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Quercetin is also known as quercetin, quercetin, the molecular formula is C15H10O7, and the chemical structural formula is as follows:
It is often widely distributed in the form of glycosides in dicotyledonous plants, especially in the flowers and leaves of some woody plants, including Fagaceae Iberian oak, Berberis red star anise, hypericaceae red Eclipta and oleander, kenaf, etc., play an important role in plant growth, development, flowering, fruiting, and antibacterial and disease prevention.
There is a ketone carbonyl group in the molecule of quercetin, and the oxygen atom on the first carbon is basic and can form salt with strong acid. Its molecular structure contains 4 active groups, namely: A inter-ring dihydroxy, B-ring ortho-dihydroxy, C ring C2, C3 double bond, 4-carbonyl, etc. The existence of phenolic hydroxyl and double bond makes quercetin Has strong antioxidant activity. The dihydrate of quercetin is yellow needle crystal or crystalline powder, which becomes anhydrous at 95～97℃ and decomposes at 312～314℃. It is almost insoluble in water, hardly soluble in ethanol, but soluble in glacial acetic acid, and the alkaline aqueous solution is yellow.
Free radicals can lead to cell membrane lesions, gene mutations, and erosion of body tissues, inducing diseases of various tissues and organs of the body. The antioxidant properties of quercetin can effectively reduce or scavenge the damage caused by free radicals. Zhao Liting et al. (2009) found that serum total antioxidant capacity (P < 0.01), vitamin C and vitamin E ( P < 0.05) contents were significantly increased after rats ingested quercetin. This suggests that quercetin can not only directly improve the antioxidant capacity of animals, but also synergistically exert antioxidant effects with vitamin C and vitamin E by saving.
Quercetin can exert antioxidant effect by regulating the antioxidant enzyme system. Studies have found that quercetin can protect hepatocytes damaged by H2O2 oxidative stress, enhance the total antioxidant capacity of cells, and its metal complexes have obvious scavenging effects on O-2· and·OH. Studies such as Elke and Odbayar found that quercetin can increase the expression of some antioxidant enzymes, such as glutathione transferase and aldo-keto reductase, and the expression is proportional to the amount of quercetin. When astrocytes were treated with H2O2, it was found that quercetin had a strong inhibitory effect on lipid peroxidation in the rat brain, which was of great significance for maintaining the integrity of the cell membrane.
Some studies have found that quercetin has antibacterial properties. Li and Xu extracted the active ingredients from lotus leaves and conducted antimicrobial activity experiments on them, and found that quercetin may be a potential antibacterial factor. Alina Bravo studies have shown that quercetin-cadmium or mercury complexes have penicillin-like antibacterial activity against five strains. Wang Xiaoping found that quercetin contained in traditional Chinese medicine has strong antibacterial effect on 8 common pathogenic bacteria and 3 pathogenic fungi in oral cavity, and its antibacterial effect on gram-negative bacteria is stronger than that of gram-positive bacteria. . This indicates that quercetin is a broad-spectrum antibacterial substance that can be used to prevent and treat various bacterial infectious diseases. When the human immune system fights against bacterial invasion, lipopolysaccharide (LPS) can cause the body's immune response and inflammatory response. Several studies have shown that quercetin has an inhibitory effect on the inflammatory response induced by LPS. Quercetin can significantly inhibit the inflammatory response induced by Helicobacter pylori in gastric mucosa, and has a good clinical effect on non-bacterial prostatitis.
The antibacterial and anti-inflammatory mechanism of quercetin may be related to the regulation of inflammatory factors. The study found that after quercetin (40 μmol/L) treated neutrophils (Polymorphonuclear, PMN) for 30 min, LPS could induce the expression of interleukin-6 (IL-6) mRNA, but the synthesis and secretion of IL-6 was affected by the expression of interleukin-6 (IL-6) mRNA. inhibition. Jiang Fei et al. (2008) came to a similar conclusion that quercetin inhibited the expression of intercellular adhesion molecule-1 (ICAM-1) in A549 cells induced by IL-1β by regulating the activation of NF-κB. Yue Yang et al. found that quercetin inhibits the LPS-induced PMN activation effect by antagonizing the expression of LPS on the PMN adhesion molecules CD62L and CD11b/CD18, thereby preventing the adhesion of PMN to vascular endothelial cells and reducing the infiltration of inflammatory cells to the inflammatory foci. This may be an important mechanism by which quercetin exerts its anti-inflammatory effect. In addition, A. P. Rogerio also found that quercetin can reduce the number of eosinophils in the blood and lungs of rats. Quercetin exerts antibacterial and anti-inflammatory effects by negatively regulating inflammatory factors and inhibiting inflammatory cells.
Quercetin can prevent a variety of liver damage, such as fatty liver, cirrhosis and liver fibrosis. Zhou Yusheng and Yang Xuefeng (2005) found that quercetin can significantly reduce the concentration of triglyceride in serum of rats with fatty liver, inhibit the activity of aspartate aminotransferase, and has a good effect on the treatment of fatty liver. Quercetin can significantly reduce the activities of lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) in serum, and increase the antioxidant enzymes glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) levels play a protective role against hepatocyte injury by inhibiting lipid peroxidation. In addition, Pavanato found that quercetin has a significant effect on the treatment of liver cirrhosis. Quercetin has anti-fibrotic effects on a variety of cells, such as hepatocytes, lung cells and cardiomyocytes, and its mechanism of action mainly includes inhibiting fibroblast proliferation and collagen synthesis and preventing oxidative damage. Quercetin and its derivatives have certain preventive and therapeutic effects on bleomycin-induced pulmonary fibrosis, and can resist myocardial interstitial fibrosis caused by angiotensin II.
Pharmacological studies have shown that quercetin has hypoglycemic and hypolipidemic effects. Studies have found that quercetin can significantly reduce the serum levels of blood sugar, insulin, total cholesterol, triglycerides and lipid peroxides in diabetic rats, reduce the content of non-enzymatic glycation end products in renal tissue, and reduce urinary protein excretion in diabetic rats. It improves glomerular basement membrane and matrix hyperplasia. The mechanism may be that quercetin inhibits the production of PDGF-B and vascular endothelial growth factor-1 (VEGF-1).
Myocardial ischemia/reperfusion injury is an inflammatory response, and quercetin can resist myocardial inflammatory injury by inhibiting the generation of PMN. Quercetin has the effect of resisting hypoxia and reoxygenation injury and protecting cardiomyocytes. It also has the functions of lowering blood pressure, dilating blood vessels, preventing and treating coronary heart disease and arrhythmia, and inhibiting cardiovascular hydrogen peroxide and high sugar damage.