In vitro toxicity evaluation of engineered cadmium-coated silica nanoparticles on human pulmonary cells

Cytotoxicity of cadmium-containing silica nanoparticles Cd-SiO ₂NPs (0.05-100 μg/mL) versus SiO₂NPs and CdCl ₂ was evaluated by an in vitro test battery in A549 by assessing (i) mitochondrial function, (ii) membrane integrity/cell morphology, (iii) cell growth/proliferation, (iv) apoptotic pathway, (v) oxidative stress, after short- (24-48 h) and long-term (10 days) exposure. Both Cd-SiO₂NPs and CdCl₂ produced dose-dependent cytotoxic effects: (i) MTT-assay: similar cytotoxicity pattern was observed at both 24 and 48 h, with a more Cd-SiO₂NPs pronounced effect than CdCl₂. Cd-SiO ₂NPs induced mortality (about 50%) at 1 g/mL, CdCl₂ at 25 g/mL; (ii) calcein-AM/PI staining: decrease in cell viability, noticeable at 25 g/mL, enhanced markedly at 50 and 100 g/mL, after 24 h. Cd-SiO₂NPs induced higher mortality than CdCl₂ (25% versus 4%, resp., at 25 g/mL) with further exacerbation after 48h; (iii) clonogenic assay: exposure for longer period (10 days) compromised the A549 proliferative capacity at very low dose (0.05 g/mL); (iv) a progressive activation of caspase-3 immunolabelling was detected already at 1 g/mL; (v) GSH intracellular level was modified by all compounds. In summary, in vitro data demonstrated that both Cd-SiO ₂NPs and CdCl₂ affected all investigated endpoints, more markedly after Cd-SiO₂NPs, while SiO₂NPs influenced GSH only.