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 OCT1 mRNA in ARBEC. Capacity for uptake of MPTP and nicotine was much higher than that for MPP+ (Km and Vm values of 10.94 ± 1.44 μM and 0.049 ± 0.007 pmol/mg s, respectively, for MPP+, compared to values of 35.75 ± 0.85 μM and 40.95 ± 3.56 pmol/mg s for MPTP and 25.29 ± 6.44 μM 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 (Ki) of 328 μM and 210 μM, respectively. In vivo microdialysis results showed that nicotine significantly reduced brain extracellular levels of MPTP in the first 30min (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.