Ferritins are ubiquitous iron storage proteins where Fe(II) sequestration prevents not only its spontaneous oxidation to Fe(III) but also production of toxic free radicals. Recently, scientists have subverted these nature functions and used ferritin cage structures of nanometer dimensions for encapsulation of guest molecules such as anti-cancer drugs or bioactive nutrients based on pH induced ferritin disassembly and reassembly property. However, prior to this study, ferritin nanocage was required to disassemble only under harsh pH conditions (≤2.0 or ≥11.0), followed by reassembly at near neutral pH. Such harsh conditions can cause protein or guest molecules damage to a great extent during this pH-induced unfolding-refolding process. Here, we provide evidence demonstrating that the apoferritin shell is flexible rather than rigid. Indeed, we found that two large complex molecules, uranyl acetate dihydrate and phosphotungstic acid, can reach the cavity of both plant and animal apoferritin followed by mineralization. Moreover, large organic compound such as curcumin and doxorubicin can also be encapsulated within ferritin cavity by its mixing with protein. This strategy will increase the use of ferritin in nanotechnology, and could be also applicable to other shell-like proteins as templates to prepare nanomaterials.
The objective of this study was to evaluate the effect of proanthocyanidins (PAs) on iron uptake from soybean seed ferritin (SSF) crude by rats with iron deficiency anemia (IDA) for the first time. Six groups of Sprague-Dawley (SD) rats (n = 10) were used, which contain (1) SSF crude group; (2) SSF crude + PAs group; (3) PAs group; (4) FeSO(4) group; (5) iron deficiency control group; and (6) control group. The bioavailability of iron was examined by measuring hemoglobin (Hb) concentration value, red blood cell (RBC) numbers, and serum iron stores. After 8 weeks, Hb concentration was almost recovered to the normal level upon feeding SSF crude or FeSO(4) to rats. In contrast, Hb concentration was recovered to less extent when SSF crude plus PAs was used instead of SSF crude alone (P < 0.05). A similar profile was observed with these three sample groups when serum iron and RBC were used as parameters. All rats in PAs group died at the 8th week. Taken together, all these results demonstrated that PAs inhibited iron uptake of rats from SSF, and are toxic for rats with IDA.
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