Inositol phosphates influence iron uptake in Caco-2 cells

Phytate, inositol hexaphosphate (InsP(6)), may be hydrolyzed to inositol ph osphates with lower degree of phosphorylation, i.e., inositol penta- to mon ophosphates (InsP(5)-InsP(1)), during food processing. Each of these lower inositol phosphates exists in different isomeric forms. The objective of th is study was to determine if different isomers of InsP(3)-InsP(5), (Ins(1,2 ,4)P-3, ms(1,2,3)P-3, Ins(1,2,6)P-3, Ins(1,3,4)P-3, Ins(1,2,3,4)P-4, Ins(1, 2,5,6)P-4, Ins(1,2,4,5,6)P-5, and Ins(1,3,4,5,6)P-5) and InsP(6) affect the uptake of iron. We studied the iron absorption in vitro using the human in testinal epithelial cell line, Caco-2. Addition of a 2-fold molar excess of InsP(6) or InsP(5) in proportion to Fe (1 h incubation at 37 degrees C) re duced iron uptake by 46-52% (p < 0.001). Neither InsP(4) isomers nor InsP(3 ) isomers affected iron uptake significantly at 1 h incubation with a molar InsP:Fe level of 2:1. Iron uptake was shown to not be a function of the is omeric form of inositol phosphates. The inositol phosphate isomers did not seem likely to interact with each other through iron to form more stable ir on complexes. At a molar InsP:Fe level of 20:1 an inhibitory effect of InsP (4) was found, while InsP(3) did not affect the iron absorption even at a 2 0-fold molar excess.