Cytotoxic terpene hydroperoxides from the aerial parts ofAster spathulifolius

Natural Peroxides from Plants: Historical Discovery, Biosynthesis, and Biological Activities

Naturally occurring peroxides received great interest and attention from scientific research groups worldwide due to their structural diversity, versatile biological activities, and pharmaceutical properties. In the present review, we describe the historical discovery of natural peroxides from plants systematically and update the researchers with recently explored ones justifying their structural caterogrization and biological/pharmaceutical properties intensively. Till the end of 2023, 192 peroxy natural products from plants were documented herein for the first time implying most categories of natural scaffolds (e. g. terpenes, polyketides, phenolics and alkaloids). Numerically, the reported plants' peroxides have been classified into seventy-four hydro-peroxides, hundred seven endo-peroxides and eleven acyl-peroxides. Endo-peroxides (cyclic alkyl peroxides) are an important group due to their high variety of structural frameworks, and we have further divided them into "four-, five-, six and seven"-membered rings. Biosynthetically, a shedding light on the intricate mechanisms behind the formation of plant-derived peroxides are addressed as well.

Cell death-inducing activities via Hsp inhibition of the sesquiterpenes isolated from Valeriana fauriei

Three new sesquiterpenes, valerianaterpenes I-III, and eight known compounds have been isolated from the methanol extract of the rhizomes and roots of Valeriana fauriei. The chemical structures of the three new sesquiterpenes were elucidated based on chemical and spectroscopic evidence. The absolute stereochemistry of valerianaterpene I was determined using X-ray crystallography. The cell death-inducing activity of isolated compounds alone or combination with Adriamycin (ADR) was observed by time-lapse cell imaging. Although the isolated compounds did not affect the number of mitotic entry cells and dead cells alone, kessyl glycol, kessyl glycol diacetate, and iso-teucladiol significantly increased the number of dead cells on ADR treated human cervical cancer cells. One of the mechanisms of cell death-inducing activity for the kessyl glycol acetate was suggested to be the inhibition of heat-shock protein 105 (Hsp105) expression level. This paper first deals with the naturally occurring compounds as Hsp105 inhibitor.

Germacrone: A Potent Secondary Metabolite with Therapeutic Potential in Metabolic Diseases, Cancer and Viral Infections

Natural products, an infinite reserve of bioactive molecules, will continue to serve humans as an important source of therapeutic agents. Germacrone is a bioactive natural compound found in the traditional medicinal plants of family Zingiberaceae. This multifaceted chemical entity has become a point of focus during recent years due to its numerous pharmacological applications, e.g., anticancer, anti-inflammatory, antiviral, antioxidant, anti-adipogenic, anti-androgenic, antimicrobial, insecticidal, and neuroprotective. Germacrone is an effective inducer of cell cycle arrest and apoptosis in various cancers (breast, brain, liver, skin, prostate, gastric, and esophageal) via modulation of different cell signaling molecules and pathways involved in cancer proliferation. This is the first report highlighting the wide spectrum of pharmacological activities exhibited by germacrone. The reported data collected from various shreds of evidences recommend that this multifaceted compound could serve as a potential drug candidate in the near future.

Germacrone Inhibits Cell Proliferation and Induces Apoptosis in Human Esophageal Squamous Cell Carcinoma Cells

Germacrone, a natural 10-membered monocyclic sesquiterpene with three double bonds and a ketone, was isolated from the roots of traditional Chinese medicine Saussurea costus (SC). The pharmacological value and intrinsic mechanism of germacrone in the treatment of esophageal squamous cell carcinoma (ESCC) are still unclear. Therefore, in this study, we further explored the internal molecular mechanism by which germacrone exerts its antiproliferation and antimigration ability against ESCC. 3-(4,5-Dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assays showed that germacrone dose-dependently inhibited the proliferation of ESCC cells. Flow cytometry analysis (FACS) and wound healing experiments on germacrone treated ESCC cells showed that germacrone could induce apoptosis and inhibit the migration of ESCC cells in a dose-dependent manner. In the study on the mechanism of action of germacrone in antiesophageal cancer, we found that germacrone increased the ratio of Bax/Bcl-2 in the cytoplasm of ESCC, resulting in the activation of Caspase-9 and Caspase-3 and decreased the expression of Grp78, thereby reducing the inhibition of Caspase-12 and Caspase-7. In addition, we found that germacrone also inhibited STAT3 phosphorylation in a dose-dependent manner. In conclusion, we determined that germacrone exerted an antiesophageal effect through intrinsic apoptotic signaling pathways and by inhibiting STAT3 activity in ESCC cells.

