Synthesis and antithrombotic effect of xanthone derivatives

Naturally Occurring Xanthones and Their Biological Implications

Xanthones are chemical substances in higher plants, marine organisms, and lower microorganisms. The most prevalent naturally occurring sources of xanthones are those belonging to the families Caryophyllaceae, Guttiferae, and Gentianaceae. Structurally, xanthones (9H xanthan-9-one) are heterocyclic compounds with oxygen and a γ-pyrone component. They are densely packed with a two-benzene ring structure. The carbons in xanthones are numbered from their nucleus and biosynthetic construct. They have mixed shikimate-acetate (higher plants) and acetate-malonate (lower organisms) biosynthetic origins, which influence their classification. Based on the level of oxidation of the C-ring, they are classified into monomers, dimers, and heterodimers. While based on the level of oxygenation or the type of ring residue, they can be categorized into mono-, di-, tri-, tetra-, penta- and hexa-oxygenated xanthones, bis-xanthones, prenylated and related xanthones, xanthonolignoids, and other miscellaneous xanthones. This structural diversity has made xanthones exhibit considerable biological properties as promising antioxidant, antifungal, antimicrobial, and anticancer agents. Structure-activity relationship studies suggest C-1, C-3, C-6, and C-8 as the key positions that influence the biological activity of xanthones. Furthermore, the presence of functional groups, such as prenyl, hydroxyl, glycosyl, furan, and pyran, at the key positions of xanthones, may contribute to their spectrum of biological activity. The unique chemical scaffolds of xanthones, their notable biological activities, and the structure-activity relationships of some lead molecules were discussed to identify lead molecules as possible drug candidates.

Expanding the therapeutic arsenal against cancer: a computational investigation of hybrid xanthone derivatives as selective Topoisomerase 2α ATPase inhibitors

The DNA topoisomerase II (topo II) enzyme plays an important role in the replication, recombination, and repair of DNA. Despite their widespread applications in cancer therapy, new, selective, and potent topo II inhibitors with better pharmaceutical profiles are needed to handle drug resistance and severe adverse effects. In this respect, an array of 36 new anticancer compounds was designed based on a Xanthone core tethered to multifunctional Pyridine-amines and Imidazole scaffold via alkyl chain linkers. An integrated in silico approach was used to understand the structural basis and mechanism of inhibition of the hybrid xanthone derivatives. In this study, we established an initial virtual screening workflow based on pharmacophore mapping, docking, and cancer target association to validate the target selection process. Next, a simulation-based docking was conducted along with pharmacokinetic analysis to filter out the five best compounds (7, 10, 25, 27, and 30) having binding energies within the range of -60.45 to -40.97 kcal/mol. The screened compounds were further subjected to molecular dynamics simulation for 200 ns followed by MM-GBSA and ligand properties analysis to assess the stability and binding affinity to hTOP2α. The top-ranking hits 3,7-bis(3-(2-aminopyridin-3-ylhydroxy)propoxy)-1-hydroxy-9H-xanthen-9-one (ligand 7) and 3,8-bis(3-(2-aminopyridin-3-ylhydroxy)propoxy)-1-hydroxy-9H-xanthen-9-one (ligand 25) were found to have no toxicity, optimum pharmacokinetic and, DFT properties and stable intermolecular interactions with the active site of hTopo IIα protein. In conclusion, further in vitro and in vivo experimental validation of the identified lead molecules is warranted for the discovery of new human Topoisomerase 2 alpha inhibitors.Communicated by Ramaswamy H. Sarma.

Xanthone: A Promising Antimycobacterial Scaffold

BACKGROUND

Tuberculosis (TB) is one of the infectious diseases associated with high rate of morbidity and mortality and still remains one of the top-ten leading causes of human death in the world. The development of new anti-TB drugs is mandatory due to the existence of latent infection as well as the expansion of the resistant Mycobacterium tuberculosis (MBT) strains. Xanthones encompass a wide range of structurally diverse bioactive compounds, obtained either naturally or through chemical synthesis. There is a growing body of literature that recognizes the antitubercular activity of xanthone derivatives.

