Selenium: antioxidant protection – molecular mechanisms, sources, role in health and prevention
1. Selenium: fundamental trace element
Selenium, a chemical element related to chalcogen, plays a critical role in maintaining human health due to its powerful antioxidant properties and participation in various biological processes. It is an indispensable trace element, that is, necessary for the normal functioning of the body, but required in very small quantities. The disadvantage of selenium can lead to serious health disorders, while excessive consumption can cause toxicity. The perfect balance of selenium consumption is important for the optimal functioning of the body.
1.1 chemical properties of selenium
Selenium demonstrates the properties intermediate between metal and non -metall (metalloid). It exists in several allotropic forms, including amorphous (red) and crystalline (gray) selenium. Crystalline selenium is the most stable form and has semiconductor properties, which determines its use in electronics. Selenium forms compounds with various elements, including oxygen, hydrogen and halogens. In biological systems, selenium is usually present in the form of selenocysteine (SEC), the 21st amino acid, which is part of selenoproteins.
1.2 Biological role of Selena: Selenoprotein
The main biological function of selenium is due to its inclusion in selenoproteins. Selenoproteins are a family of proteins containing selenocysteine (SEC) in their structure. SEC is integrated into the polypeptide chain during the broadcast process using a special UGA codon (usually terminal codon), which is rebuilded in the SEC codon in the presence of a specific CIS element in the 3′-unexplored MRNA and specialized transport RNA (TRNKSEC). To date, a person has 25 selenoproteins, each of which performs a certain function.
1.2.1 Glutatory Peroxidasis (GPX)
Glutathioneperoxidase (GPX) are perhaps the most studied selenoproteins. They are a family of enzymes that catalyze the restoration of hydrogen peroxide (H2O2) and organic hydroxides to water and appropriate alcohols, using glutathione (GSH) as a kosubstrat. This reaction plays an important role in protecting cells from oxidative damage caused by free radicals and active forms of oxygen (AFC). There are various GPX isoforms that differ in their localization and specificity to substrates:
- GPX1 (cytosol GPX): The most common form present in the cytosol of most cells.
- GPX2 (gastrointestinal GPX): It is expressed in the cells of the gastrointestinal tract and is involved in protection against oxidative stress that occurs during digestion.
- GPX3 (extracellular GPX): Secrets in blood plasma and lymph.
- GPX4 (phospholipid-hydrocyxide GPX): A unique form capable of restoring peroxidated phospholipids in membranes, protecting them from oxidative damage. It also plays a role in spermatogenesis and cell differentiation.
- GPx6: Found in olfactory epithelia.
1.2.2 Tirexinreduct (TrxR)
Tirdoxinreduktase (TRXR) is another important group of selenoproteins. They are a family of enzymes that catalyze the restoration of threwdoxin (TRX) using NADPH as a cofactor. Tirdoxin is a small protein involved in various cellular processes, including:
- Maintaining the radio-balance in the cage.
- Regulation of the activity of transcription factors.
- DNA replication.
- Anti -Apoptotic protection.
TRXR play a key role in ensuring antioxidant protection, restoring oxidized thirdoxin and supporting its active form. There are various TRXR isoforms that differ in their localization and functions:
- TRXR1 (cytosol TRXR): The main form present in the cytosol.
- TRXR2 (mitochondrial TRXR): Localized in mitochondria and protects them from oxidative stress.
- TrxR3 (TrxR thioredoxin reductase 3): The function is not finally set.
1.2.3 Diyodinase (DIO)
Diodinazy (DIO) is a family of selenic -dependent enzymes that catalyze the deyding of thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3). These enzymes play an important role in the regulation of metabolism and energy metabolism. There are three main DIO isoforms:
- DIO1: Converts T4 into T3 (the active form of thyroid hormone) and inactivates T4 and T3.
- Dio2: It transforms T4 into T3, mainly in the brain, pituitary gland and brown adipose tissue.
- Dio3: Inactivates T4 and T3, turning them into inactive metabolites.
1.2.4 Selenoprotein P (SEPP1)
Selenoprotein P (SEPP1) is the main selenoprotein in blood plasma. It contains several molecules of selenocysteine (up to 10) and performs the function of selenium transport in tissue, and also has antioxidant properties. SEPP1 is associated with receptors on the surface of the cells and delivers selenium inside, where it is used to synthesize other selenoproteins.
1.2.5 Other selenoproteins
In addition to the above, there are other selenoproteins that perform important functions in the body:
- Selenoprotein W (SELW): Participates in muscle function and antioxidant protection.
- Selenoprotein N (SELN): He plays a role in the development and functioning of muscles.
