Quercetin: A Functional Dietary Flavonoid
Plant-derived natural products have been used for several decades, including flavonoids, polyphenols, alkaloids, and sesquiterpenes. The therapeutic potential of these plant-based products has been explored in terms of their kinase targeting capabilities. Around 80% of the population still relies on plant-derived formulations to manage different medical issues.In recent years, there is a switch in the screening and discovery of natural products as potential kinase inhibitors. Plant-derived products have several important biological properties such as antioxidant, anticancerous, anti-inflammatory, antidiabetic, antimicrobial, and hepatoprotective and thus are used in cancer management. One such class of compound is natural polyphenols like flavonoids, which are widely distributed in plants and are generally present in food like herbs, nuts, vegetables, fruits, plant-derived teas.
These plant-based phenolic compounds target many cancer-associated signalling pathways like PI3K (EC22.214.171.124), Akt (EC 126.96.36.199), B-Raf kinase (EC188.8.131.52), and ERK or MAPK (EC 184.108.40.206).
Flavonoids are polyphenolic compounds which naturally occur in foods of plant origin and are categorised according to chemical structure into flavonols, flavones, flavanones, isoflavones, catechins, anthocyanidins and chalcones. Over 4,000 flavonoids have been identified, many of which occur in fruits, vegetables and beverages.
Flavonoids have aroused considerable interest recently because of their potential beneficial effects on human health--they have been reported to have antiviral, anti-allergic, antiplatelet, anti-inflammatory, antitumor and antioxidant activities. Quercetin (3,5,7,3′,4′-pentahydroxyflavone) is the major representative of the flavonoid subclass of flavonols. Due to its anti-oxidant, anti-tumor and anti-inflammatory activity, quercetin has been studied extensively as a chemoprevention agent in several cancer models. Quercetin has been shown to inhibit the proliferation of a wide range of cancers such as prostate, cervical, lung, breast, and colon. Recent studies have revealed that quercetin inhibits cell proliferation by causing apoptosis and/or cell cycle arrestIt has been shown that quercetin treatment causes cell cycle arrests such as G2/M arrest or G1 arrest in different cell types. Moreover, quercetin-mediated apoptosis may result from the induction of stress proteins, disruption of microtubules and mitochondria, release of cytochrome c, and activation of caspases.
Quercetin is a strong antioxidant because it can chelate metals, scavenge oxygen free radicals and inhibit xanthine oxidase and lipid peroxidation in vitro.Quercetin also exerts anti-inflammatory properties and has been shown to have membrane-stabilising capabilities and inhibits aldose reductase and low-density lipoprotein oxidation. The anti-cancer effects of quercetin are via down regulation of mutant p53 proteins; G1 phase arrest ; tyrosine kinase inhibition; and down regulation of cell survival, proliferative and anti-apoptotic proteins.
Lamson DW, Brignall MS. Antioxidant and cancer III: quercetin. Altern Med Rev 2000;5:196-208.
Graefe EU, et al. Pharmacokinetics and bioavailability of the flavonol quercetin in humans. Int J Clin Pharmacol Therapy 1999;37:219-33.
Erlund I, et al. Pharmacokinetics of quercetin aglycone and rutin in healthy volunteers. Eur J Clin Pharmacol 2000;56:545-53.
Sampson S, et al. Flavonol and flavone intakes in US health professionals. J Am Diet Assoc 2002;102:1414-20.
Akan Z, Garip AI. Antioxidants May Protect Cancer Cells from Apoptosis Signals and Enhance Cell Viability. Asian Pac J Cancer Prev. 2013;14(8):4611-4614.