Behavioral and Immunohistochemical Study of the Effects of Subchronic and Chronic Exposure to Glyphosate in Mice

The impact and toxicity of glyphosate and glyphosate-based herbicides on health and immunity

Glyphosate, or N-phosphomethyl(glycine), is an organophosphorus compound and a competitive inhibitor of the shikimate pathway that allows aromatic amino acid biosynthesis in plants and microorganisms. Its utilization in broad-spectrum herbicides, such as RoundUp®, has continued to increase since 1974; glyphosate, as well as its primary metabolite aminomethylphosphonic acid, is measured in soils, water, plants, animals and food. In humans, glyphosate is detected in blood and urine, especially in exposed workers, and is excreted within a few days. It has long been regarded as harmless in animals, but growing literature has reported health risks associated with glyphosate and glyphosate-based herbicides. In 2017, the International Agency for Research on Cancer (IARC) classified glyphosate as "probably carcinogenic" in humans. However, other national agencies did not tighten their glyphosate restrictions and even prolonged authorizations of its use. There are also discrepancies between countries' authorized levels, demonstrating an absence of a clear consensus on glyphosate to date. This review details the effects of glyphosate and glyphosate-based herbicides on fish and mammal health, focusing on the immune system. Increasing evidence shows that glyphosate and glyphosate-based herbicides exhibit cytotoxic and genotoxic effects, increase oxidative stress, disrupt the estrogen pathway, impair some cerebral functions, and allegedly correlate with some cancers. Glyphosate effects on the immune system appear to alter the complement cascade, phagocytic function, and lymphocyte responses, and increase the production of pro-inflammatory cytokines in fish. In mammals, including humans, glyphosate mainly has cytotoxic and genotoxic effects, causes inflammation, and affects lymphocyte functions and the interactions between microorganisms and the immune system. Importantly, even as many outcomes are still being debated, evidence points to a need for more studies to better decipher the risks from glyphosate and better regulation of its global utilization.

Absence of glyphosate-induced effects on ovarian folliculogenesis and steroidogenesis

Glyphosate (GLY) is an herbicidal active ingredient and both in vitro and in vivo studies suggest that GLY alters ovarian function. To determine if a chronic GLY exposure model affected steroidogenesis or folliculogenesis in vivo, postnatal day 42 C57BL6 female mice were orally delivered vehicle control (saline) or GLY (2 mg/Kg) from a pipette tip five days per week for either five or ten weeks. Mice were euthanized at the pro-estrus stage of the estrous cycle. GLY exposure did not impact body weight gain, organ weights, or healthy follicle numbers. In addition, GLY exposure did not affect abundance of ovarian mRNA encoding kit ligand (Kitlg), KIT proto-oncogene receptor tyrosine kinase (c-Kit), insulin receptor (Insr), insulin receptor substrate (Irs1 or Irs2) and protein thymoma viral proto-oncogene 1 (AKT) or phosphorylated AKT. Ovarian mRNA or protein abundance of Star, 3β-hydroxysteroid dehydrogenase (Hsd3b1), Cyp11a1 or Cyp19a were also not altered by GLY. Circulating 17β-estradiol and progesterone concentration were unaffected by GLY exposure. In conclusion, chronic GLY exposure for five or ten weeks did not affect the ovarian endpoints examined herein.

Pesticides used in Europe and autism spectrum disorder risk: can novel exposure hypotheses be formulated beyond organophosphates, organochlorines, pyrethroids and carbamates? - A systematic review

BACKGROUND

A growing body of evidences suggests an association between early exposure to organophosphates (OPs), organochlorines (OCs), pyrethroids or carbamates and autism spectrum disorder (ASD). However, there are limited data about the other pesticide groups, especially in Europe.

OBJECTIVES

Based on a systematic review, we aimed to assess the influence of neuro- and thyrotoxic agricultural and domestic pesticides (other than OPs, OCs, pyrethroids and carbamates) authorized in Europe on risk of ASD in children or ASD behavioral phenotypes in rodents.

METHODS

Pesticides were initially identified in the Hazardous Substances Data Bank. 20 currently used (10 pesticide groups) were retained based on the higher exposure potential. Epidemiological (children) and in vivo (rodents) studies were identified through PubMed, Web of Science and TOXLINE, without restriction of publication date or country (last update: November 2019). The risk of bias and level of evidence were also assessed. This systematic review is registered at the International Prospective Register of Systematic Reviews (PROSPERO, registration number CRD42019145384).

