pesticides2pd_cc_by_sparks

Parkinson’s as a ‘man-made disease’

This blog post is the second in a series of blog posts on the relationship between Parkinson’s disease and pesticide exposure. With these blog posts I want to stand up for the interests of people who will get a neurodegenerative disease like Parkinson’s in the future because they are sensitive to the adverse effects of certain pesticides.  In part I, I spoke about my own exposure to pesticides and introduced the subject. In part II, I explore the neurotoxicity of the two most commonly used pesticides in the Netherlands and try to formulate meaningful follow-up questions. 

8th of December 2019

Part II: The pile of literature

Everyone is not equal, and safety standards need to be updated in order to protect those who are more susceptible and may not even know it | Scott Ryan

It’s the 19th of September 2019.

In a broadcast by the Dutch TV show Zembla we see distressing cases of Parkinson’s disease in farmers who have been using and use pesticides, among which the fungicide (weed killer) mancozeb. People living in the surroundings also report having Parkinson’s.

The broadcast lights up a smouldering fire in many people, including myself and the Dutch Parkinson’s Foundation (De Parkinson Vereniging). After the episode, the Parkinson Vereniging receives more than 60 reports from people who associate their Parkinson’s disease with exposure to pesticides. One of them is a ticked pesticide box on my own personal Parkinson’s bingo card.

The Dutch media pays attention to Zembla’s broadcast, members of the Dutch parliament ask ‘Kamervragen‘  and our minister of agriculture – Carala Schouten – responds. Her response is so not-actionable, that the Parkinson Vereniging is preparing a letter in return for which I provide my input (in Dutch, sorry English readers). In addition, I start working on a pile of scientific literature for myself and for the Parkinson Vereniging, draw conclusions and try to formulate meaningful follow-up questions in this blog.

A visual summary

The pile of literature is overwhelming. I’m worried that the findings might not all be equally readable and interesting for you, readers of my blog.

That’s why I decide to make a visual summary of the most important observations and follow-up questions that keep me occupied. You can find this summary below. And if you so desire, you can find the scientific literature on which the summary is based below the presentation.

The scientific basis for the three conclusions

To see what the claims from the slideshow above are based on, you can read the part of this blog below. You’ll see that I repeat the observations from the slideshow, with a more detailed explanation and a source.

It seems safe to conclude that occupational exposure to pesticides brings about at least 50% increased risk for contracting a neurodegenerative disease | Gunnarsson, 2019

Are you exposed to pesticides on a day to day basis? That doesn’t mean you’re going to get Parkinson’s disease. If only it were that simple, I would almost say …. Parkinson’s disease is a complex disease that develops over the years and the disease manifests itself through an interaction of genetic and environmental factors. (e.g. Johnson, 2018). Some people are – unknowingly – more vulnerable to exposure to pesticides than others.

However, it is beyond any scientific doubt that the use of pesticides increases the chance that people will develop a neurodegenerative disease such as Parkinson’s disease. A review of studies on occupational exposure to pesticides (meaning long term exposure and in relatively high concentrations) shows that the higher chance of getting a neurodegenerative disease is at least 50% (Gunnarsson, 2019). In order to understand what this 50% means, you have to imagine that for every two people who get Parkinson’s disease, there will be an extra one who would not have Parkinson’s if he or she had not been professionally exposed to certain pesticides.

Nayaran, e.a. (2017) draw similar conclusions and show how the actual risk depends on the duration, proximity and intensity of exposure and on the pesticide/pesticide mixture used. A salient detail from this study is that those who had used personal protective equipment were more likely to develop Parkinson’s disease. The authors think this is because they were probably in a situation of higher exposure (otherwise you wouldn’t be wearing protective clothing) and/or because the personal protection failed.

The problem with pesticides is that the molecular target of a pesticide is often also present in non-target organisms, leading to the potential for undesirable effects (Richardson, 2019). Furthermore, chemicals often have multiple modes of action and therefore will probably work in more ways than the pesticide designer has thought about (Cuhra, 2016)

Sources:

Cuhra, M., Bohn, T., Cuhra, P. (2016). Glyphosate: Too much of a good thing? Frontiers in Environmental Science. https://doi.org/10.3389/fenvs.2016.00028 (Open Access)

Johnson, M. E. , Stecher, B. , Labrie, V., Brundin, L., Brundin, P., (2018),  Triggers, Facilitators, and Aggravators: Redefining Parkinson’s Disease Pathogenesis. Trends in Neurosciences, 2 (1), 4-13. https://doi.org/10.1016/j.tins.2018.09.007 (Open Access)

Gunnarsson, L-G., Bodin, L. (2019). Occupational Exposures and Neurodegenerative Diseases—A Systematic Literature Review and Meta-Analyses. Int. J. Environ. Res. Public Health, 16(3), 337 https://doi.org/10.3390/ijerph16030337 (Open Access)

Narayan, S., Liew, Z., Bronstein J.M., Ritz, B. (2017). Occupational pesticide use and Parkinson’s disease in the Parkinson Environment Gene (PEG) study. Environ Int. 2017 Oct;107 266-273. https://doi.org/10.1016/j.envint.2017.04.010 (Te bekijken via https://europepmc.org/articles/pmc5629094)

Richardson, J. R., Fitsanakis, V., Westerink, R. H. S., & Kanthasamy, A. G. (2019). Neurotoxicity of pesticides. Acta Neuropathologica. 138: 343. https://doi.org/10.1007/s00401-019-02033-9 (Closed Access)

Exposure to pesticides and toxic metals were both associated with an earlier onset of PD, an effect that was greater with higher levels of exposure, both in terms of frequency and proximity | Gamache, 2019

Several studies show that exposure to pesticides lowers the age at which you get Parkinson’s disease. And that effect increases as people are exposed for a longer duration and/or in higher doses:

