INFLAMMATATION, IRON AND FERRITINS IN IRON ABSORPTION

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The hypothesis to be tested is that changes in serum ferritin of hepatic origin are the signal for regulating intestinal iron absorption. The immediate goals are: first, to understand how certain cytokines and iron, individually and in concert, regulate secretion of serum ferritin by hepatic cells and to compare the mechanism of this regulation which preliminary data suggest is transcriptional in contrast to the translational regulation of cytosolic ferritin; second, to further characterize the structural differences between secreted and cytosolic ferritins; and, finally, to determine whether iron absorption by administering various forms of secreted ferritin intravenously into rats to establish whether iron absorption by the intestine is altered. The research design includes continues use of physical techniques such as sedimentation velocity and equilibrium centrifugation together with electron microscopy to analyze the overall size and shape of the serum ferritin and determination of N-terminal and internal amino acid sequences both directly from the protein subunits and from the cloned cDNA, carbohydrate content using lectin binding and glycosidase treatment. The rate and extent of ferritin biosynthesis will be determined in response to iron, cytokines IL-1 and TNF, alone or in combination, and the role of NO as a regulator will be quantitated by metabolically labeling the protein with 35S-Methionine and by immunoelectrophoresis. Isolated forms of serum ferritin will be infused in intact iron-deficient rats and the absorption in radioactive iron (59FeC13) measured using tied off upper intestinal segments in anesthetized rats. The significance of the proposed research is that it will determine whether and how levels of SFt change in relations to inflammation and iron status and examine whether SFt plays a role in controlling iron absorption. This is important since very little is currently known about these process at the molecular level and aberrations result in chronic over-absorption and iron overload. This is an adaptive response which is poorly understood.