Nobiletin, a citrus flavonoid, activates vasodilator-stimulated phosphoprotein in human platelets through non-cyclic nucleotide-related mechanisms

1,8-Cineole Affects Agonists-Induced Platelet Activation, Thrombus Formation and Haemostasis

1,8-cineole, a monoterpenoid is a major component of eucalyptus oil and has been proven to possess numerous beneficial effects in humans. Notably, 1,8-cineole is the primary active ingredient of a clinically approved drug, Soledum® which is being mainly used for the maintenance of sinus and respiratory health. Due to its clinically valuable properties, 1,8-cineole has gained significant scientific interest over the recent years specifically to investigate its anti-inflammatory and antioxidant effects. However, the impact of 1,8-cineole on the modulation of platelet activation, thrombosis and haemostasis was not fully established. Therefore, in this study, we demonstrate the effects of 1,8-cineole on agonists-induced platelet activation, thrombus formation under arterial flow conditions and haemostasis in mice. 1,8-cineole largely inhibits platelet activation stimulated by glycoprotein VI (GPVI) agonists such as collagen and cross-linked collagen-related peptide (CRP-XL), while it displays minimal inhibitory effects on thrombin or ADP-induced platelet aggregation. It inhibited inside-out signalling to integrin αIIbβ3 and outside-in signalling triggered by the same integrin as well as granule secretion and intracellular calcium mobilisation in platelets. 1,8-cineole affected thrombus formation on collagen-coated surface under arterial flow conditions and displayed a minimal effect on haemostasis of mice at a lower concentration of 6.25 µM. Notably, 1,8-cineole was found to be non-toxic to platelets up to 50 µM concentration. The investigation on the molecular mechanisms through which 1,8-cineole inhibits platelet function suggests that this compound affects signalling mediated by various molecules such as AKT, Syk, LAT, and cAMP in platelets. Based on these results, we conclude that 1,8-cineole may act as a potential therapeutic agent to control unwarranted platelet reactivity under various pathophysiological settings.

A review of in vitro studies of the anti-platelet potential of citrus fruit flavonoids

The citrus plants of the Rutaceae, such as oranges, grapefruits and mandarins, are cultivated worldwide. Their fruits and their juices are rich sources of flavonoids: for example, hesperidin and narirutin in oranges, and narirutin and naringin in grapefruits. Although these flavonoids have been found to potentially modulate blood platelet activity, most studies have been performed in vitro; in addition, the body of evidence regarding antiplatelet activity is relatively weak and the exact mechanisms remain poorly understood. More importantly, the concentrations of flavonoids studied in vitro (i.e. 3.125-300 μM) with washed blood platelets did not always correspond with their physiological concentrations in vivo, i.e. in whole blood after oral administration, and citrus fruit flavonoids are also characterized by low bioavailability. Therefore, more detailed studies on the antiplatelet potential of citrus flavonoids are needed, especially in in vivo models.

Citrus flavonoids and their antioxidant evaluation

The antioxidant ability is the link and bridge connecting a variety of biological activities. Citrus flavonoids play an essential role in regulating oxidative stress and are an important source of daily intake of antioxidant supplements. Many studies have shown that citrus flavonoids promote health through antioxidation. In this review, the biosynthesis, composition and distribution of citrus flavonoids were concluded. The detection methods of antioxidant capacity of citrus flavonoids were divided into four categories: chemical, cellular, animal and clinical antioxidant capacity evaluation systems. The modeling methods, applicable scenarios, and their relative merits were compared based on these four systems. The antioxidant functions of citrus flavonoids under different evaluation systems were also discussed, especially the regulation of the Nrf2-antioxidases pathway. Some shortcomings in the current research were pointed out, and some suggestions for progress were put forward.

Flavones as a Privileged Scaffold in Drug Discovery: Current Developments

BACKGROUND

Flavones are one of the main subclasses of flavonoids with diverse pharmacological properties. They have been reported to possess antimalarial, antimicrobial, anti-tuberculosis, anti-allergic, antioxidant, anti-inflammatory activities, among others.

