Seung Hwan Hwang

Identification of tyrosinase specific inhibitors from Xanthium strumarium fruit extract using ultrafiltration-high performance liquid chromatography

In this study, a strategy based on ultrafiltration-high performance liquid chromatography coupled with diode array detection (UF-HPLC-DAD) was proposed for screening tyrosinase specific inhibitors in Xanthii fructus. The false negatives were distinguished by optimizing the UF-HPLC-DAD parameters to reduce the background noise; the false positives were distinguished by introducing a blocked tyrosinase in the control group for comparison. To obtain the best blocker, the competitive experiments were performed using various known ligands. Using this strategy, three competitive inhibitors (protocatechuic acid; 3,5-di-O-caffeoylquinic acid; and 1,5-di-O-caffeoylquinic acid) and one mixed-type inhibitor (chlorogenic acid) were identified. These results were verified using tyrosinase inhibition assay, kinetic analysis, and structural simulation of the complex. Our experimental results suggest that the proposed strategy could be useful for high-throughput identification of tyrosinase specific inhibitors in natural products.

Inhibitory Effects of Colocasia esculenta (L.) Schott Constituents on Aldose Reductase

The goal of this study was to determine the rat lens aldose reductase-inhibitory effects of 95% ethanol extracts from the leaves of C. esculenta and, its organic solvent soluble fractions, including the dichloromethane (CH2Cl2), ethyl acetate (EtOAc), n-butanol (BuOH) and water (H2O) layers, using dl-glyceraldehyde as a substrate. Ten compounds, namely tryptophan (1), orientin (2), isoorientin (3), vitexin (4), isovitexin (5), luteolin-7-O-glucoside (6), luteolin-7-O-rutinoside (7), rosmarinic acid (8), 1-O-feruloyl-d-glucoside (9) and 1-O-caffeoyl-d-glucoside (10) were isolated from the EtOAc and BuOH fractions of C. esculenta. The structures of compounds 1–10 were elucidated by spectroscopic methods and comparison with previous reports. All the isolates were subjected to an in vitro bioassay to evaluate their inhibitory activity against rat lens aldose reductase. Among tested compounds, compounds 2 and 3 significantly inhibited rat lens aldose reductase, with IC50 values of 1.65 and 1.92 μM, respectively. Notably, the inhibitory activity of orientin was 3.9 times greater than that of the positive control, quercetin (4.12 μM). However, the isolated compounds showed only moderate ABTS+ [2,29-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] activity. These results suggest that flavonoid derivatives from Colocasia esculenta (L.) Schott represent potential compounds for the prevention and/or treatment of diabetic complications.

Advanced Growth Factor Delivery Systems in Wound Management and Skin Regeneration

Growth factors are endogenous signaling molecules that regulate cellular responses required for wound healing processes such as migration, proliferation, and differentiation. However, exogenous application of growth factors has limited effectiveness in clinical settings due to their low in vivo stability, restricted absorption through skin around wound lesions, elimination by exudation prior to reaching the wound area, and other unwanted side effects. Sophisticated systems to control the spatio-temporal delivery of growth factors are required for the effective and safe use of growth factors as regenerative treatments in clinical practice, such as biomaterial-based drug delivery systems (DDSs). The current review describes the roles of growth factors in wound healing, their clinical applications for the treatment of chronic wounds, and advances in growth factor-loaded DDSs for enhanced wound healing, focusing on micro- and nano-particulate systems, scaffolds, hydrogels, and other miscellaneous systems.

Phytochemical Analysis of Agrimonia pilosa Ledeb, Its Antioxidant Activity and Aldose Reductase Inhibitory Potential.

The aim of this study was to determine aldose reductase (AR) inhibitory activity and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity of compounds from Agrimonia pilosa Ledeb (AP). We isolated agrimoniin (AM), four flavonoid glucosides and two flavonoid glucuronides from the n-butanol fraction of AP 50% methanol extract. In addition to isolated compounds, the AR-inhibitory activity and the DPPH free radical scavenging activity of catechin, 5-flavonoids, and 4-flavonoid glucosides (known components of AP) against rat lens AR (RLAR) and DPPH assay were measured. AM showed IC50 values of 1.6 and 13.0 μM against RLAR and DPPH scavenging activity, respectively. Additionally, AM, luteolin-7-O-glucuronide (LGN), quercitrin (QU), luteolin (LT) and afzelin (AZ) showed high inhibitory activity against AR and were first observed to decrease sorbitol accumulation in the rat lens under high-sorbitol conditions ex vivo with inhibitory values of 47.6%, 91.8%, 76.9%, 91.8% and 93.2%, respectively. Inhibition of recombinant human AR by AM, LGN and AZ exhibited a noncompetitive inhibition pattern. Based on our results, AP and its constituents may play partial roles in RLAR and oxidative radical inhibition. Our results suggest that AM, LGN, QU, LT and AZ may potentially be used as natural drugs for treating diabetic complications.

