Silica dioxide nanoparticles combined with cold exposure induce stronger systemic inflammatory response

Growing concern has been raised over the potential hazard of nanoparticles (NPs) on human health from ambient particulate air pollution. Silicon dioxide (SiO₂) NPs are one of the most widely used nanoparticles in many sectors of industry. Research on NPs has focused mainly on their toxicity in organs. Meanwhile, NPs are present in the air year-round, but are more serious in winter. Thus, the aim of this study was to evaluate the inflammatory response to SiO₂ NPs using in vivo test systems. The composition of particulate matter is complicated; however, elemental silicon accounts for a significant proportion. Cold exposure can induce many kinds of systemic reactions. Thus, the second aim of this study was also to evaluate the combined effect of NPs and cold exposure on human health. There is little research on the combined effects of nanoparticles and cold on inflammation. Sprague-Dawley rats were randomly divided into four groups: those exposed to SiO₂ NPs by intratracheal instillation, those exposed to at 4 °C 4 h/day for 4 weeks, a combined SiO₂ NPs and cold exposure group, and a control group. Inflammatory cell infiltration in the lungs was mainly observed after exposure to SiO₂ NPs or cold. Hematoxylin and eosin staining revealed that inflammation of the lungs was more serious in the combined group. In the white adipose tissue and brown adipose tissue of the combined groups, the mRNA expressions of pro-inflammatory cytokines were upregulated. In conclusion, SiO₂ NPs combined with cold exposure induced a stronger systemic inflammatory response, accompanied by more serious health hazards.