OBJECTIVE

The present review summarizes the recent information on the pharmacological properties of naturally occurring and synthetic flavones.

METHODS

Scientific publications referring to natural and synthetic flavones in relation to their biological activities were hand-searched in databases such as SciFinder, PubMed (National Library of Medicine), Science Direct, Wiley, ACS, SciELO, Springer, among others.

RESULTS

As per the literature, seventy-five natural flavones were predicted as active compounds with reference to their IC50 (<20 µg/mL) in in vitro studies. Also, synthetic flavones were found active against several diseases.

CONCLUSION

As per the literature, flavones are important sources for the potential treatment of multifactorial diseases. However, efforts toward the development of flavone-based therapeutic agents are still needed. The appearance of new catalysts and chemical transformations is expected to provide avenues for the synthesis of unexplored flavones, leading to the discovery of flavones with new properties and biological activities.

Myricetin, the Main Flavonoid in Syzygium cumini Leaf, Is a Novel Inhibitor of Platelet Thiol Isomerases PDI and ERp5

BACKGROUND

Flavonoids have been characterized as a prominent class of compounds to treat thrombotic diseases through the inhibition of thiol isomerases. Syzygium cumini is a flavonoid-rich medicinal plant that contains myricetin and gallic acid. Little is known about the potential antiplatelet properties of S. cumini and its constituent flavonoids.

OBJECTIVE

To evaluate the antiplatelet effects and mechanism of action of a polyphenol-rich extract (PESc) from S. cumini leaf and its most prevalent polyphenols, myricetin and gallic acid.

METHODS

PESc, myricetin, and gallic acid were incubated with platelet-rich plasma and washed platelets to assess platelet aggregation and activation. In vitro platelet adhesion and thrombus formation as well as in vivo bleeding time were performed. Finally, myricetin was incubated with recombinant thiol isomerases to assess its potential to bind and inhibit these, while molecular docking studies predicted possible binding sites.

RESULTS

PESc decreased platelet activation and aggregation induced by different agonists. Myricetin exerted potent antiplatelet effects, whereas gallic acid did not. Myricetin reduced the ability of platelets to spread on collagen, form thrombi in vitro without affecting hemostasis in vivo. Fluorescence quenching studies suggested myricetin binds to different thiol isomerases with similar affinity, despite inhibiting only protein disulfide isomerase (PDI) and ERp5 reductase activities. Finally, molecular docking studies suggested myricetin formed non-covalent bonds with PDI and ERp5.

CONCLUSIONS

PESc and its most abundant flavonoid myricetin strongly inhibit platelet function. Additionally, myricetin is a novel inhibitor of ERp5 and PDI, unveiling a new therapeutic perspective for the treatment of thrombotic disorders.

Beneficial Effects of Citrus Flavonoids on Cardiovascular and Metabolic Health

The prevalence of cardiovascular disease (CVD) is increasing over time. CVD is a comorbidity in diabetes and contributes to premature death. Citrus flavonoids possess several biological activities and have emerged as efficient therapeutics for the treatment of CVD. Citrus flavonoids scavenge free radicals, improve glucose tolerance and insulin sensitivity, modulate lipid metabolism and adipocyte differentiation, suppress inflammation and apoptosis, and improve endothelial dysfunction. The intake of citrus flavonoids has been associated with improved cardiovascular outcomes. Although citrus flavonoids exerted multiple beneficial effects, their mechanisms of action are not completely established. In this review, we summarized recent findings and advances in understanding the mechanisms underlying the protective effects of citrus flavonoids against oxidative stress, inflammation, diabetes, dyslipidemia, endothelial dysfunction, and atherosclerosis. Further studies and clinical trials to assess the efficacy and to explore the underlying mechanism(s) of action of citrus flavonoids are recommended.