New Sesquiterpenoids from the Fermented Broth of Termitomyces albuminosus and their Anti-Acetylcholinesterase Activity

Termitomyces albuminosus is the symbiotic edible mushroom of termites and cannot be artificially cultivated at present. In the project of exploring its pharmaceutical metabolites by microbial fermentation, four new selinane type sesquiterpenoids—teucdiol C (1), D (2), E (3), and F (4), together with two known sesquiterpenoids teucdiol B (5) and epi-guaidiol A (6)—were obtained from its fermented broth of T. albuminosus. Their structures were elucidated by the analysis of NMR data, HR Q-TOF MS spectral data, CD, IR, UV, and single crystal X-ray diffraction. Epi-guaidiol A showed obvious anti-acetylcholinesterase activity in a dose-dependent manner. The experimental results displayed that T. albuminosus possess the pharmaceutical potential for Alzheimer’s disease, and it was an effective way to dig new pharmaceutical agent of T. albuminosus with the microbial fermentation technique.

Bioactivity-based analysis and chemical characterization of anti-inflammatory compounds from Curcuma zedoaria rhizomes using LPS-stimulated RAW264.7 cells

Inflammation is not only a self-defense response of the innate immune system, but also the pathogenesis mechanism of multiple diseases such as arthritis, neurodegeneration, and cancer. Curcuma zedoaria Roscoe (Zingiberaceae), an indigenous plant of India, has been used traditionally in Ayurveda and folk medicine. As part of our ongoing efforts to screen traditional medicinal plants exhibiting pharmacological potential and to characterize the compounds involved, we examined the anti-inflammatory effects of the MeOH extract of C. zedoaria rhizomes using lipopolysaccharide (LPS)-stimulated RAW264.7 murine macrophage cells and found that MeOH extract inhibited the synthesis of nitric oxide (NO) in a dose-dependent manner (IC₅₀: 23.44 ± 0.77 μg/mL). In our efforts to characterize the compounds responsible for these anti-inflammatory effects, bioactivity-guided fractionation of the MeOH extract and chemical investigation of its active hexane-soluble fraction led to the successful isolation of five sesquiterpenes (1-5), the structures of which were elucidated by NMR spectroscopic analysis and LC/MS analysis. Among them, curcuzedoalide (5) exhibited potent inhibitory effects on NO synthesis (IC₅₀: 12.21 ± 1.67 μM) and also suppressed pre-inflammatory protein expression of iNOS and COX-2. Curcuzedoalide (5) was thus determined to be a contributor to the anti-inflammatory effect of C. zedoaria rhizomes and could be a potential candidate for therapeutic applications.

Sesquiterpenoids from Vitex pierreana

A new germacrane sesquiterpenoid with an epoxy moiety, pierreanin A (1), and a pair of unique cyclobutyl-containing sesquiterpenoid diastereoisomers, pierreanins B and C (2 and 3), were isolated from the branches and leaves of Vitex pierreana, together with 2 known analogues, identified as germacrone (4) and epiprocurcumenol (5). The structures of all isolates were evaluated by detailed analyses of NMR, IR, and MS data. The absolute configurations of 1-3 were determined by comparison of the experimental ECD spectra with reported data of analogues containing the same chromophore. The ability of three new compounds to inhibit the growth of DU145 prostate cancer cells was also evaluated, as well as their inhibitory effects against the production of NO in LPS-stimulated RAW264.7 cells.

