The effect of vitamin C and the flavonoid Quercetin on immunity during Covid-19

Flavonoids are a powerful weapon in the fight against atherosclerosis, oncology, cardiovascular and neurological diseases. The use of one of them, quercetin, has a particularly beneficial effect on the body.

This substance prevents damage and death of nerve cells, the development of varicose veins, and produces strong anti-inflammatory, antioxidant, antiviral and antitumor effects. Therefore, the presence of even minimal portions of bioflavonoid in the daily diet can relieve many problems.

Benefits for the body

Quercetin is a glycoside of the vitamin P group. Helps fight aging, strengthens capillary walls, has a membrane-stabilizing and strong regenerative effect. This substance also accelerates the healing of the mucous membrane and prevents the destruction of bone tissue in joint pathologies.

The compound is also similar to rutin, lowering high blood pressure, protecting brain cells from damage, and having estrogen-like effects. Therefore, doctors often prescribe it during radiation therapy.

You can get more information about the beneficial properties of plant flavonoid from the video:

Quercetin granules - video instructions, indications, description, reviews, dosage

Indications for use

In medical practice, the use of quercetin is not uncommon. As a single drug, it is used to prevent erosive and ulcerative lesions of the gastrointestinal tract caused by prolonged use of nonsteroidal anti-inflammatory drugs (NSAIDs).

As a component of complex treatment, quercetin is taken for the following disorders:

• local radiation injuries and burns after exposure to x-ray and radiotherapy;
• oncology;
• diseases of the mucous membrane of the mouth and tongue (stomatitis, glossitis), periodontal disease;
• hepatitis B virus;
• varicose veins of the deep veins of the lower extremities;
• systemic lupus erythematosus;
• purulent inflammation of soft tissues;
• ulcerative colitis;
• chronic glomerulonephritis;
• vegetative-vascular (neurocirculatory) dystonia;
• joint pathologies (arthritis);
• thrombophlebitis;
• coronary heart disease (CHD), angina pectoris, arrhythmia;
• seasonal allergies;
• neuroreflex manifestations of spinal osteochondrosis (lumbago, sensitivity disorders, circulatory failure in the extremities, extracardialgia).

Another indication for the use of quercetin is menopausal syndrome. The bioflavonoid reduces unpleasant symptoms, prevents disturbances in the activity of the cardiovascular system, restores the function of the sex glands, and relieves neurasthenia.

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Cancer

Preparations based on plant polyphenols are used both for the prevention and treatment of cancer, to reduce postoperative complications and when receiving chemotherapy for cancer.

Attention! Studies have shown that taking quercetin supplements slows the development of leukemia and breast tumors.

In 1996, the medical publication Clinical Cancer Research published the work of Dr. D. R. Ferri, proving the unique ability of quercetin to restore the functionality of cancer cells. Many experts also believe that the combination of polyphenol with the antitumor drug Dasatinib enhances the therapeutic effect of the latter and speeds up recovery or prolongs life.

Rheumatoid arthritis

With arthritis of any type, autoimmune reactions occur in the body, accompanied by inflammation of the joint tissues and severe discomfort. To alleviate the condition and restore performance, it is necessary to block the destructive process as quickly as possible, strengthen antioxidant protection, and accelerate the regeneration of affected cartilage. Quercetin copes with all this.

By blocking the action of histamine, the flavonoid prevents bone destruction, relieves pain, eliminates morning stiffness, and prolongs the period of performance.

Anti-aging

With age, the body becomes more and more senescent (old) cells. This natural phenomenon is associated with the influence of free radicals and a weakened immune system. Aged cells stop dividing and can mutate. And the accumulation of fibroblasts in the skin causes the appearance of wrinkles. Therefore, it is so important to constantly reduce the number of senescent cells.

For this purpose, special senile drugs (Dasatinib) have been developed, but quercetin copes with the task of rejuvenation no worse. Thanks to its unique antioxidant properties, the flavonoid destroys aging cells, slows down vascular calcification, and improves the synthesis of collagen and elastin.

Studies on mice have shown the high efficiency of complex use of quercetin with Dasatinib. The combination of drugs not only removes spent cells, but also reduces the risk of mortality from cardiovascular diseases and speeds up recovery.

