Mechanisms of selective copper removal by tetrathiomolybdate from metallothionein in LEC rats

Copper (Cu) was selectively removed from metallothionein (MT) in the liver of LEC rats (Long-Evans rats with a cinnamon-like coat color) in vivo and in vitro by tetrathiomolybdate (TTM). Female LEC rats were injected intraperitoneally with TTM at a dose of 10 mg/kg body weight for 8 consecutive days. More than 2/3 of the Cu accumulating in the liver was removed by TTM treatment 24 h after the last injection. Although most Cu was bound to MT in the soluble fraction before TTM treatment, the Cu remaining in the liver was present almost exclusively in the non-soluble fraction together with molybdenum (Mo). Cu,Zn,Cd-MT was separated from the liver of LEC rats that had been injected with cadmium (Cd) and reacted with TTM at mol ratios of 0, 0.25, 0.50, 1.0, 2.0 and 4.0 to Cu bound to MT for 10 min at 37 degrees C. When TTM was added at a mol ratio of less than 1.0, a Cu,Zn,Cd-MT/TTM complex was detected, while addition of TTM at a mol ratio of greater than 1.0 selectively removed Cu from MT and produced a Cu/TTM complex via liberation of Zn,Cd-MT from the Cu,Zn,Cd-MT/TTM complex. Excessive TTM appeared to facilitate polymerization of the Cu/TTM complex to insoluble polymers. The dose-related formation of differing MT/TTM complexes explains the findings observed in vivo.