Germacrone Attenuates Hyperlipidemia and Improves Lipid Metabolism in High-Fat Diet-Induced Obese C57BL/6J Mice

We previously showed that Aster spathulifolius Maxim extract (ASE) reduced body weight gain and serum and liver lipid levels and significantly suppressed serum insulin and leptin concentrations in high-fat diet (HFD)-induced obese rats. Germacrone (GM) was identified as a potent bioactive constituent of ASE. In this study, we hypothesized that GM can attenuate hyperlipidemia by alleviating fatty acid (FA) synthesis/uptake and improve lipid metabolism by stimulating FA β-oxidation in HFD-induced obese C57BL/6J mice. To induce obesity, mice were fed an HFD for 6 weeks, while control mice were fed a commercial standard diet. The mice were allocated to six groups and fed either a normal diet, HFD, HFD with GM (5, 10, and 20 mg/kg), or HFD with 200 mg/kg Garcinia cambogia extract for 30 days. In the GM groups, body weight gain, visceral fat pad weight, fasting plasma glucose, serum insulin and leptin, and serum, as well as hepatic lipid, levels were attenuated. Transcriptional factors related to lipid metabolism, such as AMP-activated protein kinase α, sterol regulatory element-binding protein (SREBP) 1, SREBP 2, acetyl-CoA carboxylase, peroxisome proliferator-activated receptor (PPAR)-α, PPAR-γ, FA synthase, and carnitine palmitoyltransferase 1, showed higher expression in the GM groups. In summary, GM may help attenuate hyperlipidemia by suppressing FA synthesis and uptake by inhibiting SREBP signaling pathway activation and improve lipid metabolism by stimulating FA β-oxidation by activating the AMPKα signaling pathway in HFD-induced obesity.

Germacrone inhibits adipogenesis and stimulates lipolysis via the AMP-activated protein kinase signalling pathway in 3T3-L1 preadipocytes

OBJECTIVES

In a previous study, we reported that Aster spathulifolius Maxim extract (ASE) inhibited lipid accumulation and adipocyte differentiation in 3T3-L1 cells. Of the components in ASE, germacrone (GM) was identified as a potent bioactive constituent. GM is known for its anticancer and antiviral activity. However, the effects of GM and the molecular mechanism by which GM regulates adipogenesis and lipolysis were not reported. Therefore, we investigated the effect of GM on adipogenesis and lipolysis and to elucidate its underlying molecular mechanism.

METHODS

We analysed the contents of intracellular triglyceride and carried out Western blotting and RT-qPCR to investigate the underlying mechanism.

KEY FINDINGS

We demonstrate that GM suppresses adipogenic differentiation and the increase in lipolysis in 3T3-L1 cells. In particular, GM down-regulates the expression of early adipogenesis-related genes (e.g. KLF4, KLF5, C/EBP-β and C/EBP-δ) and major adipogenesis-related genes (C/EBP-α and PPAR-γ). Furthermore, GM increases the protein levels of phosphorylated AMP-activated protein kinase α (AMPKα), phosphorylated acetyl-coenzyme A carboxylase (ACC) and carnitine palmitoyltransferase (CPT1).

CONCLUSIONS

Our results suggest that GM may be a potent bioactive anti-adipogenic and lipolytic constituent via the regulation of adipogenesis, lipolysis and the AMPKα pathway.

Anti-melanogenic effects of Aster spathulifolius extract in UVB-exposed C57BL/6J mice and B16F10 melanoma cells through the regulation of MAPK/ERK and AKT/GSK3β signalling

OBJECTIVES

Pharmacological studies of Aster spathulifolius Maxim(AS) have demonstrated its anti-allergy, anti-viral and anti-obesity effects, however, its anti-melanogenic effects is still unclear. In this study, the effects of AS extract (ASE) on the inhibition of melanin synthesis were investigated in vitro and in vivo.

METHODS

To perform this study, the contents of melanin and tyrosinase activity were analysed in B16F10 melanoma cells. Western blotting was carried out to determine the underlyling mechanism. Additionally, we investigated the effect of this extract on hyperpigmentation in C57bL/6J mice induced by 3, 6 and 9 weeks of UVB irradiation.

KEY FINDINGS

AS extract led to reduced melanin synthesis through the regulation of MITF and its downstream signals. Furthermore, ASE increased the phosphorylation of MAPK/ERK and Akt/GSK3β signalling pathway components. In vivo study, hypopigmentation effects were also observed. The melanocyte activity and the distribution of melanin granules were decreased in UVB-irradiated mice treated with ASE.

CONCLUSIONS

These results suggest that the ASE may be promising as an active anti-melanogenic component, and further investigations should be performed regarding its potential as a whitening agent in the field of cosmetics.