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Quercetin 250 mg capsules 90 pcs - Instructions

Dosage form

Capsules, 90 pieces per pack.

Compound

1 capsule contains 250 mg of the active substance Quercetin.

pharmachologic effect

The flavonoid quercetin is an aglycone of many plant flavonoid glycosides, including rutin, and belongs to the P vitamin preparations.

As a result of capillary-stabilizing properties associated with antioxidant, membrane-stabilizing effects, the drug reduces capillary permeability. Quercetin has an anti-inflammatory effect due to the blockade of the lipoxygenase pathway of arachidonic acid metabolism, reducing the synthesis of leukotrienes, serotonin and other inflammatory mediators.

Quercetin has an antiulcer effect associated with the use of non-steroidal anti-inflammatory drugs, as well as radioprotective activity (after X-ray and gamma irradiation).

The cardioprotective properties of quercetin are associated with an increase in the energy supply of cardiomyocytes due to its antioxidant effect and improved blood circulation.

The reparative properties of quercetin include accelerating wound healing. The drug can influence the processes of bone tissue remodeling; it exhibits persistent immunomodulatory activity. Diuretic, antispasmodic, and antisclerotic properties have also been experimentally determined. Quercetin is able to normalize blood pressure and stimulate the release of insulin, accelerate platelet aggregation, and inhibit thromboxane synthesis.

Quercetin also binds to estrogen receptors.

Indications for use

In complex treatment:

• To prevent erosive and ulcerative lesions of the upper digestive tract caused by taking non-steroidal anti-inflammatory drugs;
• Local radiation injuries after x-ray and gamma radiation therapy and their prevention;
• periodontal disease, erosive and ulcerative diseases of the oral mucosa;
• purulent-inflammatory diseases of soft tissues
• menopause, vertebral pain syndrome, neuroreflex manifestations of spinal osteochondrosis;
• chronic glomerulonephritis;
• neurocirculatory dystonia, coronary heart disease, angina pectoris
• II-III functional class.

Directions for use and dosage

Adults should take the drug during meals, 2 times a day, 1 capsule. Admission period is 30 days. If necessary, the dose can be increased to 3 capsules per day.

Contraindications

Hypersensitivity to quercetin and other components of the drug, as well as to drugs with P-vitamin activity.

Pregnancy and breastfeeding

It is not recommended to use the drug during pregnancy and breastfeeding. If it is necessary to prescribe the drug, breastfeeding should be stopped for the period of treatment.

Adverse reactions

Headache, tingling sensation in the extremities, nausea, hypersensitivity reactions, including rash, itching may occur.

Interaction with other drugs and other types of interactions

When using quercetin:

• with ascorbic acid preparations there is a summation of effects
• with non-steroidal anti-inflammatory drugs, the anti-inflammatory effect of the latter is enhanced while the ulcerogenic effect is reduced;
• with digoxin, the maximum serum concentration and the total area under the concentration-time curve of digoxin increase;
• with cyclosporine, the bioavailability and concentration of cyclosporine in the blood increases;
• with paclitaxel - effects on the metabolism of the latter;
• with verapamil the bioavailability of the latter increases;
• with tamoxifen, bioavailability increases, metabolism and excretion of the latter decreases.

Storage conditions

In original packaging at a temperature not exceeding 25 ° C.

Vacation category

Over the counter.

Contraindications and precautions

The instructions for quercetin-based drugs indicate a number of conditions in which the flavonoid is prohibited:

• increased sensitivity to rutin;
• pregnancy and breastfeeding;
• children under 16 years of age;
• arterial hypotension.

A safe dose of quercetin for pregnant women is unknown. Therefore, expectant mothers carrying a child should treat the supplement with caution and not take the product without a doctor’s permission. It is assumed that during gestation, quercetin is much safer to obtain from food than from dietary supplements.

Minor age is also a contraindication for use. Therefore, quercetin is not prescribed to children and adolescents. Pediatricians try not to take risks and not use insufficiently studied medicine when treating young patients.

Attention! Quercetin-based products often contain sugar, which can be dangerous for people with fructose intolerance and diabetes.

Another contraindication for use is hypertensive-hydrocephalic malabsorption syndrome.

