Source Distribution
Plant Origin: It is widely found in the stem bark, flowers, leaves, buds, seeds, and fruits of numerous plants, primarily in the form of glycosides like rutin, quercitrin, and hyperoside. Quercetin can be obtained through acid hydrolysis. Among these, higher concentrations are found in the stems and leaves of buckwheat, seabuckthorn, hawthorn, and onion. Additionally, many medicinal plants, such as Sophora japonica, Platycodon grandiflorus leaves, Galangal, Sophora flavescens, Mulberry Parasitic, Panax notoginseng, Ginkgo biloba, elderberry, and others, all contain quercetin, with Sophora japonica having a content of approximately 4%.
Effects
Antioxidant: It is one of the most potent antioxidants in nature, possessing an antioxidant capacity 50 times that of vitamin E and 20 times that of vitamin C.
Hypolipidemic: It can inhibit the breakdown of cholesterol esters into free cholesterol, reduce the solubility of cholesterol in micelle solutions, inhibit the absorption of cholesterol by the small intestine, and thus achieve the goal of lowering lipids.
Hypoglycemic: It can inhibit the transport of glucose by glucose transporters, as well as the activity of alpha amylase and alpha glucosidase, hindering the digestion and absorption of glucose.
Uric Acid Reduction: By forming hydrogen bonds around the molybdenum atom in the active center of xanthine oxidase (XO), it hinders the substrate xanthine from entering the XO active center, inhibiting XO's catalytic activity towards xanthine and thereby reducing uric acid production.
Anticancer: It has cytotoxicity towards cancer cells without damaging healthy cells and can be used as a chemopreventive and therapeutic agent for various cancers. Due to its lipophilicity, it can easily penetrate the cell membrane and exert antitumor effects through various pathways, such as regulating and inhibiting oncogene expression, blocking the cell cycle, inducing apoptosis, and inhibiting invasion and metastasis.
Neuroprotective: It can exert neuroprotective effects by directly clearing reactive oxygen species (ROS) and inhibiting β-amyloid (Aβ) deposition, tau protein hyperphosphorylation, neurofibrillary tangles (NFTs), amyloid precursor proteins (APP), and lytic enzymes (BACE1) in nerve cells through various mechanisms.
Antithrombotic: It can significantly inhibit platelet aggregation, selectively bind to blood clots on the vascular wall, and release thrombolytic agents and vascular membrane protective mediators from the vascular endothelium by inhibiting platelet lipoxygenase and cyclooxygenase, thereby exerting antithrombotic effects.
Antiviral: It exhibits antiviral activity against many viruses, such as herpes simplex virus type I, respiratory syncytial virus, rabies virus, type III parainfluenza virus, and the novel coronavirus. Its antiviral mechanism involves binding to viral proteins and interfering with the synthesis of viral nucleic acids.
Pharmacokinetics
Absorption: In nature, quercetin primarily exists in the form of glucosides, and the absorption of quercetin glucosides varies depending on the type of sugar attached. Its glucuronide and sulfate derivatives are more easily absorbed by the human body than quercetin itself. Glycosides are effectively hydrolyzed by β-glucosidase in the small intestine to form aglycones, which are then absorbed and metabolized in organs such as the small intestine, colon, liver, and kidneys.
Excretion: Approximately 20% of orally administered quercetin is absorbed by the digestive tract, 30% is metabolized, and 30% is excreted in its original form through feces. The absorbed quercetin quickly enters the bile and urine in the form of glucuronide and sulfate esters within 48 hours and is excreted.
