Identification of caffeoylquinic acid derivatives as natural protein tyrosine phosphatase 1B inhibitors from Artemisia princeps.

Considerable attention has been paid to protein tyrosine phosphatase 1B (PTP1B) inhibitors as a potential therapy for diabetes, obesity, and cancer. Ten caffeoylquinic acid derivatives (1-10) from leaves of Artemisia princeps Pamp. (Asteraceae) were identified as natural PTP1B inhibitors. Among them, chlorogenic acid (3) showed the most potent inhibitory activity (IC50 11.1 µM). Compound 3 was demonstrated to be a noncompetitive inhibitor by a kinetic analysis. Molecular docking simulation suggested that compound 3 bound to the allosteric site of PTP1B. Furthermore, compound 3 showed remarkable selectivity against four homologous PTPs. According to these findings, compound 3 might be potentially valuable for further drug development.

Identification of flavonolignans from Silybum marianum seeds as allosteric protein tyrosine phosphatase 1B inhibitors.

Protein tyrosine phosphatase 1B (PTP1B) is an attractive molecular target for anti-diabetes, anti-obesity, and anti-cancer drug development. From the seeds of Silybum marianum, nine flavonolignans, namely, silybins A, B (1, 2), isosilybins A, B (3, 4), silychristins A, B (5, 6), isosilychristin A (7), dehydrosilychristin A (8), and silydianin (11) were identified as a novel class of natural PTP1B inhibitors (IC50 1.3 7-23.87 µM). Analysis of structure-activity relationship suggested that the absolute configurations at C-7" and C-8" greatly affected the PTP1B inhibitory activity. Compounds 1-5 were demonstrated to be non-competitive inhibitors of PTP1B based on kinetic analyses. Molecular docking simulations resulted that 1-5 docked into the allosteric site, including α3, α6, and α7 helix of PTP1B. At a concentration inhibiting PTP1B completely, compounds 1-5 moderately inhibited VHR and SHP-2, and weakly inhibited TCPTP and SHP-1. These results suggested the potentiality of these PTP1B inhibitors as lead compounds for further drug developments.

Evaluation of canthinone alkaloids as cerebral protective agents.

Considerable attention has been paid to cerebral protective drugs as a potential therapy for dementia. Screening of a natural compound library here resulted in identification of five canthinone alkaloids, viz., picrasidine L (1), picrasidine O (2), eurycomine E (3), 3-ethyl-canthin-5,6-dione (4), and 3-ethyl-4-methoxy-canthin-5,6-dione (5), as novel cerebral protective agents. The structure-activity relationship indicated that C-4, C-9, and N-3 substitutions greatly affected their cerebral protective effect. Among these, compound 2 exhibited a cerebral protective effect through suppressing neuronal hyperexcitability due to an increase in the excitatory neurotransmitter glutamic acid. Furthermore, compound 2 did not affect heart rate and mean systolic blood pressure. This investigation suggests that compound 2 has potential for further development as a cerebral protective drug.

Picrasidine N Is a Subtype-Selective PPARß/δ Agonist.

Recently, growing evidence of the pivotal roles of peroxisome proliferator-activated receptor (PPAR) ß/δ in various physiological functions, including lipid homeostasis, cancer, and inflammation, has raised interest in this receptor. In this study, the naturally occurring dimeric alkaloid picrasidine N (1) from Picrasma quassioides was identified as a novel PPARß/δ agonist from a library consisting of plant extracts and natural compounds using a mammalian one-hybrid assay, and this compound was characterized. Compound 1 activated PPARß/δ but did not activate or slightly activated PPARα and PPARγ. Furthermore, a peroxisome proliferator response element-driven luciferase reporter gene assay demonstrated that 1 enhanced PPARß/δ transcriptional activity. Moreover, 1 selectively induced mRNA expression of ANGPTL4, which is a PPAR target gene. This observation is quite different from previously identified synthetic PPARß/δ agonists, which can induce the expression of not only ANGPTL4 but also other PPAR target genes, such as ADRP, PDK4, and CPT-1. These results demonstrate that 1 is a potent subtype-selective and gene-selective PPARß/δ agonist, suggesting its potential as a lead compound for further drug development. This compound would also be a useful chemical tool for elucidating the mechanism of PPARß/δ-regulated specific gene expression and the biological significance of PPARß/δ.

