The interactions of penicillamine with copper in vivo and the effect on hepatic metallothionein levels and copper/zinc distribution: the implications for Wilson's disease and arthritis therapy.

D-penicillamine does not remove copper from metallothionein, but it has been suggested that it may increase hepatic metallothionein levels. D-penicillamine was shown to increase rat hepatic metallothionein levels; however, the effect was dependent on an interaction with copper. The drug accelerated the excretion of exogenous copper but increased the amount retained on metallothionein. This interaction of penicillamine and copper also provoked changes in the distribution of zinc and in particular an increase in the heat-stable cytosol zinc fraction. In contrast, thiomolybdates were much more effective in eliminating exogenous copper and even removed copper that was already bound to metallothionein; thus, the copper level in the heat-stable cytosol fraction decreased. The observations support the view that patients with Wilson's disease may not be truly "decoppered" but that treatment with d-penicillamine is effective because the accumulated copper in the liver is bound in a nontoxic form by the increased metallothionein. The results explain why cessation of treatment is dangerous. The results may also partially explain the effectiveness of D-penicillamine copper chelates as antiinflammatory drugs.