  • In a study by Ratner (2014) 58 residents of Boston with Parkinson’s disease were questioned. 36 of them had been chronically exposed to pesticides and 22 had not. Since it is known that genetic risk factors can also hasten the age of onset of Parkinson’s, people who had family members with Parkinson’s disease were excluded from participation. Only people with so-called idiopathic Parkinson’s were allowed to participate. The word idiopathic comes from the Greek words ἴδιος (idios) – which means ‘self’ – and from πάθος (pathos), which translates as ‘disorder’, ‘pain’ or ‘emotion’. Idiopathic is therefore a difficult word for ‘selfdisease’, which means that you have a disease ‘without a known cause’.
    The 58 were interviewed via a structured questionnaire. The group that was chronically exposed to pesticides had on average received Parkinson’s disease at 53 years of age and the unexposed group at 60 years of age. However, the variation between individuals was very large and the total group studied was small.
  • In 2019 a similar study took place among 290 Canadians with idiopathic Parkinson’s disease. They were questioned about their occupational exposure to pesticides. On average, the 53 chronically exposed were found to have acquired Parkinson’s disease about five years earlier than the people who had not been exposed (Gamache, 2019).
Sources:

Gamache, P., Haj Salem, I., Roux-Dubois, N., Le Bouthillier, J., Gan-Or, Z., & Dupré, N. (2019). Exposure to Pesticides and Welding Hastens the Age-at-Onset of Parkinson’s Disease. Canadian Journal of Neurological Sciences / Journal Canadien Des Sciences Neurologiques, 46 (6), 711-716. https://doi.org/10.1017/cjn.2019.248 (Closed Access)

Ratner, M.H, Farb, D.H, Ozer, J., Feldman, R.G., Durso, R. (2014).  Younger age at onset of sporadic Parkinson’s disease among subjects occupationally exposed to metals and pesticides. Interdiscip. Toxicol. 7:123-133. https://doi.org/10.2478/intox-2014-0017 (Open Access)

In reviews that look at the relationship between pesticide exposure and Parkinson’s disease prevention, reference is also made to pesticides that have now been banned in Europe. The fact that these substances are banned is good news. But even so, we must be alert to the fact that the effects of exposure are still lagging behind. The bingo card of people who now have Parkinson’s disease – or are in the process of getting it – may have been filled with one of these banned substances in the past. That is the frustration thing in this matter. We are always lagging behind, and once a pesticide has been authorised, the burden of proof lies with the exposed.

To check the (neuro)toxicity of drugs that are still on the market, I started to look at the scientific literature for glyphosate and mancozeb. According to the Dutch CBS these two pesticides were used on the largest area of agricultural soil in the Netherlands in 2016 (more recent data are not available). Mancozeb was used on 168000 ha of agricultural land and glyphosate on 156000 ha. The fact that a substance is the most commonly used does not mean that it is the most dangerous substance, but we have to start somewhere.

For glyphosate and mancozeb I scanned the scientific literature for associations with (neuro)toxicity. Some of these studies are shown below:

Glyphosate

De molecular structure of glyphosate

Glyphosate (N-fosfonomethylglycine) is a small molecule that mainly acts as a herbicide – weed killer – by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an important component of the so-called Shikimate-route. The Shikimate route is a seven-step metabolic route used by bacteria, archaea, fungi, algae, some protozoa and plants for the biosynthesis of folates and aromatic amino acids such as phenylalanine, tyrosine and tryptophan.

Folate is a general name for a group of compounds that have the same effect as folic acid (vitamin B11). Aromatic amino acids are important starting substances for the production of hormones and neurotransmitters. A shortage of tyrosine, for example, causes a shortage of dopamine and norepinephrine.

Inhibition of the Shikimate-route blocks the production of folates and aromatic amino acids in plants, resulting in the death of weeds. Of course, the pesticide does not only have these effects on the weeds for which it is intended. In fact, in order to ensure that the plant that has to grow in the fields does not suffer from the herbicide, genetically modified seeds have been produced. These glyphosate resistant seeds (produced by the same manufacturer as that of glyphosate itself) have made glyphosate one of the most widely used herbicides in the world.

Glyphosate has an amino acid-like structure and is probably able to cross the blood-brain barrier via so-called amino acid transporters.

The reassessment

At the end of March 2016, the Dutch government imposed a ban on the professional spraying of glyphosate on the pavement and with results, according to data of the Dutch CBS. However, the product is still for sale for consumers and for agricultural purposes. In data from the CBS you can see that the use of glyphosate increased between 2012 and 2016.

In December 2017, the European Commission allowed glypohosate for a limited period of five years, and not for the usual period of 10 years. The substance should therefore be reassessed after five years, i.e. by December 2022 at the latest. The reassessment of glyphosate in the EU will start on 15 December 2019 when the applicant(s) have to apply for a renewed approval. The reassessment is carried out by an Assessment Group on Glyphosate consisting of the Member States France, Hungary, the Netherlands and Sweden.

Austria did not wait for the reassessment and was the first EU country to ban glyphosate. According to the EU this isn’t legitimate (Dutch source).

In October 2019, the Dutch ‘College voor toelating van gewasbeschermingsmiddelen en biociden (Ctgb)’ decided the following (Dutch source). It wants to limit the use of glyphosate as a so-called ‘full-field application’ and is introducing an area-limiting measure for the Meuse basin. The first restriction means that glyphosate may no longer be used shortly before harvesting to accelerate uniform ripening of the crop. The Ctgb only allows the product to be used as a herbicide (weed control). The area limitation measure is a consequence of our drinking water standard. In the Meuse basin, the Ctgb has found concentrations of glyphosate above the drinking water standard at various measuring points in the vicinity of drinking water collection points. The standard is exceeded as soon as the Meuse enters the Netherlands, but Dutch use also contributes to the standard being exceeded further down the river basin.

