The dosage makes either a poison or a remedy” (Paracelsus, 1393-1441). Selenium is a mineral so appreciated, how insidious when taken up or down. Side effects deficiency or overload are not negligible. Symptoms of excess are dermatitis, nail disorders, hair loss, neurological abnormalities, gastrointestinal disorders and the characteristic smell of garlic in the expired air (dimethyl selenide). Conversely, the chronic deficiency has serious consequences on the heart health, but the excess can result in toxicity and / or developing diabetes type 2. The daily population reference intake (PRI) of selenium is 55 micrograms while the maximum tolerable level (UL): 300 micrograms (LARN, IV rev. 2014). Selenium is a mineral found mostly in meat and fish and vegetables grown in soils rich in the mineral. Selenium enters the food chain starting from the vegetables. The selenium absorption depends on a number of factors including the soil and its pH, the amount of organic matter, the concentration of the mineral, the presence of more or less high bacteria. The essentiality of selenium is related to its presence in the active site of enzymes such as glutathione peroxidases (GPx1-4), thioredoxin reductase, iodothyronine deiodinase. The selenium absorption is not dependent on the amount present in the body. The excretion is the homeostatic mechanism for the regulation of selenium in the body. In addition, the selenium introduced with food shows a high bioavailability. Selenomethionine (Se-Met) is the principal form of selenium taken with diet; it is absorbed by means of the same mechanism of methionine absorption and incorporated into a higher number of different proteins. When required for the synthesis of new selenoproteins, the proteins release Se-Met and made it available with a mechanism transulfuration. Selenocysteine (Se-Cys) is highly bioavailable but it is still unknown the mechanism of absorption. Se-Cys is the active form of selenium pool. The body synthesizes Se-Cys starting from Se-Met. In the human body selenium, as Se-Cys, is in large part inserted to the glutathione peroxidase, the other part is present in several proteins, including the selenoprotein P, which probably acts a function of storage. The main biological functions, in which selenium is involved when incorporated in selenoproteins as Se-Cys, are wide-ranging, including the defense against oxidative stress, the activation of thyroid hormones, the improving of the redox state of several molecules including vitamin C, the regulation of the immune defense and the prevention of several types of cancer.
|Titolo:||Selenium from toxic to essential: main functions|
CIAPPELLANO, SALVATORE (Primo)
|Parole Chiave:||Selenium; selenoprotein; functions|
|Settore Scientifico Disciplinare:||Settore BIO/09 - Fisiologia|
|Data di pubblicazione:||set-2015|
|Tipologia:||Book Part (author)|
|Appare nelle tipologie:||03 - Contributo in volume|