Monitoring of metallothionein level in cancer tissue cultures exposed to cadmium

Introduction: The association of heavy metal exposure and the risk of cancer is known. Arsenic, cadmium, chromium and nickel have been formally classified as carcinogens. Heavy metals are thought to promote cancer by a number of common mechanisms, e.g. formation of free radicals, influence of cell control via alteringgene regulation etc. Heavy metals are also strong co-carcinogens, promoting synergistic effects in the presence of other carcinogenic agents. Metallothioneins (MT) are low-molecular mass proteins capable of binding to heavy metals. They are involved in transporting and/or detoxifying metal ions. It is also known that MTs contribute to the development of resistance to heavy metal-based cytostatics. Apart from heavy metal homeostasis and detoxification, their regulatory functions in many cell processes, e.g. apoptosis inhibition, transcription and enzyme regulation are known. It is assumed that heavy metal-induced metallothioneins serve as a host-derived factor in malignant diseases and closely relate to metastasis.

Aims: the aim of this research was to determine metallothionein levels in human fibroblast cell cultures (derived from an individual with cancer) exposed to cadmium.

Materials and methods: BR-175 (tumour) and BR-142 (control) human fibroblast cell cultures were exposed to CdNO3 in concentrations 0, 1, 5 and 10 uM. In intervals of 0, 1, 3, 6, 12 and 24 hours the cells were harvested. MT level was determined by using Western blotting, Dot-Immunobinding Assay (DIA) and Differential-Pulse Voltammetry-Brdicka reaction (DPV).

Results: MT levels determined in studied cell lines were within the range from 180 to 48.900 ug/mg of the soluble proteins. We observed a different behaviour of tumour cells in response to heavy metal exposure compared to controls. In control cells (0 uM Cd2+) MT levels were 2-3 mg/g of soluble proteins and did not change over time compared to treated cells, in which we observed a marked enhancement of MT level even after one hour long treatment. Compared to controls (BR 142) the MT level was three-times greater in tumour cells (BR 175) at the beginning of the experiment. The increase in MT content in BR 142 cells exhibited a linear trend over time, while for BR 175 cells MT induction was faster, but with prolonged exposure, MT content in tumour cell was below 75 % compared to control cells in relation to Cd concentration.

Conclusions: The increase in MT synthesis and different kinetics of MT induction after cadmium exposure in tumour cells in comparison to controls, found by analytical methods used, indicates a possible role of MT in carcinogenesis and metastasis

Acknowledgement: This project was supported from grants Liga proti rakovine and KAN208130801.