Daphnoretin-induced respiratory burst in rat neutrophils is, probably, mainly through protein kinase C activation

Wikstroemia: A Review on its Phytochemistry and Pharmacology

BACKGROUND

Wikstroemia (the family Thymelaeaceae) consists of medicinal plants which established great value in traditional medicines for many years. For instance, W. indica is always recommended for treatments of syphilis, arthritis, whooping cough, and cancer. No systematic review of bioactive compounds from this genus has been recorded to date.

OBJECTIVES

The objective of the current study is to review phytochemical investigations and pharmacological effects of Wikstroemia plant extracts and isolates.

METHODS

By searching on the internet, the relevant data about Wikstroemia medicinal plants were retrieved from internationally renowned scientific databases, such as Web of Science, Google Scholar, Sci-Finder, Pubmed, and so on.

RESULTS

More than 290 structurally diverse metabolites were separated and identified from this genus. They include terpenoids, lignans, flavonoids, coumarins, mono-phenols, diarylpentanoids, fatty acids, phytosterols, anthraquinones, and others. Pharmacological records indicated that Wikstroemia plant crude extracts and their isolated compounds bring out various beneficial effects, such as anticancer, antiinflammatory, anti-aging, anti-viral, antimicrobacterial, antimalarial, neuroprotective, and hepatoprotective activities.

CONCLUSION

Wikstroemia has been regarded as a worthy genus with numerous phytochemicals and various pharmacological potentials. Modern pharmacological studies have successfully provided evidence for traditional uses. Nonetheless, their action mechanisms need to be further investigated. Although various secondary metabolites were identified from Wikstroemia plants, the current pharmacological research mainly concentrated on terpenoids, lignans, flavonoids, and coumarins.

Daphnoretin Arrests the Cell Cycle and Induces Apoptosis in Human Breast Cancer Cells

Emerging evidence has shown that daphnoretin, one of the main active ingredients of Daphne giraldii Nitsche, processes antitumor activities in several tumor cells (e.g., colon cancer, lung cancer, cervical cancer, and osteosarcoma). However, the antitumor effect and its mechanism in breast cancer are unexplored. In this study, our data indicated that daphnoretin obviously suppressed the proliferation of breast cancer MCF-7 and MDA-MB-231 cells. Further studies showed that daphnoretin remarkably increased the p21 level, decreased cyclin E and CDK2 levels, and then arrested the cell cycle at the S phase. Moreover, daphnoretin obviously lowered the BCL-2 level and raised the levels of BAX and cleaved caspase-9 and -3, leading to cell apoptosis. Furthermore, daphnoretin remarkably decreased the ratio of p-PI3K/PI3K and p-AKT/AKT in breast cancer cells. Collectively, these findings demonstrated that daphnoretin could suppress breast cancer cell proliferation through cell cycle arrest and inducing apoptosis, which is related to the PI3K/AKT pathway.

Daphnoretin from Carthamus tinctorius as a Potential Inflammatory Inhibitor in COVID-19 by Binding to Toll-like Receptor-4: An in silico Molecular Docking Study

BACKGROUND: Cytokine storm in COVID-19 patients has contributed to many morbidities and mortalities in patients. Studies have found that toll-like receptors (TLRs) and some Fc receptors play essential roles in the hyperactivation of the immune system. Up to date, researchers are still in progress to discover effective and safe drugs to alleviate the hyperinflammatory state in COVID-19. The previous studies had shown that Carthamus tinctorius and its bioactive compounds might have anti-inflammatory activities in animal models. AIM: We aimed to investigate the possible interactions of several flavonoids from C. tinctorius with several immune system components using a biocomputational approach. METHODS: Molecular docking was done using the AutoDock program based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) COVID-19 pathway. The most suitable receptors found were studied to study the interactions with several flavonoids from C. tinctorius. RESULTS: TLR4, TLR8, and FcγRIIa were found to bind with SARS CoV2 inflammatory pathway and further selected as macromolecules for potential interactions study with 22 flavonoids from C. tinctorius. Of the 22 flavonoids studied, daphnoretin showed the best binding affinity with TLR4 and Rutin was shown to attach best with FcγRIIa. Unlike its excellent binding to TLR4, daphnoretin showed weak binding to TLR8. CONCLUSION: Daphnoretin showed an excellent affinity with TLR4 and might be a good candidate as an inhibitor in hyperinflammatory reactions in COVID-19 DTLR8.

Daphnoretin modulates differentiation and maturation of human dendritic cells through down-regulation of c-Jun N-terminal kinase

Daphnoretin, an active constituent of Wikstroemia indica C.A. Meys, has been shown possessing anti-cancer activity. In this study, we examined the effect of daphnoretin on differentiation and maturation of human myeloid dendritic cells (DCs). After treatment with daphnoretin (0, 1.1, 3.3, 10 and 30μM) to initiate monocytes, the recovery rate of DCs was reduced in a dose-dependent manner. The mature DCs differentiated in the presence of daphnoretin had fewer and shorter dendrites. Daphnoretin modulated DCs differentiation and maturation in terms of lower expression of CD1a, CD40, CD83, DC-SIGN, and HLA-DR. Daphnoretin inhibited the allostimulatory activity of DCs on proliferation of naive CD4⁺CD45⁺RA⁺ T cell. On the mitogen-activated protein kinase, daphnoretin down-regulated the lipopolysaccharide-augmented expression of phosphorylated c-Jun N-terminal kinase (pJNK), but not p38 and extracellular signal-regulated kinase 1/2 (ERK1/2). Activation of JNK by anisomycin reversed the effect of daphnoretin on daphnoretin-inhibited pJNK expression and dendrite formation of DCs. In disease model related to maturation of DCs, daphnoretin suppressed the acute rejection of skin allografts in mice. Our results suggest that daphnoretin modulated differentiation and maturation of DCs toward a state of atypical maturation with impaired allostimulatory function and this effect may go through down-regulation of phosphorylated JNK.

Protein kinase C as a target for new anti-cancer agents

Cancer joins the category of diseases involving abnormalities in the rate of proliferation of cells and is associated with uncontrolled cell division, where cells either generate their own growth-promoting stimuli or neighboring cells or do not respond to growth inhibitory signals. Protein kinase C (PKC) is one of the key elements in the tumor growth signal transduction pathways and is found to be overexpressed in several malignant cell types. A way to control cell proliferation and cell differentiation is by influencing signal transduction pathways by modulation of PKC. PKC encloses 12 different isoenzymes, and each isoenzyme is found to have a different functional property. Because specific PKC isoenzyme types are present in different (malignant) cell species, they may be an attractive target in the development of anti-cancer agents. Classification and identification of the available PKC isoenzymes in different tumor cells could be useful in targeting specific tumors. PKC also tends to be overexpressed in association with the multidrug resistance pheno-type. This concise review deals with the role of PKC isoenzymes in (tumor) cell biology and evaluates the antineoplastic agents interacting on PKC isoenzymes.

The Chemistry and Biological Activities of Natural Products from Northern African Plant Families: From Taccaceae to Zygophyllaceae

Traditional medicinal practices have a profound influence on the daily lives of people living in developing countries, particularly in Africa, since the populations cannot generally afford the cost of Western medicines. We have undertaken to investigate the correlation between the uses of plants in Traditional African medicine and the biological activities of the derived natural products, with the aim to validate the use of traditional medicine in Northern African communities. The literature is covered for the period 1959-2015 and part III of this review series focuses on plant families with names beginning with letters T to Z. The authors have focused on curating data from journals in natural products and phytomedicine. Within each journal home page, a query search based on country name was conducted. All articles "hits" were then verified, one at a time, that the species was harvested within the Northern African geographical regions. The current data partly constitutes the bases for the development of the Northern African natural compounds database. The review discusses 284 plant-based natural compounds from 34 species and 11 families. It was observed that the ethnobotanical uses of less than 40 % of the plant species surveyed correlated with the bioactivities of compounds identified.

