New Eremophilane Sesquiterpenoid Compounds, Eremoxylarins A and B Directly Inhibit Calcineurin in a Manner Independent of Immunophilin

A yeast-based screening system identified bakkenolide B contained in Petasites japonicus as an inhibitor of interleukin-2 production in a human T cell line

Ca2+ signaling is related to various diseases such as allergies, diabetes, and cancer. We explored Ca2+ signaling inhibitors in natural resources using a yeast-based screening method and found bakkenolide B from the flower buds of edible wild plant, Petasites japonicus, using the YNS17 strain (zds1Δ erg3Δ pdr1/3Δ). Bakkenolide B exhibited growth-restoring activity against the YNS17 strain and induced Li+ sensitivity of wild-type yeast cells, suggesting that it inhibits the calcineurin pathway. Additionally, bakkenolide B inhibited interleukin-2 production at gene and protein levels in Jurkat cells, a human T cell line, but not the in vitro phosphatase activity of human recombinant calcineurin, an upstream regulator of interleukin-2 production. Furthermore, bakkenolide A showed weak activity in YNS17 and Jurkat cells compared with bakkenolide B. These findings revealed new biological effects and the structure-activity relationships of bakkenolides contained in P. japonicus as inhibitors of interleukin-2 production in human T cells.

Eremophilane Sesquiterpenes and Benzene Derivatives from the Endophyte Microdiplodia sp. WGHS5

Three new eremophilane sesquiterpenes phomadecalins G-I (1-3) and two new benzene derivatives microdiplzenes A and B (12 and 13), together with nine known eremophilane sesquiterpenes (4-11 and 14) were isolated from an endophytic fungus, Microdiplodia sp. WGHS5. Their structures were elucidated by the interpretation of HR-ESI-MS and NMR data; meanwhile, the absolute configurations of new compounds were determined on the base of ECD calculations. All compounds were evaluated for the antimicrobial activities and antiproliferative effect on human gastric cancer cell lines (BGC-823).

Inhibition of melanin production and promotion of collagen production by the extract of Kuji amber

Kuji amber is fossilized tree resin of the Late Cretaceous in Japan. In this study, new biological activities of ethanol extract of Kuji amber (EtOH ext.) and supercritical carbon dioxide fluid extract of Kuji amber (scCO2 ext.) were examined. Both EtOH ext. and scCO2 ext. inhibited melanin production in B16 mouse melanoma cells and promoted collagen production in human skin fibroblast SF-TY cells. The scCO2 ext. had more potent activity than that of EtOH ext. and may depend on the efficiency of the extraction. The main new biologically active compound in Kuji amber, kujigamberol had no activities against melanin production, however, it promoted collagen production at low concentrations. A biologically active compound having a different structure, spirolactone norditerpenoid, showed both the inhibition activity against melanin production and the promotion activity of collagen production in a dose dependent manner. EtOH ext. and scCO2 ext., which include both kujigamberol and spirolactone norditerpenoid, have not only anti-allergy activity, but also inhibit melanin production and promote collagen production.

Inhibition of Calcineurin and Glycogen Synthase Kinase-3β by Ricinoleic Acid Derived from Castor Oil

