Abstract:
Parkinson’s disease (PD) is a progressive neurodegenerative disease that
affects between 1% and 2% of the population over age 65. Despite decades of
research and the development of many molecular models of PD, there is far from a
consensus as to the etiology of this disease. Current molecular models, such as the
role of the quaternary ammonium ion MPP+ and its effect on cell death, in the
presence/absence of monoamine transporters as opposed to distinct intracellular
activity are still disputed.
The 3-amino-2-phenylpropene (APP) class of compounds has been previously
characterized as reversible inhibitors for the bovine adrenal chromaffin granule vesicular
monoamine transporter (VMAT) as well as potent irreversible dopamine-β-
monooxygenase (DβM) and monoamine oxidase (MAO) inhibitors. These effects result
in perturbation of catecholamine uptake, storage and/or metabolism, leading to the
potential for increased oxidative stress.
Herein, we report that halogen substitution on the 4'-position of the aromatic ring
gradually increases VMAT inhibition potency from 4'-F to 4'-I, parallel to the
hydrophobicity of the halogen. We show that these derivatives are taken up into both
neuronal and non-neuronal cells, and into resealed chromaffin granule ghosts efficiently
through passive diffusion. In addition, these derivatives are highly toxic to human
neuroblastoma SH-SY5Y cells, they are not toxic to several non-neuronal cell lines at
similar concentrations. These compounds drastically perturb DA uptake and
metabolism in SH-SY5Y cells under sub-lethal conditions, and are able to deplete both
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vesicular and cytosolic catecholamines similar to amphetamines. Additionally, (4'-iodo)
3-amino-2-phenylpropene (4'-IAPP) treatment significantly increases intracellular
reactive oxygen species (ROS) and decreases glutathione reduced form (GSH) levels in
SH-SY5Y cells, and cell death is significantly attenuated by the common antioxidants α-
tocopherol, N-acetyl-L-cysteine (NAC) and glutathione (GSH).
This suggests that ROS production is intricately involved with the mechanism of
cell death. Although DNA fragmentation analysis supports that apoptosis occurs, the
fact that a non-specific caspase inhibitor provided no significant protection suggests that
that cell death is likely due to a caspase-independent ROS-mediated apoptotic pathway.
Based on these and other findings, we propose that drastic perturbation of DA
metabolism in SH-SY5Y cells by 4'-halo APP derivatives causes increased oxidative
stress leading to apoptotic cell death. These compounds, which induce catecholaminespecific
neurotoxic effects following nonspecific cellular entry may be a unique resource
in the modeling of PD both in vitro and in vivo.
