Flow-through dialysis of zinc(II) from model and human sera

Formation of Zinc-Containing Nanoparticles from Zn2+ Ions in Cell Culture Media: Implications for the Nanotoxicology of ZnO

“…We also cannot exclude the possibility that some of these small Zn-binding molecular or protein species may adsorb on the membrane itself. Our conclusions support earlier flow-through dialysis experiments of Zn(II) solubility in human serum . These observations raise the issue of actual Zn speciation in the numerous studies involving the bioactivity of either ionic Zn salts or ZnO nanoparticles.…”

“…This is particularly interesting given the 2 kDa cutoff of the dialysis membrane and the knowledge that Zn initially binds to the major serum components albumin (67 kDa), transferrin (80 kDa), and insulin (Zn-bound hexamer, 36 kDa). − We postulate that some of the Zn initially bound to the major serum proteins is transferred to low molecular weight, high affinity components present among the plethora of proteins, cytokines, and growth factors found in FBS, allowing it to dialyse more freely . These results are broadly consistent with observations by Martins, who found that Zn was less readily dialyzed when treated by serum, which itself had its low molecular weight components previously removed by dialysis …”

“…We suggest that unbound ionic Zn will enter cells via zinc transmembrane receptors and as bound elements to proteins, while nanoparticles require some form of endocytosis to cross the cellular membrane. Ions will not be subject to active scavenging processes, such as phagocytosis and the uptake behavior of ion-bound proteins may be very different from that of a nanoparticle with a protein corona. − Given the very low concentrations of Zn ions measured in this study, it is far more likely that ZnO NP cytotoxicity was being driven by intracellular dissolution of NPs after uptake and exposure of the particle agglomerates to the low pH of endosomes and phagosomes. This Trojan horse effect has been previously postulated, though the precise details of this intracellular dissolution process remains to be adequately described.…”

“…20 These results are broadly consistent with observations by Martins, who found that Zn was less readily dialyzed when treated by serum, which itself had its low molecular weight components previously removed by dialysis. 42 We find that a Zn precipitate can be formed not only in cell culture media but also in pure serum (Figure 5c). In medium containing serum, residual soluble zinc levels are around 12 μM, quite similar to those found in mammalian blood.…”

“…Our conclusions support earlier flow-through dialysis experiments of Zn(II) solubility in human serum. 42 These observations raise the issue of actual Zn speciation in the numerous studies involving the bioactivity of either ionic Zn salts or ZnO nanoparticles. In a thorough study of the mechanism of toxicity of ZnO nanoparticles, Xia et al 16 43 for ZnO nanoparticles in RPMI-1640/FBS, with ∼100% cytotoxicity toward murine fibroblasts and mesothelioma cells at [Zn] of 230 μM, and we have made very similar observations in our own studies, which include numerous measurements of total cell viability, apoptosis, and cytokine profiles on both ZnCl 2 solutions and nanoparticle ZnO under the experimental conditions also used in this study.…”