Indications of (neuro)toxicity

The neurochemical effects observed in the present study are an important public health concern. Although we have no data on humans, glyphosate could exert its neurotoxicity, notably on monoamine systems, by inducing DNA damage, neuronal inflammation and oxidative stress mechanisms …..  Our results support the hazard of glyphosate herbicide and show the importance of minimizing its herbicide use | Martinez, 2018

Glyphosate is associated with neurotoxicity, behavioural change, transgenerational toxicology and impairment of the microbioom (intestinal inhabitants) of various organisms. In addition, case studies of Parkinsonism in humans are known. Below you find a selection from the scientific literature:

While a large body of work involving pesticide exposure has focused on dopaminergic neurons, greater recognition of the role of other neurotransmitters has become the focus of more recent studies | Negga, 2012

C. Elegans is a worm that is genetically very similar to humans. The worm is often used as a model organism for research into disease mechanisms, including neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease.

Exposure to a commercial formulation of glyphosate led to the degeneration of C. Elegans’ GABA neurons (Negga, 2012). GABA – an abbreviation for gamma-aminobutyric acid – is a so-called neurotransmitter. A neurotransmitter is a signalling substance that transmits nerve impulses between nerve cells. In addition, the researchers show that acute exposure to glyphosate does not lead to the death of dopamine neurons, but chronic exposure does (24 hours is chronic for worms, it appears : )). The researchers conclude that neurotoxicity studies should not only look at dopaminergic neurons but also at other types of neurons. Furthermore, the authors think that C. Elegans is a suitable worm to study the neurotoxicity of (future) pesticides.

The reason for the observed neurodegeneration in C. Elegans is attributed to a reduced activity of the mitochondria and increased oxidative stress (Bailey, 2018).

Sources:

Negga, R., Stuart, J.A., Machen, M.L., Salva, J., Lizek, A.J., Richardson, S.J. et al (2012). Exposure to glyphosate- and/or Mn/Zn-ethylenebis-dithiocarbamate-containing pesticides leads to degeneration of gamma-aminobutyric acid and dopamine neurons in Caenorhabditis elegans. Neurotox Res 21:281–290. https://doi.org/10.1007/s1264 0-011-9274-7 (Te bekijken via http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3288661&blobtype=pdf

Bailey, D.C., Todt, C.E., Burchfield, S.L., Pressley, A.S., Denney, R.D., Snapp, I.B. (2018). Chronic exposure to a glyphosate-containing pesticide leads to mitochondrial dysfunction and increased reactive oxygen species production in Caenorhabditis elegans. Environ Toxicol Pharmacol 57:46–52. https://doi.org/10.1016/j.etap.2017.11.005 (Open Access)

Not only C. Elegans, but also the zebrafish is widely used as a laboratory animal. The zebrafish is 70 percent genetically similar to humans and is easy to breed.

Glyphosate appears to influence the behaviour of zebrafish. It affects their memory and they become more passive. Zebrafish larvae reduce their ‘exploratory behaviour’ at concentrations of glyphosate currently permitted in surface water. The larvae do not go out as much, which may make them vulnerable as prey.

The researchers not only tested glyphosate as a single substance but also tested the herbicide ‘Roundup’. In addition to glyphosate, this herbicide contains a number of unknown excipients that can lead to a so-called compound toxicity. Both glyphosate and ‘Roundup’ had similar effects.

Source:

Bridi, D., Altenhofen, S., Gonzalez, J.B., Reolon, G.K., Bonan, C.D. (2017). Glyphosate and Roundup((R)) alter morphology and behavior in zebrafish. Toxicology 392:32–39. https://doi.org/10.1016/j.tox.2017.10.007 (Open Access)

Oral exposure to glyphosate in rats leads to changes in their central nervous system (CNS) in a dose-dependent manner. A higher exposure leads to lower levels of the neurotransmitters dopamine, norepinephrine and serotonin. The authors argue that this proves that glyphosate can enter the brain through the blood-brain barrier, accumulate there and then exert its neurotoxic effect.

Source:

Martínez, M.-A., Ares, I., Rodríguez, J.-L., Martínez, M., Martínez-Larrañaga, M.-R., & Anadón, A. (2018). Neurotransmitter changes in rat brain regions following glyphosate exposure. Environmental Research, 161, 212–219. https://doi.org/10.1016/j.envres.2017.10.051 (Closed Access)

It has been exhaustively demonstrated that the developing brain is more susceptible to the neurotoxic effects of pesticides than the adultbrain | Cattani, 2017

Exposure of female rats to glyphosate led to a toxic accumulation of calcium ions in the hippocampus of her offspring which led to depression and cell death (Cattani, 2017). 

According to the researchers, the toxicity in the offspring is caused by an overactivation of the glutamate metabolism. Glutamate is one of the neurotransmitters in our brain and has a stimulating effect on neurons. Exposure to glyphosate leads to an excess of glutamate between the glutamate neurons and – as a result – also to an excessive activation of the NMDA-glutamate receptor (N-methyl Dextro Aspartic Acid Receptor). Furthermore, the researchers show that glyphosate itself fits the NMDA receptor, which further reinforces the overactivation. When the NDMA receptor is overactivated, an excessive amount of Ca2+ flows into the cells. This in turn leads to oxidative stress. The researchers also showed that the amount of glutathione (GSH) – an antioxidant – in the brains of rats decreased. Increased oxidative stress and a reduced ability to do something about it eventually leads to cell death.

Research on glutamergic neurotransmission in our basal nuclei reveals a complex and interconnected network with back-and-forth interactions between glutamergic and dopaminergic systems. A shortage of dopaminergic neurons can lead to over-stimulation of the glutamergic system, which in turn can lead to all kinds of parkinsonian symptoms (Jenner, 2019).