RESULTS

In total, two epidemiological and 15 in vivo studies were retained, focusing on the azole, neonicotinoid, phenylpyrazole and phosphonoglycine pesticide groups. No study was conducted in Europe. Glyphosate, imidacloprid, clothianidin, myclobutanil, acetamiprid, tebuconazole, thiabendazole and fipronil, globally reported an association with an increased risk of ASD in children and/or ASD behavioral phenotypes in rodents. In children, glyphosate and myclobutanil showed a "moderate level of evidence" in their association with ASD, whereas imidacloprid showed an "inadequate level of evidence". In rodents, clothianidin, imidacloprid and glyphosate showed a "high level of evidence" in their association with altered behavioral, learning and memory skills.

CONCLUSION

In the framework of environmental risk factors of ASD, novel hypotheses can be formulated about early exposure to eight pesticides. Glyphosate presented the most salient level of evidence. Given their neuro- and thyrotoxic properties, additional studies are needed for the 12 other pesticides not yet studied as potential ASD risk factors according to our inclusion criteria.

Repeated exposure of pyriproxyfen to pregnant female mice causes developmental abnormalities in prenatal pups

The continuous exposure to conventional pesticides leads to severe health and environmental issues especially at prenatal stage during developmental period. Herein, we aimed to investigate the anomalies due to repeated exposure of pyriproxyfen in pregnant female mice and their neonates. Twenty-four pregnant female mice were repeatedly administered with pyriproxyfen at 30, 100, 300, and 1000 mg/kg by oral gauge from gestation day (GD) 7 to gestation day 17 and six females were given distilled water in the control group. All the live pups were euthanized at postnatal day (PND) 7 and their organs (heart, liver, kidney, and brain) were dissected out, weighed, and assessed for further histopathological examinations. The results exhibited a significant (P < 0.001) decrease in the body weight gain of all treated pregnant mice in comparison to the controls and a significant increase in the gestational length was observed in group IV (P < 0.01) and group V (P < 0.001). In addition, no live pups were born in groups IV and V and one pregnant female mouse was also found dead in both treatments. The body weights of the pups were significantly decreased in group II (P < 0.05) and group III (P < 0.001) and the relative organ (liver, heart, and kidney) weight of the pups was increased significantly (P < 0.001, P < 0.01, P < 0.05) due to prenatal exposure in group II as compared to group I. The relative brain weights of the pups were decreased significantly (P < 0.001) in groups II and III as compared to group I. The liver, kidney, heart, and brain sections exhibited various histological alterations in groups II and III by hematoxylin and eosin staining. Furthermore, immunohistochemical staining of the coronal sections of pup's brain showed significant (P < 0.001) reduction in cortical radial thickness and total neural count in group II and III as compared to group I. Therefore, the prenatal exposure to pyriproxyfen provoked the damage to various organs in mice offspring and an increase in fetal death at higher doses.

Pre- and postnatal exposure to glyphosate-based herbicide causes behavioral and cognitive impairments in adult mice: evidence of cortical ad hippocampal dysfunction

Glyphosate-based herbicides (GBH) are the most widely used pesticides worldwide. Despite considerable progress in describing the neurotoxic potential of GBH, the harmful effects on brain cytoarchitecture and behavior are still unclear. Here, we addressed the developmental impact of GBH by exposing female mice to 250 or 500 mg/kg doses of GBH during both pregnancy and lactation and then examined the downstream effects at the behavioral, neurochemical and molecular levels. We show that pre- and neonatal exposure to GBH impairs fertility and reproduction parameters as well as maternal behavior of exposed mothers. In offspring, GBH was responsible for a global delay in innate reflexes and a deficit in motor development. At the adult age, exposed animals showed a decrease of locomotor activity, sociability, learning and short- and long-term memory associated with alterations of cholinergic and dopaminergic systems. Furthermore, GBH-activated microglia and astrocytes, sign of neuroinflammation event in the medial prefrontal cortex and hippocampus. At the molecular level, a down-regulation of brain-derived neurotrophic factor (BDNF) expression and an up-regulation of tyrosine-related kinase receptor (TrkB), NR1 subunit of NMDA receptor as well as tumor necrosis factor α (TNFα) were found in the brain of GBH-exposed mice. The present work demonstrates that GBH induces numerous behavioral and cognitive abnormalities closely associated with significant histological, neurochemical and molecular impairments. It also raises fundamental concerns about the ability of current safety testing to assess risks of pesticide exposure during developmental periods of central nervous system.

