ABSTRACT
Metal ions such as lead and cadmium inhibit enzymes containing sulphydryl (thiol) moieties via mercaptide formation. Other endogenous ligands also contribute to binding in tissues. The aim of therapy is to administer relatively non-toxic compounds that bind toxic metal ions more strongly than cellular macromolecules, thus forming nontoxic complexes that may in turn be readily excreted (Aaseth, 1983; Jones, 1991; Klaassen, 1996). A range of chelating and other agents is used to treat poisoning with metal ions, in the treatment of metal storage diseases, in particular in Wilson’s disease (genetic caeruloplasmin deficiency), and in haemochromatosis, and to aid the elimination of metallic radionuclides from the body. A list of chelating agents and related compounds that have been suggested for clinical use is given in Table 2.1. A further non-water-soluble compound, potassium iron(III) hexacyanoferrate(II) (Prussian Blue), is given orally to sequester thallium in the intestine prior to elimination in faeces. A second metal-complexing agent, ammonium tetrathiomolybdate, has been suggested for use in symptomatic patients with Wilson’s disease, although Dpenicillamine is much more widely used in practice to treat this condition.