Sources:

Cattani, D., Cesconetto, P.A., Tavares, M.K., Parisotto, E.B., De Oliveira, P.A., Rieg, C.E.H. et al. (2017). Developmental exposure to glyphosate-based herbicide and depressive-like behavior in adult offspring: implication of glutamate excitotoxicity and oxidative stress. Toxicology 387:67–80. https://doi.org/10.1016/j.tox.2017.06.001 (Open Access)

Jenner, P., Caccia, C. (2019). The Role of Glutamate in the Healthy Brain and in the Pathophysiology of Parkinson’s Disease. European Neurological Review. 14(Suppl. 2):2–12. (Te bekijken via https://pdfs.semanticscholar.org/3d84/816ab476ef6243f9f95ab69a27797c58cfc0.pdf)

There is increasing evidence of the association between microbiome dysfunction and CNS-related co-morbidities, such as anxiety, depression, autism spectrum disorders, Alzheimer’s disease and PD | Santos, 2019

One of the common prodromal symptoms of Parkinson’s disease are problems in the gastrointestinal tract. προδρομή (prodrome) means ‘running ahead’ in Greek. The prodromal symptoms run in front of the troops and show a possible future.

It is even suggested that a subtype of Parkinson’s disease begins in the intestines (Borghammer, 2019) and various studies show that people with Parkinson’s disease have a different composition of intestinal bacteria than their healthy counterparts (e.g. Boertien, 2019). This altered composition of the intestinal microbiome leads to a decrease in the biosynthesis of aromatic amino acids such as phenylalanine, tyrosine and tryptophan in people with Parkinson’s disease (Pietrucci, 2019). 

For this reason, I found it interesting to consider studies that link glyphosate to changes in the intestinal microbiome. Some hits:

  • Glyphosate changes the intestinal flora of bees and increases the susceptibility to infections and bee mortality (Motta, 2018). The researchers showed that the gene encoding EPSPS, the enzyme that is the target of glyphosate, was present in two variants in most of the bees studied. Bees with ‘variant I’ appeared to be much more sensitive to pathogens after exposure.
  • Exposure to glyphosate and ‘Roundup’ of female rats – in concentrations that are now considered ‘safe’ – leads to a changing intestinal microbiome in their offspring. (Mao, 2018). These effects were not found in the mother rat herself. The researchers point out that this shows that we have to be extra careful with exposure of pregnant women, children and adolescents.  The effects of glyphosate and ‘Roundup’ were different. Both led to an altered intestinal microbiome, but with a different composition. The authors conclude that it is not only important to understand the individual effects of glyphosate, but also to look at the impact of mixed formulations.
  • A study on the effects of glyphosate on various potential pathogens and beneficial bacteria present in the poultry stomach shows that pathogenic bacteria such as Salmonella and Clostridium are resistant to glyphosate. (Shehata, 2012). Useful bacteria such as enterococci, lactobacillus and bifidobacteria appear to be sensitive to herbicide infestation. According to the researchers, a reduction of useful bacteria in the gastrointestinal tract by intake of glyphosate can make poultry vulnerable to infections.
  • In a study on glyphosate exposure in mice, the researchers observed an increase in anxiety and depression. At the same time, they saw a change in the composition of intestinal bacteria occur and the authors describe how the observed behaviour may have been triggered by a decrease in the quantity of bacteroids, firmicutes and lactobacilli (Aitbali, 2018).

Sources:

Aitbali, Y., Ba-M’hamed, S., Elhidar, N., Nafis, A., Soraa, N., & Bennis, M. (2018). Glyphosate based- herbicide exposure affects gut microbiota, anxiety and depression-like behaviors in mice. Neurotoxicology and Teratology, 67, 44–49. https://doi.org/10.1016/j.ntt.2018.04.002 (Closed Access)

Boertien, J.M., Pereira, P.A., Velma. A., Scheperjans, F. (2019). Increasing Comparability and Utility of Gut Microbiome Studies in Parkinson’s Disease: A Systematic Review. Journal of Parkinson’s Disease, vol. 9, no. s2, pp. S297-S312, 2019. https://doi.org/10.3233/JPD-191711 (Open Acccess)

Borghammer, P., Van den Berg, N. (2019). Brain-First versus Gut-First. Parkinson’s Disease: A Hypothesis. Journal of Parkinson’s Disease. vol. 9, no. s2, pp. S281-S295, 2019. https://doi.org/10.3233/JPD-191721 (Open Access)

Mao, Q., Manservisi, F., Panzacchi, S., Mandrioli, D., Menghetti, I., Vornoli, A., … Hu, J. (2018). The Ramazzini Institute 13-week pilot study on glyphosate and Roundup administered at human-equivalent dose to Sprague Dawley rats: effects on the microbiome. Environmental health : a global access science source, 17(1), 50. https://doi.org/10.1186/s12940-018-0394-x (Open Access)

Motta, E., Rayman, K., Moran, N.A. (2018). Glyphosate perturbs the gut microbiota of honey bees. PNAS.15 (41) 10305-10310. https://doi.org/10.1073/pnas.1803880115 (Open Access)

Piettruci,D., e.a. (2019). Dysbiosis of gut microbiota in a selected population of Parkinson’s patients. Parkinsonism & Related Disorders, Volume 65, 124 – 130. https://doi.org/10.1016/j.parkreldis.2019.06.003 (Closed Access)

Santos, S. F., de Oliveira, H. L., Yamada, E. S., Neves, B. C., & Pereira, A., Jr (2019). The Gut and Parkinson’s Disease-A Bidirectional Pathway. Frontiers in neurology, 10, 574. https://doi.org/10.3389/fneur.2019.00574 (Open Access)

Shesheta, A.A., Schrödl, W., Aldin, A.A., Hafez, H.M., Krüger, M.(2012). The effect of glyphosate on potential pathogens and beneficial members of poultry microbiota in vitro. Curr Microbiol 66: 350-358. https://doi.org/10.1007/s00284-012-0277-2. Te bekijken via http://www.nvlv.nl/downloads/2012-Krueger,%20M-glyphosate%20effects.pdf

Generational toxicology needs to be incorporated into the risk assessment of glyphosate and all other potential toxicants. The ability of glyphosate and other environmental toxicants to impact our future generations needs to be considered, and is potentially as important as the direct exposure toxicology done today for risk assessment | Kubsad, 2019

Ancestral exposures can promote the onset of disease in future generations. A study in rats has shown that glyphosate exhibits such a transgenerational effect. The grandchildren and great-grandchildren (who had never been exposed themselves) showed striking effects such as obesity, various types of cancer and premature births.

