Transepithelial transport of fusariotoxin nivalenol: mediation of secretion by ABC transporters.

Mycotoxin nivalenol (NIV) is a natural contaminant of various cereal crops, animal feed and processed grains throughout the world. Human and animal contamination occurs mainly orally, and the toxin must traverse the intestinal epithelial barrier before inducing potential health effects. In this study, we investigated the mechanisms involved in NIV transepithelial transfer. The human intestinal Caco-2 cell line showed a basal-to-apical polarized transport of NIV. Using metabolic inhibitors and temperature-dependent experiments, we demonstrated that basolateral-apical (BL-AP) transfer of NIV involved an energy-dependent transport whereas apical-basolateral (AP-BL) transfer was governed by passive diffusion. NIV efflux was significantly decreased in the presence of the P-glycoprotein (P-gp) inhibitor valspodar, the multi-drug resistance-associated proteins (MRPs) inhibitor MK571, but was not modified by the breast cancer resistance protein (BCRP) inhibitor Ko143. Intracellular NIV accumulation was investigated using epithelial cell lines transfected with either human P-glycoprotein or MRP2. This accumulation was significantly decreased in LLCPK1/MDR1 and MDCKII/MRP2 cells, compared to wild-type cells, and this effect was reversed by valspodar and MK571, respectively. These in vitro results suggested that NIV was a substrate for both P-glycoprotein and MRP2. This interaction may play a key role in weak intestinal absorption of NIV and the mainly predominant excretion of NIV in faeces in animal studies.

Effect of organophosphate pesticide diazinon on expression and activity of intestinal P-glycoprotein.

Organophosphate insecticide diazinon is widely used in agricultural practices, submitting farmers to repeated exposure. Because efflux pumps, as P-glycoprotein (P-gp), serve both as natural defense mechanisms and influence the bioavailability and disposition of drugs, we analyzed the ability of diazinon to act as efflux modulator. Oral administration of diazinon (2-20 mg/kg, 5 days, or 10 mg/kg, 2-12 days) increased intestinal mdr1a mRNA of rats, in both dose- and time-dependent manner, and increased the expression of intestinal P-gp. Using the intestinal cell-line Caco-2, we found that 100 microM diazinon significantly inhibited digoxin and vinblastine secretive flux through the cell monolayers, whereas digoxin and vinblastine absorptive flux increased. The 25 microM diazinon was transported preferentially in basolateral (BL) to apical (AP) direction, suggesting a net secretion. The efflux rate significantly decreased in the presence of metabolic inhibitors sodium azide and 2-deoxy-d-glucose, P-gp inhibitors cyclosporin A and valspodar, but not in the presence of MRPs inhibitor MK571. Repeated exposure of Caco-2 cells to diazinon increased P-glycoprotein expression and activity. These results suggested the involvement of P-gp in the transfer of diazinon, leading to potential consequences for xenobiotic interactions, and showed that repeated exposure to low doses of pesticide may lead to up-regulated P-gp functions in the intestine of mammals.