St. John's wort extract Ze 117 alters the membrane fluidity of C6 glioma cells by influencing cellular cholesterol metabolism.

Chronic stress is associated with major depressive disorder (MDD). Increased glucocorticoid levels caused by uncontrolled release through the hypothalamic‒pituitary‒adrenal (HPA) axis can cause changes in the lipid content of the cellular plasma membrane. These changes are suspected to be involved in the development of depressive disorders. St. John's wort extract (SJW) Ze 117 has long been used as an alternative to synthetic antidepressants. Part of its effect may be due to an effect on the cellular lipid composition and thus on the properties of plasma membranes and receptor systems embedded therein. In this study, we investigated the effect of Ze 117 on that of dexamethasone and simvastatin. Dexamethasone increases the fluidity of C6 cell plasma membranes. This effect is counteracted by administration of Ze 117. Here we demonstrate that this is not due to a change in C16:1/16:0 and C18:1/18:0 ratios in C6 cell fatty acids. On the other hand, Ze 117 increased the cellular cholesterol content by 42.5%, whereas dexamethasone reduced cholesterol levels similarly to simvastatin. Lowering cholesterol levels by dexamethasone or simvastatin resulted in decreased ß-arrestin 2 recruitment to the 5-HT1a receptor. This effect was counterbalanced by Ze 117, whereas the SJW extract had little effect on ß-arrestin 2 recruitment in non-stressed cells. Taken together, in C6 cells, Ze 117 induces changes in membrane fluidity through its effect on cellular cholesterol metabolism rather than by affecting fatty acid saturation. This effect is reflected in an altered signal transduction of the 5-HT1a receptor under Ze 117 administration. The current in vitro results support the hypothesis that Ze 117 addresses relevant parts of the cellular lipid metabolism, possibly explaining some of the antidepressant actions of Ze 117.

Ivy Leaf Dry Extract EA 575® Has an Inhibitory Effect on the Signalling Cascade of Adenosine Receptor A2B.

Ivy leaf dry extract EA 575® is used to improve complaints of chronic inflammatory bronchial diseases and acute inflammation of the respiratory tract accompanied by coughing. Its mechanism of action has so far been explained by influencing ß2-adrenergic signal transduction. In the present study, we investigated a possible influence on adenosine receptor A2B (A2BAR) signalling, as it has been described to play a significant and detrimental role in chronic inflammatory airway diseases. The influence of EA 575® on A2BAR signalling was assessed with measurements of dynamic mass redistribution. Subsequently, the effects on A2BAR-mediated second messenger cAMP levels, ß-arrestin 2 recruitment, and cAMP response element (CRE) activation were examined using luciferase-based HEK293 reporter cell lines. Lastly, the impact on A2BAR-mediated IL-6 release in Calu-3 epithelial lung cells was investigated via the Lumit™ Immunoassay. Additionally, the adenosine receptor subtype mediating these effects was specified, and A2BAR was found to be responsible. The present study demonstrates an inhibitory influence of EA 575® on A2BAR-mediated general cellular response, cAMP levels, ß-arrestin 2 recruitment, CRE activation, and IL-6 release. Since these EA 575®-mediated effects occur within a time frame of several hours of incubation, its mode of action can be described as indirect. The present data are the first to describe an inhibitory effect of EA 575® on A2BAR signalling. This may offer an explanation for the beneficial clinical effects of the extract in adjuvant asthma therapy.

Investigation of adenosine A1 receptor-mediated ß-arrestin 2 recruitment using a split-luciferase assay.

