Sook Kyung Hyun

Angiotensin-converting enzyme I inhibitory activity of phlorotannins from Ecklonia stolonifera

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 sea-weeds, 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 μg/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 (IC50) values of 70.82±0.25, 12.74¯0.15, and 34.25±3.56 μM, respectively.

In Vitro Free Radical and ONOO- Scavengers from Sophora flavescens

Activity-guided fractionation of the CH2CI2-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)-3β,7,4’-trihydroxy-5-methoxy-8-(γ,γ-dimethylallyl)-flavanone (10), (2S)-7,4’-dihydroxy-5-methoxy-8-(γ,γ-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 ¼M, respectively. L-Ascorbic acid, when used as a positive control, exhibited an IC50 value of 7.39 ± 0.01 ¼M. 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 ¼M, respectively. Penicillamine (IC50= 2.36 ± 0.79 μM) was used as a positive control. In addition, compounds 2, 4, 6, 8, and 10 were isolated from this plant for the first time.

Inhibitory Activities of Cassia tora and its Anthraquinone Constituents on Angiotensin-Converting Enzyme

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 µg/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 IC50 value of 30.24 ± 0.20 µM. 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 × 10−5 M. Moreover, compound 7 showed marked inhibitory and scavenging activities with an IC50 value of 49.64 ± 0.37 µM (positive control; trolox: 26.07 ± 1.05 µM) for total reactive oxygen species generation, and 4.60 ± 1.12 µM (positive control; penicillamine: 0.24 ± 0.04 µM) for ONOO−. Copyright

Alaternin and emodin with hydroxyl radical inhibitory and/or scavenging activities and hepatoprotective activity on tacrine-induced cytotoxicity in HepG2 cells.

The antioxidative and hepatoprotective potentials of two anthraquinones, alaternin (2-hydroxy-emodin) 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-/V-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 μM and 13.29 ± 3.20 μM, respectively. In addition, the two anthraquinones, alaternin and emodin showed their hepatoprotective activities on tacrine-induced cytotoxicity, and the EC50 values were 4.02 μM and 2.37 μM, respectively. Silymarin, an antihepatotoxic agent used as a positive control exhibited the EC50 value of 2.00 μM. These results demonstrated that both alaternin and emodin had the simultaneous antioxidant and hepatoprotective activities.

Isorhamnetin glycosides with free radical and ONOO− scavenging activities from the stamens ofNelumbo nucifera

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 then-BuOH fraction ofNelumbo nucifera stamens. The structures of the two new compounds were then determined, using chemical and spectroscopic techniques. All isolated isorhamnetin glycosides1–4 showed marked antioxidant activities in the DPPH, and ONOO− assays.

In vitro peroxynitrite scavenging activity of 6-hydroxykynurenic acid and other flavonoids fromGingko biloba yellow leaves

As part of our research on phytochemicals that exert protective effects against diseases related to reactive nitrogen specie, we have evaluated the scavenging activity of the yellow leaves ofGinkgo biloba on ONOO−. The methanol extract and ethyl acetate fraction obtained from yellow leaves ofG. biloba evidenced a marked scavenging activity on authentic, ONOO−. Repeated column chromatography of the active ethyl acetate soluble fraction on silica gel, Sephadex LH-20, and RP-18, resulted in the purification of 15 known compounds, including sciadopitysin (1), ginkgolide B (2), bilobalide (3), isoginkgetin (4), kaempferol (5), luteolin (6), protocatechuic acid (7), bilobetin (8), amentoflavone (9), β-sitosterol glucopyranoside (10), kaempferol 3-O-rhamnopyranoside (11), kaempferol 3-O-glucopyranoside (12), kaempferol 3-O-[6‴-O-p-coumaroyl-β-D-glucopyranosyl(1→2)-α-L-rhamnopyranoside] (13), kaempferol 3-O-rutinoside (14), and 6-hydroxykynurenic acid (15). Among the compounds isolated, flavonoids (5, 6 and11–14), protocatechuic acid (7), and 6-hydroxykynurenic acid (15) all exhibited marked scavenging activities on authentic ONOO−. The IC50 values of5–7, 11–14 and 15 were as follows: 2.86±0.70, 2.30±0.04, 2.85±0.10, 5.60±0.47, 4.16±1.65, 2.47±0.15, 3.02±0.48, and 6.24±0.27 μM respectively. DL-Penicillamine (IC50=4.98±0.27 μM) was utilized as a positive control. However, the other compounds (1–4, 8–10) exerted no effects against ONOO−.

Alaternin attenuates delayed neuronal cell death induced by transient cerebral hypoperfusion in mice.

The aim of this study was to determine whether alaternin exhibits neuroprotective activity after transient cerebral hypoperfusion induced by bilateral common carotid artery occlusion (BCCAO). Mice were subjected to BCCAO, and circulation was restored after 20 min. Alaternin (10 mg/kg, p.o) treatment significantly prevented nitrotyrosine and lipid peroxidation, as well as BCCAO induced-inducible nitric oxide synthase (iNOS) expression. Alaternin also significantly reduced microglial activation (a marker of inflammation). The number of viable neurons detected by Nissl staining increased with alaternin (10 mg/kg, p.o) treatment at 7 days post-BCCAO. In the passive avoidance task, alaternin significantly ameliorated BCCAO-induced cognitive impairments (P<0.05). These results suggest that the neuroprotective effects of alaternin are mediated by its anti-inflammatory and radical scavenging activities.

A phenolic glucoside isolated fromPrunus serrulata var.spontanea and its peroxynitrite scavenging activity

A new phenolic glucoside (1), pursargentoside, was isolated from the leaves ofPrunus serrulata var.spontanea, along with three other known compounds, orobol 7-O-glucoside (2), 1β, 2α, 3α, 24-tetrahydroxy-urs-12-en-28-oic acid (3), and chlorogenic acid (4). The structure of pursargentoside (1) was identified by spectroscopic data analysis including 1D and 2D NMR spectroscopy, as 2-O-β-(6′-benzoyl)-glucopyranosylo-(Z)-coumaric acid. Compounds1, 2, and4 exhibited ONOO− scavenging activity, whereas compound3 was determined to be virtually inactive.