Inhibitory Activities of Stauntonia hexaphylla Leaf Constituents on Rat Lens Aldose Reductase and Formation of Advanced Glycation End Products and Antioxidant

Stauntonia hexaphylla (Thunb.) Decne. (Lardizabalaceae) leaves (SHL) have been used traditionally as analgesics, sedatives, diuretics, and so on, in China. To date, no data have been reported on the inhibitory effect of SHL and its constituents on rat lens aldose reductase (RLAR) and advanced glycation end products (AGEs). Therefore, the inhibitory effect of compounds isolated from SHL extract on RLAR and AGEs was investigated to evaluate potential treatments of diabetic complications. The ethyl acetate (EtOAC) fraction of SHL extract showed strong inhibitory activity on RLAR and AGEs; therefore, EtOAc fraction (3.0 g) was subjected to Sephadex LH-20 column chromatography, for further fractionation, with 100% MeOH solvent system to investigate its effect on RLAR and AGEs. Phytochemical investigation of SHL led to the isolation of seven compounds. Among the isolated compounds, chlorogenic acid, calceolarioside B, luteolin-3′-O-β-D-glucopyranoside, quercetin-3-O-β-D-glucopyranoside, and luteolin-7-O-β-D-glucopyranoside exhibited significant inhibitory activity against RLAR with IC50 in the range of 7.34–23.99 μM. In addition, 3-(3,4-dihydroxyphenyl) propionic acid, neochlorogenic acid, and luteolin-3′-O-β-D-glucopyranoside exhibited the most potent inhibitory activity against formation of AGEs, with an IC50 value of 115.07–184.06 μM, compared to the positive control aminoguanidine (820.44 μM). Based on these findings, SHL dietary supplements could be considered for the prevention and/or treatment of diabetes complication.

Isolation of Fucosterol from Pelvetia siliquosa by High-speed Countercurrent Chromatography

We report here the use of high-speed countercurrent chromatography (HSCCC) in the preparative isolation and purification of the bioactive component, fucosterol, from Pelvetia siliquosa. A crude extract was obtained by ultrasonic extraction of powdered P. siliquosa using methylene chloride and was then subjected to separation and purification by HSCCC, coupled with evaporative lightscattering detection. Preparative HSCCC was performed successfully using a two-phase solvent system, n-heptane:methanol (3:2, v/v), to obtain 10.96 mg fucosterol with 96.8% purity from 50 mg of crude extract; the recovery rate was approximately 90.5%.

Rapid Identification and Isolation of Inhibitors of Rat Lens Aldose Reductase and Antioxidant in Maackia amurensis

Oxidative stress and aldose reductase activity have been implicated in the development of diabetic complications. In this study, the antioxidant and aldose reductase (AR) inhibitory effects of Maackia amurensis (MA) were investigated. The ethyl acetate fraction of the MA extract showed the highest inhibitory activity in antioxidant and rat lens AR (RLAR). To identify and isolate the active components in the ethyl acetate fraction of the MA extract, high-speed countercurrent chromatography and Sephadex LH-20 column chromatography were performed and guided by an offline HPLC-ABTS assay and HPLC microfractionation AR assay. Four antioxidants, namely, piceatannol (IC50 = 6.73 μM), resveratrol (IC50 = 11.05 μM), trans-ferulic acid (IC50 = 13.51 μM), and chlorogenic acid (IC50 = 27.23 μM), and six AR inhibitors, namely, chlorogenic acid (IC50 = 4.2 μM), tectoridin (IC50 = 50.4 μM), genistein (IC50 = 57.1 μM), formononetin (IC50 = 69.2 μM), resveratrol (IC50 = 117.6 μM), and daidzein (IC50 = 151.9 μM), were isolated and identified. The screening results of the offline HPLC-ABTS assay and HPLC microfractionation AR assay matched the activity of isolated compounds. Thus, MA is potentially valuable for antioxidant and AR inhibitor discovery and efficient drug design for the prevention and treatment of diabetic complications.