- Selenoprotein H (SELH): Presumably participates in antioxidant protection and maintaining the stability of the genome.
- Selenoprotein and (villages): The function is not fully set.
- Selenoprotein K (SELK): Participates in calcium homeostasis and immune response.
- Selenoprotein M (SELM): The function is not fully set.
- Selenoprotein O (village): The function is not fully set.
- Selenoprotein T (SELT): Participates in the endoplasmic reticulum of-assed degradation (ERAD).
- 15kda selenoprotein (SEP15): Participates as a chaperon in endoplasmic reticulum.
- Methynin Sulphoxy Redukyzi B1 (MSRB1): Restores methionine sulfoxide to methionine, protecting proteins from oxidative damage.
2. The mechanisms of antioxidant protection of selenium
Selenium provides antioxidant protection through several mechanisms mainly related to the functioning of selenoproteins.
2.1 direct recovery of peroxides (GPX)
Glutathioneperoxidases (GPX) catalyze the direct restoration of hydrogen peroxide (H2O2) and organic hydraxides, turning them into water and alcohols, respectively. This prevents the accumulation of these harmful substances that can cause oxidative damage to DNA, proteins and lipids. The reaction looks as follows:
ROOH + 2GSH -> Spirit + H2O + GSSG
Where:
- ROOH – hydraoxide (for example, H2O2 or lipid hydraoxide)
- GSH – Restored glutathione
- ROH – alcohol
- GSSG – oxidized glutathione
GPX contain selenocystein in an active center, which plays a key role in the catalytic mechanism. Selehenol (SEH) The selenocysteine group restores hydraoxide, turning into selenic acid (SEOH). Then selenic acid is restored by glutathione, regenerating Selenol and completing the catalytic cycle.
2.2 Tiedxin regeneration (TRXR)
Tirdoxynreduktase (TRXR) maintain rare ox-balance in a cage, restoring threwdoxin (TRX). Tirdoxin, in turn, is involved in the restoration of other proteins and molecules, protecting them from oxidative damage. TRXR also play a role in the restoration of Kilikhinon (Coenzyme Q10), an important antioxidant in mitochondria.
2.3 Protection of lipid membranes (GPX4)
GPX4 has a unique ability to restore peroxidated phospholipids in membranes, protecting them from oxidative damage. Lipid peroxidation is a chain reaction, which can lead to the destruction of membranes and impaired their functions. GPX4 interrupts this chain reaction, restoring damaged phospholipids.
2.4 indirect mechanisms of antioxidant protection
In addition to direct restoration of peroxides and regeneration of antioxidants, selenium can also have an antioxidant effect through other mechanisms:
- Regulation of the expression of antioxidant enzymes: Selenium can affect the expression of genes encoding antioxidant enzymes, such as superoxidsmouth (SOD) and catalase.
- Reducing the formation of free radicals: Selenium can reduce the formation of free radicals, suppressing the activity of enzymes involved in their generation, such as NOX (Nadph Oxidase).
- Helating of metals: Some compounds of selenium can bind metals, such as iron and copper, which are involved in the reactions of the Fenton and Habera Wesis, leading to the formation of free radicals.
3. Sources of Selena in nutrition
The content of selenium in food products depends on the content of selenium in the soil on which they were grown. In some regions of the world, such as China and Russia, the content of selenium in the soil is low, which can lead to selenium deficiency in the population.
3.1 The main food sources of Selena:
- Brazil nut: It is one of the richest sources of Selena. Several nuts per day can provide sufficient daily dose of selenium.
- Seafood: Fish (tuna, cod, halve), mollusks (oysters, mussels) and shrimp are good sources of selenium.
- Meat: Beef, pork and chicken contain selenium.
- Eggs: Eggs contain a moderate amount of selenium.
- Grain products: Whole grain products, such as wheat, rice and oats, contain selenium, although its content can vary depending on the region.
- Seeds: Sunflower seeds and pumpkin seeds contain selenium.
- Vegetables and fruits: The content of selenium in vegetables and fruits is usually lower than in other foods, but some vegetables, such as garlic and broccoli, may contain a significant amount of selenium.
3.2 Selena supplements
For people who do not receive enough selenium from food, selenium additives are available. The most common forms of selenium in addition:
- Selenomethumentin: The organic form of selenium, which is well absorbed by the body. Seleenomeinine is the main form of selenium contained in plants.
- Sodium selenite: The inorganic form of selenium, which is also absorbed by the body, but less effective than selenometyonin.
- Sodium Selevenat: Another inorganic form of selenium.
- Selenocysteine: The form contained in selenoproteins.
It is recommended to consult a doctor or nutritionist before taking Selena additives to determine the optimal dosage and avoid toxicity.
