Glyphosate as a direct or indirect activator of pro-inflammatory signaling and cognitive impairment

Abstract

Glyphosate-based herbicides are widely used around the world, making it likely that most humans have significant exposure. Because of habitual exposure, there are concerns about toxicity including neurotoxicity that could result in neurological, psychiatric, or cognitive impairment. We recently found that a single injection of glyphosate inhibits long-term potentiation, a cellular model of learning and memory, in rat hippocampal slices dissected 1 day after injection, indicating that glyphosate-based herbicides can alter cognitive function. Glyphosate-based herbicides could adversely affect cognitive function either indirectly and/or directly. Indirectly, glyphosate could affect gut microbiota, and if dysbiosis results in endotoxemia (leaky gut), infiltrated bacterial by-products such as lipopolysaccharides could activate pro-inflammatory cascades. Glyphosate can also directly trigger pro-inflammatory cascades. Indeed, we observed that acute glyphosate exposure inhibits long-term potentiation in rat hippocampal slices. Interestingly, direct inhibition of long-term potentiation by glyphosate appears to be similar to that of lipopolysaccharides. There are several possible measures to control dysbiosis and neuroinflammation caused by glyphosate. Dietary intake of polyphenols, such as quercetin, which overcome the inhibitory effect of glyphosate on long-term potentiation, could be one effective strategy. The aim of this narrative review is to discuss possible mechanisms underlying neurotoxicity following glyphosate exposure as a means to identify potential treatments.

Introduction

Glyphosate-based herbicides (GBH), which have often been associated with the original trade name, Roundup, are ubiquitous in the environment. In many regions around the world, it is extremely difficult to avoid exposure. The increase in the use of these herbicides since the development of genetically modified plants and the surge of some health conditions may simply be a coincidence. However, it is also important to understand the potential toxicity of glyphosate in order to promote public health and avoid potential adverse outcomes from exposure. In this review, we discuss (I) the history and general features of glyphosate, (II) possible mechanisms underlying glypohosate neurotoxicity, (III) the effects of glyphosate on neuroinflammation, and (IV) possible ways of dealing with glyphosate exposure.

Search Strategy

Our review of the literature used PubMed as the search engine with search terms including herbicide, Roundup, glyphosate, GBH, ER, UPR, CXCL, CXCR, LPS, TLR, NLRP, and MTOR. We also used the Google search engine for glyphosate use and history.

History and General Features of Glyphosate

Glyphosate, which was first developed in 1950, was originally patented as a cation chelator (Fon and Uhing, 1964). In the 1960’s, it was used as a descaling agent to clean pipes. Because glyphosate inhibits the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase in the aromatic amino acid biosynthetic pathway, it was patented as a herbicide in 1970 and brought to market under the trade name Roundup®. GBH are now produced by multiple companies including Bayer, Adama, OPL, BASF SE, Snyngenta AG, and Nissan Chemical among others under brand names such as Eraser, Rodeo Aquatic Herbicide, and Kesuda. The market for glyphosate expanded exponentially as genetically modified plants were developed in the 1990s (Soares et al., 2021). In the US, about 140,000 tons of glyphosate was applied to 120 million Hectares annually in agricultural settings and 11,000 tons for non-crop sites (No author listed, 2019). Across the world, 825,000 tons of glyphosate were used in 2014 compared to 67,000 tons in 1995 (Statista Research Department, 2016).

