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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.

The metabolisms of five xanthones isolated from a Tibetan medicinal herb Halenia elliptica D. Don, 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) and 1,5-dihydroxy-2,3-dimethoxy-xanthone (HM-5), were studied in rat liver microsomes in vitro. High performance liquid chromatography coupled to ion trap time-of-flight mass spectrometry (LC-ESI-IT-TOF) was applied for identification of metabolites of five xanthones mentioned above and (1)H NMR was used to elucidate the major metabolites. The structures of thirteen metabolites were identified and seven of them had not been reported before. Moreover, xanthone isomers herein could be distinguished by difference of fragmentation behaviors with increase of stages or relative abundances. The results indicated that in vitro metabolic transformation of HM-1, HM-2, HM-3, HM-4 and HM-5 occurred mainly at 2-, 4-, 5-, 7-carbonic positions on their structures of parent drugs. The metabolites could be new vasoactive substances. This work will provide a basis for study on the structure-activity relationships of these xanthones and their derivatives from Tibetan herbal in the next work.

Metabolism study has been carried out on 1-hydroxy-2,3,5-trimethoxyxanthone (HM-1) and 1-hydroxy-2,3,4,7-tetramethoxyxanthone (HM-2), which are two biologically active ingredients isolated from the Tibetan herb, Halenia elliptica D. Don., in rat liver microsomes in vitro . A method of high performance liquid chromatography coupled to ion trap time-of-flight mass spectrometry (LCMS n -ESI-IT-TOF) was applied to analyze metabolites of HM-1 and HM-2 on line, and five metabolites were identified containing 1,5-dihydroxy-2,3-dimethoxyxanthone (HM-5), 1,7-dihydroxy-2,3,4-trimethoxyxanthone (HM-9), 1,4, 7-trihydroxy-2,3-dimethoxyxanthone (HM-10), 1,4-dihydroxy-2,3,7-trimethoxyxanthone (HM-11) and 1,2-dihydroxy-3,4,7-trimethoxyxanthone (HM-12). Among these metabolites, HM-9, HM-11, and HM-12 were isomers mutually. The results indicated that HM-1 and HM-2 occurred Phase I metabolic reaction of demethylation in rat microsomes in vitro .

A novel 1:1 natural product complex ( 1 ) containing luteoskyrin ( 2 ) and rugulosin ( 3 ) was isolated from the acetone extract of culture broth of Myrothecium sp. In DMSO solution, the 1 H and 13 C NMR spectra showed only half proton and carbon signals indicating that both compounds exist as a symmetric enol–enol form. In contrast, in the solid state, X-ray analysis revealed that 2 bound 3 with high specificity through intermolecular hydrogen bonds and π–π interactions, and both 2 and 3 tautomerized to a non-symmetric enol–ketone form due to the strong linear hydrogen bonding between the ketone group and the alcoholic hydroxyl group. In addition, complex 1 showed potent cytotoxic activity against cell lines KB (human epidermoid carcinoma cell), HT-29 (human colon cancer cell) and 3T3 (mouse embryonic fibroblast cell) with IC 50 values of 0.57, 3.11 and 5.83 μM, respectively.

Dopamine, as a neurotoxin, can elicit severe Parkinson's disease-like syndrome by elevating intracellular reactive oxygen species levels and apoptotic activity. In this study, we examined the effect of 6,7-di-O-glucopyranosyl-esculetin, which was extracted from Fraxinus sieboldiana bloom, on dopamine-induced cytotoxicity and the underlying mechanism in human neuroblastoma SH-SY5Y cells. Our results suggest that the protective effects of 6,7-di-O-glucopyranosyl-esculetin (0.1, 1 and 10 microM) on dopamine-induced cytotoxicity may be ascribed to its anti-oxidative properties by reducing reactive oxygen species levels, and its anti-apoptotic effect via protecting mitochondrion membrane potential (Delta Psi m), enhancing superoxide dismutaese (SOD) activity and reduced glutathione (GSH) levels, and regulating p53, Bax and Bcl-2 expression. In addition, 6,7-di-O-glucopyranosyl-esculetin inhibited the release of cytochrome c and apoptosis-inducing factor (AIF), and the protein expression of activated caspase 3. These data indicate that 6,7-di-O-glucopyranosyl-esculetin may provide a useful therapeutic strategy for the treatment of progressive neurodegenerative diseases such as Parkinson's disease.

