Neuroprotective effect of intranasal delivery of asiatic acid against amyloid beta1-42-induced alzheimer's disease in mice

Asiatic acid (AA) is an active natural compound that can be derived from Centella asiatica extract. Several pharmacological studies were reported that AA has potential as neuroprotector in the central nervous system disorders. AA penetration in the brain was limited due to its low bioavailability. Nasal delivery system of solid lipid nanoparticles (SLNs) loaded-AA was developed to increase AA penetration in the brain. The current study aimed to investigate neuroprotective effect and protective mechanisms of AA in SLNs by nasal-to-brain delivery technique against Aβ1–42 induced memory impairment by in vivo study. Male ICR mice were divided into six groups (n=11-12/group); Sham, AD, AD-DON, AD-INAA, AD-POAA3 and AD-POAA30. Aggregated Aβ1–42 was injected into lateral ventricle of all AD mice while Sham mice was injected with 10% Dimethylsulfoxide (DMSO) in normal saline solution (NSS). One day after Aβ1–42 injection, Sham and AD mice received 0.5% carboxymethylcellulose (CMC) (1 mL/kg, p.o.) while donepezil (3 mg/kg, p.o.), AA in SLNs (2.26 mg/kg, i.n.), AA (3 and 30 mg/kg p.o) were given to AD-DON, AD-INAA, AD-POAA3 and AD-POAA30, respectively. The treatments were given 28 consecutive days, 60 min before the behaviour test except donepezil was given only during memory behaviour test (7 days). Open field-test (OFT) was performed on days 7 and 18 followed by novel object recognition (NOR) on days 19-20, elevated-plus maze (EPM) on day 21, and Morris water maze (MWM) on days 22-27. 24-hours after the last treatment, brains were collected for further analysis of phosphorylated tau (pTau) protein expression, glial activation (detected by glial fibrillary acidic protein (GFAP) and transmembrane protein 119 (TMEM119)), proinflammatory cytokines (IL-1b and TNF-a) level, malondialdehyde (MDA) level, amyloid beta deposits and neuronal counts. The results showed that spatial learning memory and recognition memory of AD mice significantly reduced, while INAA treatment significantly alleviated memory deficits in AD-INAA mice compared AD mice on days 2-5 of MWM (escape latency: p < 0.01, p < 0.05, p < 0.001 and p < 0.01, respectively; swimming distance: p < 0.001, p < 0.01, p < 0.001 and p < 0.001, respectively) and on the testing phase of NOR (discrimination and preference index: p < 0.5 and  p < 0.5, respectively). INAA treatment also significantly reduced pTau Serine-396 (p < 0.5) and pTau Threonine-231 (p < 0.01) protein expression in the hippocampus, GFAP and TMEM119 immunoreactivity in CA1 (p < 0.001 and p < 0.5, respectively) and CA3 (p < 0.01 and p < 0.5, respectively) subregion of the hippocampus, IL-1b (p < 0.001) and MDA levels (0.5) in the brain tissue. Additionally, Aβ1–42 injection did not induce neuronal loss in the hippocampus. To summarize, INAA had neuroprotective effect against Aβ1–42 in vivo. The underlying neuroprotective mechanisms are hyperphosphorylated tau protein inhibition, prevention of glial activation and proinflammatory cytokines and lipid peroxidation reduction. Taken together, the present study suggest that nasal delivery of AA in SLNs is a potential in drug development for the treatment of Alzheimer’s disease