In silico and cell studies on the interaction of the herbicide glyphosate with estrogen receptors

Glyphosate is the active constituent of Roundup, the world’s most widely used herbicide; it is now ubiquitous in the environment with residues commonly found in the air, soil, waterways, and food. As such, understanding the full extent of glyphosate’s toxicological effects on humans and the environment is crucial to minimise the risks of increasing glyphosate use. Glyphosate has been shown to activate estrogen receptors (ERs), which may lead to adverse effects in humans and other species, however, there remains significant conjecture in this area. This thesis explores the interactions of glyphosate and its environmentally persistent metabolite, aminomethylphosphonic acid (AMPA), with ERs. In silico ligand docking studies performed in the Schrödinger platform showed that both glyphosate and AMPA interact with the ligand-binding cleft (LBC) of ERɑ, with predicted binding affinities of -18.04 and -19.09 kJ/mol respectively, considerably weaker than the natural ligand 17β-estradiol (-50.4 kJ/mol). The interactions formed by glyphosate and AMPA with ERɑ are insufficient to initiate receptor activation, therefore neither are likely to be estrogenic by a ligand-dependent mechanism. In silico molecular dynamics (MD) simulations performed using Desmond software showed that glyphosate is capable of linking critical ERɑ LBC amino acid residues by formation of a transient water bridge, and therefore has the potential to be weakly estrogenic via a ligand- dependent mechanism. AMPA was unable to form these interactions, thus is highly unlikely to be estrogenic via a ligand-dependent mechanism. Exposure studies in ER-expressing (ER+) human cells revealed that glyphosate does not induce estrogenic effects, while AMPA elicited a minor ER-mediated effect. Glyphosate and AMPA are therefore unlikely to have any major implications on human health with respect to estrogenicity. Together, the evidence presented in this thesis suggests that glyphosate is not estrogenic, while AMPA might have minor ER-mediated effects via a ligand-independent mechanism. Future studies are necessary to uncover the extent and mechanism of AMPA’s proposed ER-mediated effects and their implications for environmental toxicity