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

Abstract

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 (0-5000μM) for 24h 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(+), b(0,+) 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.

Keywords: Arginine; Choline; Lysine; Paraquat intestinal uptake; Putrescine; y(+) transport system.