Background: Adenosine A1 receptor (A1AR) plays a prominent role in neurological and cardiac diseases and inflammatory processes. Its endogenous ligand adenosine is known to be one of the key players in the sleep-wake cycle. Like other G protein-coupled receptors (GPCRs), stimulation of A1AR leads to the recruitment of arrestins in addition to the activation of G proteins. So far, little is known about the role of these proteins in signal transduction and regulation of A1AR compared to the activation of G proteins. In this work, we characterized a live cell assay for A1AR-mediated ß-arrestin 2 recruitment. We have applied this assay to a set of different compounds that interact with this receptor. Methods: Based on NanoBit® technology, a protein complementation assay was developed in which the A1AR is coupled to the large part of the nanoluciferase (LgBiT), whereas its small part (SmBiT) is fused to the N-terminus of ß-arrestin 2. Stimulation of A1AR results in the recruitment of ß-arrestin 2 and subsequent complementation of a functional nanoluciferase. For comparison, corresponding data on the effect of receptor stimulation on intracellular cAMP levels were collected for some data sets using the GloSensor™ assay. Results: The assay gives highly reproducible results with a very good signal-to-noise ratio. Capadenoson, in contrast to adenosine, CPA, or NECA, shows only partial agonism in this assay with respect to the recruitment of ß-arrestin 2, whereas it shows full agonism in the case of the inhibitory effect of A1AR on cAMP production. By using a GRK2 inhibitor, it becomes clear that the recruitment is at least partially dependent on the phosphorylation of the receptor by this kinase. Interestingly, this was also the first time that we demonstrate the A1AR-mediated recruitment of ß-arrestin 2 by stimulation with a valerian extract. Conclusion: The presented assay is a useful tool for the quantitative study of A1AR-mediated ß-arrestin 2 recruitment. It allows data collection for stimulatory, inhibitory, and modulatory substances and is also suitable for more complex substance mixtures such as valerian extract.

Impact of St. John's wort extract Ze 117 on stress induced changes in the lipidome of PBMC.

BACKGROUND: Membrane lipids have an important function in the brain as they not only provide a physical barrier segregating the inner and outer cellular environments, but are also involved in cell signaling. It has been shown that the lipid composition effects membrane fluidity which affects lateral mobility and activity of membrane-bound receptors. METHODS: Since changes in cellular membrane properties are considered to play an important role in the development of depression, the effect of St. John's wort extract Ze 117 on plasma membrane fluidity in peripheral blood mononuclear cells (PBMC) was investigated using fluorescence anisotropy measurements. Changes in fatty acid residues in phospholipids after treatment of cortisol-stressed [1 µM] PBMCs with Ze 117 [10-50 µg/ml] were analyzed by mass spectrometry. RESULTS: Cortisol increased membrane fluidity significantly by 3%, co-treatment with Ze 117 [50 µg/ml] counteracted this by 4.6%. The increased membrane rigidity by Ze 117 in cortisol-stressed [1 µM] PBMC can be explained by a reduced average number of double bonds and shortened chain length of fatty acid residues in phospholipids, as shown by lipidomics experiments. CONCLUSION: The increase in membrane rigidity after Ze 117 treatment and therefore the ability to normalize membrane structure points to a new mechanism of antidepressant action of the extract.

Effect of St. John's wort extract Ze 117 on the lateral mobility of ß1-adrenergic receptors in C6 cells.

Depression has been associated with altered signal transduction of serotonergic, dopaminergic and adrenergic neurotransmitter systems in the brain. Signaling relies on receptor-ligand interactions and subsequent regulatory processes, but also on lateral receptor mobility. The aim of this study was to investigate the effect of the St. John's wort extract Ze 117 on the lateral mobility of SNAP-tagged ß1-adrenergic receptors (ß1AR) in the plasma membrane of C6 cells under both, non-stimulating and isoprenaline-stimulating conditions. Single particle tracking (SPT) was used, whereby the registered trajectories were evaluated by variational Bayesian treatment of a hidden Markov model (vbSPT) and packing coefficient (Pc) analysis with respect to diffusion coefficients, receptor state occupancies and confinement. Three different diffusion states were identified, differing in their diffusion coefficients. Treatment with Ze 117 [25 µg/ml] decreased the mobility of the ß1AR, which was manifested by a relative increase in the slow-diffusing state S1 (0.21-0.30) compared to control and by an increase in receptor confinement (79.4-68.1 nm). After isoprenaline stimulation of control cells, the slow-diffusing state was more pronounced, whereas confinement was not affected. In summary, SPT has been shown to be a powerful method to analyze lateral receptor mobility. Furthermore, the present study identified a correlation between Ze 117 treatment and ß1AR mobility.

Ivy leaves dry extract EA 575® mediates biased ß2-adrenergic receptor signaling.

