Using DARC to assess neuroprotection of intranasal curcumin in an Alzheimer’s model

Abstract

Purpose : Alzheimer’s disease (AD) is the major cause of dementia in the world with increasing evidence of the retina being affected. Since no cure exists, the development of new treatments is an urgent unmet need. Curcumin, a natural polyphenol, has been advocated as a potential neuroprotectant in AD. However, its poor solubility in water and low bioavailability have limited its clinical translation. In this study we describe a novel curcumin nanoparticle (CN) formulation and evaluate its neuroprotective efficacy in vitro and in vivo.

Methods : CN were formulated using a thin film rehydration technique. Their stability and characteristics were investigated with spectrophotometry and dynamic light scattering. R28 cells were used to assess CN toxicity and neuroprotective activity (alamarBlue assay). For in vivo studies 3xTg-AD mice were treated intranasally 5 days/week from the age of 10 months with 3 µL of either CN (n=7) or vehicle (n=6). After three months of treatment, animals had retinal imaging performed using DARC (Detection of Apoptosing Retinal Cells) technology. Fluorescent spots (DARC count) were counted by someone masked to treatment groups. All results were given with the standard error and the statistical test used was a one-way ANOVA with a Tukey post-test.

Results : CN formulation incorporating over 4 mg/ml of curcumin was stable over 90 days when stored at 4°C with a particle size of 13 nm and a polydispersity index <0.3. This formulation was well tolerated by R28 cells and protected against a) glutamate excitotoxicity with an IC50 of 22.36±0.50 mM vs 4.54±0.32 mM for control group (p<0.0001) and b) hypoxia mimetic cobalt chloride with an IC50 of 427.9±37.62 µM vs 259.4±15.34 µM for control group (p<0.05). No adverse effects were seen in vivo either systemically or in the eye. 3xTg-AD mice receiving CN were found to have a significant reduction in the DARC count (p<0.05) compared to vehicle control (17.36±3.34 vs 49.08±13.28).

Conclusions : These promising results show that CN is non-toxic and neuroprotective in vitro against insults mimicking cellular stress of AD. CN was found in vivo to be neuroprotective in 3xTg-AD mouse eyes, as evidenced by the reduction in retinal cell apoptosis. This suggests that systemic CN has a potential therapeutic effect in AD, and that the effects of AD therapy can be assessed through the eye. However, further histological studies are needed to validate these findings.