Effects of Flavonoid Quercetin on Thrombo-Inflammatory Processes in Patients with Sickle Cell Disease

Introduction: Altered erythrocyte physiology in Sickle Cell Disease (SCD) results in severe vascular complications, including vaso-occlusion (VOC) along with various other manifestations, such as thrombosis and end organ damage. Moreover, platelet activation endothelial dysfunction and fibrin formation, are critical processes implicated in thrombo-inflammatory vasculopathy in SCD. Since flavonoids intake is associated with lowered adverse cardiovascular disease outcomes and cancer associated thrombosis, we are evaluating the effects of the flavonoid Isoquercetin (IQ) on thrombo-inflammatory biomarkers in patients with SCD (NCT:04514510). Here we report the mechanistic effects of Quercetin (Que), an aglycone that differs from IQ by the absence of 3-linked glucoside moiety, on markers of erythrocyte and platelet activation in patients with SCD. Methods: We studied patients with SCD (Genotype SS, mean age: 39 yrs, N=8) and ethnic matched controls (Genotype AA, mean age: 42 yrs, N=8). Erythrocyte reactive oxygen species (ROS) was measured in washed red cells by flow cytometry using the fluorescent probe 2', 7'-dichlorofluorescein diacetate (DCFDA) in the presence or absence of Quercetin (Que) (100 µM). Effects of in vitro erythrocyte ROS induction by hydrogen peroxide (H 2O 2) and ROS inhibition by N-acetyl-L-cysteine (NAC) were evaluated. Baseline and agonist-induced (ADP 20 µM) platelet P-selectin expression in vitro in the presence or absence of Que (100 µM) was assessed by flow cytometry. Results: At baseline, SS erythrocytes demonstrated elevated levels of ROS reflected by greater florescent intensity with DCFDA when compared with erythrocytes from ethnic matched controls (SS mean= 1884, SD: 508.8 vs. AA mean: 1604, SD: 554.5; p value= 0.3798). Stimulation of AA erythrocytes in vitro with H 2O 2 led to accumulation of ROS that approached levels similar to those exhibited by SS erythrocytes at baseline (AA mean: 1890, SD: 748.3). Pre-treatment of SS and AA erythrocytes in vitro with the antioxidant NAC exhibited minimal effects on ROS in SS erythrocytes (SS baseline+NAC mean: 1942, SD: 526.8, p value 0.4609 and SS H 2O 2+NAC mean: 1889, SD: 437.4, p value 0.5469) but lowered ROS levels in both baseline and H 2O 2 treated AA erythrocytes (AA baseline+NAC mean: 1442, SD: 453.9, p value 0.1563 and AA H 2O 2+NAC mean: 1581, SD: 518.7, p value 0.078). Pre-treatment of SS and AA erythrocytes in vitro with Que substantially lowered erythrocyte ROS in patients and controls at the baseline (SS baseline ROS with Que mean: 1582, SD: 542.0, p value 0.0078; AA baseline ROS with Que mean: 1341, SD: 490.9, p value 0.0313; Fig. 1A), and after H 2O 2 stimulation (SS H 2O 2 induced ROS+Que mean: 1677, SD: 572.5, p value 0.0156; AA H 2O 2 induced ROS+Que mean: 1417, SD: 512, p value 0.0078). Pre-treatment of erythrocytes with a combination of Que and NAC did not reveal synergistic anti-oxidant activity (SS NAC+Que mean: 1616, SD: 464.8; AA NAC+Que mean: 1333, SD: 524.1). We simultaneously investigated the effects of Que on platelet P-selectin expression in the same subjects. As expected, baseline platelet surface P-selectin expression was higher in SS patients compared with controls (SS N=5, mean: 1.48%, Max: 4.9%, Min: 0.03%; AA N=4, mean: 0.89%, Max: 2.3%, Min: 0%; p value 0.55). Stimulation of platelet rich plasma (PRP) with ADP increased surface P-selectin expression in comparison with baseline, in both patients and controls (SS N=5, mean: 18.04%, Max: 40.4%, Min: 5.8%, p value 0.0047; AA N=4, mean: 20.60%, Max: 43.8%, Min: 5.4%; p value 0.0140). Pre-treatment of PRP with Que prior to ADP stimulation revealed a trend toward decreased platelet surface P-selectin expression in both patients and controls (SS N=5, mean: 10.49%, Max: 24.8%, Min: 3.1%; AA N=4, mean: 12.09%, Max: 21.9%, Min: 3.4%; Fig 1B) although this did not return to baseline. Conclusion: The flavonoid Quercetin appears to have a beneficial effect in lowering erythrocyte ROS and platelet surface P-selectin and warrant further evaluation as a strategy to ameliorate thrombo-inflammatory pathophysiology in sickle hemoglobinopathies. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

In Silico Prediction of the Phosphorylation of NS3 as an Essential Mechanism for Dengue Virus Replication and the Antiviral Activity of Quercetin

Dengue virus infection is a global health problem for which there have been challenges to obtaining a cure. Current vaccines and anti-viral drugs can only be narrowly applied in ongoing clinical trials. We employed computational methods based on structure-function relationships between human host kinases and viral nonstructural protein 3 (NS3) to understand viral replication inhibitors’ therapeutic effect. Phosphorylation at each of the two most evolutionarily conserved sites of NS3, serine 137 and threonine 189, compared to the unphosphorylated state were studied with molecular dynamics and docking simulations. The simulations suggested that phosphorylation at serine 137 caused a more remarkable structural change than phosphorylation at threonine 189, specifically located at amino acid residues 49–95. Docking studies supported the idea that phosphorylation at serine 137 increased the binding affinity between NS3 and nonstructural Protein 5 (NS5), whereas phosphorylation at threonine 189 decreased it. The interaction between NS3 and NS5 is essential for viral replication. Docking studies with the antiviral plant flavonoid Quercetin with NS3 indicated that Quercetin physically occluded the serine 137 phosphorylation site. Taken together, these findings suggested a specific site and mechanism by which Quercetin inhibits dengue and possible other flaviviruses.