It is estimated that 3.9% of applied glyphosate is lost to run off and another 6.9% enters the atmosphere (Lupi et al., 2019). The USA, Brazil, and China have the largest exposure to glyphosate with at least 0.1 mg/kg of dry soil (Maggi et al., 2020). In spite of its low vapor pressure (< 1 × 10^–5 Pa), glyphosate is commonly detected in both air (86%) and rain (77%) in the US Mississippi Delta agricultural region (Majewski et al., 2014). In Argentine tree-less planes (pampas), more than 80% of rain samples contain glyphosate (max 67.4 µg/L; Alonso et al., 2018). Glyphosate is also commonly detected in water samples of streams in the US (median 0.05 µg/L, maximal 8.1 µg/L; Medalie et al., 2020)

Glyphosate is routinely detected in genetically engineered crops and food based on these crops. For example, dry pasta contains glyphosate at levels of 60–150 µg/kg (Environmental Working Group, 2019). The US Food and Drug Administration (FDA) reports that no samples contained violative levels but non-violative levels of glyphosate were found in 63.1% of corn samples and 67.0% of soybean samples (Nutrition, 2023). The use of glyphosate is not limited to genetically engineered crops. Glyphosate is often used for early-season burn-down weed control and harvest aid by accelerating the drying of wheat, barley, oats, and beans that are not glyphosate-resistant. High levels of glyphosate are sometimes detected in chickpeas, lentils beans, and oats even if grown organically (Environmental Working Group, 2020).

Accordingly, human exposure to glyphosate has become routine across populations. In France, glyphosate was detected in over 99% of human urine samples (Grau et al., 2022) while in central India, glyphosate was detected in 93% of urine samples with a mean (SD) concentration of 3.4 (1.2) µg/L (Parvez et al., 2018). Because only 1% of ingested glyphosate is secreted in urine (Zoller et al., 2020), this level indicates possibly significant exposure.

Possible Mechanisms of Neurotoxicity

Disruption of the gut microbiota and the gut barrier

As noted above, glyphosate has long been deemed safe for humans because the shikimate pathway, which is selectively blocked by glyphosate, does not exist in animal cells (Herrmann and Weaver, 1999). However, this pathway is not limited to plants and could be important for some microorganisms. In 2013, Samsel and Seneff hypothesized that the microbiota, the microorganisms comprising bacteria, archae, viruses, and fungi colonizing the gut, could be imbalanced by glyphosate and that the imbalance may impair sulfate transport to inhibit cytochrome P450, possibly resulting in obesity and psychiatric illnesses including autism spectrum disorder (Samsel and Seneff, 2013). Their paper and publisher have been criticized because of the lack of experimental evidence for this hypothesis (Mesnage and Antoniou, 2017).

Recent experimental evidence, subsequent to the Samsel and Seneff (2013) paper, shows some diversities in the effects of glyphosate on gut microbiota. In rats after 2 weeks of exposure to glyphosate or Glyfonova 450 PLUS (which contains 450 g/kg glyphosate) at 25 mg/kg per day, the pH of feces was significantly higher than controls, although bacterial compositions were not robustly altered (Nielsen et al., 2018). Similarly, a 3-day exposure of 228 mg/day of glyphosate acid equivalents from Roundup LB Plus® on the colon content of pigs resulted in only subtle changes in the concentration of aromatic amino acids (Krause et al., 2020). With regard to microbial growth, it was reported that Roundup® but not glyphosate had an inhibitory effect (Clair et al., 2012). These differences could depend on how glyphosate is formulated and administered. Additionally, surfactants in the product may have more toxic effects than glyphosate itself (Mesnage et al., 2019). It is also possible that the duration and route of exposure affect the gut microbiome (Del Castilo et al., 2022). In a prenatal exposure paradigm, the gut microbiota of rats treated with water containing glyphosate or Roundup® (1.75 mg/kg per day) from embryonic day 6 (E6) to postnatal day 31 (P31), showed increased Prevotella in the Roundup-exposed group, while Lactobacillus was reduced in both groups (Mao et al., 2018). Prenatal exposure to lower doses also alters the gut microbiome in rat offspring (treated from E5-P21 with 0.098% glyphosate as Roundup Maxload® in drinking water). Moreover, this developmental exposure results in social interaction deficits in offspring (Pu et al., 2020). Autism spectrum disorder-like behaviors are also observed in offspring after prenatal exposure to pure glyphosate (Pu et al., 2021). Even in adult animals, long exposures to glyphosate alter microbiota. For example, in mice, the composition of microbiota was altered by only 10 µg/mL glyphosate in drinking water for 60 days (Lehman et al., 2023).