OBJECTIVE

The objective of this review is to highlight the main natural sources along with the critical design elements, structure-activity relationships (SARs), modes of action and pharmacokinetic profiles of xanthone-based anti-TB compounds.

METHODS

In the present review, the anti-TB activity of xanthones reported in the literature from 1972 to date is presented and discussed.

RESULTS

Exploration of xanthone scaffold led to the identification of several members of this class having superior activity against both sensitive and resistant MBT strains with distinctive mycobacterial membrane disrupting properties. However, studies regarding their modes of action, pharmacokinetic properties and safety are limited.

CONCLUSION

Comprehendible data and information are afforded by this review and it would certainly provide scientists with new thoughts and means which will be conducive to design and develop new drugs with excellent anti-TB activity through exploration of xanthone scaffold.

Euxanthone inhibits traumatic spinal cord injury via anti-oxidative stress and suppression of p38 and PI3K/Akt signaling pathway in a rat model

BACKGROUND

Owing to neurite promoting, antioxidant and anti-inflammatory effects of Euxanthone (Eux), the investigation was aimed to probe the neuroprotective efficacy of Eux against traumatic spinal cord injury (t-SCI) in rats and whether Eux can improve neuropathic function in t-SCI.

METHOD

Sprague-Dawley (SD) rats were randomized in - Sham, t-SCI, Eux30, and Eux60 (t-SCI + 30 and 60 mg/kg respectively). Animals with compression force-induced t-SCI were subjected to estimation of locomotor functions. Spinal cord water content and Evans blue (EB) effusion were determined for quantifying edema and intactness of the spinal cord. Oxidative stress and immunochemical markers were quantified by ELISA and western blotting.

RESULTS

Findings revealed that Eux60 group animals had greater Basso, Beattie, and Bresnahan (BBB) and (incline plane test) IPT score indicating improved locomotor functions. There was a reduction in the spinal edema and water content after Eux treatment, together with lowering of oxidative stress markers. The expression of IL-6, IL-12, IL-1β, caspase-3, RANKL, TLR4, NF-κB, p-38, PI3K, and Akt in spinal cord tissues of t-SCI-induced rats was lowered after Eux treatment.

CONCLUSION

Overall, the investigation advocates that Eux attenuates t-SCI and associated inflammation, oxidative damage, and resulting apoptosis via modulation of TLR4/NF-κB/p38 and PI3K/Akt signaling cascade.

Discrimination of geographical origin of cultivated Polygala tenuifolia based on multi-element fingerprinting by inductively coupled plasma mass spectrometry

Inorganic elements are important components of medicinal herbs, and provide valuable experimental evidence for the quality evaluation and control of traditional Chinese medicine (TCM). In this study, to investigate the relationship between the inorganic elemental fingerprint and geographical origin identification of cultivated Polygala tenuifolia, 41 elemental fingerprints of P. tenuifolia from four major polygala-producing regions (Shanxi, Hebei, Henan, and Shaanxi) were evaluated to determine the importance of inorganic elements to cultivated P. tenuifolia. A total of 15 elemental (B, Ca, Cl, Cu, Fe, K, Mg, Mn, Na, N, Mo, S, Sr, P, and Zn) concentrations of cultivated P. tenuifolia were measured using inductively coupled plasma mass spectroscopy (ICP-MS). The element composition samples were classified by radar plot, elemental fingerprint, and multivariate data analyses, such as hierarchical cluster analysis (HCA), principle component analysis (PCA), and discriminant analysis (DA). This study shows that radar plots and multivariate data analysis can satisfactorily distinguish the geographical origin of cultivated P. tenuifolia. Furthermore, PCA results revealed that N, Cu, K, Mo, Sr, Ca, and Zn are the characteristic elements of cultivated P. tenuifolia. Therefore, multi-element fingerprinting coupled with multivariate statistical techniques can be considered an effective tool to discriminate geographical origin of cultivated P. tenuifolia.

