Dr. Joachim Clement (Jena, DE), Dr. Frank Mickoleit (Bayreuth, DE), Cornelia Jörke (Jena, DE), Dr. Reinhard Richter (Bayreuth, DE), Dr. Sabine Rosenfeldt (Bayreuth, DE), Simon Markert (Bayreuth, DE), Jula Tropschug (Jena, DE), Professor Anna Schenk (Bayreuth, DE), Professor Dirk Schüler (Bayreuth, DE)
Abstract text (incl. figure legends and references)
Introduction Bacterial magnetosomes are promising tools for biomedicine. In Magnetospirillum gryphiswaldense, they consist of a cuboctahedral magnetite core surrounded by a biological membrane. An important quality parameter for future applications is the long-term stability.
Objective We investigated the colloidal stability of isolated particles, their magnetic properties, the integrity of the magnetosome membrane, as well as potential cytotoxic effects when applied to human cell lines.
Methods Magnetosomes were isolated from bacteria by magnetic separation techniques. The particles were resuspended in 10 mM HEPES with 1 mM EDTA, pH 7.2, and stored under a nitrogen atmosphere at 4°C. The iron concentration was determined by atomic absorption spectroscopy. Physico-chemical characterization was performed by dynamic light scattering, vibrating sample magnetometry and TEM. Biocompatibility of magnetosomes was evaluated on the cell lines FaDu (hypopharynx carcinoma) and HCC78 (lung adenocarcinoma) using the PrestoBlue cell viability assay and the SYTOX assay.
Results Over a period of one year, aliquots of purified magnetosomes were analyzed monthly. The size distribution, morphology and colloidal stability remained constant (overall particle diameter: month 1: 40.2±5.7 nm; month 12: 39.6±5.1 nm; zeta-potential: month 1: ‑35.8±3.4 mV; month 12: -35.7±3.7 mV). Due to potential oxidation effects, the saturation magnetization dropped to one-third of its initial value, however, the particles could still be efficiently attracted by magnetic fields. Magnetosomes exhibited a concentration-dependent effect on the viability. For the FaDu and HCC78 cell lines average viability values of 73 (67-91; month 12: 67)% (FaDu) and 73 (36-90; month 12: 58)% (HCC78) were determined for 50 μg Fe cm−2 and 48 h of incubation.
Conclusion Our investigations demonstrate that magnetosomes can be safely stored for at least one year as an aqueous suspension without significant quality deficits.