Effects of Flavone Derivatives on Antigen‐Stimulated Degranulation in RBL‐2H3 Cells

Mast cells are primarily responsible for IgE‐mediated allergic responses. The activation level of mast cells is reflected in their degree of degranulation. This can in turn be determined by measuring the amount of β‐hexosaminidase release, a key parameter in degranulation. In this study, 40 flavone derivatives, including flavone, 14 methoxyflavones, 13 hydroxyflavones, and 12 hydroxymethoxyflavones, were evaluated for their inhibition of degranulation in rat basophilic leukemia RBL‐2H3 cells. 3′,7‐Dihydroxyflavone inhibited degranulation (IC₅₀ = 13.56 μm ), which was comparable to PP2 (3‐(4‐chlorophenyl)‐1‐(1,1‐dimethylethyl)‐1H‐pyrazolo[3,4‐d]pyrimidin‐4‐amine) used as a control. In addition, we report quantitative relationships between the structural properties of flavones and their inhibitory effects on degranulation.     

Inhibition of IgE‐induced mast cell activation by ethyl tertiary‐butyl ether,a bioethanol‐derived fuel oxygenate

Objectives The effect of ethyl tertiary‐butyl ether (ETBE), which is widely used as a fuel oxygenate commonly produced from bioethanol, on immunoglobulin (Ig)E‐dependent mast cell activation was investigated. Methods The rat mast cell line RBL2H3 sensitised with monoclonal anti‐ovalbumin IgE was challenged with ovalbumin in the presence or absence of ETBE, tert‐butanol (TBA), which is the main metabolite of ETBE in humans, and ethanol. Degranulation of RBL2H3 was examined by the release of β‐hexosaminidase. To understand the mechanisms responsible for regulating mast cell function, the effects of ETBE, TBA and ethanol on the levels of intracellular calcium, phosphorylation of Akt (as a marker of phosphatidylinositol 3‐kinase) and global tyrosine phosphorylation were also measured as indicators of mast cell activation. Key findings In the presence of ETBE, TBA or ethanol, IgE‐induced release of β‐hexosaminidase was decreased. These compounds also attenuated the IgE‐mediated increase in the levels of intracellular Ca²⁺, phosphorylation of Akt and global tyrosine phosphorylation in RBL2H3 cells. Conclusions ETBE, TBA and ethanol inhibited mast cell degranulation by inhibiting the increase in intracellular calcium ion concentration and activation of phosphatidylinositol 3‐kinase and protein tyrosine kinase activation, suggesting that exposure to ETBE might affect immune responses, particularly in allergic diseases.     

Inorganic arsenite inhibits IgE receptor‐mediated degranulation of mast cells

Millions of people worldwide are exposed to arsenic (As), a toxicant which increases the risk of various cancers, cardiovascular disease and several other health problems. Arsenic is a potent endocrine disruptor, including of the estrogen receptor. It was recently shown that environmental estrogen‐receptor disruptors can affect the signaling of mast cells, which are important players in parasite defense, asthma and allergy. Antigen (Ag) or allergen crosslinking of IgE‐bound receptors on mast cells leads to signaling, culminating in degranulation, the release of histamine and other mediators. Because As is an endocrine disruptor and because endocrine disruptors have been found to affect degranulation, here we have tested whether sodium arsenite affects degranulation. Using the rat basophilic leukemia (RBL) mast cell model, we have measured degranulation in a fluorescence assay. Arsenic alone had no effect on basal levels of degranulation. However, As strongly inhibited Ag‐stimulated degranulation at environmentally relevant concentrations, in a manner that is very dependent on concentrations of both As and Ag. The concentrations of As effective at inhibiting degranulation were not cytotoxic. This inhibition may be a mechanism underlying the traditional Chinese medicinal use of As to treat asthma. These data indicate that As may inhibit the ability of humans to fight off parasitic disease. Copyright © 2010 John Wiley & Sons, Ltd.     

β‐eudesmol suppresses allergic reactions via inhibiting mast cell degranulation

The regulatory effect of β‐eudesmol, which is an active constituent of Pyeongwee‐San (KMP6), is evaluated for allergic reactions induced by mast cell degranulation. Phorbol 12‐myristate 13‐acetate (PMA) plus calcium ionophore A23187‐stimulated human mast cell line, HMC‐1 cells, and compound 48/80‐stimulated rat peritoneal mast cells (RPMCs) are used as the in vitro models; mice models of systemic anaphylaxis, ear swelling, and IgE‐dependent passive cutaneous anaphylaxis (PCA) are used as the in vivo allergic models. The results demonstrate that β‐eudesmol suppressed the histamine and tryptase releases from the PMA plus calcium ionophore A23187‐stimulated HMC‐1 cells. β‐eudesmol inhibits the expression and activity of histidine decarboxylase in the activated HMC‐1 cells. In addition, β‐eudesmol inhibits the levels of histamine and tryptase released from the compound 48/80‐stimulated RPMCs. Furthermore, β‐eudesmol decreases the intracellular calcium level in the activated RPMCs. β‐eudesmol also decreases the compound 48/80‐induced mortality and ear swelling response. β‐eudesmol suppresses the serum levels of histamine, IgE, interleukin (IL)‐1β, IL‐4, IL‐5, IL‐6, IL‐13, and vascular endothelial growth factor (VEGF) under PCA mice as well as PCA reactions. Therefore, the results from this study indicate the potential of β‐eudesmol as an anti‐allergic drug with respect to its pharmacological properties against mast cell‐mediated allergic reactions.     

