Aldosterone Activation of Trans-epithelial Iron Absorption in Human Colon

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PROJECT SUMMARY/ABSTRACT The aim of this project is to identify the aldosterone (“aldo”) activation of iron (Fe2+) absorption in a human colon. The duodenum is the primary site for iron absorption. Duodenal Fe2+ absorption is hampered in patients with celiac sprue and peptic ulcer diseases, during gastric bypass surgery, and in patients that develop iron deficiency and iron deficiency anemia (IDA). Coordinated regulation of apical divalent metal transporter-1 (DMT1) and basolateral ferroportin-1 (FPN1) mediate the trans-epithelial iron absorption. Although the duodenum is the primary site for iron absorption, both DMT1 and FPN1 are also expressed with decreasing levels along the entire length of the intestinal tract, including the colon. In general, hypoxia and iron deficiency up-regulate iron absorption, and DMT1 and FPN1 expression. We were pleasantly surprised during our preliminary studies, when we identified that aldosterone enhanced DMT1 and FPN1 expression, and increased iron absorption in a rat colon. Since “aldo” stimulates the epithelial Na+ channel (ENaC) in both rats and humans, we propose that “aldo” would also stimulate iron absorption by enhancing DMT1 and FPN1 expression in a human colon. Identification of the “aldo” enhanced colonic iron absorption would serve as an alternate site and distinct mechanism to stimulate iron absorption in patients with hampered duodenal iron absorption. Thus, we are proposing the following aims. Specific Aim-1 will identify and establish the iron transporters and iron absorption capacity of a normal human colon. We will accomplish this task by characterizing iron transporters and trans-epithelial iron absorption by measuring 59FeSO4 fluxes in epithelial layers and organoids; and by establishing trans-epithelial iron absorption requires coordinated regulation of apical (DMT1) and basolateral (FPN1) transporters by selective knockdown using siRNA transfection. Specific Aim-2 will address identifying the mechanisms to stimulate iron transporters and iron absorption in a normal human colon. This will be accomplished by establishing that “aldo” enhances iron transporters and trans- epithelial iron absorption and by identifying one or more pro-inflammatory cytokines that specifically up-regulate DMT1 and FPN1 expression, and iron absorption capacity in colonic epithelial layers and colonoids.