Xanthium strumarium as an Inhibitor of α-Glucosidase, Protein Tyrosine Phosphatase 1β, Protein Glycation and ABTS+ for Diabetic and Its Complication

Phytochemical investigation of the natural products from Xanthium strumarium led to the isolation of fourteen compounds including seven caffeoylquinic acid (CQA) derivatives. The individual compounds were screened for inhibition of α-glucosidase, protein tyrosine phosphatase 1β (PTP1β), advanced glycation end products (AGEs), and ABTS+ radical scavenging activity using in vitro assays. Among the isolated compounds, methyl-3,5-di-caffeoyquinic acid exhibited significant inhibitory activity against α-glucosidase (18.42 μM), PTP1β (1.88 μM), AGEs (82.79 μM), and ABTS+ (6.03 μM). This effect was marked compared to that of the positive controls (acarbose 584.79 μM, sumarin 5.51 μM, aminoguanidine 1410.00 μM, and trolox 29.72 μM respectively). In addition, 3,5-di-O-CQA (88.14 μM) and protocatechuic acid (32.93 μM) had a considerable inhibitory effect against α-glucosidase and ABTS+. Based on these findings, methyl-3,5-di-caffeoyquinic acid was assumed to be potentially responsible for the anti-diabetic actions of X. strumarium.

Screening of Peruvian Medicinal Plants for Tyrosinase Inhibitory Properties: Identification of Tyrosinase Inhibitors in Hypericum laricifolium Juss

Tyrosinase inhibitors are of far-ranging importance in cosmetics, medicinal products, and food industries. Peru is a diverse country with a wide variety of plants that may contain excellent anti-tyrosinase inhibitors. In the present study, the tyrosinase inhibitory properties of 50 medicinal plant extracts from Peru were investigated using tyrosinase assay. Among plant extracts, those that showed an inhibition rate >50% were Hypericum laricifolium Juss., Taraxacum officinale F.H.Wigg., and Muehlenbeckia vulcanica Meisn., with H. laricifolium Juss. showing the greatest anti-tyrosinase activity. Although H. laricifolium Juss. has been widely used as a medicinal plant by Peruvians, little is known regarding its bioactive components and effects on tyrosinase activity. For this reason, we attempted to discover tyrosinase inhibitors in H. laricifolium Juss. for the first time. The bioactive components were separated by Sephadex LH-20 chromatography and eluted with 100% methanol. Eight compounds were discovered and characterized by high-performance liquid chromatography coupled with diode array detection (HPLC-DAD): protocatechuic acid, p-hydroxybenzoic acid, chlorogenic acid, vanilic acid, caffeic acid, kaempferol 3-O-glucuronide, quercetin, and kaempferol. In addition, the concentration of these compounds required for 50% inhibition (IC50) of tyrosinase activity were evaluated. Quercetin exhibited the strongest tyrosinase inhibition (IC50 14.29 ± 0.3 μM). Therefore, the Peruvian plant H. laricifolium Juss. could be a novel source for anti-tyrosinase activity.

Enzymatic Synthesis of a Novel Kaempferol-3-O-β-d-glucopyranosyl-(1→4)-O-α-d-glucopyranoside Using Cyclodextrin Glucanotransferase and Its Inhibitory Effects on Aldose Reductase, Inflammation, and Oxidative Stress

Kaempferol-3-O-β-d-glucopyranoside (astragalin, AS), a major flavonoid that exists in various plants, exerts antioxidant, antitumor, anti-human immunodeficiency virus (HIV), and anti-inflammatory effects. However, the low water solubility of AS limits its use. In this study, we used cyclodextrin glucanotransferase (CGTase) with maltose (G2) as a donor molecule to enzymatically modify AS to improve its water solubility and physiochemical properties. We isolated the glycosylated astragalin (G1-AS) and identified the structure of G1-AS as kaempferol-3-O-β-d-glucopyranosyl-(1→4)-O-α-d-glucopyranoside, where one glucose residue was transferred to AS. G1-AS retained the antioxidative activity of the original AS compound; however, the solubility of G1-AS was 65-fold higher than that of AS. In addition, G1-AS showed enhanced anti-inflammatory effects and aldose reductase inhibitory activity compared to AS when applied to rat lenses.