Eva-Maria Pferschy-Wenzig

Discovery and resupply of pharmacologically active plant-derived natural products: A review.

Medicinal plants have historically proven their value as a source of molecules with therapeutic potential, and nowadays still represent an important pool for the identification of novel drug leads. In the past decades, pharmaceutical industry focused mainly on libraries of synthetic compounds as drug discovery source. They are comparably easy to produce and resupply, and demonstrate good compatibility with established high throughput screening (HTS) platforms. However, at the same time there has been a declining trend in the number of new drugs reaching the market, raising renewed scientific interest in drug discovery from natural sources, despite of its known challenges. In this survey, a brief outline of historical development is provided together with a comprehensive overview of used approaches and recent developments relevant to plant-derived natural product drug discovery. Associated challenges and major strengths of natural product-based drug discovery are critically discussed. A snapshot of the advanced plant-derived natural products that are currently in actively recruiting clinical trials is also presented. Importantly, the transition of a natural compound from a “screening hit” through a “drug lead” to a “marketed drug” is associated with increasingly challenging demands for compound amount, which often cannot be met by re-isolation from the respective plant sources. In this regard, existing alternatives for resupply are also discussed, including different biotechnology approaches and total organic synthesis. While the intrinsic complexity of natural product-based drug discovery necessitates highly integrated interdisciplinary approaches, the reviewed scientific developments, recent technological advances, and research trends clearly indicate that natural products will be among the most important sources of new drugs also in the future.

Natural product agonists of peroxisome proliferator-activated receptor gamma (PPARγ): a review.

Graphical abstract

Identification of Isosilybin A from Milk Thistle Seeds as an Agonist of Peroxisome Proliferator-Activated Receptor Gamma

Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of glucose and lipid metabolism. Agonists of this nuclear receptor are used in the treatment of type 2 diabetes and are also studied as a potential treatment of other metabolic diseases, including nonalcoholic fatty liver disease. Silymarin, a concentrated phenolic mixture from milk thistle (Silybum marianum) seeds, is used widely as a supportive agent in the treatment of a variety of liver diseases. In this study, the PPARγ activation potential of silymarin and its main constituents was investigated. Isosilybin A (3) caused transactivation of a PPARγ-dependent luciferase reporter in a concentration-dependent manner. This effect could be reversed upon co-treatment with the PPARγ antagonist T0070907. In silico docking studies suggested a binding mode for 3 distinct from that of the inactive silymarin constituents, with one additional hydrogen bond to Ser342 in the entrance region of the ligand-binding domain of the receptor. Hence, isosilybin A (3) has been identified as the first flavonolignan PPARγ agonist, suggesting its further investigation as a modulator of this nuclear receptor.

Characterization and identification of mycosporines-like compounds in cyanolichens. Isolation of mycosporine hydroxyglutamicol from Nephroma laevigatum Ach.

Mycosporine-like compounds, comprising mycosporines and mycosporine-like amino acids (MAAs) are UV protecting secondary metabolites described in organisms such as fungi, algae, cyanobacteria or animals. Lichens however, were only poorly investigated for such constituents so far. Here, a method for the characterization of mycosporines and MAAs in purified aqueous extracts, involving HPTLC coupled to spectrophotodensitometry, HPLC-DAD-MS(n) and UPLC-HRMS analysis, is described. This optimized protocol was validated on three algae and one cyanolichen containing known MAAs and mycosporines, and then applied to 18 cyanolichen species. Analyses revealed the presence of five already described mycosporine-like compounds in the investigated species, including mycosporine serinol in Lichina and Peltigera species and mycosporine glutamicol in Degelia plumbea. Apart from that, eight unknown mycosporine-like compounds were detected and tentatively characterized on the basis of their DAD spectra and their MS(n) and HRMS data: two in the alga Porphyra dioica and six in cyanolichen species belonging to the genera Degelia, Nephroma and Stereocaulon. From Nephroma laevigatum, the mycosporine hydroxyglutamicol was preparatively isolated and identified through HRMS, 1D and 2D NMR spectroscopic data. The optimized analytical protocol allowed the characterization of mycosporine-like compounds in small amounts of material and confirmed the potential of cyanolichens as a source of mycosporine compounds. It should also be applicable to investigate lichen species with green algae photobionts for mycosporine-like compounds.

