Inhibitory effect of norathyriol, a xanthone from Tripterospermum lanceolatum, on cutaneous plasma extravasation

Structure-Activity-Relationship and Mechanistic Insights for Anti-HIV Natural Products

Acquired Immunodeficiency Syndrome (AIDS), which chiefly originatesfroma retrovirus named Human Immunodeficiency Virus (HIV), has impacted about 70 million people worldwide. Even though several advances have been made in the field of antiretroviral combination therapy, HIV is still responsible for a considerable number of deaths in Africa. The current antiretroviral therapies have achieved success in providing instant HIV suppression but with countless undesirable adverse effects. Presently, the biodiversity of the plant kingdom is being explored by several researchers for the discovery of potent anti-HIV drugs with different mechanisms of action. The primary challenge is to afford a treatment that is free from any sort of risk of drug resistance and serious side effects. Hence, there is a strong demand to evaluate drugs derived from plants as well as their derivatives. Several plants, such as Andrographis paniculata, Dioscorea bulbifera, Aegle marmelos, Wistaria floribunda, Lindera chunii, Xanthoceras sorbifolia and others have displayed significant anti-HIV activity. Here, weattempt to summarize the main results, which focus on the structures of most potent plant-based natural products having anti-HIV activity along with their mechanisms of action and IC50 values, structure-activity-relationships and important key findings.

Intermolecular C-O Addition of Carboxylic Acids to Arynes: Synthesis of o-Hydroxyaryl Ketones, Xanthones, 4-Chromanones, and Flavones

An efficient and simple route to biologically and pharmaceutically important o-hydroxyaryl ketones, xanthones, 4-chromanones, and flavones has been developed utilizing readily available carboxylic acids and commercially available o-(trimethylsilyl)aryl triflates.

Norathyriol suppresses skin cancers induced by solar ultraviolet radiation by targeting ERK kinases

Ultraviolet (UV) irradiation is the leading factor in the development of skin cancer, prompting great interest in chemopreventive agents for this disease. In this study, we report the discovery of norathyriol, a plant-derived chemopreventive compound identified through an in silico virtual screening of the Chinese Medicine Library. Norathyriol is a metabolite of mangiferin found in mango, Hypericum elegans, and Tripterospermum lanceolatum and is known to have anticancer activity. Mechanistic investigations determined that norathyriol acted as an inhibitor of extracellular signal-regulated kinase (ERK)1/2 activity to attenuate UVB-induced phosphorylation in mitogen-activated protein kinases signaling cascades. We confirmed the direct and specific binding of norathyriol with ERK2 through a cocrystal structural analysis. The xanthone moiety in norathyriol acted as an adenine mimetic to anchor the compound by hydrogen bonds to the hinge region of the protein ATP-binding site on ERK2. Norathyriol inhibited in vitro cell growth in mouse skin epidermal JB6 P+ cells at the level of G(2)-M phase arrest. In mouse skin tumorigenesis assays, norathyriol significantly suppressed solar UV-induced skin carcinogenesis. Further analysis indicated that norathyriol mediates its chemopreventive activity by inhibiting the ERK-dependent activity of transcriptional factors AP-1 and NF-κB during UV-induced skin carcinogenesis. Taken together, our results identify norathyriol as a safe new chemopreventive agent that is highly effective against development of UV-induced skin cancer.

Inhibition of the arachidonic acid cascade by norathyriol via blockade of cyclooxygenase and lipoxygenase activity in neutrophils

