Nitric oxide inhibitory daphnane diterpenoids as potential anti-neuroinflammatory agents for AD from the twigs of Trigonostemon thyrsoideus

The extensive pathology studies revealed that Alzheimer’s disease (AD) is closely related to neuroinflammation and anti-neuroinflammatory agents may be potentially useful for the treatment of AD. A continuous search for new nitric oxide (NO) inhibitory compounds as anti-neuroinflammatory agents for AD resulted in the isolation of four new (1−4) and eight known (5−12) daphnane diterpenoids from the twigs of Trigonostemon thyrsoideus. Their structures were elucidated on the basis of extensive nuclear magnetic resonance (NMR) spectroscopic data analysis and the time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. Compounds 1–4 represent new examples of daphnane diterpenoid orthoesters and 4 features a rare and complex macroring diterpenoid structure. The anti-neuroinflammatory effects were examined by inhibiting NO release in lipopolysaccharide (LPS)-induced murine microglial BV-2 cells. The possible mechanism of NO inhibition of some bioactive compounds was also investigated using molecular docking, which revealed the interactions of bioactive compounds with the inducible nitric oxide synthase (iNOS) protein.     

Withanolides from Physalis peruviana showing nitric oxide inhibitory effects and affinities with iNOS

A phytochemical study to obtain new nitric oxide (NO) inhibitors resulted in the isolation of five new withanolides from the whole plants of Physalis peruviana. The structures were determined on the basis of extensive NMR spectroscopic data analysis as well as the time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The NO inhibitory effects were examined by inhibiting NO release in lipopolysaccharide-stimulated murine microglial BV-2 cells. Molecular docking studies showed the strong interactions of bioactive compounds with the inducible nitric oxide synthase (iNOS) protein, revealing the potential mechanism of NO inhibition of bioactive compounds.     

Anti-inflammatory abietane diterpenoids from the seeds of Podocarpus nagi

In searching for naturally occurring anti-inflammatory agents, three new abietane-type diterpenoids, named 16-hydroxylambertic acid (1), 7-oxo-18-hydroxyferruginol (2), and 5α,12-dihydroxy-6-oxa-abieta-8,11,13-trien-7-one (3), were isolated from the seeds of Podocarpus nagi, together with three known compounds. The structures of the new compounds were elucidated by extensive analysis of NMR and HR-ESIMS data. All the new compounds were tested for nitric oxide (NO) inhibitory activities on lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Compound 1 significantly inhibited NO production with IC₅₀ value of 5.38 ± 0.17 μM, and suppressed inducible NO synthase (iNOS) expression in a dose-dependent manner, which were mediated through inhibiting the mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) activation.     

Steroidal glycosides from Marsdenia tenacissima

Three new compounds 1–3 as C₂₁ steroidal glycosides of diester derivatives of tenacigenin B were isolated from the ethanolic extract of stems of Marsdenia tenacissima. All compounds were prepared and evaluated inhibitory activity of nitric oxide in RAW276.4 macrophages. Compounds 1–3 exhibited inhibitory effects against nitric oxide (NO).     

Rearranged limonoids and chromones from Harrisonia perforata and their anti-inflammatory activity

Two new rearranged limonoids, harperforatin (1) and harperfolide (2), and a new chromone, harperamone (3), were isolated from fruits and roots of Harrisonia perforata, together with eight known compounds. Their structures were elucidated on the basis of spectroscopic data. Harperfolide (2) exhibited potent anti-inflammatory activity by suppressing nitric oxide (NO) production from activated macrophages with IC₅₀ value of 6.51 μM. Furthermore, its effect is mediated by reduction of iNOS protein expression, attributable to the inhibitory action of LPS-induced NO production.     

