General description

Selenium is a nonmetallic chemical element found in trace amounts in human body. Selenium primarily occurs in vivo as selenocompounds, mostly selenoproteins such as glutathione peroxidase and thioredoxin reductase (enzymes responsible for detoxification). Alone or in combination with Vitamin E, selenocompounds act as antioxidants. These agents scavenge free radicals; prevent blood clots by inhibiting platelet aggregation; strengthen the immune system; and have been shown, in some instances, to inhibit chromosomal damage and mutations. Exhibiting chemopreventive activity, selenocompounds also inhibit the induction of protein kinase C.

Application and pharmacology

Selenium is a naturally occurring mineral element that is distributed widely in nature in most rocks and soils. In its pure form, it exists as metallic gray to black hexagonal crystals, but in nature it is usually combined with sulfide or with silver, copper, lead, and nickel minerals. Most processed selenium is used in the electronics industry, but it is also used: as a nutritional supplement; in the glass industry; as a component of pigments in plastics, paints, enamels, inks, and rubber; in the preparation of pharmaceuticals; as a nutritional feed additive for poultry and livestock; in pesticide formulations; in rubber production; as an ingredient in antidandruff shampoos; and as a constituent of fungicides. Radioactive selenium is used in diagnostic medicine.

Selenium is incorporated into selenoproteins that have a wide range of pleiotropic effects, ranging from anti oxidant and anti-inflammatory eff ects to the production of active thyroid hormone. In the past 10 years, the discovery of diseaseassociated polymorphisms in seleno protein genes has drawn attention to the relevance of selenoproteins to health. Low selenium status has been associated with increased risk of mortality, poor immune function, and cognitive decline. Higher selenium status or selenium supplementation has antiviral effects, is essential for successful male and female reproduction, and reduces the risk of autoimmune thyroid disease. Prospective studies have generally shown some benefit of higher selenium status on the risk of prostate, lung, colorectal, and bladder cancers, but findings from trials have been mixed, which probably emphasises the fact that supplementation will confer benefi t only if intake of a nutrient is inadequate. Supplementation of people who already have adequate intake with additional selenium might increase their risk of type-2 diabetes. The crucial factor that needs to be emphasised with regard to the health effects of selenium is the inextricable U-shaped link with status; whereas additional selenium intake may benefit people with low status, those with adequate-to-high status might be affected adversely and should not take selenium supplements.
1.In human beings, the nutritional functions of selenium are achieved by 25 selenoproteins that have selenocysteine at their active centre.3 The insertion of selenocysteine to form a selenoprotein is specifi ed by the UGA codon in mRNA under specifi c conditions, but many other interacting factors are necessary.3,4 In low selenium supply, the synthesis of some selenoproteins (eg, glutathione peroxidase, GPx4) is prioritised over that of others.4 Many selenoproteins are important enzymes and their importance to human health is shown by the effect of single nucleotide polymorphisms (SNPs) in selenoprotein genes 
on disease risk or mortality [1]
2.The essential trace mineral, selenium, is of fundamental importance to human health. As a constituent of selenoproteins, selenium has structural and enzymic roles, in the latter context being best-known as an antioxidant and catalyst for the production of active thyroid hormone. Selenium is needed for the proper functioning of the immune system, and appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression
to AIDS. It is required for sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking selenium to cardiovascular disease risk although other
conditions involving oxidative stress and inflammation have shown benefits of a higher selenium status. An elevated selenium intake may be associated with reduced cancer risk. Large clinical trials are now planned to confirm or refute
this hypothesis. In the context of these health effects, low or diminishing selenium status in some parts of the world, notably in some European countries, is giving cause for concern.[2,3]

   
Figure 1.A summary of selenium and immune responses

History

The discoverer, J ö ns Jakob Berzelius, named it Selene, which means moon in Greek. Discovery year: 1817 discovery process: in 1817, bezelius of Sweden prepared selenium from the red powder at the bottom of the lead chamber of the sulfuric acid plant. He also found allotropic forms of selenium. He reduced the oxide of selenium to obtain orange amorphous selenium; Slowly cool the molten selenium to obtain Gray Crystal selenium; The selenide is naturally decomposed in the air to obtain black crystalline selenium. Selenium is a multifunctional nutrient for life. It is often used in 40 diseases such as Keshan disease, Kaschin Beck disease, cardiovascular disease, diabetes, liver disease, prostatic disease, heart disease, cancer and so on. It is widely used in cancer, surgery, radiotherapy and chemotherapy.
Selenium is also divided into plant active selenium and inorganic selenium. Inorganic selenium generally refers to sodium selenite and sodium selenate, including yeast selenium and malt selenium with a large amount of inorganic selenium residues. It is obtained from the by-products of metal minerals. Inorganic selenium has great toxicity, is not easy to be absorbed, and is not suitable for human and animal use. Plant active selenium is formed by biotransformation combined with amino acids and generally exists in the form of selenomethionine. Plant active selenium is a selenium source allowed for human and animals.

Toxicity

1.Selenium is an essential micronutrient that plays a crucial role in development and a wide variety of physiological processes including effect immune responses. The immune system relies on adequate dietary selenium intake and this nutrient exerts its biological effects mostly through its incorporation into selenoproteins. [2]
2.Selenium is a reddish colored powder that may become black upon exposure to air. It is toxic by ingestion. It is used to manufacture electronic components and rubber.

Storage

Drugs are generally stored in a closed, dry and dark place in a cool place with low temperature at home. If the tablets are found to be moldy, deteriorated, discolored or have strange smell during storage, or flocs appear in the liquid medicine, do not use it again.

Reference

1., "Selenium and human health,".

2. Rayman M. P., "The importance of selenium to human health," The Lancet (British edition), Vol.356, No.9225(2000), pp.233-241.

3. Avery J. & Hoffmann P., "Selenium, Selenoproteins, and Immunity," Nutrients, Vol.10, No.9(2018), p.1203.