BACKGROUND: ß2-adrenergic receptor (ß2-AR) stimulation activates the G protein/cAMP pathway, which is opposed by the GRK2/ß-arrestin 2 pathway. The latter is undesirable in the treatment of respiratory diseases. HYPOTHESIS/PURPOSE: EA 575® is capable of mediating a biased ß2-adrenergic signaling pathway. METHODS: The impact of the ivy leaves dry extract EA 575® on ß2-adrenergic signaling was tested in a dynamic mass redistribution assay in HEK wild-type and in HEK ß-arrestin knock-out cells. cAMP formation and recruitment of ß-arrestin 2 were investigated using GloSensor™ and PathHunter® assays, respectively. NFκB transcriptional activity was determined in both HEK wild-type as well as HEK ß-arrestin knock-out cells. RESULTS: EA 575® inhibits the recruitment of ß-arrestin 2 and thereby enhances G protein/cAMP signaling under ß2-stimulating conditions, as evidenced by a corresponding increase in cAMP formation. While ß2-AR-mediated inhibition of NFκB transcriptional activity is ß-arrestin-dependent, EA 575® leads to significant inhibition of NFκB transcriptional activity in ß-arrestin knock-out cells and thus via a ß-arrestin-independent signaling pathway. CONCLUSION: EA 575® is the first active phytopharmaceutical ingredient for which biased ß2-adrenergic activation has been described. This shift towards G protein/cAMP signaling provides the molecular basis for the clinically proven efficacy of EA 575® in the treatment of lower respiratory tract diseases. In this light, EA 575® could potentially reduce ß-arrestin-mediated adverse effects in new combinatorial therapeutic approaches.

A comparative study on the influence of an ivy preparation and an ivy/thyme combination on the ß2-adrenergic signal transduction.

The ß2-adrenergic receptor (ß2AR) is relevant for surfactant formation in alveolar type 2 cells and reduction of intracellular calcium concentration in bronchial muscle cells and thus for secretolytic and bronchospasmolytic effects. Herbal medicinal products that affect the ß2AR system are used to treat common cold and bronchitis accompanied with mucus covered and narrowed airways. The present work compares the influence of an ivy preparation and an ivy/thyme combination on the ß2-adrenergic signal transduction. For receptor binding studies and characterization of the lateral mobility of ß2AR we have used single molecule detection by fluorescence correlation spectroscopy and single particle tracking. For the determination of both the second messenger cAMP and the internalization of ß2AR we have generated luciferase based reporter cell lines, which produce a cAMP-dependent luciferase in the cytosol and express ß2AR with extracellular luciferase moiety in the plasma membrane. While both preparations increased the ß2AR binding, a significant increase of the cAMP level was observed only for the ivy preparation, which can be explained by the inhibited internalization of HiBiT-tagged ß2AR under stimulating conditions. In contrast, isoprenaline-mediated internalization of HiBiT-tagged ß2AR of ivy/thyme combination pre-treated cells was not inhibited. Cells comparatively pre-treated with a thyme preparation did not show inhibition of ß2AR internalization either. Furthermore, SNAP-tagged ß2AR of ivy preparation pre-treated cells, which were not internalized after isoprenaline stimulation, showed a redistribution from fast-to-slowly diffusing ß2AR. A corresponding redistribution of these receptors was not observed after pre-treatment with both the ivy/thyme combination and the thyme preparation. Comparable to the ivy/thyme combination, no decrease in the intratrack transitioning probability ratio (p23/p32) for fast and slow diffusing ß2AR was found for the thyme preparation, which, however, significantly decreased for control cells and for pre-treatment with the ivy preparation under stimulating conditions. It can therefore be concluded that the thyme fluid extract fraction in the ivy/thyme combination may have in part a negative effect on the ß2-adrenergic signal transduction.

St John's wort extract influences membrane fluidity and composition of phosphatidylcholine and phosphatidylethanolamine in rat C6 glioblastoma cells.