Anti-Obesity Effects of Aster spathulifolius Extract in High-Fat Diet-Induced Obese Rats

The aim of this study was to investigate the anti-obesity and antihyperlipidemic efficacy and molecular mechanisms of Aster spathulifolius Maxim extract (ASE) in rats with high-fat diet (HFD)-induced obesity. Rats were separately fed a normal diet or a HFD for 8 weeks, then they were treated with ASE (62.5, 125, or 250 mg/kg) for another 4.5 weeks. The ASE supplementation significantly lowered body weight gain, visceral fat pad weights, serum lipid levels, as well as hepatic lipid levels in HFD-induced obese rats. Histological analysis showed that the ASE-treated group showed lowered numbers of lipid droplets and smaller size of adipocytes compared to the HFD group. To understand the mechanism of action of ASE, the expression of genes and proteins involved in obesity were measured in liver and skeletal muscle. The expression of fatty acid oxidation and thermogenesis-related genes (e.g., PPAR-α, ACO, CPT1, UCP2, and UCP3) of HFD-induced obese rats were increased by ASE treatment. On the other hand, ASE treatment resulted in decreased expression of fat intake-related gene ACC2 and lipogenesis-related genes (e.g., SREBP-1c, ACC1, FAS, SCD1, GPATR, AGPAT, and DGAT). Furthermore, ASE treatment increased the level of phosphorylated AMPKα in obese rats. Similarly, the level of phosphorylated ACC, a target protein of AMPKα in ASE groups, was increased by ASE treatment compared with the HFD group. These results suggest that ASE attenuated visceral fat accumulation and improved hyperlipidemia in HFD-induced obese rats by increasing lipid metabolism through the regulation of AMPK activity and the expression of genes and proteins involved in lipolysis and lipogenesis.

Cardiac Glycosides from the Seeds of Thevetia peruviana

Investigation of the seeds of Thevetia peruviana resulted in the isolation of 15 new (2-16) and 18 known (1 and 17-33) cardiac glycosides. Eight 19-nor-cardenolides (1-8), including two rare 19-nor-10-hydroperoxycardenolides, were obtained from T. peruviana for the first time. All the structures were characterized by NMR spectroscopy and chemical derivatization. The inhibitory effects of cardiac glycosides 1-33 against three cancer cell lines (human lung cancer cells, P15; human gastric cancer cells, MGC-803; and human pancreatic cancer cells, SW1990) and one normal hepatocyte cell line, LO2, were evaluated, and a preliminary structure-activity relationship is discussed. In addition, cardiac glycosides 1, 22, 26, and 28 were evaluated for their apoptosis-inducing activities in MGC-803 cells, showing IC50 values in the range 0.02-0.53 μM.

Inhibitory effects of Aster spathulifolius extract on adipogenesis and lipid accumulation in 3T3-L1 preadipocytes

OBJECTIVES

Aster spathulifolius Maxim (AS), known for its anti-viral and anti-allergic activity, is also known to reduce body weight gain in high fat diet-induced obese rats. But its molecular mechanism of the anti-obesity effects is still unclear. So, we investigated the inhibitory effect of AS extract (ASE) on adipogenesis and lipid accumulation to determine the underlying cellular molecular mechanism.

METHODS

To perform this study, the contents of intracellular triglyceride were analysed. Real-time polymerase chain reaction and Western blotting were carried out to investigate the expression of adipogenic transcriptional factors.

KEY FINDINGS

ASE showed the suppression of adipogenic differentiation and the considerable reduction of the lipid accumulation in 3T3-L1 cells. Especially, ASE inhibited the early stage of differentiation via the downregulation of C/EBP-β and C/EBP-δ, which are early adipogenic factors. Major adipogenic factors, such as PPAR-γ and C/EBP-α, were also subsequently inhibited. These findings were supported by Oil Red O staining and intracellular triglyceride levels. A molecular mechanism liking the effect of ASE was identified through the activation of AMPKα pathway. ASE increased protein levels of phosphorylated AMPKα and phosphorylated ACC.

CONCLUSIONS

ASE showed anti-adipogenic and anti-lipogenic effects through the regulation of adipogenic factors and AMPKα pathway.