Effect of daphnoretin on the proliferation and apoptosis of A549 lung cancer cells in vitro

Daphnoretin is an active constituent of Wikstroemia indica C.A. Mey., which is widely distributed in the northwest and southwest regions of China. Previous studies have shown that daphnoretin has anticancer effects on leukemia, osteosarcoma and uterine cervix cancer cells. However, the effect of daphnoretin on human lung cancer cells has yet to be elucidated. In the present study, daphnoretin was observed to inhibit A549 lung cancer cell proliferation in a concentration- and time-dependent manner. Fluorescent microscopy and flow cytometric analysis showed that daphnoretin induced A549 cell apoptosis in a concentration-dependent manner. Western blot analysis also revealed that daphnoretin induced apoptosis through the regulation of the B-cell lymphoma-2 gene family in A549 cells. These findings indicate that daphnoretin may have potential as a therapeutic agent for the management of lung cancer.

Daphnoretin-induced apoptosis in HeLa cells: a possible mitochondria-dependent pathway

Daphnoretin is a bicoumarin compound isolated from a natural product, Wikstroemia indica, which has been used to treat many diseases. It has strong antiviral and anti-tumor activities. Taking the anti-tumor activity of daphnoretin as a starting point, the present study aimed to test the pro-apoptotic effect of daphnoretin and its underlying mechanism in HeLa cells. The inhibitory effects of daphnoretin on viability and proliferation of HeLa cells were determined by the MTT assay. Daphnoretin-induced apoptotic morphological changes were analyzed by mitochondrial membrane potential and Hoechst staining. The number and stage of apoptotic HeLa cells were determined by flow cytometry. Gene expression was determined by reverse-transcription polymerase chain reaction. Protein expression was determined by western blot. The caspase activity of HeLa cells was detected by a caspase-3 and caspase-9 colorimetric assay kit. We found that daphnoretin significantly inhibited HeLa cells' viability by the MTT assay and flow cytometry. The nuclei of the apoptotic cells exhibited strong, blue fluorescence in Hoechst staining. Bax mRNA and protein levels were increased while bcl-2 mRNA levels were decreased after daphnoretin treatment. Daphnoretin also activated both caspase-3 and caspase-9. These findings suggest that daphnoretin promotes apoptosis of HeLa cells in a mitochondria-mediated way. Daphnoretin therefore has potential to be a promising drug to treat uterine cervix cancer.

Oleodaphnoic acid and coriaceol, two new natural products from the stem bark of Wikstroemia coriacea

Fractionation of the chloroform extract of Wikstroemia coriacea led to the isolation of two new compounds, oleodaphnoic acid (1), a guaiane-type sesquiterpenoid, and coriaceol (2), an 1,5-diphenyl-1-pentanone analogue, together with nine known compounds. The structures of 1 and 2 were elucidated by extensive spectroscopic data analysis. The known compounds were oleodaphnal (3), indicanone (4), (5R,8R,8aR)-3,8-dimethyl-4,5,6,7,8,8a-hexahydro-5-(1-methylethenyl)-2(1H)-azulenone, (5), 1,5 diphenyl-1-pentanone (6), (+)-3-hydroxy-1,5-diphenyl-1-pentanone (7), umbelliferone (8), daphnoretin (9), β-sitostenone (10) and (−)-hinokinin (11).

Small-molecule NOX inhibitors: ROS-generating NADPH oxidases as therapeutic targets

NOX NADPH oxidases are electron-transporting membrane enzymes whose primary function is the generation of reactive oxygen species (ROS). ROS produced by NOX enzymes show a variety of biologic functions, such as microbial killing, blood pressure regulation, and otoconia formation. Strong evidence suggests that NOX enzymes are major contributors to oxidative damage in pathologic conditions. Blocking the undesirable actions of NOX enzymes, therefore, is a therapeutic strategy for treating oxidative stress-related pathologies, such as ischemia/reperfusion tissue injury, and neurodegenerative and metabolic diseases. Most currently available NOX inhibitors have low selectivity, potency, and bioavailability, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. This review has two main purposes. First, we describe a systematic approach that we believe should be followed in the search for truly selective NOX inhibitors. Second, we present a critical review of small-molecule NOX inhibitors described over the last two decades, including recently published patents from the pharmaceutical industry. Structures, activities, and in vitro/in vivo specificity of these NOX inhibitors are discussed. We conclude that NOX inhibition is a pertinent and promising novel pharmacologic concept, but that major efforts will be necessary to develop specific NOX inhibitors suited for clinical application.

Activation of phosphoinositide 3-kinase and Src family kinase is required for respiratory burst in rat neutrophils stimulated with artocarpol A

Artocarpol A (ART), a natural product isolated from Artocarpus rigida, stimulated superoxide anion (O2*-) generation, which was inhibited by 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294002), a phosphoinositide 3-kinase (PI3K) inhibitor, in rat neutrophils. ART stimulated phosphorylation of protein kinase B (PKB/Akt) on both T308 and S473 residues, and LY 294002 inhibited these effects. Rat neutrophils expressed both class IA PI3K subunits (p85, p110alpha, p110beta, and p110delta) and a class IB PI3K subunit (p110gamma) as assessed by a combination of Western blotting and reverse transcription-polymerase chain reaction (RT-PCR) approaches. Stimulation of neutrophils with ART evoked phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) formation, which reached a maximal level at 2 min and was attenuated by LY 294002, as evidenced by immunofluorescence microscopy and by flow cytometry. Detectable membrane-association of class IA PI3Ks, class IB PI3K and Ras was seen as early as 1.5, 0.5 and 1.5 min, respectively, after stimulation with ART. The kinetics of ART-induced Ras activation paralleled the kinetics of class IA PI3Ks recruitment to membrane caused by ART, and the p85 and p110gamma immunoprecipitates contain Ras. ART stimulated Src family kinase activation, which was detectable within 1.5 min of incubation with ART. Both Src kinase activity and PtdIns(3,4,5)P3 formation in ART-stimulated neutrophils were inhibited by 4-amino-1-tert-butyl-3-(1'-naphthyl)pyrazolo[3,4-d]pyrimidine (PP1 analog). PP1 analog also attenuated the ART-stimulated O2*- generation in rat neutrophils. These results indicate that the stimulation of respiratory burst by ART in neutrophils implicates PI3K signaling.

Synthesis of (2E)-3-{2-[(substituted benzyl)oxy]phenyl}acrylaldehydes as novel anti-inflammatory agents

As part of our continuing effort for development of novel anti-inflammatory agents, the highly potential agent CCY1a, which we reported recently, was selected as lead compound to synthesize a series of its derivatives for evaluation. Most of the newly synthesized compounds exhibited superior inhibitory activity than both the lead compound and the positive control (trifluoperazine) toward fMLP-stimulated neutrophil superoxide formation. (2E)-3-[2-(Benzyloxy)-5-methoxyphenyl]-acrylaldehyde (31) was among the most potent with action mechanism different from CCY1a in that it does not act as cAMP-elevating agent but inhibits the increase in cellular Ca(2+) with greater potency.

