The Diverse Role of Selenium within Selenoproteins: A Review

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Abstract

Selenium functions within mammalian systems primarily in the form of selenoproteins. Selenoproteins contain selenium as selenocysteine and perform a variety of physiological roles. Eleven selenoproteins have been identified: cellular or classical glutathione peroxidase; plasma (or extracellular) glutathione peroxidase; phospholipid hydroperoxide glutathione peroxidase; gastrointestinal glutathione peroxidase; selenoprotein P; types 1, 2, and 3 iodothyronine deiodinase; selenoprotein W; thioredoxin reductase; and selenophosphate synthetase. Of these, cellular and plasma glutathione peroxidase are the functional parameters used for the assessment of selenium status. Glutathione peroxidases catalyze the reduction of peroxides that can cause cellular damage. Thioredoxin reductase provides reducing power for several biochemical processes and defends against oxidative stress. Selenoprotein P appears to play a role in oxidant defense. Selenoprotein W may play a role in oxidant defense and be involved with muscle metabolism. Thyroid deiodtnases function in the formation and regulation of active thyroid hormone. Selenophosphate synthetase is an enzyme required for the incorporation of selenocysteine into selenoproteins. In addition, a protein in the sperm mitochondrial capsule, which is vital to the integrity of sperm flagella, may be a unique selenoprotein. Recommended intakes, food sources, and status assessment of selenium, as well as selenium's role in health and disease processes, are reviewed. J Am Diet Assoc. 1999;99:836–843.

Section snippets

Dietary Selenium

Selenium is associated with protein in animal tissues (2). Consequently, muscle meats, organ meats, and seafood are dependable dietary sources of the mineral (5), (6). Grains and seeds, however, vary in selenium content depending on the selenium content of the soils in which they were grown (5), (6). Fruits, vegetables, and drinking water do not provide substantial quantities of selenium (6). In general, beef, white bread, pork, chicken, and eggs account for about half of the selenium in diets

Selenium Deficiency

In human beings, an association between low selenium status and Keshan disease, a cardiomyopathy endemic to parts of China, was documented in 1979 (11). Human selenium deficiencies are rare. The primary group of people who have developed selenium deficiency have been those receiving total parenteral nutrition without selenium for extended periods (12), (13), (14), (15). Brown et al (12) described an association between muscle weakness and severe selenium deficiency in a female patient with

Selenium Toxicity

In the 13th century, Marco Polo noticed seleniferous plants in the mountainous region of western China that, if eaten, would cause the hoofs of animals to drop off (23). Similar observations were recorded in Nebraska, the Dakotas, and other western territories in the late 19th and early 20th centuries (23).

In the 20th century the most widespread occurrence of selenium toxicity occurred in the Enshi County of China between 1961 and 1964 (24). Large quantities of selenium were ingested when a

Selenoproteins

Selenoproteins are proteins that contain the selenocysteine form of selenium, now recognized as the 21st amino acid (27). Eleven selenoproteins have been identified: 4 glutathione peroxidases (cellular or classical [1], plasma or extracellular [28], phospholipid hydroperoxide [29], and gastrointestinal [30], selenoprotein P (31), 3 iodothyronine deiodinases (type 1 [32], type 2 [33], and type 3 [34], selenoprotein W (35), thioredoxin reductase (36) and selenophosphate synthetase (37). In

Assessment

Selenium functions within mammalian systems primarily in the form of selenoproteins. Assessment of a person's selenium status can be accomplished through a variety of means, including measurement of specific selenoproteins. Estimation of dietary selenium intakes; measurement of selenium concentrations in blood, tissues, or excreta; and determination of glutathione peroxidase activity in various blood components are the common techniques used for assessing selenium status. Cellular and plasma

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    Copyright © 1999 American Dietetic Association. Published by Elsevier Inc. All rights reserved.