Ricinoleic acid (RA) is the main fatty acid component of castor oil and was found to inhibit Ca²⁺ -signal transduction pathway-mediated cell cycle regulation in a yeast-based drug screening assay. RA is expected to have antidiabetic, antiallergy, and/or anticancer properties but its target molecule is unknown. To identify a novel pharmacological effect of RA, we investigated its target molecule in the Ca²⁺ -signal transduction pathway. RA inhibition of calcineurin (CN) was examined in a yeast-based CN inhibitor screening assay using the rsp5^A401E mutant and in a phosphatase assay using recombinant human CN. RA showed growth-restoration activity at 5 μg/spot in the CN inhibitor screening assay with the rsp5^A401E yeast strain. Furthermore, it directly inhibited CN without immunophilins at K_i = 33.7 μM in a substrate-competitive manner. The effects of RA on CN in mammalian cells were further evaluated by measuring β-hexosaminidase (β-HEX) release in RBL-2H3 cells. RA at 50 μM suppressed the release of β-HEX from RBL-2H3 cells. Moreover, this compound was found to inhibit glycogen synthase kinase-3β (GSK-3β), as determined by a kinase assay using recombinant human GSK-3β. RA inhibited GSK-3β at K_i = 1.43 μM in a peptide substrate-competitive manner. The inhibition of GSK-3β by this molecule was further assessed in mammalian cells by measuring the inhibition of glucose production in H4IIE rat hepatoma cells. RA at 25 μM suppressed glucose production in these cells. These findings indicate that RA and/or castor oil could be a useful functional fatty acid to treat allergy or type 2 diabetes.

A novel Ca2+-signal transduction inhibitor, kujigamberol C, isolated from Kuji amber

A novel labdane type diterpenoid, 15-nor-8-labden-13-ol, named kujigamberol C, was isolated from Kuji amber using a modified isolation method to increase the yield of biologically active compounds. The structure was determined using HREIMS, 1D and 2D NMR. Kujigamberol C showed growth-restoring activity against mutant yeast via Ca2+-signal transduction.

Kujigamberoic acid A, a carboxylic acid derivative of kujigamberol, has potent inhibitory activity against the degranulation of RBL-2H3 cells

The aldehyde and carboxylic acid derivatives of kujigamberol were synthesized using pyridinium dichromate (PDC). The carboxylic acid derivative exhibited lower cytotoxicity and inhibited the degranulation of rat basophilic leukemia-2H3 (RBL-2H3) cells stimulated by thapsigargin more than kujigamberol. The carboxylic acid derivative was detected and isolated from the methanol extract of Kuji amber (MEKA) by the modified isolation procedure. Thus, it has been named as kujigamberoic acid A.

Isolation of yeast Ca2+ signal transduction inhibitors from the Early Cretaceous Burmese amber

Two kinds of biologically active compounds were isolated from the MeOH extract of the Early Cretaceous Burmese amber [99 million years ago (Ma)], which is older than the K-Pg boundary (65 Ma). These compounds had inhibitory activity against the hypersensitive mutant yeast strain (zds1∆ erg3∆ pdr1∆ pdr3∆) with respect to Ca²⁺ signal transduction. They were identified as 16,17-bisnordehydroabietic acid (1) and 16,17-bisnorcallitrisic acid (2), respectively, on the basis of spectral analyses including HREIMS, 1D, and 2D NMR. Both have faint growth restoring activities around the clear inhibition zone against the mutant yeast on the 0.31-0.16 μg/spot. This is the first report of direct structural elucidation of 1 and 2 and the biologically active compounds derived from Burmese amber.

Isolation of a spirolactone norditerpenoid as a yeast Ca2+ signal transduction inhibitor from Kuji amber and evaluation of its effects on PPM1A activity

A different type of biologically active compound from Kuji amber (Late Cretaceous, Japan) before the K-Pg boundary [65 million years ago (Ma)] was isolated based on the growth-restoring activity of a mutant yeast involving Ca²⁺ signal transduction. It was identified as a spirolactone norditerpenoid, (4R*, 5S*, 8R*, 9R*, 10S*)-14,15,16,19-tetranor-labdan-13,9-olide (1) from spectral analyses with high-resolution electron ionization mass spectrometry (HREIMS), 1D and 2D nuclear magnetic resonance (NMR). Although the planar structure of 1 is known as an artificial derivative from marrubiin, it was isolated as a natural product from Kuji amber and its structure was elucidated for the first time. It had a growth-restoring activity against the mutant yeast through the direct or indirect inhibition of calcineurin activity [protein phosphatase, Mg²⁺/Mn²⁺-dependent 1A (PPM1A) activation]. Furthermore, the compound had potent inhibitory effect against the degranulation of rat basophilic leukemia 2H3 (RBL-2H3) cells.