It is also known that glyphosate disrupts tight junctions between the small bowel and colonic epithelium cells (Vasiluk et al., 2005; Qiu et al., 2020), suggesting the possibility that leaky gut syndrome can be induced by glyphosate, as it is by gluten. As the relation between coeliac disease and autism has been speculated for decades 1969 (Croall et al., 2021), the possible link between glyphosate exposure and autism spectrum disorder could be explained by leaky gut syndrome directly induced by glyphosate. Thus, dysbiosis, an imbalanced bacterial composition in the gut, by glyphosate could impact the central nervous system (CNS) (Rueda-Ruzafa et al., 2019).

Epigenetic modifications

There are also concerns that glyphosate exposure might increase risks of non-Hodgkin lymphoma (Weisenburger, 2021), effects that could involve epigenetic mechanisms. Epigenetic modifications include differential expression of non-coding RNAs, DNA methylation, and histone modifications.

In the prefrontal cortex of murine offspring after perinatal exposure to 1% Roundup®, aberrant expression of microRNAs is detected that likely target genes regulating the Wnt/β-catenin and Notch pathways (Ji et al., 2018). Dysregulation of micro RNAs could also be a cause of neurodegenerative diseases (Juźwik et al., 2019). In the hippocampus of murine offspring after perinatal 1% Roundup® indirect exposure (from E14 to P7), aberrant expression of circular RNAs, non-coding RNAs that critically regulate gene expression via interaction with microRNA, was detected and some of these changes were related to stress-associated steroid metabolism pathways (Yu et al., 2018). Recent lines of evidence indicate that circular RNAs may be important for homeostasis in the CNS and may play a pivotal role in the occurrence or prevention of neurodegenerative illnesses such as Parkinson’s disease (Li et al., 2021; Dorostgou et al., 2022).

DNA methylation is another mechanism through which glyphosate could produce epigenetic changes. In vitro exposure of human leukocytes to 0.25 mM glyphosate for 24 hours, which corresponds to 42 mg/L, results in increased DNA methylation and, at 0.5 mM, glyphosate damages DNA (Kwiatkowska et al., 2017). In contrast, in human peripheral blood mononuclear cells treatment with as little as 0.5 µM glyphosate for 24 hours decreases global DNA methylation (Woźniak et al., 2020). DNA methylation is currently thought to be an epigenetic mechanism contributing to various neurological diseases (Reichard and Zimmer-Bensch, 2021).

Wozniak et al. (2021) analyzed genes related to histone methylation (EHMT1,2) and histone deacetylation (HDAC3 and 5) with glyphosate and its metabolite. These authors found that glyphosate, even at 0.5 µM, increased the expression of HDAC3. HDAC3 induces neurodegeneration in various animal models through targeting Neuronal PAS domain protein 4, an immediate early gene induced by neuronal activity, and brain-derived neurotrophic factor, a member of the neurotrophin family (Louis Sam Titus et al., 2019). HDAC3 is a gene related to the pathogenesis of AD. In the triple transgenic mouse model of Alzheimer’s disease (3×Tg-AD), RGFP-966, a selective HDAC3 inhibitor, reversed pathological tau phosphorylation and decreased Aβ_1–12 protein levels in the brain (Janczura et al., 2018).

Metal chelation

Glyphosate strongly chelates divalent cations, such as calcium, zinc, iron, cobalt, copper, and molybdenum (Duke, 2018; Mertens et al., 2018). Chelation of iron results in inactivation of cytochrome P450 enzymes. When rats drink water containing 0.7 mg/L glyphosate (intake 0.09 mg/kg per day) for 90 days there is a substantial (approximately 50%) reduction in hepatic cytochrome P450 enzymes (Larsen et al., 2014). If similar reductions occur in the CNS, glyphosate exposure could induce significant neuronal dysfunction because cytochrome P450 enzymes play a pivotal role in the production of neurosteroids. For instance, several lines of evidence indicate that allopregnanolone, a key neurosteroid, is crucial to prevent cellular stress and modulate stressful conditions related to psychiatric illnesses (Zorumski et al., 2019).