Recent studies have suggested that dual inhibitors of cyclooxygenase (COX) and lipoxygenase (LO) may be more beneficial in the treatment of inflammatory diseases in which platelet-leukocyte interaction dominates the underlying inflammatory process, than inhibitors of COX or LO alone. In this study, we examined oxygenated xanthones, shown previously to inhibit platelet and neutrophil activation, with respect to the potency of COX inhibition. 1,3,6,7-Tetrahydroxyxanthone (norathyriol) was the most potent. Norathyriol suppressed thromboxane B(2) (TXB(2)) and leukotriene B(4) (LTB(4)) formation in calcium ionophore (A23187)- and formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated rat neutrophils. Norathyriol was 3-4 times more active against LTB(4) formation than against TXB(2) formation (IC(50) about 2.8 vs. 10 microM, respectively). Norathyriol also inhibited prostaglandin D(2) (PGD(2)) formation in A23187-stimulated rat mast cells (IC(50) 3.0+/-1.2 microM) and in arachidonic acid (AA)-activated mast cell lysate. Norathyriol was a more effective inhibitor of 5-LO activity than of COX, as shown also by analyses of enzyme activities in a cell-free system, of COX and 5-LO metabolic capacity in neutrophils and of ex vivo TXB(2) and LTB(4) formation in A23187-stimulated neutrophils. Moreover, norathyriol inhibited COX-2 and 12-LO with IC(50) values (19.6+/-1.5 and 1.2+/-0.1 microM, respectively) similar to those required for the inhibition of COX-1 and 5-LO (16.2+/-1.5 and 1.8+/-0.4 microM, respectively). Inhibition of 15-LO by norathyriol was slightly less active. Norathyriol had no effect on A23187-induced AA release from neutrophils and did not affect phospholipase A(2) (PLA(2)) activity in a cell-free system. These results indicate that norathyriol inhibits the formation of PGs and LTs in neutrophils probably through direct blockade of COX and 5-LO activities. Norathyriol, a single molecule with multiple targets, might provide a potential therapeutic benefit in the treatment of inflammatory diseases.

1,4-Dihydroxyxanthone modulates the adhesive property of endothelial cells by inhibiting intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin

Cell adhesion molecules, particularly intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule (VCAM-1) and E-selectin, play important roles in the recruitment of leukocytes to the site of inflammation. Blocking the expression of these molecules or preventing their interaction with the receptors has been shown to be important in controlling various inflammatory diseases. These cell adhesion molecules are induced on endothelial cells by various proinflammatory cytokines like IL-1beta and TNF-alpha and also by bacterial LPS. We demonstrate here that 1,4-Dihydroxyxanthone (1,4 DHX) inhibits the expression of cell adhesion molecules, such as ICAM-1, VCAM-1 and E-selectin, on endothelial cells in a concentration and time dependent manner. The inhibition by 1,4 DHX is reversible. On further analysis, our results also show that 1,4 DHX inhibits the adhesion of peripheral neutrophils to the endothelial cell monolayers. 1,4 DHX, therefore, could be used as a novel target for controlling various pathological conditions associated with upregulation of endothelial leukocyte adhesion molecules.

Structure-activity relationship studies on chalcone derivatives. the potent inhibition of chemical mediators release

Some chalcones exert potent anti-inflammatory activities. 2',5'-Dialkoxychalcones and 2',5'-dihydroxy-4-chloro-dihydrochalcone inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma)-activated N9 microglial cells and in LPS-activated RAW 264.7 macrophage-like cells have been demonstrated in our previous reports. These compounds also suppressed the inducible NO synthase (iNOS) expression and cyclooxygenase-2 (COX-2) activity in RAW 264.7 cells. In an effort to continually develop potent anti-inflammatory agent, a series of chalcones were prepared by Claisen-Schmidt condensation of appropriate acetophenones with appropriate aromatic aldehyde and then evaluated their inhibitory effects on the activation of mast cells, neutrophils, macrophages, and microglial cells. Most of the 2',5'-dihydroxychaclone derivatives exhibited potent inhibitory effects on the release of beta-glucuronidase and lysozyme from rat neutrophils stimulated with formyl-Met-Leu-Phe (fMLP)/cytochalasin B (CB). Some chalcones showed potent inhibitory effects on superoxide anion generation in rat neutrophils in response to fMLP/CB. Compounds 1 and 5 exhibited potent inhibitory effects on NO production in macrophages and microglial cells. Compound 11 showed inhibitory effect on NO production and iNOS protein expression in RAW 264.7 cells. The present results demonstrated that most of the 2',5'-dihydroxychaclones have anti-inflammatory effects. The potent inhibitory effect of 2',5'-dihydroxy-dihydrochaclones on NO production in LPS-activated macrophage, probably through the suppression of iNOS protein expression, is proposed to be useful for the relief of septic shock.