Novel xanthone-polyamine conjugates as catalytic inhibitors of human topoisomerase IIα

It has been proposed that xanthone derivatives with anticancer potential act as topoisomerase II inhibitors because they interfere with the ability of the enzyme to bind its ATP cofactor. In order to further characterize xanthone mechanism and generate compounds with potential as anticancer drugs, we synthesized a series of derivatives in which position 3 was substituted with different polyamine chains. As determined by DNA relaxation and decatenation assays, the resulting compounds are potent topoisomerase IIα inhibitors. Although xanthone derivatives inhibit topoisomerase IIα-catalyzed ATP hydrolysis, mechanistic studies indicate that they do not act at the ATPase site. Rather, they appear to function by blocking the ability of DNA to stimulate ATP hydrolysis. On the basis of activity, competition, and modeling studies, we propose that xanthones interact with the DNA cleavage/ligation active site of topoisomerase IIα and inhibit the catalytic activity of the enzyme by interfering with the DNA strand passage step.

Synthesis and biological evaluation of C1-O-substituted-3-(3-butylamino-2-hydroxy-propoxy)-xanthen-9-one as topoisomerase IIα catalytic inhibitors

Topoisomerase II poison blocks the transitorily generated DNA double-strand breaks (DSBs) from religation, thereby causes severe DNA damage and gene toxicity. While topoisomerase II catalytic inhibitor does not form cleavable DNA-enzyme complex because its function attributes to inhibition of the catalytic steps of the enzyme such as before generating DNA DSBs or in the last step of the catalytic cycle after religation. It has been reported that the stabilizing effect of etoposide on transient cleavable DNA-topoisomerase IIβ complex attributes to its secondary malignancy. Therefore, topoisomerase IIα has been considered as more attractive target than topoisomerase IIβ for the development of chemotherapeutic agents. In the previous work, we reported compounds I and II as novel topoisomerase IIα catalytic inhibitors targeting for ATP binding site of human topoisomerase IIα ATP-binding domain. As a continuous work, we have designed and synthesized 43 compounds of C1-O-alkyl and arylalkyl substitiuted compounds with or without methoxy group on ring A. In the topoisomerase IIα inhibitory test, among the tested C1-O-4-chlorophenethyl substituted compounds 37 and 47 were more active than others, and compound 37 showed strongest topoisomerase IIα inhibitory activity with 94.4% and 23.0% inhibition, respectively, at 100 and 20 μM. Compounds 37 and 47 have also showed much enhanced cytotoxic activity against T47D cells; IC50 (μM): 0.63 ± 0.01 and 0.19 ± 0.02, respectively, which are stronger than reference drugs. Band depletion assay and cleavage complex assay results showed compounds 37 and 47 were potential topoisomerase IIα catalytic inhibitor with low DNA damage.

Xanthones from the Leaves of Garcinia cowa Induce Cell Cycle Arrest, Apoptosis, and Autophagy in Cancer Cells

Two new xanthones, cowaxanthones G (1) and H (2), and 23 known analogues were isolated from an acetone extract of the leaves of Garcinia cowa. The isolated compounds were evaluated for cytotoxicity against three cancer cell lines and immortalized HL7702 normal liver cells, whereby compounds 1, 5, 8, and 15-17 exhibited significant cytotoxicity. Cell cycle analysis using flow cytometry showed that 5 induced cell cycle arrest at the S phase in a dose-dependent manner, 1 and 16 at the G2/M phase, and 17 at the G1 phase, while 16 and 17 induced apoptosis. Moreover, autophagy analysis by GFP-LC3 puncta formation and western blotting suggested that 17 induced autophagy. Taken together, our results suggest that these xanthones possess anticancer activities targeting cell cycle, apoptosis, and autophagy signaling pathways.