BACKGROUND: Chronic stress, an important factor in the development of depressive disorders, leads to an increased formation of cortisol, which causes a hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. In addition, cortisol mediates an adaptive effect on plasma membrane fluidity which may affect signal transduction of membrane-bound receptors and contribute to pathophysiological changes. METHODS: Membrane fluidity was measured by fluorescence anisotropy using DPH (1,6-diphenyl-1,3,5-hexatriene) and TMA-DPH (1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene). Changes in cellular content of phosphatidylcholine species was determined by pulse-chase experiments using deuterated choline and mass spectrometry. Single molecule tracking was used to examine the lateral mobility of ß1-adrenoceptors and changes in cAMP formation were measured by ELISA. RESULTS: Chronic exposure (6 - 8 days) of C6 cells to cortisol dose-dependently decreased DPH and TMA-DPH fluorescence anisotropy, reflecting increased membrane fluidity. In contrast, cells pretreated with St. John's wort extract Ze117 showed increased DPH and TMA-DPH fluorescence anisotropy values, indicating a membrane rigidification effect which was mediated at least by the constituents hypericin, hyperforin, quercetin, amentoflavone and biapigenin. The observed membrane fluidizing effect of cortisol could be reversed by cotreatment with Ze117. The membrane rigidification of Ze117 was in line with the in parallel observed decrease in the phosphatidylcholine/phosphatidylethanolamine ratio determined in whole cell lipid extracts. Interestingly, pulse-chase experiments demonstrated, that Ze117 inhibited the incorporation of choline-D9 in phosphatidylcholine species with saturated or monounsaturated fatty acids compared to control cells, while the synthesis of phosphatidylcholine species with polyunsaturated fatty acids was not affected. C6 cells whose membranes have become more rigid by Ze117 showed altered lateral mobility of ß1-adrenoceptors as well as reduced cAMP formation after stimulation with the ß1-adrenoceptor agonist dobutamine. CONCLUSION: Obviously, the signaling of ß1-adrenoceptors depends on the nature of the membrane environment. It can therefore be assumed that Ze117 has a normalizing effect not only on the membrane fluidity of "stressed" cells, but also on lateral mobility and subsequently on the signal transduction of membrane-associated receptors.

Anti-inflammatory effects of ivy leaves dry extract: influence on transcriptional activity of NFκB.

EA 575® is an ivy leaves dry extract (DER 5-7.5:1, 30% ethanol) used against diseases of the lower respiratory tract associated with productive cough. EA 575® improves symptoms associated with chronic inflammatory bronchial conditions. Compared to its bronchospasmolytic and secretolytic properties, the anti-inflammatory effects of EA 575® are mostly untried. Therefore, we addressed the question of whether the anti-inflammatory effect of EA 575® is due to an impact on the NFκB pathway. NFκB nuclear translocation was visualized by immunofluorescence in J774.2 as well as HEK293 cells. In the latter, a luciferase-based reporter was used to monitor NFκB transcriptional activity. Phosphorylation of RelA and its inhibitor IκB was measured by Western blot analysis. Additionally, changes in the stability of NFκB:IκB complex were shown by protein fragment complementation. Decreased transcriptional activity of NFκB under treatment with EA 575® was also shown for a human monocytic as well as a human lung epithelial cell line. EA 575® is able to inhibit NFκB transcriptional activity by partially inhibiting its translocation to the nucleus after stimulation with TNFα. Furthermore, phosphorylation of IκBα is reduced while phosphorylation of RelA is enhanced after pre-incubation with EA 575®, leading to an enhanced stability of NFκB:IκBα complex. EA 575® has an regulatory impact on the NFκB pathway, possibly by switching specificity of IKK from IκBα to RelA, resulting in enhanced stability of NFκB:IκBα complex and reduced RelA translocation into the nucleus.

α-Hederin inhibits G protein-coupled receptor kinase 2-mediated phosphorylation of ß2-adrenergic receptors.

BACKGROUND: Recently is has been shown that α- and ß-hederin increase the ß2-adrenergic responsiveness of alveolar type II cells (A549) and human airway smooth muscle cells (HASM), respectively, by inhibiting the internalization of ß2-adrenergic receptors (ß2AR) under stimulating conditions. Internalization of ß2AR is initiated by phosphorylations of certain serines and threonines by cAMP dependent protein kinase A (PKA) and G protein-coupled receptor kinases (GRK). PURPOSE: To evaluate the effect of α-hederin on PKA and GRK2 mediated phosphorylation of GFP-tagged ß2AR. STUDY DESIGN: To study this process we performed In-Cell Western using isoprenaline stimulated HEK293 cells overexpressing ß2AR as GFP fusion protein and specific antibodies against PKA (Ser345/346) and GRK2 (Ser355/356) phosphorylation sites. RESULTS: There was no effect found on the PKA mediated phosphorylation (n = 14) but we could show that α-hederin (1 µM, 12 h) significantly inhibits GRK2 mediated phosphorylation at Ser355/356 by 11 ± 5% (n ≥ 29, p ≤ 0.01) under stimulating conditions compared to the positive control. In Förster resonance energy transfer (FRET) experiments using the isolated kinases in solution α-hederin did not show any influence neither to GRK2 nor to PKA. CONCLUSION: Taken together, these results indicate that α-hederin acts as an indirect GRK2 inhibitor leading to a reduced homologous desensitization of ß2AR-GFP in HEK293 cells.