4. Selena deficit: health consequences
Selenium deficiency can lead to various health disorders, mainly associated with impaired antioxidant protection and functioning of selenoproteins.
4.1 Keshan disease
Keshan’s disease is endemic cardiomyopathy, which is found in regions with a low selenium content in the soil. It is characterized by an increase in the heart, heart failure and arrhythmias. Selenium deficiency increases the susceptibility to the Coksaki B virus, which is believed to be the main factor that causes Keshan’s disease.
4.2 Kashin-Bek’s disease
Kashin -bek disease is endemic osteoarthritis, which is also found in regions with a low content of selenium in the soil. It is characterized by degeneration of the articular cartilage and bones, leading to pain in the joints, limiting mobility and disability.
4.3 Dysfunction of the thyroid gland
Selenium plays an important role in the functioning of the thyroid gland, participating in the deedification of thyroid hormones. Selena deficiency can lead to hypothyroidism (decreased thyroid function) and autoimmune thyroid diseases such as Hashimoto thyroiditis.
4.4 Violation of the immune function
Selenium is necessary for the normal functioning of the immune system. Selena deficiency can weaken the immune response and increase susceptibility to infections.
4.5 infertility
Selenium plays an important role in spermatogenesis and fertility. Selena deficiency can lead to a decrease in sperm mobility and infertility in men.
4.6 increased risk of cancer
Some studies have shown that selenium deficiency can be associated with an increased risk of some types of cancer, such as prostate cancer, lung cancer and colon cancer.
5. The toxicity of Selena: Selenosis
Although selenium is necessary for health, excess selenium consumption can cause toxicity known as selenosis. Selenosis can occur when using high doses of selenium additives or when eating food, grown on soils with very high selenium content.
5.1 Symptoms of selenosis
Symptoms of selenosis can vary depending on the dose and duration of exposure. The main symptoms:
- Hair loss
- Fragility of nails
- Nausea
- Diarrhea
- Fatigue
- Irritability
- Neurological disorders
- The smell of garlic from the mouth
In severe cases, selenosis can lead to serious complications, such as damage to the liver, kidneys and nervous system.
5.2 Prevention of selenium toxicity
To prevent selenium toxicity, it is recommended:
- Do not exceed the recommended daily dose of selenium (55 μg for adults).
- Get selenium mainly from food, not from additives.
- Consult a doctor or nutritionist before taking Selena’s additives.
- Avoid the use of high doses of selenium additives, especially for a long time.
- Control the level of selenium in the blood if you take selenium additives in high doses.
6. Selenium and Health: Clinical Research and Application
Numerous clinical studies studied the role of selenium in the prevention and treatment of various diseases.
6.1 Cancer
Some studies have shown that selenium supplements can reduce the risk of some types of cancer, especially prostate cancer, lung cancer and colon cancer. However, the results of the studies are contradictory, and further research is necessary to confirm these results. The mechanism of the anti -cancer action of selenium can be associated with its antioxidant properties, the regulation of apoptosis and inhibiting angiogenesis.
6.2 Cardiovascular diseases
Some studies have shown that selenium additives can reduce the risk of cardiovascular diseases, such as coronary heart disease and stroke. Selenium can improve the function of endothelium, reduce LDL cholesterol (poor cholesterol) and prevent blood clots.
6.3 Autoimmune diseases
Selenium can play a role in the regulation of the immune system and can be useful in the treatment of autoimmune diseases, such as Hashimoto thyroiditis and rheumatoid arthritis. Selena additives can reduce the level of antibodies to the thyroid gland and improve the function of the thyroid gland in patients with hashimoto thyroiditis.
6.4 infertility
Selena additives can improve sperm quality and increase fertility in men with selenium deficiency. Selenium protects sperm from oxidative damage and improves their mobility.
6.5 Other applications
Selenium was also studied as a potential remedy for the treatment of other diseases, such as HIV/AIDS, Alzheimer’s disease and asthma. However, further research is needed to confirm these results.
7. Selenium and sports
Intensive physical activity can increase the formation of free radicals and cause oxidative stress. Selenium, thanks to its antioxidant properties, can be useful for athletes, helping to protect muscles from damage and improve recovery after training. However, it is important to observe caution and not exceed the recommended daily dose of selenium, since excessive consumption can have a negative effect on health.
8. Selenium and aging
Oxidative stress plays an important role in the aging process. Selenium, as an antioxidant, can help slow down the aging process, protecting the cells from damage caused by free radicals. Some studies have shown that the elderly with a high level of selenium in the blood has a better cognitive function and a lower risk of developing age diseases.
9. Conclusion (do not include)
10. References (do not include)