Antioxidant and anti-inflammatory activities of zinc oxide nanoparticles synthesized using Polygala tenuifolia root extract

The exploitation of various plant materials for the green synthesis of nanoparticles is considered an eco-friendly technology because it does not involve toxic chemicals. In this study, zinc oxide nanoparticles (ZnO NPs) were synthesized using the root extract of Polygala tenuifolia. Synthesized ZnO NPs were characterized by UV-Vis spectroscopy, FTIR, TGA, TEM, SEM and EDX. Anti-inflammatory activity was investigated in LPS-stimulated RAW 264.7 macrophages, whereas antioxidant activity was examined using a DPPH free radical assay. ZnO NPs demonstrated moderate antioxidant activity by scavenging 45.47% DPPH at 1mg/mL and revealed excellent anti-inflammatory activity by dose-dependently suppressing both mRNA and protein expressions of iNOS, COX-2, IL-1β, IL-6 and TNF-α.

Polysulfated xanthones: multipathway development of a new generation of dual anticoagulant/antiplatelet agents

A multipathway strategy was used to evaluate the in vitro and in vivo antithrombotic effects of a new synthetic family of sulfated small molecules. Polysulfated xanthonosides showed highly effective anticoagulation effects in vitro, both in plasma (clotting times) and in whole human blood (thromboelastography), as well as in vivo (ip administration, mice). Physicochemical properties were assessed for mangiferin heptasulfate (7), which showed high solubility and stability in water and in human plasma and no putative hepatotoxicity in vivo. Mangiferin heptasulfate (7) was found to be a direct inhibitor of FXa, while persulfated 3,6-(O-β-glucopyranosyl)xanthone (13) acted as a dual inhibitor of FXa (directly and by antithrombin III activation). By impedance aggregometry, compounds 7 and 13 exhibited the antiplatelet effect by inhibition of both arachidonic acid and ADP-induced platelet aggregation. Dual anticoagulant/antiplatelet agents, such as sulfated xanthonosides 7 and 13, are expected to lead to a new therapeutic approach for the treatment of both venous and arterial thrombosis.

Synthesis, biological evaluation, and molecular docking study of 3-(3'-heteroatom substituted-2'-hydroxy-1'-propyloxy) xanthone analogues as novel topoisomerase IIα catalytic inhibitor

Epoxide ring-opened xanthone derivatives were synthesized and tested for their topoisomerase inhibitory activity and cytotoxicity. Most of the compounds showed topo IIα specific inhibitory activity. To clarify the mechanism of action of these compounds, the most potent compound (compound 14) of the synthesized analogues was further studied by testing its ATPase inhibitory activity and through molecular docking experiments. The results showed that the topo IIα inhibitory activity of compound 14 was inversely proportional to ATP concentration. In the ATPase inhibitory test, ATP hydrolysis was reduced less efficiently by compound 14 (28.5±4.6%) than novobiocin (60.4±8.1%). Molecular docking study revealed compound 14 to have a stable binding pattern to the ATP-binding domain of human topo II.

Mechanism of the vasodilator effect of Euxanthone in rat small mesenteric arteries

In the present work we investigated the mechanism involved in the vasodilator effect induced by euxanthone in rat small mesenteric arteries. We observed that euxanthone induced concentration-dependent vasodilatation in arteries by a mechanism independent on the release of endothelial factors, such as nitric oxide (NO) and cyclooxygenase-derived factors. In addition our results also suggest that euxanthone induced its vasodilator effect through inhibition of calcium-sensitive mechanisms activated by protein kinase C, rather than by inhibition of contractions dependent on the release of the intracellular calcium stores or by inhibition of voltage-operated calcium channels.