A systematic study on the influence of the main ingredients of an ivy leaves dry extract on the ß2-adrenergic responsiveness of human airway smooth muscle cells.

The bronchospasmolytic and secretolytic effects of ivy leaves dry extracts can be explained by an increased ß2-adrenergic responsiveness of the bronchi. Recently, it was shown that α-hederin inhibits the internalization of ß2-adrenergic receptors (ß2AR) under stimulating conditions. α-Hederin pretreated alveolar type II cells and human airway smooth muscle cells revealed an increased ß2AR binding and an elevated intracellular cAMP level, respectively. In order to identify whether additional compounds also mediate an increased ß2-adrenergic responsiveness, we examined the ingredients of an ivy leaves dry extract (EA 575) protocatechuic acid, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, rutin, kaempferol-3-O-rutinoside, 3,4-, 3,5- and 4,5-dicaffeoylquinic acid, hederacoside B, and ß-hederin. Within all the tested substances, only ß-hederin inhibited the internalization of GFP-tagged ß2AR in stably transfected HEK293 cells. Using fluorescence correlation spectroscopy ß-hederin (1 µM, 24 h) pretreated HASM cells showed a statistically significant increase in the ß2AR binding from 33.0 ± 8.9% to 44.1 ± 11.5% which was distributed with 36.0 ± 9.5% for τbound1 and 8.1 ± 2.6% for τbound2, respectively (n = 8, p < 0.05). The increased binding was selectively found for the receptor-ligand complex with unrestricted lateral mobility (τbound1 of 0.9 ± 0.1 ms, D1 = 9.1 ± 0.2 µm(2)/s, n = 8), whereas the binding of ß2AR with hindered lateral mobility (τbound2 of 64.2 ± 47.6 ms, D2 = 0.15 ± 0.02 µm(2)/s, n = 8) was not affected. Compared to control cells, a statistically significant increase of 17.5 ± 6.4% (n = 4, p < 0.05) and 24.2 ± 5.8% (n = 4, p < 0.001) in the cAMP formation was found for ß-hederin pretreated HASM cells after stimulation with 10 µM of terbutaline and simultaneous stimulation with 10 µM terbutaline and 10 µM forskolin, respectively. Within this systematic study focusing on the influence of the ingredients of an ivy leaves dry extract on HASM cells it was possible to identify ß-hederin as further component presumably responsible for the ß2-mimetic effects.

Downregulation of ß1 -adrenergic receptors in rat C6 glioblastoma cells by hyperforin and hyperoside from St John's wort.

