Role of glyphosate in disrupting the microbiota-gut-brain axis
According to a review recently published in Ecotoxicology and Environmental Safety, glyphosate severely alters the balance of the gut microbiota, the gut-brain axis, and the central and peripheral nervous systems.
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The noose tightens around glyphosate Classified as a “probable carcinogen” by the International Agency for Research on Cancer (IARC) – but not by regulatory agencies (see text box) – and suspected of being an endocrine disruptor, glyphosate may also cause various neurodevelopmental and neurobehavioral disorders.
So suggests an analysis by a team of Belgian and Polish researchers, who sifted through studies on the toxic effects of glyphosate (experiments on cell cultures and animal models, clinical cases, epidemiological studies, etc.). 1
According to them, (sidenote: Glyphosate Glyphosate is the active compound in Roundup, a “broad-spectrum” weedkiller introduced by Monsanto in 1974. It kills all weeds by blocking the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase enzyme, which is involved in the synthesis of certain amino acids essential to their growth. Extremely effective, easy to use, and inexpensive, glyphosate is the most widely used pesticide in the world. Three hundred and fifty million hectares of crops in 140 countries are currently treated with glyphosate. It is considered a probable human carcinogen by the International Agency for Research on Cancer (IARC) and is also thought to be an endocrine disruptor (although this remains controversial). Since 2000, when its patent expired, it has been used in a large number of agricultural herbicides. In several countries, including France, the Netherlands, and Belgium, it is banned for private use and in public spaces. ) and its metabolites, such as aminomethylphosphonic acid (AMPA), the adjuvants found in the composition of glyphosate-based herbicides (surfactants), or the heavy metals in these preparations, exert what they describe as “devastating” effects at various levels.
Gut microbiota
Scientific studies on animals have shown that prolonged exposure to glyphosate-based herbicides leads to a change in the composition of the gut microbiota that favors pathogenic bacteria.
A 16S rRNA analysis of 141 bacterial families showed a deviation in the Firmicutes-to-Bacteroidetes ratio, a significant marker of (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232. ) , as well as a decrease in the abundance of beneficial bacteria, such as Enterococcus spp. and Bacillus spp. Some pathogenic bacteria, such as E. coli, Salmonella spp., and Clostridia spp. also became resistant to glyphosate as a result of this exposure.
In the studies, these changes in the microbiota were associated with increased oxidative stress and inflammation levels. Glyphosate exposure may also cause anatomical changes in the jejunum and duodenum.
Gut-brain axis
By destabilizing the gut microbiota, glyphosate herbicides appear capable of disrupting the functioning of the gut-brain axis, mediated by the vagus nerve, as well as that of the hypothalamic–pituitary axis. This may lead to neuronal and endocrine dysfunction, with multiple hormonal, emotional, cognitive, or behavioral consequences.
Neurons
Glyphosate may cause a variety of neuronal disturbances, which may or may not be linked to the microbiota and the gut-brain axis. Individuals with high exposure (farmers and chemical plant workers) are known to be at greater risk of neurodegenerative diseases. These diseases may be linked to a decrease in axon projections from neurons and the degeneration of the myelin sheath of motor and sensory nerves caused by glyphosate. Glyphosate also appears to inhibit neuronal differentiation and growth, with the disappearance of certain axon branches and dendritic underdevelopment potentially leading to neuromuscular and locomotor disabilities.
Blood-brain barrier (BBB)
The BBB is a selectively permeable membrane that regulates the transport of molecules, immune cells, xenobiotics, and pathogens between blood vessels and the microenvironment of the central nervous system, thus contributing to paracrine and endocrine signaling. In co-cultures of endothelial cells and neurons (a model for studying the BBB), exposure to glyphosate for 24 hours had a range of adverse effects, including the depletion of tight junction proteins, increased vascular permeability, and altered neuronal activity.
Nerve communication
As an organophosphate, glyphosate inhibits the enzyme acetylcholinesterase, which may lead to paralysis, memory impairment, psychomotor disorders, and anxiety.
A study of adolescents living in agricultural regions of the Andes found a correlation between acetylcholinesterase markers and depression. Glyphosate herbicides may also cause a disruption to monoaminergic transmission linked to major depression.
These results are worrying, since glyphosate is found everywhere, whether in the air, water, or the food we eat. It affects everyone, even if farmers and herbicide factory workers are the most exposed. What daily dose can affect the human brain and microbiota? Which exposure routes have the greatest impact? Which age groups are the most sensitive? This study raises many questions, with further studies required to answer them.
