As part of our study of the isolation of antihypertensive agents derived from natural marine products, the bioactivity of 10 edible Korean seaweeds were screened by angiotensin converting enzyme (ACE) inhibitory and peroxynitrite assays. Among the crude extracts of selected seaweeds, including five Phaeophyta ( Ecklonia stolonifera , E. cava , Pelvetia siliquosa , Hizikia fusiforme , and Undaria pinnatifida ), four Rhodophyta ( Gigartina tenella , Gelidium amansii , Chondria crassicaulis , and Porphyra tenera ) and one Chlorophyta ( Capsosiphon fulvescens ), the ethanol extracts of E. stolonifera , E. cava , P. siliquosa , U. pinnatifida , and G. tenella exhibited significant inhibitory properties against ACE at more than 50% inhibition at a concentration of 163.93 µ g/mL. Phloroglucinol 1 , eckstolonol 2 , eckol 3 , phlorofucofuroeckol A 4 , and dieckol 5 had been isolated previously, and triphlorethol-A 6 and fucosterol 7 were isolated for the first time from E. stolonifera. Also, the ACE inhibitory and peroxynitrite scavenging properties of phlorotannins 1-6 were evaluated, along with fucosterol 7 obtained from E. stolonifera . Among profound peroxynitrite scavenging compounds 1-6 , phlorotannins 3 , 4 and 5 were also determined to manifest marked inhibitory activity against ACE, with 50% inhibition concentration (IC 50 ) values of 70.82 ± 0.25, 12.74 ± 0.15, and 34.25 ± 3.56 µ M, respectively.

Aldose reductase, the principal enzyme of the polyol pathway, has been shown to play an important role in the complications associated with diabetes. A methanol extract of the stamens of Nelumbo nucifera Gaertn. was shown to exert an inhibitory effect on rat lens aldose reductase (RLAR), and thus was fractionated using several organic solvents, including dichloromethane, ethyl acetate and n-butanol. The ethyl acetate-soluble fraction, which manifested potent RLAR-inhibitory properties, was then purified further via repeated measures of silica gel and Sephadex LH-20 column chromatography. Thirteen flavonoids: kaempferol (1) and seven of its glycosides (2-9), myricetin 3',5'-dimethylether 3-O-beta-d-glucopyranoside (10), quercetin 3-O-beta-d-glucopyranoside (11) and two isorhamnetin glycosides (12, 13) were isolated from N. nucifera, as well as four non-flavonoid compounds: adenine (14), myo-inositol (15), arbutin (16) and beta-sitosterol glucopyranoside (17). These compounds were all assessed with regard to their RLAR-inhibitory properties. Among the isolated flavonoids, those harboring 3-O-alpha-l-rhamnopyranosyl-(1-->6)-beta-d-glucopyranoside groups in their C rings, including kaempferol 3-O-alpha-l-rhamnopyranosyl-(1-->6)-beta-d-glucopyranoside (5) and isorhamnetin 3-O-alpha-l-rhamnopyranosyl-(1-->6)-beta-d-glucopyranoside (13), were determined to exhibit the highest degree of rat lens aldose reductase inhibitory activity in vitro, evidencing IC(50) values (concentration required for a 50% inhibition of enzyme activity) of 5.6 and 9.0 microm, respectively.

Previously, it was reported that some prenylated flavonoids contained in the dichloromethane fraction of the ethanolic extract of Sophora flavescens, such as kuraridin, sophoraflavanone G, kurarinone, and kushenol F, are tyrosinase inhibitors; however, based on the level of these inhibitors in the extract, its inhibitory effect on tyrosinase activity was higher than expected. This has led us to further investigate other possible constituents that may contribute to the extract's strong inhibitory activity. The results of this study indicate that kurarinol (1), kuraridinol (2), and trifolirhizin (3), from the ethyl acetate fraction of Sophora extract, can inhibit tyrosinase activity. Compared with kojic acid (16.22؎1.71 m mM), compounds 1-3 possessed potent tyrosinase inhibitory activity with IC 50 values of 8.60؎0.51, 0.88؎0.06, and 506.77؎4.94 m mM, respectively. These three compounds were further tested for their inhibitory effects on melanogenesis. In cultured B16 melanoma cells, 1-3 markedly inhibited (Ͼ50%) melanin synthesis at 50 m mM. This is the first study indicating that 1-3 exert varying degrees of inhibition on tyrosinase-dependent melanin biosynthesis, and therefore, are candidates as skin-whitening agents.

