Inhibition of c-Kit signaling by diosmetin isolated from Chrysanthemum morifolium.

The interaction of stem cell factor (SCF) with its cognate receptor c-Kit is closely associated with the survival and maturation of melanocytes. To investigate novel depigmentation agents, we screened 2,000 plant extracts for c-Kit inhibitors to identify active small molecules by using time-resolved fluorescence enzyme assays. For the active extracts identified as inhibitors of c-Kit enzyme, we evaluated the effects of the active extracts and isolated flavonoids on c-Kit phosphorylation in MO7e/melanocytes. Anti-melanogenic activity was also examined in melanocytes and melanoderm model. The flavonoids such as diosmetin, apigenin, acacetin and luteolin isolated from Chrysanthemum morifolium were found to be active in inhibiting c-Kit both at enzyme and cellular levels. In addition, these flavonoids attenuated SCF-induced proliferation of human primary melanocytes without toxicity and suppressed ultraviolet (UV) B irradiation-mediated melanin synthesis significantly. Among the active flavonoids, diosmetin was found to inhibit SCF-induced melanogenesis in a human melanoderm model. These results strongly suggest that C. morifolium extract and diosmetin have potential to suppress SCF-/UVB-induced melanogenesis, and could be developed as anti-pigmentation agents.

Synthesis and evaluation of a series of 3,4,5-trimethoxycinnamic acid derivatives as potential antinarcotic agents.

A series of 3,4,5-trimethoxycinnamic acid derivatives was prepared and evaluated for antinarcotic effects on morphine dependence in mice and binding affinities on serotonergic receptors. The key synthetic strategies involve generation of ketones 6-7, esters 9-12 through condensation reaction, and amides 13-19 via coupling reaction using 1-hydroxybenzotriazole/ethyl(dimethylaminopropryl)carbodiimide system in high yield. We found that the naloxone-induced morphine withdrawal syndrome was significantly suppressed by new synthetic 3,4,5-trimethoxycinnamic acid derivatives (20 mg/kg/day). Most of 3,4,5-trimethoxycinnamic acid derivatives were found to have high affinity to 5-HT(1A) receptor. The naloxone-induced morphine withdrawal syndrome was attenuated by (+)8-OH-DPAT (0.1 mg/kg/day, i.p.), a 5-HT(1A) receptor agonist. In cortical neuronal cells, (+)8-OH-DPAT (1 µM) produced an elevation of the pERK 1/2 expression, and the elevated pERK levels were inhibited by WAY 100635, a 5-HT(1A) receptor-specific antagonist. Interestingly, the pERK levels were increased by the 3,4,5-trimethoxycinnamic acid derivatives and the derivatives-mediated changes in pERK levels were blocked by the WAY 100635. These results suggested that new synthetic 3,4,5-trimethoxycinnamic acid derivatives have a potential antinarcotic effect through acting as a 5-HT(1A) receptor agonist in mice.

In vitro BACE-1 inhibitory activity of resveratrol oligomers from the seed extract of Paeonia lactiflora.

A new resveratrol oligomer (1) together with eight related components (2- 9) were isolated from the seed extract of Paeonia lactiflora (Paeoniaceae) as active principles responsible for the inhibition of beta-site APP-cleaving enzyme 1 (BACE-1) in vitro. The chemical structure of 1 was established as (-)-7a,8a- CIS- ε-viniferin with the aid of spectroscopic analyses including NOESY experiments. All isolated resveratrol oligomers (1- 9) demonstrated significant inhibition on baculovirus-expressed BACE-1 in a dose-dependent manner, which was assessed by the FRET assay using Rh-EVNLDAEFK as a substrate in vitro.

Screening of Kit inhibitors: suppression of Kit signaling and melanogenesis by emodin.

In search of novel antipigmentation agents, a set of 3,840 compounds with natural-like synthetic or natural origin were screened against Kit (stem cell factor receptor). Emodin from the seed of Cassia tora and baicalin from Scutellariae radix showed potent inhibitory effects (IC(50) = 4.9 and 9.0 microM, respectively) on the phosphorylation of Kit. Emodin also blocked other receptor tyrosine kinase activities, such as epithelial growth factor receptor (EGFR), vascular endothelial growth factor receptor 2 (VEGFR-2), fibroblast growth factor receptor 1 (FGFR-1), platelet-derived growth factor receptor b (PDGFR-b). In contrast to emodin, aloe-emodin did not inhibit Kit activity at all. Emodin also blocked the cellular kinase activities of Kit and its down-stream p44/42 mitogen activated protein kinase (MAPK) in MO7e cells and human primary melanocytes. Emodin strongly suppressed the melanin synthesis triggered by stem cell factor (SCF) treatment. Also, emodin showed almost no toxicity up to 10 microM on cultured melanocytes as reported previously by other researchers. The results indicate that emodin is a good candidate for the development of antipigmentation agents since it can radically block the differentiation and proliferation of pigment cells by reducing Kit signaling.

