Several transport systems contribute to the intestinal uptake of Paraquat, modulating its cytotoxic effects

•Paraquat uptake into Caco-2 cells is partially mediated by the y+ transport system.•PQ uptake is regulated by a Ca++/calmodulin complex-dependent mechanism.•The carrier-mediated transport system for choline is involved on PQ uptake.•Several transport systems contribute to the intestinal uptake of paraquat.•Specific and potent inhibitors of these transporters may be potential new antidotes.

Paraquat (PQ) is an extremely toxic herbicide upon oral ingestion that lacks a specific antidote. In case of intoxication, treatment primarily relies on limiting its intestinal absorption. In this study, we elucidate the intestinal transport mechanisms of PQ uptake using Caco-2 cells as a model of the human intestinal epithelium. The cells were incubated with a wide range of PQ concentrations (0-5000 μM) for 24 h with or without simultaneous exposure to different transporters substrates/inhibitors including, choline or hemicolinium-3 (for choline carrier-mediated transport system inhibition) and putrescine, trifluoperazine, valine, lysine, arginine or N-ethylmaleimide (for basic amino acid transport systems inhibition). PQ cytotoxicity was evaluated by the MTT reduction assay and correlated with PQ intracellular levels quantified by gas chromatography-ion trap-mass spectrometry (GC-IT/MS). Potential interactions of PQ with the substrates/inhibitors of the transport systems were investigated and discarded by infrared spectroscopy.Our results showed a significant reduction in PQ intracellular accumulation and, consequently, in PQ cytotoxicity, in the presence of both choline and hemicolinium-3, demonstrating that the choline carrier-mediated transport system is partially involved in PQ intestinal uptake. Likewise, PQ cytotoxicity and intracellular accumulation were significantly attenuated by simultaneous exposure to putrescine, trifluoperazine, valine, lysine, arginine and N-ethylmaleimide. These data suggested the involvement of more than one of the basic amino acids transport systems, including the y+, b0,+ or y+L systems.In conclusion, this study demonstrated that several transport systems mediate PQ intestinal absorption and, therefore, their modulation may provide alternative efficient pathways for limiting PQ toxicity in intoxication scenarios.