Intranasal glyphosate-based herbicide administration alters the redox balance and the cholinergic system in the mouse brain

Pesticide exposure is associated with cognitive and psychomotor disorders. Glyphosate-based herbicides (GlyBH) are among the most used agrochemicals, and inhalation of GlyBH sprays may arise from frequent aerial pulverizations. Previously, we described that intranasal (IN) administration of GlyBH in mice decreases locomotor activity, increases anxiety, and impairs recognition memory. Then, the aim of the present study was to investigate the mechanisms involved in GlyBH neurotoxicity after IN administration. Adult male CF-1 mice were exposed to GlyBH IN administration (equivalent to 50 mg/kg/day of Gly acid, 3 days a week, during 4 weeks). Total thiol content and the activity of the enzymes catalase, acetylcholinesterase and transaminases were evaluated in different brain areas. In addition, markers of the cholinergic and the nigrostriatal pathways, as well as of astrocytes were evaluated by fluorescence microscopy in coronal brain sections. The brain areas chosen for analysis were those seen to be affected in our previous study. GlyBH IN administration impaired the redox balance of the brain and modified the activities of enzymes involved in cholinergic and glutamatergic pathways. Moreover, GlyBH treatment decreased the number of cholinergic neurons in the medial septum as well as the expression of the α7-acetylcholine receptor in the hippocampus. Also, the number of astrocytes increased in the anterior olfactory nucleus of the exposed mice. Taken together, these disturbances may contribute to the neurobehavioural impairments reported previously by us after IN GlyBH administration in mice.

Glyphosate and glyphosate-based herbicide exposure during the peripartum period affects maternal brain plasticity, maternal behaviour and microbiome

Glyphosate is found in a large array of non-selective herbicides such as Roundup® (Monsanto, Creve Coeur, MO, USA) and is by far the most widely used herbicide. Recent work in rodent models suggests that glyphosate-based herbicides during development can affect neuronal communication and result in altered behaviours, albeit through undefined mechanisms of action. To our knowledge, no study has investigated the effects glyphosate or its formulation in herbicide on maternal behaviour and physiology. In the present study, relatively low doses of glyphosate (5 mg kg-1  d-1 ), Roundup® (5 mg kg-1  d-1 glyphosate equivalent), or vehicle were administered by ingestion to Sprague-Dawley rats from gestational day (GD) 10 to postpartum day (PD)22. The treatments significantly altered licking behaviour toward pups between PD2 and PD6. We also show in the dams at PD22 that Roundup exposure affected the maturation of doublecortin-immunoreactive new neurones in the dorsal dentate gyrus of the hippocampus of the mother. In addition, the expression of synaptophysin was up-regulated by glyphosate in the dorsal and ventral dentate gyrus and CA3 regions of the hippocampus, and down-regulated in the cingulate gyrus. Although a direct effect of glyphosate alone or its formulation on the central nervous system is currently not clear, we show that gut microbiota is significantly altered by the exposure to the pesticides, with significant alteration of the phyla Bacteroidetes and Firmicutes. This is the first study to provide evidence that glyphosate alone or in formulation (Roundup) differentially affects maternal behaviour and modulates neuroplasticity and gut microbiota in the mother.

