Zinc-Based Nanoparticles, but Not Silicon-Based Nanoparticles, Accumulate in Mitochondria and Promote Cell Death in Liver Cancer Cells.

Introduction: Hepatocellular carcinoma (HCC) is the main hepatic primary malignancy. Patients with advanced HCC receiving the recommended therapies have a poor outcome. In different settings, nanotechnology has gained attraction as a potential alternative strategy for improving therapeutic effectiveness. Among several nanoparticles (NPs), inorganic NPs, such as zinc and silicon oxides (ZnO and SiO₂), are mainly chosen as drug nanocarriers, as both present great adsorption properties and biocompatibility.

Aim: The objective is to identify the molecular mechanisms underlying the proapoptotic effects of ZnO and SiO₂ NPs in differentiated hepatoblastoma cells (HepG2) and mesenchymal liver cancer cells (SNU449).

Methods: Dose-dependent induction of cell cytotoxicity by ZnO and SiO₂ NPs (5 to 50 µg/mL) was determined in HepG2 and SNU449 cells. NPs intracellular localization was assessed using transmission electron microscopy (TEM). Cell death was determined by trypan blue staining and caspase-3 and -8 activities. Cell respiration was determined using MitroStress assay (Seahorse, Agilent).

Results: ZnO NPs, but not SiO₂ NPs, reduced cell viability in HepG2 and SNU449. Interestingly, SNU449 appeared to be more susceptible than HepG2 to ZnO NPs (IC50 of 27.4 ± 1.4 µg/mL and 41.8 ± 0.4 µg/mL, respectively). SiO₂ NPs tended to be localized in lysosomes in both cell lines, while ZnO NPs demonstrated a random distribution with a high presence in mitochondria and related structures. As expected, SiO₂ NPs did not reduce cell survival and cell respiration, while ZnO NPs promoted cell death and decreased oxygen consumption rate. ZnO NPs mitochondrial accumulation was associated with increased apoptosis in HepG2, while necroapoptosis was mainly involved in ZnO-induced cell death in SNU449.

Conclusion: SiO₂ demonstrated no cytotoxic profile against liver cancer cells. ZnO NPs demonstrated to accumulate in mitochondria impacting cell respiration and cell death in liver cancer cells. ZnO induced apoptosis and necroptosis in HepG2 and SNU449, respectively.