Caco-2 cell acquisition of dietary iron(III) invokes a nanoparticulate endocytic pathway

Enhancement of non-heme iron absorption by anchovy (Engraulis japonicus) muscle protein hydrolysate involves a nanoparticle-mediated mechanism

The mechanisms by which meat enhances human absorption of non-heme iron remain unknown. Recently, anchovy (Engraulis japonicus) muscle protein hydrolysate (AMPH) was found to mediate the formation of nanosized ferric hydrolysis products in vitro. The current paper evaluates the effects of AMPH on the bioavailability and the intestinal speciation of non-heme iron in rats, followed by an investigation of cellular uptake pathways of in vitro-formed AMPH-stabilized nanosized ferric hydrolysis products (ANPs) by polarized human intestinal epithelial (Caco-2) cells. The hemoglobin regeneration efficiencies in anemic rats followed the order ferric citrate (9.79 ± 2.02%) < commercial bare α-Fe2O3 nanoparticles (16.37 ± 6.65%) < mixture of ferric citrate and AMPH (40.33 ± 6.36%) ≈ ferrous sulfate (40.88 ± 7.67%) < ANPs (56.25 ± 11.35%). Percentage contents of intestinal low-molecular-weight iron in the groups of FC+AMPH, FeSO4, and ANPs were significantly lower than the corresponding hemoglobin regeneration efficiencies (P < 0.05), providing strong evidence for the involvement of nanosized iron in intestinal iron absorption from FC+AMPH, FeSO4, and ANPs. Calcein-fluorescence measurements of the labile iron pool of polarized Caco-2 cells revealed the involvement of both divalent transporter 1 and endocytosis in apical uptake of ANPs, with endocytosis dominating at acidic extracellular pH. Overall, AMPH enhancement of non-heme iron absorption involves a nanoparticle-mediated mechanism.

Ferroportin mediates the intestinal absorption of iron from a nanoparticulate ferritin core mimetic in mice

The ferritin core is composed of fine nanoparticulate Fe(3+) oxohydroxide, and we have developed a synthetic mimetic, nanoparticulate Fe(3+) polyoxohydroxide (nanoFe(3+)). The aim of this study was to determine how dietary iron derived in this fashion is absorbed in the duodenum. Following a 4 wk run-in on an Fe-deficient diet, mice with intestinal-specific disruption of the Fpn-1 gene (Fpn-KO), or littermate wild-type (WT) controls, were supplemented with Fe(2+) sulfate (FeSO4), nanoFe(3+), or no added Fe for a further 4 wk. A control group was Fe sufficient throughout. Direct intestinal absorption of nanoFe(3+) was investigated using isolated duodenal loops. Our data show that FeSO4 and nanoFe(3+) are equally bioavailable in WT mice, and at wk 8 the mean ± SEM hemoglobin increase was 18 ± 7 g/L in the FeSO4 group and 30 ± 5 g/L in the nanoFe(3+) group. Oral iron failed to be utilized by Fpn-KO mice and was retained in enterocytes, irrespective of the iron source. In summary, although nanoFe(3+) is taken up directly by the duodenum its homeostasis is under the normal regulatory control of dietary iron absorption, namely via ferroportin-dependent efflux from enterocytes, and thus offers potential as a novel oral iron supplement.

A nano-disperse ferritin-core mimetic that efficiently corrects anemia without luminal iron redox activity

The 2-5 nm Fe(III) oxo-hydroxide core of ferritin is less ordered and readily bioavailable compared to its pure synthetic analogue, ferrihydrite. We report the facile synthesis of tartrate-modified, nano-disperse ferrihydrite of small primary particle size, but with enlarged or strained lattice structure (~ 2.7 Å for the main Bragg peak versus 2.6 Å for synthetic ferrihydrite). Analysis indicated that co-precipitation conditions can be achieved for tartrate inclusion into the developing ferrihydrite particles, retarding both growth and crystallization and favoring stabilization of the cross-linked polymeric structure. In murine models, gastrointestinal uptake was independent of luminal Fe(III) reduction to Fe(II) and, yet, absorption was equivalent to that of ferrous sulphate, efficiently correcting the induced anemia. This process may model dietary Fe(III) absorption and potentially provide a side effect-free form of cheap supplemental iron.

From the Clinical Editor

Small size tartrate-modified, nano-disperse ferrihydrite was used for efficient gastrointestinal delivery of soluble Fe(III) without the risk for free radical generation in murine models. This method may provide a potentially side effect-free form iron supplementation.