Depression, anxiety-like behavior, and memory impairment in mice exposed to chitosan-coated zein nanoparticles

The advent of biotechnology provided the synthesis of nanoproducts with diverse applications in the field of medicine, agriculture, food, among others. However, the toxicity of many nanoparticles (NP) currently used, which can penetrate natural systems and impact organisms, is not known. Thus, in this study, we evaluated whether the short exposure (5 days) to low concentrations of chitosan-coated zein nanoparticles (ZNP-CS) (0.2 ng/kg, 40 ng/kg, and 400.00 ng/kg) was capable of causing behavioral alterations compatible with cognitive deficit, as well as anxiety and depression-like behavior in Swiss mice. However, we observed an anxiogenic effect in the animals exposed to the highest ZNP-CS concentration (400.00 ng/kg), without locomotor alterations suggestive of sedation or hyperactivity in the elevated plus maze (EPM) test. We also observed that the ZNP-CS caused depressive-like behavior, indicated by the longer immobile time in the tail suspension test and the animals exposed to ZNP-CS presented deficit in recognition of the new object, not related to locomotor alteration in this test. To the best of our knowledge, this is the first report of the neurotoxicity of ZNP in a mammal animal model, contributing to the biological safety assessment of these nanocomposites.

Learning and memory impairments associated to acetylcholinesterase inhibition and oxidative stress following glyphosate based-herbicide exposure in mice

Numerous clinical and epidemiological data have reported the deleterious effects of glyphosate on learning and memory. The ability of this herbicide to cross the blood-brain barrier may have adverse effects on the structure and various functions of the nervous system. This study was conducted to highlight the effects of Glyphosate-based herbicide (GBH) on these two functions in mice treated daily with 250 or 500 mg/kg following acute (unique administration), subchronic (6 weeks) and chronic (12 weeks) treatments. The integrity of learning and memory was assessed by using a specific behavioral test battery: Novel object recognition, Y-maze and passive avoidance tasks. The acetylcholinesterase (AChE) and anti-oxidant enzyme activities, especially superoxide dismutase (SOD) and peroxidase (PO) were evaluated. Our results indicated that unlike acute treatment, both subchronic and chronic exposure to GBH decreased discrimination index and the step-through-latency indicating recognition and retention memory impairments, respectively. In contrast, only chronic exposure affected working memory manifested by decreased spontaneous alternation. Furthermore, our results showed also a prominent decrease in AChE, SOD and PO specific activities within the brain of treated mice following repeated exposures. This study demonstrates that GBH induced numerous cognitive abnormalities referred to different forms of memory likely associated with a significant inhibition of AChE activity and oxidative stress induction.

Propamocarb exposure decreases the secretion of neurotransmitters and causes behavioral impairments in mice

Propamocarb (PM) is a type of fungicide, which is widely used in the greenhouse-based production of vegetables and fruits globally. It has been considered to have generally low toxicity. However, the teratogenicity or neurotoxicity for mammals remains unclear. In this study, we aimed to explore its effect on the secretion of neurotransmitters and behavioral impairments. Male adult mice were exposed to 10 and 40 mg/L PM for 2 weeks (acute exposure) or 3 and 10 mg/L PM for 10 weeks (chronic exposure). It was observed that acute or chronic exposure to PM changed the levels of serotonin (5-HT) and dopamine in the serum and colon and the transcription of TPH2 and DRD2 in the colons of mice. In addition, the locomotor test, the open field test, and the Morris water maze analysis also showed that acute exposure to PM caused behavioral impairments to some extent. The results obtained in the present study indicated that PM has the potential to induce neurotoxicity in animals.

Glyphosate based- herbicide exposure affects gut microbiota, anxiety and depression-like behaviors in mice

Recently, a number of studies have demonstrated the profound relationship between gut microbiota (GM) alterations and behavioral changes. Glyphosate-based herbicides (GBH) have been shown to induce behavioral impairments, and it is possible that they mediate the effects through an altered GM. In this study, we investigated the toxic effects of GBH on GM and its subsequent effects on the neurobehavioral functions in mice following acute, subchronic and chronic exposure to 250 or 500 mg/kg/day. The effect of these acute and repeated treatments was assessed at the behavioral level using the open field, the elevated plus maze, the tail suspension and splash tests. Then, mice were sacrificed and the intestinal samples were collected for GM analysis. Subchronic and chronic exposure to GBH induced an increase of anxiety and depression-like behaviors. In addition, GBH significantly altered the GM composition in terms of relative abundance and phylogenic diversity of the key microbes. Indeed, it decreased more specifically, Corynebacterium, Firmicutes, Bacteroidetes and Lactobacillus in treated mice. These data reinforce the essential link between GM and GBH toxicity in mice and suggest that observed intestinal dysbiosis could increase the prevalence of neurobehavioral alterations.