Hye Sook Kang

Inhibitory phlorotannins from the edible brown algaecklonia stolonifera on total reactive oxygen species (ROS) generation

Reactive oxygen species (ROS) play an important role in the pathogenesis of many human degenerative diseases such as cancer, aging, arteriosclerosis, and rheumatism. Much attention has been focused on the development of safe and effective antioxidants. To discover sources of antioxidative activity in marine algae, extracts from 17 kinds of seaweed were screened for their inhibitory effect on total ROS generation in kidney homogenate using 2′,7′-dichlorofluorescein diacetate (DCFH-DA). ROS inhibition was seen in three species:Ulva pertusa, Symphyocladia latiuscula, andEcklonia stolonifera. At a final concentration of 25 μg/mL,U. pertusa inhibited 85.65±20.28% of total ROS generation,S. latiscula caused 50.63±0.09% inhibitory, and theEcklonia species was 44.30±7.33% inhibition.E. stolonifera Okamura (Laminariaceae), which belongs to the brown algae, has been further investigated because it is commonly used as a foodstuff in Korea. Five compounds, phloroglucinol (1), eckstolonol (2), eckol (3), phlorofucofuroeckol A (4), and dieckol (5), isolated from the ethyl acetate soluble fraction of the methanolic extract ofE. stolonifera inhibited total ROS generation.

Tyrosinase inhibitors isolated from the edible brown alga Ecklonia stolonifera.

Extracts from seventeen seaweeds were determined for tyrosinase inhibitory activity using mushroom tyrosinase with L-tyrosine as a substrate. Only one of them,Ecklonia stoloniferaOkamura (Laminariaceae) belonging to brown algae, showed high tyrosinase inhibitory activity. Bioassay-guided fractionation of the active ethyl acetate (EtOAc) soluble fraction from the methanolic extract ofE. stolonifera, led us to the isolation of phloroglucinol derivatives [phloroglucinol (1), eckstolonol (2), eckol (3), phlorofucofuroeckol A (4), and dieckol (5)]. Compounds1~5 were found to inhibit the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with IC50 values of 92.8, 126, 33.2, 177, and 2.16 μg/mL, respectively. It was compared with those of kojic acid and arbutin, well-known tyrosinase inhibitors, with IC50 values of 6.32 and 112 μg/ mL, respectively. The inhibitory kinetics analyzed from Lineweaver-Burk plots, showed compounds1 and2 to be competitive inhibitors with Ki of 2.3×10-4 and 3.1×10-4 M, and compounds3×5 to be noncompetitive inhibitors with Ki of 1.9×10-5, 1.4×10-3 and 1.5×10-5 M, respectively. This work showed that phloroglucinol derivatives, natural compounds found in brown algae, could be involved in the control of pigmentation in plants and other organisms through inhibition of tyrosinase activity using L-tyrosine as a substrate.

A sphingolipid and tyrosinase inhibitors from the fruiting body of Phellinus linteus.

This paper for the first time reports the isolation of 5 compounds fromPhellinus linteus. A sphingolipid (1) and two tyrosinase inhibitory compounds (2, 3) along with two carboxylic acids (4, 5), were isolated from the fruiting body ofPhellinus linteus (Berk & Curt) Aoshima. The structure of compound 1 was identified as 1-O-β-D-glucopyranosyl-(2S, 3R, 4E, 8E)-2-[(2R)-2-hydroxyhexadecanoylamino]-9-methyl-4,8-octadecadiene-1,3-diol, known as cerebroside B, based on spectroscopic methods such as 1D and 2D NMR as well as by acid hydrolysis. Compounds2~5 were identified as protocatechualdehyde (2), 5-hydroxymethyl-2-furaldehyde (HMF) (3), succinic acid (4), and fumaric acid (5) based on the spectroscopic evidence. Compounds2 and3 inhibited the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with an IC50 of 0.40 and 90.8 μg/mL, respectively. The inhibitory kinetics, which were analyzed by the Lineweaver-Burk plots, were found to be competitive and noncompetitive inhibitors with a Ki of 1.1 μM and 1.4 mM, respectively.

Antioxidant effect ofSalvia miltiorrhiza.

A strong antioxidant activity, which was measured by the radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl(DPPH) radical, was detected in the methanol extract ofSalvia miltiorrhiza Bunge (Labiatae). By activity-directed fractionation, compounds 1 and 2 were isolated as antioxidant principles ofS. miltiorrhiza. Compounds 1 and 2 were identified as dimethyl lithospermate and 3-(3,4-dihydroxyphenyl)lactamide, respectively, on the basis of spectral data. The radical scavenging effect of compounds 1 and 2 on DPPH radical exceeded that of L-ascorbic acid which is a well known antioxidant. These two compounds also showed prominent inhibitory activity against free radical generation in dichlorofluorescein (DCF) method and cytoprotective effect againstt-BHP in cultured liver cell.

Antioxidant potential of dimethyl lithospermate isolated from Salvia miltiorrhiza (red sage) against peroxynitrite.

Peroxynitrite (ONOO(-)) is a reactive oxidant formed from superoxide and nitric oxide that can readily oxidize cellular components, including essential protein, non-protein thiols, and DNA. ONOO(-) has contributed to the pathogenesis of diseases such as stroke, heart disease, Alzheimers disease, and atherosclerosis. In this study, the ability of dimethyl lithospermate (DML), isolated from Salvia miltiorrhiza, to scavenge ONOO(-) and to protect cells against reactive species and ONOO(-) was investigated. The data obtained show that DML can efficiently scavenge native ONOO(-) as well as ONOO(-) derived from the ONOO(-) donor 3-morpholinosydnonimine hydrochloride. Spectrophotometric analysis revealed that DML led to decreased ONOO(-)-mediated nitration of tyrosine through electron donation. DML significantly inhibited nitration of bovine serum albumin by ONOO(-) in a dose-dependent manner. DML also manifested cytoprotection from cell damage induced by ONOO(-). The present study suggests that DML is an effective ONOO(-) scavenger and promotes cellular defense activity in the protection against ONOO(-)-involved diseases.

Further isolation of antioxidative (+)-1-hydroxypinoresinol-1-O-β-d-glucoside from the rhizome ofSalvia miltiorrhiza that acts on peroxynitrite, total ROS and 1,1-diphenyl-2-picrylhydrazyl radical

A furanofuranoid lignan glycoside, with radical scavenging on peroxynitrite, total reactive oxygen species (ROS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, was isolated from the rhizome ofSalvia miltiorrhiza and characterized as (+)-1-hydroxypinoresinol-1-O-β-d-glucoside based on spectroscopic evidence. The compound exhibited peroxynitrite, total ROS and DPPH radical scavenging activities with IC50 values of 3.23 ± 0.04, 2.26 ± 0.07 and 32.3 ± 0.13 μM, respectively. Penicillamine, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) andL-ascorbic acid, acting as positive controls, showed radical scavenging activities with IC50 values of 6.72 ± 0.25, 1.43 ± 0.04 and 11.4 ± 0.07 μM, respectively.

A new cyclic phenyllactamide from Salvia miltiorrhiza

From the rhizome of Salvia miltiorrhiza, a new cyclic phenyllactamide was isolated and characterized as 2,10,11-trihydroxy-8-methoxy-1,6,7,8-tetrahydro-2H-benzo[e]azecine-3,5-dione (1) from spectroscopic evidence. The new compound was found to be a scavenger of 1,1-diphenyl-2-picrylhydrazyl radical.

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.