Identification of Picrasidine C as a Subtype-Selective PPARα Agonist.

Picrasidine C (1), a dimeric ß-carboline-type alkaloid isolated from the root of Picrasma quassioides, was identified to have PPARα agonistic activity by a mammalian one-hybrid assay from a compound library. Among the PPAR subtypes, 1 selectively activated PPARα in a concentration-dependent manner. Remarkably, 1 also promoted PPARα transcriptional activity by a peroxisome proliferator response element-driven luciferase reporter assay. Furthermore, 1 induced the expression of PPARα-regulated genes involved in lipid, glucose, and cholesterol metabolism, such as CPT-1, PPARα, PDK4, and ABCA1, which was abrogated by the PPARα antagonist MK-886, indicating that the effect of 1 was dependent on PPARα activation. This is the first report to demonstrate 1 to be a subtype-selective PPARα agonist with potential application in treating metabolic diseases, such as hyperlipidemia, atherosclerosis, and hypercholesterolemia.

Canthinone alkaloids are novel protein tyrosine phosphatase 1B inhibitors.

Considerable attention has been paid to protein tyrosine phosphatase 1B (PTP1B) inhibitors as a potential therapy for diabetes. Screening of a natural compound library resulted in six canthinone alkaloids, namely, picrasidine L (1), 3,4-dimethyl-canthin-5,6-dione (2), 4-ethyl-3-methyl-canthin-5,6-dione (3), eurycomine E (4), 5-methoxy-canthin-6-one (5), and 5-acethoxy-canthin-6-one (6), as novel PTP1B inhibitors. Among these, 1 is the competitive PTP1B inhibitor with the best inhibitory selectivity between PTP1B and other PTPs and was shown to promote activity in the insulin signaling pathway in cell-based assays. Molecular docking simulations and structure-activity relationship analysis of 1 will add to its potential as a lead compound in future anti-insulin-resistant drug developments.

Protein tyrosine phosphatase 1B inhibitory activity of lavandulyl flavonoids from roots of Sophora flavescens.

Protein tyrosine phosphatase 1B is a non-transmembrane protein tyrosine phosphatase and major negative regulator in insulin signaling cascades, and much attention has been paid to protein tyrosine phosphatase 1B inhibitors as potential therapies for diabetes. The screening of a natural compound library led to the discovery of five lavandulyl flavonoids, which were isolated from the roots of Sophora flavescens, as novel PTP1B inhibitors: kuraridin (1), norkurarinone (2), kurarinone (3), 2'-methoxykurarinone (4), and kushenol T (5). The three most potent compounds, 1, 2, and 4 (IC50 < 30 µM), were demonstrated to be noncompetitive inhibitors of protein tyrosine phosphatase 1B based on a kinetic analysis, and they exhibited different inhibitory selectivities against four homologous protein tyrosine phosphatases (T cell protein tyrosine phosphatase, vaccinia H1-related phosphatase, and Src homology domain 2-containing protein tyrosine phosphatases 1 and 2). Compounds 1, 2, and 4 also exhibited cellular activity in the insulin signaling pathway by increasing the insulin-stimulated Akt phosphorylation level in human hepatocellular liver carcinoma HepG2 cells, suggesting their potential for new anti-insulin-resistant drug developments.

Evaluation of licorice flavonoids as protein tyrosine phosphatase 1B inhibitors.

Protein tyrosine phosphatase 1B (PTP1B) is a major negative regulator in insulin- and leptin-signaling cascades as well as a positive regulator in tumorigenesis, and much attention has been paid to PTP1B inhibitors as potential therapies for diabetes, obesity, and cancer. In the present study, the screening of a compound library of licorice flavonoids allowed for the discovery of several compounds, including licoagrone (3), licoagrodin (4), licoagroaurone (5), and isobavachalcone (6), as new PTP1B inhibitors. It was revealed that these compounds inhibit the activity of PTP1B in different modes and with different selectivities and that they exhibit different cellular activity in the insulin-signaling pathway. Glycybenzofuran (1), a competitive PTP1B inhibitor, showed both excellent inhibitory selectivity against PTP1B and cellular activity on the insulin-stimulated Akt phosphorylation level. The similarity of its action profiling in the insulin-signaling pathway suggested its potential as a new anti-insulin-resistant drug candidate.

