Titanium Dioxide Nanoparticles Disturb the Fibronectin-Mediated Adhesion and Spreading of Pre-osteoblastic Cells

In the context of rapid development of nanoparticles (NPs) for industrial applications, the question of their toxicity and biological effects must be considered. In this work, we have assessed the influence of titanium dioxide NPs on the adhesion and spreading of MC-3T3 pre-osteoblasts by using a cell subclone that does not produce its own extracellular matrix. Petri dishes were coated with the important adhesion protein fibronectin (Fn). By incubating these Fn-coated surfaces with different amounts of TiO₂ NPs, we have shown that the adhesion of pre-osteoblasts is disturbed, with an important decrease in the number of adherent cells (from 40 to 75% depending upon the concentration and type of NPs). Petri-dish surfaces were analyzed with environmental scanning electron microscropy (ESEM), with images showing that TiO₂ NP aggregates are bound to the layer of adsorbed Fn molecules. The cells cultured on these Fn/NP surfaces adopted an irregular shape and an aberrant organization of actin cytoskeleton, as revealed by fluorescence microscopy. Most importantly, these results, taken together, have revealed that the actin cytoskeleton forms abnormal aggregates, even on top of the nucleus, that coincide with the presence of large aggregates of NPs on top of cells. On the basis of these observations, we propose that some Fn molecules are able to desorb from the Petri dish surface to coat TiO₂ NPs. Fn/NP complexes are not attached firmly enough on the surface to allow for normal cell adhesion/spreading and the development of tense actin fibers. These results stress the paramount need for the assessment of the toxicology of NPs, with special attention to their interactions with biomolecules

Topological Effects and Binding Modes Operating with Multivalent Iminosugar-Based Glycoclusters and Mannosidases

Multivalent iminosugars have been recently explored for glycosidase inhibition. Affinity enhancements due to multivalency have been reported for specific targets, which are particularly appealing when a gain in enzyme selectivity is achieved but raise the question of the binding mode operating with this new class of inhibitors. Here we describe the development of a set of tetra- and octavalent iminosugar probes with specific topologies and an assessment of their binding affinities toward a panel of glycosidases including the Jack Bean α-mannosidase (JBαMan) and the biologically relevant class II α-mannosidases from <i>Drosophila melanogaster</i> belonging to glycohydrolase family 38, namely Golgi α-mannosidase ManIIb (GM) and lysosomal α-mannosidase LManII (LM). Very different inhibitory profiles were observed for compounds with identical valencies, indicating that the spatial distribution of the iminosugars is critical to fine-tune the enzymatic inhibitory activity. Compared to the monovalent reference, the best multivalent compound showed a dramatic 800-fold improvement in the inhibitory potency for JBαMan, which is outstanding for just a tetravalent ligand. The compound was also shown to increase both the inhibitory activity and the selectivity for GM over LM. This suggests that multivalency could be an alternative strategy in developing therapeutic GM inhibitors not affecting the lysosomal mannosidases. Dynamic light scattering experiments and atomic force microscopy performed with coincubated solutions of the compounds with JBαMan shed light on the multivalent binding mode. The multivalent compounds were shown to promote the formation of JBαMan aggregates with different sizes and shapes. The dimeric nature of the JBαMan allows such intermolecular cross-linking mechanisms to occur

Correction to “Topological Effects and Binding Modes Operating with Multivalent Iminosugar-Based Glycoclusters and Mannosidases”

Correction to “Topological Effects and Binding Modes Operating with Multivalent Iminosugar-Based Glycoclusters and Mannosidases