Immunolocalization of Metallothionein in Different Tissues of Fresh Water Catfish, Clarias Gariepinus on Exposure to Cadmium

Metallothionein (MT) is a cysteine-rich protein that binds to heavy metals, and it is induced by them. The objective of this study to identify the MT protein induction/expression and localization in liver and kidney tissues (treated with 20 mg/L of CdCl2 for 72 hours) by immunohistochemical techniques and Western Blotting methods in the fresh water catfish, Clarias gariepinus. MT expression (MT-I and MT-II) levels were analyzed by Western blot method (using Mouse Monoclonal Anti-Metallothionein primary and Horseradish Peroxidase (HRP) secondary antibody). MT bands were detected using enhanced chemiluminescence system (West Femto Super Signal detection kit, Thermo Scientific Inc. USA) method. Antibodies showed a positive cross reactivity with MT proteins, MT immune activity was high in the cytoplasm of hepatocytes in Cd exposed fish liver and also detected in the nephrocytes present in the proximal tubules of the nephron and more precisely in their basal labyrinth in kidney. Western blotting showed increased MT expression levels in Cd treated tissues when compared with control tissue. The differential induction/localization of MTs in different cell types described in this study suggests that the presence and quantification of MT can be used in biomonitoring programs as a biomarker of Cd exposure in aquatic environments. INTRODUCTION Cadmium is a toxic heavy metal, which is a common pollutant of aquatic medium. Organisms like fish living in contaminated aquatic systems can absorb this heavy metal, show bioaccumulation, damaged tissues, vertebral alterations, necrosis and ultimately apoptosis and death 1 . The release of discharge of large number of pollutants, especially heavy metals and pesticides, pose a threat to human life 2 . The water pollution is no longer considered to be an aesthetic problem, but a serious economic and public health problem as well.