The search for chelate antagonists for chronic cadmium intoxication

Cadmium is unique among the metals because of its combination of toxicity in low dosages, long biological half-life (of about 30 years in humans), its low rate of excretion from the body and the fact that it is stored predominantly in the soft tissues (liver and kidney). There has been an increase in exposure to cadmium because its presence in fertilizers and sewage sludge and also its increased industrial use in Cd-Ni batteries. Although there are a number of reports on occupational and environmental exposures to cadmium compounds, treatment of cadmium poisoning has been difficult because there is neither a safe practical means of evaluating bioavailable body burden nor is there a recommended therapeutic chelating agent for chronic cadmium intoxication. In this review, the various factors affecting the chelation of cadmium such as its binding to intracellular metallothionein, the structural requirements of compounds for effective removal of cadmium, the excretion pattern of cadmium after its mobilization from intracellular stores and the recent developments in the design and synthesis of new compounds for cadmium chelation are discussed. The importance of protecting sensitive organs such as kidney and brain during cadmium chelation is addressed. The progress made during the last decade on the synthesis of new compounds, especially derivatives of dithiocarbamates, is remarkable. Some of these compounds provide promise for development of a useful and safe therapeutic chelating agent which can be used for the assessment of cadmium body burden and for preventive removal of cadmium as well as for use in overt cadmium poisoning in humans.