Source:

Kubsad, D. et al. Assessment of Glyphosate Induced Epigenetic Transgenerational Inheritance of Pathologies and Sperm Epimutations: Generational Toxicology. Scientific Reports, volume 9, Article number: 6372 (2019). https://doi.org/10.1038/s41598-019-42860-0 (Open Access)

A number of case studies in which exposure to glyphosate is linked to parkinson’s disease (isme) are reported in the scientific literature:

  • Parkinsonism
    Barbosa (2001) reports the case of a 54-year-old man who accidentally sprayed himself with glyphosate and who developed parkinsonism a month later. A year later, this patient showed a slowly resting tremor in his left hand and arm, accompanied by a limitation of his short term memory.
  • Parkinsonism
    Wang (2011) reports a case of parkinsonism following chronic exposure to glyphosate in a previously healthy 44-year-old woman who worked for 3 years in a chemical plant in the department where glyphosate was produced. She showed rigidity, slowness and resting tremor in the limbs, without affecting short-term memory.
  • Reversible parkinsonism
    Zheng (2018) describes a case study of reversible Parkinsonism after acute exposure to glyphosate. A previously healthy 58-year-old woman comes to the hospital with a headache and in the coming days develops inertia, tremors and difficulty walking. Fifteen days later she has a mask face, bradykinesia, the gear phenomenon, a clearly curved posture, reduced arm swing and a russtremor in all limbs. She had been spraying glyphosate for more than 3 hours a day for a week without using any protective equipment. After being treated with ATP, pralidoxime iodide and scopolamine hydrobromide, her headache and parkinsonism disappeared.
  • Parkinsonisme
    A man who wanted to commit suicide by drinking 200 ml of glyphosate, at the age of 34, develops parkinsonism four years later (Eriguchi, 2019). He swallowed the glyphosate and after 10 minutes he vomited. His stomach was pumped at the hospital and he was given activated carbon. Four years later, he developed right-sided parkinsonian symptoms that responded well to the administration of levodopa.

Sources:

Barbosa, E.R., Leiras da Costa, M.D, Bacheschi, L.A, Scaff, M., Leite, C.C. (2001). Parkinsonism after glycine-derivate exposureMov Disord 16: 565-568. https://doi.org/10.1002/mds.1105 (Closed Access)

Eriguchi, M., Iida, K., Ikeda, S., Osoegawa, M., Nishioka, K., Hattori, N., … Hara, H. (2019). Parkinsonism Relating to Intoxication with Glyphosate. Internal medicine (Tokyo, Japan)58(13), 1935–1938. https://doi.org/10.2169/internalmedicine.2028-18 (Open Access)

Wang, G., Fan, X.N., Tan, Y.Y., Cheng, Q., Chen, S.D., 2011. Parkinsonism after chronic occupational exposure to glyphosate. Parkinsonism Relat. Disord. 17, 486–487. https://doi.org/10.1016/j.parkreldis.2011.02.003 (Closed Access)

Zheng, Q., Yin, J., Zhu, L., Jiao, L., & Xu, Z. (2018). Reversible Parkinsonism induced by acute exposure glyphosate. Parkinsonism & Related Disorders, 50, 121. https://doi.org/10.1016/j.parkreldis.2018.01.021 (Closed Access)

Mancozeb

Mancozeb is a non-systemic contact fungicide with protective multi-side activity, effective on the germination of spores. It acts by blocking the pathogenic fungal metabolism at the cellular level, at several stages of the physiologically important Citrate cycle, known as the main pathway of the Acetyl coenzyme-A metabolism, and strongly linked to the cellular energy metabolism and the amino-acid synthesis | Commission Directive 2005/72/EC

The proposed molecular structure of mancozeb (C4H6MnN2S4)x(Zn)y), a polymer complex of ‘maneb entitites’ (Maneb is already banned in the EU

Mancozeb (MZ) is an organometallic fungicide mainly used on fruit and vegetables. MZ belongs to the so-called dithiocarbamates (DTCs). It is a polymer complex of ethylenebisdithiocarbamate with manganese and zinc.

Mancozeb was approved in the EU on 1 July 2006 (Commission Directive 2005/72/EC). According to the accompanying document, Mancozeb intervenes in the citric acid cycle of the fungi being controlled and exposure ensures that the spores of moulds do not germinate. Therefore, the fungi cannot reproduce. The citric acid cycle that mancozeb is involved in does not only occur in fungi. It occurs in all living organisms and is important for energy management.

In addition, it has been investigated how MZ inhibits the activity of certain proteins/enzymes. The interaction of MZ with enzymes is probably caused by its high affinity to form a complex with the SH-groups on enzymes. For maneb this has been proven.

In humans, MZ is absorbed by the skin, mucous membranes and respiratory and gastrointestinal tracts and metabolized via the liver enzymes.

Indications of (neuro)toxicity

We observed a higher PD prevalence in farmers who used pesticides, on almost all French crops and livestock. Particularly, the present study provides further support for specific active ingredients applied to crops, which have previously been associated with PD such as rotenone, a natural insecticide, diquat and paraquat, bipyridil herbicides and the dithiocarbamate fungicides maneb, mancozeb and ziram | Pouchieu, 2018

Exposure to mancozeb (MZ) is associated with an increased risk of Parkinson’s disease and immunotoxicity in humans. In addition, exposure leads to neurodegeneration, genotoxicity and behavioural disorders in a variety of organisms. Below you find a selection from the scientific literature:

In the context of the expanding interest of neurotransmitters other than dopamine involved in Parkinson’s disease, it is timely that our research has shown a potentially increased vulnerability of GABAergic neurons to a widely used glyphosate-containing herbicide and a popular Mn-containing fungicide, Mancozeb | Negga, 2012

C. Elegans is a worm that is genetically very similar to humans. The worm is often used as a model organism for research into disease mechanisms, including neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease.

