New Study Has Shown That RoundUp Glyphosate and Rodeo disrupt the gut microbiome by inhibiting the Shikimate pathway, causing imbalances that can lead to cancer, diabetes, obesity, and depression.
By Graciela Vizcay Gomez
The main mechanism of how glyphosate herbicides kill plants is by inhibiting an enzyme called EPSPS, which is part of a biochemical pathway known as the shikimate pathway. The shikimate pathway is responsible for the synthesis of certain aromatic amino acids that are vital for the production of proteins, the building blocks of life. Thus, when the synthesis of aromatic amino acids is blocked by the inhibition of EPSPS glyphosate, the plant dies, according to the note published in the English medium Sustainable Pulse.
Humans and animals do not have the shikimate pathway, which is why industry and regulators have claimed that glyphosate is not toxic to humans.  However, some strains of gut bacteria have the shikimate pathway, leading to much debate as to whether Roundup and glyphosate might affect the gut microbiome (bacterial populations).
Imbalances in gut bacteria have been found to be linked to many diseases, including cancer, type 2 diabetes, obesity, and depression.
As many species of gut bacteria have the shikimate pathway, scientists have hypothesized that glyphosate herbicides could inhibit the EPSPS enzyme of the shikimate pathway in these organisms, causing an imbalance in the microbiome, with potentially negative consequences for health. Some have proposed that if glyphosate herbicides disrupt the gut microbiome, EPSPS inhibition will be the primary mechanism through which this occurs.
However, the proof that glyphosate herbicides can inhibit the EPSPS enzyme and the shikimate pathway in gut bacteria has been lacking. But a new study has shown without question that this actually happens.
The study on rats by an international team of scientists based in London, France, Italy and the Netherlands, led by Dr. Michael Antoniou of King's College London and published on the BioRxiv pre-review site, found that the herbicide Roundup and its active ingredient glyphosate causes a dramatic increase in the levels of two substances, shikimic acid and 3-dehydroshikimic acid, in the intestine, which are a direct indication that the EPSPS enzyme of the shikimic acid pathway has been severely inhibited.
Additionally, the researchers found that both Roundup and glyphosate affected the microbiome at all dose levels tested, causing changes in bacterial populations.
The levels tested were previously assumed to have no adverse effect
For the study, female rats (12 per group) received a daily dose of glyphosate or a Roundup formulation approved in Europe, called MON 52276. Glyphosate and Roundup were administered through drinking water to give a daily intake of glyphosate from 0.5 mg, 50 mg and 175 mg / kg body weight per day (mg / kg bw / day), respectively representing the EU Acceptable Daily Intake (ADI), the EU No Observed Adverse Effects Level (NOAEL ) and the US NOAEL.
The study found certain adverse effects at all doses tested, disproving regulators' assumptions that these levels have no adverse effects.
Some previous studies have also reported changes in the gut microbiome of laboratory animals exposed to glyphosate and / or Roundup. However, as they did not use the deeper molecular profiling techniques (multi-omics) used in the last investigation, they could not observe the inhibition of the shikimate pathway.
Unique comprehensive analysis
The unique aspect of the new study is that a more comprehensive analysis was conducted than ever to see if changes in the gut microbiome could affect the health of the rats.
The researchers applied two levels of analysis to investigate the changes:
1) a metagenomic analysis, which analyzed all the DNA in the gut and identified all the organisms present.
2) an analysis of metabolomics, which analyzed alterations in the biochemistry of the environment of the gut microbiome.
Dr Antoniou commented: “We are the first to use this combination of metagenomics and metabolomics profiling to look for the effects of glyphosate herbicides on the gut microbiome. Through this exhaustive multicomics analysis, we obtained definitive results that demonstrate the impact of glyphosate and Roundup on both the bacterial population and the biochemistry of the gut microbiome ”.
Metagenomic analysis found that both Roundup and glyphosate affected the microbiome at all dose levels, causing changes in bacterial populations. Metabolomics revealed that levels of two substances, shikimic acid and 3-dehydroshikimic acid, increased dramatically at the two highest doses in the gut of rats fed glyphosate and Roundup. These two acids were undetectable in the intestine of control animals. This is a clear indication that the EPSPS enzyme of the shikimate acid pathway was inhibited by glyphosate and Roundup, as if it were active it would rapidly convert shikimic acid to the next substance in the pathway, but that did not happen.
Dr Antoniou said that this effect had previously been hypothesized but not proven: “Our study provides the first evidence that glyphosate and Roundup with these allowed regulations and therefore presume safe doses inhibit the shikimic acid pathway in intestinal bacteria ”.
The researchers also saw other changes in the intestinal metabolome that indicated oxidative stress, a type of imbalance that can lead to DNA mutations, damage to cells and tissues, and diseases such as cancer. Gut bacteria respond to oxidative stress by producing certain substances that fight it. [two]
Biomarkers of glyphosate exposure
Dr Antoniou said the study has broken new ground in identifying the first biomarker of glyphosate exposure, which could be relevant to humans: “Our findings suggest that surveys of human populations should be urgently carried out to show if there is a correlation between glyphosate and shikimate levels. If such a correlation is found, then shikimate levels could be used as a measure of the biological effects of glyphosate exposure. "
This means that it is possible to see if a certain disease in a person is associated with glyphosate exposure by looking at their fecal microbiome, although a causal link between the disease and glyphosate could not be established.