OBJECTIVES: While the use of St John's wort extracts as treatment for mild to moderate depression is well established the mode of action is still under investigation. Individual constituents of St John's wort extract were tested for possible effects on the ß1 AR density and a subsequent change in downstream signalling in rat C6 glioblastoma cells. METHODS: The effect of compounds from St John's wort extract on the downregulation of ß1 -adrenergic receptor-GFP fusion proteins (ß1 AR-green fluorescent protein (GFP)) of transfected rat C6 gliobastoma cells (C6-ß1 AR-GFP) was investigated by means of confocal laser scanning microscopy (LSM). The influence on the lateral mobility of ß1 AR-GFP in C6-ß1 AR-GFP was investigated by fluorescence correlation spectroscopy. The formation of second messenger was determined by c-AMP-assay. KEY FINDINGS: Confocal LSM revealed that pretreatment of cells with 1 µm of hyperforin and hyperoside for 6 days, respectively, led to an internalization of ß1 AR-GFP under non-stimulating conditions. Observation by fluorescence correlation spectroscopy showed two diffusion time constants for control cells, with τdiff1 = 0.78 ± 0.18 ms and τdiff2 = 122.53 ± 69.41 ms, similarly distributed. Pretreatment with 1 µm hyperforin or 1 µm hyperoside for 3 days did not alter the τdiff values but decreased the fraction of τdiff1 whereas the fraction of τdiff2 increased significantly. An elevated level of ß1 AR-GFP with hindered lateral mobility was in line with ß1 AR-GFP internalization induced by hyperforin and hyperoside, respectively. A reduced ß1 -adrenergic responsiveness was assumed for C6 gliobastoma cells after pretreatment for 6 days with 1 µm of both hyperforin and hyperoside, which was confirmed by decreased cAMP formation of about 10% and 5% under non-stimulating conditions. Decrease in cAMP formation by 23% for hyperforin and 15% for hyperoside was more pronounced after stimulation with 10 µm dobutamine for 30 min. CONCLUSIONS: The treatment of C6 gliobastoma cells with hyperforin and hyperoside results in a reduced ß1 AR density in the plasma membrane and a subsequent reduced downstream signalling.

Bisphenol A inhibits voltage-activated Ca(2+) channels in vitro: mechanisms and structural requirements.

Bisphenol A (BPA), a high volume production chemical compound attracts growing attention as a health-relevant xenobiotic in humans. It can directly bind to hormone receptors, enzymes, and ion channels to become biologically active. In this study we show that BPA acts as a potent blocker of voltage-activated Ca(2+) channels. We determined the mechanisms of block and the structural elements of BPA essential for its action. Macroscopic Ba(2+) / Ca(2+) currents through native L-, N-, P/Q-, T-type Ca(2+) channels in rat endocrine GH(3) cells, mouse dorsal root ganglion neurons or cardiac myocytes, and recombinant human R-type Ca(2+) channels expressed in human embryonic kidney (HEK) 293 cells were rapidly and reversibly inhibited by BPA with similar potency (EC(50) values: 26-35 µM). Pharmacological and biophysical analysis of R-type Ca(2+) channels revealed that BPA interacts with the extracellular part of the channel protein. Its action does not require intracellular signaling pathways, is neither voltage- nor use-dependent, and does not affect channel gating. This indicates that BPA interacts with the channel in its resting state by directly binding to an external site outside the pore-forming region. Structure-effect analyses of various phenolic and bisphenolic compounds revealed that 1) a double-alkylated (R-C(CH(3))(2)-R, R-C(CH(3))(CH(2)CH(3))-R), or double-trifluoromethylated sp(3)-hybridized carbon atom between the two aromatic rings and 2) the two aromatic moieties in angulated orientation are optimal for BPA's effectiveness. Since BPA highly pollutes the environment and is incorporated into the human organism, our data may provide a basis for future studies relevant for human health and development.

Fluorescence correlation spectroscopy in drug discovery: study of Alexa532-endothelin 1 binding to the endothelin ETA receptor to describe the pharmacological profile of natural products.

Fluorescence correlation spectroscopy and the newly synthesized Alexa532-ET1 were used to study the dynamics of the endothelin ET(A) receptor-ligand complex alone and under the influence of a semisynthetic selective antagonist and a fungal extract on living A10 cells. Dose-dependent increase of inositol phosphate production was seen for Alexa532-ET1, and its binding was reduced to 8% by the selective endothelin ET(A) antagonist BQ-123, confirming the specific binding of Alexa532-ET1 to the endothelin ET(A) receptor. Two different lateral mobilities of the receptor-ligand complexes within the cell membrane were found allowing the discrimination of different states for this complex. BQ-123 showed a strong binding affinity to the "inactive" receptor state characterized by the slow diffusion time constant. A similar effect was observed for the fungal extract, which completely displaced Alexa532-ET1 from its binding to the "inactive" receptor state. These findings suggest that both BQ-123 and the fungal extract act as inverse agonists.

Terbutaline causes immobilization of single ß2-adrenergic receptor-ligand complexes in the plasma membrane of living A549 cells as revealed by single-molecule microscopy.