Nitric oxide inhibitory limonoids as potential anti-neuroinflammatory agents from Swietenia mahagoni

Recent studies have revealed that there is a close relationship between neuroinflammation and Alzheimer's disease (AD) and compounds with anti-neuroinflammatory effects are potentially useful for the treatment of AD. A phytochemical investigation to obtain new neuroinflammatory inhibitors resulted in the isolation of four new and three known limonoids from Swietenia mahagoni. The structures of these limonoids were established by NMR, MS, and electronic circular dichroism (ECD) data analysis. Compounds 1–3 feature complicated polycyclic caged structures of limonoid orthoester and represent new examples of phragmalin-type limonoids. All of the isolates showed anti-neuroinflammatory activities by inhibiting nitric oxide (NO) release in LPS-induced murine microglial BV-2 cells with compounds 1 and 3–6 having IC₅₀ values of 26.8, 26.1, 26.0, 37.1, and 16.5 μM, respectively. The possible mechanism of NO inhibition of some bioactive compounds was also investigated using molecular docking, which revealed the interactions of bioactive compounds with the inducible nitric oxide synthase (iNOS) protein.     

Chemical constituents isolated from Disporum viridescens leaves and their inhibitory effect on nitric oxide production in BV2 microglial cells

Excessive NO (nitric oxide) has been associated with the pathogenesis of various neurodegenerative diseases including Alzheimer’s disease (AD). In our screening system using LPS-activated BV2 microglial cells, the methanolic extract of Disporum viridescens leaves was found to have significant NO inhibitory activity. Bioactivity-guided isolation yielded a new phenylpropanoid characterized as 4-ally-2,6-dimethoxyphenyl 1-O-β-d-apiofuranosyl (1 → 6)-β-d-glucopyranoside (12) with 21 known compounds from the leaves of D. viridescens. Among them, compounds 2 and 4 significantly inhibited NO production. Thus, we further elucidated the anti-inflammatory mechanism of these lignans. Especially, compound 4 inhibited the expression of both inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) through the suppression of the MAPK signaling pathway. Taken together, the anti-inflammatory activities of the active constituents isolated from D. viridescens leaves could have therapeutic potential against neurodegenerative diseases.     

Bioactive triterpene glycosides from the fruit of Stauntonia hexaphylla and insights into the molecular mechanism of its inflammatory effects

Chromatography of the ethanol extract of the medicinal fruit Stauntonia hexaphylla resulted in the purification of 26 compounds (1–26), including two undescribed triterpene saponins 1 and 2 (hexaphylosides A and B). Their structures were confirmed by spectroscopic data, including IR, HR QTOF MS, ¹H, ¹³C NMR, COSY, HMQC, HMBC, and TOCSY, and HPLC sugar analysis after acid hydrolysis. The anti-inflammatory effects of the high-purity constituents (1–26) on lipopolysaccharide (LPS)-induced RAW264.7 macrophage cells were investigated by screening nitric oxide production. The NO inhibitory activity of compounds 6 and 10 with the IC₅₀ values of 1.33 and 1.10 µM, respectively. The structure-activity relationships (SAR) of the isolated compounds were also analyzed. Furthermore, compounds 6 and 10 inhibited the protein expression inducible nitric oxide synthase (iNOS), and cyclooxygenase (COX)-2 via Western blotting analysis. This showed that compounds 6 and 10 contributed to the anti-inflammatory effects of S. hexaphylla fruit, which could be developed as a natural nutraceutical and functional food ingredient.     

Trichosanhemiketal A and B: Two 13,14-seco-13,14-epoxyporiferastanes from the root of Trichosanthes kirilowii Maxim.