Effect of natsudaidain isolated from Citrus plants on TNF‐α and cyclooxygenase‐2 expression in RBL‐2H3 cells

Objectives Flavonoids inhibit the activity of chemical mediators released from mast cells. Our aim was to investigate the effects of natsudaidain, a polymethoxyflavone isolated from Citrus plants, on mast cells. Methods We investigated the inhibitory effects of natsudaidain, which is a polymethoxy‐flavone isolated from Citrus plants, on histamine release, tumour necrosis factor‐α production and cyclooxygenase‐2 expression in Ca ionophore‐stimulated rat basophilic leukemia cells (A23187‐stimulated RBL‐2H3 cells) by spectrofluorometric, ELISA and immunoblotting methods. Key findings The percent of histamine release from A23187‐stimulated RBL‐2H3 cells pretreated with natsudaidain at 5, 25 and 50 μM was not changed as compared with non‐treated A23187‐stimulated cells. At 100 and 200 μM, natsudaidain pretreatment resulted in slightly reduced histamine release (% histamine release, 89.8 ± 3.5% and 71.5 ± 5.6% at 100 and 200 μM). Thus, natsudaidain hardly affects histamine release from RBL‐2H3 cells, except at high concentrations. On the other hand, natsudaidain dose‐dependently inhibited tumour necrosis factor‐α protein and mRNA levels in A23187‐stimulated RBL‐2H3 cells; a concentration of 6.8 μM was required for a 50% reduction. In addition, all concentrations of this compound that we tested also inhibited cyclooxygenase‐2 protein expression. The mRNA levels of cyclooxygenase‐2 in A23187‐stimulated RBL‐2H3 cells treated with natsudaidain were also markedly decreased. The phosphorylated‐p38 MAPK protein levels in A23187‐stimulated RBL‐2H3 cells treated with natsudaidain were lower than in the non‐treated cells. Conclusions These findings suggest that natsudaidain inhibits tumour necrosis factor‐α and cyclooxygenase‐2 production by suppressing p38 MAPK phosphorylation but not p65 NFKB phosphorylation, and that natsudaidain might alleviate inflammatory diseases.     

Synthesis of stable isotopically labelled 3‐methylfuran‐2(5H)‐one and the corresponding strigolactones

Conventional synthetic procedures of strigolactones (SLs) involve the independent synthesis of ring ABC and ring D, followed by a coupling of the two fragments. Here we prepared three kinds of stable, isotopically labelled D‐ring analogues productively using a facile protocol. Then, a coupling of the D‐rings to ring ABC produced three isotope‐labelled SL derivatives. Moreover, (+)‐D₃‐2′‐epi‐ 1A and (?)‐ent‐D₃‐2′‐epi‐ 1A with high enantiomeric purity were obtained via chiral resolution.     

Entrapping unusual folding characteristics of the β‐Ala residues in a model peptide: Boc‐β‐Ala‐Aib‐β‐Ala‐NHCH3

Abstract: Crystal structure analysis of a model peptide: Boc‐β‐Ala‐Aib‐β‐Ala‐NHCH₃ (β‐Ala: 3‐amino propionic acid; Aib: α‐aminoisobutyric acid) revealed distinct conformational preferences for folded [φ≈136°, µ ≈ ?62°, ψ ≈100°] and semifolded [φ ≈ 83°, µ ≈ ?177°, ψ ≈ ?117°] structures of the N‐ and C‐terminus β‐Ala residues, respectively. The overall folded conformation is stabilized by unusual N_i···H‐N_i+1 and nonconventional C–H···O intramolecular hydrogen bonding interactions.     

