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, 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 Pi/min/mg protein, respectively, and Km values of 9.72 ± 3.91 and 1.62 ± 0.51 µM, respectively, compared to the P-gp substrate verapamil with Vmax of 20.8 ± 0.7 nmol Pi/min/mg protein and Km of 0.871 ± 0.172 μM. None of the other pesticides stimulated ATPase activity. We observed increased resistance to MPP+ and rotenone in LLC-MDR1-WT cells compared to LLC-vector, 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 demonstrates 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.
- The American Society for Pharmacology and Experimental Therapeutics