Quercetin and inflammation

How inflammation occurs in the body

Poor health is associated with the opening of the intestinal barrier, as a result of which substances from foods and additives in them are recognized as an enemy molecule, that is, an antigen. In such a situation, the uncoordinated immune system begins to fight the intruder, which often leads to an increase in pro-inflammatory cytokines such as IL-2, IL-6 or IFN-gamma. Inflammation accompanying heavy training seems to be a desirable phenomenon. This leads to tissue reconstruction and allows you to build strong muscles. However, you need to use a thick line to separate the inflammation that accompanies microdamage to the muscle mass. Occurred after intense training, from chronic inflammation, which is compared to a fire that cannot be extinguished. Inflammation occurs as a result of:

• injury,
• when tissue integrity is compromised due to a sudden unfavorable vector of force.
• poor oral hygiene, where caries, dry sockets and infections associated with root canal treatment cause inflammation.
• parasitic infections, sometimes difficult to diagnose due to the relatively low sensitivity of tests, increased permeability of the intestinal barrier, where elevated levels of markers such as zonulin or alpha-1 antitrypsin show the extent of the problem.

Considering a person's lifestyle, a common cause of chronic inflammation is a diet containing stimulants, coffee, alcohol and energy drinks. As well as anti-nutrient ingredients, including sugar, wheat, trans fatty acids. Lots of dietary lectins and dairy. Pharmacotherapy, including NSAIDs, antibiotics and PPIs, also negatively affects the microbiome. The resulting intestinal damage is corrected as soon as possible with appropriate dietary therapy, which consists of an elimination-rotation diet and intestinal barrier restoration therapy based on the use of antioxidants, probiotics, colostrum and short-chain fatty acids. Sometimes they start a natural anti-inflammatory that is safe for our intestinal ecosystem. This brings up the question of flavonoids such as quercetin. This compound is known for its beneficial effects.

Quercetin

Quercetin, classified as a flavone, is also a flavonoid compound often used in the pharmacy. Due to its structure, quercetin is considered an example of how spatial structure influences the biological properties of chemical compounds. The presence of a double bond in the C-ring enhances the antioxidant properties of quercetin. The presence of hydroxyl group at positions 3, 5, 7, 3', 4' not only affects the antioxidant properties but also increases the chelating ability of divalent metals. This is important because chelation of divalent cations, which catalyze oxidation periods, has the effect of inhibiting oxidative processes that are more likely to have a negative effect on cells.

Acting multidimensionally, quercetin enhances the protective actions occurring in the body, and the main one is the regulation of epigenetic changes in the body. This phenomenon refers to processes that occur as a result of changes in gene expression, rather than the genetic code itself. This means that epigenetic changes caused by environmental factors are associated with the development of tumor diseases. Following this example, substances that manipulate epigenetic changes have been shown to have a positive effect on reducing the likelihood of cancer and supporting the treatment period. Recent research suggests that methylation of several types of tumor suppressor genes has an impact on cancer status. Quercetin has demonstrated the ability to inhibit methylation of suppressor genes. Quercetin's ability to inhibit and demethylate these genes may help in both the prevention and treatment of cancer.

Another function of quercetin in cancer is that quercetin helps normal gene transcription. This is the first step towards expressing the P53 gene, also known as a tumor suppressor gene. The function of suppressor genes, as the name suggests, is to protect cells against malignancy and tumor formation. Disruptions of the tumor suppressor gene P53 appear to be a common abnormality observed in human cancers, as already demonstrated in 1998 by Bray, Schorl and Hall. Administration of quercetin to humans results in increased transcription of the P53 tumor suppressor gene through stimulation by a substance called Nrf2. Helps regulate gene expression. In addition, quercetin has antioxidant properties. Although small concentrations of this flavone have an antioxidant effect, higher concentrations cause pro-oxidant effects. These oxidative effects are beneficial because the effects appear to be anticancer—meaning they inhibit the growth of cancer. Excessive concentrations of quercetin lead to oxidation to substances called o-quinones. These compounds have demonstrated the effect of apoptosis, programmed death, of cancer cells, closely related to the reaction of tyrosinase with quercetin to form o-quinones, which then exhibit anti-cancer effects on melanoma cells, as confirmed in 2021 by Harris. Donovan, Branco, Limes and Bird.