Quantitative and qualitative determination of six xanthones in Garcinia mangostana L. by LC-PDA and LC-ESI-MS

A new method was developed for the simultaneous analysis of six naturally occurring xanthones (3-isomangostin, 8-desoxygartanin, gartanin, alpha-mangostin, 9-hydroxycalabaxanthone and beta-mangostin). The quantitative determination was conducted by reversed phase high performance liquid chromatography with photodiode array detector (LC-PDA). Separation was performed on a Phenomenex Luna C18(2) (150 mm x 3.00 mm, 5 microm) column. The xanthones were identified by retention time, ultraviolet (UV) spectra and quantified by LC-PDA at 320 nm. The precision of the method was confirmed by the relative standard deviation (R.S.D.), which was < or =4.6%. The recovery was in the range from 96.58% to 113.45%. A good linear relationship was established in over two orders of magnitude range. The limits of detection (LOD) for six xanthone compounds were < or =0.248 microg/mL. The identity of the peaks was further confirmed by high performance liquid chromatography with time-of-flight mass spectrometry (LC-TOF MS) system coupled with electrospray ionization (ESI) interface. The developed methods were applied to the determination of six xanthones in Garcinia mangostana products. The satisfactory results showed that the methods are effective for the analysis of real samples.

Synthesis and pharmacological activities of xanthone derivatives as α-glucosidase inhibitors

Considerable interest has been attracted in xanthone and its derivatives because of their large variety of pharmacological activities. In this project, a series of hydroxylxanthones and their acetoxy and alkoxy derivatives were synthesized and evaluated as alpha-glucosidase inhibitors, aimed at clarifying the structure-activity correlation. The results indicated that these xanthone derivatives were capable of inhibiting in vitro alpha-glucosidase with moderate to good activities. Among them, polyhydroxylxanthones exhibited the highest activities and thus may be exploitable as a lead compound for the development of potent alpha-glucosidase inhibitors.

Photophysics of aminoxanthone derivatives and their application as binding probes for DNA

Xanthones with amino substituents were synthesized to diminish the photoreactivity of the xanthone chromophore with DNA, with the objective of using these molecules to study their binding dynamics with DNA. The aminoxanthones showed a strong solvatochromic effect on their singlet and triplet excited-state photophysics, where polar solvents led to a decrease of the energies for the excited states. Quenching of the triplet excited states by nitrite anions was used to determine the binding dynamics, and a residence time in the microsecond time domain was estimated for the bound 2-aminoxanthone with DNA. The quenching experiments performed showed that this methodology will not be applicable to study the binding dynamics of a wide variety of guests with DNA.

Pharmacological Effects of Xanthones as Cardiovascular Protective Agents

Many epidemiological studies indicate that consumption of dietary polyphenolic compounds is beneficial in the prevention of cardiovascular diseases. Xanthones are a class of polyphenolic compounds that commonly occur in plants and have been shown to have extensive biological and pharmacological activities. Recently, the pharmacological properties of xanthones in the cardiovascular system have attracted great interest. Xanthones and xanthone derivatives have been shown to have beneficial effects on some cardiovascular diseases, including ischemic heart disease, atherosclerosis, hypertension and thrombosis. The protective effects of xanthones in the cardiovascular system may be due to their antioxidant, antiinflammatory, platelet aggregation inhibitory, antithrombotic and/or vasorelaxant activities. In particular, the antagonism of endogenous nitric oxide synthase inhibitors by xanthones may represent the basis for improved endothelial function and for reduction of events associated with atherosclerosis.