New polyketides, paralactonic acids A-E produced by Paraconiothyrium sp. SW-B-1, an endophytic fungus associated with a seaweed, Chondrus ocellatus Holmes

Five polyketides, paralactonic acids A-E (1-5) were isolated from Paraconiothyrium sp. SW-B-1, an endophytic fungus isolated from the seaweed, Chondrus ocellatus Holmes. Their structures were determined by various spectroscopic methods, predominantly by 2D NMR spectroscopic analyses. The absolute configurations of compounds 1-5 were determined by comparison of the experimental and calculated ECD spectra. Compound 5 showed moderate antibacterial activity and restored the growth of a mutant yeast strain inhibited by hyperactivated Ca²⁺-signaling.

Ca2+-Signal Transduction Inhibitors, Kujiol A and Kujigamberol B, Isolated from Kuji Amber Using a Mutant Yeast

A podocarpatriene and a labdatriene derivative, named kujiol A [13-methyl-8,11,13-podocarpatrien-19-ol (1)] and kujigamberol B [15,20-dinor-5,7,9-labdatrien-13-ol (2)], respectively, were isolated from Kuji amber through detection with the aid of their growth-restoring activity against a mutant yeast strain ( zds1Δ erg3Δ pdr1Δ pdr3Δ), which is known to be hypersensitive with respect to Ca²⁺-signal transduction. The structures were elucidated by spectroscopic data analysis. Compounds 1 and 2 are rare organic compounds from Late Cretaceous amber, and the mutant yeast used seems useful for elucidating a variety of new compounds from Kuji amber specimens, produced before the K-Pg boundary.

Eremophilane-type sesquiterpenes from fungi and their medicinal potential

Eremophilanes are sesquiterpenes with a rearranged carbon skeleton formed both by plants and fungi, however, almost no plant eremophilanes are found in fungi. These eremophilanes possess mainly phytotoxic, antimicrobial, anticancer and immunomodulatory properties and in this review fungal eremophilanes with bioactivities of potential medicinal applications are reviewed and discussed. A special focus is set on natural products bearing highly functionalized fatty acids at C-1 or C-3 position of the eremophilane backbone. Many of these fatty acids seem to contribute to the bioactivity of the metabolites enhancing the activity of the sesquiterpene moieties. Several approaches for optimization of these natural products for clinical needs and testing of the resulting derivatives are presented and discussed. The combination of identification of bioactive natural products with their subsequent improvement using a variety of genetical or chemical tools and the pharmacokinetic assessment of the products is presented here as a promising approach to new drugs.

A new eremophilane sesquiterpene from the fungus Xylaria sp. V-27 and inhibition activity against degranulation in RBL-2H3 cells

A new eremophilane sesquiterpene, 13,13-dimethoxyintegric acid (1), together with known compound integric acid (2) have been isolated from a fungus, Xylaria sp. V-27, obtained from a dead branch. The structure of 1 was established by means of spectroscopic analyses. 1 and 2 promoted growth restoring activity against the mutant yeast strain (Saccharomyces cerevisiae (zds1Δ erg3Δ pdr1Δ pdr3Δ)) and inhibited degranulation of rat basophilic leukemia RBL-2H3 cells stimulated by immnunoglobulin G + 2,4-dinitrophenylated-bovine serum albumin (IgE+DNP-BSA), thapsigargin and A23187.

