Objective/Rationale:
N-Acetylcysteine (NAC) is an orally absorbed compound that supports neuronal synthesis of glutathione, a key neuronal antioxidant. Our objective here is to establish the blood and cerebrospinal levels of NAC in mouse that correlate with changes in neuronal glutathione content in mouse brain. This will serve to establish target human blood and cerebrospinal levels in a subsequent clinical trial to determine if NAC can slow progression of PD.
Project Description:
The studies will use a mouse strain in which there is impaired neuronal uptake of cysteine resulting in reduced neuronal glutathione content. NAC has been shown to restore normal neuronal glutathione levels in this mouse strain. In the present studies, the mice will be given NAC at several test doses. The brains will then be harvested and analyzed for neuronal glutathione content. In addition, samples of cerebrospinal fluid (CSF) and blood will be for measurements of NAC and thiol intermediates. Our aim is to establish the blood and CSF concentrations of NAC that correlate with normalized neuronal glutathione content. Parallel studies will be conducted in mice treated with NACA or glutathione itself, since these thiol compounds may also influence neuronal glutathione content.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
It has long been recognized that reduced neuronal glutathione is an early and characteristic hallmark of PD, and that reductions in glutathione lead to death of dopaminergic and other neurons. However, direct repletion of glutathione levels has not previously been studied as an approach to slowing PD progression. NAC can restore glutathione levels in mice, but it is difficult to estimate the dose of NAC required to obtain this same effect in humans. The studies proposed will identify biomarkers that can be used to guide NAC dosing in a clinical trial of NAC in PD.
Anticipated Outcome:
We expect to establish a CSF or blood marker to use in guiding NAC dosing in a clinical trial. We will at the same time obtain important comparative data on the biological efficacy of exogenous glutathione and NACA in the same experimental model.
Final Outcome
Neuronal death in PD is preceded by oxidative stress and neuronal glutathione (GSH) depletion. Accordingly, the use of N-acetyl cysteine (NAC) and other thiol antioxidants has been proposed as a disease modifying therapy. However, there is a lack of information about thiol drug penetrance into the brain and the doses required to influence neuronal GSH content in humans. Here we aimed to establish the minimal doses of three thiol agents—NAC, N-acetyl cysteine amide (NACA), and GSH itself—that normalize GSH content in neurons of the EAAC1-/- mouse (a strain with chronically reduced neuronal GSH content). In order to provide a clinically accessible measure to guide human dosing, we aimed in addition to use CSF from mice treated with these agents to identify CSF metabolite levels or other biomarkers that correlate with neuronal GSH normalization. Studies accomplished to date have established sensitive methods for measuring both neuronal GSH content and neuronal antioxidant capacity in mouse brain in situ. NAC at a dose of 7.5 mg/kg or higher (by i.p. delivery) were found to normalize GSH content and antioxidant capacity in EAAC1-/- mouse neurons. Full dose response curves for NACA and GSH are pending. Studies have not identified CSF biomarkers suitable for predicting drug efficacy. Ongoing studies are refining the CSF analyses and the time points of CSF collection.
Publication Based on MJFF Funding:
Berman AE, Chan WY, Brennan AM, Adler BL, Swanson RA, N-Acetylcysteine Prevents Loss of Dopaminergic Neurons in the EAAC1-/- Mouse. In press, Ann Neurology.