Since the pathogenesis of AD is caused by complex and multiple factors, it is reasonable to prescribe a combination of drugs with different pharmacological activities for AD patients, rather than a single drug [29–31]. In fact, it has been reported that donepezil, an AChEI, is widely prescribed for patients with moderate to severe AD, and that although it is highly effective during the early administration period, it is somewhat less effective during the later administration period [32, 33]. Here, we demonstrated that co-treatment with donepezil and a mixture of three herbal extracts, SIP3, results in improved pharmacological activity in the late dementing stage in AD mouse model, in comparison with donepezil alone.
Originally this study, was boost up higher cell viability as well as donepezil in SH-SY5Y (Neuroblastoma cell line) cells, and progressed a combo of herbal extracts SIP3. Initially 33 medicinal herbs in SH-SY5Y cells were isolated them for Aβ toxicity [34]. Among them Santalum album, Polygala tenuifolia, Illicium verum were the perfect herb [22, 35, 36]. After evaluated the neuroprotective effect of SIP3 with donepezil using Drosophila AD models. Drosophila was a well-developed genetic and cell biological system has been examining neurodegenerative disease [37]. S. album, I. verum, and P. tenuifolia separately and also mixed (SIP3) together or SIP3 with dopepezil analyzed the neuroprotective effect against Aβ42 toxicity in Drosophila. The survival rate was significantly increased during the combination of SIP3 and donepezil, compared to the group in which donepezil only. Also, the intake of SIP3 with donepezil significantly improved locomotive dysfunction and strongly suppressed Aβ42-induced cell death. These results suggest that SIP3 with donepezil is effective for protecting the cells from Aβ42 cytotoxicity and neuronal functions [15].
Then, we investigated the effects of donepezil and SIP3 co-treatment on learning and memory in the APP/PS1 AD mouse model, in comparison with donepezil alone, using the PAT methodology [38, 39]. In the early stage of dementia (1 to 3 months), both treatments resulted in improved memory when compared to control mice, with no noticeable difference seen between the two groups. However, in the later stage of dementia (5 to 6 months), memory was significantly improved in the group co-treated with SIP3 than that in the group treated with donepezil alone. Based on these results, we conducted MWM test on animals at the late stage of dementia to compare cognitive abilities between the two groups [40]. In the SIP3L co-treatment group, the time to reach the target quadrant was shorter and the time spent in the target quadrant was longer, indicating that the animals in this group had a more improved cognitive ability than those treated with donepezil alone [41, 42].
During that time AD patients are well known to progress depression, which affects the development and progression of AD, we have regulated FST as well as TST experiments through study depression-like behavior in AD animals [43]. In contrary the donepezil alone group, depression was significantly enhanced in the SIP3 and donepezil co-treatment group. In addition, co-administration of SIP3 and donepezil inhibited the increase in corticosterone levels seen in the serum of the AD animals. In this study we have implemented that the SIP3 was ready to regulate serum corticosterone level in APP/PS1 mice. The outcomes were carried both peripheral and central origins over a direct action of SIP3 on adrenal glands and hypothalamic-pituitary-adrenal axis respectively. In contrary, the relationship between memory performance and corticosterone level in APP/PS1 was approved the damaging effects on memory [44]. In addition, a long term depression has influenced the spatial memory [45].
These results suggest that SIP3 and donepezil co-treatment could improve some side effects, such as anxiety and insomnia, reported in donepezil-treated AD patients.
MicroRNA is small nucleic acids consisting of about ~ 20 nucleic acids, which involved in various biological pathways, and recent studies have reported that miRNA plays a key role in neurological diseases. In this study, we found that the expressions of miRNAs were reversed its abnormal changes by DON and SIP3L cotreatment, including miRNA-15a, -27a, 32, which are linked with inflammation or apoptosis pathways [46–49], indicating that the therapeutic mechanism of SIP3 and DON might underlie miRNA regulation. Further studies are required to unravel the detailed mechanism.
RNA-seq was used to study gene expression profiles in relation to the improved cognitive ability seen in the SIP3 co-treated AD animals. Genes involved in exercise behaviors, the neuropeptide signaling pathway, and visual learning were differentially expressed in the mice of the SIP3L group in comparison to those expressed in the AD control mice. These results are consistent with the improved learning and memory seen in the animals of the SIP3L group. Noticeably, the gene expression profiles in the SIP3L group were more similar to those of normal mice than those of the control APP/PS1 mice, those treated with donepezil alone, or those co-treated with donepezil and SIP3H. In this study, we found that co-treatment of low dose of SIP3 and donepezil can improve impaired learning, memory, and depression.