In this study, we isolated two new isorhamnetin glycosides, designated as nelumboroside A (3) and nelumboroside B (4), as well as the previously-characterized isorhamnetin glucoside (1) and isorhamnetin rutinoside (2), from the n-BuOH fraction of Nelumbo nucifera stamens. The structures of the two new compounds were then determined, using chemical and spectroscopic techniques. All isolated isorhamnetin glycosides 1-4 showed marked antioxidant activities in the DPPH, and ONOO- assays.

As a component of our program that pertains to the isolation of antihypertensive agents derived from natural products, we screened the bioactivity of seeds from raw and roasted Cassia tora via angiotensin converting enzyme (ACE) inhibitory assays. We found that both of the MeOH extracts from the raw and roasted C. tora exhibited significant inhibitory properties against ACE, demonstrating more than 50% inhibition at a concentration of 163.93 microg/mL. Emodin (3), alaternin (4), gluco-obtusifolin (5), cassiaside (6), gluco-aurantioobtusin (7), cassitoroside (8), toralactone gentiobioside (9), and chrysophanol triglucoside (10) had been previously isolated; however, questin (1) and 2-hydroxyemodin 1-methylether (2) were isolated from C. tora for the first time in this study. Among them, only anthraquinone glycoside (7) demonstrated marked inhibitory activity against ACE, with an IC(50) value of 30.24 +/- 0.20 microM. Conversely, aurantioobtusin (7a), obtained from the acid hydrolysis of 7, showed no activity. Further inhibitory kinetics analyzed from Lineweaver-Burk plots showed 7 to be a competitive inhibitor with a Ki value of 8.3 x 10(-5) M. Moreover, compound 7 showed marked inhibitory and scavenging activities with an IC(50) value of 49.64 +/- 0.37 microM (positive control; trolox: 26.07 +/- 1.05 microM) for total reactive oxygen species generation, and 4.60 +/- 1.12 microM (positive control; penicillamine: 0.24 +/- 0.04 microM) for ONOO(-).

Activity-guided fractionation of the CH2Cl2-soluble fraction of the roots of Sophora flavescens furnished five 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavengers: trans-hexadecyl ferulic acid (1), cis-octadecyl ferulic acid (2), trans-hexadecyl sinapic acid (3), (-)-4-hydroxy-3-methoxy-(6aR,11aR)-8,9-methylenedioxypterocarpan (4) and desmethylanhydroicaritin (8), along with nine known inactive compounds: (-)-maackiain (5), xanthohumol (6), formononetin (7), (2S)-2'-methoxykurarinone (9), (2S)-3beta,7,4'-trihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (10), (2S)-7,4'-dihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (11), umbelliferone (12), kuraridin (13), and trifolirhizin (14). Compounds 1-4 and 8 exhibited DPPH free radical scavenging effects at IC50 values of 33.01 +/- 0.20, 57.06 +/- 0.16, 39.84 +/- 0.36, 35.83 +/- 0.47, and 18.11 +/- 0.04 microM, respectively. L-Ascorbic acid, when used as a positive control, exhibited an IC50 value of 7.39 +/- 0.01 microM. Compounds 1-4 and 8 also appeared to exert significant scavenging effects on authentic ONOO-, with IC50 values of 5.76 +/- 1.19, 15.06 +/- 1.64, 8.17 +/- 4.97, 1.95 +/- 0.29, and 4.06 +/- 2.41 microM, respectively. Penicillamine (IC50 = 2.36 +/- 0.79 microM) was used as a positive control. In addition, compounds 2, 4, 6, 8, and 10 were isolated from this plant for the first time.