Vasorelaxant effect of euxanthone in the rat thoracic aorta

This study was undertaken to investigate the effect of euxanthone on isolated rat thoracic aorta. Euxanthone concentration-dependently relaxed high K+-induced sustained contractions with IC50 values of 32.28+/-1.73 microM and this inhibition was antagonized by increasing the Ca2+ concentration in the medium. These results indicated that euxanthone may have calcium antagonistic property. Euxanthone also relaxed norepinephrine (NE)-induced sustained contractions with IC50 values of 32.50+/-2.15 microM and this relaxant effect was unaffected by the removal of endothelium or by the presence of propranolol, indomethacin, glibenclamide or N(omega)-nitro-L-arginine. Moreover, euxanthone inhibited both the phasic and tonic contractions induced by NE in a concentration-dependent manner and showed more potent inhibition on phasic contraction (P < 0.01). Pre-treatment with euxanthone inhibited vascular contraction induced by phorbol 12, 13-dibutyrate (PDBu), a protein kinase C (PKC) agonist, in either the presence or absence of Ca2+ in the solution with IC50 values of 20.15+/-1.56 and 18.30+/-1.62 microM, respectively. However, when the tissues were treated with euxanthone after the PDBu-induced contraction had reached a steady state, the tension was not affected by euxanthone. This study also showed that the inhibitory effect of pre-treatment of euxanthone was more potent than the post-treatment after the tension had reached a steady state. These results suggested that the vasorelaxation of euxanthone may be through multiple pathways involved PKC-mediated signal pathway and calcium-independent pathway besides the direct inhibition of calcium influx and its vasorelaxant effect is more active on calcium-independent pathway and more sensitive to the initial stage of contraction.

Involvement of protein kinase C and E2F-5 in euxanthone-induced neurite differentiation of neuroblastoma

Euxanthone, a neuritogenic agent isolated from the medicinal herb Polygala caudata, has been shown to induce morphological differentiation and neurite outgrowth in murine neuroblastoma Neuro 2a cells (BU-1 subclone). In order to elucidate the underlying mechanisms of euxanthone-induced neurite outgrowth, a proteomic approach was employed. In the present study, two dimensional (2-D) gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight (MALDI-ToF) mass spectrometry were performed to investigate the alterations in protein expression profile of euxanthone-treated BU-1 cells. Fourteen identified proteins were changed in expression levels after induction of neurite growth. These proteins included participants in transcription and cell cycle regulation, calcium influx and calcium signaling, fatty acid metabolism, cytoskeleton reorganization, casein kinase signal transduction, putative transbilayer amphipath transport and protein biosynthesis. Among the 14 identified proteins, E2F transcription factor 5 (E2F-5) was significantly up-regulated after euxanthone treatment. Go6976, a protein kinase C (PKC) alpha/betaI inhibitor, was found to inhibit neuritogenesis and expression of E2F-5 in the euxanthone-treated BU-1 cells, while SH-6, the Akt/PKB inhibitor, had no inhibitory effect. The gene silencing of E2F-5 by small interfering RNA (siRNA) was found to abolish the euxanthone-induced neurite outgrowth. In conclusion, these results indicated that the transcription factor E2F-5 was actively involved in the regulation of euxanthone-induced neurite outgrowth via PKC pathway.

Relationship between protective effect of xanthone on endothelial cells and endogenous nitric oxide synthase inhibitors

1,3,5,6-tetrahydroxyxanthone was synthesized. The relationship between protective effect of xanthone on endothelial cells and endogenous nitric oxide synthase inhibitors was investigated. Endothelial cells were treated with ox-LDL (100 microg/mL) for 48 h. Adhesion of monocytes to endothelial cells and release of lactate dehydrogenase (LDH) was determined. Levels of tumor necrosis factor-alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1), nitric oxide (NO) and asymmetric dimethylarginine (ADMA, an endogenous inhibitor of nitric oxide synthase) in conditioned medium and activity of dimethylarginine dimethylaminohydrolase (DDAH) in endothelial cells were measured. Incubation of endothelial cells with ox-LDL (100 microg/mL) for 48 h markedly enhanced the adhesion of monocytes to endothelial cells, increased the release of LDH, the levels of TNF-alpha, MCP-1 and ADMA, and decreased the content of NO and the activity of DDAH. Xanthone (1,3,5,6-tetrahydroxyxanthone) (1, 3 or 10 micromol/L) significantly inhibited the increased adhesion of monocytes to endothelial cells and attenuated the increased levels of LDH, MCP-1 and ADMA induced by ox-LDL. Xanthone (1,3,5,6-tetrahydroxyxanthone) (3 or 10 micromol/L) significantly attenuated the increased level of TNF-alpha and decreased level of NO and activity of DDAH by ox-LDL. The present results suggest that xanthone (1,3,5,6-tetrahydroxyxanthone) preserves endothelial cells and inhibits the increased adhesion of monocytes to endothelial cells induced by ox-LDL, and that the protective effect of xanthone (1,3,5,6-tetrahydroxyxanthone) on endothelial cells is related to reduction of ADMA concentration via increase of DDAH activity.

