DDT exposure induces cell cycle arrest and apoptosis of skin fibroblasts from Indo-Pacific humpback dolphin via mitochondria dysfunction.

Abstract

Although the global use of the 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (p,p -DDT) has been prohibited, its persistence in the environment has caused long-lasting exposure on marine mammals. Our previous studies revealed exceedingly high residue levels of DDTs in Indo-Pacific humpback dolphins (Sousa chinensis) from the Pearl River Estuary region, China. However, the molecular mechanisms of p,p -DDT toxicity on the dolphin are largely unknown. This study conducted the first cytotoxicity effect exploration of p,p -DDT on the dolphin skin fibroblasts (ScSFs) to enhance the understanding of the cellular and molecular regulation impacts. ScSF cells were exposed to p,p -DDT (28∼168\u202fμM) for 24, 48 and 72\u202fh. The exposure remarkably decreased viability of ScSF cells, possibly due to the synergetic effects of cell cycle arrest and apoptosis via DNA damage and mitochondria dysfunction. The DNA damage and mitochondria dysfunction were likely triggered by an increase of cellular reactive oxygen species (ROS), alteration in mitochondrial membrane potential, reduction in the cellular ATP levels, decreased expression of the genes CDK1, CDK4, cyclin B1, cyclin D1 and apoptosis regulator Bcl-2, release of cytochrome c, and activation of caspase-3, caspase-8 and caspase-9. Moreover, caspase inhibitor displayed protective activity against p,p -DDT-induced apoptosis, indicating that caspases played a central role in p,p -DDT-triggered apoptosis in the ScSF cells. We hypothesize apoptosis likely plays a minor role in cytocidal effects induced by p,p -DDT exposure, but the mechanisms remain unclear. Overall, this research provides new evidence of the cytotoxic mechanisms underlying p,p -DDT exposure on humpback dolphin skin cells, and suggests that p,p -DDT contamination is one of key health concern issues for the protection of this marine mammal.