Mechanisms of the vasorelaxant effect of 1-hydroxy-2, 3, 5-trimethoxy-xanthone, isolated from a Tibetan herb, Halenia elliptica, on rat coronary artery

Xanthones: Biosynthesis and Trafficking in Plants, Fungi and Lichens

Xanthones are a class of secondary metabolites produced by plant organisms. They are characterized by a wide structural variety and numerous biological activities that make them valuable metabolites for use in the pharmaceutical field. This review shows the current knowledge of the xanthone biosynthetic pathway with a focus on the precursors and the enzymes involved, as well as on the cellular and organ localization of xanthones in plants. Xanthone biosynthesis in plants involves the shikimate and the acetate pathways which originate in plastids and endoplasmic reticulum, respectively. The pathway continues following three alternative routes, two phenylalanine-dependent and one phenylalanine-independent. All three routes lead to the biosynthesis of 2,3',4,6-tetrahydroxybenzophenone, which is the central intermediate. Unlike plants, the xanthone core in fungi and lichens is wholly derived from polyketide. Although organs and tissues synthesizing and accumulating xanthones are known in plants, no information is yet available on their subcellular and cellular localization in fungi and lichens. This review highlights the studies published to date on xanthone biosynthesis and trafficking in plant organisms, from which it emerges that the mechanisms underlying their synthesis need to be further investigated in order to exploit them for application purposes.

Interaction effects on cytochrome P450 both in vitro and in vivo studies by two major bioactive xanthones from Halenia elliptica D. Don

The major components, 1-hydroxy-2,3,5-trimethoxy-xanthone (HM-1) and 1,5-dihydroxy-2,3-dimethoxy-xanthone (HM-5) isolated from Halenia elliptica D. Don (Gentianaceae), could cause vasodilatation in rat coronary artery with different mechanisms. In this work, high-performance liquid chromatography coupled to ion trap time-of-flight mass spectrometry (LCMS-IT-TOF) was used to clarify the metabolic pathways, and CYP450 isoform involvement of HM-1 and HM-5 were also studied in rat. At the same time, in vivo inhibition effects of HM-1 and ethyl acetate extracts from origin herb were studied. Three metabolites of HM-5 were found in rat liver microsomes (RLMs); demethylation and hydroxylation were the major phase I metabolic reactions for HM-5. Multiple CYP450s were involved in metabolism of HM-1 and HM-5. The inhibition study showed that HM-5 inhibited Cyp1a2, 2c6 and 2d2 in RLMs. HM-1 inhibited activities of Cyp1a2, Cyp2c6 and Cyp3a2. In vivo experiment demonstrated that both HM-1 and ethyl acetate extracts could inhibit Cyp3a2 in rats. In conclusion, the metabolism of xanthones from the origin herb involved multiple CYP450 isoforms; in vitro, metabolism of HM-5 was similar to that of its parent drug HM-1, but their inhibition effects upon CYP450s were different; in vivo, Cyp3a2 could be inhibited by HM-1 and ethyl acetate extracts.

Ethnopharmacological, chemical, and pharmacological aspects of Halenia elliptica: A comprehensive review

Traditional Tibetan medicine (TTM) is an old traditional medical system, which is an effective and natural method of improving physical and mental health, and has been widely spread in the western part of China for centuries. Halenia elliptica (H. elliptica) D. Don, known as "Jiadiranguo" (Tibetan medicine name) is one of the most important herbal medicine in TTM that is from the genus Halenia (family: Gentianaceae). The whole herb can be used as a medicine to treat hepatobiliary diseases and xeransis, and possesses many biological and pharmacological activities including heat clearing, bile benefiting, liver soothing, digestion promoting, blood nursing, detoxification activities, and so on. In modern research, H. elliptica can be used to treat acute or chronic hepatitis, especially hepatitis B. In addition, the chemical compounds of the herb have potent antihepatitis B virus (anti-HBV) activity in vitro. As an important TTM, further studies on H. elliptica can lead to the development of new drugs and therapeutics for various diseases, and more attention should be paid on the aspects of how to utilize it better.

Biofunctional studies of new 2-methoxyphenylpiperazine xanthone derivatives with α₁-adrenolytic properties

BACKGROUND

The aim of this study was to assess the selectivity of the studied xanthone derivatives for α1-adrenoceptor subtypes (α1A, α1B, α1D, α1L) in functional experiments in order to verify if they possess any selectivity for a distinct subtype of α1-adrenoceptor. Moreover, several pharmacological tests were carried out to assess whether they reveal other than α1-adrenoceptor blocking properties such as: antagonistic for 5-HT2 receptors, vasorelaxant or spasmolytic.