Artocarpol A stimulation of superoxide anion generation in neutrophils involved the activation of PLC, PKC and p38 mitogen-activated PK signaling pathways

1 Artocarpol A (ART), a natural phenolic compound isolated from Artocarpus rigida, stimulated a slow onset and long-lasting superoxide anion generation in rat neutrophils, whereas only slightly activated the NADPH oxidase in a cell-free system. 2 Pretreatment of neutrophils with pertussis toxin (1 microg ml(-1)), 50 microM 2'-amino-3'-methoxyflavone (PD 98059), or 1 microM 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126) had no effect on ART-stimulated superoxide anion generation. ART (30 microM) did not induce extracellular signal-regulated kinase (ERK) phosphorylation. 3 4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB 203580) markedly attenuated the ART-stimulated superoxide anion generation (IC50 value of 4.3+/-0.3 microM). Moreover, ART induced p38 mitogen-activated PK (MAPK) phosphorylation and activation. 4 The superoxide anion generation in response to ART was also substantially inhibited in a Ca2+-free medium, and by pretreatment with 1 microM 1-[6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U-73122) and 100 microM 2-aminoethyldiphenyl borate (2-APB). ART (30 microM) stimulated the [Ca2+]i elevation in the presence or absence of external Ca2+, and also increased the D-myo-inositol 1,4,5-trisphosphate formation. 5 2-[1-(3-Dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide (GF 109203X) greatly inhibited the ART-stimulated superoxide anion generation (IC50 value of 7.8+/-1.0 nM). ART increased the recruitment of PKC-alpha, -betaI, and -betaII to the plasma membrane of neutrophils, and stimulated Ca2+-dependent PKC activation in the cytosol preparation. 6 ART induced the phosphorylation of p47phox, which was attenuated by GF 109203X. Moreover, ART evoked the membrane association of p47(phox), which was inhibited by GF 109203X and SB 203580. 7 These results indicate that the ART stimulation of superoxide anion generation involved the activation of p38 MAPK, PLC/Ca2+, and PKC signaling pathways in rat neutrophils.

Measurement of daphnoretin in plasma of freely moving rat by liquid chromatography

Daphnoretin (7-hydroxyl-6-methoxy-3,7'-dicoumaryl ether), isolated from Wikstronemia indica C.A. Mey. (Thymelaceae), has been reported to induce rabbit platelet aggregation through protein kinase C activation and anticancer activity. In this study, we developed an automated blood sampling system coupled to a simple and sensitive HPLC system to determine plasma concentration of daphnoretin in rats. This method was applied to investigate the pharmacokinetics of daphnoretin in a freely moving rat. Separation of daphnoretin in the rat plasma was achieved using a reversed-phase C18 column (250 mm x 4.6 mm, 5 microm) with a mobile phase of methanol-10 mM NaH2PO4 (adjusted to pH 3.0 with H3PO4) (55:45, v/v), and the flow rate of 1.0 ml/min. The UV detector was set at 345 nm. The automated blood sampling system (DR-II has been applied for blood sampling in a conscious and freely moving rat. The blood samples were centrifuged at 3000 x g for 10 min and the plasma samples were then deproteinized by acetonitrile containing an internal standard (khellin 1 microg/ml). After centrifugation (8000 x g for 10 min), the aliquot of supernatant was injected into the HPLC system for analysis. The concentration-response relationship from the present method indicated linearity over a concentration range of 0.05-1.00 and 1.00-100 microg/ml. Intra- and inter-assay precision and accuracy of daphnoretin fell well within the predefined limits of acceptability (< or = 15%). After daphnoretin (500 mg/kg) was given orally, the maximum concentration was 0.17 microg/ml at the time of 5 min. The oral bioavailability was about 0.15%.

The conditioned enhancement of neutrophil activity is catecholamine dependent

Neutrophil activity was elevated in the conditioned mice for the first time through an established conditioned training process. Catecholamines were proved to be important in the regulation of this conditioned innate immunity. In the study, the camphor odor (as the conditioned stimulus, CS) and poly I: C (as the unconditioned stimulus, US) was used to conditionally elevate the activity of the splenic neutrophils. The mechanism(s) responsible for the conditioned enhancement of neutrophil activity was further investigated using the neurochemical blocking assay and immunohistochemical analysis. Results showed that the neutrophil activity was significantly enhanced through the conditioned training process; both reserpine and 6-hydroxydopamine (6-OHDA) significantly blocked this conditioned innate immunity at the conditioned recall stage. Dexamethasone (Dex), however, showed no effect on the conditioned neutrophil response. Tyrosine hydroxylase (TH)-positive cells significantly increased in the locus coeruleus (LC), hypothalamus, and cortex but not in the spleen of the conditioned animals. These results indicate that during the conditioned recall stage, the brain signals the splenic neutrophils via the sympathetic nervous system (SNS) by releasing the peripheral catecholamines in spleen. The activation of the SNS, on the other hand, is also under the influence of catecholamines released in the LC. The hypothalamic pituitary (HP) axis, on the other hand, plays no role in the regulation of the conditioned neutrophil response.

The blockade of cyclopiazonic acid-induced store-operated Ca2+ entry pathway by YC-1 in neutrophils

In the presence of external Ca2+, pretreatment of neutrophils with 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) inhibited the cyclopiazonic acid (CPA)-induced [Ca2+](i) elevation in a concentration- but not a time-dependent manner, while YC-1 had no effect on the Ca2+ signals in a Ca2+-free medium. YC-1 failed to inhibit ATP- and interleukin-8 (IL-8)-induced [Ca2+](i) changes. Addition of YC-1 after cell activation strongly inhibited the CPA-induced [Ca2+](i) changes. In a classical Ca2+ readdition protocol, a similar extent inhibition of Ca2+ spike by YC-1 introduced either prior to or after CPA stimulation was obtained. In rat neutrophils, mRNA for endothelial differentiation gene (edg)1, edg5, edg6 and edg8, the putative targets for sphingosine 1-phosphate (S1P), could be detected. However, S1P was found to have little effect on Ca(2+) signals. YC-1 did not inhibit but enhanced the sphingosine-induced [Ca2+](i) changes. Inhibition by YC-1 of CPA-induced [Ca2+](i) changes was not prevented by 7-nitroindazole and N-(3-aminomethyl)benzylacetamidine (1400W), two nitric oxide synthase (NOS) inhibitors, by aristolochic acid, a phospholipase A(2) inhibitor, or by suspension in a Na(+)-deprived medium. YC-1 did not affect the mitochondrial membrane potential. Moreover, YC-1 did not alter [Ca2+](i) changes in response to ionomycin after CPA and formyl-Met-Leu-Phe (fMLP) stimulation in a Ca2+-free medium. YC-1 had no effect on the basal [Ca2+](i) level, the pharmacologically isolated plasma membrane Ca2+-ATPase activity, and Ba2+ entry into CPA-activated cells. YC-1 alone resulted in the accumulation of actin filaments in neutrophils, while significantly reduced the intensity of actin filament staining in the subsequent activation with CPA. These results indicate that YC-1 inhibited CPA-activated store-operated Ca2+ entry (SOCE) probably through the direct blockade of channel activation and/or the disruption of the integrity of the actin cytoskeleton necessary for supporting Ca2+ entry pathway in neutrophils.

2-Benzyloxybenzaldehyde inhibits formyl peptide-stimulated increase in intracellular Ca2+ in neutrophils mainly by blocking Ca2+ entry

2-Benzyloxybenzaldehyde (CCY1a) inhibited the formyl-Met-Leu-Phe (fMLP)-induced elevation of cytosolic [Ca(2+)]() ([Ca(2+)](i)) in rat neutrophils. The late plateau phase, but not the initial Ca(2+) spike, of the fMLP-induced [Ca(2+)](i) change was inhibited by CCY1a. In the absence of external Ca(2+), CCY1a had no appreciable effect on either the fMLP- or cyclopiazonic acid (CPA)-induced [Ca(2+)](i) elevation. CCY1a failed to inhibit [Ca(2+)](i) changes induced by N-ethylmaleimide, GEA3162, ionomycin or sphingosine, but slightly inhibited the Ca(2+) signals elicited by ATP or interleukin-8 (IL-8). In a classical Ca(2+) readdition protocol, addition of CCY1a after cell activation strongly inhibited the [Ca(2+)](i) response to fMLP, whilst that to CPA was only slightly reduced. CCY1a nearly abrogated the fMLP-stimulated Mn(2+) influx but was less effective on the CPA-induced response. CCY1a attenuated the levels of tyrosine-phosphorylated bands in the 70-85 kDa molecular mass range. CCY1a had no effect on the basal [Ca(2+)](i) level, the pharmacologically isolated plasma membrane Ca(2+)-ATPase activity or on the mitochondrial membrane potential. Thus, CCY1a blocks fMLP-induced Ca(2+) entry into neutrophils probably by blocking the relevant Ca(2+) channel directly or, alternatively, indirectly through the attenuation of tyrosine phosphorylation of some cellular proteins.