Xanthones as inhibitors of microsomal lipid peroxidation and TNF-alpha induced ICAM-1 expression on human umbilical vein endothelial cells (HUVECs)

Xanthones bearing different functionalities, namely 1-hydroxyxanthone (1), 3-hydroxyxanthone (2), 1,4-dihydroxyxanthone (3), 2,6-dihydroxyxanthone (4), 1,2-diacetoxyxanthone (5), 2,6-diacetoxyxanthone (6), 3-methoxyxanthone (7), 1,3,7-trimethoxyxanthone (8) and 1,5-dihydroxy-6-methoxyxanthone (9) were synthesised and examined for their effect on nicotinamide adenine dinucleotide phosphate (NADPH)-catalysed liver microsomal lipid peroxidation and on tumour necrosis factor-alpha (TNF-alpha) induced expression of intercellular adhesion moledule-1 (ICAM-1) on endothelial cells, with a view to establish structure-activity relationship. Hydroxy- and acetoxyxanthones showed potent inhibitory effects on NADPH-catalysed lipid peroxidation and TNF-alpha induced expression of ICAM-1 on endothelial cells.

Synthesis and anti-inflammatory effect of chalcones

The process of degranulation of mast cells and neutrophils contributes to inflammatory disorders. Activation of microglial cells and macrophages is believed to be involved in inflammatory, infectious and degenerative diseases of the CNS. Combining the potent inhibition of chemical mediators released by the degranulation of mast cells or neutrophils and from the activated microglial cells or macrophages, would lead to a promising anti-inflammatory agent for the treatment of peripheral and central inflammation. A series of chalcone derivatives have been reported to have potent anti-inflammatory activity. In an effort to continually develop potent anti-inflammatory agents, novel series of chalcones, 2'-hydroxy- and 2',5'-dihydroxychalcones were synthesized and their inhibitory effects on the activation of mast cells, neutrophils, microglial cells and macrophages were evaluated in-vitro. The chalcones were prepared by Claisen-Schmidt condensation of appropriate acetophenones with an appropriate aromatic aldehyde. The alkoxychalcones were prepared with appropriate hydroxychalcones and alkyl iodide and the dihydroxychalcones were prepared by hydrogenation of an appropriate chalcone with Pd/C. Almost all of the hydroxychalcones exhibited potent inhibitory effects on the release of beta-glucuronidase and lysozyme from rat neutrophils stimulated with formyl-Met-Leu-Phe/cytochalasin B (fMLP/CB). Of the hydroxychalcones, compound 1 was the most potent inhibitor of the release of beta-glucuronidase (IC50=1.6+/-0.2 microM) and lysozyme (IC50=1.4+/-0.2 microM) from rat neutrophils stimulated with fMLP/CB. Almost all of the 2',5'-dialkoxychalcones exhibited potent inhibitory effects on nitric oxide (NO) formation from murine microglial cell lines N9 stimulated with lipopolysaccharide (LPS). Of these, compound 11 showed the greatest effect (IC50=0.7+/-0.06 microM). The present results demonstrated that most of the chalcone derivatives have an anti-inflammatory effect. The inhibitory effects of dialkoxychalcones, 10-12 on inflammation are probably not due to the inhibition of mast cells and neutrophil degranulation, but are mediated through the suppression of NO formation from N9 cells.

Chemistry and biological activities of constituents from Morus australis

A novel constituent named australone B (1) was further isolated from the cortex of Morus australis (Moraceae). The structure of 1 has been elucidated by one- and two-dimension spectra. In human citrated platelet-rich plasma, 1 showed strong inhibition of aggregation induced by adrenaline in a concentration-dependent manner with an IC(50) value of about 33.3 microM. Compound 1 (30 microM) also showed inhibitory effects on superoxide anion formation from rat neutrophils stimulated with formyl-Met-Leu-Phe (fMLP)/cytochalasin B (CB). Morusin (2) inhibited superoxide anion formation from rat neutrophils stimulated with phorbol myristate acetate (PMA) in a concentration-dependent manner with an IC(50) value of 66.9+/-2.5 microM.

