The enzyme CYP2D6 can metabolize many centrally acting drugs and endogenous neural compounds (e.g. catecholamines); it can also inactivate neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1,2,3,4-tetrahydroisoquinoline (TIQ) and β-carbolines that have been associated with Parkinson’s disease (PD). CYP2D6 is ideally situated in the brain to inactivate these neurotoxins. The CYP2D6 gene is also highly polymorphic, which leads to large variation in substrate metabolism. Furthermore, CYP2D6 genetically poor metabolizers are known to be at higher risk for developing PD, a risk that increases with exposure to pesticides. Conversely, smokers have a reduced risk for PD and smokers are suggested to have higher brain CYP2D6 levels. Our studies furthered the characterization and involvement of CYP2D6 in neuroprotection against PD. METHODS: We investigated the effects of CYP2D6 inhibition on MPP+-induced cell death in SH-SHY5Y human neuroblastoma cells. We compared levels of brain CYP2D6, measured by western blotting, between human smokers and non-smokers, between African Green monkeys treated with saline or nicotine, and between PD cases and controls. In addition, we assessed changes in human brain CYP2D6 expression with age. RESULTS: Blocking CYP2D6 activity in SH-SY5Y cells with four diverse inhibitors significantly increased MPP+-induced neurotoxicity. Smokers have higher brain CYP2D6 compared to non-smokers. In monkeys, basal expression of CYP2D6 varied across brain regions and was increased by chronic nicotine treatment in select regions (notably the basal ganglia) and specific cell types. Expression of human brain CYP2D6 increased from fetal to 80 years of age in the frontal cortex; the influence of age on CYP2D6 expression was brain region specific. Compared to age-matched controls, PD cases had ~40% lower CYP2D6 levels in the frontal cortex, cerebellum and hippocampus consistent with lower CYP2D6 increasing the risk for PD. In the caudate and substantia nigra, CYP2D6 levels were similar between PD case and controls using Western blotting. This is likely due to the increase in CYP2D6-expressing astrocytes and much higher cellular CYP2D6 in PD affected areas as observed with immunocytochemical staining. CONCLUSIONS: Brain CYP2D6 can meaningfully inactivate neurotoxins, and it can be increased by nicotine in brain regions of interest to PD. These findings support the contention that higher brain CYP2D6 is protective and lower levels may contribute to increased risk for PD.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/31853 |
| Date | 10 January 2012 |
| Creators | Mann, Amandeep |
| Contributors | Tyndale, Rachel |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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