G-protein-coupled receptors are important targets for various drugs. After signal transduction, regulatory processes, such as receptor desensitization and internalization, change the lateral receptor mobility. In order to study the lateral diffusion of ß(2)-adrenergic receptors (ß(2)AR) complexed with fluorescently labeled noradrenaline (Alexa-NA) in plasma membranes of A549 cells, trajectories of single receptor-ligand complexes were monitored using single-particle tracking. We found that a fraction of 18% of all ß(2)ARs are constitutively immobile. About 2/3 of the ß(2)ARs moved with a diffusion constant of D(2) = 0.03 ± 0.001 µm(2)/s and about 17% were diffusing five-fold faster (D(3) = 0.15 ± 0.02 µm(2)/s). The mobile receptors moved within restricted domains and also showed a discontinuous diffusion behavior. Analysis of the trajectory lengths revealed two different binding durations with τ(1) = 77 ± 1 ms and τ(2) = 388 ± 11 ms. Agonistic stimulation of the ß(2)AR-Alexa-NA complexes with 1 µM terbutaline caused immobilization of almost 50% of the receptors within 35 min. Simultaneously, the mean area covered by the mobile receptors decreased significantly. Thus, we demonstrated that agonistic stimulation followed by cell regulatory processes results in a change in ß(2)AR mobility suggesting that different receptor dynamics characterize different receptor states.

Pre-treatment with α-hederin increases ß-adrenoceptor mediated relaxation of airway smooth muscle.

Preparations of ivy leaves dry extract with secretolytic and bronchiolytic efficacy are widely used for the treatment of acute and chronic obstructive airway diseases. The mechanism by which ivy preparations improve lung functions is not fully understood. Here, we tested the influence of the three main saponins of ivy, α-hederin, hederacoside C and hederagenin, on the contraction and relaxation behaviour of isolated bovine tracheal smooth muscle strips by isometric tension measurements. None of the tested compounds altered histamine or methacholine-induced contraction of the smooth muscle strips. In contrast, the isoprenaline-induced relaxation of 100µM methacholine precontracted muscle strips was significantly enhanced when pre-treated with 1µM of α-hederin for 18h. The pre-treatment with hederacoside C or hederagenin had no effect on isoprenaline-induced relaxation. For the first time the bronchiolytic effect of α-hederin was demonstrated by isometric tension measurements using bovine tracheal smooth muscle strips. α-Hederin increases isoprenaline-induced relaxation indirectly, probably by inhibiting heterologous desensitization induced by high concentrations of muscarinic ligands like methacholine.

Balbiani ring mRNPs diffuse through and bind to clusters of large intranuclear molecular structures.

A detailed conception of intranuclear messenger ribonucleoprotein particle (mRNP) dynamics is required for the understanding of mRNP processing and gene expression outcome. We used complementary state-of-the-art fluorescence techniques to quantify native mRNP mobility at the single particle level in living salivary gland cell nuclei. Molecular beacons and fluorescent oligonucleotides were used to specifically label BR2.1 mRNPs by an in vivo fluorescence in situ hybridization approach. We characterized two major mobility components of the BR2.1 mRNPs. These components with diffusion coefficients of 0.3 ± 0.02 µm²/s and 0.73 ± 0.03 µm²/s were observed independently of the staining method and measurement technique used. The mobility analysis of inert tracer molecules revealed that the gland cell nuclei contain large molecular nonchromatin structures, which hinder the mobility of large molecules and particles. The mRNPs are not only hindered by these mobility barriers, but in addition also interact presumably with these structures, what further reduces their mobility and effectively leads to the occurrence of the two diffusion coefficients. In addition, we provide evidence that the remarkably high mobility of the large, 50 nm-sized BR2.1 mRNPs was due to the absence of retarding chromatin.

Transport of a hyaluronan-binding protein in brain tissue.