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.

Mechanisms of the influence of magnolol on eicosanoid metabolism in neutrophils

We have demonstrated that magnolol suppressed thromboxane B2 (TXB2) and leukotriene B4 (LTB4) formation in A23187-stimulated rat neutrophils. Maximum inhibition was obtained with about 10 microM magnolol. Magnolol was more effective in the inhibition of cyclooxygenase (COX) activity than in the inhibition of 5-lipoxygenase (5-LO) activity as assessed by means of enzyme activity determination in vitro and COX and 5-LO metabolic capacity analyses in vivo. Magnolol alone stimulated cytosolic phospholipase A2 (cPLA2) phosphorylation and the translocation of 5-LO and cPLA2 to the membrane, and evoked arachidonic acid (AA) release. Recruitment of both 5-LO and cPLA2 to the membranes was suppressed by EGTA. Arachidonyl trifluoromethyl ketone (AACOCF3), a PLA2 inhibitor, bromoenol lactone (BEL), a Ca2+-independent PLA2 (iPLA2) inhibitor, and EGTA suppressed the magnolol-induced AA release. However, none of the follows affected magnolol-induced AA-release: 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580), a p38 mitogen-activated protein kinase (MAPK) inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), a MAPK kinase (MEK) inhibitor, or 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide (GF109203X), a protein kinase C (PKC) inhibitor. In addition, magnolol at 30 microM did not stimulate the p38 MAPK and extracellular signal-regulated kinase 2 (ERK2) enzyme activities. These results indicated that magnolol inhibits the formation of prostaglandins and leukotrienes in A23187-stimulated rat neutrophils, probably through a direct blockade of COX and 5-LO activities. The stimulatory effects of magnolol at high concentration on the membrane association of 5-LO and cPLA2 are attributable to the elevation of [Ca2+]i, and on the AA release is likely via activation of cPLA2 and iPLA2.

The blockade of formyl peptide-induced respiratory burst by 2',5'-dihydroxy-2-furfurylchalcone involves phospholipase D signaling in neutrophils

The inhibition of formyl-methionyl-leucyl-phenylalanine (fMLP)-induced respiratory burst by 2',5'-dihydroxy-2-furfurylchalcone (DHFC) was investigated in rat neutrophils, and the underlying mechanism of this inhibition was assessed. DHFC concentration-dependently inhibited superoxide anion (O(2)) generation (IC(50) 4.2+/-1.2 microM), reaching a plateau within 5-10 min preincubation time, and inhibited oxygen consumption (IC(50) 6.9+/-1.9 microM) in rat neutrophils. In cell-free systems, DHFC failed to scavenge the generated during dihydroxyfumaric acid auto-oxidation. DHFC was less effective in the inhibition of both phorbol 12-myristate 13-acetate-activated neutrophil particulate NADPH oxidase activity and arachidonic acid-induced NADPH oxidase activation. In rat neutrophils, DHFC did not exert a cAMP-elevating effect, nor did it affect fMLP-induced [Ca(2+)](i) change to a considerable extent. DHFC slightly reduced fMLP-induced phosphatidylinositol 3-kinase (PI3 K) activation but showed moderate inhibition of Akt phosphorylation. fMLP-induced cellular phospholipase D (PLD) activation was markedly inhibited by DHFC (IC(50) 8.9+/-2.0 microM). In addition, DHFC effectively attenuated the membrane association of protein kinase C (PKC)-alpha, ADP-ribosylation factor (ARF) and Rho A in fMLP-stimulated cells. However, DHFC had no effect on the membrane association of ARF and Rho A caused by guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) in cell lysate. fMLP-stimulated protein tyrosine phosphorylation was weakly attenuated by DHFC. DHFC was more efficient in the inhibition of extracellular signal-regulated kinase (ERK) phosphorylation than p38 mitogen-activated protein kinase (MAPK) phosphorylation. Collectively, these results indicate that the suppression of fMLP-induced respiratory burst by DHFC in rat neutrophils is probably mainly attributable to the inhibition of PLD activation, via the blockade of PKC-alpha, ARF and Rho A membrane association.

Characterization of maleimide-activated Ca2+ entry in neutrophils

N-Ethylmaleimide (NEM), a thio-alkylating agent, concentration-dependently stimulated the elevation of [Ca(2+)](i) in rat neutrophils in the presence of external Ca(2+). This effect was not observed in Ca(2+)-free medium and was abrogated by dithiothreitol pretreatment. The application of NEM after cyclopiazonic acid (CPA) stimulated the store-emptying activation of Ca(2+) entry. Unlike CPA-induced cation entry, NEM showed poor uptake of Ba(2+) and Sr(2+) and did not induce Mn(2+) influx. NEM diminished CPA-induced Mn(2+) influx, an effect that was blocked by dithiothreitol. Both Ni(2+) and La(3+) attenuated the elevation of [Ca(2+)](i) in response to NEM; however, greater resistance was observed to Ni(2+) inhibition of NEM-induced Ca(2+) influx than inhibition of store-operated Ca(2+) entry. Both cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL-12,330A) and 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole (SKF-96365), Ca(2+) channel blockers, and calyculin A, an inhibitor of protein serine/threonine phosphatases 1/2, diminished the NEM-induced Ca(2+) entry. Treatment of cells with genistein, a general tyrosine kinase inhibitor, or with wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), phosphatidylinositol 3-kinase inhibitors, had no appreciable inhibitory effects on the action of NEM. However, 2-aminoethyldiphenyl borate, an inositol trisphosphate receptor antagonist, enhanced rather than inhibited the [Ca(2+)](i) change in response to NEM. These results indicate that NEM stimulates Ca(2+) entry and regulates Ca(2+) signaling through direct thiol oxidation, bypassing the cellular signal transduction pathway. The NEM-regulated Ca(2+) signal demonstrates characteristics that distinguish it from the store-emptying operation in neutrophils, and therefore represents two distinct modes of Ca(2+) regulation.

Expression of adenylyl cyclase isoforms in neutrophils

In the present study, we have identified the expression of adenylyl cyclase (AC) isoforms in rat neutrophils according to the mRNA analysis and the distinct mode of regulation of isoform activity. Agarose gel electrophoresis of reverse transcription-polymerase chain reaction (RT-PCR)-amplified products resulted in a single band of the expected size for each product with nucleotide sequences corresponding to AC1 to AC9. AC1 was abundant, while AC2, 6 and 9 were of moderate expression among the AC isoforms in neutrophils based on the quantitative real-time RT-PCR analysis. Exposure of neutrophils to Ca(2+) ionophore A23187, isoproterenol and forskolin stimulated cellular cyclic AMP accumulation. EDTA and the calmodulin (CaM) antagonist, trifluoperazine, prevented the A23187-induced response. Pretreatment with pertussis toxin (PTX) inhibited the alpha(2)-adrenergic agonist, UK14304-induced cellular cyclic AMP elevation. In addition, UK14304 augmented the cyclic AMP elevation when cells were stimulated by isoproterenol. Phorbol 12-myristate 13-acetate (PMA) attenuated the augmentation response of UK14304 and isoproterenol. Treatment of the membrane preparations from rat neutrophils with Ca(2+)/CaM, forskolin, isoproterenol, GTPgammaS or Gbetagamma all increased cyclic AMP production. The addition of protein kinase C (PKC) catalytic fragment and Gbetagamma augmented the Ca(2+)/CaM- and isoproterenol-stimulated AC activity, respectively. However, forskolin and the activated protein kinase A (PKA) attenuated the GTPgammaS- and isoproterenol-stimulated AC activity, respectively. KT5720, a PKA inhibitor, reversed the inhibition by PKA. Taken together, these data suggest the presence of four groups of AC isoforms in rat neutrophils.