Release forms

There are several forms of release of the supplement. In Russian pharmacies it is easier to buy the drug in tablet form - Quertin. According to the instructions for use, it contains 40 mg of quercetin in each pill. The medicine is slowly absorbed, but produces a prolonged effect, is convenient to take and does not require dosage.

An interesting dosage form is granules. They can be dissolved in liquid and used internally and externally. The drug is taken only with water, dosing in grams or measuring with a teaspoon, which is not always convenient for the patient.

Quercetin capsules are most often produced by foreign manufacturers. The powder contained in the shell is protected from the influence of gastric juice, does not contain additional substances and rarely causes allergies or other side effects.

The effect of vitamin C and the flavonoid Quercetin on immunity during Covid-19

Recent studies have shown that the combined use of ascorbic acid (vitamin C) and quercetin (vitamin P) enhances the antiviral and immunomodulatory properties of these substances, increasing each other's effectiveness.

Both of these substances, necessary for the proper functioning of the immune system, were discovered back in the 30s of the last century by the Hungarian-American biochemist Albert Szent-Györgyi, who later became a Nobel Prize laureate.

It is now well known that vitamin C has antiviral properties. It supports lymphocyte activity, increases interferon-α production, modulates cytokine, reduces inflammation, improves and restores endothelial and mitochondrial function. It plays a critical role in the stress response and has shown promising results in the prevention and treatment of patients with coronavirus infection.

Quercetin is also a well-known flavonoid whose antiviral, anti-inflammatory and antioxidant properties have been shown in numerous studies. This substance can affect several stages of pathogen virulence—virus entry, virus replication, and protein assembly.

So, the beneficial properties of quercetin are:

• Prevents the virus from entering cells by blocking the receptors through which the virus enters the cell;
• Stops the reproduction of the virus in infected cells;
• Reduces inflammation by inhibiting the synthesis and release of inflammatory mediators;
• Binds free radicals and reactive oxygen species, protecting all tissues and organs from them;
• Reduces allergic reactions by reducing the release of histamine from mast cells;
• Reduces the risk of developing atherosclerosis;
• Prevents blood thickening, which can cause severe complications during coronavirus infection.

Vitamin P (quercetin) and vitamin C

Evidence has been obtained that Quercetin supplementation can enhance the anti-inflammatory, antiviral and immunoprotective effects of vitamin C. And at the same time, the therapeutic effects of Quercetin can be enhanced by the joint administration of vitamin C. This interesting fact can be used for effective prevention of coronavirus infection in high-risk groups , and for the treatment of patients with Covid-19 as an adjunct to drugs such as Remdesivir or convalescent plasma.

Scientists and doctors believe that in the context of a global pandemic, attention should be paid to such simple and inexpensive methods that have a reasonable biological basis.

The beneficial properties of vitamin C have previously been widely used for various conditions and diseases, including respiratory diseases, but Quercetin is not so well known.

Where is Quercetin found?

Quercetin is a natural flavonoid that is found in plants predominantly red, purple in color: lovage, capers, buckwheat, onions (especially red; in larger quantities in the outer shells), apples, peppers, garlic, red grapes, tea, citrus fruits , dark cherries, lingonberries, tomatoes, broccoli, raspberries, blueberries, cranberries, chokeberries, rowan berries, sea buckthorn, some types of honey (eucalyptus, tea tree), nuts, cauliflower and cabbage, red wine, olive oil, acorns - in the form of water-soluble routine. You can get quercetin not only from food. This substance is also found in some drinks. The leaders in terms of volumes of this antioxidant are rosehip decoction, green and black tea.

By following the link you can find a detailed list of products, indicating the amount of quercetin they contain/

To prevent colds, it is enough to take 100-200 mg of ascorbic acid and 250-400 mg of quercetin per day.

Vitamin C is produced and sold in pharmacy chains in the form of tablets, powders, ampoules, Quercetin - in the form of granules, tablets, capsules.

Dosage and regimen

Tablets based on a plant flavonoid are prescribed orally. The prophylactic dose of the drug, according to most scientists, is 300–400 mg per day.

Some experts recommend calculating the dose of quercetin based on the patient’s body weight - 25 mg per 1 kg. Thus, for an adult weighing 70 kg, 1,750 mg of the substance will be required daily. If there are medical indications, the portion of bioflavonoid is increased.

