New In Vitro Model to Evaluate Nanomaterial-Induced Adverse Effects on CNS: 3D Spheroids from Human Neuronal- and Astrocyte-like Cells

The rapid spread of nanotechnology raises serious questions about its impact on the population’s health and the environment. Thousands of nanoproducts are already available on the market, raising concerns of extensive consumer exposure by different routes. Several studies have already pointed to possible respiratory and cardiovascular system damage following nanoparticle (NPs) exposure, other studies have also looked at NP impact on the highly vulnerable nervous system. Available evidence suggests incomplete effectiveness of blood brain barrier (BBB) protection of the brain against NPs translocation. Regardless of the route of exposure, NPs could reach the blood and translocate to brain. The distribution of NPs in the bloodstream raises also a particular concern of NP transfer from placenta to the fetal CNS and because BBB develops gradually in the fetal brain this type of direct exposure to NP in utero may have the most damaging consequences. A recognized need is to combine nanotoxicology and neurology and calls for novel specific tools and investigation methods for this discipline. Although standardized procedures for the evaluation of NPs toxicity have not yet been defined, the integration of validated in vitro-studies into safety assessment strategies is claimed by several Institutions. Moreover, the increasing number of newly developed NPs entering the production and use quickly, in combination with the growth in societal risk aversion, is forcing gradually but steadily the shift from the traditional in vivo toxicological approaches towards alternative testing strategies including in vitro assays. The majority of current in vitro investigations for the assessment of NPs neurotoxicity are performed mainly in 2D cell cultures. With the advent of three dimensional (3D) cell culture models, in vitro studies are now mimicking better the mammalian tissues properties in many features including recreate aspects of the spatial and mechanical environmental of the tissue, permitting cells to interact. Additionally, the 3D spheroid model allows for detection of effects caused not only after short-term by even longer (and repeated) exposure of lower compound concentrations, which appears frequently in vivo. They also allow evaluating long–lasting effects which may derive from an acute exposure. Another advantage of applying the 3D cell culture in high-throughput (HT)-friendly 96-well format is the possibility for real-time monitoring of the effects during the multiple re-dosing of the tested compound. Two types of CNS cell spheroid models are now being developed and optimised using astrocytes and neurons of human origin for investigating CNS injury caused by neurotoxicants: (i) 3D neuronal- and astrocyte-like spheroids derived from human brain SH-SY5Y and D384 cell lines, respectively (ii) 3D human neurospheres differentiated from mesenchymal stem cells (hMSCs) isolated and expanded from umbilical cords obtained from full-term infants.