Nelumbo nucifera GAERTN., the family of Nelumbonaceae, is a perennial, rhizomatous, aquatic plant distributed throughout Asia, including India, China, and Egypt. The plant is comprised of: membranous, peltate, orbicular, and concave leaves; nut-contained and ovoid fruits; black, hard, and ovoid seeds; nodal roots. In Korea, China and India, various parts of N. nucifera have been used in foodstuffs and traditional medicine for the treatment of diarrhea, gastritis, insomnia, nervous prostration and as a haemostatic.1-3) In particular, numerous biological activities, including antioxidant, 4,5) anti-human immunodeficiency virus (HIV), 6) antihyperlipidemic, 1) hepatoprotective, and antiobesity effects [7][8][9] have been reported from the leaves of N. nucifera. In addition, Mukherjee et al. reported 24) Recently, N. nucifera semen extract was reported to improve memory in rats with scopolamine-induced dementia through the induction of choline acetyltransferase expression and inhibition of acetylcholinesterase (AChE).25) Even though individual parts of this plant have been the target of distinct biological and pharmacological research, there are limited studies of the stamens, with the exception of research focusing upon the antioxidant and rat lens aldose reductase (RLAR) inhibition [26][27][28] and anti-allergic activities 29) attributed to the flavonoids. Alzheimer's disease (AD) is a neurodegenerative disease and the most frequent and predominant cause of dementia in the elderly, provoking progressive cognitive decline, psychobehavior disturbances, memory loss, the presence of senile plaques, neurofibrillary tangles, and a decrease in cholinergic transmission. 30,31) Although the pathogenesis of AD is complicated and involved in numerous pathways, two major hypotheses are currently under consideration regarding the molecular mechanism, the cholinergic hypothesis and the amyloid cascade hypothesis. Thus, the focus herein is upon inhibitors of select cholinesterases (ChEs) to alleviate cholinergic deficits and improve neurotransmission and b-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1; aspartyl protease, b-secretase, and memapsin2) inhibitors to preclude formation and accumulation of amyloid b peptide (Ab). Pursuant to this, both could then be established as viable therapeutic targets for AD. [31][32][33][34] Given that numerous promising pharmaceuticals and nutraceuticals are constantly isolated from effective natural products, and that a previous study from this lab indicated potent antioxidant and RLAR inhibitory activities of N. nucifera stamens, this plant was chosen for ongoing investigations into anti-AD activities. The present work deals with the isolation and characterization of a new b-cyclogeraniol diglycoside (5), and four known compounds: cycloartenol (1); p-hydroxybenzoic acid (2); vanilloloside (3); 5Ј-Omethyladenosine (4). Furthermore, the inhibitory activities of 1-5 toward ChEs, including AChE and butyrylcholinesterase (BChE), and BACE1 were evaluated. Busanjin-gu, Busan 61...

The antioxidative and hepatoprotective potentials of two anthraquinones, alaternin (2-hydroxyemodin) and emodin, to scavenge and/or inhibit hydroxyl radicals generated by the Fenton reaction and to protect tacrine-induced cytotoxicity in human liver derived HepG2 cells were evaluated, respectively. The inhibitory activity on hydroxyl radical generated in a cell-free chemical system (FeSO4/H2O2) was investigated by a fluorescence spectrophotometer using a highly fluorescent probe, 2',7'-dichlorofluorescein. The hydroxyl radical scavenging activity was determined by electron spin resonance spectroscopy using 5,5-dimethy-1-pyrroline-N-oxide as hydroxyl radicals trapping agents. Tacrine-induced HepG2 cell toxicity was determined by a 3-[4,5-dimethylthiazole-2yl]-2,5-diphenyltertrazolium bromide assay. Although the scavenging activity of alaternin on hydroxyl radical was similar to that of emodin in dose-dependent patterns, the inhibitory activity exhibited by the former on hydroxyl radical generation was stronger than that of the latter, with IC50 values of 3.05 +/- 0.26 microM and 13.29 +/- 3.20 microM, respectively. In addition, the two anthraquinones, alaternin and emodin showed their hepatoprotective activities on tacrine-induced cytotoxicity, and the EC50 values were 4.02 microM and 2.37 microM, respectively. Silymarin, an antihepatotoxic agent used as a positive control exhibited the EC50 value of 2.00 microM. These results demonstrated that both alaternin and emodin had the simultaneous antioxidant and hepatoprotective activities.