Renal cadmium deposition and injury as a result of accumulation of cadmium-metallothionein (CdMT) by the proximal convoluted tubules--A light microscopic autoradiography study with 109CdMT.

Chronic, but not acute, exposure to inorganic Cd produces renal damage. However, a single injection of cadmium bound to metallothionein (CdMT) produces renal injury. It is hypothesized that an interorgan redistribution of Cd as CdMT is responsible for the chronic nephrotoxic effect of Cd. To better understand the mechanism(s) of CdMT-induced nephrotoxicity, the intrarenal distribution of 109CdMT was examined. 109CdMT isolated from rat liver was injected into mice at a nonnephrotoxic dose (0.1 mg Cd/kg, iv). The radioactivity in the kidney reached a maximum level (85% of the dose) as early as 30 min following administration and remained essentially constant for up to 7 days after injection. Within the kidney, 109Cd distributed almost entirely to the cortex. Light microscopic autoradiography of the kidney showed that, within the cortex, 109Cd distributed preferentially to the S1 and S2 segments of the proximal convoluted tubules. Within the S1 and S2 segments, the concentration of 109Cd in the basal and apical parts of the cells was similar to that after the nonnephrotoxic dose of CdMT, but after a nephrotoxic dose (0.3 mg Cd/kg) the radioactivity distributed preferentially to the apical portion of the cells. In contrast, light microscopic autoradiography studies with 109CdCl2 revealed that 109Cd was more evenly distributed throughout the proximal tubules. Moreover, after administration of a large dose of inorganic Cd (3 mg Cd/kg), a similar concentration of Cd was found in the convoluted and straight proximal tubules. These data support the hypothesis that CdMT-induced nephrotoxicity might be due, at least in part, to its preferential uptake of CdMT into the S1 and S2 segments of the proximal tubules, the site of Cd-induced nephrotoxicity.

Carbon tetrachloride-induced hepatotoxicity: studies in developing rats and protection by zinc.

This investigation was designed to evaluate carbon tetrachlorid (CCl4)-induced hepatotoxicity in developing rats and in adult rats pretreated with zinc. Hepatotoxicity of CCl4 in rats as young as 4 days of age was similar to that in adults. However, CCl4 metabolism, measured by in vitro binding of 14CCl4 to hepatic microsomal protein and lipid, was significantly lower in 4- and 14-day old rats than in adults. The sensitivity of young animals to CCl4 toxicity may be due to metabolic ketosis since blood concentrations of acetoacetate were 3-5 times higher in young rats than in adult animals. It has previously been shown that adult rats are more sensitive to CCl4 toxicity when they are in the ketonic state. The protection from CCl4 toxicity that was afforded adult rats pretreated with zinc was determined to be independent of the effect of zinc on CCl4 metabolism. Since treatment with zinc results in a large increase in hepatic concentration of metallothionein and that some product of 14CCl4 appeared to bind to zinc-induced metallothionein, it was suggested that metallothionein may protect against CCl4-induced liver damage by sequestering reactive metabolites of CCl4. These studies represent two examples of how the toxicity of a chemical whose toxicity is mediated via a metabolite can be modified by factors independent of metabolic activation.