Inhibition of protein kinase C by synthetic xanthone derivatives

The modulatory activity of two xanthones (3,4-dihydroxyxanthone and 1-formyl-4-hydroxy-3-methoxyxanthone) on isoforms alpha, betaI, delta, eta and zeta of protein kinase C (PKC) was evaluated using an in vivo yeast phenotypic assay. Both xanthones caused an effect compatible with PKC inhibition, similar to that elicited by known PKC inhibitors (chelerythrine and NPC 15437). PKC inhibition caused by xanthones was confirmed using an in vitro kinase assay. The yeast phenotypic assay revealed that xanthones present differences on their potency towards the distinct PKC isoforms tested. It is concluded that 3,4-dihydroxyxanthone and 1-formyl-4-hydroxy-3-methoxyxanthone may become useful PKC inhibitors and xanthone derivatives can be explored to develop new isoform-selective PKC inhibitors.

Antihypertensive and vasorelaxing activities of synthetic xanthone derivatives

A series of xanthones and xanthonoxypropanolamines have been synthesized. The activity of compounds on cardiovascular system was evaluated. All the compounds tested exhibited effective hypotensive activity in anesthetized rats. An oxypropanolamine side chain substituted at the C-3 position of the xanthone nucleus significantly enhanced the hypotensive activity. In rat thoracic aorta, all the compounds tested significantly depressed the contractions induced by Ca(2+) (1.9mM) in high K+(80mM) medium and the phasic and tonic contractions caused by norepinephrine (3 microM). In the rat thoracic aorta, the phenylephrine- and high K+ -induced 45Ca(2+) influx were both inhibited by a selective xanthone derivative, 13. In addition to the previously reported result of 13, evaluated as beta adrenoceptor blocker, the depressor and bradycardia effects of 9 are independent of the parasympathetic passway. These results suggest that 13 showed inhibitory effects on the contractile response caused by high K+ and norepinephrine in rat thoracic aorta are mainly due to inhibition of Ca(2+) influx through both voltage-dependent and receptor-operated Ca(2+) channels. The vasodilating properties of 13 is due to its calcium channel and beta adrenergic blocking effects.

Effects of euxanthone on neuronal differentiation

The growth inhibitory and differentiation inducing effects of euxanthone (1,7-dihydroxyxanthone) from the medicinal plant Polygala caudata on the neuroblastoma (Neural 2A, subclone BU-1) were investigated. At the concentration range of 0-100 microM, euxanthone inhibits the growth of BU-1 cells in a dose dependent manner. The 50% growth inhibitory concentration (IC50) was 41 microM. Significant induction of morphological differentiation and neurite growth was observed at the concentration of 100 microM. Frequency of proliferative neuroblastoma cells was determined after induction of differentiation. The frequency of proliferating BU-1 cells was markedly reduced from 1/1.1 to <1/99. Confocal microscopy also confirmed that the morphological differentiation of BU-1 was associated with the expression of neurite specific marker MAP-2 protein in neurites. These data suggest that euxanthone may be one of the neuropharmacological active compounds in the medicinal plant Polygala caudata.