Table - Daily intake of quercetin for some pathologies

People living in contaminated areas are recommended to take 1 g of quercetin daily. Lower doses of the substance, from 50 to 400 mg per day, may be ineffective.

The optimal portions and duration of treatment depend on the clinical picture of the disease and are determined by the doctor. Typically, it takes a long time for the beneficial properties of quercetin to manifest itself - from 3 to 4 months.

Dosage

To avoid any side effects, you should stick to the dosage. For example, for prevention, 500 mg of the substance per day will be enough, for the treatment of hypertension - 730 mg, for relief of joint pain - 250 mg. Your doctor will help you determine the exact daily dose, taking into account the individual characteristics of your body.

Thus, quercetin is a beneficial supplement that can be obtained from food or in tablet form. It helps in the fight against various diseases, inflammatory processes, and allergies. Almost everyone can take it, but it is better to consult with a specialist to avoid negative consequences.

Side effects and allergies

The substance quercetin is an organic compound that rarely causes unpleasant symptoms. Adverse reactions were observed in laboratory animals; in cases with humans, such effects were not observed. However, their appearance cannot be ruled out.

Expected consequences:

• toxic effect on brain neurons;
• increased homocysteine ​​levels;
• dysfunction of the thyroid gland.

But the following side effects occurred in people:

• nausea, loose stools;
• dry mouth;
• headache;
• increased blood pressure;
• tingling in fingertips.

Patients with intolerance to the substance are likely to develop allergies. The reaction is manifested by a skin rash, itching, swelling of the mucous membranes, and redness of the dermis.

Overdose

Bioflavonoid, obtained from food, even in large quantities, is not capable of harming the body. However, tablets taken in high doses (over 4 g daily) can cause an excess of the substance.

Attention! There is not yet enough information about the consequences of an overdose. It is assumed that the symptoms of excess manifest themselves in the form of adverse reactions, only in an intensified form.

To eliminate the consequences of an overdose, the drug is discontinued and symptomatic therapy is carried out. If you do not feel better, you should consult a doctor.

Reviews about the application

Official medicine is suspicious of quercetin-based supplements. For specialists, the main condition for safety and effectiveness is clinical trials, and these are not yet sufficient for the flavonoid. All studies confirming the beneficial properties of the substance were carried out mainly on laboratory animals.

Despite the limited evidence base, consumer reviews of the effects of quercetin are mostly positive.

Buyers note that the additive:

• quickly stops allergy symptoms;
• increases immunity;
• helps fight infections and viruses;
• relieves heaviness in the legs due to varicose veins;
• accelerates recovery after long-term illnesses and operations.

Quercetin is especially praised by people suffering from rheumatoid arthritis. About 80% of patients who took dietary supplements against the background of exacerbation of pathology noted a decrease in pain, improved mobility, and increased muscle tone. The use of bioflavonoid allows you to obtain long-term and stable remission, reduce the number of medications taken, stop bone deformation and protect the gastrointestinal tract from the harmful effects of NSAIDs.

But the medicine also has disadvantages: some patients did not notice the effect after using the supplement, other people were not satisfied with the high price. There are also those who complained of allergies and other unpleasant sensations.

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Quercetin
CAS number:
117-39-5
Gross formula:
C15H10O7
Chemical name:
3,3′,4′,5,7-Pentahydroxyflavone;
2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one Physico-chemical data:
Molecular formula: C15H10O7 Molecular weight: 302.24g/mol Melting point 314-317 ° C Solubility in water <0.1 g / 100 ml at 21 ° C Quercetin substance is stable under recommended storage conditions. Dangerous decomposition products formed in fire conditions are carbon monoxide.

Description:

Quercetin, a plant flavonol from the flavonoid group of polyphenols, is found in many fruits, vegetables, leaves and grains. Has a bitter taste.

Quercetin is known for its antioxidant activity against radicals, antiallergic properties characterized by stimulation of the immune system, antiviral activity, inhibition of histamine release, reduction of pro-inflammatory cytokines, formation of leukotrienes and suppression of interleukin IL-4 production. This improves the Th1/Th2 balance and limits the formation of antigen-specific IgE antibodies. Quercetin is also effective in inhibiting enzymes such as lipoxygenase, eosinophil and peroxidase, and in suppressing inflammatory mediators. All the mentioned mechanisms of action contribute to the anti-inflammatory and immunomodulatory properties of quercetin, which can be effectively used in the treatment of late-phase bronchial asthma, allergic rhinitis and anaphylactic reactions caused by peanuts. The plant extract of quercetin is a major ingredient in many potential antiallergy drugs, supplements and fortified foods, and is more potent at inhibiting IL-8 than cromolyn (the antiallergy drug disodium chromoglycate), suppressing IL-6 and cytosolic calcium levels.

