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Paraquat (PQ), an herbicide widely used in agriculture, is considered a highly toxic compound. In hepatocytes, P-glycoprotein (P-gp/Abcb1) is a canalicular transporter involved in PQ extrusion from the cell. Previously, we demonstrated that genistein (GNT) induces P-gp in rat liver. In this study, the protective role of GNT pretreatment towards hepatic damage in a model of acute intoxication with PQ in rats, was investigated. Wistar rats were randomized in 4 groups: Control, GNT (5 mg/kg/day sc, 4 days), PQ (50 mg/kg/day ip, last day) and GNT+ PQ. Hepatic lipoperoxidation (LPO) was evaluated by the thiobarbituric acid reactive substances method. Hepatic levels of 4-hydroxynonenal protein adducts (4-HNEp-add) and glutathione-S-transferase alpha (GSTα) protein expression were evaluated by Western blotting. Hepatic glutathione levels and plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST) were also measured. Biliary excretion of PQ was studied in vivo and in isolated perfused liver. PQ was quantified by HPLC. PQ significantly increased AST and ALT activities, malondialdehyde and 4-HNEp-add levels, whereby pretreatment with GNT ameliorated this effect. PQ biliary excretion remained unchanged after treatments in both experimental models. Hepatic GSTα expression was augmented in GNT group. GNT pretreatment increased hepatic glutathione levels in PQ + GNT group. These results agree with the lower content of 4-HNEp-adds in GNT + PQ group respect to PQ group. Unexpectedly, increased activity of P-gp did not enhance PQ biliary excretion. Thus, GNT protective mechanism is likely through the induction of GSTα which results in increased 4-HNE metabolism before formation of protein adducts., (Copyright © 2021. Published by Elsevier Inc.)

The multidrug resistance-associated protein 2 (MRP2/ABCC2) is a transporter that belongs to the ATP-binding cassette (ABC) superfamily. In the intestine, it is localized to the apical membrane of the enterocyte and plays a key role in limiting the absorption of xenobiotics incorporated orally. MRP2 may also play a role in systemic clearance of xenobiotics available from the serosal side of the intestine. MRP2 transports a wide range of substrates, mainly organic anions conjugated with glucuronic acid, glutathione and sulfate and its expression can be modulated by xenobiotics at transcriptional- and post-transcriptional levels. Transcriptional regulation is usually mediated by a group of nuclear receptors. The pregnane X receptor (PXR) is a major member of this group. Relevant drugs described to up-regulate intestinal MRP2 via PXR are rifampicin, spironolactone and carbamazepine, among others. The constitutive androstane receptor (CAR, NR1I3) was also reported to modulate MRP2 expression, phenobarbital being a typical activator. Dietary compounds, including micronutrients and other natural products, are also capable of regulating intestinal MRP2 expression transcriptionally. We have given them particular attention since the composition of the food ingested daily is not necessarily supervised and may result in interactions with therapeutic drugs. Post-transcriptional regulation of MRP2 activity by xenobiotics, e.g. as a consequence of inhibitory actions, is also described in this review. Unfortunately, only few studies report on drug-drug or nutrient-drug interactions as a consequence of modulation of intestinal MRP2 activity by xenobiotics. Future clinical studies are expected to identify additional interactions resulting in changes in efficacy or safety of therapeutic drugs., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The cAMP pathway is a universal signaling pathway regulating many cellular processes including metabolic routes, growth and differentiation. However, its effects on xenobiotic biotransformation and transport systems are poorly characterized. The effect of cAMP on expression and activity of GST and MRP2 was evaluated in Caco-2 cells, a model of intestinal epithelium. Cells incubated with the cAMP permeable analog dibutyryl cyclic AMP (db-cAMP: 1,10,100 μM) for 48 h exhibited a dose-response increase in GST class α and MRP2 protein expression. Incubation with forskolin, an activator of adenylyl cyclase, confirmed the association between intracellular cAMP and upregulation of MRP2. Consistent with increased expression of GSTα and MRP2, db-cAMP enhanced their activities, as well as cytoprotection against the common substrate 1-chloro-2,4-dinitrobenzene. Pretreatment with protein kinase A (PKA) inhibitors totally abolished upregulation of MRP2 and GSTα induced by db-cAMP. In silico analysis together with experiments consisting of treatment with db-cAMP of Caco-2 cells transfected with a reporter construct containing CRE and AP-1 sites evidenced participation of these sites in MRP2 upregulation. Further studies involving the transcription factors CREB and AP-1 (c-JUN, c-FOS and ATF2) demonstrated increased levels of total c-JUN and phosphorylation of c-JUN and ATF2 by db-cAMP, which were suppressed by a PKA inhibitor. Co-immunoprecipitation and ChIP assay studies demonstrated that db-cAMP increased c-JUN/ATF2 interaction, with further recruitment to the region of the MRP2 promoter containing CRE and AP-1 sites. We conclude that cAMP induces GSTα and MRP2 expression and activity in Caco-2 cells via the PKA pathway, thus regulating detoxification of specific xenobiotics., (Copyright © 2015 Elsevier Inc. All rights reserved.)