C.Elegans’ GABA neurons appear to be extremely sensitive to exposure to MZ. GABA – an abbreviation for gamma-aminobutyric acid – is a so-called neurotransmitter. A neurotransmitter is a signalling substance that transmits nerve impulses between nerve cells. The authors conclude that in toxicity studies not only dopaminergic neurons should be considered, but also other neurons.

Source:

Negga, R., Stuart, J.A., Machen, M.L., Salva, J., Lizek, A.J., Richardson, S.J. et al (2012). Exposure to glyphosate- and/or Mn/Zn-ethylenebis-dithiocarbamate-containing pesticides leads to degeneration of gamma-aminobutyric acid and dopamine neurons in Caenorhabditis elegans. Neurotox Res 21:281–290. https://doi.org/10.1007/s1264 0-011-9274-7 (Te bekijken via http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3288661&blobtype=pdf

A pre-treatment of C. Elegans with a dopamine transporter antagonist protects dopaminergic neurons against chronic MZ-treatment (24 hours). A dopamine transporter is a transmembrane protein, responsible for the reuptake of dopamine from the synaptic cleft tween two neurons. A DAT antagonist blocks the reuptake of dopamine and all other substances that may use this channel, such as presumably MZ. The authors conclude that DAT transporters may play a role in the neurotoxicity of MZ for dopamine neurons.

Source:

Montgomery, K., Corona, C., Frye, R., Barnett, R., Bailey, A., Fitsanakis, V.A. (2018). Transport of a manganese/zinc ethylene-bis-dithiocarbamate fungicide may involve pre-synaptic dopaminergic transporters. Neurotoxicology and Teratology, 68, 66-71. https://doi.org/10.1016/j.ntt.2018.05.004 (Closed Access)

At higher levels of MZ, the behavior of C. Elegans changes. The worm stops laying eggs.

The concentration used by the researchers was within the current LC50 value for MZ (LC50 is the concentration in the air that causes death in inhalation in 50 % of the test animals. LC stands for Lethal Concentration).

The authors conclude that behavioural disorders can be a biomarker of the toxicity of MZ.

Source:

Brody, A.H., Chou, E., Gray, J.M., Pokyrwka, N.J., Raley-Susman, K.M. (2013). Mancozeb-induced behavioral deficits precede structural neural degeneration. Neurotoxicology, 34, 74-81. https://doi.org/10.1016/j.neuro.2012.10.007 (Open Access)

Researchers find increased levels of manganese in the brain of common carps exposed to MZ. At non-lethal concentrations, they see perceptible behavioural changes.

In addition, the researchers see a significant increase in ROS (Reactive Oxygen Species) levels in the brain of carp after exposure to MZ.

Futhermore, they see a significant increase in the amount of Nrf2 protein in the brain (Nuclear Factor Erythroid 2-Related Factor 2). Nrf2 is a so-called transcription factor (or sequence-specific DNA binder). A transcription factor is a protein that determines the rate at which genetic information from DNA is read and converted into messenger RNA. Nrf2 activates a large number of so-called cell-protective genes. For example, Nrf2 triggers the transcription of the body’s own antioxidant and detoxification enzymes. The increase in Nrf2 may expose a mechanism by which organisms try to limit damage from MZ.

Source:

Costa-Silva, D.G., Lopes, A.R., Martins, I.K. et al. (2018). Mancozeb exposure results in manganese accumulation and Nrf2-related antioxidant responses in the brain of common carp Cyprinus carpio. Environmental Science and Pollution Research, 25(16), 15529–15540. https://doi.org/10.1007/s11356-018-1724-9 (Closed Access)

Meer weten over Nrf2? Lees de blog van Simon Stott op Science of Parkinson’s

In addition to neurons, other cells exist in the brain. These cells are called glia cells (glia is Greek for “glue”). One of the types of glia cells are astrocytes. Astrocytes are also part of the blood-brain barrier.

Mancozeb appears to be cytotoxic to astrocytes, isolated from the hippocampus of rats, in a dose-dependent manner. If cells were exposed to MZ for 1 hour, they would not recover. With atomic absorption, the researchers showed a significant accumulation of manganese in the astrocytes.

If the researchers administered chelators – compounds that form complexes with metal ions – and antioxidants together with MZ, then neurotoxicity did not occur. This seems to indicate that neurotoxicity is at least partly caused by an accumulation of manganese.

Source:

Tsang, M. & Trombetta, L. (2007). The protective role of chelators and antioxidants on mancozeb-induced toxicity in rat hippocampal astrocytes. Toxicology and industrial health. 23. 459-70. https://doi.org/10.1177/0748233708089039 (Closed Access)

Male mice were exposed to low and high doses of MZ (30 and 90 mg/kg body weight respectively) from late pregnancy to adolescence. The hypothalamus of the mice was then examined for neurotoxicity. The researchers saw cell death, neuroinflammation and demyelination (loss of myelin, the substance that can be present as an insulating layer around nerves and that accelerates the conduction of impulses). In addition, they saw an imbalance in the proportions of the neurotransmitters glutamate and GABA (gamma-aminobutyric acid) (Moralles-Ovales, 2018).

A neurotransmitter is a signalling substance that transmits nerve impulses between neurons in the synapses. Some neurotransmitters stimulate signal transmission (such as glutamate) and others inhibit it (such as GABA). In this study, with an increasing dose of MZ, the ratio of stimulating to inhibitory neurotransmitters increased, leading, according to the authors, to increased toxicity and neuronal vulnerability.