METHODS

The influence on α1A-adrenoceptors was examined in biofunctional studies employing isolated rat vas deferens, on α1B-adrenoceptors in guinea-pig spleen, on α1D-adrenoceptors in rat aorta, and on α1L-adrenoceptors in rabbit spleen. Affinity for 5-HT2 receptors was measured in radioligand binding assay, whereas antagonistic potency for 5-HT2 receptors was studied on isolated rat aorta. Vasorelaxant effect of tested compounds was assessed in functional study employing rat aorta, whereas direct spasmolytic activity was investigated using the isolated rabbit small intestine.

RESULTS

The present study provides evidences that the tested 2-methoxyphenylpiperazine xanthone derivatives are non-selective α1-adrenoceptor blockers. However, at higher concentrations the direct spasmolytic effect could enhance their hypotensive activity. The obtained results indicate that the studied xanthones possessed weak calcium entry blocking activity, as well as antagonistic properties for 5-HT2A receptors.

CONCLUSIONS

The results of the present study support the idea that the hypotensive activity of the studied compounds is related to their α1-adrenolytic properties.

Enzyme kinetic and molecular docking studies on the metabolic interactions of 1-hydroxy-2,3,5-trimethoxy-xanthone, isolated from Halenia elliptica D. Don, with model probe substrates of human cytochrome P450 enzymes

Halenia elliptica D. Don is a Tibetan herb and medicinal preparations containing Halenia elliptica have been commonly used for the treatment of hepatitis B virus infection in China. The metabolism of 1-hydroxy-2,3,5-trimethoxy-xanthone (HM-1) to its metabolites is mediated through cytochrome P450 enzymes. This study aimed to investigate the herb-drug interaction potential of HM-1 by studying its effects on the metabolism of model probe substrates of five major CYP450 isoforms in human liver microsomes. HM-1 showed moderate inhibitory effects on CYP1A2 (IC₅₀ = 1.06 μM) and CYP2C9 (IC₅₀ = 3.89 μM), minimal inhibition on CYP3A4 (IC₂₀ = 11.94 μM), but no inhibition on model CYP2D6 (dextromethorphan) and CYP2E1 (chlorzoxazone) probe substrates. Inhibition kinetic studies showed that the K(i) values of HM-1 on CYP1A2, CYP2C9 and CYP3A4 were 5.12 μM, 2.00 μM and 95.03 μM, respectively. HM-1 competitively inhibited testosterone 6β-hydroxylation (CYP3A4) but displayed mixed type inhibitions for phenacetin O-deethylation (CYP1A2) and tolbutamide 4-hydroxylation (CYP2C9). Molecular docking study confirmed the inhibition modes of HM-1 on these human CYP isoforms.

Chromone derivatives from Halenia elliptica and their anti-HBV activities

Nine water-soluble chromone derivatives, including chromone-2-carboxylic acids, 2-methylchromones and their structural hybrids, were isolated from aerial tissues of Halenia elliptica (Gentianaceae), six of which were previously unknown. Their structures were elucidated by comprehensive mass, 1D and 2D NMR spectroscopic analyses and chemical derivatization. Two unstable structural hybrids of chromone-2-carboxylic acids and 2-methylchromones, viz. 3-acetyl-8-hydroxy-4H-1-benzopyran-4-one-2-carboxylic acid (halenic acid C) and 2-(8-hydroxy-2-methyl-4H-1-benzopyran-4-one-3-yl)-2-oxoacetic acid (halenichromone A), were isomers and were interconvertible. The proposed mechanism of their acid-catalyzed isomerization in aqueous solvent is described. In addition, 2-methylchromones, 8-hydroxy-2-methyl-4H-1-benzopyran-4-one, and 8-methoxy-2-methyl-4H-1-benzopyran-4-one, were found to exhibit a strong inhibitory effect towards hepatitis B virus (HBV) in vitro without showing significant cytotoxicity.

Tibetan medicine: a unique heritage of person-centered medicine

With a history going back approximately 2,500 years, the Tibetan medicine, known as Sowa Rigpa in the Tibetan language, is one of the world’s oldest known traditional medicine. It originally developed during the pre-Buddhist era in the kingdom known as Shang Shung. As a traditional medicine, the future development of Tibetan medicine in Western countries is linked to being recognized as a popular and viable healthcare option providing an alternative clinical reality. Its inherent ability to incorparate predictive diagnostics, targeted prevention, and the creation of individualized medical treatment give Tibetan medicine great potential for assessing and treating patients.

