In Parkinson’s disease (PD) dopaminergic neurons in the midbrain region substantia nigra pars compacta die. There is currently no treatment available that prevents this cell death. We have screened for FDA-approved drugs that increase the expression of two molecules, Engrailed 1 and FoxA2, that are important for the function and survival of the vulnerable midbrain dopamine neurons. The serotonin and norepinephrine re-uptake inhibitor duloxetine hydrochloride increases the expression of these molecules in cultured dopaminergic neurons in vitro and in the substantia nigra pre-clinical models. We will perform pre-clinical experiments to test if this drug has potential to be preventive against PD.
We will test the neuroprotective capacity of duloxetine hydrochloride against PD-like processes in cultured dopaminergic neurons as well as in pre-clinical models for PD. Specifically, we will (1) treat cultured dopaminergic neurons with duloxetine hydrochloride and determine neuronal survival after challenge with four PD associated toxins in vitro, and (2) determine neuroprotective effects in PD pre-clinical models after systemic drug administration in vivo. We are using three different pre-clinical models that simulate progressive PD, intra-striatal 6-OHDA injection, chronic MPTP and AAV-alpha-synucleinopathy. We will determine pathological and biochemical changes such as dopaminergic cell death in the substantia nigra, neuroinflammation, and striatal dopamine content as well as behavior and motor function.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
The development of new clinically approved drugs is a long process compared to repositioning of FDA approved drugs. Duloxetine hydrochloride is an FDA approved drug used for a number of neurological indications including major depressive disorder, anxiety and pain. We will test if this drug also has potential therapeutic value in preventing the midbrain dopaminergic cell loss seen in PD. We believe that initiating early treatment with duloxetine hydrochloride may make these vulnerable neurons more resilient to degeneration associated with PD.
We have proposed an extensive plan for cell and pre-clinical model based testing of duloxetine hydrochloride as a potential therapeutic for PD. We are using several progressive models of PD that allows us to study the neuroprotective effect of duloxetine hydrochloride against different PD etiologies. Our expectation is that the data obtained from these studies will be sufficient to determine suitability of this drug for clinical testing towards repositioning for PD.
We have previously observed that FoxA2 and En-1 are up-regulated in the substantia nigra of male pre-clinical models when duloxetine is administered at a dose of 20 mg/kg daily subcutaneously for 12 days. We have now optimized the dosing route and treatment regimen for long term chronic administration. These experiments confirm up-regulation of FoxA2 and En-1 in models of both genders. Experiments in a model of PD are currently ongoing to determine whether duloxetine increases the resilience of the midbrain dopaminergic neurons to PD-related degeneration. In parallel, we are also determining the effect of duloxetine HCl on cultured dopaminergic neurons subjected to various different PD-related toxins.
We have observed that the transcription factors FoxA2 and En-1, which are important for dopaminergic neuron survival, are up-regulated in the substantia nigra of pre-clinical models when duloxetine is administered for two weeks. Despite the up-regulation of these transcription factors, experiments where duloxetine HCl was administrated in a three-week toxin-induced model of PD did not result in a significantly increased survival of neurons in substantia nigra as compared to control models. Consistent with the lack of neuronal survival, the models did not improve in behavioral studies aimed at assessing the function of the dopaminergic circuitry. Additionally, we determined if duloxetine HCl has a neuroprotective effect in a 24-week alpha-synucleinopathy model of PD. One interesting finding in duloxetine HCl-treated models and in dopaminergic cells exposed to duloxetine HCl in a culture dish was that the expression of the enzyme tyrosine hydroxylase involved in the synthesis of dopamine was reduced. We are uncertain as to what this decrease in tyrosine hydroxylase expression mean,s and we have as of yet no data on the effect of duloxetine HCl on tyrosine hydroxylase expression in humans.