New eremophilane and dichlororesorcinol derivatives produced by endophytes isolated from Ficus ampelas

The novel compound, 11-O-methylpetasitol (1), was isolated from Penicillium sp. N-175-1, and two new compounds, cosmochlorins D (5) and E (6), were isolated from Phomopsis sp. N-125. In addition, three known eremophilane sesquiterpenes, sporogen-AO1 (2), petasol (3) and 6-dehydropetasol (4), were isolated from Penicillium sp. N-175-1. The structures of 1, 5 and 6 were elucidated by a combination of extensive spectroscopic analyses, including 2D NMR, high-resolution electrospray ionization time-of-flight mass spectrometry (HRESITOFMS) and chemical reactions. Compounds 2, 3, 5 and 6 exhibited cytotoxicity to HL60 and 2 and 3 to HeLa cells. Furthermore, 2 and 3 showed robust growth-restoring activity of a Saccharomyces cerevisiae (cdc2-1 rad9Δ) mutant strain, whereas 5 and 6 exhibited minor growth-restoring activity in this strain. Thus, these compounds may inhibit the growth of HL60 and HeLa cells by blocking the cell cycle, and they may be utilized as new lead compounds that act as inhibitors of survival signal transduction pathways.

Triterpene saponins from the roots of Acacia albida Del. (Mimosaceae)

Seven previously undescribed bidesmosidic triterpenoid saponins named albidosides A - G, were isolated from a methanol extract of the roots of Acacia albida. Their structures were elucidated using 1D and 2D NMR spectroscopy and mass spectrometry and determined to be bidesmosides of oleanolic acid and of 16α-hydroxyoleanolic acid. Albidosides B - G were assayed for their cytotoxicity against HeLa and HL60 cells using MTT method and microscopic observation.

Eremophilane-Type Sesquiterpenoids from an Acremonium sp. Fungus Isolated from Deep-Sea Sediments

Chemical examination of an EtOAc extract of a cultured Acremonium sp. fungus from deep-sea sediments resulted in the isolation of 15 new eremophilane-type sesquiterpenoids, namely, acremeremophilanes A-O (1-15), together with seven known analogues. The structures of new compounds were determined through extensive spectroscopic analyses, in association with chemical conversions and ECD calculations for configurational assignments. The PKS-derived 4-hexenoic acid unit in 2-6 is rarely found in nature. All compounds were evaluated for inhibitory effects toward nitric oxide production induced by lipopolysaccharide in RAW 264.7 macrophage cells. Compounds 2-6 and 14 exhibited inhibitory effects with IC50 values ranging from 8 to 45 μM.

High-Throughput Screening Platform for the Discovery of New Immunomodulator Molecules from Natural Product Extract Libraries

It is widely accepted that central nervous system inflammation and systemic inflammation play a significant role in the progression of chronic neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, neurotropic viral infections, stroke, paraneoplastic disorders, traumatic brain injury, and multiple sclerosis. Therefore, it seems reasonable to propose that the use of anti-inflammatory drugs might diminish the cumulative effects of inflammation. Indeed, some epidemiological studies suggest that sustained use of anti-inflammatory drugs may prevent or slow down the progression of neurodegenerative diseases. However, the anti-inflammatory drugs and biologics used clinically have the disadvantage of causing side effects and a high cost of treatment. Alternatively, natural products offer great potential for the identification and development of bioactive lead compounds into drugs for treating inflammatory diseases with an improved safety profile. In this work, we present a validated high-throughput screening approach in 96-well plate format for the discovery of new molecules with anti-inflammatory/immunomodulatory activity. The in vitro models are based on the quantitation of nitrite levels in RAW264.7 murine macrophages and interleukin-8 in Caco-2 cells. We have used this platform in a pilot project to screen a subset of 5976 noncytotoxic crude microbial extracts from the MEDINA microbial natural product collection. To our knowledge, this is the first report on an high-throughput screening of microbial natural product extracts for the discovery of immunomodulators.

