New biofunctional effects of oleanane-type triterpene saponins.

In the current review, we describe the novel biofunctional effects of oleanane-type triterpene saponins, including elatosides, momordins, senegasaponins, camelliasaponins, and escins, obtained from Aralia elata (bark, root cortex, young shoot), Kochia scoparia (fruit), Polygala senega var. latifolia (roots), Camellia japonica (seeds), and Aesculus hippocastanum (seeds), considering the following biofunctional activities: (1) inhibitory effects on elevated levels of blood alcohol and glucose in alcohol and glucose-loaded rats, respectively, (2) inhibitory effects on gastric emptying in rats and mice, (3) accelerative effects on gastrointestinal transit in mice, and (4) protective effects against gastric mucosal lesions in rats. In addition, we describe (5) suppressive effects of the extract and chakasaponins from Camellia sinensis (flower buds) on obesity based on inhibition of food intake in mice. The active saponins were classified into the following three types: (1) olean-12-en-28-oic acid 3-O-monodesmoside, (2) olean-12-ene 3,28-O-acylated bisdesmoside, and (3) acylated polyhydroxyolean-12-ene 3-O-monodesmoside. Furthermore, common modes of action, such as involvements of capsaicin-sensitive nerves, endogenous NO and PGs, and possibly sympathetic nerves, as well as common structural requirements, were observed. Based on our findings, a common mechanism of action might mediate the pharmacological effects of active saponins. It should be noted that the gastrointestinal tract is an important action site of saponins, and the role of the saponins in the gastrointestinal tract should be carefully considered.

Structures of Mammeasins P and Q, Coumarin-Related Polysubstituted Benzofurans, from the Thai Medicinal Plant Mammea siamensis (Miq.) T. Anders.: Anti-Proliferative Activity of Coumarin Constituents against Human Prostate Carcinoma Cell Line LNCaP.

A methanol extract of the flowers of Mammea siamensis (Miq.) T. Anders. (Calophyllaceae) showed anti-proliferative activity against human prostate carcinoma LNCaP cells (IC50 = 2.0 µg/mL). Two new coumarin-related polysubstituted benzofurans, mammeasins P (1) and Q (2), and a known polysubstituted coumarin mammea B/AC cyclo F (39) were isolated from the extract along with 44 previously reported polysubstituted coumarin constituents (3-38 and 40-47). The structures of two new compounds (1 and 2) were determined based on their spectroscopic properties derived from the physicochemical evidence including NMR and MS analyses and taking the plausible generative pathway into account. Among the coumarin constituents, mammeasins A (3, IC50 = 1.2 µM) and B (4, 0.63 µM), sugangin B (18, 1.5 µM), kayeassamins E (24, 3.0 µM) and G (26, 3.5 µM), and mammeas E/BA (40, 0.88 µM), E/BB (41, 0.52 µM), and E/BC (42, 0.12 µM) showed relatively potent anti-proliferative activity.

Hepatoprotective Principles from the Rhizomes of Picrorhiza kurroa.

A methanol extract of rhizomes of Picrorhiza kurroa Royle ex Benth. (Plantaginaceae) showed hepatoprotective effects against D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced liver injury in mice. We had previously isolated 46 compounds, including several types of iridoid glycosides, phenylethanoid glycosides, and aromatics, etc., from the extract. Among them, picroside II, androsin, and 4-hydroxy-3-methoxyacetophenone exhibited active hepatoprotective effects at doses of 50-100 mg/kg, per os (p.o.) To characterize the mechanisms of action of these isolates and to clarify the structural requirements of phenylethanoid glycosides for their hepatoprotective effects, their effects were assessed in in vitro studies on (i) D-GalN-induced cytotoxicity in mouse primary hepatocytes, (ii) LPS-induced nitric oxide (NO) production in mouse peritoneal macrophages, and (iii) tumor necrosis factor-α (TNF-α)-induced cytotoxicity in L929 cells. These isolates decreased the cytotoxicity caused by D-GalN without inhibiting LPS-induced macrophage activation and also reduced the sensitivity of hepatocytes to TNF-α. In addition, the structural requirements of phenylethanoids for the protective effects of D-GalN-induced cytotoxicity in mouse primary hepatocytes were evaluated.

A Gedunin-Type Limonoid, 7-Deacetoxy-7-Oxogedunin, from Andiroba (Carapa guianensis Aublet) Reduced Intracellular Triglyceride Content and Enhanced Autophagy in HepG2 Cells.