Investigation of the cellular mechanism of inhibition of formyl-methionyl-leucyl-phenylalanine-induced superoxide anion generation in rat neutrophils by 2-benzyloxybenzaldehyde

The inhibition of formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O2(.-)) generation by 2-benzyloxybenzaldehyde (CCY1a) was investigated in rat neutrophils, and the underlying mechanism of this inhibition was assessed. CCY1a concentration-dependently inhibited O2(.-) generation (IC(50)=18.5+/-4.3 microM). In cell-free systems, CCY1a failed to alter O2(.-) generation during dihydroxyfumaric acid autoxidation, in phorbol 12-myristate 13-acetate (PMA)-activated neutrophil particulate NADPH oxidase preparations, or during arachidonic acid-induced NADPH oxidase activation. CCY1a increased cellular cyclic AMP (cAMP) levels in a time- and concentration-dependent manner, and this cAMP-elevating effect was inhibited by the adenylyl cyclase inhibitor 9-(tetrahydro-2'-furyl)adenine (SQ22536), adenosine deaminase (ADA), and the adenosine receptor antagonist 8-(p-sulfophenyl)theophylline. In neutrophils, inhibition of O2(.-) generation by CCY1a was partially reversed by the protein kinase A inhibitor (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-l][1,6]benzodiazocine-10-carboxylic acid, hexyl ester (KT5720). CCY1a did not affect fMLP-induced p38 mitogen-activated protein kinase phosphorylation, but concentration-dependently attenuated the phosphorylation of extracellular signal-regulated kinase (ERK) and Akt (IC(50) about 31.3 and 19.4 microM, respectively). The plateau phase, but not the initial spike, of fMLP-induced [Ca2+](i) changes was inhibited by CCY1a in a concentration-dependent manner. CCY1a inhibition of Ca2+ entry, ERK, and Akt phosphorylation was not prevented by SQ22536 or ADA. fMLP-induced phospholipase D (PLD) activation was inhibited by CCY1a (IC(50)=13.9+/-2.0 microM). ADA and KT5720 did not prevent the inhibition of PLD activation by CCY1a. Collectively, these results indicate that the inhibition by CCY1a of fMLP-induced O2(.-) generation in rat neutrophils can probably be attributed to the increase in cAMP levels, and to the blockade of Ca2+ entry, suppression of Akt, and PLD activation via cAMP-independent mechanisms.

Inhibition of formyl-methionyl-leucyl-phenylalanine-stimulated phospholipase D activation in rat neutrophils by the synthetic isoquinoline DMDI

The expression of phospholipase D (PLD) isoenzymes in neutrophils was investigated using reverse transcription-polymerase chain reaction analysis. Amplification products of predicted size were obtained from rat neutrophils with nucleotide sequences corresponding to PLD1a and PLD2. 1-(3',4'-Dimethoxybenzyl)-6,7-dichloroisoquinoline (DMDI) inhibited the formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PLD activation in rat neutrophils. The underlying cellular signaling mechanism of DMDI inhibition was investigated. The fMLP-induced protein tyrosine phosphorylation and the membrane translocation of ADP-ribosylation factor (ARF) and Rho A in neutrophils was attenuated by DMDI in a concentration-dependent manner. However, neither the membrane association of protein kinase C-alpha and -beta isoenzymes in fMLP-stimulated cells nor the GTPgammaS- and phorbol 12-myristate 13-acetate-stimulated membrane translocation of ARF and Rho A in a cell-free system was affected significantly by DMDI. These results indicate that the expression of PLD1a and PLD2 mRNA in neutrophils. Attenuation of protein tyrosine phosphorylation and the membrane association of ARF and Rho A probably play a concerted role in the inhibition of PLD by DMDI in rat neutrophils in response to fMLP.

GEA3162 stimulates Ca2+ entry in neutrophils

We showed that 5-amino-3-(3,4-dichlorophenyl)1,2,3,4-oxatriazolium (GEA3162), a lipophilic nitric oxide (NO)-releasing agent, induced Ca(2+) entry into rat neutrophils in a concentration-dependent manner, whereas the guanylyl cyclase inhibitors, 6-anilino-5,8-quinolinequinone (LY83583) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), had no effect on GEA3162-induced response. The GEA3162-induced Ca(2+) entry was not observed in a Ca(2+)-free medium. GEA3162 did not potentiate but reduced the store-emptying activated Ca(2+) entry caused by cyclopiazonic acid. Stimulation of cells with GEA3162 in the absence of extracellular Ca(2+) followed by addition of cations showed that only Ca(2+) but not Ba(2+) and Sr(2+) entry occurs. Store-operated Ca(2+) entry was sensitive to La(3+) and Ni(2+) inhibition, whereas the GEA3162-induced Ca(2+) entry was sensitive to La(3+) but resistant to Ni(2+). cis-N-(2-Phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL-12,330A) and calyculin A diminished the Ca(2+) entry activated by cyclopiazonic acid as well as by GEA3162. In contrast, 2-aminoethyldiphenyl borate (2-APB) diminished cyclopiazonic acid-but enhanced GEA3162-induced [Ca(2+)](i) change. Genistein effectively attenuated the cyclopiazonic acid-but slightly inhibited GEA3162-induced [Ca(2+)](i) change. Application of neomycin and high extracellular Ca(2+) concentration did not induce [Ca(2+)](i) rise. These data suggest that GEA3162 induced Ca(2+) entry and regulated Ca(2+) signal, through direct protein thiol oxidation. The action of GEA3162 demonstrates characteristics that distinguish it from the store-operated mechanism in neutrophils and therefore is likely to represent an entirely distinct pathway. Extracellular Ca(2+)-sensing receptor is not existing in neutrophils.

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.

Distinct role for microglia in rotenone-induced degeneration of dopaminergic neurons

Increasing evidence has suggested an important role for environmental factors such as exposure to pesticides in the pathogenesis of Parkinson's disease. In experimental animals the exposure to a common herbicide, rotenone, induces features of parkinsonism; mechanistically, rotenone-induced destruction of dopaminergic neurons has been attributed to its inhibition of the activity of neuronal mitochondrial complex I. However, the role of microglia, the resident brain immune cells in rotenone-induced neurodegeneration, has not been reported. Using primary neuron-enriched and neuron/glia cultures from the rat mesencephalon, we discovered an extraordinary feature for rotenone-induced degeneration of cultured dopaminergic neurons. Although little neurotoxicity was detected in neuron-enriched cultures after treatment for 8 d with up to 20 nm rotenone, significant and selective dopaminergic neurodegeneration was observed in neuron/glia cultures 2 d after treatment with 20 nm rotenone or 8 d after treatment with 1 nm rotenone. The greatly enhanced neurodegenerative ability of rotenone was attributed to the presence of glia, especially microglia, because the addition of microglia to neuron-enriched cultures markedly increased their susceptibility to rotenone. Mechanistically, rotenone stimulated the release of superoxide from microglia that was attenuated by inhibitors of NADPH oxidase. Furthermore, inhibition of NADPH oxidase or scavenging of superoxide significantly reduced the rotenone-induced neurotoxicity. This is the first report demonstrating that microglia play a pivotal role in rotenone-induced degeneration of dopaminergic neurons. The results of this study should advance our understanding of the mechanism of action for pesticides in the pathogenesis of Parkinson's disease.

