The Role of Natural Products in COVID-19
Hanadi Talal Ahmedah, Muhammad Riaz, Sagheer Ahmed, Marius Alexandru Moga in The Covid-19 Pandemic, 2023
Quercetin is a common flavonoid that is found in a number of medicinal plants. Lemon (C. limon) is also rich in quercetin. It has shown strong anti-influenza virus activity previously [84]. Quercetin is known to impair the expression of influenza virus protein [85]. It was particularly found very active against initial stages of viral attack. It has also been in common use since a long for treating common cold [86]. Quercetin also showed predominant detrimental effects on hepatitis C virus (HCV) by hindering the replication of virus inside the host cells quercetin can control the viral load directly itself or by host mediated interference to the viral life cycle [87]. It can suppress the activities of various viral enzymes like proteases, reverse transcriptases, DNA gyrases and polymerases [88–91]. The half-life of quercetin in human body is 25 hours, so its higher levels in blood plasma can be easily maintained for longer to treat viral infections without multiple doses [92].
Anti-Proliferative Properties of Various South African Buddleja Species
Namrita Lall in Medicinal Plants for Cosmetics, Health and Diseases, 2022
The isolated compounds from this plant include flavonoids (apigenin-7-O-glucoside, quercetin and luteolin) and phenylpropanoids (2-acetylmartynoside and isomartynoside). The presence of inflammation within the body allows the development of cancer and aids in the progression of all stages of tumorigenesis. If the immune response is not restored to homeostasis, it could lead to chronic inflammation, immunosuppression and excessive proliferation. Apigenin-7-O-glucoside is a stable natural flavonoid that has anti-inflammatory activity and exhibits anti-proliferative activity against the colon cancer cell line HCT116 with an IC50 of 15 µM (Smiljkovic et al., 2017). Apoptosis in these cells was induced by the pro-apoptotic proteins Bcl-2-association X protein (Bax) and tumor protein p53 (Smiljkovic et al., 2017). Quercetin has anti-inflammatory activity, due to its ability to inhibit the COX-2 protein, and has immune-modulatory activity (Pendota et al., 2014).
The Treatment of Hypertension with Nutrition, Nutritional Supplements, Lifestyle and Pharmacologic Therapies
Stephen T. Sinatra, Mark C. Houston in Nutritional and Integrative Strategies in Cardiovascular Medicine, 2022
Quercetin is an antioxidant flavonol found in apples, berries and onions that reduces BP in hypertensive individuals [391–393], but the hypotensive effects do not appear to be mediated by changes in HSCRP, TNF-alpha, ACE activity, ET-1, NO, vascular reactivity or FMD [391]. Quercetin is metabolized by CYP 3A4 and should be used with caution in patients on drugs metabolized by this cytochrome system [391–393]. Quercetin was administered to 12 hypertensive men at an oral dose of 1,095 mg with reduction in mean BP by 5 mmHg, SBP by 7 mmHg and DBP by 3 mmHg [391]. Forty-one prehypertensive and stage I hypertensive subjects were enrolled in a randomized, double-blind, placebo-controlled, crossover study with 500 mg of quercetin per day vs placebo [392]. In the stage I hypertensive patients, the BP was reduced by 7/5 mmHg (p < 0.05) [392]. Quercetin administered to 93 overweight or obese subjects at 150 mg/day (plasma levels of 269 nmol/L) over 6 weeks lowered SBP by 2.9 mmHg in the hypertensive group and up to 3.7 mmHg in SBP in the patients 25–50 years of age [393]. The recommended dose of quercetin is 500 mg twice daily.
Recent advances towards natural plants as potential inhibitors of SARS-Cov-2 targets
Published in Pharmaceutical Biology, 2023
Zhouman He, Jia Yuan, Yuanwen Zhang, Runfeng Li, Meilan Mo, Yutao Wang, Huihui Ti
Researchers have reported that herbacetin, rhoifolin, apigenin, luteolin, quercetin, daidzein, puerarin, and kaempferol inhibit the proteolytic activity of SARS-CoV 3CLpro (Jo et al. 2020; Bilginer et al. 2022). Quercetin, a plant flavonoid, is widely distributed in vegetables, seeds, leaves, and other plant tissues. Quercetin may be an effective inhibitor of SARS-CoV-2 3CLpro based on MD study (Khaerunnisa et al. 2020). Abian et al. (2020) confirmed quercetin as a stronger SARS-CoV-2 3CLpro inhibitor and assumed that quercetin was a competitive inhibitor for the same active site as 3CLpro. The experimental data showed that its Ki value is 7.4 μmol/L, which is similar to that of the first discovered SARS-CoV-2 3CLpro inhibitor. Based on the thermal shift assay, quercetin also dose-dependently alters the thermal stability of 3CLpro, rendering 3CLpro unstable. Moreover, the interaction of quercetin and 3CLpro reduces the activity of 3CLpro. Quercetin was identified as the top ligand of the S protein, and its molecular model binds to the host-receptor binding domain or interface of the S protein-hACE2 receptor. The complex of the S protein-hACE2 receptor has low binding energy (Pandey et al. 2021). Both of the abovementioned factors might restrict the virus from entering into host cells and/or interfere with host-virus interactions. Quercetin might serve as a suitable scaffold for designing new functional groups and developing new SARS-CoV-2 3CLpro inhibitors, and it might become an extremely promising antiviral small molecule.
Quercetin improves the imbalance of Th1/Th2 cells and Treg/Th17 cells to attenuate allergic rhinitis
Published in Autoimmunity, 2023
Xia Ke, Ziqi Chen, Xiaoqiang Wang, Houyong Kang, Suling Hong
Chinese medicine has been widely concerned in the treatment of diseases due to its effectiveness and safety. Quercetin is a hydroxyl phenolic compound, which is an important representative of the flavonoid subclass. It exists in a variety of plants and regulates plant growth and development [10]. Moreover, quercetin has many biological activities, such as antioxidant, antiviral, anti-inflammatory, and anti-allergic effects [11,12]. Accumulating evidence has shown that quercetin is used to treat and prevent diseases, including cancers, cardiac diseases, inflammation, and metabolic diseases [13]. Quercetin plays a central role in a variety of allergic diseases, including AR. It regulates the Th1/Th2 balance and reduces the release of IgE antibodies [12,14]. However, the regulation of quercetin in the Treg/Th17 balance remains largely unknown.
Neuroprotective effects of quercetin on the cerebellum of zinc oxide nanoparticles (ZnoNps)-exposed rats
Published in Tissue Barriers, 2023
Shaimaa A. Abdelrahman, Amal S. El-Shal, Abeer A. Abdelrahman, Ebtehal Zaid Hassen Saleh, Abeer A. Mahmoud
Much prior research suggested that Quercetin may possess antioxidant and anti-inflammatory properties due to its free radical scavenging and metal-chelating capacities.48–50 The anti-inflammatory/anti-allergic property of Quercetin was attributed to mast cell membranes stabilization so, preventing the release of histamine and other inflammatory mediators in the body. It was shown to reduce IL-6 and TNFα in lipopolysaccharide in murine macrophages.51 Quercetin also prevents glial cells from releasing proinflammatory cytokines. It protects against neuroinflammation by decreasing the formation of nitric oxide (NO) in microglial cells, which inhibits NF-B signaling.52–55 Similarly, Quercetin has been shown to reduce manganese neurotoxicity via reducing neuroinflammation-mediated neurodegeneration, by regulating the heme oxygenase-1 (HO-1)/nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear NF-B pathways.56
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