The effects of combined exposure to nano-plastics and cadmium on Chinese soft-shelled turtle embryo fibroblasts.

Cadmium (Cd) is a persistent heavy metal pollutant that accumulates in aquatic organisms and poses severe threats to reptiles. Meanwhile, nano-plastics (NPs), as emerging contaminants, have been detected extensively in aquatic environments and can act as carriers for other pollutants. This study employed Chinese soft-shelled turtle embryonic fibroblast (CSSTEF) as an in vitro model to investigate the individual and combined toxicological effects of Cd and NPs. The objectives were to determine the half-maximal inhibitory concentration (IC50) of Cd in CSSTEF cells, evaluate the cytotoxic interactions between Cd and NPs through multiple endpoints including cell viability, membrane integrity, and oxidative stress biomarkers, and elucidate the underlying molecular mechanisms using transcriptomic and model analyses. Our results demonstrated that Cd exhibited concentration-dependent cytotoxicity with an IC50 value of 102.9 μM at 72 h exposure. Both Cd exposure and combined exposure obviously altered cell morphology and exacerbated oxidative stress. Under combined exposure, antagonistic effects were observed on superoxide dismutase (SOD), catalase activities (CAT) and lactate dehydrogenase (LDH), while additive effects were detected on glutathione S-transferase (GST). Transcriptomic analysis revealed significant enrichment of pathways related to glycosaminoglycan biosynthesis and extracellular matrix (ECM) receptor interactions in the Cd and NPs combined exposure group, indicating activated extracellular matrix metabolism and cellular stress responses. Quantitative real-time polymerase chain reaction confirmed the differential expression of key genes involved in these pathways. These findings establish CSSTEF cells as a valuable model for reptilian toxicology research and highlight the necessity of multi-biomarker approaches in assessing the risks of contaminant mixtures in freshwater ecosystems relevant to turtle conservation.