Secoiridoid glucosides and related compounds from Syringa reticulata and their antioxidant activities.

A 70% EtOH extract from the bark of Syringareticulata has shown significant antioxidant activity. Chemical study on the extract resulted in the isolation of seventeen compounds (1-17), including a novel oleoside-type secoiridoid glucoside, reticuloside (1), and the structures were elucidated on the basis of extensive spectroscopic analyses. Among the isolated compounds, jaspolyoside (2), oleuropein (4) and 2-(3,4-dihydroxy)-phenylethyl-ß-d-glucopyranoside (17), showed the most potent superoxide anion scavenging activity with the EC(50) values of 4.97, 2.57 and 4.97µM, respectively. The structure-activity relationship indicated that the presence of 2-(3,4-dihydroxyphenyl)-ethoxy group is important for exhibiting the activity.

Chemical constituents from Sambucus adnata and their protein-tyrosine phosphatase 1B inhibitory activities.

The MeOH extract from the whole plants of Sambucus adnata has shown significant protein-tyrosine phosphatase 1B (PTP1B) inhibitory activity. Chemical study on the extract resulted in the isolation of thirteen compounds, including a novel triterpene (1). The structure of 1 was determined to be 1α,3ß-dihydroxy-urs-12-en-11-one-3-yl palmitate on the basis of extensive spectroscopic analyses. Among the isolated compounds, ursolic acid, oleanolic acid and (±)-boehmenan showed the most potent PTP1B inhibitory activity in vitro with the IC(50) values of 4.1, 14.4 and 43.5 µm, respectively. The kinetic analysis indicated that (±)-boehmenan inhibits PTP1B activity in a competitive manner.

Two novel steroidal alkaloid glycosides from the seeds of Lycium barbarum.

Two novel steroidal alkaloid glycosides, lycioside A (1) and lycioside B (2) were isolated from the seeds of Lycium barbarum. Their structures were determined by various spectroscopic analyses. Compounds 1 and 2 showed inhibitory activities with the IC(50) values of 75.3 and 72.8 µM against rat intestinal sucrase, and 63.4 and 59.1 µM against rat intestinal maltase.

Triterpenoid saponins from Rubus ellipticus var. obcordatus.

Ten new triterpenoid saponins (1-10), named rubusides A-J, and 21 known saponins (11-31) were isolated from the roots of Rubus ellipticus var. obcordatus. The structures of 1-10 were established on the basis of spectroscopic analyses, mainly NMR and MS, and chemical degradations. The compounds demonstrated inhibitory activities against alpha-glucosidase with IC50 values in the range 0.65-3.09 mM.

Isolation, Structural Elucidation, and Liquid Chromatography-Mass Spectrometry Analysis of Steroidal Glycosides from Polygonatum odoratum.

The rhizomes of Polygonatum odoratum represent a traditional Chinese medicine and functional food. A phytochemical investigation resulted in the isolation of eight steroidal glycosides (1-8), including two new compounds, polygonatumosides F (1) and G (2). The structures were elucidated by spectroscopic data and chemical reactions. Compound 7 showed antiproliferation activity against human hepatocellular carcinoma cell line HepG2 (IC50 of 3.2 µM). The chemical profile and contents of steroidal glycosides of P. odoratum rhizomes collected at different dates and geographical locations were also investigated, indicating that the rational harvest of P. odoratum in spring and autumn is preferable to obtain higher levels of steroidal glycosides. Compounds 1 and 7 showed the highest contents in all P. odoratum samples and have potential to serve as chemotaxonomic and chemical markers for quality control of this important plant material. 14-Hydroxylation may be a key step for the biosynthesis of compounds 1-7.

