Lead (Pb) toxicity is the most common preventable disease in the pediatric age group today in the United States. In its 1988 report to Congress, the U.S. Public Health Service estimated that 5 million or more young children are at high risk from all sources of Pb, including food, drinking water, dust, dirt and gasoline, and paint. Unfortunately, this disease will continue for many years, because there are still over 40 million dwellings nationally that contain hazardous quantities of leaded paint. Numerous studies have investigated the actions of chelating agents on lead metabolism in animals and humans, including selective removal from soft tissues and the skeleton, and altered tissue deposition of metal-chelator complexes. The most critical measure(s) of chelator efficacy are the ability to (a) reduce cellular lead burden, (b) restore or prevent Pb- induced loss of cell function, and (c) not produce adverse effects by interfering with homeostasis and utilization of essential trace elements. Little is currently known regarding the action of meso-2,3- dimercaptosuccinic acid (DMSA), an orphan chelating drug, on cellular lead metabolism. The questions to be addressed in this application include, How much lead must be removed, and from which subcellular kinetic pool, to provide restoration of biochemical function (porphyrin, heme, and osteocalcin production) to the cells? together, these experiments will test the hypothesis that DMSA will decrease the cellular burden of lead in critical target within kinetically distinct intracellular kinetic pools of lead, and that reduction the amount of lead in these pools leads to a selective restoration of cell function. The experiments will be conducted in cultured renal proximal tubule cells (PCT) and in clonal osteoblastic bone cells (ROS 17/2.8).
Three specific aims are to: 1. Characterize and compare the ability of DMSA to reduce the cellular burden of lead by evaluating the action of DMSA on the steady state kinetics of 210Pb in cultured renal tubule and osteoblastic bone cells. 2. Characterize the potential for DMSA to increase movement of Pb2+ into cells by evaluating the steady state kinetics of 210Pb administered as the 210Pb-DMSA complex, in cultured renal tubule and osteoblastic bone cells. 3. Characterize the ability of DMSA to restore cellular function in lead intoxicated cells by evaluating the restoration of porphyrin and hemoprotein production in renal tubule and osteoblastic bone cells, and the recovery of osteocalcin production in osteoblasts. In summary, this project will characterize the ability of DMSA to reduce the subcellular burden of lead in two important target cells for lead toxicity using a kinetic model for 210Pb metabolism and correlate these changes in intracellular lead metabolism with three important biochemical and clinical measures of lead toxicity. These studies will (a) contribute to understanding the basic mechanisms and processes of chelator action at the cellular level, (b) provide a basis for designing more effective and safer chelating drugs, and (c) provide a link between chelator action at the cellular level with clinical and animal studies.