Pentacyclic triterpenoids and ceramide mediate the vasorelaxant activity of Vitex cienkowskii via involvement of NO/cGMP pathway in isolated rat aortic rings

ETHNOPHARMACOLOGICAL RELEVANCE

Vitex cienkowskii Kotschy & Peyritsch is a deciduous tree, prescribed by Cameroonian traditional healers as one of the most popular plant widely used in many disorders including cardiovascular diseases. The preliminary pharmacological studies carried out on Vitex cienkowskii showed its vasorelaxant activities on guinea-pig aortic rings.

AIM OF THE STUDY

The present work evaluated the vasorelaxant activity of extract and isolated compounds from Vitex cienkowskii.

MATERIALS AND METHODS

Rat aortic rings were used to evaluate the in vitro vascular effect of the extract. The antioxidant activity was determined by measuring the reduction of the free radical 1,1-diphenyl-1-picryl-hydrazyl (DPPH).

RESULTS

Vitex cienkowskii induced significant relaxation in a concentration- and endothelium-dependent manner (EC(50)=12.12 μg/ml, CH(2)Cl(2)-MeOH, 1:1) and did not produce a vasorelaxant effect on contraction evoked by KCl (60 mM). In order to determine its mode of action, Vitex cienkowskii-induced relaxant effect was evaluated in the presence of indomethacin (10 μM), L-NAME (100 μM), ODQ (1 μM) and SQ22356 (100 μM). Relaxation was significantly blocked by L-NAME and ODQ. These results indicate that Vitex cienkowskii-mediated relaxation is endothelium dependent, probably due to NO release, and the consequent activation of vascular smooth muscle soluble guanylate cyclase (sGC), a signal transduction enzyme that forms the second messenger cGMP. Bio-guided study of Vitex cienkowskii allowed the isolation of the known pentacyclic triterpenoids and a ceramide. It is the first report of salvin A, maslinic acid and a ceramide from Vitex cienkowskii. The activity induced by these compounds indicated that they may be partly responsible for the vasorelaxant effect of the plant extract. A dose of 40 mg/kg of CH(2)Cl(2)-MeOH (1:1) extract administered intravenously induced a decrease of mean arterial pressure but did not affect the heart rate. Moreover the plant extracts were found to be highly active in the DPPH radical scavenging assay.

CONCLUSION

Vitex cienkowskii extract possesses antioxidant property, vasorelaxing, and hypotensive effect linked to the endothelium related factors, where nitric oxide is involved.

A new xanthone from Halenia elliptica D. Don

A new xanthone, 1,5-dihydroxy-2,3,4-trimethoxyxanthone (1), together with 15 known compounds (2-16), was isolated from an ethanolic extract of Halenia elliptica D. Don. Their structures were elucidated by spectroscopic methods. Among the known compounds, the (13)C NMR spectroscopic data of 2,3,4,5-tetramethoxyxanthone-1-O-gentiobioside (2) were reported for the first time.

Vasodilatory actions of xanthones isolated from a Tibetan herb, Halenia elliptica

In this study, six major xanthones, isolated and identified from Halenia elliptica were investigated for their vasodilatory actions in isolated rat coronary artery. The xanthones, including 1-hydroxy-2,3,5-trimethoxy-xanthone (HM-1), 1-hydroxy-2,3,4,7-tetramethoxy-xanthone (HM-2), 1-hydroxy-2,3,4,5-tetramethoxy-xanthone (HM-3), 1,7-dihydroxy-2,3,4,5-tetramethoxy-xanthone (HM-4), 1,5-dihydroxy-2,3-dimethoxy-xanthone (HM-5) and 1,7-dihydroxy-2,3-dimethoxy-xanthone (HM-7) caused vasodilation in the coronary artery pre-contracted with 1 microM 5-hydroxytryptamine (5-HT), with EC(50) values ranging from 1.4+/-0.1 microM (HM-1) to 6.6+/-1.4 microM (HM-2). The EC(50) values of the other xanthones were between those of HM-1 and HM-2. Removal of endothelium of the coronary artery led to decreases in the vasorelaxant effects of HM-1, HM-7 but not HM-2, HM-3, HM-4 and HM-5. Our results showed that xanthones isolated from Halenia elliptica are vasoactive substances which exhibit either endothelium-dependent or endothelium-independent mechanisms in rat coronary artery. The potency and mechanism(s) of the vasorelaxant effects of these xanthones may be relevant to the structure-activity differences in the level and the position of the substituent groups with the primary xanthone structure.