Formulation and optimization of fisetin nanoemulsion for the treatment of Alzheimer's disease in rats: Pharmacokinetic and pharmacodynamic assessment

Fiestin (FS) is a polyphenolic flavonoid that possesses various neuroprotective effects by attenuating the levels of AChE enzyme, accumulated amyloid β, free radicals and neuroinflammation against Alzheimer's disease (AD). It is also helpful in reducing cellular senescence. However, FS suffers from a dissolution rate-limited oral bioavailability, and poor blood-brain barrier (BBB) permeability leading to decreased therapeutic efficacy. To address these challenges, an attempt has been made to formulate a nanoemulsion (NE) of FS using Box-Behnken design (BBD) as optimization tool. The optimized NE contained 10 mg of FS, 164 μL of Capmul MCM EP/NF® (oil), 618 μL of T80 (surfactant), 218 μL of Transcutol P®, (co-surfactant) and 4000 μL of distilled water. The optimized formulation resulted in a mean droplet size, drug loading, polydispersity index (PDI), and zeta potential (ZP) of 32 nm, 95.5 %, 0.26, and −15.99 mV, respectively. In the pharmacokinetic studies, FS-NE showed 9.2-fold increase in Cmax as compared to naïve FS. Relative oral bioavailability FS loaded in FS-NE was 842.93 %. Further the concentration of FS loaded in FS-NE was 8.81-fold higher in brain than naive FS. To evaluate pharmacodynamic effects, an aluminum chloride (AlCl₃)-induced AD rat model was used. Cognitive functions were assessed using the Morris water maze and open field tests. The formulation showed dose-dependent effects. Rats treated with both, low and high doses of FS-NE (groups VI and VII) showed significant improvements (P < 0.001) in cognitive functions in AD-induced rats. The biochemical studies showed that FS-NE at both doses attenuated the levels of AChE enzyme, amyloid β, oxidative stress, and neuroinflammation. Results of histopathology indicated that FS-NE attenuated the degeneration of neurons in the cerebral cortex and hippocampus parts of the brain.