Inflammation induces a plethora of changes in iron metabolism. These include a depression in iron and transferrin in the serum and a rise in the concentration of serum ferritin. In addition, chronic inflammation is associated with a mild to moderate anemia. The mechanism by which these abnormalities develop is unknown. A lowering in the availability of iron in the cell may be some defense against infection and may help to limit oxidant damage from free radicals generated by the inflammatory response. Cytokines such as Il-1beta activate the immune response by stimulating T- cells. T-cells also need iron for proliferation. The decrease in serum iron induced by cytokines may be a counter regulatory response which helps to dampen the immune reaction to inflammation. Work in our laboratory using the human hepatoma cell line HepG2 as a model system shows that ferritin translation is stimulated by the cytokine interleukin-1beta. The mechanism is a recruitment to polyribosomes of preexisting ferritin mRNA, leading to an increase in the amount of free iron in the cell. Il-6 also stimulates ferritin synthesis in these cells by activating translation of the ferritin message. These cytokines also simulate ferritin synthesis in human umbilical vein endothelial cells, indicating that the phenomenon is not limited to cells in permanent culture. Present knowledge of these phenomena will be expanded by i) examining in greater detail the effects of cytokines on ferritin synthesis in HepG2 cells and other cell lines, ii) determining the mechanism of the effect by subcloning into the expression vector PSV2-CAT constructs of the 5 untranslated region of the ferritin message, since specific segments of the 5 UT of the ferritin message are important in the translational control of the message by iron, iii) determining the metabolic consequences of the induction of ferritin synthesis by cytokines. In particular, we shall determine whether alterations in ferritin synthesis in monocytic cells lead to a sequestration of iron which contributes to the anemia of chronic inflammation. Primary effects of cytokines on ferritin synthesis and hemoglobin production in erythroid cell lines will also be examined. We will determine whether ferritin synthesis and iron sequestration protect HepG2 cells from oxidant injury by limiting the generation of damaging free radicals by the iron-catalyzed Fenton reaction. These data will provide insight into possible means of limiting cell damage mediated by inflammation. Finally, we have preliminary evidence for ferritin secretion by endothelial cells, a finding which could explain the heretofore unknown origin of serum ferritin. These findings will be confirmed and extended by biochemical analysis of the secretory process in endothelial cells. Serum ferritin levels are widely used as an index of body iron stores. The utility of the test, unfortunately is limited by the disturbances in serum ferritin levels which occur with inflammation. The series of investigations proposed in this application will help to explain a number of the perturbations in iron metabolism which accompany chronic inflammation and which contribute to pathology in disease processes ranging from rheumatoid arthritis to tuberculosis.