Decreased protein kinase C activation mediates inhibitory effect of norathyriol on serotonin-mediated endothelial permeability

We examined the mechanisms of norathyriol on the serotonin-induced increased permeability of rat heart endothelial cell monolayers. The present study showed that the activation of rat heart endothelial cell protein kinase C by phorbol myristate acetate led to the dose-dependent increase in endothelial permeability to albumin, an effect that was inhibited by staurosporine (a protein kinase inhibitor). Staurosporine also attenuated the serotonin-induced increase in permeability. Norathyriol abolished both serotonin- and phorbol myristate acetate-induced permeability. We investigated whether norathyriol, by inhibiting protein kinase C activation, attenuated the serotonin-induced permeability. Immunofluorescence studies demonstrated that norathyriol prevented the redistribution of protein kinase C isozymes following stimulation with serotonin. Western blot analysis showed that norathyriol significantly inhibited the serotonin-induced translocation of the alpha protein kinase C isozyme from the cytosolic to the particulate fraction. In conclusion, norathyriol attenuates the serotonin-induced permeability of rat heart endothelial cells to macromolecules in association with inhibition of protein kinase C activation. This decrease in endothelial cell permeability may be one of the mechanisms for the protective effects of norathyriol against edema formation in response to inflammatory agonists in vivo.

Stereochemistry and biological activities of constituents from Cynanchum taiwanianum

The stereochemistry of new acetophenones, cynandione B-D (2-4), isolated from Cynanchum taiwanianum, elucidated by computer modelling calculation and NOESY spectrum. It establishes the absolute configurations of cynandiones B-D (2-4) as 7R; 7"S, 7S; 7"S and 7R; 7"R, respectively. Cynandione B (2) strongly inhibited the release of beta-glucuronidase and lysozyme in formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated rat neutrophils in a concentration-dependent manner with IC50 values of 1.5 +/- 0.2 and 1.6 +/- 0.2 microM, respectively. 2,5-Dihydroxyacetophenone (6) strongly inhibited the aggregation of washed rabbit platelets induced by arachidonic acid in a concentration-dependent manner with an IC50 value of about 4.8 microM. In human citrated platelet-rich plasma, 2,5-dihydroxyacetophenone (6) inhibited the secondary phase, but not the primary phase, of aggregation induced by adrenaline and ADP. These results suggest that the antiplatelet effect of 2,5-dihydroxyacetophenone (6) is due to inhibition of the formation of thromboxane A2.

A new pharyngitis model using capsaicin in rats

1. Application of capsaicin solution onto the rat pharyngeal mucosa caused a well-reproducible increase in vascular permeability in the pharynx. 2. Capsaicin-induced pharyngeal inflammation was unaffected by a histamine H1 blocker and non-steroidal anti-inflammatory agents, whereas dexamethasone was effective in its inhibition. 3. FK224, a dual antagonist of tachykinin NK1 and NK2 receptors, and FK888, a selective antagonist of NK1 receptor, significantly inhibited capsaicin-induced plasma exudation in the pharynx. 4. In capsaicinized animals, the application of capsaicin solution in the pharyngeal mucosa did not induce pharyngitis. 5. These results suggest that the mechanism of the capsaicin-induced pharyngitis primarily involves tachykinins.

Synthesis and anti-inflammatory effect of chalcones and related compounds

PURPOSE

Mast cell and neutrophil degranulations are the important players in inflammatory disorders. Combined with potent inhibition of chemical mediators released from mast cells and neutrophil degranulations, it could be a promising anti-inflammatory agent. 2',5'-Dihydroxychalcone has been reported as a potent chemical mediator and cyclooxygenase inhibitor. In an effort to continually develop potent anti-inflammatory agents, a novel series of chalcone, 2'- and 3'-hydroxychalcones, 2',5'-dihydroxychalcones and flavanones were continually synthesized to evaluate their inhibitory effects on the activation of mast cells and neutrophils and the inhibitory effect on phlogist-induced hind-paw edema in mice.

