Manganese in Diagnostics: A Preformulatory Study

Abstract

This investigation aims to find lipid-based nanosystems to be used as tools to deliver manganese for diagnostic purposes in multimodal imaging techniques. In particular, the study describes the production and characterization of aqueous dispersions of anionic liposomes as delivery systems for two model manganese-based compounds, namely manganese chloride and manganese acetylacetonate. Negatively charged liposomes were obtained using four different anionic surfactants, namely sodium docusate (SD), N-lauroylsarcosine (NLS), Protelan AG8 (PAG) and sodium lauroyl lactylate (SLL). Liposomes were produced by the direct hydration method followed by extrusion and characterized in terms of size, polydispersity, surface charge and stability over time. After extrusion, liposomes are homogeneous and monodispersed with an average diameter not exceeding 200 nm and a negative surface charge as confirmed by ζ potential measurement. Moreover, as indicated by atomic absorption spectroscopy analyses, the loading of manganese-based compounds was almost quantitative. Liposomes containing NLS or SLL were the most stable over time and the presence of manganese-based compounds did not affect their size distribution. Liposomes containing PAG and SD were instable and therefore discarded. The in vitro cytotoxicity of the selected anionic liposomes was evaluated by MTT assay on human keratinocyte. The obtained results highlighted that the toxicity of the formulations is dose dependent.

Synthetic and Nanotechnological Approaches for a Diagnostic Use of Manganese

“…To this aim, the ζ potential of unloaded and MP-loaded LS and LN was measured, with MP being the more hydrophilic manganese complex here considered. Notwithstanding the maintenance of a net negative charge of the systems, the obtained results confirmed previous published data [ 16 ] and indicated a reduction in ζ potential after MP loading, from −67.12 ± 0.64 mV to −51.18 ± 1.83 mV for LS and from −57.77 ± 0.26 mV to −49.21 ± 1.42 mV for LN, corroborating our hypothesis and the data obtained for liposomes loaded with manganese chloride [ 16 ].…”

“…In our previous study, a pre-formulatory study allowed us to select NLS and SLL as optimal anionic surfactants for the delivery of both hydrophilic and lipophilic manganese-based compounds [ 16 ].…”

“…In order to verify the association of the different compounds with the lipid bilayer of vesicles, ultracentrifugation was used to separate the lipid phase from aqueous phase, and the amount of Mn ions in the lipid phase was quantified. Indeed, as recently discussed, manganese was successfully encapsulated into anionic liposomes and retained by its lipid portion possibly intercalated or associated to the phospholipid bilayer, depending on the hydrophilic or lipophilic characteristics of the complex [ 16 ]. Indeed, FT-IR spectroscopy analysis revealed that hydrophilic complexes could establish electrostatic interactions between Mn 2+ and the negatively charged phospholipid surface.…”

“…The preliminary study conducted on plain LP and unloaded LN and LS demonstrated the safety of the formulations at different concentrations with a dose-dependent profile [ 16 ]. In this study, with the aim of verifying the effect of the encapsulated complexes in LN and LS aimed at screening of the formulations, HaCaT cells were selected as a human nontumor cell line.…”

“…A potential strategy to exploit manganese bimodal contrast properties by limiting the drawback of a poor water solubility is represented by their loading into liposomes, known for their wide range of applications in the biomedical field, including in diagnostics and theranostics [ 12 , 13 , 14 , 15 ]. Accordingly, we recently reported a pre-formulation study of anionic liposomes as delivery systems for manganese [ 16 ].…”