Mariana Zancan Tonel

Interaction of single‐walled carbon nanotubes and saxitoxin: Ab initio simulations and biological responses in hippocampal cell line HT‐22

Saxitoxins (STXs) are potent neurotoxins that also induce cytotoxicity through the generation of reactive oxygen species. Carbon nanotubes (CNTs) are nanomaterials that can promote a Trojan horse effect, facilitating the entry of toxic molecules to cells when adsorbed to nanomaterials. The interaction of pristine single-walled (SW)CNTs and carboxylated (SWCNT-COOH) nanotubes with STX was evaluated by ab initio simulation and bioassays using the cell line HT-22. Cells (5 × 104  cells/mL) were exposed to SWCNT and SWCNT-COOH (5 μg mL-1 ), STX (200 μg L-1 ), SWCNT+STX, and SWCNT-COOH+STX for 30 min or 24 h. Results of ab initio simulation showed that the interaction between SWCNT and SWCNT-COOH with STX occurs in a physisorption. The interaction of SWCNT+STX induced a decrease in cell viability. Cell proliferation was not affected in any treatment after 30 min or 24 h of exposure (p > 0.05). Treatment with SWCNT-COOH induced high reactive oxygen species levels, an effect attenuated in SWCNT-COOH+STX treatment. In terms of cellular oxygen consumption, both CNTs when coexposed with STX antagonize the toxin effect. Based on these results, it can be concluded that the results obtained in vitro corroborate the semiempirical evidence found using density functional theory ab initio simulation. Environ Toxicol Chem 2017;36:1728-1737.

Cytoprotection of lipoic acid against toxicity induced by saxitoxin in hippocampal cell line HT-22 through in silico modeling and in vitro assays

Saxitoxins (STXs) are potent neurotoxins that block voltage-gated channels in neurons and induce cytotoxicity. These toxins not only can generate reactive oxygen species but also can alter antioxidant levels, promoting oxidative stress. Under this pro-oxidant situation, the use of the antioxidant lipoic acid (LA) can represent a chemoprotective alternative to minimize the deleterious effects induced by neurotoxins as STXs. P-glycoprotein (P-gp) is a well-known ATP-binding cassette (ABC) transporter that plays a crucial role in the extrusion of toxic substances, decreasing their accumulation and potential intracellular effects in virtue of its broad substrate specificity, its expression in many excretory tissues and its large efflux capacity. The interaction of STXs with LA was evaluated by ab initio simulation, molecular docking and bioassays using the cell line HT-22. The interaction of STXs with LA occurs by physisorption. Molecular docking indicated that STXs can be a substrate of P-gp and, estimating the Free Energy of Binding (FEB), LA has lower amino acids residues binding sites, similar to verapamil, while STX and STX+LA_1 have similar amino acids residues and binding sites with similar FEB between this ligands.Cells were exposed to STXs and LA for 30min and 24h. LA treatment minimizes STX cytotoxicity, evaluated by trypan blue and MTT assay and both STX and STX-LA treatments were efficient to induce P-gp activity measured by rhodamine 123 dye extrusion. LA and STX+LA treatments induced low reactive oxygen species levels and low oxygen consumption. Based on our results, it can be concluded that LA was able to induce cytoprotection, including induction of cellular glutathione levels, and that STX+LA interaction reduced toxicity effects induced by STX. Overall, the in vitro results corroborated the semi-empirical evidences found using density functional theory ab initio simulation and molecular docking.