Pyrrocidine A, a metabolite of endophytic fungi, has a potent apoptosis-inducing activity against HL60 cells through caspase activation via the Michael addition

Pyrrocidine A is a known antimicrobial compound produced by endophytic fungi and has a unique 13-membered macrocyclic alkaloid structure with an α,β-unsaturated carbonyl group. We have previously reported that pyrrocidine A shows potent cytotoxicity against human acute promyelocytic leukemia HL60 cells, and the activity is 70-fold higher than that of pyrrocidine B which is the analog lacking the α,β-unsaturated carbonyl group. Pyrrocidine A induced nuclear condensation, DNA fragmentation and caspase activation in HL60 cells. Since the DNA fragmentation was suppressed by pretreatment with the pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone (z-VAD-fmk), caspase-mediated apoptosis contributes to pyrrocidine A-induced cytotoxicity. JFCR39 human cancer cells panel indicated that the mechanism of action of pyrrocidine A is different from other clinical anticancer drugs, and this compound broadly inhibited the growth of various cancer cell lines. The apoptosis induction by pyrrocidine A was suppressed by both N-acetyl-l-cysteine (NAC) and glutathione, both of which are thiol-containing antioxidants. Furthermore, pyrrocidine A directly bound to N-acetyl-l-cysteine methyl ester (NACM) through the Michael-type addition at the α,β-unsaturated carbonyl group and was detected by HPLC and liquid chromatography-ESI-tandem MS (LC-ESI-MS/MS) analyses. This indicates that this moiety is crucial for the potent apoptosis-inducing activity of pyrrocidine A.

Inhibition of glycogen synthase kinase-3β by falcarindiol isolated from Japanese Parsley (Oenanthe javanica)

A new biological activity of falcarindiol isolated from Japanese parsley (Oenanthe javanica) using the mutant yeast YNS17 strain (zds1Δ erg3Δ pdr1Δ pdr3Δ) was discovered as an inhibitor of glycogen synthase kinase-3β (GSK-3β). Falcarindiol inhibited GSK-3β in an ATP noncompetitive manner with a Ki value of 86.9 μM using a human enzyme and luminescent kinase assay platform. Falcarindiol also both suppressed gene expression of glucose-6-phosphatase (G6Pase) in rat hepatoma H4IIE cells and protected mouse neuroblastoma HT22 cells from glutamate-induced oxidative cell death at 10 μM. During an oral glucose tolerance test (OGTT), the blood glucose level was significantly decreased in the rats treated with oral administration of O. javanica extract containing falcarindiol (15 mg/kg). These findings indicate that Japanese parsley could be a useful food ingredient against type-2 diabetes and Alzheimer's disease.

Pisiferdiol and pisiferic acid isolated from Chamaecyparis pisifera activate protein phosphatase 2C in vitro and induce caspase-3/7-dependent apoptosis via dephosphorylation of Bad in HL60 cells

Protein phosphatase 2C (PP2C) dephosphorylates a broad range of substrates and regulates apoptosis, stress response and growth-related pathways. In the course of screening for PP2C activators from natural sources, we isolated abietane-type diterpenes, pisiferdiol and pisiferic acid from Chamaecyparis pisifera. Pisiferdiol having a unique seven-membered ring showed more specific PP2C activation activity (1.3-fold at 100 microM) than pisiferic acid having a normal six-membered ring and oleic acid, which is known to activate PP2C. Pisiferdiol and pisiferic acid showed mixed-type activation with respect to alpha-casein, and this differed from the non-competitive activation of oleic acid in vitro. In vivo, the cytotoxicity of pisiferdiol toward human promyelocytic leukemia cell line HL60 with an IC(50) value of 18.3 microM was 2-fold and 7-fold stronger than those of pisiferic acid and oleic acid, and pisiferdiol induced apoptosis through a caspase 3/7-dependent mechanism involving the dephosphorylation of Bad(1), which is a PP2C substrate. We thus conclude that pisiferdiol and pisiferic acid are novel PP2C activators, and the more specific activator, pisiferdiol, may be a useful chemical probe to study PP2C-mediated signaling pathways, and a lead compound for pharmaceutical agents.