Inhibition of superoxide anion generation by YC-1 in rat neutrophils through cyclic GMP-dependent and -independent mechanisms

3-(5'-Hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), a soluble guanylyl cyclase (sGC) activator, inhibited formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O(2)*(-)) generation and O(2) consumption in rat neutrophils (IC(50) values of 12.7+/-3.1 and 17.7+/-6.9 microM, respectively). Inhibition of O(2)*(-) generation by YC-1 was partially reversed by the cyclic GMP-lowering agent 6-anilinoquinoline-5,8-quinone (LY83583) and by the Rp isomer of 8-(4-chlorophenylthio)guanosine-3',5'-monophosphorothioate (Rp-8-pCPT-cGMPS), a cyclic GMP-dependent protein kinase inhibitor. In cell-free systems, YC-1 failed to alter O(2)*(-) generation during dihydroxyfumaric acid autoxidation, phorbol 12-myristate 13-acetate (PMA)-activated neutrophil particulate NADPH oxidase preparation, and arachidonic acid-induced NADPH oxidase activation. YC-1 increased cellular cyclic GMP levels through the activation of sGC and the inhibition of cyclic GMP-hydrolyzing phosphodiesterase activity. The plateau phase, but not the initial spike, of fMLP-induced [Ca(2+)](i) changes was inhibited by YC-1 (IC(50) about 15 microM). fMLP- but not PMA-induced phospholipase D activation was inhibited by YC-1 (IC(50) about 28 microM). Membrane-associated ADP-ribosylation factor and Rho A in cell activation was also reduced by YC-1 at a similar concentration range. Neither cytosolic protein kinase C (PKC) activity nor PKC membrane translocation was altered by YC-1. YC-1 did not affect either fMLP-induced phosphatidylinositol 3-kinase activation or p38 mitogen-activated protein kinase phosphorylation, but slightly attenuated the phosphorylation of extracellular signal-regulated kinase. Collectively, these results indicate that the inhibition of the fMLP-induced respiratory burst by YC-1 is mediated by cyclic GMP-dependent and -independent signaling mechanisms.

Cellular mechanisms of inhibition of superoxide anion generation in rat neutrophils by the synthetic isoquinoline DMDI

This study was undertaken to assess the cellular localization of the inhibitory effect of a chemically synthetic isoquinoline compound 1-(3',4'-dimethoxybenzyl)-6,7-dichloroisoquinoline (DMDI) on the formyl-methionyl-leucyl-phenylalanine (fMLP)-induced respiratory burst in rat neutrophils. The DMDI concentration dependently inhibited the superoxide anion (O(2)(*-)) generation and O(2) consumption (IC(50) 12.2+/-4.9 and 15.2+/-8.4 microM, respectively) of neutrophils. DMDI did not scavenge the O(2)(*-) generated during the autoxidation of dihydroxyfumaric acid in a cell-free system. DMDI did not elevate cellular cyclic AMP levels. Inhibition of O(2)(*-) generation by DMDI in neutrophils was not reversed by a cyclic AMP-dependent protein kinase inhibitor, (8R,9S,11S)-(-)-9-hydroxy-9-hexoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a,g]cycloocta[cde]trinden-1-one (KT5720). The DMDI concentration dependently inhibited the late plateau phase but not the initial spike of fMLP-induced [Ca(2+)](i) changes in the presence of extracellular Ca(2+). However, DMDI had no effect on the fMLP-induced [Ca(2+)](i) changes in the absence of extracellular Ca(2+). In addition, DMDI did not affect the fMLP-stimulated phosphatidylinositol 3-kinase (PI3-kinase) activation. DMDI produced a concentration-dependent reduction in the formation of phosphatidic acid and phosphatidylethanol in the presence of ethanol from fMLP-stimulated neutrophils (IC(50) 13.3+/-4.0 and 9.4+/-4.3 microM, respectively). On the basis of the immunoblot analysis of the phosphorylation of the mitogen-activated protein (MAP) kinase, DMDI attenuated the fMLP-stimulated MAP kinase phosphorylation in a similar concentration range. Collectively, these results indicate that the inhibition of the respiratory burst by DMDI in rat neutrophils is mediated through the blockade of phospholipase D and MAP kinase signaling pathways.

Investigation of the inhibitory effects of HA-1077 and Y-32885 on the translocation of PKCbetaI, PKCbetaII and PKCzeta in human neutrophils

To transmit the information inside the cell, one possibility is the action of an enzyme called kinase that phosphorylates other proteins. To study these enzymes, chemical compound synthesis was needed to know the function and the mechanism of activation. The major difficulty is creating a specific molecule for one kinase. In this study, we test the action of Rho-kinase inhibitors (HA-1077 and Y-32885) on protein kinase C (PKC) in the respiratory burst in the human polymorphonuclear neutrophils. We have shown that these compounds could inhibit the anion superoxide production. To prove their action on PKC, we have shown a decrease of binding of a specific ligand (phorbol-12,13-dibutyrate) with each inhibitor. During its activation, PKC was translocated from the cytoplasm to the plasmic membrane. We have also shown an inhibition of this translocation, proving an inhibition of PKC by HA-1077 and Y-32885.

Investigation of the inhibitory effects of chelerythrine chloride on the translocation of the protein kinase C betaI, betaII, zeta in human neutrophils

The protein kinase C (PKC) is a serine/threonine kinase, consisting of different isoforms, implicated in numerous processes of signal transduction. To understand this enzyme well, different pharmacological tools were developed. To activate PKC specifically, phorbol esters were previously used but recent research has shown that these compounds are able to stimulate other proteins. Our model is the respiratory burst in the polymorphonuclear neutrophils. A decrease in the inflammatory process was measured using chelerythrine chloride. Action on PKC was proved by a binding study and by showing the absence of translocation of this enzyme from the cytoplasm to the plasmic membrane during stimulation.

Inhibition of extracellular Ca(2+) entry by YC-1, an activator of soluble guanylyl cyclase, through a cyclic GMP-independent pathway in rat neutrophils

The effects of a soluble guanylyl cyclase (sGC) activator, 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), on formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated [Ca(2+)](i) elevation in rat neutrophils were examined. YC-1 produced a concentration-dependent inhibition of [Ca(2+)](i) elevation. Pretreatment of neutrophils with YC-1 did not enhance its inhibitory effect. YC-1 also inhibited the [Ca(2+)](i) changes caused by ionomycin. In a biphasic model, measuring the [Ca(2+)](i) stimulation by fMLP in a Ca(2+)-free medium followed by reintroduction of Ca(2+), YC-1 mainly affected Ca(2+) influx. YC-1 also inhibited active and passive Mn(2+) influx, and this inhibitory effect was not attenuated by the sGC inhibitor 6-anilino-5,8-quinolinequinone (LY83583). Sodium nitroprusside did not affect the fMLP-stimulated [Ca(2+)](i) changes. Pretreatment of neutrophils with the cyclic GMP-dependent protein kinase inhibitor 8-(4-chlorophenylthio) guanosine-3',5'-monophosphorothioate, Rp-isomer (Rp-8-pCPT-cGMPS), LY83583, the protein phosphatase 2B inhibitor cyclosporin A, or the protein kinase inhibitor staurosporine did not attenuate the inhibition of [Ca(2+)](i) by YC-1. YC-1 inhibited the fMLP-stimulated protein tyrosine phosphorylation. These results indicate that cyclic GMP does not play an important role in the regulation of [Ca(2+)](i) in rat neutrophils. Inhibition of fMLP-stimulated [Ca(2+)](i) changes by YC-1 is mainly via the blockade of Ca(2+) entry through the inhibition of tyrosine kinase activity, but not the stimulation of protein kinase C and protein phosphatase 2B.

