Abstract Body: Introduction: Glyphosate, marketed as Roundup®, is a widely used potent herbicide in the US. Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase of the shikimate pathway, a non-mammalian signaling pathway present in plants and microbes. Therefore, glyphosate has been deemed safe for humans. However, humans are holobionts with symbiotic gut microbiota susceptible to gut dysbiosis when exposed to glyphosate. Because gut microbiota is an important contributor to hypertension (HTN), we hypothesized that exposure to glyphosate leads to gut dysbiosis and HTN.

Methods: Dahl salt-sensitive (S) rats were administered either vehicle or glyphosate (175 mg/kg/day) in drinking water for three weeks ad libitum. In one group of rats (N=4/group), sympathetic nerve activity was assessed using in situ whole nerve recordings and by measuring circulating norepinephrine (NE) levels by ELISA. In separate rats (N=6–8/group), blood pressure (BP) was measured once a week for three weeks by radiotelemetry, and circulating NE was determined by ELISA. At the endpoint, fecal microbiome analyses were performed using the Illumina and Oxford Nanopore platforms.

Results: Exposure to glyphosate for just one week was sufficient to significantly increase systolic (173 mmHg vs 160 mmHg, p<0.0001) and mean arterial pressure (MAP) (148 mmHg vs 141 mmHg, p<0.0002), but not diastolic BP of S rats. Through week three, BP continued to rise in glyphosate-treated rats with greater differences in the systolic (195 mmHg vs 176 mmHg, p<0.0001), diastolic (142 mmHg vs 135 mmHg, p<0.0001), and MAP (168 mmHg vs 155 mmHg, p<0.0001). This was accompanied by increased sympathetic nerve activity and serum NE as early as one week of exposure to glyphosate (5.85 ng/mL vs 4.77 ng/mL, p<0.001), which continued at week three of glyphosate exposure (13.31 ng/mL vs 6.16 ng/mL, p<0.001), indicative of adrenergic overdrive. 16S data showed that glyphosate altered the composition of commensal gut microbiota, reducing bacterial α-diversity (Shannon entropy; p<0.05) and β-diversity (Bray-Curtis; p<0.02). Whole metagenomic analysis revealed a higher abundance of several bacterial species, including Candidatus spp., Erysipelaclostridium ramosum, and Clostridium sporogenes in the glyphosate-treated rats.

Conclusions: Glyphosate exposure elevated BP, increased sympathetic nerve activity, and altered gut microbiota composition. This is the first proof-of-concept study to demonstrate that glyphosate contributes to HTN.