1, 5-Dihydroxy-2, 3-dimethoxy-xanthone (HM-5) is one of the naturally-occurring xanthones of a Tibetan medicinal herb Halenia elliptica. Recently, it has been shown that HM-5 is one of the phase I metabolites of 1-hydroxy-2, 3, 5-trimethoxy-xanthone (HM-1), the major active component of H. elliptica with potent vasorelaxant actions. This study investigated the vasorelaxant effect of HM-5 and its mechanism(s). HM-5 (0.35-21.9 microM) produced a concentration-dependent relaxation in rat coronary artery rings pre-contracted with 1 microM 5-hydroxytryptamine (5-HT), with an EC(50) of 4.40+/-1.08 microM. Unlike HM-1, the effect of HM-5 was endothelial-independent such that removal of the endothelium did not affect its vasodilator potency. Nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME, 100 microM), the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ, 10 microM) did not affect the vasodilatory effects of HM-5, thus confirming the non-involvement of endothelium related mechanisms. In endothelium-denuded coronary artery rings, the vasorelaxant effect of HM-5 was inhibited by a potassium channel blocker, TEA (10 mM), and 4-aminopyridine (4-AP, a K(v) blocker; 1 mM) but not by other K+ channel blockers such as iberiotoxin (100 nM), barium chloride (100 microM) and glibenclamide (10 microM). The involvement of Ca2+ channel was studied in artery rings pre-incubated with Ca2+-free buffer (intact endothelium or endothelium-denuded) and primed with 1 microM 5-HT or 60 mM KCl prior to the addition of CaCl2 to elicit contraction. In the 5-HT-primed preparations, HM-5 (34.7 microM) significantly inhibited the CaCl(2)-induced vasoconstriction (89.9% inhibition in intact endothelium artery rings; 83.3% inhibition in endothelium-denuded rings). In the KCl-primed preparations, HM-5 (34.7 microM) produced a 34% inhibition in endothelium-denuded rings. The same concentration of HM-5 inhibited (by 62.3%) the contractile response to 10 microM phorbol 12, 13-diacetate (PDA), a protein kinase C activator, in Ca2+-free solutions. Taken together, this study showed that the mechanisms of the vasorelaxant effects of HM-5 were distinctly different from those of its parent drug HM-1. The vasorelaxant effect of HM-5 was mediated through opening of potassium channel (4-AP) and altering intracellular calcium by partial inhibition of Ca2+ influx through L-type voltage-operated Ca2+ channels and intracellular Ca2+ stores.

1-Hydroxy-2, 3, 5-trimethoxyxanthone (HM-1) is a xanthone isolated from Halenia elliptica, a Tibetan medicinal herb. HM-1 (0.33-42.1 microM) produced a concentration-dependent relaxation in rat coronary artery rings pre-contracted with 1 microM 5-hydroxytryptamine (5-HT), with an EC(50) of 1.67+/-0.27 microM. Removal of the endothelium significantly affected the vasodilator potency of HM-1, resulting in 46% decrease in E(max) value. The endothelium-dependent effects of HM-1 was confirmed when its vasorelaxant effect was inhibited after addition of nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (100 microM) or the soluble guanylate cyclase inhibitor 1H-[1, 2, 4] oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ, 10 microM). Atropine (100 nM), flurbiprofen (10 microM), propranolol (100 microM), pyrilamine (10 microM), cimetidine (10 microM) and SQ22536 (100 microM) had no effect on the vasorelaxant activity of HM-1 indicated the non-involvement of other receptor/enzyme systems. In endothelium-denuded coronary artery rings, the vasorelaxant effect of HM-1 was unaffected by potassium channel blockers such as tetraethylammonium (10 mM), iberiotoxin (100 nM), barium chloride (100 microM) and 4-aminopyridine (1 mM). The involvement of Ca(2+) channel in 5-HT-primed artery ring preparations incubated with Ca(2+)-free buffer was confirmed when HM-1 (9.93 microM) partially abolished the CaCl(2)-induced vasoconstriction (87% inhibition in intact-endothelium artery rings; 50% inhibition in endothelium-denuded rings). In the KCl-primed preparations incubated with Ca(2+)-free buffer, HM-1 (9.93 microM) produced a 27.3% inhibition in endothelium-denuded rings. HM-1 (3.31-33.1 microM) had minimal relaxant effects (14.4%-20.3%) on the contractile response generated by 10 microM phorbol 12,13-diacetate (PDA) in Ca(2+)-free solutions, suggesting minimal effects on intracellular Ca(2+) mechanisms. These findings suggest the vasodilator action of HM-1 involved both an endothelium-dependent mechanism involving NO and an endothelium-independent mechanism by inhibiting Ca(2+) influx through L-type voltage-operated Ca(2+) channels; a minor contribution to the effects of HM-1 may be related to inhibition of the protein kinase C-mediated release of intracellular Ca(2+) stores.

Two new diterpenoids were isolated from Euphorbia micractina. Their structures were elucidated on the basis of two dimensional NMR (1H-1H COSY, 13C-1H COSY and long range 13C-1 H COSY) and X-ray crystallography.