Hyaluronan is an unsulfated linear glycosaminoglycan with the ability to nucleate extracellular matrices by the formation of aggregates with lecticans. These matrices are essential during development of the central nervous system. In the prospective white matter of the developing brain hyaluronan is organized into fiber-like structures according to confocal microscopy of fixed slices which may guide the migration of neural precursor cells [Baier, C., S.L. Baader, J. Jankowski, V. Gieselmann, K. Schilling, U. Rauch, and J. Kappler. 2007. Hyaluronan is organized into fiber-like structures along migratory pathways in the developing mouse cerebellum. Matrix Biol. 26: 348-58]. By using plasmon surface resonance, microinjection into brain slices and fluorescence correlation spectroscopy, we show that the brain-specific lecticans bind to, but also dissociate rather rapidly from hyaluronan. After microinjection into native cerebellar slices a GFP-tagged hyaluronan-binding neurocan fragment was enriched at binding sites in the prospective white matter, which had a directional orientation and formed local stationary concentration gradients in areas where binding sites are abundant. Fluorescence correlation spectroscopy measurements at fixed brain slices revealed that fiber-bound neurocan-GFP was mobile with D(fiber(neurocan-GFP))=4x10(-10)cm(2)/s. Therefore, we propose that hyaluronan-rich fibers in the prospective white matter of the developing mouse cerebellum can guide the diffusion of lecticans. Since lecticans bind a variety of growth and mobility factors, their guided diffusion may contribute to the transport of these polypeptides and to the formation of concentration gradients. This mechanism could serve to encode positional information during development.

Alpha-hederin, but not hederacoside C and hederagenin from Hedera helix, affects the binding behavior, dynamics, and regulation of beta 2-adrenergic receptors.

Hederacoside C, alpha-hederin, and hederagenin are saponins of dry extracts obtained from the leaves of ivy (Hedera helix L.). Internalization of beta(2)-adrenergic receptor-GFP fusion proteins after stimulation with 1 microM terbutaline was inhibited by preincubation of stably transfected HEK293 cells with 1 microM alpha-hederin for 24 h, whereas neither hederacoside C nor hederagenin (1 microM each) influenced this receptor regulation. After incubation of A549 cells with 5 nM Alexa532-NA, two different diffusion time constants were found for beta(2)AR-Alexa532-NA complexes by fluorescence correlation spectroscopy. Evaluation of the autocorrelation curve revealed diffusion time constants: tau(bound1) = 1.4 +/- 1.1 ms (n = 6) found for receptor-ligand complexes with unrestricted lateral mobility, and tau(bound2) = 34.7 +/- 14.1 ms (n = 6) for receptor-ligand complexes with hindered mobility. The distribution of diffusion time constants was 24.3 +/- 2.5% for tau(bound1) and 8.7 +/- 4.3% for tau(bound2) (n = 6). A549 cells pretreated with 1 microM alpha-hederin for 24 h showed dose-dependent alterations in this distribution with 37.1 +/- 5.5% for tau(bound1) and 4.1 +/- 1.1% for tau(bound2). Simultaneously, the level of Alexa532-NA binding was significantly increased from 33.0 +/- 6.8 to 41.2 +/- 4.6%. In saturation experiments, alpha-hederin did not influence the beta(2)-adrenergic receptor density (B(max)), whereas the K(D) value for Alexa532-NA binding decreased from 36.1 +/- 9.2 to 24.3 +/- 11.1 nM. Pretreatment of HASM cells with alpha-hederin (1 microM, 24 h) revealed an increased intracellular cAMP level of 13.5 +/- 7.0% under stimulating conditions. Remarkably, structure-related saponins like hederacoside C and hederagenin did not influence either the binding behavior of beta(2)AR or the intracellular cAMP level.

Cerebroside sulfotransferase forms homodimers in living cells.

Cerebroside sulfotransferase (CST) catalyzes the 3'-sulfation of galactose residues in several glycolipids. Its major product in the mammalian brain is sulfatide, which is an essential myelin component. Using epitope-tagged variants, murine CST was found to localize to the Golgi apparatus, but in contrast to previous assumptions, not to the trans-Golgi network. An examination of enhanced green fluorescent protein (EGFP)-tagged CST suggests that CST forms homodimers and that dimerization is mediated by the lumenal domain of the enzyme, as shown by immunoprecipitation and density gradient centrifugation. In order to verify that dimerization of CST observed by biochemical methods reflects the behavior of the native protein within living cells, the mobility of CST-EGFP was examined using fluorescence correlation spectroscopy. These experiments confirmed the homodimerization of CST-EGFP fusion proteins in vivo. In contrast to full-length CST, a fusion protein of the amino-terminal 36 amino acids of CST fused to EGFP was exclusively found as a monomer but nevertheless showed Golgi localization.