METHODS

A series of chalcones and related compounds were prepared by Claisen-Schmidt condensation of appropriate acetophenones with appropriate aromatic aldehyde and the anti-inflammatory activities of these synthetic compounds were studied on inhibitory effects on the activation of mast cells and neutrophils.

RESULTS

Some chalcones showed strong inhibitory effects on the release of beta-glucuronidase and histamine from rat peritoneal mast cells stimulated with compound 48/80. Almost all chalcones and 4'-hydroxyflavanone exhibited potent inhibitory effects on the release of beta-glucuronidase and lysozyme from rat neutrophils stimulated with formyl-Met-Leu-Phe (fMLP). Some chalcones showed potent inhibitory effects on superoxide formation of rat neutrophils stimulated with fMLP/cytochalasin B (CB) or phorbol myristate acetate (PMA). 2',3-Dihydroxy-, 2',5'-dihydroxy-4-chloro-, and 2',5'-dihydroxychalcone showed remarkable inhibitory effects on hind-paw edema induced by polymyxin B in normal as well as in adrenalectomized mice.

CONCLUSIONS

These results indicated that the anti-inflammatory effects of these compounds were mediated, at least partly, through the suppression of chemical mediators released from mast cells and neutrophils.

Mechanism of vasorelaxation of thoracic aorta caused by xanthone

The effect of xanthone on smooth muscle was studied in thoracic aorta isolated from rats. Xanthone relaxed the norepinephrine-induced contraction of rat thoracic aorta. This relaxing effect of xanthone persisted in endothelium-denuded aorta suggesting that the relaxation induced by xanthone is endothelium-independent. The norepinephrine and high-K+-induced vasoconstriction was inhibited dose dependently in aorta pretreated with xanthone with IC50 values of 60.26 +/- 8.43 and 82.9 +/- 13.21 microM, respectively. The inositol 1,4,5-trisphosphate formation induced by norepinephrine (3 microM) in rat aorta was not affected by xanthone (10-100 microM), suggesting that the vasorelaxant effect of xanthone was not exerted on the receptor. Xanthone concentration dependently inhibited the 45Ca2+ influx induced by either norepinephrine or high-K+, suggesting that xanthone might act as a blocker of both receptor-operated and voltage-dependent Ca2+ channels. Furthermore, xanthone caused an increase in the level of intracellular cyclic adenosine 3',5'-monophosphate (cAMP), but not cyclic guanosine 3',5'-monophosphate (cGMP) content. These data suggested that the mechanism of xanthone-induced vasorelaxation might involve the increase of intracellular cyclic adenosine 3',5'-monophosphate (cAMP) content and block of Ca2+ channels.

Evidence for the involvement of protein kinase C inhibition by norathyriol in the reduction of phorbol ester-induced neutrophil superoxide anion generation and aggregation

Norathyriol, a xanthone aglycone, inhibited superoxide anion (O2-) generation and O2 consumption in phorbol 12-myristate 13-acetate (PMA)-activated rat neutrophils in a concentration-dependent manner. In addition, norathyriol inhibited PMA- but enhanced formylmethionyl-leucyl-phenylalanine (fMLP)-induced neutrophil aggregation. Norathyriol suppressed neutrophil cytosolic protein kinase C as well as rat brain protein kinase C over the same range of concentrations at which it inhibited the respiratory burst. Norathyriol did not affect [3H]phorbol 12,13-dibutyrate ([3H]PDB) binding to neutrophil cytosolic protein kinase C, but effectively attenuated trypsin-treated rat brain protein kinase C activity. Moreover, norathyriol was found to be a noncompetitive inhibitor with respect to ATP and peptide substrate (N-terminal acetylated, amino acid sequence 4-14 of the myelin basic protein, Ac-MBP-(4-14)). Unlike staurosporine, norathyriol did not affect porcine heart protein kinase A activity. On the immunoblot analysis of protein kinase C subcellular distribution, the PMA-induced translocation of protein kinase C-beta from the cytosol to the membrane was not affected by norathyriol. These results show that the inhibition by a plant product, norathyriol, of PMA-induced respiratory burst and aggregation is, at least partly, attributed to the direct suppression of protein kinase C activity through blockade of the catalytic region, but is not due to interference with the membrane translocation of protein kinase C during PMA-induced cell activation.