Benzyloxybenzaldehyde analogues as novel adenylyl cyclase activators

Several benzyloxybenzaldehyde analogues were prepared and found to have significant inhibitory activity toward neutrophil superoxide formation. Consequently, these compounds were evaluated for cAMP-elevating capability. Among them, benzyloxybenzaldehyde (7), exhibiting activity equivalent to forskolin, was determined as an adenylyl cyclase activator since it elevates cAMP levels by activation of adenylyl cyclase but not by inhibition of phosphodiesterase. Having a chemical structure very different from known adenylyl cyclase activators, compound 7 is recommended by us for use as a new lead compound in the future development of adenylyl cyclase activators.

The upstream regulation of p38 mitogen-activated protein kinase phosphorylation by arachidonic acid in rat neutrophils

The signal transduction pathways activated by arachidonic acid that lead to p38 mitogen-activated protein kinase (MAPK) activation in neutrophils remains unclear. In this study, selective inhibitors of several signalling pathways were utilized to investigate the mechanisms of activation of p38 MAPK by arachidonic acid in rat neutrophils. Stimulation of p38 MAPK phosphorylation by arachidonic acid and its trifluoromethyl ketone analogue AACOCF3 was transient, peaking at 1 min, and was concentration-dependent. Arachidonic acid-stimulated p38 MAPK phosphorylation was attenuated in cells pretreated with the Gi/o inhibitor (pertussis toxin), but not with the dual cyclooxygenase/lipoxygenase inhibitor (BW755C) or the leukotriene biosynthesis inhibitor (MK886). Tyrosine kinase inhibitor (genistein), but not the extracellular signal-regulated kinase kinase inhibitors (PD98059 and U0126), attenuated the phosphorylation of p38 MAPK by arachidonic acid. Phosphoinositide 3-kinase inhibitors (wortmannin and LY294002) did not affect the arachidonic acid-induced response. After pretreatment of the cells with protein kinase C inhibitors (Gö6976, Gö6983 and GF109203X), only Gö6976 significantly attenuated the phosphorylation of p38 MAPK by arachidonic acid. In addition, phosphorylation of p38 MAPK by arachidonic acid was greatly attenuated by the phospholipase C inhibitor (U73122) and the Ca2+ chelator BAPTA ((1,2-bis-o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid), but not altered by the nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester. Arachidonic acid did not cause an increase in cellular cyclic GMP level. This study revealed the involvement of pertussis toxin-sensitive G protein, non-receptor tyrosine kinase, phospholipase C/Ca2+, and probably Ca2+-dependent protein kinase C in arachidonic acid-stimulated p38 MAPK activation.

Activation of p38 mitogen-activated protein kinase by formyl-methionyl-leucyl-phenylalanine in rat neutrophils

The signaling pathways leading to p38 mitogen-activated protein kinase (MAPK) activation in formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated rat neutrophils were examined. Immunoblot analysis with antibodies against a phosphorylated form of p38 MAPK showed that fMLP-stimulated p38 MAPK activation was dependent on a pertussis toxin-sensitive G protein. Two phosphatidylinositol 3-kinase inhibitors, wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), did not affect the p38 MAPK activation. Phosphorylation of p38 MAPK was concentration dependently attenuated by a tyrosine kinase inhibitor, genistein, and by a Ca(2+)-dependent protein kinase C inhibitor, 13-cyanoethyl-12-methyl-6,7,12,13-tetrahydroindolo[2,3-a]pyrrolo[3 , 4-c]carbazole-7-one (Gö6976). However, the protein kinase C inhibitors with a broader spectrum, 2-[1-(3-dimethylaminopropyl)-5-methoxy-1H-indol-3-yl]-3-(1H-indol-3-y l)-maleimide (Gö6983) and 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimi de (GF109203X), had no inhibitory effect. fMLP-stimulated p38 MAPK phosphorylation was also reduced in cells pretreated with a phospholipase C inhibitor, 1-[6-((17beta-3-methoxyestra-1,3, 5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U73122), or preloaded with an intracellular Ca(2+) chelator, 1, 2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA). We conclude that phosphorylation of p38 MAPK by fMLP stimulation in rat neutrophils is dependent on G(i/o) protein, nonreceptor tyrosine kinase, phospholipase C/Ca(2+), and probably Ca(2+)-dependent protein kinase C pathways.

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.

Examination of the signal transduction pathways leading to activation of extracellular signal-regulated kinase by formyl-methionyl-leucyl-phenylalanine in rat neutrophils

The signaling pathways leading to extracellular signal-regulated kinase (ERK) activation in formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated rat neutrophils were examined. fMLP-stimulated ERK activation based on immunoblot analysis with antibodies against the phosphorylation form of ERK was attenuated by the pretreatment of cells with pertussis toxin but not with a dual cyclo-oxygenase/lipoxygenase inhibitor BW755C. Exposure of cells to the tyrosine kinase inhibitor genistein, phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002, or protein kinase C (PKC) inhibitors Gö6976, Gö6983, and GF109203X inhibited fMLP-stimulated ERK phosphorylation in a concentration-dependent manner. In addition, both the phospholipase C (PLC) inhibitor U73122 and the Ca2+ chelator BAPTA attenuated ERK activation. These results indicate that G(i/o) protein, tyrosine kinase, P13K, PKC, and PLC/Ca2+, but not arachidonate metabolites, act upstream of fMLP-stimulated ERK activation.

2-Hydroxymethyl-1-naphthol diacetate (TAC) suppresses the superoxide anion generation in rat neutrophils

We have investigated the inhibitory effect of 2-hydroxymethyl-1-naphthol diacetate (TAC) on the respiratory burst of rat neutrophils and the underlying mechanism of action was also assessed in this study. TAC caused concentration-related inhibition of the formylmethionyl-leucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2*-) generation (IC50 10.2+/-2.3 and 14.1+/-2.4 microM, respectively) and O2 consumption (IC50 9.6+/-2.9 and 13.3+/-2.7 microM, respectively) of neutrophils. TAC did not scavenge the generated O2*- during dihydroxyfumaric acid autoxidation. TAC inhibited both the transient elevation of [Ca2+]i in the presence or absence of [Ca2+]o (IC50 75.9+/-8.9 and 84.7+/-7.9 microM, respectively) and the generation of inositol trisphosphate (IP3) (IC50 72.0+/-9.7 microM) in response to fMLP. Cytosolic phospholipase C (PLC) activity was also reduced by TAC at a same range of concentrations. The PMA-induced PKC-beta associated to membrane was attenuated by TAC (about 80% inhibition at 30 microM). Upon exposure to fMLP, the cellular cyclic AMP level was decreased in neutrophils pretreated with TAC. TAC attenuated fMLP-induced phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 (IC50 17.4+/-1.7 microM), but not p38. The cellular formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt) induced by fMLP was inhibited by TAC in a concentration-dependent manner (IC50 25.4+/-2.4 and 25.9+/-1.4 microM, respectively). TAC had no effect on the O2*- generation of PMA-stimulated and arachidonic acid (AA)-stimulated NADPH oxidase preparations. However, TAC caused concentration-related decrease of the membrane associated p47phoX in PMA-stimulated neutrophils (about 80% inhibition at 30 microM). We conclude that inhibition by TAC of the neutrophil respiratory burst is probably attributable to the blockade of the p42/44 MAPK and phospholipase D (PLD) pathways, the membrane translocation of PKC, and to the failure in assembly of a functional NADPH oxidase complex. Blockade of the PLC pathway by TAC probably plays a minor role.

