Induction and activation of P-glycoprotein by dihydroxylated xanthones protect against the cytotoxicity of the P-glycoprotein substrate paraquat

Abstract

Xanthones are a family of compounds with several known biological activities and therapeutic potential for which information on their interaction with membrane transporters is lacking. Knowing that P-glycoprotein (P-gp) acts as a cellular defense mechanism by effluxing its toxic substrates, the aim of this study was to investigate the potential of five dihydroxylated xanthones as inducers of P-gp expression and/or activity and to evaluate whether they could protect Caco-2 cells against the cytotoxicity induced by the toxic P-gp substrate paraquat (PQ). After 24 h of incubation, all tested xanthones caused a significant increase in both P-gp expression and activity, as evaluated by flow cytometry using the UIC2 antibody and rhodamine 123, respectively. Additionally, after a short 45-min incubation, all the tested xanthones induced a rapid increase in P-gp activity, indicating direct pump activation without increased P-gp protein expression. The tested compounds also increased P-gp ATPase activity in MDR1-Sf9 membrane vesicles, demonstrating to be P-gp substrates. Moreover, when simultaneously incubated with PQ, all xanthones significantly reduced the cytotoxicity of the herbicide, and these protective effects were completely reversed upon incubation with a specific P-gp inhibitor. In silico studies evaluating the interactions between xanthones and P-gp in the presence of PQ suggested that a co-transport mechanism may be operating. A quantitative structure-activity relationship model was developed and validated, and the maximal partial charge for an oxygen atom was the descriptor predicted as being implicated in P-gp activation by the dihydroxylated xanthones. These results disclose new perspectives in preventing PQ- and other P-gp substrates-induced poisonings.

P-glycoprotein induction in Caco-2 cells by newly synthetized thioxanthones prevents paraquat cytotoxicity

“…2b, c). P-glycoprotein transport activity RHO 123 is a P-gp fluorescent substrate widely used for the evaluation of P-gp activity (Palmeira et al 2011;Silva et al 2011Silva et al , 2014bVilas-Boas et al 2011). In the present study, two different approaches for the evaluation of transport activity were performed.…”

Effect of MDR1 gene polymorphisms on mortality in paraquat intoxicated patients

“…Some reports have shown that inducing P-gp can protect cells against PQ induced toxicity in vivo and in vitro 91012131415. Silva et al have demonstrated that inducing P-gp in Caco-2 cells using newly synthesized thioxanthones can prevent PQ cytotoxicity15.…”

“…One study has shown that P-gp is involved in removing PQ from the kidneys and attenuating toxicity enhanced in MDR 1a/1b knockout mice12. Some reports have suggested that inducing P-gp might be used as a therapeutic approach to treat PQ intoxication13141516.…”

Quantification of 1‐(propan‐2‐ylamino)‐4‐propoxy‐9H‐thioxanthen‐9‐one (TX5), a newly synthetized P‐glycoprotein inducer/activator, in biological samples: method development and validation

“…Xanthones (Xs) and thioxanthones (TXs) are two families of heterocyclic compounds with several known biological activities and recognized therapeutic potential (Masters & Brase, ; Pinto et al ., ; Silva et al ., ). In fact, in recent years, the interaction of Xs and TXs with membrane transporters, like P‐gp, has been an important research target for medicinal chemists, who describe these classes as privileged structures given their pronounced biological effects (Silva et al ., ; Sousa & Pinto, ). Several xanthonic and thioxanthonic derivatives have been synthesized in recent years and some compounds have been screened in vitro to find a compound able to increase P‐gp activity and/or expression.…”

“…Considering all of the mechanisms in which P‐gp is involved, it can be concluded that P‐gp plays a very important role in defending cells against its toxic substrates, avoiding their intracellular accumulation. Accordingly, strategies to increase P‐gp expression and/or activity may be viewed as potential antidotal pathways to prevent P‐gp substrate‐mediated toxicity and, therefore, an alternative therapeutic strategy to implement in the near future, in intoxication scenarios (Dinis‐Oliveira et al ., ; Silva et al ., ; Vilas‐Boas et al ., ).…”