2',5'-Dihydroxychalcone as a potent chemical mediator and cyclooxygenase inhibitor

Eleven chalcone derivatives have been tested for their inhibitory effects on platelet aggregation in rabbit platelet suspension and the activation of mast cells and neutrophils. Arachidonic acid-induced platelet aggregation was potently inhibited by almost all the compounds and some also had a potent inhibitory effect on collagen-induced platelet aggregation and cyclooxygenase. Some hydroxychalcone derivatives showed strong inhibitory effects on the release of beta-glucuronidase and lysozyme, and on superoxide formation by rat neutrophils stimulated with the peptide fMet-Leu-Phe (fMLP). We found that the anti-inflammatory effect of 2',5'-dihydroxychalcone was greater than that of trifluoperazine. 2'5'-Dihydroxy and 2',3,4,5'-tetrahydroxyl chalcones, even at low concentration (50 microM), tested in platelet-rich plasma from man almost completely inhibited secondary aggregation induced by adrenaline. These results suggest that the anti-platelet effects of the chalcones are mainly a result of inhibition of thromboxane formation.

Examination of the inhibitory effect of norathyriol in formylmethionyl-leucyl-phenylalanine-induced respiratory burst in rat neutrophils

Norathyriol, aglycone of a xanthone C-glycoside mangiferin isolated from Tripterospermum lanceolatum, concentration dependently inhibited the formylmethionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O2.-) generation and O2 consumption in rat neutrophils. In cell-free oxygen radical generating system, norathyriol inhibited the O2.- generation during dihydroxyfumaric acid (DHF) autoxidation and in hypoxanthine-xanthine oxidase system. fMLP-induced transient elevation of [Ca2/]i and the formation of inositol trisphosphate (IP3) were significantly inhibited by norathyriol (30 microM) (about 30 and 46% inhibition, respectively). Norathyriol concentration dependently suppressed the neutrophil cytosolic phospholipase C (PLC). In contrast with the marked attenuation of fMLP-induced protein tyrosine phosphorylation (about 70% inhibition at 10 microM norathyriol), norathyriol only slightly modulated the phospholipase D (PLD) activity as determined by the formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt). Norathyriol did not modulate the intracellular cyclic AMP level. In the presence of NADPH, the phorbol 12-myristate 13-acetate (PMA)-activated particulate NADPH oxidase activity was suppressed by norathyriol in a concentration-dependent manner and the inhibition was noncompetitive with respect to NADPH. Norathyriol inhibited the iodonitrotetrazolium violet (INT) reduction in arachidonic acid (AA)-activated cell-free NADPH oxidase system at the same concentration range as those used in the suppression of PMA-activated particulate NADPH oxidase activity. Taken together, these results suggest that the scavenging ability of norathyriol contributes to the reduction of generated O2.-, however, the inhibition of O2.- generation from neutrophils by norathyriol is attributed to the blockade of PLC pathway, the attenuation of protein tyrosine phosphorylation, and to the suppression of NADPH oxidase through the interruption of electrons transport.

Inhibitory effect of glycyrrhetinic acid derivatives on capsaicin-induced ear edema in mice

We examined the effect of glycyrrhetinic acid (Ia) and its derivatives on ear edema induced by topical application of capsaicin in mice. Three dihemiphthalate compounds: di-sodium salt of 18 beta-olean-12-ene-3 beta,30-diol (deoxoglycyrrhetol, IIa) di-O-hemiphthalate (IIb); 18 beta-olean-9(11),12-diene-3 beta, 30-diol di-O-hemiphthalate (IIIa); and olean-11,13(18)-diene-3 beta,30-diol di-O-hemiphthalate (IVa) inhibited capsaicin-induced edema with ED50 values of 52.6, 41.0 and 51.8 mg/kg (p.o.), respectively. However, glycyrrhetinic acid and deoxoglycyrrhetol at a dose of 200 mg/kg (p.o.) had no effect. Compound IIIa (100 mg/kg, p.o.) also inhibited the edema response to capsaicin in mast cell-deficient mice. Furthermore, compounds IIb, IIIa and IVa (25-100 mg/kg, p.o.) prevented ear edema in response to intradermal injection of substance P (SP) and compound 48/80. In addition, these compounds at a high dose of 100 mg/kg (p.o.) produced a significant inhibition of the plasma extravasation in ear skin induced by i.v. administration of SP. The above results suggest that the effect of these compounds on capsaicin-induced ear edema is due at least in part to an inhibition of the increase of vascular permeability induced by vasoactive agents released from mast cells. Moreover, it seems likely that these compounds at a high dose can suppress vasodilatation and plasma extravasation induced by SP involved in capsaicin-induced edema.