Polychlorinated biphenyls (PCBs) exert toxic effects by binding to the aryl hydrocarbon receptor, leading to cell dysfunction by altering gene transcription. One study conducted at the University of Kentucky (USA) showed that treatment of endothelial cells with quercetin significantly reduced the expression of pro-inflammatory genes induced by polychlorinated biphenyls (PCBs). The scientists also found that the flavonoid suppresses inflammatory pathways through mechanisms related to functional caveolae.

A study conducted by the Niger Delta University examined the inhibitory effect of quercetin and its metabolite 3-O-methylquercetin on lipopolysaccharide-mediated macrophage cell activation. The scientists measured inflammatory markers (catalase activity, nitric oxide, tumor necrosis factor-alpha, interleukin 6, and interleukin 1) in the supernatant of cell cultures exposed to lipopolysaccharide and quercetin or 3-O-methyl quercetin. They found that both quercetin and 3-O-methylquercetin (at 30 mM) reduced levels of all markers. 3-O-methylquercetin showed a stronger effect than quercetin. Tan and colleagues also found that quercetin attenuated the release of the late proinflammatory mediator HMGB1 in animals with established endotoxemia. Their in vitro test with macrophages confirmed that quercetin inhibited the release as well as the cytokine activity of HMGB1.

However, scientists from the University of Maastricht (Netherlands) were unable to demonstrate the anti-inflammatory effects of quercetin in an intervention study. After treating volunteers for 4 weeks with quercetin, they found no effect on lipopolysaccharide-induced tumor necrosis factor alpha levels, although plasma total antioxidant status was increased. Their in vitro study with blood in a test tube showed that quercetin dose-dependently inhibited lipopolysaccharide-induced tumor necrosis factor-alpha production. The lack of effect in this intervention study was likely due to low levels of cytokines and high levels of antioxidants at baseline, indicating a lack of inflammation and oxidative stress. They concluded that only patients with elevated levels of inflammation and oxidative stress may benefit from quercetin supplementation.

Quercetin exerts anti-inflammatory effects on epithelial cells through mechanisms that inhibit cofactor recruitment to the chromatin of proinflammatory genes. Ruiz and collaborators at the Technical University of Munich came to this conclusion after studying the effect of quercetin and its metabolites on intestinal bacteria, taxifolin, alfitonin and 3,4-dihydroxyphenylacetic acid on the epithelial cell of the small intestine of mice with experimental ileitis.

Application:

Despite all the “useful” properties of this substance, it is still not a medicine. Included in dietary supplements, food additives, and food products. Widely used in Ayurvedic, alternative medicine, as well as in the cosmetic industry.

Receipt:

The method for producing quercetin includes the following stages: dissolution of rutin in an alcohol solution and hydrolysis under the action of a catalyst to obtain quercetin, glucose and rhamnose. This method of obtaining quercetin develops a new inexpensive "green" method and has the following advantages: since the acid in the original process is replaced by a catalyst, no acidic waste liquid is formed, and the preparation process is environmentally friendly.

Effect on the body:

In plants, phenylalanine is converted to 4-coumaroyl-CoA in a series of steps known as the general phenylpropanoid pathway, using phenylalanine ammonia lyase, cinnamate 4-hydroxylase, and 4-coumaroyl-CoA ligase. One molecule of 4-coumaroyl-CoA is added to three molecules of malonyl-CoA to form tetrahydroxychalcone using 7,2′-dihydroxy-4′-methoxyisoflavanol synthase. Tetrahydroxychalcone is then converted to naringenin using chalconesomerase, and naringinin to erydictyl using flavonoid 3′-hydroxylase. Eriodictol is then converted to dihydroquercetin with flavanone 3-hydroxylase, which in turn is converted to quercetin using flavonol synthase.