Chelation of zinc may result in dysfunction of synaptic transmission in the CNS. It appears that all zinc-containing neurons are glutamatergic (Frederickson CJ 2000) and zinc is important for the regulation of N-methyl-D-aspartic acid (NMDA) receptors, and glutamate-gated cation channels with high calcium permeability (Sandstead et al., 2000). Calcium-EDTA, but not zinc-EDTA, inhibits the induction of long-term potentiation (LTP), a cellular model of learning and memory (Izumi et al., 2006), suggesting the possibility that zinc chelation by glyphosate may have a significant impact on cognitive function. In hippocampal slices from immature 15-day-old rats, 0.01% Roundup® increases calcium uptake and induces cell death, as demonstrated by increased lactate dehydrogenase release (Cattani et al., 2014). The increase in calcium uptake is prevented by an NMDA receptor antagonist, suggesting the involvement of excitotoxicity through NMDA receptors.

The involvement of excitotoxicity is also speculated from the structure of glyphosate. Since glyphosate has structural similarities to both glutamate and glycine, both of which are important for regulating NMDA receptors, it is possible that glyphosate behaves like an NMDA receptor agonist (Cattani et al., 2017; Madani and Carpenter, 2022). Alternatively, glyphosate may promote the release or accumulation of glutamate in the brain (Costas-Ferreira et al., 2022). In 1969, Olney described a significant increase in obesity with exogenous monosodium glutamate exposure during development mediated by excitotoxic damage to the arcuate nucleus of the hypothalamus that resulted in hypothalamic dysfunction. It has been reported that glyphosate exposure during gestation also induces obesity in offspring (F2 and F3) (Kubsad et al., 2019). Thus, the effects of glyphosate on the glutamate system could contribute to its possible neurotoxicity.

Co-forumlants in GBH such as surfactants

Surfactants in GBH are another possible mechanism that could contribute to neurotoxicity. Because diverse and variable surfactants (such as alkyl polyglucoside, polyethoxylatedd amines (POEA), dodecanamine, TN-20, or cocoamine) are used in the preparation of herbicides, it is not easy to understand the role of these agents in toxicity. However, it is believed that certain surfactants can disrupt cell membranes (Aguirre-Ramírez et al., 2021). It has been reported that alkyl polyglucoside and POEA were 15–18 times and 1200–2000 times more cytotoxic in human placental cells than glyphosate, respectively (Defarge et al., 2016). Furthermore, in human tumor cell lines POE-15, the most commonly used POEA, but not glyphosate itself, is responsible for endoplasmic reticulum stress (Mesnage et al., 2022).

Glyphosate and Neuroinflammation

Ultimately, the mechanisms outlined above may cause synaptic dysfunction, cognitive impairment, and neurodegeneration via activation of neuroinflammation. Neuroinflammation typically involves microglial activation. Morphological modification of microglia to an active form has been observed in zebrafish kept in water containing 0.1 µg/L glyphosate (Forner-Piquer et al., 2021). After perinatal exposure to 250 or 500 mg/kg glyphosate (E0-P21 to mother), interleukin-1β (IL-1β) was increased in the prefrontal cortex and hippocampus of grown offspring (Ait-Bali et al., 2020). Increases in microglia are also observed In pubescent mice when their mothers are exposed to 0.3 mg/kg of oral glyphosate during the gestational period (de Castro Vieira Carneiro et al., 2023). A major question concerns how microglia are activated by glyphosate exposure. In the following section, we focus on the potential role of pro-inflammatory signaling in mediating the effects of glyphosate in the brain.