γ‐H2AX formation in the urinary bladder of rats treated with two norharman derivatives obtained from o‐toluidine and aniline

Aminomethylphenylnorharman (AMPNH) and aminophenylnorharman (APNH) are mutagenic norharman derivatives obtained from o‐toluidine and aniline, respectively. APNH is carcinogenic to the urinary bladder of rats and present in urine samples of healthy volunteers, indicating that norharman derivatives may be associated with cancer development in the urinary bladder of humans. To evaluate the possible role of AMPNH and APNH in bladder carcinogenesis, we examined the formation of γ‐H2AX, a DNA damage response marker, in the urinary bladder of rats. Seven‐week‐old male F344 rats were treated with 400 ppm AMPNH or 40 ppm APNH in the diet for 4 weeks. Animals were killed at the end of administration or after 2 weeks of recovery, and immunohistochemistry for γ‐H2AX and Ki67, a cell proliferation marker, was performed. At week 4, γ‐H2AX formation in bladder epithelial cells was significantly increased by APNH treatment as compared with that in controls. AMPNH also induced upregulation of γ‐H2AX formation, although there was no statistical significance. After the recovery period, γ‐H2AX‐positive cells were reduced but remained significantly higher in AMPNH and APNH groups than in the control group. Ki67‐positive cells were significantly increased by AMPNH and APNH at week 4 and reduced to the same level as the control after 2 weeks of recovery. Expression of KRT14, a bladder stem cell marker, was also increased in the basal layer by the two norharman derivatives. Thus, AMPNH and APNH showed in vivo genotoxicity in the bladder epithelium of rats, and APNH may be a potent causative agent of bladder carcinogenesis.     

A new [2H]‐labelled α‐trichloroimidate glucuronic ester for the synthesis of deuterated drug conjugates

A new reaction pathway for the synthesis of a [²H]‐labelled trichloroacetimidate precursor for the preparation of glucuronides is described. Therewith, stable isotope‐labelled drug glucuronides become accessible on a preparative scale, which can further be used as internal standards for quantitative analysis.     

2‐Pyridinyl‐4(3H)‐Quinazolinone: A Scaffold for Anti‐influenza A Virus Compounds

A series of 2‐pyridinyl‐3‐substituted‐4(3H)‐quinazolinones were synthesized, and their anti‐influenza A virus activities were determined using the cytopathic effect inhibition assay. Most of the compounds were potent with IC₅₀ values ranging from 51.6 to 93.0 μm , which are better than that of the currently marketed drug ribavirin. The molecular mechanisms of the new compounds were investigated using neuraminidase inhibition assay, cellular NF‐κB signaling pathway inhibition assay, and computational docking. Compound 4e , which is a N3 imidazol‐1‐ylpropyl‐substituted derivative of 2‐pyridinyl‐4(3H)‐quinazolinone, had the most potent anti‐influenza A virus activity in vitro, and inhibited both virus neuraminidase and cellular NF‐κB signaling pathway. In conclusion, 2‐pyridinyl‐4(3H)‐quinazolinone is a new scaffold for the design of potent anti‐influenza A virus compounds, offering an alternative approach to tackle influenza drug resistance.     

Synthesis,biological evaluation,and docking studies of some 5‐chloro‐2(3H)‐benzoxazolone Mannich bases derivatives as cholinesterase inhibitors

A series of N‐substituted‐5‐chloro‐2(3H)‐benzoxazolone derivatives were synthesized and evaluated for their acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) inhibitory, and antioxidant activities. The structures of the title compounds were confirmed by spectral and elemental analyses. The cholinesterase (ChE) inhibitory activity studies were carried out using Ellman's colorimetric method. The free radical scavenging activity was also determined by in vitro ABTS (2,2‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid)) assay. The biological activity results revealed that all of the title compounds displayed higher AChE inhibitory activity than the reference compound, rivastigmine, and were selective for AChE. Among the tested compounds, compound 7 exhibited the highest inhibition against AChE (IC₅₀ = 7.53 ± 0.17 μM), while compound 11 was found to be the most active compound against BuChE (IC₅₀ = 17.50 ± 0.29 μM). The molecular docking study of compound 7 showed that this compound can interact with the catalytic active site (CAS) of AChE and also has potential metal chelating ability and a proper log P value. On the other hand, compound 2 bearing a methyl substituent at the ortho position on the phenyl ring showed better radical scavenging activity (IC₅₀ = 1.04 ± 0.04 mM) than Trolox (IC₅₀ = 1.50 ± 0.05 mM).

     

Functional expressions of adenosine triphosphate‐binding cassette transporters during the development of zebrafish embryos and their effects on the detoxification of cadmium chloride and β‐naphthoflavone