Of the 32 Trichosanthes species in China, T. kirilowii Maxim. is the most renowned species used in traditional Chinese medicine and has diverse pharmacological properties. However, most of the phytochemical studies of T. kirilowii have focused on the fruits and seeds. In our investigation of the chemical constituents of T. kirilowii roots, two previously undescribed sterols [trichosanhemiketal A and B (1 and 2)], together with 13 known compounds, were isolated and their structures were elucidated. To the best of our knowledge, this represents the first isolation of compounds with a 13,14-seco-13,14-epoxyporiferastane (1–2) skeleton from the Cucurbitaceae family. The anti-inflammatory activity of the isolated compounds was determined through an analysis of their inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in macrophage RAW264.7 cells. Of the compounds, 4, 5, 6, and 8 showed significant inhibitory activities, with IC₅₀ values of 8.5, 15.1, 25.4, and 28.5 µM, respectively. In addition, compound 4 inhibited inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 expression in a concentration-dependent manner.     

Phenolic constituents from the rhizomes of Acorus gramineus and their biological evaluation on antitumor and anti-inflammatory activities

On the search for anti-cancer compounds from natural Korean medicinal sources, a bioassay-guided fractionation and chemical investigation of the MeOH extract from the rhizomes of Acorus gramineus resulted in the isolation and identification of thirteen phenolic derivatives (1–13) including two new 8-O-4′-neolignans, named surinamensinols A (1) and B (2) and a new phenolic compound, named acoramol (9). The structures of these new compounds were elucidated on the basis of 1D and 2D NMR spectroscopic data analyses as well as circular dichroism (CD) spectroscopy studies. The cytotoxic activities of the isolates (1–13) were evaluated by determining their inhibitory effects on human tumor cell lines. The new 8-O-4′-neolignans, compounds 1 and 2, showed moderate antiproliferative activities against A549, SK-OV-3, SK-MEL-2, and HCT-15 cell lines with IC₅₀ values in the range of 4.17–26.18 μM. On the basis of the expanded understanding that inflammation is a crucial cause of tumor progression, anti-inflammatory activities of these compounds were determined by measuring nitric oxide (NO) levels in the medium using murine microglia BV-2 cells. Compounds 1, 2, 4, 7 and 10 inhibited NO production in BV-2 stimulated by lipopolysaccharide with IC₅₀ values of 8.17–18.73 μM via NO scavenging, inhibition of iNOS activity, and/or suppression of iNOS expression.     

NO inhibitory phytochemicals as potential anti-inflammatory agents from the twigs of Trigonostemon heterophyllus

Studies on the relationship of nitric oxide (NO) and inflammation have revealed that compounds with NO inhibitory effects are potentially useful for inflammation and related inflammatory disorders. A phytochemical investigation to obtain new NO inhibitors resulted in the isolation of two new cleistanthane diterpenoids (1 and 2) and 11 known terpenoids (3–13) from Trigonostemon heterophyllus. The structures of these terpenoids were established by analysis of their NMR, MS, and electronic circular dichroism (ECD) data. Compounds 1 and 2 possess rare 3,4-seco-cleistanthane diterpenoid skeletons. All of the isolates were evaluated biologically for their NO inhibitory effects in lipopolysaccharide (LPS)-induced murine microglial BV-2 cells and compounds 1, 6, and 8–10 showed strong NO inhibitory effects with IC₅₀ values less than 40 μM. Using Western blotting experiments and molecular docking, the possible mechanism of NO inhibition was investigated.     

Anti-inflammatory activity of halogenated secondary metabolites of Laurencia snackeyi (Weber-van Bosse) Masuda in LPS-stimulated RAW 264.7 macrophages

Secondary metabolites of tropical seaweed are proven to exhibit variety of biological activities. Six species of seaweed (Caulerpa racemosa var. laete-virens, Caulerpa sertularioides f. longipes, Halymenia dilatata, Laurencia snackeyi, Padina boryana, and Sargassum swartzii) were tested for anti-inflammatory activity in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Crude L. snackeyi extract exhibit potent activity, and upon bioassay-guided isolation, it contained four halogenated compounds that exert profound inhibitory effects against nitric oxide (NO) production in LPS-stimulated RAW 264.7 cells. These compounds were subjected to spectroscopic measurements and were identified as palisadin A (1), aplysistatin (2), 5-acetoxypalisadin B (3), and palisol (4). Further experiments showed aplysistatin (2) to significantly inhibit NO production and prostaglandin-E2 (PGE2) production, and suppress inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression in LPS-stimulated RAW 264.7 cells. Therefore, aplysistatin (2) is suggested to inhibit NO and PGE2 production via the inhibition of iNOS and COX-2, indicating that its activity may be attributed to the modulation of anti-inflammatory agents.     

