Metallothionein as biomarker of metal exposure and disease in translational medicine

With the introduction of molecular biology techniques in medicine, new biochemical tools are available for determining a diagnosis. Transcriptional profiling and proteomics represent a major subject in translational clinical research. Metallothionein is a small molecular weight protein, having a strong affinity for heavy metals. However, despite to the increasing experimental data, the true function of this elusive protein remains to be identified. Due to the induction by a variety of stimuli, metallothioneins are considered valid biomarkers in environmental and medical fields. In this respect we present data related to the isolation and quantification of metallothionein in tissues of reptiles and mammals naturally exposed to heavy metals. In green turtles from the Caribbean Sea, copper-metallothionein in the liver was 10 times higher than the concentration found in the liver of loggerhead turtles from the Mediterranean Sea. As regards to mammals, the badger kidney metallothionein was rich in zinc, copper and cadmium, while in fox from the same area, only traces of the protein were found. These results are indicative of a different environmental metal exposure or a different mechanism in the control of metallothionein transcription. Moreover, in our laboratory, preliminary studies were conducted to evaluate the expression of metallothionein in mammary tumors of bitches. Western blotting patterns failed to identify the monomeric form of the protein; immunoreactive bands were present in correspondence of higher molecular weight molecules, which could be related to polymeric forms of metallothionein caused by disulphide bridges.