hERG Channel Blocking Ipecac Alkaloids Identified by Combined In Silico - In Vitro Screening.

Human ether-a-go-go-related gene channel blocking is associated with QT interval prolongation and increased risk of potentially fatal arrhythmias. As natural products keep increasing in popularity, there is an urgent need for studies assessing human ether-a-go-go-related gene channel-related cardiotoxic risks. We selected 49 plant species based on the results of a pharmacophore-based virtual screening campaign, in parallel with a literature data survey concerning highly consumed herbal medicines with reported cardiac liabilities. Lead-like enhanced extracts were prepared, an initial in vitro screening was performed at 100 µg/mL by voltage clamp on Xenopus oocytes, and five human ether-a-go-go-related gene channel blocking extracts were identified. In accordance to the six virtually predicted alkaloids, the root extract of Carapichea ipecacuanha inhibited human ether-a-go-go-related gene channel currents by 32.5 %. A phytochemical workflow resulted in the isolation and identification of five out of the six virtually predicted alkaloids. All isolates blocked human ether-a-go-go-related gene channel currents to different extents. The major ipecac constituents emetine (1) and cephaeline (2) showed IC50 values of 21.4 and 5.3 µM, respectively, measured by whole-cell patch clamp in HEK293 cells. This is the first report on human ether-a-go-go-related gene channel blockers from C. ipecacuanha. Its roots and rhizomes are used to produce different pharmacopeial ipecac preparations that are mainly used as emetics for poisoning treatment. Our findings raise further questions regarding the safety and over-the-counter appropriateness of these herbal products.

Dereplication of depsides from the lichen Pseudevernia furfuracea by centrifugal partition chromatography combined to 13C nuclear magnetic resonance pattern recognition.

Lichens produce a diversity of secondary metabolites, among them depsides comprised of two or more hydroxybenzoic acid units linked by ester, ether, or CC-bonds. During classic solid support-based purification processes, depsides are often hydrolyzed and in many cases time, consuming procedures result only in the isolation of decomposition products. In an attempt to avoid extensive purification steps while maintaining metabolite structure integrity, we propose an alternative method to identify the major depsides of a lichen crude extract (Pseudevernia furfuracea var. ceratea (Ach.) D. Hawksw., Parmeliaceae) directly within mixtures. Exploiting the acidic character of depsides and differences in polarity, the extract was fractionated by centrifugal partition chromatography in the pH-zone refining mode resulting in twelve simplified mixtures of depsides. After (13)C nuclear magnetic resonance analysis of the produced fractions, the major molecular structures were directly identified within the fraction series by using a recently developed pattern recognition method, which combines spectral data alignment and hierarchical clustering analysis. The obtained clusters of (13)C chemical shifts were assigned to their corresponding molecular structures with the help of an in-house (13)C NMR chemical shift database, resulting in six unambiguously identified compounds, namely methyl ß-orcinolcarboxylate (1), atranorin (2), 5-chloroatranorin (3), olivetol carboxylic acid (4), olivetoric acid (5), and olivetonide (6).

Imbricaric acid and perlatolic acid: multi-targeting anti-inflammatory depsides from Cetrelia monachorum.

In vitro screening of 17 Alpine lichen species for their inhibitory activity against 5-lipoxygenase, microsomal prostaglandin E2 synthase-1 and nuclear factor kappa B revealed Cetrelia monachorum (Zahlbr.) W.L. Culb. & C.F. Culb. As conceivable source for novel anti-inflammatory compounds. Phytochemical investigation of the ethanolic crude extract resulted in the isolation and identification of 11 constituents, belonging to depsides and derivatives of orsellinic acid, olivetolic acid and olivetol. The two depsides imbricaric acid (4) and perlatolic acid (5) approved dual inhibitory activities on microsomal prostaglandin E2 synthase-1 (IC50 = 1.9 and 0.4 µM, resp.) and on 5-lipoxygenase tested in a cell-based assay (IC50 = 5.3 and 1.8 µM, resp.) and on purified enzyme (IC50 = 3.5 and 0.4 µM, resp.). Additionally, these two main constituents quantified in the extract with 15.22% (4) and 9.10% (5) showed significant inhibition of tumor necrosis factor alpha-induced nuclear factor kappa B activation in luciferase reporter cells with IC50 values of 2.0 and 7.0 µM, respectively. In a murine in vivo model of inflammation, 5 impaired the inflammatory, thioglycollate-induced recruitment of leukocytes to the peritoneum. The potent inhibitory effects on the three identified targets attest 4 and 5 a pronounced multi-target anti-inflammatory profile which warrants further investigation on their pharmacokinetics and in vivo efficacy.