Abstract
Previous studies have reported that Hedyotis diffusa Willdenow extract shows various biological activities on cerebropathia, such as neuroprotection and short-term memory enhancement. However, there has been a lack of studies on the inhibitory activity on neurodegenerative diseases such as Alzheimer’s disease (AD) through enzyme assays of H. diffusa. Therefore, H. diffusa extract and fractions were evaluated for their inhibitory effects through assays of enzymes related to AD, including acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and β-site amyloid precursor protein cleaving enzyme 1 (BACE1), and on the formation of advanced glycation end-product (AGE). In this study, ten bioactive compounds, including nine iridoid glycosides 1–9 and one flavonol glycoside 10, were isolated from the ethyl acetate and n-butanol fractions of H. diffusa using a bioassay-guided approach. Compound 10 was the strongest inhibitor of cholinesterase, BACE1, and the formation of AGEs of all isolated compounds, while compound 5 had the lowest inhibitory activity. Compounds 3, 6, and 9 exhibited better inhibitory activity than other compounds on AChE, and two pairs of diastereomeric iridoid glycoside structures (compounds 4, 8, and 6, 7) showed higher inhibitory activity than others on BChE. In the BACE1 inhibitory assay, compounds 1–3 were good inhibitors, and compound 10 showed higher inhibitory activity than quercetin, the positive control. Moreover, compounds 1 and 3 were stronger inhibitors of the formation of AGE than aminoguanidine (AMG), the positive control. In conclusion, this study is significant since it demonstrated that the potential inhibitory activity of H. diffusa on enzymes related to AD and showed the potential use for further study as a natural medicine for AD treatment on the basis of the bioactive components isolated from H. diffusa.
Highlights
Hedyotis diffusa Willdenow, a member of the Rubiaceae family, is mainly distributed in tropical and sub-tropical Asia, especially in China, Japan, and Indonesia
We aimed to evaluate the potential efficacy of the extracts, fractions, and compounds isolated from H. diffusa against Alzheimer’s disease (AD), that is, against cholinesterase, BACE1, and advanced glycation end-product (AGE) formation
Compounds 1–10 from H. diffusa were evaluated for their anti-AD potencies, by conducting inhibitory assays of AChE, BChE, BACE1, and the formation of AGE
Summary
Hedyotis diffusa Willdenow, a member of the Rubiaceae family, is mainly distributed in tropical and sub-tropical Asia, especially in China, Japan, and Indonesia. H. diffusa has various biological activities, including neuroprotection [2], short-term memory enhancement [3], anti-oxidant [4], anticancer [5,6], anti-inflammatory [7], antitumor [8], antibacterial [9], and hepatoprotection effects [10]. H. diffusa, including iridoid glycosides, flavonol glycosides, triterpenoids, flavonoids, anthraquinones, and phenolic acids, such as E-6-O-p-coumaroyl scandoside methyl ester, E-6-O-p-methoxycinnamoyl. 17 species of the Hedyotis herba genus are used as herbal medicines. H. diffusa Willdenow has been used as a representative herbal medicine; it can often be confused for H. corymbosa Lamark owing to their similar external appearance. It is necessary to identify a specific potential biomarker that makes it possible to distinguish H. diffusa from counterfeits
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