Mitochondrial dysfunction and DNA damage reveal nanoplastic-induced cytotoxicity in the sea cucumber Apostichopus...

Nanoplastics (NPs), as an emerging class of pollutants, have become pervasive in marine environments due to the fragmentation of larger plastic debris and intentional production for industrial applications. In this study, we investigated the cytotoxic effects of NPs on intestinal and respiratory tree cells of the sea cucumber Apostichopus japonicus, focusing on oxidative stress, mitochondrial integrity, and DNA damage. Cells were exposed to 100 nm NPs dispersed in culture media at concentrations of 0.1, 1.0 and 10.0 μg mL^-1 for 24 h, with untreated cells serving as the control. Transmission electron microscopy revealed progressive cell membrane rupture, extensive vacuolation, and the presence of bilayered autophagy-like structures and monolayered lysosome-like vesicles following NP exposure. TUNEL assays revealed a significant increase in TUNEL-positive DNA fragmentation across PS-NP exposure levels, suggesting enhanced apoptosis-like cell death. A 1.0-1.4-fold increase in ROS production confirmed that NPs induced significant oxidative stress. Mitochondrial disruption was evident by increased ADP levels and reduced ATP content, oxygen consumption rate, and activities of respiratory chain complex I-V, suggesting impaired oxidative phosphorylation. Transcriptomic analysis further supported the involvement of mitochondrial pathways in NP-induced apoptosis. Moreover, after 24 h of exposure, both olive tail moment (with an 8.0-11.8-fold increase) and DNA-protein crosslinking (25.7-30.2%) were markedly elevated, even at the lowest NP concentration of 0.1 μg mL^-1, demonstrating substantial genotoxic effects. Overall, NPs induced cytotoxicity and apoptosis in A. japonicus cells in a dose-dependent manner, with time-dependent changes in mitochondrial function. These findings highlight the sensitivity of A. japonicus cells to nanoplastic exposure and propose cellular response indicators such as ROS accumulation, ATP/ADP imbalance, and MPTP opening as potential biomarkers for ecological risk assessment in marine benthic systems.