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.

New benzoquinone pigments from the hydnoid fungus Sarcodontia setosa and their biosynthetic relationship.

Chemical investigation of the hydnoid fungus Sarcodontia setosa resulted in the isolation of five compounds, including two new sarcodontic acid derivatives - setosic acid (1) and 7,8-dehydrohomosarcodontic acid (2) along with three known benzoquinone pigments - sarcodontic acid (3), 4,5-dehydrosarcodontic acid (4) and dihydrosarcodontic acid (5). The structures were elucidated using spectroscopic methods (UV, NMR and HR-ESIMS). The biosynthetic relationship of the isolated compounds is proposed and discussed. Antibacterial activity screening of compounds 1-5 against ESKAPE bacterial strains in vitro with zones of inhibition was performed and MIC values were established for the most active compounds (3 and 5).

The Ability of Acid-Based Natural Deep Eutectic Solvents to Co-Extract Elements from the Roots of Glycyrrhiza glabra L. and Associated Health Risks.

The roots of licorice (Glycyrrhiza glabra L.) have been widely used in traditional and officinal medicines for the treatment of different diseases. Natural deep eutectic solvents (NADES) have become popular for the extraction of active principles from medicinal plants. However, the ability of NADES to co-extract trace elements during the isolation of target active compounds is rarely investigated. The aim of this study was to analyze the content of trace elements in acid-based NADES extracts from the roots of G. glabra and the health risks associated with them. In this study, we have tested for the first time the ability of several acid-based NADES to co-extract glycyrrhizic acid (GA) and trace elements from the roots of G. glabra. GA has been identified as the dominant phytochemical in G. glabra NADES extracts (0.145-0.495 mg/g). Due to the close pKa of lactic acid and GA, the yield of GA in lactic acid-based NADES was higher in comparison with other tested NADES. The yield of GA in NADES3-NADES5 was statistically significant and surpassed the yield of GA in water. The recovery of all elements (except Li) by all tested NADES was low (less than 6%). According to an ANOVA test, the hydrogen bond donor type plays a decisive role in the extraction of elements. A strong positive correlation between the recovery of GA and MPI was noted. The metal pollution index, hazard quotient, hazard index, and chronic daily intake were calculated and suggest that all tested NADES extracts of G. glabra roots were nontoxic and possess no health risk for both ingestion and topical application.

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.

Isolation and Characterization of a New Flavone C-glycoside Isoembinin from Iris lacteal along with its Effects on Platelet Activation.

One new compound isoembinin 1 along with ten known compounds 2-11 were isolated from the terrestrial parts of Iris lactea Pall. All of the compound structures were determined through extensive 1D and 2D NMR experiments along with HR-ESIMS analysis and comparison with literature data. Because many flavonoids exert antiplatelet and antioxidant activity we tested the effects of the isolated flavone C-glycosides 1-9 on platelet activation and reactive oxygen species (ROS) production. Platelet reactivity was assessed by activation of αIIbß3 integrins activation and ROS production by DCF-DA fluorescence. For the analysis of whether protein kinase A or G are involved in the platelet inhibition, the activity of these kinases was analyzed by phosphorylation of their common substrate in platelets. In all experiments apigenin, which inhibit platelet activation was used as a positive control. All isolated flavone C-glycosides inhibited platelet αIIbß3 integrins activation with IC50 in the µM range, however this inhibitory effect was found to not be mediated through the prevention of ROS formation or by the activation of cyclic nucleotide pathways. Structure-activity comparison between apigenin and compounds 1-9 shows that the presence of C-glycoside and O-glycoside residues on the aglycone apigenin diminish the degree of platelet inhibition.

A new dimethoxy dihydrochalcone isolated from the shoots of Empetrum nigrum L.

A new dihydrochalcone, 2',4'-dimethoxydihydrochalcone (1), together with 7 known compounds, 2',4'-dihydroxydihydrochalcone (2), 2'-hydroxy-4'-methoxydihydrochalcone (3), 2'-hydroxy-4'-methoxychalcone (4), 1-(3,5-dihydroxy-4-methoxyphenyl)-2-(3-hydroxyphenyl) ethane (5), 2,3,4,7-tetramethoxy-9,10-dihydrophenanthrene (6), 5-hydroxy-2,3,4-trimethoxy-9,10-dihydrophenanthrene (7) and 5,7-dihydroxy-6,8-dimethyl flavanone (8) were isolated from the shoots of Empetrum nigrum L. The structures of these compounds were elucidated using 1D and 2D NMR experiments along with HR-ESI-MS. Compound 6 is reported for the genus Empetrum for the first time.[Formula: see text].

New cyclic diarylheptanoids from the false heartwood of Betula pubescens Ehrh.

Two undescribed (1-2) and five known cyclic diarylheptanoids (3-7) were isolated from the false heartwood of white birch (Betula pubescens Ehrh.). All structures were elucidated through extensive 1D and 2D NMR experiments and HR-ESI-MS data, along with comparison of their spectroscopic data with those reported in the literature. The two new cyclic diarylheptanoids are betuladiol (1) and betulondiol (2). Extracts from false heartwood were evaluated for their antimicrobial activity against Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, Staphylococcus aureus and Cutibacterium acnes together with their antifungal activity against Candida albicans and Candida glabrata.

Synthesis of N-succinyl- and N-glutaryl-chitosan derivatives and their antioxidant, antiplatelet, and anticoagulant activity.

The effects of temperature, reactant ratio, pH, and reaction time were studied on the polymers formed by the reactions of succinic and glutaric anhydrides with chitosan under both homogeneous and heterogeneous conditions. As a result, protocols were developed for the synthesis of succinyl- and glutaryl-chitosan derivatives (SC and GC, respectively) with a specific degree of substitution. The polymers were characterized by NMR spectroscopy, including two-dimensional NMR techniques, that confirms N-substitution of chitosan under reaction conditions used. SC and GC both show pronounced and similar antioxidant activity, which slightly increases with an increase in the degree of substitution. Both SC and GC showed antiplatelet and anticoagulant activity. The platelet aggregation is suppressed more strongly in the experiments with GC than with SC, although the latter exhibits a more pronounced anticoagulant activity.