Furthermore, the results showed distinct changes in the profile of the intestinal bacterial populations. Glyphosate and MON 52276 increased the levels of Eggerthella spp. and Homeothermacea spp, while MON 52276 also increased levels of Shinella zoogleoides. These changes in bacterial species, if confirmed by additional studies, could also act as additional biomarkers of exposure to glyphosate and Roundup.
Dr. Antoniou said: “We see definite and consistent changes in all doses of MON 52276 and glyphosate. So even at the level of ADI (Acceptable Daily Intake, the regulators believe that it can be ingested daily in the long term without adverse effects) we see these changes in bacterial populations. In the long term there may be health implications. Currently, science does not understand enough about what the biological and health consequences of these changes could be, but the alterations are in themselves a cause for concern ”.
Liver damage in rats fed Roundup and glyphosate
The study also revealed that Roundup, and to a lesser extent glyphosate, damaged the liver and kidneys of rats, even during the relatively short study period of 90 days. Histopathological (microscopic) examination of the liver showed that the two highest doses of Roundup caused a statistically significant and dose-dependent increase in lesions, changes in fatty liver disease, and necrosis (tissue death).
In the new study, in the glyphosate treatment group, there was also an increase in the incidence of this liver damage, but it was not at a statistically significant level. In contrast, none of the control animals showed the same liver effects, so the changes in glyphosate-fed animals may be biologically significant. As the authors state, they may not have reached statistical significance because the number of animals was too low and the duration of exposure too short. Another month or two additional to the duration of the study could have resulted in statistical significance for glyphosate and the effects of Roundup.
The findings of fatty liver disease confirm and extend the observations of a previous study by Dr. Antoniou's team. In this earlier study, rats were given a dose of Roundup that was a staggering 125,000 times lower, based on glyphosate dose, than the lowest dose group in the new research. However, they were fed this dose for a period longer than two years. This lower dose also caused fatty liver disease. "We now know that a lower dose of Roundup for a longer time or a higher dose for a shorter time produces the same result," said Dr. Antoniou.
There were clear increases in kidney dysfunction (injury, mineralization, and necrosis) in the Roundup and glyphosate groups, but they were mostly not statistically significant. Again, this may be because there were too few animals or the study was too short. Anyone wishing to replicate these effects in other studies should extend the duration of the study and use a larger number of animals to see if there is serious long-term damage to the kidneys.
Biochemistry of blood
The researchers expected that the signs of damage to liver and kidney function in the Roundup groups and, to a lesser extent, in the glyphosate groups would be reflected in the biochemistry of the blood. Surprisingly, however, they saw little change at this level. Dr. Antoniou commented: “While biochemical measurements of blood are routinely used to assess liver or kidney dysfunction in humans, they are relatively crude methods that could lose the effects of pesticides. And this was demonstrated in our study.
"But using 'omics' that looked at hundreds of measurements, we saw liver toxicity from glyphosate and Roundup. We saw all of these changes after just 90 days of feeding at levels that regulators say produce no ill effects.
“Our study shows that the most superficial physiological and biochemical measurements are not deep enough. We must use state-of-the-art multi-omics analysis methods as part of the risk assessment process, to ensure that we do not miss anything of public health importance. "
Until now, regulators have not incorporated these methods into the risk assessment process.
New mechanism for glyphosate-cancer linkage?
In 2015, glyphosate was classified as a probable carcinogen by the International Agency for Research on Cancer (IARC). Agency experts identified oxidative stress and genotoxicity (DNA damage) as possible mechanisms.
The new study proposes a new mechanism through which exposure to glyphosate-based herbicides can cause cancer. Animals fed Roundup and glyphosate showed elevated levels of shikimic acid in their intestines. Shikimic acid can have many different biological effects, including protecting the body against oxidative stress. But it has also been proposed as a cancer promoter, and a recent study found that shikimate can stimulate the proliferation of human breast cancer cells. The authors state in their article: "The new mechanism of action of glyphosate in the gut microbiome that we describe in the study presented here could be relevant in the debate on the ability of glyphosate to act as a carcinogen."
Power of multi-omics
In their article, the authors explain that their study "demonstrates the power of using multimic molecular profiling to reveal changes in the gut microbiome after exposure to chemical contaminants that would otherwise be lost using more standard and less exhaustive analytical methods."
The researchers identified the first biomarker for the effects of glyphosate on the rat gut microbiome, namely a marked increase in shikimate and 3-dehydroshikimate, indicating EPSPS inhibition of the shikimate pathway. Furthermore, they found increased levels of certain substances that suggest a response to oxidative stress. They also showed that Roundup and glyphosate caused different changes in the profile of intestinal bacterial populations, which could also act as additional biomarkers of exposure to glyphosate and Roundup.
The researchers concluded: “Although more studies are needed to understand the health implications of glyphosate inhibition of the shikimate pathway in the gut microbiome, our findings can be used in environmental epidemiological studies to understand whether glyphosate may have biological effects on human populations ”.
1. In the final addendum to the Glyphosate Renewal Assessment Report (October 2015), p23, Rapporteur Member State Germany and Co-Rapporteur Member State Slovak State, based on industry claims, “Action on the Shikimic Acid path it is exclusive to glyphosate and the absence of this pathway in animals is an important factor in its low toxicity for vertebrates ”.
2. Increased levels of γ-glutamylglutamine, cysteinylglycine and valylglycine were found in the intestine.
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