Induction of calcium release from sarcoplasmic reticulum of skeletal muscle by xanthone and norathyriol

1. Effects of xanthone and its derivative, 1,3,6,7-tetrahydroxyxanthone (norathyriol), on Ca2+ release and ryanodine binding were studied in isolated sarcoplasmic reticulum (SR) vesicles from rabbit skeletal muscle. 2. Both xanthone and norathyriol dose-dependently induced Ca2+ release from the actively loaded SR vesicles which was blocked by ruthenium red, a specific Ca2+ release inhibitor, and Mg2+. 3. Xanthone and norathyriol also dose-dependently increased apparent [3H]-ryanodine binding. Norathyriol, but not xanthone, produced a synergistic effect on binding activation when added concurrently with caffeine. 4. In the presence of Mg2+, which inhibits ryanodine binding, both caffeine and norathyriol, but not xanthone, could restore the binding to the level observed in the absence of Mg2+. 5. Xanthone activated the Ca(2+)-ATPase activity of isolated SR vesicles dose-dependently reaching 70% activation at 300 microM. 6. When tested in mouse diaphragm, norathyriol potentiated the muscle contraction followed by twitch depression and contracture in either a Ca(2+) -free bathing solution or one containing 2.5 mM Ca2+. These norathyriol-induced effects on muscle were inhibited by pretreatment with ruthenium red or ryanodine. 7. These data suggest that xanthone and norathyriol can induce Ca2+ release from the SR of skeletal muscle through a direct interaction with the Ca2+ release channel, also known as the ryanodine receptor.

Synthesis and anti-inflammatory effects of xanthone derivatives

Eighteen synthetic xanthone derivatives were tested for their inhibitory effects on the activation of mast cells and neutrophils. 1,3- and 3,5-Dihydroxyxanthone showed strong inhibitory effects on the release of beta-glucuronidase and histamine from rat peritoneal mast cells stimulated with compound 48/80. 1,6-Dihydroxyxanthone and 1,3,8-trihydroxyxanthone showed strong inhibitory effects on the release of beta-glucuronidase, and beta-glucuronidase and lysozyme, respectively, from rat neutrophils stimulated with formyl-Met-Leu-Phe (fMLP). 1,3- and 1,6-Dihydroxyxanthone, 1,3,7-trihydroxyxanthone, and 1,3,5,6-, 2,3,6,7-, and 3,4,5,6-tetrahydroxyxanthone showed potent inhibitory effects on superoxide formation of rat neutrophils stimulated with fMLP. 1,6- and 3,5-Dihydroxyxanthone showed remarkable inhibitory effects on hind-paw oedema induced by polymyxin B in normal as well as in adrenalectomized mice. These data indicated that the anti-inflammatory effect of these compounds is mediated through the suppression of chemical mediators released from mast cell and neutrophil degranulation.