Two additional articles with the same type of conclusions:

  • On exposure to MZ, an increase in oxidative stress markers (ROS, reactive oxygen species) and mitochondrial inhibition has been observed in rats (Domico, 2012). 
  • In cell cultures of the cerebral cortex of the mouse, mitochondria are damaged and there are signs of neuroinflammation. According to the authors, this can lead to neuronal damage (Pena-Contreras, 2016)

Sources:

Domico, L.M., Zeevalk, G.D., Bernard, L.P., Cooper, K.R. (2006). Acute neurotoxic effects of mancozeb and maneb in mesencephalic neuronal cultures are associated with mitochondrial dysfunction. NeuroToxicology, 27, 816-825. https://doi.org/10.1016/j.neuro.2006.07.0 (Closed Access)

Peña-Contreras, Z., Miranda-Contreras, L., Morales-Ovalles, Y., Colmenares-Sulbarán, M., Dávila-Vera, D., Balza-Quintero, A., Salmen, S., Mendoza-Briceño, R.V. (2016). Atrazine and mancozeb induce excitotoxicity and cytotoxicity in primary cultures of mouse cerebellar cortex. Toxicological & Environmental Chemistry, 98:8, 959-976. https://doi.org/10.1080/02772248.2016.1151020 (Closed Access)

Morales-Ovalles, Y., Miranda-Contreras, L., & Peña-Contreras, Z. (2018). Developmental Exposure to Mancozeb Induced Neurochemical and Morphological Alterations in Adult Male Mouse Hypothalamus. Environmental Toxicology and Pharmacology. https://doi.org/10.1016/j.etap.2018.10.004 (Closed Access)

Maneb and Mancozeb are both equally toxic to cell cultures grown from human intestinal epithelium. Exposure leads to metal accumulation of manganese, copper and zinc in and between large intestinal cells called HT-29 and Caco2. The authors conclude that the rapid increase in metal concentrations affects the ability of individual cells to maintain a healthy level of metals in the cell. Metal overload occurs, which in turn leads to oxidative stress and cell death. According to the authors, the toxicity of MZ is caused both by the metal part and by the organic part of the polymer complex.

Source:

Hoffman, L., Trombetta, L., Hardej, D. (2015). Maneb and Mancozeb cause metal overload in human colon cells. Environmental Toxicology and Pharmacology. https://doi.org/10.1016/j.etap.2015.11.002 (Closed Access)

A lymphocyte is a type of white blood cell and lymphocytes play an important role in our immune system. In cell cultures of human lymphocytes, exposure to MZ leads to DNA damage and cell death. The lymphocytes tested were isolated from blood from healthy, non-smoking blood donors. The cytotoxic effects of MZ were studied at various concentrations (0.2-10μg/ml) at 6, 12, and 24-hour exposure.

As exposure increased, the researchers found that cytochrome c, ROS (Reactive Oxygen Species) and caspace-9 and caspace-3 increased, among other things. Cytochrome c and caspaces each play their own role in ‘programmed cell death’. Different signals can incite the cells to ‘suicide’ via a process called apoptosis. When mitochondria are damaged, cytochrome C can signal that it is time for ‘suicide’. Caspaces are proteins that help break down enzymes. In this case, the researchers saw an increase in the breakdown of the DNA repair enzyme PARP (poly (ADP-ribose) polymerase). The breakdown of PARP meant that DNA damage could not be repaired. The research also shows the involvement of oxidative stress in MZ-induced genotoxicity and cell death.

Source:

Srivastava, A. K., Ali, W., Singh, R., Bhui, K., Tyagi, S., Al-Khedhairy, A. A., … Shukla, Y. (2012). Mancozeb-induced genotoxicity and apoptosis in cultured human lymphocytes. Life Sciences, 90(21-22), 815–824. https://doi.org/10.1016/j.lfs.2011.12.013

A small 2005 study with 13 winegrowers working with Mancozeb and 13 control subjects showed that exposure to a low concentration of MZ changed the functioning of the immune system. First, the researchers showed that the farmers were actually exposed by measuring the level of ethylenethiourea (ETU) in urine. ETU is a degradation product of MZ. In addition, they took blood samples and looked at the samples for factors that say something about the functioning of the immune system. For example, in exposed farmers, they saw an increase in the amount of white blood cells and also in CD19+ cells, a sign that the amount of B cells was increasing. A decrease in CD25+ cells indicated that the number of T-helper cells actually decreased. They also saw a decrease in TNF-alpha (Tumor Necrosis Factor), a substance that normally increases with an infection.

Sources:

Corsini, E., Birindelli, S., Fustinoni, S., De Paschale, G., Mammone, T., Visentin, S., … Colosio, C. (2005). Immunomodulatory effects of the fungicide Mancozeb in agricultural workers. Toxicology and Applied Pharmacology, 208(2), 178–185. https://doi.org/10.1016/j.taap.2005.02.011 (Closed Access)

Corsini, E., Viviani, B., Birindelli, S., Gilardi, F., Torri, A., Codecà, I., … Colosio, C. (2006). Molecular mechanisms underlying mancozeb-induced inhibition of TNF-alpha production. Toxicology and Applied Pharmacology, 212(2), 89–98. https://doi.org/10.1016/j.taap.2005.07.002 (Closed Access)

Researchers have used data from the cohort study AGRICAN to investigate relationships between the occurrence of Parkinson’s disease and exposure to certain pesticide/pesticide mixtures. Research among 1732 farmers with Parkinson’s disease showed, among other things, that the risk of Parkinson’s disease increases with exposure to MZ.

This study provides much more information. The researchers saw that Parkinson’s disease is more common among farmers who use pesticides anyway, regardless of the crop or cattle with which they farm. The study provides further support for already established relationships between certain pesticides and Parkinson’s disease, such as rotenone, diquat and paraquat, bipyridil herbicides and the dithiocarbamate fungicides maneb, mancozeb and ziram. The researchers also found – for the first time – positive associations between Parkinson’s disease and exposure to other dithiocarbamate fungicides such as cupreb, ferbam, mancopper, metiram, propineb, thiram and zineb.

Source:

Pouchieu, C., Piel, C., Carles, C., Gruber, A., Helmer, C. (2017). Pesticide use in agriculture and Parkinson’s disease in the AGRICAN cohort study. International Journal of Epidemiology, 299-310. https://doi.org/10.1093/ije/dyx225 (Open Access)

The burden of proof

After reading the scientific literature, we can at least conclude that there is ‘reasonable doubt’. Pesticides in general – and mancozeb and glyphosate in particular – should justify themselves.

