Acute, Nontoxic Cadmium Exposure Inhibits Pancreatic Protease Activities in the Mouse

Toxic effects of cadmium on liver, kidney, lung, and testes have been well established in experimental animals and in cell model systems. However, little is known about the effect of cadmium on pancreas, though the pancreas has been reported to accumulate high concentrations of cadmium. Therefore, in this study we examined the effects of cadmium on the pancreas of mice. A single sc injection of 1 mg Cd/kg to mice had no obvious toxic effects on the liver, kidney, and pancreas at both 1 and 5 days after cadmium treatment. Within the pancreas, however, the activities of trypsin, chymotrypsin, and carboxypeptidase A were significantly decreased at 1 day after cadmium treatment, whereas the activity of carboxypeptidase B was not changed. All pancreatic enzyme activities returned to the control levels by 5 days after cadmium treatment. The concentrations of cadmium in pancreas were very similar at 1 and 5 days after cadmium treatment, indicating a stable deposition of the metal. The concentration of zinc in pancreas was markedly increased at 5 days after cadmium treatment. In order to more fully examine the inhibitory effects of cadmium on these protease activities in pancreas, the direct effects of cadmium on purified proteases were studied in vitro. Contrary to the results in vivo, cadmium increased the activity of purified trypsin in a concentration-dependent manner. Consistent with the in vivo results, the activity of purified carboxypeptidase A was decreased by cadmium treatment in a concentration-dependent fashion in vitro. The activities of chymotrypsin and carboxypeptidase B did not change by the cadmium exposure in vitro. The enhanced activity of trypsin by cadmium was returned to the control levels by subsequent treatment with EDTA, indicating that enhancement was reversible. In addition, the zinc normally contained in purified carboxypeptidase A and carboxypeptidase B was released by the cadmium treatment. These results indicate that cadmium inhibits protease activities within the pancreas in vivo at doses that do not induce overt hepatic, renal, or pancreatic toxicity. Based on in vitro study, the decreases seen in trypsin and chymotrypsin activities might be based on indirect effects of cadmium, whereas the decreases in carboxypeptidase A are probably due to the direct inhibition by the metal.