Curcuminoids possess acetylcholinesterase inhibitory and memory enhancing activities
Curcuminoids, a mixture of curcumin, bisdemethoxycurcumin and demethoxycurcumin are considered to represent turmeric, a well known curry spice useful in Alzheimer's disease (AD). The aim of this study was to investigate if curcuminoids possess combination of activities beneficial for AD. Acetylcholinesterase (AChE) inhibitory activity was evaluated in the in-vitro and ex-vivo AChE assay in rats . Morris water maze test  was used to study the effect of compounds on memory in rats. Curcuminoids inhibited AChE in the in-vitro assay with IC50 values of 19.67µM (14.31–25.02; 95% CI; n=5), bisdemethoxycurcumin 16.84µM (15.07–18.60), demethoxycurcumin 33.14µM (29.08–37.19) and curcumin 67.69µM (63.71–71.66) being the least potent. The mixture of curcuminoids was compared with individual components at a fixed dose (10mg/kg) in the ex-vivo AChE assay, where it showed 58.18±3.51% inhibition (mean±SEM; n=5) in rat frontal cortex and 65.79±2.00% in hippocampus. Similarly, bisdemethoxycurcumin and demethoxycurcumin showed 47.56±3.52 and 46.69±2.38% inhibition in frontal cortex and 55.28±3.65 and 44.63±3.99% in hippocampus respectively, while curcumin showed negligible effect (p>0.05). Curcuminoids and all of the individual components showed significant (p<0.01) and comparable memory enhancing effect in scopolamine-induced amnesia. These data indicate that curcuminoids possess AChE inhibitory activity along with memory enhancing effect, which is mediated possibly through more than one mechanisms and this study may explain the medicinal use of turmeric in AD.
Acknowledgements: This study was supported by the Aga Khan University, Karachi and Higher Education Commission, Pakistan.
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