Selenium in Biology

Abstract

The role of Se in biology appears from the evidence now at hand to be as a catalyst par excellence. As unique prosthetic group of a variety of enzymes, presumably as Se(2-), Se functions with tocopherol to protect cell and organelle membranes from oxidative damage, to facilitate the union between oxygen and hydrogen at the end of the metabolic chain, and to transfer ions across cell membranes, in protein synthesis in erythrocytes and in liver organelles, in immunoglobulin synthesis, and in ubiquinone syntheses. As perhaps the most versatile and rapid nucleophile, Se is thought to amplify and orient SH in equilibrium -S-S-interactions involving glutathione and proteins. Its toxicity appears to be due to overaccumulation of selenite ions, which act as oxidants to inhibit SH interactions. Such toxicity is readily avoided or reversed in many ways. Although not yet recognized as essential for man, Se is clearly essential for many animal species and some microorganisms. As the active selenide, Se emerged as the target for many heavy metal toxicities; contrariwise, as a specific antidote against heavy metal toxicities. Despite all this, its unusual toxicity and the many preconceived notions about Se continue to confuse attitudes toward the safe uses of selenicals. From a suspected cause of cancer, Se metamorphosed, via evidence over many years, into something of possible anticancer value. Interrelations between Se, Vitamin E, the ubiquinones, and various chronic diseases appear as beckoning research areas. The reported veterinary values of Se-tocopherol combinations in animals, together with clinical evidence, plus human and animal evidence for safety, offer promise for intensive medical investigation. The historical confusion and misunderstandings regarding Se must be corrected, however, before advantage can be taken of its potential for human welfare. The many misjudgments about Se, ever since 1900 and more obviously since the 1930s, have involved other trace elements. Unrealistic regulations stemming from these misunderstandings prevail worldwide. Evidence suggests that, once the nutrition biochemistry and toxicology of Se is sufficiently understood and appreciated, major breakthroughs in agriculture, medicine, and public health can result. Much has been accomplished along these lines in New Zealand in animal agriculture, in the US and other countries in veterinary medicine, and in Mexico in human medicine.

How to use the world's scarce selenium resources efficiently to increase the selenium concentration in food

“…In the majority of the European countries and other parts of China, classical symptoms associated with severe Se deficiency diseases are not commonly reported, but the daily Se intake is lower than the recommended Se intake (46). In these countries Se Efficient use of selenium resources 213 supplementation of the diet may possibly improve several different measures of health (3,4,12,47,53,56,57), such as reduction in cancer risk (53,58Á60), better immune function (61Á64), reduction of blood lipid oxidation (65,66), anti-ischaemic protection (67Á80), reduction of morbidity and mortality from HIV disease (81Á98), anti-ageing effects (99Á102), improved fertility (3,56,103Á105) and protection against allergic diseases and asthma (106Á111).…”

Involvement of ROS and JNK1 in selenite-induced a poptosisin Chang liver cells

“…In addition, selenite is known to induce apoptosis in many malignant cells such as hepatoma, prostate cancer, lung cancer and gastric cancer cell lines (El-Bayoumy, 2001;Gasparian et al, 2002). The cytotoxic activity of selenite is suggested to be associated with the oxidative stress (Shen et al, 2001) and interaction with thiol groups in proteins (Frost and Lish, 1975). The type of cytotoxicity was reflected closely with apoptosis of various tumor cell lines (Shen et al, 2001;Jiang et al, 2002), and the underlying apoptotic signaling pathway is widely investigated.…”

Activation of selenate by adenosine 5′-triphosphate sulphurylase from Saccharomyces cerevisiae

“…Animal diseases have been related to the toxic effects of seleniumcontaining compounds (Rosenfeld & Beath, 1964) and the role of selenium as an essential trace element in animal and bacterial nutrition has been established (Frost & List, 1975;Stadtman, 1974). Early studies on selenium compounds focused on the ability of other compounds to protect livestock from the toxic effects of selenium.…”