The seed oil of Carapa guianensis Aublet (Andiroba) has been used in folk medicine for its insect-repelling, anti-inflammatory, and anti-malarial activities. This study aimed to examine the triglyceride (TG) reducing effects of C. guianensis-derived limonoids or other commercially available limonoids in human hepatoblastoma HepG2 cells and evaluate the expression of lipid metabolism or autophagy-related proteins by treatment with 7-deacetoxy-7-oxogedunin (DAOG; 1), a principal limonoid of C. guianensis. The gedunin-type limonoids, such as DAOG (% of control at 20 µM: 70.9 ± 0.9%), gedunin (2, 74.0 ± 1.1%), epoxyazadiradione (4, 73.4 ± 2.0%), 17ß-hydroxyazadiradione (5, 79.9 ± 0.6%), 7-deacetoxy-7α-hydroxygedunin (6, 61.0 ± 1.2%), andirolide H (7, 87.4 ± 2.2%), and 6α-hydroxygedunin (8, 84.5 ± 1.1%), were observed to reduce the TG content at lower concentrations than berberine chloride (BBR, a positive control, 84.1 ± 0.3% at 30 µM) in HepG2 cells pretreated with high glucose and oleic acid. Andirobin-, obacunol-, nimbin-, and salannin-type limonoids showed no effect on the intracellular TG content in HepG2 cells. The TG-reducing effect of DAOG was attenuated by the concomitant use of compound C (dorsomorphin), an AMPK inhibitor. Further investigation on the detailed mechanism of action of DAOG at non-cytotoxic concentrations revealed that the expressions of autophagy-related proteins, LC3 and p62, were upregulated by treatment with DAOG. These findings suggested that gedunin-type limonoids from Andiroba could ameliorate fatty liver, and that the action of DAOG in particular is mediated by autophagy.

Phytochemicals with Chemopreventive Activity Obtained from the Thai Medicinal Plant Mammea siamensis (Miq.) T. Anders.: Isolation and Structure Determination of New Prenylcoumarins with Inhibitory Activity against Aromatase.

With the aim of searching for phytochemicals with aromatase inhibitory activity, five new prenylcoumarins, mammeasins K (1), L (2), M (3), N (4), and O (5), were isolated from the methanolic extract of Mammea siamensis (Miq.) T. Anders. flowers (fam. Calophyllaceae), originating in Thailand. The stereostructures of 1-5 were elucidated based on their spectroscopic properties. Among the new compounds, 1 (IC50 = 7.6 µM) and 5 (9.1 µM) possessed relatively strong inhibitory activity against aromatase, which is a target of drugs already used in clinical practice for the treatment and prevention of estrogen-dependent breast cancer. The analysis through Lineweaver-Burk plots showed that they competitively inhibit aromatase (1, Ki = 3.4 µM and 5, 2.3 µM). Additionally, the most potent coumarin constituent, mammea B/AB cyclo D (31, Ki = 0.84 µM), had a competitive inhibitory activity equivalent to that of aminoglutethimide (0.84 µM), an aromatase inhibitor used in therapeutics.

Ursane-type triterpene oligoglycosides with anti-hepatosteatosis and anti-hyperlipidemic activity from the leaves of Ilex paraguariensis A. St.-Hil.

The methanol extract from the leaves of Ilex paraguariensis A. St.-Hil. (Aquifoliaceae), popularly known as mate, maté, or yerba maté, inhibits the intracellular triglyceride accumulation in HepG2 cells and suppresses the plasma triglyceride elevation in olive oil-treated mice. Three new triterpene saponins, termed mateosides I (1), II (2), and III (3), were isolated from the extract along with 29 known compounds. The structures of 1-3 were elucidated based on chemical and spectroscopic evidence. Among the isolates, principal saponin constituents, 2 and matesaponins 1 (7) and 2 (9), potently inhibited the triglyceride accumulation in HepG2 cells simultaneously treated with oleic acid and high glucose. In vivo assay of the methanol extract of I. paraguariensis revealed that 7 and 9 showed anti-hyperlipidemic activities in olive oil-treated mice. These results suggested that the saponin constituents of I. paraguariensis could be valuable bioactive marker for the anti-obesogenic activity.

A review of antidiabetic active thiosugar sulfoniums, salacinol and neokotalanol, from plants of the genus Salacia.

