Common Herbicide a Player in Neurodegeneration?

Chronic exposure to glyphosate — the most widely used herbicide globally — may be a risk factor for Alzheimer’s disease (AD), new research showed. 

Researchers found that glyphosate exposure even at regulated levels was associated with increased neuroinflammation and accelerated AD-like pathology in mice — an effect that persisted 6 months after a recovery period when exposure was stopped.

“More research is needed to understand the consequences of glyphosate exposure to the brain in humans and to understand the appropriate dose of exposure to limit detrimental outcomes,” co-senior author Ramon Velazquez, PhD, with Arizona State University in Tempe, told Medscape Medical News.

The study was published online December 4 in the Journal of Neuroinflammation. 

Persistent Accumulation Within the Brain

Glyphosate is the most heavily applied herbicide in the United States, with roughly 300 million pounds used annually in agricultural communities throughout the US. It is also used for weed control in parks, residential areas, and personal gardens.

The US Environmental Protection Agency (EPA) has determined that glyphosate poses no risks to human health when used as directed. But the World Health Organization’s International Agency for Research on Cancer disagrees, classifying the herbicide as “possibly carcinogenic to humans.”

In addition to the possible cancer risk, multiple reports have also suggested potential harmful effects of glyphosate exposure on the brain. 

In earlier work, Velazquez and colleagues showed that glyphosate crosses the blood-brain barrier and infiltrates the brains of mice, contributing to neuroinflammation and other detrimental effects on brain function. 

In their latest study, they examined the long-term effects of glyphosate exposure on neuroinflammation and AD-like pathology using a mouse model.

They dosed 4.5-month-old mice genetically predisposed to AD and non-transgenic control mice with either 0-, 50-, or 500-mg/kg of glyphosate daily for 13 weeks followed by a 6-month recovery period. 

The high dose is similar to levels used in earlier research, and the low dose is close to the limit used to establish the current EPA acceptable dose in humans.

Glyphosate’s metabolite, aminomethylphosphonic acid, was detectable and persisted in mouse brain tissue even 6 months after exposure ceased, the researchers reported. 

Additionally, there was a significant increase in soluble and insoluble fractions of amyloid-beta (Aβ), Aβ42 plaque load and plaque size, and phosphorylated tau at Threonine 181 and Serine 396 in hippocampus and cortex brain tissue from glyphosate-exposed mice, “highlighting an exacerbation of hallmark AD-like proteinopathies,” they noted. 

Glyphosate exposure was also associated with significant elevations in both pro- and anti-inflammatory cytokines and chemokines in brain tissue of transgenic and normal mice and in peripheral blood plasma of transgenic mice. 

Glyphosate-exposed transgenic mice also showed heightened anxiety-like behaviors and reduced survival. 

“These findings highlight that many chemicals we regularly encounter, previously considered safe, may pose potential health risks,” co-senior author Patrick Pirrotte, PhD, with the Translational Genomics Research Institute, Phoenix, Arizona, said in a statement.

“However, further research is needed to fully assess the public health impact and identify safer alternatives,” Pirrotte added. 

Funding for the study was provided by the National Institutes on Aging, National Cancer Institute and the Arizona State University (ASU) Biodesign Institute. The authors have declared no relevant conflicts of interest.