The binding of iron-laden transferrin to the cell-surface transferrin receptor (TfR) 1 results in endocytosis and uptake of the metal cargo. Iron is delivered to tissues by circulating transferrin, a transporter that captures iron released into the plasma mainly from intestinal enterocytes or reticuloendothelial macrophages. Figure 1 shows a schematic diagram of iron cycle in the body. Iron is recycled and thus conserved by the body. Almost two-thirds of the body iron is found in the hemoglobin present in circulating erythrocytes, 25% is contained in a readily mobilizable iron store, and the remaining 15% is bound to myoglobin in muscle tissue and in a variety of enzymes involved in the oxidative metabolism and many other cell functions. The body requires iron for the synthesis of its oxygen transport proteins, in particular hemoglobin and myoglobin, and for the formation of heme enzymes and other iron-containing enzymes involved in electron transfer and oxidation-reductions. In the human body, iron mainly exists in complex forms bound to protein (hemoprotein) as heme compounds (hemoglobin or myoglobin), heme enzymes, or nonheme compounds (flavin-iron enzymes, transferring, and ferritin). Many of the mechanisms found in lower organisms, have analogous counterparts in higher organisms, including humans.
Examples are siderophores secreted by microbes to capture iron in a highly specific complex or mechanisms to reduce iron from the insoluble ferric iron (Fe +3) to the soluble ferrous form (Fe +2) as in yeasts. In response, various cellular mechanisms have evolved to capture iron from the environment in biologically useful forms. This apparent paradox is due to the fact that in contact with oxygen iron forms oxides, which are highly insoluble, and thus is not readily available for uptake by organisms. However, despite its geologic abundance, iron is often a growth limiting factor in the environment. In contrast to zinc, iron is an abundant element on earth and is a biologically essential component of every living organism. Nowadays, although low iron intake and/or bioavailability are responsible for most anemia in industrialized countries, they account for only about half of the anemia in developing countries, where infectious and inflammatory diseases (especially malaria), blood loss from parasitic infections, and other nutrient deficiencies (vitamin A, riboflavin, folic acid, and vitamin B12) are also important causes. For many years, nutritional interest in iron focused on its role in hemoglobin formation and oxygen transport. However, it was not until 1932 that the importance of iron was finally settled by the convincing proof that inorganic iron was needed for hemoglobin synthesis. During the 17 th century, iron was used to treat chlorosis (green disease), a condition often resulting from the iron deficiency. Iron had early medicinal uses by Egyptians, Hindus, Greeks, and Romans. Finally, we discuss strategies for prevention of iron deficiency.įrom ancient times, man has recognized the special role of iron in health and disease. In this review, we discuss the latest progress in studies of iron metabolism and bioavailability, and our current understanding of human iron requirement and consequences and causes of iron deficiency.
Disorders of iron metabolism are among the most common diseases of humans and encompass a broad spectrum of diseases with diverse clinical manifestations, ranging from anemia to iron overload, and possibly to neurodegenerative diseases.
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However, as iron can form free radicals, its concentration in body tissues must be tightly regulated because in excessive amounts, it can lead to tissue damage. Iron is an essential element for almost all living organisms as it participates in a wide variety of metabolic processes, including oxygen transport, deoxyribonucleic acid (DNA) synthesis, and electron transport. The effect of an element is determined by several characteristics, including absorption, metabolism, and degree of interaction with physiological processes.
It is well-known that deficiency or over exposure to various elements has noticeable effects on human health.
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