During our studies characterizing functional substances from food resources for the prevention and treatment of lifestyle-related diseases, we isolated the active constituents, salacinol (1) and neokotalanol (4), and related thiosugar sulfoniums, from the roots and stems of the genus Salacia plants [Celastraceae (Hippocrateaceae)] such as Salacia reticulata Wight, S. oblonga Wall., and S. chinensis L., and observed their antidiabetic effects. These plant materials have been used traditionally in Ayurvedic medicine as a specific remedy at the early stage of diabetes, and have been extensively consumed in Japan, the United States, and other countries as a food supplement for the prevention of obesity and diabetes. Here, we review our studies on the antidiabetic effects of plants from the genus Salacia, from basic chemical and pharmacological research to their application and development as new functional food ingredients.

Anti-proliferative activities of coumarins from the Thai medicinal plant Mammea siamensis (Miq.) T. Anders. against human digestive tract carcinoma cell lines.

Geranylated coumarins named mammeasins G-J (1-4) were isolated from the methanol extract of the flowers of Mammea siamensis (Miq.) T. Anders. (Calophyllaceae) originating in Thailand. Their structures were established based on detailed spectroscopic analyses. The isolates, including previously reported coumarin constituents (5-28), exhibited anti-proliferative activities against human carcinoma cell lines HSC-2, HSC-4, MKN-45, and MCF-7. Mammeasin A (7, IC50 = 13.6 µM) and surangin B (15, 15.2 µM), both consisting of the geranyl group, were found to show relatively strong activities against HSC-4 cells and their mechanisms of action were found to involve apoptotic cell death.

Dose-Dependent Suppression of Postprandial Hyperglycemia and Improvement of Blood Glucose Parameters by Salacia chinensis Extract: Two Randomized, Double-Blind, Placebo-Controlled Studies.

The number of diabetes mellitus and borderline diabetes cases is increasing and poses a serious problem worldwide. Plants of the genus Salacia are known to have α-glucosidase inhibitory activity and to lower postprandial hyperglycemia. Two randomized, double-blind, placebo-controlled clinical trials were conducted to evaluate the efficacy of Salacia chinensis extract. Study 1 was a single-dose crossover study of 150, 300, or 600 mg of Salacia extract or placebo to determine the dose dependency of the effect on postprandial hyperglycemia. The duration of the washout period between each experimental day was a minimum of 6 days. Study 2 was a 12-week, multiple-dose, parallel-group study to evaluate the effects of 600 mg/day of Salacia extract on blood glucose parameters. In Study 1, Salacia induced significant dose-dependent suppression of postprandial blood glucose, insulin, and their incremental area under the curve values. The dose of 600 mg appeared to have the most significant effect. In Study 2, Salacia significantly improved several blood glucose-related parameters, such as hemoglobin A1c, and glucose tolerance after glucose challenge. These results suggest that S. chinensis extract may have beneficial effects in patients with diabetes.

Collagen synthesis-promoting and collagenase inhibitory activities of constituents isolated from the rhizomes of Picrorhiza kurroa Royle ex Benth.

Three new acylated phenylethanoid glycosides, kurroaosides A (14), B (15), and C (16), and a new acylated cucurbitane-type triterpene glycoside, kurroaoside D (17), were isolated from a methanol extract of the rhizomes of Picrorhiza kurroa Royle ex Benth. (Plantaginaceae) along with 29 known isolates including 10 acylated phenylethanoid glycosides (18-27), three cucurbitane-type triterpene glycosides (32-34), and a nortriterpene glycoside (35). The structures of these new compounds (14-17), including their stereochemistry, were determined based on chemical and physicochemical evidence derived from NMR and MS analysis. Among the isolates, acylated iridoid glycosides, picrosides I (8), II (9), III (10), and IV (11) and 6-feruloylcatalpol (12), phenylethanoid glycosides (14-16), triterpene glycosides, cucurbitacin B 2-O-ß-D-glucopyranoside (32) and 25-acetoxy-2-ß-D-glucopyranosyloxy-3,16,20-trihydroxy-9-methyl-19-norlanosta-5-en-22-one (35), and an acetophenone glycoside, picein (36), significantly promoted collagen synthesis at 10-30 µM, with no cytotoxicity being observed at the effective concentrations. Furthermore, acylated phenylethanoid glycosides, calceolarioside A (19, IC50 = 69.2 µM), plantamajoside (20, 51.8 µM), isoplantamajoside (21, 76.8 µM), and scroside E (23, 65.5 µM), exhibited collagenase inhibitory activity equivalent to that of positive agents caffeic acid (75.6 µM) and epigallocatechin 3-O-gallate (75.4 µM).

Geranylated Coumarins From Thai Medicinal Plant Mammea siamensis With Testosterone 5α-Reductase Inhibitory Activity.