Stimulation of respiratory burst by cyclocommunin in rat neutrophils is associated with the increase in cellular Ca2+ and protein kinase C activity

In this study, the underlying mechanisms of stimulation by cyclocommunin, a natural pyranoflavonoid, of respiratory burst in rat neutrophils was investigated. Cyclocommunin evoked a concentration-dependent stimulation of superoxide anion (O2*-) generation with a slow onset and long lasting profile. The maximum response (16.4+/-2.3 nmol O2*-/10 min per 10(6) cells) was observed at 3-10 microM cyclocommunin. Cyclocommunin did not activate NADPH oxidase in a cell-free system. Cells pretreated with pertussis toxin or n-butanol did not affect the cyclocommunin-induced O2*- generation. However, a protein kinase inhibitor staurosporine and EGTA greatly reduced the O2*-generation caused by cyclocommunin. Treatment of neutrophils with phorbol 12-myristate 13-acetate (PMA), but not with formylmethionyl-leucyl-phenylalanine (fMLP), for 20 min significantly reduced the O2*- generation following the subsequent stimulation of cells with cyclocommunin. Cyclocommunin did not affect the cellular mass of phosphatidic acid (PA). Neither the tyrosine kinase inhibitor, genistein, nor the p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, affected cyclocommunin-induced O2*- generation. The enzyme activities of neutrophil cytosolic and membrane-associated protein kinase C (PKC) were both increased significantly with 100 microM cyclocommunin. The membrane-associated PKC-theta and PKC-beta were increased following the stimulation of neutrophils with 30 and 100 microM cyclocommunin, respectively. Cyclocommunin reduced the [3H]phorbol 12,13-dibutyrate ([3H]PDB) binding to cytosolic PKC in a concentration-dependent manner. Cyclocommunin (> or =3 microM) significantly evoked a slow and long lasting [Ca2+]i elevation in neutrophils, and a phospholipase C (PLC) inhibitor U73122 greatly inhibited these Ca2+ responses. Moreover, the increase in cellular inositol bis- and trisphosphate (IP2 and IP3) levels were observed in neutrophils stimulated with 30 microM cyclocommunin for 3 min. Collectively, these results indicate that the stimulation of respiratory burst by cyclocommunin is probably mediated by the synergism of PKC activation and [Ca2+]i elevation in rat neutrophils.

Involvement of cyclic AMP generation in the inhibition of respiratory burst by 2-phenyl-4-quinolone (YT-1) in rat neutrophils

The inhibitory effect of 2-phenyl-4-quinolone (YT-1) on respiratory burst in rat neutrophils was investigated, and the underlying mechanism of action was assessed. YT-1 caused a concentration-dependent inhibition of the rate of O2.- release from rat neutrophils in response to formylmethionyl-leucyl-phenylalanine (fMLP), but not to phorbol 12-myristate 13-acetate (PMA), with an IC50 value of 60.7+/-8.2 microM. A comparable effect was also demonstrated in the inhibition of O2 consumption. Unlike superoxide dismutase, YT-1 had no effect on O2.- generation in the xanthine-xanthine oxidase system and during dihydroxyfumaric acid autoxidation. The fMLP-induced inositol trisphosphate (IP3) formation was unaffected by YT-1. In addition, YT-1 did not affect the initial spike of [Ca2+]i, but it accelerated the rate of [Ca2+]i decline in cells in response to fMLP. YT-1 was found to have little effect on the activity of neutrophil cytosolic protein kinase C (PKC). YT-1 increased the cellular cyclic AMP level, while having no effect on the cyclic GMP level. In addition, YT-1 increased neutrophil cytosolic protein kinase A (PKA) activity, but had no direct effect on the enzyme activity of pure porcine heart PKA. When neutrophils were treated with (8R,9S,11S)-(-)-9-hydroxy-9-hexoxycarbonyl-8-methyl-2,3,9,10-tetra hydro-8,11-epoxy- 1H,8H,11H-2,7b,11a-triazadibenzo[a,g]cycloocta[cde]trinde n-1-one, (KT 5720), a PKA inhibitor, the inhibition of O2.- generation by YT-1, as well as by prostaglandin E1 (PGE1) and dibutyryl cyclic AMP, was attenuated effectively. YT-1 did not activate the adenylate cyclase associated with neutrophil particulate fraction but inhibited the cytosolic phosphodiesterase (PDE) activity in a concentration-dependent manner. Neutrophils treated with YT-1 had a more pronounced increase in cellular cyclic AMP level by PGE1. Moreover, the ability of PGE1 to inhibit the respiratory burst in neutrophils was greatly enhanced by YT-1. These results suggest that the increase in cellular cyclic AMP levels by YT-1 through the inhibition of PDE (probably PDE4 isoenzyme) activity is involved in its inhibition of fMLP-induced respiratory burst in rat neutrophils.

The signal transduction mechanism involved in kazinol B-stimulated superoxide anion generation in rat neutrophils

1. In this study, the underlying mechanism of stimulation of respiratory burst by kazinol B, a natural isoprenylated flavan, in rat neutrophils in vitro was investigated. 2. Kazinol B concentration-dependently stimulated the superoxide anion (O2*-) generation, with a lag but transient activation profile, in neutrophils but not in a cell-free system. The maximum response (13.2+/-1.4 nmol O2*- 10 min(-1) per 10(6) cells) was observed at 10 microM kazinol B. 3. Pretreatment of neutrophils with phorbol 12-myristate 13-acetate (PMA) or formylmethionyl-leucyl-phenylalanine (fMLP) significantly enhanced the O2*- generation following the subsequent stimulation of cells with kazinol B. 4. Cells pretreated with EGTA or a protein kinase inhibitor staurosporine effectively attenuated the kazinol B-induced O2*- generation. However, a p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 and a phosphoinositide 3-kinase (PI3K) inhibitor wortmannin had no effect on the kazinol B-induced response. 5. Kazinol B significantly stimulated [Ca2+]i elevation in neutrophils, with a lag and slow rate of rise activation profile, and this response was attenuated by a phospholipase C (PLC) inhibitor U73122. Kazinol B also stimulated the inositol bis- and trisphosphate (IP2 and IP3) formation with a 1 min lag time. 6. The membrane-associated PKC-alpha and PKC-theta but not PKC-iota were increased following the stimulation of neutrophils with kazinol B. It was more rapid and sensitive in the activation of PKC-theta than PKC-alpha by kazinol B. Kazinol B partially inhibited the [3H]phorbol 12,13-dibutyrate ([3H]PDB) binding to the neutrophil cytosolic PKC. 7. Neither the cellular mass of phosphatidic acid (PA) and phosphatidylethanol (PEt), in the presence of ethanol, nor the protein tyrosine phosphorylation were stimulated by kazinol B. In addition, the kazinol B-induced O2*- generation remained relatively unchanged in cells pretreated with ethanol or a tyrosine kinase inhibitor genistein. 8. Collectively, these results indicate that the stimulation of the respiratory burst by kazinol B is probably mediated by the synergism of PKC activation and [Ca2+]i elevation in rat neutrophils.

Possible involvement of protein kinase c inhibition in the reduction of phorbol ester-induced neutrophil aggregation by magnolol in the rat

The influence of the plant product magnolol on neutrophil aggregation has been investigated in the rat. Magnolol inhibited phorbol 12-myristate 13-acetate (PMA)-activated rat neutrophil aggregation in a concentration-dependent manner with an IC50 (concentration resulting in 50% inhibition) of 24.2 +/- 1.7 microM. Magnolol suppressed the enzyme activity of neutrophil cytosolic and rat brain protein kinase C (PKC) over the same range of concentrations at which it inhibited the aggregation. Magnolol did not affect PMA-induced cytosolic PKC-alpha and -delta membrane translocation or trypsin-treated rat-brain PKC activity, but attenuated [3H]phorbol 12,13-dibutyrate binding to neutrophil cytosolic PKC. These results suggest that the inhibition of PMA-induced rat neutrophil aggregation by magnolol is probably attributable, at least in part, to the direct suppression of PKC activity through blockade of the regulatory region of PKC.