Quercetin is the aglycone form of a number of other flavonoid glycosides, such as rutin and quercitrin, which are found in citrus fruits, buckwheat and onion peels. Quercetin forms the glycosides quercitrin and rutin together with rhamnose and rutin, respectively. Similarly, guaeverine is a 3-O-arabinoside, hyperoside is a 3-O-galactoside, isoquercetin is a 3-O-glucoside, and spireoside is a 4′-O-glucoside. CTN-986 is a quercetin derivative found in cottonseed and cottonseed oil. Mikelianin is the 3-O-β-D-glucuronopyranoside quercetin.

The path of degradation is routine. The enzyme quercitrinase can be found in Aspergillus flavus. This enzyme hydrolyzes quercitrin glycoside to release quercetin and L-rhamnose. It is an enzyme in the rutin catabolic pathway.

There is evidence that quercetin inhibits the oxidation of other molecules and is therefore classified as an antioxidant. Quercetin contains a polyphenolic chemical substructure that stops oxidation by acting as a scavenger of free radicals responsible for oxidative chain reactions.

Quercetin also activates or inhibits the activity of a number of proteins. For example, it is a nonspecific inhibitor of the protein kinase enzyme. Quercetin is reported to have estrogenic (female sex hormone-like) activity by activating estrogen receptors.

Quercetin is generally thought to be poorly absorbed. About 25% of the administered dose of quercetin is absorbed from the small intestine. Although a recent study by Hollman et al found that people absorb significant amounts of quercetin, this contradicts the assumption. Quercetin has been detected in human plasma as conjugates with glucuronic acid, sulfate or methyl groups without significant amounts of free quercetin. Quercetin has been shown to reach levels of 0.1-10 µmol/L (micromoles per liter) in the bloodstream. Quercetin concentration was mainly due to the presence of quercetin metabolites rather than its aglycone, which was recently reexamined by Murota and Terao. Regarding the pharmacokinetics of quercetin-glucoside conjugates. The main determinant of absorption of these conjugates appears to be the nature of the sugar moiety. For example, quercetin glucoside is absorbed from the small intestine, while quercetin rutinosides are absorbed from the colon after removal of the carbohydrate moiety by bacterial enzymes. In addition to the chemical form of flavonol, dietary fat content also influences the oral bioavailability of quercetin. Lesser et al examined the effect of dietary fat on the oral bioavailability of quercetin. According to them, the bioavailability of quercetin from each diet was always higher from the glucoside than from the aglycone, but regardless of the chemical form used, the bioavailability of quercetin was also higher in the 17% fat diet compared to the 3% fat diet (P < 0.05 ) .

Research has shown that bromelain, an enzyme derived from pineapple, improves the absorption of quercetin. Bromelain is a complex substance mainly composed of proteolytic enzymes. Several studies have proven that bromelain is a fibrinolytic agent. Bromelain is also known to have many of the same histamine and leukotriene inhibitory properties as quercetin. Thus, they improve each other's properties.

After absorption in the small intestine, quercetin is transported to the liver through the portal circulation, where it undergoes metabolism. Quercetin and its metabolites are distributed throughout various tissues of the body. Quercetin is closely associated with albumin in plasma. Peak plasma levels reach 0.7 hours to 7.0 hours after administration. The half-life of quercetin is approximately 25 hours. Elimination of quercetin was significantly delayed following its administration to fat-enriched diets (P < 0.05).

Toxicological data:

Acute toxicity in rats following oral administration

LD50 Oral - rat - 161 mg/kg.

Drug interactions

Quercetin, being a biologically active substance, can interact with some medications and dietary supplements:

• combined use with vitamin C and anti-inflammatory non-steroidal drugs enhances their effect;
• combination with organic nitrates (Cardiket, Cardix, Monizide, Nitroglycerin, Pentacard, etc.) can cause a sharp decrease in blood pressure;
• simultaneous use of quercetin with drugs such as Cyclosporine, Verapamil and Tamoxifen improves the bioavailability of the latter;
• in combination with thrombolytics (Streptase, Thromboflux, Urokinase Medak, Actilyse), polyphenol enhances the effectiveness of antithrombotic therapy.

Attention! It is known that flavonoids work well in combination with each other - in the form in which they exist in nature. Therefore, it is useful to combine quercetin with resveratrol and green tea catechins.