Flavonoids and hERG channels: Friends or foes?

The cardiac action potential is regulated by several ion channels. Drugs capable to block these channels, in particular the human ether-à-go-go-related gene (hERG) channel, also known as K_V11.1 channel, may lead to a potentially lethal ventricular tachyarrhythmia called "Torsades de Pointes". Thus, evaluation of the hERG channel off-target activity of novel chemical entities is nowadays required to safeguard patients as well as to avoid attrition in drug development. Flavonoids, a large class of natural compounds abundantly present in food, beverages, herbal medicines, and dietary food supplements, generally escape this assessment, though consumed in consistent amounts. Continuously growing evidence indicates that these compounds may interact with the hERG channel and block it. The present review, by examining numerous studies, summarizes the state-of-the-art in this field, describing the most significant examples of direct and indirect inhibition of the hERG channel current operated by flavonoids. A description of the molecular interactions between a few of these natural molecules and the Rattus norvegicus channel protein, achieved by an in silico approach, is also presented.

Hispidulin, a constituent of Clerodendrum inerme that remitted motor tics, alleviated methamphetamine-induced hyperlocomotion without motor impairment in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Previously, we found a patient with an intractable motor tic disorder that could be ameliorated by the ground leaf juice of Clerodendrum inerme (CI). Furthermore, the ethanol extract of CI leaves effectively ameliorated methamphetamine-induced hyperlocomotion (MIH) in mice, an animal model mimicking the hyper-dopaminergic status of tic disorders/Tourette syndrome, schizophrenia, or obsessive-compulsive disorder. Here, we for the first time identified a constituent able to reduce MIH from the CI ethanol extract that might represent a novel lead for the treatment of such disorders.

MATERIALS AND METHODS

The ethanol extract of CI was sub-divided into n-hexane, dichloromethane, n-butanol and water fractions. Using MIH alleviation as a bioassay, active compounds were identified in these fractions using silica gel chromatography, recrystallization and proton NMR spectroscopy.

RESULTS

The dichloromethane and n-hexane fractions were active in the bioassay. Further subfractionation and re-crystallization resulted in an active compound that was identified to be hispidulin by proton NMR spectroscopy. Hispidulin significantly alleviated MIH in mice at doses that did not affect their spontaneous locomotor activity or performance in the rotarod test, a measure for motor coordination.

CONCLUSIONS

Hispidulin is a flavonoid that has been isolated from several plants and reported to have anti-oxidative, anti-inflammatory and anti-cancer activities. Here, we for the very first time found that hispidulin can also alleviate MIH at doses that did not impair motor activity, suggesting a therapeutic potential of hispidulin in hyper-dopaminergic disorders.

Bioassay-guided isolation and mechanistic action of anti-inflammatory agents from Clerodendrum inerme leaves

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves of Clerodendrum inerme (L.) Gaertn. have commonly been used in Thai traditional medicine for treatment of inflammatory diseases. However, the bioactive compounds responsible for the anti-inflammatory effect of leaves have not been yet determined. The objective of the present study was to isolate these bioactive compounds by bioassay-guided isolation technique and to determine the mode of action of isolated compounds in LPS-induced macrophages.

MATERIALS AND METHODS

Anti-inflammatory effect of various fractions (hexane, ethyl acetate and water) of ethanol extract of C. inerme leaves was determined from the production of nitric oxide (NO) in RAW 264.7 macrophage stimulated with LPS. The mRNA and protein levels were determined also by real-time reverse transcription-polymerase chain reaction and western blot analysis, respectively. Leaf bioactive compounds were isolated by bioassay-guided fractionation technique using column chromatography.

RESULTS

The ethyl acetate fraction (EA) among solvent extracts provided the most potent inhibitory activity on NO production. Also, EA reduced the mRNA and protein expressions of inducible nitric oxide synthase (iNOS) in LPS-stimulated macrophages. Three known flavones, acacetin (1), hispidulin (2) and diosmetin (3), were isolated based on inhibition of NO production. Furthermore, hispidulin also inhibited PGE2 production as well as iNOS and cyclooxygenase-2 expressions via the blockade of NF-κB DNA-binding activity and JNKway.

CONCLUSIONS

Our results found acacetin (1), hispidulin (2) and diosmetin (3), were responsible for the anti-inflammatory properties of C. inerme leaves. We provide scientific evidence to support the usefulness of C. inerme leaves in traditional medicine for the treatment of inflammation-related diseases.