Adenosine triphosphate‐binding cassette (ABC) transporters, including ABCB, ABCC and ABCG families represent general biological defenses against environmental toxicants in varieties of marine and freshwater organisms, but their physiological functions at differential developmental stages of zebrafish embryos remain undefined. In this work, functional expressions of typical ABC transporters including P‐glycoprotein (Pgp), multiresistance associated protein 1 (Mrp1) and Mrp2 were studied in zebrafish embryos at 4, 24, 48 and 72 h post‐fertilization (hpf). As a result, both the gene expressions and activities of Pgp and Mrps increased with the development of embryos. Correspondingly, 4–72 hpf embryos exhibited an increased tolerance to the toxicity caused by cadmium chloride (CdCl₂) and β‐naphthoflavone (BNF) with time. Such a correlation was assumed caused by the involvement of ABC transporters in the detoxification of chemicals. In addition, the assumption was supported by the fact that model efflux inhibitors of Pgp and Mrps such as reversine 205 and MK571 significantly inhibited the efflux of toxicants and increased the toxicity of Cd and BNF in zebrafish embryos. Moreover, exposure to CdCl₂ and BNF induced the gene expressions of Pgp and Mrp1 in 72 hpf embryos. Thus, functional expressions of Pgp and Mrps increased with the development of zebrafish embryos, which could cause an increasing tolerance of zebrafish embryos to CdCl₂ and BNF. Copyright © 2015 John Wiley & Sons, Ltd.     

Bis‐2(5H)‐furanone derivatives as new anticancer agents: Design,synthesis, biological evaluation,and mechanism studies

New bis‐2(5H)‐furanone derivatives containing a benzidine core were synthesized via a one‐step transition‐metal‐free reaction of benzidine with 5‐substituted 3,4‐dihalo‐2(5H)‐furanones. Their antitumor activities against various tumor cells have been evaluated by MTT assay. Among them, compound 4e exhibits significant inhibitory activity against C6 glioma cells with an IC₅₀ value of 12.1 μm and low toxicity toward HaCaT human normal cells. Studies on the antitumor mechanism reveal that cell cycle arrest at S‐phase in C6 cells is induced by compound 4e . Furthermore, investigations with electronic, fluorescence emission and circular dichroism spectra show that compound 4e can significantly interact with C6‐DNA. These data indicate that DNA may be one of the potential targets for bis‐2(5H)‐furanone derivatives as anticancer drugs.     

Radiosynthesis of 1‐(4‐(2‐[18F]fluoroethoxy)benzenesulfonyl)‐3‐butyl urea: a potential β‐cell imaging agent

Tolbutamide ( 1 ) is a sulfonurea agent used to stimulate insulin secretion in type 2 diabetic patients. Its analogue 1‐(4‐(2‐[¹⁸F]fluoroethoxy)benzenesulfonyl)‐3‐butyl urea ( 3 ) was synthesized in overall radiochemical yields of 45% as a potential β‐cell imaging agent. Compound 3 was synthesized by ¹⁸F‐fluoroalkylation of the corresponding hydroxy precursor ( 2 ) with 2‐[¹⁸F]fluoroethyltosylate in DMF at 120°C for 10 min followed by purification with HPLC in a synthesis time of 50 min. Insulin secretion experiments of the authentic ¹⁹F‐standard compound on rat islets showed that the compound has a similar stimulating effect on insulin secretion as that of tolbutamide ( 1 ). The partition coefficient of compound 3 between octanol/water was determined to be 1.3±0.3 (n=5). Copyright © 2002 John Wiley & Sons, Ltd.     

Immunohistochemistry of γ‐H2AX as a method of early detection of urinary bladder carcinogenicity in mice

Phosphorylated histone H2AX (γ‐H2AX) has been demonstrated as a DNA damage marker both in vitro and in vivo. We previously reported the effects of genotoxic carcinogens in the urinary bladder of rats by immunohistochemical analysis of γ‐H2AX using samples from 28‐day repeated‐dose tests. To evaluate the application of γ‐H2AX as a biomarker of carcinogenicity in the bladder, we examined species differences in γ‐H2AX formation in the urinary bladder of mice. Six‐week‐old male B6C3F₁ mice were treated orally with 12 chemicals for 4 weeks. Immunohistochemical analysis demonstrated that N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine, p‐cresidine and 2‐acetylaminofluorene (2‐AAF), classified as genotoxic bladder carcinogens, induced significant increases in γ‐H2AX levels in the bladder urothelium. In contrast, genotoxic (2‐nitroanisole, glycidol, N‐nitrosodiethylamine and acrylamide) and non‐genotoxic (dimethylarsinic acid and melamine) non‐bladder carcinogens did not upregulate γ‐H2AX. Importantly, 2‐nitroanisole, a potent genotoxic bladder carcinogen in rats, significantly increased the proportion of γ‐H2AX‐positive cells in rats only, reflecting differences in carcinogenicity in the urinary bladder between rats and mice. Significant upregulation of γ‐H2AX was also induced by uracil, a non‐genotoxic bladder carcinogen that may be associated with cell proliferation, as demonstrated by increased Ki67 expression. 2‐AAF caused γ‐H2AX formation mainly in the superficial layer, together with reduced and disorganized expression of uroplakin III, unlike in rats, suggesting the mouse‐specific cytotoxicity of 2‐AAF in umbrella cells. These results suggest γ‐H2AX is a useful biomarker reflecting species differences in carcinogenicity in the urinary bladder.