Knockdown of RAC1 and VASP gene expression inhibits breast cancer cell migration

The ability of tumor cells to migrate is biologically fundamental for tumorigenesis, growth, metastasis and invasion. The present study examined the role of Ras-related C3 botulinum toxin substrate (RAC1) and vasodilator-stimulated phosphoprotein (VASP) in breast cancer cell migration. According to data in Kaplan, Oncomine and The Cancer Genome Atlas, increased expression levels of RAC1 and VASP in breast cancer are associated with decreased cancer cell differentiation, advanced pathological stage and more aggressive tumor subtypes, while increased VASP mRNA expression levels are positively correlated with a poor prognosis in patients with breast cancer. The short hairpin (sh)RNA technique was employed to knock down the expression of RAC1 or VASP. Stable interference with the expression of RAC1 or VASP using RAC1-shRNA or VASP-shRNA, respectively, was established in MCF-7 breast cancer cells. In RAC1-shRNA or VASP-shRNA cells, the protein expression levels of RAC1 or VASP were significantly downregulated compared with control cells. The proliferation and migration rates of the RAC1-shRNA or VASP-shRNA cells were significantly lower compared with control cells. It was observed that the protein expression levels of VASP also decreased in RAC1-shRNA cells compared with control cells. The results revealed that RAC1 and VASP may serve important roles in promoting the migration of MCF-7 breast cancer cells, and that VASP may among the downstream signaling molecules associated with RAC1.

Label-Free Quantitative Phosphoproteomics Reveals Regulation of Vasodilator-Stimulated Phosphoprotein upon Stathmin-1 Silencing in a Pair of Isogenic Colorectal Cancer Cell Lines

In this communication, we present the phosphoproteome changes in an isogenic pair of colorectal cancer cell lines, viz., the poorly metastatic HCT-116 and the highly metastatic derivative E1, upon stathmin-1 (STMN1) knockdown. The aim was to better understand how the alterations of the phosphoproteins in these cells are involved in cancer metastasis. After the phosphopeptides were enriched using the TiO₂ HAMMOC approach, comparative proteomics analysis was carried out using sequential window acquisition of all theoretical mass spectra-MS. Following bioinformatics analysis using MarkerView and OneOmics platforms, we identified a list of regulated phosphoproteins that may play a potential role in signaling, maintenance of cytoskeletal structure, and focal adhesion. Among these phosphoproteins, was the actin cytoskeleton regulator protein, vasodilator-stimulated phosphoprotein (VASP), where its change in phosphorylation status was found to be concomitant with STMN1-associated roles in metastasis. We further showed that silencing of stathmin-1 altered the expression, subcellular localization and phosphorylation status of VASP, which suggested that it might be associated with remodeling of the cell cytoskeleton in colorectal cancer metastasis.

Hawthorn Leaf Flavonoids Protect against Diabetes-Induced Cardiomyopathy in Rats via PKC-α Signaling Pathway

Objectives

DCM has become one of the main reasons of death in diabetic patients. In this study, we aimed to explore the hawthorn leaf flavonoids (HLF) protective effect against diabetes-induced cardiac injury and the underlying mechanisms in experimental rats.

Methods

Experimental diabetic model was induced by intraperitoneal injection of streptozotocin (STZ, 40 mg/kg) in rats after feeding with high-fat diet for 8 weeks. The diabetic rats received a 16-week treatment of different doses of HLF (50, 100, and 200). The morphological changes of myocardial cells were observed by light microscope; the concentration of antioxidant indicator and TNF-α and the expression of PKC-α mRNA, PKC-α, and NF-κB proteins were assessed as well.

Results

STZ-induced diabetes mellitus prompted blood glucose, cardiac injury, oxidative stress, and inflammation, accompanied with suppressed body weight. On the contrary, HLF administration improved body weight and blood glucose and attenuated myocardial structural abnormalities in diabetic rats. In addition, HLF decreased MDA level and enhanced SOD activities, inhibited TNF-α expression, and downregulated PKC-α mRNA, PKC-α, and NF-κB which were induced by diabetes.

Conclusions

HLF has a protective effect against diabetic cardiomyopathy in rats. The mechanism may be involved in reducing oxidative stress and inflammation via inactivation of the PKC-α signaling pathway.