One possibility is that glyphosate triggers proinflammatiory cascades in the CNS via lipopolysaccharide (LPS). Dysbiosis may alter the permeability of not only the gut barrier but also the blood-brain barrier (BBB). Compared to pathogen-free mice with normal gut microbiota, germ-free mice show reduced expression of the tight junction proteins occludin and claudin-5, which results in increased permeability of the BBB (Braniste et al., 2014). The disruption of both the gut barrier and the BBB allows infiltration of LPS, endotoxins derived from the outer leaflet of the cell membrane of Gram-negative bacteria such as Escherichia coli, into the systemic circulation and CNS. LPS in turn activates immune cells, and microglia in the CNS, leading to the release of pro-inflammatory mediators such as the cytokines IL-1 and tumor necrosis factor alpha (TNF-α) as part of the inflammatory process. In the CNS, pro-inflammation in the presence of LPS results in synaptic dysfunction and learning impairment (Sheppard et al., 2019). In our studies, we found that LPS acutely disrupts LTP induction in rat hippocampal slices through microglial activation and synthesis of the oxysterol, 25-hydroxycholesterol, an important microglial- and cholesterol-derived modulator that helps to regulate immune responses (Izumi et al., 2021) in both the peripheral and central immune systems. Consistent with these results, LPS also induced memory impairment when administered in vivo via a mechanism involving 25-hydroxycholesterol. The link of neuroinflammation induced by dysbiosis is now widely considered in various neurodegenerative disorders including Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis (Roy Sarkar and Banerjee, 2019).

Prenatal administration of penicillin V to mice (31 mg/kg per day from 1 week before birth to weaning) disrupts the gut microbiota and alters the integrity of BBB preceding neuroinflammation in the frontal cortex, changes that result in aggressive behaviors. These changes occur without disrupting the gut barrier and without systemic inflammation (Leclercq et al., 2017), and suggest that dysbiosis could induce neuroinflammation even if LPS and other microbiota metabolites do not infiltrate the body. It is also possible that glyphosate can directly induce neuroinflammation even without altering the gut barrier. Thus, neuroinflammation and dysbiosis can occur separately without necessarily altering the integrity of the gut barrier. Consistent with this, we have found that synaptic plasticity (LTP) is inhibited in hippocampal slices from rats in which 30 mg/kg glyphosate was injected one day prior to dissection (Figure 1). This result suggests that, even if the gut microbiota remains intact, glyphosate may directly activate proinflammatory cascades to impair cognitive function.

Figure 1.

Glyphosate injection inhibits LTP.

One day after intraperitoneal injection of 30 mg/kg glyphosate or saline, 30–34-day-old rats were dissected for LTP studies in the CA1 region of hippocampal slices. Slices were prepared using a previously described method (Izumi et al., 2023). HFS (100 Hz for 1 second, arrow) was delivered at the time marked by the arrow. EPSPs evoked by Schaffer collateral pathway stimulation were potentiated by HFS in slices from control rats (open circles, n = 5) but not in slices from rats exposed to glyphosate (closed circles, n = 8). Created with Sigmaplot (14.5). These original data have not been submitted or published elsewhere. EPSP: Excitatory postsynaptic potentials; HFS: high frequency stimulation; LTP: long-term potentiation.

Even in the mature human CNS, orally ingested glyphosate can acutely infiltrate the brain and induce inflammation. It has been reported that 2 days after ingesting approximately 150 mL GBH (41% glyphosate) a patient presented with aseptic meningitis and elevated glyphosate concentrations in serum and CSF (1294 and 123 µg/mL, respectively; Sato et al., 2011). Winstone et al. (2022) exposed mice to 125, 250, and 500 mg/kg per day glyphosate via oral gavage for 14 days and detected glyphosate in the brain. TNF-α is detected in both plasma and brain after 500 mg/kg exposure but only in the brain after 125 mg/kg exposure. Moreover, brain glyphosate correlates with increased TNF-α levels (Winstone et al., 2022). Prenatal exposure of mice to a low dose of GBH (0.3 mg/kg glyphosate administered orally to the mother throughout the gestational period until birth) increased microimmunoactivity and TNF-α in the prefrontal cortex and resulted in increased anxiety detected by the Marble-Burying Test along with behavioral hyperactivity (de Castro Vieira Carneiro et al., 2023).