A new specific BACE-1 inhibitor from the stembark extract of Vitis vinifera.

A new resveratrol dimer, (+)-vitisinol E (1) which demonstrated inhibitory activity on BACE-1 (beta-site APP-cleaving enzyme 1) in vitro, was isolated from the stembark extract of Vitis vinifera (Vitaceae) together with four known resveratrol oligomers, (+)-epsilon-viniferin (2), (+)-ampelopsin A (3), (+)-vitisin A (4) and (-)-vitisin B (5). The chemical structure of 1 was established by MR spectroscopic analyses, including HMBC. All isolated resveratrol derivatives (1-5) demonstrated significant inhibition on baculovirus-expressed BACE-1 in a dose-dependent manner, which was assessed with the FRET assay using Rh-EVNLDAEFK as a substrate in vitro.

In vitro BACE-1 inhibitory phenolic components from the seeds of Psoralea corylifolia.

A new isoflavone, neocorylin ( 1) was isolated from the seeds extract of Psoralea corylifolia L. (Fabaceae), together with eight known constituents ( 2 - 9), i. e., bakuchiol ( 2), psoralen ( 3), bavachromene ( 4), isobavachromene ( 5), bavachalcone ( 6), isobavachalcone ( 7), 7,8-dihydro-8-(4-hydrophenyl)-2,2-dimethyl-2 H,6 H-[1,2- B:5,4- B']dipyran-6-one ( 8), and bavachinin ( 9). The structure of the new isoflavone 1 was elucidated as 7-hydroxy-3-[2-methyl-2-(4-methylpenten-3-yl)-2 H-chromen-6-yl]-4 H-chromen-4-one by spectroscopic analyses. Neocorylin ( 1) as well as related compounds 2, 4 - 6, 8 and 9 exhibited a significant inhibitory effect on baculovirus-expressed BACE-1 in vitro.

Preparation of piperazine derivatives as 5-HT7 receptor antagonists.

Twenty-four compounds of 4-methoxy-N-[3-(4-substituted phenyl-piperazine-1-yl)propyl] benzene sulfonamides and N-[3-(4-substituted phenyl-piperazine-1-yl)propyl] naphthyl sulfonamides were prepared and evaluated as 5-HT(7) receptor antagonists. Most of the compounds showed the IC(50) values of 12-580nM. Four methyl branched analogues were also obtained, but the activity for methyl branched analogues was almost same as its straight chain congeners. Among the synthesized compounds, 3c showed a good activity on 5-HT(7) receptors and a good selectivity on 5-HT(1a), 5-HT(2a), 5-HT(2c), and 5-HT(6) receptors.

Ginsenoside Rg3 antagonizes NMDA receptors through a glycine modulatory site in rat cultured hippocampal neurons.

We previously reported that ginseng, a well-known herbal medicine, inhibited NMDA receptors in cultured hippocampal neurons. Here, we further examined the detailed mechanism of ginseng-mediated inhibition using its main active ingredient, ginsenoside Rg3. Co-application of ginsenoside Rg3 with increasing concentrations of NMDA did not change the EC50 of NMDA to the receptor, suggesting that ginsenoside Rg3 inhibits NMDA receptors without competing with the NMDA-binding site. Ginsenoside Rg3-mediated inhibition also occurred in a distinctive manner from the well-characterized NMDA receptor open channel blocker, MK-801. However, ginsenoside Rg3 produced its effect in a glycine concentration-dependent manner and shifted the glycine concentration-response curve to the right without changing the maximal response, suggesting the role of ginsenoside Rg3 as a competitive NMDA receptor antagonist. We also demonstrated that ginsenoside Rg3 significantly protected neurons against NMDA insults. Therefore, these results suggest that ginsenoside Rg3 protects NMDA-induced neuronal death via a competitive interaction with the glycine-binding site of NMDA receptors in cultured hippocampal neurons.