Antiplatelet Effects of Flavonoid Aglycones Are Mediated by Activation of Cyclic Nucleotide-Dependent Protein Kinases.

Flavonoid aglycones are secondary plant metabolites that exhibit a broad spectrum of pharmacological activities, including anti-inflammatory, antioxidant, anticancer, and antiplatelet effects. However, the precise molecular mechanisms underlying their inhibitory effect on platelet activation remain poorly understood. In this study, we applied flow cytometry to analyze the effects of six flavonoid aglycones (luteolin, myricetin, quercetin, eriodictyol, kaempferol, and apigenin) on platelet activation, phosphatidylserine externalization, formation of reactive oxygen species, and intracellular esterase activity. We found that these compounds significantly inhibit thrombin-induced platelet activation and decrease formation of reactive oxygen species in activated platelets. The tested aglycones did not affect platelet viability, apoptosis induction, or procoagulant platelet formation. Notably, luteolin, myricetin, quercetin, and apigenin increased thrombin-induced thromboxane synthase activity, which was analyzed by a spectrofluorimetric method. Our results obtained from Western blot analysis and liquid chromatography-tandem mass spectrometry demonstrated that the antiplatelet properties of the studied phytochemicals are mediated by activation of cyclic nucleotide-dependent signaling pathways. Specifically, we established by using Förster resonance energy transfer that the molecular mechanisms are, at least partly, associated with the inhibition of phosphodiesterases 2 and/or 5. These findings underscore the therapeutic potential of flavonoid aglycones for clinical application as antiplatelet agents.

Thrombin-induced platelet inhibition by 2',4'-dihydroxychalcone and 2',4'-dihydroxydihydrochalcone is mediated by inhibition of ROS production and Thromboxane synthase a activity: structure-activity relationship of polyphenol secondary metabolites from Empetrum nigrum.

In this study, we expanded our previous work by testing compounds 1-12 for their ability to inhibit platelet activation at low (30 µM) concentration by inhibition of ROS production, thromboxane synthase (TxS) activity, and activation of cyclic nucleotide pathways. We also investigated whether some of these compounds could potentiate the effects of P2Y12 ADP receptor inhibitor action and discussed possible structure-activity relationships of the tested compounds. We showed that at this concentration only compounds 7 and 12 significantly inhibited thrombin-induced platelet activation which was accompanied by inhibition of ROS production and thromboxane synthase activity. Correspondingly, these compounds significantly potentiated the inhibitory effect of cangrelor on thrombin-induced platelet activation. In some other cases, inhibition of ROS production and thromboxane synthase activity did not correlate with platelet inhibition, indicating that these compounds could affect some, still unidentified, activatory pathways in platelets that counteract their inhibitory effects.

Polyacetylene Derivatives from the Polypore Fungus (Fistulina hepatica, Agaricomycetes) and Their Antimicrobial Activity.

Chemical investigation of the polypore fungus Fistulina hepatica resulted in the isolation of five compounds, including four new polyacetylenic fatty acid derivatives - isocinnatriacetin B (1), isocinnatriacetin A (2), cinna-triacetin C (3) and ethylcinnatriacetin A (4) together with one known polyacetylene fatty acid derivative - cinnatriacetin A (5). The structures were elucidated using spectroscopic methods (UV, NMR, HR-ESIMS) along with comparison to literature data. Antibacterial activity screening of compounds 1-5 against ESKAPE bacterial strains in vitro with zones of inhibition (ZOI) was performed and MIC values were established for the most active compounds (3 and 4). Together with that morphological and growth parameters under solid-phase cultivation were also researched.

Bracteatinine and isogroenlandicine, two new isoquinoline alkaloids isolated from Corydalis bracteata and their effect on platelet function.

Two previously undescribed isoquinoline alkaloids, bracteatinine (1) and isogroenlandicine (2), together with four known alkaloids - coptisine (3), dehydrocorydaline (4), palmatine (5) and jatrorrhizine (6) were isolated from the aerial parts of Corydalis bracteata (Steph. Ex. Willd.) Pers. The structures of the compounds were elucidated using 1D and 2D NMR data along with HRESI-MS. The isolated new compounds bracteatinine and isogroenlandicine are close structural derivatives and isomers of corgoine and groenlandicine, respectively. Bracteatinine is also notable, being a representative of the rare 2-benzylisoquinoline alkaloids. Many natural products isolated from different plants are used as adjuvants, in addition to standard chemotherapy, in treatment of different cancers. Cancer-associated thrombosis remains a common complication and leading cause of mortality for cancer patients. Because platelets play the key role in thrombotic complications, we investigated effects of the isolated alkaloids 1-6 on platelet reactivity and showed that they did not significantly affect platelet function.

Phytochemical Characterization of Water Avens (Geum rivale L.) Extracts: Structure Assignment and Biological Activity of the Major Phenolic Constituents.

Water avens (Geum rivale L.) is a common Rosaceae plant widely spread in Europe and North America. It is rich in biologically active natural products, some of which are promising as prospective pharmaceuticals. The extracts of water avens are well known for their triterpenoid metabolites and associated anti-inflammatory, antimicrobial and antioxidant activities. However, the polyphenolic profiles of G. rivale L. are still awaiting complete characterization. Accordingly, the contribution of its individual components to the antioxidant, antibacterial and neuroprotective activity of the extracts is still unknown. As this plant can be available on an industrial scale, a better knowledge of its properly-relevant constituents might give access to new highly-efficient pharmaceutical substances and functional products. Therefore, herein we comprehensively characterize the secondary metabolome of G. rivale by ESI-HR-MS, ESI-HR-MSn and NMR spectroscopy with a special emphasis on the polyphenolic composition of its aerial parts. Furthermore, a multilateral evaluation of the antioxidant, neuroprotective and antibacterial properties of the aqueous and ethyl acetate fractions of the total aqueous alcoholic extract as well as individual isolated polyphenols was accomplished. Altogether four phenolic acid derivatives (trigalloyl hexose, caffeoyl-hexoside malate, ellagic acid and ellagic acid pentoside), six flavonoids (three quercetin derivatives, kaempferol and three its derivatives and two isorhamnetin derivatives) and four tannins (HHDP-hexoside, proantocyanidin dimer, pedunculagin I and galloyl-bis-HHDP-hexose) were identified in this plant for the first time. The obtained aqueous and ethyl acetate fractions of the total extract as well as the isolated individual compounds showed pronounced antioxidant activity. In addition, a pronounced antibacterial activity against several strains was proved for the studied fractions (for ethyl acetate fraction the highest activity against E. coli АТСС 25922 and S. aureus strains ATCC 27853 and SG-511 (MIC 15.6 µg/mL) was observed; for aqueous fraction-against Staphylococcus aureus SG-511 (MIC 31.2 µg/mL)). However, the anti-neurodegenerative (neuroprotective) properties could not be found with the employed methods. However, the antibacterial activity of the fractions could not be associated with any of the isolated individual major phenolics (excepting 3-O-methylellagic acid). Thus, the aerial parts of water avens represent a promising source of polyphenolic compounds with antioxidant activity and therefrom derived human health benefits, although the single constituents isolated so far lack a dominant selectively bioactive constituent in the bioassays performed.