Neuroprotective Effects of Triterpenoids from Camellia japonica against Amyloid β-Induced Neuronal Damage

Alzheimer's disease (AD), a neurocognitive impairment affecting human mental capacity, is related to the accumulation of amyloid-β peptide (Aβ) and the hyperphosphorylation of tau protein. In addition to modern therapies approved for AD treatment, natural products with antioxidant and anti-inflammatory properties have been studied for their potential to prevent AD pathogenesis. Six new noroleanane triterpenoids from the fruit peels of Camellia japonica were isolated, and their structures were determined by diverse spectroscopic methods. The neuroprotective effects of the six new compounds were tested against Aβ-induced neurotoxicity and neuroinflammation in mouse hippocampal and microglial cells. In the model of HT22-transfected cells, compounds 1-4 showed strongly neuroprotective effects via antioxidant response element gene activation and decreased the level of glutamate uptake. Compounds 1-4 also appeared to have strong inhibitory effects on NO production in Aβ_1-42-transfected BV2 microglial cells. A docking simulation study was used to explain the inhibitory effects of compounds 1-4 on β-secretase 1 (BACE1). Noroleanane triterpenoids 1-4 had potential neuroprotective and anti-inflammatory effects against Aβ-induced neuronal damage. The structure-activity relationships of the 30 oleanane triterpenoids from C. japonica were assessed in a model of Aβ_1-42-transfected HT22 cells.

Prenylated Phenolic Compounds from the Leaves of Sabia limoniacea and Their Antiviral Activities against Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV), a serious swine epidemic, has been rampant in Asia since the 1990s. Despite the widespread use of PEDV vaccines, the occurrence of PEDV variants requires the discovery of new substances that inhibit these viruses. During a search for PEDV inhibitory materials from natural sources, seven new sabphenosides (1-7) and a new flavonoid (8), as well as eight known phenolic compounds (9-16), were obtained from the leaves of Sabia limoniacea. The structural determination of the new phenolic derivatives (1-8) was accomplished using comprehensive spectroscopic methods. Their absolute configurations were assigned by a combination of the ECD exciton chirality method following selective reduction and calculation of their ECD spectra. The bioactivities of the isolated compounds were measured based on their abilities to inhibit viral replication of PEDV. Among the test compounds, 15 and 16 exhibited the most promising antiviral activities, with IC₅₀ values of 7.5 ± 0.7 μM and 8.0 ± 2.5 μM against PEDV replication. This study suggests that compounds 15 and 16 could serve as new scaffolds for the treatment of PEDV infection through the inhibition of PEDV replication.

Antiviral escin derivatives from the seeds of Aesculus turbinata Blume (Japanese horse chestnut)

Porcine epidemic diarrhea virus (PEDV) causes severe diarrhea and high fatality of piglets, influencing the swine industry. Japanese horse chestnut (seed of Aesculus turbinata) contains many saponin mixtures, called escins, and has been used for a long time as a traditional medicinal plant. Structure-activity relationship (SAR) studies on escins have revealed that acylations at C-21 and C-22 with angeloyl or tigloyl groups were important for their cytotoxic effects. However, the strong cytotoxicity of escins makes them hard to utilize for other diseases and to develop as nutraceuticals. In this research, we investigated whether escin derivatives 1-7 (including new compounds 2, 3, 5 and 6), without the angeloyl or tigloyl groups and with modified glycosidic linkages by hydrolysis, have PEDV inhibitory effects with less cytotoxicity. Compounds 1-7 had no cytotoxicity at 20μM on VERO cells, while compounds 8-10 showed strong cytotoxicity at similar concentrations on PEDV. Our results suggest that escin derivatives showed strong inhibitory activities on PEDV replication with lowered cytotoxicity. These studies propose a method to utilize Japanese horse chestnut for treating PEDV and to increase the diversity of its bioactive compounds.