STL1, a New AKT Inhibitor, Synergizes with Flavonoid Quercetin in Enhancing Cell Death in A Chronic Lymphocytic Leukemia Cell Line

Using a pharmacophore model based on the experimental structure of AKT-1, we recently identified the compound STL1 (ZINC2429155) as an allosteric inhibitor of AKT-1. STL1, was able to reduce Ser473 phosphorylation, thus inhibiting the PI3K/AKT pathway. Moreover, we demonstrated that the flavonoid quercetin downregulated the phosphorylated and active form of AKT. However, in this case, quercetin inhibited the PI3K/AKT pathway by directly binding the kinases CK2 and PI3K. In the present work, we investigated the antiproliferative effects of the co-treatment quercetin plus STL1 in HG-3 cells, derived from a patient affected by chronic lymphocytic leukemia. Quercetin and STL1 in the mono-treatment maintained the capacity to inhibit AKT phosphorylation on Ser473, but did not significantly reduce cell viability. On the contrary, they activated a protective form of autophagy. When the HG-3 cells were co-treated with quercetin and STL1, their association synergistically (combination index < 1) inhibited cell growth and induced apoptosis. The combined treatment caused the switch from protective to non-protective autophagy. This work demonstrated that cytotoxicity could be enhanced in a drug-resistant cell line by combining the effects of different inhibitors acting in concert on PI3K and AKT kinases.

Polyphenolic Flavonoid Compound Quercetin Effects in the Treatment of Acute Myeloid Leukemia and Myelodysplastic Syndromes

Flavonoids are ubiquitous groups of polyphenolic compounds present in most natural products and plants. These substances have been shown to have promising chemopreventive and chemotherapeutic properties with multiple target interactions and multiple pathway regulations against various human cancers. Polyphenolic flavonoid compounds can block the initiation or reverse the promotion stage of multistep carcinogenesis. Quercetin is one of the most abundant flavonoids found in fruits and vegetables and has been shown to have multiple properties capable of reducing cell growth in cancer cells. Acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) therapy remains a challenge for hematologists worldwide, and the outcomes for patients with both disorders continue to be poor. This scenario indicates the increasing demand for innovative drugs and rational combinative therapies. Herein, we discuss the multitarget effects of the flavonoid quercetin, a naturally occurring flavonol, on AML and MDS.

Targeting the Nervous System of the Parasitic Worm, Haemonchus Contortus, With Quercetin.

Prevalence of infection, limited choice of drugs, and emerging resistance against contemporary drugs lead to a pressing need to develop new anthelmintic drugs and drug targets. However, limited understanding of the physiology of worms has delayed the process substantially. Here, for the first time, we are reporting the tissue morphology of Haemonchus contortus and targeting its nervous system with quercetin, a naturally occurring flavonoid. Quercetin showed anthelmintic activity against all of the developmental stages of the H. contortus. Further, histological analysis demonstrated damage of various body parts, including isthmus, brut, pseudocoele, and other organs due to quercetin treatment. Mechanistic studies revealed the generation of oxidative stress and alterations in activities of the stress response enzymes, such as catalase, superoxide dismutase, and glutathione peroxidase. Moreover, the time-dependent imaging of ROS-generation disclosed neuropils as the primary targets of quercetin in the adult worms, which eventually lead to the paralysis and death of the worms. Thus, altogether, this work demonstrates that the nervous system of the parasitic helminth, H. contortus, is a novel target of the drug quercetin.

Control of Gene Expression With Quercetin-Responsive Modular Circuits

Control of gene expression is crucial for several biotechnological applications, especially for implementing predictable and controllable genetic circuits. Such circuits are often implemented with a transcriptional regulator activated by a specific signal. These regulators should work independently of the host machinery, with low gratuitous induction or crosstalk with host components. Moreover, the signal should also be orthogonal, recognized only by the regulator with minimal interference with the host operation. In this context, transcriptional regulators activated by plant metabolites as flavonoids emerge as candidates to control gene expression in bacteria. However, engineering novel circuits requires the characterization of the genetic parts (e.g., genes, promoters, ribosome binding sites, and terminators) in the host of interest. Therefore, we decomposed the QdoR regulatory system of B. subtilis, responsive to the flavonoid quercetin, and reassembled its parts into genetic circuits programmed to have different levels of gene expression and noise dependent on the concentration of quercetin. We showed that only one of the promoters regulated by QdoR worked well in E. coli, enabling the construction of other circuits induced by quercetin. The QdoR expression was modulated with constitutive promoters of different transcriptional strengths, leading to low expression levels when QdoR was highly expressed and vice versa. E. coli strains expressing high and low levels of QdoR were mixed and induced with the same quercetin concentration, resulting in two stable populations expressing different levels of their gene reporters. Besides, we demonstrated that the level of QdoR repression generated different noise levels in gene expression dependent on the concentration of quercetin. The circuits presented here can be exploited in applications requiring adjustment of gene expression and noise using a highly available and natural inducer as quercetin.