Susceptibility of MT-Null Mice to Chronic CdCl2-Induced Nephrotoxicity Indicates That Renal Injury Is Not Mediated by the CdMT Complex

Abstract

Chronic human exposure to Cd results in kidney injury. It has been proposed that nephrotoxicity produced by chronic Cd exposure is via the Cd-metallothionein complex (CdMT) and not by inorganic forms of Cd. If this hypothesis is correct, then MT-null mice, which cannot form CdMT, should not develop nephrotoxicity. Control and MT-null mice were injected sc with a wide range of CdCl2 doses, six times/week for up to 10 weeks, and their renal Cd burden, renal MT concentration, and nephrotoxicity were quantified. In control mice, renal Cd burden increased in a dose-and time-dependent manner, reaching as high as 140 μg Cd/g kidney, along with 150-fold increases in renal MT concentrations, reaching 800 μg MT/g kidney. In MT-null mice, renal Cd concentration (10 μg/g) was much lower, and renal MT was nonexistent. The maximum tolerated dose of Cd in MT-null mice was approximately one-eighth that of controls. MT-null mice were more susceptible than controls to Cd-induced renal injury, as evidenced by increased urinary excretion of protein, glucose, γ-glutamyl-transferase, and N-acetyl-β-D-glucosaminidase, as well as by increased blood urea nitrogen levels. Kidneys of Cd-treated mice were enlarged and histopathology showed various types of lesions, including proximal tubular degeneration, apoptosis, atrophy, interstitial inflammation, and glomerular swelling. These lesions were more severe in MT-null than in control mice, mirroring the biochemical analyses. These data indicate that Cd-induced renal injury is not necessarily mediated through the CdMT complex and that MT is an important intracellular protein in protecting against chronic Cd nephrotoxicity.