Physiological responses and expression of metallothionein (MT) and superoxide dismutase (SOD) mRNAs in olive flounder, Paralichthys olivaceus exposed to benzo[a]pyrene

We cloned complementary DNA (cDNA) encoding metallothionein (MT) and superoxide dismutase (SOD) from the liver of olive flounder, Paralichthys olivaceus. The full-length MT cDNA consists of 183 base pairs (bp) and encodes a protein of 60 amino acids; partial SOD cDNA consists of 326 bp and encodes a protein of 109 amino acids. We investigated the dose- and time-related effects of the polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) on MT and SOD mRNA using quantitative polymerase chain reaction (QPCR). The expression levels of MT mRNA were highest at 24 h (about five times) in 10 microg/L BaP, and at 6 h (about twelve times) in 30 microg/L BaP. The expression levels of SOD mRNA were highest at 12 h (about three times) in 10 microg/L BaP, and at 6 h (about six times) in 30 microg/L BaP, and then decreased toward the end of the experiment. We also measured plasma glucose and cortisol, all of which increased with BaP exposure. These results suggest that MT and SOD play an important role in the detoxification of reactive oxygen species (ROS) caused by BaP exposure, and thus may be indicators of oxidative stress responses.