Geranylated coumarin constituents, kayeassamin I (1) and mammeasins E (2) and F (3) were newly isolated from the methanol extract of the flowers of Mammea siamensis (Calophyllaceae) originating in Thailand, along with five known isolates, such as mammea E/BC (23), deacetylmammea E/AA cyclo D (31), deacetylmammea E/BB cyclo D (32), mammea A/AA cyclo F (34), and mammea A/AC cyclo F (35). These compounds (1-3) were obtained as an inseparable mixture (ca. 1:1 ratio) of the 3″R and 3″S forms, respectively. Among the isolated coumarins from the extract, mammeasins E (2, 22.6 µM), A (4, 19.0 µM), and B (5, 24.0 µM), kayeassamins E (9, 33.8 µM), F (10, 15.9 µM), and G (11, 17.7 µM), surangin C (13, 5.9 µM), and mammeas A/AA (17, 19.5 µM), E/BB (22, 16.8 µM), and A/AA cyclo F (34, 23.6 µM), were found to inhibit testosterone 5α-reductase.

Acylated iridoid glycosides with hyaluronidase inhibitory activity from the rhizomes of Picrorhiza kurroa Royle ex Benth.

Seven new acylated iridoid glycosides, picrorhizaosides A-G (1-7), were isolated from the methanol extract of the rhizomes of Picrorhiza kurroa Royle ex Benth. (Plantaginaceae), in addition to six known iridoid glycosides (8-13). The structures of these new iridoids, including their stereochemistry, were determined based on chemical and physicochemical evidence derived from NMR and MS analysis. Of the isolates, picrorhizaosides D (4, IC50 = 43.4 µM) and E (5, 35.8 µM); picrosides I (8, 60.7 µM), II (9, 22.3 µM), and IV (11, 59.2 µM); and minecoside (13, 57.2 µM), exhibited a similar or stronger hyaluronidase inhibitory activity than those of the antiallergic medicines disodium cromoglycate (64.8 µM), ketotifen fumarate (76.5 µM), and tranilast (227 µM).

Glucose Tolerance-Improving Activity of Helichrysoside in Mice and Its Structural Requirements for Promoting Glucose and Lipid Metabolism.

An acylated flavonol glycoside, helichrysoside, at a dose of 10 mg/kg/day per os for 14 days, improved the glucose tolerance in mice without affecting the food intake, visceral fat weight, liver weight, and other plasma parameters. In this study, using hepatoblastoma-derived HepG2 cells, helichrysoside, trans-tiliroside, and kaempferol 3-O-ß-D-glucopyranoside enhanced glucose consumption from the medium, but their aglycones and p-coumaric acid did not show this activity. In addition, several acylated flavonol glycosides were synthesized to clarify the structural requirements for lipid metabolism using HepG2 cells. The results showed that helichrysoside and related analogs significantly inhibited triglyceride (TG) accumulation in these cells. The inhibition by helichrysoside was more potent than that by other acylated flavonol glycosides, related flavonol glycosides, and organic acids. As for the TG metabolism-promoting activity in high glucose-pretreated HepG2 cells, helichrysoside, related analogs, and their aglycones were found to significantly reduce the TG contents in HepG2 cells. However, the desacyl flavonol glycosides and organic acids derived from the acyl groups did not exhibit an inhibitory impact on the TG contents in HepG2 cells. These results suggest that the existence of the acyl moiety at the 6'' position in the D-glucopyranosyl part is essential for glucose and lipid metabolism-promoting activities.

Salacia chinensis stem extract and its thiosugar sulfonium constituent, neokotalanol, improves HbA1c levels in ob/ob mice.

The antidiabetic effects of a hot water extract of the stems of Salacia chinensis (SCE) were evaluated in vivo in ob/ob mice (genetically obese hyperglycemic mice). Administration of dietary feed containing 0.20 and 0.50% of SCE for 23 days to ob/ob mice significantly suppressed the elevation of both blood glucose and HbA1c levels, without significantly changing body weight and food intake. To characterize the antidiabetic effects of the thiosugar sulfonium constituent neokotalanol (1), which has potent α-glucosidase inhibitory activity, we performed a similar in vivo study. HbA1c levels were significantly suppressed in ob/ob mice after the administration of dietary feed containing 0.0003% of neokotalanol (1) for 20 days. These results indicate that SCE and neokotalanol (1) are potential leads for the development of novel antidiabetic agents.

Collagen Synthesis-Promoting Effects of Andiroba Oil and its Limonoid Constituents in Normal Human Dermal Fibroblasts.

