The role of metallothionein in the elevated excretion of copper in urine from people living in a cadmium-polluted area

Abstract

Gel chromatographic analysis of urine specimens obtained from three women environmentally exposed to cadmium (Cd) was carried out to study the relationship between urinary excretion of heavy metals and metallothionein (MT). In one of the three Cd-exposed women MT was detected in the fraction corresponding to molecular weight of about 10,000 (MT-F) by radioimmunoassay, and Cd and copper (Cu) peaks were also observed in the MT-F. However, in the other two Cd-exposed women no metal peak was found in the MT-F although MT alone was detected in it. When urine speciments from these subjects were treated with 2-mercaptoethanol before chromatography, appreciable amounts of Cd and Cu were recovered in the MT-F. In a sample to which dithiothreitol was added at the time of urine collection more than 60% of both Cd and Cu were recovered in the MT-F. These results support the suggestion that MT is so susceptible to oxidation that metals bound to MT can be released from it and distribute in high or low molecular weight fractions. It is also suggested that most urinary Cd and Cu is excreted with MT and that MT is directly involved in the increased excretion of these metals, espcially Cu, in people environmentally exposed to Cd.