Does a Graphical Abstract Bring More Visibility to Your Paper

A graphical abstract (GA) represents a piece of artwork that is intended to summarize the main findings of an article for readers at a single glance. Many publishers currently encourage authors to supplement their articles with GAs, in the hope that such a convenient visual summary will facilitate readers with a clearer outline of papers that are of interest and will result in improved overall visibility of the respective publication. To test this assumption, we statistically compared publications with or without GA published in Molecules between March 2014 and March 2015 with regard to several output parameters reflecting visibility. Contrary to our expectations, manuscripts published without GA performed significantly better in terms of PDF downloads, abstract views, and total citations than manuscripts with GA. To the best of our knowledge, this is the first empirical study on the effectiveness of GA for attracting attention to scientific publications.

Inhibition of NO Production by Grindelia argentina and Isolation of Three New Cytotoxic Saponins

A bioassay‐guided phytochemical analysis of the ethanolic extract of Grindelia argentina Deble & Oliveira‐Deble (Asteraceae) allowed the isolation of a known flavone, hispidulin, and three new oleanane‐type saponins, 3‐O‐β‐D‐xylopyranosyl‐(1→3)‐β‐D‐glucopyranosyl‐2β,3β,16α,23‐tetrahydroxyolean‐12‐en‐28‐oic acid 28‐O‐β‐D‐xylopyranosyl‐(1→2)‐β‐D‐apiofuranosyl‐(1→3)‐β‐D‐xylopyranosyl‐(1→3)‐α‐L‐rhamnopyranosyl‐(1→2)‐α‐L‐arabinopyranosyl ester (2), 3‐O‐β‐D‐glucopyranosyl‐2β,3β,23‐trihydroxyolean‐12‐en‐28‐oic acid 28‐O‐β‐D‐xylopyranosyl‐(1→2)‐β‐D‐apiofuranosyl‐(1→3)‐β‐D‐xylopyranosyl‐(1→3)‐α‐L‐rhamnopyranosyl‐(1→2)‐α‐L‐arabinopyranosyl ester, (3) and 3‐O‐β‐D‐xylopyranosyl‐(1→3)‐β‐D‐glucopyranosyl‐2β,3β,23‐trihydroxyolean‐12‐en‐28‐oic acid 28‐O‐β‐D‐xylopyranosyl‐(1→2)‐β‐D‐apiofuranosyl‐(1→3)‐β‐D‐xylopyranosyl‐(1→3)‐α‐L‐rhamnopyranosyl‐(1→2)‐α‐L‐arabinopyranosyl ester (4), named grindeliosides A–C, respectively. Their structures were determined by extensive 1D‐ and 2D‐NMR experiments along with mass spectrometry and chemical evidence. The isolated compounds were evaluated for their inhibitory activities against LPS/IFN‐γ‐induced NO production in RAW 264.7 macrophages and for their cytotoxic activities against the human leukemic cell line CCRF‐CEM and MRC‐5 lung fibroblasts. Hispidulin markedly reduced LPS/IFN‐γ‐induced NO production (IC50 51.4 μM), while grindeliosides A–C were found to be cytotoxic, with grindelioside C being the most active against both CCRF‐CEM (IC50 4.2±0.1 μM) and MRC‐5 (IC50 4.5±0.1 μM) cell lines.

A Combined LC-MS Metabolomics- and 16S rRNA Sequencing Platform to Assess Interactions between Herbal Medicinal Products and Human Gut Bacteria in Vitro: a Pilot Study on Willow Bark Extract

Herbal preparations are complex mixtures of natural products, many of which are able to reach the distal gut due to low oral bioavailability. There, they can influence the microbial communities, and can be metabolized into potentially absorbable bioactive compounds by the intestinal bacteria. This aspect has often been disregarded when searching for the active principles of medicinal plants and herbal medicinal products. The aim of this study was to establish an interdisciplinary platform to unravel interactions of herbal medicine and intestinal microbiota, using a combined LC-MS metabolomics and 16S rRNA microbiome sequencing approach. Willow bark extract (WBE), a herbal medicinal product with a long history of traditional use and a well-established anti-inflammatory activity, was incubated with human fecal suspension under anoxic conditions. Samples were taken after 0.5, 4, and 24 h of incubation. Microbiome analyses revealed that incubation with WBE had a marked effect on microbial community composition and functions. For example, the proportion of Bacteroides sp. was clearly enhanced when the fecal sample used in this study was incubated with WBE. LC-MS analysis showed that WBE constituents were readily metabolized by fecal bacteria. Numerous microbial metabolites could be annotated, allowing the construction of putative microbial degradation pathways for the main groups of WBE constituents. We suggest that studies of this type help to increase the knowledge on bioactive principles of medicinal plants, since gut microbial metabolites might have been underestimated as a source of bioactive compounds in the past.