The seed oil of andiroba (Carapa guianensis, Meliaceae) was found to promote collagen synthesis in normal human dermal fibroblasts. To characterize the active constituents of this oil, the collagen synthesis-promoting activities of 10 principal limonoid constituents, gedunin (1), 6α-acetoxygedunin (2), 7-deacetoxy-7-oxogedunin (3), 7-deacetoxy-7α-hydroxygedunin (4), andirolide H (5), 6α-hydroxygedunin (6), methyl angolensate (7), 17ß-hydroxyazadiradione (8), and carapanosides C (9) and R (10), were examined. Among them, 1-4, 6, 7, and 9 were found to significantly promote collagen synthesis without cytotoxicity at the effective concentrations.

Total Synthesis of γ-Alkylidenebutenolides, Potent Melanogenesis Inhibitors from Thai Medicinal Plant Melodorum fruticosum.

A hitherto unreported member of γ-alkylidenebutenolides in Melodorum fruticosum (Annonaceae), (4 E)-6-benzoyloxy-7-hydroxy-2,4-heptadiene-4-olide, named as isofruticosinol (4) was isolated from the methanol extract of flowers, along with the known related butenolides, namely, the (4 Z)-isomer (3) of 4, melodrinol (1), and its (4 E)-isomer (2). To unambiguously determine the absolute configuration at the C-6 position in these butenolides, the first total syntheses of both enantiomers of 2-4 were achieved over 6-7 steps from commercially available D- or L-ribose (D- and L-5). Using the same protocol, both enantiomers of 1 were also synthesized. Based on chiral HPLC analysis of all synthetic compounds ( S- and R-1-4), all naturally occurring butenolides were assigned as partial racemic mixtures with respect to the chiral center at C-6 (enantiomeric ratio, 6 S/6 R = ∼83/17). Furthermore, the melanogenesis inhibitory activities of S- and R-1-4 were evaluated, with all shown to be potent inhibitors with IC50 values in the range 0.29-2.9 µM, regardless of differences in the stereochemistry at C-6. In particular, S-4 (IC50 = 0.29 µM) and R-4 (0.39 µM) showed potent inhibitory activities compared with that of reference standard arbutin (174 µM).

Degranulation inhibitors from the arils of Myristica fragrans in antigen-stimulated rat basophilic leukemia cells.

A methanol extract of mace, the aril of Myristica fragrans (Myristicaceae), was found to inhibit the release of ß-hexosaminidase, a marker of antigen-IgE-stimulated degranulation in rat basophilic leukemia cells (RBL-2H3, IC50 = 45.7 µg/ml). From the extract, three new 8-O-4' type neolignans, maceneolignans I-K (1-3), were isolated, and the stereostructures of 1-3 were elucidated based on spectroscopic and chemical evidence. Among the isolates, maceneolignans A (5), D (6), and H (8), (-)-(8R)-∆8'-4-hydroxy-3,3',5'-trimethoxy-8-O-4'-neolignan (13), (-)-(8R)-∆8'-3,4,5,3',5'-pentamethoxy-8-O-4'-neolignan (14), (-)-erythro-(7R,8S)-∆8'-7-acetoxy-3,4-methylenedioxy-3',5'-dimethoxy-8-O-4'-neolignan (17), (+)-licarin A (20), nectandrin B (24), verrucosin (25), and malabaricone C (29) were investigated as possible degranulation inhibitors (IC50 = 20.7-63.7 µM). These inhibitory activities were more potent than those of the antiallergic agents tranilast (282 µM) and ketotifen fumalate (158 µM). Compounds 5, 25, and 29 also inhibited antigen-stimulated tumor necrosis factor-α production (IC50 = 39.5-51.2 µM), an important process in the late phase of type I allergic reactions.

Ellagic acid glycosides with hepatoprotective activity from traditional Tibetan medicine Potentilla anserina.

Two new gallic acid glycosides, potentillanosides G (1) and H (2), were newly isolated from the methanol extract of the tuberous roots of Potentilla anserina (Rosaceae), together with a known compound, ellagic acid 3-O-α-L-rhamnopyranoside (3). Their structures were elucidated on the basis of chemical and physicochemical evidence. Among the constituents, potentillanoside H (2, IC50 = 99.5 µM) was found to show hepatoprotective activity.

Two new aromatic glycosides, elengiosides A and B, from the flowers of Mimusops elengi.

Two new aromatic glycosides, elengiosides A (1) and B (2), were isolated from the methanolic extract of the flowers of Mimusops elengi (Sapotaceae) together with 26 known compounds. Their stereostructures were elucidated based on their spectroscopic properties and chemical evidence. Among the isolates, a phenylethanoid glycoside, undatuside C (14), was found to exhibit hyaluronidase inhibitory activity.