Characterization of Metallothionein from Asian Sea Bass (Lates calcarifer,Bloch) and Application as a Biomarker for Heavy Metal Exposure in Thailand

Abstract

In the present study, metallothionein (MT) proteins and cDNA were isolated from Asian sea bass (Lates calcarifer) livers. Immunochemical protocols (i.e. an enzyme-linked immunosorbent assay (ELISA) and Western blot) were developed for quantification of MT protein levels in Asian sea bass. These were applied to analyze MT protein levels in 15 different feral fish species from two different areas, one urban area Angsila and one industrial area Map Ta Phut in the Gulf of Thailand. An MT protein band was detected in Shrimp scad (Alepes djadaba) and Indian ilisha (Ilisha melastoma) from both areas. Higher MT protein expressions were seen in shrimp scad from cadmium-contaminated areas near shore as well as off shore. These results suggest that induction of hepatic MT immunoreactive proteins in the shrimp scad may be a good early warning signal for heavy metal exposure in environmental monitoring programmes in Thailand waters. Protocol for quantification of MT mRNA levels in Asian sea bass was developed using quantitative PCR. Asian sea bass were exposed in the lab to different doses of CdNO $_3$ and sampled at different times after injection. There appears to be a bi-phasic dose-response pattern with highest MT mRNA levels in fish injected with 4 mg CdNO $_3$ /kg. In these fish, the highest expression was seen after one day and lowest induction after three days. These results suggest that induction of MT mRNA levels in Asian sea bass liver can be used as a sensitive early warning signal for cadmium exposure in tropical waters.