NO inhibitory constituents as potential anti-neuroinflammatory agents for AD from Blumea balsamifera

Our continuous search for new nitric oxide (NO) inhibitory substances as anti-neuroinflammatory agents for AD resulted in the isolation of one new labdane diterpenoid and three new guaiane sesquiterpenoids, as well as ten known compounds from Blumea balsamifera. Their structures were elucidated by NMR spectroscopic data analysis and the time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The anti-neuroinflammatory effects were examined by inhibiting NO release in LPS-induced murine microglial BV-2 cells. The possible mechanism of NO inhibition of some bioactive compounds was also investigated using molecular docking, which revealed the interactions of bioactive compounds with the iNOS protein.     

NO inhibitors function as potential anti-neuroinflammatory agents for AD from the flowers of Inula japonica

The extensive pathology studies revealed that Alzheimer’s disease (AD) is closely related to neuroinflammation and anti-neuroinflammatory agents may be potentially useful for the treatment of AD. Inula japonica is a member of the Asteraceae plant family and its flowers have been used as a healthy tea and a traditional Chinese medicine. Our continuous search for new nitric oxide (NO) inhibitory substances as anti-neuroinflammatory agents for AD resulted in the isolation of two new sesquiterpenes and ten known terpenes from the flowers of I. japonica. Their structures were established on the basis of extensive analysis of NMR and MS spectroscopic data, as well as calculated and experimental electronic circular dichroism (ECD) spectra. Among these isolates, compound 1 is a new sesquiterpene with a rare tricyclic fused skeleton, and 2 processes a 1,10-seco-eudesmane skeleton. The anti-neuroinflammatory effects were examined by inhibiting NO release in LPS-induced murine microglial BV-2 cells. The possible mechanism of NO inhibition was also investigated using molecular docking, which revealed the interactions of bioactive compounds with the iNOS protein. The present study disclosed that the flowers of I. japonica as a healthy tea are potentially useful for AD and related neuroinflammatory diseases.     

Synthesis of a novel series of diphenolic chromone derivatives as inhibitors of NO production in LPS-activated RAW264.7 macrophages

A novel series of diphenolic chromone derivatives were synthesized and their inhibitory activity on nitric oxide (NO) production and cytotoxicity were evaluated using LPS-activated murine macrophages RAW264.7 assay and MTT method, respectively. Among these compounds, (5,7-dihydroxy-4-oxo-4H-chromen-3-yl) methyl esters (6b, 6c, 6f, 6g, and 6h) showed quite potent inhibitory activities with IC₅₀ values of 2.20, 3.48, 0.35, 0.80, and 0.61 μM, respectively. The MTT results showed that all of the active compounds exhibited no cytotoxicity at the effective concentrations. The preliminary mechanism of the most potent compounds (6b, 6c, 6f, 6g, and 6h) was further examined based on the RT-PCR results and the compounds 6f, 6g, and 6h inhibited NO production by suppressing the expression of iNOS mRNA in a dose dependent manner. Furthermore, a computational analysis of physicochemical parameters revealed that the most of the compounds possessed drug-like properties.     

Phytochemicals with NO inhibitory effects and interactions with iNOS protein from Trigonostemon howii

A phytochemical investigation to obtain new NO inhibitors led to the isolation of nine compounds including one new guaiane-type sesquiterpenoid (1) and two new cleistanthane diterpenoids (2 and 3) from the stems of Trigonostemon howii. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic data analysis, and the absolute configurations of new compounds 1–3 were established via comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compounds 2 and 3 possess a rare 3,4-seco-cleistanthane diterpenoid skeleton. All of the compounds showed inhibitory effects on lipopolysaccharide-induced NO production in murine microglial BV-2 cells. The further molecular docking studies indicated the strong interactions between some bioactive compounds with the iNOS protein, which revealed the possible and potential mechanism of NO inhibition of bioactive compounds.     