In Vitro Antileishmanial Activity of Sterols from Trametes versicolor (Bres. Rivarden).

Two ergostanes, 5α,8α-epidioxy-22E-ergosta-6,22-dien-3β-ol (1) and 5α-ergost-7,22-dien-3β-ol (2), and a lanostane, 3β-hydroxylanostan-8,24-diene-21-oic acid (trametenolic acid) (3), were isolated from an n-hexane extract prepared from the fruiting body of Trametes versicolor (Bres. Rivarden). The activity of the isolated sterols was evaluated against promastigotes and amastigotes of Leishmania amazonensis Lainson and Shaw, 1972. The lanostane, compound (3), showed the best inhibitory response (IC50 promastigotes 2.9 ± 0.1 μM and IC50 amastigotes 1.6 ± 0.1 μM). This effect was 25-fold higher compared with its cytotoxic effect on peritoneal macrophages from BALB/c mice. Therefore, trametenolic acid could be regarded as a promising lead for the synthesis of compounds with antileishmanial activity.

Antiproliferative Carvotacetones from Sphaeranthus africanus

Five carvotacetone derivatives, including two known ones, 3,5-diangeloyloxy-7-hydroxycarvotacetone (1) and 3-angeloyloxy-5-[2″,3″-epoxy-2″-methylbutanoyloxy]-7-hydroxycarvotacetone (2), along with three new compounds, 3-angeloyloxy-5-[3″-chloro-2″-hydroxy-2″-methylbutanoyloxy]-7-hydroxycarvotacetone (3), 5-angeloyloxy-7-hydroxy-3-tigloyloxycarvotacetone (4), and 3-angeloyloxy-5,7-dihydroxycarvotacetone (5), were isolated from the aerial parts of Sphaeranthus africanus collected in Vietnam. Bioassay-guided fractionation was monitored by the antiproliferative activity on CCRF-CEM human cancer cells. The structures of compounds 1-5 were determined on the basis of NMR spectroscopic and mass spectrometric data. Activities of compounds 1-5 were evaluated in vitro against the human cancer cell lines CCRF-CEM, MDA-MB-231, U-251, and HCT-116. All compounds exhibited significant antiproliferative activity against all four cancer cell lines. CCRF-CEM was most sensitive to the compounds, with IC50 values ranging from 0.6 to 1.5 μM. Compounds 3 and 4 possessed the highest activity, with IC50 values in the four cell lines ranging from 0.6 to 2.9 μM and 1.3 to 2.5 μM, respectively. These compounds also showed inhibitory activity toward the HEK-293 human embryonic kidney cells with IC50 values ranging from 2.5 to 5.5 μM. This is the first time that antiproliferative activity of S. africanus has been reported, and 1-5 are the most cytotoxic carvotacetone derivatives reported so far.

Phytochemical analysis and anti-inflammatory effects of Filipendula vulgaris Moench extracts

Filipendula vulgaris Moench (dropwort) is used in traditional medicine for relieving various inflammation-related diseases. In the present study, the phytochemical profile of F. vulgaris aerial part (FVA) and root (FVR) methanolic extracts was evaluated by LC-DAD-HRMS analysis. Furthermore, their in vitro and in vivo anti-inflammatory effects, as well as their potential cytotoxicity, were assessed. Results showed that the extracts mainly contain phenolics like flavonoids, hydrolyzable tannins, procyanidins, and phenolic acid derivatives, including gaultherin. No in vitro cytotoxicity was found at the highest concentration (50 μg/mL). FVA extract (50 μg/mL) significantly inhibited cyclooxygenase-1 and -2 (COX-1 and COX-2) activities in vitro (>50% inhibition), and FVR extract considerably inhibited COX-2 activity (52.5 ± 2.7%) without affecting COX-2 gene expression in LPS-stimulated THP-1 cells. The extracts demonstrated prominent in vivo anti-inflammatory potential upon oral administration in rats. Especially FVA extract at 100 and 200 mg/kg significantly inhibited carrageenan-induced edema formation. From these results, it can be concluded that F. vulgaris extracts possess interesting anti-inflammatory properties.