Souichi Nakashima

Melanogenesis inhibitors from the desert plant Anastatica hierochuntica in B16 melanoma cells.

The methanolic extract from the whole plants of Anastatica hierochuntica, an Egyptian herbal medicine, was found to inhibit melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. Among the constituents isolated, anastatin A, silybin A, isosilybins A and B, eriodictyol, luteolin, kaempferol, quercetin, hierochins A and B, (2R,3S)-2,3-dihydro-2-(3,4-dimethoxyphenyl)-3-hydroxymethyl-5-(2-formylvinyl)-7-hydroxybenzofuran, (+)-dehydrodiconiferyl alcohol, (+)-balanophonin, 1-(4-hydroxy-3-methoxyphenyl)-2-{4-[(E)-3-hydroxy-1-propenyl]-2-methoxyphenoxy}-1,3-propanediol, and 3,4-dihydroxybenzaldehyde substantially inhibited melanogenesis with IC(50) values of 6.1-32 microM. With regard to the mechanism of action of silybins and isosilybins, the inhibition of tyrosinase activity suggested to be important. In addition, isosilybins A and B inhibited the mRNA expression of TRP-2, but silybins A and B oppositely enhanced the mRNA expression of tyrosinase and TRP-1 and -2 at 10 and/or 30 microM, and the inhibition of phosphorylation of extracellular signal-regulated kinases (ERK1/2) is involved in the enhanced expression of mRNA, at least in part, similar to that of PD98059.

Alkaloid constituents from flower buds and leaves of sacred lotus (Nelumbo nucifera, Nymphaeaceae) with melanogenesis inhibitory activity in B16 melanoma cells.

Methanolic extracts from the flower buds and leaves of sacred lotus (Nelumbo nucifera, Nymphaeaceae) were found to show inhibitory effects on melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. From the methanolic extracts, a new alkaloid, N-methylasimilobine N-oxide, was isolated together with eleven benzylisoquinoline alkaloids. The absolute stereostructure of the new alkaloid was determined from chemical and physicochemical evidence. Among the constituents isolated, nuciferine, N-methylasimilobine, (-)-lirinidine, and 2-hydroxy-1-methoxy-6a,7-dehydroaporphine showed potent inhibition of melanogenesis. Comparison of the inhibitory activities of synthetic related alkaloids facilitated characterization of the structure-activity relationships of aporphine- and benzylisoquinoline-type alkaloids. In addition, 3-30 μM nuciferine and N-methylasimilobine inhibited the expression of tyrosinase mRNA, 3-30 μM N-methylasimilobine inhibited the expression of TRP-1 mRNA, and 10-30 μM nuciferine inhibited the expression of TRP-2 mRNA.

Cucurbitacin E as a new inhibitor of cofilin phosphorylation in human leukemia U937 cells

Cucurbitane-type triterpenes, cucurbitacins B and E, were reported to exhibit cytotoxic effects in several cell lines mediated by JAK/STAT3 signaling. However, neither compound inhibited phosphorylation of STAT3 in human leukemia (U937) cells at low concentrations. We therefore synthesized a biotin-linked cucurbitacin E to isolate target proteins based on affinity for the molecule. As a result, cofilin, which regulates the depolymerization of actin, was isolated and suggested to be a target. Cucurbitacins E and I inhibited the phosphorylation of cofilin in a concentration-dependent manner, and their effective concentrations having the same range as the concentrations at which they had cytotoxic effects in U937 cells. In addition, the fibrous-/globular-actin ratio was decreased after treatment with cucurbitacin E in HT1080 cells. These findings suggested that the inhibition of cofilins phosphorylation increased the severing activity of cofilin, and then the depolymerization of actin was enhanced after treatment with cucurbitacin E at lower concentrations.

Alkaloids from Sri Lankan curry-leaf (Murraya koenigii) display melanogenesis inhibitory activity: Structures of karapinchamines A and B

A methanolic extract and its ethyl acetate-soluble fraction from Sri Lankan curry-leaf, the leaves of Murraya koenigii, inhibited melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. Two new carbazole alkaloids, karapinchamines A and B, were isolated from the ethyl acetate-soluble fraction together with 12 known carbazole alkaloids. The structures of karapinchamines A and B were determined by physicochemical analyses. The principal alkaloid constituents were found to display potent melanogenesis inhibitory activity. The structural requirements of the carbazole alkaloids for melanogenesis inhibitory activity were discussed.

Acylated sucroses and acylated quinic acids analogs from the flower buds of Prunus mume and their inhibitory effect on melanogenesis

The methanolic extract from the flower buds of Prunus mume, cultivated in Zhejiang Province, China, showed an inhibitory effect on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells. From the methanolic extract, five acylated sucroses, mumeoses A-E, and three acylated quinic acid analogs, 5-O-(E)-p-coumaroylquinic acid ethyl ester, and mumeic acid-A and its methyl ester, were isolated together with 13 known compounds. The chemical structures of the compounds were elucidated on the basis of chemical and physicochemical evidence. Inhibitory effects of the isolated compounds on melanogenesis in theophylline-stimulated B16 melanoma 4A5 cells were also investigated. Acylated quinic acid analogs substantially inhibited melanogenesis. In particular, 5-O-(E)-feruloylquinic acid methyl ester exhibited a potent inhibitory effect [inhibition (%): 21.5±1.0 (P<0.01) at 0.1 μM]. Moreover, its biological effect was much stronger than that of the reference compound, arbutin [inhibition (%): 10.6±0.6 (P<0.01) at 10 μM]. Interestingly, the obtained acylated quinic acid analogs displaying melanogenesis inhibitory activity showed no cytotoxicity [cell viability >97% at 10 μM]. It is concluded that acylated quinic acid analogs are promising therapeutic agents for the treatment of skin disorders.

