Interaction between Nicotine and Mptp/Mpp+ in Rat Brain Endothelial Cells

To examine the interaction between nicotine and MPTP/MPP+ in the blood- brain barrier, cellular uptake of MPTP and MPP+ was studied in the presence of nicotine and several compounds, including MPTP/MPP+ analogs and a specific inhibitor of organic cation transporter (OCT) in an adult rat brain microvascular endothelial cell line (ARBEC). The kinetic properties of the uptake of MPTP, MPP+, and nicotine were also examined. In addition, a microdialysis study was performed to evaluate the in vivo effect of nicotine (i.p.) on extracellular levels of MPTP and MPP+ in the brain after intravenous administration of MPTP The results showed that uptake of MPTP, MPP+, and nicotine was partly mediated by a carrier system that was sensitive to decynium22, a specific OCT inhibitor. RT-PCR showed the presence of OCT I mRNA in ARBEC. Capacity for uptake of MPTP and nicotine was much higher than that for MPP+ (K-m and V-m values of 10.94 + /- 1 .44 mu M and 0.049 +/- 0.007 pmol/mg s, respectively, for MPP+, compared to values of 35.75 +/- 0.85 mu M and 40.95 +/ - 3.56 pmol/mg s for MPTP and 25.29 +/- 6.44 mu M and 51.15+ /- 14.18 pmol/mg s for nicotine). In addition, nicotine competitively inhibited the uptake of both MPTP and MPP+, with inhibition constants (K-i) of 328 mu M and 210 mu M, respectively. In vivo microdialysis results showed that nicotine significantly reduced brain extracellular levels of MPTP in the first 30 min (507.4 +/- 8.5 ng/ml vs. 637.9 +/- 30.8 ng/ml with and without nicotine pre-treatment, respectively), but did not have significant effect on those of MPP+. In conclusion, nicotine can inhibit in vitro cellular uptake and in vivo transfer of MPTP across the blood-brain barrier, which can be mediated by multiple pathways including OCT1. (c) 2007 Elsevier Inc . All rights reserved