Disruptions in microtubule and mitochondrial dynamics as indicators for assessing nano- and microparticle toxicity

Nano- and microparticles (NMPs) hold great promise for applications in medicine, industry, and agriculture, but concerns about their impact on human health persist due to their small size and unique properties. This study investigates the cytotoxic effects of three representative NMPs: titanium dioxide (TiO₂), polystyrene (Psty), and a chitosan-based biopolymer (CSFe). Two of these (TiO₂ and Psty) are known for potential toxicity, while CSFe is less studied. Here, we examined the impact of these particles on two critical regulators of cellular homeostasis: microtubules and mitochondria. Cell viability assays revealed that CSFe particles were the least harmful, whereas TiO₂ and Psty particles, particularly the larger (0.5 μm) ones, which were significantly toxic. Interestingly, 0.2 μm Psty particles caused less toxicity than both smaller (0.1 μm) and larger Psty, likely due to lower cellular uptake. Further investigation showed that only CSFe and 0.2 μm Psty particles induced microtubule hyperacetylation, a stress response associated with cell survival. TiO₂ damaged microtubule networks without inducing hyperacetylation but altered the distribution of the +TIP protein CLIP-170, indicating impaired microtubule function and more particularly in growth rate capacity. Mitochondrial analysis revealed that CSFe did not affect mitochondrial morphology, while Psty (0.1 and 0.5 μm) caused fragmentation, a sign of cellular stress. TiO₂ had a milder impact. Overall, the study highlights the importance of particle size and composition in determining cellular impact and underscores the relevance of microtubules and mitochondrial alterations as markers of NMP toxicity.