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FOLATE (FOLIC ACID) PLAYS A CRUCIAL ROLE IN RED BLOOD CELL FORMATION
Koury MJ, Ponka P (2004). New insights into erythropoiesis: the roles of folate, vitamin B12, and iron. Annu Rev
Nutr. 24:105-31.
Erythropoiesis is the process in which new erythrocytes are produced. These new erythrocytes replace the oldest
erythrocytes (normally about one percent) that are phagocytosed and destroyed each day. Folate, vitamin B12, and
iron have crucial roles in erythropoiesis. Erythroblasts require folate and vitamin B12 for proliferation during
their differentiation. Deficiency of folate or vitamin B12 inhibits purine and thymidylate syntheses, impairs DNA
synthesis, and causes erythroblast apoptosis, resulting in anemia from ineffective erythropoiesis. Erythroblasts
require large amounts of iron for hemoglobin synthesis. Large amounts of iron are recycled daily with hemoglobin
breakdown from destroyed old erythrocytes. Many recently identified proteins are involved in absorption, storage,
and cellular export of nonheme iron and in erythroblast uptake and utilization of iron. Erythroblast heme levels
regulate uptake of iron and globin synthesis such that iron deficiency causes anemia by retarded production rates
with smaller, less hemoglobinized erythrocytes.
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Casadevall N. (1995). Cellular mechanism of resistance to erythropoietin. Nephrol Dial
Transplant. 10 Suppl 6:27-30.
Erythropoiesis is controlled by different regulators. Interleukin 3, granulocyte-macrophage colony-stimulating
factor and stem cell factor play regulatory functions in the early steps of erythropoiesis. Erythropoietin (Epo) is
the main factor which acts positively on the last steps of the production of erythrocytes in mammals. Epo is
specific for the erythroid progenitor cells and has only little effect on other cells. The target cells for Epo are
the erythroid progenitors (BFUe and CFUe). Epo acts on these progenitors through surface receptors specific for
Epo. Epo induces the proliferation and differentiation of erythroid progenitors leading finally to reticulocytes.
During this process, certain conditions are required to permit this differentiation: progenitors must be present in
sufficient numbers, the bone marrow environment must be normal, and nutrients such as folic acid, vitamin B12 and
particularly iron must be available. Elemental iron is an absolute requirement for adequate haemoglobin formation.
Indeed, in a normal adult, without any stimulation, the bone marrow synthesizes 4 x 10(14) molecules of haemoglobin
per second, each molecule containing four atoms of iron, which roughly corresponds to 20 mg iron. On the other
hand, erythropoiesis is negatively regulated by several cytokines. These are macrophage-derived cytokines,
including tumour necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), interleukin-6 (IL-6) and transforming
growth factor-beta (TGF-beta). All these factors are elevated in the inflammatory state and are implicated in the
pathogenesis of anaemia of chronic disease. TNF-alpha has an inhibitory effect on erythroid progenitors either
directly or mediated by interferon-beta (INF-beta). IL-1 inhibits erythropoiesis in vivo in mice and in vitro in
humans.
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