Cadmium (Cd) is an environmental pollutant with high toxic potential. Over half of the body burden of Cd is concentrated in liver and kidney and bound to metallothionein (MT). MT is a low molecular weight, cysteine-rich metal-binding protein. The long-term goal of the research is to explore the mechanism of Cd toxicity and the role of MT in the toxicity of Cd. The target organ of toxicity for acute Cd exposure is liver, while kidney is the target organ of chronic exposure. The current theory holds that Cd-induced nephrotoxicity is mediated through the Cd-metallothionein (CdMT) complex which """"""""leaks"""""""" out of the liver and is taken up by the kidney to produce renal toxicity. However, a single CdMT injection model does not mimic, in many aspects, the nephrotoxicity produced by human chronic exposure to the metal. Therefore, the first aim (1) is to test the hypothesis that Cd-induced nephrotoxicity is not necessarily mediated through CdMT, and a single injection of CdMT is not an appropriate model to study chronic Cd nephropathy.
This aim i s essential so that efforts will not be directed at the mechanism of acute CdMT -induced nephrotoxicity, if it has no relevance to human exposure. In the second (2) aim, the hypothesis that MT protects against chronic Cd-induced renal injury as well as other toxic effects will be tested. Using MT-null mice, which are identical to control mice but cannot synthesize MT, the role of MT in chronic Cd toxicity will be determined with certainty. In the third (3) aim, the link between chronic Cd exposure, oxidative stress, and renal injury will be explored via (a) urine analysis (urinary lipid metabolites vs proteinuria, glucosuria and enzymuria), (b) blood analysis (serum tumor necrosis factor-alpha, interleukin-1 and interleukin-6 vs blood urea nitrogen), (c) histology (localization of 4-hydroxynonenal- and malondialdehyde-adducts vs histopathology), (d) tissue analysis (antioxidant components vs tissue Cd content), and (e) electron paramagnetic resonance (ESR)-spin trapping to detect free radical metabolites generated in vivo during chronic Cd exposure. These studies with MT-null mice will determine the role of MT in chronic Cd nephrotoxicity and other toxicities and will be helpful in developing strategies for treating Cd poisoning as well as setting criteria for the protection of human health.
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