Antiviral Indolosesquiterpenoid Xiamycins C-E from a Halophilic Actinomycete

New metabolites, xiamycins C-E (1-3), were isolated from a Streptomyces. sp (#HK18) culture inhabiting the topsoil in a Korean solar saltern. The planar structures of the xiamycins C-E were elucidated as carbazole-bearing indolosesquiterpenoids using a combined analysis of NMR, MS, UV, and IR spectroscopic data. The absolute configurations of these new compounds were determined by analyses of NOESY and ECD data. When the xiamycins were tested for inhibitory activity on porcine epidemic diarrhea virus (PEDV), xiamycin D (2) showed the strongest inhibitory effect on PEDV replication (EC50 = 0.93 μM) with low cytotoxicity (CC50 = 56.03 μM), thus displaying a high selective index (60.31). Quantitative real-time PCR data revealed the inhibitory effect of 2 on genes encoding essential structural proteins (GP6 nucleocapsid, GP2 spike, and GP5 membrane) for PEDV replication in a dose-dependent manner. The antiviral activity of xiamycin D (2) was also supported by both Western blotting of the GP2 spike and GP6 nucleocapsid protein synthesis of PEDV. Therefore, xiamycin D shows the potential of indolosesquiterpenoids as new and promising chemical skeletons against PEDV-related viruses.

Jubanines F-J, cyclopeptide alkaloids from the roots of Ziziphus jujuba

Five Ib-type cyclopeptide alkaloids, jubanines F-J (1-5), and three known compounds, nummularine B (6), daechuine-S3 (7), and mucronine K (8) were isolated from the roots of Ziziphus jujuba. Their structures were fully characterized by spectroscopic analyses in combination with chemical derivatization. Compounds 1-3, and 6 were evaluated for their antiviral activity against the porcine epidemic diarrhea virus (PEDV). Compounds 2, 3, and 6 showed potent inhibitory effects on PEDV replication.

Oleanane triterpenes from the flowers of Camellia japonica inhibit porcine epidemic diarrhea virus (PEDV) replication

Porcine epidemic diarrhea virus (PEDV) infections have resulted in a severe economic loss in the swine industry in many countries due to no effective treatment approach. Fifteen oleanane triterpenes (1-15), including nine new ones (1-4 and 10-14), were isolated from the flowers of Camellia japonica, and their molecular structures were determined by extensive spectroscopic methods. These compounds were evaluated for their antiviral activity against PEDV replication, and the structure-activity relationships (SARs) were discussed. Compounds 6, 9, 11, and 13 showed most potent inhibitory effects on PEDV replication. They were found to inhibit PEDV genes encoding GP6 nucleocapsid, GP2 spike, and GP5 membrane protein synthesis based on RT-PCR data. Western blot analysis also demonstrated their inhibitory effects on PEDV GP6 nucleocapsid and GP2 spike protein synthesis during viral replication. The present study suggested the potential of compounds 6, 9, 11, and 13 as promising scaffolds for treating PEDV infection via inhibiting viral replication.

Dammarane triterpenes as potential SIRT1 activators from the leaves of Panax ginseng

During a search for SIRT1 activators originating in nature, three new dammarane triterpenes, 6α,20(S)-dihydroxydammar-3,12-dione-24-ene (1), 6α,20(S),24(S)-trihydroxydammar-3,12-dione-25-ene (2), and 6α,20(S),25-trihydroxydammar-3,12-dione-23-ene (3), as well as two known triterpenes, dammar-20(22),24-diene-3β,6α,12β-triol (4) and 20(S)-ginsenoside Rg3 (5), were isolated from Panax ginseng leaves. Compounds 1 and 3-5 showed potential as SIRT1 activators, as analyzed by in vitro enzyme-based SIRT1-NAD/NADH and SIRT1-p53 luciferase cell-based assays. They were also found to increase the level of NAD(+)/NADH ratio in HEK293 cells. This study presents a new class of chemical entities that may be able to be developed as SIRT1 activators for antiaging and treatment of age-associated diseases.