Identification and evaluation of magnolol and chrysophanol as the principle protein tyrosine phosphatase-1B inhibitory compounds in a Kampo medicine, Masiningan.

ETHNOPHARMACOLOGICAL RELEVANCE: Masiningan is a traditional medicine consisting of six crude drugs that have been used for treating constipation and diabetes mellitus in both Japan and China. Masiningan has been reported to have significant PTP1B inhibitory activity and to affect cells in the insulin-signaling pathway. The aim of the present study is to identify the PTP1B inhibitory compounds in Masiningan. MATERIALS AND METHODS: Bioactivity peaks were identified by analytical HPLC profiling and PTP1B inhibitory activity profiling of sub-fractions from Masiningan extract. The bioactive compounds were isolated by tracking two identified bioactive peaks, and the chemical structures were determined by spectroscopic analyses. The bioactive compounds were further investigated for their inhibitory effect against PTP1B by enzymatic kinetic analysis, molecular docking simulation, inhibitory selectivity against other PTPs, and cellular activity in the insulin signal transduction pathway. RESULTS: From Masiningan, magnolol (1) and chrysophanol (2) were isolated as compounds that exhibited significant dose-dependent inhibitory activities against PTP1B, with IC50 values of 24.6 and 12.3µM, respectively. Kinetic analysis revealed that 1 is a non-competitive and that 2 is a competitive PTP1B inhibitor. In the molecular docking simulation, compound 2 was stably positioned in the active pocket of PTP1B, and the CDOCKER energy was calculated to be 24.3411kcal/mol. Both compounds demonstrated remarkably high selectivity against four PTPs and revealed cellular activity against the insulin signal transduction pathway. CONCLUSIONS: Magnolol (1) and chrysophanol (2) were identified as the principle PTP1B inhibitory active compounds in Masiningan, and their actions were investigated in detail. These findings demonstrated the effectiveness of Masiningan on diabetes mellitus through the inhibition of PTP1B at a molecular level as well as the potential of magnolol (1) and chrysophanol (2) as lead compounds in future anti-diabetes drug development.

A new flavonoid glycoside and other chemical constituents from leaves of Rosa davurica and their antioxidant activity.

A 70% ethanol extract from the leaves of Rosa davurica showed significant antioxidant activity in both superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging assays. Phytochemical study of this extract resulted in the isolation of eight compounds, including a new flavonoid glycoside. The chemical structure was determined by various spectroscopic analyses. The isolated compounds and their structurally related compounds, belonging to two classes: quercetin 3-O-glycosides and gallic acid derivates, were evaluated for their superoxide anion- and DPPH free radical-scavenging activities. These compounds showed significant superoxide anion-scavenging activity with the EC50 values ranging from 1.68 to 18.09 µM, and DPPH free radical-scavenging activity with the EC50 values ranging from 7.18 to 67.62 µM. The structure-activity relationship was also reported.

Antioxidant lignoids from leaves of Ribes nigrum.

Phytochemical investigation of the leaves of Ribes nigrum resulted in the isolation of fourteen compounds, including four 7,7'-epoxylignans, three tetrahydrofuran-type sesquilignans, and a spirocyclic dilignan. Their structures were elucidated by extensive spectroscopic analyses and by chemical transformations. The isolated compounds were evaluated for their antioxidant activities using superoxide anion scavenging assay and DPPH free radical scavenging assay. Ribesin D and ribesin G showed the most potent superoxide anion scavenging activity with EC50 values of 1.24 and 1.12 µM, respectively, and the structure-activity relationship was discussed.

Juglanone, a novel α-tetralonyl derivative with potent antioxidant activity from Juglans mandshurica.

A novel alpha-tetralonyl derivative, juglanone, was isolated from the fresh unripe fruits of Juglans mandshurica. Its structure was determined by spectroscopic analyses and from chemical evidence. Juglanone exhibited significant antioxidant activity in assays for 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and superoxide dismutase-like activity with IC(50) values of 10.1 and 9.0 microM, respectively. It also showed moderate cytotoxic activity against HL-60 human myeloid leukemia with an IC(50) value of 19.7 microM.