Using rat hippocampal slices, we observed that synaptic transmission in the hippocampal Cornu Ammonis 1 (CA1) region was completely suppressed by perfusion of 800 ppm Roundup®. Furthermore, LTP was inhibited when slices were preincubated with 1 µM glyphosate. Acute inhibition of LTP by administration of 100 µM glyphosate for 15 minutes was prevented by minocycline, an inhibitor of microglial activation, and by LPS-RS, an inhibitor of toll-like receptor 4 (TLR4), suggesting the involvement of TLR4 signaling after microglial activation (Izumi et al., 2023). We previously reported that LPS and acrylamide, a product formed by asparagine and sugars after high-temperature cooking, inhibit LTP induction in a similar manner (Izumi et al., 2022, 2021). However, a distinct difference is that direct inhibition of LTP induction by glyphosate is independent from the NLR family pyrin domain containing 3 (NLRP3) inflammasome activation. MCC-950, an inhibitor of NLRP3, overcomes the inhibitory effects on LTP induction by acrylamide, but not the inhibition by glyphosate.

It is also possible that glyphosate induces neuroinflammation via epigenetic changes (Bukowska et al., 2022). Increases in hippocampal mRNA expression of glucocorticoid receptors were accompanied by the reversal of DNA methylation. Trichostatin A, a histone deacetylase inhibitor, reverses epigenetic alterations and restores glucocorticoid receptor expression in mice that had experienced maternal separation before weaning. Trichostatin A also reverses the effect on the activation of nuclear factor-κB signaling and neuroinflammatory responses to sevoflurane (Zhu et al., 2017).

Epigenetic alterations could also result from chelation of divalent cations, particularly zinc (Mertens et al., 2018). In THP-1 cells, zinc deficiency over several weeks decreased IL-6 promoter methylation that likely contributed to increased IL-6 production (Wong et al., 2015). Several lines of evidence indicate that zinc deficiency, induced by chelation, could trigger neuroinflammation and cognitive impairment. Human monocytic cell line THP-1 cultured in zinc-deficient media, shows that expression of TNFα and IL1β mRNA was almost doubled by 10 ng/mL LPS compared to zinc-sufficient media (Wong et al., 2013; Wong, 2014), indicating that zinc deficiency facilitates proinflammatory responses. Zinc chelation also results in cognitive impairment via dysbiosis. Zinc deficiency can also alter microbiota and intestinal biota. In chickens, chronic dietary Zn depletion induces significant changes in the microbiota (Reed et al., 2015). Prenatal zinc depletion in mice results in changes in microbiota composition and increases in Zonulin-1 levels, indicating intestinal barrier dysfunction. Neuroinflammation and ALS-related behavioral changes are also seen in these mice (Sauer et al., 2022).

Taken together, glyphosate, if it enters the CNS, can directly initiate neuroinflammation, largely mimicking the ability of LPS to generate pro-inflammatory responses. Glyphosate may also disrupt the gut barrier, and bacterial by-products such as LPS could activate proinflammation cascades. Whichever is the case, the resulting neuroinflammation can result in behavioral abnormalities and cognitive impairment (Figure 2).

Figure 2.

Potential mechanisms depicting how glyphosate induces neuroinflammation.