Anti-neuroinflammatory effects of sesquiterpenoids isolated from Nardostachys jatamansi

Two new nardosinone-type sesquiterpenoids, namely kanshone J (1) and kanshone K (2) along with seven known terpenoids (3–9) were isolated from the rhizomes and roots of Nardostachys jatamansi DC (Valerianaceae). The structures of these compounds were determined mainly by analysis of 1D-, 2D-NMR and MS data. In addition, the absolute configuration of compound 1 was assigned by application of the modified Mosher’s method. In an initial assay to evaluate their anti-neuroinflammatory effects, compounds 1–5 and 9 exhibited dose-dependent inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in BV2 cells, with IC₅₀ values ranging from 2.43 to 46.54?μM. Particularly, desoxo-narchinol A (3) and narchinol B (4) significantly inhibited LPS-induced NO overproduction in BV2 cells with IC₅₀ values of 3.48?±?0.47 and 2.43?±?0.23?μM, respectively. Furthermore, compounds 3 and 4 exhibited anti-neuroinflammatory effects by inhibiting the production of pro-inflammatory mediators, including prostaglandin E₂ (PGE₂), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) proteins, and pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF)-α, in LPS-stimulated BV2 and primary microglial cells.     

Synthesis and anti-inflammatory activities of 1-O-acetylbritannilactone analogues

Natural product 1-O-acetylbritannilactone (ABL) is a major sesquiterpene in Inula Britannica and Inula Japonica. To investigate the chemistry properties of ABL, 12 analogues were synthesized. Compound 1, a new 6-deoxybrintanilactone with a methylene at C-14 position, was characterized by 1D, 2D NMR and HR-MS spectrum. The studies of anti-inflammatory activities showed that compounds 1 and 4 exhibited significant inhibitory effects on the nitric oxide production and inducible nitric oxide synthase (iNOS) expressions. The preparation of compounds 1 and 2 from ABL was also studied. We also speculated a proposed mechanism for the formation of 1, 2 and 3.     

Synthesis of azaisoflavones and their inhibitory activities of NO production in activated microglia

A series of azaisoflavones were synthesized and their biological activities were evaluated for nitric oxide (NO) production and inducible NO synthase (iNOS) expression in BV-2 microglia cell lines. Among these compounds, compound 8d was the most potent with IC₅₀ 7.83 μM for inhibition of NO production. Also, compound 8d inhibited expression of iNOS in LPS-induced BV2 cells. This result suggests that compound 8d inhibited the production of NO by suppressing the expression of iNOS.     

Corrigendum to “A new phenylethyl glycoside and a new dibenzocyclooctadiene lignan from the leaves of Kadsura coccinea (Lem.) A. C. Smith” [Phytochem. Lett. 45 (2021) 57–62]

A new phenylethyl glycoside (1), (S)-1-phenylethyl-6-α-L-arabinopyranosyl-β-D-glucopyranoside), and a new dibenzocyclooctadiene lignan (7), Kasuracin A, together with seven known compounds, were isolated and identified from the leaves of Kadsura coccinea. Their structures were determined by analysis of multinuclear and multidimensional nuclear magnetic resonance (NMR), circular dichroism (CD), mass spectrometry, hydrolysis analysis, or comparison to those reported in the literature. Then, all the isolates 1‒9 were evaluated for their inhibitory eff ;ects against nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Among them, compounds 2 and 3 were isolated for the first time from this plant and compounds 3, 7, 8, and 9 significantly inhibited NO production with IC₅₀ values of 36.4, 10.2, 12.3, and 21.7 μM, respectively.