Cytotoxic Effects of ZnO and Ag Nanoparticles Synthesized in Microalgae Extracts on PC12 Cells

The green synthesis of silver (Ag) and zinc oxide (ZnO) nanoparticles (NPs), as well as Ag/Ag₂O/ZnO nanocomposites (NCs), using polar and apolar extracts of <i>Chlorella vulgaris</i>, offers a sustainable method for producing nanomaterials with tunable properties. The impact of the synthesis environment and the nanomaterials' characteristics on cytotoxicity was evaluated by examining reactive species production and their effects on mitochondrial bioenergetic functions. Cytotoxicity assays on PC12 cells, a cell line originated from a rat pheochromocytoma, an adrenal medulla tumor, demonstrated that Ag/Ag₂O NPs synthesized with apolar (Ag/Ag₂O NPs A) and polar (Ag/Ag₂O NPs P) extracts exhibited significant cytotoxic effects, primarily driven by Ag⁺ ion release and the disruption of mitochondrial function. However, it is more likely the organic content, rather than size, influenced anticancer activity, as commercial Ag NPs, despite smaller crystallite sizes, exhibit less effective activity. ZnO NPs P showed increased reactive oxygen species (ROS) generation, correlated with higher cytotoxicity, while ZnO NPs A produced lower ROS levels, resulting in diminished cytotoxic effects. A comparative analysis revealed significant differences in LD₅₀ values and toxicity profiles. Differentiated PC12 cells showed higher resistance to ZnO, while AgNPs and Ag/Ag₂O-based materials had similar effects on both cell types. This study emphasizes the crucial role of the synthesis environment and bioactive compounds from <i>C. vulgaris</i> in modulating nanoparticle surface chemistry, ROS generation, and cytotoxicity. The results provide valuable insights for designing safer and more effective nanomaterials for biomedical applications, especially for targeting tumor-like cells, by exploring the relationships between nanoparticle size, polarity, capping agents, and nanocomposite structures.