Lignan Dicarboxylates and Terpenoids from the Flower Buds of Cananga odorata and Their Inhibitory Effects on Melanogenesis

The methanolic extract from the flower buds of Cananga odorata showed an inhibitory effect on melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. From the methanolic extract, two new lignan dicarboxylates, canangalignans I and II, three new terpenoids, canangaterpenes I, II, and III, and eight known compounds were isolated. The structures of these compounds were elucidated on the basis of chemical/physicochemical evidence. Several mono- and sesquiterpene analogues significantly inhibited melanogenesis. In particular, canangaterpene I and (3R,3aR,8aS)-3-isopropyl-8a-methyl-8-oxo-1,2,3,3a,6,7,8,8a-octahydroazulene-5-carbaldehyde exhibited a potent inhibitory effect on melanogenesis [inhibition (%): 34.7±4.2 (p<0.01), 45.5±5.7 (p<0.01) at 1 μM, respectively] without inducing cytotoxicity. Moreover, the biological effect of these compounds was much stronger than that of the reference compound, arbutin. Thus, these isolated terpenoid derivatives may be promising therapeutic agents for the treatment of several skin disorders.

Diarylheptanoids with inhibitory effects on melanogenesis from the rhizomes of Curcuma comosa in B16 melanoma cells

The methanolic extract from the dried rhizomes of Curcuma comosa cultivated in Thailand was found to inhibit melanogenesis in theophylline-stimulated murine B16 melanoma 4A5 cells. From the methanolic extract, three new diarylheptanoids, diarylcomosols I-III, were isolated together with 12 known diarylheptanoids. Their chemical structures were elucidated on the basis of chemical and physicochemical evidence. The diarylheptanoids inhibited melanogenesis, and several structural requirements of the active constituents for the inhibition were clarified. In particular, (3R)-1,7-bis(4-hydroxyphenyl)-(6E)-6-hepten-3-ol exhibited stronger inhibitory effect [IC50=0.36 μM] without inducing cytotoxicity. The biological effect was much stronger than that of a reference compound, arbutin [IC50=174 μM]. We conclude that diarylheptanoid analogs are promising therapeutic agents for the treatment of skin disorders.

Anti-obesity effects of the methanolic extract and chakasaponins from the flower buds of Camellia sinensis in mice.

The methanolic extract from the flower buds of Camellia sinensis cultivated in Fujian Province showed inhibitory effects on body weight gain and the weight of visceral fats in high-fat diet-fed mice and/or Tsumura Suzuki Obese Diabetic (TSOD) mice. A suppressive effect of the extract on food intake was suggested to contribute to the anti-obesity effect. The n-butanol (BuOH)-soluble fraction also reduced food intake in normal diet-fed mice. A principal constituent, chakasaponin II, inhibited gastric emptying (GE) as well as food intake. These inhibitory effects were partly reduced by pretreatment with a high dose of capsaicin. The n-BuOH-soluble fraction and chakasaponin II suppressed mRNA levels of neuropeptide Y (NPY), an important regulator of body weight through its effects on food intake and energy expenditure, in the hypothalamus. Furthermore, chakasaponin II enhanced the release of serotonin (5-HT) from the isolated ilea of mice in vitro. These findings suggested that the active saponins suppressed the appetite signals in the hypothalamus through stimulation of the capsaicin-sensitive sensory nerves, probably vagal afferent nerves, or enhancement of 5-HT release from the ilea, leading to reduced food intake and body weight gain.

Neolignan and megastigmane glucosides from the aerial parts of Isodon japonicus with cell protective effects on BaP-induced cytotoxicity

Six neolignan glucosides, named isodonosides I-VI, and a megastigmane glucoside named isodonmegastigmane I, were isolated together with 15 known compounds from the methanolic extract of aerial parts of Isodon japonicus cultivated in Tokushima, Japan. The chemical structures of the compounds were elucidated based on their MS and NMR spectroscopic analysis. The absolute configurations of the neolignan and megastigmane glucosides were determined by derivatizations, by ECD (electronic circular dicroism) Cotton effect approximation, and by the modified Moshers method. In addition, a significant cell protective effects of neolignan glucosides on benzo[a]pyrene-induced cytotoxicity was found.

Chemical structures of constituents from the whole plant of Bacopa monniera

Two new dammarane-type triterpene oligoglycosides, bacomosaponins A and B, and three new phenylethanoid glycosides, bacomosides A, B1, and B2, were isolated from the whole plant of Bacopa monniera Wettst. The chemical structures of the new constituents were characterized on the basis of chemical and physicochemical evidence. In the present study, bacomosaponins A and B with acyl groups were obtained from the whole plant of B. monniera. This is the first report of acylated dammarane-type triterpene oligoglycosides isolated from B. monniera. In addition, dammarane-type triterpene saponins significantly inhibited the aggregation of 42-mer amyloid β-protein.