Suppression of Inflammatory cytokine production by ar-Turmerone isolated from Curcuma phaeocaulis

Rhizomes of Curcuma phaeocaulis Valeton (Zingiberaceae) have traditionally been used for controlling inflammatory conditions. Numerous studies have aimed to isolate and characterize the bioactive constituents of C. phaeocaulis. It has been reported that its anti-inflammatory properties are a result of cyclooxygenase-2 inhibition; however, its effect on the T-cell function remains to be elucidated. In this study, four known sesquiterpenoids, viz., ar-turmerone (TM), germacrone (GM), (+)-(4S,5S)-germacrone-4,5-epoxide (GE), and curzerenone (CZ), were isolated from C. phaeocaulis rhizomes and evaluated for their effects on the CD4(+) T-cell function. While GM, GE, and CZ had no effect on the activation of splenic T cells or CD4(+) T cells, TM suppressed the interferon (IFN)-γ production, without affecting the interleukin (IL)-4 expression. TM also decreased the expression of IL-2 in CD4(+) T cells, but did not change their cell-division rates upon stimulation. These results suggest that TM, a major constituent of C. phaeocaulis rhizomes selectively exerts potent anti-inflammatory effects via suppression of the inflammatory cytokines IFN-γ and IL-2.

Mechanistic studies on the autoxidation of α-guaiene: structural diversity of the sesquiterpenoid downstream products

Two unstable hydroperoxides, 6b and 10a, and 13 downstream sesquiterpenoids have been isolated from the autoxidation mixture of the bicyclic sesquiterpene α-guaiene (1) on cellulose filter paper. One of the significant natural products isolated was rotundone (2), which is the only known impact odorant displaying a peppery aroma. Other products included corymbolone (4a) and its C-6 epimer 4b, the (2R)- and (2S)-rotundols (7a/b), and several hitherto unknown epimers of natural chabrolidione A, namely, 7-epi-chabrolidione A (3a) and 1,7-epi-chabrolidione A (3b). Two 4-hydroxyrotundones (8a/b) and a range of epoxides (9a/b and 5a/b) were also formed in significant amounts after autoxidation. Their structures were elucidated on the basis of spectroscopic data and X-ray crystallography, and a number of them were confirmed through total synthesis. The mechanisms of formation of the majority of the products may be accounted for by initial formation of the 2- and 4-hydroperoxyguaienes (6a/b and 10a/b) followed by various fragmentation or degradation pathways. Given that α-guaiene (1) is well known to exist in the essential oils of numerous plants, coupled with the fact that aerial oxidation to form this myriad of downstream oxidation products occurs readily at ambient temperature, suggests that many of them have been overlooked during previous isolation studies from natural sources.

Sesquiterpenes inhibiting the microglial activation from Laurus nobilis

The inhibitory reagents to inhibit the activation of microglial cells may be potentially useful for the treatment of neurodegenerative diseases. The leaves of the plant Laurus nobilis belonging to the family Lauraceae, namely, bay leaves, have been used as a popular spice, and their extract showed moderate inhibition on microglial activation. A further phytochemical investigation of the leaves led to the isolation of two new (1, 2) and eight known (3-10) sesquiterpenes. Their structures were elucidated on the basis of extensive 1D and 2D NMR (HMQC, HMBC, (1)H-(1)H COSY, and NOESY) spectroscopic data analyses and Chem3D modeling. The following biological studies disclosed that these isolated compounds showed inhibitory activities on LPS-induced microglial activation. The results of our phytochemical investigation, including two new sesquiterpenes (1 and 2) and the first report of two compounds (3 and 4) from this species, further revealed the chemical composition of bay leaves as a popular spice, and the biological studies implied that bay leaves, containing bioactive substances with the inhibition of microglial activation, were potentially beneficial to human health.

A New Eudesmane Sesquiterpene from Dichrocephala integrifolia

A new sesquiterpene, eudesm-11-ene-4α,7β,9β-triol, was isolated from the EtOH extract of aerial parts of Dichrocephala integrifolia. Its structure was determined on the basis of spectral analysis of 1D and 2D NMR data.

Peroxy natural products

This review covers the structures and biological activities of peroxy natural products from a wide variety of terrestrial fungi, higher plants, and marine organisms. Syntheses that confirm or revise structures or stereochemistries have also been included, and 406 references are cited.