supported by the Japanese Ministry of Agriculture, Forestry and Fisheries.

In one of the latest experiments, GM maize Bt 11 and the corresponding non-GM maize line, purchased from Novartis Seed, Inc  (now Syngenta) was processed into corn meal, and incorporated into the diet of 5 control and 5 experimental castrated male pigs for 4 weeks (comprising 60% of the diet).

Contents of the intestine and peripheral blood were screened for fragments of maize genes: invertase (226 base pairs, bp, a unit of DNA length), chloroplast gene ribulose-1,5­biphosphate carboxylase/oxygenase (rubisco) large subunit (1 028 bp), ze 1 (242 bp) and crylAb (437 bp and 110 bp). The protein CrylAb was detected by immunochemical methods.

Most of the DNA extracted from the gut contents was partially degraded, whereas the extracted DNA from blood cells was less degraded and more than 10 thousand bp in size.

The stomach, duodenum and caecum samples were positive for the rubisco gene in all 10 pigs; samples from the ileum were positive for seven pigs and rectal samples positive for 5 pigs. The invertase gene was detected in the stomach and ileum of all 10 pigs, in the duodenum and caecum of eight pigs and the rectum of seven pigs. The ze 1 was detected in the stomach of seven pigs, and 3 pigs had it in the duodenum, ileum, caecum and rectum.

The crylAb 110bp fragment was detected in all of the stomach, duodenum, ileum and caecum contents and in the rectal contents in three out of 5 pigs fed GM maize. In addition, the larger 437 bp fragment of crylAb was detected in the stomach of all five pigs, and in the duodenum, ileum, and caecum of 3 pigs, and the rectal contents of one pig out of the five that were fed GM maize. None of the pigs fed non-GM showed positive results for crylAb fragments.

No gene fragments of either maize DNA or crylAb DNA were detected in the peripheral blood, because the PCR (polymerase chain reaction) did not work in blood. This is very important, as negative findings of transgenic DNA in peripheral blood and tissues have been reported which had not been accompanied by appropriate tests on whether the detection method was working. There are many unknown inhibitors of the PCR in different tissues, and very careful work has to be done to determine whether transgenic DNA is present or not.

CrylAb protein is present at a level of 600 nanograms/g in the Bt 11 diet (a nanogram is 10-9g). It is not very digestible; compared with the totally indigestible chromic oxide included as a standard in the diet, Cry1Ab’s digestibility was 92%.

Cry1Ab protein was detected in the contents of stomach, duodenum, ileum, caecum and rectum of mice fed Bt 11 GM maize. Similar results were found in previous experiments in which calves were fed Bt 11 maize.

The researchers concluded, on the basis of scant evidence obtained after only 4 weeks feeding, that: “The present results suggest that no difference in general health and growth rate is detected between Bt 11 corn-fed and control pigs.”

While they admitted, “antigenecity [sic] of the [Cry1Ab] protein is retained”, that is considered not harmful to the mammalian gut cells because of “the lack of Cry protein receptors”. Unfortunately, other scientists have indeed identified specific ‘receptors’ in the mammalian gut that binds Cry proteins (see “Bt toxin binds to mouse intestine”, this series).

These researchers also downplayed the environmental impacts resulting from the excretion of transgenic toxin and DNA into the environment, again, without any empirical evidence.

Article first published 2004



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