There certainly remains an important challenge in translating cellular work to human populations. And epidemiological studies, while revealing links between pesticide exposure and the risk of developing Parkinson’s disease, do not tell us anything about the mechanism by which toxicity is generated (Richardson, 2019). The problem, however, is that while we look for ‘certainty’ through scientific research (a certainty that really isn’t within our grasp) our population and our environment continue to be exposed to suspicious pesticides.

The burden of proof lies on the wrong side of the table.

I feel this is partly due to the fact that the discussion is too easily diluted. For what would happen if we would take a closer look?

In the space of a few weeks, the Parkinson Vereniging received 60 reports from people who associate their Parkinson’s disease with exposure to pesticides. The FNV (a trade union in the Netherlands) received zero reports. A fact from which you can quickly draw the wrong conclusions. Does zero reporting mean that the problem does not exist? Or are we looking in the wrong places?

Many farmers are not affiliated with the FNV and will not see a company phyisician either. After all, they are self-employed. Also, not everyone who becomes ill will make the connection with pesticides. This requires a great deal of information and admitting that this relationship exists.

Furthermore, it is not only the working population that has filed a report at the Parkinson Vereniging, It’s also residents living nearby exposed areas, children of farmers and people who have worked with pesticides in the laboratory. In addition, scientific studies show that children in the abdomen are already susceptible to the harmful effects of pesticides and they are certainly not able to report any future negative effects of exposure. The same applies, of course, to future generations.

Earlier this year, an RIVM report about the risk for residents living nearby exposed areas was published. In the report, RIVM concluded that the concentrations in residential areas did not exceed the accepted standards. But what if these standards are not right for vulnerable groups? Following the report, our Minister of Health – Minister Bruins – asked the Dutch Health Council (Gezondheidsraad) for advice:

I would ask you to advise on the extent to which the current assessment procedure is sufficiently protective of the health of local residents – in particular of vulnerable groups such as pregnant women and children – and whether the assessment procedure takes account of possible cognitive effects. | Minister Bruins

This recognition is important, but the report is not expected until the summer of 2020, and in the meantime exposure will continue, even though we have known for a long time from the literature that these groups should be better protected.

This blog post focuses on two pesticides. There is a huge amount of potential (neuro)toxic agents on the market and looking at each one after another like I did in this post will of course take far too much time. In this way, we will continue to lag behind. In addition, we know very little about the effects of combined, cumulative and chronic low grade exposure.

Minster Bruins understands this and writes:

I also ask you to describe to what extent the assessment procedure is sufficiently protective of the cumulative effects of several crop protection products | Minister Bruins

Apart from the fact that I find it shocking that this has apparently not been looked at before, it will be ‘business as usual’ for the duration of the study.

In the meantime, more action is really needed and possible.

A few examples:

  • Maneb is already banned in the EU and mancozeb isn’t. In addition, there are other so-called dithiocarbamate fungicides such as cupreb, ferbam, mancopper, metiram, propineb, thiram, zineb and ziram on the market. For all these substances, the AGRICAN cohort study found a relationship with Parkinson’s disease. Perhaps this is a hint to (re)assess substances that have the same mechanism of action as a group of chemicals instead of per substance?
  • Why are there pesticides such as glyphosate on the market that can penetrate the blood-brain barrier? That certainly wouldn’t be my tip of the day to protect people from contracting a neurodegenerative disease.

Source:

Pouchieu, C., Piel, C., Carles, C., Gruber, A., Helmer, C. (2017). Pesticide use in agriculture and Parkinson’s disease in the AGRICAN cohort study. International Journal of Epidemiology, 299-310. https://doi.org/10.1093/ije/dyx225 (Open Access)

The scientific literature shows that behavioural disorders can be a biomarker of toxicity (e.g. Brody, 2013). A biomarker can tell us something about a process going on in our bodies.

It’s not just that exposure to pesticides increases the chance that we will eventually visibly have Parkinson’s disease. The possible prodromal symptoms that have preceded the visual onset for years are also important to take into account. Think of symptoms such as behavioural change, but also of changes in the intestinal microbiome and a weakening of our immune system.

In addition, Parkinson’s disease is only one of the many (neuro)degenerative diseases. Martins (2019) for example, describes a number of mechanisms that may underlie manganese induced neurodegeneration. According to the authors, a multitude of neurodegenerative disorders such as Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS) are characterized by metal dyshomeostasis which may contribute to disease-specific protein accumulation. 

Sources:

Brody, A.H., Chou, E., Gray, J.M., Pokyrwka, N.J., Raley-Susman, K.M. (2013). Mancozeb-induced behavioral deficits precede structural neural degeneration. Neurotoxicology, 34, 74-81. https://doi.org/10.1016/j.neuro.2012.10.007 (Open Access)

Martins, A.C., Morcillo, P., Ijomone, O.M., Venkataramani, V., Harrison, F.E., Lee, E., Bowman, A.B., Ascher, M. (2019). New insights on the rol of Manganes in Alzheimer’s Disease and Parkinson’s Disease. Int. J. Environmental Research and Publich Health. 16(19), 3546. https://doi.org/10.3390/ijerph16193546 (Open Access)

Final musings

This has been a very challenging blogpost to write. The question is:

What happens when the report has been completed, the parliamentary questions have been asked, the Zembla episode has been viewed, the scientific publication has been written, the conclusion has been drawn, the blog has been written and the statement has been made? Who feels responsible for continuing to put the individual actions into a larger context?

Do we want to wait until science ‘knows’ how current agricultural practices are damaging our (future) health?
Or is doubt sufficiently sown to want to harvest innovation instead?

With these questions in mind, I will continue my journey.

I will keep you posted.

Sparks

Disclaimer: I write these posts on my own account and not on behalf of the Dutch Parkinson’s Association (de Parkinson Vereniging).
You can find official statements from de Parkinson Vereniging on their own website.

Leave a Comment

Deze website gebruikt Akismet om spam te verminderen. Bekijk hoe je reactie-gegevens worden verwerkt.