Participation of serotonin in capsaicin-induced mouse ear edema

We investigated the involvement of serotonin (5-HT) in mouse ear edema induced by topical application of capsaicin (250 micrograms/ear). Application of capsaicin to the ear caused degranulation of mast cells in skin connective tissue. Capsaicin-induced ear edema was significantly inhibited by preadministration of 5-HT2 receptor antagonists such as ketanserin (2 mg/kg, i.v.) and LY 53857 (1 mg/kg, i.v.), but not 5-HT1-, 5-HT3- and 5-HT4-receptor antagonists. Intradermal injection of alpha-methyl 5-HT (5-HT2-receptor agonist) and 5-HT into ear skin produced edema formation more potently than 8-OH-DPAT (5-HT1A agonist) and 2-methyl 5-HT (5-HT3 agonist). 5-HT2 antagonists markedly suppressed the edema response to 5-HT and its receptor agonists, whereas any antagonist for 5-HT1, 5-HT3 and 5-HT4-receptors had no effect. Furthermore, 5-HT2-receptor antagonists partly prevented ear edema in response to substance P (SP), a putative mediator or capsaicin-induced edema, and compound 48/80, a releaser of vasoactive amines form mast cells. These results suggest that 5-HT released from mast cells is partly involved in the development of capsaicin-induced mouse ear edema via 5-HT2 receptors in the ear skin.

Inhibition of plasma extravasation by abruquinone A, a natural isoflavanquinone isolated from Abrus precatorius

Polymyxin B-induced hind-paw edema was suppressed by abruquinone A, an isoflavanquinone isolated from Abrus precatorius, in normal as well in adrenalectomized mice. Unlike dexamethasone, abruquinone A did not increase the liver glycogen content in fasting adrenalectomized mice. The volume of exuded plasma was significantly reduced by abruquinone A in neurogenic inflammation, passive cutaneous anaphylactic reaction and compound 48/80-induced ear edema. Histamine-, serotonin-, bradykinin- and substance P-induced plasma extravasation in ear edema was also suppressed by abruquinone A. Abruquinone A, like isoproterenol, significantly reduced the bradykinin- and substance P-induced plasma extravasation in normal as well as in compound 48/80-pretreated mice. In addition, abruquinone A suppressed the bradykinin- and substance P-induced ear edema to a significantly greater extent than diphenhydramine/methysergide did. In the in vitro experiments, abruquinone A suppressed the compound 48/80-induced histamine and beta-glucuronidase released from isolated rat peritoneal mast cell preparations. These results suggest that the anti-inflammatory effect of abruquinone A is mediated partly via the suppression of the release of chemical mediators from mast cells and partly via the prevention of vascular permeability changes caused by mediators. The glucocorticoid activity and the release of glucocorticoid hormones from the adrenal gland are probably not involved.

Inhibition of hind-paw edema and cutaneous vascular plasma extravasation in mice by acetylshikonin

Acetylshikonin, a naphthoquinone isolated from the Chinese herb medicine, tzu ts'ao, was demonstrated to inhibit the polymyxin B-induced hind-paw edema in normal as well as in adrenalectomized mice. Liver glycogen content was increased in adrenalectomized mice pretreated with dexamethasone, but not with acetylshikonin. Like diphenhydramine, methysergide and isoproterenol, acetylshikonin reduced the plasma exudation evoked in dorsal hind-paw skin by antidromic stimulation of the saphenous nerve, and in passive cutaneous anaphylactic reaction, bradykinin-, substance P-, compound 48/80-, histamine- and serotonin-induced ear edema. Indomethacin was ineffective in these respects. Bradykinin- and substance P-induced plasma exudation were also significantly reduced when [Thi5,8,D-Phe7]bradykinin and [D-Pro2,D-Trp7,9]substance P were coinjected with bradykinin and substance P, respectively. In isolated rat peritoneal mast cell preparation, acetylshikonin produced a concentration-dependent inhibition of histamine and beta-glucuronidase release from mast cells challenged by compound 48/80. In compound 48/80-pretreated mice, acetylshikonin and isoproterenol produced significantly more inhibitory effect on bradykinin- and substance P-induced plasma exudation than did diphenhydramine in combination with methysergide. Pretreatment with diphenhydramine/methysergide in compound 48/80-pretreated mice significantly further reduced the bradykinin- and substance P-induced plasma exudation if [Thi5,8,D-Phe7]bradykinin and [D-Pro2,D-Trp7,9]substance P were coinjected with bradykinin or substance P, respectively. The results suggest that the inhibitory effect of acetylshikonin on the edematous response is due neither to the release of steroid hormones from the adrenal gland nor to the glucocorticoid activity, but probably partly to the suppression of mast cell degranulation and partly to protection of the vasculature from mediator challenge.