LAUSR

We recently synthesized ZnO nanomaterials (denoted as ZnO nanorods [NRs] and Mini‐NRs) and suggested that their cytotoxicity could be related with the activation of endoplasmic reticulum (ER) stress apoptosis. However, in a complex biological microenvironment, the ER stress‐apoptosis pathway could also be modulated by biological molecules, such as free fatty acids, leading to unpredicted biological effects. In this study, we investigated the combined toxicity of ZnO NRs/Mini‐NRs and palmitate (PA) to THP‐1 macrophages. PA influenced the zeta potential and solubility of ZnO NRs and ZnO Mini‐NRs in water, which indicated a change of colloidal stability. Exposure to ZnO NRs and Mini‐NRs dose‐dependent decreased cellular viability and release of soluble monocyte chemotactic protein 1 (sMCP‐1), and these effects were significantly promoted with the presence of PA. However, ZnO NR‐ and Mini‐NR‐induced intracellular Zn ions or reactive oxygen species were not significantly affected by PA. ZnO NRs and ZnO Mini‐NRs significantly promoted the expression of ER stress genes HSPA5, DDIT3, XBP‐1s and apoptotic gene CASP3, whereas PA also modestly promoted the expression of HSPA5, DDIT3 and CASP3. Interestingly, the ER stress inducer thapsigargin showed a similar effect as PA to promote the cytotoxicity of ZnO NRs and ZnO Mini‐NRs. It is suggested that PA might promote the cytotoxicity of ZnO NRs and ZnO Mini‐NRs possibly by promoting ER stress.