Ascorbic acid (vitamin C) is crucial to health and well-being. Scurvy (extreme vitamin deficiency) markedly disturbs iron metabolism and storage, and produces the """"""""classical"""""""" findings of perifollicular hemorrhages and """"""""cork-screw"""""""" hair. The investigation of many aspects of human disease depends on cells in long-term culture. These cells are almost universally ascorbate-deficient because the vitamin is extremely labile in solution. These investigators have unveiled a number of important aspects of the cell biology of ascorbic acid. Their work showed that ascorbic acid slows the cellular degradation of the iron storage protein, ferritin. The result is greater quantities of """"""""free"""""""" iron within cells. This """"""""free"""""""" iron can cause cell injury, including peroxidation of lipid, protein and nucleic acid. On the other hand, the iron chelator, desferrioxamine, removes this """"""""free"""""""" iron more readily in patients with transfusional iron overload. These investigators have also shown that ascorbic acid alters ferritin synthesis by changing the structure and enzymatic activity of iron responsive protein 1 (IRP1). The central role of IRP1 in the metabolism of the transferrin receptor and the erythroid form of delta-aminolevulinic acid synthase raises the possibility of a role of ascorbic acid in these proteins as well. These investigators propose to continue scrutiny of ascorbic acid and iron metabolism. They will determine the mechanism by which ascorbic acid alters IRP1 aconitase activity. In particular, they will explore the in vivo phosphorylation of this protein and the role of ascorbic acid. The investigators will also explore the role of ascorbic acid in transferrin receptor biology, since this receptor mediates iron uptake by most cells. They will also examine the impact of ascorbic acid on heme biosynthesis that is important in the production of hemoglobin by erythroid precursors. Heme is also a prosthetic group to a number of important proteins such as cytochromes. The fact that most studies of iron metabolism have involved ascorbate-deficient cells raises questions about the interpretation of this work. In order to better understand and intervene in the disturbances of iron metabolism in disorders as diverse as the relatively rare sideroblastic anemia and the extremely common thalassemia, we must have more accurate infirmation on cellular iron metabolism.
