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.

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.