Abstract
P-glycoprotein (P-gp) has been associated with a number of neurodegenerative diseases, including Parkinson’s disease, although the mechanisms remain unclear. Altered transport of neurotoxic pesticides has been proposed in Parkinson’s disease, but it is unknown whether these pesticides are P-gp substrates. We used three in vitro transport models, stimulation of ATPase activity, xenobiotic-induced cytotoxicity, and inhibition of rhodamine-123 efflux, to evaluate P-gp transport of diazinon, dieldrin, endosulfan, ivermectin, maneb, 1-methyl-4-phenyl-4-phenylpyridinium ion (MPP+), and rotenone. Diazinon and rotenone stimulated ATPase activity in P-gp–expressing membranes, with Vmax values of 22.4 ± 2.1 and 16.8 ± 1.0 nmol inorganic phosphate/min per mg protein, respectively, and Km values of 9.72 ± 3.91 and 1.62 ± 0.51 µM, respectively, compared with the P-gp substrate verapamil, with a Vmax of 20.8 ± 0.7 nmol inorganic phosphate/min per mg protein and Km of 0.871 ± 0.172 μM. None of the other pesticides stimulated ATPase activity. We observed an increased resistance to MPP+ and rotenone in LLC-MDR1-WT cells compared with LLC-vector cells, with 15.4- and 2.2-fold increases in EC50 values, respectively. The resistance was reversed in the presence of the P-gp inhibitor verapamil. None of the other pesticides displayed differential cytotoxicity. Ivermectin was the only pesticide to inhibit P-gp transport of rhodamine-123, with an IC50 of 0.249 ± 0.048 μM. Our data demonstrate that dieldrin, endosulfan, and maneb are not P-gp substrates or inhibitors. We identified diazinon, MPP+, and rotenone as P-gp substrates, although further investigation is needed to understand the role of P-gp transport in their disposition in vivo and associations with Parkinson’s disease.
Footnotes
- Received May 29, 2015.
- Accepted August 12, 2015.
↵1 Current affiliation: Department of Biomedical Sciences, University of Minnesota Duluth, Duluth, Minnesota.
This work was supported by the National Institutes of Health Center of Biomedical Research Excellence grants that support the Center for Biomolecular Structure and Dynamics [Grant P20GM103546], the Center for Environmental Health Sciences [Grant P20RR017670], and the Center for Structural and Functional Neuroscience [Grant P20RR015583]; the American Foundation for Pharmaceutical Education, American Association of College of Pharmacy, New Investigators Program (E.L.W.); the Institute of Translational Health Sciences [Grant UL1TR000423 to E.L.W.]; and the American Foundation for Pharmacy Education Pre-Doctoral Fellowship (S.E.L.).
- Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics
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