Glyphosate can facilitate LPS release in the circulation, and can also directly infiltrate the CNS and mimic the actions of LPS. In addition, metal chelation and epigenetic alterations by glyphosate may contribute to neuroinflammation. Metabolites of glyphosate and other components in GBH, such as surfactants, could also participate. Created with Microsoft PowerPoint 2016. CNS: Central nervous system; GBH: glyphosate-based herbicides; LPS: lipopolysaccharide.

Possible Prevention and Treatment of Glyphosate Toxicity

Avoiding glyphosate is the primary way to prevent possible neuropsychiatric sequelae resulting from exposure. This, however, is extremely difficult because glyphosate is present ubiquitously, even in tap water and non-GMO crops. While it is important to know how to protect the brain from glyphosate, protection also depends on the acuteness of exposure and the dose. It has been reported that enhanced dopamine release from the striatum when mice are exposed to glyphosate (75 or 150 mg/kg, intraperitoneally) is prevented by reserpine (Costas-Ferreira et al., 2023). Reserpine could thus be considered when severe agitation appears after glyphosate intoxication. For more chronic exposures, alternative approaches could be considered. For example, consuming a fermented diet (such as yogurt, kimchi, miso, and sauerkraut) rich in Lactobacillus could be beneficial to preserve the microbiome (Rastogi and Singh, 2022). In small bowel and colonic epithelial cell lines, a lignite extract supplement (Terrahydrite (Restore®)) prevents glyphosate-mediated intestinal barrier dysfunction (Gildea et al., 2017). Disruption of the blood-brain barrier by LPS can be prevented by polyphenols such as isoflavone (Johnson et al., 2019). These remedies may have therapeutic potential if dysbiosis is responsible for neuronal dysfunction during chronic glyphosate exposure. Quercetin is a major polyphenol that attenuates inflammatory processes through inhibition of endoplasmic reticulum and oxidative stress (Feng et al., 2019). Quercetin has been shown to prevent neuronal damage and neuroinflammation induced by LPS. For instance, quercetin overcomes the reduction of synaptosomal-associated protein in the cortex and hippocampus of mice after LPS injection (Khan et al., 2018). Quercetin may also improve dysbiosis by LPS (Feng et al., 2023). In mice, depressive-like behaviors induced by glyphosate (50 mg/kg for 30 days via gavage) are prevented by simultaneous administration of quercetin (30 mg/kg; Bicca et al., 2021). We have recently found that the inhibition of LTP by 100 µM glyphosate in rat hippocampal slices was overcome by co-administration of 50 µM quercetin (Izumi et al., 2023). A diet rich in quercetin, which is found in apples, berries, tea, and especially onions, may be another way to protect against glyphosate-induced neurotoxicity.

Astrocytes are major contributors to brain function, and astrocytic dysfunction, which is often initiated by microglia, can influence not only neuronal survival but also stimulate further microglial activation (Yu et al., 2023). In the rat hypothalamus, glyphosate and GBH increase the expression of glial fibrillary acidic protein, an astrocyte marker (Duque-Díaz et al., 2022), and GBH activates mitochondrial respiratory chain enzymes in a rat astroglioma cell line (Neto da Silva et al., 2020). Thus, GBH-induced changes in astrocytic function could contribute to inflammatory changes and neuronal dysfunction (Anderson, 2022). Attenuating GBH-driven changes in astrocytes could provide an important early target to limit the impact of GBH on CNS function.

Conclusion

Glyphosate, the active ingredient in the most widely used herbicides, can cause neuroinflammation by directly infiltrating the CNS or by indirectly inducing dysbiosis and leaky gut. In either case, prevention of neuroinflammation could be a possible countermeasure to deal with the potential adverse effects of glyphosate exposure. While definitive answers about the toxicity of glyphosate are presently lacking, it is clear that further systematic study of glyphosate’s potential neurotoxicity is warranted given widespread exposure in humans.

Funding Statement

Funding: This work was supported by MH101874 (to CFZ), MH122379 (to CFZ), and the Taylor Family Institute for Innovative Psychiatric Research and the Bantly Foundation (to CFZ).