Inhibitory effect of curcuminoids on acetylcholinesterase activity and attenuation of scopolamine-induced amnesia may explain medicinal use of turmeric in Alzheimer's disease

Curcuminoids (a mixture of curcumin, bisdemethoxycurcumin and demethoxycurcumin) share vital pharmacological properties possessed by turmeric, a well known curry spice, considered useful in Alzheimer's disease (AD). The aim of this study was to evaluate if curcuminoids possess acetylcholinesterase (AChE) inhibitory and memory enhancing activities. The in-vitro and ex-vivo models of AChE inhibitory activity were used along with Morris water maze test to study the effect on memory in rats. Curcuminoids inhibited AChE in the in-vitro assay with IC₅₀ value of 19.67, bisdemethoxycurcumin 16.84, demethoxycurcumin 33.14 and curcumin 67.69 µM. In the ex-vivo AChE assay, curcuminoids and its individual components except curcumin showed dose-dependent (3-10 mg/kg) inhibition in frontal cortex and hippocampus. When studied for their effect on memory at a fixed dose (10 mg/kg), all compounds showed significant (p < 0.001) and comparable effect in scopolamine-induced amnesia. These data indicate that curcuminoids and all individual components except curcumin possess pronounced AChE inhibitory activity. Curcumin was relatively weak in the in-vitro assay and without effect in the ex-vivo AChE model, while equally effective in memory enhancing effect, suggestive of additional mechanism(s) involved. Thus curcuminoids mixture might possess better therapeutic profile than curcumin for its medicinal use in AD.