Effects of multi-walled carbon nanotube (MWCNT) on antioxidant depletion, the ERK signaling pathway, and copper bioavailability in the copepod (Tigriopus japonicus)

Multi-walled carbon nanotubes (MWCNTs) are nanoparticles widely applicable in various industrial fields. However, despite the usefulness of MWCNTs in industry, their oxidative stress-induced toxicity, combined toxicity with metal, and mitogen-activated protein kinase (MAPK) activation have not been widely investigated in marine organisms. We used the intertidal copepod Tigriopus japonicus as a test organism to demonstrate the adverse effects induced by MWCNTs in aquatic test organisms. The dispersion of the MWCNTs in seawater was maintained over 48 h without aggregation. MWCNTs caused a decrease in acute copper toxicity compared to the copper-only group in response to 20 and 100 mg/L MWCNTs, but not in response to 4 mg/L MWCNT, indicating that MWCNT may suppress acute copper toxicity. Reactive oxygen species (ROS) and enzymatic activities of glutathione S-transferase (GST) and catalase were significantly down-regulated in response to 100 mg/L MWCNT exposure. Glutathione (GSH) and glutathione reductase (GR) activity did not change significantly, indicating that MWCNTs may cause failure of the antioxidant system in T. japonicus. However, MWCNT induced extracellular signal-regulated kinase (ERK) activation without p38 and c-jun NH2-terminal kinase (JNK) activation, suggesting that ERK activation plays a key role in cell signaling pathways downstream of CNT exposure. This suggests that this pathway can be used as a biomarker for CNT exposure in T. japonicus. This study provides a better understanding of the cellular-damage response to MWCNTs.